GB2026185A - The manufacture of transfer materials - Google Patents

Abstract

Making dry transfer materials by imagewise exposing a positive working photosensitive material (e.g. naphthoquinone diazides) is described. In the method, the positive working layer, on development, constitutes (in the unexposed areas), the indicia or other transferable design. In the exposed areas, it is wholly or partly removed during development. Preferably the photosensitive material has a photosensitive layer overcoated by a shearable adhesive layer: the adhesive in exposed areas shears and is removed during development leaving adhesive for effecting transfer precisely where desired, i.e. on the transferable film areas.

Description

SPECIFICATION The Manufacture of Transfer Materials.

This invention relates to the manufacture of transfer materials.

In recent years a number of suggestions have been made for the manufacture of dry transfer materials, particularly transfer lettering sheets, by photographic proceses ratherthan by printing processes. Exemplary of such processes are those described in British Patent Specifications 1291960,1364627 and 1441982.

In the systems proposed in Specifications 1364627 and 1441982 a photographically sensitive material is exposed imagewise to light through a negative of the desired transferable image. Where the light impinges on the photosensitive material, the material hardens and after exposure is not removed during a development process to which the material is then subjected. During that development process unexposed portions of the photosensitive material are removed by solvent action.

Specification 1291960 describes a method of producing transfer materials photographically using a positive working photosensitive material to form the desired transferable indicia. The use of a positive working system brings substantial advantages, but these are not fully realised in the materials disclosed in Specification 1291960.

According to the present invention there is provided a method of making a dry transfer material which comprises imagewise exposing a positive working photosensitive layer on a carrier sheet, and developing the layer to remove, at least in part, exposed areas of the layer, and accordingly leave on the carrier sheet visible transferable positive images constituted by unexposed developed areas of the layer. In a highly preferred method, the carrier sheet bears, on top of the positive working photosensitive coating, a shearable coating of a substantially non-tacky pressure sensitive adhesive. During development, parts of the shearable coating overlying exposed areas are removed, leaving adhesive precisely in register with the indicia produced.

The indicia are preferably rendered visible by incorporating a pigment and/or a dye into the photosensitive layer.

Positive working systems are well known. Technically, when using positive working systems the aqueous alkali developer used promotes coupling of two components in the unexposed areas of the coating. Such elements are e.g. a quinone or napthoquinone diazide and an alkali soluble resin. The final image so formed is substantially insoluble in water and aqueous alkali. In the exposed areas, the coating is dissolved and washed off during the development. An automatic advantage is achieved using a positive working system is that the full thickness of indicium desired is automatically achieved, it corresponding to the full thickness of the photosensitive layer on the base material which is exposed. Full film thickness using negative working systems such as described in the specifications referred to above can only be achieved with certainty by using long exposure times.If such negative working material is exposed through the carrier film, an image of increasing thickness after development builds up on the carrier film, so for thick images, long exposure times are needed. If such negative working material is exposed from the side carrying the photosensitive layer, full film thickness is obtained, since the image after development builds up from the outside surface of the photosensitive layer towards the carrier, and no image is formed after development at all unless the exposure has penetrated through the whole of the photosensitive layer. Thus in either case, long exposure is needed. In the case of the present invention, any exposure gives full film thickness in the image areas; any underexposure merely leaves the possibility of residues between the images after development.This is unimportant if these residues are non-adhesive since they will remain on the carrier sheet of the transfer material so produced, and accordingly, it is particularly preferred to provide a layer of adhesive on the positive working photosensitive material. Such adhesive should not be soluble in the developer, but sufficiently porous to enable the developer to develop the unexposed areas of the photosensitive layer and to remove exposed portions of the photosensitive layer and therewith portions of the adhesive in the exposed areas.

Exposure of the sensitised material can take place through the carrier sheet or directly on to the photosensitive layer (through an adhesive layer if provided.) In the former case, the carrier sheet needs to be transparent or translucent; flexible plastics films are preferred.

Positive working materials have the advantage that a positive to positive imaging process is obtained in one step and it is for example possible to manufacture a transferable image directly from artwork in a few simple processing steps without having to go through the intermediate stage of producing a negative version of that artwork. They also have the advantage that image resolution depends less on exposure time than in negative working systems; a corollary of this is that for a given resolution, greater film thickness can be achieved using positive working systems than using negative working systems.

A number of positive working photosensitive systems are known from the manufacture of presensitised lithographic plates, as are development systems designed for use therewith. Modifications to particular formulations for photosensitive layers and developers are of course necessary in order to adapt those positive working systems to the requirements of the manufacture of a transfer material, but there is no fundamental difference in the systems employed. One particular modification which may be undertaken is to ensure that the developed, no longer photosensitive, layer has appropriate mechanical properties enabling it to be easily and cleanly removed from the flexible transparent or translucent substrate.This removal may be effected either solely using the power of an adhesive applied over the indicium or with the aid of the so-called stretch release technique described in British Patent Specification 959,670.

The method of the present invention specifically avoids the drawback of the method described in Specification 1291960 where the positive working photosensitive layer is used only as a masking layer and not as an image4orming or indicia4orming layer. The problems associated with the use of microencapsulated adhesives disclosed in that specification may also be avoided.

The following Examples will serve to illustrate the invention.

