WO2014096785A1 - Utilisation d'un film de polyester pour amélioration d'extraction de lumière de sources de lumière oled et ensemble multicouche comprenant une source de lumière oled et un film de polyester - Google Patents

Utilisation d'un film de polyester pour amélioration d'extraction de lumière de sources de lumière oled et ensemble multicouche comprenant une source de lumière oled et un film de polyester Download PDF

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Publication number
WO2014096785A1
WO2014096785A1 PCT/GB2013/053276 GB2013053276W WO2014096785A1 WO 2014096785 A1 WO2014096785 A1 WO 2014096785A1 GB 2013053276 W GB2013053276 W GB 2013053276W WO 2014096785 A1 WO2014096785 A1 WO 2014096785A1
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WIPO (PCT)
Prior art keywords
oled
light
polyester film
film
particles
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PCT/GB2013/053276
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English (en)
Inventor
Duncan Henry Mackerron
Stephan Harkema
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Dupont Teijin Films U.S. Limited Partnership
Nederlandse Organisatie Voor Toegepast Natuurwetenschappelijk Onderzoek Tno
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Publication of WO2014096785A1 publication Critical patent/WO2014096785A1/fr

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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/80—Constructional details
    • H10K50/85—Arrangements for extracting light from the devices
    • H10K50/854—Arrangements for extracting light from the devices comprising scattering means
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/02—Diffusing elements; Afocal elements
    • G02B5/0205—Diffusing elements; Afocal elements characterised by the diffusing properties
    • G02B5/0236—Diffusing elements; Afocal elements characterised by the diffusing properties the diffusion taking place within the volume of the element
    • G02B5/0242—Diffusing elements; Afocal elements characterised by the diffusing properties the diffusion taking place within the volume of the element by means of dispersed particles
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K2102/00—Constructional details relating to the organic devices covered by this subclass
    • H10K2102/301—Details of OLEDs
    • H10K2102/331—Nanoparticles used in non-emissive layers, e.g. in packaging layer
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/80—Constructional details
    • H10K50/805—Electrodes
    • H10K50/81—Anodes
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K50/00—Organic light-emitting devices
    • H10K50/80—Constructional details
    • H10K50/84—Passivation; Containers; Encapsulations
    • H10K50/844—Encapsulations

Definitions

  • the present invention relates to polyester film suitable for improving light extraction from organic light-emitting diode (OLED) light sources, and to a method of improving light extraction from such OLEDs.
  • OLED organic light-emitting diode
  • OLEDs are electroluminescent devices which have been intensively studied over the past two decades, and have become competitive with established solutions in illumination tasks requiring large-area light sources.
  • OLEDS have consisted of one or more light-emitting organic layers (generally referred to as the light-emitting organic stack) sandwiched between a metallic cathode and a transparent anode deposited on a transparent substrate.
  • Current flowing through the OLED causes the charges carriers (holes and electrons) to recombine in the emissive layer and emit photons.
  • the light-emitting organic layer(s) may be polymeric, and such OLEDs are sometimes referred to as PLEDs.
  • the light-emitting organic layer(s) may comprise a non-polymeric, small-molecule organic compound, and such OLEDs are sometimes referred to as SMOLEDs.
  • the visible light emitted from an organic layer or layer stack may be white light, or a narrower range of wavelengths in the visible region, depending on the organic molecule and the intended application.
  • Suitable light-emitting organic compounds include the commercially available LiviluxTM materials (Merck).
  • the output of an OLED light source should be independent of the emission wavelength over the visible spectrum, i.e. a white light is desired.
  • the thickness of the OLED stack including the electrodes is not more than 1 ⁇ , whereas the substrate thickness is up to and around 1 mm. Because the organic light-emitting layers are very sensitive to air and moisture, the OLED stack is encapsulated within a barrier.
  • the majority of commercially available devices are currently fabricated on rigid glass substrates, although flexible plastic substrates are now being adopted, which will be increasingly important when utilized with roll-to-roll continuous manufacturing techniques.
  • OLEDs which are transparent (TOLEDs) have been proposed for integration into buildings and vehicles as smart-windows. Additionally, the control of electromagnetic radiation across a window may enable cost savings in terms of the heating and cooling of rooms.
  • OLEDs and photovoltaic (PV) cells has also been proposed.
  • the manufacture and application of OLED light sources are now well known and a variety of architectures has been developed, for instance "bottom emission” and "top emission” designs.
  • the bottom-emitting device comprises a transparent bottom substrate layer (typically glass), a transparent anode layer, a light-emitting organic layer, a reflective cathode and an encapsulating layer, in that order.
  • the top-emitting device comprises a bottom substrate layer, a reflecting layer and an anode layer (or a reflecting anode layer), a light-emitting organic layer, a transparent cathode and an encapsulating layer, in that order.
  • the OLEDs comprise at least one transparent electrode, for instance a transparent conductive oxide (TCO) such as indium tin oxide (ITO).
  • TCO transparent conductive oxide
  • ITO indium tin oxide
  • ITO is commonly used in OLEDs because of its high transparency, thermal stability and conductivity.
  • Conductive organic materials alone or in combination with TCOs, are also now being investigated for use as transparent electrodes.
  • One advantage of organic materials as electrodes is the ability to tune their refractive index either to match or intentionally mismatch the organic light-emitting layers.
  • the resulting external quantum efficiency (EQE; photons emitted into air from the device per injected electron) from an optical point of view is therefore at most about 20% when using high efficiency (phosphorescent) materials. This value quickly drops by roughly a factor 4 when using less efficient (fluorescent) materials.
  • wave-guiding refers to the internal reflection of light within a layer and the refraction of light at layer boundaries, which occurs as a result of refractive index differences between adjacent layers, to which Snellius' law can be applied. Wave-guiding results in propagation of light parallel to the plane of the OLED.
  • the refractive index of a glass substrate is around 1.5 whereas the light-emitting organic layers typically have refractive indices of about 1.7 to 1.9. Wave-guiding within the organic/inorganic thin film layer(s) and/or substrate of the stack means absorption losses become more significant.
  • OLED-based lighting In further contrast to incandescent lighting, fluorescent lighting, and inorganic LED-based lighting (for instance, AIGalnP devices and InGaN devices), an advantage of OLED-based lighting is that the OLED device itself may be the luminaire, rather than merely the light bulb in a luminaire, and so does not suffer from the fixture losses associated with such other light sources.
  • substrate wave-guiding can account for losses of up to about 30% of the total power emitted by a radiating dipole (depending on the design of the OLED), and a number of studies have addressed modification of the substrate in order to improve light extraction and increase the efficiency of the OLED.
  • micro-spheres For instance, it is known to modify the topography of the external surface of the substrate by introducing periodic micro-structures of sufficient size with respect to the active area of the OLED, which increases the direct emission of light from the substrate, and such structures include micro-spheres, micro-pyramids and other micro-lens arrays (see, for instance, Greiner et al., Jap. J. Appl. Phys., 2007, 46 (7A), p4125; and Yang et al., Appl. Phys. Lett. 2010, 97, p223303). It is also known to dispose a volume-scattering layer containing light- scattering particles such as Ti0 2 in an organic layer on the external surface of the OLED (Greiner et al., supra).
  • a particular problem with conventional OLED light sources is that one or more optical properties including emission intensity or emission colour deteriorate as the viewing angle changes from 0° (i.e. the normal direction; forward emission) through to 90°.
  • Angular variations in colour and intensity are a particular problem, and it would be desirable to provide a more homogeneous emission colour and/or emission intensity over the entire viewing angle range. Only a portion of the light emitted by the OLED escapes into air and as a result of limited refraction from a dense to rare medium (e.g. glass or plastic to air) much of the angle dependence is hidden in the substrate. It is therefore important to evaluate the enhancement provided to the OLED emission based on the emission by the OLED into the substrate.
  • a method for reducing the angular dependence of emission colour and/or emission intensity of an OLED light source and/or increasing light extraction from said OLED comprising the step of disposing a biaxially oriented polyester film as a layer in a multi-layer assembly further comprising an OLED light source, wherein said polyester film is disposed on a light-emitting surface of said OLED or within said OLED, wherein said polyester film comprises light-scattering particles.
  • a biaxially oriented polyester film comprising light-scattering particles as a layer in a multi-layer assembly further comprising an OLED light source, wherein said polyester film is disposed on a light- emitting surface of said OLED or within said OLED, for the purpose of reducing the angular dependence of emission colour and/or emission intensity of said OLED and/or increasing light extraction from said OLED.
  • reducing angular dependence means that the angular dependence of the assembly comprising said OLED and said polyester film is reduced (and hence improved) relative to the assembly comprising said OLED in the absence of said polyester film.
  • the present invention is of particular utility for reducing the angular dependence of emission colour and/or emission intensity of an OLED light source, and particularly for reducing the angular dependence of emission colour of an OLED light source.
  • polyester films used in the present invention exhibit surprisingly superior performance with regard to the angular dependence of emission colour and/or emission intensity, relative to the micro-lenticular arrays, for a given OLED the outer surface of which has been modified by the film or micro-lens array.
  • the polyester films used in the present invention preferably reduce the angular dependence of emission colour of the OLED light source, as measured by CD avg described hereinbelow, by at least 50%, preferably at least 75% and preferably at least 90%, relative to the value of CD avg of the OLED in the absence of said polyester film.
