US2766688A - Planographic printing plate - Google Patents

Description

Get 6, 56 G. HALPERN ET AL 2,766,688

PLANOGRAPHIC PRINTING PLATE Filed Feb. 24, 1955 INVE gkEGO-QY awn? BY W TORS PLANOGRAPHIC PRINTING PLATE Gregory Halpern and Robert Gumbinner, Tarrytown, N. Y., assignors to Polychrome Corporation, Yonkers, N. Y., a corporation of New York Application February 24, 1955, Serial No. 490,268

20 Claims. (Cl. 101-1492) Our present invention is a continuation-in-part of copending applications Serial No. 214,176, filed March 6, 1951, Halpern application Serial No. 378,136, filed September 2, 1953, Halpern application Serial No. 378,135, filed September 2, 1953, and Gumbinner application Serial No. 378,137, filed September 2, 1953, and relates to an improvement in planographic printing, and particularly to a novel plate or sheet having a water impervious coating and a hydrophilic coating bonded to each other in a novel manner and by novel means.

The art of planographic printing depends, as does the older lithographic art, upon the immiscibility of oil and water and upon the preferential retention of a greasy image-forming substance by the image areas, and a similar retention of an aqueous dampening fluid by the nonimage areas.

In the preparation of planographic printing plate surfaces, it was at first customary to employ metal plates as substitutes for the printing stone originally used. The surfaces of these metal plates were grained by an expensive marble operation which rendered the surfaces capable of retaining films of water and becoming thereby grease-repellent.

In addition to its cost in time, labor and equipment, the graining operation is objectionable due to the fact that plates prepared by it must be subjected to etching, gumming and other operations both during the preparation and operation of the plate. Furthermore, satisfactory grained metal lithographic surfaces can be prepared on only a few relatively expensive metals.

In order to eliminate the necessity for the expensive graining operations, and the use of expensive bases, various hydrophilic coatings in combination with metal or non-metal supports were developed. However, these nonmetallic base planographic printing plates have considerable limitations with regard to durability, curling tendency, stretching, cohesive strength, and the number of satisfactory copies obtainable.

Accordingly an object of the present invention is to provide a planographic plate or sheet which is durable, does not curl or stretch, avoids graining, is of the necessary strength to withstand the various printing operations, and which permits a desirable number of copies to be produced.

Another object of our invention is the provision of a novel starch-type printing element which will give truer reproduction, result in a longer running plate, and provide a good base for a presensitized plate.

A further object of the present invention is the provision of a novel planographic printing plate or sheet having a strong wear resistant base, a water impervious coating which does not decrease substantially the original flexibility of the base and a novel hydrophilic coating receptive to grease or water and repellent to either grease or water when the other is applied first.

Further objects will be apparent from a consideration of the following description and the accompanying draw ings wherein- Figure 1 is an enlarged fragmentary cross-section of a planographic printing plate or sheet of the invention.

Figure 2 is an enlarged fragmentary cross-section of another planographic printing plate or sheet.

Figure 3 is an enlarged fragmentary cross-sectional view of another planographic sheet showing the modification of the invention.

Figure 4 is an enlarged fragmentary view of a further planographic sheet showing another modification of the invention.

Figure 5 is an enlarged fragmentary view of another planographic sheet showing still another modification of the invention which employs a light sensitive coating.

Figure 6 is an enlarged cross-sectional view of a simplified short-run plate made in accordance with another modification of our invention.

Referring first to Figure 1, we have here shown a cross-sectional view of our novel planographic printing sheet in which the base 10 is preferably a wet strength kraft type paper or other appropriate cellulose stock having a formation which is uniform and may be impressed or calendered to have a fine surface.

Necessary and inherent characteristics of the paper material which will form the base 10 will be described after a general description of our planographic printing sheet of Figure 1.

The paper or other flexible base 10 is coated on both sides with water impervious coatings 12, 22 preferably a ureaformaldehyde material, so applied that it will be bonded to the paper base by impregnation of a portion thereof to the extent of approximately .001" below the surface as shown at 12a and 22a and extending above the original surface of the paper base on both sides totaling an amount of the order of .001", as shown at 12 and 22.

A hydrophilic layer 14 containing starch carbamate is coated on the water impervious coating or surface 22.

