US3168491A

US3168491A - Printing plate compositions

Info

Publication number: US3168491A
Application number: US66434A
Authority: US
Inventors: Philip K Isaacs; Norman G Tompkins; Nimoy Melvin; Jr Russell L Haden
Original assignee: WR Grace and Co
Current assignee: WR Grace and Co
Priority date: 1960-11-01
Filing date: 1960-11-01
Publication date: 1965-02-02
Anticipated expiration: 1982-02-02

Description

United States Patent M 3,168,491 PRG PLATE COMPQSITIUNS Philip K. Isaacs, Broolrline, Norman G. Tompkins, Melrose, Melvin Nimoy, Hyde Park, and Russell L. Harlan, Jr., Lincoln, ,Mass., assignors to W. R. Grace 8: ;Co., Cambridge, Mass a corporation of Connecticut No Drawing. Filed Nov. 1, 1964 Ser. No. 66,434

15 Claims. (Cl. 26tl-3ll.6)

This invention relates to compositions of matter suitable for use in preparing printing plates. In a specific aspect it relates to flexible printing plates derived from thermosetting liquid polymers which are particularly useful in letterpress printing including rotary press and flat bed printing.

In large-scale printing runs, such as newspapers, national magazines and books, printing directly from type involves extreme difficulties. First, there is the difiiculty of keeping the type pages tightly locked within the frame during printing with the result that the printed image emerges unevenly. Even if the type remains rigid in one plane against the pressure of printing, the lead type wears away faster than the zinc or other metal which is used for pictorial matter, causing the printing surface to become ragged. Second, attempts to keep all the type for a complete book or newspaper ties up an enormous amount of metal and requires huge storage space. Consequently, large-scale printing is performed from reproductions or duplicates of the type rather than the type itself.

The use of duplicate plates avoids wear on the original type form, the preparation of which is usually expensive and time-consuming. In addition, several duplicate plates may be made of the same form which permits reproduction of the printed matter in more than one location on more than one press at the same time. Moreover, the use of duplicate plates eliminates handling, shipping and mounting of heavy type forms and makes possible the preparation of curved plates for use on rotary printing equipment. 1

The principal types of duplicating plates used in letterpress printing are stereotypes, electrotypes, rigid and flexible plastic plates, and rubber plates. Stereotypes are metal plates which may be used in fiat bed or rotary presses. Flat plates are prepared by pressing a mat consisting of a damp, lightly calendered, uniformly thick sheet of paper over a type form and drying the resulting mold. Molten metal; predominantly lead, is then poured into the mold and upon solidification and cooling of the metal, a cast or stereotype is obtained. The stereotype is used as the printing plate. Rotary stereotypes are made by holding a mat by vacuum in a curved casting chamber While molten metal is poured and cast centrifugally. The curved stereotype readily fits the press -cylinders after a series of finishing operations. Rotary stereotypes are used mostly in newspaper presses since the process permits preparation of many plates in a short period of time. In such use, the standard of production required is not high and the presses operate at high speeds to produce a large number of copies over a relatively short time period.

. Electrotype plate preparation starts with a type form, made by any typesetting process, and complete with halftone etchings so mounted that their surfaces are level with the type faces. An impression of this form is then 3,168,491 Patented Feb. 2, 1965 molded in a sheet of thermoplastic resin, such as a vinyl chloride-vinyl acetate copolymer. The surface of the mold is thoroughly cleaned with a detergent and the clean surface is then sprayed with solutions of nickel salts and reducing agents, thus coating it with a conducting layer of nickel. The thickness of the nickel deposit is generally about 0.0010.002 inch. The nickel-coated mold is then suspended in an electrolytic bath containing a copper salt solution, e.g., copper sulfate, and copper is deposited on the nickel surface until an overall thickness of both metals of about 0.0080.0l5 inch is obtained. Electrodeposition normally requires about 2 /2 hours. The back of the shell is then reinforced so that the plate will stand up under printing pressures. Reinforcement is accomplished by first tinning the back surface, using tinfoil and flux, pouring molten lead on the tinned surface, and then cooling in a casting machine. The plate is bumped to bring all printing portions into one plane and shaved to fix the thickness of the plate accurately. It is then proofed and any low areas are raised by hammering at the appropriate points on the rear of the plate. Trimming and bevelling follow as well as bending if the electrotype is to be used on a rotary press, followed by final proofing. In addition to all of these operations, an electrotype frequently requires many hours of make-ready time on the press where the plates are moved slightly to bring them into register and handout underlays are placed under low areas so that all matter will print in the correct position and with the required definition and blackness.

