Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1996-02-21
1998-11-10
Cooney, Jr., John M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
264 451, 2642358, 2642884, 2642902, 4283155, 428422, C08F 1402
Patent
active
058345280
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a production process of a polytetrafluoroethylene (hereinafter, referred to as also "PTFE") porous composite film (or membrane) and a PTFE porous composite film produced by such process. Further, the present invention relates to a filter, in particular a high performance air filter for the removal of fine particles in a fluid (for example air) in which the PTFE porous composite film is used.
The porous film according to the present invention can be used as a filter medium for an air filter, in particular a filter medium for an ULPA (ultra low penetration air) or HEPA (high efficiency particulate air) filter which cleans an inside atmosphere of a cleanroom of semiconductor industries or a production equipment for precise electronic devices, chemical agents or biochemical products, or as a filter medium for a liquid filter.
Recently, completely cleaned air or highly cleaned liquid agents have been required in production processes of semiconductor industries, precision industries, biotechnology industries and so on. Particularly, a highly cleaned atmosphere inside the production equipments achieved by, for example by the removal of fine particles has been demanded with the recent highly integration in the semiconductor industries. With respect to the cleaned air, it has been obtained by recirculating and filtering air through an air filter. Also, with respect to the liquid agents used particularly in the semiconductor industries, highly cleaning thereof has been required and it is achieved by recirculating and filtering the agents through a filter.
Various filters have been hitherto proposed and practically used for the above purposes. Particularly, with respect to the air filter, a filter medium which is now popularly used is produced by paper-making with addition of a binder to glass fibers. However, such a filter medium has some defects. For example, dusts are formed due to the presence of micro-fibers depositing on the filter medium, dust self-formation when the medium is processed or folded, or binder and glass degradation when the medium contacts with certain agents such as hydrofluoric acid.
In order to solve the above problems, the use of an electret filter medium made of a synthesized fiber is proposed (Japanese Patent Kokai Publication No. 53365/79), but it is stated that its static electric force is shielded by fine particles collected on the medium so that its effect disappears and collection performance is reduced (see preprint of "The 11th Symposium of Air Cleaning and Contamination Control" (Apr. 21 to 22, 1992), pp. 153-156). Accordingly, it is proposed to use a stretched polytetrafluoroethylene porous film so as to provide means to overcome those disadvantages and to form a cleaned atmosphere (Japanese Patent Kokoku Publication No. 10364/1992 and Japanese Patent Kokai Publication No. 284614/1990).
In the above proposals, a stretched PTFE film is used which has a pore diameter not less than 1 .mu.m so as to prevent increase of a pressure loss. A theory in which fine particles having a diameter less than the pore diameter of the film can be trapped is as follows:
Particles contained in a fluid are said to be removed according to the following main mechanisms ("Cleanroom Handbook" edited by Japanese Air Cleaning Association published by Ohm Publishing Co. on Jan. 10, 1990): stopped and removed by micro-fibers as if they were sieve-separated; tortuous passage between micro-fibers, they cannot change their going directions so rapidly as a gas does so that they collide with and deposit on the micro-fibers; spirally move in a gas under controls of an intermolecular force and an electrostatic force so that their diameter apparently becomes larger and particles collide the micro-fibers as in the case of the inertia collision; and collection of electret fibers.
However, it is seen from data shown in Japanese Patent Kokai Publication No. 284614/1990 that such a PTFE film cannot completely collect particles of which diameter is not more than 1 .mu.m.
Generally, in order t
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Preprint of The 11th Symposium of Air Cleaning and Contamination Control, Apr. 21-22, 1992, pp. 153-156.
"Cleanroom Handbook" edited by Japanese Air Cleaning Association, published by Ohm Publishing Co. on Jan. 10, 1990.
Asano Jun
Chaen Shinichi
Inoue Osamu
Kusumi Toshio
Tanaka Osamu
Cooney Jr. John M.
Daikin Industries Ltd.
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