US2373287A - Method of preparing printing plates - Google Patents

Description

April 10, 1945. E, BASSIST 2,373,237

METHOD OF PREPARING A PRINTING PLATE Filed July 27, 1943- PAPER COATING IMPREGNATED WITH TANN/C ACID While he was debating the Y I suggested a. fourteen days tra v GREASE RECEPT/ v1: TYPE- ond ac Ks where he p1 anned. to do WRITTEN -SUBJCTMATTR and Sam happily accepte' JGREASE RECEPT/VE TYPE WRITTENSUBJ'ECT MATTER Mile he was debating t suggested. a. fourteen days tra Macks Planned to do COATING SURFACE GUMMEO WITH WATER 'RECEP T/VE MATERIAL and Sam happi 1y ace epted.

Patented Apr. 10, 1945 2.373.287 ME'1'HOD F PREPARING PRINTING PLATES Ellis Bassist, Brookllne,

Craig Toland,

Masa, assignor to William trustee, Brookline, Mass.

Application July 27, 1943, Serial No. 496,329 6 Claims. (01. 101-1492) This invention relates to a planographic printing plate and its method of preparation, and more especially to a "direct-image type of plate.

By the term fidirect-image printing plate" is meant a planographic printing plate inwhich greasy material, constituting printing portions of the plate, is directly applied to the surface of the plate, as by typewriting, hand drafting and the like, as distinguished from photolithographic plates in which printing portions are formed by photographic methods. While not being limitedthereto, the invention is particularly directed to plates formed by direct application of printing portions with a. typewriter to sheets of paper.

An object of the invention is to improve planographic printing plates and methods of preparation therefor, and to devise a direct-image type of paper printing plate which is simple, cheap and efllcient, and which aflords greatly improved quality of reproduction and marked increase in durability. I

The nature of the invention and its objects will be more fully understood from the following description of the drawing and discussion relating thereto.

In the accompanying drawing:

Fig. 1 is an enlarged cross-sectional view illustrating a sheet material employed in forming the plate of the invention;

Fig. 2 is a fragmentary plan view illustrating a step in preparing the plate of the invention; and

Fig. 3 is a fragmentary plan view illustrating another step resulting in a finished printing plate.

.In connection with forming typewritten printing portions on a printing plate base, difficulty is experienced in getting enough of the typewriter ribbon ink transferred to furnish a sufiiciently strong ink body for a printing image. It is also diillcult to anchor the ink body to the base so that it will not be separated or dislodged, and finally it is diflicult to maintain the ink body in a sumciently hardened condition so that it will not smudge and its original outline and character lost.

The plate of the invention is characterized by printing images or printing portions which, when formed by typewriting as well as by other modes of application, present a relatively heavy ink body, which are very tenaciously attached to the base, and finally which are of a relatively tough, durable character adapted to preserving and-reproducing accurately the original subject matter.

In general, these characteristics of a relatively heavy ink body hardened to resist smudging and limited impregnation, the

by introducing into a normally water-receptive base limited amounts of an agent for imparting a superficial grease-retentive character to the surface of the base. The grease-retentive surface is utilized to insure transfer of a relatively heavy typewritten image. The entire surface ofthe plate is then treated with a lithographic etching mixture which eliminates the superficial greaseretentive character from those areas surrounding the typewritten image. At the same time the lithographic etching agent cooperates with the impregnating agent in the base to convert the ink image to an exceedingly tough ink body fixed in the base.

Referring more in detail to the invention, Fig. 1 illustrates a sheet of paper. I whichpreferably consists of a strong kraft paper impregnated with a sizing adapted to impart wet strength to the paper. Examples of a suitable sizin'g for this purpose are resinous or colloidal materials such as polyvinyl alcohol, gelatin, and the like. The paper also preferably includes waterrepellent material applied at either side thereof.

