US2028710A - Printing plate - Google Patents

Description

Patented Jan. 21, 1936 PATENT OFFICE PRINTING PLATE Hylton Swan, Upper Montclair, and Sigfried Higgins, Verona, N. J., assignors to Bakelite Cor- Dur i n, New York, N. Y., a corporation of Delaware Application May 26, 1934, Serial No. 727,723

21 Claims.

This invention relates to a printing plateand method of preparing same.

The printing trade at the present time greatly desires a printing plate which is of general application, that is, one which may be used with smooth or rough paper and which is applicable either to flat-bed or cylindrical types of presses.

In an effort to provide such a plate, rubber plates have found favor but the rubber printing surfaces are subject to attack by the oils which are in the common inks. In order to prevent the deterioration of the printing surface of the plate, it has been proposed to make plates with either a synthetic resin face or a metal face. A difliculty with a plate faced with synthetic resin, however, is that the resin sets to a hard, brittle condition so that it must be molded either flat or curved for a particulartype of press. A difficulty with the metal faced plates is that they cannot be used for a high grade printing job on rough finished or antique papers. Plates composed entirely of cellulose acetate or nitrate have been proposed but have not found favor with the trade. The cellulose nitrate is dangerously inflammable and is unsatisfactory due to the tendency to warp or shrink under variable atmospheric conditions. Cellulose acetate is less water absorbent but a thick plate cannot readily be curved for application to a cylindrical plate without distorting the type faces.

An object and feature of the present invention is a plate which can be made easily and quickly from materials readily obtainable in the open market and which, when prepared, may be used either on a flat-bed press or a rotary cylinder press without material distortion of the type face. Furthermore, the plate is resilient so that it may be used to print on either smooth or rough paper, and by virtue of its resiliency such a plate has the definite advantage of materially reducing the time required in accurately setting up the plate on the printing press, technically known as make-ready. Moreover, in its manufacture the printing surface of the plate does not stick to' the synthetic resin matrices which are highly desirable for use in forming a plate, due to their strength, light weight, durab lity and fidelity in reproducing "the original type or other printing areas.

Other objects and features of the invention will be pointed out in the claims and will be understood from the following part of the speci fication wherein one of the preferred forms of the invention is disclosed, together with the drawing illustrating a plate and matrix.

We have discovered that-a plate including a printing face comprising a thin sheet of cellulose acetate and a rubber body which is softer than the cellulose acetate, and preferably with a layer of stretch resisting material next to the 5 cellulose acetate, has the desirable characteristic which adapt it for almost universal use.

The cellulose acetate is extremely tough and wear resistant and has sufficient strength so that fine lines and small dots do not mushroom or 10 spread when printing pressure is applied yet, on the other hand, when backed up with a rubber body of the desired resiliency, it is sufficiently flexible and compressible to print satisfactorily on rough paper. The printing surface is not 15 attacked by the oils in the common printing inks, and is resistant to wear and deterioration both in use and in storage before or after use. The printing surface takes ink very well from inking rollers or other inking devices and. gives it up 2 very readily to the material upon which the printing is being done. Furthermore, the printing surface faithfully reproduces the smallest hairlines and dots on the matrix as well as the largest printing areas, and can beformed to 25 reproduce a matrix with great fidelity and without the use of extremely high forming pressures which may damage the matrix surface. In thin sheets, the cellulose acetate for instance that obtained in the open market including such plasticizers, oils, waxes, etc. as may be desired, can when heated rather easily be forced into, and can readily be made to conform to, the finest detail in the matrix. The sheets of cellulose acetate which we use may, for example, be from .001 to .035 of an inch in thickness. They may also be roughened on'one side for instance by sand blasting, to assist the bonding of the surface to the rubber body or intermediate stretch resisting layer.

