Patent GB-642734-A (GB)
Title: Improvements in or relating to magnetic sheet material having an insulating coating
IPC: H01F41/16
Filed: 1947-06-06
Abstract: Insulated magnetic sheet material, e.g. for rotor and stator laminations and for transformer punchings comprises magnetic sheet material and an insulating film not exceeding 2 per cent of the thickness of the sheet material applied to the surface of the sheet material, the film being composed of a thermoset aminotriazine-aldehyde resin, as defined below, and finely divided solids distributed therein in an amount of less than 35 per cent of the weight of the resin, the solids being selected from carbon, iron oxide, silica, alumina, magnesia, asbestos, mica dust and bentonite. The resin is prepared by reacting one mole. of a compound of the formula <FORM:0642734/IV (a)/1> where R is an amino, alkyl, halogen, substituted amino, alkoxy or hydroxy radical with from 0.8 to 4.5 moles. of an aldehyde, the resin being condensed to the state where it is still water-soluble.  Suitable aldehydes are formaldehyde, para-formaldehyde, butyraldehyde, furfural and acetaldehyde.  The coating may be applied, e.g. by felt or rubber rolls, as a composition comprising from 5 to 70 per cent by weight of the partially reacted resin, from 90 to 25 per cent of water, 5 to 25 per cent of organic solvent and up to 35 per cent of the finely divided solids.  Suitable organic solvents are ethanol, propanol, isopropanol, butanol, ethanolamine, morpholine and acetone. Wetting agents, e.g. sulphonated alcohols, long carbon chain sulphates, e.g. lauryl sulphate, and soaps, e.g. sodium stearate, may also be included in the coating compositions.  In examples, coatings of (1) melamine-formaldehyde resin and lampblack in a mixture of isopropanol are applied to magnetic sheet material, dried at 150 DEG  C., and then cured; (2) iron oxide (FeO) replaces the lampblack of (1).  A graph shows the resistance of a number of laminations coated with composition (1).  The Specification as open to inspection under Sect. 91 comprises also magnetic sheet material coated with the melamine-aldehyde resin without filler.  It is also stated that powdered magnetic material, e.g. iron and nickel, may be coated with the resin and compacted under heat and pressure to form magnetic cores suitable for applications in radio.  Examples (now cancelled) describe coating magnetic material with a composition of melamine-formaldehyde resin and (1) ethanol, water, methyl cellulose and the di-octyl ester of sodium sulphosuccinic acid, (2) iso-propyl alcohol, water and wetting agent.  This subject-matter does not appear in the Specification as accepted.ALSO:Insulated magnetic sheet material, e.g. for rotor and stator laminations and for transformer punchings comprises magnetic sheet material and an insulating film not exceeding 2 per cent of the thickness of the sheet material applied to the surface of the sheet material, the film being composed of a thermoset amino-triazine-aldehyde resin, as defined below, and finely divided solids distributed therein in an amount of less than 35 per cent of the weight of the resin, the solids being selected from carbon, iron oxide, silica, alumina, magnesia, asbestos, mica dust and bentonite.  The resin is prepared by reacting one mole, a compound of the formula <FORM:0642734/III/1> where R is an amino, alkyl, halogen, substituted amino, alkoxy or hydroxy radical with from 0.8 to 4.5 moles. of an aldehyde, the resin being condensed to the state where it is still water-soluble.  Suitable aldehydes are formaldehyde, p  para-formaldehyde, butyraldehyde, furfural and acetaldehyde.  The coating may be applied e.g. by felt or rubber rolls as a composition comprising from 5 to 70 per cent by weight of the partially reacted resin, from 90 to 25 per cent of water, 5 to 25 per cent of organic solvent and up to 35 per cent of the finely divided solids.  Suitable organic solvents are ethanol, propanol, isopropanol, butanol, ethanolamine, morpholine and acetone. Wetting agents, e.g. sulphonated alcohols, long carbon chain sulphates, e.g. lauryl sulphate, and soaps, e.g. sodium stearate, may also be included in the coating compositions.  In examples, coatings of (1) melamine-formaldehyde resin and lampblack in a mixture of isopropanol are applied to magnetic sheet material, dried at 150 DEG  C., and then cured; (2) iron oxide (FeO) replaces the lampblack of (1).  A graph shows the resistance of a number of laminations coated with composition (1).  The Specification as open to inspection under Sect. 91 comprises also magnetic sheet material coated with the melamine-aldehyde resin without filler.  It is also stated that powdered magnetic material, e.g. iron and nickel, may be coated with the resin and compacted under heat and pressure to form magnetic cores suitable for applications in radio.  Examples (now cancelled) describe coating magnetic material with a composition of melamine-formaldehyde resin, and (1) ethanol, water, methyl cellulose, and the di-octyl ester of sodium sulphosuccinic acid, (2) iso-propyl alcohol, water and wetting agent.  This subject-matter does not appear in the Specification as accepted.