  • the out-coupled multi-layer assemblies comprising said OLED light source and said biaxially oriented polyester film exhibit a value for CD avg of no more than 1x10 "2 , preferably no more than 5x10 "3 , preferably no more than 2.5x10 "3 , preferably no more than 1x10 "3 , and preferably no more than 5x10 "4 .
  • the films used in the present invention exhibit excellent out-coupling performance with significant increases in external extraction efficiency of OLED light sources, providing an enhancement factor (when measured normal to the OLED surface according to the method described hereinbelow) of at least 10%.
  • the enhancement factor is at least 40%; in a further embodiment, the enhancement factor is at least 70%; and in a further embodiment, the enhancement factor is at least 85%.
  • novel and advantageous multilayer assemblies comprising an OLED light source and a biaxially oriented polyester film comprising light-scattering particles, wherein said polyester film is disposed on a light-emitting surface of said OLED or within said OLED, as identified hereinbelow.
  • novel and advantageous multi-layer assemblies identified hereinbelow provide novel and advantageous methods and uses for increasing light extraction from said OLED.
  • the OLED light sources can have a variety of different architectures and may comprise one or more organic light-emitting layers.
  • At least one of the electrodes is transparent, and in one embodiment both electrodes are transparent.
  • a transparent electrode may comprise a transparent conductive oxide (TCO) and/or a conductive organic material.
  • a transparent electrode (preferably the anode) comprises a layer of conductive organic material, optionally in association with a TCO layer.
  • a transparent electrode comprises a layer of conductive organic material in the absence of a TCO layer.
  • Suitable conductive organic materials include poly(3,4- ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT/PSS), commercially available as OrgaconTM conductive polymers (Agfa Materials).
  • One of the electrodes may be a reflective electrode, and such electrodes are conventional in the art and include, for instance barium/silver or barium/aluminium layers or other combinations involving a material beneficial to electron injection, such as LiF, NaF, CsF, Cs2C03, metal oxides or the like.
  • the substrate may be glass or a polymeric material. Polymeric substrates have the advantage of providing flexibility to the OLED light source, but require additional barrier layers to prevent ingress of air or moisture into the OLED in order to protect the sensitive organic light-emitting stack.
  • the OLED light sources may be categorised depending on the characteristics of (i) specular reflectance (Rs), and (ii) angle-independence (Al) of emitted light.
  • the angle independence (Al) of emitted light within the optical window of the OLED structure is herein defined as the angle (measured from the normal) at which the intensity of the emission (measured as normalised radiance) deviates by more than 10% from its initial level.
  • the emission intensity and threshold angle are obtained by measuring the emission characteristics of a point source OLED device while it is covered with a half-sphere. In its simplest form, this categorisation generates four classes, in which these characteristics are as follows (and as illustrated in Figure 1):
  • Class I a specular reflectance of no more than a threshold value Rs y ;
  • Class II a specular reflectance of greater than Rs y and
  • Class III a specular reflectance of greater than Rs y ;
  • Class IV a specular reflectance of no more than Rs y ;
  • the threshold value (Rs y ) of specular reflectance is 70%.
  • Preferred OLEDs of Class II and Class III in the present invention exhibit a specular reflection of at least 80%, and preferably at least 85%
  • the threshold value (Al x ) of angle independence is 45°.
  • Preferred OLEDs of Class III and Class IV in the present invention exhibit an angle independence of at least 70°.
  • the present inventors have found that the out-coupling response for a given out- coupling film depends on the class of OLED, and also that out-coupling response for a given class of OLED depends on the out-coupling film, and this varies in a manner which could not have been predicted.
  • the differences in response include: (i) differences in the enhancement factor (i.e. the increase in the amount of light extracted from the OLED by the out-coupling film); and
  • the present inventors have been able to formulate specific out-coupling films for combination with specific OLED classes.
  • the out-coupling films utilised in the present invention reduce the angle- dependence of one or more of said optical properties (emission intensity and emission colour) of an OLED light source, particularly with regard to colour.
  • the out- coupled OLED light sources of the present invention exhibit angle-dependence represented by plot (d) in Figure 2, wherein the angle-dependence plot of the out-coupled OLEDs more closely approximates to the ideal Lambertian behaviour of plot (a) when compared to the angle- dependence plot of the OLED in the absence of the out-coupling film.
  • the presence of the out-coupling film shifts the angle-dependent plot (d) of the OLED closer to the angle-independent plot (a).
  • the polyester films described herein may be used as an external extraction structure (EES) applied to the surface of a conventional OLED light source, which may comprise either a glass or polymeric transparent substrate.
  • EES external extraction structure
  • the polyester film may comprise part or all of the transparent substrate on which is deposited the active layers of the OLED during its fabrication, and which forms the transparent substrate in the OLED.
  • the polyester film preferably replaces the glass substrate, resulting in a flexible device.
  • the polyester film is a self-supporting film or sheet by which is meant a film or sheet capable of independent existence in the absence of a supporting base.
  • the polyester film is preferably a biaxially oriented film.
  • the polyester of said polyester film is preferably polyethylene terephthalate or polyethylene naphthalate, and more preferably polyethylene naphthalate.
  • the polyethylene naphthalate is preferably derived from 2,6-naphthalenedicarboxylic acid.
  • the polyester may also contain relatively minor amounts of one or more residues derived from other dicarboxylic acids and/or diols.
  • dicarboxylic acids include isophathalic acid, phthalic acid, 1 ,4-, 2,5-, 2,6- or 2,7- naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, hexahydro-terephthalic acid, 1 ,10- decanedicarboxylic acid and aliphatic dicarboxylic acids of the general formula C n H2n(COOH) 2 wherein n is 2 to 8, such as succinic acid, glutaric acid sebacic acid, adipic acid, azelaic acid, suberic acid or pimelic acid.
  • diols include aliphatic and cycloaliphatic glycols, such as 1 ,4- cyclohexanedimethanol.
  • the polyester film contains only one dicarboxylic acid, i.e. terephthalic acid or naphthalenedicarboxylic acid, and preferably naphthalenedicarboxylic acid.
  • the polyester contains only one glycol, i.e. ethylene glycol.
  • the polyester resin is the major component of the film, and makes up at least 50%, preferably at least 65%, preferably at least 80%, preferably at least 90%, and preferably at least 95% by weight of the total weight of the film.
  • the intrinsic viscosity of the polyester from which the film is manufactured is preferably at least about 0.65, preferably at least about 0.70, preferably at least about 0.75 and preferably at least about 0.80.
  • Formation of the polyester is conveniently effected in a known manner by condensation or ester interchange, generally at temperatures up to about 295 °C.
  • Solid state polymerisation may be used to increase the intrinsic viscosity to the desired value, using conventional techniques well- known in the art, for instance using a fluidised bed such as a nitrogen fluidised bed or a vacuum fluidised bed using a rotary vacuum drier.
  • the film comprises light-scattering particles which increase the degree of internal scattering of the polyester film, but without significant reduction in the total light transmittance of the film.
  • the particles may be non-voiding inorganic particles, voiding inorganic particles or incompatible resin filler particles.
  • inorganic particles which do not give rise to voiding in polyester film are metal or metalloid oxides, such as alumina, silica (especially precipitated or diatomaceous silica and silica gels) and titanium dioxide, and are preferably titanium dioxide particles or organic particles.
  • An example of inorganic particles which give rise to voiding in polyester film is barium sulphate.
  • incompatible resin filler particles are polyolefins, particularly polypropylene.
  • the light-scattering particles in the polyester film comprise or consist of non-voiding inorganic particles.
  • the light-scattering particles consist of non-voiding inorganic particles, preferably titanium dioxide particles.
  • the titanium dioxide may be in anatase or rutile form.
  • Non-voiding inorganic particles are preferably present in an amount of no more than about 1.0 wt%, preferably no more than about 0.95 wt%, preferably no more than about 0.90wt%, preferably no more than about 0.85 wt%, and preferably at least about 0.03 wt%, preferably at least about 0.05 wt%, preferably at least about 0.10 wt%, preferably at least about 0.15 wt%, preferably at least about 0.20 wt%.
  • Particle concentrations described herein are calculated relative to the total weight of the polyester film, unless otherwise stated.
  • Voiding inorganic particles are preferably present in an amount of no more than about 5.0 wt%, preferably no more than about 4.0 wt%, and preferably at least about 0.50 wt%, preferably at least about 1.0 wt%, preferably at least about 2.0 wt%, and preferably at least about 3.0 wt%.
  • Incompatible resin particles are preferably present in an amount of no more than about 1.5 wt%, in one embodiment no more than about 1.0 wt%, and in a further embodiment no more than about 0.50 wt%; preferably at least about 0.01 wt%, preferably at least about 0.05 wt%, preferably at least about 0.10 wt%, and preferably at least about 0.20 wt%.
  • the film comprises mixtures of the afore-mentioned different types of light-scattering particles
  • the relative proportions thereof may be adjusted to provide the required haze characteristics, as discussed hereinbelow.
  • the non-voiding inorganic particles make up greater than 50 wt% of the total amount of light-scattering particles in the film, and in one embodiment at least 60 wt%, in a further embodiment at least 70 wt%, in a further embodiment at least 80 wt%, in a further embodiment at least 90wt%, in a further embodiment at least 95 wt%, and in a further embodiment at least 99 wt% of the light scattering particles in the film.
  • the light-scattering particles are non-voiding inorganic particles.
