US3161518A

US3161518A - Diazo sensitized lithographic plate comprising a hydrophilic amine formaldehyde intermediate layer

Info

Publication number: US3161518A
Application number: US193338A
Authority: US
Inventors: Elmer F Deal; Isadore M Richlin
Original assignee: Lithoplate Inc
Current assignee: Lithoplate Inc
Priority date: 1957-11-01
Filing date: 1962-05-08
Publication date: 1964-12-15
Anticipated expiration: 1981-12-15
Also published as: DE1169467B; GB907289A

Description

' silicate. v

a support base to' form a water-insoluble hydrophilic subbase or-barrier. Inasmuch as a chemical reaction with a United States Patent f 3,161,518 7 1 DIAZO SENSHTIZED LITHQGRAPHIC PLATE (30M- PRISING A HYDROPHILIC AMHIE FORMALDE- HYDE INTERMEDIATE LAYER Elmer EDeal, West Covina, and Isadore M. Richlin, San

Gabriel, Calif., assignors to Lithoplate, Inc, a corporation-of (laliiornia N0 Drawing. Filed May 8, 1962, Ser. No. 193,338

19 Claims. (Cl. 96-75) This application is a continuation-impart of our application Serial No. 120,188, which in turn wasa continua- I tion-in-part of our application Serial No. 693,814.

g In the manufacture, sale and use of diazo presensitized lithographic plates, various factors are important Among these are uniformity of product, quality of product, ease of'control during manufacture, storage life prior to use, length of run on, the press, and ease of control of the 1 printing on the press; For example, it is well known that commonly used'diazo compounds react with metals and that for this reason, where the lithographic plate is to comprise a metal support sheet, it is necessary to provide a barrier layer or sub-base between the diazo and the metal surface to prevent such reaction. Such barrier layer or sub-base must of course adhere to the support and provide a hydrophilic outer surface to which the light-exposed diazo compound will permanently adhere during printing and to which'the unexposed diazo compound will releasably adhere.

One of the difficulties experienced with diazo presensitized plates having a metal support is that the sub-base may be. discontinuous or the sub-base is so thin that reaction between the metal and diazo resin results. Such imperfections appear as flaws in the printed impressions from the plate. To avoid such conditions requires very carefulco'ntrol of the' various stages in the manufacture of the presensitized plate and in the subsequent handling. Frequently, a high percentage of spoilage results.

Another .difliculty which has. been experienced is that the water attractive character of the sub-base disappears after a time of use on the press and the plates begin to scum. Thus the life of the-plate is shortened or limited by a wearing off or deterioration of the hydrophilic subbase. This may be due tothe thinness of the sub-base or lack of toughness under operation'conditions of the press. In an eifort tominirnize this effect and lengthen the useful life of the plate, the press operator must exercise careful control of operating conditions.

Two sub-base materials that have been proposed are polyacrylic acid and a' siliceous substance such as sodium Inthis case, the material reacts with a metal metal base is'needed to form the sub-base, it follows that the sub-base is necessarily quite thin, since the chemical reaction isconiinedto the interface between themetal base and the sub-base'mate'r ia'l. Especially in the case of the silicate, the 'sub -baseis very thin and may, in fact,

be only a few, molecules thick. It has been our experience that this sub-base fails to prevent the metal from destroying a diazo compound or resin. Further, there is no way of building the sub-base or barrier to a suitable thickness which can adequately protect the diazo material from decomposition. Still further, if a siliceous sub-base becomes dry as by loss of water during storage, thesiliceous subbase deteriorates and becomes ink receptive, making it unsuitable for use as a lithographic surface for lack of a contrasting oleophilic surface.

