U.S. patent application number 10/638498 was filed with the patent office on 2004-02-12 for water and oil repellent porous particles and methods for making the same.
This patent application is currently assigned to Porex Technologies Corporation. Invention is credited to Yao, Li.
Application Number | 20040028890 10/638498 |
Document ID | / |
Family ID | 24068953 |
Filed Date | 2004-02-12 |
United States Patent
Application |
20040028890 |
Kind Code |
A1 |
Yao, Li |
February 12, 2004 |
Water and oil repellent porous particles and methods for making the
same
Abstract
This invention relates to a hydrophobic and oleophobic porous
materials and processes for making the same. In a first process of
the invention, a thermoplastic substrate is at least partially
coated and/or impregnated with a surface treatment material. In a
second process of the invention, thermoplastic particles which
comprise a surface treatment material are sintered together.
Preferred surface treatment materials are fluorochemicals.
Inventors: |
Yao, Li; (Peachtree City,
GA) |
Correspondence
Address: |
PENNIE & EDMONDS LLP
1667 K STREET NW
SUITE 1000
WASHINGTON
DC
20006
|
Assignee: |
Porex Technologies
Corporation
|
Family ID: |
24068953 |
Appl. No.: |
10/638498 |
Filed: |
August 12, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10638498 |
Aug 12, 2003 |
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09519590 |
Mar 6, 2000 |
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6638610 |
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Current U.S.
Class: |
428/304.4 ;
428/341; 428/421; 428/523 |
Current CPC
Class: |
Y10T 428/249953
20150401; Y10T 428/273 20150115; Y10T 428/31938 20150401; Y10T
428/3154 20150401; B05D 2201/02 20130101; B05D 5/083 20130101 |
Class at
Publication: |
428/304.4 ;
428/341; 428/421; 428/523 |
International
Class: |
B32B 003/26 |
Claims
What is claimed is:
1. A porous hydrophobic and/or oleophobic material having a surface
energy of from about 5 dynes/cm.sup.2 to about 30 dynes/cm.sup.2
which comprises a sintered porous thermoplastic substrate having a
surface at least part of which is coated with a high molecular
weight fluorochemical.
2. The material of claim 1 wherein the porous thermoplastic
substrate is made of a thermoplastic selected from the group
consisting of: 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.
3. The material of claim 2 wherein thermoplastic is
polyethylene.
4. The material of claim 3 wherein the polyethylene is ultra-high
molecular weight polyethylene.
5. The material of claim 1 wherein the high molecular weight
fluorochemical is selected from the group consisting of fluorinated
acrylates, methacrylates, acrylic esters, and mixtures thereof.
6. The material of claim 5 wherein the high molecular weight
fluorochemical is polymerized from a compound selected from the
group consisting of: 11and mixtures thereof, wherein R.sub.f is
--CF.sub.3(CF.sub.2).sub.n, n is 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.
7. The material of claim 6 wherein the high molecular weight
fluorochemical is polymerized from a compound selected from the
group consisting of: 12wherein R.sub.f is
--CF.sub.3(CF.sub.2).sub.n, and n is an integer of from about 1 to
about 18.
8. 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.
9. The material of claim 8 wherein the porous thermoplastic
substrate is made of a thermoplastic selected from the group
consisting of: 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.
10. The material of claim 9 wherein the porous thermoplastic
substrate is made of polyethylene.
11. The material of claim 8 wherein the surface treatment material
is a low molecular weight fluorochemical.
12. The material of claim 11 wherein the low molecular weight
fluorochemical is selected from the group consisting of:
fluorinated urethanes, allophanates, oxazolidones, piperazines, and
mixtures thereof.
13. The material of claim 11 wherein the low molecular weight
fluorochemical is of the formula: 13wherein each R.sub.f is
independently --CF.sub.3(CF.sub.2).sub.n, n is an integer of from
about 1 to about 18, and R' is selected from the group consisting
of: 14and derivatives thereof, wherein m is an integer of from
about 1 to about 20.
14. The material of claim 13 wherein the low molecular weight
fluorochemical is of the formula: 15wherein each R.sub.f is
independently --CF.sub.3(CF.sub.2).sub.n, and n is an integer of
from about 1 to about 18.
15. A particle comprised of surface treatment material disposed
about a thermoplastic core.
16. The particle of claim 15 wherein the surface treatment material
is a low molecular weight fluorochemical.
17. The particle of claim 15 wherein the thermoplastic core is made
of polyethylene.
18. A particle which comprises a surface treatment material of the
formula: 16disposed about a polyethylene core, wherein each R.sub.f
is independently --CF.sub.3(CF.sub.2).sub.n, and n is an integer of
from about 1 to about 18.
19. The particle of claim 18 wherein said particle has a diameter
of from about 5 .mu.M to about 1000 .mu.M.
20. A process for making a porous hydrophobic and/or oleophobic
material which comprises contacting a sintered porous thermoplastic
substrate with a high molecular weight fluorochemical, wherein the
substrate is made of polyethylene.
21. The product of the process of claim 20.
22. A process for making a particle which comprises cooling a
molten pre-particle, wherein the pre-particle is comprised of a
thermoplastic and a surface treatment material.
23. The process of claim 22 wherein the surface treatment material
is a low molecular weight fluorochemical.
