Patent GB-1087815-A (GB)
Title: Improvements in or relating to heating using alternating magnetic fields
Inventor: WHITE JEROME RUSSELL
IPC: B29C65/14
Filed: 1964-08-07
Abstract: A method of heating a material (such as a heat-activatable adhesive) comprises associating the material with finely-divided multi-domain ferrimagnetic particles and subjecting these particles to an alternating magnetic field having a frequency greater than 10 Mc/s. to generate heat within them whereby the material is heated.  The material may be an adhesive coated on a surface of paper, metal, plastic, leather, glass or fabric and may be used to stick two such surfaces together.  Suitable adhesives are polymer-modified petroleum wax compositions, e.g. compositions containing polymers and copolymers of ethylene, propylene &c. and especially ethylene polymers containing one or more copolymerized monomers, e.g. ethylene/vinyl acetate, ethylene/ethyl acrylate, ethylene/1,4-hexadiene, ethylene/methyl methacrylate.  A specified adhesive is a polymer-modified petroleum wax comprising 50-99.9% petroleum wax, 50-0.1% of an ethylene/vinyl acetate copolymer having a vinyl acetate content of 15-35% and a melt index of 0.1 to 500, and 0-40% of a resin, esterified resin, rosin, or esterified rosin.  The ferrimagnetic particles may be simple or mixed oxides of metals which include the alkali metals, the alkaline earth metals, the rare earth metals and Cu, Zn, Va, Ti, Al, Cr, Mn, Fe, Co and Ni.  It may have spinel, garnet, perovskite or pyrrhotite structure, and may have resistivity above 10-2 ohm cm.  The particles may be up to 5 microns in size.  The applied field may have a frequency between 10 and 2500 Mc/s. and a strength of 50-500 gauss.  The material may be used in the manufacture of milk cartons, food containers and similar boxes. Paper or cardboard carton blanks having portions to be sealed together are coated with the adhesive materials, at least one of the adhering surfaces being also provided with an undercoating which comprises the magnetic particles in a binder such as resin, glue or polyvinyl acetate in a solvent such as methanol, isopropanol or ethanol.  The blanks are then folded to bring together the associating surfaces and subjected to a magnetic field.  The material may also be a printing ink, the magnetic particles being dispersed therein so that on application of the magnetic field the heat produced rapidly evaporates the solvent of the ink. Alternatively with inks which contain an oxidizable vehicle such as linseed oil this may be rapidly heated to the proper oxidizing temperature.ALSO:A method of heating a material (such as a heat activatable adhesive) comprises associating the material with finely divided multidomain ferrimagnetic particles and subjecting these particles to an alternating magnetic field having a frequency greater than 10 Mc/s. to generate heat within them whereby the material is heated.  The material may be an adhesive coated on a surface of paper, metal, plastic, leather, glass, or fabric and may be used to stick two such surfaces together.  Suitable adhesives are polymer-modified petroleum wax compositions, e.g. composition containing polymers and copolymers of ethylene, propylene, and especially ethylene polymers containing one or more copolymerised monomers, e.g. ethylene/vinyl acetate, ethylene/ethyl acrylate, ethylene/1, 4-hexadiene, ethylene/methyl methacrylate.  A specified adhesive is a polymer-modified petroleum wax comprising 50-99.9% petroleum wax, 50-0.1% of an ethylene/vinyl acetate copolymer having a vinyl acetate content of 15-35% and a melt index of 0.1 to 500, and 0-40% of a resin, esterified resin, rosin, or esterified rosin.  The ferrimagnetic material may be simple or mixed oxides of metals which include the alkali metals, the alkaline earth metals, the rare earth metals and Cu, Zn, Va, Ti, Al, Cr, Mn, Fe, Co and Ni. It may have spinel, garnet, perovskite or pyrrhotite structure, and may have resistivity above 10-2 ohm cm.  The particles may be up to 5 microns in size.  The applied field may have a frequency between 10 and 2500 Mc/s and a strength of 50-500 gauss. The material may be used in the manufacture of milk carton, food containers and similar boxes.  Paper or cardboard cartons blanks having portions to be sealed together are coated with the adhesive material, at least one of the adhering surfaces being also provided with an undercoating which comprises the magnetic p  particles in a binder such as resin, glue or polyvinyl acetate in a solvent such as methanol, isopropanol or ethanol.  The blanks are then folded to bring together the associating surfaces and subjected to a magnetic field.  The material may also be a printing ink, the magnetic particles being dispersed therein so that on application of the magnetic field the heat produced rapidly evaporates the solvent of the ink. Alternatively with inks which contain an oxidisable vehicle this may be rapidly heated to the proper oxidising temperature.