Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Producing or treating porous product
Reexamination Certificate
2000-05-25
2002-07-16
Chiesa, Richard L. (Department: 1724)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Producing or treating porous product
C055S524000, C055S528000, C055SDIG005, C055SDIG003, C095S059000, C096S066000, C096S069000, C096S098000, C264S455000, C264S466000, C264S469000, C264S483000, C264SDIG008, C264SDIG004, C442S092000
Reexamination Certificate
active
06419871
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the improvement of electrostatic filter media by the use of a fluorine-containing plasma.
2. Description of the Related Arts
Filters having an electrostatic charge are known in the art and have a variety of uses. The electrostatic charge provides for increased filter efficiency against a variety of substances, especially charged particulates such as dust. Charged filters are commonly used today in household heating and air conditioning filters and in vacuum bags.
The filters typically contain a non-woven web of electret fibers. These webs can be formed by a variety methods. For example, a thin film or monolayer of polymer material can be extruded and charged via corona discharge. The charged film is then fibrillated and the resulting fibrils formed into a non-woven web via needle punching or other known means. In another method, a polymer is melt blown as a fine fiber and then fashioned into a non-woven web. The fibers are charged either as they exit the orifice of the extruder during melt blowing or after they are assembled into a web. Charging can be carried out by corona exposure, ion bombardment, etc.
The conventional electrostatic filters, however, suffer from unstable charging. The electrostatic charge possessed by the fiber electrets tends to dissipate over time. This presents a problem with respect to storage stability. The consumer may be confronted with fluctuating filtering efficiency based on the duration between manufacture and use.
Furthermore, the charge loss may be accelerated during use, thereby requiring a premature change of the filter. This accelerated charge loss during use is normally caused by the make up of the composition being filtered. One known problem in this regard is the presence of oily aerosols. It is known that oil is especially problematic with respect to a polyolefin based filter web such as polypropylene.
One proposal for dealing with this problem is set forth in U.S. Pat. No. 5,411,576. Here, oily aerosol resistance is stated to be improved by incorporating a fluorochemical additive into a polypropylene fiber electret. The fluorochemical is blended with the polypropylene before extrusion and is taught to be used in an amount of 0.2 to 10% by weight. The fluorochemical must be melt processable and preferably has a molecular weight in the range of about 500 to 2500.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a filter having improved electrostatic charge stability.
It is another object of the invention to provide a filter having good resistance against oils.
A further of object of the invention is to provide a washable electrostatic media.
Another object of the present invention is to provide a process for making electrets having improved charge stability.
A further object of the present invention is to provide a process for making a filter having improved properties.
These and other objects of the invention are achieved by a filter medium, comprising a web of electret fibers, said fibers having been formed from a material that was treated with a fluorine-containing plasma at a deposition amount of about 0.03 g/m
2
to about 1.5 g/m
2
; electrostatically charged; rinsed; and dried.
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Strobel et al, “Plasma Fluorination of Polyolefins”,Journal of Polymer Science, vol. 25, pp. 1295-1307, 1987.
Birch Stewart Kolasch & Birch, LLP.
Chiesa Richard L.
Transweb, LLC.
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