Background of the Invention

The present invention relates generally to photosensitive imaging compositions and more specifi- cally to bi-layer photosensitive imaging films.

Probably the most commonly used photosensitive imaging systems employ silver halide based compositions- Silver halide contact films, for example, have been widely used for many years and are still the standard of the industry. Similarly, a wide variety of silver halide color proofing films and contact papers are in common use. Even printed circuit resists generally rely on silver halide based photosensitive systems.

Silver halide photosensitive imaging compo- sitions are inconvenient to store and to use. They must be stored in light-tight containers. Their shelf life is very limited. Furthermore, processing must be carried out in the dark or under subdued, safelight conditions. Development of silver halide based compositions is gen- erally a multi-step process requiring separate development, fixing and washing procedures. The chemicals utilized in these procedures are also ecologically undesirable, being oftentimes toxic and difficult to dispose of. Furthermore, even after processing, the silver halide based images deteriorate quickly and are readily scrat¬ ched and otherwise susceptible to surface damage.

Silver halide films pose further diffi¬ culties when attempting to produce halftone images. For example, the production of halftone images of uniform optical density is quite difficult, particularly in those applications where it is further necessary to reduce image surface area by etching image dots and holes.

Silver halide imaging compositions offer very limited etching latitude. When the silver halide image is subjected to an etching solution, the solution attacks the perimeter of the image (dots in highlight areas, holes in shadow areas) and the top surface of the image as well. Thus, the thickness of the image is reduced along with its perimeter resulting in an image of re¬ duced optical density. Since significant reductions in optical density are generally unacceptable in many app¬ lications (e.g. color proofing) , only very limited etch¬ ing of silver halide halftone images is possible. Further¬ more, similar problems arise in non-silver halide based images where the image surface is unprotected from the etching solution.

Although alternatives to silver halide photo¬ sensitive imaging compositions have been proposed and are now offered in the marketplace, these alternative materials have not significantly displaced the silver halide materials for a number of reasons. For example, these alternative materials suffer many of the same dis¬ advantages found in the silver halide materials, inclu¬ ding storage difficul ies, short shelf life, safelight and multi-step development, and ecologically undesir- able processing procedures. These alternative compositions are also susceptible to scratching and other damage, both before exposure and development and after. As a result, post-development protective overcoats are of¬ ten necessary. Furthermore, unlike the silver halide compositions, these alternative compositions often

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require multi-step exposures. Finally, and perhaps most importantly, these alternative materials usually have very limited development and exposure latitude and pro¬ duce images of inadequate optical density and definition.

Summary of the Invention and Objects

The present invention is directed to a bi- layer photosensitive imaging article which overcomes the various difficulties associated with prior photosensi¬ tive imaging compositions.

In its broadest sense, the present invention is directed to photosensitive imaging articles consist¬ ing of a substrate, an organic image layer disposed upon the substrate and an organic resist layer disposed upon the image layer. Important novel aspects of the present invention reside in the provision of specific layer components and thicknesses. Further' important feature are attributable to the discovery of a method of halftone etching involving the production and etching of this bi-layer halftone image.

The photosensitive imaging articles of the present invention comprise a substrate bearing an image layer of from about 0.3 microns to about 3.0 microns in thickness. The image layer must be soluble in a given developer and generally consists of an organic film- forming vehicle.

The film-forming vehicle is preferably chosen from a particular group of styrene-maleic anhydride copoly ers, which will be described in further detail below. Within this group of copolymers, a particularly important subgrouping is bimodal styrene-maleic anhydride copolymers, which will also be described in detail below.

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The resist layer, which is disposed upon the image layer, should be from about 0.5 to about 2.0 microns in thickness. This layer consists of an organic-based material whose solubility with respect to the given de- veloper is changed upon exposure of the resist layer to actinic electromagnetic radiation. Particular resist materials suitable in the practice of the present in¬ vention will be described below.

It is therefore an important object of the present invention to provide a bi-layer photosensitive imaging article which does not require special handling and may be stored and developed under daylight conditions.

It is a further object of the present inven¬ tion to provide a photosensitive imaging article which may be readily processed with water or mildly alkaline developer solutions to produce durable images.

It is yet another object of the present invention to provide a photosensitive imaging article capable of producing images with outstanding definition and optical density which furthermore are durable, long lasting and reasonably resistant to scratching and other surface damage even without a protective overcoating.

A further object of the invention is to pro¬ vide a photosensitive imaging article which does not require multiple step exposure or development.

An important object of the present invention is to provide a photosensitive imaging article capable of producing high quality halftone images that may be readily etched to varying degrees without significantly affecting image optical density.

Another important object of the present in¬ vention is to provide an improved method of etching a halftone image.

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Other objects and features of the present in¬ vention will become apparent upon examination of the following specification and drawings, together with the claims. While the invention is described herein in con- nection with preferred or illustrative embodiments, these embodiments are not intended to be exhaustive or limit¬ ing of the invention. Rather, the present invention is intended to cover all alternatives, modifications and equivalents that may be included within its spririt and scope, as defined by the appended claims.

Brief Description of the Drawings

Figure 1 is a cross-sectional view illustra¬ ting the photosensitive imaging article of the present invention as conventionally exposed to electromagnetic actinic radiation through a halftone screen;

Figure 2 is an illustration of the element of Fig. 1 after exposure through the halftone screen showing the formation of a latent image in the resist layer of the article;

Figure 3 is an illustration of the article of Fig. 2 after removal of unexposed portions of the resist layer and corresponding portions of the image lay¬ er to leave a halftone highlight (dot) image on the sub¬ strate;

Figure 4 is a representation, in section, of the halftone image of Fig. 3 after etching of the pig- mented image layer;

Figure 5 is a top view of the etched article of Fig. 4;

Figure 6 is a top view similar to that of

Fig. 5 __.owing an etched halftone shadow (hole) image

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produced with a photosensitive imaging article according to the present invention.

Similar reference numerals are applied to cor¬ responding features throughout the different figures of the drawings.

Detailed Description of the Preferred Embodiments

With brief reference to the drawings, a photo¬ sensitive imagine article 10 is illustrated in Figure 1 including a substrate 12, an image layer 14 containing a coloring medium and a resist layer 16. Above the resist layer 16 is a halftone screen 18 positioned for image-wise exposure of the article.

