US2892711A - Process for producing gelatin relief images on printing plates - Google Patents

Description

R. SANFORD ET AL PROCESS FOR PRODUCING GELATIN RELIEF IMAGES ON PRINTING PLATES June 30, 1959 Filed Aug. 15, 1954 GELATIN PAPER BREAK -AWAY ADHE SIVE STABLE BACKING PA PER $TA5LE BACKING MTA M PLIQSTIC 2 SheetsSheet l sspmm PAPER BREAK-AWAY ADHESIVE NON WATER SOLUBl-i ADHESIV! LATIN PAPER BREAK-AWAY ADNEQIVE NON WATER SOLUBLE ADHESWE Non WATER sowaua GELATIN STABLE BACKING a (METAL 0R PLASTIC) 8 smaue BACKING INVENTOR5 BYJW ATTORNEYS R- .SPSANFORD ET AL PROCESS FOR PRODUCING GELATIN RELIEF June 30, 1959 IMAGES ON PRINTING PLATES 2 Sheets-Sheet 2 Filed Aug. 15, 1954 S 5 m w m m L E O 0 T n R 1 A H E T T O N IG N O w m R E Nw um 7 .w T 8 O R s T l o N N W E U r ww m m N mm w /m j c c R w m 0 A R R C u 0 IO M 03 6 Y w B v L 4 v a 5) o 4 W o o o o o o o o o o o o o c o O 4 niuw lkmmmam mmmu naacr dun. mmIOZ IU-rmdPW Z mIm United PROCESS FOR PRODUCING GELATIN RELIEF lNlAGES N PRINTING PLATES Application August 13, 1954, Serial No. 449,540 3 Claims. (Cl. 96-35) This invention relates to printing and more particularly to methods and materials useful in the preparation of printing plates or cylinders, such as intaglio plates and cylinders by photo'mechanical means.

One of the common methods of producing high quality intaglio plates and cylinders, hereinafter referred to as plates, is by the use of so-called carbon tissue, a product comprising a paper backing sheet which is water permeable and hygroscopic, and consequently dimensionally unstable under changing humidity conditions, and a coating of unsensitized pigmented gelatin on one surface thereof.

In the normal course of this process, which is generally carried out in air conditioned plants, the carbon tissue is sensitized in an aqueous bichromate solution, squeegeed gelatin side down on a ferrotype plate, dried and stripped from the ferrotype plate, placed in a refrigerator for a period of several hours, removed from the refrigerator and allowed to stabilize in the air-conditioned room for a further period, and thereafter exposed to light through a transparency as well as through a suitable screen, generally by contact in a vacuum printing frame, the use and characteristics of which are well known in the art. The gelatin is selectively hardened by exposure to light in accordance with the varying density of the image on the transparency and screen, the hardened portions being insoluble in warm water at a temperature of about 110 F., and the unhardened portions being soluble therein.

Following the exposure in the vacuum printing frame, the carbon tissue is rolled gelatin side down on a copper printing plate or cylinder wet with distilled water, which causes the gelatin to adhere firmly to the cylinder. The plate is then developed in warm water, and since the paper backing of the carbon tissue is hygroscopic and water-permeable, the warm water softens the unhardened gelatin adjacent the surface of the paper, allowing the latter to be peeled ofi the gelatin. The plate is further developed in warm water to remove all the unhardened gelatin, and the result is a gelatin relief image on the plate. The plate is thereafter subjected to an etching bath, such as a ferric chloride solution, which selectively etches the plate in accordance with the thickness of the gelatin relief image. The end result is a depressed relief image on the copper plate, which is then used for printing by the well-known intaglio process.

The above process gives perhaps the highest quality reproduction of any of the photo-mechanical processes utilized in the preparation of printing plates, but due to the lack of dimensional stability of the carbon tissue under changing conditions of temperature and humidity, which occur even in air conditioned plants, it has been found extremely difiicult, particularly in multi-color work, to produce plates for the diiferent colors each having the same size image. It is also diificult in black and white work to produce plates having the same size image as the original, and difiiculty is also experienced when multiple exposures are made on the same sheet of carbon tissue,

Patent 0 M Patented June 30, 1959 2 as is done in some cases, and it is accordingly an object of the present invention to provide means and methods for overcoming these ditficulties.

Another object is the provision of means and methods for maintaining materials such as carbon tissue dimensionally stable during processing without interfering with the normal processing procedure.