A nitrocellulose layer 15 is coated on impervious layer 12 to reduce curling tendencies. However, it is also possible to utilize any other suitable anti-curling backing.

In the making of a planographic printing sheet in accordance with our invention, we have found that several necessary and inherent characteristics must be present in each of the components; base layer 10, water impervious coatings 12 and 22, the hydrophilic layer 14 and layer 15. In the following we shall describe our invention in connection with a flexible paper base.

Paper base 10 In accordance with the present invention various bases may be used for planographic printing plates as metal, cloth, plastic, cellulose acetate or paper for base 10.

It is essential that base 10, where a paper is used, be of relatively long fibres, such as kraft, having a thickness of .003 to .010 inches depending upon the printing press on which it is to be used. The most suitable thickness is between .004 and .008 inch, the thicker paper being used to provide for longevity of use and the thinner paper for short runs.

One of the main considerations in selecting the stock is the amount of wear and tear on the plate due to the pressures of the blankets, the ink rolls and the water fountain roll. The base paper is hung on either hooks or pegs. These give rise to various tensile stresses which can cause distortion. This, coupled with the additional fact that lithographic offset printing usually calls for long runs, requires the use of strong bases.

Paper itself initially has poor resistance to moisture. The moisture stretches, wrinkles and reduces the tensile strength of the paper.

Wet strength paper is a paper which is treated chemically or in any way so as to reduce the deleterious effects of water upon the paper.

We have discovered that paper treated with a 22 /2% by weight melamine formaldehyde resin based on the weight of fiber in the paper mill will provide desired wet strength for planograph printing reducing these effects of moisture. The melamine formaldehyde resin is applied as a part of the paper manufacturing process.

Due to the mechanical stresses exerted by the prongs and hooks, the raw stock should be of such a nature as to have a good fibre distribution in both directions with and against the grain.

Preferably, the paper should be made on a Fourdrinier with an equal strength or close to an equal strength in both directions.

The raw stock should be resistant to brittleness caused upon the application of heat, etching or chemicals. A pure cellulose paper, of a cellulose sulphate stock, would be preferred for base 10. The formation should be of uniform type and preferably compressed so as to have a very fine surface.

The paper as thus formed in accordance with the above has substantially no imperfections or non-uniformities on the surface or the interior and is calendered as hereinafter described to give it the desirable gloss or texture and density to keep it from being too spongy.

Waterproof layers urerzformaldehyde 12, 22

The wet strength paper base it) formed in accordance with the above described procedure is next coated with the water impervious layers 12 and 22. This waterproof composition may be ureaforrnaldehyde solution or emulsion or one of the following: melamine formaldehyde resin, nitrocellulose, neoprene, nylon, phenolformaldehyde resin, vinyl, alkyd, polyester or rubber hydrochloride resins.

The specific ureaformaldehyde is a 65% solid dispersion of a low molecular weight ureaformaldehyde in water. This material polymerizes after being applied to the paper by the action of heat and the loss of water. The ureaformaldehyde coating is calendered to a uniform caliper and desired finish depending on the caliper and finish of the original stock.

In addition, further curing or polymerization and flowing of the ureaformaldehyde occurs at the calender when heat is applied to the rolls. The paper is contacted with hot calender rolls from 3 to 10 seconds at 170 F.

Ureaformaldehyde coated paper is aged for two to seven days in order to permit stabilization of setting so that top coats will not curl the base paper when applied and also so that ureaformaldehyde will not dissolve in the top coat solution. If cured for too long a period, the top coats will not bond. In fact, in order to provide a more effective bond with the top coat, it is often desirable to use a second ureaformaldehyde prime coat. The hydrophilic starch carbamate coating is then applied to this second prime within 48 hours. This embodiment is set forth in more detail in Halpern patent application Serial No. 378,136, hereinbefore referred to.

Ureaformaldehyde in a thin film is more flexible than a thick film. The surface must be coated with ureaformaldehyde in addition to the ureaformaldehyde absorbed inasmuch as the paper would be still affected by moisture without the surface coat, as in Figure 2. Thus, too little ureaformaldehyde results in a paper affected by moisture, Figure 2, and too much ureaformaldehyde results in a paper that is too brittle. It should be noted, however, that the ureaformaldehyde may be dispensed with in the plate of Figure 6, hereinafter referred to in more detail, in which the hydrophilic coating contains a large amount of melamineformaldehyde.

