US1992966A - Dampening method and means for planographic printing - Google Patents

Description

March 5, 1935. G, s, RowELL DAMPENING METHODAND MEANS FOR PLANOGRAP'HIC PRINTING Filed sept. 19, 1932 Patented Mar. 5, 1935 Y PAT-ENT OFFICE nAMPENmG METHOD AND MEANS Fon.

- l rLANoGnAPmc rmN'rnzG George S. Rowell, Cleveland, Ohio, assigner to Multigraph Company, Wilmington, Del., a corporation of Delaware' Application September 19, 1932, Serial No. 833,824

12 Claims.

'This invention relates to a method and means for dampening planographic printing plates and it comprises a dampening roller provided with a covering layer of a thixotropic glycerin gel, sometimes, but not always, mutually coextensive with a foraminous body such as sponge rubber or an open-textured fibrous body as felt, all as more fully hereinafter described and claimed.

Lithography, or planographic printing, depends upon the immiscibility of oil and water. stated the process consists of applying a greasy image to the surface of a dry printing plate and thereafter, during printing, maintaining the nonprinting areas of the plate in a damp and consequently ink-repellent condition.

The use of water as a dampening fluid has several serious objections, among which may be mentioned the fact that it is volatile, that its viscosity is very low and that a high degree of skill is required to feed to and to maintain on the printing surface such a nicely adjusted amount of water as will protect the non-printing areas from contamination by ink and prevent the dampening iiuid from encroaching on the printing areas with consequent degradation of the tinctorial value of the printed image. These dilculties'have been long recognized in the art and many attempts have been made to eliminate or mitigate them. 'I'hus it has been proposed to substitute glycerin or other viscous non-volatile polyhydric alcohols of the saturated series for the usual dampening water. However, the viscosity of glycerin, whichmakes it much more effective than water, presents at` the same time a serious diillculty in that it has been found extremely dilcult heretofore to apply to the nonprinting areas a film which was both sumciently thin and uniform to avoid the detrimental effect produced by the aforementioned encroachment by the dampening fluid on the printing image. If the amount of glycerin on the non-printing areas be such that the ink roller passing thereover is capable of imparting substantial motion to the glycerin, a minute wave of glycerin is moved forward by the ink roll and is forced over the printing image. Because of its viscosity the glycerin produces markedly greater degradation of the printed image than that produced by water under similar circumstances. In order to take advantage of the desirable characteristics of glycerin, i. e., its viscosity and hygroscopicity, and avoid the heretofore insurmountable dimculties of obtaining from a glycerin-charged dampening roll a sufficiently tenuous illmiform layer of glycerin over the non-printing areas without degradation Simply f of the printing image, it has been lsuggested to incorporate the glycerin -as minute, dispersed emulsoid particles inthe printingr ink itself, it

vhaving been discovered that such emulsoid ink,

when the ratio of Ldispersed glycerin to pigmented 5 oily vehicle was properly adjusted, would deliver a just adequate amount of glycerin to the nonprinting areas. So far as the maintenance of the non-printing areas in an ink-repellent condition by an extremely thin Vfilmiform layer of glycerin replenished from the ink carried by the ink roller, the process left nothing to be desired. The advantages derived from the use of glycerin and its just adequate supply to the plate were, however, more than offset by the facts that such emulsoid inksv are unstable and tend to break, with separation of the glycerin from the pigmented vehicle, in the ink fountain; that such emulsoid inks by reason of the contained hydroscopic glycerin remain tacky for weeks and 20 sometimes for months and after printing; and further that containing, as they must, a substantial proportion of the non-pigmented fluid, i. e. glycerin, their covering power is greatly reduced and in consequence to obtain good tinctorial values such emulsoid inks must be so heavily loaded with pigment as to adversely affect their physical characteristics, as is well recognized by those skilled in the art.

It is an object of this invention to provide means whereby an extremely thinflmiform layer of glycerin, neithermotile nor mobile, may be deposited on the non-printing areas of planographic printing plates without the necessity for human intervention or control. It is a further object of this invention to provide means whereby such a film of glycerin may be so replenished between successive inkings as to effectively protect the non-printing areas of the plate from contaminationby ink throughout long editions, without the necessity for adjustment of the glycerin supply. Other objects and advantagesof the invention will become apparent from its more detailed description.

I have discovered that a thixotropic glycerin gel, i. e. a glycerin gel which, although exhibiting the characteristic properties of a. solid gel when at rest, is capable of being liquefied by mechanical means and when so liquefied tends to resume its previous gel state, may be so liqueed by frictional contact with the surface of a planographic printing plate as to leave thereon an extremely thin but continuous and unbroken illmiform layer of glycerin which remains remarkably adherent to the plate. I believe the tendency for glycerin, derived from a thixotropic gel state, at least to the extent of a marked increase in viscosity in a short period of time, accounts for the observed fact that a film of such glycerin is less mobile and more resistant to grease under pressure, as of ink rollers passing thereover, than is a lm of ordinary glycerin of the same thickness.

The thixotropic effect is most markedly exhibited in glycerin gels when such gels are very delicate and I find it desirable therefore to provide a foundation and at least a partial structural support for such gels, for use as the dampening means of this invention, by forming such gels in part at least -in the interstices of a foraminous or open-textured base therefor. Both sponge rubber and felt have been found to be satisfactory for this purpose.

An understanding of the mechanical features of a dampening roll suitable for the purpose of my invention may be had from an inspection of the drawing in which:

Fig. 1 is an isometric view of a roller carrying a covering of `thixotropic glycerinv gel;

Fig. 2 is an enlarged sectional view of a portion of the roller illustrated in Fig. 1 covered with sponge rubber; and

Fig. 3 is a similar view of a portion of the roller illustrated in Fig. 1 covered with felt.

