US2681617A - Planographic printing - Google Patents

Description

Patented June 22, 1954 UNITED STATES PATENT OFFICE PLAN GRAPmC PRINTING ware No Drawing. Application November 28, 1947, Serial No. 788,660

4 Claims.

This invention relates to paper or like cellulose base planographic printing plates and to a method of and compositions for use in treating such planographic printing plates.

Among the problems involved in the use of paper or like cellulose base planographic printing plates are the problems incidental to the rerunning of such planographic printing plates upon a planographic printing press after the initial use or run thereof which include preventing of image spread during the time the plate is in storage and elimination of excess or residual ink on the printing surface of the plate prior to rerunning. Heretofore in the art it has been customary to treat planographic printing plates, after use, with a preservative, such as gum arabic, to preserve the image thereon during the time the plate is in storage and to facilitate clean up of the printing surface of the plate prior to rerunning. However, the use of gum arable, as a plate preservativais objectionable in that it must be removed before a planographic printing plate treated therewith may be reimaged and rerun. Moreover, gum arabic requires considerable care in its application as a plate preservative to avoid danger of blinding the image.

We have now found, however, that if a limited quantity of a finely divided water-wettable mineral pigment is incorporated in and is loosely bound upon the printing surface of a paper or like cellulose base planographic printing plate during manufacture thereof, the removal of inadvertent ink smears from the printing surface of the plate is facilitated and erasures may be more easily efiected, and the thus prepared plate may be readily cleaned and conditioned for rerunning by the application of a water dispersion of such finely divided mineral pigment to the printing surface of the plate, after use and prior to stor age, without the necessity for removal of the plate preservative composition thus applied as is necessary in the use of gum arabic or similar plate preservative compositions.

More specifically, we have found that if the new platepreservative composition, in the form of a water dispersion of a finely divided water- ,wettable mineral pigment, is applied to the printing surface of a coated paper or like cellulose base planographic printing plate having a limited quantity of such finely divided water-wettable loosely bound mineral pigment incorporated therein in the manufacture thereof, after use, and. before rerunning, image spread during storage is effectively prevented and residual ink on the printing surface of the plate is quickly and nil-14.9.2)

effectively removed. Thus the plate may be removed from storage and rerun without the necessity for the removal of the plate preservative composition and with the result that in the rerunning of the plate satisfactory numbers of excellent copies are obtained which are substan tially free of ink specks and generally as good in quality as the copies obtained in the first edition or run of the plate.

Accordingly, an object of the present invention is to provide a new and improved coated paper or like cellulose base planographic printing plate having incorporated in the printing surface thereof a limited quantity of a finely divided Water-wettable loosely bound mineral pigment which not only affords an excellent planographic printing surface but promotes and facilitates quick and easy clean up of the plate and prevention of image spread during the time the plate is in storage.

Another object of the invention is to provide a new and improved method of and clean-up and plate preservative compositions for use in eifecting quick and easy clean-up of the printing surface of a planographic printing plate, of the character contemplated by the present invention, after use, and prevention of image spread While the thus treated plate is in storage, without the necessity for removing the plate preservative composition from the printing surface of the plate after storage in order to add further images to the plate prior to rerunning it, as is necessary in the use of gum arabic and like plate preservative compositions.

A further object of the present invention is to provide a new and hnproved method of and clean-up and plate preservative compositions for use in efiecting quick and easy clean up of the new planographic printing plates after running and before storage and to the end that the plates may be removed from storage and immediately applied to and rerun upon a rotary offset pianographic printing press with the result that copies are obtained which are substantially free of ink specks and are otherwise as good in quality as the copies obtained in the first run or edition of the plate.

Other objects will appear hereinafter.

In the practice of the present invention the finely divided, water-wettable mineral pigment may be applied to and incorporated in the printing surface of the new coated planographic printing plate as a loosely bound pigment as distinguished from the usual practice of tightly binding pigments in or upon the coated surfaces of paper sheets by means of a suitable adhesive hinder or the like. When the thus finely divided water-wettable loosely bound mineral pigment is incorporated in the printing surface of the plate it provides a pattern of capillary spaces which are water-receptive and ink-receptive but are be lieved to prevent image spread by preventing lateral difiusion of the oil component of the printing ink applied thereto. At the same time, the abrasive surface of the thus formed plate permits of ready ink removal and thus makes possible quick and easy clean up of the plate after use.

