US2411109A - Etching rotogravure printing members - Google Patents

Description

Nov. 12, 1 946. POWERS 2,411,109

ETCHING- ROTOGRAVURE PRINTING MEMBERS Filed Feb. 26, 1944 'to explain the principles Patented Nov. 12, 1946 MEMBERS ETCHING ROTOGRAVURE PRINTING Frank T. Powers, Glen Cove, N. Y.

Application February 26, 1944, Serial No. 524,075

2 Claims. (Cl. 955.'7)

The present invention relates to new and useful improvements in the preparation of rotary and intaglio printing members and particularly rotary photogravure cylinders.

Objects and advantages of the invention will be set forth inpart 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 processes, steps and combinations pointed out in the appended claims.

The invention consists in the novel steps, processes, combinations and improvements herein shown and described.

The accompanying drawing, referred to herein and constituting a part hereof, illustrates one manner of carrying out the process of the inven tion, and together with the description, serves of the invention.

Of the drawing:

Figure 1 is a perspective view showing diagrammatically one step of the process of the present invention;

Figure 2 is adiagrammatic View, with certain parts exaggerated, showing a transparency applied to the surface of the coated cylinder for exposure of the resist prior to etching; and

Figure 3 is a diagram showing the method of exposing the cylinder resist beneath the transparency.

The present invention has for its object the provision of a novel and improved process .of

photoengraving, particularly for rotary, intaglio printing members. A further object is the provision of an improved process of preparing rotary photogravure cylinders. provides an improved process of coating a cylinder with photosensitive resist, exposing the resist and developing the resist so that it may be etched to provide a rotary photogravure printing cylinder.

In the conventional process of rotary photogravure, the ground and polished cylinder of copper is cleansed and on it is transferred a layer of exposed photosensitive gelatin which has been exposed to a continuous tone transparency of the picture to be reproduced, as well as a rotogravure screen, after which the layer is developed and etched in varying strengths of ferric chloride. However, such a process depends upon the transfer of a previously exposed layer of colloid, the precise and skilful development of the layer, and then the etching in selected strengths of etch, which not only etch the copper, but also wear away the gelatin film so as to etch the copper to varying depths in the various intagliated cells.

The invention further In accordance with the present invention, the copper cylinderis coated with a solution of gelatin and a bichromate to provide a thin, uniform layer of resist'on the surface of the cylinder. Preferably warm bichromate gelatin solution is poured on the cylinder as it is rotated to form the uniform film, and the cylinder is revolved until dry, in a current of warm air, if desired. When dry, the layer is exposed through a combined screen and continuous tone transparency, preferably comprising the positive transparenc print on strip film of a conventional halftone photoengraving negative which provides a' uniform number of dots per unit area, which dots vary in size or area in'accordance with the tones to be reproduced. This strip film transparency is wrapped around the coated cylinder in intimate contact therewith, preferably in page size areas, with the sheets held in place by scotch tape or otherwise until after exposure. When the cylinder has been completely covered by the transparencies, it is exposed in actinic light, preferably a longitudinally extending beam of light, as the cylinder is revolved to distribute the exposure uniformly. When sufficiently exposed, the transparency is removed, the cylinder developed in water considerabl warmer than the body of the cylinder and when the cylinder has been completely developed, the cylinder is suitably etched, as for instance in an aqueous solution of ferric chloride. When fully etched, the remaining resist may be removed from the cylinder by means of an alkaline solution, such as dilute caustic soda, thereby rendering the cylinder ready for printing in the usual manner.

The printing member produced by thejpresent invention ,is superior to the conventional rotogravure member, as the image on the printing member is formed of intagliated cellular cavities of substantially uniform depth which vary in area in accordance with the tone to be reproduced. Furthermore the etching is accomplished with much more certainty than is usual and depends in no way upon the humidity of the gelatin. or ambient atmosphere.

It will be understood that the foregoing general description and the following detailed description as Well are exemplary and explanatory of the invention but are not restrictive thereof.

