US2778735A - Photo-sensitive coated paper plate for photo-lithography - Google Patents

Description

Jan. 22, 1957 F. E. BRINNICK ETAL PHOTO-SENSITIVE COATED PAPER PLATE FOR PHOTO-LITHOGRAPHY Filed Oct. 1, 1953 /W/QFA 577.55

5 5 2 HYLWUAV/L/C (OFF/V6 United States Patent PHOTO-SENSITIVE COATED PAPER PLATE FOR PHOTO-LITI-IOGRAPHY Frederic E. Brinnick, Westbrook, Towers Doggett, Windham, and Raymond L. Oransky, Portland, Maine, assignors to S. D. Warren Company, Boston, Mass., a corporation of Massachusetts Application October 1, 1953, Serial No. 383,696

Claims. (Cl. 96-75) This application is a continuation-in-part of our application Serial No. 356,887, filed May 22, 1953, now abandoned.

This invention relates to a new photosensitive coated paper product useful as a photo-lithographic printing plate for use in planographic printing.

Planographic printing is a form of lithographic printing which uses plates that are substantially plane, having image areas which are neither intaglioed nor raised above the adjacent surface. In use the blank or unimaged areas are kept wet with aqueous lithographic solution and so are ink-repellent. The imaged areas, being water-repellent, are not wet by the aqueous solution and so are free to accept ink from the inking-rolls of the printing press, and when so inked can thereafter print the image in reverse on any ink-receptive surface brought into contact therewith. In practice the print i first made on a rubber offset blanket from which it is transferred to paper so that the final print is identical with the design on the Plate.

U. S. Patents Nos. 2,626,866 and 2,649,373 disclose photo-sensitive coated paper lithographic printing plates in which paper bearing-a clay-casein coating has applied thereto a diazonium salt corresponding to the following Formula No. 1.

\N-AI-NE X- wherein or the condensate of such a salt with an aldehyde, or a sulfonate formed by the reaction of a sulfite with said diazonium salt or its condensate with an aldehyde. A preferred material is the product produced by the action of an alkali-metal sulfite such as sodium sulfite upon the condensation product of a zinc double salt of diazotized para-amino-diphenylamine and formaldehyde in equimolecular proportions.

The light-sensitive coated paper product so made can be kept in a package for at least a year with substantially no deterioration, so that at the end of that time it can be used for printing by exposure through a negative transparency to actinic-light. The light insolubilizes the exposed'areas which thereupon become receptive to greasy ink; the unexposed areas remain water-soluble and subsequently are washed away.

The coated paper plate made as described is an excellent product and has come into wide use. Such plates are capable of printing about 2000 excellent halftone prints and at least twice as many prints of line-cuts or type. For some purposes, however, plates capable of yielding a greater number of prints are desired.

The present invention is directed to an improvement over the above described plate by which improvement a photo-sensitive coated paper plate is produced which is capable of making up to 15,000 or more satisfactory halftone prints.

The accompanying drawing is a diagrammatic crosssectional illustration of a sheet of paper in accordance with the present invention. In the drawing 5 is the paper base, 6 is an optional back coating, 4 is an optional barrier coating, 3 and 2 are base and top hydrophilic coatings, respectively, and 1 is the photo-sensitive coating all of which will be described in detail hereinafter.

The production of a plate capable of making up to 15,000 or more satisfactory halftone prints is attained by use of the same photosensitive compounds disclosed in said Patents Nos. 2,626,866 and 2,649,373, in combination with a mineral-coated surface of specific composition having the ability of coacting with said photosensitive compound to yield images capable of making many thousands of prints. The particular coated surface which coacts with the photo-sensitive compound comprises finely divided mineral pigment of a non-hydrous type such as titanium dioxideand being entirely free from clay or hydrous aluminum silicate, and containing for each 100 parts of said non-hydrous pigment from 20 to parts and preferably from 35 to 50 parts of a water-soluble carboxyalkylhydroxyalkyl cellulose com pound, such, for example, a sodium carboxymethylhydroxyethyl cellulose. The particular cellulose derivative used should have a ratio of carboxyalkyl groups to hydroxyalkyl groups of less than 1.0 and preferably of between 0.3 and 1.0. The degree of substitution of the anhydroglucose units present should be greater than 0.8 The so-called aluminum-resistant varieties :of carboxymethyl-hydroxyethyl cellulose fall in this range and are very suitable for use under the invention. Products of medium to low viscosity are preferred in order to make possible coating compositions of reasonably high solids content. It is possible to use compounds of higher viscosity, however, provided repeated applications are made to build up the layer of coating to the desired weight.

