Patent GB-1108303-A (GB)
Title: Porous abrasive and process for producing the same
IPC: B24D11/00
Filed: 1965-03-03
Abstract: A process for producing porous abrasives, comprises spinning into filaments a mixture of a spinnable natural or artificial highly polymerized substance and a sufficient proportion of natural or artificial abrasive agent grains as to obtain a filamentary abrasive containing said abrasive grains uniformly distributed therein, the mixture prior to spinning having added thereto an additive which after spinning creates pores in the filaments formed.  Filaments may be dry-spun, melt-spun, or wet-spun, and the spun filamentary material may be stretched before collection.  Specified materials for dry spinning include cellulose acetate, polyacrylonitrile, polyvinyl chloride, vinyl chloride-vinyl-acetate copolymers and vinyl chloride-acrylo-nitrile copolymers.  A solution prepared by dissolving any individual or mixture of these in a suitable solvent may be used.  For melt spinning, polyolefines, polyamides, polyesters, polyurethanes, polyureas, polyethers and inorganic highly polymerized substances, e.g. glass fibres, may be used. For wet spinning, regenerated cellulose made from viscose or cuprammonium solutions, polyvinyl alcohol, polyacrylonitrile, alginate fibre materials, protein fibre materials and polyvinyl chloride may be used.  Where polyvinyl alcohol is used, an acetalizing agent may be added to the coagulating bath. Specified abrasives include diamond, emery powder, corundum, emery, garnet, pumice, quartz, iron sand, diatomaceous earth, chalk, colcothar, magnetite, limestone, lime, alumina, silicon carbide, boron carbide, metal powders, glass powders, metallic oxide powders, silicate powders and natural or synthetic lustring agents.  These materials may be used singly as a mixture of two or more of them.  The additive may be a substance soluble in a non-solvent for said spinnable natural or artificial highly polymerized substance, this additive being mixed into the spinnable mixture, then treated after filament formation with said solvent to remove the additive thereby to leave pores in place of the additive grains in said filament. Thermally-decomposing blowing agents of the azo-bisisobutyronitrile type or the type comprising a hydrazine derivative of an organic sulphonic acid may be used.  To simplify spinning, the abrasive agent grains may be coated on their surfaces with a binder or lubricant before mixing with the polymer. Grease, wax, stearic acid, or polyethylene glycol may be used for this purpose.  In Example 1, polyethylene terephthalate and poly-e -caprolactam were mixed and melted to a ratio of 2:1.  Five kilograms of emery of 500 meshes per inch, 0.07 parts of dioctyl phthalate plasticizer and 0.01 parts of an azo-bisisobutyronitrile type blowing agent were added to 30 litres of the melt, which was then spun at 280 DEG  C.  When the product was stretched and crimped at 320 DEG  C., there was obtained a crimped filamentary abrasive having low specific gravity and high elasticity.  In Example 2, 16 kilograms of an abrasive agent composed mostly of silicon carbide of 80 meshes per inch and a blowing agent composed of a hydrazine derivative of an organic sulphonic acid having a decomposing point above 100 DEG  C. were mixed and suspended in 20 litres of an aqueous solution of 15% polyvinyl alcohol.  The mixture at about 80 DEG  C., was extruded through a nozzle into a coagulating bath 3 metres long and containing a saturated aqueous solution of sodium sulphate at 40 DEG  to 60 DEG C., and was solidified and separated at a delivering velocity of 10 metres per minute, a product in the form of a string being continuously obtained.  When it was passed through an air bath at 220 DEG  to 230 DEG C under tension so as to be stretched and foamed simultaneously with heat treatment, passed through a formalization bath at 350 DEG  C. consisting of formalin, sulphuric acid and sodium sulphate, washed with water and dried, a porous abrasive in the form of a thick string was continuously obtained.  In Example 3, an aqueous solution of 50% by weight anhydrous sodium sulphate, 15% by weight formalin and 20% by weight hydrochloric acid was used for the coagulating bath in the method of Example 2, to produce a similar porous abrasive.ALSO:Porous abrasives are made by spinning into filaments a mixture of a spinnable natural or artificial highly polymerized substance and a sufficient proportion of natural or artificial abrasive agent grains as to obtain a filamentary abrasive containing said abrasive grains uniformly distributed therein, the mixture prior to spinning having added thereto an additive which after spinning creates pores in the filaments formed.  Filaments so made may be woven or knitted to form an abrasive material in a fabric form or may be cut into staple fibres and set in a form of a felt, or may be cut uniformly to be of a length of less than ten millimetres and electrically planted on a paper, cloth, leather or synthetic resin sheet previously coated with a binder.  