In making duplicate rigid plastic plates, a matrix or mold is first made from a type form using a coated phenolic impregnated paperboard as the molding medium. Molding is carried out at a high temperature and results in about one percent shrinkage from the original. A thermoplastic resin powder is placed in the mold to prescribed thickness, with extra powder being added at the corners of the mold, and the entire assembly is preheated in an oven to molding temperature. Following the preheating period, the assembly is finally molded in a press to a thickness slightly over that which is desired. The resulting plates are processed in the same manner as electrotypes, requiring substantially the same finishing operations. Because of their rigidity, however, they cannot be bent for rotary press use nor can they be levelled by bumping.

Duplicate rubber plates are made from sheets of uncured rubber material in the same type of mold that is used in preparing rigid plastic plates. vulcanization of the rubber occurs during the molding operation. Usually, the rubber material rnust be kept under refrigeration to avoid partial curing at room temperature which cure would introduce molding difiiculties. Molding is usually carried out at about 280 F. and a shrinkage of about two percent from the matrix dimensions occurs. The resulting plates are usually ground or buffed to the desired thickness on semi-automatic equipment. Ordinary plate rubber is not a hard material and usually has a hardness of about 50 to 60 (Shore A durometer). Because of the softness of the plates, thickness tolerances for reasonably good quality printing are wider and make-ready time on the press is minimized. On the other hand, the softness of the material places a limit on the fineness of detail which may be accurately reproduced and rubber plates are normally considered unsatisfactory, for example, for reproducing half-tone illustrations.

Flexible plastic plates are usually molded from plas ticized polyvinyl chloride or other thermoplastic materials, such as nylon. With nylon, flexibility can be preserved while hardness is materially increased over soft plastic or rubber, thus making the reproduction of halftone material possible. Flexible plastic plates are made and finished in substantially the same manner as rubber plates but require a cooling period before the plates can be removed from the mold. The cooling step necessitates the need for additional equipment or an extension of the molding cycle.

Of the foregoing major commercial types of duplicating plates, the electrotype represents the standard in dimensional stability, quality of reproduction and durability. The preparation of electrotypes, however, is a slow process which requires at least a three-hour span starting from the type form until the plate is finished and ready for mounting on the press. In addition, several hours of make-ready time on the press is necessary before printing can commence. Electrotype preparation also requires a large area of floor space, large amounts of heavy equipment, and a force of at least seven or eight skilled operators.

Rigid plastic plates require less time to manufacture than electrotypes since the two and one-half hour plating cycle is eliminated. However, they require many of the same finishing operations, make-ready time is comparable to electrotypes, and they cannot readily be curved for use on rotary press equipment.

Rubber plates are light in weight and are prepared quickly, easily and economically. The required equipment is usually a molding press and a grinder, both of which may be operated by a single or a maximum of two operators. Make-ready time on the press is practically negligible, With rubber plates, however, the printing quality is sacrificed and fine detail and half-tones cannot be reproduced satisfactorily. Shrinkage of the rubber plates of about two percent from the dimensions of the matrix occurs and allowance for this must be taken into account in making the type form.

Flexible plastic plates shrink about the same as rubber plates. In addition, the molding cycle must include a cooling period before the plate can be withdrawn from the mold. Even when provision is made for an adequate cooling time, distortion may result from the excessive stresses which are applied in removing the plate from the mold or in subsequent handling. Rubber and flexible plastic plates are generally molded from solid sheets or granular resinous materials and considerable difiiculty is frequently experienced with the use of these materials in capturing fine detail due to their inability to fill all impressions in the mold. In addition, they are not readily finished to the final shape by means of the ordinary bending and routing equipment. While liquid materials, such as plastisols, may fill the mold with greater facility, the resulting plates are readily affected by ink solvents and because of their thermoplastic nature they are amenable to distortion.

It is, therefore, a principal object of this invention to provide improved duplicate printing plates which can be prepared rapidly and economically. It is a further object of this invention to provide plastic printing plates which reproduce fine detail and half-tone cuts of a quality comparable to electrotypes. It is another object of this invention to provide thermosetting compositions of matter suitable for preparing plastic printing plates of various hardness. Still another object is to provide flexible plastic printing plates which are adaptable to rotary and fiat bed letterpresses and which can be finished by ordinary bending, grinding and routing equipment.