The preferred ureaformaldehyde may be combined with a catalyst to hasten the polymerization of the ureaformaldehyde. As described, the ureaformaldehyde penetrates the base 10 at 22c and 12a to a depth of about .001" on each side of the paper base 10 and extends above the surface of base 10 to a thickness of about .0005," as

at 12 and 22 so that thickness of the paper base is increased by about .001". The weight is then approximately 1 to 7 of dry ureaformaldehyde to paper.

The extent of saturation by the coating which in turn determines the brittleness of the base is controlled by the absorbency of the raw stock; the viscosity of the solution; and by the time the coating takes to set. Material that will bend around at least a mandrel 4:", on which it is turned, without cracking, has the desired flexibility.

Hydrophilic layer 14 To the paper base 10 thus formed and made water impervious by coating layers 12, 22, 12a and 22a, the hydrophilic coating 14 is now applied as hereinafter described. The hydrophilic layer 14 is a composition of a starch carbamate, fillers, a hardener, water and a wetting agent, being .0003 to .0005 inch thick. One or a multiplicity of coating may be used.

We have discovered that a marked improvement in grease and water selectivity is secured by the use of starch carbamate. The use of starch carbamate in the hydrophilic layer has been found to be particularly advantageous. For one thing, the starch carbamate gives much better balance; that is, it is highly grease receptive when,

dry and grease repellent when wet, thereby providing an improved balance between the hydrophilic and hydrophobic properties. Moreover, it is readily hardened to make it water receptive, gives much truer reproductions LIL.

To the starch carbamate is added a filler consisting of clays and/ or pigments. The fillers fulfill specific purposes, giving porosity, absorbency and imbibition and thus acting as a trap for the greasy ink as well as assisting in the necessary absorption of wetting fluid from the Water fountain roll.

An example of medium oil absorption filler is titanium dioxide which is added 25 parts to 10 parts of starch carbamate by weight. 'Another filler is china clay which can be used parts to 10 parts of starch. Still another filler is a combinaiton of titanium dioxide and china clay which can be used 25 parts of titanium dioxide and 30 parts of china clay to 20 parts of starch. The titanium dioxide or antimony oxide hardens, adding to grease receptivity. The hardening of the titanium dioxide, however, makes corrections ditficult. China clay, on the other hand, softens the coating and makes erasures easy. Blancfixe, silica, bentonite or carbon black may be used as substitutes for the china clay.

Incorporating some carbon black 2% solution will allow accelerated curing at lower temperature using a system of infra-red bulbs as the carbon black absorbs the heat.

The water added to the solution is a distilled or d,6-

ionized water to assure a given pH value of the emulsion and freedom from unwanted impurities.

There is added to the above solution another solution consisting of 1 /2 parts of oxalic acid, parts of glyoxal, 10 parts of water, basing everything on 10 parts of starch carbamate. A small amount of a detergent such as Tergitol 7 is also added to insure spreading of the coatrngs.

A typical formulation is as follows:

The hydrophilic layers 16 and 17 consist of the following mixture in the proportions indicated:

30 lbs. dry starch carbamate 600 lbs. water 3 lbs. ozs. titanium dioxide 4 lbs. 11 /2 ozs. china clay To this is added, just before using, the following mixture in the proportions indicated:

107 gm. oxalic acid 2520 cc. water 35.4 gm. Parez resin 611 (melamine formaldehyde) 71 cc. Tergitol (sodium alkyl sulfate surface) active agent The starch carbamate serves as the hydrophilic material. Utilization of the carbamate derivative allows for a greater grease receptiveness than using starch per se, and a marked improvement in grease and Water selectivity is secured.

The inclusion of the Parez No. 611 melamine-formaldehyde resin in the starch carbamate layer produces a particularly desirable plate as the melamine resin assures that the plate will remain water-receptive when hardened.

The starch carbamate coated papers as described above store well, have good hydrophilic qualities, hold moisture on the press, are easily cleaned, have high cohesive strength and yield a large number of good copies.

