GB2609710A - Electro-conductive transfer films - Google Patents

Abstract

An electro-conductive transfer film is described which can be hot- or cold-stamped onto a receiving substrate to quickly, simply, easily and very cost-effectively render that substrate electro-conductive, preferably with a pattern reflecting that of the stamp shape, such as for PCB (fig 5) or antenna (fig 6) manufacture. The film may comprises at least a flexible plastics carrier layer 4a, a release coat layer 6a, a lacquer coat layer 8a, an electro-conductive layer, such as a metal 10A and a (preferably adhesive) size coat layer 12A. The release coat, may remain on the carrier, or may at least partially be transferred on the conductive layer during stamping. An alternative film has no lacquer layer, instead with at least some of the releases coat left on the transferred conductive layer. The upper layer of the lacquer or the release coat may be made partially conducing so that a top (point) contacts can be made to the underlying conductive layer via the accessible upper layer such that the majority of current flow between said contacts within the released layers of the transfer film occurs within the patterned electro-conductive layer.

Description

Electro-conductive transfer films

Field of the Invention

The present invention relates to electro-conductive transfer films, and more specifically to electroconductive transfer films having a substantially multi-laminar structure comprising at least a carrier layer and at least one electro-conductive layer which is capable of being both released or otherwise separated from said carrier layer by means of the localised or unilateral application of heat, pressure, light or other energy or combination thereof, and also substantially simultaneously adhered to a substrate material with which the said transfer film is in physical contact at the time said energy or energies are applied.

For the avoidance of doubt, the term 'electro-conductive' as appearing herein and in the context of the transfer films with which this application is concerned should be understood to mean that the transfer film includes at least one layer of an electrically conductive material capable of carrying an electrical current and which therefore, in isolation, may be regarded as an electrical conductor, despite possibly being sandwiched between other substantially more insulating layers of the transfer film which would generally tend to prevent or significantly hinder a ready, direct electrical connection with said electrically conductive layer. In this regard, it is entirely possible that an electro-conductive transfer film of the present invention may actually be quite electrically inert prior to the transfer of said electrically conductive layer to a substrate material by applying some form of energy to one or both of said substrate material and said transfer film.

Background to the Invention

In the printing industry, the embellishment of printed substrates with metallic elements is most commonly achieved using a hot-or cold-stamping technique in which the printed substrate material is nipped together with what is commonly referred to in the printing industry as a foil between a hot or cold stamping die, the result of which is that a metallised layer of the foil is both released from the foil and simultaneously adhered to the printed substrate. Such techniques are widely practised, and largely beyond the scope of this application, except to mention that although the techniques are relatively simple scientifically, a very high degree of accuracy and resolution can be achieved so that, firstly, the pattern of metallic elements being transferred from foil to substrate, as determined by the stamping die, can be applied in precise registration with the printed substrate and secondly, the size and shape of said metallic elements essentially precisely and accurately replicate the stamping die which releases them from the foil without such imperfections as tearing, cracking, and partial or incomplete transfer. Of course, it will be understood by those skilled in the art that some edge artefacts around the perimeter of the transferred metallic elements will be inevitable because the release thereof essentially involves a tearing or ripping of said metallic elements from the metallised layer of which they originally formed part -however, such edge artefacts are almost always invisible to the naked eye in the finished article.

A typical modern foil will generally be multi-laminar in construction, and may consist of, for example, the following different layers: (1) A carrier layer, typically being a film of a polyester, polyethylene or other durable polymeric plastics material; depending on a variety of factors such as the ultimate application, the parameters of the stamping technique to which the film is to be subjected, and the thickness of the other layers of which the foil is comprised, the carrier layer may vary significantly in thickness, but typical foils include a carrier layer of between 10 and 25km: (2) At least one, and possibly two release coat layers; typically (and especially so for hot stamping techniques) release coatings are wax-based compositions which at elevated temperature and/or pressures liquefy such that subsequent constituent layers of the foil can be selectively released from the carrier in those areas of the release layer(s) having been so liquefied; in other areas of course, the still-solid release layer will continue to provide adhesion and prevent any such release of other layers; release coat layer thicknesses may range between 0.04 and 0.12 lam; the wax content of release coat layers, and indeed the overall composition of a release coat, may be different depending on whether only relatively small, precisely defined areas of foil are to be released, or whether relatively much larger areas are to be released -e.g. fine detail foiling or large area foiling; (3) A temperature-resistant lacquer layer, typically having a thickness in the range 1-2 km; lacquers are well known in the printing industry, and in foils, lacquers will often include dyes or pigments so as to provide a colouring of the underlying base metal appearance (most commonly silver, if Aluminium is used); additionally, the lacquer provides scuff/abrasion resistance for the foil and determines the chemical resistance of the foil; the lacquer is a very important part of the overall laminar construction of modern foils, notably because the lacquer, like other layers which are separated from the carrier film during stamping, must be brittle enough to give sharp definition to the metallic elements stamped from the foil, and said lacquer must of course be transparent or translucent to achieve the proper metallic finish; In the foil manufacturing process, the lacquer coat must be applied by an exceedingly consistent coating system, as it contributes significantly to the ultimate stamping performance of the foil; (4) A metallic layer ranging in thickness from about 0.02-0.1 pm, which provides reflectivity and, depending on thickness, a degree of opacity; most commonly, the metal employed is Aluminium, although other metals such as Copper, Gold, Silver (the best metal conductor) Nickel, Zinc may be used, as well as alloys of such metals, e.g. "Monel"; and such are usually applied to the foil by means of vacuum metallisation which results in an extremely thin but uniform, continuous and mirror-bright metallized layer; (5) A adhesive or "size coat" layer, with a thickness of 0.1-0.3 pm; the size coat serves to bond the released foil elements to the substrate and is usually a mixture of low melting point resins which melt at the stamping temperature or under sufficient pressure to form a chemical or physical bond with the stamped surface of the substrate which must be of greater adhesive strength than the bond between the release coat and the carrier to ensure a successful transfer.

