US1892682A - Method of making a printing plate - Google Patents

Description

' Jan. 3, 1933.

T. E. RICHARDS METHOD OF MAKING A PRINTING PLATE 4 "Fin; 1..

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BY m J 2 a TORNEYR Patented Jan. 3, 1933 PATENT OFFICE UNITED STATES Original application fled October 80, 1987,

Serial No. 827,623, and. in New zealand November 88, 1888.

Divided and Hill application filed June 4, 1828, SerlaI'No. 388,424. Renewed Kay 81, 1988.

This invention relates to lithographic printing plates and to the method of preparmg the same, especially when prepared photographically; and has for its object the production of plates which will be superior to the plates heretofore in use with respect to cost and rapidity of preparation, durability, speed at which the plates may be run in the printing machines and quality of the work produced. This ap lication is a division of my co-pendin application Serial No. 227,- 623, filed Octo r 20, 1927.

The present invention is particularly adapted to the production of planographic plates for offset printing purposes, especially for newspaper work, but it is nevertheless contemplated applying the invention to the preparation of photolithographic plates of ang type.

y the present invention, one is enabled to produce a planographic printing plate having a very strong, distinct and durable image which may be put in an offset printing press,

7 for example, and copies taken therefrom at a higher rate of sp and in greater quantit than have heretofore been practicable in this class of work. The image is defined by a coating material which is made hard and firmly united with the plate by partial penetration of the metal in a manner more specifically pointed out hereinafter.

he invention accordingly comprises the several steps and relation and order of one or more of such steps with respect to each of the others, and the printing plate possessing the features, properties, and the relation of elements, which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detail description taken in connection with the accompanying drawing, in which:

Fig. 1 is an enlarged cross section showing schematically a ained plate having an image-receiving fifill;

Fig. 2 shows a plate of the character shown in Fig. 1 having a developed image to which is'applied a coating containing an agent of durable characterin accordance with the invention; and

Fig. 3 is a similar view showing the late with the image film removed to yield a lithographic printing plate of the present invention.

Referring now to the drawing, 10 denotes a grained metallic plate of any suitable inkrepellant metal, for example, zinc or aluminum, to which is applied a film 11 adapted to take an image, for example, a film of bichromate emulsion for receiving an image photographically. When an image has been formed or developed by removing portions of the film from the plate, there remain upstanding portions as indicated at 12 in Fig. 2, about which the image-reproducin material is applied. To this end, a coating 13 containing an agent of durable character is applied evenly over the plate. The late w en finally prepared in accordance wit the process of the resent invention, has the im age-receiving lm removed and the coating hardened and made firmly adherent to the plate. This coating represents the image orm to be reproduced by planographic printin and stands alone on the finished plate as in icated in Fig. 3, the height shown being greatly exaggerated. The bonding of this coatin to t e metal by partial penetration thereo is indicated at 14.

When producing lithographic plates photographically, there are in general four main ste s to be followed, namely, 1) producin a p otogra hic ibmage upon a sensliltized melta printing p ate exposin a oto a ic film thereon, (2i dlSSOlVlig dif the u exposed sensitive substance, (3) a plying to the plate a coating material capable of taking and holding a desired image form and of absorbing printers ink, (4) and finally developing the image on the plate according to any known or suitable method of removing the exposed or relatively exposed port-ions of the sensitized substances.

In the practice of the present invention, the coating material is made to have metal penetrating and adhering properties, and is so applied to the plate and the whole so treated by means of heat that the coating becomes highly adherent and relatively hard whereby clear sharply defined images result and the plate produced capable of giving a relatively large. number of impressions without sign of deterioration. In accomplishing'this effect, a coating material is employed containing a body-giving agent of durable character, an ink-absorbing substance and a metal'penetrating agent, which is applied to the plate about the developed image and heated in two stages, in the first of which the coating material is made closely adherent to the plate whereby the developed image substance may be removed in a clean and efiicient manner, while in the second the coating is hardened and firmly bonded with the plate.

Certain other steps which will be hereinafter described with reference to an illustrative example of the invention are of minor importance and, except as hereafter noted and pointed out in the appended claims, are common practice and comprise no part ofthe invention.

