GB2049210A - Photographic formation of visible images - Google Patents

Abstract

A visible image is photographically formed on a substrate employing a light insensitive layer 2 intermediate between a substrate 1 and a light sensitive photoresist top coat 3. The top coat 3 is exposed to activating radiation in an image pattern and developed to yield a relief image following contact with a developer system that removes the top coat 3 and intermediate layer 2 yielding the desired image pattern. Following formation of the relief image, the remaining top coat is removed leaving only the intermediate layer 2 comprising the image pattern and thereafter, the intermediate layer 2 is preferably encased or sealed in a suitable transparent material to protect the image and provide a smooth surface. The process can be used in the manufacture of keybuttons. <IMAGE>

Description

SPECIFICATION Photographic formation of visible images CROSS REFERENCE TO RELATED APPLICA TIONS This applicaton is a continuation-in-part of U.S. Patent Application Serial No. 829,998 filed September 1, 1977 (now pending) which latter application is a continuation of U.S. Patent Application Serial No. 665,082 filed March 8, 1976 which application is a continuation of U.S. Patent Application Serial No. 409,646 filed October 25, 1973, said latter two applications now being abandoned.

BACKGROUND OF THE INVENTION 1. Introduction This invention relates to the photographic formation of a visible image over a substrate and, more particularly, to the formation of such an image over a substrate employing a light insensitive layer intermediate between a light sensitive photoresist top coat and a substrate.

2. Description of the Prior Art Processes for the formation of visible images over substrates such as in the manufacture of keybuttons having visible legends thereon are known in the art and disclosed, for example, in IBM Technical Disclosure Bulletin, Volume 20, No. 7, December, 1977, Page 2861. In said bulletin, it is disclosed that one method for introducing a legend on a keybutton comprises double-shot molding which is described as satisfactory for high volume production but too high in cost for low volume production due to the cost of mold fabrication. Another process described in the bulletin as low cost utilizes photosensitive polymers with metal chelates. The process comprises the following steps: 1. A homogeneous mixture of a photoresist with a metal chelate is prepared, applied to a keybutton surface and permitted to form a dry coating.

2. The metal chelate-photoresist coating is exposed to a computer-controlled actinic radiation source such as a UV source, laser beam or electron beam tp decompose the metal chelate to yield a base metal.

3. The base metak having the keybutton image is subjected to electroless metal deposition to enhance the definition of the image.

4. A clear, wear-resistant overcoat is applied as necessary.

The process utilizing the photosensitive polymers is satisfactory, but also suffers certain disadvantages. For example, the mixture of the metal chelate with the photopolymer interferes with the light sensitivity of the same and image definition and development may be affected. Moreover, the further step of metal plating is costly and limits color selections to the color of the metal plate.

The process described hereinafter provides a method for the photographic formation of visible image over a substrate such as a keybutton using photosensitive resists. These materials are coatings which, when exposed to light of the proper wave length, are chemically changed in their solubility characteristics to certain solvents or developers. Two types are available-negative-acting and positiveacting resists. Prior to exposure, negativeacting resists are soluble in developer, but with light exposure, they undergo chemical change and become insoluble in developer.

Exposure is done through a film having an image pattern and the unexposed photoresist is selectively dissolved, softened or washed away, leaving the desired resist pattern on a substrate in a relief image. Positive-acting resists work in the opposite manner, light exposure making the resist soluble in developer. The resist relief pattern that remains after development is insoluble in chemicals normally used in processes employing such resists.

Resist coatings have been applied to substrates in liquid form using squeegies, rollers or wicks or by dipping or wiping to form a layer of liquid resist over the substrate which is dried to-yield a film of the resist over the substrate. Alternatively, photoresists may be applied to a substrate in dry form such as disclosed in U.S. Patent No. 3,469,982 (incorporated herein by reference) where a resist is coated as a film on a backing sheet and dried. While still on the backing sheet, the film is adhered to a substrate by means of heat and/or pressure. The backing sheet may be transparent and the film may be exposed through the backing sheet. Before developing the photoresist, the backing sheet is cut to size and removed by stripping it from the photo-resist layer thereby exposing the same for development.

