US6030428A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Porous polytetrafluoroethylene membrane, process for producing the same, sheet-form polytetrafluoroethylene molding, and air filter medium
Assignee: Nitto Denko Corp
•
Filing: 1998-08-28
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Granted: 2000-02-29
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Expires: 2018-08-28
Abstract
Abstract A fine powder of polytetrafluoroethylene is mixed with a liquid lubricant, and the mixture is molded into an unsintered sheet by at least one of an extrusion method and a rolling method. The liquid lubricant is removed from the sheet by at least one of a heating method and an extrusion method. This sheet-form molding is stretched in the machine direction to produce a sheet-form polytetrafluoroethylene molding which, upon analysis with a differential scanning calorimeter, gives a crystal fusion curve having an endothermic peak in the temperature range of 345±5° C. and which has a degree of crystallization of from 0.1 to 0.85 and a specific gravity of 1.4 or lower. The molding is then stretched in the transverse direction to produce a porous polytetrafluoroethylene (PTFE) membrane. The process is effective in producing, with good reproducibility, a useful porous PTFE membrane which has a high collection efficiency and a low pressure loss and is reduced in the leakage of coarse particles.
Inventors
- 👤 Toshiaki Ishino
- 👤 Norikane Nabata
- 👤 Takuya Maeoka
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 19:14
CPC Classifications
B; B32; B32B; B32B27/00; B32B27/06; B32B27/08; C; C08; C08J; C08J5/00; C08J5/20; C08J5/22; C08J5/2206; C08J5/2218; C08J5/2231; C08J5/2237; B01; B01D; B01D39/00; B01D39/08; B01D39/083; B01D39/14; B01D39/16; B01D39/1692; B01D67/00; B01D67/0002; B01D67/0023; B01D67/0025; B01D67/0027; B01D71/00; B01D71/06; B01D71/30; B01D71/32; B01D71/36; B29; B29C; B29C55/00; B29C55/005; B29C55/02; B29C55/10; B29C55/12; B29C55/14; B29D; B29D7/00; B29D7/01; B32B27/12; B32B27/32; B32B27/322; B32B38/00; B32B38/0012; B32B38/16; B32B38/164; B32B5/00; B32B5/02; B32B5/022; B32B7/00; B32B7/04; B32B7/12; C08J7/00; C08J7/08; C08J7/12; C08J7/16; C08J7/18; C08J9/00; C08J9/28; B01D2239/00; B01D2239/02; B01D2239/0216; B01D2239/0233; B01D2239/04; B01D2239/0464; B01D2239/06; B01D2239/0604; B01D2239/0627; B01D2239/065; B01D2239/0654; B01D2239/0668; B01D2239/0681; B01D2239/069; B01D2239/0695; B01D2239/12; B01D2239/1241; B01D2325/00; B01D2325/24; B01D2325/40; B29K; B29K2027/00; B29K2027/12; B29K2027/18; B29K2105/00; B29K2105/04; B32B2038/0028; B32B2262/00; B32B2262/02; B32B2305/00; B32B2305/02; B32B2305/026; B32B2307/00; B32B2307/70; B32B2307/724; B32B2309/00; B32B2309/02; B32B2327/00; B32B2327/12; B32B2327/18; C08J2327/00; C08J2327/02; C08J2327/12; C08J2327/18; C08L; C08L27/00; C08L27/02; C08L27/12; C08L27/18
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
79 words
A sheet-form polytetrafluoroethylene molding obtained by stretching an unsintered polytetrafluorothethylene sheet-form molding in the machine direction at a temperature lower than the melting point of sintered polytetrafluoroethylene, wherein analysis of said sheet-form polytetrafluoroethylene molding with a differential scanning calorimeter gives a crystal fusion curve having an endothermic peak in the temperature range of 345±5° C., and wherein said sheet-form polytetrafluoroethylene molding has a degree of crystallization of from 0.1 to 0.85 and a specific gravity of 1.4 or lower.
Claim 2
Dependent Claim
79 words
A sheet-form polytetrafluoroethylene molding obtained by stretching an unsintered polytetrafluorothethylene sheet-form molding in the machine direction at a temperature lower than the melting point of sintered polytetrafluoroethylene, wherein analysis of said sheet-form polytetrafluoroethylene molding with a differential scanning calorimeter gives a crystal fusion curve having an endothermic peak in the temperature range of 345±5° C., and wherein said sheet-form polytetrafluoroethylene molding has a degree of crystallization of from 0.1 to 0.85 and a specific gravity of 1.4 or lower.
Claim 3
Dependent Claim
58 words
A porous polytetrafluoroethylene membrane produced by stretching an unsintered polytetrafluoroethylene sheet-form molding in the machine direction at a temperature lower than the melting point of sintered polytetrafluoroethylene, and then stretching the polytetrafluoroethylene sheet-form molding in the transverse direction, said membrane having a pressure loss lower than 20 mmH 2 O and a PF value of 22 or higher.
Claim 4
Dependent Claim
58 words
A porous polytetrafluoroethylene membrane produced by stretching an unsintered polytetrafluoroethylene sheet-form molding in the machine direction at a temperature lower than the melting point of sintered polytetrafluoroethylene, and then stretching the polytetrafluoroethylene sheet-form molding in the transverse direction, said membrane having a pressure loss lower than 20 mmH 2 O and a PF value of 22 or higher.
Claim 5
Dependent Claim
45 words
An air filter medium which comprises at least two stacked layers, each layer consisting of a porous polytetrafluoroethylene membrane according to claim 2, wherein said polytetrafluoroethylene membrane has a pressure loss lower than 20 mmH 2 O and a PF value of 22 or higher.
Claim 6
Dependent Claim
22 words
The air filter medium of claim 3, which contains a reinforcing material interposed between the stacked layers of the porous polytetrafluoroethylene membranes.
Claim 7
Dependent Claim
15 words
The air filter medium of claim 4, wherein the reinforcing material is a nonwoven fabric.
Claim 8
Dependent Claim
33 words
The air filter medium of claim 5, wherein the nonwoven fabric is constituted of composite synthetic fibers having a core/sheath structure, in which the cores have a higher melting point than the sheaths.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2003-02-28 | 2003-08-30 | 2004-02-29 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2007-02-28 | 2007-08-30 | 2008-02-29 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2011-02-28 | 2011-08-30 | 2012-02-29 | $7700.00 | Window Closed / Lapsed |