WO2018106784A2

WO2018106784A2 - Preparation of large area signage stack

Info

Publication number: WO2018106784A2
Application number: PCT/US2017/064872
Authority: WO
Inventors: Ranjanben Chhaganbhai BAKER; David J. Gerber
Original assignee: Djg Holdings, Llc
Priority date: 2016-12-07
Filing date: 2017-12-06
Publication date: 2018-06-14
Also published as: WO2018106784A3

Abstract

The invention relates to a process for producing a signage stack that includes a luminescent device stack and a receiver substrate. The process includes providing a flexible luminescent device stack comprising a luminescent layer; providing a receiver substrate; and interfacially fixing a portion of the luminescent device stack to the receiver substrate. The portion of the luminescent device may have a large scale area and a predetermined size and shape.

Description

Preparation of Large Area Signage Stack Cross Reference to Related Applications

The present application claims priority to U.S. Provisional Application Serial No. 62/431 , 100, filed December 7, 2016 and U.S. Provisional Application Serial No. 62/531 ,530, filed July 12, 2017, and hereby incorporates herein by reference the disclosures thereof.

Background

Signage is a communication medium that employs alphanumeric characters, graphics and / or pictures (collectively referred to herein as "graphic content") to convey information for a range of purposes, such as identification, advertising, decoration, providing directions, relaying safety information and so forth. As used herein, "signage" includes signs (collectively) and various other decorative, graphical, textual or display applications, such as billboards, labels, banners, flags, nameplates, posters, plaques, menu boards, fleet graphics, wraps, wallpaper, architectural lighting, packaging and point of purchase / sale, tradeshow and dashboard displays. Signage will frequently be installed in outdoor settings and in a variety of locations such as storefronts, floors, vehicle exteriors or the like.

Signs may be produced in high volume to display standard graphic content messages, such as FOR SALE, in common fonts, sizes and layouts. However, there is also demand for custom made signs to display information specific to the particular use and setting.

Signs may be internally illuminated for functional, visual, or aesthetic purposes, such as greater conspicuousness, visibility and legibility, or for use in exterior locations outside of, as well as during, the hours of daylight.

Internally illuminated signs often comprise a "light box" with one or more sources of light, such as neon, incandescent, fluorescent, or light emitting diode (LED) bulbs, housed in a protective framework comprising front, back and side panels, where at least one panel, typically the front, transmits light. This light transmitting panel often comprises a color filter, which may include printed graphic content such as letters, graphics or pictures.

Different types of such signage may include backlit channel letters, cabinets, pans and awning signs, among others, formed from various materials, to different designs, using a range of sign making techniques. The graphic content (e.g. letters, graphics and / or pictures) may be formed either from the (boundary) size and shape of the light transmitting panel itself or from distinct light filtering properties (such as intensity and frequency) of different regions of the panel. Certain such conventional arrangements (specifically illuminated channel graphic content, e.g channel letters and cabinet signs) are illustrated in Figure 1.

As can be seen, internally illuminated channel graphic content, e.g. channel letters (shown in the top row of Figure 1 ) are physically separate light boxes, each fabricated to embody a three dimensional (3D) letter so that the light emitting panel itself forms an individual letter. Multiple visually distinct and physically separate items of internally illuminated channel graphic content (e.g. channel letters), each representing graphic content, e.g. a letter of the sign message or other component of the sign may be placed on a sign surface to form the sign. Internally illuminated cabinet signs (shown in the middle and bottom rows of Figure 1 ) are single boxes with a light transmitting panel displaying the entire sign graphic content message. The graphic content message is formed by a patterned opaque mask placed over the panel surface, allowing the transmission of light only through letter size and shaped openings ("masked cabinet") or by a differentially colored or shaded sign graphic content message and background region ("standard cabinet").

Strategies for forming static graphic content (e.g. sign letters and graphics) have also been applied to other types of light emitting signs. For example, edge lit signs, which trap light inside of a smooth piece of light transmitting material, have specific regions engraved to reflect the light out thereby creating an image. Other types of signs (e.g. those disclosed in US Patent Publication No. 2010/0009588 and US Patent No. 7144289, the contents of both of which are incorporated by reference), have employed electroluminescent sheets to produce static signs. Such sheets typically comprise phosphor layers having a thickness in the order of 1 .5mm to 2.0mm. These phosphor layers comprise, for example, ZnS powders having relatively large crystal sizes of, e.g. 30 microns to 40 microns. However, it has been found that the operational lifetimes of such thick electroluminescent sheets are not sufficient for long term use. The useful emission is also limited. Some of these issues are considered in US Patent No. 7323816 which describes luminosity issues and also in US Patent No. 7989088 which describes issues in manufacture. The contents of both documents are incorporated by reference. US Patent No. 5432015 provides further background on the technology of electroluminescent displays and its contents are incorporated by reference. US Patent No. 7719187, the contents of which are also incorporated by reference, describes static and addressable emissive displays using phosphors.

Further, some thinner conventional electroluminescent devices comprise films with still relatively thick phosphor sheets (e.g. in the order of 5 microns to 30 microns). Working with such layers in sign making applications is not easy and can result in considerable defects in operation of the eventual sign. For example, cutting of such films is not easy, leading to gross edge defects. These defects significantly increase the risk of failure, as well as the increased potential of dust formation, which can be hazardous to those engaged in the sign making process and which debris can also effect operation of the eventual sign. The thick phosphor sheets are also opaque, limiting the applications for signs comprising such sheets. Although most traditional forms of signage use static graphic content such as letters and graphics, systems capable of displaying changing content (known variously as "variable" "changeable" "electronic" or "dynamic message" displays) provide for the presentation of new or varying content over time. For example, variable message displays include static signs with prefabricated graphic content, such as words or graphical shapes that illuminate or appear on rotating trilons to change the content being displayed. Such signs may also include passive or active dot matrix displays that are capable of displaying a wider range of messages and other graphic content, including colored text and graphics. Thus the combination of static content with changeable dynamic content in signs is of interest, especially in billboard and very large signage. In context of billboard applications, the diameter of the billboard pixel ranges from 15mm to 50mm, with inter pixel pitch ranging from 16 mm to 28mm, as found for LED based billboards. New signage technology is desired which can provide such pixel sizes to make up the dynamic part of large area signs, as well as much larger area sizes of the electroluminescent sign.

A more recent form of signage, termed "dynamic digital signage" is able to display dynamically changeable full color digital images, digital video and streaming media. Such signs typically have rectangular overall shape and rigid frames, regardless of the size and shape of the graphic content displayed in the sign. Such signs conventionally employ a passive or active full matrix display with rows and columns of addressable electrodes including a vast number of separate orthogonally arranged, miniscule (relative to the displayed graphic) and uniformly sized and shaped (for example circular) pixels. Further each electrode comprises a separate transistor for each pixel and complex software and multiple drivers are required to actuate the display.

While dynamic digital signage displays can of course be programmed to display static content, owing to their relative complexity, such displays are constrained by the size of the display units. Further, such displays are expensive, owing in part to the incorporation of complex electronics and data communications capabilities required for dynamic capability. Further, some such displays may not be suitable for outdoor use. Thus, there remains a need for efficient processes for preparing static luminescent signage in which the illuminated regions are large scale (i.e. not subject to the limitations of using pixel scale display systems) and / or that obviate the need for complex electronics and data communications capabilities, as well as signage obtainable from such processes.

Large format signs and billboards, comprising static and dynamic digital signage, is often viewed from a greater distance compared to smaller format images and therefore may have larger pixels. Larger pixels offer advantages, such as reduced production cost (e.g., simpler electronics), data requirements, and power consumption.

The cost to date of producing large scale signs for static luminescent displays has been expensive, prohibitively so for many applications. Further, the technology of the transfer of or in situ production of such large scale anisotropic objects comprising thin layers has not been reproducibly developed. Further, methods of efficiently electrifying large scale static signs have not been properly developed. The production of large scale signs which have both static and dynamic digital content has also not been successfully addressed.

As those skilled in the art will recognise, the production of materials for displaying graphic content requires different issues and requirements to be balanced and there is a need for an improved process which achieves this while delivering a cost effective and reproducible product.

One such requirement in electroluminescent signage is brightness uniformity. Most internally illuminated static displays, e.g. channel letter and cabinet signs, have an enclosed structure that has a faceplate and light source/s that are commonly based on line or point sources, e.g. neon or fluorescent tubes or incandescent or LED bulbs. The faceplate is transparent (in its entirety or at least a predesignated portion), and the light source/s illuminate this transparent region. However, conventionally used light source/s which typically emit lines or points of light, rather than providing the planar emission of light, tend to produce uneven illumination across the faceplate, e.g., bright areas or hot spots near the light source/s and also dim corner areas. This non uniform brightness is aesthetically displeasing and may distract and confuse the sign viewer. Attempts to address the problem of non uniform lighting have been made in US Patent No. 6566824 and US Patent No. 6878436, the contents of which are incorporated by reference.

Sign makers employ strategies to increase the brightness uniformity of light box signs. However, these strategies often still leave non uniform brightness and / or create additional problems. For example, the sign maker may employ a faceplate that diffuses the light. However, diffusor plates also absorb a significant amount of light and thus decrease brightness and energy efficiency and increase heat of the display. This issue is recognised in US Patent No. 6641880 and US Patent No. 7162821 , the contents of which are incorporated by reference.

Another conventionally deployed approach for improving the uniformity of brightness is the use of additional light sources. The sign maker can increase the number of light sources in the light box as a whole or in certain strategic locations, and this approach is considered in US Patent No. 7748148, the contents of which are incorporated by reference. However, additional light sources generally require additional cost for materials (light sources, fixtures) and labour (layout, installation, wiring). The approach also increases the overall weight of the sign which may require the use of greater structural support and complicates installation.

An additional strategy for improving light uniformity is to increase the depth of the light box so that the cone of light emitted from light sources located on the back plate will widen and thereby become more diffuse before reaching the faceplate. However, increasing the depth adds materials cost and fabrication complexity as well as weight. It may also impose aesthetic design limitations as this strategy will preclude shallow light box designs.

It may also impose restrictions on the graphic content that can be displayed. For example, the reliance on more diffuse light may preclude the incorporation of narrow features such as the thin serif of a letter because narrow channels defy full illumination. This issue has been discussed in International Patent Publication No. WO2015/148167, the contents of which are incorporated by reference.

One further way in which sign makers may attempt to improve light uniformity is to increase the diffusion of light internally within the sign. The sign maker can line the interior sidewalls and backplate with material that diffusively reflects light and / or position and direct the light sources at oblique angles to increase diffusion, for example, as discussed in US Patent No. 5697175, the contents of which are incorporated herein. However, as with the use of a diffusion plate (discussed above), light absorption will reduce the intensity of emitted light.

Additionally or alternatively to brightness uniformity, a further issue that sign makers face is the challenge of colour filtering. Sign makers often produce illuminated static displays, such as the light boxes described above, based on white light sources and colored faceplates that filter the emitted white light to project colored light. The faceplates may be a single color, may have a patterned opaque photomask or may employ a multicolor graphic (e.g. , an inkjet printed image). However, these faceplate light filters present multiple issues.

Firstly, the faceplate filters absorb a significant amount of light and thus decrease brightness and energy efficiency and increase heat of the display. This issue is discussed in US Patent Publication No. 2014/098515, the contents of which are incorporated by reference.

A further challenge with colour filtering is that intense light emission can cause the faceplate color to be less saturated and appear to be "washed out" and even color shifted and this issue is considered in US Patent No. 8631598, the contents of which are incorporated by reference.

The colored faceplate may also effect a different color between the night time and the daylight hours when ambient light will be absorbed and reflected in addition to the light being emitted. US Patent No. 6878436, the contents of which are incorporated by reference, discusses this challenge.

Further, graphic content that has been printed on a faceplate, e.g. by inkjet using pigmented dispersions, may have black areas which require that the pigment layer completely absorbs the backlight. Such "true" blacks are difficult to achieve and failure to provide "true" black impairs legibility and aesthetics and increases light trespass.

A further issue with which the experienced sign maker will be familiar is that each lighting technology with which he or she is familiar has its relative strengths and weaknesses, and may be best suited for certain specific types of displays. A useful discussion of these strengths and weaknesses is provided in the "Background" section in US Patent Publication No. 2014/0098515, the contents of which are incorporated by reference.

The production and installation of these different lighting technologies requires different specialized tools, materials and skills that are specific to the particular lighting technologies and related signage types. Among the requirements for many illuminated displays is the ability to generate bright and highly saturated colors, high color fidelity, a wide spectrum of possible colors, stability, a high contrast ratio, wide and conformable viewing angles, energy efficiency and typically low cost of manufacture. A review of recent advances and remaining challenges in OLED signage applications is disclosed by Sprengard et al., Proceedings of SPIE, 2004, 5519 (1 ), 173 to 183, the contents of which are incorporated by reference.

There is a need for a lighting technology possessing these attributes, which sign makers may use to form custom shaped and sized rigid and flexible displays based on a limited array of tools and materials and limited skill intensiveness, preferably those already possessed by sign makers.

A further challenge faced by sign makers is the provision of thin, bright and separate graphic content, such as lettering. Whereas thin non illuminated static signs, with visually distinct sections of graphic content (e.g. separate letters) such as cut vinyl or screen printed signs are ubiquitous, internally illuminated versions of these signs are relatively uncommon. Sign makers can produce signs based on planar lighting technologies, including (i) edge lit rigid plastic sheets and (ii) cut or screen printed traditional electroluminescent material.

The edge lit sheets may be provided with custom engravings that refract light outward. In sheets with these engravings, brightness and complexity of the design are limited and the entire sheet covers the sign surface. With edge lit or waveguide designs, white scattering dots are sometimes printed on a waveguide or film coupled to a waveguide, these dots scatter the light asymmetrically with much of the light scattered aimlessly resulting in the inefficiency of emission. Prismatic films may be used to direct points of light toward the forward direction and a diffuser is may be added to the top of the waveguide to blend the non uniformities of the white points together and scatter the light. However, these components and films are costly and add bulk.

Additionally, conventionally employed electroluminescent material is not especially bright, a problem considered in US Patent Publication No. 2016/0158099 and US Patent No. 5491377, the contents of which are incorporated by reference. Electroluminescent material may be cut into selected sizes and shapes, but the freedom of the sign maker regarding the size and shape is limited, for example by the challenge of establishing the required electrical connections, as discussed in US Patent No. 5821691 , the contents of which are incorporated by reference.

Thus, bright, durable graphic content displays are generally limited to three dimensional signage, such as channel letters, which involve costly materials, complex fabrication, wiring, cumbersome handling of individual characters of graphic content and challenges of aligning separate individual characters with precision when mounting the sign.

There is therefore a need for a process for preparing signage (or components thereof) which provides some or all of the following advantages over the prior art: greater ease of production, with greater possibilities for sign types, both for large area static and/or dynamic signs (e.g. for creating large pixels suitable for large format digital (static or dynamic) billboards), greater flexibility in providing a wider gamut of emitted colour, reduced electrical circuitry requirements and better energy efficiency, greater flexibility in assembling different signage types including graphic content of custom shapes and sizes, the ability to provide signage (or component thereof) which provide special effects (e.g. three dimensional graphic content), greater ease of incorporating light management schemes for greater efficiency of operation and convenience of incorporating emerging technologies in the field such as quantum dots which achieve steady state emission within on optimised thermal management environment and enable the preparation of thin signage displays.

Aspects of the Present Invention

Thus according to a first aspect of the present invention, there is provided a process for providing a signage stack comprising an luminescent device stack and a receiver substrate, comprising the steps of: · providing a flexible luminescent device stack comprising a luminescent layer;

• providing a receiver substrate; and

• interfacially fixing a portion of the luminescent device stack to the receiver substrate, the portion of the luminescent device having a large scale area and a predetermined size and shape.

The process of this aspect of the present invention advantageously permits the production of large scale luminescent (including electroluminescent) signs using a range of techniques including those conventionally used in sign making.

In embodiments of the invention, the flexible luminescent device stack is an electroluminescent device stack and the luminescent layer is an emissive electroluminescent layer. In such embodiments, the flexible electroluminescent device stack may comprise (i) an anode layer having an outer surface and an inner surface and (ii) a cathode layer having an outer surface and an inner surface and (iii) the emissive electroluminescent layer disposed between the inner surface of the anode layer and the inner surface of the cathode layer. In alternative embodiments, the luminescent layer may not be an emissive electroluminescent layer, but may be a photoluminescent layer. In such embodiments, the signage stack may comprise a light source, e.g. a further luminescent layer which may be emissive, one or more LEDs, OLEDs, QLEDs and / or any other type of light source. Additionally or alternatively, the signage stack may be intended for mounting onto a light box or other mounting surface comprising, or at least being lit by, a light source.

Whether the luminescent layer is an emissive electroluminescent layer or not, it may comprise nano phosphors including single component nanophosphors. In certain embodiments, the luminescent layer (whether or not an emissive electroluminescent layer) may comprise quantum dots and / or comprise mixtures of nanophosphors.

The luminescent stack may comprise one or a plurality of luminescent layers. Additionally or alternatively, the luminescent layer may comprise a single type of nanophosphors or a mixture of two or more types of nanophosphors. In certain embodiments, the luminescent stack comprises a plurality of layers each comprising a single type of nanophosphor. In embodiments in which a plurality of luminescent layers are present, these may have the same size and shape and be arranged to fully overlap each other. Alternatively, the luminescent layers may have alternating sizes and / or shapes and / or be arranged such that they do not fully overlap each other. In this way, a composite sign may be made of different shapes and / or sizes of luminescent material potentially having differently coloured regions.

In embodiments in which a plurality of types of nanophosphor are present (in the same luminescent layer and / or in separate luminescent layers), this enables luminescence in defined wavelength regions permitting the generation of a broad gamut of luminescent (including electroluminescent) colours.

For the avoidance of doubt, as used herein, the term "signage stack" is used to encompass a multi layered arrangement which, when provided with the appropriate electrical current or voltage in the case of an electroluminescent stack, or when provided with a light source in the case of a photoluminescent stack, is capable of emitting light and which can be employed either as a sign without further modification or which can be used in the preparation of a sign upon the addition or possibly the removal of supplementary components or layers.

For ease of comprehension, when considered in cross section, the signage stack may be considered to have upper and lower surfaces. The upper surface is the outwardly facing surface of the signage stack which is furthest from the receiver substrate. This may be the outer surface of the electroluminescent device stack or (if present) the outer surface of a protector layer, if present. The lower surface of the stack is the outwardly facing surface of the signage stack or receiver substrate facing opposite to the upper surface. As used herein, the term "large scale" in its broadest interpretation means greater than the size of pixels employed within dynamic digital displays such as consumer TV or personal computer screens. For example, the term comprises portions of electroluminescent device stack having an area of about 100pm² or greater, about 200pm² or greater, about 500pm² or greater, about 1 mm² or greater, about 10mm² or greater, about 15mm² or greater, about 20mm² or greater, 50mm² or greater, 100mm² or greater, about 1 cm² or greater, about 2cm² or greater, about 5cm² or greater, about 10cm² or greater, about 20cm² or greater, about 50cm² or greater or about 1 m² or greater. The portion of the luminescent device stack which is interfacially fixed to the receiver substrate may correspond to an item of graphic content, e.g. a letter, image, symbol or the like.

The thickness of one, some or all of the individual layers in the signage stack may be less than about 2 microns, less than about 1 micron, less than about 0.5 microns, less than about 0.3 microns, less than about 0.2 microns, less than about 0.1 microns or less than about 0.05 microns. The layers in the signage stack may have a combination of layer thicknesses, such that the individual layers making up the luminescent device stack may have differing thicknesses, tailored according to the purpose of specific function for in situ sign optimising operations (e.g., ablation, dim out, patterning) for the layers.

The production, e.g. by transfer, of large scale areas of anisotropic luminescent device stacks has conventionally been challenging. While pixel scale transfer of such material will be familiar to those skilled in the art (e.g. in the context of organic light emitting diode (OLED), electroluminescent TV or computer screens or quantum dot light emitting diode (QLED) consumer applications), the production and interfacial treatment of large scale signage stack has not been properly addressed until now. This is especially the case for thin layered large scale signage stacks, for example where the stack comprises thin layers which are sub micron or less in thickness.

In embodiments of the invention, the luminescent device stack may be configured such that it comprises one or more of the following elements / effects (which are discussed herein in detail): (i) simulated versions of standard types of illuminated channel graphic content (e.g. channel letters), such as open faced, reverse halo, and front/back lit and / or pan. These effects may be achieved through the control of text shadow, reflection, glow/soft edges, outline and 3D format based on (a) controlling illumination levels selectively and differentially within the sign graphic and (b) patterning the sign surface to produce optical effects, e.g. prismatic and holographic effects,

(ii) simulated versions of molded graphic content (e.g. letters), with rounded protruding or receding portions, (iii) colors outside the process color gamut,

(iv) control of luminance levels which may be achieved by (a) creating preferred luminance contrast between the graphic content displayed in the sign, sign background and non sign background, (b) providing different luminous intensity to different (analog) sections of the decal for varied levels across the sign (e.g. pan face with multiple different intensities) and (c) creating the impression of highly reflective and luminous elements within a photographic image, such as a glowing sunset or a highly reflective mirror,

(v) directionality and scope of light control,

(vi) control of the design and form of the conductive layers to minimise their visual impact and optimize their efficiency. This may be achieved by (a) creating the optimal form of the conductive layer, e.g. grids or lines which electrically connect separate items of graphic content (e.g. characters) with automated design (for example standard wiring designs for each letter and grading rules), (b) camouflaging the conductive layer that connects separate items of graphic content (e.g. independent letters) for example through the use of conductive layers which are transparent or colored to match the intended sign background, (c) arranging the conductive layer between separate items of graphic content (e.g. separate letters) for various different connection schemes and (d) arranging electrically conductive components so that they conform to the layout of the surface between items of graphic content (e.g. letters) and / or

(vii) simulated dynamic effects such as (a) changeable coloring of the entirety or certain portions of the luminescent device stack over time (e.g. to provide varying information, such as OPEN / CLOSED), (b) simulating motion, such as a timed series of arrows, or (c) modifying the color and brightness in response to changes in ambient lighting conditions that vary over the course of the day. Embodiments of (vii) may use large scale, dynamic segmented characters.

As mentioned above, in this aspect of the present invention, a large scale portion of luminescent device stack having a predetermined size and shape is interfacially fixed to a receiver substrate. This may be achieved through the transfer of a portion of the luminescent device stack on to the receiver substrate. However, it also encompasses the opposite arrangement, where a receiver substrate is transferred on to an luminescent device stack. It may also be achieved by the layerwise application (e.g. via printing, deposition, or the like, for example by ink jet printing) of the layers making up the luminescent device stack onto the receiver substrate (or vice versa). In embodiments of the invention, the process comprises the step of providing an luminescent device stack web and then separating the large scale portion of luminescent device stack having a predetermined size and shape from the luminescent device stack web. The step of separating the large scale portion of luminescent device stack having a predetermined size and shape from the luminescent device stack web may be carried out prior to, simultaneous with and / or following the interfacial fixing of the large scale portion of luminescent device stack having a predetermined size and shape to the receiver substrate.

The portion of the luminescent device stack of predetermined size and shape may be cut from a luminescent device stack web or roll prior to interfacial fixing on the receiver substrate. Those skilled in the art will be familiar with techniques for cutting luminescent device stacks and further guidance is provided below. In embodiments of the invention, the portion of the luminescent device stack of predetermined size and shape may be separated from the remainder of the luminescent device stack web using any cutting technique known to those skilled in the art. In a preferred embodiment, the stack is cut with a knife and / or a laser. In an embodiment of this cutting process, the resulting separated shape, in the case of an electroluminescent device stack, may then be powered to emit light selectively from this shape.

Where a knife is used to separate the portion of the luminescent device stack of predetermined size and shape from the remainder of the luminescent device stack web, this may be (or comprise) a blade having a single or double bevel edge, a chiseled edge or a modified chisel edge. Additionally or alternatively, the knife may be (or comprise) a pointed tip blade, a concave / hook blade, a formed blade, a multiple edged blade, a straight blade, a combination edge geometry blade, a scored strip blade, a convex / curved blade, a toothed edge blade or a circular blade. The knife may be part of larger cutting apparatus, for example a cutting wheel, a flatbed cutter or a plotter.

The knife used to separate the portion of the luminescent device stack of predetermined size and shape from the remainder of the luminescent device stack web may optionally be heated to a temperature of about 25°C to about 50°C, about 70°C or about 100°C.

Where a laser is used to separate the portion of the luminescent device stack of predetermined size and shape from the remainder of the luminescent device stack web, the laser may have a power density of about 0.1 J/cm², about 1 J/cm², about 3J/cm² or about 5J/cm² to about 10J/cm², about 15J/cm² or about 20J/cm². Alternatively, the portion of the luminescent device stack of predetermined size and shape may be cut and / or transferred and / or otherwise removed from a luminescent device stack web (which may be in the form of a sheet or roll) prior to or following interfacial fixing on the receiver substrate. For example, in some embodiments of the invention, the interfacial fixing of the portion of the luminescent device stack may be achieved by fixing the luminescent device stack to a receiver substrate layer and removing a selected portion of unwanted luminescent device stack, leaving only the portion of luminescent device stack having the predetermined size and shape fixed to the receiver substrate. In some embodiments of the invention, the interfacial fixing of the portion of the luminescent device stack may be achieved by fixing the luminescent device stack to a receiver substrate layer and removing a selected portion of both the unwanted luminescent device stack and interfacially positioned receiver substrate, leaving only the portion of luminescent device stack having the predetermined size and shape fixed to a correspondingly sized and shaped portion of the receiver substrate.

