US1991697A - Process of etching - Google Patents

Description

1935. TfPowE s 1,991,697

frnocmss 0F ETCHING" Filed" Nov. 11, 1951 INVENTOR Patented Feb. 19 1935 UNITED STATES -PA TENT OFFICE I 3 Claims.

5 during the process of etching.

The purposes and advantages of my invention will be set forthin part hereinafter and in part will be obvious herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the instru- -mentalities and-procedures pointed outin the appended claims.

In the process of etching plates to be used for printing, it is now customary to produce on the surface of the plate by photographic methods an image composed of a thin coating of a material resistant to the'action of the etchant to be used.

There are various well known coatings or sensitizers in general use for producing the desired image,- such, for example, :as' a light sensitive solution of albumen or glue mixed with bichromate of potash, or a so-called cold enamel coating may be used. After the usual printing and developing of the image, the plate is prepared in the usual mannerfor receiving'the first bite of the etchant. This first bite is usually a very light one, that is, the'pla'te is exposedbut a few seconds to the action of the etching fluid, and consequently the depth of the bite is very slight, only about 0.001 inch. The next step is ,to protect the sides or shoulders of the first bite against further action by the etching fluid and against undercutting, by the appliesztion thereto of a suitable resist. There are two commonly used forms of resist employed. One is a powder known as dragon's blood, and the other is a suitable ink applied to thedesign on the surface of the plate by means of a leather covered roller or a composition roller having a surface of resilient material. My present invention is concerned with the application of the second named forms of resist, namely, the ink resist.

All of the various types of rollers heretofore in common use for the application of an ink resist have more or less resilient or yielding surfaces. When such a roller is passed over the surface of the plate being etched to deposit ink resist on the design, the yielding surface of the roller permits it to touch not only the unetched top surface of the plate, but also to touch those portions of the plate which have been etched to slight depths, thus tending to-deposit ink upon areas which should not receive it. If ink is deposited upon those portions of the surface which Application November 11, 1931, Serial No. 514,322 (on. 41-43) it is desired to continue to etch, the plate will not be satisfactorily etched. To prevent this ad.- herence of ink tothose portions of the plate, various treatments are applied, such as a weak, aqueous solution of gum arabic. Such applications are for the purpose of preventing the ink 0n; .the roller adhering to etched areas of the plate, but still permitting the ink to adhere to the design portion of the plate. The application of such a solution or fluid is intended to cause the ink to selectively adhere to portions of the plate and not to other portions, but it is not always entirely effective and at times ink does adhere to portions of the plate that should be further etched, but which the presence of the ink prevents. This adhering of the inkto these spots results in a rough bottom on the plate and necessitates additional routing. In' other instances the application of the fluid intended to prevent the adherence of the ink may not be thorough and parts of the plate may not receive the fluid. In these cases the ink adheres to areas which should not receive it, thus preventing further etching of portions which should be etched more 25 deeply.

This application of a fluid to prevent adherence of the ink is a separate step in the process and takes time and labour, which by my invention I eliminate.

I have found that transferring the ink from a hard metal surface to the surface of the plate to be etched gives far better results than does transferring the ink from a resilient, compressible or yielding surface, and inmy co-pending application, Serial Number 574,286, I have described a cylindrical, metal roller for this purpose.

In my present invention I employ a smooth metal surface accurately finished to a substantially true plane. I then apply the etchant resisting ink to the surface of this metal plate by means of an ordinary composition or leather co'vered ink roller, and evenly distribute the ink over its surface. I then bring the inked surface of the metal plate into close contact w'th the surface of the etched plate by any suita le and convenient means, and firmly press them together, so that every portion of the etched plate which is still of its original thickness and is unetched is pressed into intimate contact with the inked plate, and by so doing I transfer ink from the inked plate to all those areas on the etched plate which form a part of the design thereon.

When the first application of ink is to be made to a plate which has had its first bite, I place a very thin coating of ink on my inking surface so that when the inking surface is pressed against the etched surface of the plate only a small quantity of ink is squeezed out from between the surfaces in contact and over the shoulders or edges of the unetched portions of the design on the etched plate.