Foils are in general typically an order of magnitude more expensive than printed substrate materials such as common paper, board or card stock, and therefore their use is somewhat restricted to premium printed products or where it is desired to provide the finished printed article with a degree of quality or exclusivity. However, when compared to conventional wet chemical processes such as etching used in the manufacture of, for example, printed circuit boards (PCBs), dry stamping processes are known to be much less expensive, not to mention significantly cleaner because wet chemical processes necessarily involve chemically aggressive solvents.

For such reasons, together with the common understanding that the Aluminium metallised layer present in most modern foils is electro-conductive to at least some degree, the stamping of foils has been proposed as a means of applying an electrically conductive pattern to substrate materials such as common paper, board and card stock, as well as to more rigid plastics materials, whether extruded or otherwise manufactured. For example, US2002/0018880 describes a stamping foil comprising a carrier film, a layer of heat activated adhesive, a layer of vacuum deposited copper, and a release layer which facilitates transfer of the copper layer to a substrate material. Analagously to the known hot-stamping technique, relevant layers are activated by heat and pressure by a stamping die which causes the layers beneath the release layer to delaminate from the carrier film and adhere to a surface of a substrate in a predetermined electrically conductive pattern. The release layer releasably couples the layer of vacuum deposited copper to the carrier film in conventional fashion, but in contrast to conventional purely decorative foils of the time, wherein only miniscule quantities of copper were deposited (in a layer less than 0.005 rim thick), the vacuum deposited copper layer is required to be in the range 0.005-0.1 Rm thick. As a further example, US4495232 also teaches the use of an electro-conductive stamping foil to form printed circuit patterns on a non-conductive substrate.

Thus, the use of pressure-initiated techniques on foils possessing an electro-conductive layer to apply an electro-conductive pattern to an essentially electrically insulating substrate material is seemingly known. However, despite the existence of relevant prior art, there has been no universal adoption of such techniques, for a variety of reasons. Firstly, although the raw material costs may be low compared to those used in the manufacture of PCBs and the like, PCB manufacture his highly developed and at scale, the cost per item is significantly less than would be the case for a comparable item manufactured using any foil stamping technique, most notably because only a relatively small amount of the foil is actually applied to the substrate, the remainder being rather wastefully discarded. Therefore, foil stamping is only really a viable production process at relatively low volumes, and for which wet chemical processes such as etching (by which PCBs are commonly mass produced) are not at all cost effective. Secondly, research and experimentation by the applicant herefor has revealed that although stamping a standard and essentially purely decorative aluminium foil in a predetermined pattern on simple card, paper or board stock may be relatively straightforward, the electrical circuit thus produced on the substrate is somewhat unreliable, and furthermore, and equally if not more importantly, it has proved somewhat difficult to form a good electrical connection with any part of the pattern so stamped.

There are various reasons why standard decorative foils suffer such problems. Firstly, although Aluminium is a relatively good conductor, elemental aluminium is immediately oxidised in air and becomes coated with an electrically insulating layer of Aluminium (Ill) Oxide. Elemental Aluminium is a particularly reactive material, and in ambient atmospheric conditions, oxidation of the surface of the bare metal occurs almost instantaneously such that it becomes impossible to obtain a direct electrical connection with the conducting metal beneath the oxide layer without creating the connection in very controlled conditions, e.g. in a vacuum. Even in the case where a vacuum metallisation technique is initially used to apply a layer of elemental Aluminium to a coated and lacquered carrier film during foil manufacture, and this metallic layer is then immediately coated with a size coat of adhesive such that little oxidation of the metallic Aluminium occurs, any puncturing of either the size coat (pre-stamping) or lacquer coat (post-stamping) would cause the bare metal to be exposed to air whereupon an Aluminium Oxide layer would immediately be formed on the exposed area rendering it electrically inactive.

Secondly, as previously mentioned, in conventional foils the layers above and below the metallised layer (the lacquer and the size coat layers respectively) tend to be somewhat if not completely electrically insulating, so even if the metallised layer between them is electrically conductive, the making of any electrical connection with the encapsulated metallised layer would always entail a further process step of firstly removing, in at least two predetermined spaced apart locations, portions of at least one of said insulating layers so as to expose portions of the metallised layer and permit contact therewith so that electrical current could flow from one contact to the other along the path determined by the transferred foil pattern. The necessity of any further process steps in the manufacturing technique of course necessarily increases costs. Furthermore, the delicacy of the respective layers is such that any additional process step which might be considered as a means for making an electrical connection with the metallised layer must be similarly delicate to ensure that said metallised layer is not damaged during said process. Thus aggressive or brute force methods of forming said electrical connection, such as soldering or spot welding, while nevertheless being simple and cost-efficient, are precluded, and only more intricate and thus costly methods can be considered.

