US2108822A - Printing plate and formation thereof - Google Patents

Description

Feb. 22', 1938.

w. A. LIPPINCOTT PRINTING PLATE AND FORMATION THEREOF Filed Nov. 11, 1955 3 Sheets-Sheet l mog W26 (flki'upinc Feb. 22, 1938 V 1 w; LiPPlNCOTT 2 .PRINTING PLATE AND FORMATION THEREOF Filed Nov. 11, 1935 3 Sheets-Sheet 2 ////////////A/ III W. A. LIPPINCOTT PRINTING PLATE AND FORMATION THEREOF Feb. 22, 1938.

Filed Nov. 11, 1955 s Sheets-Sheet 3 V v NVENTOIQ/ QM); wwammfi Patented Feb. 22, 1938 PRINTING PLATE AND FORMATION THEREOF Wells A. Lippincott, Chicago, Ill. Application November 11, 1935, Serial No. 49,186

7 Claims.

This invention relates in general to printing plates and the formation and mounting thereof and more particularly to printing plates of the kind in which all or part of the type projections defining the printing surface are formed in a molding operation.

One object of the invention is to simplify and reduce the cost of manufacturing and mounting of printing surfaces by providing a printing plate having type projections composed of readily moldable material capable of withstanding the pressure encountered during printing and of being bent readily to the curvature of the press support upon which the plate is mounting during 16 printing. In carrying out this object, it is preferred to employ a moldable material having thermoplastic properties, that is to say, a material which after being initially molded will soften gradually upon being heated.

Another object is to provide a novel mounting for a type surface of the above general character.

A further object is to provide a novel construction of the different color plates for use in multicolor printing which permits exact color registration to be obtained after bending thereof to conform to curved printing press supports.

Another object is to provide a novel method by which molded printing plates of the above character may be formed to produce a high degree of accuracy in the location of the printing surfaces relative to the back surface of the plate.

The invention also aims to provide a novel method of curving printing plates of the general 35 character referred to above.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in which Figure 1 is a fragmentary perspective view of a printing press cylinder equipped with a printing plate embodying the features of the present invention, the plate being partially detached from the cylinder.

Fig. 2 is a fragmentary sectional view illustrating the arrangement of the parts preparatory to molding of the printing plate.

Fig. 3 is a fragmentary sectional view of the printing plate attached to a press cylinder.

Figs. 4, 5 and 6 are fragmentary sectional views on a small scale illustrating the method of bending the printing plate.

Figs. 7 and 8 are fragmentary cross-sectional views on an enlarged scale of two different color plates to be used in multi-color printing.

Figs. 9 and 10 are views similar to Figs. '7 and 8 of plates constructed in accordance with the present invention.

Fig. 11 is a cross-sectional view showing a modified form of printing plate in the process of 5 manufacture.

Fig. 12 is a cross-sectional view on a substantially enlarged scale illustrating a modified form of printing surface.

The invention is susceptible of various modi- 10 fications and therefore I do not, by the present exemplary disclosure, intend to limit the invention but aim to cover all modifications and alternatives falling within the spirit and scope of the invention as expressed in the appended claims.

In the drawings, the invention is embodied for purposes of illustration in a rectangularly shaped printing plate generally indicated at 9 carrying type II), the faces ll of which define a surface for printing part or all of one page of a magazine 20 or the like. In the present instance, the type are in the form of solid projections integral with and standing out in relief from a base or layer i2 composed of the same material as the type and of uniform thickness. For reasons to appear later, 25 the layer I2 is made as thin as practicable and yet thick enough to unit the type projections integrally and enable the same to be secured properly to a reinforcing member or carrying sheet l3.

The present invention contemplates formation 30 of the type II] and the layer l2 in whole or in part of a readily moldable material which is sufficiently ductile or elastic to bend readily. Preferably, the material has thermoplastic characteristics; that is to say, will, after initial setting, soften gradually upon being reheated. -A material known to the trade as Vinylite and formed by the polymerization of a vinyl compound has been found to possess a degree of hardness sufficient to withstand "the wear and tear incident to use in the modern high speed printing press. By the addition of well' known plasticizers, such for example as dibutylphthalate, the degree of ductility of the layer l2 may be varied as desired in order to attain the required flexibility of the printing plate as a whole.

The carrying sheet i3 serves to reinforce the molded type layer and enable the same to be fastened detachably on the printing press support 14 and securely held thereon during printing. Preferably, the sheet I3 is substantially thinner than the base l2 and is composed of metal such as steel possessing a relatively high degree of flexibility and yet is substantially nonextensible as compared to the type layer l2, that is, is capable of withstanding a substantial edgewise tension and compression without appreciable change in surface dimensions.

