GB2129952A

GB2129952A - 'Peel apart' coloured photosensitive materials

Info

Publication number: GB2129952A
Application number: GB08329691A
Authority: GB
Inventors: John Philip Gasson; John Victor Shepherd; John Stirk Thornley
Original assignee: Letraset International Ltd; Letraset Ltd
Current assignee: Letraset International Ltd; Letraset Ltd
Priority date: 1982-11-05
Filing date: 1983-11-07
Publication date: 1984-05-23
Also published as: GB8329691D0; GB2129952B

Abstract

Photosensitive materials comprising two carrier sheets having therebetween a photo-polymerisable layer which contains a light- attenuating, non-photosensitive dye or pigment and material which changes colour under the influence of actinic radiation. When the photosensitive material is imagewise exposed to actinic radiation the photo- polymerisable material is polymerised and the colour changeable material changes colour in the exposed areas. Thus there is obtained an image which is immediately visible after the imagewise exposure step and accordingly can be used to check that exposure has correctly taken place and which is developable by peeling apart of the two carrier sheets whereby the material therebetween shears imagewise along the edges of the image areas. The photosensitive material according to this invention is particularly useful in the production of sign making materials and in the production of dry transfer materials.

Description

SPECIFICATION Photosensitive materials This invention relates to photosensitive materials and their use. In particular the invention relates to photosensitive materials which, after imagewise exposure, can be developed by mechanical rather than chemical means to give the reproduced image.

The reproduction of images using photosensitive materials is of course well known. One particular area to which attention has recently been directed is the development of photosensitive materials which, after imagewise exposure, can be "developed" without the aid of developer liquids.

Rather than by chemical means, the images of such materials are developed mechanically. The materials generally comprise two carrier sheets having at least one photosensitive layer therebetween which carrier sheets, after imagewise exposure of the photosensitive layer through one of the carrier sheets, are peeled apart to give the desired image adhered to a carrier sheet.

Such "peel apart" systems have been proposed for different uses. For example British Patent Specification No: 2053497A proposes a sign-making material which consists of a pair of carrier sheets which can be peeled apart and which are held together via intermediate layers. At least one of the carrier sheets is transparent or translucent and adjacent this is a layer of adhesive and between this layer and the other carrier sheet is an, e.g. pigmented, imaging layer which, after imagewise exposure, shears along the edges of the image areas when the sheets are peeled apart to form the final image adhered to the first carrier sheet. Suitably the imaging layer comprises a first photopolymer layer and an adjacent, separate shearable pigmented layer.Using such photosensitive materials, after imagewise exposure and peeling apart, there is obtained a transparent or translucent carrier sheet bearing on its adhesive side a desired legend or image formed from the sheared image forming layer which can be a photopolymer layer and adjacent shearable pigmented layer. The legend will normally be in the form of a plurality of indicia such as signs, symbols, letters and figures each surrounded by adhesive which serves to adhere the whole sheet to a desired location. Thus there is obtained a sign which is protected against for example abrasion by the overlying carrier sheet.

British Patent Specification No: 2029039A discusses various other prior art approaches to peel apart systems and itself proposes photosensitive materials useful in particular for the production of dry transfer materials. Thus British Patent Specification No: 2029039A describes a photosensitive material comprising, in order, a first carrier sheet, a photosensitive layer, a non-photosensitive pigment or dye-containing image forming layer and a second carrier sheet, wherein an imagewise exposure of the material and peeling apart of the sheets the image forming layer is caused to shear imagewise, wherein, prior to exposure, on peeling apart the sheets, the photosensitive layer and image forming layer are both retained wholly on the second carrier sheet and wherein, after exposure, the photosensitive layer and at least part of the image forming layer are on the first carrier sheet.By incorporating adhesive in or adjacent the shearable image forming layer, this photosensitive material may constitute a material from which dry transfers may be manufactured simply by imagewise exposure and peeling apart.