An improvement in photoresist technology, as well as a cost savings, is disclosed in copending U.S. Patent Application Serial No.

829,998 assigned to the same assignee as herein and incorporated herein by reference.

In said application there is disclosed an essentially light insensitive layer intermediate between a substrate and a light sensitive photoresist layer. The image definition in the light insensitive layer depends upon the development of the layer of photoresist which it underlies, rather than on a photochemical reaction. Thus, upon exposure of the photoresist layer and development of the same, the light insensitive intermediate layer is bared, and may be developed by the developer for the photoresist layer if the developer is also a solvent for the intermediate layer or by contact with a separate solvent therefor. In effect, the developed photoresist top coat creates a protective stencil over the intermediate layer permitting the same to be removed by contact with a solvent either-in a positive image pattern or in a negative image pattern.

As disclosed in said co-pending- application, while it might be expected that the use of a layer beneath the photoresist layer soluble in developer could result in lift-off of the entire photoresist layer, or at least severe undercutting into the intermediate layer during development, it has been found in practice that with suitable selection of the light insensitive layer, little undercutting occurs even with light insensitive layers having thicknesses of 1 mil of greater. In fact, it has been found that extremely fine resolution can be obtained using very thin layers of photoresist over light insensitive layers in excess of 1 mil in thickness.

The resolution can be optimized by selection of materials used in the photoresist and light insensitive layers.

It should be understood that with respect to the light insensitive layer, a material can be used that is soluble in the developer for the photoresist, or alternatively, to provide sub stantially greater freedom of selection of materials, a material can be selected that is not soluble in the developer for the photoresist in which case there would be two development steps, one to develop the photoresist and the second to develop the light insensitive layer.

The invention of said co-pending application provides numerous advantages over the wet and dry methods for the use of photoresist described above. For example, the light insensitive layer can be relatively thick, thereby requiring only thin photoresist layers and thus, proportionally small amounts of expensive light sensitive material, since the light insensitive layer can be selected to provide the requisite strength and toughness properties required in processes for their use. Thus, the cost is substantially reduced.

In addition to the above, the use of a thin photoresist layer results in a faster exposure speed since exposure time is a function of resist thickness. Moreover, because of the relatively thin resist layer, development of the exposed element is more complete leaving a cleaner surface on the- substrate since separation of the photoresist from the substrate by the light insensitive layer prevents reaction between the substrate and the photoresist.

Further to the above, as described in said co-pending application, dyes have been added to photoresist layers in the prior art to facilitate inspection of the developed layers. However, the addition of dyes greatly slows exposure speed of the photoresist. With the use of an intermediate layer, the dye can be added to the light insensitive layer rather than the photoresist layer thus providing a photoresist layer not having an exposure speed effected or reduced by the presence of extraneous dyes. In fact, practically any dye or pigment can be used since it need not be compatible with the light sensitive material of the photoresist layer and the effect of a dye or pigment on a light insensitive layer is frequently minimal. This permits higher loadings of dye or pigment than in the prior art.

As a further advantage to the use of an intermediate layer underlying a photoresist top coat, properties can be built into the light insensitive layer that cannot be built into a photoresist layer without affecting the light insensitivity or developability of the same. For example, resin systems can be used having physical properties desirable for specific applications such as hardness, adhesion and the like.

STATEMENT OF THE INVENTION In accordance with this invention, there is provided a photographic means for formation of a visible image over a substrate such as for use in the manufacture of name plates, keyboards such as typewriter keyboards, and the like.

One process in accordance with the invention comprises formation of a composite of at least a substrate material, a light insensitive intermediate layer color-contrasting with the substrate, and a photoresist top coat over the light insensitive intermediate layer. The composite can be formed by liquid application of each layer over the substrate, by application of each layer as a dry film, either as separate films or as a multilayered film, or by combination of a liquid layer and a dry layer. Thereafter, the composite structure is exposed to activating radiation in an image pattern with the photoresist top coat facing the source of activating radiation. The top coat is developed, thereby providing a relief image with the intermediate layer bared in the desired image pattern. In effect, the photoresist layer defines a stencil over the intermediate layer.

