Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
2000-03-06
2003-10-28
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S341000, C428S421000, C428S523000
Reexamination Certificate
active
06638610
ABSTRACT:
1. FIELD OF THE INVENTION
The invention relates to hydrophobic and/or oleophobic porous materials and to processes for making the same.
2. BACKGROUND OF THE INVENTION
Materials that repel water (i.e., hydrophobic materials) and materials that repel oils (i.e., oleophobic materials) are useful in a variety of applications. For example, U.S. Pat. No. 5,853,894 discloses a method that allegedly increases the ability of laboratory vessels, such as test tubes and graduated cylinders, to repel water and oils. See also, Schmidt, D. L., et al.,
Nature
368:39-41 (1994); and Brady, R. F.,
Nature
368:16-17 (1994).
In other applications, porous (i.e., gas permeable) hydrophobic and oleophobic materials are desired. For example, such materials may be used to provide vents or filters that allow the passage of gases but resist the passage of liquids. Porous hydrophobic and oleophobic materials may also be used to prevent the transmission of viral pathogens. See, e.g., U.S. Pat. Nos. 5,690,949 and 5,738,111. Until now, however, attempts at providing hydrophobic and oleophobic porous materials have yielded materials of limited use.
In one prior method of providing a porous hydrophobic material, a porous substrate is coated with silicone oil. Although materials with surface energies as low as 25 to 30 dynes/cm can be obtained by this method, large amounts (e.g., greater than two percent by weight of the material) of silicone oil are often required. More important, because silicone oil can easily leach from these materials, they are of little use in applications that require a contaminate-free environment.
An alternate method of providing an allegedly hydrophobic porous material is disclosed by U.S. Pat. No. 5,156,780. According to this method, a microporous substrate is impregnated with a solution containing a fluorinated monomer, after which the carrier solvent is evaporated and the monomers are polymerized in situ to form a coating.
Another method of providing an allegedly hydrophobic porous material is disclosed by U.S. Pat. Nos. 5,260,360 and 5,352,513. According to this method, a microporous material is made by stretching a phase-separated membrane. Unfortunately, this method is of little use in providing hydrophobic and oleophobic materials that have desirable mechanical properties such as stiffness and strength.
In view of the inadequacies of prior porous materials, there exists a need for porous hydrophobic and/or oleophobic materials that can be used in a wide range of applications. There further exists a need for low cost, efficient methods of making porous hydrophobic and/or oleophobic materials.
3. SUMMARY OF THE INVENTION
This invention is directed to porous hydrophobic and/or oleophobic materials and methods of their manufacture and use. Particular materials of the invention comprise a porous thermoplastic substrate and a surface treatment material. The invention is further directed to methods of using the novel porous materials disclosed herein, as well as to filters, vents, and pipette tips made of, or comprising, the novel porous materials disclosed herein.
Preferred hydrophobic and/or oleophobic materials of the invention have a surface energy of from about 5 dynes/cm
2
to about 30 dynes/cm
2
, more preferably from about 6 dynes/cm
2
to about 20 dynes/cm
2
, and most preferably from about 6 dynes/cm
2
to about 15 dynes/cm
2
.
Suitable thermoplastics that can be used to provide porous thermoplastic substrates of the invention include, but arc not limited to, polyolefins, nylons, polycarbonates, poly(ether sulfones), and mixtures thereof. A preferred thermoplastic is a polyolefin. Examples of suitable polyolefins include, but are not limited to: ethylene vinyl acetate; ethylene methyl acrylate; polyethylenes; polypropylenes; ethylene-propylene rubbers; ethylene-propylene-diene rubbers; poly(1-butene); polystyrene; poly(2-butene); poly(1-pentene); poly(2-pentene); poly(3-methyl-1-pentene); poly(4-methyl-1-pentene); 1,2-poly-1,3-butadiene; 1,4-poly-1,3-butadiene; polyisoprene; polychloroprene; poly(vinyl acetate); poly(vinylidene chloride); and mixtures and derivatives thereof. A preferred polyolefin is polyethylene. Examples of suitable polyethylenes include, but are not limited to, low density polyethylene, linear low density polyethylene, high density polyethylene, ultra-high molecular weight polyethylene, and derivatives thereof.
A first embodiment of the invention encompasses a porous hydrophobic and/or oleophobic material which comprises a sintered porous thermoplastic substrate having a surface at least part of which is coated with a surface treatment material.
Although the thermoplastic substrate can be made of any thermoplastic, including those disclosed herein, it is preferably made of polyethylene, more preferably ultra-high molecular weight polyethylene. Preferred surface treatment materials include, but are not limited to, fluorochemicals. Preferred fluorochemicals are high molecular weight fluorochemicals polymerized from compounds such as, but not limited to, fluorinated acrylates, methacrylates, acrylic esters, and mixtures thereof. Specific preferred fluorochemicals are high molecular weight fluorochemicals polymerized from compounds such as:
and mixtures thereof, wherein each R
f
is independently —CF
3
(CF
2
)
n
, each n is independently an integer of from about 1 to about 18, preferably of from 1 to 4, and R is hydrogen or substituted or unsubstituted alkyl, aryl, or aralkyl.
A specific porous hydrophobic and/or oleophobic material of the invention thus comprises a sintered porous thermoplastic substrate having a surface at least part of which is coated with a surface treatment material, wherein the porous thermoplastic substrate is ultra-high molecular weight polyethylene and the surface treatment material is a perfluoro polyacrylate. Specific preferred perfluoro polyacrylates are polymerized from compounds such as:
wherein R
f
is —CF
3
(CF
2
)
n
, and n is an integer of from about 1 to about 18, preferably of from 1 to 4.
A second embodiment of the invention encompasses a porous hydrophobic and/or oleophobic material which comprises a sintered porous thermoplastic substrate and a surface treatment material disposed throughout at least part of the substrate.
Although the thermoplastic substrate can be made of any thermoplastic, including those disclosed herein, it is it is preferably polyethylene. Preferred surface treatment materials include, but are not limited to, fluorochemicals. Preferred fluorochemicals are low molecular weight fluorochemicals such as, but not limited to, fluorinated urethanes, allophanates, oxazolidones, piperazines, and mixtures thereof. Specific preferred low molecular weight fluorochemicals include, but are not limited to, those of the formula:
wherein each R
f
is independently —CF
3
(CF
2
)
n
, n is an integer of from about 1 to about 18, preferably of from 1 to 4, and R′ can by any suitable organic moiety including, but not limited to:
and derivatives thereof, wherein m is an integer of from about 1 to about 20, preferably of from 1 to 6.
A specific porous hydrophobic and/or oleophobic material of the invention thus comprises a sintered porous thermoplastic substrate and a surface treatment material disposed within at least part of the sintered porous thermoplastic substrate, wherein the porous thermoplastic substrate is polyethylene and the surface treatment material is of the formula:
wherein each R
f
is independently —CF
3
(CF
2
)
n
, and n is an integer of from about 1 to about 18, preferably of from 1 to 4. In an even more specific material of the invention, the surface treatment material is disposed uniformly within at least about 75 percent, more preferably at least about 90 percent, and most preferably at least about 95 percent of the porous thermoplastic substrate.
A third embodiment of the invention encompasses a particle comprised of surface treatment material disposed about a thermoplastic core. Preferred surface treatment materials are low molecular weight fluorochemicals such as those described h
Le H. Thi
Pennie & Edmonds LLP
Porex Technologies Corp.
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