24. The product of the process of claim 22.
25. A process for making a porous hydrophobic and/or oleophobic
material which comprises sintering particles which are comprised of
a surface treatment material disposed about a thermoplastic
core.
26. The process of claim 25 wherein the surface treatment material
is a low molecular weight fluorochemical and the thermoplastic core
is polyethylene.
27. The product of the process of claim 25.
Description
[0001] This is a divisional of U.S. application Ser. No.
09/519,590, filed Mar. 6, 2000, the entirety of which is
incorporated herein by reference.
1. FIELD OF THE INVENTION
[0002] The invention relates to hydrophobic and/or oleophobic
porous materials and to processes for making the same.
2. BACKGROUND OF THE INVENTION
[0003] 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).
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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
[0009] 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.
[0010] Preferred hydrophobic and/or oleophobic materials of the
invention have a surface energy of from about 5 dynes/cm.sup.2 to
about 30 dynes/cm.sup.2, more preferably from about 6
dynes/cm.sup.2 to about 20 dynes/cm.sup.2, and most preferably from
about 6 dynes/cm.sup.2 to about 15 dynes/cm.sup.2.
[0011] Suitable thermoplastics that can be used to provide porous
thermoplastic substrates of the invention include, but are 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.
[0012] 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.
[0013] 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: 1
[0014] and mixtures thereof, wherein each R.sub.f is independently
--CF.sub.3(CF.sub.2).sub.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.
[0015] 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: 2
[0016] wherein R.sub.f is --CF.sub.3(CF.sub.2).sub.n, and n is an
integer of from about 1 to about 18, preferably of from 1 to 4.
[0017] 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.
[0018] 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: 3
[0019] wherein each R.sub.f is independently
--CF.sub.3(CF.sub.2).sub.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: 4
[0020] and derivatives thereof, wherein m is an integer of from
about 1 to about 20, preferably of from 1 to 6.
[0021] 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: 5
[0022] wherein each R.sub.f is independently
--CF.sub.3(CF.sub.2).sub.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.
[0023] 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 herein.
Although the thermoplastic core can be made of any thermoplastic,
it is preferably made of polyethylene.
[0024] A specific particle of the invention thus comprises a
surface treatment material of the formula: 6
[0025] disposed about a polyethylene core, wherein each R.sub.f is
independently --CF.sub.3(CF.sub.2).sub.n, and n is an integer of
from about 1 to about 18, preferably of from 1 to 4. A specific
particle of the invention has a diameter of from about 5 .mu.M to
about 1000 .mu.M, more preferably from about 10 .mu.M to about 500
.mu.M, and most preferably from about 20 .mu.M to about 300
.mu.M.
[0026] A fourth embodiment of the invention encompasses a process
for making a porous hydrophobic and/or oleophobic material, and the
products of that process. The process comprises contacting a
sintered porous thermoplastic substrate with a surface treatment
material, or a solution (e.g., a liquid or aerosol), suspension or
powder comprising a surface treatment material, to provide a coated
and/or impregnated substrate which is optionally dried and/or
treated. Optional treatment includes, but is not limited to,
radiation- and chemical-induced crosslinking. Preferred surface
treatment materials are fluorochemicals, and more preferred surface
treatment materials are high molecular weight fluorochemicals.
[0027] A fifth embodiment of the invention encompasses a process
for making a particle and the products of that process. The process
comprises cooling a molten pre-particle, wherein the pre-particle
is comprised of a thermoplastic and a surface treatment material.
Preferably, the molten pre-particle is formed by chopping a molten
extrudate. Preferably, the pre-particle is cooled under a coolant
such as, but not limited to, water. Preferably, the surface
treatment material is a fluorochemical, more preferably a low
molecular weight fluorochemical.
[0028] A sixth embodiment of the invention encompasses a process
for making a porous hydrophobic and/or oleophobic material and the
products of that process. This process comprises sintering
particles which are comprised of a surface treatment material
disposed about a thermoplastic core. Preferred surface treatment
materials are low molecular weight fluorochemicals such as those
described herein. Although the thermoplastic core can be made of
any thermoplastic, including those disclosed herein, it is it is
preferably polyethylene. Preferred particles are formed by cooling
a molten pre-particle comprised of a thermoplastic and a surface
treatment material.
3.1 Definitions
[0029] As used herein to describe a particle, the term
"substantially spherical" means that the particle is spherical or
that the length of its longest radius is no greater than about 2.0
times, more preferably no greater than about 1.5 times, even more
preferably no greater than about 1.2 times the length of its
shortest radius. When used to describe a mixture or collection of
particles, the term "substantially spherical" means that greater
than about 50%, more preferably greater than about 75%, even more
preferably greater than about 90%, and most preferably greater than
about 95% of the particles are substantially spherical.
[0030] As used herein, the term "substantial portion" means greater
than about 80%, more preferably greater than about 90%, and most
preferably greater than about 95%.
[0031] As used herein, the terms "degradation temperature" and
"decomposition temperature" mean the temperature at which a
particular chemical compound (e.g., a surface treatment material)
decomposes or loses its ability to repel water and/or oil. As those
skilled in the art will recognize, the degradation temperature of a
particular material will vary as a function of, for example,
pressure and exposure to oxidants, reductants, or other reactive
chemical moieties.