The bared intermediate layer is then developed by contact with a solvent to remove the same thereby baring the underlying substrate.

The development of the photoresist layer and the dissolution of the bared intermediate layer can be accomplished using a single treatment solution with a developer that is also a solvent for the intermediate layer or two separate treatments with different solutions (developers). Two separate treatment solutions are preferred. The next step comprises removal of the remaining photoresist leaving the intermediate layer in the image pattern. Finally, as an optional step, the intermediate layer in the image pattern is preferably encased in a suitable transparent or translucent material to provide a uniform, hard and wear-resistant surface.

Based upon the above, an object of this invention is to provide a photographic method for formation of a visible image over a substrate that is color-contrasting with the sub trate and hard and durable.

Another object of this invention is to provide a composite structure suitable for use in the process of the invention.

Other subjects and advantages will be apparent from the description which follows.

DESCRIPTION OF THE DRAWINGS Figure 1 represents a cross-section of a composite structure in accordance with the invention; Figure 2 represents a flow sheet of a processing sequence for formation of a visible image on a substrate in accordance with the invention; and Figure 3 represents an encased image over a substrate which is the reverse of that represented in Fig. 2E.

DESCRIPTION OF THE PREFERRED EMBODI MENTS With reference to the drawings, Fig. 1 represents a cross-section of a composite useful for the formation of a visible image in accordance with this invention. As represented in the drawing, there is shown a substrate (1) overcoated with intermediate layer (2) of a light insensitive material and provided with a light sensitive photoresist top coat (3). Though not shown in the drawing, there may also be provided over the photoresist top coat a protective layer to protect the photoresist during storage and handling and an adhesion promoting layer between interme- diate layer (2) and substrate (1) to enhance adhesion between the substrate and the intermediate layer. Other layers may be employed as might be apparent to those skilled in the art.

The light sensitive, photoresist top coat may be either a positive-working or negative-working material. Any of the photoresist materials known in the art can be used. Examples of suitable photoresist materials are disclosed in U.S. Patent Nos. 3,046,110; 3,046,118; 3,102,804; 3,130,049; 3,174,860; 3,230,089; 3,264,837; 3,149,983; 3,264,104; 3,288,608; and 3,427,162 and in Kosar, Jaromir, Light-Sensitive Systems: Chemistry and Application of Non-Silver Halide Photographic Processes, New York, John Wiley 8 Sons, Inc., Copyright 1965, all incorporated herein by reference. Preferred light sensitive materials are diazo materials, both positive and negative-working diazo materials being suitable. The most preferred material is a naphthoquinone diazide sulfonic acid ester.

Other suitable light sensitive materials include cinnamic acid, vinylcinnamalacetophenone polymers such as those disclosed in U.S. Patent No. 2,716,102; vinyl benzal acetophenones as disclosed in U.S. Patent No. 2,854,388; vinylazidophthalate polymers of U.S. Patent No. 2,870,011; dichromate materials; and free radical materials such as those disclosed in the Institute of Graphic Communications Monthly, August, 1972, at pp. 4-19.

Materials suitable for use as the light insensitive intermediate may vary widely. Where it is desired that the light insensitive layer be soluble in aqueous developers, that layer may comprise materials such as, for example, water soluble salts of the group consisting of polyvinyl ether-maleic anhydride copolymers, water soluble cellulose ethers, water soluble salts of carboxy alkyl cellulose, water soluble salts of carboxy alkyl starch, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamides, water soluble salts of polyacrylic acid or ethylene oxide polymers.Where it is desired to use materials insoluble in aqueous developers, materials soluble in organic solvents may be used providing, of course, that the resist top coat is insoluble in the solvent used to dissolve the intermediate layer, such polymers include polystyrene and its copolymers such as acrylonitrile-butadiene styrene (ABS) copolymers, polymethyl methacrylate, polyamides and polyester.

The preferred light sensitive resist is the positive working naphthoquinone diazide sulfonic acid esters in a binder of a Novolac resin. Since these materials are developable in aqueous alkali solution, where two step development is desired, the preferred intermediate layer is acid soluble such as a melamine resin soluble in acids such as sulfuric acid.