Backing layer 15 The plates may be coated at 15 on the back 12 to prevent curling. One of the reasons for curling is the fact that one side may, by the nature of the coating process or because of unforeseeable causes, have a slightly thicker coating than the other side and when the coating contracts, the plate warps. Starch tends to curl papers less than other hydrophilic coatings, as for example, polyvinyl alcohol. A starch carbamate therefore is also useful as the back coating 15 to stiffen the base slightly and prevent curling.

Modifications In one embodiment of the present invention we prefer to utilize two thin coats 16 and 17 as illustrated in Figure 3 in preference to one thick coat.

Utilizing two thin coats 16 and 17 helps to cover flaws, gives more uniform drying throughout the final thickness, and provides better depth of printing surface. The first coat 17 is primarily a bonding coating and not necessarily a printing coat.

In bonding to this partially cured ureaformaldehyde 22, the coat 17 hardens somewhat and it is only in the second coat 16 that complete control is achieved as the urea-formaldehyde 22 is by this time cured.

The second coat 16 may differ from the first coat 17 in an additional manner by having the filler proportioned differently. For example, titanium dioxide 15 parts, osmo-kaolin 18 parts. Although the original composition of the two coats may be the same, the application of the second coat 16 allows some of the colloid and water to seep into the first coat 17 essentially changing the composition of the second coat 16.

Where the plate on which the information to be printed is recorded by a typewriter, the base must be a thin supple paper to provide the necessary flexing required of typewriter paper. There are many applications where several plates are put in a pack, all to be at least in part typed up together through the used carbon. For example, they have common information and also in dividual information. The final sheet will then have information from several different lithographic plates. In order to have good transfer of copy through a system pack, the plate must be thin and supple and transfer the character of the type. Hence the paper would be as thin as possible, i. e., .004 inch or even thinner, and at the same time have the strength necessary for offset printing.

There are applications wherein a single plate is typed, as for example, letters, advertising, etc. The plate would then be more rugged.

The multiple stock, as above, should have a weight of approximately 60 pounds of 24" x 36"500 and the single plate direct image stock, as above, should be between 70 and pounds for the same dimensioned paper.

Figure 4 illustrates an embodiment wherein two hydrophilic coatings are used as referred to in Halpern copending application Serial No. 378,135, filed Septembr 2, 1953. A first hydrophilic coating 24 is coated on the plate 20 on the side away from the tendency to curl; in this case, on coating 22. The coating 24 is a polyvinyl alcohol coating having the following composition:

Polyvinyl alcohol 35 pounds. Water 600 pounds. Titanium dioxide 4pounds 1 ounce. China clay 5 pounds.

Oxalic acid 50 grams.

Polyvinyl alcohol coatings bind satisfactorily to the flexible urea formaldehyde coating 22 as described above.

A second hydrophilic coating 25 is coated over the coating 24. The coating 25 is of essentially a starch carbamate composition and similar to the coatings 14, 16 and 17 of the planographic printing plates described above in reference to Figures 1 to 3.

The formulation of the hydrophilic layer 24 consists of dry starch carbamate 30 pounds, water 600 pounds, titanium dioxide 3 pounds 15 ounces, china clay 4 pounds 11 /2 ounces, to which is added just before using oxalic acid 107 gm., water 2520 cc., Parez resin 607 35.4 gm. and Tergitol 71 cc.

Figure 5 illustrates a plate where the hydrophilic layer 30 is the base for a photographic coating of the type referred to in Gumbinner copending application Serial No. 378,137, filed September 2, 1953. Here the paper base 10 is covered with first prime coats 12 and 22 which in turn may be covered with second prime coats, applied to both sides of the plates, 28 and 29. These coats have fillers in them. The first prime coat has walnut shell flour, in addition to the ureaformaldehyde. In the second prime coat, we add an amount of titanium dioxide approximately 50% of the ureaformaldehyde. The hydrophilic layer 30 is then placed on second prime coat 28 and serves as a suitable base for the application of lightsensitive compound.

There are two types of photographic plates; the presensitized plate and the customers sensitized plate. The customers sensitized plate utilizes an application of sensitizing material on the plate before exposing the negative. The presensitized plates, however, are exposed directly through the negative without any previous treatment. The customers sensitized plate solution applied is ammonium dichromate and egg albumen, prepared from an egg albumen solution of approximately a 9 percent solution of egg albumen in water and ammonium dichromate of approximately a 25 percent solution in water, the ratio of egg albumen to ammonium dichromate being approximately 3 to 1 by Weight in the final sensitizing solution.