[0032] As used herein, the term "substantial degradation" means the
degradation of a substantial portion of the material described.
[0033] As used herein to describe a compound or moiety, the term
"derivative" means a compound or moiety wherein the degree of
saturation of at least one bond has been changed (e.g., a single
bond has been changed to a double or triple bond) or wherein at
least one hydrogen atom has been replaced with a different atom or
with a chemical moiety. Examples of different atoms and chemical
moieties include, but are not limited to, alkyl, aryl, halogen,
oxygen, nitrogen, sulfur, hydroxy, methoxy, alkyl, amine, amide,
ketone, and aldehyde.
[0034] As used herein, the term "surface treatment material" refers
to a material which is or which comprises a compound or mixture of
compounds that, when disposed on the surface of a material, will
reduce its surface energy. The term "surface treatment material"
also encompasses materials that require further processing after
having been disposed on the surface of a material in order to
reduce its surface energy. Examples of further processing include,
but are not limited to, chemical- or radiation-induced crosslinking
and the formation of chemical.
4. DETAILED DESCRIPTION OF THE INVENTION
[0035] This invention is directed to novel porous materials that
repel water and/or oil. The materials of the invention can be
molded or formed into any of a variety of shapes, and can thus be
used to provide, for example, filters or vents that are useful in a
variety of medical, research, consumer and industrial applications.
The mechanical strength and uniform porosity of specific materials
of the invention further enable their use in applications for which
prior hydrophobic and oleophobic materials are not suited. For
example, pipette tips can be made from the materials of this
invention. Examples of pipette tips include those disclosed by U.S.
Pat. Nos. 5,156,811 and 5,364,595, both of which are incorporated
herein by reference.
[0036] The specific properties of a particular porous material of
the invention will depend on its specific composition and
structure. These, in turn, depend on the materials and processes
used in the manufacture of the porous material.
4.1. Materials
[0037] Porous materials of the invention comprise a porous
substrate and a surface treatment material. The surface treatment
material can be disposed on the exterior of the porous substrate,
within its interior, or both.
[0038] Using methods such as, but not limited to, those described
herein, porous substrates are made from at least one type of
thermoplastic. Examples of suitable thermoplastics include, but are
not limited to, polyolefins, nylons, polycarbonates, and poly(ether
sulfones). Preferred thermoplastics are polyolefins.
[0039] Examples of polyolefins suitable for use in the invention
include, but are not limited to: ethylene vinyl acetate (EVA);
ethylene methyl acrylate (EMA); polyethylenes such as, but not
limited to, low density polyethylene (LDPE), linear low density
polyethylene (LLDPE), high density polyethylene (HDPE), and
ultra-high molecular weight polyethylene (UHMWPE); 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. Specific EVA materials include, but are not limited to,
those in the Microthene MU.RTM. and Microthene FE.RTM. series
manufactured by Equistar, Houston, Tex., such as Microthene MU
763-00 (9% vinyl acetate) and Microthene FE 532-00 (9% vinyl
acetate). Specific EMA materials include, but are not limited to,
those in the Optema TC.RTM. series manufactured by Exxon Chemical
Company, Baton Rouge, La., such as Optema TC-110 (21.5% methyl
acrylate). Specific polyethylene materials include, but are not
limited to, those in the Exact.RTM. series manufactured by Exxon
Chemical Company, such as Exact SLX-9090, Exact 3024, Exact, 3030,
Exact 3033, Exact 4011, Exact 4041, Exact SLP-9053, Exact SLP-9072,
and Exact SLP-9095. Specific examples of LDPE include, but are not
limited to, those in the 20 series manufactured by DuPont Chemical
Company, Wilmington, Del., such as 20 series 20, 20 series 20-6064,
20 series 2005, 20 series 2010, and 20 series 2020T. Specific
examples of LLDPE include, but are not limited to, those in the
Exact.RTM. series manufactured by Exxon Chemical Company, such as
Exact 3022 and Exact 4006. Specific examples of HDPE include, but
are not limited to, those in the Escorene HX.RTM. series
manufactured by Exxon Chemical Company, such as Escorene
HX-0358.
[0040] Ultra-high molecular weight polyethylenes suitable for use
in the invention include, but are not limited to, UHMWPE having a
molecular weight greater than about 1,000,000. Typically, UHMWPE
displays no measurable flow rate under normal test procedures. See,
U.S. Pat. No. 3,954,927, which is incorporated herein by reference.
Ultra-high molecular weight polyethylene also tends to have
enhanced mechanical properties compared to other polyethylenes,
including, but not limited to, abrasion resistance, impact
resistance and toughness. Polyethylenes having weight average
molecular weights of 1,000,000 or higher, which are included within
the class designated as UHMWPE, typically an intrinsic viscosity in
the range of about 8 or more. Specific examples of UHMWPE include,
but are not limited to, Hostalen GUR.RTM. sold by Ticona Inc.,
League City, Tex.