The foregoing objectives are realized by providing compositions of matter which comprise principally a vinyl polymer such as polymers and copolymers of vinyl chloride and the reaction product of a complex polyimidazoline and an epoxy compound. These compositions may be modified by the addition of certain agents and additives, such as fillers, plasticizers, cure control agents, etc. The resulting mixtures are thick, readily flowable liquids, stable at room temperature and cure rapidly under heat and pressure during the molding process to form flexible printing plates of superior quality.

The compositions of this invention are unique in that printing plates may be molded from the compositions in liquid form or the liqiud may be partially processed into a solid sheet before molding. The use of the liquid form enables penetration of the composition into the minutest impressions of the mold and thus assures reproduction of the fine details of the image. The liquid compositions are stable at room temperature but solidify and chemically crosslink at elevated temperatures. Because of the thermosetting character of the compositions, the plates produced therefrom may be removed from the mold While hot without causing distortion, and, further,

the plates do not undergo distortion due to cold flow in subsequent handling, storing and mounting operations. The compositions may be formulated to give any hardness values to the plates and thus permit reproduction of varieties of type and line work as well as half-tone cuts. A significant advantage is the non-porosity of the plate surface which means less ink consumption. In addition, the ordinary ink solvents have less effect on the plates of this invention than on the rubber plates of commerce.

The principal constituents of the compositions include suspension, emulsion, and paste grade polyvinyl chloride, and vinyl chloride copolymerized with another polymerizable monomer such as vinyl acetate, vinylidene chloride, dibutyl maleate, vinyl laurate and a host of other polymerizable vinyl esters. It is preferred that the copolymer contain at least about 50% of vinyl chloride.

The epoxy compound-polyimidazoline reaction product is obtained by heating the reactants at temperatures between about C. and 190 C. for about 1 to 2 hours, and preferably between about C. and C. for about 1 hour. Under these conditions the reaction proceeds quite readily. The epoxy compound-polyimidazoline ratio may vary considerably to obtain desirable results. Generally, the polyirnidazoline constitutes 5-50% and the epoxy compound 95-50% by weight of the reaction product. Excellent results are obtained when the reactants are present in a 50-50 ratio.

Suitable epoxy compounds for preparing the reaction product include epoxidized triglycerides, such as epoxidized soybean oil and epoxidized castor oil and epoxidized esters of lower alkyl alcohols and fatty acids. Representative epoxy compounds of the latter group include methyl-, ethyl-, propyl-, butyl-, and hexyl -9,l0-epoxystearate; butyl 9,10,12,l3-diepoxystearate; butyl 9,10-epoxypalmitate; and butyl 12-hydroxy-9,lO-epoxystearate.

The polyimidazoline is a complex product derived by reacting triethylene tetramine and a plurality of carboxylic acids under suitable reaction conditions. Specifically, it is prepared by reacting 70.2 lbs. (0.48 mole) of triethylene tetramine, 36.4 lbs. (0.18 mole) of sebacic acid, 36 lbs. (0.06 mole) of dimerized linoleic acid, and 67.7 lbs. (0.24 mole) of oleic acid in a heated glass vacuum vessel. 0.21 lb. of powdered sodium tripolyphosphate is added to chelate catalytic pro-oxidant metals. The reaction is carried out with vigorous agitation while maintaining a nitrogen atmosphere. Temperature is carefully controlled, ranging from 150 C. at the start of the reaction to 220 C. upon completion. The reaction period covers 4 hours and the pressure is reduced from 760 mm. to 20 mm. Hg over this period to remove water of condensation. The amount of water removed corresponds with 85% conversion of carboxyl groups to irnidazoline groups, leaving a balance of 15% of the carboxyl groups in the form of amides. This result was this purpose and, in addition, its use facilitates release of the plate from the mold.

Hg (dimeric linoleie nd H L% mole 0341168 acid residue) amides is hereinafter referred to as Compound X.

, Specific details for preparing the polyimidazoline-epoxy rompound reaction product are described as follows. 100 lbs. of Compound X is heated to 130 C. and then 300 lbs. of preheated epoxidized soybean oil is added thereto. The mixture is then reacted at 130 C. for about 1 hour with gentle stirring and then cooled. Care is taken to protect the reaction mixture and cooled product from moist air and/or carbon dioxide, both of which tend to produce bubbles in the final print plate. The reaction proceeds smoothly and gives a product which is pennanently fluid at room temperature. The reaction product is hereinafter referred to as Compound Y. Upon curing with polyvinyl chloride at elevated temperatures, both the epoxy groups and the amino groups of the polyimidazoline enter into a crosslinking reaction which yields a thermoset polymer.