While these peel-apart systems offer a very convenient way of reproducing images, they suffer from the disadvantage that the image is only revealed during the peel apart development when image and non-image areas are retained on different carriers. No visible change occurs in the material itself during the imagewise exposure step; the change which takes place on imagewise exposure is a photopolymerisation. The operator is thus not able to perceive the image immediately after imagewise exposure, for example to check that imagewise exposure has been properly carried out.

G.B. 2075701A describes a peel apart system using a laminated product comprising a sensitive layer sandwiched between substrates, the sensitive layer being photopolymerisable and colourless before radiation and comprising a leucocyanide dye. On imagewise exposure the sensitive layer material becomes photopolymerised and coloured to form a product in which the image and nonimage areas can be distinguished and which can be peeled apart to give the final image. However the optical properties of the image obtained in this way is far from satisfactory.

According to the present invention there is provided a photosensitive material which comprises, in order, a first carrier sheet, a photopolymerisable layer, which layer contains a light-attenuating, nonphotosensitive dye or pigment and contains material which changes colour when exposed to actinic radiation, and a second carrier sheet, at least the first carrier sheet being transparent or translucent, in which material, on imagewise exposure to actinic radiation, the photopolymerisable layer is both polymerised and changes colour in the exposed areas and in which material, after imagewise exposure and peeling apart of the carrier sheets, the photopolymerisable layer material shears along the edges of the image areas so that in the exposed areas photopolymerisable layer material is retained on the first carrier sheet.

When the photosensitive material according to the present invention is imagewise exposed to actinic radiation not only does the material of the photopolymerisable layer polymerise in the exposed areas but also there is a color change giving an image which can be viewed even prior to peeling apart.

The photosensitive material according to the invention is imagewise exposed through the first carrier sheet. This causes polymerisation of the photopolymerisable layer in the exposed areas and in addition there is caused a change of colour. This change of colour can be checked by the operator, for example to check that all is proceeding normally. Assuming normal operation, the carrier sheets are then peeled apart, the photopolymerisable layer shearing imagewise so that the desired legend or sign is retained on the first carrier. It is to be noted that despite the fact that a visible image is obtained in the photopolymerisable layer after imagewise exposure there is not required any fixing step to deactivate the unexposed background areas since these are physically detached from the image areas in the peeling apart step.

Moreover, because the polymerisable layer also contains light-attenuating, non-photosensitive dye or pigment the final image obtained is of good optical density.

The photopolymerising and dye- or pigment-constituents of the photopolymerisable layer may be present in a single layer. Preferably however the photopolymerisable layer is made up of two sublayers; a first photopolymerisable sublayer and, adjacent thereto, a shearable dye- or pigment-containing sublayer which second sublayer changes colour under the influence of actinic radiation. By having the colour components in a separate sublayer from the photopolymerisable component better resolution of the image is generally obtained. Indeed the dye- or pigment-constituents and the constituents which cause colour change may themselves be present in different shearable sublayers.

Preferred photosensitive material according to the present invention comprises, in order, a first carrier sheet, a photopolymerisable layer, a shearable layer, adjacent the photopolymerisable layer, which shearable layer contains the light-attenuating, non-photosensitive dye or pigment and the material which changes colour on exposure to actinic radiation, and a second carrier sheet, at least the first carrier sheet being transparent or translucent, in which material, on imagewise exposure to actinic radiation, the photopolymerisable layer is polymerised and the shearable layer changes colour in the exposed areas and in which material, after imagewise exposure and peeling apart of the carrier sheets, the photopolymerisable layer material and the shearable layer material shear along the edges of the image areas so that in the exposed areas the photopolymerisable layer material and at least part of the shearable dye- or pigment-containing layer material are retained on the first carrier sheet. Preferably shearing occurs through the whole of the depth of both the photopolymerisable and the shearable layer material so that the material retained on the first carrier is substantially of the thickness of that of the photopolymerisable and shearable layers.

