GB1056745A - Dampening roller cover and its use in lithographic printing - Google Patents

Abstract

1,056,745. Dampening roller covers. MINNESOTA MINING & MANUFACTURING CO. July 15, 1963 [July 16, 1962], No. 27930/63. Heading B6C. [Also in Divisions D1 and F2] A dampening roller cover for use in lithographic printing comprises a hygroscopic, seamless, non-woven sleeve of randomly disposed hydrophilic fibres, which are substantially insoluble in water below 100‹ F. and are capable of being expanded longitudinally when water wetted, and of retaining the expanded condition on drying and of contracting longitudinally when subsequently re-wetted with water. A web 1, Fig. 1, of hydrophilic fibrous material made from polyvinyl alcohol or polypyrrolidone fibres is convolutely wrapped in multiple layers around a mandrel 2, and a wetted nylon curing tape, which shrinks upon drying is wrapped helically (Fig. 2, not shown) about the mandrel over the layers. This preformed sleeve is then heated in the presence of moisture to a temperature of 200-300‹ F. sufficient to effect at least a partial fusion of some of the non-woven fibres to each other to produce a coherent sleeve. After drying, the curing tape is removed and the sleeve 3, Fig. 3, sanded by sanding wheel to remove surface irregularities. The sleeve is then slipped over an expandible mandrel 5 (Fig. 4, not shown), wetted with water and mechanically expanded, in which state it is dried so that the sleeve retains its expanded dimensions. The dry sleeve is then slipped over a dampening roller 6, Fig. 5, and wetted with water, whereupon the sleeve contracts to the dimensions of the roller and tightly adheres to the surface. The non-woven web preferably comprises fibres of the polyvinyl alcohol type with a denier from about 0À5-6 and having a length varying between 0À25-2 inches. To improve the hydrophilic properties of the non- woven web additional hydrophilic fibres, which need not be heat fusible, may be included e.g. cotton, regenerated cellulose, viscose rayon, cellulose acetate and other rayons. A small amount of binder, such as a water-soluble polyvinyl alcohol resin, may be added to the fibres as a figuration of the web to assist in bonding the fibres into a cohesive web. By way of example, webs containing 50% by weight of cellulose acetate rayon fibres and polypyrrolidone fibres and 20% by weight of polyvinyl alcohol fibres and 80% by weight of cellulose acetate rayon fibres, are quoted.