Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Separator – retainer – spacer or materials for use therewith
Reexamination Certificate
1998-08-14
2001-09-11
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Separator, retainer, spacer or materials for use therewith
C429S250000, C429S247000, C429S246000
Reexamination Certificate
active
06287730
ABSTRACT:
FIELD OF THE INVENTION
The instant invention is a hydrophilic polyolefin article in which a hydrophobic polyolefin article is coated with a mixture of surfactant and EVOH.
BACKGROUND OF THE INVENTION
Hydrophilic refers to the ability to “wet-out” a liquid. “Wet-out” refers to the ability to cause a liquid (e.g., an aqueous solution) to penetrate more easily into, or spread over the surface of another material. Generally, polyolefins are considered hydrophobic. Hydrophobic refers to the inability to “wet-out” a liquid.
Various methods to make polyolefins more hydrophilic generally include: coating with a surfactant (or surface active agent or wetting agent); coating with a polymer(s), the polymer(s) having different (i.e., better) surface active properties than the polyolefin; surface activation (e.g., by plasma treatment); surface roughing to increase surface area (e.g., foaming the surface); and blending the polyolefins with another polymer(s), the blend having different (i.e., better) surface active properties than the polyolefin. Examples of the foregoing are illustrated in Japanese Kokai Nos.: 2-133608 (published May 22, 1990); 2-133607 (May 22, 1990); 3-55755 (Mar. 11, 1991); 4-346825 (Dec. 2, 1992); and 5-106112 (Apr. 17, 1993); and European Patent Publication Nos. 498,414 A2 (Aug. 12, 1992); 634,802 A1 (Jan. 18, 1995); and 203,459 A2 (Dec. 3, 1986).
In the foregoing methods, the hydrophilicity of the polyolefin may degrade over time. Accordingly, there is a need for a permanently hydrophilic polyolefin.
SUMMARY OF THE INVENTION
The present invention is directed to a hydrophilic polyolefin article comprising a polyolefin article having a coating containing a surfactant and an ethylene vinyl alcohol (EVOH) copolymer.
DETAILED DESCRIPTION OF THE INVENTION
Polyolefins are a class or group of thermoplastic polymers derived from simple olefins. Polyolefins generally include polyethylene, polypropylene, polybutylene, polymethyl pentene, and copolymers thereof. Polyolefins articles generally include fibers and films, but also include microporous films and microporous hollow fibers. Microporous refers to an article which has a plurality of pores with effective diameters of 1 micron or less. Hydrophobic polyolefins refer to polyolefins having surface energies equivalent to or less than the surface energy of polyethylene.
The polyolefin article is made hydrophilic by a coating. The coating contains a surfactant and an ethylene vinyl alcohol (EVOH) copolymer. Preferably, the coating is applied as a mixture of the surfactant and EVOH, but the coating may also be applied serially, e.g. first apply the surfactant, and then apply the EVOH. Preferably, the coating is added onto the article at an average weight percentage in the range of 10-25 based upon the weight of the article. It is believed that the addition of the surfactant to the EVOH facilitates the adhesion of the EVOH to the article, and thereby increases the permanency of the coating.
The coating is preferably applied to the surface in solution form. The solution may comprise an alcohol/water (preferably 60:40 propanol:water) and no more than 0.9% by weight surfactant and between 1.5-3% by weight EVOH. The amount of surfactant is balanced so that the surfactant does not cause wetting. Of the surfactants named herein, no more than 0.9% should be use. Preferably, the range should be from 0.7 to 0.9% by weight. The amount of EVOH is chosen to insure consistent wetting of the surface but to avoid pore blockage. At less than 1.5% wetting becomes erratic. At greater than 3.0% pore blockage is likely to occur. Preferably, the range should be from 2.0 to 3.0% by weight.
After application, any application method is appropriate, the alcohol/water portion is driven off, e.g., by drying including forced hot air dying, and the article is ready for use.