Suitable materials which change colour under the influence of actinic radiation for use in the photopolymerisable layer, preferably in a sublayer adjacent a photopolymerisable sublayer, according to the invention may comprise a single component or a mixture of components, for example a mixture of components which when exposed to actinic radiation, react with a colour change. The colour change can be a bleaching effect (photobleaching) or a darkening effect and may for example be a dye bleaching or dye formation reaction. The colour change may be reversible or non-reversible. For example there may be used a photochromic compound i.e. a compound in which a colour change is induced by radiation of one wavelength, which colour change is reversed either by radiation of a second wavelength or by thermal energy.The following systems can be mentioned as suitable systems for use as materials which change colour under the influence of actinic radiation: the photolysis of polyhalogen derivatives e.g. carbon tetrabromide, in the presence of diphenylamine, photochromic compounds, photobleaching compounds and light sensitive leuco dyes.

The photopolymerisable layer also contains a light-attenuating, non-photosensitive dye or pigment. The presence of this dye or pigment in the final image gives the image its satisfactory optical density. Suitably the dye or pigment should be present in the photopolymerisable layer such that the layer has an optical density of at least 0.5 to a white light source by transmission.

Particular care has to be taken to ensure that the final image has sufficient optical density when a - photobleachable dye is used. Then a balance must be struck between the optical density of the final image and its density relative to the unexposed material by adjusting the amount of dye used and the exposure of the material. If desired, to ensure sufficient optical density in the final image, carbon black may be incorporated into the photobleachable layer. Alternatively, the photosensitive material may also include (between the photobleachable layer and second carrier) a separate shearable pigmented or dyed image forming layer. Then, after imagewise exposure of the photosensitive material, the image is visible as bleached areas compared with the unexposed areas.However when the photosensitive material is developed by peeling apart in addition to the photopolymerisable layer material (and if separate therefrom photobleachable layer material) being retained on the first carrier sheet in the exposed areas there will also be retained at least part of this image forming layer to give the final image the required optical density.

The present invention is particularly useful in the production of signs in manner analogous to that described in British Patent Specification No: 2053497A. Thus in particular the invention provides a photosensitive material for use in making signs which consists of two carrier sheets, at least one of which is transparent or translucent, the sheets being held together via at least one transparent or translucent layer of adhesive (preferably pressure-sensitive adhesive) adjacent the or a transparent or translucent carrier sheet, a photopolymerisable layer adjacent the adhesive layer and a shearable layer of material which contains a light-attenuating, non-photosensitive dye or pigment and contains material which changes colour when exposed to actinic radiation adjacent the photopolymerisable layer.

When this sign making material is imagewise exposed to actinic radiation the exposed areas are visible as for example bleached or darkened areas. Then to develop the image the two carrier sheets are peeled apart and the photopolymerised layer, the exposed parts of which will have been photopolymerised under the influence of the imagewise exposure and at least part of the overlying shearable layer will shear along the edges of the image areas so that there is obtained the transparent or translucent carrier sheet having on its adhesive bearing side indicia formed of the photopolymerised material and overlying dye- or pigment-containing shearable layer material.This may then be used as a sign, the adhesive serving to adhere the whole to a receptor surface to give a sign in which the indicia are protected for example against abrasion by means of the overlying transparent or translucent carrier sheet.

Again, when the material which changes colour under the influence of light is a photobleachable material, care must be taken to ensure that there is sufficient optical density in the final image. As discussed above this can be done by balancing between the optical density of the final image and its density relative to the unexposed areas by adjusting the exposure and the amount of dye used and possibly also admixing a pigment such as carbon black into the layer.

