US1373658A - Method and apparatus for preparing photoengraving-plates - Google Patents

Description

J. S. FREEH.

METHOD AND APPARATUS FOR PREPARING PHOTOENGRAVING PLATES. APPLICATION FILED MAR. 23. I920.

1,373,658. Patented Apr. 5, 1921.

5140M 3g? i w Ja es 157 14 Mme/1 rd UNITED STATES PATENT OFFICE.

JZAIMIES S. FREER, OF RUTHERFORD, NEW JERSEY.

To all whom it may concern:

Be it known that I, JAMES S. FREER, a citizen of the United States, and resident of Rutherford, in the county of Bergen and State ofNew Jersey, have invented certain new and useful Im rovements in Methods and Apparatus for reparing Photoengraving-Plates, of which the following is a specification.

My invention relatesto improvements in the process and apparatus employed in etching, and is especially adapted for use in connection with the allied processes.

A great variety. of processes for preparing and etching metal plates are known, all of which include the application to one sideof a plate of an erosive-resisting coating. In

a great many of these processes, it is necessary to heat the coating after it has been applied to the plate to render it tacky, to bake or burn it in, to melt it, or to accomplish various other results according to the requirements of the particular process. According to the uniform practice which is now followed the coating is heated to the necessary extent by placing the plate over or.

on a suitable stove or heater, the heat being transmitted through the plate to the coating. After the coating or resist has been heated to a suitable. point it is necessary to cool the plate before the processcan be continued either by permitting the plate to cool slowly in the open air, or by subjecting it to various cooling processes, usually includ-- ing the application of water. Two common methods employed in photoengraving include placing the hot plate under a stream of water or, in the improved method, passing the plate over a roller covered with carpet saturated with water. These and other rapid cooling methods are objectionable because they tend to buckle or warp the plate, and when water is used directly, it must be removed from the plate before the next step in the process can be taken. Furthermore, sudden cooling tends to draw the tem er of copper plates, materially reducing the r usefulness. On the other hand, the slow cooling of plates wastes a great deal of valuable time; and owing to the highly paid labor Specification of Letters Patent.

photoengraving and strong aflin ty for the ink, and permeates usual practice in carrying out this process,

the plate, after exposure and rolling up, is treated a number of times with a finely powdered resinous substance such as dragons blood. This substance when melted has a the ink-bearing emulsion, forming, when cooled, an acid-resisting substance which is generally referred to as the resist.

In the process of etching by the dragons blood method the plate is ordinarily immersed in the acid bath a number of times, three or four being customary; and before each insertion in the bath, or bite, the

plate is treated with the dragons blood powder, ordinarily by the method known as powdering four ways This method consists in applying the powder to the late four or more successive times, and brus ing it across the surface of the plate each time in a diffeernt direction, it being customary to apply the powder from left to right, from right to left, from bottom to top, and from top to bottom. After each application of the" powder in a single direction, the plate is heated so that the powder will melt against the sides of the lines in the direction in which it is brushed, and the plate is then cooled to a working temperature. Conse; quently, four separate heating and cooling steps are necessary between succeeding bites, and in addition a preliminary application of the dragons blood to the entire plate after it has been rolled up is'usual. After powdering four ways it will be apparent that each line along which etching is to take place will be accurately defined, as the side walls Patented Apr. 5, 1921. Application filed March 23, 1920. Sefrial No. 368,079.

of the resist adjacent'the line'will be uni the time required for this process is con sumed in heating and cooling the plates, especlally slnce each plate, if it is chilled by the application of water in the usual way, must again be reheated to a point where the ink is tacky and adapted to take up the dr agon.s blood.

According to the method universally employed in heating the plate in carrying out this process, the plate is held in a pair oftongs over an open gas stove, the plate body 1 being heated first and imparting heat to the resist until the dragons blood is melted.

The plate is then cooled by any of the .methods above indicated, either rapidly or slowly, although under modern conditions the rapid cooling is the almost universal practice. Warped and distorted plates necessarily result, and the time of the workman is taken up in swabbing off the water on the face of the plate and in reheating the plate to the proper temperature if necessary.

The primary object of my invention is to avoid the detrimental effects produced by the present practice of heating and cooling the body of theplate. By avoiding this practice, I insure the-preservation of a normal flat condition of the.plate and reduce very materially the total time required to carry out the usual photoengraving process or other processes of the general natureabove indicated.

