US2561354A - Lithographic process - Google Patents

Description

Patented July 24, 1951 LITHOGRAPBIC PROCESS James Finno, Brooklyn, N.Y.

No Drawing. Application February 3, 1947,

Serial N0. 726,197

(Granted under the act of March 3, 1883. as

' amended April 30, 1928; 370 O. G. 757) 19 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without payment to me of any royalty thereon.

This invention relates to a planographic offset printing process and more particularly to an improvement in parchment planographic printing plates, an improved etching solution for preparing such plates for printing and an improved dampening solution for application to the parchment plates when employed in planographic duplicating machines.

This application is in part a continuation of application Serial No. 596,718, filed May 30. 1945, now abandoned.

The standard commercially available equipment for carrying out the process of planographic offset printing consists, briefly, of a duplicating machine provided with an impression cylinder, 9. moistening roll, an inking roll and a rubber transfer cylinder. A planographic printing plate having an ink receptive image formed on the surface thereof in any suitable manner is mounted on'the impression cylinder. During rotation of the impression cylinder the printin plate first comes into contact with the moistening roll which is saturated with an inkrepellent solution. The property of the nonimage portion of the surface of the printing plate is such that it is uniformly wetted by the inkrepellent solution, while the ink formin the image portion of the printing plate is unwetted by the solution. As the impression cylinder continues to rotate, the printing plate comes into contact with the inking roll which applies a lithographic or grease base type of ink to the image on the printing plate. The non-image portion of theprinting plate previously wetted with an ink-repellent solution will not pickup the ink. Further rotation of the impression cylinder. brings the printing plate into contact with a rubber transfer roll which accepts the ink from the entire image. The transfer roll is then rotated over a sheet of paper and the ink portions which correspond to the original image are deposited upon the paper to provide a final copy.

The printin plates employed in the process outlined above were, in the earlier stages of development of the process, photographically prepared metal or cellulose plates. While such plates were, and still are, satisfactory, the cost thereof and the expense of preparing them are obvious disadvantages. In recent years, the trend has been to replace such plates by employing paper printing plates or masters and to tievelop simple, direct-and inexpensive methods of formin an image on the surfaces thereof. This trend is illustrated by the patents granted to William B. Wescott, Patent No. 2.134.165, dated October 25, 1938, Patent No. 2,205,998. dated June 25, 1940; and Patent'No. 2.348.771, dated May 16. 1944. These patents are directed generally to a composite paper printing plate consisting of layers of cellulosic material adhesively or otherwise bonded. One of the layers which serves as a printing surface is formed from a dense amyloid parchment paper. The remaining layer is formed from a heavy, water-repellent paper and serves as a backin or support for the water-absorptive parchment layer. More I recently a patent granted to Arthur Garrett, Patent No. 2,363,311, dated November 21. 1944. disclosed an unbacked printing plate formed from supercalendered amyloid parchment paper. Images may be formed on these printing plates by the simple expedient of depositing an imageformin ink thereon with a pen or pencil but preferably with a typewriter provided with a ribbon saturated with an image-forming ink. The paper printing plates thus prepared for printing on an offset duplicating machine are usually treated with ink or scum-displacing solutions since plates of this type are easily smudged either in handling or during the printing operation. These scum-removin compositions usually comprise aqueous solutions of glycerine and contain small quantities of phosphates and gum arabic. The chemistry of the action of such solutions has been thoroughly studied and it is known that, heretofore solutions of this type did not improve the quality of the image, per se. In addition to scum-removing solutions it has been necessary to employ dampening or fountain solutions with these plates to render the non-image portion of the printing plate ink-repellent. Such solutions consist essentially of aqueous .solutions of glycerine and are applied to the plate with moistening rolls as previously described.