Alternatively the sign making material may comprise a further shearable pigmented or dyed image forming layer adjacent the photobleachable layer. In such a sign making material the carrier sheets would be held together via at least one transparent or translucent layer of adhesive adjacent a carrier sheet, a photopolymerisable layer adjacent the adhesive layer, a shearable photobleachable layer adjacent the photopolymerisable layer, a shearable pigmented or dyed image forming layer adjacent the photobleachable layer and the second carrier sheet. This assembly in use is imagewise exposed through the first carrier sheet to photopolymerise the material of the photopolymerisable layer in the exposed areas and at the same time the material of the photobleachable layer will become bleached in the exposed areas thus making the image inspectable.

The image is then developed by peeling apart of the composite. The photopolymerisable layer shears between the exposed (photopolymerised) areas and the unexposed (non-photopolymerised) areas and in addition the photobleached layer and at least part of the shearable image forming layer shear imagewise along the edges of the exposed area so that there is obtained the transparent or translucent carrier sheet bearing on its adhesive coated side indicia formed of photopolymerised material, overlying photobleached layer material and finally image forming layer material.

This can be used to provide a sign, the adhesive adhering the whole to the appropriate receptor surface and the carrier sheet providing an abrasion-resistant covering for the indicia.

The invention is also particularly useful in the production of dry transfers for example in a manner similar to that described in British Patent Specification No: 2029039A. Thus, according to a preferred embodiment, the invention also provides a photosensitive material for use in the production of dry transfer materials comprising, in order, a first carrier sheet, a photopolymerisable layer, a shearable layer which contains a light-attenuating, non-photosensitive dye or pigment and contains material which changes colour when exposed to actinic radiation and a second carrier sheet wherein, on imagewise exposure of the material, the shearable layer changes colour imagewise and on peeling apart of the sheets the shearable layer is caused to shear imagewise, wherein, prior to exposure, on peeling apart the sheets, the photopolymerisable and shearable layers are both retained wholly on the second carrier sheet, and wherein, after exposure, the photopolymerisable layer and at least part of the shearable layer are retained on the first carrier sheet.

Thus again after imagewise exposure of the photosensitive material the image is visible as areas of different colour, e.g. bleached or darkened areas, from the remainder of the material.

Again as discussed above when a photobleachable compound is used care may need to be taken about the optical density of the final image either for example by including carbon black in the photobleachable layer or including a further shearable pigmented or dyed image forming layer adjacent the photobleachable layer.

In the production of dry transfers the photosensitive material must be formulated so that on the one hand the final image must adhere to the first carrier sheet after exposure and on the other hand the image must be released from the carrier sheet and adhere to a receiving surface when brought in contact therewith. Thus the photosensitive material will have adhesive incorporated in or adjacent the layer forming the image layer furthest from the first carrier sheet (i.e. the shearable layer which changes colour under the influence of actinic radiation or, if present, the overlying shearable pigmented or dyed layer). Suitably the shearable layer contains permanently relatively non-tacky adhesive components sufficient to adhere the image formed on to a desired receptor surface.In that connection, the dry transfer material so produced may be arranged, by appropriate formulation of the two layers, to work solely by virtue of the adhesion generated to the desired receptor by the adhesive components in the shearable layer which act to overwhelm the bond between the exposed photosensitive layer and the first carrier sheet. However the best way of overcoming the apparent contradiction of the increase in adhesion in the photosensitive material giving rise to an image adhered to the first carrier sheet from which it is released when transferred to a receptor surface is to have a photosensitive material so formulated that the image is released from the first carrier by the so-called stretch-release principle by local manipulation e.g. by rubbing over the rear surface of the first carrier sheet with a stylus, as disclosed in British Patent Specification No: 959670.In addition preferably the adhesive face of the shearable layer may be coated onto a release paper constituting the second carrier sheet.

Alternatively to incorporating an adhesive material in the shearable layer, the adhesive may be incorporated into the photosensitive material as a layer between the shearable layer and the second carrier sheet, which layer on peeling apart the carrier sheets is retained at least partly on those areas of shearable layer which are pulled away with the first carrier sheet.

If it is not desired to incorporate adhesive into the photosensitive material itself, after exposure and development by peeling apart, the indicia it is desired to transfer may be supercoated with a conventional dry transfer low tacky pressure sensitive adhesive in known fashion.