It is therefore an object of the present invention to provide an electro-conductive transfer film which does not suffer from such disadvantages, and which facilitates the making of reliable electrical connections with the electro-conductive material layer which forms part of said transfer film.

Summary of the Invention

According to a first aspect of the present invention, there is provided an electro-conductive transfer film comprising at least a carrier layer being of a flexible plastics material, a release coat layer, a lacquer coat, an electro-conductive layer and a size coat layer wherein said release coat layer adhesively secures said carrier layer and said lacquer coat layer together and to which, through one or both of said carrier layer and said lacquer layer, one or more forms of energy can be applied in a predetermined pattern, said energy having the effect of activating the release coat layer so as to reduce or eliminate its adhesive quality within or without a perimeter boundary of said pattern so that said lacquer layer and any layers on the opposite side thereof to said carrier layer are effectively released from said carrier layer in first regions within or without said pattern but otherwise remain adhered to said carrier layer in second regions without or within said pattern and such that said released layers can be simultaneously transferred to a substrate material, characterised in that, the surface energy between the release coat layer when in its activated state and the carrier layer is greater than the surface energy between the release coat layer in said activated state and said lacquer layer such that, when in said activated state, said release layer is essentially or substantially retained on said carrier layer as other layers beneath it are released therefrom and transferred to said substrate material as a result of the application of said energy, and further characterised in that the lacquer layer is formed of or comprises an at least partially electrically conducting material having an electrical conductivity which less than that of the electro-conductive layer of the transfer film such that the surface of said lacquer layer can support at least first and second spaced apart direct physical electrical contacts into and out of which an electrical current can flow, the relative conductivities of the lacquer layer and the electro-conductive layer and the separation of the electrical contacts being such that the majority of current flow between said contacts within the released layers of the transfer film occurs within the electro-conductive layer.

According to a second similar but modified aspect of the present invention, there is provided an electro-conductive transfer film comprising at least a carrier layer being of a flexible plastics material, a release coat layer, a lacquer coat, an electro-conductive layer and a size coat layer wherein said release coat layer adhesively secures said carrier layer and said lacquer coat layer together and to which, through one or both of said carrier layer and said lacquer layer, one or more forms of energy can be applied in a predetermined pattern, said energy having the effect of activating the release coat layer so as to reduce or eliminate its adhesive quality within or without a perimeter boundary of said pattern so that said lacquer layer and any layers on the opposite side thereof to said carrier layer are effectively released from said carrier layer in first regions within or without said pattern but otherwise remain adhered to said carrier layer in second regions without or within said pattern and such that said released layers can be simultaneously transferred to a substrate material, characterised in that, the surface energy between the release coat layer when in its activated state and the carrier layer is less than the surface energy between the release coat layer in said activated state and said lacquer layer such that, when in said activated state, said release layer is essentially or substantially released from said carrier layer along with other layers beneath it and transferred to said substrate material as a result of the application of said energy, and further characterised in that both the release coat layer and the lacquer layer are formed of or comprise an at least partially electrically conducting material and have an electrical conductivities which are less than that of the electro-conductive layer of the transfer film such that the surface of said release coat layer, when in a deactivated or inactive state can support at least first and second spaced apart direct physical electrical contacts into and out of which an electrical current can flow, the relative conductivities of the release coat layer in its inactive state, the lacquer layer and the electro-conductive layer and the separation of the electrical contacts being such that the majority of current flow between said contacts within the released layers of the transfer film occurs within the electro-conductive layer.

In a third aspect of the present invention, there is provided an electro-conductive transfer film comprising at least a carrier layer being of a flexible plastics material, a release coat layer, an electro-conductive layer and a size coat layer wherein said release coat layer adhesively secures said carrier layer and said electro-conductive layer together and to which, through one or both of said carrier layer and said electro-conductive layer, one or more forms of energy can be applied in a predetermined pattern, said energy having the effect of activating the release coat layer so as to reduce or eliminate its adhesive quality within or without a perimeter boundary of said pattern so that said electro-conductive layer and any layers on the opposite side thereof to said carrier layer are effectively released from said carrier layer in first regions within or without said pattern but otherwise remain adhered to said carrier layer in second regions without or within said pattern and such that said released layers can be simultaneously transferred to a substrate material, characterised in that, the surface energy between the release coat layer when in its activated state and the carrier layer is less than the surface energy between the release coat layer in said activated state and said electro-conductive layer such that, when in said activated state, said release layer is essentially or substantially released from said carrier layer together with other layers beneath it, all such released layers being transferred to said substrate material as a result of the application of said energy, and further characterised in that the release layer is formed of or comprises an at least partially electrically conducting material having an electrical conductivity which is less than that of the electro-conductive layer of the transfer film such that the resulting surface of said release layer in its inactive or deactivated state can support at least first and second spaced apart direct physical electrical contacts into and out of which an electrical current can flow, the relative conductivities of the release coat layer and the electro-conductive layer and the separation of the electrical contacts being such that the majority of current flow between said contacts within the released layers of the transfer film occurs within the electro-conductive layer.

Preferably, the conductivity of the exposed top-most layer of the transfer film, post-transfer, whether this is the lacquer layer as in the first aspect of the present invention, or the inactive or deactivated release coat layer as in the second and third aspects of the present invention, is such that electrical connection therewith can be achieved through simple surface contact without any requirement for further modification, alteration or amelioration On terms of electrical conductivity) of said layer.