In these embodiments in which an unwanted portion of the luminescent device stack (and optionally a correspondingly shaped and sized portion of the receiver substrate) is removed (or "weeded") leaving the large scale portion of luminescent device stack having a predetermined size and shape interfacially fixed to the receiver substrate, the receiver substrate may be an adhesive layer that can then be used to fix the portion of luminescent device stack on to a mounting surface. Alternatively, the receiver substrate itself may be the mounting surface.

In embodiments of the invention, the step of interfacially fixing the portion of the luminescent device stack to the receiver substrate may be achieved by roll-to- roll processing. For example, this may be achieved by the luminescent device stack and / or the receiver substrate each being provided as a separate roll of material, unrolling a portion of the receiver substrate and / or the luminescent device stack from the roll/s to expose a portion thereof, interfacially fixing the large scale portion having a predetermined size and shape of the luminescent device stack to the receiver substrate to produce the signage stack, the signage stack itself optionally collected as a roll of material.

Interfacial fixing of the luminescent device stack to the receiver substrate may be achieved through the use of thermal energy, laser energy, pressure, adhesion or other fixing means, e.g. chemical fixing, UV curing, printing (e.g. ink jet printing) or a combination thereof. In embodiments in which laser energy is deployed to interfacially fix the large scale portion of luminescent device stack having a predetermined size and shape to the receiver substrate, the power density of the laser may be less than about 1 J/cm², less than about 0.5 J/cm², less than about 0.1 J/cm² or less than about 0.05 J/cm².

In embodiments of the invention, the process comprises the step of providing a web of luminescent device stack material and separating the large scale portion of luminescent device stack having a predetermined size and shape from an unused portion of the luminescent device stack web. This separation can be achieved using any means known to those skilled in the art. For example, separation may be achieved through a cutting step (e.g. using a knife, laser and / or saw). Additionally or alternatively, separation may be achieved through the application of heat, laser energy and / or pressure (e.g. using a transfer printer). Additionally or alternatively, separation may be achieved through the physical removal (e.g. mechanical) of the large scale portion of luminescent device stack having a predetermined size and shape from the unused portion of the luminescent device stack web (or vice versa). In embodiments, some or all of these separation techniques may be used in combination.

In embodiments of the invention, separation of the large scale portion of luminescent device stack having a predetermined size and shape from the unused portion of the luminescent device stack web may be carried out prior to interfacially fixing a portion of the luminescent device stack to the receiver substrate.

In embodiments of the invention, the luminescent device stack web may comprise a transfer substrate and, following separation of the large scale portion of luminescent device stack having a predetermined size and shape from an unused portion of the luminescent device stack web, the unused portion of the luminescent device stack web may be removed (e.g. weeded) from the large scale portion of luminescent device stack having a predetermined size and shape. In such embodiments, the process may also comprise the step of separating a portion of the transfer substrate which corresponds to the large scale portion of luminescent device stack having a predetermined size and shape from an unused portion of the transfer substrate which corresponds to the unused portion of the luminescent device stack web, and optionally removing (e.g. weeding) the unused portion of transfer substrate from the portion of the transfer substrate which corresponds to the large scale portion of luminescent device stack having a predetermined size and shape.

Alternatively, after the separation of the large scale device stack having a predetermined size and shape from the remainder of the web, the whole of the web may be interfacially fixed to the receiver substrate. The signage stack may be configured such that upon the application of power (in the case of an electroluminescent device stack), only the separated portion/s of the luminescent device stacks of predetermined size and shape will emit light. This type of construction may be useful for production of static / dynamic digital billboard signs.

In an embodiment of the invention, the signage stack may comprise a patterned anode and / or cathode (e.g. which anode and / or cathode may be in the form of a grid of conducting lines) and the separation of the electroluminescent device stack of predetermined size and shape is done without cutting the grid lines, thereby permitting the delivery of electrical power to the emissive electroluminescent layer in the electroluminescent device stack of predetermined size and shape.

In embodiments in which the luminescent device stack comprises a transfer substrate, the transfer substrate may be provided with adhesive and interfacial fixing of large scale portion of luminescent device stack having a predetermined size and shape to the receiver substrate may be achieved by adhering the transfer substrate to the receiver substrate. Adhesion may be achieved through the use of adhesives, for example a pressure and / or thermal adhesive which may advantageously protect the large area device stack from the ingress of oxygen, moisture and / or other contaminants. An acrylic resin adhesive having acrylic acid groups may be usefully employed as an adhesive.

In certain embodiments of the invention, the step of separating the large scale portion of luminescent device stack having a predetermined size and shape from an unused portion of the luminescent device stack web may be carried out simultaneously with interfacially fixing of the portion of the luminescent device stack to the receiver substrate. In such embodiments, the luminescent device stack web may comprise a transfer substrate and interfacial fixing of the luminescent device stack may be achieved through the application of heat, laser energy and / or pressure (e.g. using a transfer printer), resulting in separation of the large scale portion of luminescent device stack having a predetermined size and shape from an unused portion of the luminescent device stack web.

In embodiments of the invention, following the interfacial fixing of the large scale portion of luminescent device stack having a predetermined size and shape to the receiver substrate, the large scale portion of luminescent device stack having a predetermined size and shape may be separated from the unused portion, possibly by removing (e.g. physically) the unused portion from the interfacially fixed large scale portion of luminescent device stack having a predetermined size and shape, or vice versa. Additionally or alternatively, separation may be facilitated by a cutting step optionally one in which only the luminescent device stack, or one or more of the layers the luminescent stack, and not the receiver substrate, is cut.

In embodiments of the invention, the luminescent device stack is provided in the form of a web.

The web may be provided in the form of a roll. In such embodiments, the roll may be produced by roll-to-roll processing, a more detailed discussion of which is provided below.

In embodiments of the invention, the roll of luminescent device stack may be manufactured using ink jet technologies, such as array printheads from Fujifilm e.g. "Dimatix". Such technologies are useful for depositing the luminescent layer (including those comprising nanophosphors such as quantum dots), the cathode and / or anode or conductive layer/s (including those comprising graphene, nano silver or the like). Further, such technologies enable the direct application of large volumetric areas, in a pre-determined manner, such that the upper / lower surfaces may be large scale and flat while the layers of the stack (and thus their exposed edges) are very thin having the dimensions described herein. The use of ink jet technologies readily permits the production of complex device stacks in which there is molecular interfacial separation of the luminescent layer and the anode and / or cathode layers from surrounding polymer as illustrated in Figure 10 and described in greater detail below. In alternative embodiments, the luminescent device stack web may be provided in sheet form, e.g. as a plurality of sheets. The sheets may be flexible or be somewhat rigid. Whether in sheet, roll or any other form, the large scale portion of the luminescent device stack of predetermined shape and size may be removed from the remainder of the luminescent device stack prior to the step of interfacially fixing of it to the receiver substrate. Alternatively, the shape and size of the large scale portion of the luminescent device stack may be marked, for example by scoring, intermittent cutting, marking or the like to facilitate its separation from the remainder of the web or roll. Alternatively, the shape and size of the large scale portion of the luminescent device stack may be marked, for example by scoring, intermittent cutting, marking or the like, and only that shape is then selectively powered, in the case of an electroluminescent device stack.

To facilitate separation of the large scale portion of the luminescent device stack of predetermined shape and size from the remainder of the web and to minimise wastage of luminescent device web material, the large scale portion of the luminescent device stack of predetermined shape and size may be surrounded in the web by non-optically active material (e.g. which does not comprise a luminescent layer).

To facilitate fabrication and handling of the luminescent device stack and / or interfacial fixing of portions of the luminescent device stack to the receiver substrate, the luminescent device stack may comprise a transfer substrate. The structure and / or composition of the transfer substrate may be selected depending on the intended means of interfacially fixing the luminescent device stack to the receiver substrate. A more detailed discussion of the structure and compositions of transfer substrates that may be employed in the present invention is provided below.

Once the portion of the luminescent device stack has been interfacially fixed to the receiver substrate, the process may comprise the step of removing residual transfer substrate from the fixed portion of luminescent device stack to form a signage stack.

In embodiments, the step of interfacially fixing the luminescent device stack to the receiver substrate is preferably carried out in a clean room, e.g. under class 100 or lower conditions. Additionally or alternatively, the environment in which interfacial fixing of the luminescent device stack to the receiver substrate is carried out may have low moisture and / or oxygen content. This can be achieved, for example through the use of an inert atmosphere, e.g. as can be achieved through nitrogen blanketing.

However, in embodiments of the invention, environmental control measures may not be necessary or may need to be less stringent through the use of stable or stabilised quantum dots for example core shell quantum dots comprising a protective shell e.g. an aluminium oxide shell and / or which stack comprises a stabilising polymer matrix, e.g. an acrylic acid or epoxy adhesive matrix.

In embodiments of the invention, signage stacks comprising a plurality of luminescent device stacks may be desirable, and thus the process may further comprise the provision of signage stacks comprising a plurality of (e.g. 2, 3, 4, 5 or more than 5) luminescent device stacks.

The plurality of the luminescent device stacks may be arranged (i) on top of each other (vertically) and/or (ii) adjacent to each other (horizontally). The luminescent device stacks may be formed of different luminescent materials and/or have different relative areas. The use of a plurality of luminescent device stacks in a signage stack provides a wide choice of emission possibilities. Figures 9 and 10 show examples of signage stacks of the present invention which comprise a plurality of luminescent emissive layers from which an extensive gamut of emitted color combinations may be achieved.

Thus, in such embodiments, the process of the invention further comprises the step of interfacially fixing a further large scale portion of luminescent device stack having a predetermined shape and size to (i) the portion of luminescent device stack previously interfacially fixed to the receiver substrate or (ii) the receiver substrate. This further step may be repeated once, twice, three times, four times or more than four times.

In the manufacture of arrangements comprising a plurality of luminescent device stacks, interfacial fixing of the stacks to the receiver substrate or the production of those stacks may achieved by printing, e.g. ink jet printing may be usefully employed. The use of such an approach permits the preparation of signage containing multiple shapes which may emit the same colour or different colours. Luminescent layers of different shapes and sizes (including those comprising quantum dots), may be deposited using ink jet technology.

In embodiments in which luminescent layers are deposited using ink jet technologies, this may be done using compositions which comprise quantum dots optionally stabilised with acidic or amine containing organic ligands in a suitable solvent (e.g. a hydrocarbon such as hexane and / or octane, or water). In such compositions, the concentrations of quantum dots may be at least about 1 mg/ml, about 5mg/ml, about 10mg/ml, about 15mg/ml, about 20mg/ml, about 30mg/ml, about 40mg/ml, or about 50mg/ml.

The regions of luminescent device stack of predetermined size and shape may be surrounded by non-optically active web. This non-optically active web may be formed by depositing polymer in between the regions of luminescent device stack of predetermined size and shape, so that those regions are separated from each other. This type of manufacture is particularly useful for web manufacture of signage stacks in volume.

In embodiments of the invention, luminescent layers of different shapes and sizes containing same or different compositions may be deposited using printing, e.g. ink jet technology directly onto a receiver substrate or onto other layers making up the luminescent device stack. In an embodiment, these regions of luminescent device stack of different size and shape may be separated from each other by a non-optically active region of the web, e.g. a polymeric region comprising no luminescent layer. Both the luminescent device stacks and the non-optically active regions of the web can advantageously be printed, e.g. ink jetted in a roll to roll method according to programmed designs. The regions of luminescent device stack of predetermined size and shape may then be interfacially fixed to a receiver substrate separately from the non- optically active regions, or together with the non-optically active regions.

In embodiments, the materials comprised in the different luminescent device stacks may vary, with each such layer having different emission profiles and / or emitting light at different wavelengths. Examples of emissive electroluminescent layers which may be employed as luminescent layers in the present invention with such varying emissive properties are disclosed in US Patent Publication No. 2014/0374697, US Patent No. 9379344 and US Patent No. 7615800, the contents of each of which are incorporated by reference. Thus, the materials comprised in the different luminescent device stacks may vary according to the optimum electronic set up required for the electroluminescent layers, where used.

Advantageously, signage stacks comprising a plurality of luminescent layers (including emissive electroluminescent layers) provide flexibility in terms of the choice of the emission color (e.g. by combining different OLEDS and / or nano phosphors, e.g. quantum dot materials), choice in the layer area positioning, choice in the layer pattern and size (e.g. large or small dots versus whole area transfer, stochastic/random dots for more even emitted color), choice in providing different local area emission intensity and the possibility to create "vignettes" (colored regions having a gradual transition from one color shade to another or to or between black, white, grey or transparent).

The present invention also permits the production of large scale signs that can be made into decals (i.e. signs provided on backing layers for convenient mounting) enabling ready attachment to surfaces such as shop windows, walls or vehicle bodies which may include curved or 3D shaped surfaces. In embodiments of the invention, the luminescent device stack and / or receiver substrate is conformable and / or elastic in nature.

In embodiments of the invention, the luminescent device stack may be applied to a receiver substrate or mounting surface which is three dimensional. For example the luminescent device stack may be conformed or wrapped around a final support, or conformed or wrapped in or around a mold (e.g., for vacuum molding a sign). In such embodiments, the luminescent device stack may require flexibility both within the stack layers, in the transfer substrate and / or in the receiver substrate. Accordingly, one or more layers within the luminescent device stack may comprise materials to impart flexibility. Suitable flexibilising compounds which may be used are polyols (e.g. polyether ester polyols, urethane polyols), polyaminoamides, polysulfides, aliphatic polyamines and / or dimerised fatty acids, or the like. These may be present as reactive diluents in the layers comprising nano particulate materials used in the production of the luminescent stack.

The luminescent device stacks comprising thin layers of nano particulate materials, such as graphene and / or quantum dots, are particularly of interest where such flexibility is required. There may be compression or stretching of the luminescent device stack during its transfer on to a mounting surface, especially if the mounting surface has a three dimensional profile. Thus, in embodiments of the invention, layers comprising nanoparticulate materials (e.g. graphene and / or quantum dots) may additionally comprise flexibilising compounds. For example, a layer comprising quantum dots the luminescent device stack may additionally comprise an epoxy - amine matrix and optionally polyether ester polyols to render that layer flexible.

In embodiments of the invention, the transfer substrate and/or the receiver substrate may have a thickness of less than about 25 microns, less than about 20 microns, less than about 15 microns, less than about 10 microns, or less than about 5 microns. Additionally or alternatively, the transfer substrate and / or the receiver substrate may comprise flexible plastics such as vinyl, or acrylic, or epoxy optionally those comprising flexibilising groups, e.g. polyols.

In embodiments of the invention, the process may comprise the additional step of folding sign components (e.g., individual letters) along fold lines to create a three-dimensional shape. In such embodiments, the luminescent device stack may be provided with fold lines, e.g. by weakening or otherwise altering the luminescent device stack in predetermined regions e.g., heating or creasing (including the use of a creasing rule/wheel and preferably also a creasing matrix). In embodiments, the luminescent device stack may be applied to a foldable substrate material, which may be provided with fold lines and / or which may be draped over a three dimensional shape, which shape may have been formed by folding, molding, vacuum forming, and/or other means (e.g., additive or subtractive means).

In embodiments, the sign may be designed so that the various different panels/sides of the three-dimensional sign may have different colors, intensities, optical effects, and/or surface treatments. In embodiments, the fold lines may be non-emissive, such that the folded sign does not maintain functionality across a crease or bend, provided that electrical connections are made.

In embodiments, the luminescent device stack may maintain its functional integrity through the bend of preferably less 90 degrees or less, 80 degrees or less, 70 degrees or less, 60 degrees or less, 50 degrees or less, or 40 degrees (e.g., the interior angle of a Times New Roman letter "V") or less. This may be achieved by the luminescent device stack having sufficient durability, flexibility, and / or layer thickness. In embodiments of the invention, the luminescent device stack may comprise nano particulate materials such as graphene and / or quantum dots, and optionally a flexible matrix which has flexibilising compounds such as polyols, polyaminoamides, polysulfides, aliphatic polyamines and / or dimerised fatty acids, etc.

In embodiments, especially where material is to be folded without being applied to a 3D form, the material is sufficiently rigid. This may be achieved through the provision of adequate support (e.g. a flat receiver substrate), at least until additional support may be provided (e.g. upon transfer to a mounting surface), to maintain its desired/folded form between the fold lines. In such a configuration, the sign comprising the luminescent device stack may require a degree of rigidity, either within a stack layer or in the transfer or receiver substrate. Similarly, the luminescent device stack may be set-able along the fold line (e.g., temporarily made flexible, for example, by heating during the folding or forming process, but thereafter retaining its folded form).

The signage stack is particularly suitable for use in the preparation of static and / or dynamic analog signage, although embodiments of the invention may additionally or alternatively be suitable for use in static or dynamic digital signage. As used herein, "static analog signs" and/or "dynamic analog signs" comprise discrete luminescent graphic content (e.g. letters, symbols or other graphics) that are together or separately electrically powered.

One benefit of the present invention is that it permits the production of signage stacks comprising large scale discrete portions of luminescent device stack material which may be very thin and highly anisotropic and which may be discretely maintained with integrity for effective luminescent performance.

This disclosure relates to methods, materials and systems for making large scale patterned luminescent devices, especially light emitting signage stacks for use in sign displays and the luminescent devices so made. Thus, according to a further aspect of the present invention, there is provided a signage stack comprising an luminescent device stack comprising a luminescent layer and a receiver substrate; the receiver substrate being fixed interfacially with at least one portion of the luminescent device stack having a large scale area.

In this aspect of the invention, the luminescent device stack may be an electroluminescent device stack and the luminescent layer may be an emissive electroluminescent layer. In such embodiments, the electroluminescent device stack may comprise (i) an anode layer having an outer surface and an inner surface and (ii) a cathode layer having an outer surface and an inner surface and (iii) the emissive electroluminescent layer disposed between the inner surface of the anode layer and the inner surface of the cathode layer The signage stack of this aspect of the invention may be obtained from the processes described herein. This may involve the use of a printing apparatus, as described below.

In embodiments of the invention, the present invention may comprise the additional step of mounting the signage stack on to a mounting surface. The mounting surface may be for example, a wall, window, billboard base, vehicle body, or the like. Alternatively, the mounting surface may be comprised in a sign holder, and the sign holder may then be affixed to a wall, window, billboard base, vehicle body or the like.

In some embodiments, the receiver substrate may provide a mounting surface which can then be loaded into or onto a sign holder.

An advantage of using a sign holder with the signage stack of the invention is that this facilitates the replacement of specific components of the graphic content (e.g. individual characters) or layers in the event of partial failure of the sign.

The sign holder may be formed of stable materials, e.g. rigid plastic or metal. The plastic and / or metal may optionally have a coating for example of glass and / or metal. It may optionally be provided in the form of a casing holder defining a housing comprising a transparent front cover into which the signage stack is placed. The transparent front cover may be formed of glass, a transparent polymer (e.g., polycarbonate, CAB) or the like. Alternatively, the signage stack may be applied directly to a mounting surface forming part of the sign holder. Such a signage stack may be configured to display non-static signage (e.g. images which may scroll from one static sign image to another).

In embodiments, the sign holder defines an interior which is configured to prevent the ingress of oxygen, moisture and / or other contaminants, which may otherwise adversely affect the sign. Additionally or alternatively, the sign holder may also offer protection from additional environmental elements, such as abrasion (from e.g. dust particles, chemicals, etc.) and / or comprise means for heat dissipation.

Additionally or alternatively, the sign holder may be provided with guidance means to facilitate the correct positioning of the signage stack and / or other layers to be used with the signage stack in or on the holder. For example, in embodiments in which the sign holder includes or defines an interior, the interior may be provided with guiding markings or grooves or other mechanical means such as registration or alignment pins to facilitate the correct insertion and / or removal of the signage stack and / or other layers. The sign holder is preferably configured to house the large scale signage stack and may optionally house other films, e.g. graphic films, light management layers (e.g. light channeling layers, imaged layers), registration layers or the like. These other films may comprise graphic content shaped and sized to correspond to that shown by the signage stack. These other films may be interfacially fixed to the signage stack.

In embodiments, the sign holder has an opening (e.g. in its side) through which the signage stack and other films (e.g. can be inserted, positioned, repositioned and / or replaced).

The sign holder may have a shape corresponding generally to the graphic content of the signage stack (i.e. the portion of the luminescent device stack having a predetermined size and shape which is fixed to the receiver layer), but potentially having a larger area to incorporate margins and / or additional graphic content.

Additionally or alternatively, the sign holder may have a flat and / or seamless profile. Depending on the intended end use of the sign, low profile signage stacks (i.e. those having minimal bulk around the surround of the sign) may be preferred.

In practice of the invention, the assembled signage stack may be brought to the mounting surface (for example, in a sign making shop or at the final sign location). Mounting of the signage stack may then be achieved by removing the release liner (if present) and / or applying sign fixing means, e.g. adhesive or mechanical coupling means and mounting the signage stack on to the mounting surface. Alternatively, the receiving substrate may provide the mounting surface which can then be loaded into or onto the sign holder.

In certain embodiments, a plurality of large scale portions of luminescent device stack may be interfacially fixed to the receiver substrate. In such embodiments, where those portions are interfacially fixed to the receiver substrate at adjacent positions, they may be subjected to a seaming process (e.g. using laser treatment) to increase diffusion along any seams and thus meld or stitch together those adjacent portions and make the seams invisible or at least less noticeable to the viewer.

Additionally or alternatively, in processes in which a plurality of portions of luminescent device stack are mounted on to a mounting surface, such a seaming process may be carried out.

To facilitate the correct positioning of the signage stack when mounting and / or the correct positioning of other layers with which the signage stack is to be used (e.g. light management layers, such as light channeling layers), in embodiments of the invention, registration indicia and / or a registration layer may be provided. The registration layer may be provided with indicia and/or other positioning means to facilitate the correct positioning of the signage stack and / or the other layers on or with respect to the mounting surface.

Additionally or alternatively, the signage stack and / or mounting surface may be provided with registration indicia. Further, in arrangements where the signage stack is to be used with other layers, those layers may also be provided with registration indicia preferably corresponding to those provided in the registration layer, the signage stack and / or the mounting surface.

As mentioned above, the purpose of the registration layer / indicia is to ensure that the signage stack is correctly positioned and / or mounted on the mounting surface and / or that any other layers (e.g. light management layers such as light channeling layers and / or color filtering layers) used with the signage stack are correctly positioned. Additionally, registration indicia may facilitate the correct loading of components of the signage stack during its fabrication. Conventionally, certain sign making systems employ cut to print registration, in which the printer prints a target and the plotter (or plotter operator) registers the plot starting point to the printed graphic. Other sign making systems cut and print on the same machine, so the machine can facilitate the registration. Thus the manufacturing process may provide images (on the various sheets) that are already aligned with the edges of the sheets. Such approaches may be employed in the present invention. Additionally or alternatively, registration may be facilitated in the present invention using a mechanical or other key, with an additional visual guide. A transparent film having graphic content (e.g. an image) corresponding to the predetermined size and shape of the luminescent device stack may be positioned in front of the light channeling film and behind the front glass or transparent polymer cover. Such an image may be a transparent colored image on a transparent plastic.

Steps may also be taken during the production of the signage stack to improve its barrier properties, for example to provide enhanced protection against the ingress of oxygen, moisture and / or other contaminants. This can be achieved by, for example fusing the portion of the luminescent device stack to the receiver substrate. Such fusing could be achieved using heat, pressure and / or laser treatment. This fusing step may be carried out during the interfacial fixing step, i.e. fixing conditions / techniques may be selected to both effect fixing of the luminescent device stack to the receiver substrate and fusion of the luminescent device stack to the receiver substrate. This fusion may be at the edges, on the surface of and / or between luminescent device stacks (if a plurality of them are present) of various sizes and shapes.

Additionally or alternatively, the edges of the stack may have sealant and / or adhesive applied to them prior to, simultaneous with or following cutting, fusing, laser melting or ablation sealing of those edges.

These treatments to the stack edges may precede any cutting steps carried out on the luminescent device stack and / or the receiver substrate. By such pre- treatment, this helps to prevent the ingress of oxygen, moisture and / or other contaminants and / or minimise the liberation or formation of hazardous material which may arise during subsequent processing steps, for example cutting steps. The pre-treatment will also assist with sealing the edges of the layers of the stack.

Thus, in embodiments, the process may further comprise the step of fusing the edges of the portion of the luminescent device stack to the receiver substrate.

Additionally or alternatively, the process may comprise the step of fusing the edges of multiple layers of the luminescent device stack to one another. This step may be performed prior to, simultaneous with or following interfacial fixing of the luminescent device stack to the receiver substrate.

Owing to the manner of production or handling of the luminescent device stack, it may comprise microcracks on its surface and / or edges. Accordingly, the process of the present invention may further comprise the step of smoothing or passivating microcracks present in the luminescent device stack. This may be achieved through the application of heat and / or pressure to the luminescent device stack, either prior to, simultaneous with or following interfacial fixing to the receiver substrate

In embodiments of the invention, the receiver substrate may be provided with indentations which are optionally sized and shaped to correspond to the size and shape of the portion of the luminescent device stack to be fixed to the receiver substrate. Fixing of the portion of luminescent device stack to the receiver substrate results in a signage stack having the luminescent device stack inlaid into the receiver substrate, an example of which is shown in Figure 10.

In embodiments of the present invention, the sign is a static and / or dynamic, analog sign, comprising contiguous layers, composed of organic and/or inorganic polymer matrixes, which layers operate to provide daylight and nighttime readable signs.

