US2032779A - Flexible composite planographic plate - Google Patents

Description

March 3, 1936,

w. B. wEscoTT 2,032,779 FLEXIBLE COMPOSITE PLANOGRAPHIC PLATE Filed Jan. 26, 1934 Jay-@7120? Patented Mar. 3, 1936 PATENT OFFICE FLEXIBLE COMPOSITE PLANOGRAPHIC PLATE William Wescott, Dover, Mass, assignor' to Multigraph Company, Wilmington, Del., a cornotation of Delaware Application January 26, 1934, Serial No. 708,398

10 Claims. (01. 101-401) This invention relates to an improvement in a planographic plate, and more particularly to aflexible composite planographic plate which comprises a flexible cellulosic base surfaced with closely packed discrete metallic particles firmly adherent thereto. I

The planographic plates of this invention, while useful for planographic printing generally, have particular utility in connection with w printing images produced thereon by direct typewriting. The ordinary sheet-metal planographic plate is not adapted to take a printing image directly from a typewriter.

I am aware that thin paperebacked metal foil has heretofore been proposed and used for the production of a printing image by direct typewriting; but, if the foil is thin enough to afford the requisite flexibility, it is disadvantageously embossed by the action of graining marbles; 20 and, if thick enough to prevent embossing thereby, it will not readily conform to the platen roll of, nor take a clean impression in, the usual typewriter. I am also aware that it has heretofore been proposed to overcome the difficulties 25 inherent in sheet-metal plates by spraying molten metal on a flexible nonmetallic backing; but, the surface, of the sprayed particles, becomes oxidized during the spraying operation and hence the facings obtained therefrom are 30 disadvantageously permeated with oxide which cannot be eliminated by the customary treatment for the removal of surface oxide from planographic plates; moreover the metal facings so obtained have little tensile strength, and dis- 35 advantageously crack when bent around the typewriter platen and, what is more important, about the form roll of the press.

.One object of this invention is to provide a planographic plate adapted to take a clean im- 40 age by direct typewriting in a usual typewriter. Another object is to provide a composite plate of high flexibility which may be made to conform to typewriter platens of small radius without detriment. Still another object'is to'provide a composite plate having a metallized printing surface, comprising closely packed-discrete'particles of metal, preferably zinc, which, while firmly adherent to the supporting base, are so exposed as to be chemically reactive with image- 50 forming inks and ink-repellent solutions. Other objects and advantages of the invention will become apparent as its description proceeds.

The art of planographic printing depends upon the immiscibility of oil and water and the 55 ability of water to displace or repel ink from a.

surface more readily wet by water than by oils. In direct planography a greasy image is produccd directly on a metal surface by any convenient means. The effective retention of this image by the metal, under printing conditions, 5 depends upon a chemical reaction between constituents of the greasy image-forming material and the metal. The preservation of the nonprinting areas of the plate during the inking and printing operations alsodepends upon avchemical reaction between the metal and constituents of a dampening solution applied thereto, whereby the metal of the non-printing areas is rendered preferentially water-receptive, or lyophilic. The metal constituting the printing surrace of the plate, to be effective for the purpose, must therefore be so exposed as to be chemically reactive. It is generally considered essential and it is certainly highly desirable, that the printing surface be slightly rough or "grained.

Fora clear understanding of the present invention, it is necessary to consider the role played by the grain of a planographic plate. A film of water on a smooth plate has two surfaces of equal extent; whereas on a grained plate the extent of the water-air surface is much less than is the extent of the watermetal surface. If the surface tension of the aqueous fluid and the wettability of the metal thereby are respectively the same in both cases, it is obvious that a film-of the aqueous fluid will offer a greater resistance to displacement from the grained sur-. face than from the smooth surface, because the ratio of water-metal surface to water-air surface is greater in the former than in the latter, while the ratio of surface tension to metal-wettability remains the same in both cases. It is, however, also obvious that any attritionalwear of the grained surface must occur at the apices of the grain; and it is common experience that, unless continuously treated during printing to maintain these apices in a lyophilic condition, they soon lose their preferential water-wettability, pick up ink, and produce a speckled effect on the whites of the print. From this observation it has been generally held that, to obtain ,clean prints from a planographic plate, the entire non-printing area thereof must be rendered and maintained in a preferentially water-wettable condition throughout the printing operation.