A mandrel 1, Fig. l, is covered with a continuous layer of a thixotropic glycerin gel 2. In Figs. 2 and 3 the disposition of a foraminous base 3 in shown in section surrounding the mandrel 1, and permeated and covered by the gel comprising the layer 2.

While for relatively short runs or small editions I find it satisfactory to cast a covering layer of thixotropic gel directly on the mandrel, I prefer to cover the mandrel with a thin layer, such as one-eighth of an inch, of sponge rubber, as in Fig. 2, felt, as shown in Fig. 3, or other resiliently deformable material not detrimentally affected by moisture and to saturate this material with such a fluid mixture of glycerin and gelatin as will upon setting yield a thixotropic gel. By rotating the roll in a horizontal position while the glycerin-gelatin mixture is setting I may readily obtain a thin layer of gel covering the foraminous base. In use it will be found that after the outer layer 2, in either Fig. 2 or Fig. 3, has been liquefied by frictional contact with and delivered to the non-printing areas of a planographic printing plate, the dampening roll of this invention will continue to deliver glycerin by reason of the resilient deformability of the foraminous base and its comprised gel. For use on coarse grained plates I prefer to make the gel covering co-extensive with the foraminous base in order that the amount of glycerin delivered to the plate by the liquefaction of the gel may be limited by the resilient deformability of the base and thus offset the increased frictional effect of the coarse grain Iof the plate surface.

As the water content of commercial glycerin varies somewhat and as the gel consistency of gelatin-glycerin gels may vary as the gelatin may vary from batch to batch, the ratios given in the following illustrative formula should be considered as approximate only, but anyone skilled in the art will have no difficulty in determining for any given lot of glycerin and/or gelatin the ratio which will yield a gel of the desired degree of thixotropia Formula: to 100 grs. of gelatin add 250 cc. ,of water containing 20 grs. of chloral hydrate; soaking for at least three hours, or preferably over night, adding to the mixture 300 cc. of water and heat to between 60 C. and 65 C. until solution takes place and mixing equal parts of the dissolved gelatin and high-grade glycerin. This will yield on cooling to room temperature a solid. although delicate, gel capable of exhibiting the thixotropic effect to approximately the desired extent. Slight variations in the ratio of the glycerin-gelatin components will produce corresponding differences in the stiffness of the gel and its thixotropic response to light frictional forces. It is to be noted that the liquefaction of the gelatin should be so carried out, preferably on a water bath at a temperature well below 70 C. because of the danger of the transformation of the gelatin by excessive heat into the nongelling state. It is further desirable that the chloral hydrate or other suitable germicide, such as hexylresorcinol, be added to the `water used to soften the gelatin in the rst instance. It may be Vstated in passing,'although this fact is well known, that a germicide is required to prevent bacterial liquefaction of the gelatin. However, in the selection of such reagent, one should be chosen which is compatible or inert with respect to the plate or colloid or other image thereon. The precautions of maintaining the temperature below 70, as above mentioned, apply as well to the liquefaction of the glycerin-gelatin gel by heating, for the purpose of impregnating foraminous material and coating the outer or roll surface therewith...

As pointed out in my copending application No. 631,588 it is sometimes desirable to add such saltsas ammonium nitrate and ammonium -phosphate to glycerin used as a dampening fluid on metal printing plates and particularly on zinc printing plates. When it is desired to include such salts in the dampening means of this invention it is merely necessary to dissolve the desired amount in the water to be added to the softened gelatin and when so added and the mixture brought to 60 C., more water, if needed, may be added until complete solution of salts and gelatin has been effected. Dampening reagents which are suitable for application to this invention include viscous liquid polyhydric alcohols such as glycerin, glycol, diethylene glycol, or others, having the common characteristics of high viscosity and miscibility with water.

While the foregoing description has referred to gelatin, it will be obvious to those skilled in the art that Aga Aga, or other like material may be used without departing from the spirit and scope of the invention as set forth in the following claims.

I claim:

1. Method of dampening planographic image bearing printing plates and like surfaces, comprising the step of applying a thixotropic gel thereto.

2. Method of dampening planographic image bearing printing plates and like surfaces, comprising the step of applying a thixotropic gel thereto containing a viscous, liquid, polyhydric alcohol.

3. Method of dampening planographic image bearing printing plates and like surfaces, comprising the step of applying a thixotropic glycerin gel thereto.

4. Method of dampening planographic image bearing printing plates and like surfaces, comprising the step of applying a thixotropic diethylene glycol gel thereto.

5. Method of dampening planographic image bearing printing plates and like surfaces, comprising the step of applying a thixotropic glycerin-gelatin gel thereto.

6. Method ,of dampening planographic printing plates and like surfaces, comprising the step of impregnating an open foraminous material with a thixotropic gel and passing the impregnated material over the surface.

7. Method of dampening planographic printing plates and like surfaces, comprising the step of impregnating an open foraminous material with a thixotropic gel and rolling the impregnated material over `the surface.

8. Means for dampening planographic printing plates and like surfaces comprising an open foraminous material impregnated with a thixotropic gel.

9. Means for dampening planographic printing plates and like surfaces comprising a roller, having an open foraminous material impregnated with a thixotropic gel.

10. Means for dampening planographic printing plates and like surfaces comprising an open foraminous material impregnated with a thixotropic gel containing a viscous, liquid, polyhydric alcohol.

11. Means for dampening planographic printing plates and like surfaces comprising an open foraminous material impregnated with a thixotropic gel containing glycerin.

12. Means for dampening planographic printing plates and like surfaces comprising an open foraminous material impregnated with a thixotropic gel containing diethylene glycol.

v GEORGE S. ROWELL.

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