The Luminescent Device Stack

In embodiments of the invention, the luminescent device stack may be an electroluminescent device stack in which the luminescent layer is an emissive electroluminescent layer

The electroluminescent device stack comprises an anode layer, a cathode layer and the emissive electroluminescent layer. A detailed discussion of exemplary structures and compositions of these layers, as well as that of other optional layers that may be comprised in the electroluminescent device stack, is provided below.

As will be recognised by those skilled in the art, the disclosure herein provides numerous examples of materials and techniques for preparing luminescent device stacks (whether electroluminescent or not) which permit the production of ultra thin, anisotropic luminescent device stacks.

In preferred embodiments of the invention, the luminescent device stack has a total thickness of less than about 5 microns, less than about 2 microns, less than about 1 micron, less than about 800nm, less than about 700nm, less than about 600nm, less than about 500nm or less than about 300nm. In the case of photoluminescent device stack the thickness maybe 75 micron, or 50 micron, or 25 micron or less. For the avoidance of doubt, when the thickness of the luminescent device stack is assessed, any transfer substrate should be discounted from that assessment.

The use of anisotropic luminescent device stacks (especially electroluminescent device stacks) is advantageous for many reasons, not least because the reduced thickness of the stack means that when it is cut, the amount of dust and discharge of other materials from within the stack (which may be hazardous to health) is minimised. This is especially so in arrangements comprising particles, such as colloidal phosphors (e.g. quantum dots) or metallic particles (such as nano silver, nano copper or the like), are comprised within a polymer matrix (such as a polyethyeleneimine or acrylic or epoxy matrix) as this limits or even prevents their liberation during the processes described herein.

Thus, according to a further aspect of the present invention, there is provided an electroluminescent device stack comprising (i) an anode layer having an outer surface and an inner surface and (ii) a cathode layer having an outer surface and an inner surface, and (iii) an emissive electroluminescent layer disposed between the inner surface of the anode layer and the inner surface of the cathode layer, wherein the total thickness of the stack is less than about 5 microns, less than about 2 microns, less than about 1 micron, less than about 800nm, less than about 700nm, less than about 600nm or less than about 500nm.

The individual layers making up the luminescent device stack may have differing thicknesses, tailored according to the purpose of specific function for in situ sign optimising operations (e.g., ablation, dim out, patterning), as explained further on.

The luminescent device stack may be produced according to any technique known in the art. In a preferred embodiment, the luminescent device stack may be prepared by a roll-to-roll process. While such processes will be familiar to those skilled in the art, guidance regarding the preparation of OLED containing luminescent devices is disclosed in design lines Automotive by Mogck et al., accessible via http://www.eetimes.com/document.asp?doc_id=1279752. Some aspects of this method are disclosed in German Patent Publication No. DE102014202945.

The luminescent device stack may be produced using roll-to-roll fabrication which advantageously provides (i) lower fabrication cost, (ii) no exposed front/back edges prior to cutting of the roll, (iii) and greater user freedom regarding the placement of graphic content of the final sign, (iv) the ability to pattern the stack (or layers comprised therein) in situ which is of benefit when fabricating large scale signage and (v) improved material utilization, (vi) greater range of sizes of signs, letters, and other symbols, such as long arrows, without seaming, (vi) compatibility of use with conventional sign printing and cutting equipment, and (vii) the ability to produce standard rolls comprising multiple luminescent device stack types comprising a predetermined combination of visual effects for example provided by quantum dot arrangements which rolls would be feedstock for use by a sign maker.

In embodiments of the invention, the luminescent device stack (for example an electroluminescent device stack) comprises nano particles. Examples of nano particles that may be employed include colloidal phosphors such as quantum dots (e.g. core shell quantum dots), nano metals (e.g. nano silver, nano copper) and / or nano flakes of graphene. Where such particulate materials are employed in the present invention, they are preferably stabilised with organic ligands such as oleic acid and / or octyl amine and other ligand discussed herein and / or may be comprised within a polymer matrix (e.g. polyethylenimine ethoxylated (PEIE) for the quantum dots).

Layers comprising nano particles are preferably applied in thin layers, e.g. having a thickness of about 20nm, about 30nm, about 40nm, about 50nm, about 60nm, about 70nm to about 100nm, about 200nm, about 500nm or about 1000nm (e.g. where those layers form emissive electroluminescent layers) or about 1 micron, about 2 microns, about 5 microns, about 10 microns about 25 microns or about 50 microns to about 100 microns, about 200 microns, about 500 microns or about 1000 microns (e.g. where those layers form photoluminescent layers). Nano particles of the type discussed herein are preferably comprised within the luminescent layer of the luminescent device stack (and in the case of electroluminescent device stacks, in the emissive electroluminescent layer). Further examples of ligands which may be used to stabilize nano particulate layers include those comprising carboxylic groups (such as oleic acid), amino groups (such as octyldecylamine), phosphine groups, and / or hydroxy groups (such as from polyethylene glycol, etc.) Examples of attempts to utilise quantum dot technology in a range of applications are disclosed in US6744960, US9199842, US9085728 and US9548009, the contents of which are incorporated by reference.

The use of luminescent devices comprising colloidal phosphors, e.g. quantum dots is known in the context of small test devices. They are of potential interest to those engaged in the development of consumer products such as QLED TVs or computer screens.

Methods of preparing signage stacks comprising such materials are described herein which enable the efficient preparation of signage with large scale graphic content to (i) achieve luminescent signage with greater and stable luminosity as compared to that obtained from conventional devices and (ii) provide greater flexibility for achieving signage displaying graphic content having a range of sizes, shapes and colors, in a broad gamut of possibilities for emitted colors.

The use of nanoparticulate materials in the luminescent layer (which may be an emissive electroluminescent layer and/or a photoluminescent layer) provides useful properties during the preparation of signage comprising the luminescent device stack of the invention. For example, where the sign maker is required to cut that stack, the thinness of the obtained stack results in sharp, clean edges being achieved. Such sharp edges are important to prevent microcracks, (and overcuts), which may otherwise propagate potentially leading to degradation of performance of the luminescent device stack. Thus according to a further aspect of the present invention, there is provided a process for preparing an luminescent device stack web comprising: providing a first roll of a first web material having a first surface, unrolling a portion of the first roll to expose the first surface of the first web material, sequentially applying a plurality of layers upon the first surface of the web material to form a luminescent device stack and optionally rolling up the electroluminescent device stack to obtain the luminescent device stack roll, wherein the total thickness of the stack is less than about 5 microns, less than about 2 microns, less than about 1 micron, less than about 800nm, less than about 700nm, less than about 600nm, less than about 500nm or less than about 300nm.

In embodiments of the invention, the luminescent device stack web which is produced may be an electroluminescent device stack comprising an emissive electroluminescent layer as the luminescent layer. In such embodiments, the electroluminescent device stack comprises (i) an anode layer having an outer surface and an inner surface and (ii) a cathode layer having an outer surface and an inner surface and (iii) the emissive electroluminescent layer disposed between the inner surface of the anode layer and the inner surface of the cathode layer.

In embodiments of the invention, the first web material may be a transfer substrate on to which the components of the luminescent device stack are applied. In embodiments in which the luminescent device stack web which is produced is an electroluminescent device stack web, the plurality of layers subsequently applied will comprise a cathode layer, the emissive electroluminescent layer and an anode layer and the cathode or anode layer may be applied on to the transfer substrate. Alternatively, a conductive layer may be applied on to the transfer substrate which may then be followed by the cathode or anode layer.

Thus, in embodiments of the invention, the luminescent device stack (whether electroluminescent or not) may be provided with and comprise a transfer substrate. In an alternative embodiment, no transfer substrate may be employed. In such an embodiment in which an electroluminescent device stack is prepared, the first web material may be the anode layer, meaning that the plurality of layers subsequently applied will comprise the emissive electroluminescent layer and the cathode layer. Alternatively, the first web material may be the cathode layer, meaning that the plurality of layers subsequently applied will comprise the emissive electroluminescent layer and the anode layer. As a further alternative, the first web material may be a conductive layer, and thus the plurality of layers subsequently applied will comprise the cathode layer, the emissive electroluminescent layer and the anode layer.

Application of the plurality of layers to the first web material may be achieved using any technique known to those skilled in the art, for example vacuum deposition, spray coating, solution deposition, thin film deposition (e.g. e-beam deposition or sputtering), thermal and / or pressure transfer, laser deposition, printhead transfer, ink jetting, filament deposition, atomic layer epitaxy (ALE) or the like. A suitable inkjet device is commercialized by FujiFilm under the name "Dimatix". Between deposition of each layer, there maybe heating applied to ensure thorough removal of solvents whilst ensuring microcracking is prevented from occuring.

In such methods, the materials that are deposited may have compositions facilitating their deposition. For example, where a layer of the luminescent device stack is to be applied by ink jetting, ink jettable compositions will be employed. Examples of such compositions which are capable of deposition via ink jetting are disclosed in US Patent No. 6576155 and US Patent No. 8765014, the contents of which are incorporated by reference. Additionally or alternatively, the ink jettable compositions employed in the present invention may be colloidal dispersions of nanophosphors at a concentration of about 1 mg/ml, about 2mg/ml, about 5mg/ml, about 10mg/ml, about 15mg/ml, about 20mg/ml, about 30mg/ml, about 40mg/ml, or about 50mg/ml to about 100mg/ml, about 200mg/ml, about 500mg/ml, in carrier liquids such as water, or alcohols, or hydrocarbons (such as hexane, octane), etc.

In embodiments of the invention, a layer may be provided on a separate donor sheet and applied via transfer, e.g. thermal, laser and / or pressure transfer. An example of such a sheet for use in the present invention is 3M BT3F.

Certain layers may be deposited by means other than transfer from carriers. For example, the barrier layer may be provided by means other than a carrier sheet, using different technologies. These include atomic layer deposition (ALD) technology, e.g. as provided by Veeco, Lotus Applied Technology, Beneq, Encapsulix; PECVD e.g. from Aixtron or Applied Materials; vacuum evaporation e.g. from Vitex; or printing, such as inkjet printing e.g. as provided by Kateeva. The stacks of the present invention may comprise alternating layers of different compositions and thicknesses. To provide protection to the stack, a film such as a Vitriflex all metal oxide barrier film or a UDC single hybrid organic / inorganic layer may be employed. Manufacturing of alternating organic / inorganic barrier layers may employ different sets of deposition methods, e.g. inorganic layers may be deposited using sputtering, ALD and / or PECVD and organic layers may be deposited using vacuum evaporation and / or inkjet printing. For other layer structures, sputtering may be employed, e.g. Vitriflex's metal-oxide film. There may be grading in the deposited layers, e.g. GE Graded UHB.

The provision of such layers may be comprised within the protector layer, the receiver substrate and / or the transfer substrate and optionally provide a water vapour transmission rate (VWTR) of less than about 10^"2 gm/m²/day, less than about 5 x 10^"3 gm/m²/day, less than about 5 x 10^"4 gm/m²/day, less than about 5 x 10^"5 gm/m²/day, or less than about 5 x 10^"6 gm/m²/day.

In embodiments, the production of the luminescent device stack may be carried out in a clean room, e.g. under class 100 or lower conditions. Additionally or alternatively, the environment in which production of the luminescent device stack is carried out may have low moisture and / or oxygen content. This can be achieved, for example through the use of an inert atmosphere, e.g. as can be achieved through nitrogen blanketing, in for example a dry box. However, in embodiments of the invention, environmental control measures may not be necessary or may need to be less stringent through the use of stable or stabilised quantum dots for example core shell quantum dots comprising a protective shell e.g. an aluminium oxide shell and / or which stack comprises a stabilising polymer matrix.

In embodiments, the roll-to-roll produced luminescent device stack and / or the roll-to-roll produced conductive layers may have barrier layers to ensure stability of the thin layers from the ingress of oxygen, moisture and / or other contaminants during storage, transport, handling and / or processing before use and at the sign maker and even the sign site. The composition and structure of barrier layers is discussed below in more detail.

In embodiments of the invention, one or more of the layers comprised in the signage stack, for example in the luminescent device stack, may be produced or modified (e.g. to impart desirable properties on a specific layer) using deposition methods such as vacuum deposition, spray coating, solution deposition, thin film deposition (e.g. e-beam deposition or sputtering), thermal and / or pressure transfer, laser deposition, printhead transfer, ink jetting, filament deposition, atomic layer epitaxy (ALE) or the like.

Advantageously, owing to the construction and potentially the method of the interfacial treatment, the luminescent device stacks of the invention are resistant to forming microcracks or delaminating during the interfacial fixing process, which is important given that large scale portions of them will be handled and fixed e.g. by transfer.

In embodiments of the invention, the compositions which are deposited on or within layers in the signage stack may be selected such that they can be deposited using the same apparatus (e.g. inkjet, laser or printhead transfer) as needed to effect interfacial fixing (e.g. of the luminescent device layer to the receiver substrate). Examples of such compositions include curable liquid monomers, e.g. acrylic, epoxy, polyamine, polyols or the like. In embodiments of the invention, the luminescent device stack may be fabricated using automated apparatus, for example a printer, such as an environmentally controlled printer, which preferably permits the roll-to-roll fabrication of the luminescent device stack in its entirety, as described for example by "Center of Organic Materials and Electronic Devices Dresden" (COMEDD) of Fraunhofer IPMS in

Advantageously, the use of automated apparatus may be employed to produce the signage stacks having a predetermined portion of the luminescent device stack of required size and shape interfacially fixed to the receiver substrate, and also having predetermined emission color. The use of such apparatus may facilitate the efficient workflow by a sign maker for the production of large scale signage with reduced wastage of materials. Such an approach is particularly appropriate for volume production of (standard) stacks of required size and shapes.

In embodiments of this aspect, the luminescent device stack having a predetermined size and shape may be deposited on a transfer substrate, using the automated apparatus. The transfer substrate may then be used at a signmaker to facilitate the interfacial fixing of a predetermined portion of the luminescent device stack to the receiver substrate optionally to achieve optimum oxygen and moisture impermeability.

Additionally or alternatively, layers in the signage stack may be subjected to property modifying techniques such as microreplication and / or embossing techniques. Such techniques may be employed to, for example, modify the barrier and / or light management properties. International Patent Publication NO. WO2017/014100, the contents of which are incorporated by reference, provides examples of such property modifying techniques. In embodiments of the invention, the luminescent device stack, whether produced in web, roll, sheet, pre-cut or any other form, may be stored and / or transported in an inert atmosphere (for example, under nitrogen blanketing). Use of luminescent device stacks including layers comprising stable quantum dots and / or quantum dots dispersed in stabilising polymer matrix may diminish the need for such environment requirements.

In embodiments of the invention in which emissive electroluminescent layers are employed, the electroluminescent device stack exhibits luminance of at least about 10 cd/m², about 20 cd/m², about 30 cd/m², about 40 cd/m² or about 50 cd/m². Additionally or alternatively, the electroluminescent device stack exhibits luminance of less than about 300 cd/m², about 400 cd/m² or about 500 cd/m²

The operating voltages of the electroluminescent device stacks which may be employed in the present invention may be from about 1V or more, about 2V or more, about 5V or more, or about 50V or less, about 30V or less or about 20V or less.

Additionally or alternatively, electroluminescent device stack/s employed in the present invention may have a significantly higher operating voltage, e.g. for field driven electroluminescent device stack/s, about 30V or higher, about 50V or higher or about 100V or higher and / or about 300V or lower, about 250V or lower or about 200V or lower.

The operating voltages of the electroluminescent device stacks may be varied according to the requirements of the area of the shape and the composition of the layers.

In embodiments of the invention, electroluminescent device stacks which may be employed emit light at an intensity of about 5cd/m² or higher, about 10cd/m² or higher, about 15cd/m² or higher, or about 20cd/m² or higher. The emissive electroluminescent layer employed in aspects of the present invention may be formed from any material known to those skilled in the art that emits light upon exposure to electrical energy. Additionally, the emissive electroluminescent layer may be structured in any way provided that it achieves this goal.

In embodiments of the invention, the emissive electroluminescent layer may comprise semiconductor organic materials such as OLEDS, PLEDS and/or semiconductor nanoparticles e.g. nanophosphors, such as quantum dots. Such materials may also be employed in non-emissive luminescent layers (e.g. photoluminescent layers) either alone or in combination with organic materials such as OLEDS, PLEDS.

Commercial sources of quantum dots include those from Nanoco, Storedot, Quantum Materials, and Crystalplex.

Quantum dots employed in emissive and / or non-emissive luminescent layers which may be employed in any aspect of the present invention may be particles having an average diameter of less than about 60nm, less than about 50nm, less than about 40nm, less than about 30nm, less than about 20nm, less than about 15nm, less than about 10nm or less than about 5nm. The quantum dots may be spherical and / or rod-shaped.

In such embodiments, the quantum dots may comprise inorganic compounds selected from one or more of: compounds of Group II to VI, such as CdSe, CdS, CdTe, ZnSe, ZnO, ZnS, ZnTe, HgS, HgSe, HgTe and alloys thereof such as CdZnSe; compounds of Group III to V, such as InAs, InP, GaAs, GaP, InN, GaN, InSb, GaSb, AIP, AIAs, AlSb and alloys such as InAsP, CdSeTe, ZnCdSe, InGaAs; compounds of Group IV to VI, such as PbSe, PbTe and PbS and alloys thereof; compounds of Group III to VI, such as InSe, InTe, InS, GaSe and alloys such as InGaSe, InSeS; compounds of Group IV semiconductors, such as Si and Ge alloys thereof and combinations thereof in composite structures (e.g. CsPbBr3, CulnSe2 nanocrystals); metal oxide nanoparticles; core shell structured nanocrystals; semiconductor nanocrystals doped with rare earth elements or transition metal elements or any combination of the foregoing.

The quantum dots may be composite particles, for example comprising one or more of the materials above in combination with other compounds. In embodiments of the invention, in addition to an inorganic component, the quantum dots may also comprise fluorescent dyes or quantum dots comprising graphene structures. The quantum dots may comprise a shell and a core. The quantum dots may be thin shell quantum dots, thick shell quantum dots and / or gradient shell quantum dots (i.e. where the composition of the core gradually grades into the composition of the shell). In embodiments of the invention, the quantum dots are coated with a thin layer of an inorganic compound such as aluminium oxide to reduce or prevent the ingress of oxygen, moisture and / or other contaminants. Examples of quantum dots configured in this way are provided commercially by Crystalplex Corp. Advantageously, the present invention enables the production of signage bearing large scale graphic content in which the advantages of quantum dot technology can be utilised. These advantages include (i) theoretical internal quantum efficiency potentially as high as 100%, compared to levels in the order of 25% which is understood to be typical of a conventional organic (OLED) emitter; (ii) the quantum dots are dispersible in common organic solvents and can be made successfully as dispersions in formulations to be used for coatings; (iii) emission wavelength from the quantum dots can be tailored by the core size or semiconductor ratios to achieve a broader gamut of emitted colors, including custom colors, than is understood to be possible with conventionally sized (i.e. non colloidal) phosphors; (iv) the emission spectrum is narrow and (v) the intrinsic stability is good in inorganic materials.

The optimum thickness of a luminescent layer (including an emissive electroluminescent layer) which may be employed in the present invention comprising quantum dots may depend on the type and dispersion of the quantum dots, as well as the composition and construction of the adjacent layers in the signage stack. In embodiments of the invention, the luminescent layer may have a thickness of about 10nm or more, about 20nm or more, or about 30nm or more.

Using quantum dots with generally constant diameter and shape, but with differing internal chemical compositions and / or coating thicknesses / types advantageously provides flexibility in achieving effective thin layers for deposition.

Further examples of materials which may be comprised in the luminescent layer are disclosed in US Patent No. 6765349, the contents of which are incorporated by reference. Additionally, examples of nanophosphors that may be incorporated in the luminescent layer in the present invention are described in International Patent Publication No. WO201 1/005859, the contents of which are incorporated by reference. Particularly preferred are non toxic nanoparticles, such as those nontoxic quantum dots composed of carbon, silicon and some Group l-lll-VI elements, for example quantum dots made of indium phosphide (InP), CulnS2 or doped ZnS/ZnSe. Organic fluorescent dyes embedded within solid matrixes, as described in US Patent Publication No. 2017137626 (the contents of which are incorporated by reference), may be used.

In embodiments of the invention in which signage stacks comprising luminescent layers (including emissive electroluminescent layers) of the type discussed above (e.g. OLEDS, PLEDS, nanophosphors, graphene quantum dots and / or nano metals) are prepared, those signage stacks (and optionally the luminescent device stacks thereof) can be prepared (for example on a roll- to-roll basis) using various deposition methods, such as vacuum deposition, laser or printhead transfer, ink jetting, spraying, filament deposition or the like. As those skilled in the art will recognise, for each of these methods, specialist compositions may be employed, for example inkjet compositions as described in US Patent No. 6576155 and US Patent No. 8765014 (the contents of which are incorporated by reference); and/or microreplication / embossing techniques, to produce functionalized layers such as active, protective or light management layers.

In embodiments of the invention, the luminescent device stack comprises a single luminescent layer and (in arrangements in which the luminescent device stack is electroluminescent) thus a single cathode layer / anode layer pair.

However, in alternative embodiments, the luminescent device stack may comprise a plurality of (e.g. 2, 3, 4, 5 or more than 5) luminescent layers. One, some or all of these may be emissive electroluminescent layers.

In such embodiments in which a multiplicity of emissive electroluminescent layers are provided in an electroluminescent device stack, the stack may comprise a plurality (e.g. 2, 3, 4, 5 or more than 5) of cathode and anode pairs may be provided, although this is not essential; a single cathode and anode pair may be provided. Figure 12 depicts an example of a multiplicity of luminescent device stacks making up a multicolour sign.

As used herein, the terms "anode layer" and "cathode layer" should be interpreted broadly not only to encompass conventional layers of conductive materials, but also positive charge promotion and negative charge promotion layers, respectively. Charge promotion layers function by producing, promoting or injecting electrons or holes. In embodiments of the invention in which charge promotion layers are employed, these may be dielectric layers which are polarised by applied current which may be provided by conductive layers. This causes the charge promotion layers to produce positive or negative charges (or carriers) necessary to result in luminescence from the emissive electroluminescent layer, where used.

In embodiments in which the anode layer comprises a charge promotion layer, the signage stack may additionally comprise a conductive layer in electrical communication with the charge promotion layer. The conductive layer may be comprised in the anode layer, elsewhere in the electroluminescent device stack, in the receiving substrate or in a protective layer (if present).

The charge promotion layers may comprise materials with low dielectric constant (K), e.g. of less than about 5, or less than about 3. Examples of such materials that may be employed in charge promotion layers include inorganic oxides, inorganic nitrides or insulating polymers, specific examples of which include silicon oxide, aluminium oxide, zinc oxide, benzocyclobutene polymers, polyphenylenes, polyarylenes, silsesquioxanes or the like. The charge promotion layers may additionally or alternatively be provided with coatings to produce the required dielectric, semi conduction effects, such as coatings containing e.g. pentacene.

The deposition of charge promoting layers may be achieved using low pressure processes such as physical vapor deposition (PVD), sputtering, plasma deposition and chemical vapor deposition (CVD) or solution processing (e.g. jetting, spraying).

The anode and cathode layers may be formed of any material known by those skilled in the art to be useful for the preparation of electroluminescent device layers.

More specifically, the anode layer may be formed of any high work function conductive material known to the skilled reader. The anode layer may be disposed adjacent to at least one other layer in the electroluminescent device stack, for example the emissive electroluminescent layer, a conductive layer, a hole transport layer, a passivating layer or the like.

In embodiments of the invention in which the anode layer is disposed adjacent to another layer, deposition techniques known to those skilled in the art may be employed, for example, vacuum deposition, spray coating, solution deposition, thin-film deposition (e.g. e-beam deposition or sputtering), thermal and / or pressure transfer, laser deposition, printhead transfer, ink jetting, filament deposition, atomic layer epitaxy (ALE) or the like.

The work function of the anode may be about 4.0 ev or higher, about 4.2 ev or higher or about 4.5 ev or higher. As an example of a material from which the anode may be formed, indium tin oxide may have a work function in the range of about 4.2 to 5.2 ev. The specific work function value of an anode layer may depend on the method of its deposition and other preparatory steps e.g. chemical treatment, cleaning or the like. The anode layer preferably has a low thickness. In embodiments of the invention, the anode layer has a thickness of at least about 1000 angstroms, about 2000 angstroms, about 3000 angstroms, about 4000 angstroms or about 5000 angstroms. Additionally or alternatively, the anode layer has a thickness of less than about 50000 angstroms, about 40000 angstroms, about 30000 angstroms, about 20000 angstroms, about 10000 angstroms or about 5000 angstroms.

In embodiments of the present invention, the anode layer may be formed of or comprise metals (in sheet and / or particulate form) such as silver, indium, tin (e.g. tin oxide, indium/tin oxide), yttrium (e.g. yttrium oxide), zinc (e.g. aluminium doped zinc oxide) and / or other conductive materials such graphene or carbon nanotubes. In embodiments in which the anode layer comprises graphene, this may be provided in sheet form and / or in particulate form (e.g. in the form of flakes).