[0041] Polypropylenes suitable for use in the invention include,
but are not limited to: the Polyfort.RTM. series manufactured by A
Shulman Co., Akron, Ohio, such as FPP 2320E, 2321E, 2322E, 2345E,
PP2130, and PP2258; the Acctuf.RTM. series manufactured by BP Amoco
Corporation, Atlanta, Ga., such as Acctuf 3045, Amoco 6014, and
Amoco 6015; the Aristech.RTM. series manufactured by Aristech
Chemical Corp., Pittsburgh, Pa., such as D-007-2, LP-230-S, and
TI-4007-A; the Borealis.RTM. series manufactured by BASF
Thermoplastic Materials, Saint Paul, Minn., such as BA101E, BA110E,
BA122B, BA204E, BA202E, and BA124B; the Polypro.RTM. series
manufactured by Chisso America Inc., Schaumburg, Ill. such as F1177
and F3020; the Noblen.RTM. series manufactured by Mitsubishi
Petrochemical Co. Ltd., Tokyo, Japan, such as MA8; the Astryn.RTM.
series manufactured by Montell USA Inc., Wilmington, Del., such as
68F4-4 and PD451; the Moplen.RTM. series manufactured by Montell
USA Inc., such as D 50S, D 60P, and D 78PJ; and the Pro-Fax.RTM.
series manufactured by Montell USA Inc., such as 6723, 6823, and
6824.
[0042] Sinterable thermoplastics in addition to those recited
herein can also be used in this invention. As those skilled in the
art are well aware, the ability of a thermoplastic to be sintered
can be determined, at least in part, from its melt flow index
(MFI). Melt flow indices of individual thermoplastics are known or
can be readily determined by methods well known to those skilled in
the art. For example, the extrusion plastometer made by Tinius
Olsen Testing Machine Company, Willow Grove, Pa., can be used. As
discussed elsewhere herein, the MFIs of thermoplastics suitable for
use in this invention will depend on the particular porous
thermoplastic material and/or the method used to prepare it. In
general, however, the MFI of a thermoplastic suitable for use in
the materials and methods of the invention is from about 0 to about
15, more preferably from about 0.2 to about 12, and most preferably
from about 0.5 to about 10. The temperatures at which individual
thermoplastics sinter (i.e., their sintering temperatures) are also
well known, or can be readily determined by routine methods such
as, but not limited to, thermal mechanical analysis and dynamic
mechanical thermal analysis.
[0043] The materials of this invention next comprise a surface
treatment material. Preferred surface treatment materials are
fluorochemicals. Depending on the material and method of the
invention, preferred fluorochemicals are either high or low
molecular weight fluorochemicals.
[0044] High molecular weight fluorochemicals typically have a
molecular weight greater than about 10.sup.4, more preferably
greater than about 10.sup.5, and most preferably greater than about
10.sup.6 grams/mole. Mixtures of high molecular weight
fluorochemicals typically have an average molecular greater than
about 10.sup.4, more preferably greater than about 10.sup.5, and
most preferably greater than about 10.sup.6.
[0045] Examples of high molecular fluorochemicals that can be used
in the materials and processes of the invention include, but are
not limited to, fluorinated acrylates, methacrylates, acrylic
esters, and mixtures thereof.
[0046] Examples of fluorinated acrylates include, but are not
limited to, perfluorohexyl acrylates. Specific, commercially
available fluorinated acrylates suitable for use in this invention
include, but are not limited to: those disclosed in U.S. Pat. Nos.
4,954,256, 5,156,780, and 5,853,894, each of which is incorporated
herein by reference; those sold under the tradenames
PerFluoroCoat.RTM. and FluoroPel.RTM. by Cytonix Corporation,
Beltsville, Md.; Fluorad.RTM. FC-722, FC-724, FC-725, and FC-732,
and Fluorel.RTM. FC-2174 and FC-2181, all of which are sold by the
Commercial Chemicals Divisions of 3M Corporation, St. Paul, Minn.
Suitable fluorinated acrylates can also be prepared by methods well
known to those skilled in the art using starting materials such as,
but not limited to: Zonyl.RTM. TA-N, sold by DuPont Dow Elastomers,
Wilmington, Del.; and FX-13 and FX-189 sold by the Commercial
Chemicals Divisions of 3M Corporation.
[0047] Examples of fluorinated methacrylates include, but are not
limited to, perfluorohexyl methacrylate, perfluoroheptyl
methacrylate, perfluoroocytyl methacrylate, perfluorononyl
methacrylate, perfluorodecyl methacrylate, perfluoroundecyl
methacrylate, perfluorododecyl methacrylate, and mixtures thereof.
Specific, commercially available fluorochemical methacrylates that
can be used in the materials and methods of the invention include,
but are not limited to, those prepared from the monomer sold under
the tradename FX-14 by the Commercial Chemicals Divisions of 3M
Corporation.
[0048] Examples of fluorinated acrylic esters include, but are not
limited to, acrylic esters comprising a perfluoropolyoxyalkylene
moiety such as described in U.S. Pat. No. 4,681,925, which is
incorporated herein by reference.
[0049] Preferred high molecular weight fluorochemicals include, but
are not limited to, these sold under the tradenames Fluorad.RTM.
FC-722 and FluoroPel.RTM..