Suitable additives to impart various desired properties to the light insensitive layer may also be added as would be well known to the art. Further, additives may be included in the intermediate layer to render the same color contrasting with the substrate such as dyes and pigments. These materials may be added in high loading to render the layer opaque and highly colored-e.g., for pigments in amounts from 1 to 50% by weight of the resin, preferably from 20 to 40% by weight.

Typical pigments include titanium dioxide, carbon black and molybdates and dyes include phthalocyanines. Pigments are preferred to dyes for the applications disclosed herein.

The photoresist layer and the light insensitive layer may each be applied to the substrate in liquid form, by whirl coating, roller coating or by other methods known to the art.

Preferably, however, the two layers are formed into a unitary film which is adhered to the substrate with the light insensitive layer in contact with the substrate. As noted, the light insensitive layer may be of strong material and/or in relatively thick sections so that additional support sheets or layers are not required. However, additional sheets or layers can be used if found desirable for particular circumstances. For example, a release sheet, such as polyethylene terephthalate release sheet, may be applied over the photoresist top coat so that it is protected on one side by the release sheet and on the other by the interme diate layer. Other suitable release sheets are well known, including polyethylene, polypropylene, vinyl resins, cellulose materials, treated paper release sheets, etc.

Methods for forming a unitary film comprising a photoresist top coat and a light insensitive layer should be apparent to those skilled in the art. For example, one of the materials may be formed into a film which is thereafter coated. with a layer of the other material.

The thickness of the light insensitive layer depends on the properties desired of it. Generally, the layer may be between about 0.05 and 5. mils thick. It is preferred that it has a thickness of from about 0.2 mils to about 2 mils. Likewise, the thickness of the photoresist layer depends on the properties desired of that layer. As noted above, the amount of expensive photoresist material required in acdordance with this, invention may be reduced and the exposure speed increased by use of a thinner layer, the light insensitive layer providing the required strength. Accordingly, though the ratio of the resist layer to the light insensitive layer may vary between about 20:1 to 1:20, preferably the ratio is at least 1:1 and preferably varies between 1:1 and 1:20 and more preferably between 1:1 and 1:5 if desired.The photoresist layer should not, however, be so thin that it becomes pervious and fails to protect the underlaying light insensitive material. If the developed photoresist layer does not satisfactorily protect the light insensitive layer, the protective stencil for the substrate will not be formed and the visible image of the intermediate layer will be poorly formed.

A photographic image is formed in the composite of Fig. 1 by exposure to activating radiation through a transparency which may be a negative or positive record of the desired image. The radiation source and the use of a positive or negative image is dependent upon the photoresist top coat as would be apparent to those skilled in the art.

Following exposure through the transparency for a time sufficient to form a latent image, the composite is developed by contact with a developer which may be a solvent for the intermediate layer. In a preferred embodiment, the developer for the photoresist is not a solvent for the intermediate layer. Hence, two development steps are required, the first comprising development of the latent image in the photoresist top coat by contact with a developer for the top coat thereby forming a relief image in the top coat, the remaining photoresist acting as a protective layer over bared areas of the intermediate layer and acting as a stencil therefore and then the bared layer of the intermediate layer is removed by contact with a solvent which is-not a solvent for the protective photoresist top coat.This embodiment is preferred as it gives a greater latitude to the selection of materials used to form the visible image and greater control over the processing sequence.

A lesser preferred embodiment of the invention is that where the intermediate layer is soluble in developer for the photoresist layer.

For example, where the photoresist layer is of a light sensitive material in combination with a developer soluble resin such as an alkali soluble Novolac phenol-formaldehyde resin in combination with a naphthoquinone diazide sulfonic acid ester, the light insensitive intermediate layer would be of the same developer soluble Novolac resin absent the light sensitive material.

The preferred procedure for formation of the image in accordance with the invention is illustrated in the flow sheet of Fig. 2 where, for purposes of illustration, the composite of Fig. 1 consisting of substrate (1), intermediate layer (2) and a photoresist top coat (3) is used. As illustrated in Fig. 2, the photoresist is positive acting.