Referring now in detail to the details of the preferred process according to the present invenetched comprises a ground and polished cylinder l0 having a surface layer which is preferably a Water c" 4000 Soft gelatin grams 400 Ammonium bichromate do 80 Ferric ammonium citrate do 80 This sensitized resist is slowly poured on the surface of the rotating cylinder to provide an excess of resist as the stream is moved from one end of the cylinder to the other, and rotation of the cylinder is continued until the resist has gelled and dried, preferably assisted by a current of warm air directed against the cylinder l0.

When the thin layer of resist it has dried, the cylinder is ready to receive the transparency for the photographic exposure. This transparency is preferably made from a conventional photoengraving' .halftone camera negative on- -paper strip film and is developed, fixed and Washed in the usual manner. Alternatively, the transparency may be formed by making a halftone copy of a continuous tone negative-of the desired copy through a halftone screen,-(in the. conventional manner of making a halftone negative except that a negative rather than positive copy is used). Thus in the shadows, the transparency comprises sma11 transparent dots, while in the highlights, the transparency comprises large transparent dots which maymerge to leave-only small opaque dots. a

After processing, the transparency comprises a'thin flexible film Ilwhich wheh dry may be wrapped on the surface of the resist-coated cylinder I to bringit into intimate contact with the resist on the surface of the cylinder where it may beheld by scotch tapel2 around the edges of each sheet of film, the-several'sheets of eachconsition on the cylinder surfacethe resist is ex posed to actinic light through the transparencies for a tim sufiicient to render it fully exposed. This exposure is preferably carried out by rotating the cylinder at a fairly slowate adjacent to a light source l6 of actinic light extendin'glongirtudinally of the cylinder, such as a mercury vapor lamp which may be shielded by the opaquemembers l8. The-rotating of the cylinder l0, con tinued forv a considerableperiod of time, produces a uniform illumination of the transparencies M andresistlayerll. A

After the exposure is complete, the transparencie'sv M are removed and the cylinder I B, which isat room temperatureof about 70 to 80 F., is

4 ready for development which may be carried out by spraying with, or rotation in Water at 120 to 140 F., approximately. Alternatively, the resist may be developed in a 1% aqueous solution of a substantive dye such as brilliantbenzoechtvi-olett (Schultz 1931 Edition No. 610 EL, 2 RL). The resist may then be hardened by immersion for a few moments in a dilute solution 1% or 2% of a chromic acid compound or other hardening agent which reacts with the dye to harden the gelatin in accordance with the process of my 00- pending application Serial No. 524,074, filed February 26,1944.

After drying and rinsing with water, the cylinder may be etched by treatment with a suitable mordant such as aqueous ferric chloride in the usual manner of photoengraving, not requiring the varying strengths of mordant as is usual with rotogravure.

When the proper depth is attained, the cylinder I!) may be rinsed, dried and proved, after which the resist I I may be strip ed Ebyrneans of a dilute alkaline solution. 1 I

The process is highly advantageous inconnection with multicolor work, as the etching is much more readily controlled than usual, requires less hand work andthe cylinders may be proved and if needing correction may be again etchedbefore the resist is removed. j

The invention in its broader aSPGC tS iS -HOt limited to the specific processes andist epsshown and described but departures may be made; therefrom within the scope of the accompanying claims Without departing from the'principles of the invention and without sacrificing itschief advantages j WhatIclaimis: Y g 1. The process of photoengraving a' cylinder which comprises coating the surface of the cylinder with a layer of photosensitive: gelatin resist, exposing the resist to the desired imageand developing the exposed resist by treatment with water substantially warmerwthan the bodyI-of-the cylinder to wash-away the not fully exposed gelatin resists,dyeing the resist with a substantive dye, and hardening the resist by a compound re activewiththe dye. 2. The process of photoengraving ajcylin'der which comprises coating the surface of the cyliinder with a layer of photosensitive gelatinresist, exposing the resist to the desired imag and'developing the exposed resist by ,treatmentQwith water substantially warmer. than the body of the cylinder to wash away the not fully exposed gelajtin resists, dyeing the'resistwith asubstantive dye, hardening theresist by a chromic'acidsolution, and etching the cylinder.

. 7 FRANK T. POWERS}

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