Substrates useful in the practice of the pre¬ sent invention may be clear, as in the case of clear plastic films or glass; they may be opaque, as in the case of papers or metal plates and foils; or they may be translucent, as in the case of matte films, useful clear substrates include polyethylene, polyethylene tereph- thalate and polycarbonate films, such as thermoplastic polycarbonate condensation products of bisphenol-A and phosgene (Lexan) . These clear films can be used to produce photosensitive imaging articles such as general purpose contact films and color proofing films. Useful opaque substrates include papers of various kinds such as filled polypropylene synthetic papers and poly¬ ethylene coated cellulose papers. Also tinted opaque substrates can be used to produce print papers, as well as negative and/or positive proofing papers. Since the present photosensitive imaging articles ay be used to produce lithographic plates, useful litho¬ graphic substrates would also include metal plates and other rigid supports. Finally, useful translucent substrates include polyethylene and polyethylene terephth- alate films which are matted during their manufacture or

with subsequently applied coatings. The imaging articles produced with these substrates can be used as engineering drawing intermediates suitable for diazo-type white prints, sepias, and for other purposes which would be apparent to those skilled in the art.

The image layer used in the articles of the present invention should be of a composition soluble in a developer for the particular resist layer employed. De¬ velopers particularly useful in the practice of the pre¬ sent invention include water and mild aqueous alkaline solutions. These developers will be discussed further in connection with the resist layers and in the Examples set forth below.

Many of the important advantages inherent in the composition of the present invention are the result of careful control of the thicknesses of the image and resist layers.

Turning first to the image layer, it has been found that the thickness of this layer must be within the range of about 0.3 to about 3.0 microns. Thicker image layers result in slow and difficult development, as well as poor resolution. Image layers below about 0.3 microns in thickness generally lack the requisite film strength and adhesion, and cannot develop optical density for con¬ tact papers and color proofing films.

Within the specified thickness range for the image layer, it has been found that certain applications require yet further thickness limitations. Thus, for exam¬ ple, optimal color proofing films require image layers of from about 0.3 to about 1.0 micron in thickness. The produces optimal color intensity and purity, as well as outstanding resolution. General purpose contact films, on the other hand, should optimally have image layers in the

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broader thickness range of about 1.0 to about 3.0 microns.

As noted earlier, the image layer contains an organic film-forming vehicle soluble in the resist devel¬ oper*. Although a number of organic film-forming vehicles are known, certain styrene-maleic anhydride copolymers have been found to exhibit unexpectedly superior perfor¬ mance in the context of the present invention. Furthermore, these copolymers have been found to be readily tailorable to specific applications such as the production of photo- sensitive imaging articles suitable for halftone image formation and etching.

The styrene maleic anhydride (SMA) copolymers found to be particularly useful in the practice of the pre¬ sent invention include those having a molecular weight in the range of 1,000 to 150,000 and a formulation as follows:

1.

where m = 1-3, n = 1-10

2. Half esters and ammonium half amides of SMA copolvmer

where X is OH, ONH- ONH, OR, ONH-R, ONH_R ₂ ,

ONHR ₃ , ONH ₃ , NH ₂ , ONa, OK, OLi, R is an alkyl group in the range C1-C10 optionally including a functional group such as ketone, alcohol, ether ether alcohol, or aryl and m = 1-3, n =* 1-10.

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Useful additives which may be blended with the identified SMA compositions include film-forming polymers also of molecular .weight in the range 1,000 - 150,000:

where x, y, m, and n are as described in connection with the SMA formulas 1 and 2 above, P is ethylene or methylvinyl ether, and R is hydrogen, alkyl or aryl.

In some applications it may be desireable to tailor the characteristics of the above-described polymers. For example, recognizing that higher molecular weight polymers tend to be less soluble in aqueous developers , it may be necessary to introduce additives to improve image layer solubility. Low molecular weight polymers of the above-described structures may be used in such cases to improve solubility. For example, a SMA resin based on formula 1., where m = 1-3, n = 6-8 and molecular weight - 1500-3000, as well as half esters and amine salts thereof are particularly useful in increasing image layer solu- bility. Other useful solubilizing agents would include generally linear ethylene maleic anhydride resins having a molecular weight between 8000 and 10,000, as well as their acid, single ammonium salt, double ammonium salt, half ester and diester forms. Another useful class would be poly(methylvinylether) maleic anhydride resins and their corresponding half ester forms, of molecular weight 5000-100,000. Yet another class of water-soluble materi¬ als useful in this connection would be glycols .

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In addition to the above solubilizing agents, film modifiers may be added to the organic film-forming vehicle of the image layer. For example, compounds such as polyvinylacetate may be used to improve image layer flexibility and epoxy esters can be used to improve abr- sion resistance.

The image layer 14 may be applied to the sub¬ strate 12 by any one of a number of conventional coating techniques well known to those skilled in the art. For example, both solvent and aqueous casting techniques may be employed, as well as conventional roller and gravure application procedures.

As those skilled in the art will recognize, adhesion can present a problem when applying a thin coat¬ ing to a substrate as in the present invention. This prob¬ lem may be overcome by selection of image layer and sub¬ strate materials which exhibit a greater degree of adhe¬ sive compatability. In other cases, as where polyethylene and polyethylene terephthalate films are used, it may be necessary to apply a subcoating to the substrate or to use- specially pre-treated substrates. For example, where the image layer is aqueous cast, it may be particularly helpful to subcoat the substrate with a high molecular weight SMA copolymer (average molecular weight approxi¬ mately 50,000) in methyl ethyl ketone. With solvent cast films, similar subcoating of high molecular weight SMA may also prove helpful. The use of this sublayer has a further unexpected advantage for both acqueous and sol- vent castings in that the resultant imaging article will produce clearer backgrounds due to the absence of pigment retention on (or staining of) the substrate. A less pre¬ ferred alternative, would be to use pretreated films carrying an adhesive coating to improve image layer ad- hesion to the substrate.

In applications such as photosensitive imaging articles for use as lithographic plates, it is not neces-

sary to introduce a coloring medium into the image layer. However, in a preferred embodiment of the present inven¬ tion, the image layer will contain a coloring medium uni¬ formly dispersed within the film-forming vehicle.

The coloring medium may be chosen from among the numerous commercially available pigments and dyes. The coloring medium may be used in an aqueous form, in a solvent-soluble form, or in the form of a dispersion. Where a particulate material is used, the particle size must be less than the image layer thickness. Preferably, the coloring medium particles will lie in the range of 100 to 5000 Angstroms. More preferably, the particles will lie in the range of 250 to 2500 Angstroms. Generally, smaller particle sizes will give better coverage, opacity, and film strength.

The quantity of coloring medium used should be sufficient to produce an optical density in the overall article of at least 3.0. On a weight basis, the ratio of coloring medium to film-forming vehicle should be in the range of 9:1 to 1:1 and preferably in the range of 2:1 to 1:1. The amount of pigment actually used will depend upon the intended application, since coloring medium to vehicle ratios affect many film characteristics such as adhesion, flexibility and development speed.

Although numerous pigments and dyes useful in the practice of the present invention will be apparent to those skilled in the art, a number of such useful materials are listed in Tables A and B below.