In step 2 A, activating-radiation is passed through transparency (4) striking photoresist top coat (3). A portion of the radiation is blocked- by opaque portions (5) of transparency (4). A latent image is formed in the photoresist top coat (3).

Since a positive working photoresist is illustrated in. Fig. 2, the activating radiation solubilizes the photoresist layer where is strikes the same. In step 2 B, there is illustrated the composite as it would appear following exposure and contact of the top coat with a developer. There remains intermediate layer (2) overlying substrate (1) and having photoresist top coat (3) defining an image pattern over intermediate layer (2).

Step 2 C represents the composite following contact of intermediate layer (2) with a solvent. The photoresist top coat (3) protects the intermediate layer which it overlies and only portions of the intermediate layer not protected by the top coat are removed by the solvent. Consequently, following contact of the intermediate layer with the solvent, the intermediate layer and photoresist top coat both overlie the substrate in an image pattern.

In step 2 D, the photoresist top coat (3) has been removed by contact with a solvent that is not a solvent for intermediate layer (2). This leaves only intermediate layer (2) in the image pattern over the substrate. Removal of the photoresist top coat is desirable as it is light sensitive and possesses its own coloration. If not removed, it will slowly darken and discolor the desired appearance of the intermediate layer.

As represented in Fig. 2, in step 2 E, intermediate layer (2) in the desired image pattern is preferably encased in a protective lacquer (6) to protect the image and provide a hard, relatively smooth and durable coating.

This step is not required, but is desirable.The material used to encase the intermediate layer should be transparent or translucent. Polyurethane and derivatives are suitable materials.

With further reference to Fig. 2, if the photoresist used was a negative working material instead of a positive material, the top coat would be soluble in developer prior to exposure, but would become insoluble by exposure. Hence, a reverse image would be obtained following the procedure set forth in Fig. 2 using the same transparency. Fig. 3 represents a composite formed in this manner.

The following examples will more fully illustrate the invention.

Example 1 This represents the currently preferred embodiment of the invention.

A solution of an adhesive comprising 30% by weight of hexamethoxymethyl melamine (Cymel 303 from Am Cyanamid) is prepared and an acid catalyst added prior to use.

The adhesive is sprayed onto a plaque of a styrene acrylonitrile polymer using a hand sprayer activated with compressed, air. The layer is dried in an oven maintained at about 50 C for ten (10 minutes. The final dry thickness is about 0.1 mils.

A second solution is prepared comprising a methylated melamine resin (Resimine 730 of Monsanto Corporation) in an amount of 40% by weight, titanium dioxide in an amount 26% by weight and an acid catalyst in an amount of 6% by weight of the resimine resin. This solution is sprayed over the adhesive layer using the same sprayer and dried in an oven maintained at 70 C for thirty (30) minutes. The total dry coat thickness is approximately 0.4 mils. The plaques are then cooled to room temperature.Finally, a solution of AZ 120 Photoresist of Shipley Company Inc. comprising a light sensitive compound of a naphthoquinone diazide sulfonic acid ester and a novolak phenolformaldehyde resin dissolved in a cellosolve solvent system is sprayed over the melamine intermediate layer and dried in an oven maintained at 50 C for ten (10) minutes to yield a dry thickness coating of about 0.2-0.3 mils.

The composite formed above is exposed to activating radiation from an aristogrid light source (aristo Grid Lamp Products Inc.) through a transparency having a desired image pattern for two (2) minutes to form a latent image in the photoresist top coat. The latent image is developed with AZ 220 or AZ 303A of Shipley Company Inc. used at a strength of 40% and 12% respectively, by immersion of the plaque in the developer.

Contact with the developer gives a relief image in the top coat with the underlying intermediate layer exposed in a negative of the desired image. Thereafter, the exposed portions of the intermediate layer are removed by immersion of the plaque in a 20% solution of sulfuric acid containing a surfactant. The top coat protects the intermediate layer which it covers while the intermediate layer, and subsequently the bottom layer, in contact with the sulfuric acid are dissolved. The next step in the process comprises removal of the remaining top coat by dissolution in a solution of AZ 420 Remover of Shipley Company Inc.