The foregoing paper printing plates have met with commercial success but are. albeit, subject to numerous objections. The multi-ply type of paper printing plates are expensive and un-. economical for preparing a small number of copies; The composite .or multi-ply printing plates lack flexibility and may not be erased satisfactorily. It has been found that multipiy' printing plates which have been erased will. upon being moistened with standard ink-repellent solutions. demonstrate swelling in the areas which have been erased with the result that images subsequently applied to the erased areas are broken by distension or bucklin of the swollen surface. In the case of single-ply supercalendered amyloid parchment plates erasures produce a similar type of failure. This latter action is not understood but it is believed that supercalendering forms a tough skin on the surface of parchment paper so treated which is broken by the erasing action and that when the latter occurs the fibers, which are uncoated or the coatings of which have been broken, absorb water and swell. Aside from the above obJections, the principal disadvantages which both multi-ply composite sheets and supercalendered sheets have been found to possess lies in the lack of permanency of the images formed thereon.

This has been found to be due to the surface characteristics of the paper employed and not merely to any property of the image-forming ink used. For example, various commercially available image-forming inks have been applied to both multi-ply sheets and supercalendered parchment sheets and it has been determined that such plates will last in storage no longer than approximately three days at which time the images were found to have disintegrated completely and become useless. The images formed on such plates. furthermore, failed to last as long as the paper printin plate upon which they were deposited when employed immediately-following preparation in an offset printing process.

This invention is an improvement over the inventions disclosed in the above patents and is based essentially on the use of a single-ply, unsized and substantially uncalendered parchment paper in forming the planographic printing plate. The plates are thus formed of an inexpensive parchment paper stock which is not coated with any sizing material, does not contain any fillers, pigments or the like which increases the transparency and, furthermore, requires no backing or support. The parchment paper stock employed must be substantially uncalendered for the purposes of this invention since the absence of calendering imparts flexibility to the plate formed therefrom and provides a slightly rough surface which possesses an afllnity for image-forming ink not heretofore demonstrated by any paper planographic printing plate. The lack of calendering of the parchment paper stock, furthermore, provides a printing plate which may be erased with a minimum loss of the original surface characteristics of the plate. The use of these parchment plates in standard duplicating or printing machines is limited, however, in that the dampening solution forming a part of this invention must be employed therewith to produce the desired result and, if the use of a scum-removing etching solution is desired, only the etching solution forming a part of this invention may be used in conjunction with the parchment plates and dampening solutions disclosed herein.

The etching or scum displacing solutions forming a part of this invention are applied to the plates in the usual manner prior to, their use in the printing process. The etching solution consists of an aqueous solution of glycerine and preferably a minor amount of sodium sulfate. The most essential components of the solution, however, are sodium thiosulfate and citric acid. A minor portion of these latter ingredients are dissolved in equal quantities in the solution and serve to impart permanency to the printing plate image. The dampening solution which forms a part of this invention consists of glycerine, a

small amount of gum acacia and as essential ingredients small amounts of sodium sulfate and boric acid dissolved in water. This solution is applied to the printing plate by the moistening roll of the duplicating machine and renders the non-image portion of the uncalendered parchment plate ink-repellent without causing swelling or buckling.

As an additional feature, the parchment plates of this invention may be provided with a preprinted image on the printing surface thereof consisting of a quick drying synthetic resin base ink. This image may be applied simply with a metal offset planographic printing plate and the image formed dries without offset practically instantaneously. Imprints of marginal scales or other guides may be applied to the reverse side of the printing plate as a reversed image employing a water soluble or other printing or nonprinting ink. The transparency of the parchment paper plate permits the reversed image on the non-printing face of the plate to be viewed through the body of the plate from the printing surface thereof and thus provides a visual copy layout guide in the form of an unreversed or normal image.

It is, therefore, the principal object of this invention to provide an inexpensive flexible cellu losic planographic printing plate formed of a single ply, unsized, unbacked, and substantially uncalendered amyloid parchment characterized by low gloss and low smoothness.

Another object of this invention is to provide an unbacked, substantially uncalendered parchment planographic printing plate having an image-forming ink deposited thereon which may be stored for extended periods of time without image deterioration or loss of the printing quality thereof.

Another object of the invention is to provide a single-ply, substantially uncalendered parchment printing plate having a pre-printed image formed from a quick drying synthetic resin image-forming ink.

Another object of this invention is to provide a single-ply, substantially uncalendered parchment printing plate which may be erased without altering the original surface characteristics of the plate.