While the polyimidazoline is a highly effective curing agent for polyvinyl chloride and copolymers of vinyl chloride, its curing action must be controlled, else the polymer will degrade upon heating. Degradation is evidenced by blackening and stiffening of the polymer, attendant with evolution of HCl, and it is difiicult to obtain ahigh degree of crosslinking without encountering these signs of degradation. To regulate the curing action of the polyimidazoline, a metallic compound, such as zinc oxide, is added to the print plate composition. The Zinc oxide retards blackening on heating, prevents gas evolution and augments resistance to moisture while maintaining the advantage of polyirnidazoline cure. The grade of zinc oxide is not a critical factor so long as good dispersion is obtained and a particle size of about .5 micron is quite eifecrtive.

An agent is also added to sequester any moisture which may remain in the composition after it is manufactured or which may accidentally reach the composition during storage and use. Such moisture is undesirable as it tends l The above polyimidazoline together with the residual its cause bubbles in the molded plate which consequently adversely affects the plate printing surface. Any material which would from a compound with water at room temperature and which would not decompose at about 350 F. would be a suitable moisture-sequestering agent provided it could be reduced to a finely divided state so I as to obtain good dispersion and would not cause any undesirable side effects. Quicklime, Portland .cement, and barium oxide have been found satisfactory for this purpose.

geneous print plate.

The foregoing constituents form a print plate composition which is quite viscous and, although a satisfactory plate can be manufactured therefrom, its viscous nature makes handling and workability difficult. In order to alleviate these conditions, a viscosity-lowering agent is added. Suitable agents include polyethylene glycol stearate, condensation products of ethylene oxide and polypropylene glycol, sorbitan monopalmitate, sorbitan monoleate, 3,5-dimethyl-l-hexyn-3-ol and the fatty acid esters of polyethylene glycol 200600 series (the designation numbers approximate the molecular weight of the polymeric glycol ex the weight of the fatty acid portion). Polyethylene glycol 400 monooleate is quite effective for White Portland cement is preferred since it can be readily dispersed and results in a more homo Plasticizers are generally not incorporated into the printing plate compositions of this invention since Compound Y ordinarily performs this function. Compound Y is an excellent plasticizer for polyvinyl chloride in which the epoxy groups help to control and even enhance crosslinking without degradation. However, some uses of the plates may dictate the need of an additional plasticizer and either the straight ester or polymeric type of plasticizer, such as diisooctyl adipate, dioctyl phthalate, and polyester resins based on long chain polycarboxylic acids esterified with polyhydric alcohols, may be added to the composition.

The composition may be prepared by combining the constituents in toto or by incremental addition and the mass is then thoroughly mixed in a suitable mixing apparatus until all constituents are thoroughly and uniformly dispersed to form a homogeneous liquid. A preferred embodiment of carrying out the mixing operation is to first form a masterbatch to assure intimate dispersion of the components and then gradually add the remaining portions of the formulation to the masterbatch. A typical masterb'atch comprises zinc oxide, the moisture-sequestering agent, and Compound Y, the total amounting to about 2 percent of the final weight of the composition. It is processed through a Manton-Gaulin homogenizer, or through a pebble mill when large quantifies are desired. After a prescribed preliminary mixing period, the masterbatch is withdrawn and, to complete its mixing cycle, it is passed to a mixing kettle in which a low pressure of about 25 mm. Hg or less can be reached and maintained. The complete formulation of the'printing plate composition is prepared by placing the major portion of Compound Y in a vacuum mixer, and theniadding the masterbatch thereto with agitation. These components are mixed for a prescribed period, agitation is then stopped, polyvinyl chloride is added until the head space is filled, and the mixer is closed and evacuated. Agitation is resumed and continued until all of the polyvinyl chloride has been incorporated into the liquid. Agitation is again halted, the vacuum is released .and the kettle opened and the process is repeated until all of the polyvinyl chloride which is required by the formulation has been added and thoroughly blended. Agitation under vacuum is then continued until all specks and lumps have been completely dispersed. Finally, the viscosity-lowering agent is added and stirred in under vacuum. Upon completion of the latter step, the liquid composition is ready for use in molding printing plates directly or manufacturing sheet material for use in the sheet plate-making process. 5

The invention is further illustrated by the following examples. Examples 1 to 3 are representative masterbatches of compositions which are used to prepare print ing plates having various degrees of hardness. The designations A95, A60 and A40 represent hardness values as determined by the Shore A Durometer.