In the pre-sensitized plate, the application of a coating of a light sensitive diazo compound 31 to the surface of the hydrophilic layer 30 has been found to be particularly advantageous. Instead of having a laminated plate in which the light sensitive material is in the form of a film 7 which has been glued to the surface, the diazo liquid may be simply applied to the surface of the plate.

When films were applied as in the prior art, the expansion and contraction of the paper was always found to be different from that of the film and, therefore, there was a tendency for the film to separate from this paper base.

The diazo compound applied as the light sensitive surface provides an increased sharpness in the character of the half-tones due to the closer contact which the chemical has with the paper than can be obtained by a film through which the light must pass.

In the preferred form of my invention this light sensitive material is a formaldehyde condensation product of diazo diphenylamine sulphate. This is applied as a coating of the following solution:

100 parts of water 2 parts of this diazo .65 part of zinc chloride part of wetting agent (10% solution Saponin) This compound is sprayed on to a pair of squeeze rolls made of rubber about 4" in diameter between which the plate is passed.

The resulting coating is of micron depth, less than one ten-thousandth of an inch and results in a reduction of the light fraction.

Accordingly, there is less tendency for the light rays to angle off as occurs where laminated coatings are employed. Because of the thinness of the light sensitive coating, the negative is so close to the base that light does not have a chance to spread. This results in an image of finer composition and increased sensitivity. Moreover, with the novel coating as here described, a single application of the chemicals desensitizes the non-printing areas making the image highly ink receptive and visible.

After the present plates have been exposed, it is free from light or grease susceptibility. This builds up a high grease-receptive coating which makes the image visible on the plate.

More specifically, the diazo may be the condensation product of paraformaldehyde and paradiazodiphenylamine (4 parts of formaldehyde to 30 parts of paradiazodiphenylamine by weight).

Referring now to Figure 6, it can be seen that a simple short run plate may be made in which the starch carbamate-melamine formaldehyde, coating 17, hereinbefore referred to, is applied directly to a wet strength or surface treated sizing paper. In this modification, however, it is necessary to employ a considerably larger quantity of the Pare-z No. 611 melamine formaldehyde resin. Thus, in the formulation referred to previously, the amount of melamine formaldehyde would be increased 10-40 times to about 350l500 gms., or to about 2 to percent of of the weight of dry starch carbamate. In this modifica tion, one or both sides may be coated with the starch carbamate-melamine-formaldehyde layer, as desired. If only one side is coated, it would be advisable to coat the opposite side with an anticurl compound.

Methods of manufacture Our invention is capable of embodiment in many different forms of processes for producing the above described plates, and we shall choose, for the purpose of H ture of ureaformaldehyde with flour, which may be walnut shell flour8% by weight. The dry material is mixed with water in approximately the proportion of 40% ureaformaldehyde dry to water by weight. To that may In actual practice we have found that the catalyst acts immediately to cause a thickening and change of the viscosity of the ureaformaldehyde. This thickening occurs before the coating has been applied and is un-' desirable. The viscosity of the ureaformaldehyde alone is 13 seconds at 27 C. with a 150 gram load using a Stormer viscosimeter. In order to predetermine the viscosity of the mixture ideally, each drop of ureaformaldehyde would be mixed immediately preceding its ap plication to the paper. Mixing the ureaformaldehyde with the catalyst, for example, two hours prior to application causes the viscosity to double in this time. An additional problem is presented by the fact that some of the solution remains in the coating machine when the new batch is added. Accordingly we propose to effect a continuous mixing just before the coating.

In the coating process, the ureaformaldehyde penetrates to about .001 inch on each side of the paper and the remainder remains on the surface to a height of about .0005 inch.

The paper is then squeezed, polished and dried between about C. and 0, thereby partially curing the resin.

When the resin is in the partially polymerized state, the paper is calendered and brought to the desired finish. The calendering smooths out ridges in the partially cured paper by melting and plasticizing the resin, forcing it into the paper and resulting in a solid sheet of ureaformaldehyde without grain.