A coated paper planographic printing plate designed to produce 15,000 or more prints requires more strength than one designed to produce only 50 copies. The strength demanded is not great, however, and is easily provided by a paper base made from moderately beaten chemical wood-pulp fiber and weighing about to pounds per ream of 500 sheets 25 x 38 inches in size. A specific example of a suitable paper base i one weighing 87 pounds per ream made from a furnish containing beaten wood-pulp fibers from both coniferous and. deciduous trees, a small proportion of clay filler, rosin-size, alum, and acidified melamine-formaldehyde condensate. The formed web is surface sized with about 2. pounds per ream of the evaporation residue of a solution of ammonical casein made slightly acidic by formaldehyde, dried and calendered.

For a paper plate expected to give really long printing runs it is essential that the fibrous base of the plate shall not become saturated with aqueous lithographic solution, with consequent weakening and distortion of the base. Such aqueous saturation can be prevented by impregnation of the paper base with a water-proofing agent,

c g,asphalt. Preferably, however, a Water-impervious barrier-coat is interposed between the fibrous base and the p l anographic printing surface to prevent saturation and to ensure long printing runs. When such a barriercgat .used substantially no -aqueous liquid reaches the fibrous base and consequentlyit is not essential for the paper base to. have wet-strength properties. Nevertheless, si 1ce some penetration of aqueous liquid maybe expected through the cut edges of the plate it i preferable to give the paper base some degree of wet-strength, as, fonexample, by includingurea-formaldehyde er melamine-formaldehyde condensate in the paper-making furnish.

Paper cqated only on one side is liable to exhibit a tepdency to curl. Hence it is preferable in producing seated, .Pau -p am. aphic. pr n ingp at s h h a k or non-printing side of the plate also be coated in order to otfsertosorne degree the tendency towardsyctuling which the coating on the printing-side may induce. The actual composition of vthecoating on the bac-kof the plate is of little importance, but it is desirable that the coating be. sufliciently water-resistant that if it inadvertently becomes wetted it will not adhere to the plate cylinder of the printing press or to other objects with which it may come into contact. One suitable coating for th e purpose is about 10 pounds per ream of 500 ts cut IZS x 38 inches, of the evaporation residue, of V rnposition in parts by weight shown in following o mula .NQ-

Clay 100 Casein (solvated by ammonia) 18 Dimethylol urea (to insolubilize the casein) 2 Water to make solids content about 40%.

factory coating for this purpose is one deposited from.

the composition, given in parts by weight, shown in the following Formula No. 3:

Clay; 50 A latex ofaemulsion polymerized mixture of 3 moles.

of styrene and 2 moles of butadiene 60 A latex of emulsion polymerized polystyrene mol. wt.

about. 80,000. 40 Water to make solids content about 40%.

The dry weight of such barrier-coat required per ream of paper will vary considerably, depending upon the surface characteristics of the base stock. It is necessary to apply suflicient so that all fibers are covered. The usual range is from about 4 pounds to about 10 pounds per ream. In any case the coating is adequate if when .subjectedfor 2 minutes to the Cobb absorption test (see Standard Test No. T441 of the Technical Association of the Pulp and Paper Industry) it absorbs not over 0.04 gram of water over an area of 78.5 square centimeters or not over 5.1 grams per square meter. Paper with such a degree of resistance may for our purpose be considered to be substantially impervious to water. I A suitable, weight of coatir 1g is 7 pounds. per eam I barriercoat v previously described is oleophilic rather than hydrophilic Consequently it must be completelycovered by the coating which is to provide the planographic printing surface. Otherwise any portions not so covered will pick up ink and so spoil any matter printed therefrom. Complete coverage of the barriercoat is ensured by the preferred practice of the invention in which two successive hydrophilic coatings are appliedoventhe barrier-coat. Other advantages also ensue from use of two successive layers of hydrophilic coating. Among'these are the possibility of using for thefirst. layerof hydrophilic coating acomposition having stronger adhesion to the aforesaid barrier-coat than is given by the top coating containing carboxy-alkylhydroxyalkyl cellulose. In such a case the cellulosic coating is less liable to crack than. whenit. is applied directly over the barrier-coat. Moreover the total cost of the composite hydrophilic coating tcanbc less than a. coating of equal weight composed of the preferred top coating alone.