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Table A-Piqments

Titanium Dioxide (rutile form)

Zinc ^" Oxide

Iron Oxides (natural)

Chrome Oxide Green

Molybdate Orange

Ultra Marine Blue

Hansa Yellow G

Toluidine Red

Lithol Red

Lithol Rubine

Diarylide Yellow

Quinacridone Violet 19

Phthalo cyanine Blue

Carbon Black

Raven 100OR

Regal 400R,300

Elftex 8

Special Schwarz 4A

Mogul A

Monarch 74

Aqua Black Dispersion

Auresperse W7012

Table B-Dyes

Methyl violet Rhodamine B Fuchsine Methyl ene Blue Victoria Blue B Malachite Green Bismark Brown R Alizarine Orange

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The resist layer 16 may be applied to the image layer again using conventional coating techniques. It is generally required that the thickness of this layer lie in the range of about 0.5 microns to about 2.0 microns, in order to obtain the outstanding exposure, development and resolution characteristics of the present photosensitive imagine articles. Resist layers of thickness below 0.5 micron are generally of insufficient resist strength and adhesion, and display poor scratch resistance. Excessively thick resist layers, on the other hand, result in poor resolution and poor shelf life. Furthermore, thick resist layers should be avoided because they require in¬ creased development time and are generally uneconomic.

The resist layer consists of a material whose solubility with respect to a given developer is changed upon exposure to actinic radiation. While a great variety of such materials are well known in the art, the outstanding advantages of the present invention may best be obtained with the resist materials described below.

One particularly suitable resist material is de¬ scribed in U.S. patent application Serial No. 588,334, filed 6/19/75 and abandoned in favor of continuation-in-part application Serial No. 815,899, filed 7/15/77 and now abandoned in favor of continuation application Serial No. 051,652, filed 6/25/79, the disclosures of which are incor¬ porated herein by reference. The resist material of these patent applications comprises a generally continuous phase and a generally discontinuous phase, with the continuous phase being a minor constituent of the overall structure. The continuous phase consists of a photosensitive materials whose solubility with respect to a developer is changed upon exposure to actinic radiation. The discontinuous phase which is a major constituent of the overall structure consists of a polymeric emulsion-dispersion made up of a particulate material which is substantially insoluble in the developer. The two phases --?,ie uniformly interdispersed throughout the entire resist ^η 'ayer 16.

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The minor phase material of the above resist composition may be selected from the group consisting of diazo compounds, photopolymers, light sensitive dyestuffs, azo compound, and dichromates. The polymeric major phase material of the emulsion-dispersion of the resist film may be selected from the group consisting of polyacrylics, copolymers of acetate and ethylene, copolymers of styrene and acrylates, polyvinyl acetates and copolymers of vinyl acetate and acrylates.

Preferred compositions of the above described continuous phase-discontinuous phase resist layer may be formed from a polyvinyl acetate-acrylic polymer emulsion dispersion in water with paradiazo diphenyla ine sulfate condensation product with paraformaldehyde (stabilized with zinc chloride) . Preferred alternate discontinuous phase materials include polyacrylamide, polyvinyl acetate, polystyrene allyl alcohol and polyvinyl butyral.

Other photosensitive material useful as resist composition in the present invention include aqueous based diazo/colloid mixtures such as: paradiazo diphenylamine sulfate condensation product/hydroxy ethyl cellulose (Natrosol HHR 250 from Hercules) or paradiazo diphenylamine sulfate condensation product/polyaerylamide (high molecular weight) .

Useful solvent based alternate resist materials would include mixtures of solvent soluble diazos and resins. Such diazos are typified by those listed in Table C. The resins useful in such cases are typified by those found in Table D. These tables, however, should not be considered restrictive.

A post-exposure treatment solution or developer particularly useful in connection with the above-described diazo materials is disclosed in U.S. patent application Serial No. 875,367, filed February 6, 1978, now abandoned

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-15a-

Table C

1.) Sulfoesters of napthaquinone 1, 2 diazides such as:

2.) Sulfonamides of naphaquinone 1, 2 diazides such as:

3.) Reaction products of paradiazo diphenylamine sulfate - formaldehyde resins with: phosphotungstic acid, phospomolybdic acid, tetrafluoroboric acid, hexa- fluorophosphoric acid, toluene sulfonic acid, napthalen 1,5 disulfonic acid, vinyl phosphonic acid, 2, 2', 4, 4' tetrahydroxy benzophenone.

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-15b-

Table D

Phenolfo__maldehyde novalak m-cresol formaldehyde novalak

Epoxy resin (epichlorohydrin-bisphenol A)

Poly vinyl acetate

Poly vinyl butyral

Ethyl acrylate-acrylic acid apolymer

Vinyl acetate-vinyl phthalate copolymer

Poly amide resins

Phenolic resins

Phenoxy resins

Epoxy ester resins

Polyimide resins

Vinylidene-acrylonitrile copolymer

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-16- in favor of U.S. patent application Serial No. 051,478 filed June 25, 1979. The treatment solution described therein includes a water soluble desensitizing agent cap¬ able of reacting with residual photosensitive diazo to render it incapable of forming an oleophillic substance, and a filming agent selected from water soluble aliphatic polyols having less than eight carbon units, the acid de¬ rived monoesters of these polyo s, and the alkaline metal salts of the monoesters. The entire disclosure of the app- lication Serial No. 875,367 is hereby incorporated by reference.

Once again, the photosensitive imaging articles of the present invention are formed by conventional methods. The image layer is first coated onto the substrate, op- tionally by successive passes, and followed by the resist layer which may be also applied by successive passes. The layers may be cast from solvents or from aqueous media, depending upon the choice of resist material and image layer film-forming vehicle. It is, of course, necessary, in most instances, that the image layer first be dried before the resist layer is applied and itself dried. Particular drying temperature requirements will depend upon the nature of formulations being used and will be apparent to those skilledin the art.

Exposure of the photosensitive imaging articles of the present invention will depend upon the thicknesses and composition of the resist and image layers. For color proofing films, for example, exposures of 10-30 seconds under a five kilowatt mercury vapor source (2800 micro- 2 watt/cm ) will produce satisfactory images. For litho¬ graphic films, 20-180 seconds under a similar source will suffice while 30-60 seconds are preferred.

As those skilled in the art would expect, de¬ velopment time is directly related to the thickness of the resist and image layers, as well as to the coloring medium to vehicle ratio, polymer molecular weight, polymer acid

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-17- value, developer strength (e.g., concentration, pH, sur¬ face tension, ionic components) and thermal treatment history of the image layer. Generally development times will range from 15-120 seconds while 30-90 seconds are preferred. For positive working resists, where the posi¬ tive working resist material is rendered soluble upon ex¬ posure, exposure time is, of course, a more significant factor in determining the development time.

Although photosensitive imaging articles gen- erally following the above teaching are useful in pro¬ ducing halftone images, photosensitive imaging articles utilizing a particular subgrouping of organic film-forming vehicles exhibit unexpectedly outstanding performance in halftone applications.

