Abstract: A method of laminating at least two gas permeable sheet materials includes: (1) providing at least a first gas permeable sheet material, wherein at least a portion of at least a surface region of the first sheet material is thermoplastic material; (2) providing at least a second gas permeable sheet material of polytetrafluoroethylene; (3) superposing the sheet materials; and (4) contacting the sheet materials with a heating means to heat the thermoplastic material to a temperature from 140° to 230° C., so as to melt the thermoplastic material and laminate the sheet materials to one another, without the application of direct pressure in the thickness direction of the sheet materials during the contacting step so as to form a gas permeable laminate.

Abstract: A filter medium with excellent flame-resistant properties and an air filter unit using the same are provided which have a flame-resistant air permeable supporting material on at least one surface of a polytetrafluoroethylene (PTFE) porous film and which can be used as a ceiling device, etc.

Abstract: The present invention provides a novel group of particles for air filter inspection which solves problems caused by volatilization and scattering of those particles at the downstream side of the air filter in use, enables an air filter inspection with superior stability and reproducibility, and may be produced by using a comparative inexpensive manufacturing device, and manufacturing methods as well as inspection methods of such a group of particles. The group of particles for air filter inspection consists of a plurality of aggregate particles having a particle size of not less than 0.1 &mgr;m, each aggregate particle being constituted by solid primary particles having an average particle size of less than 55 nm.

Abstract: A filter medium which has an average pore diameter of more than 0.5 &mgr;m, a pressure loss of 2-50 mmH2O determined when air is permeated therethrough at a velocity of flow of 5.3 cm/sec, and a PF value of 18-12, which is calculated in accordance with the following equation on the basis of this pressure loss and a collection efficiency using DOP of a grain size of 0.10-0.12 &mgr;m.

Abstract: A fibrous material of fluorine-containing resins such as polytetrafluoroethylene which has a high deodorizing antibacterial activity is obtained. A monofilament, staple fiber, split yarn or finished yarn thereof comprising a fluorine-containing resin such as polytetrafluoroethylene containing a photodegrading catalyst such as an anatase-type titanium dioxide in an amount of from 5 to 50% by weight, and a deodorizing antibacterial woven fabric, knitted fabric, and non-woven fabric which are produced by using the monofilament, staple fiber, split yarn or finished yarn thereof.

Abstract: An air filter unit in which the generation of organic substances is restrained by controlling at least the amount of organic substances detected from a square test piece of 5.times.5 cm (25 cm.sup.2) of a filter medium so as to be 100 ng or less in the total amount of organic substances detected from the whole air filter unit at a temperature of 40.degree. C. before using. The air filter unit is assembled by housing a filter medium that has been bent in a waveform in a frame composed of 4 outer frame members and sealing the gap between the frame and the filter medium using a sealing compound. Organic substances adhering to the air filter unit are removed by blowing a cleaned air heated at 80.degree. C. against the air filter unit at a velocity of 50 ml/min for 60 minutes. Then, an air suction port and an air exhaust port of the air filter unit are sealed with a film (for example, a PET film) which keeps the unit from contacting with organic substances and from which organic substances are not generated.

Abstract: An object is to provide a polytetrafluoroethylene (PTFE) porous composite film which has substantially no defect portion.There is provided the PTFE porous composite film by stretching a composite along its width direction which composite is composed of at least two overlapped films longitudinally stretched at a temperature not higher than a melting point of a sintered PTFE material, each film being obtained by paste-extruding and semi-sintering thereafter a PTFE produced by emulsion polymerization.

Abstract: A porous polytetrafluoroethylene film which is excellent as an air filter used in clean rooms in a semiconductor industry, which is suitable for the collection of microparticles floating in a gas such as air and exhibits a low pressure drop is provided. The film has an average pore size of from 0.2 to 0.4 .mu.m and exhibits a pressure drop of from 20 to 50 mmH.sub.2 O when air is passed through it at a flow rate of 5.3 cm/sec. The film is prepared by stretching biaxially unsintered polytetrafluoroethylene at specific temperatures.

Abstract: Cotton-like polytetrafluoroethylene materials are obtained by opening a uniaxially stretched article of molded polytetrafluoroethylene by a mechanical force. Those cotton-like materials comprise the 5 to 150 mm long fibers having branches and crimps and non-uniform section. The cotton-like materials are excellent in intermingling property and can be easily made into non-woven fabrics.

Abstract: A filter apparatus that is compact and that provides a large filtration area includes filter elements each constructed in cylindrical form by spirally winding a filter medium. Such medium includes a porous membrane of a polytetrafluoroethylene having a pore diameter of 0.1 to 5 .mu.m and low pressure loss and one or a pair of sheets composed of fibers made of a thermally melting synthetic resin. One end of the cylindrical filter element is connected to a respective through hole in a rigid support plate, and the opposite end is blocked.

Abstract: A polytetrafluoroethylene porous film, which is prepared by stretching a semisintered polytetrafluoroethylene material and heating the stretched material at a temperature higher than the melting point of sintered polytetrafluoroethylene, has an area ratio of fibrils to nodes of from 99:1 to 75:25, an average fibril diameter of from 0.05 to 0.2 .mu.m, a largest node area of not larger than 2 .mu.m.sup.2 and an average pore size of from 0.2 to 0.5 .mu.m and achieves low pressure loss.