The rubber body should have sufficient yield to pemiit the plate to be used on rough paper and it should also have sufficient yield to be compressed when the plate is curved so that the strains and stresses set up in curving the plate are absorbed in the rubber body instead of forcing the cellulose acetate facing to stretch. The underlying rubber body may be of varying flexibility, thus, for instance, it should be less soft when the plates are made with a thick'rubber underlayer, else the plate will not be solid enough to resist pull or movement in planes parallel to the surface, for accurate register, for instance in color work. This lateral displacement is particularlynoticeable on rotary presses where, if the plate is too yieldable, there is a tendency for the printing surface of the plate to shift laterally with relation to the base at the time that the leading edge of the plate meets the impact of the impression cylinder. Thus a plate which has a relatively thin rubber body should contain rubber which is softer than the rubber in a plate having a thick rubber body because with a thin rubber body, there is less of the elastic yieldable rubber to permit the plate to yield on rough paper and there is less tendency for the printing surface to shift laterally with regard to the base. In the case where a thick rubber body is used, it is preferably of harder rubber, sumciently yieldable to permit of some compression when printing on rough paper, but hard enough to resist lateral displacement of the printing surface. For relatively thin rubber bodies, for example where the rubber is from .125 to .150 of an inch in thickness, 'the body may test between 50 and 65 durometer test and if a relatively thick rubber body, for example where the rubber is from .180 to .250 of an inch in thickness, the body may test between 60 and '75 on the durometer. The intermediate stretch resisting layer is particularly desirable where the rubber body is of the thicker and harder rubber since the harder rubber resists compression more than the softer rubber of a thinner body and thus has a greater tendency to cause stretch of the cellulose acetate facing. The proper amount of yield of the rubber may be obtained by regulating the amount of vulcanizing agent, accelerators, etc. incorporated with the rubber, or by incorporating fillers, for instance, zinc oxide, carbon, barium sulphate, asbestos, etc. The rubber body may also have included in it, one or more sheets of absorbent paper, fabric or similar material, for instance rubber impregnated blotting paper, or cloth which is readily compressible and adapted to be curved but has relatively great resistance to stretch or movement in a plane parallel to the plane of the printing surface.

If desired, a metallic foundation plate or sheet may be fastened to the rear face of the rubber body to assist in holding the plate on the press. The rubber or rubber filler composition may thus be of a thickness sufiicient to give a plate of the desired cross section or it may be thinner to allow for the thickness of the metal or similar sheet. This metallic foundation plate or sheet should, however, not be applied to plates which are to be curved, prior to the curving operation, else it will prevent the free compression of. the rubber body when the plate is curved and thus will have a tendency to cause stretch and distortion of the cellulose acetate printing surface. For plates designed for fiat-bed presses, the metallic sheet may be applied to the plate or plate blank at any time but for plates which are to be curved after molding, the metallic sheet should first be given the required curvature and then cemented to the curved plate after the rubber has absorbed the stresses or strains due to curving.

An illustrative method of making the plate will now be described, it being understood that the description is by way of example only and that variations thereof may be made as desired. The" sheet of rubber either with or without filler or embedded fibrous material is first procured; This sheet should contain sufficient vulcanizing or curing agent to produce the required stifiness upon heating but yet not harden the rubber sufllciently to prevent it from compressing when the plate is curved. The rubber sheet is coated with an adhesive which adheres to both the rubber and cellulose acetate. A general example of a suitable adhesive is an acid degenerated rubber in a solvent or an emulsion or dispersion, comprising ingredients which render tacky the cellulose acetate, for instance a solvent for the cellulose acetate such as acetone. The adhesive may be used to coat the adjoining. surface of the rubber and cellulose acetate or a sheet of fibrous material, for example paper, blotting paper or cloth may be coated or impregnated with this adhesive and used as an intermediate bond between the rubber and cellulose acetate. Also, the stretch resisting material may be coated on one side with a rubber adhesive, for instance a rubber solution, and on the other side, with a cellulose acetate adhesive for instance a solution of cellulose acetate. Under the influence of heat and pressure when the plate is molded, the cellulose acetate adhesive on one surface of the intermediate sheet and the rubber adhesive on the other surface. bond with the cellulose acetate facing sheet and the rubber body, respectively.