Still another object of the invention is to provide: means and methods for maintaining carbon tissue dimen-- sionally stable during the period of exposure and subse-- quent application to the printing plate.

A further object of the invention is the provision of. means and methods for securing a dimensionally stable: strippable backing to the carbon tissue during processing.

A still further object of the invention is to provide a. novel dimensionally stable strippable backing member for carbon tissue.

Another object is the provision of a photographic stripping material.

These and other objects and novel features of the invention will appear more fully hereinafter from the following detailed description when taken in connection with the accompanying drawings, wherein several embodiments of the invention are illustrated. It is to be expressly understood, however, that the drawings are employed for purposes of illustration only, and are not designed as a definition of the limits of the invention, reference being had for this purpose to the appended claims.

In the drawings, wherein similar reference characters refer to similar parts throughout the several views:

Fig. l is a representation of the structure of a sheet of carbon tissue of conventional type;

Fig. 2 shows the carbon tissue at one stage of one modification of the process;

Fig. 3 shows another stage of the modification of the process referred to in Fig. 2;

Fig. 4 is illustrative of another modification of the invention;

Fig. 5 shows a stable backing member utilized in the preferred form of the invention;

Fig. 6 shows a stage in the performance of the invention in its preferred form as referred to in connection with Fig. 5; and

Fig. 7 is a graph showing the effect of humidity variations on carbon tissue with and without a dimensionally stable backing.

Although the present invention is particularly adapted to use in connection with carbon tissue, as the term is commonly 'used in the trade, it is to be understood that the invention is also suitable for use in other photo-mechanical reproduction processes, such as those utilizing a paper base sheet coated with a light sensitive emulsion which may be developed in suitable chemical solutions after exposure and transfer to a printing plate. The term carbon tissue, as used in this specification, is accordingly intended to include such other photo materials as maybe adhered to a printing plate and thereafter have the backing removed by treatment in aqueous solutions to leave the image receiving coating of the material on the plate. In like manner, the term gelatin is intended to include other colloidal materials and the like, which may be coated on a backing sheet, and which are adapted to receive a photographic image.

As indicated heretofore, in the application of the carbon tissue process to multi-color work requiring the production of a separate printing plate for each color, great diificulty has been experienced in producing a set of plates all having the same image size. Carbon tissue is normally sensitized in an aqueous bichromate solution a short time before it is to be used, as it will only keep ashort time in the sensitized condition, and since it is normally squeegeed to a metal ferrotype plate after being sensitized, the backing of'the' carbon tissue must'be a water-permeable material, such as paper, in order to allow the water of the sensitizing solution to escape from the gelatin during'drying of-the carbon tissue on the ferrotypeplate. the carbon tissue thereto, is developed in water or in an aqueous solution to release the backing fromthe gelatin which also necessitates the use of a water permeable.

backing sheet on the carbon tissue.

Paper, however, is hygroscopic, and changes dimensionally in response to humidity changes, which is the basic cause of the difficulty in producing a set of printing plates all having the same image size. The critical period as regards registration starts when the image is printed on the carbon tissue in the printing frame, and ends when the gelatin of the carbon tissue has been firmly adhered to the surface of the printing plate. Although this is a relatively short period of time, the relative humidity in an air conditioned plant has been found in some cases to have a variation of from 50 to 68%, an amount sufiicient to expand or contract the carbon tissue during processing by an amount suflicient to throw some of the plates out of registry so that new plates had to be made.

The present invention overcomes these difficulties, and in the preferred form of the invention a sheet of carbon tissue 4, shown in Fig. 1 and having a paper backing sheet 5 with a gelatin coating 6 on one surface thereof, is sensitized in the usual manner, squeegeed gelatin side down to a ferrotype plate, dried and stripped from the plate, placed in a refrigerator, and then conditioned in the work room for a period suflicient to allow the carbon tissue to reach substantially the temperature and humidity conditions obtaining in the work room at the time.

Prior to placing of the carbon tissue in the vacuum printing frame, a stable backing sheet 7, shown in Fig. 5, is placed against the paper backing of the carbon tissue, as will be more fully explained hereinafter. Although different materials may be utilized for the backing sheet, the preferred form includes a thin sheet 8 of flexible, substantially non-extensible and non-moisture-permeable plastic. A sheet of unplasticized vinyl chloride-acetate copolymer having about 87% vinyl chloride and 13% vinyl acetate, and having a thickness of .005", has been used successfully, although other materials may be utilized, suchas polystyrene, polyethylene, polyvinyl butyrol, polyvinyl acetal and polyvinyl aceto-butyrate, or sheets of thin metal maybe used. These materials should be so constituted, however, as to be substantially non-extensible during handling, and should preferably be sufficiently transparent to permit the viewing therethrough of registration marks on the carbon tissue.

