GB151299A - Improvements in and relating to printing plates and method of making the same - Google Patents

Abstract

151,299. Alexander, A. E., (Stokes, J. S.). March 20, 1919. Printing-surfaces.-A printing-plate comprises a body or backing of fibrous material impregnated short of saturation with a phenolic, condensation product and having a facing layer of phenolic condensation product or of metal. The plate is moulded under heat and pressure against a matrix or mould, and in the preparation of the matrix from the type forme an underlay may be employed so that the moulded plate is made-ready for printing. Alternatively, the plate may be " madeready " by subjecting it to pressure with an overlay in contact with its printing-surface. The plate may also be formed with means by which it can be easily registered on the bed of the press. Fig. 1 shows one form of plate blank comprising a number of sheets a of fibrous material, preferably fibre board made from old newspaper stock, impregnated short of saturation with phenolic condensation product and secured together by an adhesive consisting of phenolic condensation product, wood flour, and a solvent such as amyl alcohol, mononitro-naphthalene or penta-chlorophenol. The outer faces are coated with layers d of phenolic condensation product, and the blank heated in a press for about one minute to harden the layers d into a smooth non-flowing skin. The mould or matrix preferably consists of a fibrous backing impregnated with phenolic condensation product and faced with an alloy of equal parts of tin and lead. Before moulding the plate, the face of the matrix is treated with a solution of bicarbonate of soda and is then coated with a layer of a composition consisting of phenolic condensation product, a so]- vent of phenol such as mono-nitro-naphthalene or penta-chlorophenol, and small quantities of stearic acid and of fillers such as lamp black, iron oxide or copper peroxide. The matrix is then heated until the layer forms a dry skin. The matrix and plate blank are then placed face to face in a heated press to mould the blank and cause the layer to adhere firmly to the plate. The heating is continued until the phenolic condensation product in the plate is hardened to infusible form, and the plate is then separated from the matrix while hot. Instead of facing layers d of phenolic condensation product, metallic facings secured to the body by the adhesive described above may be employed, but in this case the matrix is used without the coating layer described above. The plate may be " made-ready " for printing before the phenolic condensation produce in the body of the plate is set to infusible form, by placing the plate C, Fig. 6, in a steam-heated press with an overlay 7 in contact with the printing surface 5. The non- printing hollows of the plate may afterwards be deepened by a sand blast, the printing parts being protected by a paste of beeswax and resin oil. To facilitate registration of the plate 21, Fig. 7, on the bed 20 of the printing press, the bed may have a number of sockets 42 and the plate 21 is moulded with corresponding bosses 39, Fig. 11, by means of the specially formed moulding-press plate 34, and the matrix 29 is positioned in the moulding press so that the bosses are formed in a predetermined position with respect to the marginal lines of the printing characters on the plate. Screws 43 in the plate 34 may be provided to form threaded bores in the bosses 39 to receive fastening screws for holding the plate on the printing- press bed. In the manufacture of curved printing plates, the plate is moulded in the flat condition with grooves 47, Fig. 14, on the back, and while still flexible is bent over a cylindrical mandrel and held thereon by a weighted cover or hood.