The carrying sheet l3 and the molded type layer l2 are firmly bonded together during the molding operation in which the type projections are formed. For this purpose, the upper surface of the sheet is covered by and firmly cemented by a suitable adhesive such as water glass to a sheet l5 of muslin or other material to which the resin will adhere readily.

The metal sheet affords a convenient medium through which the printing plate may be stretched over and securely but detachably fastened to a backing surface mounted on the printing press support l4. Herein, the backing surface is formed by a plate [6 preferably preformed to the curvature of the cylinder i4 and of a uniform thickness sufficient to locate the printing surfaces H in proper position with respect to the cooperating impression cylinder of the printing press. In the embodiment shown, the backing plate comprises two substantially rigid plate sections 11 and 18 connected in edge-to-edge relation at a hinge joint l9. The two opposite edges of the backing plate are adapted to be received between shoulders 20 formed along the opposite side edges of the sheet l3 immediately beyond the edges of the layer l2. These shoulders may be formed by bending the outermost portions of the sheet 13 reversely on the underside of the layer l2 so as to form inturned flanges 2i.

In securing the printing plate to the press cylinder through the medium of the backing member above described, the plate section I! is first clamped to the cylinder, the free edge of the section I8 is swung upwardly and the printing plate applied as shown in Fig. 1. Now, when the section 18 is pressed downwardly against the cylinder, the plate will be expanded with a toggle action as the sections l1 and I8 are brought into edgewise alinement thereby stretching the sheet 13 and drawing the printing plate over the surface of the backing member and effectually securing the sheet l4 and backing member together. By applying clamps 22 to the free edge of the backing section l8, the sheet and backing member assembly will be securely fastened to the press cylinder ready for printing.

The vinyl resin of which the type are formed in the printing plate above described possesses certain properties which adapt the resin for such use. The resin does not shrink as much in molding as most synthetic resins and takes a sharp impression. The thermoplastic character renders the plate readily usable in rotary printing presses requiring a curved type surface. The plate above described possesses sufficient flexibility to respond to a detail make-ready placed beneath the backing member l6 instead of on the impression cylinder as is done in standard practice.

The printing plate is preferably formed in a single molding operation from a mold 23 having indentations therein corresponding to the type to be formed and formed from an original engraving or form in the manner disclosed in a copending application of Arthur B. Davis, Serial No. 736,222, filed July 20, 1934.

The plate molding operation is carried on in a suitable press preferably operated hydraulically and having platens 24 and 25 heated to the temperature necessary for softening the resin ingredients to the degree required for molding. This may be accomplished by circulating heating fluid through coils 28. During molding, the mold is supported on the lower platen 25 and covered with a layer 26 of the resin ingredients in powdered or sheet form suflicient in amount to more than fill all of the mold cavities when in the plastic state. The carrying sheet l3 may be fastened to a filler plate 21 against which the upper platen 24 acts. To prevent the resin from adhering to those parts of the carrying sheet corresponding to the so-called dead metal areas of the original form, a suitable mast l4 may be interposed between the material 26 and the sheet I3.

With the parts thus assembled, the platens are first maintained in close proximity to each other until the resin has been softened properly. Then, the platens are moved together under pressure to compress the plastic ingredients to a thickness determined by bearers 28 after which the resin is allowed to set.

Upon cooling, the finished plate may be stripped from the mold and thereafter bent to the proper curvature. This is accomplished by reheating the printing plate to a temperature suflicient to soften the resin slightly, bending the plate around a cylindrical surface of slightly smaller radius than the printing press support on which the plate isto be used, and allowing the bent plate to cool. If desired, such bending may be effected by the same general method which is used in attaching the printing plate to the printing press cylinder. To this end, a backing plate and cylinder as shown in Figs. 4 to 6 would be employed having a radius slightly smaller than the radius of curvature desired in the finished plate. One flange of the reheated plate would first be hooked around the backing plate section ll as shown in Fig. 4 and the other end then hooked around the section 18 as shown in Fig. 5. By moving the sections 11 and I8 into alinement as shown in Fig. 6, the carrying sheet i3 is stretched over and bent around the backing plate after which the plate is allowed to cool and take a permanent set. By bending the plate to a smaller radius than the printing press support on which the plate is to operate, any slight shrinkage which may occur upon cooling of the resin is compensated for and the final curvature desired thus obtained.