One surface of the plastic sheet is coated with a very thin layer 9 of a permanently pressure sensitive nonoxidizing adhesive, the thickness of the coating being of the order of .0005". The adhesive should be so constituted as to be substantially non-offsetting on the paper of the carbon tissue, of sufficient strength to substantially prevent relative expansion or contraction of the carbon tissue when adhered to the paper backing thereof, and of insuflicient strength to effect appreciable tearing of the carbon tissue during stripping therefrom. A certain amount of tearing of the paper backing of the carbon tissue is permissible provided such tearing is insufficient to effect tearing of the gelatin coating of the tissue. It would also be desirable that the adhesive, when coated on one surface of the plastic, have the property of nonadherence to the other surface of the plastic, thus permitting rolls or sheets to be stored and stripped without resorting to the use of interleaving sheets to prevent blocking. There is also a further requirement, regardless of whether a pressure sensitive or other type adhesive is used. The stable backing sheet must be secured to the. paper of the carbon tissue with an adhesive that does not require the evaporation ,of any appreciable amount Also theprinting plate, after application of of solvent as after the lamination is made, such solvent can only be absorbed by or escape'through the carbon tissue.

Although the plastic backing sheet may be separately laminated to the backing of the carbon tissue before placing the resulting assembly inthe printing frame, it is sufficient, particularly when a vacuum printing frame is used, to lay the plastic sheet on the back of the carbon tissue with the adhesive against the paper, and then place the assembly in the frame. When the frame is evacuated, the two sheets are brought into intimate contact, and maybe subsequently removed from the frame, trimmed, and transferred to the printing plate or cylinder without separation. The laminated assembly as it comes from the printing frame is shown in Fig. 6, and comprises the gelatin layer 6, paper layer 5, adhesive layer 9, and plas tic sheet 8.

In the. printing operation, a transparency, usually on a glass plate, is supported by the glass front of the printing frame, and the gelatin of the carbon tissue is placed in contact with thetransparency. When the novel backing member 7 is used as above described, the carbon tissue is. protected against dimensional changes during printing in the following manner. against humidity changes by engagement with the transparency. The paper is sealed against humidity changes by the plastic backing. Since the plastic backing and the pressure sensitive adhesive are non-hygroscopic, there is no tendency for the latter to absorb moisture from the paper or to increase the moisture content of the paper. The. plastic backing is moisture-impermeable, and prevents any tendency for the paper to dry out due to evacuation of the printing frame. Thus theonly portions of the carbon tissue subject to humidity changes during printing are the edges of the paper and its gelatin coating, and due to the extremely small area thus exposed, any resulting humidity changes are negligible. In addition to being held together during printing by the action of the vacuum frame, the carbon tissue and plastic backing are further mechanically held together against relative expansion or contraction by the adhesive layer 9. Thus any humidity change or dimensional change in the carbon tissue during the printing operation is to all intents and purposes entirely eliminated.

Immediately after the printing operation, the assembly is removed from the frame, and then placed on the printing plate or cylinder as soon as possible. This is done by aligning the assembly on the plate, and then wetting the surface of the plate with distilled water and rolling the gelatin surface of the assembly into intimate contact therewith. The gelatin immediately adheres firmly to the plate, and the plastic backing member is then stripped off, the adhesive, as before stated, being so constituted as to permit this without tearing the paper of the carbon tissue, and without offsetting the adhesive on to the paper, which would interfere with the subsequent water development. The plate is then treated in a warm aqueous solution in the usual manner to permit stripping of the paper of the carbon tissue and subsequent development of the gelatin image.

As will be understood from the foregoing description, the carbon tissue is sealed against humidity changes during printing, and is held mechanically against dimensional changes. On removal from the printing frame, the entire assembly except the gelatin surface is sealed against humidity changes. The interval between removal of the assembly from the frame and application to the printing plate is short, and it has been found that with the paper sealed and mechanically held by the plastic backing duringthis period, changes in the gelatin occur which are suflicient to affect registration, and repeated trials under commercial conditions have resulted in perfect registration of the finished printing plates in each case.