[0050] Low molecular weight fluorochemicals, some of which are
referred to as "waxes," are fluorochemicals that are not high
molecular weight fluorochemicals. Mixtures of low molecular weight
fluorochemicals are mixtures of fluorochemicals that are not
mixtures of high molecular weight fluorochemicals. Low molecular
weight fluorochemicals typically have a molecular weight of less
than about 10.sup.4, more preferably from about 8000 to about 2000
grams/mole. Mixtures of low molecular weight fluorochemicals
typically have an average molecular weight of less than about
10.sup.4, more preferably from about 8000 to about 2000.
[0051] Examples of low molecular fluorochemicals (e.g.,
fluoro-waxes) that can be used in the materials and methods of the
invention include, but are not limited to: those disclosed by U.S.
Pat. Nos. 4,668,726, 5,156,780, 5,342,434, and 5,853,894, each of
which is incorporated herein by reference; and fluorinated
urethanes, allophanates, oxazolidinones, and piperazines, and
mixtures thereof.
[0052] Specific, commercially available fluorinated urethanes
include those sold under the tradenames FX-1801 and FX-1808 by the
Commercial Chemical Division of 3M Corporation, St. Paul, Minn.
[0053] Methods well known in the art can also be used to provide
fluorinated urethanes such as, but not limited to, those of the
formula: 7
[0054] wherein each R.sub.f is independently
--CF.sub.3(CF.sub.2).sub.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: 8
[0055] and derivatives thereof, wherein m is an integer of from
about 1 to about 20, preferably of from 1 to 6. Fluorinated
urethanes such as these can be prepared from starting materials
such as, but not limited to, methylene-di-p-phenyl diisocyanate,
available from Eastman Kodak Corp., Rochester, N.Y., and
perfluoroalkyl alkyl alcohols such as perfluoroalkyl ethyl alcohol,
which is sold under the tradename Zonyl BA-N.RTM. by DuPont Dow
Elastomers, Wilmington, Del.
[0056] Examples of fluorinated oxazolidinones include, but are not
limited to, those disclosed by U.S. Pat. Nos. 5,025,052, 5,352,513,
5,690,949, and 5,738,111, each of which is incorporated herein by
reference. Suitable fluorinated oxazolidinones can also be prepared
by methods known to those skilled in the art. For example, suitable
fluorinated oxazolidinones can be prepared by reactions such as,
but not limited to: 9
[0057] Examples of fluorinated allophanates include, but are not
limited to, those disclosed by U.S. Pat. No. 4,606,737, which is
incorporated herein by reference. Suitable fluorinated allophanates
can also be prepared by methods known to those skilled in the art
from starting materials such as, but not limited to: 10
[0058] Preferred low molecular weight fluorochemicals include, but
are not limited to, those sold under the tradenames FX-1801 and
FX-1808.
[0059] The porous materials of the invention can optionally
comprise materials in addition to surface treatment materials.
These additional materials are typically incorporated within the
porous substrate, but can also be used to provide a coating or
external layer. Examples of optional additional ingredients
include, but are not limited to, lubricants, colorants, and
fillers. Examples of fillers include, but are not limited to,
carbon black, cellulose fiber powder, siliceous fillers,
polyethylene fibers and filaments, and mixtures thereof Specific
polyethylene fibers and filaments include, but are not limited to,
those disclosed by U.S. Pat. Nos. 5,093,197 and 5,126,219, each of
which is incorporated herein by reference.
[0060] Using materials such as, but not limited to, those described
herein, novel porous thermoplastic materials of the invention can
be made using any technique known in the art. It is preferred,
however, that they be made using at least one of the processes
disclosed herein. In a first of these processes, a porous
thermoplastic substrate is contacted with at least one surface
treatment material. In a second process, thermoplastic particles
that comprise at least one surface treatment material are sintered
together.
4.2. Coating- or Impregnating Porous Substrates
[0061] In a first process of the invention, a porous thermoplastic
substrate is contacted with at least one surface treatment
material. Preferably, the porous thermoplastic substrate is made by
sintering together thermoplastic particles.
[0062] Preferred thermoplastic particles have an average diameter
of from about 5 .mu.M to about 1000 .mu.M, more preferably from
about 10 .mu.M to about 500 .mu.M, and most preferably from about
20 .mu.M to about 300 .mu.M. It is also preferred that the
particles are all of about the same size. In other words, it is
preferred that the particles' size distribution be narrow (e.g., as
determined using commercially available screens). It has been found
that particles of about the same size can be consistently packed
into molds. A narrow particle size distribution further allows the
production of a substrate with uniform porosity (i.e., a substrate
comprising pores that are evenly distributed throughout it and/or
are of about the same size). This is advantageous because solutions
and gases tend to flow more evenly through uniformly porous filters
and vents than through filters and vents which contain regions of
high and low permeability. Uniformly porous substrates are also
less likely to have structural weak spots than substrates that
comprise unevenly distributed pores of substantially different
sizes. In view of these benefits, if a thermoplastic is
commercially available in powder (i.e., particulate) form, it is
preferably screened prior to use to ensure a desired average size
and size distribution. However, most thermoplastics are not
commercially available in powder form, and must therefore be
converted into powder form by methods well known to those skilled
in the art such as, but not limited to, cryogenic grinding and
underwater pelletizing.
[0063] Cryogenic grinding can be used to prepare thermoplastic
particles of varying sizes. But because cryogenic grinding provides
little control over the sizes of the particles it produces, powders
formed using this technique can be screened to ensure that the
particles to be sintered are of a desired average size and size
distribution.