An example of the configuration of an anode which may be employed in the present invention is the indium tin oxide anode disclosed in US Patent No. 6764368, the contents of which are incorporated by reference. Where the anode layer is formed of or comprises particulate conductive material, this may be disposed in a conductive material such as a conductive monomer (e.g. one including an aromatic benzene ring) or a conductive polymer. Additionally or alternatively, the conductive material may be applied by vacuum deposition. In arrangements in which the anode layer comprises graphene (whether in sheet and / or particulate form), the graphene may be provided as two layered graphene arrangement (i.e. a layer comprising two layers of the two dimensional graphene ring network). Further, as mentioned above, the graphene may be provided in a conductive polymer, for example one having a benzene ring in the monomeric unit.

In embodiments of the invention in which the anode comprises graphene flakes, these preferably have a length along their longest axis of about 100nm or less, about 50nm or less, about 30nm or less or about 10nm or less. The use of flakes of such dimensions is especially preferred in arrangements in which transparency of the anode layer is desirable. In embodiments in which the anode layer comprises graphene, it may additionally comprise metallic particles such as nanoparticulate metal to optimise the electroluminescent emission. Nanoparticulate gold may be employed for this purpose. Additionally or alternatively, in embodiments in which the anode layer comprises graphene, the anode layer may be a patterned or unpatterned layer. The pattern may be one or more lines, a grid of lines or a mesh.

To the inventors' knowledge, the use of large scale electroluminescent signs comprising anodes formed partially or totally from graphene is advantageous as such an approach means that the use of metallic materials traditionally employed in electrodes for electroluminescent displays (e.g. indium tin oxide) may be avoided, saving cost, reducing weight and minimising the environmental burden of obtaining large quantities of such components. Additionally, deposition, treatment and transfer of anode layers comprising graphene is relatively straightforward; graphene may be coated in situ by vacuum deposition or by incorporating suitable treated graphene flakes in e.g. a curable resin, for ink jetting, spraying or other application techniques. Thus, according to a further aspect of the present disclosure, there is provided an electroluminescent device comprising (i) an anode layer having an outer surface and an inner surface and (ii) a cathode layer having an outer surface and an inner surface, the anode layer and cathode layer having an emissive electroluminescent layer disposed between the inner surface of the anode layer and the inner surface of the cathode layer, wherein the anode and/or the cathode layer comprises graphene. Preferably the anode comprises graphene.

Graphene containing layers may require the selection of appropriate hole and/or electron transport materials, either together with the graphene or in adjacent layers, so that the semi conduction electronic properties of the graphene are suitably adjusted for optimum efficiency of electroluminescence.

The cathode layer may be formed of any low work function conductive material known to the skilled reader. The cathode layer will be disposed adjacent to at least one other layer in the electroluminescent device stack, for example the emissive electroluminescent layer, a conductive layer, a passivating layer or the like. In embodiments of the invention in which the cathode layer is deposited on to another layer, deposition techniques known to those skilled in the art may be employed, for example, vacuum deposition, spray coating, solution deposition, thin film deposition (e.g. e-beam deposition or sputtering), thermal and / or pressure transfer, laser deposition, printhead transfer, ink jetting, filament deposition, atomic layer epitaxy (ALE) or the like. The cathode layer may comprise a metal having a work function of about 4.2 eV or lower, about 3.5 eV or lower or about 3 eV or lower.

In embodiments of the invention, the cathode layer may comprise metals which readily release electrons into the emissive electroluminescent layer. Examples of such metals include alkali metals, such as magnesium, calcium, aluminium or alloys comprising any of those metals. For example, the cathode layer may comprise greater than 50 percent by weight of a first metal such as magnesium and at least 0.1 percent by weight of a second metal having a work function of about 4 eV or lower or optionally a combination of metals having a work function of about 4 eV or lower.

In certain embodiments, the cathode layer may comprise graphene. In such embodiments, the graphene may be provided in sheet form and / or in particulate form (e.g. in the form of flakes). In embodiments in which the cathode comprises graphene, it may additionally comprise particulate (e.g. nanoparticulate) metal such as nano silver to optimise the electroluminescent function of the electroluminescent device stack. Additionally or alternatively, in embodiments in which the cathode layer comprises graphene, the cathode layer may be a patterned or unpatterned layer. The pattern may be one or more lines, a grid of lines or a mesh.

Where the cathode layer is formed of or comprises particulate conductive material, this may be disposed in a conductive material such as a conductive monomer (e.g. one including an aromatic benzene ring) or a conductive polymer. Additionally or alternatively, the conductive material may be applied by vacuum deposition. In arrangements in which the cathode layer comprises graphene (whether in sheet and / or particulate form), the graphene may be provided as two layered graphene arrangement (i.e. a layer comprising two layers of the 2 dimensional [2D] graphene ring network). Further, as mentioned above, the graphene may be provided in a polymer, for example one having a benzene ring in the monomeric unit.

In embodiments of the invention in which the cathode comprises graphene flakes, these preferably have a longest axis of about 100nm or less, about 50nm or less, about 30nm or less, about 20nm or less or about 10nm or less. The use of flakes of such dimensions is especially preferred in arrangements in which transparency of the cathode layer is desirable.

In embodiments of the present disclosure, the anode and / or cathode layers may comprise or be accompanied by one or more (e.g. 1 , 2, 3, 4, 5, 6 or more than 6) conductive layers. The conductive layers may be disposed adjacent to or at least in electrically conductive proximity to the anode and / or cathode layers. If so disposed, the conductive layer may be referred to herein as an "anode conductive layer" or a "cathode conductive layer" respectively. The anode conductive layer/s may be comprised within the electroluminescent device stack, the receiver substrate (discussed below) or the protector layer (discussed below). The cathode conductive layer/s may be comprised within the electroluminescent device stack, the receiver substrate (discussed below) or the protector layer (discussed below).

The function of the anode and cathode conductive layers is advantageously (i) to provide electrification of the appropriate anode and / or cathode layers for an individual signage stack and / or (ii) to provide a common electrification pathway for a plurality of electroluminescent signage stacks which are comprised in a sign. Such an arrangement conveniently enables large scale signage comprising separate items of graphic content of different shapes and sizes.

These anode and / or cathode conductive layers may be provided in the form of line/s, grid/s and / or mesh/es. Examples of a grid pattern are provided in US Patent No. 9235298, the contents of which are incorporated by reference. Additionally or alternatively, one or both of the anode and / or cathode conductive layers may be in sheet form.

The anode and / or cathode conductive layers, when in non sheet form (e.g. when present as lines and / or grids) may be positioned in their respective layer in a predetermined location, e.g. to meet the requirements of successful electroluminescent performance of the signage stack.

Accordingly, the process of preparing the electroluminescent device stack of the present invention may comprise the step of designing a layout of an anode and / or cathode conductive layer and forming such layer/s in accordance with the design. The layout of the conductive layer/s may be selected so as to electrify a single signage stack or connect a number of signage stacks for common electrification. The layout may be formed advantageously during the fabrication of the sign at a sign maker's facility.

The conductive layer/s may be prepared from conductive materials, such as thin metal foils (made of conductive metals or metal alloys, for example silver, gold, aluminum, copper, tin, titanium, tungsten and nickel or alloys thereof, etc.), compositions of nano particles (e.g. indium tin oxide, nano silver, nano copper, carbon nano tubes, graphene) and / or conductive organic materials. As explained above, the conductive layers may be provided in the form of a plurality of lines, a grid and / or a mesh.

The conductive layers may be deposited using e.g. FDM (fused deposition modelling) conductive pastes, be produced by laser thermal processing using suitable donor films, e.g. as disclosed in International Patent Publication No. WO2010/082151 the contents of which are incorporated by reference, be prepared using thermal processing of coalescence phenomena, e.g. as disclosed in US Patent No. 9235298 the contents of which are incorporated by reference, and/or formed using inkjetting techniques and inkjettable conductive inks such as AgCite™ available from Nano Dimension. The resistance of the conductive layer/s may be in the range of about 1000 to about 0.1 ohms/sq or about 300 to about 0.5 ohms/sq. The conductive layer/s may be formed from conductive organic material having a resistance of around 1000 ohms/sq to about 500 ohms/sq and / or a metal grid having a resistance of about 50 to about 0.5 ohms/sq.

Overall transparency of the signage stack (or at least portions thereof) prepared using the luminescent device stack may be an important requirement. For the avoidance of doubt, unless stated otherwise, where reference is made herein to the transparency of a layer, stack or other component, this should be understood as meaning transparency of that layer, stack or other component at least with respect to the frequency/ies of the emitted light.

The requisite level of transparency may be achieved by the use of transparent layers in the preparation of that stack. Thus, in one embodiment of the present invention, all layers disposed between the emissive luminescent layer (or hole transport layer, if present) and the upper surface of the signage stack are transparent. In embodiments, transparency of layers present in the signage stack can be achieved through the use of very thin layers. Thus, in embodiments of the invention, the hole transport layer (if present), the electron transport layer (if present) and / or the luminescent layer may have a thickness of less than about 0.5pm, less than about 0.2pm or less than about 0.1 pm.

Further, the anode layer and any anode conductive layer/s present may be transparent. In such embodiments, the cathode layer and any cathode conductive layer/s present may be transparent or alternatively may be reflective, opaque or retroflective.

Conversely, the cathode layer and any cathode conductive layer/s present may be transparent. In such embodiments, the anode layer and any anode conductive layer/s present may be transparent or alternatively may be reflective, opaque or retroflective.

Transparency of the anode layer, the cathode layer and / or the anode and / or cathode conductive layers may be achieved through any technique known to those skilled in the art. For example, they may be formed of a substantially or totally transparent material optionally provided with conductive organic or nano particles of e.g. metal, such as silver, such that the layer/s are not visible at human viewing distance.

In embodiments the transmission of light through the luminescent stack is greater than about 20%, greater than about 30%, greater than about 40%, greater than about 50%, greater than about 60%, greater than about 70%, or greater than about 80%.

As an alternative to ensuring that multiple layers in the signage stack of the present invention are transparent, the visual impact of layers in the stack, whether present as sheets, lines and / or grids, may be colored to match the portion of the luminescent device stack which is to be fixed to the receiver substrate. Additionally or alternatively, the luminescent device stack may be further subjected to one or more of the following measures: (i) in situ laser treatment of one or more of the layers present in the luminescent device stack (e.g. the luminescent layer, anode layer, cathode layer and / or hole transport layer) in non illuminating region/s of those layers (e.g. between portions of the signage stack configured to display graphic content), to disable or otherwise render those region/s non light emitting but leave them transparent and, if necessary, conductive (e.g. subtractive process), (ii) treatment of wiring regions (e.g. laser treatment or thermal transfer) if present, to introduce opaque material that emulates the appearance of the sign background / surface thus blocking light transmission and / or camouflaging the wiring regions, (iii) treatment (e.g. laser treatment) of areas covered by non transparent portions of conductive grids / lines (if present) to retain and / or increase light scattering thus making distinct (thin) lines less visible and / or (iv) providing conductive layers, if needed, in the form of full grids (i.e. which cover all of the portions of the electroluminescent device stack which are to be fixed to the receiver substrate), that are substantially transparent.

The anode and / or cathode layers (if present) preferably exhibit hole or electron release properties.

In embodiments of the invention, the electroluminescent device stack may additionally comprise charge generation and / or transport layers, such as hole transport and / or electron transport layers. Advantageously, the inclusion of hole transport and / or electron transport layers contributes to the efficient production of electroluminescence from the emissive electroluminescent layer. Examples of hole transport and electron transport layers which may be incorporated in the electroluminescent device stacks of the present invention are disclosed in US Patent No. 9093656, the contents of which are incorporated by reference. In embodiments of the present invention, a hole transport layer may be present. The function of the hole transport layer is to promote high efficiency of positive charge generation and / or transport. The construction and composition of the hole transport layer will be selected to meet the specific requirements of the anode and also the type of electroluminescent material in the emissive electroluminescent layer.

By way of example, where the emissive electroluminescent layer is an OLED layer, the hole transport layer may comprise additives and / or dopants which have a highest occupied molecular orbital (HOMO) of about -6 eV or higher, or about -5eV or higher, and / or a lowest unoccupied molecular orbital (LUMO) of about -2 eV or lower, about -3 eV or lower, or about -4eV or lower. Additives and / or dopants which can impact the HOMO / LUMO values will be known to those skilled in the art. Specific examples of additives and dopants which may be employed in the present invention are those comprising biphenyl or benzene groups.

Where the luminescent layer comprises quantum dots, the charge generation and / or transport layers (if present) may comprise organic and / or inorganic compounds such as those described in e.g. International Patent Publication No. WO2012/013272, the contents of which are incorporated by reference. Specific compounds that may be employed in charge generation and / or transport layers in the present invention include inorganic compounds selected from transition metal oxides, such as vanadium oxide, molybdenum oxide, ruthenium oxide and tungsten oxide.

As those skilled in the art will recognise, it is important to keep discrete electroluminescent device stacks separate from each other to prevent electrical shorting. To ensure separation of those stacks, especially at edges where transfer, fixing or in situ processing occurs, the use of hole transport, electron transport and / or passivating layers is contemplated to provide buffer function during the treatment (for example when a sign maker is separating or cutting the web and / or laying out the components of the sign), preparation and operation of a sign comprising the large scale portions of electroluminescent device stack. Such layers preferably have adhesive and flexible properties so that microcracking is prevented. In arrangements in which the luminescent device stack is an electroluminescent device stack, this emits light when activated. In terms of the quality of the emitted light, the electroluminescent device stack, in embodiments of the invention, may emit electromagnetic radiation in the range of about 350 nm to about 700 nm and / or provide ambient nighttime (nit) lighting levels of at least about 100 nits, at least about 150 nits or at least about 200 nits and/or luminance of at least about 10 cd/m², about 20 cd/m², about 30 cd/m², about 40 cd/m², or about 50 cd/m². Additionally or alternatively, the electroluminescent device stack exhibits luminance of less than about 300 cd/m², about 400 cd/m² or about 500 cd/m².

Additionally or alternatively, the luminescent device stack may be capable of near infra red emission (whether emitted by the luminescent layer itself or, for example, in embodiments in which the luminescent layer is non-emissive but the signage stack is used with an alternative light source), e.g. in the range of about 700nm to about 900nm, about 750nm to about 850nm or about 780nm to about 820nm. Such emission can be achieved, for example, through the use of a rutile ΤΊΟ2 emissive electroluminescent layer. The use of near infra red emission may be of interest for machine readable signage, e.g. by mobile phone or vehicular devices.

The luminescent device of the present invention produces high luminous intensity, among other benefits. Advantageously, those stacks may have higher density of luminescent material compared to the pixelated approach of conventional TVs and thus the graphic content is overall brighter.

In embodiments of the invention, the signage stack, the receiver substrate, the protector layer, the luminescent device layer or specific layers therein, such as the anode layer, the cathode layer, the conductive layers and / or the luminescent layer, may be modified (either in their entirety, or in predetermined regions) to modify their properties. Thus, the processes of the present invention may include the step of modifying the properties of one or more of the layers provided in the signage stack, the receiver substrate, the protector layer or the luminescent device layer. Such a modifying step may be carried out after the subject layer has been applied to a stack (i.e. the modification step may be carried out in situ) or prior to the layer in question being applied into a stack.

Additionally or alternatively, the modifying step may be carried out before the portion of luminescent device stack having a predetermined size and shape is fixed to the receiver substrate or after.

In embodiments of the invention, a plurality of modifying steps may be carried out on the same or different layers of the signage stack, the receiver substrate, the protector layer or the luminescent device layer.

An example of such a modifying step is patterning. Accordingly, the processes of the present invention may comprise the step of patterning one or more of the layers present in the signage stack, the receiver substrate, the protector layer and / or the luminescent device layer.

In such embodiments, one or more of the conductive layers may be patterned.

For example layers within the luminescent device stack and / or any conductive layers may be patterned in a predetermined manner depending on factors such as sign type, design and manufacturing method. In a particular arrangement, the conductive layers (if present) and the luminescent layer may be patterned in the same way such that all large scale objects in the sign are correspondingly arranged, meaning that (for emissive arrangements) power will be supplied for electroluminescence in those areas of the signage stack but the electrical link lines comprised in the conductive layer/s are not visible.

Patterning can be achieved using any technique known to those skilled in the art. One technique for achieving patterning of the luminescent device stack (or specific layers thereof) is for example via the selective deposition of some or all of the layers making up the luminescent device stack optionally according to a predetermined design.

Thus, the conductive layers of predetermined configuration may be deposited using e.g. FDM (fused deposition modelling) conductive pastes, be produced by laser thermal processing using suitable donor films, e.g. International Patent Publication No. WO2010/082151 the contents of which are incorporated by reference, by thermal processing of coalescence phenomena e.g. as in US Patent No. 9235298 the contents of which are incorporated by reference or by using inkjetting techniques and inkjettable conductive inks, such as AgCite™ available from Nano Dimension.

The resistance of the conductive layer may be in the range of about 1000 ohms/sq to about 0.1 ohms/sq or about 300 ohms/sq to about 0.5 ohms/sq. Additionally or alternatively, the conductive layer may comprise conductive organic material having a resistance in the range of about 1000 ohms/sq to about 500 ohms/sq and / or a metal grid having a resistance in the range of about 50 ohms/sq to about 0.5 ohms/sq. In embodiments, the luminescent device stack may be modified at the roll-to-roll manufacture stage. For example, the stack may be patterned, e.g. by printing the stack layers as dots or grids or lines as shown in Figure 5, optionally within a supporting polymer matrix so that a whole polymer transferable layer is achieved in which there are the patterned stacks, as seen in Figure 10a. This embodiment provides for additional protection of the stack during the interfacial fixing treatments to produce the large scale signs and afterwards during use during mounting at e.g. a shop front.

Additionally or alternatively, patterning of the luminescent device stack (or specific layers thereof) may be achieved by selective transfer using, e.g. thermal means.

As a further technique to achieve patterning of the luminescent device stack (or specific layers thereof), the layer/s in question may be selectively ablated and / or deactivated, e.g. using a laser and / or thermal means, to create a pattern in the luminescent device stack (either in its entirety, or in selected layers thereof) as desired. In such embodiments, for example, portions of the conductive layers and / or the exposed wiring regions (if present) may be modified to render them non conductive, thereby preventing them from being able to induce field effects in the emissive electroluminescent layer (and thus controlling the regions of the sign which, in use, will be emissive) but may still be transparent.

In embodiments of the present disclosure, deactivation and / or ablation means (e.g. a laser) may be employed to ablate away or otherwise deactivate predetermined regions of specific layers (e.g. the conductive layer/s, the luminescent layer, the hole transport layer, the electron transport layer and / or the anode and / or cathode layers) so that light is not emitted from these regions but will be emitted or luminesced from the non ablated / deactivated regions. Such a step may be carried out in situ (i.e. once the layer in question has been applied to a stack) or prior to application of the layer to a stack. In embodiments of the invention, where performed, the ablation and / or deactivation step/s may be carried out on one or more of the following layers: the luminescent layer, conductive layer, anode layer, cathode layer, hole transport layer and / or the electron transport layer. Such step/s should not undermine transparency of the layer/s being treated and / or should not cause fusion of the layer/s.

In arrangements of the invention in which the signage stack comprises a plurality of conductive layers in a grid or mesh configuration, the ablation / deactivation step, if performed, preferably ablates / deactivates regions of the conductive grid layers in situ.

Those skilled in the art will recognise that causing a change in the visual effect of the signage stack may be achieved by subjecting different layers to ablation / deactivation steps. In other words, there is a degree of choice as to which layer/s should be treated in this way to obtain the intended result. In embodiments of the present invention, the thickest layers of the conductive layer/s, anode layer, cathode layer and / or luminescent layer may be subjected to ablation / deactivation, optionally in situ. Thus, in embodiments in which the conductive layers (if present) are thicker than the emissive electroluminescent layer, the anode layer or the cathode layer, the conductive layers may be the most feasible layers to disable in situ.

Thus, the individual layers making up the luminescent device stack may have differing thicknesses, tailored according to the purpose of specific function for in situ sign optimising operations (e.g., ablation, dim out, patterning)

In addition to altering the visual effects of the signage stack, ablation / deactivation step/s may be deployed for functional purposes. For example, in embodiments of the invention, a portion of the protector layer and / or the receiver substrate may be ablated to expose a portion of one or more conductive layer (e.g. the anode conductive layer and / or the cathode conductive layer) and / or the cathode and / or anode layer. This may facilitate the connection of those layers to an electrical supply, which may be connected to the conductive layers and / or the anode and / or in cathode layers, for example using a conductive adhesive.

In embodiments of the present invention, one, some or all of the layers present in the signage stack, in the luminescent device stack, in the receiver substrate and / or the protector layer may be unpatterned.

As those skilled in the art will recognise, ablation steps of the type discussed herein may cause the production of vapour, dust or other debris. Accordingly, in the processes of the invention, any ablation step which is carried out may take place in a controlled environment, e.g. a room or a printer which may be provided with a filter, exhaust extraction or the like.

The process of the present invention may be conducted so as to prevent or minimise the liberation or formation of hazardous material which may arise during the process steps, such as of laser address, thermal address or cutting. Thus, the following may be carried out: (i) the construction and preparation of layers which when the material making up the layer is severed e.g., by printing, slicing, melting, do not create dust; (ii) use of nonconductive layers that melt and fuse when heated/severed (e.g. by thermal means during cutting), thereby being self sealing; (iii) use of safer (non toxic, for example cadmium free) versions of the components in, for example the luminescent layer and / or (iv) use of specific stable conductor materials, for example air stable graphene, titanium dioxide or zinc oxide as the cathode material.

A further example of a layer modifying step that may be carried out in the process of the present invention includes a step to improve barrier properties, for example to provide enhanced protection against the ingress of oxygen, moisture and / or other contaminants. This can be achieved by, for example (i) treatment (e.g. folding in, heated knife / stylus cutting / fusing and / or laser treatment) of the edges of the luminescent device stack (or at least layers thereof for example the luminescent layer, the anode layer (if present), the cathode layer (if present) and / or the hole transport layer (if present)) to seal them thus preventing or at least minimising the ingress of oxygen, moisture and / or other contaminants, (ii) treatment (e.g. folding in, heated knife / stylus cutting / fusing and / or laser treatment) of the luminescent device stack around the portion which is fixed on to the receiver substrate, before or after interfacial fixing, to prevent or at least minimise the ingress of oxygen, moisture and / or other contaminants and/or (iii) laminating the luminescent stack with protector layers such as SCOTCHCAL films, e.g. 8518, or BTF3, which may comprise a layer of adhesive, e.g. acrylic adhesive. The use of heat and / or laser treatment to carry out these sealing operations is advantageous as this results in polymerisation of polymeric material present, thus acting as a barrier. Such modifying steps may precede any cutting operations in order to prevent the ingress of oxygen, moisture and / or other contaminants and / or the liberation or formation of hazardous material which may arise during subsequent processing steps, for example cutting steps. Additionally or alternatively, the edges of the stack may have sealant and / or adhesive applied to them prior to, simultaneous with or following cutting, fusing, laser melting or ablation sealing of those edges.

One or more layers in the luminescent device stack, the protector layer and / or the receiver substrate may be subjected to treatment (e.g. laser treatment and / or thermal treatment, e.g. thermal embossing) to produce optical effects, such as prismatic or holographic effects. Such optical effects may be used, e.g. to create the impression of three dimensionality of the sign and the spatial relationship between the sign and the sign surface when viewed by a stationary or moving observer. Additionally or alternatively, one or more layers may be provided with additive or subtractive color e.g. nanopigment dots. A further step which may be carried out in the processes of the invention is to enhance the luminance of the signage stack, for example, by (i) laser treatment to modify the luminescent device stack (or parts thereof) for greater luminance/brightness, (ii) employing a highly reflective layer (for example a layer which may also be a conductive layer, e.g. aluminium) which may be disposed between the luminescent layer and the lower surface of the signage stack or the upper surface of the signage stack and / or (iii) including a one or more electroluminescent device stacks in the signage stack to increase light output. Additionally or alternatively, the luminescent device stack may be configured to direct the light in desired viewing angles (e.g., control the angular spread of light), vertically (e.g. from horizontal to slight vertical downward direction consistent with the normal viewing angle) and / or horizontally to the optimal field of view. This can be achieved by, for example (i) subjecting the luminescent device stack to treatment (e.g. in situ laser treatment) to modify its properties (e.g. to align the molecules or nano particles using the properties of laser coherence), (ii) subjecting a layer disposed between the upper surface of the protector layer and the luminescent layer to treatment (e.g. in situ laser treatment) to modify its properties, for example to create Fresnel and / or (iii) providing the luminescent device stack with effects that may be transferred by laser or thermal transfer or by cutting and laminating.

Doing so provides a number of advantages, for example improving brightness of the sign as viewed, increasing electrical efficiency and hence reducing electricity cost, improving luminance contrast (e.g. to improve visibility and legibility) and decreasing light pollution.

A further way in which one or more layers in the signage stack can be modified is via the process of "dimming out". The skilled person will be familiar with how such an effect can be created, and examples of such a process are disclosed in US Patent Publication No 2003/0214248, the contents of which are incorporated by reference. Dimming out of layer/s in the signage stack may be achieved through the use of laser energy. In such embodiments, the laser is operated at very short pulses, e.g. in the range of 50fs to about 10ps. Additionally or alternatively, the laser is operated at an energy density of about 1 J/cm² or less. In embodiments, the predetermined portion of the luminescent device stack (e.g. which may be disposed behind a non emissive colored layer or in a stack of a plurality of luminescent device stacks configured to emit light of different colors) may be dimmed. The degree of dimming may be selected to provide a desired intensity of emitted light. For example, dimming to provide less than about 90%, less than about 80%, less than about 70%, less than about 60% or less than about 50% luminous intensity may be effected. Embodiments in which a dimming effect have been deployed are described below.