The present invention provides a lithographic plate base for receiving a diazo compound reactive to light to produce a diazo presensitized lithographic plate which obviates the foregoing objections. In particular, we have found that lithographic plates can be made with especial advantage by applying to a support member or base a novel hydrophilic, water-insoluble sub-base coat or layer formed from modified water-soluble melamine-aldehyde resins. These. materials have been discovered to be uniquely adapted for use on lithographic plates.

related purposes and, in view of their water-solubility, are

easily applied to a plate from a water medium. The

present modified curable melamine-aldehyde resins can be deposited on a backing member as a film or coat to provide after curing a Water-insoluble layer which exhibits a hydrophilic character for lithographicapplications. The subbase or barrier of our lithographic plate is believed not to react chemically with a metal or other type of support member. In any event, a sub-base coat can be deposited having a sufficient thickness to protect an overlay of a diazo material by a single dip of the-plate into awater solution of the melamine-aldehyde resin, followed by a water rinse of the plate. Further, the present modified melamine-aldehyde'resins adhere well to a support member or base and are not stripped therefrom or otherwise damaged during the handling, shipping and use of our lithographic plate. Moreover, the sub-base material-of the present invention permits the diazo compound to form a film thereover which is sufificiently bonded thereto to permit handling and the like of the plate and whose photodecomposition products become tightly bonded to the subbase material after exposure to light.

It is, therefore, a principal object of the present invention to provide an improved plate base receptive to a diazo. compound reactive to light 'to provide a plate for lithographic printing and related uses and to provide a process for making it. i

Another object is to provide an improved sub-base material for such a plate.

.A further object isto provide a metallic lithographic plate base having an improved sub-base coat adapted toreceive a light-sensitive diazo material thereover.

A still further object istoprovide an aluminum lithe: graphic plate base having an improved sub-base material comprising a modified melamine-aldehyde resin'adapted to receive thereover -as.a continuous film a light-sensitive water-soluble diazo material. a

Other objects will become apparent as, the description proceeds.

To the accomplishment of the foregoing and related a hydrophilic character, to which can then be applied an overcoat or film of a light-sensitive diazo materiaL.

Such. materials are suitably hydrophilic for lithographic and For purposes of the invention, the modified melaminealdehyde resin may be a water-soluble alkylated methylol melamine or a polyalkylenepolyarnine-melarnine-aldehyde, or a compatible mixture of the two may be used. The aldehyde preferred and usually employed is formaldehyde, although paraformaldehyde may be used.

Since the alkylated methylol melamines employed are water-soluble, they can be applied to a plate from a preferred aqueous medium. The preparation of an alkylated methylol melamine resin is fully disclosed in U.S. Patent No. 2,715,619 and accordingly is not here disclosed in detail.

In general, melamine and formaldehyde are reacted in a mixture of water and an aliphatic alcohol at a temperature between 50 C. and reflux temperatures and at a pH between 7 and 12. Thereafter, an additional amount of aliphatic alcohol is added to bring the mol ratio of the total alcohol charged to the total water charged to at least about 2:1. The mixture is then further reacted so as to effect substantially complete alkylation under acid conditions and the resulting syrup then neutralized.

The first step of the preparation, that is, the reaction of melamine with formaldehyde in an alcohol-water mixture, is considered to be the most critical, particularly the relative proportions of the formaldehyde, alcohol and water. In this first step, the mol ratio of alcohol to water to be introduced into the sphere of reaction should be between about :1 to about 0.5 :1 and preferably between about 2:1 and 1:1. After this first step has been completed, additional alcohol is added sufiicient to bring the mol ratio of the total amount of alcohol charged to the total amount of water charged to at least about 2:1 to :1 and preferably to about 3:1 to 10:1. The mol ratio of alcohol to formaldehyde should be within the range of 0.4:1 to 5:1 and preferably within the range of 0.5 :1 to 1:1 in the described first step.

The alcohol may be added initially in full amount, or part of the alcohol may be added initially and the remainder may be added after the methylol melamine has formed. In view of the fact that in the reaction of the first step the proportion of formaldehyde, alcohol and water is very critical, the latter course is greatly preferred. The total amount of alcohol employed of course depends on the degree of methylation desired.

The amount of melamine employed in the reaction should be such that the molar ratio of melamine to formaldehyde is within the range of 1:15 to 1:6, respectively, although the preferred range is from 122.5 to 1:4, respectively.

The etherifying alcohol used is not critical as long as the resin prepared in accordance with the procedure outlined in Patent No. 2,715,619 is water-soluble. Accordingly, the simpler alcohols are used such as methyl alco hol and ethyl alcohol. Aliphatic alcohols of more than two carbon atoms result in products of limited watersolubility or water-dispersibility.