[0064] Underwater pelletizing can also be used to form
thermoplastic particles suitable for sintering. Although typically
limited to the production of particles having diameters of greater
than about 36 .mu.M, underwater pelletizing offers several
advantages. First, it provides accurate control over the average
size of the particles produced, in many cases thereby eliminating
the need for an additional screening step and reducing the amount
of wasted material. A second advantage of underwater pelletizing,
which is discussed further herein, is that it allows significant
control over the particles' shape.
[0065] Underwater pelletizing is described, for example, in U.S.
patent application Ser. No. 09/064,786, filed Apr. 23, 1998, and
U.S. provisional patent application No. 60/044,238, filed Apr. 24,
1999, both of which are incorporated herein by reference.
Thermoplastic particle formation using underwater pelletizing
typically requires an extruder or melt pump, an underwater
pelletizer, and a drier. The thermoplastic resin is fed into an
extruder or a melt pump and heated until semi-molten. The
semi-molten material is then forced through a die. As the material
emerges from the die, at least one rotating blade cuts it into
pieces herein referred to as "pre-particles." The rate of extrusion
and the speed of the rotating blade(s) determine the shape of the
particles formed from the pre-particles, while the diameter of the
die holes determine their average size. Water, or some other liquid
or gas capable of increasing the rate at which the pre-particles
cool, flows over the cutting blade(s) and through the cutting
chamber. This coagulates the cut material (i.e., the pre-particles)
into particles, which are then separated from the coolant (e.g.,
water), dried, and expelled into a holding container.
[0066] The average size of particles produced by underwater
pelletizing can be accurately controlled and can range from about
0.014" (35.6 .mu.M) to about 0.125" (318 .mu.M) in diameter,
depending upon the thermoplastic. Average particle size can be
adjusted simply by changing dies, with larger pore dies yielding
proportionally larger particles. The average shape of the particles
can be optimized by manipulating the extrusion rate and the
temperature of the water used in the process.
[0067] While the characteristics of a porous material can depend on
the average size and size distribution of the particles used to
make it, they can also be affected by the particles' average shape.
Consequently, in another embodiment of the invention, the
thermoplastic particles are substantially spherical. This shape
provides specific benefits. First, it facilitates the efficient
packing of the particles within a mold. Second, substantially
spherical particles, and in particular those with smooth edges,
tend to sinter evenly over a well defined temperature range to
provide a final product with desirable mechanical properties and
porosity.
[0068] In a specific embodiment of the invention, the thermoplastic
particles are substantially spherical and free of rough edges.
Consequently, if the thermoplastic particles used in this preferred
method are commercially available, they are thermal fined to ensure
smooth edges and screened to ensure a proper average size and size
distribution. Thermal fining, which is well known to those skilled
in the art, is a process wherein particles are rapidly mixed and
optionally heated such that their rough edges become smooth. Mixers
suitable for thermal fining include the W series high-intensity
mixers available from Littleford Day, Inc., Florence, Ky.
[0069] Thermoplastic particles made using cryogenic grinding are
likewise preferably thermal fined to ensure smooth edges and
screened to ensure a proper average size and size distribution.
Advantageously, however, if the particles are made using underwater
pelletizing, which allows precise control over particle size and
typically provides smooth, substantially spherical particles,
subsequent thermal fining and screening are typically not
required.
[0070] Once thermoplastic particles of a desired average size
and/or shape have been obtained, they are optionally combined with
additional materials such as, but not limited to, lubricants,
colorants, and fillers such as those described above in Section
4.1. As those skilled in the art will recognize, the types and
amounts of optional materials incorporated into a porous substrate
will typically depend on the application for which the final porous
hydrophobic and/or oleophobic material will be used.
[0071] After the thermoplastic particles and optional additional
materials have been blended, preferably to provide a uniform
mixture, the mixture is sintered. Depending on the desired size and
shape of the final product (e.g., a block, tube, cone, cylinder,
sheet, or membrane), this can be accomplished using a mold, a belt
line such as that disclosed by U.S. Pat. No. 3,405,206, which is
hereby incorporated by reference, or using other techniques known
to those skilled in the art. In a preferred embodiment of the
invention, the mixture is sintered in a mold. Suitable molds are
commercially available and are well known to those skilled in the
art. Specific examples of molds include, but are not limited to,
flat sheets with thickness ranging from about 1/8 inch to about 0.5
inch, round cylinders of varying heights and diameters, and small
conical parts molded to fit snugly into a pipette tip. Suitable
mold materials include, but are not limited to, metals and alloys
such as aluminum and stainless steel, high temperature
thermoplastics, and other materials both known in the art and
disclosed herein.
[0072] In a specific embodiment of the invention, a compression
mold is used to provide the sintered material. In this embodiment,
the mold is heated to the sintering temperature, allowed to
equilibrate, and then subjected to pressure. This pressure
typically ranges from about 1 psi to about 10 psi, depending on the
composition of the mixture being sintered and the desired porosity
of the final product. In general, the greater the pressure applied
to the mold, the smaller the average pore size and the greater the
mechanical strength of the final product. The duration of time
during which the pressure is applied also varies depending on the
desired porosity of the final product, and is typically from about
2 to about 10, more typically from about 4 to about 6 minutes. In
another embodiment of the invention, the thermoplastic particles
are sintered in a mold without the application of pressure.
