Verfahren zur Herstellung einer magnetischen Registrierschicht

991,676. Magnetic recording members. GEVAERT PHOTO-PRODUCTEN N.V. Jan. 18, 1963 [Jan. 22, 1962], No. 2256/63. Heading H1H. A magnetic recording member is formed by depositing on a substrate a dispersion of magnetic particles in a solution of a fully latent polyisocyanate and a binder which reacts above a certain temperature with isocyanate groups, then evaporating the solution below the reaction temperature and finally heating above the reaction temperature allowing the isocyanate groups and the binder to react. By fully latent polyisocyanate is meant the reaction product produced by the addition of a compound containing an active methylene group to any isocyanate group of a polyisocyanate compound. From this latent polyisocyanate the free polyisocyanate is regenerated by heat between 100‹ and 200‹ C. The magnetic particles are preferably oriented by a magnetic field during the evaporation process and the member is calendered before or during the chemical reaction. The substrate may be stretched polyethylene terephthalate coated with a copolymer of acrylonitrile and vinylidene chloride as in Specification 991,675. The binder may be of thermoplastic macromolecular compound containing groups which react with isocyanate groups, such as polymers containing free hydroxyl, carboxyl, amino or sulfhydroxyl groups. Suitable polyhydroxy compounds include cellulose esters and cellulose ethers containing free hydroxyl groups such as nitro-, acetyl-, propionyl-, butyryl-, acetylbutyryl-, benzyl- and ethylcellulose. And also partially saponified polyvinyl esters, soluble reaction products of polyamides and epoxy resins and polyesters containing hydroxyl groups, such as the soluble reaction products of polyesters containing hydroxyl groups with polyisocyanates. Other suitable binders are polyvinyl acetals with free hydroxyl groups, such as the non-stoichiometric reaction products of polyvinyl alcohol and butyraldehyde. Solvents for these binding agents are chlorinated lower aliphatic hydrocarbons, lower aliphatic alcohols and aromatic hydrocarbons such as toluene. Latent polyisocyanates which may be used include the addition products of lower alkyl acetoacetates, such as ethyl acetoacetate, and polyisocyanates, such as 1,4-cyclohexyl di-isocyanate or 1,6-hexane di-isocyanate. However these cause pores and irregularities in the film due to the escape of the volatile alkylacetoacetates. This can be overcome by using a compound of, for example, 2,4-toluene di-isocyanate wit