Preferably, one or both of the lacquer layer (where the transfer film includes one) and the release coat layer are one of: - formed of materials which both possess the required characteristics as far as the requisite lacquer and release functions are concerned, and are also inherently electro-conductive to the required degree, and - formed of materials which possess the required characteristics as far as the requisite lacquer and release functions but are comparatively or completely electrically insulating in that an exposed surface of such a layer would not generally support a direct surface-based electrical connection, and provided with a sufficient amount of an electro-conductive additive element, composition, or material to render said layer both electrically conductive to the required degree so that an exposed upper surface of said material is capable of supporting a direct surface-based electrical connection, with the latter of these two options being most preferred.

In the case where a conductive additive is used to provide the relevant layer with the sufficient degree of electrical conductivity, preferably the additive is one of, or any combination of: - particles of a conductive elemental metal such as Copper, Silver, Gold, Molybdenum, Zinc, Nickel, - particles of a conductive metal alloy such as Bronze, Brass, or any Monel alloy, - particles of an organic or inorganic conductive element, compound or polymer, such as Carbon (in any conductive form, such as carbon nano-tubes, graphene, Buckminsterfullerine), polyfluorines, polyacetylenes, polypyrroles, polythiophenes.

Preferably, where a particulate conductive additive is provided in the lacquer and/or release coat layer, the particle size is less than 100pm, more preferably less than 10pm, yet further preferably less than 1pm, and most preferably less than 100nm. Of course, the skilled reader will understand that all these sizes are much less than the human eye can perceive, but importantly for smaller particle sizes, a greater density of particulate material can be added without compromising the overall appearance and physical and/or functional characteristics of the material of which that or the relevant layer is constituted, while nevertheless promoting the electrical conductivity of said layer to the required degree, both as compared with the underlying electro-conductive metallised layer in the transfer film, and as regards the requirement for providing an electrically conductive surface.

Preferably the surface-based electrical contact locations are spaced apart by an amount which is at least 103, further preferably 104, and yet further preferably 10' orders of magnitude greater than the thickness of the lacquer or other layer (e.g. the release coat layer) through the exposed upper surface thereof and which supports said contacts. For example, in a most preferred embodiment, the contact locations will be spaced apart by a distance in the order of centimetres, whereas the thickness of the relevant layer support said contacts will be of the order of microns (pm), i.e. a difference in order of magnitude of 104. By ensuring such a large ratio of contact separation to layer thickness, and taking into account the tendency of current flow to occur along the path of least resistance within those respective layers of the transfer film transferred to a substrate, although both the contact-supporting layer and the underlying electro-conductive metallised layer are conductive, the relatively greater electrical resistance of the contact-supporting layer ensures that current would tend to flow from the first electrical contact vertically first downwardly into the metallised electro-conductive layer, and then horizontally therealong until reaching the second electrical contact whereupon the current would flow vertically upwardly through the contact supporting layer. Such a current flow is ensured because this path offers the lease electrical resistance, particularly if the conductivity of the contact-supporting uppermost layer is chosen carefully to be much less, than that of the electro-conductive metallised layer.

In a further aspect of the present invention, there is provided a substrate material to which has been applied a predetermined pattern of a plurality of layers of material released from a transfer film as previously described.

In terms of the specific advantages, benefits and other ancillary features of the present invention, as may have already been noted, hhot-or cold-stamping of foils is an essentially dry, solvent-free method of application, and far more ecologically considerate than mass-printing with wet inks which traditionally include a number of pollutant chemicals. Note also here that the both printed circuit boards themselves, and the etching thereof, both include or are heavily dependent on aggressive, toxic, pollutant and/or otherwise dangerous chemicals. By contrast, substrates such as commonplace card, paper, paperboard, and the like, to which the electro-conductive transfer films of the present invention may be most commonly applied, can be repulped and thus recycled, and Applicant has conducted various tests on foils generally to demonstrate their recyclability. Although the present invention is ideally suited to rendering paper, card, board and like materials electroconductive by application of foils thereto, it is to be mentioned that the present invention is not substrate dependent, and may be applied to a very wide number of different substrate materials, for example, plastics materials.

It should also be mentioned here that, aside from the surface mounted contacts that are provided on the stamp electro-conductive tracks that may be applied to substrates using the invention, a wide variety of other electric and electronic components may be similarly applied directly to the tracks, for example light emitting diodes (LEDs), switches, buzzers, sensors (e.g passive infrared -P I R -sensors) and the like. In terms of the provision of a source of electric power to the conductive tracks of the present invention, this can be provided by 3V coin batteries (e.g. that commonly power electric watches and the like), standard 9V batteries or transformers.

Applicant considers that the present invention may have wide application in the field of packaging for drinks, toys, and cosmetics and other high value products, especially where it would be of benefit to provide high-impact packaging, by, for example, providing illumination or some other electronically interactive feature on, around, or inside the packaging. Applicant is aware of prior art packaging incorporating simply electric or electronic circuits to provide, e.g., lighting, but those that have been inspected use simple PCBs and copper wires, and cannot thus be easily recycled or do otherwise not meet environmental requirements. Applicant is also aware that electrically conducting tracks can be created on substrates by printing, but conductive inks are expensive, and not striaghforwardly printed onto absorbent substrates such as paper, card, and board.