As discussed herein, in embodiments of the present invention, the color of the light emitted from a signage stack may be controlled, partially or totally, through the use of additive color, such as different nano phosphor, quantum dot or OLED characteristics, or subtractive (filtered light) color. Additionally or alternatively, dimming may be applied to one or more luminescent device stacks included in the signage stack, if multiple luminescent device stacks are present. The dimming property may be applied by the sign maker to produce desired effects in the luminescent sign.

Those skilled in the art will recognise that color of light emitted or luminesced by the signage stack (i.e. that seen by viewers of the sign) will depend on, among other factors, the color of the light emitted or luminesced by the luminescent layer (or layers, if multiple layers are present), the order and area in which multiple luminescent layers are provided and / or the degree of dim out.

In embodiments of the present invention, partial or full dimming out may be applied to predetermined, selected portions of the signage stack to create multicolored visual effects.

For example, selected dimming out of the signage stack may be employed to provide a static posterised effect, a variable image effect (i.e., colors that may be changed by electrifying the specific regions of the signage stack separately and differently over time) and / or an image from dots to produce a photographic, optionally static effect.

In one embodiment of the present disclosure, a sign having luminescent regions of desired shapes and sizes may be prepared by (i) providing a consumable material comprising a complete signage stack which includes conductive layers in the form of a grid which provide power to different regions of the electroluminescent layers within the large scale sign, (ii) alternatively rendering the corresponding top and bottom portions of the conductive grid layers non conducting (by removing a region or just separating the region with a thin gap) and (iii) ablating away a band around the graphic, with the potential exception of the region/s in which electrical connectors are required.

Preparing a sign in this way advantageously permits the edges of the sign to be sealed (for example by heating and softening the edges with a laser, pressing the stack into the base, etc.) while minimising the risk of creating a short circuit or leaving conductive grid edges exposed.

The Transfer Substrate

As explained above, to facilitate fabrication and handling of the luminescent device stack and / or fixing of portions of the luminescent device stack to the receiver substrate, the luminescent device stack may comprise a transfer substrate. The transfer substrate may be interfacially fixed to the luminescent device stack.

Any material/s which is capable of maintaining integrity during the process in which the luminescent device stack is prepared may be employed in the present invention. These may be woven or non woven. The transfer substrate may comprise a stack of one or more layers. Examples of materials that may be employed as transfer substrates (or as layers within a transfer substrate in the form of a stack) in the present invention include polymeric materials such as vinyl polymers, polyester, paper, foil or the like and / or rigid materials such as aluminum, polycarbonate or Plexiglas.

The transfer substrate may have a thickness of at least about 2 microns, at least about 5 microns, at least about 10 microns, at least about 15 microns or at least about 20 microns. Additionally or alternatively, the transfer substrate may have a thickness of about 100 microns or lower, about 80 microns or lower, about 50 microns or lower, about 40 microns or lower or about 30 microns or lower. In certain embodiments, a transfer substrate having a thickness of greater than about 50 microns may be employed.

In embodiments of the invention, the transfer substrate may comprise two principal surfaces, one of which is fixed to the luminescent device stack. The other may be provided with an adhesive, e.g. a pressure sensitive adhesive, such as an acrylic adhesive comprising acrylic acid groups. The adhesive may be protected with a release liner. The transfer substrate may be transparent, translucent or opaque. Additionally or alternatively, the transfer substrate may be colorless, solidly colored or include a coloured pattern. Further, the transfer substrate may be transmissive, reflective or retroreflective.

Examples of suitable transfer substrates that may be employed in the present invention include those described in US Patent Publication No. 2002/0086914, the contents of which are incorporated by reference. Additional examples of transfer films that may be employed in the present invention include films commercialized by 3M Company under the trade names Panaflex, Nomad, Scotchcal, Scotchlite, Controltac and Controltac-Plus, the carrier films comprised in Kurz-Hastings or iiMak thermal transfer ribbons, and / or water vapour barrier films developed by companies such as Veeco, 3M, Lotus Applied Technology, Beneq, Encapsulix, Aixtron, Applied Materials, Vitex or Kateeva.

To provide protection to the stack, a film such as a Vitriflex all metal oxide barrier film or a UDC single hybrid organic / inorganic layer may be employed. Manufacturing of alternating organic / inorganic barrier layers may employ different sets of deposition methods, e.g. inorganic layers may be deposited using sputtering, ALD and / or PECVD and organic layers may be deposited using vacuum evaporation and / or inkjet printing. For other layer structures, sputtering may be employed, e.g. Vitriflex's metal-oxide film. There may be grading in the deposited layers, e.g. GE Graded UHB. Additionally, the transfer substrate may be provided with transfer facilitation materials. If present, these may be applied to a surface of the transfer substrate, or incorporated within that substrate. As an example, an infra red absorber may be employed as a transfer facilitation material for an luminescent device stack which is intended to be transferred on to the receiver substrate using (infra red) laser energy. The absorber will cause local heating when exposed to the laser radiation which will facilitate the transfer of the portion of the luminescent device stack having a predetermined size and shape.

Advantageously, the use of transfer facilitation materials, for example those comprising adhesive layers, such as those from acrylic and/or epoxy oligomers or polymers, minimise cracking of the luminescent device stack during transfer even when large scale portions of the stack are interfacially fixed to the receiver substrate.

A factor which will influence the choice of transfer substrate to be employed may be the means via which fixing of the luminescent device stack to the receiver substrate is effected. For example, if conventional cutting (of the full luminescent device stack), followed by lamination and / or use of laser energy is used to facilitate the fixing of the luminescent device stack to the receiver substrate, then a transfer substrate formed of a polymer such as vinyl polymer, having a thickness in the region of about 10 to about 75 pm may be used.

Alternatively, for thermal printhead fixing, the transfer substrate may be a polyester film or foil having a thickness in the region of about 10 to about 15 pm.

In an embodiment, the process of the invention comprises the step of providing the luminescent device stack comprising a transfer substrate, where the luminescent device stack is interfacially fixed to the transfer substrate. This step is carried out prior to the step of interfacially fixing the portion of the luminescent device stack to the receiver substrate.

To facilitate the interfacial fixing of the predetermined portion of the luminescent device stack to the receiver substrate, the luminescent device stack and optionally the transfer substrate as well may be cut in a predetermined pattern, and the unwanted portion of the luminescent device stack (and optionally a correspondingly shaped and sized portion of the transfer substrate) may be separated (or weeded) from the desired, large scale portion of the luminescent device stack of predetermined shape.

Fixing of the portion of the luminescent device stack to the receiver substrate may then be achieved by removing the release liner from the transfer substrate (if present) and adhering the transfer substrate layer of the luminescent device stack to the receiver substrate. Advantageously, in such embodiments, the transfer substrate additionally operates as a protector layer for the luminescent device stack. Alternatively, the transfer substrate may be sacrificial and merely used to facilitate fixing of the large scale portion of the luminescent device stack onto the receiver substrate before being disposed of. For example it may be separated using mechanical pressure or thermal energy from the luminescent device stack and disposed of.

The Receiver Substrate

In the present invention, a large scale portion of the luminescent device stack is fixed to the receiver substrate.

The receiver substrate, as its name suggests, is the substrate which receives the luminescent device stack, i.e. to which it is fixed.

The receiver substrate may be flexible (e.g. a plastic film, textile or the like) or rigid (e.g. a glass sheet, a polycarbonate or acrylic sheet, cardboard or the like).

The receiver substrate may be provided in the form of a stack comprising one or more functional layers, for example a barrier layer to provide protection to the luminescent device stack, an adhesive layer to facilitate adhesion to the mounting surface, a release liner to prevent premature exposure of the adhesive layer, a rigid / structural layer (e.g. an aluminum or a polycarbonate or Plexiglas sheet), a reflective layer to reflect light, an opaque layer to act as a light barrier, and / or a layer which directs light of a particular wavelength range in a particular direction. In a preferred embodiment, the receiver substrate is fabricated using roll-to-roll processing and / or is provided in roll form.

The receiver substrate may or may not comprise the mounting surface. In embodiments in which the receiver substrate does comprise the mounting surface, the functional layers will have been pre applied to the mounting surface, prior to fixing of the luminescent device stack to the receiver substrate. Thus, the process of the invention may comprise the step of applying functional layers of the receiver substrate to the mounting surface prior to fixing of the luminescent device stack to the receiver substrate.

In embodiments in which the receiver substrate does not comprise the mounting surface, fixing of the luminescent device stack to the receiver substrate takes place prior to the signage stack being mounted on the mounting surface. Thus, in such embodiments, the process of the invention comprises the step of mounting the signage stack on to the mounting surface, following the fixing of the luminescent device stack to the receiver substrate.

In a still further embodiment, the receiver substrate is the mounting surface. Thus, the luminescent device stack, for example if provided with all layers and components required to provide functionality, is fixed directly on to the mounting surface. The mounting surface may itself have a predetermined shape that may correspond to the predetermined size and / or shape of the luminescent device stack interfacially fixed thereto. Regarding the functional layers that may be comprised in the receiver substrate, the receiver substrate may be provided with one or more adhesive layers optionally provided with a release liner, to facilitate mounting of the signage stack on to the mounting surface. Examples of layers that may be comprised in the receiver substrate include those having two major surfaces, one to which the large scale predetermined portion of the luminescent device stack is fixed. The other may comprise pressure sensitive adhesive provided on it, or may comprise a further adhesive layer. In embodiments, the receiver substrate may have the adhesive layer on its upper and / or lower surface. The adhesive applied to the receiver substrate may comprise ligand groups such as carboxylic acid and / or amino groups. In such embodiments, the receiver substrate may additionally be provided with a release liner. Examples of films which may be employed as receiver substrates in the present invention are described in US Patent Publication No. 2002/0086914, the contents of which are incorporated by reference. Commercially available films known to those skilled in the art include films marketed by the 3M Company under the trade names Panaflex, Nomad, Scotchcal, Scotchlite, Controltac and Controltac-Plus, the carrier films comprised in Kurz-Hastings or iiMak thermal transfer ribbons, and / or water vapour barrier films developed by companies such as Veeco, 3M, Lotus Applied Technology, Beneq, Encapsulix, Aixtron, Applied Materials, Vitex or Kateeva.

To provide protection to the stack, a film such as a Vitriflex all metal oxide barrier film or a UDC single hybrid organic / inorganic layer may be employed. Manufacturing of alternating organic / inorganic barrier layers may employ different sets of deposition methods, e.g. inorganic layers may be deposited using sputtering, ALD and / or PECVD and organic layers may be deposited using vacuum evaporation and / or inkjet printing. For other layer structures, sputtering may be employed, e.g. Vitriflex's metal-oxide film. There may be grading in the deposited layers, e.g. GE Graded UHB. The receiver substrate may be clear, translucent or opaque, and / or may be colorless, solidly colored or provided with a colored pattern. Additionally or alternatively, the receiver substrate may be transmissive, reflective, retroreflective or absortptive. In embodiments in which a surface of the receiver substrate is provided with a pressure sensitive adhesive, these may be acrylic functional polymers e.g. EL8154 or siloxane polymers e.g. IS8026 or barrier rubber PSA EL-92734.

Additionally or alternatively to pressure sensitive adhesives, the receiver substrate may be provided with a hot melt adhesive (e.g. an ethylene-vinyl acetate hot melt layer), heat curing adhesives such as those comprising a pre made mixture of two or more components (e.g. thermoset epoxies, urethane acrylates and polyimides) and / or ultraviolet (UV) light curing adhesives. The organic materials of the various layers, e.g. the stack layers, conductive layers, the passivation layers, the barrier layers, etc. can have adhesive properties; for example organic materials, e.g. the plastics, can melt slightly and adhere to each other or other materials when exposed to heat or pressure.

In embodiments of the invention, the adhesive layer may be top coated or treated to improve the bond with adjacent layers in the receiver substrate.

The receiver substrate may also be provided with a release liner. This may comprise a web material (e.g. paper optionally having a release coating on at least one side) that can be easily removed to expose an adhesive layer, e.g. by peeling it away. Additionally or alternatively, the release liner may comprise a rigid material, e.g. cardboard, wood, metal sheeting, signboard or the like. In embodiments of the invention, the release liner may be resistant to being cut through.

In embodiments of the invention in which an electroluminescent layer is present, the receiver substrate may include a conductive layer, for example a cathode and / or an anode conductive layer. As mentioned above, the conductive layer may be provided in the form of line/s and / or grid/s, which may optionally be shaped to provide electrification to the large scale portion of the electroluminescent device stack to which the receiver substrate will be fixed. Additionally or alternatively, the conductive layer may be provided in sheet form. In embodiments in which the receiver substrate is provided with a conductive layer, the receiver substrate and electroluminescent device stack are preferably configured such that, following interfacial fixing of the electroluminescent device stack to the receiver substrate, the conductive layer in the receiver substrate is either (i) directly adjacent to the anode layer, the cathode layer, the cathode conductive layer (if present) or anode conductive layer (if present) in the electroluminescent device stack or (ii) separated from the anode layer, cathode layer, anode conductive layer (if present) or cathode conductive layer (if present) by a passivating layer. Such passivating layers keep the conductive layer separated and stable from the adjacent layers. In the case of scenario (ii), the passivating layer may be provided in the electroluminescent device stack or the receiver substrate.

In certain embodiments of the invention in which the receiver substrate comprises a conductive layer, this may be the anode conductive layer or cathode conductive layer.

A passivating layer (in addition to or in place of that mentioned above) may be provided in the receiver substrate in embodiments of the invention.

The primary purpose of the passivating layer is to cover any pinhole defects in the conductive layer and/or the other electroluminescent device stack layers, and to provide protection of these layers during storage, transport or treatment of the signage stack while signs comprising the large scale portions of luminescent device stack are made.

The passivating layer may have adhesive properties to enable adhesion or lamination between the conductive layer and the luminescent device stack. Thermoset or UV curable compositions may be used to produce the layer, for example acrylic and / or epoxy based passivating layers may be used.

The receiver substrate may comprise a barrier layer to prevent mechanical damage to and / or the ingress of oxygen, moisture and / or other contaminants into the luminescent device stack. The passivating and the barrier layer may be the same or different.

In embodiments of the invention, the receiver substrate may be opaque. Additionally or alternatively, the receiver substrate may comprise a reflective layer.

In alternative embodiments of the invention, the receiver substrate (excluding the release liner and mounting surface) may be transparent. In such embodiments, where a transparent receiver substrate is desirable and a conductive layer is present in that substrate, the conductive layer may be transparent. Transparency of the conductive layer may be achieved through any technique known to those skilled in the art, for example, it may be formed of a substantially or totally transparent material provided with conductive organic or nano particles of e.g. metal, e.g. silver, such that the layer/s are not visible at human viewing distance.

Additionally or alternatively, the thickness of the receiver substrate may be controlled so as to provide transparency. For example, the receiver substrate may be about 10 micron or less, 5 micron or less, 3 micron or less or 1 micron or less excluding the release liner or mounting surface, if present.

In embodiments of the invention, for example those in which the eventual sign is intended to comprise visually distinct and physically separate light emitting graphic content objects (e.g. the style of illuminated "channel letter" signs or of an illuminated version of cut vinyl letter signs), the receiver substrate may be subjected to a cutting step. Such a cutting step may be carried out before, during or after fixing of the portion of the luminescent device stack of predetermined size and shape to the receiver substrate. In embodiments, the receiver substrate may be cut such that it has a size and shape corresponding to the predetermined size and shape of the luminescent device stack. Alternatively, the size and shape into which the receiver substrate is cut may conform substantially to the predetermined size and shape of the luminescent device stack. However, it may additionally incorporate margins and / or other modifications which may optionally (i) facilitate the mounting of the signage stack on to the mounting surface, (ii) improve the adhesion of the signage stack on to the mounting surface, (iii) enable the formation of a protective moisture/oxygen barrier around the signage stack or at least the luminescent device stack and / or (iv) facilitate the electrification of the sign.

Cutting of the receiver substrate may be carried out by any means known to those skilled in the art. In embodiments of the invention, when the cutting is carried out, this may not result in cutting of the release liner (if present). This may be achieved by, for example, careful control of the depth of the cut and / or selection of a material for the release liner that is resistant to being cut through.

In embodiments of the invention, the receiver substrate cutting means may be an analog die or a computer controlled cutter. For example, the means may comprise a "vinyl cutter" or "vector plotter" which utilises a cutting tool e.g. a knife or stylus that is guided in accordance with design data. In embodiments, a computer-controlled machine that moves a sheet material, in a y-axis and a knife in an x-axis to produce a shape based on the co-ordinated (x,y) movement may be employed. In a variation, a flat bed cutting table may be used where the knife is vector driven over a sheet material.

One such apparatus that is produced for signmaking is a cutter marketed under the brand name "SignMaker" by Gerber Scientific Products, Inc. , features of which are disclosed in detail in US Patent No. 4467525 and US Patent No. 4799172, the contents of which are incorporated by reference.

Others include Gerber Scientific Products' "GS15" and "GSx Plus"™ cutters. Still other cutters include the following: folding carton sample maker (Misomex), matboard cutter (Wizard), laser sign-making cutter, or Sabre router as a drag- knife cutter, e.g. using a diamond-tip blade.

In embodiments of the present invention, the cutting means may comprise a heated cutting tool (e.g. , a heated knife or heated stylus), which (if cutting of the receiver substrate is carried out after fixing of the luminescent device stack to the receiver substrate) may (i) fuse the edges of the luminescent device stack to seal (or improve a preformed seal) preventing the ingress of oxygen, moisture and / or other contaminants into the luminescent device stack, (ii) ablate a gap along the contour of the luminescent device stack to prevent fusing / shorting of the conductive layers, the anode layer and / or the cathode layer and / or (iii) melt / fuse the luminescent device stack into the receiver substrate to improve seal.

Where a knife is used, this may be (or comprise) a blade having a single or double bevel edge, a chiseled edge or a modified chisel edge. Additionally or alternatively, the knife may be (or comprise) a pointed tip blade, a concave / hook blade, a formed blade, a multiple edged blade, a straight blade, a combination edge geometry blade, a scored strip blade, a convex / curved blade, a toothed edge blade or a circular blade. The knife may be part of larger cutting apparatus, for example a cutting wheel, a flatbed cutter or a plotter.

In embodiments of the invention, the cutting means may comprise a cutting laser. This laser may have a vector or a raster path. It may not only cut the outline, but it may also or alternatively ablate away the whole area of excess material (thus a separate weeding step to remove undesired parts of the luminescent device stack is unnecessary).

As those skilled in the art will recognise, cutting steps of the type discussed herein may cause the production of vapour, dust or other debris. Accordingly, in the processes of the invention, any cutting step which is carried out may take place in a controlled environment, e.g. a room or using a suitable cutting tool which may be provided with a filter, exhaust extraction or the like.

In embodiments in which the receiver substrate is subjected to a cutting step, following that step being carried out, a "weeding" step may be carried out in which the surrounding material is weeded away (i.e. stripped, removed) from the cut sizes and shapes leaving the cut size and shapes (which may correspond to graphic content, e.g. letters or graphics) leaving the portion of luminescent device stack of predetermined size and shape mounted on a cut receiver substrate.

The various shapes of the graphic content (e.g. characters and graphics) cut from the sign material may be mounted on the mounting surface as a group in fixed spatial orientation by overlaying the cut sections of graphic content (e.g. characters) with transfer medium (e.g. tape) that pulls and thus removes that graphic content characters from the release liner.

Details of how this step may be performed using a transfer medium are provided in US Patent No. 4467525 and US Patent No. 5026584, the contents of which are incorporated by reference.

Thus, in embodiments of the invention, the process may comprise the steps of

(i) fixing (of the portion of the luminescent device stack of predetermined size and shape to the receiver substrate), (ii) cutting (of the receiver substrate) and

(iii) weeding (to remove the unwanted portion of the receiver substrate). In alternative embodiments, these same three steps may be performed but in a different order; for example, cut-fix-weed; or cut-weed-fix. As explained above, such processes are particularly advantageous when the luminescent layer comprises nano particles such as nano phosphors (quantum dots), nano fluorescent particles with fluorescing dyes, nano metals and / or graphene nano flakes or graphene quantum dots as these enable cutting and weeding operations with the formation of clean edges and much reduced microcracks.

A fix-cut-weed process configuration advantageously provides (i) the ability to print registration marks, which might be useful in cut-to-print registration; and,

(ii) the opportunity to seal the marginal area around the luminescent device stack before cutting of the receiver substrate, so moisture and oxygen will not have the (limited time) access to an exposed edge as a result of the cutting process.

A cut-fix-weed configuration advantageously facilitates the printing of an added margin of protective layer material. The added margin permits fusing of the edges surrounding the luminescent device stacks to achieve edge encapsulation and protection of the edges of the stacks from the ingress of oxygen, moisture and / or other contaminants as well as the liberation or formation of hazardous material which may arise during subsequent processing steps, for example cutting steps.

A cut-weed-fix configuration potentially provides the lowest cost arrangement, as where the receiver substrate is cut and weeded in advance of the fixing of the luminescent device stack to it, the receiver substrate has a raised profile, and thus an imagewise transfer of the luminescent device stack can be achieved more simply, e.g. by using a heated plate to press the raised receiver substrate against the luminescent device stack. Although this configuration might lack the opportunity to print an additional/outer margin of protective layer material, a heated stylus or other implement might be used to provide edge protection.

In embodiments of the present invention, a treatment step to increase the adhesive bond between the release liner (if present) and the unused receiver substrate (i.e., the region not associated with the luminescent device stack) may be carried out (e.g. using laser and / or thermal treatment) so that the transfer means, when placed on the entire non weeded receiver substrate and then removed, will only strip away the used region of the receiver substrate (i.e., the region associated with the luminescent device stack) leaving behind the unused receiver substrate.

The Protector Layer

In embodiments of the invention, the signage stack is provided with a protector layer. This may be fixed directly to the luminescent device stack, or to an intermediate layer. In embodiments it is fixed directly to the luminescent layer.

The protector layer functions to protect the luminescent device stack from environmentally caused or surface degradation caused effects on the stack, during fabrication, transport, storage and use of the large scale signage stack.

The protector layer may be provided in the form of a stack comprising one or more functional layers, for example a barrier layer to provide protection to the luminescent device stack, an adhesive layer to facilitate adhesion to the mounting surface, a rigid / structural layer (e.g. an aluminum or a polycarbonate or Plexiglas sheet), a release liner to prevent premature exposure of the adhesive layer, a reflective layer to reflect light and / or an opaque layer to act as a light barrier. Additionally or alternatively, the protector layer may comprise a protector carrier to facilitate its fabrication, handling or transfer on to the luminescent device stack. In a preferred embodiment, the protector layer is fabricated using roll-to-roll processing and / or is provided in roll form.

The barrier layer is provided to serve as a barrier to protect the layers in the sign stack, especially those present in the luminescent device stack and any conductive layers present, against damage from environmental elements such as the ingress of oxygen, moisture and / or other contaminants. The accompanying figures depict various embodiments in which a barrier layer may be employed in the present invention, and how it may be applied.

For example, the barrier layer may be provided to be a mirror image of the portion of the luminescent device stack fixed to the receiver substrate. Alternatively or additionally, the barrier may be an envelope shape, having an additional margin extending beyond one or more edges of the luminescent device stack, thus surrounding the stack and protecting it from the ingress of moisture, oxygen and / or other contaminants. Upon application of the barrier layer to the luminescent device stack, the barrier layer may be positioned so as to cover the surfaces of the stacks as shown in Figures 6, 7, 8 and 10. The barrier layer may comprise a polymeric (organic) film (e.g. acrylic, epoxy and / or siloxane resins which may optionally be deposited by web coating, inkjet, etc., using formulations which are liquid and curable), a thin inorganic (e.g. glass) coating (which may be vapor deposited) or a combination of such organic / inorganic coatings.

The barrier layer preferably has low water and / or oxygen permeability. The barrier layer may comprise inorganic oxide coatings which can be applied, for example using an ALD process. Examples of films which may be employed as barrier layers include 3M FTB3 Barrier Film, Meyer Burger CONx TFE thin film, and / or films from Tera Barrier Films Pte Ltd, etc. The 3M FTB3-50 and FTB3- 125 films comprise a base polyester layer having a thickness of 50 to 125 microns with a very thin (less than 2 microns) barrier coating made up of layers of polymer and oxide. Additional examples of barrier layer films that may be employed in the present invention include films commercialized by 3M Company under the trade names Panaflex, Nomad, Scotchcal, Scotchlite, Controltac and Controltac-Plus, the carrier films comprised in Kurz-Hastings or iiMak thermal transfer ribbons, and / or water vapour barrier films developed by companies such as Veeco, 3M, Lotus Applied Technology, Beneq, Encapsulix, Aixtron, Applied Materials, Vitex or Kateeva.

To provide protection to the stack, a film such as a Vitriflex all metal oxide barrier film or a UDC single hybrid organic / inorganic layer may be employed. Manufacturing of alternating organic / inorganic barrier layers may employ different sets of deposition methods, e.g. inorganic layers may be deposited using sputtering, ALD and / or PECVD and organic layers may be deposited using vacuum evaporation and / or inkjet printing. For other layer structures, sputtering may be employed, e.g. Vitriflex's metal-oxide film. There may be grading in the deposited layers, e.g. GE Graded UHB.

In embodiments, the protector layer preferably has a moisture and/or oxygen permeability of less than about 10^"2 gm/m²/day, less than about 5 x 10^"3 gm/m²/day, less than about 5 x 10^"4 gm/m²/day, less than about 5 x 10^"5 gm/m²/day, or less than about 5 x 10^"6 gm/m²/day.