Preferably the photopolymerisable layer comprises a monomer, a photoinitiator and a filmforming binder and/or reactive oligomer with the optional addition of reaction enhancers (e.g. amines, perhalogenated alkanes) and thermal stabilisers (e.g. polyhydric phenols), which act by inhibiting polymerisation. The monomer should be added only in as far as it is retained by the film-forming binder thus enabling the layer to be completely removed from the first carrier sheet on peel apart in the unexposed areas. In formulations where the monomer can be added in large quantities (i.e. where it is fully compatible with the binder in all proportions) then care should be exercised such that the cohesion of the photopolymerisable layer is maintained during peel apart.Similarly, the combination of initiator, monomer and oligomer should be added to the binder only to develop photoadhesion properties and not in excess such that internal cohesive failure occurs. The monomers, initiator and oligomers should be absorbed by the binder such that they are entirely removed from the first carrier sheet in the unexposed areas.

Binders can be selected from a wide range of polymeric materials but must be carefully matched to the monomers, oligomers and initiators and to the supporting substrates since it is the binder which has the major effect on image definition and release. Polyvinyl acetates, polyvinyl alcohols, polyvinylpyrrolidone and acrylic polymers are generally suitable. The photoinitiator layer should be as thin as is convenient to manufacture and compatible with good image release. A thickness of between 1 and 30 ,u gives the best results.

The materials according to the present invention may also be imaged by a method which permits visual spacing using a negative which in the non-image areas is transparent to visible light and e.g. U.V.

opaque and which in the image areas is transparent to e.g. U.V. light and opaque to visible light. When material according to the present invention appropriately sensitive is imagewise exposed through this negative to a U.V. light source, the U.V. light is transmitted through the negative in the image areas causing both polymerisation and a change of colour imagewise in the material according to the invention. The image formed will accordingly be visible in particular through the non-image areas of the negative.

This method is for example suitable for the building up of words. Thus the material according to the invention can be imagewise exposed to a negative comprising a first U.V. transparent/visible opaque letter with a visible transparent/U.V. opaque non-image areas. Then the visible image of this letter is used visually to position the negative of the next letter. There is a second imagewise exposure step so that an appropriately positioned image of that letter is formed in the photosensitive material.

This can be continued until the whole word, text etc. has been built up.

In this way by using a photographic font and a light source a dry transfer can be assembled by visual inspection and thus the alignment and spacing determined prior to peel apart. This is particularly useful in the photosetting field.

The invention is further illustrated by way of example in the accompanying drawings wherein Figure 1 shows generally the construction of a sign making material according to the present invention and diagrammatically shows what may happen when it is exposed and developed by peeling apart the carrier sheets; Figure 2 shows another sign making material according to the present invention and diagrammatically shows its use; and Figure 3 shows material according to the invention and diagrammatically shows its use in the production of dry transfers.

Referring first to Figure 1, the sign making material comprises a first clear carrier sheet C1, e.g. of polyethylene terephthalate film, which is provided with an adhesive layer A, a photopolymerisable layer PL, a shearable photobleachable layer PBL which layer also contains a light-attenuating non photosensitive dye or pigment and a carrier sheet C2.

This sign making material is imagewise exposed through a photographic negative PN having a pair of light-transmitting areas. The photosensitive material is contact exposed therewith through the clear carrier sheet Cl to the irradiation from a generally parallel beam of light. In the exposed areas the material of the photopolymerisable layer PL becomes hardened by photopolymerisation though there will be no change in colour of this layer. In addition however the image is visible because also in the exposed areas the material of the photobleachable layer PBL becomes bleached. Thus the exposed areas can be seen in the imagewise exposed material as bleached areas compared with the unexposed areas.

