Gas separation – Two or more separators – Plies or layers of different characteristics or orientation
Reexamination Certificate
1999-05-27
2002-01-08
Smith, Duane (Department: 1724)
Gas separation
Two or more separators
Plies or layers of different characteristics or orientation
C055S487000, C055S497000, C055S521000, C055S524000
Reexamination Certificate
active
06336948
ABSTRACT:
TECHNICAL FIELD
This invention relates to a filter medium applied for cleaning air in e.g., a clean room, and an air filter unit using the same. More specifically, this invention relates to a filter medium applied for cleaning air in manufacturing electronic members such as semiconductors and liquid crystals, and an air filter unit using the same.
BACKGROUND ART
As filters applied for cleaning air in e.g., a clean room, the inventors of this invention have already disclosed a polytetrafluoroethylene (referred to as PTFE hereinafter) porous film (for example, Japanese Patent Application Tokkai Hei 5-202217). In addition, the lamination of a thermoplastic material such as a span bond nonwoven cloth made of sheath-core structured long fibers onto both the surfaces of the PTFE porous film was also proposed so as to protect the porous film from scratches and pin holes (Japanese Patent Application Tokkai Hei 6-218899).
However, the inventors of this invention found in accordance with the Standard of Test Method for Combustion of Air Filter Media (JACA No. 11-1977) that the prior art mentioned above has unsatisfactory flame-resistant properties.
A flame-resistant filter medium, and an air filter unit using the same are sometimes fixed to a ceiling as equipment. In this case, particularly, flame-resistant properties are required so as to prevent fire.
DISCLOSURE OF INVENTION
This invention aims to solve the above-mentioned conventional problems by providing a flame-resistant filter medium and an air filter unit using the same.
In order to achieve the above purposes, the flame-resistant filter medium of this invention is a filter medium comprising a gas permeable supporting material on at least one surface of a PTFE porous film and which has 150 mm or less maximum carbonized length based on the Standard of Test Method for Combustion of Air Filter Media (JACA No. 11-1977). The flame-resistant properties in this invention are measured by the Standard of Test Method for Combustion of Air Filter Media (JACA No. 11-1977) prepared by the Filter Standard Committee of JAPAN AIR CLEANING ASSOCIATION (JACA).
It is preferable that the air permeable supporting material of the flame-resistant filter medium is a flame-resistant air permeable supporting material.
The PTFE porous film can be one or more layers in the flame-resistant filter medium of this invention. As the flame-resistant filter medium, an air permeable supporting material is applied on one surface of the PTFE porous film, on both surfaces of the porous film, or is alternately or randomly applied altogether with the porous film. Particularly, the filter medium in which the supporting material is applied on both surfaces of the porous film is preferable.
There is no particular limitation on the PTFE porous film, and a conventional PTFE porous film may be applied to the flame-resistant filter medium. A PTFE porous film that can provide the efficient scavenging of floating fine particles and has properties such as pressure loss (the same or better properties than an HEPA filter and ULPA filter) required for a filter unit applied in a clean room for manufacturing semiconductors, liquid crystals, etc. and in manufacturing devices is especially preferable. For instance, pressure loss is preferably 10-100 mmH
2
O when air is permeated at the flow velocity of 5.3 cm/second, and the scavenging efficiency of 0.10-0.12 &mgr;m dioctylphthalate (DOP) is preferably 99.0% or more. The PTFE porous films with such properties are described in detail in Japanese Patent Application Tokkai Hei 5-202217 and WO 94/16802, the disclosure of which are incorporated herein by reference.
The above-noted PTFE porous films applied in this invention can easily be prepared by a conventional method. The method includes, for example, the steps of extruding a paste of a PTFE fine powder and an extrusion assistant, providing a tape by pressing and spreading the extruded paste, and stretching out the non-baked or semi-baked paste in two axial directions. This method is specifically explained in Tokkai Hei 5-202217, WO 94/16802, etc.
In the flame-resistant filter medium of the invention, the air permeable supporting material is preferably a flame-resistant air permeable supporting material, or more preferably an organic-particularly, resinous-flame-resistant air permeable supporting material.
The air permeable supporting material of the flame-resistant filter medium is preferably a nonwoven fabric or woven cloth, or more preferably a resinous nonwoven fabric. Air permeable supporting materials made of glass fibers such as glass fiber nonwoven fabric, glass fiber paper and a glass fiber air filter medium are not preferable since they generate boron (B).
It is also preferable that the air permeable supporting material of the flame-resistant filter medium is made of at least one material selected from the group consisting of polyester and polyamide. It is further preferable that the air permeable supporting material is made of polyester fibers, and contains no polyolefin. The polyester mentioned above indicates polyethylene terephthalate (PEI), polybutylene terephthalate (PBI), and the like.
A flame retardant in the flame-resistant filter medium is preferably copolymerized. It is preferable that the flame retardant is copolymerized particularly to polyester fibers. In adding flame-resistant properties by e.g., organic phosphorous compounds, phosphorus (P) would not be detected from a filter medium if the flame retardant is copolymerized.
The polyester fiber material of the flame-resistant filter medium may be filaments nonwoven fabric.
The air filter unit of this invention uses a filter medium having an air permeable supporting material at least on one surface of the PTFE porous film. The filter medium is bent in wave forms and kept in the supporting body (frame), and the periphery is sealed. The filter medium has 150 mm or less maximum carbonized length according to the Standard of Test Method for Combustion of Air Filter Method (JACA No. 11-1977).
Conventional methods of kneading, copolymerizing or coating compounds having flame-resistant properties onto the fiber surface may be used as a means to add flame-resistant properties. For example, polyester fibers become flame-resistant after a flame retardant such as an organic phosphorous compound is copolymerized or kneaded to the fiber, or the fiber can be given flame-resistant properties by polymer blend or the like. More specifically, the following methods can be applied.
(1) Use of Flame-Resistant Materials
Flame-resistant fibers having flame-resistant properties in themselves include organic or inorganic fibers such as aromatic polyamide fibers, modified acrylic fibers, flame-resistant polynosic, flame-resistant vinylon, flame-resistant polyester, oxidation acrylic fibers (flame proof fibers), rayon carbonized fibers (flame proof fibers), aramid fibers, polyarylate fibers, phenol fibers, polybutylene isocyanate fibers (PBI fibers), polyvinylidene chloride fibers, asbestos, carbon fibers, metalfibers, and silica fibers, PTFE fibers, tetrafluoroethyleneperfluoroalkylvinylether copolymer (PFA) fibers, and polyvinylidene fluoride (PVdF) fibers.
(2) Flame-resistance Treatments
Flame-proof and flame-resistant properties are added by treatments such as a method of applying a flame retardant by a dipping or a coating process after preparing a thread, woven cloth, or nonwoven fabric from fibers.
In case of synthetic fibers, the treatments include a method of introducing a flame retardant by chemical bonding such as covalent bonding in preparing polymer, and a method where the fibers are kneaded in polymer or blended with polymer in melting, extruding and spinning processes.
The flame retardant includes inorganic flame retardants such as aluminum hydroxide, decabro-based bromine flame retardants such as decabromodiphenyloxide, nondeca-based bromine tetrabromobisphenol, chlorine-based flame retardants, and phosphorous flame retardants.
By mixing (spinning) flame-resistant and non-flame resistant fibers together, a thread, woven clot
Asano Jun
Chaen Shinichi
Hara Satoshi
Hirano Seiichi
Inoue Osamu
Daikin Industries Ltd.
Greene Jason M.
Merchant & Gould P.C.
Smith Duane
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