In some embodiments, the present invention may be used in conjunction with the plastic mouldings which together constitute some electrical appliance or other, in which case the electric or electronic feature provided by the tracks may become an integral part of the appliance. For instance, a plastic extrusion may have applied to it various conductive tracks by the present invention, and could be used to create shelf edges, offering highlighting, illuminating, or some other interactive feature.

It is also posited that the present invention may be capable of application to non-rigid substrates such as fabrics, and thus it may be possible to create electrically conducting clothing, bandages, plasters and other forms of medical and non-medical fabric or pliable materials. One can easily envisage a very low cost, localised heat-treatment bandage may be easily created using the present invention. Similarly, a wide variety of educational articles might be created using the invention.

A specific embodiment of the invention is now described by way of example and with reference to the accompanying drawings wherein.

Brief Description of the Drawings

Figure 1 provides a schematic sectional elevation to demonstrate the laminar structure of a conventional (prior art) hot-or cold-stamping foil, Figure 2 provides an expanded schematic sectional elevation of a transfer film according to a first aspect of the present invention, Figure 3 schematically depicts how a transfer film of the present invention may be stamped together with a substrate material in order to apply requisite layers of the transfer film to said substrate, Figure 4 shows a sectional elevation through a substrate after completion of the stamping operation shown in Figure 3, Figure 5 shows a plan view of a substrate having been stamped as shown in Figures 3 and 4 and thus provided with a predetermined pattern of released layers of the transfer film according to the present invention, Figure 6 shows a schematic resistive electrical circuit representative of the electrical characteristics of released layers of a transfer film in situ on a substrate, and Figure 7 shows a plan view of a further conductor pattern which may be applied to a substrate by the method of the present invention and which may provide the function of an antenna.

Detailed Description

Referring firstly to Figure 1, there is shown (sectionally) one prior art configuration of a common hot-or cold-stamping foil 2 which is usually provided in roll or web form. Foil 2 comprises a (usually) plastics material carrier layer 4 which supports the various other layers and to which said other layers are, at ambient temperature and pressure, adhered by means of a heat-and/or pressure activated release coat layer 6. In its inactive state, the release coat layer provides generally uniform adhesion between subsequent layers of the foil and the carrier layer, and possesses the physical and/or chemical characteristics of being liquefiable with the application of heat and/or pressure (or possibly when chilled or ambient pressure is reduced). Furthermore, the nature and composition of the release layer is such that the liquefaction (by which is meant some non-negligible reduction in adhesive characteristics) is achieved quite precisely and only in those regions where the requisite energy is applied (or removed). Beneath said release coat layer is (usually, but not mandatorily) provided a temperature-and/or pressure-(or other energy) resistant lacquer layer 8, such that there is essentially no physical or chemical change in the lacquer layer when the energy is applied to the foil during a conventional hot-or cold-stamping operation. During said stamping operation therefor, the release coat layer effectively melts in a predetermined pattern corresponding essentially exactly to that in which the energy is applied (usually) to the carrier layer allowing other subsequent layers of the foil to be released from said carrier film in regions where the release coat no longer provides sufficient adhesion, whereas in other regions, said other layers remain adhered to the carrier layer.

The metallic effect provided by common foils is provided by a metallised layer 10 which is usually formed by a well know vacuum metallisation technique beyond the scope of this application, except to mention that the technique creates an essentially continuous, but exceedingly thin (e.g. <1 micron) layer of particles of metallic element, alloy or other compound capable of conducting electricity if the metallic element, alloy or other compound is itself electrically conductive. In most cases, elemental Aluminium is used.

The final layer of the foil is a size or adhesive coat layer 12 which is again capable of adopted different states with the application of a suitable energy, e.g. an active state when the adhesive is liquefied and its adhesive qualities are significantly reduced, and an inactive state when the adhesive is solidified and provides good adhesion. In most cases, the size coat layer will be any of a number of well known hot melt adhesives, and similarly to the release coat layer, the size coat layer can be caused to liquefy only in predetermined regions by the application of suitable energy thereto, either directly, or indirectly through the carrier film layer above.

Referring now to Figure 2, there is shown an exploded sectional view of a transfer film 20 of the present invention which, similarly to the prior art foil of Figure 1 comprises a plastics carrier layer 4A, a release coat layer 6A, a lacquer layer 8A, a metallised layer 10A, and a size coat layer 12A. The important difference as far as the present invention is concerned, in the particular embodiment illustrated, is that the lacquer layer 8A of the transfer film 20, which in prior art foils is traditionally electrically insulating, is modified such that it is not only electrically conductive to at least some degree, but such electrical conductivity is carefully selected so that it is non-negligibly less than that of the underlying, and conventionally electro-conductive metallised layer 10A. The modification of the lacquer layer may take many forms, but one particular enhancement is the provision within the lacquer layer 8A of electrically conductive particulate material in such a density or concentration that firstly does not significantly otherwise affect the physical characteristics and/or function that lacquer compounds usually perform, i.e. heat and or pressure resistance, their translucence and or transparency, and their capacity for imparting a smooth glossy finish to the underlying metallised layer after having been transferred to a substrate material. As an alternative, it is certainly possible and within the scope of the present invention that an inherently electroconductive lacquer composition may be used which nevertheless provides the requisite function physical and or chemical characteristics.