Still another object of this invention is to provide a quick drying, image-forming synthetic resin ink which may be applied to a single-ply, substantially uncalendered parchment printing plate by standard offset methods without spreading or feathering.

A further object of this invention is to provide a planographic printing plate scum-removing etching solution which has the property of hardening lithographic image-forming ink to impart permanency thereto without damaging the printing plate.

A further object of this invention is to provide a planographic printing plate etching solution which is non-toxic and non-irritating to skin and which is characterized by the property of removing scum and ink blemishes'upon direct application to the printing plate or of forming a coating upon the plate from which scum and ink blemishes may be easily removed merely by the normal application of a fountain solution thereto.

A further object of this invention is to provide an etching solution for planographic printing plates which will not coat the image portion of the plate and will, upon application to metallic planographic printing plates, etch the non-image portion thereof, thereby improving the clarity of the image portion,

A still further object of this invention is to provide'a dampening solution for use with singleply, substantially uncalendered parchment printing plates which will render the non-image portion of the plates ink-repellent without causing distension of the-plate.

It is furthermore, an object of this invention to provide a dampening solution for use with a single-ply, substantially uncalendered parchment printing plate which is characterized by the property of producing an evenly distributed film of water on the non-image surface of the plate to render it ink-repellent but which will not saturatethe body of theplate and from which. film the water evaporates sufiiciently rapidly to prevent water from puddling on the plate surface.

The parchment planographic printing plate comprising this invention is prepared from parchment paper produced from high alpha cellulose pulp in the following manner. A waterleaf prepared from the pulp as a web on a paper making machine in the usual manner is 'sub jected to the action of sulfuric acid under controlled conditions.- The cellulose fibers or the surfaces thereof are gelatinized by thesulfuric acid to produce a substance known in the art asamyloid. The fibers of thepaper are thus attacked by the acid which forms a coating or film of gelatinous cellulose, covering the fibers and filling the interstices of the sheet, cementing or bonding the fibers into a coherent mass. Subsequently the excess acid is removed from the paper by both physical and chemical action and the web thereafter passed through drying rolls.

6 desired translucency of the paper is enhanced by omitting fillers and pigments.

The parchment paper made as above described and possessing the foregoing properties provided with marginal scales and other lay-out The web is preferably not calendered within the industrial meaning of the term, or, if so, only slightly." While the art has heretofore recognized that the impression factor of paper printing plates increases with an increase in the gloss and degree of calendering of the paper stock from which the plates are formed, contrary to this teaching the invention herein is predicated upon the use of a parchment paper stock, the surface of which is characterized by a minute grain finish similar to fine grain ground glass. The parchment paper stock must also possess low gloss and low smoothness values. The paper produced in the manner above described should have a smoothness measure of less than approximately seconds when tested on a Bekk smoothness tester and preferably a smoothness measure of from 10 to 15 seconds. The gloss of this paper should be appromixately 25.0 per cent when measured in an Ingersoll Glarimeter. The weight of the parchment paper may vary from to 110 pounds per ream (500 sheets. 24 x 36) but it is preferred to employ a paper having a weight of approximately 60 pounds per ream (500 sheets, 24 x 36). The thickness of the paper varies according to the weight but in the case of paper having a weight of 60 pounds per ream the thickness should be approximately .0035". Regardless of the weight per ream this parchment paper possesses very nearly uniform texture throughout its cross-section. Owing to the lack of calendering it is highly flexible and it does not possess a high machine finish but rather a fine grain finish which does not differ materially'from the texture of the paper beneath the surface. This characteristic is furthermore insured by excluding the use of paper sizes. The

guides formed by printing such material in the form of a reversed image on the non-printing face of the plate. Owing to the translucency of the plate, such images are visually perceptible as normal images throughjthe plate from the printing surface thereof.