Typical procedures which may be followed in the practice of the present invention will now be described.

Example No. 1

A coated paper base planographic printing plate was provided with a typewritten image and with a crayon image and three hundred (300) copies were run therefrom upon a rotary offset planographic printing press. The plate was then removed from the press and while still wet, was wiped lightly with a cotton swab saturated with a clean-up and plate preservative composition in the form of a water dispersion of a finely divided water-wettable mineral pigment consisting of a one (1) per cent silica aquasol prepared according to the process disclosed in United States Patent No. 2,375,738 granted May 8, 1945, to John Example No. 2

The procedure set forth in'the foregoing Example No. l was followed except that the cleanup and plate preservative composition was in the form of a two (2) per cent silica aquasol or aqueous suspension of colloidal silica in place of the one (1) per cent solution as employed in Example In place of the silica aquasol specified in the foregoing Examples Nos. 1 and Z'other forms of finely divided silica may be used and these materials may be employed in water dispersions thereof in which the silica component is maintained within the limits of from about 0.2 per cent to about 5.0 per cent,'by weight, of the complete clean-up and plate preservative composition with an optimum of about one (1) per cent.

' Likewise, place of the silica aquasol specified in the foregoing Examples Nos. 1 and 2, water dispersions of any of the 'finely divided waterwettable mineral pigments specified in the followmg examples may be employed-as the new cleanup and plate preservative composition:

Example N o. 3

Hydrated aluminum oxide "grams" Water c.'c 495 Example No. 4

Kaolin (china clay) r grams 5 Water -ic. c. 495

4 7 Example No. 5 Bentonite grams 5 Water c.c 495 Example No. 6

Zinc Oxide grams 5 Water c.c 495 sample No. 7

Talc "grams" 5 Water c.c 495 Example No. 8 Diatomaceous earth (finely divided) grams a Water c,c 396 Example No. 9

Calcium carbonate (finely divided) grams 4 Water c.c' 396 Example No, 10'

Barium sulphate (iine ly divided) grarns a Water l c.ci 396 The materiais referred to in the foregoing Examples Nos, 3 to 10, inclusive, may be prepared .for use as clean-up and plate preservative compositions by dispersing the solid component, in finely divided form, in the liquid component (water) by vigorous agitation, redispersion being effected by shaking the plate preservative composition after standing and before application to the printing surface of a paper or like cellulose base planographic printing plate. In some instances, as in the case of bentonite, redispersion may be more difficult than in other cases and may require more prolonged shaking before application. 7

All of the solid components of the compositions referred to in the foregoing Examples Nos. 1 to 10, inclusive, are characterized b being finely divided water-wettable mineral pigments which are insoluble in water while being otherwise. suit able for their intended uses, as described.

In the practice of the present invention, in one phase thereof, the finely divided water-wettable mineral pigment may be incorporated in and loosely bound upon the wash-coat or a coated paper or like cellulose base planographic printing plate, as illustrated in the following examples i Example No. 11

A paper sheet having wet strength properties and weighing about 25 pounds per thousand square feet was coated on each side with 6 pounds dr weight per thousand square feet of a coating containing clay 100 parts and casein 20 parts.

The coated sheet was calendered and then given a wash-coat, on one side, of about 0.5 lb.'dry weight per thousand square feet of an aqueous solution containing 1 percent or sodium alginate and 0.6 per cent of ammonium bichromate. The

sheet was then washed with a 2 per cent aqueous dispersion of a slice aquasol. The silica thus applied was loosely bound upon the surface or" the sheet which, when dried and used. as a pianographic plate, was very clean after 300 satisfactory impressions had been'made therefrom.

The printing surfaces prepared according to Example l or Example 2 above may be further improved as follows:

Example No. 12 The dried surfaces of the paper product to which a dispersion of silica aquasol had been applied, as describedin Example No; 11, were treated with a wash coat in the form of an aqueous solution of a water-soluble and waterstable divalent metal salt, after the manner described for treating planographic printing surfaces in the copending application of the applicant, Stephen V. Worthen, Serial No. 170,486 filed June 26, 1950, now Patent No. 2,534,650.