My invention in its broad aspect consists in the accomplishment of this object by the application of heat directly to the resist, as

. distinguished from application of the heat to the metal plate and the transmission of such heat from the plate to the resist. By this method it is possible to maintain the metal plate at practically normal temperature, as suitable means can readily be applied to the back of the plate for keeping it cool.

Furthermore, in photoengraving the resin- -exposing the entire plate and resist to an even heat, as in an oven, where the dragons blood on the surface will melt long before the plate reaches an equal temperature, I prefer to apply the heat only to the resist carrying surface of the plate, leaving the bottom of the plate protected or free fromthe heat. With this arrangement, the temperature of the plate will not be raised appreciably, and it will be ready for the next step'of the process, such as powdering or plates.

aeraeee a bite, almost immediately upon withdrawal from the heating ap aratus. Consequently, a very large par-to the time necessary in properly etching a plate is eliminated, a

feature of the greatest value commercially.

Obviously, this method of heating may be accomplished in a great variety of ways, and my invention is not restricted in its 7 broad aspect to any particular method of the accompanying drawings, in

oven, part of the door being broken away,

and

Fig. 2 is a perspective view of another form of heatingapparatus, a portion of the front being broken away.

The type of apparatus illustrated in Fig.

1 is adapted to supply heat to all sides of the plate, and preferably can be adjusted so that an even predetermined heat may be employed. Heaters of the oven type are especially suitable for this purpose, the form illustrated including an oven body 11 which may be made of sheet metal, having the usual door 12 and preferably a thermometer 13 to permit the etcher to regulate accurately the heat applied. If desired, suitable transparent windows may be provided to permit the observation of the plates while being heated. Any suitable type of heating element, such as gas burner 14-, may be employed and when the heater is located within the body 11 it preferably isprovided with a baflie plate 15 located thereabove to prevent uneven application of heat to the Suitable plate supports, such as grates 16, are mounted in the, oven body 11, and are preferably so constructed that the heated air from burner-14 may pass up-' -wardly around the supports onto the top or resist-carrying portion of plates located on the supports. I also prefer to ount on grates 16 a suitable insulating or heat-resisting substance, such as sheets 17, which may be of asbestos or other material and may be laid on, connected to, or a permanent part of the supports 16. It will be apparent that with this arrangement the oven may be maintained at a temperature suitable for heating the resist, the temperature being very readily regulated by observation of thermometer 13, and correspondlng manipulation of the heat supply.

in carrying out my process with th1s apparatus plates 18 are placed on the asbestos sheets 17 and door 12 is closed. In a short time, the dragons blood or other part of aavaeaa the resist to be heated will be raised to the the heat must be transmitted to the plates through the resist. Consequently, when the resist has been suitably heated and the plates are removed, the-temperatureof the latter will be so low that very little orno cooling is required, the ordinary chilling process being entirely unnecessary and the plate being ready almost'immediately for the next operation c It will be apparent that many variations are possible in the oven type of heater, and I do not consider myself as restricted to any specific form of heat-producing apparatus, nor to the specific construction and arran ement of the plate supports or the oven b0 y. Obviously, heated air from an outside source may be introduced to equal advane ta e.

It secondtype of apparatus bywhichmy invention may be carried out consists of means for applying heat directly to the re,

sist-carrying surface of the plate only, the plate preferably being sup orted in the open air. A great many evices, including various burners, electric heating coils and the like are suitable. These heating elementsmay be-mounted in any desired way, so that the plates may be placed adjacent thereto with the resist portions near the burners, or if desired, the heating elements may be movable into position over a suitably located plate. One convenient illustration of the former arrangement is shown in'Fig. 2, in which a hot plate 20 is mounted above and adjacent to a suitable plate support, such as grill 21, the plate and grill belng mounted on suitable supports,

such as legs 22. Any preferred form of heating unit may be employed to maintain hot plate 20 at a suitable temperature, the form illustrated including a common type of gas burner 23, which preferably is inclosed in a housin 24 over hot p1ate20, to direct the heat ownwardly against the plate. With this arrangement, the plate 18 carrying the resist may be placed on grill 21 beneath hot pl'ate20, exposing the resist to the heat,.while the plate itself is only heated through the resist, and consequently will rise in" temperature very slowly. The operator is free to observe the action of the heat upon the resist, and can withdraw the plate as soon as the operation is completed,

leaving the plate ready for the next step without any delay for cooling. While I have described and shown a hot plate construction in Fig. 2 it will be evident that variolusforms of open burners may be used with-equal facility. F urthermore, while I have shown the plateas located below the burner, this position may be reversed if the resist contains no necessaw material which will fall off when the plate is inverted.