It has been found especially desirable to prepare preprinted planographic printing plates of parchment paper. Thus, oflices employing standard forms'such as contracts, leases, lists or the like have a need for a printing plate having standard clauses, tables and columns preprinted thereon and to which a typist may add additional special information with a standard image forming ink. Parchment printing plates so prepared may be used in duplicating machines to provide a large number of copies of both the preprinted portion and the subsequently applied indicia. An image forming ink suitable for preparing preprinted parchment printing plates has been developed which comprises an oil modified phenol-formaldehyde resin, partially polymerized linseed oil, polymerized linseed oil gel, driers and pigments. One ink composition which has been found to give satisfactory results appears in the following example:

Example Parts by weight Alkali blue-oil modified phenol-formaldehyde resin dispersion 40 Iron blue-No. 1 lithographic varnish dispersion 10 Lead tetroxideNo. 3 lithographic varnish dispersion 20 Metallic soap drier-polymerizable oil dispersion 20 Polymerized linseed oil gel having a viscosity substantially equal to that of a. #5 varnish 10 The foregoing may be prepared by mixing the Alkali blue and oil modified phenol-formaldehyde resin in the proportion of 3 parts to 5 parts by weight respectively. The Iron blue pigment is mixed in equal parts by weight with No. 1 Lithographic varnish which is a commercially available oil consisting of partially polymerized linseed oil. The numerical designation of the oil indicates the degree of polymerization thereof and as the numerical designation increases the oil identified thereby is more completely polymerized. The lead tetroxide and No. 3 Lithographic varnish are mixed in the proportion of 5 parts to 1 part by weight respectively. The metallic soap drier may be any of the common driers of this type available on the market such as cobalt linoleate or a mixture of lead and manganese soaps and are employed in small amounts dispersed in polymerizable oils. The polymerized linseed oil gel is a thickener and consists of a partially polymerized linseed oil mixed with a soap, which serves as a gelatinizing agent.

The proportions of the various ingredients may be varied according to the distribution and transfer required by a specific printing operation. Thus, the oil vehicles are increased if greater distribution and transfer are required. The synthetic resin binder employed may be any oil modified phenolic or alkyd type of resin which is quick drying. The ink sets as a result of both polymerization and oxidation and the rate thereof may be controlled by the amount and type of driers employed. The ink prepared in the manner described above may be applied to planegraphic parchment printing plates by offset printing methods, preferably by means of planographic metal printing plates. The images formed on the parchment plates dry practically immediately without offset. If necessary, the drying time may be reduced by warming the preprinted parchment plates slightly. The images thus formed are lasting and the preprinted parchment plates may be stored for from 6 months to one year without loss of the printing quality of the image. The same lasting quality of images formed from standard rease-base image forming inks is obtained with the uncalendered parchment printing plates described above; It is believed that this property is due to the surface characteristics of the plate and that the presence of a minutely fibrous surface on the uncalendered printing plate protects the images deposited thereon from failure due to abrasion as well as to oxidation.

Theetching solution forming a part of this invention is especially adapted for use with the uncalendered parchment printing plates previously described. These solutions perform not only the function of removing or displacing ink scum blemishes from the non-image areas of the printing plates but also act as hardening agents for grease-base type of image forming inks. The etching solution comprises an aqueous solution of glycerine, sodium sulfate and equal amounts by .weights of sodium thiosulfate and citric acid. On the basis of a gallon of solution it is preferred to use one ounce each of sodium thiosulfate and citric acid. These quantities may be increased up to four ounces each of the citric acid and sodium 'thiosulfate, equal amounts by weight thereof always being employed. More than four ounces each of these ingredients tend to destroy the image on the printing plate rather than to harden and preserve it. The glycerine content of a gallon of the solution may be varied from 1 to 64 ounces by volume. It is preferred to employ approximately ounces of glycerine. If the glycerine content is increased above 64 ounces it has been determined that the sensitivity of the printing image to the lithographic ink is retarded. The quantity of sodium sulfate may be varied from 1 to 8 ounces per gallon of solution with 2 ounces being the preferred quantity. If more than 8 ounces of sodium sulfate are employed, the action resulting from the combination of sodium thiosulfate and citric acid is neutralized. In the foregoing composition glycerine functions as a wetting agent while the sodium sulfate serves to impart a soapy texture to the surface of the printing plate and distributes the etching solution over the printing plate surface. The sodium thiosulate and citric acid react to produce free SO: which imparts hardness to the grease-base type of image forming ink. This hardening effect lengthens the life of image and improves the printing quality thereof.