The first hydrophilic coating, whentwo coatings. are used, may comprise nonrhydrous finely divided pigment such as blanc fixe or titaniumdioxide, but. should not contain a hydrous pigment such as clay. The coating may contain a hydrophilic protein adhesive such as casein, soy protein, animal glue, or the like, said adhesive being set-up or insolubilized by known agents such, for example, as formaldehyde or formaldehyde-containing compounds.

A preferred first hydrophilic coating to be applied over the previously mentioned barrier-coat :is' about 10-12 pounds per ream of the; evaporationresiduecofthe coating composition, in parts by weight, shown in. 1 following Formula No. .4:

lrecipitated barium sulfate (blanc 'fixe) 100 Casein (solvated by ammonia) 20 Dimethylol urea 4 Water to make solids content. about 34%.

While, as has been pointed out, the preferred .practice is to apply in succession two hydrophilic coatings of. different compositions, the invention lS'. not limited to such practice. Very satisfactoryresults can be obtained by application of a single. layer of. hydrophilic coating composition comprising titanium dioxide, a water-soluble carboxyalkylhydroxyalkyl cellulose compound such as sodium carboxymethylhydroxyethyl cellulose, and an agent. to render the driedocoating waterainsolublebut stillhydrophilic.

The coating composition used to provide the top orsurface .coat'whether-a singleordoublecoating is used, however, must contain a water-soluble carboxymethylhydroxyethyl cellulose compound, or other carboxyalkylhydroxyalkyl cellulose, in quantity. amounting to from 20-10 70 parts, and preferably from to parts, for'each parts of mineral pigment present. The mineral pigment will contain no clay or other hydrous pigment, but will contain non-hydrous finely divided pigmentary materials such as titanium dioxide. Blanc fixe may be used but is somewhat less satisfactory than titanium dioxide in the top coating. The rutile form of titanium dioxide appears to giveslightly better results .than'the anatase. form in respect to greater length of. printing runs given. by. the

esulting plate.

The originally water-soluble cellulose adhesive must be rendered water-insoluble before thecoated sheet can be used as a printing plate. The treatment used toinsolubilize the adhesive should not appreciably impair ethehydrophilic properties or" the adhesive, for the..-adhesive must not become water-repellent or. water-shedding. There are, however, various known treatments for insolubilizing such a hydrophilic cellulosieadhesive Without seriously afiectingthe hydrophilic properties thereof. Oneinsolubilizing treatment that is very effective upon sodium carboxyalkylhydroxyal-kyl cellulose iscarried' out by in clusion' in the coating composition" of significant quantities of partiallycondensed amino-resins, such as-water-soluble urea-formaldehyde or melamine-forma-idehydecondensates, together with sufficient acidic material'to'keep the pH value of the coating composition below 7. Coating containing such amino-resin insolubilizers should be force-dried with heat in order to promote curing of the resin, and consequential insolubilization of the coating, within a reasonable time. The temperature and/or time required for curing will vary'depending upon the particular'amino-resin used. Particularly useful amino resinsare melamine-formaldehyde resins'preparedby the partial condensation of one mole of melamine with two to three moles of formaldehyde, for in general such condensates are satisfactorily cured merely by the heating required to dry the water from the coating. One such satisfactory resin is the condensate of 1 mole of melamine with 3 moles of formaldehyde. A quantity of such aminoresin in the range from A to 1 part for each part of cellulose derivative will ordinarily ensure satisfactory insolubilization of the latter without sensibly reducing its hydrophilic properties.

Besides the previously mentioned essential components of the top coating composition, i. e. non-hydrous pigment, sodium carboxyalkylhydroxyalkyl cellulose, and insolubilizer for the latter, the aqueous coating composition may contain small quantities of various additives generally used in aqueous coating compositions. Such additives include anti-foam agents, flexibilizers, wetting agents, eveners, and the like, in each category of which a great number of items are found. For use in the present invention, however, care should be exercised to avoid use of additives which will impart appreciable oleophilic properties to the dried coated surface.