In embodiments, the luminescent device stack and the protector layer together preferably have a moisture and/or oxygen permeability of less than about 10^"2 gm/m²/day, less than about 5 x 10^"3 gm/m²/day, less than about 5 x 10^"4 gm/m²/day, less than about 5 x 10^"5 gm/m²/day, or less than about 5 x 10^"6 gm/m²/day.

In embodiments, a sign mounted onto a mounting surface and comprising the protector layer preferably has a moisture and/or oxygen permeability of less than about 10^"2 gm/m²/day, less than about 5 x 10^"3 gm/m²/day, less than about 5 x 10^"4 gm/m²/day, less than about 5 x 10^"5 gm/m²/day, or less than about 5 x 10^"6 gm/m²/day. In embodiments of the invention, the protector layer may be applied on to the luminescent device stack by methods known to those skilled in the art, for example vacuum deposition, spray coating, solution deposition, thin film deposition (e.g. e-beam deposition or sputtering), thermal and / or pressure transfer, laser deposition, printhead transfer, ink jetting, filament deposition, atomic layer epitaxy (ALE) or the like.

In embodiments in which the protector layer is applied on to the luminescent device layer using heat and / or pressure, a suitable device which may be employed is a laminating machine marketed under the brand name "SIGNMASTER" by Ledco Incorporated.

In the processes of the invention, the step of applying the protector layer on to the luminescent device stack may be carried out before or after a predetermined portion of the luminescent device stack is fixed to the receiver substrate.

In embodiments the application of the protector layer may be "full sheet", i.e. the protector layer is applied to the luminescent device stack such that it covers the entirety of that stack, around the stack and be attached to the receiver substrate. Additionally, the protector layer may comprise a small or extended margin, as may be required by the design features of the sign and cover the areas where electrification connections (which provide the power input to e.g. conductive layers) are made.

Alternatively, the application of the protector layer may be selective such that only selected regions of the luminescent device stack and / or the receiver substrate are covered by the protector layer. Such selective application may be imagewise, i.e. such that the portion of the protector layer which is applied corresponds to the predetermined portion of the luminescent device stack (with the possible exception of electrical connection points from the transfer of barrier material), and may also cover the conductive lines and / or grids.

The protector layer may comprise a protector carrier to facilitate its preparation, handling and / or transfer. In such embodiments, the protector layer may be transferred on to the luminescent device stack, using one or more of the techniques mentioned above. This step may be carried out before or after fixing of the luminescent device stack to the receiver substrate.

Where present, the protector layer may be conformable, i.e. such that it is capable of conforming around projecting regions of the luminescent device stack. In other words, the protector layer may be configured to conform round the individual components of the signage stack, optionally maintain the required low resistivity in the conductive layers, and seal the edges of that stack to prevent the ingress of oxygen, water and / or other contaminants. Furthermore, conformability of the protector layer also minimizes or eliminates problematic pockets of air which may form around the envelope shape. Thus conformability assists in extending the range of shapes which can be formed and minimises or ideally prevents the ingress of oxygen, moisture and / or other contaminants.

To facilitate such requirements, the protector layer may have overall low glass transition temperature (Tg) to impart flexibility (thus conformability) at the required operational temperatures. Epoxy, acrylic and/or siloxane polymers having flexibilising groups / additives may be used to provide such flexibility, as well as providing additional oxygen and moisture impermeability properties.

In embodiments of the invention, the protector layer may include a conductive layer, for example a cathode and / or an anode conductive layer. As mentioned above, the conductive layer may be provided in the form of line/s and / or grid/s. Additionally or alternatively, the conductive layer may be provided in sheet form.

In embodiments in which the protector layer is provided with a conductive layer, the protector layer and luminescent device stack are preferably configured such that, following application of the protector layer on to the luminescent device stack, the conductive layer in the protector layer is either (i) directly adjacent to the anode layer, the cathode layer, the cathode conductive layer (if present) or anode conductive layer (if present) in the luminescent device stack or (ii) separated from the anode layer, cathode layer, anode conductive layer (if present) or cathode conductive layer (if present) by a passivating layer. In the case of scenario (ii), the passivating layer may be provided in the luminescent device stack or the protector layer. In embodiments of the invention in which the protector layer is provided in a stack comprising a barrier layer and a conductive layer, that stack is preferably transferred on to the luminescent device stack such that the conductive layer and barrier layer cover and seal the luminescent device stack. In certain embodiments of the invention in which the protector layer comprises a conductive layer, this conductive layer may be the anode conductive layer or cathode conductive layer.

In embodiments of the invention, a passivating layer (in addition to or in place of that mentioned above) may be provided in the receiver substrate.

In embodiments of the invention, the protector layer (discounting the protector carrier) is transparent. In such embodiments, where a transparent protector layer is desirable and a conductive layer is present in that layer, the conductive layer may be transparent. Transparency of the conductive layer may be achieved through any technique known to those skilled in the art, for example, it may be formed of a substantially or totally transparent material provided with conductive organic or nano particles of e.g. metal, e.g. silver, such that the layer/s are not visible at human viewing distance.

Additionally or alternatively, the thickness of the protector layer may be controlled so as to meet the requirements of providing the necessary barrier function while maintaining transparency. For example, the thickness of the protector layer may be about 2 microns or less, about 1 micron or less, about 0.5 microns or less, about 0.2 microns or less or about 0.1 microns or less, excluding the protector carrier, if present.

In embodiments of the invention, the protector layer may be opaque. Additionally or alternatively, the protector layer may comprise a reflective or retroflective layer.

Commercially available films which may be comprised in the protector layer include films marketed by the 3M Company under the trade names Panaflex, Nomad, Scotchcal, Scotchlite, Controltac and Controltac-Plus. Suitable specific examples are barrier films such as 3M FTB3, or Graphic Protection Films 8518, 8519, 8520, 8914, 8528.

Additional examples of commercially available films that may be comprised in the protector layer in the present invention are marketed by Lintec Corporation under the product names MS-A thermal curing adhesive sheet or MS-lamination sheet.

Other examples of protector layers may comprise the barrier layers as mentioned in earlier sections.

The Conductive Layers

As explained above, in embodiments in which the luminescent device stack is electroluminescent, the electroluminescent device stack, the receiver substrate and / or the protector layer (if present) may be provided with a conductive layer (e.g. a cathode conductive layer and / or an anode conductive layer). The purpose of these layers is to deliver the requisite power for the conductive or field ionisation effects, which provide the holes and electrons whose combination in the electroluminescent device stack results in electrolum inescence.

The conductive layers provided in the signage stack of the present invention may comprise metals or their alloys (such as copper, aluminium, silver, gold tin, nickel, etc.) or compositions or dispersions comprising conductive materials such as indium tin oxide, zinc oxide, silver, copper, graphene flakes, gold particles, carbon tube particles, all suitably doped as required. Where present, the particulate components may be nanoparticulate. The conductive layers may be produced using any technique known to those skilled in the art, for example vacuum deposition or using compositions or dispersions of conductive particles. The conductive layers may comprise polymeric binders, formed of materials such as epoxy and / or acrylic polymers, which may themselves be conductive.

Resistivity in the conductive layers is less than 500 ohms/sq, less than 300 ohms/sq, less than 100 ohms/sq, less than 50 ohms/sq, less than 25 ohms/sq or less than 10 ohms/sq.

Flexibility may be required in such layers to provide layer conformability and reduction in microcracking of the layer during preparation of the electroluminescent device stack. Thus, the conductive layers may be provided with flexibilisers such as polyether polyols, polyester polyols, polyurethane polyols, etc. Alternatively, siloxane polymers may be used. Such molecules may impart flexibility properties of up to 10% elongation before break. The use of such flexibilisers may be particularly desirable when using higher loadings of particles in the conductive layer and especially as they may additionally assist with the dispersibility of such particles

The conductive layers advantageously retain their low resistivity in the processing steps and during and after any bending and / or flexing of the completed signage stack. In embodiments of the invention, the conductive layer comprises particles in an amount of about 2% or more, about 5% or more, about 10% or more, about 20% or more, about 30% or more, about 40% or more or about 50% or more by weight. Conductive layers, where present, may be patterned. For example the conductive layer/s may be provided in the form of grids and / or one or more lines.

In arrangements in which (i) the signage stack comprises a plurality of conductive layers and (ii) the conductive layers are in the form of grids and / or one or more lines, then the conductive layers may be offset with respect to each other to minimise the risk of any contact between those layers during the fabrication (e.g. cutting) and / or use of the signage stack.

For example, if the conductive layers comprise (optionally transparent) conductive lines, which connect to respective anode and cathode layers, the signage stack may be configured such that those conductive lines do not line up and instead run at different paths (selected to maximise efficiency of operation of the electroluminescent device stack).

In some embodiments, the conductive layers may be aligned in order to achieve the optimum electrification. Additionally, if the conductive layers comprise (optionally transparent) grids which connect to the respective anode and cathode layers, the conductive grids may be aligned. For example, the conductive grid could be run at different paths. In embodiments of the invention, the conductive layers are patterned during fabrication of the respective layer in which the conductive layer is disposed, e.g. the electroluminescent device stack, the protector layer or the receiver substrate. The conductive layer/s may be patterned using any technique known to those skilled in the art. For example, a conductive layer may be patterned by the selective deposition of suitable conductive material (e.g. in the form of paste, ink and / or films) during fabrication. Particularly useful are conductive tracks and/or patterns created by ink jetting suitable compositions of conductive ink onto the required surface of the receptor or transfer layers. Multi-jet arrays, such as the Fuji Dimatix printhead may be utilised, to jet e.g. nano silver or graphene containing conductive compositions.

The conductivity of the patterns may be adjusted according to the electrical requirements of the size of the large scale stack. For example, in a billboard application, there may be a mixture of static and/or dynamic graphic content of the individual stacks comprising different scale of size of the luminescent layer in the different shapes and thus different scale of conductivity may be required.

Additionally or alternatively, a conductive layer may be selectively transferred (or a prepatterned conductive layer may be transferred) e.g. using thermal means from a donor film to the electroluminescent device stack, the receiver substrate and / or the protector layer. A further example of how patterning of a conductive layer may be achieved in the processes of the invention is via the selective deactivation of a conductive web, for example by thermal means, such that the required pattern is created. Alternatively, selective activation may be achieved in a designed manner by e.g. causing agglomeration of dispersed conductive particles in a coating.

Thus, in embodiments of the invention, the process includes the step of applying a conductive layer (e.g. an anode and / or cathode layer) to the electroluminescent device stack, the protector layer and / or the receiver substrate, which conductive layer may be optionally patterned or prepatterned.

In embodiments of the present invention, the process comprises the step of applying an anode and / or cathode conductive layer to the electroluminescent device stack, for example, to the anode and / or cathode respectively, which conductive layer may be optionally patterned or prepatterned.

Additionally or alternatively, the process of the present invention may comprise the step of applying a conductive layer to the receiver substrate and / or the protector layer (if present), which conductive layer may be optionally patterned or prepatterned.

Application of the conductive layer/s may be achieved by applying conductive material, e.g. in the form of paste, ink and / or films, optionally at predetermined locations. In embodiments the conductivity in the patterns may adjusted according to the electrical requirements of the size of the large scale stack

For the avoidance of doubt, conductive layer/s, where present, may not necessarily be disposed directly adjacent to the anode or cathode layer. In embodiments, this may be the case; but in alternative embodiments, one or more additional layers may be disposed between the conductive layer and the outer surface of the anode layer and / or cathode layer. Passivating Layers

In embodiments of the present invention, the luminescent device stack, the receiver substrate and / or the protector layer may comprise one or more passivating layers. The primary purpose of the passivating layer/s is to protect the luminescent device stacks after fabrication. In embodiments of the invention, passivating layer/s, where present may exhibit one or more of the following properties: free of pin holes, highly even, highly smooth, flexible and durable to protect the luminescent device stack during transport and fixing to the receiver substrate. The passivating layer/s may also aid in the successful production of a defect / crack free luminescent device stack. In embodiments of the invention, a passivating layer may be disposed between the cathode layer and the cathode conductive layer and / or between the anode layer and the anode conductive layer. Additionally or alternatively, a passivating layer may be provided between all conductive layers present in the signage stack.

Advantageously, the inclusion of a passivating layer facilitates patterning of the layers present in the stack, minimising the risk of damage to the luminescent device stack. Additionally, the use of passivating layers protects the conductive layers during manufacture.

In embodiments, the passivating layers exhibit latent conductivity. Thus, such passivating layers may have high resistivity after deposition and following laser or thermal treatment, may then have lower resistivity preferably corresponding to the resistivity of the conductive layers.

In embodiments of the invention, a passivating layer may be positioned between either the cathode and / or the anode, and its respective conductive layer (where present). In such embodiments, the passivating layer preferably is of sufficient thinness to permit the conduction of electrical energy from the conductive layer/s through to their respective anode or cathode, while still protecting the luminescent device stack. In embodiments of the invention, the passivating layer/s used may have a thickness of about 500nm or less, about 400nm or less, about 300nm or less, about 200nm or less or about 100nm or less. Additionally or alternatively, the passivating layer/s used may have a thickness of about 10nm or more, about 50nm or more or about 100nm or more. The passivating layer/s, where used, are preferably conformable such that they can integrate more intimately to the anode and / or cathode conductive layers, the anode and / or cathode layers and/or any additional conductive layers, e.g. upon the application of pressure and / or heat.

The passivating layers may comprise polymeric binders, formed of materials such as epoxy and / or acrylic polymers or siloxane polymers which may themselves be made conductive using conductive particles.

In embodiments, the passivating layers exhibit latent conductivity. Thus, such passivating layers may have high resistivity after deposition and following laser or thermal treatment, have lower resistivity preferably corresponding to the resistivity of the conductive layers.

Flexibility may be required in such layers to provide layer conformability and reduction in microcracking of the layer during transfer to the luminescent device stack. Thus the passivating layers may be provided with flexibilisers such as polyether polyols, polyester polyols, polyurethane polyols, etc. Alternatively siloxane polymers may be used. Such molecules may impart flexibility properties of up to 10% elongation before break.

Passivating layers useful in the present invention may comprise acrylic polymer and / or may have thermal adhesive properties permitting seam free fixing of the luminescent device stack to the receiver substrate.

Color and / or Light Management Layers

In embodiments of the present disclosure, the signage stack may comprise a color and / or light management layer. Such layer/s may be provided in the luminescent device stack, the receiver substrate and / or the protector layer. An advantage of employing a colored layer in the luminescent device stack and / or the protector layer is that light can be displayed in a specific color, providing a simpler and economic manufacturing option (through use of an luminescent device emitting white light) and roll-to-roll feedstock construction.

In embodiments in which a color layer is provided in the signage stack, this may comprise a polymeric dye and / or dispersed nano color pigments. The color layer may be provided in the luminescent device stack and / or the protector layer. The color layer preferably provides greater than about 80%, greater than about 85%, greater than about 90% or greater than about 95% transmittance for a selected color profile, e.g. a selected wavelength or a graphic image.

In embodiments of the invention, one or more layers within the signage stack may be colored using the techniques disclosed in US Patent No. 6002416, the contents of which are incorporated by reference. The colored layers, where present, may comprise additive and / or subtractive colorant material.

These colored layers may include various dot patterns and speciality effects such as prismatic and holographic features.

Such speciality effects may be non colored.

The signage stack may be configured to manage light in a predetermined manner. For example, the signage stack may be configured to direct the light into desired viewing angles (e.g. control the angular spread of light), optionally vertically (e.g. from horizontal to slight vertical downward direction consistent with the normal viewing angle) and / or horizontally to the optimal field of view.

In embodiments of the invention, the luminescent device stack may be treated to improve light output (e.g. it may be annealed and / or directionalized). In such embodiments, the treatment may be effective to mean that the x axis has a first viewing angle (e.g. at least about 60°, at least about 90° or at least about 120°) and the y axis has a second viewing angle, which may be less than the first viewing angle of the x axis (e.g. at least about 15°, at least about 30° or at least about 45°) from a plane parallel to the signage stack.

Light management can be achieved by, for example (i) subjecting one more layers (e.g. a layer in the luminescent device stack and / or the protector layer) to treatment (e.g. laser treatment, potentially in situ) to modify its properties, for example to create Fresnel and / or (ii) providing one or more layers within the signage stack (e.g. within the luminescent device stack or the protector layer) with built in effects. Such techniques advantageously may improve edge sharpness/contrast of signs, reduce the edge glow and thus create crisp distinctions, improve luminance contrast between graphical size and shapes and improve the clarity and legibility of the graphic content displayed in the sign message. A further advantage which can be provided through the use of the light management techniques discussed herein is that, in some arrangements, the blurring of light may be desirable in certain situations, for example where two separate portions of luminescent device stack collectively display a single item of graphic content and their edges need to be seamed together.

One light management technique that may be employed in the present invention is patterning of the luminescent device stack, e.g. by introducing dots or grids. This patterning may also facilitate transfer of the stacks (or at least of layers therein) and provides crisp distinctions, improves luminance contrast between graphical size and shapes, and improves the clarity and legibility of the graphic content displayed in the sign. Figure 10 illustrates one such patterned stack, where the anode-electroluminescent-cathode pattern stack is in a polymer matrix.

Additionally or alternatively, light management may be achieved through the provision of one or more functional light management layers, e.g. layers having light guiding, light polarising, reflecting, absorbing and / or other light management effects. Where present, the light management layers may be provided in the luminescent device stack, the protector layer and / or the receiver substrate. For example, a light management layer having light guiding and / or light polarising effects may be provided in the luminescent device stack and / or the protector layer such that the light flow emitted to the exterior beyond the protector layer is managed, while a reflective light management layer may be provided in the receiver substrate.

In other words, in embodiments of the invention, at least one layer disposed between the luminescent layer (comprising a hole transport layer, if present) and the bottom surface of the signage stack is reflective, retroflective or at least opaque. In such embodiments, the layers intermediate of the reflective / opaque layer and the luminescent layer (comprising a hole transport layer, if present) are transparent (at least with respect to the frequency of the light).

In an alternative embodiment, at least one layer disposed between the luminescent layer (comprising a hole transport layer, if present) and the upper surface of the signage stack is reflective, retroflective or at least opaque. In such embodiments, the layers intermediate of the reflective / opaque layer and the luminescent layer (comprising a hole transport layer, if present) are transparent (at least with respect to the frequency of the light).

Where present, the light management layer/s may be applied singly or as a stack on to the luminescent device stack, the protector layer and / or the receiver substrate. For example, Figure 12 depicts an example of a composite sign to achieve custom color comprising red, blue, green emitting stacks and light management layers to provide a custom designed emission color output from a sign which has also the desired shape and size. Each of the emitting stacks may be individually controlled so that the intensity of light emitted therefrom can be varied, e.g. by modulating the power supplied to it as to dynamically tune the overall color, e.g. to change the appearance of the graphic content displayed for aesthetic reasons or to compensate for ambient light changes. The use of light management layers is advantageous as this can also improve brightness of the sign as viewed, increase electrical efficiency and hence reduce electricity cost, improve luminance contrast (which is key to legibility), and decrease light pollution by utilising selected light of a certain light frequency, among other advantages.

As discussed elsewhere herein, some or all of the layers comprised in the luminescent device stack, the protector layer and / or the receiver substrate may be patterned, to incorporate a predetermined design. Additionally or alternatively, light management may be achieved through the use of a light channeling layer and thus, in one embodiment of the invention, the signage stack may be provided with a light channeling layer. Such a layer may be provided in the receiver substrate, the luminescent device stack and / or the protector layer and is preferably flexible.

Additionally or alternatively, light management layers, such as the light channeling layer, may be provided external of the signage stack (i.e. not comprised within the signage stack) of the invention, but may be used with that stack as a separate component (e.g. in a sign holder), to optimise the performance of the stack.

As those skilled in the art will recognise, light channeling layers can be used to maximise luminance and reduce diffusion. Light emitting signs generally must be brighter in daylight to stand out from competing distractions and to avoid appearing "washed out". Advantageously the higher intrinsic luminosity available via the use of thin luminescent device stacks, especially using quantum dots, may be utilised more efficiently by integrating the stacks with light channeling layers. Furthermore, the ready availability of a variety of nano phosphors, e.g. quantum dot materials, enables selection of optimal coloring for use in prevailing ambient conditions, for example to prevent washed out colors.

In embodiments of the invention, the light channeling layer comprises microstructuring. Examples of flexible, microstructured films are disclosed in US Patent No. 4906070, the contents of which are incorporated by reference. Additionally or alternatively, a layer comprised in the signage stack (for example in the luminescent device stack and / or the protector layer) and / or used with the signage stack may be treated to render it microstructured. In embodiments, the microstructuring guides light preferentially through the imaged areas.

The nature of the microstructuring can be selected depending on the intended use of the signage stack and / or its configuration. In US Patent No. 4497860 (the contents of which are incorporated by reference), imaged microprismatic films, created using thermal embossing are disclosed. Such processes may be employed in the process of the present invention to produce microstructuring. Additionally or alternatively, the microstructuring of a layer to be incorporated in and / or used with the signage stack of the invention may be achieved by inkjetting or filament layering In embodiments of the invention, the light channeling layer may comprise an imaged layer, i.e. a layer having an image (for example a transparent image) corresponding to the graphic content to be displayed (e.g. the graphic and / or letters of the sign or, in other words, the predetermined portion of the luminescent device stack). The imaged layer may additionally be microstructured. Conversely, the microstructured light channeling layer may be imaged. In embodiments, the light channeling layer may comprise both a microstructured layer and an imaged layer.

In embodiments in which an imaged layer is employed, this may be provided as part of the signage stack, or provided separately for use with the signage stack.

In certain embodiments in which a microstructured light channeling layer is provided in and / or used with the signage stack, the microstructured light channeling layer may have one smooth (i.e. unstructured) surface and one structured surface. In such embodiments, the layer may be provided such that the microstructured surface faces the luminescent layer.

The microstructured light channeling layer may be configured to channel light in a range of directions. For example, the microstructured light channeling layer may be configured to channel light towards the portion of the luminescent device stack which will be fixed to the receiver substrate. Additionally or alternatively, the microstructured light channeling layer may be configured so as to channel light towards the portion of the luminescent device stack having a predetermined size and shape (i.e. a graphic or character of the sign), so as to provide even or graded brightness across that portion, when the electroluminescent device stack is activated or when light is provided to the luminescent layer by a light source. Configuring the microstructured light channeling layer in this way provides greater design flexibility to manipulate the quality and / or texture of light being displayed and can improve the evenness or non evenness of light as is required.

Additionally or alternatively, there may be a microstructured or reflective image provided on the opposite surface to the microstuctured surface in the microstructured light channeling layer, which microstructured or reflective image corresponds to the portion of the luminescent device stack of predetermined size and shape (i.e. a character or graphic), thus further channeling light into the desired region of the sign. In such an embodiment, the microstructured light channeling layer may be arranged such that the microstructured or reflective image faces away from the luminescent layer.

In such an embodiment, the microstructured or reflective image may advantageously guide light from the exterior of the sign (when in use) such as sunlight or light from car headlights, and channel this to increase the luminescence of the sign.

Additionally, the microstructured light channeling layer may advantageously channel the image light into specific viewing angles, thus rendering the light visible from only selected angles.

The microstructured light channeling layer may additionally comprise fluorescing nano phosphors, such as fluorescing dyes entrained or embedded into nano particles of various matrixes, which will beneficially provide secondary light via capture of the luminescent emission. Examples of fluorescing nano phosphors are disclosed in US Patent Publication No. 2017/137626, the contents of which are incorporated by reference.

The luminescent device stacks of the present invention are especially well suited for use in analog and/or digital signage (whether static or dynamic). This is because they (i) draw light from around, between, and inside letters and other graphic content and (ii) maintain high luminance contrast, because portions of the sign that don't comprise the sign message absorb rather than reflect light. Additionally, in embodiments, the luminescent device stacks may also be employed in dynamic digital signage. The use of a light channeling layer renders the signage stack particularly appropriate for such applications. For example, the signage stack may be provided with a fully dynamic emissive electroluminescent display and a border having light channeling properties (for example provided by a light channeling layer having microstructuring around its border). The border may be configured to collect light (e.g. from the external surroundings of the sign) and channel that light to the display area.

As explained above, the use of a light channeling layer may increase the emission of light. Thus, in embodiments of the invention, the light emitted per unit of area (e.g. cm²) from the luminescent layer may intrinsically be lower than the light emitted from a corresponding unit of area of the luminescent layer and the light channeling layer. While the skilled person may be aware of light channeling layers and light channeling techniques that can be employed in the present invention, examples of such approaches are provided in International Patent Publication No. WO2002/037568, the contents of which are incorporated by reference, which focusses on minimising the total internal reflection of light, thus increasing the brightness of emitted light.

Light channeling layers may be employed in the present invention to achieve a similar goal; the collection and channeling of internal reflected light to regions where the light will be emitted.

Further examples of disclosures which discuss light channeling can be found in US Patent No. 8222804, US Patent No. 6366017 and US Patent No. 5834893, the contents of each of which are incorporated by reference.

Another type of light management layer that may be employed in the present invention is a monodirectional or dichroic layer. The skilled reader will understand that such layers control light transmission (e.g. as a result of perforations / patterning) and only permit light to pass in one direction therethrough. Such layers can therefore be considered to have an opaque surface (i.e. a surface which, if exposed to light, will not permit the transmission of light) and a transparent surface (i.e. a surface which, if exposed to light, will permit the transmission of light). US Patent No. 8136278, the contents of which are incorporated by reference, describes an electroluminescent one-way vision lamp using phosphor inks.