After coating the surface or surfaces to be joined, with the above adhesive or other suitable material, and preferably after waiting until the adhesive has a tacky surface, the sheets are assembled and pressed together to form a unitary composite sheet. The metallic foundation plate may also be included in the assembly for plates designed for flat-bed presses, the acid degenerated rubber adhesive for example, being used to cement the metallic sheet to the rubber body. A stack of the assembled sheets may be held under pressure until the cement has thoroughly set. If desired, however, the composite sheets may be molded directly after assembly, but if a wet adhesive is used,- the press should be vented to allow the escape of volatile ingredients.

Having made the plate blank, it may be formed into a printing plate in the following manner. The matrix used is preferably of a heat-hardened synthetic resin, for instance a phenol formaldehyde condensation product, which does not adhere to the cellulose acetate printing surface and which is unaffected by temperatures suitable for the vulcanization of the rubber or for softening the cellulose acetate. The surface of the cellulose acetate may 'be moistened slightly with a volatile solvent, for instance acetone, to enable it to soften and flow more easily. The composite lank is laid in a press, preferably heated, with cellulose acetate face against the matrix and is subjected to heat and pressure until the printing surfaces have been formed on the face and preferably until the rubber has reached the desired state of hardness.

It is possible to remove the plate from the press before the rubber is vulcanized suificiently to give the desired stifiness and then continue the heating in an oven, but this is not recommended as the plate may be damaged by such removal and the oven heating must be very carefully regulated so as not to melt the characters on the cellulose acetate facing. The molding of the printing surface preferably takes place in a semi-positive mold so that there is some check ofiered to the side flow of the plastic material, which gives a plate with a substantially uniform density and definition at the corners and edges, and the mold should be cooled before removal of the plate so as to harden the cellulose acetate, which is permanently thermoplastic and not heat-hardening as are the phenolic resins. The cellulose acetate softens and flows before the rubber sets, so that the soft rubber acts as a hydrostatic cushion while the cellulose acetate is taking the exact definition of the matrix face. Then the rubber hardens so that a very uniform plate is obtained. The mold is thereafter cooled sufiiciently to harden the cellulose acetate and prevent injury to the printing characters when the plate is removed from the mold and matrix.

The cellulose acetate facing gives a permanent tough printing surface which is smooth and relatively hard yet the plate is sufficiently yieldable to print on rough paper. The surface does not scratch easily as does a surface of a metal soft enough to be formed by a corresponding pressure for instance in a mold at approximately 150 C. a molding pressure of approximately 700 pounds per square inch may be used whereas with metal faces pressures in the neighborhood of 7000 pounds per square inch and upwards are usually found necessary in commercial practice. Nevertheless, the small printing areas, for instance, the fine dots on photographic-screenreproduced printing areas, do not spread or mushroom under repeated impacts of the inking rollers or impression cylinder as would the softer rubber without the cellulose acetate facing. The cellulose acetate need contain no filler and thus the printing surface is very uniform and the cellulose acetate sheet is thick enough so that the characters as well as the base layer of the printing surface are all of the same material which would not be the case if a rubber body sheet were merely varnished with the cellulose acetate solution and then molded.

A preferred form of the invention has been. described but it is not intended to exclude modification thereof. Under proper conditions, other types of yieldable bodies may be used, for instance the synthetic rubbery products now on the market, such as a hydrochloride divinyl acetylene product one form of which is sold as Duprene, vulcanized sulphur hydrocarbon-products one form of which is known as Thiocol fact-is, or a rubbery fatty oil-phenolic-methylene product. The oxidized fatty oils, for instance oxidized linseed oil, may be used in part as a modifying agent for the rubber or rubber substitute as may be other modifiers. It is therefore recognized that there are many variations of the invention and it is desired that the invention may be construed as broadly as the claims taken in conjun tion with the prior art may allow.

We claim:

1. A printing plate comprising a facing of cellulose acetate from substantially .001 to substantially .035 of an inch in thickness and a body of rubber.

2. A printing plate comprising a facing of cellulose acetate not substantially greater than .035 of an inch in thickness and a body of yieldable rubber.

3. A printing plate comprising a facing of cellulose acetate from substantially .001 to substantially .035 of an inch in thickness and a body of vulcanized rubber.

4. A printing plate comprising a molded fac-- ing of cellulose acetate and a body of rubber.

5. A printing plate comprising a facing of cellulose acetate not substantially greater than .035 of an inch in thickness and a yieldable body of another material from substantially .125 to substantially .250 of an inch in thickness.