Example 1 (A masterbatch) Constituent: Parts by weight Compound Y 20 Zinc oxide 6 Quicklime 20 7 Example 2 (A60 master-batch) Constituent: Pants by weight Compound Y 30 Zinc oxide 30 Quicklime 50 Example 3 (A40 masterbatch) Constituent:

Compound Y 36 Zinc oxide 60 Quicklime 36 Excellent dispersion of the masterbatches may be obtained by grinding the mixture in a pebble mill for approximately 16 hours or passing the mixtures through a two-stage Manton-Gaulin homogenizer with a 2000 lb. per square inch pressure difference across each valve. The amounts of the foregoing masterbatches are sufiicient to prepare four final compositions and in preparing the compositions the masterbatch is simply quartered and processed with the remaining amounts of constituents. Portland cement may be substituted in equal quantity for quicklime with no noticeable change in the results.

The following examples illustrate representative compositions of this invention and prepared via the masterbatch route, all proportions of the constituents being reported as parts by weight:

Example No. Constituent Polyvinyl chloride, paste grade 200 200 200 200 200 Compound Y 460 280 160 140 100 Zinc Oxide 10 3 1.5 1.5 3 Quicklime 6 6 5 5 3 Polyethylene glycol e e 10 5 10 10 15 Brookfield Viscosity, cps., 72

F., #4 spindle:

12 r.p.m 22, 000 178,000 6 l.p.m 170, 000 Brookfield Viscosity, eps., 100

F., #3 spindle:

60 r.p.m 6,000

42,000 6r.p.m 6,000 40,000 Molded Plates:

Press cure time, minutes, at 80 p.s.i.g. steam pressure, approximate 4 6 7 9 10 Approximate hardness,

Shore A Durometer 4O 60 80 95 100+ The hardness values are varied principally by the amounts of Compound Y which is added to the composition. High amounts of this compound give a soft plate and, conversely, lower amounts give progressively harder plates.

The following set of examples further illustrate the invention in which various constituents are combined to give acceptable printing plates. The proportions of the respective constituents are reported as parts by weight:

Example No.

Constituent Vinylite VYNV-2 (copolymcr containing 91-97% vinyl chloride and 93% vinyl acetate) 200 200 Pliovic A (copolymer containing 93-95% vinyl chloride and 75% dibutyl maleatc 200 200 200 Compound Y 280 170 140 100 Portland Cement 5 5 Quicklirne 5 Polyethylene glycol 400 m0nooleate 5 5 5 5 3,5-dimethyl'1-hexyn-3-o1 5 Zinc Oxide 3 3 3 1. 5 Approximate hardness Shore A Durometer 40 60 80 95 100+ i The proportions of the compositions may be varied depending upon the desired hardness of the final plate. In general, Compound Y may constitute between about 0.2 to 4.0 parts by weight, preferably 0.5 to 2.25; zinc oxide may be present between about 0.005 and 1.0 part by weight, preferably 0.015 to 0.05; the moisturesequestering agent may constitute between about 0.005 and 1.0 part by weight, preferably 0.015 to 0.03; and the viscosity-lowering agent may constitute between about 0.02 and 1.0 part by weight, preferably between 0.075 and 0.05. All proportions are based on the weight of the polyvinyl chloride and copolyrners of vinyl chloride taken as unity.

Duplicate printing plates may be made by one of two processes which are refererd to as the liquid and the sheet process. Both processes require the use of a standard platemaking press which is generally used in preparing matrices and rubber and plastic plates. The equipment is essentially a hydraulic press which is capable of producing platen pressure of about 1000 pounds per square inch and in which the platens can be heated uniformly with steam or electricity to a temperature of at least 325 F.

The liquid process beings with a matrix which is prepared from a type form in the same manner as is used to make a rubber plate. The matrix is laid flat with the cavity side upward and a frame, referred to as a restrictor chase, is placed on the peripheral edge of the matrix. The chase is provided with milled gates which are concave depressions of the order of about one-quarter inch wide and about 0.011 inch deep. These gates provide an escape route for excess composition during the molding operation. The thickness of the chase is such that together with the depth of the impression in the matrix, the assembly will yield a final plate having a thickness greater than that which is required.