The material is then developed by peeling part. The photopolymerised material and at least part of the photobleachable layer is retained on the first carrier and adhesive layer in the exposed areas and the photopolymerisable layer and photobleachable layer material in the unexposed areas is removed with the second carrier sheet. Thus there is obtained the sign making material comprising the first carrier having on its adhesive coated side indicia comprising photopolymerised material and shearable dye- or pigment-containing bleached photobleachable layer material. This whole can then be adhered by means of the adhesive to a suitable receptor surface. In this way the indicia are protected against for example abrasion by means of the overlying carrier sheet.

Figure 2 relates to an embodiment similar to that of Figure 1 except that the photosensitive material also comprises a shearable pigmented imaging layer IL between the photobleachable layer and the second carrier sheet to improve the optical density of the final indicia. Thus when this material is imagewise exposed and the photopolymerisable layer material photopolymerised in the exposed areas, the photobleachable layer material photobleaches in the exposed areas so that the image is visible as areas of different colours within the photobleach layer. However when the material is developed by peeling apart not only the photopolymerised and all the photobleachable layer material in the exposed areas is retained on the adhesive coating carrying surface of carrier 1 but also at least part of the shearable pigmented layer IL.

This material can be used in the same way as that of Figure 1 to make signs.

Referring to Figure 3, the material according to the present invention comprises a first clear carrier sheet e.g. of polyethylene terephthalate film C1 adjacent which is a photopolymerisable layer PL, a shearable photochromic layer PCL, an adhesive layer A and a second carrier C2, which is suitably release coated. The light-attenuating, non-photosensitive dye or pigment may be present either in layer PCL or in layer A.

The material of Figure 3 is imagewise exposed through the clear carrier sheet C1 to a photographic negative PN. In the exposed areas the material of the photopolymerisable layer PL (adjacent the clear carrier C1) becomes hardened by photopolymerisation though there is no change in colour of this layer. In addition however the image is rendered visible because also in the exposed areas there is a change in colour of the photochromic layer PCL. Thus the exposed areas can be seen in the imagewise exposed material as differently coloured areas from the unexposed areas.

The material is then developed by peeling apart. The photopolymerised material, the photochromic layer material and at least part of the adhesive layer material are retained on the clear carrier sheet Cl in the exposed areas. This material may be used as a dry transfer material in the usual way.

The invention is further illustrated in the following Examples.

Example 1 There were made up the following compositions Composition A (photobleachable composition) Parts by weight Polyisobutylene (high molecular weight) (20% by weight Oppanol B50 in Ensol ex BASF) 3.63 Polyisobutylene (low molecular weight) (Hyvis 200 ex B.P. Chemicals) 5.45 Hydrophilic Silica (Aerosil 300 ex Degussa) 2.55 Glycerol ester of hydrogenated rosin (Stabelite Ester ex Hercules) 1.45 Ethoxy ethanol 0.73 Electro neutral salt of polycarbonic acid with amine derivatives in approximately 50% higher aromatics (Product 963 ex Henkel) 0.04 Hydrocarbon solvent (Exsol ex Esso) 86.15 Silicone permanent tack adhesive, 60% in toluene (DC 282 ex Dow Corning) 1.00 Oil Soluble Nubian black BT dye (ex Williams (Hounslow) Limited) 0.50 This composition was ball milled to homogeneity.

Composition B (photopolymerisable composition) Parts by weight Polyacrylate emulsion copolymer (Bevaloid 6464 ex Bevaloid Ltd) 60.00 Unsaturated acrylate monomer (OTA 480 ex UCB Chemical Sector) 40.00 33% isopropyl thioxanthone in 2-n-butoxyethyl 4-dimethyl aminobenzoate 2 2.00 Ethoxylated sorbitan ester (HLB 4.5) (Span 80 ex Honeywill Atlas) 0.38 Ethoxylated sorbitan ester (HLB 15) (Tween 80 ex Honeywill Atlas) 0.62 Water 20.00 This mixture was emulsified using rapid stirring.

Composition A was coated onto silicone release paper using an 18 meyer bar and dried at 500 C.