The paper at its outer side further includes a lithographic printing coating 2 of polyvinyl alcohol and a filler. The polyvinyl alcohol in this case constitutes a water-receptive medium, and the filler acts as a bodying agent in the coating. Other lithographic printing coatings may be employed, as for example mixtures of albumen and other colloids with fillers, or colloidal materials alone, or other combinations.

In accordance with the invention, the. waterreceptive coating 2 is provided with a surface of superficial grease-receptive character obtained by treating the coating with a chemical reagent. A preferred example of chemical agent is a tannin or tannic acid. Fig. 2 diagrammatically illustrates a, plate having a water-receptive coating 2, and Fig. 3 illustrates the coating 2 after treatment with tannic acid. In applying a chemical reagent to the coating 2, it is essential to carry out a limited degree of impregnation, and as illustrative of suitable concentrations for efiecting a use of weak solutions, such as solutions of from 1% tion of tannic acid, may be employed, with a"3% solution giving optimum'results.

strongly bonded to a supporting base, are obtained The use of a limited amount of the tannic acid is necessary in order to control the degree of grease-retentive character which is to be built up in the colloid surface. Treatment of the polyvinyl alcohol with tannic acid results in a chem-- ical change in the nature of a hardening action as is more fully explained at a later point in the to 5% concentraspecification. By utilizing increasing amounts of the tannic acid, grease retentive character may progress to a'point where it becomes permanently sary toeffeot this change without impairing the character or the typewritten subject matter which has already been appliedto the plate.

the invention is to most affected with little hardening progressing These conditions determining the amount of grease-retentive character to be provided are satisfied by utilizing a chemical reagent of the strength and type noted with a water-receptive sheet material and also by the use of a lithographic etch as disclosed in the following description of the method of forming a printing plate from the base of the invention.

A preferred method of employing the impregnated paper of the invention consists in utilizing it in sheets of sizes suitable .ior typing as 8 /2 x 11" and the like. A sheet of this character is inserted in a typewriter and typewritten sub- Ject matter applied thereto, making use of a special typewriter ribbon which is impregnated with an ink containing a fatty acid such as oleic acid.

The typed sheet is then removed and treated with a lithographic etch containing a mixture of an iron compound and chromic acid. The typewritten subject matter forms printing portions while the areas surrounding the inked subject matter accept water and form non-printing or ink-rejecting portions. The plate may thereafter be'inked and printed in the usual manner.

The tannic acid impregnated in the coating 2 is especially efiective in establishing a superficial grease-receptive character on the surface of the coating 2 so that the coating may accept relatively large amounts of greasy printing ink from a typewriter ribbon, and thereby form a strong printing image which'can be inked and printed in a lithographic printing press. It is pointed out that the use of the tannic acid in the manner noted is generally illustrative of a method of incorporating into a water-receptive planographic base an agent which will exert a superficial hardening and produce a modified ink-receptive character.

It is known that tannic acid is an insolu-bilizing agent and hardening agent for colloids in general and for polyvinyl alcohol in particular, and it is understood that upon incorporating the tannic acid into the polyvinyl alcohol coating, a, chemical reaction takes place with the formation of tannates of polyvinyl alcohol. As comparedwith polyvinyl alcohol, such tannates are less waterreceptive and more grease-receptive. In those cases where small amounts of tannic acid, such as is obtained from a 3% solution, are impregnated in the coating, there is developed a limited hardening only which produces a superficial I grease-receptive character.

' of further importance is the limited character of the hardening exercised by the tannic acid.

The surface of the'polyvinyl alcohol coating is downwardly into the coating. On account of this only a superficial grease-retentive character is developed which may be dissipated by treatment with the etching mixture or ferric chloride and chromic acid. It is believed that the lithographic etch may either toughen the polyvinyl alcohol and convert it into a water-swollen state. at which time grease-receptive character is thrown oil, or the chromium compound may remove the tannates of polyvinyl (alcohol chemically, while causing the underlying polyvinyl alcohol to become water-swollen. This explanation is given by way i of supposition only and the invention is not intendedto be limited in any waythereby. It is again pointed out that equally important with developing grease-retentive character in the base, is elimination of this grease-retentive character after an image is applied, and this important result is-achieved by the use of a chemical reagent in the manner noted.