To avoid incorporation in the finished printing plate of any inaccuracies that may exist in the spacing of the platens of the press used in the molding operation, the invention contemplates treatment of a molded plate in a manner such as to insure a high degree of accuracy in the spacing of the type surface with respect to the back surface of the printing plate. This is accomplished by machining the back surface of the carrying sheet l3 to locate the same exactly parallel with respect to the printing surface I I of the plate. To facilitate this operation, a thin layer 30 (Fig. 11) of lead or other readily machinable metal is preferably sweated onto the underside of the carrying sheet and shaved off to the proper degree after the molding operation and while the type projections are still supported by the mold 23.

Preparatory to the machining operation, an extended end portion 3| of the carrying sheet i3 is bent around a block 32 and securely fastened by means of a clamping member 33. Then, one or more passes across the layer 30 are made in a well known manner with a shaving tool 34 to reduce the overall thickness of the printing plate to the proper degree and at the same time locate the machined surface accurately with respect to the printing surface formed by the type.

Theplate construction above described is particularly advantageous for use in multi-color printing in rotary printing presses, for with such construction, perfect color register is obtainable in spite of the bending which is necessary in order to adapt the different color plates to the cylindrical supports of rotary printing presses. This advantageous characteristic of the present plate construction may best be understood after an appreciation of the'conditions causing uneven distortion of the different color plates and lack of color register in the matter printed thereby when such plates are constructed of the same kind of material throughout or comprise ordinary lead-backed electrotypes.

Referring now to Figs. '7 to 10 which show two printing plates 35 and 36 composed of one kind of material throughout; the plate 35 has a type surface 3l adapted to print a large solid area of a length x. The plate 36 has type projections 3t separated by a distance 31 and intended to print small widely separated areas in a different color with their inner edges in register with the outer edges of the solid area printed by the type face 3?.

Itis well known that when a fiat plate of any substantial thickness, such as the solid portion of the plate 35 is bent around a cylinder, the material on the concave side is compressed while that on the convex surface is placed under tension. The magnitude of the tension produced in bending and therefore the increase in the distance between opposite sides edges of the solid area 3? is proportional to the distance of the surface from a neutral line 39 along which the material is undisturbed. For a plate composed of one kind of material, this neutral line is located about midway between the opposite side surfaces of the plate. With a thinner plate, such as that portion of the plate 36 between the projections 38, the distance between the neutral line 38 and the surface of the type 38 is greater; consequently, the distance between the projections as indicated at 1/ is increased more in bending of the plate 38 than the distance a: in the case of the plate 35 In othr words, if the distances at and y are equal before bending, the distance 11/ will be greater after bending by an amount represented in Fig. 8 between the radial line r and the inner edge of the adjacent projection 38. If such plates were used in multi-color printing, the adjacent edges of the solid area printed by the surface 31 and the areas printed by the type 38 would be separated and proper color register would. not be obtained.

This deviation from proper register will be more pronounced where, as in the lead-backed electrotypes ordinarily used in multi-color printing, the material forming the filling and backing for the electrotype shell is more readily compressible than the type face. With such a plate, the metal forming the type surface would define the neutral plane in bending and the type surface for printing a large solid area would remain practically unstretched after bending; whereas, the surfaces of widely spaced dots would, as an incident to bending, be seperated the same as in the case of the plate 36 above described.

In a printing plate constructed in accordance with the present invention, the sheet I3, being composed of material which is non-compressible as compared to the material of which the type is composed, determines the neutral line above referred to in the bending of the plate, and the distance between this plane and the type surface for the different color plates is always the same regardless of the character of the type surfaces. Therefore, in bending of'the plate, the sheet I3 will actually cause the printing face of a large solid type area to be stretched to a slight extent and in the same proportion that the surfaces of spaced dots will be separated in bending. As a result, the distance between two points on a large solid type area of one color plate will be increased in bending to the same degree as the distance between two similarly spaced points on a different color plate having type projections of small areas. Thus, by locating the sheets I3 of the plates for printing different colors equidistant from the surface defined by the type, uniform distortion of the type surfaces of all of the plates results from bending. Exact color register, therefore, will be obtained when the two plates are used in multi-color printing.

