US2741297A

US2741297A - Printing plate material

Info

Publication number: US2741297A
Application number: US286898A
Authority: US
Inventors: Vamvaketis Stephen
Original assignee: United States Rubber Co
Current assignee: Uniroyal Inc
Priority date: 1952-05-09
Filing date: 1952-05-09
Publication date: 1956-04-10
Anticipated expiration: 1973-04-10
Also published as: GB720703A

Description

April 10, 1956 s. VAMVAKETIS 2,741,297

PRINTING PLATE MATERIAL Filed May 9, 1952 14 1/4444\x'rzza azz zzz INVENTOR.

J'Tf/ HE/V V4MV4/i f7/J' BYy hg/y AGENT United States Patent '9 PRINTING PLATE MATERIAL Stephen Vamvaketis, Cranston, R. 1., assiguor to United :States Rubber Company, New York, N. Y., a corporafion of New Jersey Application May 9, 1952, set-m No. 286,898

1 Claim. c1. 154-54 'This invention relates to an improved printing plate material, and more particularly it relates to -a printing plate material that is adapted for convenient preparation of printing plates having improved characteristics.

The printing plate materials and the printing plates available in accordance with prior art practices have had certain disadvantages. Thus, printing plates made from metals or rigid plastics have lacked the flexibility that would be desirable to permit easy mounting of thepl ates on the cylinders of the printing press. Also, the lack of resiliency, in addition to the hard surface of these materials, sometimes led to cutting or undesirable embossing of delicate surfaces, such as cellophane, glassine, tissue paper, etc., on which it was desired to print. Furthermore, the handling and storing of the metal orrigidplastic plates required extreme care, since such plates were easily damaged by contact with other hard objects, or when dropped on the floor.

On the other hand, printing plates made from resilient materials do not lend themselves to the reproduction of fine details, as is required in most letterpress work, 'because of their tendency to deform and spread out under normal printing pressure.

The present invention has for its principal object the amelioration of the foregoing difiiculties by provisionof a printing plate material which is easily fabricated into a printing plate that has a printing surface capable of accurately reproducing fine detail, but that at the same time is flexible and resilient Another object is the provision of a printing plate material which is easily manufactured and can be shipped conveniently in bulk, and stored for relatively long periods without deterioration.

Still a further object of the invention is to provide a printing plate material which the ordinary rubber or plastic printing plate maker can utilize conveniently and efiiciently, in its present plate making equipment.

Additional objects and advantages of the invention will be made manifest in the following detailed description, which isintended to be read with reference to the accompanying drawing, wherein:

Fig. l is a transverse sectional view of a sheet of printing plate material made in accordance with the invention;

Fig. 2 is a similar view on a smaller scale of the material rolled up for shipment or storage;

Fig. 3 .is a view similar to Fig. 1 showing the sheet after fabrication into a printing plate; and,

Fig. 4 is a similar view of the printing plate applied to the cylinder of a printing press.

The invention provides a printing plate material in the form of a laminated sheet constituted essentially of a relatively thick resilient backing sheet of soft rubber in the unvulcanized state, having adhered to one surface a tat-ea en na- 12 '2 relatively thinner layer of a hard but flexible blend of a thermosetting resin with a synthetic rubber. The said thermosetting resin is most preferably a phenolic resin and the said synthetic rubber is most preferably of the type known as nitrile rubber (also known as Buna N, or by such trade names as Hycar-or-Paracril).

Referring to the drawing, and in particular toFig. 1, there is shown a sheet of such laminated printing plate material having a soft vulcauizable rubber backingl l, and a facing 2 composed of 'a hard phenolic resin-nitrile rubber blend. The rubber backing 1 is preferably also made of nitrile rubber for best resistance to the solvents or oils likely to be encountered in printing practice. The soft backing is typically made about 0:03 to 0.4 inch thick, and the hard facing is usually about 0.005 to 0.05 inch thick. The backing is generally made from 3 to 10 times thicker than the facing.

The backing is so compounded, in a manner that will be understood'by those skilled in the art of rubber compounding, as to be vulcanizable, at the usual molding temperatures, to a soft vulcanized state, such that the vulcanized material has a Shore hardness within the range from 15 to on the Shore A scale. When using the accelerators and activators commonly used :for sulfur vulcanization of nitrile rubber, in the amounts customarily employed, it will generally be found that the backing composition will have the proper hardness when compounded with from 0.5 to 5.0 parts of sulfur, although the skilled rubber compounder will be able to ,produce the desired hardness with amounts of sulfur outside of wthisrange.

In formulating the tough facing composition, there is employed a soluble, heat-reactive phenolic resin, prepared from phenol and formaldehyde 'byacid catalysis, suchas is described, for example, in U. S. Patent 2,203,206 of Shepard et al. The phenolic resin preferably is modified with from 2 to 10% of cashew nut oil. Such resins are mutually compatible with, or soluble in, the nitrile rubber component, and they are c'apable of being converted into a relatively infusible, insoluble state by'heating in the presence of a curing agent, which is usually a substance capable of yielding formaldehyde, as is well understood by those skilled in the art. With'from 20 to 150 parts by weight of such phenolic resin, there is admixed parts of the nitrile rubber to'make'the tQughfacing'compound. Thenitrile rubber may be any suitable rubbery butadiene-acryl'onitrile copolymer of commerce containing from 10 to 50% of'conibined acrylonit'rile by weight, and more preferably containing about 20-to 45 of acrylonitrile. The phenolic resin andthe "nitrile rubber may be blended together by any suitable procedure, such as'by mixing together on-a rubbermill.

