Patent GB-829008-A (GB)
Title: Magnetic recording tape
IPC: D21H19/62
Filed: 1957-09-16
Abstract: 829,008. Laminates and laminating. DU FONT DE NEMOURS & CO., E.I. Sept. 16, 1957 [Sept. 20, 1956], No. 29156/57. Class 140. [Also in Group XXXV] Laminated magnetic recording tape having a smooth surface is made by casting a thin layer of magnetic material dispersed in a binder on a smooth surface travelling at constant speed, guiding into contact with it a thin flexible supporting layer, providing adhesive between the layers, and stripping the laminate from the surface. As shown, the magnetic layer 3 is formed on a smooth drum 2 by delivery from a hopper 1, and a flexible web 4, delivered over a roller 5, skim-coated with adhesive 6 in a trough 7 while passing around a roller 8, and passed, if the adhesive is thermoplastic, through a heater 9, is pressed against the layer 3 by a roller 10, the laminate then being passed, if the adhesive is polymerizable, past a heating or ultraviolet polymerizing unit, and being stripped by a roller 12. In a modification the drum 2 is replaced by a highly polished endless belt. The magnetic material may comprise ferromagnetic oxides of iron and chromium described in Specifications 824,323 and 829,007, [both in Group III], or ferromagnetic complexes as disclosed in Specification 781,997. The binding materials usable include cellulose derivatives such as the acetate, nitrate, or acetate-propionate, a mixture of polymethylmethacrylate and a phenolformaldehyde condensation product, polystyrene, nylon, copolymers of vinylidene chloride with vinyl chloride, vinylacetate, isobutylene or acrylonitrile, and polyvinyl butyral; the last is preferred. The binder may also contain dispersing agents, such as tetra-isopropyl titanate, or the dioctyl ester of sodium sulphosuccinic acid alone or mixed with stearic acid, plasticizers, lubricants, and stripping agents such as mineral oil. The supporting layer may comprise paper or film-forming materials such as cellulose nitrate, triacetate, propionate, or acetate -butyrate, polyvinylchloride, polyvinyl chloride-acetate, polyvinyl acetals such as the formal or acetal or polyesters such as polyethylene terephthalate; oriented webs of the latter are preferred, and these may be precoated with materials to improve adhesion. One of the layers may be coloured. The adhesive used may be (1) pressure-sensitive, for example the composition containing rubber, para-coumarone resin, wood-rosin, and liquid paraffin disclosed in U.S.A. Specification 2,117,627, Example C, in which case no heating or polymerizing apparatus is required, (2) thermoplastic, heating and subsequent cooling means then being necessary, or (3) polyrnerizable, a thermo-sensitive or light-sensitive catalyst then being added, and heating means or a source of ultra-violet light such as a mercury vapour lamp being provided. In examples, the following adhesives are used to unite a magnetic layer to a support layer of polyethylene terephthalate-polyvinyl butyral; chlorsulphonated polyethylene; a copolyester of ethylene glycol with terephthalic and sebacic acids (1 : 1) ; an aqueous dispersion of a copolymer of vinylidene chloride (80 parts) and acrylonitrile (20 parts) containing 20% of dibutyl phthalate as plasticizer; an aqueous dispersion of a terpolymer of vinylidene chloride (80 parts) butyl acrylate (20 parts) and itaconic acid (2 parts); an Epon resin ; photopolymerizable resins comprising respectively methylmethacrylate containing 0.01-1.0% of benzoin, and equal parts of triethylene glycol diacrylate and vinyl acetate containing 0.1% of benzoin methyl ether. The magnetic layer may be made by ball milling the following ingredients for several days, filtering, and spreading on the smooth surface to produce a film 0.0005 inch in thickness; magnetic F 2 O 3 , grain size less than 1 micron, stearic acid, dioctyl ester of sulphosuccinic acid, tertiary butanol, toluene, and polyvinyl butyral in solution in the last two solvents. Specifications 700,957, 718,422, 726,736, 732,607 and U.S.A. Specification 2,367,670 also are referred to.