The etching solution is applied to the parchment printin plate by pourin the solution over the surface of the plate after the image has been applied thereto and is then gently spread over the surface of the plate with a cotton swab. Any blemishes such as finger smudges or ink stains deposited during the preparation of the plate for printing are either removed or loosened. Simultaneously the sodium thisoulfate and citric acid harden the grease base image forming ink. The plate may be placed on the impression cylinder immediately and the printing process commenced. Any blemishes which have been displaced by the etching solution during its application are removed by the fountain solution. The coating formed on the surface of the printing plate by the etching solution is such that ink scum blemishes which aredeposited on the surface of the plate during theprinting operation are likewise removed by the fountain solution.

The etching solutions described above may also be applied to metal planographic printing plates having image forming inks on the surface thereof. In addition to functioning as an ink scum blemish removing agent the sodium thiosulfate and citric acid actually etch the areas of the printing plate adjacent the ink image. This causes the image to stand out above the nonprinting surface of the plate and materially improves the printing quality of such plates. The etching solutions, furthermore, do not coat the image which is a distinct advantage in metal plates having a half-tone or shaded image.

The dampening or fountain solutions forming a part of this invention are especially developed for rendering the non-image area of the uncalendered parchment printing plates described above ink-repellent. The solutions comprise glycerine, sodium sulfate. boric acid and gum acacia dissolved in water. In lieu of sodium sulfate, calcium chloride, 1 to 16 ounces, may be used in the solutions. However, it demonstrates a tendency to remain on the image portion of the plate and will. ultimately, produce light colored copies. On the basis of one gallon of solution the glycerine content may vary from 10 per cent or 12.8 ounces to per cent or 64 ounces by volume. It is preferred to employ 64 ounces of glycerine in solutions for dampening plates formed from parchment paper having a weight of pounds per ream (500 sheets. 24 x 36). The glycerine content of the solutions may be decreased to the lower limit of 12.8 ounces in dampening printing plates formed from heavier stock; as, for example, weights ranging from 60-110 pounds per ream (500 sheets, 24 x 36). The sodium sulfate (calcium chloride) content of the solutions may vary from 1 to 16 ounces per gallon of fountain solution with from 1 to 8 ounces per gallon being the preferred range. The range of from 1 to 8 ounces of sodium sulfate produces uniform heavy black copies throughout the entire run while amounts in excess of this range produce progressively lighter copies. In a solution for dampening plates formed from parchment paper having a weight -of 60 pounds per ream (500 sheets, 24 x 36) a sodium sulfate content of 6 ounces per 'gallon has been found satisfactory. The boric acid content may range from i to 6 ounces per gallon of solution and produce the desired result. A boric acid content of approximately 2 ounces per gallon of solution is preferred. The gum acacia is employed in small amounts usually /4 to 3 ounces per gallon of solution. The glycerine functions as in fountain solutions previously employed in this field. The sodium serves, as in the case of the etching solutions described above, to distribute the solution over the surface of the plate. The most important relationship between the several ingredients of the fountain solution exists between the sodium sulfate and the boric acid. The former tends to distribute moisture over the surface of the parchment printing plate. The relationship is such that during each rotation of the impression cylinder the concentration and distribution of water on the surface of the printing plate is suilicient to render the non-image portions thereof thoroughly ink-repellent without the plate being saturated whereas the rate of evaporation is suillciently great that, during theinterval between the transfer of the ink from the printing plate to the rubber transfer cylinder and the remoistening of the plate, the great bulk of the water content of the solution is removed from the surface of the printing plate. This, in effect, prevents water from puddling on the surface of the printing plate and overcomes any tendency of the plate to swell or buckle.- The foregoing phenomenon is so marked that commercially available fountain solutions and the fountain solution described above may be deposited in thin films on an uncalendered parchment plate and, while the former solutions will saturate the printing plate substantially instantaneously, the latter will remain on the surface for several minutes without saturating the plate.