Composition B was then coated onto Composition A using a 22 meyer bar and dried at 500C.

A 15% solution in hydrocarbon solvent (Exsol ex Esso) of a high molecular weight polyisobutylene (Oppanol B50) was then coated onto polyethylene terephthalate sheet using an 18 meyer bar and dried at 500C.

The two sheets ware than laminated together with the photopolymer layer adjacent the polyisobutylene coating by passing through a nip between two rollers at a temperature of 700C and a speed of 30.5 cm per minutes.

The whole was contact exposed through the polyethylene terephthalate sheet through a photo negative. Exposure conditions were 10 seconds at 1 m from a 2 kw mercury metalide halide lamp. The image obtained was then visible with the material of the photobleachable layer being bleached in the exposed areas in contrast to the unexposed areas.

The whole was then developed by peeling apart the two carrier sheets, whereon the photopolymerisable layer and photobleachable layer were retained on the polyisobutylene adhesive coated surface of the polyethylene terephthalate sheet. This material was then suitable for use in the production of a sign.

Example 2 The following ingredients were dispersed using a ball mill over three days: Parts by weight Silicone adhesive (DC. 282 ex Dow Corning) 2 Xylene 6.4 Rutile titanium oxide (RH. 472 ex Laporte) 6 This mixture was coated onto a release paper (30/102 ex Jointine Limited) using a No. 10 meyer bar.

The following ingredients were mixed to homogeneity: Parts by weight Photochromic dye (YP ex A.B.M. Chemicals) 0.5 Polyester resin (Vitel PE 200 ex Goodyear Limited) 1.2 Methyl ethyl ketone 1.8 This mixture was coated on the first layer using a No. 10 meyer bar.

There were then mixed the following Parts by weight Acrylate monomer (AM 548 ex Synthese BV) 60 Non-ionic surface active agent (Sympenonic NP8 ex l.C.l.) 5 Photoinitiator mixture (33% Quantacure ITX (2-isopropylthioxanthone) in Quantacure BEA (2-(n-butoxy)-ethyl-4-dimethylaminobenzoate) ex Ward Blenkinsop) 5 To this mixture were added with vigorous stirring: Parts by weight Acrylic copolymer resin emulsion (EP 4711 ex National Adhesives Ltd) 40 Water 20 The mixture thus obtained was applied over the previous two coatings using a No. 20 meyer bar and the dried coating assembly was laminated to polyethylene terephthalate sheet (542 Melinex ex l.C.I.) using a nip heated to 700C and a lamination speed of 1 m/min.

The laminated product was exposed to light from a 2 kw mercury metal halide arc at 1 m through an image bearing transparency in contact with the polyethylene terephthalate for 25 secs. The areas exposed to light could be clearly differentiated from the non-exposed areas.

The whole was then developed by peeling apart the two carrier sheets. The exposed areas were retained on the polyethylene terephthalate sheet to give a dry transfer product.

Claims

1. A photosensitive material which comprises, in order, a first carrier sheet, a photopolymerisable layer, which layer contains a light-attenuating non-photosensitive dye or pigment and contains material which changes colour when exposed to actinic radiation, and a second carrier sheet, at least the first carrier sheet being transparent or translucent, in which material, on imagewise exposure to actinic radiation, the photopolymerisable layer is both polymerised and changes colour in the exposed areas and in which material, after imagewise exposure and peeling apart of the carrier sheets, the photopolymerisable layer material shears along the edges of the image areas so that in the exposed areas photopolymerisable layer material is retained on the first carrier sheet.

2. Photosensitive material according to claim 1 wherein the photopolymerisable layer, which changes colour under the influence of actinic radiation comprises a first photopolymerisable sublayer and, adjacent thereto, a shearable sublayer which contains a light-attenuating, non-photosensitive dye or pigment and contains material which changes colour when exposed to actinic radiation and wherein, after imagewise exposure and peeling apart of the carrier sheets, the photopolymerisable sublayer material and the shearable sublayer material shear along the edges of the image areas so that in the exposed areas the photopolymerisable sublayer and at least part of the shearable sublayer material are retained on the first carrier sheet.