As an alternate to the foregoing approach, the matrix may be cut to standard dimensions so that it fits into a rabbeted groove on the underside of the chase. In this manner, the thickness of the final plate will approximate the relief or depth of the impression in the matrix plus a thickness of that portion of the chase which extends over the matrix edge. This method avoids the danger of compressing the matrix material which compression would reduce the thickness of the final plate below that which is desired.

When the matrix and chase have been properly assembled, the required amount of liquid composition is poured into the center of the matrix and the entire assembly is heated in an open press at a temperature of about 325 F. for approximately three to five minutes. The purpose of this preheating period is to rise the temperature and lower the viscosity of the liquid to a point where it will fiow readily in the mold and thus reach the most difiiculty accessible recesses therein and to allow any bubbles of air, which may have been trapped during pouring, to escape. Following the preheating period, the entire assembly is covered with either a Teflon-coated aluminum plate, a sheet of glass-supported Teflon tape, or some other material which would facilitate release of the plate, and the covered assembly is placed in the molding press. The press is then slowly closed in order to allow any air bubbles accidentally included therein to escape, and the pressure is raised to about 500 pounds per square inch over the chase area. The temperature is maintained at a steady level between about 250 F. to 400 F. during the molding cycle. The preferred temperature is between 300 F. and 325 F.

After the requisite molding time has elapsed, and this ranges from about 2 to 12 minutes depending upon the hardness of the plate, the press is opened and the assembly is removed and disassembled. A striking advantage of this invention is that the resulting printing plate is removed from the matrix immediately and while it is still hot without damaging the plate in any manner. The fact 9. that the plate can be removed in a hot state from the matrix shortens the molding cycle and permits reuse of the matrix after a short period and while it is warm to prepare additional plates. Small amounts of composition which may adhere to the chase and matrix can be removed by simply brushing or rubbing the surface with a cloth. To assist in the release of the plate from the matrix, it is preferred to spray the internal surface of the matrix with a material such as a release fluid containing a silicone oil.

The sheet process difiers slightly from the liquid process. In carrying out this process, the liquid is sheeted at a temperature and for a time sufiicient only to form a solid sheet with a minimum amount of cure of the composition. The sheet is then laid over the printing portions of the matrix without the need of the chase. Preheating times, temperatures, and press-closing cycles are more critical than in the liquid process. The preferred temperature should range between about 320 F. and 350 F. for the sheet process.

In makinga matrix for organic plates a shrinkage of about 1 percent from the original type form occurs, but this is largely regained when the matrix is reheated for castingof the plate. The main shrinkage occurs in the organic material itself because ofthermal contraction when the plate is cooled. The coefficients of thermal exexpansion of resins and rubbers average about ten times those of metal andthus shrinkage infa plate molded at 280 F .,am ounts to about 1.75 percent and when the molding temperature is raised to about 325 F. the shrinkage increases to about 2.25 percent.

For practical purposes, shrinkage can be eliminated by incorporating in the plate a material which has a low thermal expansion coefficient. By laminating either a wire screen, a perforated sheet metal, paper or cloth in the composition before molding ,the dimensional changes that occur during molding can be eliminated or reduced. These materials function by their tendency to restrict the inevitable volume shrinkage so that shrinkage occurs in thickness rather than in the plane of the printing surface.

Shrinkage may also be reduced by incorporating finely divided material of low thermal expansion coefficient in the composition. Mineral fillers, such as mica, and cotton or rayon flock are examples of such materials. Although large amounts are needed to produce significant reductions in shrinkage, this approach is useful where the inevitable deleterious efiect on physical properties, such as abrasion resistance, can be tolerated, e.g., where plates are intended for short runs 'or for printing on materials of unusually low abrasive character.

An effective method of handling shrinkage is to make allowance for it by constructing the type forms about 2 percent larger than the desired size of the printed image. In this approach, the emphasis is shifted to uniformity of shrinkage to permit accurate register in multicolor reproduction and since the principal factor in shrinkage is thermal contraction, molding temperatures must be accurately controlled. This precaution is as necessary with the compositions of this invention as with other organic plates. However, the possibility of distortion and dimensional changes occurring after the molding process is complete when using the compositions of this invention is much less than occurs with the flexible thermoplastic resins of commerce because of the thermosetting nature of the present compositions.