The present invention has its genesis in the discovery that the non-printing area of a grained planographic plate need not be rendered lyophilic throughout its entire extent, in order to effectively prevent contamination thereof by the printing ink, provided the residual ink-receptive portions thereof be minute and be restricted to the valleys formed by and between adjacent grain prominences.

. of a portion of plate of this invention, representing in line drawing the general configuration of the particles as seen at a magnification of about 500 diameters; and

Fig. 2 is an enlarged cross section thereof.

In the embodiment of the invention illustrated in the drawing, metal particles A and B are partially embedded in a bonding matrix C, which-may be either the substance of the cellu losic base D or a layer of a suitable adhesive.

In any event, close packing of the metal particles is desired in order that the area of the exposed matrix C be at a minimum, and for this purpose it has been found desirable, but not always necessary, to use particles of two widely variant sizes, as indicated by the large particles A which determine the graininess of the plate and by the small particles B which serve to reduce the uncovered areas therebetween. 'Where a- "grain" of very fine texture is desired, a single screen-sized (or, preferably air-separated) particle of very small mean dimensions may be used alone; but where a relatively coarse graininess is wanted, there is advantage in reducing, the interstices between large particles by afilxing therein particles of a lower order of size, as Binl'lgslandz While the process. of producing the plates of this invention isinot considered as being a part of the present disclosur it is, nevertheless, necessary, for clarity of presentation and understanding of the invention, to make reference to process ste when particles of two screen-sizes are used, it

will be found desirable to apply, as in the usual Bronzing machine, the larger sized particle first and to apply the smaller sized particle as a separate and subsequent operation, albeit while the bonding agent is still in a tacky condition; for

it has been observed that a more consistently uniform texture and better coverage may be so obtained than {canbe had when particles of vaare mixed and applied in one operaon. i

As stated, the bonding matrix C may be either the substance of the cellulosic base or it may be a layer of adhesive. Any bonding agent which adhesively wets the metal particles, which is not thermoplastic atordinary temperatures, and

which, in the dry and hardened state, is fiexible.

and substantially inert in the contacting presence of aqueous'solutions and siccative oils, may be used for the Purposes 01. this invention. Synthetic resinous condensation products, which, after final condensation, retain a high degree of 'flexibility, are useful for. the purposes'of this invention; particularly in that, as no solvent is required, they remain of constant tackiness until subjected to the final condensation. and hence are well adapted to the sequential application of metal particles of different size.

Any suitable cellulosic base may be used. The base material may be solid, as sheeted cellulose acetate'or nitrate, or it may be open textured as paper or cloth. Paper tends to split along its the paper base. Complete impregnation through to the back of the paper is not only not essential to the satisfactory functioning of the product,

but it involves unjustified process complications.

For reason of economy there is sometimes advantage in metallizing both surfaces of a fiexible cellulosic base. When such a double surfaced planographic plate is produced on a paper base, according to this invention, substantially complete impregnation of the pores of the paper'is, if not essential, at least highly desirable. Such a substantially complete impregnation is obtained. by the sequential treatment of the two surfaces, thereby avoiding the mentioned process.

complications.

When a cloth base is used, it is enough that the bonding agent so penetratethe interstices of thesuperficial fibers. as to obtain good anchorage, as the cloth may be'said to be inherently and structurally unified in the sense in which that expression is used herein.

Particles of metal of widely variant shapes'may be used for the surfacing of the plates of this invention. Thus pellets previously derived-from sprayed metal, or the more irregular particles derived from grinding,.may be used in theconventional bronzing machines. Metal flakes, as derived from tumbling extremely thin metal foil,

m y be used; but due to the fact that they are thin, and in consequence tend to lie parallel to the plane .of' the, base, they are not ordinarily so efiective to hold the dampening fluid in their interstices as are thethicker pellets or irregular particles. If, however, they areso oriented, as in an electrostatic field, as to first contact the adhesive at an edge rather than I be subsequently laid down in an overlapping arrangement,- somewhat similar to that of fish scales, by a unidirectional brushing operation;