The polyalkylenepolyamine melamine formaldehyde resins are also water-dispersible and can therefore be applied to a plate from a preferred aqueous medium. The preparation of a water-soluble resin of this type is fully disclosed in U.S. Patent No. 2,796,362 and therefore is not here disclosed in detail.

According to one method for preparing the resins, melamine and formaldehyde are mixed and heated at about 75 C. under alkaline conditions for about half an hour or until at least about five mols of the formaldehyde have reacted, whichever is longer. The polyalkylenepolyamine is then added and the reaction continued at a pH of about 2 to 7. The resin shows acceptable activity as a bonding agent very shortly thereafter.

The resins are characterized by a content of at least five and preferably more than'six rnols of formaldehyde per mol of melamine. The syrups are distinctly more stable when containing eight mols of formaldehyde per mol of combined melamine. There appears to be no maximum limit to the amount of formaldehyde which the syrup or resulting product may advantageously contain, but only negligible improvement in stability occurs when more than thirty mols are used. Preferably then, the syrup contains between about 8 and 30 mols of formaldehyde per mol of melamine.

If desired, the polymerization may be carried until the resin is on the verge of gelation. In practice, it has been found advantageous to terminate the reaction when the viscosity of the syrup at 35 percent solids and 25 C. is at least 50 centipoises and preferably between about 200 and 500 centipoises so as to obtain a stable watersoluble or water dilutable product of large molecular size while avoiding the danger of gelation.

Alternatively, the melamine and all the formaldehyde and polyalkylenepolyamine may be mixed together and the mixture heated to about C. for a few minutes, after which the mixture is heated at an acid pH until the desired viscosity is obtained. Alternatively still, the melamine and formaldehyde may be reacted at an alkaline pH until a low polymer has formed, after which the polyalkylenepolyamine is added and the reaction continued at an acid pH. In each instance no more than about five mols of formaldehyde need be present during the initial alkaline reaction, and the remainder of the formaldehyde may be added when the mixture is brought to the acid side.

The amount of polyalkylenepolyamine should be sufiicient to supply between about 0.3 and 10 nitrogen atoms per molecule of melamine. Less than this results in the development of a resin of inferior characteristics, either because of insuflicient stability, poor water-dispersibility, or inferior anchoring results. The use of a large amount of polyalkylenepolyamine does not increase the effectiveness of the resin as anchoring agent and results in development of a resin which cures at a considerably slower rate. As a practical matter, it is preferred to employ polyalkylenepolyamine in an amount sufiicient to supply between about 0.5 and 4 nitrogen atoms per molecule of melamine, as in this range a satisfactory stable resin is usually obtained which gives very good anchoring and which cures rapidly.

Any of the simple water-soluble polyalkylenepolyamines and/or their salts may be used. These include such polyamines as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and the corresponding polypropylenepolyamines, as well as 4,4-iminobisbutylamine and 3,3',3"-nitrilotrispropylamine. The compound 3,3- iminobispropylamine has been found to be very effective. In general, any water-soluble, aldehyde-reactive polyalkylenepolyamine may be used as long as the ratio of carbon atoms to nitrogen atoms therein is not greater than about 4: 1.

The higher polyalkylenepolyamines may likewise be used so long as they are water-soluble. Among these are specifically included polyethyleneimine (formed by homopolymerization of ethyleneimine) and the long chain polyalkylenepolyamine formed by reacting a simple alkylenediamine or a simple polyalkylenepolyamine with about 0.6 to 1.5 mols of an alkylene dichloride, an alkylene dichlorohydrin, or epichlorohydrin. Thus, ethylenediamine or trimethylenediamine may be reacted with 1,2-dichloroethane, 1,3-dichloropropane, 1,2-dichloropropane and the like; note U.S. Patent No. 2,616,874. The polyalkylenepolyamines thus formed may have a molecular size so high that 33 percent aqueous solutions thereof have a Gardner-Holdt viscosity of N at 25 C. In addition, there may be used the intermediate sized polyalkylenepolyamines formed by reaction of simple polyalkylenepolyamines with small amounts of suitable dihalides.