The compositions of this invention are stable liquids having excellent castability and ability to reproduce fine detail. The flexible plates are endowed with controlled shrinkage, long life, good solvent resistance, high dimensional stability, low ink absorption, good ink transfer, and may be formulated to obtain various degrees 'of hardness. Their properties are such as to produce thermoset plates having a printing quality comparable to electrotypes. In addition, the same plate is convertible from rotary to flatbed presses.

We claim:

1. A composition of matter which comprises a polymeric material selected from the group consisting of polyvinyl chloride and copolymers of vinyl chloride copolymerized with up to about 50 percent of a polymerizable monomer selected from the group consisting of vinyl esters, dibutyl maleate and vinylidene chloride, about 0.005 to 1.0 part by weight of zinc oxide, and about 0.2 to 4.0 parts by weight of a reaction product consisting of -50 percent of a nonresinous epoxy compound selected from the group consisting of epoxidized triglycerides and epoxidized esters of lower alkyl alcohols and fatty acids and 5-50 percentof a polyimidazoline, said polyimidaz oline being derived by reacting 8 moles of triethylene tetramine, 3 moles of sebacic acid, 1 mole of dimerized linoleic acid, and 4 moles of oleic acid at a temperature ranging from about C. to 220 C. and at a pressure of from 20 mm. to 760 mm. Hg while continuously removing the water of condensation, said proportions being based on the Weight of the polymeric material.

2. A composition of matter which comprises a polymeric material selected from the group consisting of polyvinyl chloride and copolymers of vinyl chloride copolymerized with up to 5 0 percent of a polymerizable monomer selected from the group consisting of vinyl esters, dibutyl maleate and vinylidene chloride, about 0.005 to 1.0 par-t by weight of zinc oxide, about 0.005 to 1.0 part by weight of a moisture-sequestering agent, about 0.02 to 1.0 part by weight of a viscosity-lowering agent and about 0.2 to 4.0 parts by weight of a reaction product consisting of 95-50 percent of a nonresinous epoxy compound selected from the group consisting of epoxidized triglycerides and epoxidized esters of lower alkyl alcohols and fatty acids, and 5-50 percent of a polyimidazoline, said polyimidazoline being derived by reacting 8 moles of triethylene tetramine, 3 moles of sebacic acid, 1 mole of dimerized linoleic acid, and 4 moles of oleic acid, at a temperature ranging from about 150 C. to 220 C. and at a pressure of from 20 mm. to 760 mm. Hg while continuously removing the Water of condensation, said proportions being based on the weight of the polymeric material.

3. A composition of matter which comprises a polymeric material selected from the group consisting of polyvinyl chloride and copolymers of vinyl chloride copolymerized with up to about 50 percent of a polymerizable monomer selected from the group consisting of vinyl esters, dibutyl maleate and vinylidene chloride, about 0.015 to 0.05 part by weight of zinc oxide, about 0.015 to 0.03 part by weight of Portland cement, about 0.075 to 0.05 part by Weight of polyethylene glycol 400 monooleate and about 0.5 to 2.25 parts by Weight of a reaction product consisting of 95-50 percent of a nonresinous epoxy compound selected from the group consisting of epoxidized triglycerides and epoxidized esters of lower alkyl alcohols and fatty acids, and 5-50 percent of a polyimidazoline, said p'olyimidazoline being derived by reacting 8 moles of triethylene tetramine, 3 moles of sebacic acid, 1 mole of dimerized linoleic acid, and 4 moles of oleic acid, at a temperature ranging from about 150 C. to 220 C. and at a pressure of from 20 mm. to 760 mm. Hg while continuously removing the water of condensation, and proportions being based on the weight of the polymeric material.

4. A composition of matter which comprises polyvinyl chloride, about 0.015 to 0.05 part by weight of zinc oxide, about 0.015 to 0.03 part by Weight of quicklime, about 0.075 to 0.05 part by weight of polyethylene glycol 400 monooleate and about 0.5 to 2.25 parts by weight of a reaction product consisting of 95-50 percent of a n0nresinous epoxy compound selected from the group consisting of epoxidized triglycerides and epoxidized esters of lower alkyl alcohols and fatty acids, and 5-50 percent of a polyimidazoline, said polyimidazoline being derived by reacting 8 moles of triethylene tetramine, 3 moles of sebacic acid, 1 mole of dimerized linoleic acid, and 4 1 1 moles of oleic acid, at a temperature ranging from about 150 C. to 220 C. and at a pressure of from 20 mm. to 760 mm. Hg while continuously removing the water of condensation, said proportions being based on the weight of the polyvinyl chloride.