The foregoing action will be more apparent from Figs. 9 and 10 which show plates til and iii where R is the radius of curvature of the sheet I3. The distance between the inner edges of the projections 43 of the plate M will change in the same ratio in bending. Since the distance 2 is the same for both plates, the distances :0 and y will be increased in the same ratio so that when the plates are used in multi-color printing, the inner edges of the matter printed by theprojections 43 will coincide exactly with the outer edges of the solid area printed by the type face 42. In this way, perfect color register is obtained without treatment of the plates subsequent to bend- Where extremely severe conditions prevail in service, it may be desirable toprotect the surface of the type projections by covering the same with a thin shell of metal of uniform thickness. In such a case, the resinous layer I2 and the projections III would act as a filler for the cavities inthe back of the metallic shell forming the actual printing surface.

The life of the printing plate may also be prolonged by incorporating in the material of the layer a filler which acts to increase the resistance of the hardened resinous material to flowing under the temperatures and stresses encountered during prolonged use of the plate in a high speed printing press. forms and preferably constitutes a substantially larger proportion of the moldable material than the resinous binding ingredient. For example, the filler may comprise granules 45 (Fig. 12) of a hard material such as metal, carborundum or the like of such small size that in the molding operation the dots 46 for obtaining the different color shades may be reproduced accurately. To this end, the particles of the aggregate or filler ingredient are preferably of a size capable of passing a 300 mesh sieve or smaller and are combined with a suiiicient proportion of the thermoplastic resin to insure that all of the voids Such filler may take various in the aggregate will be filled. When approximately 28 percent of the binding ingredient is used, it has been found that the resistance of the composite material flowing when cold may be increased approximately ten times. Accordingly, the service life of the plate may be increased materially.

This application is a continuation in part of. my former application Serial No. 605,418, filed April 15, 1932.

I claim as my invention:

1. For use in multi-color printing on a printing press having cylindrieal'supports for the different color plates, a plurality of plates for printing different colors each comprising a flexible sheet of metal capable of withstanding edgewise compression and a layer of a thermoplastic resin, said layer being secured to one side of said sheet and having type formed therein, said sheets for the different color plates being disposed substantially equidistant from the type surfaces and operating to produce uniform distortion of said surfaces in bending of said plates to adapt them to the curvature of said supports.

2. For use in multi-color printing on a printing press having cylindrical supports, a plurality of plates for printing different colors each comprising a flexible metal sheet substantially non-compressible edgewise, and a layer composed of material which is sufliciently ductile to permit of bending, said layer being carried by and united with said sheet and having type standing out in relief thereon and said sheets for the differentcolor plates being spaced substantially equidistant from the type surfaces and defining neutral planes in the bending of the plates whereby to produce exact color register in the use of the different color plates after bending thereof to conform to the convex curvature of said supports.

3. For use in multi-color printing on a printing press having cylindrical supports for the different color plates, a plurality of plates for printing different colors and each having type standing out in relief therefrom, and means operable to withstand edgewise compression during bending of said plates and thereby determine neutral planes of bending extending parallel to and spaced substantially equidistant from said surfaces whereby to cause uniform distortion of said surfaces in the bending.

4. A printing plate comprising, in combination, a layer of resin having type projections molded 'in one side thereof and having thermoplastic characteristics whereby to soften when reheated after molding and permit bending of the layer to a predetermined curvature, and an integral sheet of' metal secured to the other side of said layer and acting during bending of the layer to define a neutral plane of bending spaced equidistant from all parts of the surface defined by said projections whereby to cause uniform stretching of said surface.

5. For use in a printing press having a curved support, a printing plate assembly comprising a layer of moldable thermoplastic material having type projections molded in one side thereof, an integral sheet of metal secured to said layer and acting during bending thereof to define a neutral plane of bending spaced equidistant from all parts of the surface defined by said projections whereby to cause uniform stretching of said surface, fastening devices on opposite side portions of said sheet, [and means on said support interengageable with said devices for placing said sheet under tension whereby to stretch the sheet over said support and thereby attach said layer to the support.

6. The method of forming a curved printing plate to be mounted on a printing press cylinder comprising molding type projections in a layer of material which will soften upon being heated, bonding a flexible sheet of metal to the back of said layer, heating the composite plate thus formed to a temperature suflieient to soften said material, bending the plate, while thus heated, around a surface corresponding in curvature to but of smaller radius than said cylinder, and allowing the bent plate to cool.

7. The method of forming a printing plate comprising forming a mold having cavities therein corresponding to the type to be formed, forming a type carrying sheet in said mold, uniting said layer with a sheet of material which is substantially non-extensible in an edgewise direction, and machining the back of said sheet to parallelism with the surface of said type while the latter surface is backed by the mold and said sheet is held against edgewise movement.

WELLS A. LIPPINCOTT.

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