Halftone images actually comprise an array of tiny dots in highlight areas and an array of tiny holes in shadow area. The halftone image is produced by exposing a photosensitive imaging article such as a proofing film to actinic radiation through a halftone screen as illus- trated in Figure 1. In this figure, the respective portion of the overall article or film 10 are the substrate 12, the pigmented image layer 14 and negative-working resist 16. After exposure, a latent image consisting of exposed portion 20 (which have been rendered insoluble to a given solvent) and unexposed portion 22 (whose solubility with respect to the same solvent has remained unaltered) is formed. Upon development, which is carried out by contacting and optional ly rubbing the requisite developer over the surface of the film 10, the resist soluble portion 22 is removed along with corresponding soluble portion of the image layer 14. This leaves the structure depicted in Figure 3, wherein dots 23 a shown in cross section. These dots have an optical density

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18 predetermined by the optical density of the image layer 14, which is in turn a function of layer thickness, the concentration and the nature of the coloring medium dis¬ persed or dissolved therein, and the method of dispersion emplo ed.

In color proofing and in other halftone appli¬ cations, it is generally desirable and often required that the halftone images be etchable. The purpose of the etch¬ ing process is to reduce the size or cross-sectional area of the dots in highlight areas and to increase the size of the holes in shadow areas to correct color and tone reprodu tion. It is most important in these applications that the optical density of the dots and the areas surrounding holes remain generally unaltered by the etching process.

As explained earlier, prior art films used as color separations cannot be etched without affecting dot/ hole image optical density and possibly causing pinholing, because etching solutions attack both image surfaces as wel as image perimeters. This shortcoming of prior art ateri- als may be overcome to a very limited extent by using expo¬ sures that produce excessively thick dots, so percentagewis loss of density upon etching is minimized. In this case, as well as in the general case where normal dots are produc there is, however, always some danger of pinholing and some loss of optical density. When the optical density loss is excessive, the master is rendered useless, since actinic radiation can "burn through" areas of reduced density. Even without excessive density reduction, however, the change of optical density on the film limits film exposure latitude.

In contrast with prior art halftone systems, the novel structure of the present invention will undergo, upon etching, a reduction in dot diameter and an increase in hole diameter without significantly affecting optical density. Thus, it is seen from Figures 3 and 4 that the

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-19- dot resist portion will protect the surface 15 of the dot image layer 24 from the etching solution, and" from scratch¬ ing and other surface damage. When the dot image of Figure 3 is subjected to further development or etching in the form of contact with a developer of generally equal or greater strength than that originally used, portions of the perimeters of the dot image layers 24 are removed de¬ creasing the diameter from d, to d_ without altering the thickness or density of that layer. The actual dot struc- ture is illustrated in Figure 4 wherein the resist dot portion 20 is unchanged but the dot image layer 24 ' is significantly reduced in cross section. A top view of the . dot images of Figure 4 appears in Figure 5. In connection with the etched dot structure of Figure 4, it should be further noted that the unsupported edges of the resist layer will tend to fall, thereby protecting the perimeter of the halftone images from damage due to abrasion and contact with foreign substances.

Likewise, Figure 6 illustrates a shawdow area of a halftone image, after exposure and etching, the holes 30 having been enlarged from diameter d-. to diameter d. by the etching procedure while the resist layer remains unchanged by etching.

The present invention is directed to this et- hod of halftone etching exclusive of the specific compo¬ sition of the imaging article. This method entails the production of a halftone bilayer image on a substrate including a resist layer disposed on an image layer of uniform thickness and optical density. The resist layer should be insoluble in a given developer and the image layer should be soluble in that developer. Once the de¬ scribed halftone images are formed, the method then en¬ tails etching the images by treating them with the devel¬ oper to selectively remove portions of the perimeters of the image layers without significantly altering the thick¬ ness or optical density of these image layers.

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-20- Returning to the photosensitive imaging article of the present invention, it must be understood that the provisio of such an article having good exposure and development latitude accompanied by good dot etchability is completely unexpected. Good exposure and development latitude requir that the image layer utilize a film-forming vehicle which not overly soluble in the developer. An overly soluble im layer would have poor development latitude — background areas would be totally cleaned and highlight areas lost before shadow areas were adequately developed. In terms of the dot of Figure 3, an overly soluble image layer woul mean that even a slight increase in the optimal develop¬ ment time would result in unsatisfactory reproduction, pos sibly unduly reducing the size of the dot 23.

While good development latitude requires that image layer not be overly soluble in the developer, good dot etchabili requires just the opposite. That is, if dot image layer 2 is not sufficiently soluble in the developer, it will take unduly long to obtain the reduced dot image layer 24 of Figure 4.

A particularly novel image layer composition has now been developed which overcomes the conflicting requirements of development latitude and dot etchability. The novel chara teristics of this composition are obtained, in part, by th use of a group of bimodal copolymers and their derivatives as the film-forming vehicle. These bimodal copolymers con sist of a combination of high molecular weight and low molecular weight polymer portions in a weight ratio of abo 2:8 to about 8:2. The preferred weight ratio is 5:5.

The polymers useful in the bimodal composition include all of the polymers described above in connection with the mor general photosensitive imaging article. Most preferred among these copolymers is the earlier described SMA co¬ polymers.

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-21- When SMA copolymers are utilized, the low molecular weigh portion should desirably have a molecular weight of under about 5,000 and the high molecular weight portion should have a molecular weight exceeding 10,000. Preferred low molecular weights lie in the range of 1,000-2,000. Pre¬ ferred high molecular weight portions lie in the range of 10,000-150,000 and most preferably in the range of 20,000- 50,000. When the additional copolymers are utilized, thei relative molecular weights will be in keeping with the SMA copolymer teaching.

Presently preferred and practical embodiments to the prese invention are illustrated in the following examples wherei all parts are by weight, unless otherwise indicated.

Example 1 A photosensitive imaging article useful as a general pur¬ pose contact film may be prepared in accordance with the teachings of the present invention as follows. A 4 mil polyester sheet is subcoated with a 10% solution of SMA of average molecular weight 50,000 in ethylene glycol mono- methyl ether, and then dried. The subcoated polyester sheet is then coated with an image layer 1.5 - 2.3 microns in thickness of the formula:

50 grams SMA (average molecular weight 20,000) 40 grams Carbon black (Raven 1,000R) 400 grams N-butanol (as solvent)

The image layer is then top coated with a photodispersion following the teachings of the above referenced U.S. pat¬ ent application Serial No. 815,899, filed July 15, 1977:

50 grams Polyvinyl acetate - acrylic copolymer emulsion dispersion in water

55 grams Water

2 grams Paradiazo diphenylamine sulfate conden¬ sation product with para formaldehyde stabilized with zinc chloride (herein- a

-22-

This final coating has a thickness of 0.7 - 1.5 microns and the overall product thus produced is again subjected to drying to provide a final bi-layer, general purpose contact film.