The fountain solutions described above are essential in offset printing processes in which the uncalendered parchment printing plates disclosed above are employed. The use of any other fountain solution results in distension of such plates as well as the destruction of the image thereon. Furthermore, these fountain solutions can be employed only with the etching solution described above. If commercially available etching or scum-removing solutions are used in conjunction with these fountain solutions the images on the printing plates are broken. However, the etching solutions and fountain solutions may be employed in printing processes involving the use of printing plates of any other type.

The advantage of the process is apparent from the results of tests may under many conditions which indicate that a single-ply, unsized and uncalendered parchment planographic printing plate may be employed in a duplicating machine along with the fountain solutions described to produce over 3000 clear, deep black copies. Furthermore, the etching solutions and fountain solutions described herein have been employed in duplicating machines using commercially available multi-ply planographic printing plates with the result that the output thereof has been increased from approximately 3000 copies to over 10,000 copies.

Having thus described my invention, what I claim as new and wish to secure by Letters Patent is:

1. A combined ink scum removing and grease base ink hardening etching, composition for planographic printing plates comprising, in the following proportions, 1 to 64 ounces of glycerine by volume, 1 to 8 ounces of sodium sulfate, 1 to 4 ounces of sodium thiosulfate, 1 to 4 ounces of citric acid and suflicient water to prepare one gallon of solution, said sodium thiosulfate and 10 base ink hardening etching composition for planographic printing plates comprising 20 ounces of glycerine by volume, 2 ounces of sodium sulfate, 1 ounce of sodium thiosulfate, 1 ounce of citric acid and suflicient water to bring the volume of the solution up to one gallon.

3. A method of treating a planographic printing plate having an image thereon formed from a grease base type of ink which comprises the step of applying an aqueous solution of 20 ounces of glycerine by volume, 2 ounces of sodium sulfate, -l ounce'of sodium thiosulfate, 1 ounce of citric acid, and sufficient water to make one gallon of solution, to the surface of said plate for simultaneously hardening said image forming ink and forming an ink scum displacing coating on the non-image surfaces of said plate.

4. A method as set forth in claim 3 wherein said planographic printing plate comprises a planographic metal printing plate having an image thereon formed from a grease base type of ink;

5. A method of treating a planographic printing plate having an image thereon formed from a grease base type of ink which comprises the step of applying an aqueous solution of l to 64 ounces of glycerine by volume, 1 to 8 ounces of sodium sulfate, 1 to 4 ounces of sodium thiosulfate, and 1 to 4 ounces of citric acid, together with suflicient water to make one gallon of solution, to the surface of said plate for simultaneously hardening said image forming ink and forming an ink scum displacing coating onthe non-image surfaces of said plate.

6. A method as set forth in claim 5 wherein said planographic printing plate comprises a planographic metal printing plate having an image thereon formed from a grease base type of ink 7. A combined ink scum removing and grease base ink hardening etching composition for planographic printing plates comprising, in the following proportions, 20 ounces of glycerine by volume, 1 to 8 ounces of sodium sulfate, 1 to 4 ounces of sodium thiosulfate, 1 to 4 ounces of citric acid and suflicient water to prepare one gallon of solution, said sodium thiosulfate and citric acid being employed in equal amounts by weight.

8. A combined ink scum removing and grease base ink hardening etching composition for planographic printing plates comprising 4 ounces of glycerine by volume, 2 ounces of sodium sulfate, 1 ounce of sodium thiosulfate, 1 ounce of citric acid and suflicient water to bring the volume of the solution up to one gallon.

9. A method of treating a planographic printing plate having an image thereon formed from a grease base type of ink which comprises the step of applying an aqueous solution of 4 ounces of glycerine by volume, 2 ounces of sodium sulfate, 1 ounce of sodium thiosulfate and 1 ounce of citric acid, together with sufiicient water to make one gallon of solution, to the surface of said plate for simultaneously hardening said image forming ink and forming an ink scum displacing coating on the non-image surfaces of said plate.

10. A method as set forth in claim 9 wherein said planographic printing plate comprises a planographic metal printing plate having an image thereon formed from a grease base type of ink.