  • said particles are present in an amount of from about 0.20 to about 0.95 wt%, preferably in an amount of at least about 0.25 wt%, preferably at least about 0.30 wt%, preferably at least about 0.32 wt%, preferably at least about 0.33 wt%, and preferably at least about 0.35 wt%, and preferably no more than about 0.85 wt%, preferably no more than about 0.80 wt%.
  • the light-scattering particles are voiding particles.
  • Such voiding particles may be inorganic particles (Embodiment B1), or incompatible resin filler particles (Embodiment B2), or mixtures of voiding inorganic particles and incompatible resin filler particles (Embodiment B3).
  • the scattering particles are voiding particles
  • the inorganic particles of Embodiment B1 are preferred.
  • the film comprises both non-voiding and voiding particles, as defined above.
  • the particles may be non-voiding inorganic particles in combination with voiding inorganic particles (Embodiment C1 herein), but typically the non-voiding inorganic particles are in combination with the afore-mentioned voiding organic particles (Embodiment C2 herein). Less preferred is the combination of non-voiding inorganic particles with both voiding inorganic particles and incompatible resin filler particles (Embodiment C3).
  • the non-voiding inorganic particles are preferably in the present in an amount of from about 0.10 to about 0.50 wt% and the incompatible resin filler particles are preferably present in an amount of from about 0.05 to about 0.50 wt%.
  • the light scattering particles are preferably selected from voiding and non-voiding inorganic particles, optionally in combination with voiding organic particles. Where inorganic and organic scattering particles are both present, the inorganic particles are preferably of the non-voiding type, as defined herein. In this embodiment, haze is preferably at least about 30%, more preferably at least about 40%, and preferably no more than about 80%, and more preferably no more than about 75%.
  • the particle concentration is preferably at least about 0.25wt% (and preferably at least about 0.30wt%) and preferably no more than about 0.65wt% (and preferably no more than about 0.50wt%) where only non-voiding inorganic particles are present.
  • the total particle concentration is preferably at least about 0.2wt% and preferably no more than about 0.65wt%.
  • the out-coupling films described herein provide significant out- coupling (an enhancement factor of at least 10%) for OLEDs of class I, in respect of films having haze of at least 30%, preferably at least 40%, and preferably no more than 80%.
  • the light-scattering particles are preferably selected from voiding and non-voiding inorganic particles, optionally in combination with voiding organic particles. More preferably, the light-scattering particles in the film are selected from voiding and non-voiding inorganic particles in the absence of voiding organic particles. More preferably still, the light-scattering particles in the film are selected from non-voiding inorganic particles in the absence of voiding particles (inorganic and/or organic). Where inorganic and organic scattering particles are both present, the inorganic particles are preferably of the non- voiding type, as defined herein.
  • haze is at least about 10%, preferably at least about 20%, more preferably at least about 30%, more preferably at least about 40%, more preferably at least about 45%, more preferably at least about 50%, and preferably no more than about 95%, and more preferably no more than about 85%.
  • the preferred particle concentrations are the generally preferred ranges described above.
  • the present inventors have found that the combination of a scattering out-coupling film (particularly a film having the preferred particle profile as described hereinabove) with an OLED of class II provides greater out-coupling enhancement when compared to the combination of the same scattering film with an OLED of class I.
  • a preferred embodiment of the present invention is the combination of an OLED of class II with a scattering film wherein the scattering particles are selected from voiding and non-voiding inorganic particles, optionally in combination with voiding organic particles, more preferably wherein the scattering particles are selected from voiding and non-voiding inorganic particles in the absence of voiding organic particles, and more preferably still wherein the scattering particles are selected from non-voiding inorganic particles in the absence of voiding particles (inorganic and/or organic).
  • this combination provides significant out-coupling (an enhancement factor of at least 10%) at relatively low haze (about 10%), and with relatively high TLT.
  • this combination provides even greater out-coupling (an enhancement factor of at least 40%) at relatively higher haze values (around 45% and above).
  • the light-scattering particles are preferably selected from voiding and non-voiding inorganic particles, optionally in combination with voiding organic particles. More preferably, the light-scattering particles in the film are selected from voiding and non-voiding inorganic particles in the absence of voiding organic particles. More preferably still, the light-scattering particles in the film are selected from non-voiding inorganic particles in the absence of voiding particles (inorganic and/or organic). Where inorganic and organic scattering particles are both present, the inorganic particles are preferably of the non- voiding type, as defined herein.
  • haze is preferably at least about 15%, more preferably at least about 25%, more preferably at least about 40%, more preferably at least about 50%, more preferably at least about 60%, more preferably at least about 65%, and preferably no more than about 95%.
  • the particle concentration is preferably at least about 0.35wt%, preferably at least about 0.45wt%, preferably at least about 0.50wt% where only non-voiding inorganic particles are present. Where both non-voiding inorganic and voiding organic particles are present, the total particle concentration is preferably at least about 0.35wt%.
  • the present inventors have found that the combination of a scattering out-coupling film (particularly a film having the preferred particle profile as described hereinabove) with an OLED of class III provides even greater out-coupling enhancement when compared to the combination of the same scattering films with an OLED of class II.
  • a particularly preferred embodiment of the present invention is the combination of an OLED of class III with a scattering film wherein the scattering particles are selected from voiding and non-voiding inorganic particles, optionally in combination with voiding organic particles, more preferably wherein the scattering particles are selected from voiding and non-voiding inorganic particles in the absence of voiding organic particles, and more preferably still wherein the scattering particles are selected from non-voiding inorganic particles in the absence of voiding particles (inorganic and/or organic).
  • this combination provides significant out-coupling (an enhancement factor of at least 10%) at relatively low haze (about 10%), and with relatively high TLT.
  • the particle size of the light-scattering particles is preferably in the range of from about 150 nm to about 10,000 nm, preferably at least about 180nm, more preferably at least about 200nm, preferably at least about 250nm, and preferably no more than about 1000nm, preferably no more than about 5000nm.
  • particle size refers to the volume distributed median particle diameter (equivalent spherical diameter corresponding to 50% of the volume of all the particles, read on the cumulative distribution curve relating volume % to the diameter of the particles - often referred to as the "D(v,0.5)" value). Particle size is determined by scanning electron micrograph (SEM) images of sections of the manufactured film, which are subjected to image analysis to determine the distribution of sizes in situ. The median particle size may be determined by plotting a cumulative distribution curve representing the percentage of particle volume below chosen particle sizes and measuring the 50th percentile.
  • the film may comprise any other additive conventionally employed in the manufacture of polyester films.
  • agents such as hydrolysis stabilisers, anti-oxidants, UV-stabilisers, cross- linking agents, dyes, fillers, pigments, voiding agents, lubricants, radical scavengers, thermal stabilisers, flame retardants and inhibitors, anti-blocking agents, surface active agents, slip aids, gloss improvers, prodegradents, viscosity modifiers and dispersion stabilisers may be incorporated as appropriate.
  • the film of the present invention typically comprises particulate fillers to improve handling and windability during manufacture, as is conventional in the art.
  • filler is typically present in only small amounts, generally not exceeding about 0.5% and preferably less than about 0.3% by weight of the polyester, and is typically selected from silica and talc, preferably silica. Such components may be introduced into the polymer in a conventional manner.
  • the components may be mixed with the polymer by tumble or dry blending or by compounding in an extruder, followed by cooling and, usually, comminution into granules or chips. Masterbatching technology may also be employed. Formation of the polyester film may be effected by conventional extrusion techniques well- known in the art. In general terms the process comprises the steps of extruding a layer of molten polymer at a temperature within the range of from about 275 to about 300°C, quenching the extrudate and orienting the quenched extrudate.
  • Orientation may be effected by any process known in the art for producing an oriented film, for example a tubular or flat film process.
  • Biaxial orientation is effected by drawing in two mutually perpendicular directions in the plane of the film to achieve a satisfactory combination of mechanical and physical properties.
  • simultaneous biaxial orientation may be effected by extruding a thermoplastics polyester tube which is subsequently quenched, reheated and then expanded by internal gas pressure to induce transverse orientation, and withdrawn at a rate which will induce longitudinal orientation.
  • the film-forming polyester is extruded through a slot die and rapidly quenched upon a chilled casting drum to ensure that the polyester is quenched to the amorphous state.
  • Orientation is then effected by stretching the quenched extrudate in at least one direction at a temperature above the glass transition temperature of the polyester.
  • Sequential orientation may be effected by stretching a flat, quenched extrudate firstly in one direction, usually the longitudinal direction, i.e. the forward direction through the film stretching machine, and then in the transverse direction.
  • Forward stretching of the extrudate is conveniently effected over a set of rotating rolls or between two pairs of nip rolls, transverse stretching then being effected in a stenter apparatus. Stretching is generally effected so that the dimension of the oriented film is from 2 to 5, more preferably 2.5 to 4.5 times its original dimension in the or each direction of stretching.
  • stretching is effected at temperatures higher than the T g of the polyester, preferably about 15°C higher than the T g .
  • Greater draw ratios may be used if orientation in only one direction is required. It is not necessary to stretch equally in the machine and transverse directions although this is preferred if balanced properties are desired.
  • a stretched film may be, and preferably is, dimensionally stabilised by heat-setting under dimensional support at a temperature above the glass transition temperature of the polyester but below the melting temperature thereof, to induce the desired crystallisation of the polyester.
  • TD transverse direction
  • Toe-in can involve dimensional shrinkage of the order 2 to 4% but an analogous dimensional relaxation in the process or machine direction (MD) is difficult to achieve since low line tensions are required and film control and winding becomes problematic.