Regardless of the actual composition of the lacquer compound, the now electro-conductive nature of the lacquer layer should admit direct physical, surface-based electrical connection, which should occur naturally provided the conductivity of lacquer composition is sufficiently enhanced (by addition of conductive particulate material) or is inherent (as a result of employing an inherently conductive composition).

Referring now to Figure 3, a conventional stamping operation is schematically sectionally illustrated at 30 wherein a hot-or cold-stamping die 32 provided with raised patterned profile, elements of which can be seen at 34, 36, 38, 40, over its lower operative surface 42. In use, the stamping die 32, shown in this arrangement as planar and thus reciprocating but it could certainly be cylindrical and rotary in operation, is impressed onto the uppermost surface 4B of the carrier layer 4A of the transfer film 20 which is disposed above a substrate 44 which in this embodiment is supported by a static planar platen 46. As raised profile sections 34-40 of the die pressurizingly contact the transfer film and nip against the substrate 44, the release coat layer 6A liquefies, but only in the regions where significant pressure is applied through said raised profile sections. Additionally, such pressure, together with the heat of the die if heated, activates the hot melt adhesive of the size coat layer 12A such that it adheres to and bonds with the substrate in such regions. After a suitable time period, typically much less than 1s in production conditions, the die is removed, the pressure (and optionally heat) provided thereby also thus being removed, and the transfer film carcass 50 (Figure 4), being the original transfer film but with certain layers thereof having been released therefrom and permanently and securely transferred to said substrate 44 in the required predetermined pattern, can also then be removed. The released layers of the transfer film are indicated generally as layer stacks 52 in Figure 4 and are shown as standing proud of the surface in this embodiment., The skilled reader will of course understand that, depending on the relative compressibility of the substrate, the die may effect either an embossing or debossing of such released layers 52 such that they may stand proud of the substrate upper surface, or may be indented therein. The skilled reader will also understand that no embossing or debossing may occur, and the uppermost surface of the release layers stacks may be substantially flush with the substrate upper surface -in this case of course, the layer stacks will simply be embedded within the substrate by an amount equal to their height.

As regards this particular embodiment of the present invention, it is to be noted that the transfer process results in the uppermost surface of portions of the lacquer layer being exposed, such having been released by the release layer which remains substantially if not entirely with the transfer film carcass SO. It is these uppermost exposed surfaces which now facilitate and support a direct physical electrical connection, on account of the now electro-conductive nature of the lacquer layer. However, because of the relatively much lower conductivity of this layer as compared with the immediately underlying electro-conductive metallised layer, with which said lacquer layer is in electrical communication, any current flow between two spaced apart contacts made directly with the upper exposed surface of the lacquer layer is much more likely to flow predominantly through the metal lised layer than the much more resistive lacquer layer, than directly between the contacts and only through said lacquer layer. This is advantageous because with the majority of current flow effectively occurring within the metal lised layer, said current flow is at least to some extent shielded, both physically and electromagnetically by the overlying more resistive lacquer layer.

In terms of the application of the contacts themselves, it is suggested that this could be achieved by an automated process such as riveting, and the contacts themselves m ay thus take the form of pneumatic pot rivets. In an alternative and novel and inventive arrangement, the electrical contacts could be applied using an anisotropic adhesive composition, such as those available from Creative Materials Inc, Ayer, Massachusetts. Beneficially, not only do these adhesives afford electrical conductivity in the Z-direction (i.e. between the physical contact component and the underlying electr-conductive track), but initially liquid adhesives which cure to create the adhesive bond have the added advantage and benefit that they shrink on curing, thus having the additional and unexpected effect of effectively clamping the physical contact to the electro-conductive track, thus inherently improving the quality of the electrical connection between track and contact.

Referring now to figure 5, there is shown an electronic circuit pattern 60 of the type which might easily be transferred to a substrate material from a transfer film of the present invention by a stamping technique as previously described. The pattern is approximately to scale, in that the generally horizontal electrically conducting tracks 62, 64, 66, 68 may be of a length of a few centimetres. Additionally, and as can be seen in the Figure, the ends of the conducting tracks, respectively being labelled with the appropriate track number and suffixed with "A", "B" and "C" where appropriate, being those areas with which a direct physical surface electrical connection would be made, are somewhat larger, in at least one dimension, than the width of the tracks they terminate. Not only do such contact areas thus facilitate a much easier direct electrical connection, but their shape and configuration are such that they would further promote electrical current flow in the underlying metallised layer because physically because the physical reduction in size of the conductor between the contact area and the track itself increases the electrical resistance. Put simply, there is less conductor for the electrical current to flow through, and therefore there is and electrical resistance increase between contact area and the much narrower conductive track it terminates. It should be understood that this physical arrangement of tracks and their terminating contacts is to be considered as a further feature of the invention, and in certain aspects may be separately claimable.

As regards the manner in which an electrical contact may be made with the contact areas, or indeed any other area of the uppermost exposed surface of the conductive lacquer layer, any suitable may be used, for example using a simple dab or dot of a sliver or otherwise electrically conductive adhesive. By this method, it is even possible to adhere the end of a simple electrical wire directly to the upper surface of the conducting lacquer layer.