Example I 0.49 of a napthaquinone diazide ester, formed from 2-diazo-1-hydroxynapthalene-5-sulphonic acid and a napthol derivative, made by Andrews Paper and Chemical Co. Ltd. and known by the trade name Diazo Ester #41 10 and 2.0g of an alkali soluble polyvinyl acetate known by the trade name Bevaloid 170 and manufactured by Bevaloid Ltd., were dissolved in 10.09 of 1,4-dioxan. The solution was coloured by KPR black photoresist dye made by Kodak Ltd. The resulting mixture was coated with a wire wound bar on 100 micron thick polyethylene and dried in air at ambient temperature.This photosensitive layer was exposed to ultraviolet light from 2kw Addalux lamp through a positive transparency placed in contact with the uncoated side of the polyethylene substrate and the image obtained was developed by treating with a developer solution of the following composition: sodium hydroxide 2.6 g sodium silicate 3.3 g surfactant (e.g.

Crodazaline C made by Croda Chemicals Ltd) 2.0g water 92.1 g The residual non-imaged areas, which consist of the exposed parts of the coating, were removed with a spray of cold water. The polyethylene sheet was dried in air at 40 C. A pressure sensitive adhesive based on a polyacrylate was applied to the imaged side of the polyethylene by screen printing.

The result of this procedure was a sheet of dry transfer material bearing individually transferable images.

Example 2 A positive working photoresist trade name At1 19A made by Shipley Chemicals Ltd was pigmented with 0.5% by weight Elftex 150 (a carbon black pigment) and coated with a wire wound bar onto 100 micron thick polyethylene. The coating was dried and exposed to ultraviolet light through a positive transparency placed in contact with the uncoated side of the polyethylene substrate and the image obtained was developed by treating with the developer used in Example 1.

The residual non-imaged ares, which comprise the exposed parts of the coating, were removed with a spray of cold water. The polyethylene sheet was dried in air at 40 C. A pressure sensitive adhesive based on a polyacrylate was applied to the imaged side of the polyethylene by screen printing.

The result of this procedure was a sheet of dry transfer material bearing individually transferable images.

Example 3 A positive working photoresist trade name At1 19A made by Shipley Chemicals Limited was pigmented with 0.5% by weight Elftex 150 (a carbon black pigment) and coated onto 0.1 mm thick polyethylene with a barwoundwith 0.9mm diameterwire.

An d\rr adhesive was made up by mixing the following compounds in a ball mill 35 parts by weight of a low molecular weight polyvinyl isobutyl ether.

40 parts by weight of a medium mmolecular weight polyvinyl isobutyl ether.

25 parts by weight of finely divided silica.

This mixture was then diluted with nine times its weight of a mixture of white spirit and oxitol (90 : 20 by weight) to give a suitable consistency for coating. The adhesive was applied over the photosensitive layer using a bar wound with wire 0.51 mm in diameter. The coated polyethylene was then exposed to a 2 kw mercury-metal halide lamp at 1 metre distance through a positivetransparancy placed in contact with the polyethylene for 180 seconds. The exposed material was then developed in Polychrome D900 positive developer. On washing with water and drying a sheet of self adhesed dry transfer letters was obtained.

Example4 The following components were mixed together (by weight): Napthoquinone diazide ester (Diazo ester P41 10 formed from 2-diazo-1 -hydroxynaphthaline-5sulphonic acid and a napthol derivative; ex Andrews Paper and Chemical Co.Ltd) 0.4 parts Alkali-soluble polyvinyl acetate (Bevaloid 170 ex Bevaloid Ltd 2.0 parts 1,4-dioxan 10.0 parts KPR black dye (ex Kodak Ltd) 0.4 parts The resulting solution was coated onto 0.1 mm thick untreated polyethylene sheet using a bar wound with wire of diameter 0.75 mm.

An adhesive was made up and applied as in Example 3.

The coated polyethylene was then exposed to a 2kw mercury metal halide lamp at 1 m distance through a positive transparency placed in contact with the polyethylene for 180 seconds. The exposed material was then developed in the developer solution used in Example 1, and then rinsed with water and dried to leave a sheet of self adhesive dry transfer lettering.

Claims (9)

1. A method of making a dry transfer material which comprises imagewise exposing a positive working photo-sensitive layer on a carrier sheet, and developing the layer to remove, at least in part, exposed areas of the layer, and accordingly leave on the carrier sheet visible transferable positive images constituted by unexposed developed areas of the layer.

2. A method according to claim 1 wherein substantially the whole of the exposed areas of the layer are removed during development.

3. A method according to claim 1 or 2 and substantially as hereinbefore described with reference to any one of the foregoing specific Examples.

4. A photosensitive material suitable for use in the method of claim 1 and which comprises a transparent or translucent carrier sheet, and a positive working photosensitive layer thereon which, on imagewise exposure and development, forms, in unexposed areas, a visible removable film layer which can be removed from the carrier sheet by the pulling power of an adhesive.

5. A photosensitive material according to claim 4 wherein on top of the photosensitive layer is a shearable coating oa a substantially non-tacky pressure-sensitive adhesive.

6. A photosensitive material according to claim 4 or 5 wherein the photosensitive layer includes a dye or pigment.

7. A photosensitive material according to any of claims 4 to 6 wherein the photosensitive layer is so formulated that after development of an unexposed portion, the layer may be released from the carrier sheet by the application of localised stylus pressure to the rear surface of the carrier sheet.

8. A photosensitive material according to claim 4 and substantially as hereinbefore described with reference to any one of the foregoing specific Examples.

9. A dry transfer material made by the method of any of claims 1 to 3.