In addition to functioning as an agent for modifying grease-retentive character of paper. the tannic acid provides a further highly desirable result by cooperating with the mixture of .ierric chloride and chromium compound to provide a substantial hardening of the greasy ink image. The manner in which this hardening is accomplished is not fully understood although it is suggested that there is a reaction between the fatty acid of the ink (oleic acid) the tannic acid and the iron chloride and chromic acid mixture. Whatever the explanation may be, the combined action of the tannic acid and the lithographic etch converts the ink to a tough rubbery mass which is exceedingly durable. This enables a plate made in this way to stand up under several thousand impressions as compared with a few impressions which might be obtained from printing images of typewritten subject matter prepared in the usual way. f

Still another important point in connection with the use of the tannic acid in the coated paper consists in slightly varying. the strength of the tannic acid solution applied to the paper coating for the purpose of modifying the shade or weight of the printing-image to be reproduced. The printing image formed by typewriting can be obtained in either alight or dark copy in accordance with the strength of tannic acid present in the coating. This is an advantage in instances where it is desired to reproduce typewritten subject matterof either light or dark character.

Upon applying tannic acid to most papers and then allowing the paper to dry, the latter curls upon itself and is diilicult to handle. By the use of water-repellent coatings at either side of the paper, as noted earlier in the specification, curling is eliminated and the paper is maintained in a perilectly flat state. This is an advantage during the operation of converting the paper into a printing plate and affords a convenient surface upon which to work.

A modification of the invention consists in a sheet of paper which does not include the colloid coating 2 but is provided'with a water-receptive surface. One example of a paper of this nature is a parchment paper, that is, a paper which has been digested with acid. Another example of paper of this character is afiberboard or zinc chloride treated paper. Other types of base materials or coated papers, as well as plastics and resi one sheet materials may also be employed.

In any of these modified paper or similar base hardening of thegreasy ink image.

materials, the tannic acid or other impregnating agent is utilized-in the same'manner as described in connection with the polyvinyl alcohol and filler coating. that is, the tannic acid .is impregnated directly in the treated paper or plastic as the. case maybe, and typewritten subject matter may then be applied in-the manner described. It is further intended that the base may be utilized to form a plate by hand drafting or even photographic methods when this may be found desirable.

In place of the tannic acid, it may be desired to employ various other hardening agents for polyvinyl alcohol, as for example chromic acid or ammonium dichromate, formaldehyde, borates'and others.

These hardening agents are not regarded as being as satisfactory as the tannic acid in some respects, although they are all adapted to limited.use in developing grease-receptive character and may be desired to be employed in conjunction with an etch suchas the ferric chloride chromic acid mixture.

For instance, chromium compounds weak concentrations may be used to increase greasereceptive character which may be reconverted to water-receptive character with the etch. However, the chromium compounds should be used soon after. impregnation as after standing for periods of several weeks or longer, it is more diflicult to develop the water-receptive character.

It may also be desired to utilize the etch independently of any impregnating agent in the base material. One example of such a use consists in typing with a heavy typewriter ink upon asurface which is perfectly dry and free from moisture so that there is no tendency on the part of the paper to reject the ink. The etch here develops non-printing portions which are equally as good as those obtained by treatment of a tannic acid impregnated base. However the printing portions are not as durable or as satisfactory in other ways as those obtained by the combined use of the etch and tannic acid impregnated in the base. Some modification may also be resorted to in the lithograph c etch. For example an aqueous mixture of ferric chloride alone may be used to secure desirable Similarly the chromium compound may be utilized separately of the ferric chloride, and various other combinations may be employed such as those containing other iron compounds as ferric sulphate, iron oxide, and others.