After the etched plate has had its second bite, I use a somewhat heavier coating of ink on the inking surface so that slightly more ink will be pressed out from between the surfaces in contact and over the shoulders of the design. This ink so squeezed out is subsequently heated and caused to flow down over the sides or shoulders of the unetched areas of the design and so protect them from further etching and from undercutting. As the etching proceeds to greater and greater depths into the plates, I use progressively heavier coatings of ink on my inking surface and so squeeze out greater quantities of ink from between the surfaces in contact to provide sufficient ink on the shoulders to cover them completely and effectively when melted down during the heating process which follows each application of the ink to the etched plate. But at no time do I have a coating of ink on the inking surface so heavy or thick that any ink can come into contact with any etched portion of the etched plate where no ink is desired.

Each successive application of ink to the surface of the plate being etched builds up the. resistance of the top surface of the plate to the etching fluid and so protects the top.

In the accompanying drawing, in which like characters refer to the same or similar parts, I have shown in Fig. 1 an inking plate of a preferred type, in which 1 is the plate proper, hav ing its upper surface 2 made a substantially true plane, upon which is applied a layer of etchant resisting ink, 3, against which the plate to be etched is pressed by any suitable means which in the drawing, Fig. 2, is shown as a screw press 4, similar to the old-fashioned letter press. The plate being etched, 5, is placed with its face or etched side, 6, against the inked side, '7, of my new inking plate, 8, and both are placed on the platen, 12, in the screw press, 4, and tightly squeezed together by the operation of the screw, 9. It is obvious that many devices other than a screw press may be utilized to press together the two plates, and I do not confine myself to the use of any particular device for accomplishing this result.

The condition of the plate being etched at the successive stages of the etching process under my invention is shown much enlarged in Figs. 3 to '7, inclusive, which are described as follows:

Fig. 3 shows a section of a portion of a plate, 5, to be etched, on which are shown areas, 14, covered with etchant resistant coating to form the design, which has been placed thereon by photographic processes, leaving areas 13 of bare metal.

Fig. 4 shows the same section after it has received the first bite and it will be noted that the areas 13 lying between the areas 14 which were covered with resist have been etched away to a slight depth below the original surface of the plate. At this stage in the process the plate a very thin, evenly distributed layer of ink, by

means of a common inking roller, the plate to yoke, 10, to press the movable platen, 11, down against the plates which lie on the base platen, 12.

The pressure is then released and the freshly inked plate, which now has the appearance indicated in Fig. 5, with small quantities of ink, 15, squeezed out over the edges of the design, is heated to melt down the ink over the shoulders of the design. Fig. 6 shows the condition of the etched plate at this stage of the process, the ink being --melted down to cover the shoulders as shown at 16. The plate is then again subjected to the action of the etching fluid and the uncoated areas between the ink coated areas of the design are etched away to still greater depths, as shown at 17 in Fig. 7. The operations of applying ink, heating to melt the ink on the shoul-- ders and etching, are repeated a sumcient number of times to produce a plate having good printing quality.

In this description and in the appended claims I have used the work ink" to mean any viscous or semi-fluid material suitable for use as an etchant resisting coating for the purpose described.

Having fully described my invention and the manner of its application, I will now state what I claim to be new and novel, and for which I pray that Letters Patent be granted.

I claim:

1. The method of applying ink to the surface of a partially etched photomechanical printing plate during the process of etching said plate, which consists in first applying a thin, even coating of the ink to a substantially truly plane,

hard, non-yielding surface, and then pressing in- I to intimate contact with said inked surface the partially etched surface of the printing plate, thereby transferring to the printing plate a layer,

of ink and thereby squeezing out a portion of the ink from between the surfaces in contact to f the shoulders of the etched portions of the print-- mechanical printing plates, which consists in transferring a coating of ink to the surface of the partially etched plate by pressing said surface against a layer of ink previously applied to a plane, non-yielding surface, with suflicient force to squeeze a portion of the ink from between the surfaces in contact to the shoulders of the design on said printing plate.

3. The method of applying ink to the surface of a photo-mechanical printing plate in the process of etching said plate, which includes first applying a thin even coating of ink resist to a plane unyielding surface and then pressing the inked surface into contact with the surface of the printing plate with sufiicient force to squeeze out a portion of the ink from between the surfaces in contact to the shoulders of the etched portions of the printing plate.

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