A typical surface hydrophilic coating is about 5 pounds per ream of the evaporation residue of the coating composition shown in following Formula No. 5:

Parts dry weight Acid, e. g. HCl to make pH 5.7. Water to make solids content about Any of the coating compositions may be applied by conventional coating means, an air-knife coater being very satisfactory.

The paper plate made as hereinbefore described by application of a barrier-coat and two subsequent hydrophilic coats is, after being dried, subjected to a smoothing or calendering operation to render the surface level. The resulting sheet is then ready to have applied thereto a wash coat of sensitizer. While the sensitizer preferred is a sulfonate resulting from the action of a sulfite, e. g. sodium sulfite, upon one of the groups consisting of (1) the diazonium salts corresponding to the aforesaid Formula No. 1 and (2) the condensates of such a salt with an aldehyde, nevertheless surprisingly good results may also be obtained by use of the unsulfonated diazonium salt or of its condensate with formaldehyde.

By good results is meant not only that the resulting plate had excellent printing characteristics, but also that the sensitized plates, when properly packaged, had good shelf life at ordinary temperatures. Previous coated paper plates, i. e. clay-casein coated paper plates, sensitized with the unsulfonated diazonium compounds or the aldehyde condensates thereof have had practically no shelf life. In other words plates so prepared have to be exposed within a few hours after sensitization or they become spoiled. Now, contrariwise, properly packaged plates made with the same unsulfonated product, e. g. the formaldehyde condensate of a zinc double salt of diazotized para-amino-diphenylamine, applied over the improved base coating comprising carboxymethylhydroxyethyl cellulose compound and titanium dioxide keep very satisfactorily for several months.

Nevertheless, although the unsulfonated compounds may be used with good results, it is still preferred to employ the sulfonates produced by the action of sulfites on the diazonium compounds or their aldehyde condensates 6 previously described, because of the exceptional stability of these sulfonate compounds.

The sulfonate sensitizing compounds may easily be applied from aqueous solution spread on. the surface of the calendered carboxyalkylhydroxyalkyl cellulose and titanium dioxide coating, such as the one deposited from the composition of Formula No. 5, by means of a conventional air-knife coater.

In a typical example an aqueous solution containing 1 /2% of the sulfonate of the condensation product of a zinc double salt of diazotized para-amino-diphenylamine with formaldehyde in equimolecular proportions was applied by means of an air-knife to the surface of the previously described calendered carboxymethylhydroxyethyl cellulose and titanium dioxide coated paper, and the so-treated paper was then dried with heat in conventional fashion. Care was taken not to expose the coated paper to direct sunlight or other light of equivalent actinic power; ordinary illumination from incandescent lamps was used. The dried coated paper was cut to size and made into packages wrapped with opaque paper wrappers. The packaged plates were still in excellent condition after being stored for a period of 12 months.

In a printing test the printing plate coated with the composition of Formula No. 5 and subsequently treated and sensitized as described was exposed under a halftone negative transparency to actinic light from a carbon-arc for about 3 minutes. The plate was then removed from under the negative, wiped over with a cotton swab moistened with oleic acid to intensify the ink-receptiveness of the exposed image, and was then swabbed with another swab wet with water which removed from the unexposed areas the still soluble sensitizer as well as any oleic acid intensifier overlying those areas. The so-imaged plate was then wet out with a commercial aqueous lithographic solution containing glycerine and ammonium acid phosphate, and the wet-out plate was run in the usual way on a rotary offset duplicator. The prints made at the start of the run were distinct and had a clean background, and after 15,000 prints had been made the quality was still good and the background was still clean.

