Gas separation – Two or more separators – Plies or layers of different characteristics or orientation
Reexamination Certificate
1999-11-15
2001-10-30
Simmons, David A. (Department: 1724)
Gas separation
Two or more separators
Plies or layers of different characteristics or orientation
C055S528000
Reexamination Certificate
active
06309438
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a folded filter unit using a polytetrafluoroethylene (PTFE) porous film with superior dust collection efficiency. The present invention also relates to a folded chrysanthemum-shaped filter unit with high dust collection efficiency and low inhalation resistance.
BACKGROUND OF THE INVENTION
Some current dust-proof and gas-proof masks contain filter units that are made from a nonwoven synthetic fiber filter material such as polypropylene, which is also used in air filters. Electrostatic filters have been proposed to reduce breathing resistance and mechanical filters which use a fiberglass fiber as the base material have also been proposed.
Unfortunately, there are many problems with these filters. For example, in the case of electrostatic filters, microfibers adhere to the filter material and collect in the folds. Oil mist reduces the electrostatic properties and lowers the dust collection efficiency of the filter. In the case of mechanical filters whose base material is fiberglass, the high dust collection efficiency produces increased resistance (inhalation resistance in the case of masks). It would be desirable therefore to have a filter unit for air filters, dust-proof masks and gas-proof masks with low pressure drop, (i.e., low inhalation resistance) and superior dust collection efficiency. The inhalation resistance and filter area have to be such that the filter unit can be placed inside a restricted area in front of an air filter unit or dust-proof mask. Each filter also has to be designed to collect as much dust as possible. A pleated filter with an expanded filter area has been disclosed (Japanese Unexamined Patent Application Publication [Kokai] No. 8-168629) which reduces inhalation resistance and increases the amount of dust collected.
In order to filter out dust particles the size of a single micron, the inhalation resistance of the filter has to be configured to accommodate fibers the size of a single micron. When a filter consisting of fibers the size of a single micron is folded into pleats, the filter has to be reinforced so as to be strong enough to withstand the air pressure due to inhalation resistance and also to resist mechanical vibration. The mechanical strength of the material used in the folded filter is weak, but this problem can be solved by increasing the thickness of the filter using a reinforcing material. This has to be done while maximizing the dust collection efficiency, minimizing inhalation resistance, and allowing the filter unit to be easily manufactured.
SUMMARY OF THE INVENTION
Generally the present invention relates to a filter wherein the dust collection efficiency has been improved by using a highly extended porous PTFE film with a specific fiber diameter, pore diameter, film thickness and porosity. The dust collection efficiency of such a filter is further improved by folding the film in the direction of high extension.
One embodiment of the present invention is a folded filter characterized in that the extended area scaling factor is extended by a factor of 45 or higher, and that a polytetrafluoroethylene porous film is used with a fiber diameter of 0.05 to 0.2 &mgr;m, and a porosity of 40 to 97%. The polytetrafluoroethylene porous film in the folded filter is folded in the direction with the higher extended area scaling factor, and a nonwoven polyolefin spun bond with a capped structure is used as a laminate for the polytetrafluoroethylene porous film. The folded filter of the present invention is used in dust-proof masks and gas-proof masks.
Dust-proof masks and gas-proof masks using the filter of the present invention utilize a highly extended PTFE porous film as the filter material which is folded in the direction of greater extension. As a result, the dust collection efficiency of these masks exceed 99.99% and the inhalation resistance is remarkably low.
In another embodiment of the present invention, the filter material is folded into a chrysanthemum shape. In this configuration, the filter material can be an extended polytetrafluoroethylene porous film, an electret fiber nonwoven fabric, or a fiberglass nonwoven fabric.
Other details, objects and advantages of the present invention will be readily apparent from the following description of the presently-preferred embodiments.
REFERENCES:
patent: 4187390 (1980-02-01), Gore
patent: 4877433 (1989-10-01), Oshitari
patent: 5551984 (1996-09-01), Tanahashi
patent: 6027553 (2000-02-01), Hirano et al.
Kanno Tomoaki
Umezaki Hirohisa
Yamada Kunio
Hopkins Robert A.
Mine Safety Appliances Company
Simmons David A.
Uber James G.
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