  • the actual heat-set temperature and time will vary depending on the composition of the film and its desired final thermal shrinkage but should not be selected so as to substantially degrade the toughness properties of the film such as tear resistance.
  • the film may be further stabilized through use of an in-line relaxation stage.
  • the relaxation treatment can be performed off-line.
  • the film is heated at a temperature lower than that of the heat-setting stage, and with a much reduced MD and TD tension.
  • the tension experienced by the film is a low tension and typically less than 5 kg/m, preferably less than 3.5 kg/m, more preferably in the range of from 1 to about 2.5 kg/m, and typically in the range of 1.5 to 2 kg/m of film width.
  • the reduction in film speed (and therefore the strain relaxation) is typically in the range 0 to 2.5%, preferably 0.5 to 2.0%. There is no increase in the transverse dimension of the film during the heat-stabilisation step.
  • the temperature to be used for the heat stabilisation step can vary depending on the desired combination of properties from the final film, with a higher temperature giving better, i.e. lower, residual shrinkage properties.
  • a temperature of 135 to 250 °C is generally desirable, preferably 150 to 230 °C, more preferably 170 to 200 °C.
  • the duration of heating will depend on the temperature used but is typically in the range of 10 to 40 seconds, with a duration of 20 to 30 seconds being preferred.
  • This heat stabilisation process can be carried out by a variety of methods, including flat and vertical configurations and either "off-line” as a separate process step or "in-line” as a continuation of the film manufacturing process. Film thus processed will exhibit a smaller thermal shrinkage than that produced in the absence of such post heat-setting relaxation.
  • the polyester film may be either a single layer or a composite structure comprising a plurality of polyester layers. Formation of such a composite structure may be effected by co-extrusion, either by simultaneous coextrusion of the respective film-forming layers through independent orifices of a multi-orifice die, and thereafter uniting the still molten layers or, preferably, by single-channel coextrusion in which molten streams of the respective polymers are first united within a channel leading to a die manifold, and thereafter extruded together from the die orifice under conditions of streamline flow without intermixing thereby to produce a multi-layer film, which may be oriented and heat-set as hereinbefore described.
  • the polyester layers of a composite film are selected from the polyesters described hereinabove, and preferably from PET or PET-based polyesters. Any or each layer in a composite film may comprise any of the additives mentioned above, wherein the additive(s) in a given layer may be the same as or different to the additive(s) in other layers, and in the same or different amounts.
  • the film comprises 2 or 3 layers, preferably having an AB or BAB layer structure.
  • the respective layers may comprise the same or different type of polyester, but typically the same polyester is used in each layer of the composite film.
  • the layers A and B may comprise different concentrations of particulate additive. In one embodiment, the scattering particles are in one layer only.
  • the thickness of the polyester film is preferably in the range of from about 5 to about 500 ⁇ , and more preferably no more than about 250 ⁇ , and typically between about 37 ⁇ and 150 ⁇ .
  • the polyester film used in the present invention is translucent or optically clear.
  • an optically clear film has a % of scattered visible light (haze) of no more than 30%, and/or a total luminous transmission (TLT) for light in the visible region (400 nm to 700 nm) of at least 80%, and preferably both.
  • a translucent film has may have a TLT of at least 50%, preferably at least 60%, and preferably at least 70%.
  • the preferred polyester films used in the present invention have high haze, preferably at least about 20%, preferably at least about 30%, preferably at least about 40%, preferably at least about 50% and in one embodiment at least about 60%.
  • haze is no more than about 95%, preferably no more than about 90%, and in one embodiment no more than about 85%.
  • the films also have high TLT, preferably at least about 60%, preferably at least about 65%, preferably at least about 70%, preferably at least about 75%, preferably at least 80%, and more preferably at least about 85%,
  • the intrinsic viscosity of the polyester film is preferably at least 0.65, preferably at least 0.7, and in one embodiment in the range of from about 0.65 to about 0.75.
  • the use of polyester films with a relatively high intrinsic viscosity provides improved hydrolysis stability.
  • the polyester of the polyester film exhibits an endothermic high temperature peak at a temperature of (A)°C and an endothermic low temperature peak at a temperature of (B)°C, both peaks being measured by differential scanning calorimetry (DSC), wherein the value of (A-B) is in the range from 15°C to 50°C, preferably in the range from 15°C to 45°C, more preferably in the range from 15°C to 40°C, and in one embodiment in the range from 20°C to 40°C, and this characteristic may be achieved as disclosed herein by control of the heat-setting temperature for the particular polyester being used.
  • DSC differential scanning calorimetry
  • the polyester film preferably exhibits a low shrinkage, preferably less than 3% at 150 °C over 30 minutes, preferably less than 2%, preferably less than 1.5%, and preferably less than 1.0%, particularly in the machine (longitudinal dimension) of the film, particularly a biaxially oriented film, and preferably such low shrinkage values are exhibited in both dimensions of the film (i.e. the longitudinal and transverse dimensions).
  • one or both surfaces (preferably only one surface) of the polyester film has disposed thereon a scratch-resistant coating (or hardcoat).
  • the scratch-resistant coating is disposed on the external surface of the film in order to protect the OLED from mechanical damage. That is to say, the scratch-resistant coating is disposed on the surface opposite the surface which is disposed on the OLED light source, or in the embodiments where the film is (or comprises part of) the substrate the scratch-resistant coating comprises the external surface of the substrate of the OLED.
  • the scratch-resistant layer typically has the effect of planarising the surface of the polyester film, the natural surface roughness of which varies as a result of the particulate content, polymer identity and manufacturing history of the film.
  • Many of the conventional approaches to out- coupling have involved the provision of a roughened surface to improve light extraction from OLED light sources.
  • the present invention achieves scratch-resistance using a planarising coating without detriment to light extraction.
  • the scratch-resistant layer may result in an increase in measured haze of the polyester film, and this increase is preferably no more than 20%, more preferably no more than 10% and most preferably no more than 5% of the haze value of the film in the absence of the scratch-resistant layer.
  • the scratch-resistant layer may also result in a decrease in the TLT of the film and this decrease is preferably no more than 20%, more preferably no more than 10% and most preferably no more than 5% of the TLT value of the film in the absence of the scratch-resistant layer.
  • the scratch-resistant coating of the present does not adversely affect the extraction efficiency or the angular dependence of emitted light of the out-coupling film.
  • the planarising scratch-resistant coatings used in the present invention fall broadly into one of the three following classifications; organic, organic/inorganic hybrid and predominantly inorganic coats.
  • Organic planarising scratch-resistant coatings typically comprise (i) a photoinitiator, (ii) a low molecular weight reactive diluent (e.g a monomeric acrylate), (iii) an unsaturated oligomer (e.g. acrylates, urethane acrylates, polyether acrylates, epoxy acrylates or polyester acrylates) and (iv) a solvent.
  • a photoinitiator e.g a monomeric acrylate
  • an unsaturated oligomer e.g. acrylates, urethane acrylates, polyether acrylates, epoxy acrylates or polyester acrylates
  • solvent e.g. a solvent
  • the term "low molecular weight” describes a polymerisable monomeric species.
  • the term “reactive” signifies the polymerisability of the monomeric species.
  • Such organic coatings can be cured by free radical reaction, initiated by a photolytic route. Specific formulations may vary according to the desired final
  • the coating composition comprises a UV-curable mixture of monomeric and oligomeric acrylates (preferably comprising methylmethacrylate and ethylacrylate) in a solvent (such as methylethylketone), typically wherein the coating composition comprises the acrylates at about 20 to 30 wt% solids of the total weight of the composition, and further comprising a minor amount (e.g. about 1 % by weight of the solids) of photoinitiator (e.g. IrgacureTM 2959; Ciba).
  • a minor amount e.g. about 1 % by weight of the solids
  • photoinitiator e.g. IrgacureTM 2959; Ciba
  • Organic/inorganic hybrid coatings are a particularly preferred embodiment of the invention, and they comprise inorganic particles distributed throughout an organic polymeric matrix, which can contain component(s) similar to those described immediately above.
  • the coatings are cured either thermally or by free radical reaction initiated by a photolytic route, and the presence of a photoinitiator is optional.
  • the inorganic phase which is often silica or metal oxide particles is dispersed in the polymerisable organic matrix by a number of strategies.
  • an organic/inorganic hybrid coating comprises inorganic particles preferably selected from silica and metal oxides; and an organic component comprising a low molecular weight reactive component (e.g. monomeric acrylates) and/or an unsaturated oligomeric component (e.g.
  • a thermally-curable hybrid coating comprises an epoxy resin in combination with inorganic (preferably silica) particles which are preferably present at a concentration of at least about 10% (preferably at least about 20%, and preferably no more than about 75%) by weight of the solids of the coating composition (which preferably comprises from 5 to about 20% by weight total solids in alcoholic solution).
  • inorganic preferably silica
  • a UV-curable hybrid coating composition comprises monomeric acrylates (typically multi-functional acrylates) in combination with inorganic (preferably silica) particles in a solvent (such as methylethylketone), typically wherein the coating composition comprises the acrylates and silica at about 5 to 50 wt% solids of the total weight of the coating composition, and typically further comprising a minor amount (e.g. about 1 % by weight of the solids) of photoinitiator.
  • Multi-functional monomeric acrylates are known in the art, and examples include dipentaerythritol tetraacrylate and tris(2- acryloyloxyethyl) isocyanurate.