. Such a fish 'scale" disposition of metallic flakes is effective to greatly reduce .the uncovered areas. It should be noted that where metallic flakes have been laid downin overlapping arrangement, the resulting plate must, for best results, be so ;oriented on the form roll of-the press that on rotation thereof the fixededgejof the flakes are to the fore; that is, the direction in the press must be the same as that which produced the overlap,

To the extent that any areas exposed bonding agent persist, and whether the particles befiakes or granular, the same considerations obtain. "These considerations are that the largest interstitial area, between any adjacent particles, should not appreciablyexceed the mean crosssectional area of the largest of the particlesconfiat, they may the graininess tension of the dampening .larly when an effective 'as that disclosed in my copending application stituting the coating; and that the mean interstitial area between adjacentparticle's should be substantially less than the average mean crosssectional area of the particles. Absolute limits of permissible uncovered areas cannot be given because their innocuousness does not depend upon the smallness of area alone, but also depends upon the height ,of the particles bounding the area, and also upon the viscosity and surface fluid usedon the plate.

The particle size may be varied over fairly wide limits as the character of the ink to be used, the nature of the work to be printed, and the viscosity and surface tension of the dampening fluid may dictate. But, in general, it has been found that the largest useful particles are of the order of 0.01 mm. in mean diameter, and that, for the usual run of printing and particudampening solution (such Serial No. 689,285 which has matured into Patent No. 2,003,268, May 28, 1935) is used, best results'are obtained when theparticles, imparting and effecting most of the coverage, are closely sized to a mean diameter of about 7.5 microns and the smaller particles, applied to reduce the uncovered area, are 0.5 to 1.5 microns in mean diameter.

While zinc is the metal poses of this invention, aluminum, and/or other metals such as magnesium and cadmium may be used.

From the standpoint of economy, an unsized preferred for the purother metals, such as I paper is preferred as the cellulosic base of the plates of this invention. However, sheet cellulose acetate or nitrate, woven fabric, or other sheet cellulosic material, may be used.

I sometimes find it desirable to counteretch.

-or sensitize to the fatty acids of grease, the metal particles before effecting their attachment to the base material, and thereby obviate the necessity for the performance of this operation by the user of the plate. Because all the metals, useful for the purposes of this invention, oxidize more or less rapidly, and because the presence of oxide is detrimental to the formation of a persistently retentive image, it is not enough that the counteretch should remove the oxide, but it should also replace it with a basic product, as basic aluminum sulphate, for instance.

As stated, there is advantage and economy in providing a plate with both surfaces prepared for planographic use. A method of protecting one side of a double-faced plate comprises essentially rolling into contact with the to-beprotected side, a sheet of thin flexible material, as paper, regenerated cellulose, etc., coated with a dry, aggressively adhesive material, vas crude rubber and coumarone resin or Burgundy pitch. These coatings are so well known as to need no further description here except to say that they effectively protect the underlying metallized surface from such contamination as would normally be incident to the usual manipulations of the plate in preparation for and during use.

Careful investigation of the properties of commercially available'metallized papers has failed to discover any which conform to' the requirements of this invention. .So far as could be ascertained, the heretofore metallized papers had at least one objectionable is that the disposition of the metal particles, predominantly flakes, produced patches of closely packed particles with intervening uncovered for instance, and alloys of thesecharacteristic; which areas greatly in excess of the mean particle size.

Moreover the metal was not found to be uniformly chemically reactive, either because it was protectively coated with a practically unremovable layer of stearate derived from the usual method of producing metal flakes from foil, or because it was so embedded in the bonding agent as to be substantially covered thereby.

As stated, for the purposes of this invention' the metal particles must be chemically reactive; that is, they must not be submerged in the bonding agent nor coated with water-insoluble material. Moreover, in order that the area of uncovered bonding agent may be at a' minimum, it is desirable that the contact between the particles and the bonding agent be restricted to the lower portion of the former.

When the use of a very soft ink is required and the dampening fluid is incapable of preventing such ink from contacting the uncovered areas of the bonding material, it has been found possible so to modify the reactive surfaces of the metallic particles as to counteract the contaminating effect of the soft ink. This modification is obtained, in the case of zinc, by treating the reactive surfaces of the zinc particles, after the greasy image has been delineated on the plate, with a half molar solution of ammonium dihydrogen phosphate (or alternatively the sodium or potassium salt) for five to ten minutes. Microscopic inspection of so-treated zinc particles dis-v closes the fact that their reacted surfaces are covered with fine crystalline 'excrescences, and that 'these tend substantially to fill the interstices being interlaced across the interstices between adjacent grains. crystalline product of the, reaction has not been definitely, ascertained; but, for the purposes of this disclosure, it is referred to as, in the case of zinc, an insoluble zinc ammonium phosphate.