-. Moreover, while I have described my invention primarily in its application to line photoengraving towhich it is particularly adapted, it is-to be understood that I do not consider my invention to be limited to this process, as it may be applied to the very large number of processes of various types generally referred'to as etchin processes, which require the applicatlon of heat to the resist. Nor is my invention limited to processes of thisnature wherein a resist material is melted, as it may likewise be used Where the resist is burned in, as in halftone work, or where heating of the resist is required for any other purpose. My invention is also advantageous even where a surface of the metal adjacent to the resist must be heated therewith, as by the application of heat to the resist, the surface of the metal adjacent thereto can be heated to the proper temperature while the remainder of the metal, either through radiation or by application of a cooling medium to the back of the plate, maintains a lower temperature. The temperature to which the heating devices disclosed herein, or other devices of a similar nature, must be heated in carrying out my process has not been stated, as such temperature need not be confined to any articular range. Under the present practlce the operator trusts to observation to determine when the resist has been heated to the proper point; and the the apparatus herein shown, thoug obviously the temperature may be regulated,

with much greater accuracy, and the time of the exposure of the resist to heat can consequently be gaged with greater precision. While I have indicated the scope of my invention and have described several specific methods of applying it practically to well known processes, it will be apparent that many variations both in its application and in the exact type of apparatus employed can be made without departing from my invention, as set forth in this specification.

I claim:

1. In a process of etching metal plates by applying an erosive to a plate surface having selected portions covered with an erosive resisting coating and which includes the heating of such coating, the step which consists in applying heat directly to the outer surface of the coating for a restricted period of time, suflicient to heat the coating and insuflicient to considerably heat the body of the plate. T

2. In a process of etching metal platesby applying an erosive to a plate surface having selected portions covered with an erosive resisting coating and which includes the heating of such coating, the step which consists in applying heat to the coated plate only on the plate face which carries the coating for a limited time, sufiicient to heat the coating without considerably heating the plate.

3. In the process of photoengraving' on metal plates by applying an erosive to a resist car ing plate, and which includes the heating 0 such resist, thetsteps which consist in applying heat directly to the outer surface of the resist for a brief time, suflicient to properly heat the resist, and then discontinuing the heating before the plate body becomes considerably heated,-to avoid warping the plate. and loss of time in'coolihg.

4. In the process of line photoengraving on metal plates in which selected portionsof a plate surface are covered, with a suitable coating, a powdered resinous substance be ing applied to the coating and heated so that such substance will melt and adhere to the coating, forming a resist, the step which consists in melting the resinous substance by applying heat directly to the outer surface of the coating carrying such substance for a limited time, sufficient to properly heat the surface materials without greatly rais; ing the temperatureof the body of the plate.

5. In the process of line photoengraving on metal plates in which selected portions of a plate surface are covered with a suitable coating, a powdered resinous substance being applied to the coating and heated so that such substance will melt and adhere to the coating, forming a resist, the step which consists in melting the resinous substance by- I applied to the upper surface of the plate, the g step consisting in applying heat only near the upper surface of the plate for a time only suficient to melt said substance and in sufficient to considerabIy heat the body of the plate, so that delays and warping due to plate-heating and cooling are substantially avoided.

7. In a process of etching metal plates which includes heating material applied to the upper surface of the plate, the step consisting in heating the upper surface of the plate for a limited time, and protecting the body of the plate from considerable heat, to avoid delay and warping.

8. In a process of etching metal plates I whichincludes heating material applied to the upper surface of the plate, the step consisting in heating the upper surface'of the plate for a limited time, and protecting the under surface of the plate from heat, so that the body of the plate is not considerably 'L heated, and warpage and delay for cooling are avoided.

Signed at New York city, in the county of. New York and State of New York, this 20th day of March A. D. 1920.

JAMES E. FREER,

Images