Although the teachings of Patent No. 2,796,362 are to the effect that polyalkylenepolyamine melamine-formaldehyde resins prepared as described are converted to a hydrophobic form upon drying a base material which has been contacted by such resins, it has been unexpectedly found that when such resins are further polymerized onto b a support or base as hereinafter described, they not only lose their water-dispersibility, but the resins remain sufficiently hydrophilic and water attractive that they can be used as a sub-base for lithographic plates and the like. Apparently, the resins are hydrophobic in that water does not penetrate them, but We have discovered that films of such resins will carry water on their surfaces and can therefore be used as hydrophilic and oleophobic areas onalithographic plate. v

The terms methylated methylol melamine resin and "polyalkylenepolyamine-melamine-formaldehyde resin as used here and in the claims include, except Where otherwise more specifically defined, such melamine-formaldehyde resins as a Water-soluble (prior to'final cure), fully methylated heterocyclic compound having a saturated ring consisting of only carbon atoms and at least two nitrogen atoms, to which nitrogen atoms are attached only one hydrogen atom; a thermosetting, water-soluble, infinitely dilutable methyl ether of polymethylol melamine, both of such classes of resins being disclosed in U.S. Patent 2,804,402; and co-condensation products of melamine, formaldehyde, urea, and an alkanolamine as disclosed in US. Patent No. 2,917,427. Both of these last cited patents are hereby incorporated by reference.

The type of backing or support member is not critical to the invention. Ordinarily, a metallic support or plate is preferred because of its inherent strength. Metals such as aluminum, zinc, copper, tin, lead, chromium, magnesium, steel-and the like maybe used. Aluminum has been found to give very satisfactory results and is preferred. In the case of metallic surfaces, oxides may be present, either through exposure, to air or through special treatment. For example, in the case of aluminum, the surface may, if desired, be chemically or electrolytically anodized, although this is not necessary.

Other materials may-also constitute the support member, for example, a paper sheet or plate suitably backed, or a paper sheet impregnated with a resin, such as a thermosetting resin like phenol-formaldehyde, can be employed. A heat-resistant resin is preferably employed, since it protects the paper during the heating step which may be used in preparing a lithographic plate in accordance with the method herein disclosed. As used herein and in the claims, the term plate includes a plate, sheet,

film, foil and the like, foil being merely wrapped over a supporting surface.

The light-sensitivev diazo compounds used may be those known in the art. A method of preparing a very satisfactory diazo compound is described in Patent No. 2,679,498 and inPatent No. 2,063,631. This compound is a condensation product of paraformaldehyde with pdiazo-diphenylamine sulfate; Diazo compounds are also described in US. Patent No. 2,667,415 which together with the last two mentioned patents and the diazos disclosed thereby are hereby incorporated by reference;

solution of the modified melamine-aldehyde resin is ap-' plied to .a support or base in-any convenient manner, such as by roller coating, blade coating, dipping, or spraying, and removal of any excess resin as by rinsing; The

concentration of the resin in the dispersion is not critical. 1

As an example, the modified melamine-aldehyde resin may range from about 0.3 percent to about 5 percent of the solution. After applicationzof the solution,.for example by a single dip andrinsing, the water is removed I to deposit'a sub-base coat or film of the resin and to, insolubilize it on the backing member.

Conveniently, this may be 'done by heating the assembly. Any tempera- 6 ture above an ambient temperature may be used, the upper temperature limit being determined by practical considerations, such as avoiding a temperature sufiiciently high to anneal the metal of the plate.

During the heating step and removal of the water, there is further polymerization of the resin, and this aids the insolubiiization and adherence of the resin to a backing member. However, the stage or amount of polymeric growth is not in any sense critical to practicing the invention, except that the resin should adhere Well and resist a water wash so as not to bare the backing plate. The modified melamine-aldehyde resins prepared as described in Patents No. 2,715,619 and 2,796,362 are dissolved in water and applied as previously mentioned. Such resins are partially polymerized or cured at this time. The heating is then conducted at such a temperature within the limits described and for such a time as to drive off substantially all of the water and further polymerize the resin, such that a layer or coat of the resin is deposited having the desired adherence and resistance to a water wash. Such a coat has been surprisingly found to be hydrophilic and will accept a film of a diazo compound. In the case of a polyalkylene-polyamine-melamineformaldehyde resin, the latter is dried beyond its gel point.

