Patent GB-976359-A (GB)
Title: Magnetic recording element and methods of preparation thereof
IPC: C08L75/04
Filed: 1962-04-05
Abstract: A magnetic recording medium comprises a base coated with magnetic particles in a binder comprising 0-75% by weight of a polymeric matrix material and the balance of a diosocyanate-based elastomer, said matrix material comprising at least one solid, soluble thermoplastic copolymer of from 0.5 to 50% by weight vinyl alcohol and the balance at least one member of the group vinyl esters, vinyl acetals vinyl halides and vinylidene halides, said diosocyanate-based elastomer consisting of interconnected units having the formula [-NX-(B-NH-CO-O-G-O-CO-NH)n-(B-NX-R)m-] wherein O-G-O is a bivalent polymeric radical obtained by removing the terminal active hydrogen atoms from an organic compound having a M.W. of at least 750 and consisting of a polyalkylene derived glycol or a linear dihydroxy-terminated polyester or polyester amide; B is a bivalent non-polymeric radical inert to isocyanate groups; R is a bivalent radical selected from the group consisting of carbonyl, non-polymeric diacyl radicals and non-polymeric dicarbamyl radicals; and X is hydrogen, a non-polymeric dicarbamyl radical or a polymeric dicarbamyl radical of the formula -CO-NH-(B-NH-CO-O-G-O-CO-NH)n-B-NH-CO-  The magnetic particles may be iron, magnetic, Zn, Fe ferrite or acicular g Fe2O3 particles 0.2-2m long and with a length to width ratio of 2-20. The base may be a disc, drum, or tape and made of glass, paper, metal or plastic material, e.g. polyethylene terephthalate, cellulose acetate, oriented p.v.c. Thicknesses are specified. The coating may be applied by various techniques and an orientating magnetic field may be applied.  In the preparation of the diosocyanate based elastomer, a prepolymer is formed by reacting a polymeric organic compound having two terminal hydroxyl groups with a molar excess of a diosocyanate. The prepolymer may be treated in one of two ways, (a) it may be reacted with a bifunctional chain extending compound (e.g. water, a glycol or a diamine) in an amount insufficient to react with all the NCO groups, (b) it may be reacted with excess of such a compound and then further reacted with the complementary amount of an isocyanate compound.  The applied coating may constitute the final material in uncured form, which is cured on the tape.  Alternatively the coating may include the aforementioned prepolymer and the coated tape is treated with the bifunctional compound.  Specified polymeric matrix materials comprise the following vinyl resin components: copolymers of vinyl alcohol with vinyl acetate, copolymers of vinyl alcohol with vinyl butyral, copolymers of vinyl alcohol with vinyl chloride and vinyl acetates, copolymers of vinyl alcohol with vinylidene chloride and vinyl acetate.  Polyurethane forming reactants are specified as follows:-  (a) The polymeric organic compound has a higher molecular weight (molecular weight above 750) and two terminal hydroxyl groups and is selected from the group consisting of (1) polyalkyleneether glycols, such as polytetramethyleneether glycol, polyethyleneether glycol, polypropyleneether glycol and poly-1, 2-butyleneether glycol, (2) polyalkylene-aryleneether glycols, (3) polyalkyleneether-thioether glycols, (4) polyalkylene-aryleneether-thioether glycols, (5) linear, dihydroxy terminated polyesters, such as are prepared in a known manner by esterification of dihydric alcohols, such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butylene glycol with dibasic organic acids such as adipic acid, glutaric acid, suberic acid, sebacic acid and 2-ethyl suberic acid, and (6) linear, dihydroxy-terminated polyester amides.  (b) Any of a wide variety of organic diisocyanates may be used in the reaction including aromatic aliphatic and cycloaliphatic diisocyanates and combinations of these types. Representative compounds include tolylene-2, 4-diisocyanate, m-phenylene diisocyanate, 4-chloro-1, 3-phenylene diisocyanate, 4, 41-biphenylene diisocyanate, 1, 5 naphthalene diisocyanate, 1,6-hexamethylene diisocyanate, 1,4-cyclohexylene diisocyanate and 1,5-tetrahydronaphthalene diisocyanate.  (c) The non-polymeric chain-extending agent which may be used in the preparation of the diisocyanate-based elastomer may be selected from the group of bifunctional compounds having at least two hydrogen atoms capable of reacting with isocyanates.  Some suitable bifunctional compounds are water, ethylene glycol, hexamethylene glycol, monoethanolamine, m-phenylenediamine, 4,41-methylene dianiline and 4,41-methylene-bis-(2-chloroaniline).