(Alternatively, photoresist removal can be accomplished by blanket exposure to an ultraviolet light source followed by dissolving in a developer solution). The remover dissolves the photoresist without attacking the intermediate layer. Following removal of the remaining photoresist, the plaque is baked at 70 C in an air circulating oven for thirty (30) minutes.

As an optional, but preferred step, the resulting image is sprayed with a solution of polyurethane, with or without a flattening agent, to encase the same and provide a uniform, wear-resistant coating.

Example 2 This illustrates a composite that may be developed in a single development step.

A A light insensitive layer is prepared by mixing 25 grams of a 50% solution of Novolac phenol-formaldehyde resin in Toluol in 25 grams of a Cellosolve acetate solvent. The solution is whirl coated onto a copper-clad material at 80 rpm for 5 minutes. The coated substrate is then baked for 20 minutes at 80 C to provide a dry layer of about 1 mil thickness. Next, a photoresist layer is applied as a 20 by weight solid solution of AZ 120 Photoresist of Shipley Company Inc. as described above. The photoresist top coat is applied by whilr coating for 5 minutes and baking for about 20 minutes at 80 C. The dry film thickness of the photoresist top coat is about 1/4 mil.A visible image is formed in the composite following the exposure and development procedure of Example 1, but omitting the step of contact with sulfuric acid which becomes unnecessary because the intermediate layer is soluble in the developer.

The visible image comprises the copper of the substrate color contrasting with the intermediate layer.

Example 3 This illustrates another intermediate layer soluble in an alkali developer, but less soluble than that of Example 2 due to the inclusion of other insoluble resins.

The intermediate layer is formed by mixing 25 grams of the phenol-formaldehyde solution of Example 2, 25 grams of Gantrez M-555, a 50% solution of polyvinyl methyl ether, available from GAF Corporation and 50 grams of the Cellosolve acetate solvent and applying the same by whirl coating as set forth above. The layer is developable as in Example 2, but the development time is longer due to the insoluble resins in the intermediate layer.

Example 4 This represents an embodiment using a negative working dry film top coat.

Following the procedure of Example 1, the same adhesive layer and intermediate layer may be applied over the same styrene acrylon ìtrile substrate. Thereafter, a negative working dry film photoresist (Riston of DuPont Corporation) is adhered to the intermediate layer.

The dry film is believed to comprise a polyethylene protective layer, .a layer of a photoresist material believed to be a photopolymerizable ethylinically unsaturated compound described in British Patent No. 1,128.,~850 and a layer of polyethylene terephthalate (Mylar). The polyethylene protective layer is stripped from the photoresist element and the remaining element laminated to the intermediate layer using heated pressure rollers operated at about 120 C at a pressure of about 10-20 pounds per linear inch at the nip and at a feed rate of about 2 feet per minute. The resulting laminate is then exposed through the transparency used for Fig. 1 and developed.

with thrichloroethylene which removes unexposed photoresist. The remaining steps in the process sequence would be as in Example 1 but the final image would be the negative of -Example t.

Example 5 This illustrates the use of a dry film of a light insensitive layer and a photoresist layer.

A sheet of optically transparent polyethylene terephthalate (Mylar) is whirl coated with a 20% solution of AZ 11 9 photoresist in Cellosolve acetate solvent for 5 minutes at 78 rpm. The coating is dried for 20 minutes at 80 C. A next layer is applied over the photo resist layer by whirl coating a solution com prising 36 grams of phenol-formaldehyde Novolac resin and17 grams of Gantrez M-555 dissolved in 50 grams of Cellosolve acetate solvent. The solution is whirl coated onto the photoresist layer at 78 rpm for 5 minutes and dried at about 80 C for 20 minutes.

The resulting dry film is laminated onto the styrbne-acrylonitrile plaque using rubber-covered rollers operated at about 120 C at a pressure of about 10-12 pounds per linear inch at the nip and å rate of about 2 feet per minute. The so-formed composite, with the Mylar sheet removed, may be processed in the manner of Example 1.