Whether the temperature employed is suificiently high and/or the time of heating-is sufiiciently long can .be easily determined by simply observing if the deposited coat of resin has the described desired characteristics.

In practice, heating the assembly from about C. to

210 C. for approximately 3 to 12 minutes has been found to provide good results, although these ranges are not critical.

Instead of heating to deposit the resin coat as just described, it has been found possible to promote the additional polymeric growth by making the aqueous dispersion of the resin more acid. This can be accomplished by adding a salt of a strong inorganic acid and a weak inorganic base to the solution as it overlies the metal base. Salts that may be used include ammonium chloride, ammonium nitrate and ammonium sulfate. Also organic acids such as oxalic acid, gluconic acid, and lactic acid are well suited for this purpose.- Again, whether or not the amount ofisalt or acid added is sufficient to bring about the added polymeric growth can easily be determined by noting if the deposit resin has a satisfactory adherence to the support base and suitably resists a Water wash. In general, the salt or acid is added by dipping in an aqueous solution containing from /2 to 5 percent by weight of said salt or acid. A period of about five minutes at an ambient temperature is suf-. ficient to produce a satisfactory polymeric growth, although these conditions are not critical. The water may be removed by evaporation at an ambient or slightly elevated temperature, or by whirling the plate, and the like.

Following the deposition of the resin coat, an aqueous solution of the diazo compound is applied, as by roller coating, dipping, spraying and, the like. A sufiicient amount of the compound should be used to cover a desired area of the resin coat. The thickness of the diazo film is not critical, a residue of about 0.003 gram per square foot of the resin coat being an accepted practice. Aqueous solutions up to about one percent diazocompound have also been employed. The film is deposited by driving, .off the solvent. Since water isconveniently used as the, solvent, thedrying is ordinarily'performed at an ambient temperature, although temperatures up to the decomposition temperature of the diazo compound can be used, desired.

If desired, the manufacturerof a lithographic plate of the present invention can stop short of the application ofthe diazo compound, "so .that a plate having only the sub-base-material can be shipped to a consumer. The? the diazo'c'ompound at his own 7 consumer can then apply discretion. w

In order to demonstrate the invention, the following examples are set forth for the purpose of illustration only. Any specific enumeration or detail mentioned should not be interpreted as a limitation of the invention unless specified as such in one or more of the appended claims and then only in such claim or claims.

Example I A one percent aqueous solution of a methylated methylol melamine is applied over a support. While the support is still Wet, it is wiped with a squeegee and then dried at 120 F. The assembly is then heated at 150 C. for six minutes. The plate is then immersed in an aqueous solution containing about one percent of a diazo compound, consisting essentially of a condensation product of paraformaldehyde with p-diazo-diphenylamine sulfate, to deposit on the plate a continuous coat of this solution. The plate is then air dried to deposit a' film of the diazo compound thereover. The resulting presensitized plate is then packaged in a non-bleeding, plastic lined, paper backed foil and the margins thereof heat sealed together to permit storage of the plate.

Example II An aluminum plate is grained by treatment with a ten percent aqueous solution of trisodium phosphate and then washed and desmutted. The plate is then dipped into a 0.8 percent aqueous solution of a polyalkylenepolyarninemelamine-formaldehyde resin and then heated at 170 C. for six minutes. A diazo film is applied as in Example I.

Example III A zinc plate is treated with a 1.5 percent aqueous solution of methylated methylol melamine resin formed by reacting melamine, formaldehyde and methyl alcohol in accordance with Patent No. 2,715,619. Mol ratios used are: melamine to formaldehyde 1:2, alcohol to formaldehyde 1:1, alcohol to water initially 3:1, and after the melamine-formaldehyde reaction additional alcohol to maintain this ratio. The plate is heated at 120 F. until dry and then further heated at 160 C. for eight minutes. The methylated methylol melamine resin deposits as a coat over the plate and becomes strongly adhered thereto. The coat is sufficiently hydrophilic for lithographic purposes. The plate is then immersed in a one percent aqueous solution of a diazo compound and finished in the manner described in Example I.