  • a predominantly inorganic planarising scratch-resistant coating comprises inorganic particles which are contained in a polymerisable predominantly inorganic matrix such as a polysiloxane. This type of hardcoat is cured thermally.
  • planarising scratch-resistant layer Suitable examples of such a planarising scratch-resistant layer are disclosed in, for instance, US-4198465, US-3708225, US-4177315, US-4309319, US-4436851 , US-4455205, US- 0142362, WO-A-03/087247 and EP 1418197 the disclosures of which are incorporated herein by reference.
  • the hardcoat is derived from a coating composition comprising:
  • solvent comprising from about 10 to about 90 weight percent water and from about 90 to about 10 weight percent lower aliphatic alcohol
  • the coating composition has a pH of from about 3.0 to about 8.0, preferably from about 3.0 to about 6.5, preferably less than 6.2, preferably about 6.0 or less, and preferably at least 3.5, preferably at least 4.0.
  • the silica component of the preferred coating composition may be obtained, for example, by the hydrolysis of tetraethyl orthosilicate to form polysilicic acid.
  • the hydrolysis can be carried out using conventional procedures, for example, by the addition of an aliphatic alcohol and an acid.
  • the silica used in the instant coating compositions can be colloidal silica.
  • the colloidal silica should generally have a particle size of about from 5-25 nm, and preferably about from 7-15 nm.
  • Typical colloidal silicas which can be used in the instant invention include those commercially available as "Ludox SM", “Ludox HS-30" and “Ludox LS” dispersions (Grace Davison).
  • the organic silanol component has the general formula RSi(OH) 3 . At least about 60% of the R groups, and preferably about from 80% to 100% of these groups, are methyl. Up to about 40% of the R groups can be higher alkyl or aryl selected from vinyl, phenyl, gamma- glycidoxypropyl, and gamma-methacryloxypropyl.
  • the solvent component generally comprises a mixture of water and one or more lower aliphatic alcohols. The water generally comprises about from 10 to 90 weight percent of the solvent, while the lower aliphatic alcohol complementarity comprises about from 90 to 10 weight percent.
  • the aliphatic alcohols generally are those having from 1 to 4 carbon atoms, such as methanol, ethanol, n-propanol, iso- propanol, n-butanol, sec-butanol and tertiary butanol.
  • the coating composition comprises a cross-linkable organic polymer, for instance a polyethylene imine (PEI), polyester or polvinylalcohol (PVOH), and a cross-linking agent (such as CymelTM 385 or those referred to hereinbelow), in a solvent (typically an aqueous solvent).
  • the coating composition preferably comprises PEI (preferably with a molecular weight (Mw) in the range 600,000 to 900,000).
  • the coating compositions can be applied using conventional coating techniques, including continuous as well as dip coating procedures.
  • the coatings are generally applied at a dry thickness of from about 1 to about 20 microns, preferably from about 2 to 10 microns, and particularly from about 3 to about 10 microns, and in a preferred embodiment from about 4 to about 5 microns.
  • the coating composition can be applied either "off-line” as a process step distinct from the film manufacture, or "in-line” as a continuation of the film manufacturing process.
  • the coating compositions are cured after application to the substrate, either thermally or by UV irradiation as appropriate.
  • Thermal curing is typically effected at a temperature of from about 20 to about 200°C, preferably from about 20 to about 150°C. While ambient temperatures of 20°C require cure times of several days, elevated temperatures of 150°C will cure the coatings in several seconds.
  • the exposed surface of the film Prior to application of the coating, the exposed surface of the film may be subjected to a chemical or physical surface-modifying treatment to improve the bond between that surface and the subsequently applied coating.
  • a preferred treatment is to subject the exposed surface of the film to a high voltage electrical stress accompanied by corona discharge.
  • the preferred treatment by corona discharge may be effected in air at atmospheric pressure with conventional equipment using a high frequency, high voltage generator, preferably having a power output of from 1 to 20 kW at a potential of 1 to 100 kV.
  • Discharge is conventionally accomplished by passing the film over a dielectric support roller at the discharge station at a linear speed preferably of 1.0 to 500 m per minute.
  • the discharge electrodes may be positioned 0.1 to 10.0 mm from the moving film surface.
  • the polyester film may be coated with a primer layer prior to application of the afore-mentioned coating, in order to improve adhesion of the substrate to the afore-mentioned coating composition.
  • a primer layer may be any suitable adhesion-promoting polymeric composition known in the art, including polyester and acrylic resins.
  • the primer composition may also be a mixture of a polyester resin with an acrylic resin.
  • Acrylic resins may optionally comprise oxazoline groups and polyalkylene oxide chains.
  • the polymer(s) of the primer composition is/are preferably water-soluble or water-dispersible.
  • Polyester primer components include those obtained from the following dicarboxylic acids and diols. Suitable di-acids include terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, 1 ,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid, a dimer acid, and 5-sodium sulfoisophthalic acid. A copolyester using two or more dicarboxylic acid components is preferred.
  • the polyester may optionally contain a minor amount of an unsaturated di-acid component such as maleic acid or itaconic acid or a small amount of a hydroxycarboxylic acid component such as p- hydroxybenzoic acid.
  • Suitable diols include ethylene glycol, 1 ,4-butanediol, diethylene glycol, dipropylene glycol, 1 ,6-hexanediol, 1 ,4-cyclohexanedimethylol, xylene glycol, dimethylolpropane, poly(ethylene oxide) glycol, and poly(tetramethylene oxide) glycol.
  • the glass transition point of the polyester is preferably 40 to 100°C, preferably 60 to 80°C.
  • Suitable polyesters include copolyesters of PET or PEN with relatively minor amounts of one or more other dicarboxylic acid comonomers, particularly aromatic di-acids such as isophthalic acid and sodium sulphoisophthalic acid, and optionally relatively minor amounts of one or more glycols other than ethylene glycol, such as diethylene glycol.
  • the primer layer comprises an acrylate or methacrylate polymer resin.
  • the acrylic resin may comprise one or more other comonomers. Suitable comonomers include alkyl acrylates, alkyl methacrylates (where the alkyl group is preferably methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, f-butyl, 2-ethylhexyl, cyclohexyl or the like); hydroxy-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, and 2-hydroxypropyl methacrylate; epoxy group-containing monomers such as glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether; carboxyl group or its salt-containing monomers, such as acrylic acid, methacrylic acid, itaconic acid, maleic acid,
  • the acrylic resin is copolymerised with one or more monomer(s) containing oxazoline groups and polyalkylene oxide chains.
  • the oxazoline group-containing monomer includes 2-vinyl-2-oxazoline, 2-vinyl-4- methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4- methyl-2-oxazoline, and 2-isopropenyl-5-methyl-2-oxazoline.
  • One or more comonomers may be used.
  • 2-lsopropenyl-2-oxazoline is preferred.
  • the polyalkylene oxide chain-containing monomer includes a monomer obtained by adding a polyalkylene oxide to the ester portion of acrylic acid or methacrylic acid.
  • the polyalkylene oxide chain includes polymethylene oxide, polyethylene oxide, polypropylene oxide, and polybutylene oxide. It is preferable that the repeating units of the polyalkylene oxide chain are 3 to 100.
  • the primer composition comprises a mixture of polyester and acrylic components, particularly an acrylic resin comprising oxazoline groups and polyalkylene oxide chains
  • the content of the polyester is 5 to 95 % by weight, preferably 50 to 90 % by weight
  • the content of the acrylic resin is 5 to 90 % by weight, preferably 10 to 50 % by weight.
  • acrylic resins include:
  • a copolymer of (a) 35 to 40 mole % alkyl acrylate, (b) 35 to 40 % alkyl methacrylate, (c) 10 to 15 mole % of a comonomer containing a free carboxyl group such as itaconic acid, and (d) 15 to 20 mole % of an aromatic sulphonic acid and/or salt thereof such as p-styrene sulphonic acid, an example of which is a copolymer comprising ethyl acrylate/methyl methacrylate/itaconic acid/p-styrene sulphonic acid and/or a salt thereof in a ratio of 37.5/37.5/10/15 mole %, as disclosed in EP-A-0429179 the disclosure of which is incorporated herein by reference; and (ii) an acrylic and/or methacrylic polymeric resin, an example of which is a polymer comprising about 35 to 60 mole % ethyl acrylate, about
  • the primer or adherent layer may also comprise a cross-linking agent which improves adhesion to the substrate and should also be capable of internal cross-linking.
  • Suitable cross-linking agents include optionally alkoxylated condensation products of melamine with formaldehyde.
  • the primer or adherent layer may also comprise a cross-linking catalyst, such as ammonium sulphate, to facilitate the cross-linking of the cross-linking agent.
  • a cross-linking catalyst such as ammonium sulphate
  • the coating of the primer layer onto the substrate may be performed in-line or off-line, but is preferably performed "in-line", and preferably between the forward and sideways stretches of a biaxial stretching operation.
  • the scratch-resistant layer provides mechanical protection to the film, as judged for example by the Taber abraser test (ASTM Method D-1044) in which the haze on the test samples is determined by ASTM Method D-1003.
  • the Taber Abrasion test will typically cause controlled damage to the surface of unprotected film such that under the standard conditions of treatment, the haze of the film is seen to increase by 40-50%.