The waterproofed paper may then be aged if desired, after which the hydrophilic coating is applied. The hydrophilic coating comprises a starch carbamate, prefer-. ably glucosan 2-monocarbamate, distilled water, fillers, a

hardener, and a wetting agent.

The hydrophilic coating is supplied either in solution The dry powder is mixed in" After the grinding in the mill there is added to thesolution another solution consisting of 1 parts of oxalic acid, 10 parts of glyoxal, 8 parts of monoethyl ether of ethylene glycol, 10 parts of water, basing everything on ,7

10 parts of starch carbamate.

The above is prepared as follows: water is heated to F. and oxalic acid is added and dissolved. This warm solution is added to the main cold ground solution.

Following this, the monoethyl ether of ethylene glycol and glyoxal are added to the body of the solution.

The glyoxal is a tanning or hardening agent which tans the colloid. The oxalic acid also functions as a mild. hardening agent for the colloid and furnishes a source of l acidity which is necessary for the non-emulsification of inks.

The ureaformaldehyde is mixed for.

The filler is dispersed in the starch The colloid mill utilizes the shearing action' The monoethyl ether of ethylene glycol helps spread the coating and assists in the smooth setting during the last stages of drying and curing.

If the plates are treated to have photographic coats, further coating operations are necessary. There are two types of photographic plates; the pro-sensitized plate and the customers senistized plate. The customers sensitized plate solution applied is ammonium dichromate and egg albumen; the egg albumen solution is approximately a 9% solution of egg albumen and water and the ammonium dichromate is approximately a 25% solution; these are mixed into a single solution with the ratio of egg albumen to ammonium dichromate being approximately 3 to l by weight. The customers sensitizing solution is applied to the plate by means of absorbent cotton swab which achieves an even coating. The plate is then dried utilizing a blower or fan and subsequently exposed to a source of high intensity light in combination with the negative. The source of light may be carbon arc lamp, sun lamp, photoflood, or any other means which applies ultra-violet radiation.

The plate is held in contact with the negative by means of a vacuum frame or a pressure contact frame. After exposure, the plate is rubbed with a grease-receptive ink, usually of an asphaltum base. It is then placed under running Water and washed until the unexposed egg albumen and developing ink are washed off leaving the hardened sections of the plate which correspond to the light struck areas which were patterned by the negative. The plate is then gummed and is ready for the press.

The pre-sensitized plate is a plate exposed in a similar manner as the customers plate but needs no sensitizing step. After exposure, the pre-sensitized plate is wiped down with a solution of either plain water or gum solution and then is ready for the press. It is thus much faster.

In the foregoing, we have described our invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of our invention Within the scope of the description herein are obvious. Accordingly, we prefer to be bound not by the specific disclosure herein, but only by the appending claims.

We claim:

1. A planographic printing plate comprising a base of wet strength paper, a waterproof resinous coating on said paper and a hydrophilic layenon the said waterproof coating, said hydrophilic layer comprising starch carbamate.

2. A planographic printing plate comprising a base of wet strength paper containing a melamine formaldehyde resin, said base being of the order of .004 inch to .01 inch; a waterproof coating on each side, said waterproof coating being of the order of .0005 to .001 inch thick and impregnating the said paper base; a hydrophilic coating containing starch carbamate on one side of said waterproof coatings and a coating of curl resisting material on the other side of said waterproof coatings.

3. A presensitized planographic printing plate comprising a base of wet strength paper; a waterproof resinous coating on said paper, a hydrophilic layer on the said waterproof coating, said hydrophilic layer comprising starch carbamate and having superimposed thereon an organic light-sensitive material which becomes waterinsoluble and ink-receptive upon exposure to light.

4. A presensitized planographic printing plate comprising a waterproof paper base, a hydrophilic coating on said base containing starch carbamate and, having a surface comprising a film of light sensitive diazo compound.

5. A presensitized planographic printing plate comprising a waterproof paper base, a hydrophilic coating on said base containing starch carbamate therein, and a surface comprising a film of formaldehyde condensation product of diazo diphenylamine sulphate.

6. A presensitized planographic printing plate comprising a waterproof paper base, a hydrophilic coating containing starch carbamate thereon, and a surface coating comprising a film of light-sensitive diazo compound.