By the expression closely packed, as herein used, is meant such a juxtaposition of the particles that the ratio of metal-covered surface to The structure of the.

uncovered surface is substantially constant for all similar small areas, and that the mean area of the uncovered interstitial surfaces is less than the average mean cross sectional area of the particles used; and, in any event, does not exceed a mean area of 100 sq. microns.

The expression firmly adherent, as. used 7 herein, is meant to denote such an adherence as will effectively resist the pull of a tacky ink. If the strength of the bond between base and metal particles is such that the metal particles are not extirpated when rolled up with an ink of greater ink rolls, the particles are deemed to be firmly adherent within the meaning of that expression herein used, is meant to denote metallic particles which have no metallic bond with each other, even though they be in contact as may be demtack'than can be distributed by the conventional onstrated by electrical conductivity of a film composed of such contacting discrete metallic particles; and to specificallyexclude particleswhich have a metallic .bond, as by being fused together.

s Jammy 4 2,032,770 I claim: approximates a plurality of other particles, and 1. A fiexible planographic plate comprising a that the mean area of the base exposed by the unified cellulosic base, a layer of closely packed discrete metallic particles firmly adherent thereto. and an inkreceptive image applied directly tothe metallic particles. I Y 2. A flexible planographic plate comprising a unified cellulosic base, a water-insoluble bonding agent adherent to said base, a layer of closely packed discrete metallic particles firmly adherent to said bonding agent, and an ink receptive image applied directly to the metallic particles.

3. A flexible planographie plate comprising an open-textured cellulosic base, a water-insoluble bonding agent penetrating said base and coextenmve with a surface thereof, a layer of closely packed discrete metallic particles coextensive with and firmly adherent thereto, and an ink receptive image applied directly to the metallic particles.

4. A flexible planographic plate comprising an open-textured cellulosic base, a water-insoluble onding agent permeating said base, a layer of closely packed discrete metallic particles coextensive with said base and firmly adherent thereto, and an ink receptive image applied directly to the metallic particles.

5. A flexible planographic plate comprising a unified cellulosic, base, a layer of discrete metallic particles firmly adherent thereto and characterized by the fact that each of said particles closely approximates a plurality of otherparticles, and that the mean area of thebase exposed by the interstices between adjacent particles is substantially less than theaverage mean cross sectional area of the particles, and an ink receptive image applied directly tothe metallic particles. w

6. A fie'xible planographic plate comprising a unified-cellulosic base, a layer of discrete metallic particles firmly adherent thereto and characterized by the fact that each of said particles closely closely approximates ph sphate.

interstices between adjacent particles is less than and an ink recepthe metallic parone hundred square microns, tive image applied directly to ticles.

'7. A flexible planog raphicplate comprisingva uniiiled cellulosic base, a layerof discrete metjallic particles firmly adherent thereto and characterized by the fact that each of said particles a plurality of other particles, and that the mean area of the base exposed by the interstices between adjacent particles is substantially less than the average mean cross sectional area of the particles, and that the largest area so exposed between any adjacent particles is less than the mean cross sectional area of the largest of said particles, and that the mean interstitial area between adjacent particles is substantially less than the average mean cross sectional areaof said particles, and an ink receptive image applied directly to the metallic Particles.

8. A flexible planographic plate comprising a unified cellulosic-base surfaced with firmly adherent discrete particles of 'zinc characterized by the fact that the interstices between said parti- 9-. A flexible planographic plate comprising a unified cellulosic base surfaced with firmly adherent discrete particles 01' zinc characterized by that the interstices between said parsubstantially filled by zinc ammonium the fact ticles are 10. A flexible planographic plate comprising a unified cellulosic base surfaced with adherent discrete particles of zinc characterized by the fact that the said particles are substantially covered by a basic metal salt.

WILLIAM B. WESCOTT.

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