  • the surface of the scratch-resistant coating preferably exhibits a surface having an Ra value, as measured herein, of less than 0.7 nm, preferably less than 0.6 nm, preferably less than 0.5 nm, preferably less than 0.4 nm, preferably less than 0.3 nm, and ideally less than 0.25 nm, and/or an Rq value, as measured herein, of less than 0.9 nm, preferably less than 0.8 nm, preferably less than 0.75 nm, preferably less than 0.65 nm, preferably less than 0.6 nm, preferably less than 0.50 nm, preferably 0.45nm or lower, preferably less than 0.35 nm, and ideally less than 0.3 nm.
  • an Ra value as measured herein, of less than 0.7 nm, preferably less than 0.6 nm, preferably less than 0.5 nm, preferably less than 0.4 nm, preferably less than 0.3 nm, and ideally less than 0.25
  • the polyester film may have disposed thereon a barrier layer, which is particularly important where the film is used as a partial or complete replacement for glass as the substrate layer in the OLED light source, for instance in order to provide flexibility (as described hereinabove for the "second embodiment").
  • a barrier layer which is particularly important where the film is used as a partial or complete replacement for glass as the substrate layer in the OLED light source, for instance in order to provide flexibility (as described hereinabove for the "second embodiment”).
  • the organic light-emitting layers are very sensitive to air and moisture.
  • the barrier layer in particular provides barrier properties to water vapour and/or oxygen transmission, particularly such that the water vapour transmission rate is less than 10 "3 g/m 2 /day and/or the oxygen transmission rate is less than 10 "3 /ml_/m 2 /day.
  • the water vapour transmission rate is less than 10 "4 g/m 2 /day, preferably less than 10 "5 g/m 2 /day, preferably less than 10 "6 g/m 2 /day.
  • the oxygen transmission rate is less than 10 " 4 g/m 2 /day, preferably less than 10 "5 g/m 2 /day.
  • a barrier layer is typically applied in a sputtering process at elevated temperatures, and may be organic or inorganic.
  • a barrier layer can itself comprise one or more discrete layers, and may comprise one or more organic layer(s) and one or more inorganic layer(s). However, multi-layer arrangements, particularly of inorganic and organic layer combinations, are less preferred since they may increase wave-guiding and reduce extraction efficiency.
  • Materials which are suitable for use to form a barrier layer are disclosed, for instance, in US-6, 198,217.
  • Typical organic barrier layers include photocurable monomers or oligomers, or thermoplastic resins. Photocurable monomers or oligomers should have low volatility and high melting points.
  • Examples of such monomers include trimethylol acrylates such as trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate and the like; long-chain acrylates such as 1 ,6- hexanediol diacrylate, 1 ,6-hexanediol dimethacrylate and the like; and cyclohexyl acrylates such as dicyclopentenyloxyethyl acrylate, dicyclopentenyloxy acrylate, cyclohexyl methacrylate and the like.
  • trimethylol acrylates such as trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate and the like
  • long-chain acrylates such as 1 ,6- hexanediol diacrylate, 1 ,6-hexanediol dimethacrylate and the like
  • cyclohexyl acrylates such as dicyclopentenyl
  • oligomers examples include acrylate oligomers, epoxy acrylate oligomers, urethane acrylate oligomers, ether acrylate oligomers, and the like.
  • Photoinitiators such as benzoin ethers, benzophenones, acetophenones, ketals and the like, may be used to cure the resin.
  • suitable thermoplastic resins include polyethylene, polymethyl methacrylate, polyethylene terephthalate and the like. These organic materials are typically applied by vacuum deposition.
  • Typical inorganic barrier layers are made of a material which exhibits low moisture permeability and is stable against moisture.
  • oxides, nitrides and sulphides of Groups IVB, VB, VIB, IMA, MB, IVA, VA and VIA of the Periodic Table and combinations thereof include oxides such as Si0 2 , SiO, GeO, Al 2 0 3 , ZnO, Zr0 2 , Hf0 2 and the like, nitrides such as AIN, TiN, Si 3 N 4 and the like, and metals such as Al, Ag, Au, Pt, Ni and the like. Mixed oxide-nitrides such as may also be used.
  • the inorganic material is usually applied using a vapour phase technique such as vacuum deposition, sputtering and the like under standard conditions. Where the polyester film is used as a transparent substrate in the OLED, the barrier layer must also exhibit optical transparency.
  • the oxides noted above, as well as the nitrides of Si and Al are of particular utility here.
  • the thickness of the barrier layer is preferably in the range of 2nm to 100 nm, more preferably 2 to 50 nm. Thinner layers are more tolerant to flexing without causing the film to crack, which is an important property of flexible substrates in OLED light sources since cracking compromises barrier properties. Thinner barrier films are also more transparent.
  • the concentration of inorganic filler (such as Ti0 2 or BaS0 4 ) present in the polymer film, also referred to as "inorganic loading”, may be measured using gravimetric means.
  • a specimen of material is firstly weighed, then pyrolysed, and the residual mass reweighed.
  • the pyrolysis treatment involves heating a sample of known mass from 330°C to 500°C and holding at temperature overnight. The mass of the residual inorganic filler is then expressed as a weight percentage (wt%) of that of the initial sample.
  • Clarity was evaluated by measuring total luminance transmission (TLT) and haze (% of scattered transmitted visible light) through the total thickness of the film using a Haze-gard plus spherical hazemeter (BYK Gardner) according to the standard test method ASTM D1003. This test method was used herein to record haze values up to 100%.
  • the amount of Ti0 2 in the hazemeter beam may be calculated from (a) the measured weight percentage (wt%) of Ti0 2 in the film; (b) the thickness of the film; and (c) the diameter of the hazemeter beam, which in this case was 19mm.
  • Intrinsic viscosity in units of dL/g was measured by solution viscometry in accordance with ASTM D5225-98(2003) on a ViscotekTM Y-501 C Relative Viscometer (see, for instance, Hitchcock, Hammons & Yau in American Laboratory (March 1994) "The dual-capillary method for modern-day viscometry") by using a 0.5% by weight solution of polyester in o-chlorophenol at 25°C and using the Billmeyer single-point method to calculate intrinsic viscosity:
  • Hred reduced viscosity (in dL/g), which is equivalent to (n r ei-1)/c (also expressed as n, sp /c where Hs P is the specific viscosity).
  • endothermic high temperature peak (A) and endothermic low temperature peak (B), were taken as the maximum displacement above a baseline drawn from the onset of each endothermic melting process to the end of each endothermic melting process. Peak temperature measurements were derived using standard analysis procedures within the Perkin Elmer software. Precision and accuracy of the measurements was ⁇ 2 °C.
  • Oxygen transmission rate is measured using ASTM D3985.
  • Averaging Parameter - Roughness Average (Ra) the arithmetic average of the absolute values of the measured height deviations within the evaluation area and measured from the mean surface.
  • Rq Root Mean Square Roughness
  • the roughness parameters and peak heights are measured relative to the average level of the sample surface area, or "mean surface", in accordance with conventional techniques.
  • a polymeric film surface may not be perfectly flat, and often has gentle undulations across its surface.
  • the mean surface is a plane that runs centrally through undulations and surface height departures, dividing the profile such that there are equal volumes above and below the mean surface.
  • the surface profile analysis is conducted by scanning discrete regions of the film surface within the "field of view" of the surface profiler instrument, which is the area scanned in a single measurement.
  • a film sample may be analysed using a discrete field of view, or by scanning successive fields of view to form an array.
  • the analyses conducted herein utilised the full resolution of the Wyko NT3300 surface profiler, in which each field of view comprises 480x736 pixels.
  • the resolution was enhanced using an objective lens having a 50-times magnification.
  • the resultant field of view has dimensions of 90 ⁇ x 120 ⁇ , with a pixel size of 0.163 ⁇ .
  • the field of view is conveniently increased using an objective lens having a 10-times magnification in combination with a "0.5-times field of view of multiplier" to give a total magnification of 5-times.
  • the resultant field of view has dimensions of 0.9 mm x 1.2 mm, with a pixel size of 1.63 ⁇ .
  • Rp is less than 100nm, more preferably less than 60nm, more preferably less than 50nm, more preferably less than 40nm, more preferably less than 30nm, and more preferably less than 20nm.
  • the results of five successive scans over the same portion of the surface area are combined to give an average value.
  • the Rp value is typically the average value from 100 measurements. Measurements are conducted using a modulation threshold (signal:noise ratio) of 10%, i.e. data points below the threshold are identified as bad data.
  • the surface topography can also be analysed for the presence of extreme peaks having a height of greater than 200nm. In this analysis, a series of measurements of Rp are taken with a pixel size of 1.63 ⁇ over a total area of 5cm 2 .
  • the results may be presented in the form of a histogram in which the data-points are assigned to pre-determined ranges of peak heights, for instance wherein the histogram has equally-spaced channels along the x-axis of channel width 25nm.
  • the histogram may be presented in the form of a graph of peak count (y axis) versus peak height (x axis).
  • the number of surface peaks in the range 300 to 600 nm per 5cm 2 area, as determined from Rp values, may be calculated, and designated as N(300-600).
  • the coatings used in the present invention preferably result in a reduction of N(300-600) in the film, such that the reduction F, which is the ratio of N(300-600) without and with the coating, is at least 5, preferably at least 15, and more preferably at least 30.
  • the N(300-600) value of the coated film is less than 50, preferably less than 35, preferably less than 20, preferably less than 10, and preferably less than 5 peaks per 5cm 2 area.