7. A planographic printing plate comprising a base of wet strength paper, a Waterproof resinous coating on said paper and a hydrophilic layer on said Waterproof coating, said hydrophilic layer comprising a mixture of starch carbamate and melamine formaldehyde resin.

8. A planographic printing plate comprising a base of wet strength paper containing a melamine formaldehyde resin, said base being of the order of .004 inch to .01 inch; a Waterproof coating on each side, said waterproof coating being of the order of .0005 to .001 inch thick and impregnating the said paper base; a hydrophilic coating containing a mixture of starch carbamate and melamine formaldehyde on one side of said waterproof coatings and a coating of curl resisting material on the other side of said waterproof coatings.

9. A planographic printing plate comprising a base of wet strength paper containing a melamine formaldehyde resin, said base being of the order of .004 to .01 inch; a waterproof coating on each side, said Waterproof coating being of the order of .0005 to .001 inch thick and impregnating the said paper base; a hydrophilic coating containing starch carbamate on one side of said waterproof coatings and a coating of curl resisting material on the other side of said waterproof coatings.

10. A printing plate having a water impervious paper base and a plurality of hydrophilic layers superimposed on each other and mounted on said base, said hydrophilic layers comprising starch carbamate and titanium dioxide.

11. A planographic printing plate comprising a base of wet strength paper, a waterproof resinous coating on said paper and a, hydrophilic layer on the said coating, said hydrophilic layer comprising starch carbamate, melamine formaldehyde resin and a filler.

12. A planographic printing plate consisting of a wet strength paper and a hydrophilic layer on said paper comprising starch carbamate and melamine formaldehyde resin.

13. A planographic printing plate consisting of a Wet strength paper coated with a hydrophilic layer comprising starch carbamate and melamine formaldehyde, the proportion of said melamine formaldehyde to starch carbamate being between 2 to 15 percent by weight.

14. A printing plate comprising a dense, flexible base and a coating on said base containing starch carbamate and a filler.

15. A printing plate comprising a paper base and a gtlilating on said base containing starch carbamate and a 16. A planographic printing plate comprising a water impervious paper base and a hydrophilic layer mounted thereon, said hydrophilic layer containing starch carbamate.

17. A presensitized planographic printing plate comprising a dense, flexible base, a coating on said base containing starch carbamate and superimposed upon the said coating an organic light-sensitive material which becomes water-insoluble and ink-receptive upon exposure to light.

18. A planographic printing plate comprising a dense, flexible base and a hydrophilic layer on said base containing starch carbamate and melamine formaldehyde resin.

19. A planographic printing plate comprising a paper base and a plurality of hydrophilic layers on said base and superimposed on each other, each of said layers containing starch carbamate.

20. A planographic printing plate comprising a paper base treated with melamine-formaldehyde resin, a Waterproof coating on said base, a first hydrophilic coating on said waterproof coating and a second hydrophilic coating superimposed on said first hydrophilic coating, said first hydrophilic coating being of a polyvinyl alcohol composition having good bonding to said waterproof coating and 11 to said second hydrophilic coating, said second hydrophilic coating being a starch carbamate compcsition.

References Cited in the file of this patent UNITED STATES PATENTS 2,309,027 Toland et a1 Jan. 19, 1943 2,313,848 Toland et a1 Mar. 16, 1943 2,327,380 Toland et a1 Aug. 27, 1943 7 12 7 Van Epps May 9, 1944 Siifkin June 28, 1949 Worthen Dec. 19, 1950 Gaver et a1 Ian. 23, 1951 Wolff Aug. 7, 1951 Wood Mar. 18, 1952 Neugebauer et a1 Aug. 18, 1953

Claims (2)

14. A PRINTING PLATE COMPRISING A DENSE, FLEXIBLE BASE AND A COATING ON SAID BASE CONTAINING STARCH CARBAMATE AND A FILLER.

17. A PRESENSITIZED PLANOGRAPHIC PRINTING PLATE COMPRISING A DENSE, FLEXIBLE BASE, A COATING ON SAID BASE CONTAINING STARCH CARBAMATE AND SUPERIMPOSED UPON THE SAID COATING AN ORGANIC LIGHT-SENSITIVE MATERIAL WHICH BECOMES WATER-INSOLUBLE AND INK-RECEPTIVE UPON EXPOSURE TO LIGHT.

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