[0073] Once the porous substrate has been formed, the mold is
allowed to cool. If pressure has been applied to the mold, the
cooling can occur while it is still being applied or after it has
been removed. The substrate is then removed from the mold and
optionally processed. Examples of optional processing include, but
are not limited to, sterilizing, cutting, milling, polishing,
encapsulating, coating, and combinations thereof.
[0074] The substrate is then coated and/or impregnated with at
least one surface treatment material, or a mixture comprising at
least one surface treatment material. Any method can be used in
this process, including spraying, dipping, immersing, and pouring.
But whatever the method, the surface treatment materials used in
this embodiment of the invention are preferably high molecular
weight fluorochemicals.
[0075] Although some surface treatment materials are liquid at
temperatures suitable for coating and/or impregnating the porous
substrate, many fluorochemicals typically are not. Consequently, it
may be preferred that a surface treatment material be dissolved in
a solvent to form a mixture, which is then contacted with the
substrate, after with the coated and/or impregnated substrate is
dried to provide a porous material of the invention. Any solvent in
which a surface treatment material is soluble can be used. Such
solvents are either known, or are easily determined using only
routine experimentation. For example, many low molecular weight
fluorochemicals are soluble in organic solvents such as, but not
limited to, alcohols, methylene chloride, acetone, and mixtures
thereof.
[0076] Although any of the fluorochemicals disclosed herein can be
used in this method, preferred fluorochemicals are high molecular
weight fluorochemicals. These compound, however, typically are not
soluble in conventional organic solvents. Many high molecular
weight fluorochemicals are, however, soluble in fluorinated
solvents. Thus, preferred solvents used in this embodiment of the
invention include, but are not limited to,
1,3-dichloro-1,1,2,2,3-pentafluoropropane,
1,1,1,2,3,4,4,5,5,5-decafluoro- pentane, and mixtures thereof.
Example of suitable commercially available fluorinated solvents
include, but are not limited to, that sold under the tradename
Vertvel.RTM. by DuPont Chemical Company, Wilmington, Del., and that
sold under the tradename ASAHIKLIN AK-225 by Asahi Glass
Fluoropolymers USA Inc., Chadds Ford, Pa.
4.3. Sintering Particles that Comprise a Surface Treatment
Material
[0077] In a second process of the invention, a surface treatment
material is incorporated into the porous thermoplastic substrate
during, rather than after, the sintering process. This process
provides several advantages. First, it can be used to locate
surface treatment material(s) within the porous material, and in
particular at places or depths within the material that may be
inaccessible using dipping or coating methods. Second, this process
can be used to ensure that the distribution of surface treatment
material(s) within the final material is uniform; e.g., that the
density of a surface treatment material is uniform throughout the
material. A third advantage of this process is that it can be used
to trap surface treatment materials within pores that have small
openings.
[0078] This process of the invention comprises the sintering of
thermoplastic particles which comprise at least one surface
treatment material (referred to herein as "thermoplastic surface
treatment particles" or "PST particles"), optionally with
thermoplastic particles that do not comprise surface treatment
and/or additional materials such as those described above in
Section 4.1.
[0079] In a first specific embodiment of this process, a
thermoplastic resin comprising at least one surface treatment
material is cryogenically ground and optionally screened and/or
thermal fined to provide particles which can be sintered as
described above in Section 4.2. In a specific embodiment of this
process, each of the PST particles is approximately the same size.
In another specific embodiment of this process, the PST particles
are substantially spherical.
[0080] If the PST particles are combined with particles of other
thermoplastics and/or other materials such as lubricants, colorants
and fillers, it is preferred that the combination be mixed to
ensure that the components are evenly distributed. The resulting
mixture is then sintered to provide a porous material that
uniformly hydrophobic and/or oleophobic.
[0081] Suitable sintering conditions are known in the art and
include, for example, those described above in Section 4.2.
However, because some surface treatment materials may decompose
under particular sintering conditions, those skilled in the art
will recognize that the thermoplastic, the sintering conditions,
and/or the surface treatment material will have to be selected to
provide a porous thermoplastic product of the invention that is
capable of repelling water and/or oils to a desired degree. For
example, a thermoplastic with a low MFI or sintering temperature
can be selected such that the sintering temperature will not cause
the decomposition of a desired surface treatment material.
Alternatively, a temperature-resistant surface treatment material
may be selected if the preferred thermoplastic sinters only at high
temperatures.
[0082] In a second specific embodiment of this process, PST
particles are formed by underwater pelletizing. These particles are
thus preferably made by heating and mixing at least one
thermoplastic, at least one surface treatment material, and any
optional materials, to provide a molten mixture which can be
extruded and formed into pellets according to the method described
in Section 4.2 above. In this method, preferred surface treatment
materials are low molecular weight fluorochemicals. Although
typically not necessary, the resulting PST particles can optionally
be screened and/or thermal fined.
[0083] An advantage of sintering PST particles formed by underwater
pelletizing is that the surface treatment materials they comprise
are typically located at or near the particles' exteriors. Without
being limited by theory, this is believed to be due to a phenomenon
known as "surface segregation," wherein a surface treatment
material combined with a molten thermoplastic moves to the surface
of the particles during or after their formation. Surface
segregation typically occurs when the molecular weight and/or the
surface energy of the surface treatment material is lower than that
of the thermoplastic.