  • the Surface Area Index is calculated from the "3-dimensional surface area” and the “lateral surface area” as follows.
  • the "3-dimensional (3-D) surface area” of a sample area is the total exposed 3-D surface area including peaks and valleys.
  • the "lateral surface area” is the surface area measured in the lateral direction.
  • To calculate the 3-D surface area four pixels with surface height are used to generate a pixel located in the centre with X, Y and Z dimensions. The four resultant triangular areas are then used to generate approximate cubic volume. This four-pixel window moves through the entire data-set.
  • the lateral surface area is calculated by multiplying the number of pixels in the field of view by the XY size of each pixel.
  • the surface area index is calculated by dividing the 3-D surface area by the lateral area, and is a measure of the relative flatness of a surface.
  • An index which is very close to unity describes a very flat surface where the lateral (XY) area is very near the total 3-D area (XYZ).
  • a Peak-to-Valley value may be obtained from the frequency distribution of positive and negative surface heights as a function of surface height referenced to the mean surface plane.
  • the value PV 95 is the peak-to-valley height difference which envelops 95% of the peak-to-valley surface height data in the distribution curve by omitting the highest and lowest 2.5% of datapoints.
  • the PV 95 parameter provides a statistically significant measure of the overall peak-to-valley spread of surface heights.
  • (ix) Specular Reflectance (Rs) used to characterise the OLED was measured using a Perkin Elmer Lambda 950 UV-visible-NIR spectrometer equipped with integrating sphere (10cm diameter). The OLED lamp was mounted at the sample port of the sphere and the reflectance, relative to a Spectralon® standard, was expressed as an average across the wavelength range, 430nm to 800nm.
  • E F measured emission from the OLED having disposed on the light-emitting surface thereof (or otherwise comprising) the out-coupling film.
  • the emission measurements may be made at a viewing angle which is normal (perpendicular) to the surface of the OLED.
  • E 0 and E F were measured as luminance (according to the method of K. Saxena et al., Journal of Luminescence, 128, 525 (2008)) using a luminance meter (Konica Minolta model LS 1 10) equipped with a close up lens 1 10 which is specified to measure a minimum surface area p 0.4mm.
  • Each measurement was performed in a dark environment to eliminate interference from stray background light and values of luminance (cd/m 2 ) were recorded after stable emission from the OLED source had been established under a steady current of 50mA.
  • E 0 and E F are preferably measured by recording the angle and wavelength dependence of the emission from the OLEDs, using a Display Metrology System (DMS 803, Autronic Melchers GmbH; technical specification document BR001.4, April 201 1). Again, the same measurement conditions of dark environment and source stability were observed, and in this case emission was measured as spectral radiance over the wavelength range of 380nm to 800nm and at 5° intervals from normal to 70° from normal. As before, the spectrally integrated signal from an OLED supporting an out-coupling film layer and from the unmodified OLED, yielded the ratio E F / E 0 and therefore a measure of Enh. The data collected using the DMS instrument allowed several further analyses to be performed.
  • the spectral radiance measured using the DMS was also processed using dedicated software to derive a colour point at each measurement based on the CIE (1976) u'v' colour space, as a function of angle to the normal to the plane of the OLED. These data were used further to calculate CD avg , the average colour difference or change in observed colour of the OLED lamp with angle of view (as taught in "Quantifying angular color stability of organic light-emitting diodes", A. Isphording, M. Pralle, Org. Elec, H, 1916 (2010)).
  • the spectral radiance measurement was also used to derive the External Quantum Efficiency (EQE; as taught in “Organic light emitting diodes (OLEDs) and OLED-based structurally integrated optical sensors", Y. Cai, PhD Thesis, Iowa State Univ., 2010), and the Power Conversion Efficiency (PCE) of the OLED.
  • EQE External Quantum Efficiency
  • PCE Power Conversion Efficiency
  • the latter was calculated by including values of operating current and voltage measured during current-voltage-light cycles, where a voltage is supplied to the device by a Keithley 2440 source meter which also measures the current running through the device.
  • the light was detected using a photodiode connected to a Keithley 2400 multimeter and was calibrated with a luminance meter LS110 from Konica Minolta.
  • the raw optical data allows calculation of, inter alia:
  • Luminous flux (or power), the total wavelength-weighted luminous power emitted in all directions of a light source, as detected by the human eye and based on the standard CIE 1931 photopic luminosity function (a standardised model of the sensitivity of the human eye to different wavelengths), in units of lumen, and calculated by the expression:
  • S(A) measu red is the measured spectral power distribution of the emitted radiation (power per unit wavelength), in watts per metre per steradian (W/sr.nm.m 2 ), is the standard luminosity function (dimensionless), A is wavelength in metres, and
  • f is a factor that includes the measured angle independence (Al) of the OLED.
  • Luminous intensity referred to herein simply as "intensity”
  • the wavelength-weighted luminous flux (F) emitted from a surface per unit solid angle i.e. luminous flux per steradian, in units of candela (lumen/sr).
  • Luminance the wavelength-weighted luminous flux (F) emitted from a surface detected by the eye per unit solid angle per unit projected area perpendicular to the specified direction, in units of candela per square metre (cd/m 2 ), and defined by the formula:
  • ⁇ is the luminous power (lumen, Im)
  • ⁇ is the angle between the surface normal and the specified direction
  • A is the area of the surface (m 2 ), and
  • il is the solid angle (sr) subtended by the measurement.
  • the objective radiometric quantity analogous to luminance i.e. the flux emitted from a surface per unit solid angle per unit projected area perpendicular to the specified direction, in units of watts per steradian per square metre (W/sr/m 2 ), and defined by the formula: wherein:
  • L is the radiance (W/sr/m 2 ) in the direction ⁇
  • ⁇ is the total radiant power (W) emitted
  • Lambertian surfaces are unique in that they reflect incident light in a completely diffuse manner. It does not matter what the angle of incidence ⁇ of an incoming ray is, the distribution of light leaving the surface remains unchanged. In other words, a Lambertian surface has a constant radiance or luminance that is independent of the viewing angle.
  • the total luminous flux (F) (F tof in the expression below) can be calculated from the peak luminous intensity (l ma x) > by integrating the cosine law:
  • the normalised values are then compared to a Lambertian emitter (line (a) in Figure 2). If the line (a) in Figure 2 has a value of 1 (corresponding to a solid angle of ⁇ sr) then any value of less than 1 signifies an OLED with a non-Lambertian and angle-dependent emission profile.
  • EQE External Quantum Efficiency
  • ⁇ is the solid angle
  • f is a factor that includes the measured angle independence (Al) of the OLED (the factor f corrects the solid angle from Lambertian ( ⁇ ) to the actual value of the solid angle.
  • Al measured angle independence
  • ⁇ Lambertian
  • the normalization of the radiance (in 0-70° or preferably 0-90°) then yields a value around 1 where 1 means a ⁇ solid angle. (Larger than 1 means super-Lambertian, smaller than 1 means sub-Lambertian characteristics)),
  • I applied is the current applied to the OLED
  • SWmeasured is the measured spectral power distribution of the emitted radiation (power per unit wavelength), in watts per metre, per steradian (W/sr.nm.m 2 ), where sr stands for steradian, and
  • e is the unit charge
  • h Planck's constant
  • c is the speed of light.
  • Colour and the angular dependence of emission colour were derived from measurements collected using the Display Metrology System (DMS 803, Autronic Melchers GmbH). Dedicated software was used to plot x, y chromaticity diagrams of the emission of OLEDs as a function of angle while colour difference and average colour difference (CD avg ) exhibited by each OLED were derived according to the calculations of
  • CD avg is defined as the angular dependence of the chromaticity emitted from an OLED:
  • ⁇ /(Au' + ( ⁇ ) 2
  • the lamp was a white OLED, having a transparent polyester film substrate (biaxially oriented PEN film); an inorganic barrier layer from silicon nitride; a transparent anode based on PEDOT; a white electroluminescent polymer layer (LiviluxTM); and a Ba/AI cathode.
  • the bare OLED demonstrated 89% Lambertian behaviour.
  • the scattering film was disposed on the external surface of the OLED
  • the optically coupled assembly demonstrated 97-98% Lambertian behaviour.
  • the micro-lens array was similarly disposed on the OLED, the assembly exhibited only 91-92% Lambertian behaviour.
  • the viewing angle-dependence of the OLED when optically coupled to the scattering film was reduced, and hence superior, relative to both the bare OLED and the OLED optically coupled to the micro-lens array.
  • a first series of oriented composite polyester films were manufactured, varying the polyester composition of the layer, the layer structure (number and pattern) and the concentrations of scattering particle in the layer(s), as shown in Table 1.
  • the scattering particles were Ti0 2 .
  • the Ti0 2 was introduced into the film during extrusion in the form of a concentrated masterbatch of inorganic Ti0 2 particles dispersed in polyester.
  • the masterbatch was supplied by Clariant GmbH.
  • the Ti0 2 was found by analysis to be in the anatase form, and the individual particles of Ti0 2 were close to spherical in shape, with a diameter of about 250 nm.
  • the particles of Ti0 2 were present in the A-layer only, and not the B-layer, from which was calculated the total amount of Ti0 2 by weight of the composite film, and the amount of Ti0 2 in the hazemeter beam as described above. All layers comprised either PET or PEN homopolymer, as shown in Table 1 , except for film sample M12-10 (Examples 10 and 22) whose A-layer comprised a copolymer based on PET.