In-a modification of the invention as illustrated in Figs. 2 and 3, the carbon tissue ;is sensitized and squeegeed to The gelatin is sealed' a ferrotype plate, and while still wet, is coated with a uniform coating 10 of a so-called break-away adhesive. This adhesive is water-soluble, and may comprise 2 to 6 parts of an adhesive ingredient such as polyvinyl alcohol to 100 parts of an inert ingredient such as finely powdered Georgia clay, with enough Water to make a coatable composition. The adhesive acts as a binder for the clay particles, and the result is a relatively weak adhesive which on drying, is frangible and of insufficient strength to tear the paper of the carbon tissue.

When the carbon tissue and the coating of frangible adhesive is dried and stripped from the plate, it is preferably conditioned as heretofore set forth. The stable backing sheet 8 is then applied to the coating of dried adhesive 10 with a suitable adhesive 9 which does not require the removal of solvent for setting, a precedure which would be prevented by the impermeable backing sheet 8, and the carbon tissue is then printed in the printing frame and applied to the printing plate as heretofore described. Thereafter the stable backing sheet is stripped off, the separation occurring along the line of the frangible adhesive. The printing plate is then treated in warm water in the usual manner to wash olf the remaining Water-soluble frangible adhesive, remove the paper backing of the carbon tissue, and develop the gelatin image on the plate. The paper used in different makes of carbon tissue varies considerably, and in some cases tears very easily. The above described modification is particularly useful in connection with such tissue, as the frangible adhesive forms a barrier between the paper fibers and the adhesive 9, and prevents the adhesive 9, which in this case may be a relatively strong adhesive if desired, from bonding to the paper and tearing the latter during stripping.

As a further modification, it has been found that an assembly can be made up as shown in Fig. 4, the assembly comprising, in the order named, the gelatin 6 and the paper backing of the carbon tissue, the frangible or break-away adhesive 10, a layer of paper 11 held by the adhesive 10, a layer of adhesive 9, and the stable backing sheet 8. In this case the paper 11 cooperates with the frangible adhesive 10 to form an effective barrier between the paper of the carbon tissue and the adhesive 9, insuring against any tearing of the paper of the carbon tissue during stripping.

In the formation of the assembly of Fig. 4, the carbon tissue is sensitized in an aqueous bichromate solution, squeegeed to a ferrotype plate, and coated with the frangible adhesive 10, whereupon the paper sheet 11 is laminated thereto. The resulting assembly is dried and stripped from the ferrotype plate, the stable backing sheet 8 is adhered to the paper sheet 11 with the adhesive 9, and the assembly is placed in the printing frame. After printing, the assembly is applied to the printing plate as heretofore described. The stable backing and paper sheet 11 are then stripped from the paper backing 5 of the carbon tissue along the glue line of adhesive 10, and the plate developed as usual in warm water. The carbon tissue is substantially sealed against humidity changes during printing and transfer to the printing plate, and is held mechanically against expansion or contraction by adhesive 10, paper 11, adhesive 9, and stable backing 8.

The operation of the preferred form of the invention is clearly and strikingly illustrated by the graph of Fig. 7. The curved line 12 represents the expansion and contraction of a piece of carbon tissue across the grain of the paper under changing relative humidity. Lines 13 and 14 indicate the relative humidity permissible for the maintenance of the required register tolerance of .006" indicated by horizontal lines 15 and 16; line 17 shows the performance of a sample of carbon tissue having the stable backing adhered thereto as in Fig. 6. The actual relative humidity readings for this ranged from 30% to 70%. There was no change of registry over a period of several days.

With regard to the adhesive utilized to adhere the stable backing to the carbon tissue, the importance of a nonsolvent releasing adhesive is emphasized. As stated heretofore, most carbon tissue is ferrotyped after sensitizing. No moisture-impermeable backing sheet can be adhered to it until dry, as otherwise the ferrotype plate and stable backing would prevent moisture evaporation. After the carbon tissue is dried, an adhesive must be used that will not impart any appreciable amount of solvent to the carbon tissue. A solvent activated adhesive has been used on the backing sheet by barely wetting it with solvent prior to lamination, but this method is diflicult to control, and the use of pressure sensitive adhesive is preferred. A thermo-setting adhesive can possibly be used, but the strength is diflicult to control from the standpoint of stripping. In the event a metal backing sheet is used, a socalled delayed action adhesive may be used. Such adhesives are available, which after heating and subsequent cooling, retain their adhesive properties for some time. In any case, the use of any appreciable amount of heat to effect the lamination is precluded, as the gelatin will not stand high temperatures without damage.