Specified highly polymerized substances include glass fibres, regenerated cellulose, cellulose acetate, alginate fibre materials, protein fibre materials, polyvinyl alcohol, polyvinyl chloride, vinyl chloride-vinyl acetate co-polymers, polyacrylonitrile, vinyl chloride-acrylonitrile co-polyolefins, polyamides, polyesters, polyurethanes, polyureas, and polyethers. In Examples (1) a felty elastic tool is made by cutting the monofilaments of polyvinyl acetal fibres containing natural or synthetic abrasive grains into a fixed length less than seventy millimetres according to the use so as to be staples, mixing into said staples the staples of polyvinyl alcohol fibres comparatively low in the degrees of polymerization and saponification as a binder, dispersing them uniformly, wetting the mixture with water and heat-setting the mixture.  (2) A round elastic tool is made by cutting monofilaments or tows of polyvinyl acetal fibres containing natural or synthetic abrasive grains into a fixed length less than 70 millimetres according to the use. Staples so obtained are uniformly dispersed in a liquid or gas phase so as to have no directivity. The liquid or gas phase containing the staples is uniformly mixed with a natural or synthetic binder by impregnation, spraying or any other method.  The mixture is thereafter moulded into a round sheet less than 15 millimetres thick by heating and compressing it.  Such sheets may be laminated if desired, the laminations being treated with the above-mentioned binder in the same manner.  (3) A knitted elastic tool is made by bundling polyvinyl acetal monofilaments containing natural or synthetic abrasive grains and knitting the bundles from the centre towards the outer periphery.  The product obtained is in the form of a disc and can be impregnated with a natural or synthetic binder. (4) An elastic tool is obtained by winding in several layers the monofilaments of polyvinyl acetal fibres containing natural or synthetic abrasive grains filaments, tows are made by bundling such monofilaments or threads made by twisting them on a proper columnar core so as to have the threads at angles to the axis of the core and with the plane vertical to the axis and by varying the angles for each layer.  Such elastic tool can be used not only as a bar-shaped tool but also as a disc-shaped tool for mechanical polishing when cut to the form of a disc.  Such a tool may be impregnated with a natural or synthetic binder as required. (5) A felty tool is made by cutting the monofilaments of polyvinyl acetal fibres containing natural or synthetic abrasive grains into a fixed length less than 70 millimetres according to the use so as to be staples, mixing into said staples the staples of polyvinyl alcohol fibres comparatively low in the degrees of polymerization and saponification and containing the above mentioned abrasive grains in the filaments as a binder, uniformly dispersing them, wetting the mixture with water and then heat-setting it. (6) An endless belt tool may be obtained by cutting the monofilaments or tows of polyvinyl acetal fibres containing natural or synthetic abrasive grains in the filaments into a fixed length less than 70 millimetres according to the use. The staples so obtained are uniformly dispersed in a liquid or gas so as to eliminate orientation, a natural synthetic binder is uniformly mixed into the dispersion by impregnation, spraying or any other method and the mixture is moulded into a continuous sheet less than 15 millimetres thick by heating and compressing it, cutting the sheet to be of a width and length corresponding to the use and bonding or stitching the cut pieces.  It is an effective method to reinforce the belt with a cloth or net to give strength.  (7) A sheet tool may be made as in (6) but omitting the final bonding or stitching steps.  In further Examples (1) A crimped filamentary abrasive is made by melt spinning a mixture of polyethylene terephthalate and poly-e -caprolactam to which emery is added together with a blowing agent. (2) A porous abrasive in the form of a thick string is made by wet spinning polyvinyl alcohol containing silicon carbide as abrasive and a blowing agent.  In Example 4, monofilaments of a filamentary porous abrasive of polyacrylonitrile containing an abrasive agent composed mostly of ferric oxide are twisted together and knitted up from the centre toward the outer periphery so as to be in the form of a disc. When such discs are overlapped to be of a thickness of 50 millimetres, they are stitched together with filaments of the same filamentary abrasive and knitted up to obtain a long filament tool in the form of a disc.  The tools so obtained are so soft and elastic that they show excellent properties in finish-polishing wood and other materials.  In Example 5, a filamentary porous abrasive of polyvinyl acetal containing an abrasive agent composed mostly of "Alundum" (Registered Trade Mark) of 60 meshes per