Claims (24)

1. A process for the formation of a visible image over a substrate, said process compris ing the steps of: a. providing a composite of a substrate, an intermediate layer of a substantially light insensitive material over said substrate color contrasting with the substrate, and a top coat of a photoresist material capable of forming a latent image upon exposure to activating radiation which material is removable in an image pattern by development of a latent image, said top coat overlying said intermediate layer.

b. exposing said top coat to activating radiation in an image pattern to form a latent image in said top coat, c. contacting said composite with a devel .operand solvent to remove said top coat in an image pattern and the intermediate layer underlying said removed top coat, and d. removing the remainder of the photosensitive top coat without removing the intermediate layer beneath it.

2. The process of claim 1 where the intermediate layer is polymeric.

3. The process of claim 2 where the polymeric intermediate layer contains a member selected from the group of dyes and pigments.

4. The process of claim 2 where the intermediate layer is insoluble in developer for the photoresist top coat.

5. The process of claim 2 where the intermediate layer is soluble in developer for the photoresist top coat.

6. The process of claim 2 where the photoresist top coat is of a positive working photoresist.

7. The process of claim 2 where the pho toresist top coat is of a negative working photoresist.

8. The process of claim 2 where the thickness of the intermediate layer varies between about' '0. 1 mils and 2 mils and the ratio of the thickness of the resist top coat to the light insensitive layer varies between-about 1:1 and 1:20.

9. The process of claim 8 where the ratio varies between about 1:1 and 1:5.

10. A process for the formation of a visible image over a substrate, said process comprising the steps of: a. providing a composite of a substrate, a polymeric intermediate layer of a substantially light insensitive material over said substrate color-contrasting with the substrate and a top coat of a photoresist material capable of forming a latent image upon exposure to activating radiation that is removable in an image pattern by development over said intermediate layer, the thickness of said intermediate layer varying between about 0.2 and 2 mils and the ratio of the thickness of the top coat to the intermediate layer varying between about 1:20 and 20::1; b. exposing said top coat to activating radiation in an image pattern to form a latent image in said top coat; c. contacting said composite with a developer to remove said top coat in said image pattern thereby exposing the intermediate layer underlying said removed top coat in said image pattern; d. contacting said composite with a solvent for said intermediate layer to remove the same in said image pattern; and e. removing the remainder of the photoresist top coat without removing the intermediate layer beneath it.

11. The process of claim 10 where the light insensitive material and the photoresist material are applied as solutions and dried.

12. The process of claim 10 where the light insensitive material and the photoresist material are applied as a composite dry film.

13. The process of claim 11 where the ratio of the thickness of the top coat to the intermediate layer varies between about 1:1 and 1:20.

14. The process of claim 13 where the ratio varies between about 1:1 and 1:5.

15. The process of claim 13 where the photoresist is a positive working photoresist.

16. The process of claim 13 where the photoresist is a negative working photoresist.

17. The process of claim 13 where the intermediate layer contains a member selected from the group of dyes and pigments.

18. The process of claim 13 including the step of coating the visible image in the intermediate layer with a transparent and wearresistant polymer.

19. A composite comprising a substrate, an intermediate layer of a substantially light insensitive material over said substrate colorcontrasting with the substrate and a top coat of a photoresist material capable of forming a latent image upon exposure to activating radiation that is removable in an image pattern by development, said intermediate layer being polymeric and containing a member selected from the group of dyes and pigments and having a thickness ranging between about 0.2 and 2.0 mils and the ratio of the thickness of said photoresist top coat to said intermediate layer varying between about 1:20 and 20:1.

20. The composite of claim 19 where the ratio of the thickness of the photoresist top coat to the intermediate layer varies between about 1:1 and 1:20.

21. The composite of claim 20 where the ratio varies between about 1:1 and 1:5.

22. The composite of claim 20 where the photoresist is a positive acting photoresist.

23. The composite of claim 20 where the intermediate layer is insoluble in a developer for the photoresist top coat.

24. The composite of claim 20 where the intermediate layer is soluble in developer for the photoresist top coat.