Lithographic blanket

摘要

936,206. Printing processes &c. W. R. GRACE & CO. Oct. 15, 1959 [Oct. 16, 1958; Sept. 28, 1959], No. 35007/59. Drawings to Specification. Class 100 (2). [Also in Group VIII] A lithographic printing blanket has a firmness such that a pressure of at least 15 lb. per square inch must be exerted on it to reduce its initial thickness by 2 mils and a compressibility such that the additional pressure required to reduce the thickness of the blanket by 2 mils more is not more than 35 lb. per square inch. The blanket comprises a non-extensible backing, a compressible body portion, and a thin ink-transfer surface. The backing may be prestretched cotton duck fabric, several plies bonded together with neoprene latex, or a thin sheet of aluminium, stainless steel or a polyester resin, or the offset cylinder can be used as the backing. The compressible body may be a fibre paper comprising 70% mercerized cotton linters and 30% short paper fibres impregnated with rubber, e.g. rubber latex to the extent of 72% of the fibres, a mixture of 80% of a butadiene-acrylonitrile polymer latex and 20% solution of phenolic resin, to 60%, or " Buna-N " Latex (Registered Trade Mark) to 72%. The body is secured to the base with a butadiene-acrylonitrile copolymer latex and press-cured at 250‹ F. for 20 minutes or cured in a hot-air oven. The compressibility of the body is caused by small voids occupying 49-75% by volume. The ink-transfer layer may be a polyurethane elastomer cement, or a butadiene-acrylonitrile copolymer latex compound. Alternatively, the body may be used as a replacement portion of the blanket, being cured and having the transfer layer on one face and adhesive on the other, covered with silicone-treated paper until required. A worn-out body is detached from the base and replaced. In order that the blanket should have the required firmness and compressibility, the body alone should require at least 10 lb./square inch for 2 mils compression, and not more than 60 for further compression to 4 mils.