The above film is then exposed through an appropriate mask to ultraviolet radiation from a high intensity source such as a 5 kilowatt mercury'halide lamp. The bi-layer film is then developed in an aqueous solution of a mild .alkaline material such as Na2HP04 with a pH of about 9.5 - 10.5. Light mechanical action will help to accelerate development. Development results in the removal of unexposed areas of the resist layer and corresponding portions of the image layer. After a suitable development time of from 15-60 seconds, a final product is obtained consisting of the ex- posed portions of the resist layer and corresponding portions of the image layer, both on the polyester sheet substrate. If the original mask was a negative mask, the resulting bi-layer film image will be a positive image. If the original mask was a positive mask, the resulting bi-layer image will be a negative image.

The image area of the bi-layer film made in accordance with this example will have an optical density in trans¬ mission of about 3.3 - 4.2. Since carbon black absorbs radiation in a wide range of wave lengths, this composition will be useful not only as a general purpose contact film, but also as a master for color proofing films, litho plates, and in circuit board manufacture. The resolution obtainabl with this composition is at least 150 lines per inch.

Example 2 A photosensitive imaging article utilizing an image layer with a bimodal organic film-forming vehicle may be produced as follows. The subcoated polyester substrate of Example 1 is coated with a pigment base layer having a thickness of 2.0 microns and the formula: 60 grams Carbon Black

60 grams SMA (average molecular weight 20,000) 30 grams SMA (average molecular weight 2,000) _/ -^ _j ΪE 600 grams n-butanol , as solvent _ OMP

-23- After this image layer is dried, a resist layer of 1.0 micron in thickness and the following formula is applied

50 grams Polyvinyl acetate-acrylic copolymer emulsion dispersion in water

4 grams Diazo resin

60 grams Water

The bi-layer imaging article thus produced is exposed and developed as in Example 1. A negative master is used so that a positive print is obtained. Since exposure is car¬ ried out through a half tone screen, the image on the bi-layer film is made up of an array of dots in highlight areas and holes in shadow areas.

The color or tone of the halftone images may be adjusted b subjecting the bi-layer film to treatment with an alkaline etching solution like that used in development. A typical etching solution would be a a2HP0_ι/ a3P04 in water to pro duce a pH of about 11-12. This "dot etching" of the image is successful and produces the desired reduction in color and tone, without significantly affecting the optical den¬ sity of the image dots and the portions of the image surrounding shadow holes.

Example 3

The procedures of Examples 1 and 2 were followed to pro- duce a series of six different bi-layer photosensitive imaging films with organic film-forming vehicles of vary¬ ing ratios of high and low molecular weight polymer. Thes films were then tested to evaluate their development speed, development latitude and image etching speed. For present purposes, "development speed" means the time required to remove soluble portions of the resist and corresponding portions of the image layer to produce a satisfactory image on the film substrate. "Development .latitude" refers to the range of development time which permits the bi-laye film to have background areas totally cleaned and shadow

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-24- areas opened while still maintaining highlight areas of th film image. Finally, "image etching speed" refers to the minimum time required to obtain a 50% reduction in the sur face area of highlight images (and a corresponding 30% increase in the area of the shadow images) .

The various bi-layer films produced in this example and their respective properties are listed in the table below:

TABLE I

A B C D E F

SMA (Molecular 90 60 50 40 20 0 Weight 20,000)

SMA (Molecular 0 30 40 50 80 90 Weight 2,000) n-butanol 600 600 600 600 600 600

Carbon black 60 60 60 60 60 60 (Raven 10OR)

Development 60 35 30 30 20 10 Speed (seconds)

Development 1.3X 2.5X 2.8X 2.7X 1.8X 1.2X Latitude

Dot Etching 90 60 45 45 45 30 Speed (seconds)

Examination of the above table will show that the composi¬ tions B, C and D display a combination of excellent development latitude and good dot etching speed. These examples utilize ratios of high molecular weight to low molecular weight polymer respectively of 60:30, 50:40 and 40:50. The results for composition E is less desirable though acceptable for some dot etching applications.

However, it is particularly interesting to examine composi tions A and F which respectively utilize 100% of the high molecular weight polymer and 100% of the low molecular weight polymer. The composition A material has an extreme ly slow dot etching speed, making it ill suited to etching applications. The composition F material, on the other hand, has an extremely fast dot etching speed, but display

-^ ϊ E

an undesirably narrow developing latitude. The extraordin¬ ary improvements n developing latitude and dot etching speed obtained in compositions B, C D and E therefore represent an important, unexpected synergistic result.

Example 4

Imaging articles are produced as set forth in Example 2, except the concentration of carbon black is varied from below 30 parts to over 90 parts.

Concentrations of carbon black within the range of 30 parts to 90 parts give good film structures. Below 30 parts, however, it is found that the thickness of the image layer must be increased greatly (e.g. from 1.5 microns to 4.0 microns) which produces an undesirable loss of resolution and development latitude. On the other hand, concentra- tions over about 90 parts increase film porosity resulting in overly rapid development, poor development latitude and a mechanically weak film. Furthermore, the increases over 90 parts carbon did not greatly improve the film optical density. The most preferred composition, based on develop- ent and dot etch speed, may be obtained with 60-79 parts carbon black.

Example 5

Imaging articles for use as high optical density film masters are again produced as taught in Example 2 with the thickness of the image layer varied from 0.4 - 5.0 microns. Below about 1.0 micron the film obtained exhibits an undes¬ irably low optical density, loss of mechanical strength and adhesion. On the other hand, films above about 3.0 microns in thickness exhibit significantly reduced resolution and density latitude. The most preferred balance of density latitude, resolution and development speed are obtained with films having image layers of from about 1.5 to about 2.5 microns in thickness.

Example 6 The Example 2 structure was made with the exception that the hig-i-. olecular weight SMA was replaced with a somewhat

^JR ^" Λ

.- . . „-._-. OMPI

^■ -

-26- lower molecular weight species The actual composition of the image layer was:

70 grams SMA (molecular weight 10,000)

•40 grams SMA (molecular weight 2,000) 60 grams Carbon black

600 grams n-butanol

The photosensitive imaging film obtained exhibited a faste development speed than that of Example 2 while maintaining acceptable development latitude and dot etching speed.

Example 7

The effects of the molecular weights of the copolymers making up the film-forming vehicle of the image layer were evaluated in another two photosensitive imaging films pre¬ pared in accordance with the Example 2 teaching. These tw films had image layers containing respectively:

1. 10 grams SMA (molecular weight 50,000)

40 grams SMA (molecular weight 10,000)

75 grams Carbon black

650 grams n-butanol

2. 25 grams SMA (molecular weight 50,000)

60 grams SMA (molecular weight 20,000)

65 grams Carbon black

600 grams n-butanol

Both of the above image layer compositions were found to produce useful films, in terms of mechanical strength. However, in both cases the dot etchability of the films was unsatisfactory for practical applications.