Example IV Example V A copper plate is coated with a 1.2 percent aqueous solution of a polyalkylenepolyamine-melamine-formaldehyde formed by reacting formaldehyde with melamine in a molar ratio of 8:1 in the presence of a sufficient amount of iminobispropylamine to supply about 3 nitrogen atoms per molecule of melamine. The resin is prepared in accordance with Patent No. 2,796,362 and therefore is Water-dispersible.

The modified melamine-formaldehyde resin deposits as a coat over the plate and becomes strongly bonded thereto The coat is sutficientlyhydrophilic for lithographic purposes. The plate is then immersed in a 0.7 percent aqueous solution of a diazo compound. The solution adhering to the plate is reduced to a thin film by whirling the The plate is heated at 120 F. until dry and then further heated at 200 C. for five minutes.

plate as in conventional practice until dry. The plate thus prepared is ready for exposure to light.

Example VI Example VII A procedure is carried out like the procedure of Example V except that the resin used is that designated Resin E in Patent No. 2,796,362.

Example VIII A cleaned aluminum plate is treated in two percent chromic acid at F. for about 45 minutes to form an oxide layer on the surface. It is then treated as in Example I except that a water-soluble, curable ethylated methylol melamine resin is used.

In the foregoing examples, known equivalent materials such as those disclosed herein may be substituted for those stated in the example, the times and temperatures and other parameters being adjusted where and if needed as easily determined by trial and error.

We claim:

1. In a sensitized lithographic plate having a metallic support member, an overlying layer of a diazo compound reactive to light to define printing and non-printing areas and a hydrophilic intermediate coat between said metallic support member and diazo and directly above said support member, the improvement characterized by providing as said coat a resin consisting essentially of a waterinsoluble hydrophilic methylated methylol melamine resin polymer.

2. In a sensitized lithographic plate having a metallic support member, an overlying layer of a diazo compound reactive to light to define printing and non-printing areas and a hydrophilic intermediate coat between said metallic support member and diazo and directly above said support member, the improvement characterized by providing as said coat a resin consisting essentially of a waterinsoluble hydrophilic ethylated methylol melamine resin polymer.

3. In a sensitized lithographic plate having a metallic support member, an overlying layer of a diazo compound reactive to light to define printing and non-printing areas and a hydrophilic intermediate coat between said metallic support member and diazo and directly above said support member, the improvement characterized by providing as said coat a resin consisting essentially of a waterinsoluble hydrophilic polyalkylenepolyamine-melamineformaldehyde resin polymer.

4. In a sensitized lithographic plate having a support member with a metal surface, an overlying layer of a diazo compound reactive to light to define printing and non-printing areas and an intermediate coat between said support member and diazo and directly above said support member, the improvement characterized by providing as'said coat a resin consisting essentially of a modified melamine-formaldehyde resin condensation product polymerized to a water-insoluble hydrophilic state, said resin being selected from the group consisting of a methylated methylol melamine, an ethylated methylol melamine and a polyalkylenepolyamine-melamine-formaldehyde.

5. A plate as claimed in claim 4 wherein said support member consists essentially of a metal selected from the group consisting'of aluminum, zinc, tin, magnesium, lead, chromium, copper and iron.

6. In a sensitized lithographic plate having a metallic support member, an overlying layer of a diazo compound reactive to light to define printing and non-printing areas and an intermediate coat between said metallic support member and diazo and directly above said support member, the improvement characterized by providing as said coat a resin consisting essentially of a water-dispersible alkylated methylol melamine resin condensation product polymerized to a substantially water-insoluble hydrophilic state, said resin being formed from melamine and formaldehyde in a mixture of water and an aliphatic a1- cohol containing from 1 to 2 carbon atoms, said ingredients being initially reacted at a mol ratio of alcohol to water between about 5 :1 and 0.5 1, a mol ratio of alcohol I to formaldehyde between about 0.4:1 to 5:1, and a mol ratio of melamine to formaldehyde between about 1:15 to 1:6, after which said alcohol is added to bring the mol ratio of alcohol to Water to at-least about 2:1 and additional alkylation then efiected.

