Patent GB-589221-A (GB)
Title: Improvements relating to the production of curved printing plates from thermosettingand thermoplastic materials
IPC: B41C3/06
Filed: 1945-03-20
Abstract: 589,221. Printing - surfaces ; embossing. HOLE, E. S. March 20, 1945, No. 7024. [Class 100 (ii)] Curved printing-plates for use on rotary printing machines are moulded by placing a curved matrix in a concave platen, superposing one or more layers of sheet material impregnated with a thermosetting or thermoplastic synthetic resin, applying a convex platen with means for locating it accurately within the concave platen, and effecting the moulding by pressure between the two platens. As shown, a convex platen 15, Fig. 1, is supported by brackets 17 clamped on the columns 23 of a power press having hot plates 21, 22, and a concave platen 18 is carried by a tray 19 on the plate 22 which is raised to apply pressure. The platen 15 is approximately a half cylinder having ends of reduced diameter to engage arcuate stops 24, Fig. 2, screwed to the platen 18, and blocks 26 with notches to engage wedgeshaped blocks 27 on the platen 18, whereby the platens are registered : the notch depth exceeds the wedge height so that contact is at the sides leaving the stops 24 to determine the depth of engagement of the platen 15 in the platen 18. In a modification, Fig. 3 (not shown), the platen 15 is of the same diameter throughout, packing being used to fill the cavity in the platen 18. The matrix may be made of plastic material moulded fiat and bent to shape in the press, registration marks being formed on the matrix during moulding, by means of pointed members, and holes drilled to fit over studs on spring fingers 35, Fig. 2, carried by a plate 36 having a dowel fitting in a recess 38 in the platen 18 : the middle finger 35 fits over the edge of the matrix, and the other two engage under it. The original type plate may be bent and a matrix formed therefrom between curved platens. The matrix may be made from cellulose sheets impregnated with synthetic resins, the front sheets being fully impregnated and the back sheets more thinly impregnated, to facilitate bending ; also, curing may be partial in the flat and completed in the press. The sunken parts of the matrix may be filled with a plastic mouldable powder, or, alternatively, a sheet of natural or synthetic rubber may be placed behind the first or second facing sheet, or the whole of the thickness behind the impregnated sheets may be made up of natural or synthetic rubber. Where a completely semi-circular plate is required, the platen 18 has side.extensions to allow for the margins of the matrix. To reduce the number of platens required to deal with a range of printing-cylinders, (1) a series of concave platens may be used differing in diameter by one inch intervals with convex platens differing by half inch intervals, the ends of some of the latter being reduced to fit fixed stops on the associated platens, (2) convex platens as in (1) above are used with one large concave platen, (3) a single convex platen is used in conjunction with a concave platen having deep stops, (4) a range of curved metal plates of various thicknesses is provided to insert behind the matrix or on the convex platen. Thin plastic plates may be fixed to metallic or other bases pre-curved to fit the printing-cylinder, a plastic plate may be backed by rubber rendered impervious to oil or by oil-resisting synthetic rubber, the composite plate being fixed to a metal plate perforated like a nutmeg grater or to a vulcanized fibre backing, and thermoplastic plates can be moulded from a thermosetting matrix by heating the thermoplastic, placing it on a hot matrix and between hot curved metal plates and introducing the assembly into a cold press between cold curved platens. The plates may be moulded on to a textile or widemeshed fabric or wire-gauze backing. Specification 651,371, [Group VIII], is referred to.