A composition of matter according to claim 3 wherein the polymeric material is polyvinyl chloride.

6. A composition of matter according to claim 3 wherein the polymeric material is a copolymer consisting of 91-97% vinyl chloride and 93% vinyl acetate.

7. A composition of matter according to claim 3 wherein the polymeric material is a copolymer consisting of 93-95% vinyl chloride and 7-5% dibutyl maleate.

8. A process for preparing a thermoset flexible printing plate which comprises pouring the composition of claim 2 into an image-bearing mold, preheating said mold and contents for a short period of time, and heat pressing the preheated mold to a curing temperature.

9. A process for preparing a thermoset flexible printing plate which comprises pouring a requisite amount of the composition of claim 3 into an image-bearing mold, preheating said mold and contents for about 3 to 5 min- UltES at about 325 F., placing the preheated mold in a press, and heating the pressed mold at a temperature between about 250 F. to 400 F. for about 2 to 12 minutes.

10. A process for preparing a thermoset flexible printing plate which comprises pouring a requisite amount of the composition of claim 5 into an image-bearing mold, preheating said mold and contents for about 3 to 5 minutes at about 325 F., placing the preheated mold in a press, and heating the pressed mold at a temperature between about 250 F. to 400 F. for about 2 to 12 minutes.

11. A process for preparing a thermoset flexible printing plate which comprises pouring a requisite amount of the composition of claim 4 into an image-bearing mold, preheating said mold and contents for about 3 to 5 minutes at about 325 F., placing the preheated mold in a press, and heating the presesd mold at a temperature between about 250 F. and 400 F. for about 4 to 10 minutes.

12. A thermoset flexible printing plate obtained by the process of claim 8.

13. A thermoset flexible printing plate obtained by the process of claim 9.

14. A thermoset flexible printing plate obtained by the process of claim 10.

15. A thermoset flexible printing plate obtained by the process of claim 11.

References Cited in the file of this patent UNITED STATES PATENTS 2,620,516 Muller Dec. 9, 1952 2,681,901 Wiles et al. June 22, 1954 2,723,241 De Groote et al. Nov. 8, 1955 2,795,565 Newey June 11, 1957 2,819,233 Smith et al. Jan. 7, 1958 2,878,234 Peterson Mar. 17, 1959 2,912,397 Houska et al. Nov. 10, 1959

Claims

3. A COMPOSITION OF MATTER WHICH COMPRISES A POLYMERIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF POLYVINYL CHLORIDE AND COPOLYMERS OF VINYL CHLORIDE COPOLYMERIZED WITH UP TO ABOUT 50 PERCENT OF A POLYMERIZABLE MONOMER SELECTED FROM THE GROUP CONSISTING OF VINYL ESTER, DIBUTYL MALEATE AND VINYLIDENE CHLORIDE, ABOUT 0.015 TO 0.05 PART BY WEIGHT OF ZINC OXIDE, ABOUT 0.015 TO 0.03 PART BY WEIGHT OF PORTLAND CEMENT, ABOUT 0.075 TO 0.05 PART BY WEIGHT OF POLYETHYLENE GLYCOL 400 MONOOLEATE AND ABOUT 0.5 TO 2.25 PARTS BY WEIGHT OF A REACTION PRODUCT CONSISTING OF 95-50 PERCENT OF A NONRESINOUS EPOXY COMPOUND SELECTED FROM THE GROUP CONSISTING OF EPOXIDIZED TRIGLYCERIDES AND EPOXIDIZED ESTERS OF LOWER ALKYL ALCOHOLS AND FATTY ACIDS, AND 5-50 PERCENT OF A POLYIMIDAZOLINE, SAID POLYIMIDAZOLINE BEING DERIVED BY REACTING 8 MOLES OF TRIETHYLENE TETRAMINE, 3 MOLES OF SEBACIC ACID, 1 MOLE OF DIMERIZED LINOLEIC ACID, AND 4 MOLES OF OLEIC ACID, AT A TEMPERATURE RANGING FROM ABOUT 150*C. TO 220*C. AND AT A PRESSURE OF FROM 20 MM. TO 760 MM. HG WHILE CONTINOUSLY REMOVING THE WATER OF CONDENSATION, AND PROPORTIONS BEING BASED ON THE WEIGHT OF THE POLYMERIC MATERIAL.