Of course the conductive tracks shown in Figure 5 may be much longer, but what is important as far as the present invention is concerned is that they can be effectively stamped or otherwise applied to a substrate material in any desired pattern, by a variety of techniques, and furthermore in a pattern which is decorative or otherwise visually striking in appearance or which conveys some message, image or other information. Thus the released layers of a transfer film according to the present invention and extant on any substrate material can be both functional in that they can be used for conducting an electrical current between, and visually informative or appealing.

Referring now to Figure 6, there is shown a schematic electrical circuit 70 which might be equivalent to the resistive circuit offered by any particular conductive track of Figure 5 formed using a transfer film of the present invention, for example track 64. In the Figure, contacts 64A, 643 are shown with a source and sink of electrical current 72, 74 respectively which could be simply manifested by something as simple as a direct physical surface connection of an electrical wire to the exposed upper surface of the transferred conductive lacquer layer. As previously described, while the lacquer layer is conductive, it is far less conductive that the underlying metallised layer, and therefore the resistance R1 presented to current flow within the lacquer layer between contacts 64A and 64B is relatively very much greater than the sum of the following: - the resistance Rx presented to current flow from the contact 64A vertically through the lacquer layer and into the underlying metallised layer, - the resistance R2 presented to current flow within the metallised layer between contacts 64A and 64B, (R2 « RI) and - the resistance Rx presented to current flow from the metallised layer underneath contact 643 vertically upwardly into and through the lacquer layer.

In embodiments, it should also be mentioned that not only should R2 « R1 but also Rx « R1.

Various other embodiments of the present invention are possible, For example, the transfer film may include multiple lacquer layers instead of a single lacquer layer, or the lacquer layer may be entirely absent from the transfer film (corresponding to the known prior art matt pigment foils). In the former case, the invention would require any and all layers above the standard electroconductive layer to be rendered electro-conductive to the required degree, that is each such layer should be much less conductive than the metallised layer, and the uppermost or top-most layer should be conductive to a sufficient degree to permit direct surface-based electrical connection. In the latter case, in order to provide some coating or covering for the metallised layer, the release coat material would be rendered electro-conductive, and furthermore the interfacial surface energy of said release coat material as regards the carrier film and as regards the metallised layer would be selected such that the release coat layer would be released from the surface of the carrier layer as part of the transfer process instead of remaining substantially adhered thereto as described in the first embodiment above. In other respects, these other embodiments are however essentially the same in that the conventionally electro-conducting metallised layer is covered with a layer which is electrically conductive but to a much lesser degree than the metallised layer while still supporting and/or permitting a direct physical surface-based electrical connection.

Figure 7 shows a further conductor pattern 80 which may be applied by the present invention, and which essentially comprises a single conductor path 82 wound in a tight spiral and having inner and outer termini 84, 86 respectively. The conductor 82 shown in the Figure may again be to scale, but, given the accuracy and resolution with which electro-conductive foils can be applied to substrates, Figure 7 may provide a schematically enlarged illustration of a conductor pattern which may be 5, 10, 20, 50 or even 100 times smaller (i.e. the scale of Figure 7 may be 1:5, 1:10, 1:20, 1:50 or even 1:100, or anywhere in between). As will be understood by those skilled in the art, and particularly from Figure 7, the nature of the electro-conductive transfer film and the method of its application to a substrate are such that the pattern between respective termini must be continuous and unitary in that its perimeter should be continuous and discrete -that is, no portion of the perimeter should touch and thus connect with any other portion, unless the short circuit which such a connection would create actually forms part of the conductor pattern and is thus desired.

Claims (8)