It is significant that the particular cellulose derivative specified, i. e. sodium carboxylalkylhydroxyalkyl cellulose, is the only adhesive so far found that gives these excellent results with the sulfonated diazonium compounds described. When sodium carboxymethyl cellulose was substituted for the sodium carboxymethylhydroxylethyl cellulose in Formula No. 5 the resulting plate would print only less than 1500 good copies. On the other hand, when water soluble hydroxyethyl cellulose was substituted for the sodium carboxymethylhydroxyethyl cellulose in Formula No. 5 the sensitized coating of sulfonated diazonium compound could not be completely removed. The small amount of light sensitive coating remaining on the surface of the plate was acted on by light even under conditions of subdued lighting as the plate was being used on the printing press during the printing operation. After only a few hundred copies had been printed it was noted that the image had begun to fatten and after about a thousand copies the non-image areas or background began to show tone or soiling by ink.

It is also significant that if in Formula No. 5, the sodium carboxymethylhydroxyethyl cellulose is replaced by an equal weight of a mixture of sodium carboxymethyl cellulose and water-soluble hydroxyethyl cellulose in the ratios of 0.8 to 1.0, then the results obtained are entirely different than those obtained by use of Formula No. 5 as stated. In fact the results are quite similar to those given when hydroxyethylcellulose alone is used as adhesive, in that discoloration or soiling of the background soon occurs as the plate is being used on the printing press. It appears therefore that the carboxyalkyl and hydroxyalkyl groups must both be present in the same molecule in order to achieve the superior results of the invention.

Ifthere is used a carboxymethylhydroxyethyl cellulose having a carboxymethyl to hydroxyethyl ratio of less than about 0.3 unsatisfactory results will be obtained of a nature similar to those given by plain water-soluble hydroxylethyl cellulose; ,i. e., a background which cannot be completely desensitized. On the other hand, the carboxymethyl to hydroxyethyl ratio is greater than 1. the number of prints obtainable from the resulting plate will be noticeably diminished.

We Wish to point .out that the paper base Whether it contains .a material to impart wet strength or :1: Esther it has aback side coating or not and whether it has a frontside barrier coating or not forms no part of the present invention, the provision of such a paperbase .for planographic printing plates being well known in the art. We wish to point out further that the present invention doesnot reside broadly in the use of the diazo sensitizers disclosed in Patents Nos. 2,628,865 and 2,649,373. The present invention. resides in the use of a paperbase which is suitable for a ,planographic printing plate and in the useof the diazo sensitizers referred to in combhiation with an intermediate coating or layer which consists esentially of an insolublized carboxyalizylhydroxylallryl cellulose adhesive and a non-hydrous pigment, it being understood that said intermediate layer may consist of a single coating of said composition or two or more coatings thereof or a top coating thereof upon an anchoring coating of another composition, which anchoring coating however must be hydrophilic and free of hydrous pigment such as clay.

Examples of diazonium compounds of Formula No. 1 are the following:

The diazo compounds of 4--(N-benzyl-N-ethyl)-aminoaniline, 4-(N-2,6-dichloro benzyl)amino-aniline, 4(N- cyclohexyl")-amino-aniline, 4 amino-2,5,4-tribromo-diphenylamine, 4 amino2',4,6-trichloro-diphenylarnine, 4 amino-Z- [N- 2,5 -diethoxy-phenyl -sulian1idol diphenylarnine, 4 amino 3,6-dimethoxy-diphenylamine-2-carboxylic acid, 1-amino-2,5-di-n-propoXy-4-methyl-diphenylsulfide, N- (2,6-dichlorobenzyl) -3-arnino-carbazol, 4- (N- 2,3,4,6 tetrachloro-benzyl)-amino-aniline, 4-(N-2,6-dichloro-benzyl-N-ethyl)-amino-2,5-diethoXy-aniline and 4- amino2,5,4 triethoXy-diphenyiether and their aldehyde condensates and the sulfonates of both.

The prefer-red sensitizer, referred to above is made by the action of sodium sulfite upon the condensation product of the zinc double chloride of diazotized para-aminoo'iphenylamine with an equimolecular quantity of formaldehyde. This is applied in a Weight amounting to about 0.35 pound per reamv We claim:

1. A photo-sensitive coated paper product capable of being transformed by actinic light into a planograph printing plate comprising a paper base having a calendered coating layer thereon, said coating consisting essentially of an insolubilized carboxymethylhydroxyethyl cellulose adhesive in which the ratio of carboxymethyl groups to hydroxyethyl groups is within the range from 0.3 to ,1 and in which the degree of substitution of anhydroglucose n R stands for a member of the group consisting of aryl groups and aryl groups substituted by a member selected from the group consisting of aIKYL-alkQXY and carboxyl groups and halogens,