The following procedure is an illustrative example of a specific method by which the present invention is carried out:

A grained metal lithographic plate is first prepared by rinsing a suitable metal plate, for example one of aluminum, in a ten percent solution of nitric acid and then thoroughly washed. The plate is then coated with a suitable bichromate emulsion for example, the following:

Fish glue 16 ozs. Water 36 ozs. Ammonium bichromate 1 ozs. Ferric ammonium citrate ozs. Strong solution of ammonia 1% drams On the sensitized plate an exposure is made from a half-tone screened or line positive. (Obviously, a negative may be employed if it is desired to make prints having their lights and shadows reversed as compared with the original.) The image is then developed by washing the plate with water, which dissolves off the unexposed portions of the sensitized glue, leaving a negative image on the plate. The plate is next dried and afterwards coated with the penetrating ink-absorbing substance, as referred to above, which is a liquid or plastic material prepared with a suitable solvent or vehicle and a rugged material, such as asphaltum, to give it body and durability. The following formula for the coating material has been found to give satisfactory results: one gallon of pure turpentine (the solvent) is mixed with one pound of asphaltum (the body-giving material) and the mixture brought to the boiling point. This mixture is then combined with a second mixture consisting of one-half pound of transfer ink dissolved by heating in one quart of turpentine. To this is added a third or liquid mixture comprisin one dram of a preparation consisting of o eic acid and an essential oil, and one dram of substantially pure oleic acid oil. The preparation of oleic acid and an essential oil preferred is that now sold on the open market under the tradename Elbagreen-oil. This mixture has the property of penetrating and adhering to the late and, being of a greasy nature, has a ity for printers ink, as is well known in the art. The addition of thetransfer ink to this mixture increases the afinity of the coating material.

The plate is coated with such material in any convenient uniform manner, for example by the whirling method, and then given the first heating, which is to a relatively moderate temperature, for example to 112 F. This temperature is sufiiciently high to soften the coating but is not such as to crack the insoluble glue or film remaining on the plate, hence in general the figure given should not be exceeded. At this stage, the plate is entirely covered with some sort of material, the unexposed portions of the late, which were washed clean by water being covered b the metal penetrating coating material, wh' e the exposed portions are still protected by the insoluble glue or film.

The plate is now finally developed, which is accomplished by immersing it in water, so that the surplus coating material overlying the remaining glue'may be brushed away. It is then placed in a ten percent solution of phosphoric acid, so that the undeveloped glue or film may be dissolved or otherwise 1'81 moved; after this the plate is washed with water; immersed in a ten percent solution of nitric acid for about twenty seconds; again washed with water and immersed finally for is to a relatively high temperature, for example to a temperature of from- 250 to 260 F. This heating is such as materially to assist the coating material to penetrate the surface of the plate and become hard and thoroughly bonded with the metal of the plate in a firm and durable manner. It is beneficial to continue such heating for several minutes to give ample time for accomplishing this'effect. Care, however, should be exercised not to continue the second heating for such a length of time or at such intensity as to cause injury to the plate.

WVhen the plate has become cooled, it may be coated with a solution of gum arabic and dried. The plate is now ready to be put in the printing press and run.

The image thus provided on the plate is a tough, closely adhering coating of ink-absorbing nature, the remainder of the plate being clean. The image is very durable, ab-

sorbs ink readily, and gives good depth of color. In consequence the plate can be run at high speed and will produce more good prints than have heretofore been obtainable.

It will be understood that the particular ingredients mentioned in the foregoing description are not of the essence of the invention, and that some of the operations described, although practically necessary, are of a routine nature and well known in the art. The invention is not limited to the particular procedure described, except as defined in the following claims. The term film? is used throughout in its generic sense, to designate any image-receiving substance.

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

1. The method of preparing lithographic printing plates, which comprises applying a film of bichromate emulsion to a grained metallic plate, photographically exposing and developing said film so that the portions which remain provide a matrix of a desired image form, applying an ink-absorbing coat-' ing containing a metal-penetrating agent, heating said plate so that said agent penetrates the metal and thereafter removing the matrix form.

2. The method of preparing lithographic printing plates, which comprises applying a film of bichromate emulsion to a ained metallic plate, photographically exposmg and developing said film so that the portions which remain provide a matrix of a desired image form, applying an ink-absorbing coating containing a rugged agent which is softened by heat and an oily metal-penetratin agent, heating said plate so as to fuse sai rugged agent and cause said oily agent to penetrate the metal and form a bond, and thereafter removing the matrix form.

3. The method of preparing lithographic printing plates, which comprises applying a film of bichromate emulsion to a grained metallic plate, photographically exposing and devoloping said film so that the portions which remain provide a matrix of a desired image form, inlg containing asphaltum, oi y metal-penetratin same thereafter in a p removing the matrix.

4. The method of preparing lithographic printing plates, which comprises applying a 1m of ichromate emulsion to a grained meagent, heating the urality of stages, and

tallic plate, photographically exposing and developing said film so that the portions which remain provide a matrix ofa desired image form, applyingan ink-absorbing coating adapted to develop metal-penetrating properties when heated, heating saidcoated plate in a plurality of stages at progressively increasing temperatures, and removing said matrix at a time intermediate said stages;

' T. E. RICHARDS.

produces a bond, and

applying an ink-absorbing coat- I a solvent and an-

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