Example No. 13

To an aqueous dispersion containing 1.5 per cent of silica, in the form of a hydrosol, was added a 10 per cent aqueous dispersion of casein which had been solvated by ammonia, said addition being sufiicient to introduce one part of casein for each 3 parts of S102 present. The resulting suspension was then applied to a calendered paper product consisting of a wet-strength paper base Weighing 30 pounds per 1000 square feet and bearing a coating of 6 pounds per 1000 square feet containing 5 parts of clay to 1 part of casein adhesive. When so applied the finely divided silica was loosely bound upon the printing surface of the sheet which was wet-out very readily and, when used as a planographic printing plate, gave over 500 satisfactorily clean impressions.

All of the finely divided water-wettable mineral pigments referred to in the clean-up and plate preservative compositions set forth in Examples Nos. 3 to 10, inclusive, may be incorporated in and loosely bound upon the printing surface of the new planographic printing plates in the manner described in the foregoing Examples Nos. 11, 12 and 13. When so used these materials are preferably employed in a quantity of from about 0.2 to 5.0 per cent, by weight, of the aqueous dispersion in which such material may be applied to and incorporated in the printing surface of the plate.

When bentonite is employed as the finely di vided water-wettable mineral pigment, in the practice of the present invention, it is preferably employed only when preparing a colorless planographic printing plate since it may interfere with the organic or other coloring materials employed in preparing a colored planographic printing plate.

Example N0. 14

The procedure set forth in Example No. 1 was followed except that a new image was applied to a previously unimaged area and, likewise, a portion of the original image on the plate was removed by erasure and a new image typed on the erased area after storage and before rerunning. The images afforded by the newly imaged area and likewise by the erased and reimaged area were as good in quality as those obtained from the original and non-erased areas.

All of the finely divided water-wettable mineral pigments used in the practice of the present invention have the necessary tooth required for the reception of a planographic image and also for the reception of the aqueous planographic etching and dampening solutions which are employed in planographic printing upon rotary 011- set planographic printing presses and the like.

In the preparation of the clean-up and plate preservative compositions specified in each of the foregoing Examples Nos. 3 to 10, inclusive, the solid component of the water dispersion is preferably maintained at a concentration of about one 151) per cent by weight, of the total composiion.

It will thus be seen from the foregoing description that the present invention affords a novel method of and compositions for treating a paper or like cellulose base planographic printing plate, and has the desirable advantages and characteristics, and accomplishes its intended objects, including those hereinbefore specified, and others which are inherent in the invention.

We claim:

1. In the art of preparing direct image planographic printing plates, the improvement which consists in providing a paper or like cellulosic base sheet with a planographic base coating having therein finely divided pigment particles, applying directly upon the external surface only of said planographic base coating an auxiliary coating consisting of a water dispersion of a finely divided hydrophilic water insoluble non-reactive mineral pigment in the form of a silica aquasol, and then bonding the pigment particles of the said water dispersion to the said base coating by drying to form a discontinuous deposit of discrete particles of said finely divided mineral pigment over the entire external surface only of said planographic base coating.

2. A planographic printing plate which is the product of the method defined in claim 1.

3. In the art of printing from a direct image coated planographic paper or like cellulosic base planographic printing plate provided with a hydrophilic planographic image-receptive surface having thereon greasy hydrophobic images defining printing portions, the improvement which resides in printing from the said imagebearing planographic printing plate, applying to the said printing surface of said direct image planographic printing plate, after printing therefrom, a clean-up and plate preservative composition composed of a water dispersion of a finely divided water-insoluble non-reactive water-wettable hydrophilic mineral pigment whereby to cover only the unimaged areas thereof, drying the thus treated planographic printing plate, and then reprinting from the said treated and dried planographic printing plate without removing the said clean-up and plate preservative composition from the unimaged areas thereof prior to the said reprinting operation.

4. The improvement in the art of printing from a direct image paper or like cellulosic base planographic printing plate, as defined in claim 3, in which the said clean-up and plate preservative composition is in the formE of a silica aquasol.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 606,709 Five July 5, 1898 637,588 Hett Nov, 21, 1899 2,132,443 Simons Oct. 11, 1938 2,154,219 Shepherd Apr. 11, 1939 2,156,100 Simons Apr. 25, 1939 2,233,573 Ayers Mar. 4,1941 2,280,986 Toland Apr. 28, 1942 2,361,665 Toland Oct. 31, 1944 FOREIGN PATENTS Number Country Date 4,930 Great Britain Nov. 10, 1881