Patent GB-1188968-A (GB)
Title: Process for manufacture of Fibrillated Films
IPC: D01D5/42
Filed: 1967-11-30
Abstract: 1,188,968. Fibrillated films. MITSUI PETROCHEMICAL INDUSTRIES Ltd. 30 Nov., 1967 [1 Dec., 1966; 21 June, 1967], No. 54525/67. Heading B5B. [Also in Division D1] Fibrillated films are made from a film-forming synthetic thermoplastic resin, by longitudinally stretching at a stretch ratio of 2:1 to 12:1 a film of the resin having uniformly dispersed therein closed voids of average dimension in the direction of the thickness of the film of 1/40 to 30/40 of the thickness of the film and having a void ratio of 0À1 to 0À6. The void ratio is defined as the quotient obtained by dividing the volume of voids in the film by the apparent volume of the film. Thermoplastic resins exemplified include polyethylene, polypropylene, polystyrene and polyvinyl chloride. The film containing the voids is suitably made by incorporating into the resin a blowing agent in proportion sufficient to provide the required void ratio and void dimensions in the subsequently formed film, and extruding the mixture in the form of a film under conditions which activate the blowing agent. The blowing agent may be gaseous, e.g. nitrogen and carbon dioxide, liquid, e.g. water, low boiling hydrocarbons, e.g. butane and heptane, and low boiling halogenated hydrocarbons, or solid, especially powdery solids as, for example, sodium bicarbonate, a mixture of sodium bicarbonate and an organic acid, ammonium carbonate, diethylazodiformate, dinitrosopentamethylene tetramine, azodicarboamide, azoisobutyronitrile, derivatives of hydrazide as e.g. benzene sulphonyl hydrazide, and p,p<SP>1</SP>-oxybis-(benzene-sulphonyl hydrazide). Preferably, the blowing agent on being activated produces 20 to 300 mls. of gas per gram of blowing agent at the film-forming temperature. The blowing agent may also be a white, finelydivided inorganic solid containing water of crystallization, and to assist the splitting of the foamed film a finely divided solid nucleusforming agent may be used with a gas, liquid or solid blowing agent. Generally usable as the solid nucleus-forming agents are preferably white powdery inorganic solids which are not melted at the shaping temperatures of the resin, e.g. calcium sulphate, borax, barium sulphate, barium carbonate, aluminium oxide, silica, zinc oxide, and magnesium carbonate. Solid blowing agents of the type containing water of crystallization or which are wetted by water or other liquid swelling agent and so may be used to evolve a small proportion of gas may be used and these include aluminium oxide, aluminium sulphate, calcium chloride, magnesium chloride, barium chloride, sodium carbonate, sodium sulphate, borax, iron alum and potassium alum either in a form containing water of crystallization or in a form wetted by water or other liquid swelling agent. Such solids act also as nucleus-forming agents and assist splitting. The film-extrusion step may be effected by a tubular film method or by a T-die method. The film extrusion temperature is not restricted, and can vary from the upper limit of the melting range of the resin to its degradation temperature, taking into consideration the blowing temperature of the incorporated blowing agent. Desirably, the film before stretching is 0À05 to 0À3 millimeters thick, and the closed voids preferably have an average dimension in the direction of thickness of 1/25 th to 10/25 ths of the thickness of the film, the preferred void ratio being 0À15 to 0À35. Stretching may be effected at any temperature from room temperature to a point 10 C. lower than the melting point of the resin, the preferred stretch ratio being from 3:1 to 9:1. The film stretching can generally be carried out between two pairs of rolls having a different rotating speed at a stretching rate of 50 to 550 meters per minute. After stretching, the resulting fibrillated film may be developed in a direction transverse to the direction of stretch to give a network fibrillated structure. Such development necessitates little mechanical force, and may be effected by tentering, a rubbing belt, or by air ejection. The split fibre of the invention has a deformed cross-section in its single fibres owing to its being split three-dimensionally. Its cross-section is similar to that of natural fibres, and can give a web having suitable smoothness and soft touch. The denier of the single fibres of the split fibre can be predetermined depending on the proportion of the blowing agent, the degree of its dispersion, and the stretch ratio. The splitting of the fibrillated film of the invention occurs threedimensionally between the thin tubular voids. Having a complicated network structure, the yarn-like materials of the invention are bulky and pliable and have less fluff, showing properties like those of spun yarns. They are useful for clothing, as yarns for industrial purposes, non-woven web, ropes, and cords. The yarn-like material may be divided in optional widths, and made into continuous filaments of desired denier. It is also possible to draft and cut the yarn-like material in appropriate lengths, make it into continuous slivers, and spin them to make spun yarns. The obtained woven fabriclike materials having a large width can be used directly, or after having been laminated, in such applications as mats, carpets, filters, various fabrics, non-woven fabrics and fibrous stuffings.