3. Photosensitive material according to claim 1 or 2 wherein the material which changes colour when exposed to actinic radiation is photobleachable or photochromic.

4. Photosensitive material according to claim 3 wherein the material which changes colour when exposed to actinic radiation in photobleachable and which comprises a photobleachable layer and, between the photobleachable sublayer and the second carrier sheet, a shearable image-forming sublayer containing light-attenuating, non-photosensitive dye or pigment, and wherein, after imagewise exposure and peeling apart of the carrier sheets, the shearable pigmented or dyed imageforming sublayer as well as the underlying sublayer(s) shear along the edge of the image areas so that in the exposed areas the underlying sublayer(s) material and at least part of the shearable pigmented or dyed image-forming material is retained on the first carrier sheet.

5. A photosensitive material for use in making signs which consists of two carrier sheets, at least one of which is transparent or translucent, the sheets being held together via at least one transparent or translucent layer of adhesive adjacent the or a transparent or translucent carrier sheet, a photopolymerisable layer adjacent the adhesive layer and a shearable layer which contains a lightattenuating, non-photosensitive dye or pigment and contains material which changes colour when exposed to actinic radiation adjacent the photopolymerisable layer, in which material, on imagewise exposure to actinic radiation, the photopolymerisable layer is polymerised and the shearable layer changes colour in the exposed areas and in which material, after imagewise exposure and peeling apart of the carrier sheets, the photopolymerisable layer material and shearable layer material shear along the edges of the image areas so that there is obtained the transparent or translucent carrier sheet having on its adhesive bearing side indicia formed of the photopolymerisable material and at least part of the shearable layer material.

6. Photosensitive material according to claim 5 wherein the material which changes colour when exposed to actinic radiation is photobleachable.

7. Photosensitive material according to claim 6 wherein the carrier sheets are held together via at least one transparent or translucent layer of adhesive adjacent a first carrier sheet, a photopolymerisable layer adjacent the adhesive layer, a shearable photobleachable layer adjacent the photopolymerisable layer, a shearable pigmented or dyed image-forming layer adjacent the photopolymerisable layer and the second carrier sheet wherein, after imagewise exposure and peeling apart of the carrier sheets, the photopolymerisable layer material, the shearable photobleachable layer material and the shearable image-forming layer material shear along the edges of the image areas so that in the exposed areas the photopolymerisable layer material, the photobleachable layer material and at least part of the image-forming layer material are retained on the adhesive bearing side of the first carrier sheet.

8. A photosensitive material for use in the production of dry transfer materials comprising, in order, a first carrier sheet, a photopolymerisable layer, a shearable layer which contains a lightattenuating, non-photosensitive dye or pigment and material which changes colour when exposed to actinic radiation and a second carrier sheet wherein, on imagewise exposure of the material, the shearable layer changes colour imagewise and on peeling apart of the sheets the shearable layer is caused to shear imagewise, wherein, prior to exposure, on peeling apart the sheets, the photopolymerisable and shearable layers are both retained wholly on the second carrier sheet, and wherein, after exposure, the photopolymerisable layer and at least part of the shearable layer are retained on the first carrier sheet.

9. A photosensitive material according to claim 8 wherein the shearable layer comprises a sublayer containing the colour changeable material and an adhesive sublayer adjacent the second carrier, the pigment or dye being present in either sublayer.

10. A photosensitive material substantially as described in and illustrated with reference to Figure 1, 2 or 3 of the accompanying drawings.

11. A photosensitive material according to claim 1 substantially as described in either of the Examples.

12. A method of reproducing an image which method comprises imagewise exposing photosensitive material as claimed in any one of claims 1 to 11 and peeling apart the two carrier sheets.