  • the copolymer was prepared from a mixture of terephthalic acid (TA) and isophthalic acid (IPA), (having a ratio TA:IPA of 82: 18).
  • the films in Table 1 comprising either two or three layers were extruded and cast using a standard melt coextrusion system.
  • the coextrusion system was assembled using two independently operated extruders which fed separate streams of polymer melt to a standard coextrusion block or junction at which these streams were joined.
  • one stream of melt was split prior to the coextrusion junction and fed to two ports of the junction, which provided a common melt channel comprising three distinct streams.
  • the melt was thereafter transported to a simple, flat film extrusion die which allowed the melt curtain to be cast and quenched in temperature onto a rotating, chilled metal drum.
  • the extrusion temperature was about 275°C for PET (or PET-based copolymers) and 290°C for PEN.
  • the film was reheated to a temperature of about 90°C and stretched in the forward or machine direction to a stretch ratio of x3.1.
  • film sample O-U which was uniaxially oriented
  • the film was then stretched in the sideways or transverse direction to a stretch ratio x3.4 at a temperature of about 105°C in a stenter apparatus.
  • the stretched film was then heat-set at an elevated temperature to induce further crystallisation of the polyester layer.
  • the final heat-set stage was performed at an oven temperature of about 220°C.
  • the haze and the TLT of the film were measured and the results presented in Table 1.
  • the films were then disposed onto the surface of a series of OLED lamps such that the (or a) B- layer was in contact with the OLED surface.
  • OLED lamps were used:
  • L1 An OLED of Class I, as defined herein. It is a white polymer OLED (or "wPLED") having a transparent glass substrate; a transparent anode comprising a PEDOT:PSS (Clevios AI4083) layer and an ITO layer; a light-emitting polymer layer comprising LiviluxTM White (Merck KGaA, Germany); and a layered Ba/AI reflective cathode, encapsulated in a metal encapsulant on the glass substrate.
  • wPLED white polymer OLED
  • wPLED white polymer OLED
  • a transparent anode comprising a PEDOT:PSS (Clevios AI4083) layer and an ITO layer
  • a light-emitting polymer layer comprising LiviluxTM White (Merck KGaA, Germany)
  • a layered Ba/AI reflective cathode encapsulated in a metal encapsulant on the glass substrate.
  • the enhancement factor (or out-coupling value) for each film was calculated, as defined herein, by measuring the luminance of emitted light at a normal viewing angle (i.e. perpendicular to the OLED surface), for the OLED with and without the film.
  • the films contained either (a) Ti0 2 particles only, or (b) BaS0 4 particles only, or (c) polypropylene (PP) particles only, or (c) a combination of Ti0 2 and PP particles.
  • the following films were used:
  • Examples 71 to 82 Film samples M12-1 to M12-10, M 12-12 and M 12-13 in the order used in Examples 1 to 12 as shown in Table 1.
  • Examples 83 to 86 Film samples N 15-1 to N15-4 of monolayer PET films comprising various concentrations of Ti0 2 , manufactured as described hereinbelow.
  • Examples 87 to 89 Films A31-1 to A31-3 of monolayer PET films comprising various concentrations of BaS0 4 , manufactured as described hereinbelow.
  • Examples 90 and 91 Films A31-4 and A31-5 of monolayer PET films comprising various concentrations of polypropylene, manufactured as described hereinbelow.
  • Examples 92 to 101 Films A31-6 to A31-11 and N 15-5 to N 15-8 of monolayer PET films comprising various concentrations of Ti0 2 and polypropylene, manufactured as described hereinbelow.
  • the scattering particles of Ti0 2 and BaS0 4 (supplied by Sachtleben Chemie GmbH, Germany) were introduced to the film during extrusion as the appropriate concentrated masterbatch of particles in polyester.
  • polypropylene particles were added directly to the extruder and dispersed into the molten PET using the combination of heat and mechanical shear of the process.
  • the polypropylene was a homopolymer grade (GWE27 (BASF)), with melt flow index 4.5 +/- 0.5 (measured at 230°C, 2.16 kg load), and further contained around 1 wt % dispersion aid (AC wax type 316a (Allied Chemical)) and 1 wt % stabiliser (Irganox 1010 (Ciba Geigy)).
  • GWE27 BASF
  • the particle-containing molten PET was extruded through a twin-screw extruder and out of a simple, flat film extrusion die onto a rotating, chilled metal drum, where the melt curtain was quenched in temperature.
  • the extrusion temperature was about 275°C.
  • the film was reheated to a temperature of about 90°C and stretched in the forward or machine direction to a stretch ratio of x3.1.
  • the film was then stretched in the sideways or transverse direction to a stretch ratio x3.4 at a temperature of about 100°C in a stenter apparatus.
  • the stretched film was then heat-set at an elevated temperature to induce further crystallisation of the polyester layer.
  • the final heat-set stage was performed at an oven temperature of about 220°C.
  • the haze of the film was measured and the results presented in Table 2.
  • Table 2 PET film samples M12-1 to M12-13, A31-1 to A31-11 and N15-1 to N15-8from Series 2
  • Enhancement Factor* sample (AB or Mono) in film in film in film OLED L1 OLED L3 OLED L7
  • the films of Examples 71 to 101 were variously disposed onto the surface of different OLED lamps.
  • the Ti0 2 -containing layer constituted the external surface of the out-coupling film when applied to the OLED lamp, as for Series 1.
  • the OLED lamps described above as Lamp L1 (an OLED of class I) and L3 (an OLED of class II) were used, as well as a third OLED:
  • OLEDs of class III demonstrate a relatively large dependence on the identity of the scattering particles in the film, even where at least some of the particles are inorganic particles, and in this scenario the use of non-voiding inorganic particles alone provides unexpectedly superior out-coupling performance.
  • Film sample M12-10 from Series 1 was re-tested using an OLED source similar to lamp L2 described above.
  • OLED L2 was used with and without the 120nm- thick ITO layer.
  • Figure 8A The results are shown in Figure 8A, in which "device 1" is OLED L2 (i.e. with the ITO layer) and “device 2" is the modified OLED L2 (i.e. without the ITO layer).
  • the ITO-free OLED (device 2) exhibited greater power conversion efficiency, PCE (in Im/W) versus brightness (luminance, in cd/m 2 ), and hence greater light extraction from the OLED.
  • PCE in Im/W
  • the angular dependence of normalized emission brightness (in cd/m 2 ) of devices 1 and 2 (before application of the out-coupling film) is shown in Figure 8B.
  • the presence of the out-coupling film significantly increased the light extracted from the OLED for both devices 1 and 2.
  • the power conversion efficiency of the ITO-containing OLED was raised to 7.0 Im/W at 100 cd/m 2 (55%) and to 5.86 Im/W at 1000 cd/m 2 (100%) while that of the ITO-free OLED was increased to 8.3 Im/W (84 %) and 7.1 Im/W (+115 %) at the same intensities.
  • the brightness (luminance) of device 1 in the forward direction was enhanced by a factor of 1.64 by the application of the out-coupling film, while that of device 2 was enhanced by a factor of 1.83.
  • the performance of devices 1 and 2 is summarized in Table 3 below. It is estimated that the out-coupling film of the present invention enables approximately 65% of light to be extracted from device 1 , and 85% to be extracted from device 2.
  • a fourth series of coated composite films was produced using the method to make the films of Series 1 shown in Table 1. The procedure above was repeated except that a scratch-resistant coating was applied to the external surface of the out-coupling film.
  • the final coating was an organic/inorganic hybrid and was prepared from a solution of:
  • MEK methyl ethyl ketone
  • the coating solution was applied to the finished film in an off-line coating step using a Meyer bar (No.2), left to dry for 2 minutes then cured for 1 minute at 80°C and UV-cured at 1000mJ/cm 2 .
  • the coated composite films are described in Table 4 together with the Enhancement Factor, as obtained from luminance measurements. Table 4
  • Film sample M12-10 from Series 1 was retested further using the OLED lamps L1 , L3 and L7 described above.
  • a further micro-lens array textured surface layer was tested similarly.
  • the surface of the MLAF in this case was found from electron microscopy to comprise an array of close packed hemispherical micro-lenses of diameter 10 ⁇ and similar separation. Both samples were examined for their effect on the colour light emitted by L1 and L3.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Electroluminescent Light Sources (AREA)

Abstract

La présente invention concerne un procédé de réduction de la dépendance angulaire d'une couleur d'émission et/ou d'une intensité d'émission d'une source de lumière OLED et/ou d'augmentation de l'extraction de lumière de ladite OLED. Selon l'invention, le procédé fait appel à l'étape consistant à disposer un film de polyester à orientation bi-axiale en tant que couche dans un ensemble multicouche comprenant en outre une source de lumière OLED, ledit film de polyester étant disposé sur une surface électroluminescente de ladite OLED ou à l'intérieur de ladite OLED, ledit film de polyester comprenant des particules de diffusion de lumière. L'invention concerne également un ensemble multicouche comprenant une source de lumière OLED et un film de polyester à orientation bi-axiale comprenant des particules de diffusion de lumière, ledit film de polyester étant disposé sur une surface électroluminescente de ladite OLED ou à l'intérieur de ladite OLED.
PCT/GB2013/053276 2012-12-18 2013-12-12 Utilisation d'un film de polyester pour amélioration d'extraction de lumière de sources de lumière oled et ensemble multicouche comprenant une source de lumière oled et un film de polyester WO2014096785A1 (fr)

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