7. In a sensitized lithographic plate having a-metallic support member, an overlying layer of a diazo compound reactive to light to define printing and non-printing areas and an intermediate coat between said metallic support member. and diazo and directly above said support member, the improvement characterized by providing as said coat a resin consisting essentially of a formerly waterdispersible alkylated methylol melamine resin condensation product polymerized to a substantially water-insoluble hydrophilic state, said resin being formed from melamine and formaldehyde in a mixture of water and an allphatic alcohol containing from 1 to 2 carbon atoms, said ingredient being initially reacted at a mol ratio of alcohol to water between about 2:1 tolzl, a mol ratio of alcohol to formaldehyde bet een about 0.5:1 to 1:1, a mol ratio of melamine to formaldehyde between about 1:25 to 124, after which said alcohol is added to bring the mol ratio of alcohol to water to at least about 2:1 and additional alkylation theneifected.

water-dispersible hydrophilic state.

9. A plate as claimed in claim 8 wherein thepolyalkylenepolyamine of said resin is one selected from the group consisting of diethylenetriamine; triethylenetetra- 4,4-iminobisbutylamine; 3,3'-iminobispropylamine;

mine; tetraethylenepentamine; 3,3,3"-nitrilotrispropylamine; and polyethyleneimine.

10. A plate as defined, in claim 8 wherein the polyalkylenepolyamine reacted with said resin is a watersoluble aldehyde-reactive polyalkylenepolyamine having a ratio of carbon atoms to nitrogen atoms which is not greater than about 4: 1.

11, In a sensitized lithographic plate having a metallic support member, an overlying layer of a diazo compound reactive to light todefine printing and non-printing areas and an intermediate coat between said metallic support member and diazo and directly above said support member, the improvement characterized by providing as said coat a resin consisting essentially of a water-dispersible cationic. polyalkylenepolyamine-melamine-formaldehyde resin condensation product polymerized to a'substantially water-insoluble hydrophilic state, said resin being formed by drying beyond its gel point and containing more than five mols of combined formaldehyde per mol of melamine,

amine being between about 0.3:1 and 10:1.

. 12. 'Ina sensitized lithographic plate having a metallic support member, an overlying layer of adiazo compound reactive to light to define printing and non-printing areas and an intermediate coat between said metallic support member and diazo and directly above said support mem- A her, the improvement characterized by providing as said coat a resin consisting essentially of a cationic polyalkylenepolyamine-melamine formaldehyde resin condensation product polymerized to a' substantially water-insoluble 16 v hydrophilic state, said resin being formed by drying be{ yond its gel point and containing 8 to 30 mols of combined formaldehyde per mol of melamine, the ratio of the number of nitrogen atoms in saidpolyalkylenepolyamine to the number of mols of said melamine being between about 0.5:1 and 4:1. a 13. In a process of preparing a sensitizedlithographie plate by applying to a metallic support member an inselected from the group consisting of a methylated methylol melamine, an ethylated methylol melamine and a polyalkylenepolyamine-melamine-formaldehyde resin, and heating to polymerize said resin to a water-insoluble state and thereby insolubilize the resin as a hydrophilic waterinsoluble coat over said support member.

14. In a process of preparing a sensitized lithographic plate by applying to a metallic support member an intermediate coat and to said coat a diazo compound reactive to light to define printing and non-printing areas, the improvement characterized by applying directly to said support member to form said intermediate coat an aqueous dispersion of a modified curable melamine-formaldehyde resin selected from the group consisting of a methylated methylol melamine, an ethylated methylol melamine and a polyalkylenepolyamine-melamine-formaldehyde, said resin being'in an early state of polymerization, and making said aqueous dispersion more acid further to polymerize the resin to a water-insoluble state and thereby insolubilize the resin as a hydrophilic water-insoluble coat over said support member.

15. A process as claimed in claim 14 wherein said step of making the aqueous solution more acid includes adding a salt of a strong inorganic acid and a weak inorganic base.

16. A process as claimed in claim 14 wherein said step of making the aqueous solution more acid includes adding an acid ingredient selected from the group consisting of ammonium chloride, ammonium nitrate, ammonium sulfate, oxalic acid, gluconic acid and lactic acid.