6. A printing plate comprising a. facing of cellulose acetate and a body of rubber more yieldable than the cellulose acetate.

7. A printing plate comprising a facing of 6:1- lulose acetate and a yieldable body havings durometer reading from substantially 50 to substantially 75. L

8. A printing plate comprising a facing of cellulose acetate from substantially .001 to substantially .035 of an inch in thickness, a yieldable body and a layer of stretch resisting material substantially parallel to the facing.

9.A printing plate comprising a facing of cellulose acetate, a yieldable body from substantially .125 to substantially .250 of an inch in thickness and a stretch of resisting material embedded in the plate.

10. A printing plate comprising a thin facing of cellulose acetate, a yieldable body and a combined stretch resisting and bonding layer between the cellulose acetate facing and the yieldable body, said body having sufllcient yield to prevent substantial distortion of the facing when the plate is curved.

11. A curved printing plate comprising a body of rubber and a facing of cellulose acetate presenting molded printing characters of the same material, said characters being substantially undistorted due to the curving.

12. A printing plate comprising a body of rubber from substantially .125 to substantially .250 of an inch in thickness, a thin continuous facing of cellulose acetate from substantially .001 to substantially .035 of an inch in thickness, and an interior stretch resisting layer adjacent the cellulose acetate facing.

13. A curved printing plate comprising a body of rubber and a facing of cellulose acetate presenting molded printing characters of the same material, the printing characters presenting ink receiving surfaces. without filler and substantially without distortion due to curving.

14. A printing plate comprising a body of rubber and a facing of cellulose acetate up to' substantially .035 of an inch in thickness presenting molded printing characters of the same material, the printing characters presenting ink receiving surfaces without exposed filler.

15. Method of producing a printing plate comprising forming a composite sheet having a facing of cellulose acetate up to substantially .035 of an inch in thickness and a body including rubber, laying the composite sheet in molding position with the cellulose acetate toward a matrix, and subjecting the assembled part to pressure to mold a printing surface on the cellulose acetate from the matrix.

16. Method of producing a printing plate comprising forming a. composite sheet having a facing of cellulose acetate and a body including rubber and suflicient vulcanizing agent to produce a body softer than the cellulose acetate, laying the composite sheet in molding position with the cellulose acetate toward a matrix, subjecting the assembled part to pressure to mold a printing surface on the cellulose acetate from the matrix, and vulcanizing the rubber.

17. Method of producing a printing plate comprising forming a composite sheet having a facing of cellulose acetate and a body including rubber from substantially .125 to substantially .250 of an inch in thickness and a vulcanizingagent, laying the composite sheet in molding andpressuretomoldaprintingsuriaceonthe cellulose acetate from the matrix, and vulcanizing the rubber to the desired stillness.

18. Method of producing a printing plate comprising iorming a composite sheet having a facing of cellulose acetate and a body including rubber and a vulcanizing agent. laying the composite sheet in molding position with the cellulose acetate toward a matrix, subjecting the assembled parts to pressure to mold a printing surface on the cellulose acetate irom thematrix, and vulcanizing the rubber to a durometer reading from substantially 50 to substantially 75.

19. Method of manufacturing printing plates comprising printing surfaces of cellulose acetate and bodies of resilient rubber which comprises uniting the cellulose acetate and the rubber and correlating the hardness of the rubber to its thickness so that a softer rubber is used where therubberisthinnerandaharderrubberis used where the rubber is thicker.

20. A printing plate comprising a printing surface of cellulose acetate and a body of rubber from substantially 0.125 to substantially 0.250 oianinchinthicknesasaidrubberhavlnga durometer test from substantially 50 to substantially75, with the hardness and thickness of the rubber correlated so that the thinner the rubber, the harder it is.

21. Method of manufacturing plates having topically raised and depressed areas of cellulose acetate and bodies of another material which comprises uniting the cellulose acetate and body,

and molding the cellulose acetate iace against a matrix having a face of hardened synthetic resin.

HYLTON SWAN. SIGFRIED HIGGINS.

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