[0084] Thus, materials formed by sintering PST particles which
comprise a thermoplastic and a low molecular weight fluorochemical
will typically contain significant amounts of surface treatment
material near or on the walls of the pores they contain, since
these pore walls are formed by the particles' surfaces.
Consequently, this method can be used to provide porous materials
that contain surface treatment material located where it will most
likely come into contact with liquids or vapors of water and/or
oil.
[0085] Because this process can be used to position surface
treatment materials within porous materials at locations where they
are most effective, it can be used to avoid the inefficient,
expensive, and potential overuse of surface treatment materials.
Thus, PST particles can be made by combining the necessary amount
of surface treatment material(s) with at least one thermoplastic
resin.
[0086] As discussed above, if PST particles are formed from a
mixture comprised of at least one thermoplastic and at least one
surface treatment material, it is important to select the
thermoplastic(s) and surface treatment material(s) to ensure that
at least a substantial portion of the surface treatment material(s)
will not decompose during the underwater pelletizing or sintering
processes. This is easily done, however, as the decomposition
temperatures of individual surface treatment materials are well
known or can readily be determined by conventional means. For
example, a surface treatment material can be heated to a specific
temperature (e.g., the temperature at which the thermoplastic
melts) and then allowed to cool, after which its hydrophobicity
and/or olephobicity can be measured.
[0087] The flexibility of the processes of this invention allow the
production of porous materials using innumerable thermoplastics and
surface treatment materials. This and other novel and unexpected
advantages of the invention are further illustrated by the
following non-limiting examples.
5. EXAMPLES
5.1. Example 1: Coating Sintered Porous Thermoplastics
[0088] FC-722, a 2 weight percent fluorochemical acrylate solution
in perfluorocarbon solvent, was adjusted to 0.5 weight percent with
HFE-7 100, a hydrofluoroether solvent. Both chemicals are available
from the Commercial Chemical Division of 3M Corporation. Two
sintered porous thermoplastic sheets (X-7937 and X-9619, available
from Porex Technologies, Fairburn, Ga.) having an average pore size
of about 35 .mu.m and 10 .mu.m, respectively, were submerged in the
fluorochemical acrylate solution for 10 seconds, taken out and
dried in a flowing air environment for another 30 minutes.
[0089] Various physical properties of the treated and untreated
porous materials are provided in the following tables.
1 Water Entry Air Flow Oil Water Pressure Rate Pore Size Repel-
Repel- Component (psi).sup.a (ml/min).sup.b (.mu.m) lency.sup.c
lency.sup.d Porex .RTM. X-7937 1.0 154.18 35 4 320 Porex .RTM.
X-7937 1.5 157.8 35 9 230 coated with 0.5% fluorochemical Porex
.RTM. X-7937 1.2 156.8 35 8 230 coated with 0.3% fluorochemical
Porex .RTM. X-9619 5.0 19.58 10 5 270 Porex .RTM. X-9619 7.5 18.0
10 10+ 210 coated with 0.5% fluorochemical Porex .RTM. X-9619 7.2
19.2 10 10+ 210 coated with 0.3% fluorochemcial .sup.aWater Entry
Pressure was measured according to ISO 811. .sup.bAir flow test was
measured under back pressure of 4.9 inches of water. Pore Size was
measured according to ASTM D4 197. .sup.cOil repellency was
determined by the "Kit Test" described as TAPPI Useful Method 557;
the higher the value the better the repellency. .sup.dWater
repellency test was determined by the "Cobb Test" described as
TAPPI-T44 1-05-77; the lower the value, the better the water
repellency.
5.2 Surface Treatment Using Surface Segregation
[0090] FX-1801, supplied in powder form from 3M Corp., was mixed
with Escorene HX-0358 (Exxon Chemical Company) to 0.5 weight
percent. The blend was mixed thoroughly through a dry blender.
[0091] After pre-blending, the blend was fed into a SLC-5 LPU
underwater pelletizer available from Gala Industries Inc.,
Winfield, W. Va. The extruder used had three thermal zones set to
150.degree. C., 165.degree. C., and 180.degree. C. The underwater
pelletizer was fit with a die with 0.020 inch holes drilled into
it. The blends were extruded through the die and into the cutter of
the underwater pelletizer, which was rotating at 90-100 rpm to
produce a material yield of approximately 15 lb/h of 0.0 inch
diameter pellets.
[0092] The collected underwater pelletized powder was dried in a
conventional oven at 80.degree. C. for 4 hours. After it was
completely dried, the powder was placed into a 0.25 inch flat mold,
which was then heated to 140.degree. C. using an electricity-heated
plate for 10 minutes. After heating, the mold was cooled and the
sintered porous thermoplastic material of the invention was removed
from it.
[0093] The embodiments of the invention described above are
intended to be merely exemplary, and those skilled in the art will
recognize, or will be able to ascertain using no more than routine
experimentation, numerous equivalents of the specific materials,
procedures, and devices described herein. All such equivalents are
considered to be within the scope of the invention and are
encompassed by the appended claims.
* * * * *