Example 8

In this example, alternate polymers were substituted for the SMA of Examples 1 and 2. The particular formulas used to produce these image layers were the following:

-27-

1. 80 grams Poly(methyl, vinyl, ether/maleic acid) isopropyl mono ester (Gan— trez 335)

70 grams Carbon black (Regal 330R) 700 grams n-butanol

80 grams Poly(methyl, vinyl, ether/maleic acid) butyl mono ester (Gantrez

425)

70 grams Carbon black 700 grams n-butanol

40 grams Poly(methyl, vinyl, ether/maleic acid) butyl mono ester 50 grams SMA (molecular weight 10,000) 300 grams n-butanol 400 grams Ethylene glycol monomethyl ether

In cases 1 and 2, the resulting films' mechanical strength was generally unsatisfactory. In the case of formulation however, far improved mechanical strength accompanied by other desirable film properties was obtained.

Example 9

The teachings of Example 2 were followed, but alternate subcoatings of the following formulation were used:

1. 1 gram SMA (molecular weight 50,000) 9 grams Carboxylated polyvinyl acetate (Nivac ASB 516 - Air Products) 100 grams Ethylene glycol mono methyl ether

2. 3 grams SMA (molecular weight 20,000) 7 grams Carboxylated polyvinyl acetate 100 grams Methyl ethyl ketone 9 grams SMA (molecular weight 50,000) 100 grams Methyl ethyl ketone

OMPI

-28- All of the above subcoatings exhibited good adhesion betwe the polyester substrate and the image layer and produced a film with good stability and development latitude.

In'another variation, the subcoating was eliminated entire and a pretreated polyester material, such as Celanar 4500 series polyester was used. Once again, the results were good. In yet another variation, the subcoating was again eliminated but an untreated polycarbonate film was-used. And again, satisfactory adhesion was obtained.

Example 10

A series of formulations following the teaching of Example 2 were made with variations in the diazo resin of the re¬ sist layer. The resist layer formulations used in these alternative compositions were as follows:

1. 50 grams Polyvinyl acetate - acrylic copoly¬ mer emulsion dispersion in water 6 grams Diazo resin 100 grams Water

2. 50 grams PVAC emulsion 10 grams Diazo resin

120 grams Water

3. 50 grams PVAC emulsion 15 grams Diazo resin 130 grams Water

4. 50 grams PVAC emulsion 2 grams Diazo resin 100 grams Water

All of the above formulations were found to be workable. The major differences between the formulations related to exposure time requirements. Resist layers of thicknesses between about 0.75 and about 1.5 microns gave optimal - _p \TRE

•—-— —" ' 0MPI

-29- results. In addition, introduction of surfactants such as P-toluene sulfonic acid or the addition of thickening agen such as polyvinyl alcohol, or gelatin made it possible to obtain workable thicknesses up to about 2.0 microns, how¬ ever, shelf life and resolution problems begin to arise at thickness of about 2.0 microns.

Example 11

In -this example , other water-soluble resins were added to the resis layer formulations top coated onto the structure of Exampl 2 to improve the performance of the overall imaging articl Among the formulations were the following resist layers :

50 grams PVAC emulsion dispersion

10 grams Diazo resin

120 grams Water

1 gram Hydroxy ethyl cellulose

2. 50 grams PVAC emulsion dispersion 10 grams Diazo resin 120 grams Water

2 grams Polyvinyl alcohol (Monsanto PVA 20-90)

50 grams PVAC emulsion dispersion

10 grams Diazo resin

130 grams Water

2 grams Gelatin

50 grams PVAC emulsion dispersion 10 grams Diazo resin 130 grams Water

1 gram Water-soluble polyaπide (K-resin from Unitika Ltd. of Japan)

-Each of the final photosensitive imaging films produced with the above resist layers showed improved shelf life, improved optical properties and enhanced developability.

OM

-30- The addition of water-soluble or dispersible resins may therefore be desirable in some instances in order to modif and improve performance and coating properties.

Example 12 Structures similar to those of Examples 1 and 2 were made with the use of the following solvent cast resist layers:

1. 10 grams Diazo resin BBP (a P-diazo diphenylamine sulfate condensate with paraformaldehyde stabilized with hexa fluorophosphate)

100 grams Dimethyl foi-mamide

2. 10 grams P-diazo diphenylamine sulfate con¬ densate with paraformaldehyde stabilized with tetra fluorobrate (ZAL. BF 4 from Sobin Chemicals)

100 grams Dimethyl formamide Both of these formulations produced films having superior shelf life and excellent resolution, especially in very thin films in the range of about 0.2 to about 0.6 microns.

Other organic solvents may be substituted for the dimethyl formamide without effecting the final characteristics of the film. For example, such solvents as dioxane, DM acet- amide, ethylene glycol monomethyl ether and methyl ethyl ketone have been used satisfactorily.

Example 13 Resins were added to the resist layers described in Exampl 12 to determine whether film characteristics could thereby be enhanced. The following formulations were evaluated:

1. 60 grams Diazo BBP

30 grams SMA (molecular weight 20,000) 350 grams Dimethyl acetamide

- -

2 . 50 grams Diazo BBP

40 grams SMA (molecular weight 50,000]

20 grams SMA (molecular weight ^' 2, 000)

350 grams DMAC

55 grams Diazo ZAL.BF4 35 grams Alkaline soluble polyvinyl acetate 200 grams Dimethyl formamide 150 grams n-butanol

4. 50 grams Diazo ZAL.BF4

30 grams Polyvinyl butyral

5. 114 grams Diazo BBP 75 grams SMA (molecular weight 20,000) 21 grams Polyvinyl acetate 78 grams SMA (molecular weight 2,000) 900 grams DMAC

100 grams Diazo BBP 30 grams Polystyrene allyl alcohol 20 grams Novalak 1280 750 grams PMF

60 grams Diazo BBP 30 grams Phenolic resin (Hercules Vinsol

790224-B)

300 grams PMF

The results obtained in each case were good, the resin ad- ditions providing improved film formation and mechanical strength. Both alkaline soluble and non-alkaline soluble resins were useful, although alkaline soluble resins could be used in higher proportions. In ^' fact, mixtures of alka¬ line soluble and non-soluble resins may, in certain instances, provide enhanced development latitude. In this connection, formulation 5 is a preferred embodiment.