Where used, the monodirectional layer may be located between the lower surface of the signage stack and the receiver substrate. Alternatively, the monodirectional layer may be located between the upper surface of the signage stack and the protector layer.

In embodiments of the invention, one surface of the monodirectional layer is dark colored (e.g. the opaque surface) while the other is lighter (e.g. the transparent surface). In embodiments of the invention in which such layers are employed, the transmission of light through the opaque surface of the monodirectional layer is less than about 50%, less than about 40%, less than about 30%, less than about 20%, less than about 10% or less than about 5% of the transparency through the transparent surface of that layer. In practice, a pattern of opaque and transmissive areas has been found effective with the opaque pattern having an opaque surface and a reflective surface.

In embodiments, the monodirectional layer may be produced by ink jet printing and precision deposition techniques. This may be achieved, for example, through the use of an array ink jet printhead, where the required patterning is produced on a transparent receiver substrate in a roll to roll production mode. Precision deposition is required for the quality production of the monodirectional pattern, which comprises solid dots or squares or stochastic shapes within a transmissive substrate and provides the required visual properties on the surfaces, i.e. opaque on one side of the solid pattern and reflective on the other side, while being transmissive in-between the solid pattern.

Additionally, such precision deposition for patterning may be useful, not only for the preparation of one-way directing layers, but also to pattern the luminescent layer so that there is efficiency in usage of the specialist luminescent materials, e.g. nano phosphors such as quantum dots, OLEDS etc.

In embodiments of the invention, ink jet and precision deposition techniques, such as an array inkjet printhead, may used where the required one-way vision patterning and the luminescent layer, optionally also patterned, is produced on a transparent receiver surface, in a roll to roll production mode. The inkjet inks may be thermo and / or light curable and will be of different compositions according to the type of pattern. Thus, for the one-way directing pattern, the inks may be white or reflective (containing e.g. titanium oxide pigments), and black or absorbing (containing carbon black) in e.g. epoxy and/or acrylic resin compositions, whereas the inks for the luminescent layer (or pattern) may be a quantum dot, e.g. InP core shell colloid with oleic acid ligands in carrier such as hexane, octane and / or water. Such monodirectional or dichroic layers may be advantageously employed in arrangements in which signage is required which is visible from one side, and invisible or slightly visible from the opposite side. For example, in an otherwise transparent signage stack adhered to the window of a shop, the use of a monodirectional layer, arranged such that the black surface of the pattern faces towards the interior of the shop to enable people within the shop to look through the sign. However, as the reflective surface of the monodirectional layer will face the exterior of the shop, the sign will be opaque with regard to people outside the shop looking at the sign and thus the interior of the shop will not be visible from the outside, though the emissive sign is highly visible to those outside of the shop.

In such an arrangement, the monodirectional film may be provided between the upper surface of the signage stack the protector layer or between the lower surface of the signage stack and the receiver layer, depending on which side is desired to be visible.

Dichroic layers employed in the present invention may be produced comprising a patterned layer e.g. one in which the pattern consists of dots (e.g. half tone or stochastic) which are transmissive, interspersed within an opaque (e.g. white) or reflective surround, or vice versa. Examples of configurations of this type are disclosed in US Patent No. 851 1884, the contents of which are incorporated by reference. Alternatively, the dichroic surface employed in the present invention may be produced by ultra thin and anisotropic layered films where the refractive index is different between the ultra thin layers making the dichroic surface. An example of such a surface is disclosed in US Patent No. 6967778, the contents of which are incorporated by reference.

An additional example of an light management layer which may be employed in the present invention is a polarising layer. A polarising layer may comprise patterning, e.g. closely spaced transmissive or reflective parallel lines. For the avoidance of doubt, in embodiments of the present invention, layers may be selected to serve multiple functions. For example, a layer may function as both a colored layer and a light management layer. Additionally or alternatively, a given layer may function as both a light channeling layer and a moisture barrier. The use of such multifunction films is advantageous as this may permit a multifunctional stack having a reduced number of separate layers (and thus potentially thinner, lighter, more flexible and less costly) to be produced. Software

As will be recognized by those skilled in the art, aspects of the present invention are suitable for control by computer means, for example patterning step/s and particularly the design of the pattern to be applied (e.g. for non sheet form conductive layers) and / or transfer step/s particularly the design and predetermination of the portion of the luminescent device stack to be fixed to the receiver substrate. Thus, according to a further aspect of the present invention, there is provided computer software for programming, controlling and / or implementing the process of the present invention. In one embodiment, the computer software is configured to design a signage stack configuration on the basis of user requirements, for example regarding the configuration required to produce specific emitted colors or combinations thereof.

In such an embodiment, the computer software is configured to design the layout and configuration of conductive layer/s (if present), the anode layer (if present), the cathode layer (if present), and the luminescent layer, and optionally control the apparatus to implement those designs.

Additionally or alternatively, the computer software is configured to design the layout and configuration of the receiving substrate, the transfer substrate (if present), the protector layer and / or any of the light management layers (if present) and optionally control the apparatus to implement those designs.

The software is configured to optimise the layout and configurations of different sign designs, to minimise waste (e.g. film, web, stack layers).

Further, the processes of the invention may include the step of designing a sign, which typically will be carried out prior to the step of fixing the portion of the luminescent device stack of predetermined size and shape to the receiver substrate. Preferably, the step of designing the sign will be carried out on control means such as a computer, tablet or the like and the control means will generate design and preproduction data and control the luminescent device stack fixing means (i.e. the means used to effect the step of fixing the portion of the luminescent device stack of predetermined size and shape to the receiver substrate). Thus, in such an embodiment, the predetermination of the size and shape of the portion of the luminescent device stack to be fixed to the receiver substrate will be made by the control means. An example of software which may be employed in the present invention to design signage and thus predetermine the size and shape of the portion of luminescent device stack to be fixed to the receiver substrate is marketed under the brand name "Illustrator" by Adobe Systems Incorporated. Control / Electrification Features

In embodiments of the present invention, touch controls or specific light stimulation controls facilitating the operation of the emissive electroluminescent layer or other light sources and thus the illuminated display of graphic content or the selection or programming of graphic content that may be displayed (e.g. changing the analog graphic on the sign) is envisaged. Accordingly, in embodiments of the present invention, the signage stack may be provided with a touch active layer and / or film, e.g. as disclosed in US Patent No. 8294843, the contents of which are incorporated by reference.

In certain embodiments, the signage stack may be provided with an electrical connector. Those skilled in the art will be familiar with the types of connector that may be usefully employed. Examples of such connectors are disclosed in US Patent No. 7888861 , the contents of which are incorporated by reference. Circuitry for achieving optimum electroluminescence may depend on the construction of the electroluminescent device stack. In certain embodiments, alternating current may be preferable as this can deliver efficient and stable performance of the emissive electroluminescent layer.

US Patent No. 8136278, the contents of which are incorporated by reference, provides background guidance regarding the electrification requirements of electroluminescent light sources.

In certain embodiments, the circuitry and associated drivers are designed to deliver the appropriate current / voltage for operation of both static and digital dynamic content of the signage stacks. For example the shopfront sign or billboard sign may have, made from the device stacks, large area static sign letters and have also large area dynamic digital signs. Such dynamic digital signs may comprise large area dots, squares, random shapes, of stacks, having size 100pm² or greater, about 200pm² or greater, about 500pm² or greater, about 1 cm² or greater, about 2cm² or greater, about 5cm² or greater, about 10cm² or greater, about 20cm² or greater, about 50cm² or greater or about 1 m² or greater.

In embodiments of the invention, the conductive layers, the anode layer and / or the cathode layer may be attached to an electrical supply before or after fixing of the portion of the electroluminescent device stack to the receiver substrate.

The connection between the conductive layers, the anode layer and / or the cathode layer and the electrical supply can be made by accessing the conductive layers, the anode layer and / or the cathode layer via the protector layer and / or the receiver substrate. For example, the electrical supply connectors can be sealed / molded into the protector layer and / or the receiver substrate. Suitable protector and / or receiver layers include those that are effective to minimise or ideally prevent the ingress of moisture, oxygen and / or contaminants. Examples of films that may be employed as barrier layers in the present invention include 3M FTB3, Meyer Burger CONx TFE thin film and / or films from Tera Barrier Films Pte Ltd.

In embodiments, conductive lines and / or grids joining separate portions of electroluminescent device stack which are transferred to the receiver substrate can be attached at the time the signage stack is connected to an electrical supply and then sealed / molded into the protective layer and / or receiver substrate. Such conductive lines and / or grids may be designed and applied (e.g. by printing) on to adjacent layers in the luminescent device stack, the protector layer and / or the receiver substrate such that, upon interfacial fixing of the luminescent device stack onto the receiver substrate a sign comprising several shapes may be provided and have relay electrical energy from the power source to the emissive electroluminescent layer.

Light Harvesting

The present invention also permits the integration of large-scale luminescent signs with light harvesting (solar) layers to produce integrated luminescent signage displays which also function as light harvesting devices. According to a further aspect of the present disclosure, there is provided a light harvesting article comprising one or more large scale static light harvesting characters or shapes, comprising an active photovoltaic device stack comprising (i) an anode layer having an outer surface and an inner surface and (ii) a cathode layer having an outer surface and an inner surface, the anode layer and cathode layer having a photovoltaic active bilayer disposed between the inner surface of the anode layer and the inner surface of the cathode layer; and a base layer onto which the light harvesting device is mounted.

The photovoltaic active bi-layer may be made of organic or inorganic semi- conducting materials, with suitable photo hole and photo electron producing and transport properties. Nano particles of, e.g., lead sulfide PbS may be used. Graphene conductive layers may be used, as, e.g., described in US9401489 (the contents of which are incorporated by reference) for graphene in solar film application

Thus a roll to roll fabrication of a stack of layers comprising the anode-bi layer photovoltaic-cathode stack may be utilized in the methods described in this application to produce large scale light harvesting films / decals having different shapes or conformability to any receiving surface.

Such light harvesting decal to produce electricity has appropriate wiring formats to enable use in variety of ways, e.g., storage in a battery, charging a mobile device, powering an EL device, etc.

Furthermore, using the method described herein, light managing layers may be readily integrated with the light harvesting stacks in order to focus, etc. the light being harvested.

Additionally, while various embodiments have been described herein, it will be appreciated by those of ordinary skill in the art that modifications can be made to the various embodiments without departing from the spirit and scope of the present disclosure as a whole. Accordingly, the particular embodiments described in this specification are to be taken as merely illustrative and not limiting.

Figures

Description of Figures

Figure 1 - Main types of illuminated signs: channel letter (top), masked cabinet (middle); standard cabinet (bottom)

Figure 2 - Electroluminescent device stack of the present invention

Figure 3 - Signage stack of the present invention

Figure 4 - Device fabrication process

Figure 5 - Exploded view of transfer substrate and electroluminescent device stack Figure 6 - Whole layer transfer of protective layer

Figure 7 - Whole layer transfer of protective layer

Figure 8 - Imagewise transfer of electroluminescent device stack

Figure 9 - Signage stack with multiple emissive electroluminescent layers Figure 10a - Patterned signage stack

Figure 10b - Custom color using patterned signage stack with different stack areas

Figure 1 1 - Barrier layers for protection of rolls

Figure 12 - Example of a composite sign comprising different sign stacks and light channeling layers.

The invention will now be described with reference to the following examples.

Examples

Example 1 : Construction of Electroluminescent Device Stack

The electroluminescent device stack of the present invention is illustrated in Figure 2. The illustrated stack comprises an emissive electroluminescent layer and a contiguous hole transport layer, together interposed between an anode layer and a cathode layer so that the application of voltage produces light emission. The construction comprises a capacitor (not shown). The luminescent layer between the anode and cathode is a nanophosphor that gives off photons when the capacitor is charged. By making at least one of the anode or cathode layers transparent, a large area can be made to emit light in one or both directions. Transparency is preferable also in the hole transport layer if the anode is the transparent electrode.

In this illustrated arrangement, the emissive electroluminescent layer does not include individually addressable matrices of micro pixels as are found in dynamic digital displays for video presentation. However, the electroluminescent device stack may be patterned as shown in Figure 10a to provide electroluminescence from a pattern structure of electroluminescent device stacks within a large scale sign. Accordingly the displayed content is substantially static and is analog, rather than dynamic or digital in nature. Similarly, the electroluminescent device stack is planar. A stack of this type may be used to produce large, irregularly size and shaped, separate objects of graphic content, such as letters and graphics that may each be in the order of inches or feet in height and in width. The present invention permits the construction of signage that can achieve even, smooth, stable emission over a large sign comprised of images of this type. The following table details examples of materials that can be used to prepare the device stack of this example:

A stack having the configuration described above, but having additionally electron transport layer of ZnO particles, was made.

Hole Transport Layer Poly(3,4-ethylenedioxythiophene) (PEDOT)

/ polystyrene para-sulfonate (PSS), available from Sigma Aldrich, spin cast onto the ITO surface and dried at 70°C for 2

hours

Emissive Electroluminescent CdSe/ZnS, spin cast deposited from a

Layer dispersion of the CdSe/ ZnS available from

SigmaAldrich, e.g. 753777-25ML, and the spin cast layer is annealed/dried at 70C for

2 hours

Electron Transport Layer ZnO nano particles dispersed in ethanol and spin cast onto the electroluminescent layer

Cathode Layer Aluminium (100nm thickness) deposited

onto the emissive electroluminescent layer

Bright electroluminescence was observed at the edges of stack which has the ZnO layer.

The stack on the polyester was cut with a razor and examined by SEM: the aluminium and ZnO layers were clearly separately visible, with smooth edges, without mixing and without zagged edges. The substrate on the other hand was unevenly frayed. The coatings on the polyester substrate were successfully cut using the following sign cutting machines:

1 : Folding carton sample maker (Misomex) using a 45-degree V-shaped blade, which cut at a 90-degree angle (normal) to the surface entirely through.

2: Matboard cutter (Wizard) using a 45-degree chisel-shaped blade, which cut at a +45-degree, and separately at a -45-degree angle with respect to the normal entirely through.

As a comparison, an electroluminescent film was obtained from EL International. According to the supplier information, that film comprises phosphor inks (understood to comprise ZnS phosphor powder) to create initial brightness of 200 cd/m² at a low voltage and frequency of 700Hz. The film, which has thick opaque layers, and appears pink in colour, was cut with a sharp scissors and was found to delaminate in areas which form dark (non emitting) spots at the cut edges.

Example 2: Construction of Complete Signage Stack

An example of an alternative construction of a signage stack comprising an electroluminescent device stack is shown in Figure 3, which additionally comprises a receiver substrate and a protective (including a barrier) layer.

In the illustrated embodiment, the signage stack comprises additional layers for accessing electrical power and for protecting the electroluminescent device stack and the conductive materials, among additional functions. In addition to the cathode layer, emissive electroluminescent layer, hole transport layer and anode layer, the signage stack comprises passivating layers which separate the anode and cathode layers from their respective conductive layers.

The uppermost layer in the signage stack is a protector layer, and the bottom five layers make up the receiver substrate, which comprises a barrier layer to provide protection to the electroluminescent device stack, an adhesive layer, a release liner, a cathode conductive layer and a passivating layer. Removal of the release liner will expose the adhesive layer and facilitate adhesion of the stack on to the mounting surface (not shown).

The barrier layer preferably has low water and / or oxygen permeability. The barrier layer may comprise inorganic oxide coatings which can be applied, for example using an ALD process. Examples of films which may be employed as barrier layers include 3M FTB3 Barrier Film, Meyer Burger CONx TFE thin film, and / or films from Tera Barrier Films Pte Ltd, etc. The 3M FTB3-50 and FTB3- 125 films comprise a base polyester layer having a thickness of 50 to 125 microns with a very thin (less than 2 microns) barrier coating made up of layers of polymer and oxide.

Designed conductive tracks are printed on these layers and thereafter the electroluminescent stack is interfacially applied between the conductive layers.

The present invention permits the construction of a sign comprising a signage stack or several signage stacks, either separately or fully connected electrically, that can achieve even, smooth, stable emission over a sign comprised of large scale images, for over 30,000 hours operation owing, at least partly, to the encapsulation of the electroluminescent device stack in the barrier layers, which prevent the ingress of oxygen, moisture and / or other contaminants. Example 3 - Device Fabrication Process and Sign

In this example a signage stack is produced stepwise. As is apparent, the exemplified process for preparing the signage stack comprises (i) the fabrication of the electroluminescent device stack multilayer consumables a in roll-to-roll fabrication process, which is preferably conducted in an industrial setting due to exacting tolerances, clean room operations (e.g. class 100 or lower), and the need for capital intensive equipment and lengthy production runs; and (ii) the subsequent full sheet and imagewise transfers of a large scale portion of the electroluminescent device stack having a predetermined size and shape, which may be conducted in a signmaking shop.

Example 3-1 : Roll-to-roll Fabrication of Consumables

The present invention contemplates the fabrication of separate multilayered consumables (the electroluminescent device stack, the protector layer and the receiver substrate) shown in the "Stage 1 " part of Figure 4.

Figure 4 shows simplified layers to illustrate fabrication processes of the present invention. Examples of the construction of the specific layers, e.g. the receiver substrate, the electroluminescent device stack and the protector layer, are described more fully herein.

Thus, "Stage 3" of Figure 4 depicts an example of an interfacially fixed electroluminescent device stack within a protector layer and receiver substrate, where the receiver substrate is ready for attachment to the final surface, e.g. shopfront window.

The receiver substrate is a medium for receiving, supporting and protecting the electroluminescent device. In the illustrated embodiment, the receiver substrate comprises an adhesive layer and a release liner (not shown in Figure 4). This receiver substrate stack is fabricated using a roll-to-roll process.

The electroluminescent device stack shown in Figure 4 is a simplified representation of that depicted in Figure 2 and thus comprises a cathode layer, an emissive electroluminescent layer, a hole transport layer and an anode layer which, for simplicity are not individually depicted in Figure 4. That stack is produced using a roll-to-roll process on a transfer substrate. Ink jet array printers, e.g. commercialized by Fujifilm USA under the name "Dimatix", may be employed to deposit the layers using compositions which have the luminescent nanophosphors or conductive materials, e.g. nano silver or graphene, dispersed in suitable liquid carrier at the required viscosity suitable for jetting using such printers. In the illustrated embodiment, the anode layer comprises graphene and the cathode layer comprises aluminium. The emissive electroluminescent layer comprises nanophosphor, for example CdSe / ZnS core shell colloidal particles. The graphene cathode layer contains gold particles to bring the graphene into appropriate anode work function level.

The hole transport layer contains compounds that are matched to the selected anode so that optimum efficiency in the anode is obtained, such as poly(ethylenedioxythiophene):polystyrene sulphonate PEDOT: PSS, poly[(9.9- dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenylamine) and / or metal oxide nanoparticles, such as NiO, Mo03, MoS2, Cr203 and Bi203, p- type ZnO, p-type GaN or any combination thereof. Optionally, an electron transport layer, e.g. ZnO particles, maybe included between the electroluminescent layer and the cathode layer.

The protector layer includes a stack comprising a polymeric and/or inorganic protector layer, which prevents the ingress of oxygen, moisture and / or other contaminants and a protector carrier. The protector layer is fabricated via roll- to-roll processes, such as those involving the ALD process available (or under development) from Beneq Oy, or Vitriflex, etc. Ink jet array printers e.g. as commercialized by Fujifilm USA under the name "Dimatix", may be employed to deposit some of layers using compositions in suitable liquid carrier which have the required viscosity suitable for jetting using such printers.

Example 3-2: Transfer of Portion of Electroluminescent Device Stack Prior to the exemplified process being carried out, a sign having graphic content of specific size, shape and color was designed. As part of this design, a large scale size and shape to be formed from the electroluminescent device stack was pre-determined. In the second stage of this sign making process, the portion of the electroluminescent device stack of predetermined size and shape is transferred from the transfer substrate on to the receiver substrate, as shown in "Stage 2" of Figure 4. As can be seen, the electroluminescent device stack of the predetermined size and shape is transferred in its entirety, advantageously without the formation of unacceptable levels of microcracks or other defects.

In this arrangement, the imagewise transfer is accomplished by laser transfer, and more specifically by digital laser transfer printing in response to design data. An example of a digital laser printer which can be used in this way is the laser transfer technology which was marketed under the brand name "Approval Digital Color Proofing System" by Eastman Kodak Company or that marketed as "Creo Trendsetter Spectrum System".

There may be differential heating at the edges of the portion being transferred, in order to ensure clean separation during transfer, provided that excessive damage to the emissive electroluminescent layers is not caused. Thus, the laser is more focused at the edges of that portion. This may be achieved through the use of a laser focussed to 50 microns, such that the peak power density is 50kW/cm2.

The tool path may also be fashioned in a way so as to facilitate large area transfer without microcracking in the fragile electroluminescent device layers. Another means of accomplishing imagewise transfer of a portion of electroluminescent device stack is through a combination of heat and pressure. One thermal transfer printer for printing sign graphic content on to thermoplastic material is a printer marketed under the brand name "GERBER EDGE by Gerber Scientific Products, Inc. which is also disclosed in US Patent No. 5537135, the contents of which are incorporated by reference.

Again in this case, the operation of the printheads is such that there is diffusion of the thermal effect, again to ensure whole thin layer transfer as required, without forming micro cracks or damaging the electroluminescent device stack integrity. There may be differential heating at the edges of the graphic being transferred, in order to ensure clean separation during transfer without damage to the emissive electroluminescent layers.

Imagewise thermal transfer may also be accomplished by non digital (analog) means. An example is hot stamping. One thermal stamping machine for roll on applications is marketed under the name "CR3300" by Stamprite Machine Co. The stamping tooling itself may be fabricated based on imagewise machining or etching means in accordance with the design data. To facilitate transfer, the edges may be pre cut according to the desired graphic content.

Imagewise transfer may also be accomplished by (i) cutting the portion of electroluminescent device stack and weeding / removing the transfer substrate corresponding to that size and shape from the remainder of the transfer substrate, then (ii) pressing the cut portion of electroluminescent device stack against the receiver material and contacting the transfer substrate with a uniformly flat (non imaged) heated plate or heated roller.

Example 3-3: Transfer of Protector Layer

The final step of the fabrication process, shown in "Stage 3" of Figure 4 is the transfer of the protector layer (which, as explained above, comprises a barrier layer, an anode conductive layer and a passivating layer on to the electroluminescent device stack). This produces the completed signage stack.

Example 4: Device Fabrication Process

A signage stack corresponding to that shown in Figure 3, but not including passivating layers, can be prepared as follows.

In a first arrangement of the stack of this example (Version 4a), a receiver substrate was prepared by treating a Scotchcal 8150 film which is a transparent vinyl film having an adhesive and release liner on one side and an inkjet receptive surface on the other. Conductive lines comprising UV curable nano silver ink were inkjetted (using the Fujifilm USA inkjet printhead commercialised under the brand name "Dimatix" ) onto the inkjet receptive surface of the film. The ink was UV cured to produce a grid having a resistivity of 20ohms/sq.

A protector layer was prepared in the same way. In both layers, the Scotchcal 8150 film provided barrier function.

A portion of an electroluminescent device stack comprising an aluminium cathode (thickness 100nm), an electron transport layer comprising zinc oxide nanoparticles (thickness 30nm), an emissive electroluminescent layer comprising CdSE/ZnS particles (thickness 30nm) and an anode comprising ITO was interfacially fixed using a digital printer to the receiver substrate. The protector layer e.g. Scotchcal 8510 was laminated onto electroluminescent device stack, taking care to prevent any contact between the conductive grids printed on the barrier layers in the receiver substrate and protector layers. In a second arrangement of this example (Version 4b) of this example, the ITO layer was substituted with graphene flakes with gold particle doping (thickness 30nm). The protector layer i.e. Scotchcal film 8510 was laminated onto electroluminescent device stack, taking care to prevent any contact between the conductive grids printed on the barrier layers in the receiver substrate and protector layers.

The release liner on the film present in the receiver substrate was removed and the signage stack was mounted on to a glass surface. Thereafter, the release liner on the protector layer was removed and a thin glass cover was applied thereto to provide additional barrier functionality and prevent the ingress of oxygen, moisture and / or other contaminants. Example 5: Device Fabrication Process

An electroluminescent device stack having the same construction as the two arrangements discussed in Example 4 (either with the ITO anode or the graphene / gold doped as anode) is produced / fixed to a vinyl transfer substrate using a roll-to-roll manufacturing process.

The large scale portion of electroluminescent device stack of predetermined size and shape is then separated by cutting and transferred to the receiver substrate (again, based on a film) using a printer, as visually represented in Figure 5. The transfer substrate and the unused remainder of the electroluminescent device stack is then removed and disposed of.

Example 6: Device Fabrication Process A series of signage stacks of the present invention are shown in Figures 6 to 8. These may be prepared by variations on the processes of the preceding examples. For example, the arrangement shown in Figure 6 can be achieved by forming a receiver substrate by printing conductive lines / a grid onto a barrier film (such as Scotchcal 8150, or comprising BTF3), and then applying a passivating layer thereupon.

A large scale portion of electroluminescent device stack of predetermined size and shape may then be fixed to the receiver layer and a protective layer (again formed by applying conductive lines / a grid onto a barrier film such as Scotchcal 8150, or comprising BTF3) can be applied to the electroluminescent device stack / receiver substrate. Note that in this arrangement, the protector layer is conformable and thus fully envelopes and provides an effective barrier around the entirety of the electroluminescent device stack.

