GB1443455A - Method and apparatus for producing colour changes in selected areas of webs - Google Patents

Abstract

1443455 Electrolytic colour changing WIGGINS TEAPE Ltd 2 July 1974 [3 July 1973] 31658/73 Heading C7B [Also in Divisions B6 D1 and D2] A method of producing a paper or non-woven web having areas of differing colour or shades of colour comprises forming on a papermaking machine a web containing a chemical compound which generates a colour or change in colour of the web when subjected to an electrical potential difference, said compound having been introduced (a) into the web by an impregnation step after web formation, or (b) into the fibrous suspension from which the web is formed, and subjecting the web to an electrical potential difference in selected areas whilst on the papermaking machine so as to bring about a colour change in said areas. The web during or after formation may be supported on an electrically conductive carrier surface which carries the web into momentary contact with an electrically conductive zone or zones supported by a support member and corresponding in configuration with the selected areas, the carrier surface and support member being maintained at differing electrical potentials. The carrier may be an endless belt, Fourdrinier wire, or roll. The support member may be a belt, or roll e.g. dandy roll. Preferably, at the time of electrical contact, the web has a moisture content greater than 30%. The compound used may be a pigment e.g. iron oxide, dyestuff, e.g. a fluorescent dyestuff, a redox indicator, or a pH sensitive compound. Each ply of a two-ply sheet of paper may be treated according to the method. In an Example, a web was prepared from an aqueous suspension of wood pulp containing wood resin, alum, ferric chloride, and sodium ferrocyanide, and contacted with a dandy roll bearing a design through which a D.C. current was passed. A corresponding coloured design was formed in the web. The dandy roll had a metallic inner shell, a plastics non-conductive wove cover, and an electro-metal design secured to the cover. In another Example, the web was formed from an aqueous suspension of cotton linters and wood pulp, which also included wood resin, sodium aluminate, china clay, and manganese chloride. In a further Example, a web formed from an aqueous fibrous wood pulp suspension containing wood resin, aluminium sulphate, and ferric chloride, is sprayed with an aqueous solution of sodium ferrocyanide and a yellow dyestuff prior to contact with the dandy roll.