In addition to the resins referred to in the above exemplary ^* co pos__-. ons, other useful resin additives are epoxies, phenoxies, acrylics, silicones, polyesters and polyamides,. ---- ^'

-32- Example 14

The structures of Examples 1 and 2 were made by using a positive resist in place of the negative working resists de¬ scribed earlier. Use of a positive working resist will, of course, produce a negative image from a negative mask and a positive image from a positive mask.

The particular positive working resist coat used in this example was:

30 grams Quinone diazide (AZ 1350 J from Shipley)

40 grams Amyl acetate

Development of the overall film bearing the above positive working resist was carried out in a developer consisting of:

75 ml AZ 606 425 ml Water (overall pH 11.5-12.5)

Other useful developers for this resist would include the following compositions:

1. 4 grams KOH

100 grams Water

2 . 10 grams Na ₂ C0 ₃

2 grams Na ₃ P0 ₄

100 grams Water

3. 6 grams N 3P0

1 gram Sodium lauryl sulfate anionic surfactant

100 gra s Water

Examole 15

Test work with differing coloring media was carried out in this example. The image layer composition of Example 13 was replaced with the following pigme ted

-33-

1. 80 grams SMA (molecular weight 20,000) 20 grams SMA (molecular weight 2,000) 80 grams Dinitraniline orange (pigment orange No. 5, 2-4 dinitroanalin coupled with beta naphthol)

400 grams Ethylene glycol mono methyl ether

Next the positive working structure of Example,14 was modi fied by replacing the image layer with the following alternate image layer compositions:

2. 80 grams SMA (molecular weight 20,000) 20 grams SMA (molecular weight 2,000) 80 grams Dinitraniline orange (pigment orange No. 5, 2-4 dinitroanalin coupled with beta naphthol)

400 grams Ethylene glycol mono methyl ether

3. 100 grams SMA (molecular weight 20,000) 90 grams Ti0 ₂ 500 grams n-butanol

Each of the above compositions produced a film with good ultraviolet absorbing characteristics. The white image produced with the film of composition 3 was of particular interest in duplicating negative masters. This film be¬ haved like a negative but produced a positive image when viewed against a dark background. This unusual feature will be of particular usefulness to those practicing in the arts of proofing and stripping films.

Example 16

A numb'er of overlay color proofing films were made with image layers having the following exemplary compositions:

1. 29 grams Lithol rubine

110 grams SMA (molecular weight 20,000) 850 grams Ethylene glycol monobutyl ether

-34-

2. 80 grams Mogul carbon black

100 grams SMA (molecular weight 10,000)

80 grams Ethylene glycol mono methyl ether

3. 45 grams Phthalocyanine blue 110 grams SMA (molecular weight 20,000)

1,000 grams n-butyl alcohol

4. 38 grams Sun yellow AAA

90 grams SMA (molecular weight 2,000)

850 grams Ethylene glycol mono methyl ether

The above compositions were used in the structures of Exam¬ ples 1, 2, 12, 13 and 14 to produce useful overlay color proofing films .

Example 17

Image layer compositions following the teaching of Example 1, 2 , 12, 13, 14 and 16 could next be applied to white opaque substrates to produce negative and/or positive proo ing or print papers. Suitable substrate materials would include filled polypropylene synthetic paper (e.g. imdura FPG 150, Melinex 990) , and typical RC papers such as poly- ethylene coated cellulose papers. Further useful photosen sitive imaging articles could be obtained by using the Tiθ image layers suggested in Example 15 to coat paper pigment black and overcoated with polyethylene.

Yet further useful photosensitive imaging articles could b produced by coating the structure of Example 14 onto trans lucent substrates. These articles would be useful as engineering drawing intermediates such as masters for diazo-type white prints and sepias. Suitable translucent substrates for this application would include: matte poly ethylene terphthalate films, matte coated PET films

(typically with Siθ2 in a resin binder as the matte coat¬ ing) and matte finished polypropylene films.

-35- Example 18

While the image layers of the prior examples have been coated from solvent bases, aqueous base coating can also accomplished within the teaching of the present invention. Such aσueous based coatings have a number of important ad vantages, since they are oftentimes more economical, less toxic and more acceptable environmentally. Typical usefu aqueous base image layer formulations include the followi

1. 20 grams SMA (molecular weight 20,000;

10% solids solution in NH4OH)

10 grams 28% NH3 170 grams Water 0.01 grams Triton X-100 (nonionic surfactant) 70 grams Predispersed carbon black (i.e.

Aquablack 135 from Bordon Chemical)

2. 15 grams SMA (molecular weight 20,000;

15% solution in NH3.H2O)

4 grams 28% NH4OH 80 grams H2O 40 grams Predispersed carbon black 25 grams SMA (molecular weight 2,000; neutralized with NH4OH)

3. 18 grams SMA (molecular weight 20,000; 15% solution in NH3Η2O) 108 grams SMA (molecular weight 10,000; 10% solution in NH3-H ₂ 0) 36 grams Predispersed carbon black

4. 20 grams SMA (molecular weight 20,000;

15% solution in NH3.H2O) 80 grams SMA (molecular weight 10,000;

10% solution in NH3«H2θ) 30 grams SMA (molecular weight 20,000;

10% solution in NH3.H2O) 1 gram Triton X-100 (nonionic surfactnat) 25 grams Predispersed carbon black

^< _ΓOREA

OMPI

-36- The above image layers can be coated onto all of the sub¬ strates discussed earlier and may, as well, be overcoated with each of the resists of the above examples. It is als important to note that the development rate and developmen latitude of bimodal compositions 2, 3 and 4 is far superio to the results obtainable with image layers having 100% of either a high or low molecular weight styrene maleic anhy¬ dride. Dot etchability for these formulations is also exceptional.

Example 19

As noted earlier, a particularly novel and useful feature of the present invention is that all of the photosensitive imaging articles produced in accordance with the present teaching can be developed with simple aqueous base de- velopers. Organic solvents are not required.

Furthermore, systems can be formulated such that all of the products can be developed with the same de¬ veloper. Alternatively, the formulations can be optimized for each resist using slightly different developers for th different resists such as in the case of the positive resist.