1. CLAIMS1. An electro-conductive transfer film comprising at least a carrier layer being of a flexible plastics material, a release coat layer, a lacquer coat layer, an electro-conductive layer and a size coat layer wherein said release coat layer adhesively secures said carrier layer and said lacquer coat layer together and to which, through one or both of said carrier layer and said lacquer coat layer, one or more forms of energy can be applied in a predetermined pattern, said energy having the effect of activating the release coat layer so as to reduce or eliminate its adhesive quality within or without a perimeter boundary of said pattern so that said lacquer coat layer and any layers on the opposite side thereof to said carrier layer are effectively released from said carrier layer in first regions within or without said pattern but otherwise remain adhered to said carrier layer in second regions without or within said pattern and such that said released layers can be simultaneously transferred to a substrate material, characterised in that, the surface energy between the release coat layer when in its activated state and the carrier layer is greater than the surface energy between the release coat layer in said activated state and said lacquer coat layer such that, when in said activated state, said release layer is essentially or substantially retained on said carrier layer as other layers beneath it are released therefrom and transferred to said substrate material as a result of the application of said energy, and further characterised in that the lacquer coat layer is formed of or comprises an at least partially electrically conducting material having an electrical conductivity which less than that of the electro-conductive layer of the transfer film such that the surface of said lacquer coat layer can support at least first and second spaced apart direct physical electrical contacts into and out of which an electrical current can flow, the relative conductivities of the lacquer coat layer and the electro-conductive layer and the separation of the electrical contacts being such that the majority of current flow between said contacts within the released layers of the transfer film occurs within the electro-conductive layer.
2. 2. An electro-conductive transfer film comprising at least a carrier layer being of a flexible plastics material, a release coat layer, a lacquer coat layer, an electro-conductive layer and a size coat layer wherein said release coat layer adhesively secures said carrier layer and said lacquer coat layer together and to which, through one or both of said carrier layer and said lacquer coat layer, one or more forms of energy can be applied in a predetermined pattern, said energy having the effect of activating the release coat layer so as to reduce or eliminate its adhesive quality within or without a perimeter boundary of said pattern so that said lacquer coat layer and any layers on the opposite side thereof to said carrier layer are effectively released from said carrier layer in first regions within or without said pattern but otherwise remain adhered to said carrier layer in second regions without or within said pattern and such that said released layers can be simultaneously transferred to a substrate material, characterised in that, the surface energy between the release coat layer when in its activated state and the carrier layer is less than the surface energy between the release coat layer in said activated state and said lacquer coat layer such that, when in said activated state, said release layer is essentially or substantially released from said carrier layer along with other layers beneath it and transferred to said substrate material as a result of the application of said energy, and further characterised in that both the release coat layer and the lacquer coat layer are formed of or comprise an at least partially electrically conducting material and have an electrical conductivities which are less than that of the electro-conductive layer of the transfer film such that the surface of said release coat layer, when in a deactivated or inactive state can support at least first and second spaced apart direct physical electrical contacts into and out of which an electrical current can flow, the relative conductivities of the release coat layer in its inactive state, the lacquer coat layer and the electro-conductive layer and the separation of the electrical contacts being such that the majority of current flow between said contacts within the released layers of the transfer film occurs within the electro-conductive layer.3. An electro-conductive transfer film comprising at least a carrier layer being of a flexible plastics material, a release coat layer, an electro-conductive layer and a size coat layer wherein said release coat layer adhesively secures said carrier layer and said electro-conductive layer together and to which, through one or both of said carrier layer and said electro-conductive layer, one or more forms of energy can be applied in a predetermined pattern, said energy having the effect of activating the release coat layer so as to reduce or eliminate its adhesive quality within or without a perimeter boundary of said pattern so that said electro-conductive layer and any layers on the opposite side thereof to said carrier layer are effectively released from said carrier layer in first regions within or without said pattern but otherwise remain adhered to said carrier layer in second regions without or within said pattern and such that said released layers can be simultaneously transferred to a substrate material, characterised in that, the surface energy between the release coat layer when in its activated state and the carrier layer is less than the surface energy between the release coat layer in said activated state and said electro-conductive layer such that, when in said activated state, said release layer is essentially or substantially released from said carrier layer together with other layers beneath it, all such released layers being transferred to said substrate material as a result of the application of said energy, and further characterised in that the release layer is formed of or comprises an at least partially electrically conducting material having an electrical conductivity which is less than that of the electro-conductive layer of the transfer film such that the resulting surface of said release layer in its inactive or deactivated state can support at least first and second spaced apart direct physical electrical contacts into and out of which an electrical current can flow, the relative conductivities of the release coat layer and the electro-conductive layer and the separation of the electrical contacts being such that the majority of current flow between said contacts within the released layers of the transfer film occurs within the electro-conductive layer.
3. 2. An electro-conductive transfer film according to any of claims 1-3 wherein the conductivity of the exposed top-most layer of the transfer film, post-transfer, whether this is the lacquer coat layer or the release coat layer, is such that electrical connection therewith can be achieved through simple surface contact.
4. 4. An electro-conductive transfer film according to any of claims 1 wherein the lacquer coat layer is provided with a sufficient amount of an electro-conductive additive material to render said layer both electrically conductive to the required degree so that an exposed upper surface of said material is capable of supporting a direct surface-based electrical connection, said electroconductive additive element being one of, or some combination of: - particles of a conductive elemental metal such as Copper, Silver, Gold, Molybdenum, Zinc, Nickel, - particles of a conductive metal alloy such as Bronze, Brass, or any Monel alloy, - particles of an organic or inorganic conductive element, compound or polymer, such as Carbon (in any conductive form, such as carbon nano-tubes, graphene, Buckminsterfullerine), polyfluorines, polyacetylenes, polypyrroles, polythiophenes.
5. 5. An electro-conductive transfer film according to any of claims 2 or 3, or claim 4 when dependent on claim 2, wherein the release coat layer is provided with a sufficient amount of an electro-conductive additive material to render said layer both electrically conductive to the required degree so that an exposed upper surface of said material is capable of supporting a direct surface-based electrical connection, said electro-conductive additive element being one of, or some combination of: - particles of a conductive elemental metal such as Copper, Silver, Gold, Molybdenum, Zinc, Nickel, - particles of a conductive metal alloy such as Bronze, Brass, or any Monel alloy, - particles of an organic or inorganic conductive element, compound or polymer, such as Carbon (in any conductive form, such as carbon nano-tubes, graphene, Buckminsterfullerine), polyfluorines, polyacetylenes, polypyrroles, polythiophenes.
6. 6. An electro-conductive transfer film according to claim 5 wherrein the particle size is one of: less than 1vm, and less than 100nm.
7. 7. A substrate rendered electro-conductive by the application thereto of an electroconductive transfer film according to any preceding claim, and further provided with at least a pair of electric contacts applied to said film in spaced apart relation along some portion of a length of said applied film.
8. 8. An electro-conductive substrate according to claim 7 wherein the said contacts are separated from one another by an amount which is one of: at least 10, at least 104, at least 10' orders of magnitude greater than the thickness of the uppermost layer of the film with which said contacts are directly in contact.