11. A dampening composition for planographic paper printing plates comprising, in the following proportions, 12.8 to 64 ounces of glycerine by volum e, lto 16 ounces of sodium sulfate, 1 to 6 ounces of boric acid, V to 3 ounces of gum acacia, and sufficient water to bring the volume of the solution to one gallon.

12. A dampening composition for. planographic paper printing plates comprising, in the following proportions, 12.8 to 64 ounces of glycerine by volume, 1 to 16 ounces of sodium sulfate, 1 to 6 ounces of boric acid, 1 ounce of gum acacia, and sufficient water to bring the volume of the solution to one gallon.

13. A dampening composition for planographic paper printing plates comprising 64 ounces of lycerine by volume, 6 ounces of sodium sulfate. 2 ounces of boric acid, V4 to 3 ounces of gum acacia, and suflicient water to bring the volume of the solution to one gallon.

14. A method of dampening planographic paper printing plates comprising the step of treating the non-image portions thereof with an aqueous solution of 12.8 to 64 ounces of glycerine by volume, 1 to 16 ounces of sodium sulfate, 2 ounces of boric acid, V ounce of gum acacia and a water drying compound for rendering said non-image portions repellent to lithographic inks, and suflicient water to bring the volume of solution to one gallon.

15. A method of dampening planographic paper printing plates comprising the step of treating the non-image portions thereof with an aqueous solution of 12.8 to 64 ounces of glycerine by volume, 1 to 16 ounces of sodium sulfate, 2 ounces of boric acid and V to 3 ounces of gum acacia to render said non-image portions repellent to lith ographic inks, and sufllcient water to bring the volume of solution to one gallon.

16. A method as set forth in claim wherein the planographic paper printing plate comprises an unbacked, unsized sheet of uncalendered amyloid parchment paper having a minutely 12 fibrous fine grain surface characterized by having low gloss and low smoothness values.

17. A method of dampening planographic paper printing plates comprising the step of treating the non-image portions thereof with an aqueous solution of 12.8 to 64 ounces of glycerine by volume, 1 to -16 ounces of sodium sulfate, 1 to 6 ounces of boric acid, and M; to 3 ounces of gum acacia in sufilcient water to make a gallon of solution, to render said non-image portions repellent to lithographic inks.

18. A method as set forth in claim 17 wherein the planographic paper printing plates comprise unbacked, unsized sheets of uncalendered amyloid parchment paper having a minutely fibrous fine grain surface characterized by having low gloss and low smoothness values.

19. A method of preparing 'a planographic printing plate. for use in an offset printing process, said plate comprising an unbacked sheet of uncalendered parchment paper having a greasebase ink image thereon, which comprises the steps of applying an aqueous solution of 1 to 64 ounces of glycerine'by volume, 1 to 8 ounces'of sodium sulfate, 1 to 4 ounces of sodium thiosulfate and 1 to 4 ounces of citric acid, in sufllcient water to make a gallon of solution, to the surface of said plate to harden said image and form an ink scum displacing coating on the non-image portions of said plate; and thereafter applying an aqueous solution of 12.8 to 64 ounces of glycerine by volume, 1 to 16 ounces of sodium sulfate, 1 to 6 ounces of boric acid and V to 3 ounces of gum acacia, in sufllcient water to make a gallon of solution, to the non-image portions of said plate to render said portions repellent to lithographic inks.

JAMES FINNO.

No references cited.

Claims (1)

1. A COMBINED INK SCUM REMOVING AND GREASE BASE INK HARDENING ETCHING COMPOSITION FOR PLANOGRAPHIC PRINTING PLATES COMPRISING, IN THE FOLLOWING PROPORTIONS, 1 TO 64 OUNCES OF GLYCERINE BY VOLUME, 1 TO 8 OUNCES OF SODIUM SULFATE, 1 TO 4 OUNCES OF SODIUM THIOSULFATE, 1 TO 4 OUNCES OF CITRIC ACID AND SUFFICIENT WATER TO PREPARE ONE GALLON OF SOLUTION, SAID SODIUM THIOSULFATE AND CITRIC ACID BEING EMPLOYED IN EQUAL AMOUNTS BY WEIGHT.