The use of tannic acid and an iron compound, such as ferric chloride, as well as a chromium compound, to form grease-retentive printing.

portions in a-direct-image plate, may be carried out in other ways. For example in hand drafting as by a pen, a greasy ink mixture is not as readily applied since the greasy ink will not flow freely from a pen point. In this type and upon being applied to the surface of the base, gradually turn to a dense black color.

It is pointed out that when drawing with a pen which is inked with an ink mixture such as that rescribed, much greater amounts of taining both a fatty acid and aqueous materials thoroughly mixed together. The emulsion, which may or may not include any ofthe chemical reagents referred to, is adapted to adhere more readily to water-receptive surfaces by reason of the presence of small amounts of aqueous materials in the emulsion. The-result of this is to improve transfer of printing ink from a typewriter ribbon to water-receptive surfaces.

It should be observed that the method of the invention provides" for the development of a superficial grease-retentive characterin a waterreceptive base which facilitates application of I an ink image thereto, and at thesame. time the method of the invention providesior removing or dissipating the superficial grease-retentive character after application of the printing image, and at a time when the printing image itself may be converted to a hard durable mass while water-receptive character is being revived in the non-printing portions of the plate. The printing plate resulting from this method is formed with printing portions and non-printgraphic principle of printing. The printing poring portions in accordance with the usual lithotions include tannates of polyvinyl alcohol (in the case of a polyvinyl alcohol coated plate) and a chemically hardened greasy ink. The nonprinting portions of the plate consist of polyvinyl alcohol which has been toughened at its surface by chemical treatment but which nevertheless exhibits a water-swollen condition which provides a completely water-receptive character and which positively rejects ink with no 00- currence of scumming.

In forming a lithographic printing image, the typewriter action and typewriter ribbon will apply only a very small amount of typewriter ink to the surface of the paper, and the paper itself must be of a type which takes ink easily, is readily inserted in the machine, and otherwise dealt with. In view of this, formation of printing plates from typewrtten subject matter has been unsatisfactory, and at best, plates of questionable quality and very limited life have been produced.

The impregnated sheet material of the invention, substantially aids in overcoming these difii- .culties, by temporarily increasing the greasereceptive character of the paper and by thus insuring that a satisfactory amount of ink may be applied. The impregnating agent in the paper also cooperates with other chemical etch ing agents referred to in hardening the ink and providing for many impressions being made, as.

for example 25,000 impressions and more. addition, the paper is very easy to use and is not subject to difliculties in connection with development of the printing image so that an unskilled operator may very quickly prepare the printing image for use in a printing press. Various other advantages are also present in connection with the paper sheet material of the invention suchas light weight, low cost, and thelike.

While I have shown a preferred embodiment of my invention, it should be understood that various changes and modifications may be rworted to, in keeping with the spirit of theinvention as defined by theappended claims.

I claim: V

1. That improved process which comprises applying to a sheet material having a water-receptive surface a solution of tannic acid, applying ink image'on the surface. said ink contain ng oleic acid, treating the image with a lithographic etching mixture which contains ferric chloride.

aerator g a lithographic etching mixture which contains an iron compound, a chromium compound and an aqueous material. a

4. That improved process which comprises providing a. sheet ofpaper with a coating of ing the image with a lithographic etch which 2. The improved process! which comprises, I

applying to a sheetmaterial having a water-receptive'surface a, solution of tannic acid. applying an ink image on the surface, said ink con- 3. That improved process {which comprises applying to a sheet material having a water-recontains a chemical reagent adaptedto cooperate with the said first chemical agent in harden-- ing the image. f I

6. That improved process which comprises providing a. sheet material, impregnating the sheet material with a chemical agent to modify ceptive surface a solution of tannic acid, applyw its grease-receptive character, applying an ink image thereto. treating the entire surface of the sheet material with an etch which cooperates with the said first agent to harden the image.

' ELLIS nAssIs'r,

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