This aqueous, tailorable feature of the present invention permits a hitherto unimaginable variety of graphic arts articles to be developed by the same chemistry and in the same type of processing equipment. The problems associate with prior full-line contact speed graphic arts products employing silver halides, photopolymer, diazo-type, diazo resin and other technologies to produce a variety of films papers, proofs, intermediates and lithographic printing plates can be eliminated. With these prior systems, the user was confronted with a bewildering array of supplies and equipment associated with each of these different tech nologies and their differing development chemicals and processing equipment.-requirements. In sharp contrast to these prior systems, however, the photosensitive imaging article of the present invention may use a single type of exposts:-e source, as well as a single development chemistry and one t e of r c s yy> *- ^

- 37- Typical general application developers useful with the pr ent photosensitive imaging articles include :

2% solution Sodium metasilicate

1% solution Sodium lauryl sulfate

2. 5 grams Na ₂ HP0 ₄

2 grams a3P04

100 grams Water

3. 10 grams Na2C03

25 grams Sodium tripolyphosphate

1 gram Sodium lauryl sulfate

100 grams Water

4 . 3 grams KOH

1 gram Triton X-100

100 grams H ₂ 0

5. 5% solution Sodium lauryl sulfate

5% solution Sodium sulfate

1% solution Sodium xylene sulfonate

1% solution Na3P04

A particularly useful developing solution for use with the photosensitive imaging articles of the present invention i disclosed in the aforementioned U.S. patent application Serial No. 051,478, filed June 25, 1979. Typical useful formulations for this developer include:

25 grams Potassium toluene sulfonate

10 grams Disodium beta-glycero phosphate

1 gram Triton X-100

100 grams Water

7. 30 grams Potassium toluene sulfonate

5 grams Disodium beta-glycero phosphate

5 grams a2HPθ4

1 gram Triton 405

100 grams Water

-38- In connection with the teaching of the 051,478 application it is noted that the developing solutions described therei use low molecular weight film formers such as sodium glyce phosphate. The basic requirements for these developers in the present application, however, do not necessitate such restriction. Thus, high concentration (10-50%) of hydro- tropic materials such as sodium xylene sulfonate, potassiu toluene sulfonate, potassium cumene sulfonate and the like in combination with alkaline salts in a weight concentrati of from 1-15% may be used. Alkaline salts especially usef in this context are disodium phosphate, trisodium phosphat sodium tripoly phosphate, tetrapotassium pyro phosphate, . sodium hexametaphosphate, sodium glycerophosphate and the like. Other useful alkaline salts include sodium metasili cate, sodium orthosilicate, water glass and other complex sodium silicates, sodium citrate, potassium gluconate, sodium carbonate, ammonium metavanadate, potassium hydrox¬ ide, sodium acetate and the like. Of course, nonionic and anionic surfactants and combinations thereof may also be added as may film formers, thickeners, buffering agents, builders, defoamers and so on.

Example 20

In addition to the film and paper substrate products of th prior examples, the photosensitive imaging articles which may be produced according to the teaching of the present invention include lithographic plates having as substrates the rigid materials commonly employed in that field. With lithographic plates, the developing formulations of Exampl 19 are particularly useful since they make possible one chemical, one step development and gumming. Of course, wi lithographic printing plates, it is not necessary to use coloring media in the image layer although coloring media may optionally be introduced into the image layer in order to enhance visibility of the lithographic image.

One useful lithographic article may be made as follows. A grained silicated aluminum substrate is coated with both image and resist compositions comprisincr:

-39-

1. Image layer : 60 grams Phthalocyanine blue 210 grams SMA (molecular weight 20,000) 1 , 000 grams Ethylene glycol mono methyl ether

Resist layer: 100 grams Diazo resin ZAL.BF4 30 grams Epoxy resin (Araldite 7073 from

Ciba-Geigy)

30 grams Novalak 1280 (from Union Carbide) 800 grams Dimethyl formamide 200 grams MEK

Each layer is about 1 micron in thickness. Exposure is carried out with an ultraviolet radiation source through a negative mask. The lithographic plate thus produced is developed and gummed with composition 6 of Example 19. The resulting product is run on an offset press for several thousand copies which are all of acceptable definition and quality. Furthermore, these plates are resistant to the typical acidic fountain solutions used in printing operation Uniquely, these plates are dot etchable, therefore, correct¬ able after exposure.

Further lithographic plates are produced using the same grained silicated aluminum substrate with the following image layers and resist layers: 2. Image layer:

100 grams SMA (molecular weight 50,000) 20 grams SMA (molecular weight 10,000)

Resist layer: 100 grams Diazo resin BBP 10 grams Butvar B76 (from Monsanto) 50 grams Phenolic resin (Vinsol 790224-B) from Hercules)

2 grams Methylene blue dye

-40-

3. Image layer :

100 grams SMA (molecular weight 20,000) 20 grams SMA (molecular weight 2,000) 30 grams Dinitraniline orange

Resist layer:

100 grams Diazo resin BBP 50 grams Acrylic resin (DuPont 2044) 10 grams Styrene allyl alcohol resin (Monsanto RJ101) 400 grams Dimethyl acetamide

400 grams Ethylene glycol mono methyl ether

4. Image layer:

100 grams SMA (molecular weight 20,000) 900 grams n-butyl alcohol

Resist layer:

80 grams Diazo resin ZAL.BF4 20 grams SMA (molecular weight 50,000) 30 grams SMA (molecular weight 10,000) 20 grams Lithol rubine 900 grams Dimethyl acetamide

As in the case of formulation 1 of this example, each of the. above formulations is exposed and developed by one of the developers of Example 19 to produce negative working plates. Naturally, the use of the positive working resist layers of Example 14 would give the positive analogue of these plates.

The spatial separation of the image coat from the photosen sitive materials of the resist coat makes for the produc¬ tion of a more readily manufactured lithographic plate tha would be the case with single layer plates. Furthermore, by making the bottom layer ultraviolet light absorptive, i is found that superb antihalation properties can be ob¬ tained which are not found in single layer plates.

-41- Example 21

This example illustrates the outstanding dot etchability characteristics of the present photosensitive imaging art cles. A half-tone print is made following standard indus practices to produce a bi-layer image with an array of do in highlight areas an an array of holes in shadow areas. similar half-tone image is produced with a coirmercially available silver halide based film for comparison purpose

The respective dots and holes of these images are examine under 200X magnification and then subjected to etching, using the teachings of the present invention to etch the bi-layer film and conventional etching techniques to etch the silver halide film.

Typical of the etch changes obtained with the bi-layer fi were the following:

Original Half-Tone Image Etched Image Area Percen Area (% of Entire Film) (% of Entire Film) Change

90 (shadow) 65 27

60 (mid-range) 25 58 40 (mid-range) 10 75

15 (highlight) 5 67

Etching was accomplished in each of the above cases withou a significant change in through-dot density. The original density prior to etching was about 3.6-3.8. Dot density r ained in the 3.6-3.8 range after etching.

With the silver halide based films, however, it was found that an etching change of 10-20% in a mid-range, half-tone image (40-60% of surface area) was the maximum etch attain without significant reduction in through-dot density. Hig light dots (5-20% of surface area)for silver based film we even less amenable to etching before unacceptable density losses occurred. Indeed, with the silver halide base film the density upon etching was found to be reduced from an original density of 4.5 to 2.6 or less. Such a density change, either locally or across the film,

-42- acceptable window for exposure and, indeed, may render the film useless as a mask to ultraviolet light.

Of course, it should be understood that various changes and modifications to the preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is, there¬ fore, intended that such changes and modifications be covered by the following claims.