Porous polytetrafluoroethylene film and process for preparation thereof

• US 5,772,884 A
• Filed: 12/22/1994
• Issued: 06/30/1998
• Est. Priority Date: 01/25/1993
• Status: Expired due to Term

• Current Assignee: Daikin Industries Ltd
• Original Assignee: Daikin Industries Ltd
• Inventors: Uraoka, Nobuki, Inoue, Osamu, Tanaka, Osamu, Yamamoto, Katsutoshi, Asano, Jun, Chaen, Shinichi, Kusumi, Toshio, Tamaru, Shinji
• Primary Examiner(s): FORTUNA, ANA M
• Application Number:
  US08/302,913
• Time in Patent Office: 1,286 Days
• Field of Search: 210/500.36, 210/500.27, 210/490, 428/315.5, 264/210.7, 264/288.4, 264/288.8, 264/290.2
• US Class Current: 210/500.36
• CPC Class Codes: B01D 2325/02 Details relating to pores or porosity of the membranes
• CPC Class Codes: B01D 2325/02834 more than 0.1 and up to 1 µm
• CPC Class Codes: B01D 39/1692 Other shaped material, e.g. perforated or porous sheets
• CPC Class Codes: B01D 67/0027 by stretching
• CPC Class Codes: B01D 69/02 characterised by their properties
• CPC Class Codes: B01D 69/10 Supported membranes; Membrane supports
• CPC Class Codes: B01D 69/1071 Woven, non-woven or net mesh
• CPC Class Codes: B01D 71/36 Polytetrafluoroethene
• CPC Class Codes: B29C 55/005 characterised by the choice of materials
• CPC Class Codes: B29C 55/143 firstly parallel to the direction of feed and then transversely thereto
• CPC Class Codes: B29K 2027/18 PTFE, i.e. polytetrafluorethene , e.g. ePTFE, i.e. expanded polytetrafluorethene
• CPC Class Codes: B29K 2105/04 cellular or porous
• CPC Class Codes: C08J 2327/18 Homopolymers or copolymers of tetrafluoroethylene
• CPC Class Codes: C08J 5/18 Manufacture of films or sheets
• CPC Class Codes: Y10T 428/249978 Voids specified as micro

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 μm and exhibits a pressure drop of from 20 to 50 mmH₂ 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.

Claims

1. A porous polytetrafluoroethylene film which is prepared by stretching biaxially an unsintered PTFE has an average pore size of from 0.2 to 0.4 μ

m and exhibits a pressure drop of from 20 to 50 mmH₂ O when air is passed through the film at a flow rate of 5.3 cm/sec.

2. A porous polytetrafluoroethylene film as claimed in claim 1 in which a porous reinforcing material is laminated on at least one side of the porous polytetrafluoroethylene film.

3. A filter comprising the porous polyterafluoroethylene film as claimed in claim 1 or 2.

4. A process for preparing a porous polytetrafluoroethylene film comprising the steps of stretching lengthwise an unsintered polytetrafluoroethylene tape, which is obtained by paste extruding a polytetrafluoroethylene fine powder and then rolling it, at a temperature of from 250°

to 320°

C. and subsequently stretching crosswise said lengthwise stretched unsintered polytetrafluoroethylene at a temperature of from 100°

to 200°

C. to produce a porous polytetrafluoroethylene film having an average pore size of from 0.2 to 0.4 μ

m.

5. A process as claimed in claim 4, in which the stretching is carried out in a stretched area ratio of at least 100.

6. A process as claimed in claim 4, in which the stretched film is not heat set at a temperature above the melting point of polytetrafluoroethylene.

7. A process as claimed in claim 4, in which the stretched film is laminated on at least one side thereof with a porous reinforcing material.

8. A process as claimed in claim 7, in which the porous reinforcing material is laminated to the stretched film before the crosswise stretched film is wound up.

9. A porous polytetrafuloroethylene film which is prepared by stretching an unsintered polytetrafuloroethylene tape lengthwise at a temperature between 250°

to 350°

C.; and

stretching the tape crosswise at a temperature between 100°

to 200°

C., such that the total stretched area ratio is at least 100, said film having an average pore size of from 0.2 to 0.4 μ

m.