R1 stands for a member of the group consisting of hydrogen and alkyl,

N stands for nitrogen,

Ar stands for an aromatic residue selected from the group consisting of phenylene and phenylene substituted by a member of the group consisting of alkyl, alkoxy, aroxy, arylsulfamido, and halogen, and

X stands for the equivalent of an anion of an acid (2) the condensates of (l) with aldehydes, ('3) sulfonates obtained by reaction of a sulfite upon (1), and (4) sulfonates obtained by reaction of a sulfite upon (2).

2. Product according to claim 1 in which the adhesive in the calendered coating layer comprises sodium carboxymethylhydroxyethyl cellulose which has been insolubilizecl by an amino-resin.

3. Photo-sensitive coated paper product capable of bein'g'transformed into a planogi-aphic printing plate by actinic light which comprises'a paper base, on one side of said paper base a barrier-coatsubstantially impervious to water, over said barrier-coat an anchoring coat comprising non-hydrous pigment and insolubilized protein adhesive, over said anchoring coat a calendered hydrophilic coating layer consisting essentially of titanium dioxide pigment and insolubilized carboxymethylhydroxyethyl cellulose adhesive in which the ratio of carboxymethyl groups to hydroxyethyl groups is within the range from 0.3 to 1 and in which the degree of substitution of anhydroglucose units is greater than 0.8, and-over said calendered hydrophilic coating layer a photo-sensitive layer comprising a sulfonate produced by the action of a sulfite upon a member of the group consisting of (1) diazoniurn salts corresponding to the formula R-stands for a member of the group consisting of aryl groups and aryl groups substituted by a member selected from the group consisting of alkyl, alkoxy and carboxyl groups and halogens,

R1 stands for a member of the group consisting of hydrogen and alkyl,

Nstands for nitrogen,

Ar stands for an aromatic residue selected from the group consisting of phenylene and phenylene substituted by a member of the group consisting of alkyl, alkoxy, aroxy, arylsulfamido, and halogen, and

X stands for the equivalent of an anion of an acid,

and (2) the condensates of (l) with aldehydes.

4. Product according totclaim 3 in which the photosensitive diazo sulfonate is one obtained by the action of a .sulfite upon a formaldehyde condensate of a paradiazonium salt of a diphenylamine.

.5. Productas defined in claim 3 in which the non-hydrous pigment is blanc fixe.

References Cited in the file of this patent UNITED STATES PATENTS 2,474,700 Sliflrin June '28, 19.49

2,570,262 Newman Oct. 9, 1951 2,591,309 Slifkin et al Apr. 1, 1952 2,626,866 Neugebauer et al Jan. 27, 1953 2,649,373 Neugebauer et al. Aug. 18, 1953 FOREIGN PATENTS 678,599 Great Britain Sept. 3, 1952

Claims (1)

1. A PHOTO-SENSITIVE COATED PAPER PRODUCT CAPABLE OF BEING TRANSFORMED BY ACTINIC LIGHT INTO A PLANOGRAPH PRINTING PLATE COMPRISING A PAPER BASE HAVING A CALENDERED COATING LAYER THEREON, SAID COATING CONSISTING ESSENTIALLY OF AN INSOLUBILIZED CARBOXYMETHYLHYDROXYETHL CELLULOSE ADHESIVE IN WHICH THE RATIO OF CARBOXYMETHYL GROUPS TO HYDROXYETHYL GROUPS IS WITHIN THE RANGE FROM 0.3 TO 1 AND IN WHICH THE DEGREE OF SUBSTITUTION OF ANHYROGLUCOSE UNITS IS GREATER THAN 0.8 AND A GREATER QUANTITY OF A NONHYDROUS PIGMENT OF THE GROUP CONSISTING OF BLANC FIXE AND TITANIUM DIOXIDE AND A PHOTO-SENSITIVE LAYER OVER SAID COATING, SAID LAYER COMPRISING A PHOTO-SENSITIZER TAKEN FROM THE GROUP CONSISTING OF (1) DIAZONIUM SALTS CORRESPONDING TO THE FORMULA

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