The surfactant is any one capable of raising the surface energy of the polyolefin to about 48 dynes/cm. Those surfactants include, but are not limited to, polyethylene glycol diolate, nonylphenoxypoly(ethyleneoxy) ethanol, triethylene glycol divinyl ether, and combinations thereof. Polyethylene glycol diolate is available as MAPEG D0400 from PPG Industries, Inc. of Gurnee, Ill. Triethylene glycol divinyl ether is available as Rapidcure DVE-3 from ISP Technologies Inc. of Wayne, N.J. Nonylphenoxypoly (ethyleneoxy) ethanol is available as Igepal CO 660 from Rhone-Poulenc Surfactants and Specialties, Inc. of Cranberry, N.J.
The EVOH may be any commercially available EVOH copolymer. Preferably, the EVOH has about 38 mole % of ethylene monomer. Suitable EVOH copolymers include: Soarnol K3835N from Nippon Goshei of Osaka, Japan; and EVAL F104 from Eval Company of America, Lisle, Ill.
The foregoing hydrophilic polyolefin articles may be used in any application where a hydrophilic polyolefin is necessary or desirable, for example, air filtration, air cleaning, water filtration, water cleaning, water purification, medical equipment, separation equipment, semiconductor manufacture, battery cell separator (particularly for batteries having aqueous based electrolytes), ultrafiltration equipment and the like.
With regard to battery cell separators, the coating is applied to one or preferably both surfaces of the microporous polyolefin membrane. Such membranes are commercially available from: CELGARD LLC, Charlotte, N.C.; Tonen KK, Tokyo, Japan; Asahi Chemical Industry Co., Ltd., Tokyo, Japan; Nitto Denko Corp., Osaka, Japan; and Ube Industries Ltd., Tokyo, Japan. This coated separator is particularly suitable for aqueous alkaline secondary battery. Such batteries include, but are not limited, nickel metal hydride (NiMH), nickel cadmium (NiCd), and zinc air batteries. In such uses, preferably about 50-90% (most preferably 60-80%) of the separator's surface is coated. Partial coating is preferred because it facilitates gas permeability. During the recharging of alkaline secondary batteries, gases may be formed on the electrode surfaces, these gases must be able to permeate the separator to recombine.
With regard to the separation, filtration, cleaning, and purification equipment, particularly where microporous polyolefin hollow fibers or flat sheet membranes are used, higher flux rates all obtainable by use of the coatings. Suitable hollow fibers and membrane contactors (e.g., LIQUI-CEL® contactors) are available from CELGARD LLC, Charlotte, N.C.
The following examples serve only to further illustrate aspects of the present invention and should not be construed as limiting the present invention.
The Gurley value is measured using a Model 4120 or 4150 Gurley Densometer from Teledyne Gurley, and is the time in seconds required to pass 10 cc of air through 1 in
2
of membrane at a constant pressure of 12.2 in of water. [Ref. ASTM D726(B)]
The electrical resistance (or resistivity) is measured as follows: A R.A.I. AC Milliohm Resistance Meter, Model 2401 and R.A.I. test cell electrode (from RAI Research Corp., Hauppauge, N.Y.) are used. A 31% by wt KOH solution is used to wet the sample. Samples should not be dry when tested. The results, reported in milliohm-inch
2
.
REFERENCES:
patent: 4501793 (1985-02-01), Sarada
patent: 0203459 (1986-12-01), None
patent: 0498414A2 (1993-08-01), None
patent: 0203459 (1996-12-01), None
patent: 2-133607 (1990-05-01), None
patent: 2-133608 (1990-05-01), None
patent: 3-55755 (1991-03-01), None
patent: 4-346825 (1991-05-01), None
patent: 5-106112 (1991-10-01), None
patent: 8131789 (1996-05-01), None
patent: 8311771 (1996-11-01), None
Callahan Robert W.
Nguyen Khuy Van
Celgard Inc.
Hammer III Robert H.
Weiner Laura
LandOfFree
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