A variation of the signage stack is shown in Figure 7. In this arrangement, the receiver substrate comprises a vinyl layer shaped to receive the (optional) conductive layer and the large scale portion of the electroluminescent device stack of predetermined size and shape. The (optional) conductive layer and electroluminescent device stack is interfacially fixed into the vinyl layer shape through the application of heat and pressure, which advantageously simultaneously seals the edges of the stack preventing the ingress by moisture, oxygen and / or other contaminants. A flat upper surface is provided onto which the protector layer can be applied.

By configuring the signage stack in this way, at the transfer stage, it is ensured that the anode and cathode layers do not touch at the edges where transfer/cutting takes place.

Additionally or alternatively, a process can be adopted which causes top layers to fully cover the (inner) imagewise layers ideally such that they do not become damaged. This can be achieved, for example, by pressing the underlying imagewise layers into the vinyl as part of the transfer process, so that the surface is flush and / or applying pressure and quality of heat from printhead / laser so that, at the edges, there is more polymer flow and thus sealing. Alternatively or additionally, a sealing adhesive is applied around the edges of the large scale electroluminescent device stack: example adhesive may be from Addison adhesives, e.g. UV curable epoxy sealant adhesive A535-A, A535-N, AC A1428, AC A1450 or siloxane adhesive EL-92734.

A further variation, especially suitable for roll-to-roll production, is shown in Figure 10. Ink jet technologies such as array printheads from Fujifilm e.g. "Dimatix", or from Spectra Inc, e.g. Spectra are useful for depositing luminescent layers comprising nano phosphors such as quantum dots as well as the cathode or anode layers comprising graphene, nano silver, or the like. This technology enables direct deposition of large volumetric areas in a programmed manner, such that one surface is large scale and flat and the exposed edges of those layers are very thin. This method advantageously provides a programmable approach for achieving large area signs set within a polymer where there is interfacial separation of the luminescent and anode / cathode layers from the surrounding polymer. Such a method is applied to produce the stacks set within a polymer as illustrated in Figures 10a, 10b fixed to a receiver substrate, e.g. Scotchcal 8150 and protected by a protector layer, e.g. Scotchcal 8150. Both the receiver substrate and protector layer may further conveniently incorporate the required conductive layers and water vapour and oxygen impermeable technology, e.g. BTF3. Example 7: Alternative Signage Stack Arrangement

Applying the process of Example 3, a sign arrangement as shown in Figure 8 may be produced. In that arrangement, the protective layer (comprising the conductive layer) is transferred in its entirety while the electroluminescent device stack transferred is imagewise, on to the receiver substrate.

The conductive layer may be provided to cover the electroluminescent device stack plus margin (for channel letter style, where the sign comprises separate and visually distinct items of graphic content (e.g. letters or other graphical objects, whether 2D or 3D) or bounding box (for cabinet sign style, where the sign comprises physically connected if visually distinct items of graphic content, e.g. letters or other graphical objects, whether 2D or 3D). The second passivating layer may be treated with regard to the device stack image so that that area becomes selectively conductive. By doing so, the second passivating layer remains passivating and non conductive at the sides of the stack, to avoid shorting between anode and cathode layers.

Example 8: Complete Sign

Provided below is an example of a complete sign comprising the signage stack and electroluminescent device stack of the present invention.

Sign Holder. A housing made principally from materials such as thick plastic or thin metal and having a transparent front cover formed of for example glass or transparent polymer (e.g., polycarbonate), that contains, supports and protects the signage stack. The use of metallic materials or metal coated materials to form the sign holder may be advantageous owing to their heat spreading properties; localized overheating caused during operation of the electroluminescent device stack may be prevented by heat dissipation. The metal material may be applied over all of one of the surfaces or partially over the holder. The latter approach may be useful where a fully transparent sign is used, visible from both sides. The sign holder may house films in addition to the signage stack, e.g. graphic films, light management films, light harvesting films or the like. The holder has a closeable opening at its side through which these films can be inserted or slid into position, repositioned and replaced as required. Thus, the signage stack and additional films can be arranged, inspected, repaired or replaced as required from time to time.

The front cover through which the illuminated graphic is seen should remain clear and transparent for long periods, for example up to 7 years at ambient conditions. The sign holder therefore protects the electroluminescent device stack/s from exterior elements and also provides the electroluminescent device stack with a stable internal environment contributing to the required lifetime of the electroluminescent device stack/s. This is of significant benefit; modern electroluminescent panels typically have very thin active layers and these can be fragile and prone to deleterious oxygen or moisture effects. The combination of the type of barrier layers described herein, as part of the receiver and/or the protector layers encapsulating the device stacks, and the sign holder ensures optimised protection.

The sign holder may be provided with a suitable adhesive or other fixing means for mounting on to a wall, post, window or the like. Alternatively, the sign holder may be free standing

Signage Stack. The signage stack comprises a light emitting (preferably white light) emissive electroluminescent layer. The signage stack comprises a rigid receiver substrate onto which the stack is mounted. The signage stack is inserted or slid into the sign holder and is positioned adjacent to the inner side of the metal backing of the holder. The signage stack may be provided with magnetic fixing means to retain it firmly to the metal back of the sign holder.

The electroluminescent device stack preferably comprises graphene electrodes and organic or inorganic (e.g., OLED, PLED, nanophosphors, etc.) emissive electroluminescent layers. It also comprises hole / electron transport layers, barrier and passivating layers.

The signage stack is configured to be resistant to ingress by moisture, oxygen and / or other contaminants, using the approaches disclosed herein.

During fabrication of the signage stack, care is taken when cutting steps are carried out on the electroluminescent device stack to avoid rendering that stack (or the layers comprised therein) vulnerable to the ingress of oxygen, moisture and / or other contaminants and / or adversely affecting the light output and light consistency. Thus sealing the edges with an adhesive sealant may be used. Alternatively or additionally, the electroluminescent device stack film may have a border, for example provided by the receiver substrate, which is laminated to the electroluminescent device stack and which can be cut without disturbing the electroluminescent device stack.

Light Channeling Layer. A light channeling film may be provided in front of the signage stack, the light channeling film has a light channeling image corresponding to the predetermined size and shape of the electroluminescent device stack, registered to the signage stack to ensure correct positioning of the light channeling film.

Through the use of the light channeling film, the light emitted from the sign as a whole has a greater luminosity than the light emitted from the emissive electroluminescent layer.

Imaged Layer. A transparent film having an image corresponding to the predetermined size and shape of the electroluminescent device stack (i.e. the graphic or character to be displayed) is positioned in front of the light channeling film and behind the front glass or transparent polymer sheet.

The imaged layer also functions as a registration layer; that is, the transparent graphic corresponds to, and is preferably registered to, the corresponding area of the light channeling film such that greater luminosity is seen through these areas.

Preferably the graphics construction is such that any total internal reflection within the sign housing of light from the emissive electroluminescent layer is prevented, to maximise the light emitted through the transparent graphic.

The production of the graphic in the imaged layer may be achieved using photographic means, for example to produce a transparent image on a black background, or a graphic on a transparent background, such that electroluminescent light only emerges through the imaged region. The use of the imaged layer and the light channeling layer advantageously promote the collection and channeling of internally reflected light, resulting in an improvement of luminescence in the imaged areas.

Light Harvesting Layer. To optimise power efficiency when operating the sign, light harvesting film may be included in the holder. The power generated may be used directly or stored in a device (a battery) for use for the sign. The light harvesting film may be cut to fit the shape of the sign(s).

Example 9: Fabrication of Signage Stack

A direct printing machine, which facilitates processing of electroluminescent device materials under optimised environmental controls (e.g. low dew point, low oxygen content, class 100 or less rating, high cleanliness) may be used. Such a machine may be used to produce a roll-to-roll of the electroluminescent device stack layers which can then be used to transfer large scale portions of electroluminescent device stack in the form of graphic content such as characters or graphics. The size and shape of those portions is controlled by software. Further, the color and light management properties of the electroluminescent device stack may also be controlled in this way.

The printer may advantageously be suitable for the roll-to-roll fabrication of the feedstocks used to prepare the signage stack of the invention, i.e. the electroluminescent device stack and optionally the protector layer and / or receiver substrate. For example, the printer may be capable of achieving this using ink jetting, vacuum depositing and / or layer micro embossing functionality or the like to make up the stacks of interest. The same apparatus may also be capable of transferring large scale portions of the electroluminescent device stack on to the receiver substrate using roll-to-roll processing, to produce large scale signage stacks.

Ink jet technologies, such as array printheads from Fujifilm e.g. "Dimatix", are useful for depositing the luminescent layer (including those comprising nano phosphors such as quantum dots), the cathode and / or anode, and / or or the conductive layers (including those comprising graphene, nano silver, or the like). This technology enables direct interfacial application of large volumetric layers in a programmable manner, such that one surface is large scale and flat and the exposed edges of those layers are very thin. This approach leads readily to the separation of the luminescent and anode / cathode layers from surrounding polymer, as illustrated in Figure 10.

Alternatively, the direct printing machine may be used to produce the large scale portions of the signage stacks in the required predetermined sizes and shapes and relative positioning and orientation on a donor substrate, which then can be used at a signmaker for full assembly. This is particularly suitable for volume production of standardised signs, which are standardised in the bespoke color and size/shape requirements.

Example 10: Custom Color Signage Stack

The examples discussed above involve signage stacks comprising a single electroluminescent device stack. However, as explained herein, the signage stacks of the invention may comprise multiple electroluminescent device stacks, e.g. as shown in Figure 9, 10a, 10b and 12. Doing so provides flexibility in the skilled signmaker's ability to produce custom colored signs, as these can be achieved using only a limited number of colored emissive electroluminescent layers.

Sign makers often require signs to be produced accurately with specific custom colours, such as e.g. IBM Blue, which represents a key aspect of IBM's corporate identity and thus, the color must be displayed identically in all sign locations. The device shown in Figure 9 illustrates an example of the overall concept of producing large scale electroluminescent device stacks comprising e.g. red, blue, green emitting electroluminescent device layers from roll-to-roll produced films to produce composite stack sections optimised by design software to emit a required custom color. Such composite stack sections may also be produced by using cut and transfer technologies or programmed ink jet technologies, as described above.

Thus, the present invention provides flexibility in terms of the choice of the emission color (e.g. by combining different OLEDS or quantum dot materials) of the basic electroluminescent device stacks (which may be in a one contiguous stack or made of patterned stacks within a polymer matrix as shown in Figures 5, 10a and 10b), the choice in stack positioning, choice in the stack pattern and size (e.g. large or small dots versus whole area transfer, stochastic / random dots for more even emitted color), and/or the freedom to create vignettes.

Similarly, Figure 12 demonstrates the sign maker's freedom to obtain custom colour effects through the preparation of a signage stack comprising a plurality of vertically disposed (or "stacked") electroluminescent device stacks and including light channelling/directing layers.

Claims

1 . A process for producing a signage stack, comprising an luminescent device stack and a receiver substrate comprising: providing a flexible luminescent device stack comprising a luminescent layer; providing a receiver substrate; and interfacially fixing a portion of the luminescent device stack to the receiver substrate, the portion of the luminescent device having a large scale area and a predetermined size and shape.

2. The process of Claim 1 , wherein the luminescent device stack is an electroluminescent device stack and the luminescent layer is an emissive electroluminescent layer, the electroluminescent device stack comprising (i) an anode layer having an outer surface and an inner surface and (ii) a cathode layer having an outer surface and an inner surface and (iii) the emissive electroluminescent layer disposed between the inner surface of the anode layer and the inner surface of the cathode layer.

3. The process of Claim 1 , wherein the luminescent layer is a photoluminescent layer.

4. The process of Claim 1 or 2, further comprising fixing a protector layer to the luminescent device stack.

5. The process of Claim 4, wherein the protector layer and / or the receiver substrate has a moisture and / or oxygen permeability of less than about 10^"2 gm/m²/day, less than about 5 x 10^"3 gm/m²/day, less than about 5 x 10^"4 gm/m²/day, less than about 5 x 10^"5 gm/m²/day, or less than about 5 x 10^"6 gm/m²/day.

6. The process of Claim 4 or 5, wherein the protector layer and / or the receiver substrate comprise a layer which is polymeric and / or which comprises inorganic oxide.

7. The process of any one of Claims 1 to 6, wherein the fixing of the portion of the luminescent device stack to the receiver substrate is carried out using roll-to-roll processing.

8. The process of any one of Claims 1 to 7, wherein the luminescent device stack is prepared by roll-to-roll processing and / or the receiver substrate is prepared by roll-to-roll processing.

9. The process of any one of Claims 1 to 8, further comprising the step of providing a web of luminescent device stack material and separating the large scale portion of luminescent device stack having a predetermined size and shape from an unused portion of the luminescent device stack web.

10. The process of Claim 9, wherein the step of separating the large scale portion of luminescent device stack having a predetermined size and shape from an unused portion of the luminescent device stack web is carried out prior to interfacially fixing a portion of the luminescent device stack to the receiver substrate.

1 1 . The process of Claim 10, wherein the luminescent device stack web comprises a transfer substrate and, following separation of the large scale portion of luminescent device stack having a predetermined size and shape from an unused portion of the luminescent device stack web, the unused portion of the luminescent device stack web is removed (e.g. weeded) from the large scale portion of luminescent device stack having a predetermined size and shape.

12. The process of Claim 1 1 additionally comprising the step of separating a portion of the transfer substrate which corresponds to the large scale portion of luminescent device stack having a predetermined size and shape from an unused portion of the transfer substrate which corresponds to the unused portion of the luminescent device stack web, and optionally removing (e.g. weeding) the unused portion of transfer substrate from the portion of the transfer substrate which corresponds to the large scale portion of luminescent device stack having a predetermined size and shape.

13. The process of Claim 10, wherein the transfer substrate is provided with adhesive and interfacial fixing of large scale portion of luminescent device stack having a predetermined size and shape to the receiver substrate is achieved by adhering the transfer substrate to the receiver substrate.

14. The process of Claim 9, wherein the step of separating the large scale portion of luminescent device stack having a predetermined size and shape from an unused portion of the luminescent device stack web is carried out simultaneously with interfacially fixing a portion of the luminescent device stack to the receiver substrate.

15. The process of Claim 14, wherein the luminescent device stack web comprises a transfer substrate and interfacial fixing of the luminescent device stack is achieved through the application of heat, laser energy and / or pressure, resulting in separation of the large scale portion of luminescent device stack having a predetermined size and shape from an unused portion of the luminescent device stack web.

16. The process of Claim 15 wherein said interfacial fixing and separation is achieved through the use of a transfer printer.

17. The process of Claim 9, wherein following the interfacial fixing of the large scale portion of luminescent device stack having a predetermined size and shape to the receiver substrate, the large scale portion of luminescent device stack having a predetermined size and shape is separated from the unused portion.

18. The process of Claim 17, wherein separation of the large scale portion of luminescent device stack having a predetermined size and shape from the unused portion is achieved through the use of heat, laser energy and / or pressure.

19. The process of Claim 17 or 18, wherein separation of the large scale portion of luminescent device stack having a predetermined size and shape from the unused portion is achieved by removing the unused portion from the interfacially fixed large scale portion of luminescent device stack having a predetermined size and shape.

20. The process of any one of Claims 17 to 19, wherein separation of the large scale portion of luminescent device stack having a predetermined size and shape from the unused portion is achieved via a cutting step.

21 . The process of Claim 20, wherein the cutting step is carried out such that only the luminescent device stack and not the receiver substrate is cut.

22. The process of any one of Claims 9 to 21 , wherein the separation of the large scale portion of luminescent device stack having a predetermined size and shape from the unused portion of the luminescent device stack web is achieved by the application of a laser and / or thermal printing and, to prevent damage to the luminescent device stack having a predetermined size and shape, differential heating / laser focus is applied at the edge of the luminescent device stack having a predetermined size and shape.

23. The process of any one of Claims 1 to 22, wherein the process further comprises the step of cutting the receiver substrate into a size and shape corresponding at least substantially to the predetermined size and shape of the portion of the luminescent device stack.

24. The process of Claim 23, further comprising the step of weeding the cut receiver substrate size and shapes.

25. The process of any one of Claims 1 to 24, wherein the process further comprises mounting the signage stack on a mounting surface.

26. The process of Claim 25 wherein the mounting surface is provided on or in a sign holder.

27. The process of Claim 26 additionally comprising the step of providing one or more light modifying layers on or in the sign holder.

28. The process of Claim 27, wherein the one or more light modifying layers comprise one or more light channeling layers and / or one or more imaged layers.

29. The process of any one of Claims 1 to 28, wherein fixing of the luminescent device stack to the receiver substrate is achieved through the use of heat, laser energy and / or pressure.

30. The process of Claim 29, wherein the heat, laser energy and / or pressure are provided by a print head and / or stamping die.

31 . A signage stack comprising an luminescent device stack comprising a luminescent layer and a receiver substrate; the receiver substrate being fixed interfacially with at least one portion of the luminescent device stack having a large scale area.

32. The signage stack of Claim 31 , wherein the luminescent device stack is an electroluminescent device stack and the luminescent layer is an emissive electroluminescent layer, the electroluminescent device stack comprising (i) an anode layer having an outer surface and an inner surface and (ii) a cathode layer having an outer surface and an inner surface and (iii) the emissive electroluminescent layer disposed between the inner surface of the anode layer and the inner surface of the cathode layer.

33. The process of any one of Claims 1 to 30 or the signage stack of Claim 31 or 32, wherein the thickness of the luminescent device stack is about 5 microns or lower.

34. The process of any one of Claims 1 to 30 or 33 or the signage stack of any one of Claims 31 to 33, wherein the portion of luminescent device stack interfacially fixed to the receiver substrate has an area of about 100pm² or greater, about 200pm² or greater, about 500pm² or greater, about 1 cm² or greater, about 2cm² or greater, about 5cm² or greater, about 10cm² or greater, about 20cm² or greater, about 50cm² or greater or about 1 m² or greater.

35. The process of any one of Claims 1 to 30, 33 or 34 or the signage stack of any one of Claims 31 to 34, wherein the portion of luminescent device stack interfacially fixed to the receiver substrate is a nonstandard shape or a plurality of different shapes.

36. The process of any one of Claims 1 to 30, or 33 to 35 or the signage stack of any one of Claims 31 to 35, wherein the portion of luminescent device stack interfacially fixed to the receiver substrate is a nonstandard shape or a plurality of different shapes.

37. The process of any one of Claims 1 to 30, or 33 to 36 or the signage stack of any one of Claims 31 to 36, wherein the layout of conductive lines (if present) is not a grid or an orthogonal grid.

38. The process of any one of Claims 1 to 30 or 33 to 37 or the signage stack of any one of Claims 31 to 37, wherein the portion of luminescent device stack interfacially fixed to the receiver substrate has an area of about 10cm² or more.

39. The process of any one of Claims 1 to 30 or 33 to 38 or the signage stack of any one of Claims 31 to 38, wherein the signage stack is provided with two conductive layers.

40. The process of any one of Claims 1 to 30 or 33 to 39 or the signage stack of any one of Claims 31 to 39, wherein one of the conductive layers is separated from the anode layer by a passivating layer and / or the other of the conductive layers is separated from the cathode layer by a passivating layer.

41 . A process for preparing an luminescent device stack web comprising: providing a first roll of a first web material having a first surface, unrolling a portion of the first roll to expose the first surface of the first web material, and applying a plurality of layers upon the first surface of the web material to form an luminescent device stack web comprising a luminescent layer, wherein the total thickness of the stack is less than about 5 microns.

42. The process of Claim 41 , wherein the luminescent device stack web is an electroluminescent device stack web and the luminescent layer is an emissive electroluminescent layer, the electroluminescent device stack web comprising (i) an anode layer having an outer surface and an inner surface and (ii) a cathode layer having an outer surface and an inner surface and (iii) the emissive electroluminescent layer disposed between the inner surface of the anode layer and the inner surface of the cathode layer.

43. The process of Claim 41 or 42, further comprising the step of rolling up the luminescent device stack to obtain the luminescent device stack roll.

44. The process of any one of Claims 41 to 43, further comprising the step of modifying one or more layers of the luminescent device stack.

45. The process of Claim 44, wherein the step of modifying the one or more layers comprises patterning the layer.

46. An electroluminescent device stack comprising (i) an anode layer having an outer surface and an inner surface and (ii) a cathode layer having an outer surface and an inner surface and (iii) an emissive electroluminescent layer disposed between the inner surface of the anode layer and the inner surface of the cathode layer, wherein the total thickness of the stack is less than about 5 microns.

47. An luminescent device stack comprising a photoluminescent layer, wherein the total thickness of the stack is less than about 5 microns, and the area of the luminescent device stack is about 100pm2 or greater, about 200pm2 or greater, about 500pm2 or greater, about 1 cm2 or greater, about 2cm2 or greater, about 5cm2 or greater, about 10cm2 or greater, about 20cm2 or greater, about 50cm2 or greater or about 1 m2 or greater.

48. The process of any one of Claims 1 to 30 or 33 to 45, or the stack of any one of Claims 31 to 40, 46 or 47 wherein the luminescent device stack is provided with a hole transport layer and / or an electron transport layer.

49. The process of any one of Claims 1 to 30, 33 to 45 or 48 or the stack of any one of Claims 31 to 40 or 46 to 48 wherein the luminescent layer comprises OLEDs, PLEDs and / or semiconductor (e.g. nanophosphor) nanoparticles such as quantum dots.

50. The process of any one of Claims 1 to 30, 33 to 45, 48 or 49 or the stack of any one of Claims 31 to 40 or 46 to 49 wherein the anode layer and / or the cathode layer comprise graphene.

51 . The process of any one of Claims 1 to 30, 33 to 45, 48 to 50 or the stack of any one of Claims 31 to 40 or 46 to 50 wherein the luminescent layer comprises graphene.

52. The process or stack of Claims 50 or 51 , wherein the graphene is particulate and optionally comprises two layered graphene.

53. The process of any one of Claims 1 to 30, 33 to 45, 48 to 52 or the stack of any one of Claims 31 to 40 or 46 to 52, wherein the thickness of the luminescent device stack is about 1 micron or lower.

54. The process of any one of Claims 1 to 30, 33 to 45, 48 to 53 or the stack of any one of Claims 31 to 40 or 46 to 53, wherein the transmission of light through the luminescent device stack is greater than about 20%, greater than about 30%, greater than about 40%, greater than about 50%, greater than about 60%, greater than about 70%, or greater than about 80%.

55. The process of any one of Claims 1 to 30, 33 to 45, 48 to 54 or the stack of any one of Claims 31 to 40 or 46 to 54, wherein the luminescent device stack comprises a monodirectional layer which renders the luminescent device stack opaque when viewed from its upper surface and transparent when viewed from its lower surface.

56. The process of any one of Claims 1 to 30, 33 to 45, 48 to 54 or the stack of any one of Claims 31 to 40 or 46 to 54, wherein the luminescent device stack comprises a monodirectional layer which renders the luminescent device stack opaque when viewed from its lower surface and transparent when viewed from its upper surface.

57. A signage stack obtainable from the process of any one of Claims 1 to 30, 33 to 45 or 48 to 56 or comprising the luminescent device stack of any one of Claims 31 to 40 or 46 to 56.

58. A sign comprising the stack of Claim 57.

59. The sign of Claim 58, wherein, in use, the sign displays static and digital dynamic content.

60. The sign of Claim 58 or 59, wherein the sign comprises at least one static luminescent device stack and at least one dynamic luminescent device stack.

61 . A sign comprising a plurality of luminescent device stacks, at least one of which luminescent device stacks is an electroluminescent device stack comprising (i) an anode layer having an outer surface and an inner surface and (ii) a cathode layer having an outer surface and an inner surface and (iii) an emissive electroluminescent layer disposed between the inner surface of the anode layer and the inner surface of the cathode layer.

62. The sign of Claim 61 wherein each of the plurality of luminescent device stacks is an electroluminescent device stack comprising (i) an anode layer having an outer surface and an inner surface and (ii) a cathode layer having an outer surface and an inner surface and (iii) an emissive electroluminescent layer disposed between the inner surface of the anode layer and the inner surface of the cathode layer.

63. The sign of any one of Claims 58 to 62, wherein at least two of the plurality of luminescent device stacks are vertically, interfacially arranged.

64. The sign of any one of Claims 58 to 63, wherein at least two of the plurality of luminescent device stacks are horizontally separated and interfacially arranged.

65. The sign of Claim 64, wherein the at least two of the plurality of luminescent device stacks comprise conductive layers.

66. The sign of Claim 65 wherein the conductive layers have a resistance of less than 300 ohms/sq, less than 200 ohm/sq, less than 100 ohms/sq, less than 50 ohms/sq or less than 10 ohms/sq.

67. The sign of any one of Claims 58 to 66, wherein the emissive electroluminescent layers comprised within at least one of the plurality of electroluminescent device stacks comprises nano phosphors

68. The sign of any one of Claims 58 to 67, wherein the sign is used to make a billboard, banner, a wrap, a traffic control sign, an emergency sign, a facility identification sign, a wayfinding sign, or a shopfront sign.

69. The sign of any one of Claims 58 to 68 comprising at least one luminescent device stack having an area of about 100pm² or greater, about 200pm² or greater, about 500pm² or greater, about 1 cm² or greater, about 2cm² or greater, about 5cm² or greater, about 10cm² or greater, about 20cm² or greater, about 50cm² or greater or about 1 m² or greater.

70. The sign of any one of Claims 58 to 69 wherein the sign is at least partially manufactured using inkjet printing.