While the invention has been illustrated and described herein with considerable particularity, it is to be understood that other forms of the invention may suggest themselves to those skilled in the art, and reference is accordingly made to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. A process for producing a gelatin relief image on a printing plate from a transparency having a master image imprinted thereon in which the relief image and master image will have substantially identical dimensions, comprising: adhering a flexible sheet of moisture-impermeable material coated on one side with a permanently pressuresensitive, non-oxidizing, non-hygroscopic adhesive free of volatile solvents to substantially the entire uncoated side of a water-permeable paper sheet coated with a light hardenable gelatin film, said paper sheet being normally subject to expansion and contraction upon change in humidity conditions but dimensionally stabilized by the sealing action of said flexible sheet and said adhesive being non-offsetting on said paper sheet and of sutficient strength to prevent relative movement between said paper sheet and said flexible sheet While said sheets are adhered but of insuflicient strength to tear said gelatin film when said flexible sheet is stripped from said paper sheet; exposing said gelatin film to light through said transparency to selectively harden portions of said film; adhering said selectively hardened film to the surface of said printing plate; stripping said flexible sheet and said adhesive carried thereby from said paper sheet; and contacting said paper sheet and said gelatin film with water to remove said paper sheet and the unhardened portions of said gelatin film from said printing plate leaving said gelatin relief image thereon.

2. The process of claim 1 in which said flexible pressure-sensitive adhesive-coated sheet is composed of a light-transmitting plastic material.

3. The process of claim 2 wherein said plastic material is a copolymer of vinyl chloride and vinyl acetate.

References Cited in the file of this patent UNITED STATES PATENTS 2,010,188 Hagedorn et al Aug. 6, 1935 2,089,460 Wilmanns et al. Aug. 10, 1937 2,385,599 Ballet a1 Sept. 25, 1945 FOREIGN PATENTS 577,230 Great Britain May 9, 1946

Claims (1)

1. A PROCES FOR PRODUCING A GELATIN RTELIEF IMAGE ON A PRINTING PLATE FROM A TRANSPARENCY HAVING A MASTER IMAGE IMPRINTING THEREON IN WHICH THE RELIEF IMAGE AND MASTER IMAGE WILL HAVE SUBSTANTIALLY IDENTICAL DIMENSIONS, COMPRISING: ANHERING A FLEXIBLE SHEET OF MOISTURE-IMPERMEABLE MATERIAL COATED ON ONE SIDE WIWTH A PERMANEENTLY PRESSURESENSITIVE, NON-OXIDIZING, NON-HYGROSCPPIC ADHESIVE FREE OF VOLATILE SOLVENTS TO SUBSTAMTIALLY THE ENTIRE UNCOATED SIDE OF A WATER-PERMEABLE PAPER SHEET COATED WITH A LIGHT HARDENABLE GELATIN FILM, SAID PAPER SHEET BEING NORMALLY SUBJECT TO EXPLANSION AND CONATRACTION UPON CHANGE IN HUMIDITY CONDITIONS BUT DIMENSIONALLY STABILIZED BY THE SEALING ACTION OF SAID FLEXIBLE SHEET AND SAID ADHESIVE BEING NON-OFFSETTING ON SAID PAPER SHEET AND OF SUFFICIENT STRENGTH TO PREVENT RELATIVE MOVEMENT BETWEEN SAID PAPER SHEET AND SAID FLEXIBLE SHEET WHILE SAID SHEETS ARE ADHERED BUT OF INSUFFICIENT STRENGTH TO TEAR SAID FELATIN FILM WHEN SAID FLEXIBLE SHEET IS STRIPPED FROM SAID PAPER SHEET; EXPOSING SAID GELATIN FILMM TO LIGHT THROUGH SAID TRANSPARENCY TO SELECTIVELY HARDEN PORTIONS OF SAID FILM; ADHERING SAID SELECTIVELY HARDENED FILM TO THE SURFACE OF SAID PRINTING PLATE; STRIPPING SAID FLEXIBLE SHEET AND SAID ADHESIVE CARRIED THEREBY FROM SAID PAPER SHEET; AND CONTACTING SAID PAPER SHEET AND SAID GELATIN FILM EITH WATER TO REMOVE SAID PAPER SHEET AND THE UNHARDENED PORTIONS OF SAID GELATIN FILM FROM SAID PRINTING PLATE LEAVING SAID GELATIN RELIEF IMAGE THEREON.

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