17. In a process of preparing a sensitized lithographic plate by applyingto a metallic support member an intermediate coat and to said coat a diazo compound reactive to light to define printing and non-printing areas, the improvement characterized by applying directly to said support member to form said intermediate coat an aqueous dispersion of a curable alkylated methylol melamine resin formed by reacting melamine and formaldehyde in a mixture of water and an aliphatic alcohol of from 1 to 2 carbon atoms, said ingredients being initially reacted at a mol ratio of alcohol to water between about 5:1 and 0.5 :1, a mol ratio of alcohol to formaldehyde between about 0.421 to 5: 1, and a mol ratio of melamine to formaldehyde between about 1:15 to 1:6, after which additional said alcohol is added to bring the mol ratio of alcohol to water to at least about 2:1 and additional alkylation then effected, and heating to drive ofl. thewater and further polymerize said resin to deposit the resin as a hydrophilic water-insoluble coat over the support member. 1

V 18. In a process of preparing a sensitized lithographic plate by applying to a metallic support member an inter- "mediate coat and to said coat a diazo compound reactive to light to define printing and non-printing areas, the improvement characterized by applying directly to said support member to form said intermediate coat an aqueous dispersion of a curable alkylated methylol melamine resin formed by reacting melamine and formaldehyde in a mixture of water and an aliphatic alcohol of from 1 to 2 carbon atoms, said ingredients'being initially reacted at a mol ratio of alcohol to water between about 2:1 to 1:1, a mol ratio of alcohol. to formaldehyde between about 0.5:1 to 1:1, 2. mol ratio of melamine to formaldehyde between about 1:25 to 1:4, after which additional said alcohol is added to bring the mol ratio of alcohol to water to at least about 2:1 and additional alkylation then effected, and heating to drive off the water and further polymerize said resin to deposit the resin as a hydrophilic Water-insoluble coat over the support member.

19. In a process of preparing a sensitized lithographic plate by applying to a metallic support member an intermediate coat and to said coat a diazo compound reactive to light to define printing and non-printing areas, the improvement characterized by applying directly to said support member to form said intermediate coat an aqueous dispersion of a partially cured cationic polyalkylenepolyamine-melamine-formaldehyde resin formed by reacting 8 to 30 mols of formaldehyde with each mol of melamine and with a suflicient amount of a poly- References Cited in the file of this patent UNITED STATES PATENTS 2,357,273 Thurston Aug. 29, 1944 2,537,111 Wood Jan. 9, 1951 2,754,279 Hall July 10, 1956 2,778,735 Brinnick et a1. Ian. 22, 1 957 2,796,362 Wooding et al June 18, 1957 2,873,207 Weegar et al Feb. 10, 1959 OTHER REFERENCES Synthetic Resins for Coatings, 1947, Resinous Products and Chemical Co., Philadelphia, pages 66-67.

Claims

4. IN A SENSITIZED LITHOGRAPHIC PLATE HAVING A SUPPORT MEMBER WITH A METAL SURFACE, AN OVERLYING LAYER OF A DIAZO COMPOUND REACTIVE TO LIGHT TO DEFINE PRINTING AND NON-PRINTING AREAS AND AN INTERMEDIATE COAT BETWEEN SAID SUPPORT MEMBER AND DIAZO AND DIRECTLY ABOVE SAID UPPORT MEMBER AND DIAZO AND DIRECTLY ABOVE SAID SUPPORT MEMBER, THE IMPROVEMENT CHARACTERIZED BY PROVIDING AS SAID COAT A RESIN CONSISTING ESSENTIALLY OF A MODIFIED MELAMINE-FORMALDEHYDE RESIN CONDENSATION PRODUCT POLYMERIZED TO A WATER-INSOLUBLE HYDROPHILIC STATE, SAID RESIN BEING SELECTED FROM THE GROUP CONSISTING OF A METHYLATED METHYLOL MELAMINE, AN ETHYLATED METHYLOL MMELAMINE AND A POLYALKYLENEPOLYAMINE-MELAMINE-FORMALDEHYDE.