The facing formulation should include an agent capable of promoting the heat-setting of the phenolic resin, such as hexamethylenete'tramine in amount of from '4 to 12 parts per 100 parts by weight of resin. 'Frequentlythe commercial grades of phenolic resin already contain 'a'curing'agent. I

i "It is also advantageous to include a small amount of sulfur in "the -mixture,-say l 'to "10 parts per 100 parts 'of rubber, particularly if the mixture contains less than about '50 parts of phenolic resin 'in 100 parts of nitrile rubber. i i

Phenolic resin nitril'e rubber blends of this type produce, upon 'curingat elevated temperatures'ya composition which'is unusually'hard and tough, but still definitely flexible, "and having physical properties which are un- "usually well suited for printing. The cured material has a Shore hardness within the range from 65 to 100 onthe unfilled, or it may be filled with various materials, such as carbon black.

The following example will illustrate the invention in further detail.

A commercial nitrile rubber sold under the trade designation Paraeril BJ.

Face compound Paracril Bl 100.00 Phenolic resin 70.00 Zinc oxide 1 5.00 Carbon black 100.00 Stearic acid 0.75 Cumarone-indene resin 25.00 Antioxidant 0.75 Accelerator 2.00 Sulfur 5.00

A novolac type of cashew nut shell oil modified phenolic resin containing hexamethylenetetramine as a curing agent, sold under the trade designation Durez 12687.

A viscous liquid type of resin, sold under the trade designation Cumar AX.

The compounds were mixed on a roll mill and lamination of the two compounds was affected on a calender.

The heat and pressure of the calender-lug operation cause .7

the two layers to become firmly united. The adherence of the two layers is enhanced by the fact that the nitrile rubber constituting the backing layer is also present in the facing layer. 7 r

The resulting laminate was 0.125 inch thick, comprising 0.02 inch of facing and 0.105 inch of backing. The laminate was flexible and could easily be rolled up into a roll 3 as shown in Fig. 2, for storage or shipping. To prepare'a printing plate from this laminate, a piece of the material was simply cut from the roll 3 to the size of the matrix, which inthis case was made of Bakelite and was previously'prepared by spraying with a silicone mold release emulsion composition, followed by dusting with fine talc. The piece of laminate was placed on top of the matrix and the assembly wasthen placed between 'the platens of a vulcanizing press between thickness bearers to control the thickness of the finished plate. I The press was closed to effect a preliminary dwell, during which the material of the plate was pre-heated by contact with the platens, but without being actually compressed. After one minute of such dwell, a platen pressure of about 125 pounds per square inch was applied for about 8 minutes at 307 F. during which time both the backing and the face material became completely cured. The

cured plate, havingthe appearance shown in Fig. 3, with the printing impressions 4 molded in its face,-was removedfrom the matrix, the flash was trimmed off, and

of the plate, although hard and smooth, was not brittle.

It was found by actual use of such a plate, that the surface was rigid enough to print fine detail. The flexible and resilient rubber backing absorbed practically all of the printing pressure, and at the same time compensated for any irregularities in the printing surface, as well as any unequal printing pressure. Because the plate could be mounted on the press substantially as easily as a rubber plate, the present construction, permitted costly make ready time" to be minimized.

Because the printing plate material made in accordance with the invention takes the form of a sheet material, the storage, shipment and utilization of the material is greatly simplified. Since the surface of the material isrnot easily damaged, the usual hazards in storing and shipping the plate or the material are substantially eliminated.

The printing plate maker can utilize the material conveniently and efiiciently, since the material is fabricated to the prescribed thickness, and the plate maker can simply convenient than the use ofresins and the like in granular form. In molding a plate from the latter materials, it was necessary to first spread the granules over the matn'x,'and then wipe out the excess so that the granulesremained only in the crevices of the matrix. Since many matrix designs are intricate, the process of distributing the granules evenly was time consuming, and proved to be very diflicult in 'many cases. V Y

The plates made from the present material are not only capable of printing fine detail with accuracy, but they are unusually long wearing, and retain their ability to print fine detail even after prolonged periods of use.

The soft vulcanizable rubber composition used as the backing material in the present plate can be stored for relatively long periods of time without appreciable change in its vulcanizing characteristics, so that the printer will have no difficulty about fabricating a printing plate from it, even if the material has been on hand for some time. This is true also of the composition used as the facing material, since it remains in the desired heat-curable condition'throughout relatively prolonged times in shipment or storage. There is therefore no difliculty about the printing plate material deteriorating during the time elapsed between manufacture of the material and fabrication of the plate. v

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

A printing plate laminate comprising a composite flexible sheet constituted of a relatively thick resilient backing layer of soft-vulcanizable nitrile rubber directly heatlaminated on one surface to a contacting surface of' a relatively thinner facing layer of a hard but flexible composition comprising a heat-curable blendof parts of nitrile rubber with from 25 to parts of a cashew nut shell oil modified novolac phenol-formaldehyde resin, the said nitrile rubber in each said layer being a copolymer of butadiene and acrylonitrile containing from 10% to 50% of acrylonitrile and the presence of said nitrile rub her in each said layer serving to enhance the adhesion between the layers, the said laminatedlayers being characterized by the ability to retain without appreciable change their original'vulcanizing and curing characterable, when heated to softening and curing temon deiicate surfaces Without damage thereto and flexible enough to conform Without difiiculty to the curvature of 10 a printing plate cylinder.

References Cited in the file of this patent UNITED STATES PATENTS Harbison et a1. Sept. 10, Swan et a1. June 21, Freedlander July 14, Gartrell Mar. 18, Juve et a1 Jan. 27, Groten et a1 Jan. 18,