Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-08-24
2002-12-24
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S546000, C524S369000, C524S385000, C524S389000, C524S538000, C524S198000, C525S539000
Reexamination Certificate
active
06498207
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a PTFE aqueous dispersion composition containing fine particles of polytetrafluoroethylene (hereinafter referred to as PTFE).
BACKGROUND ART
PTFE by an emulsion polymerization method is usually produced by injecting and polymerizing tetrafluoroethylene (hereinafter referred to as TFE) monomer under pressure while adding and stirring a peroxide type polymerization initiator, an anionic dispersant and a higher paraffin or the like as a polymerization stabilizer, to pure water. Usually, an aqueous dispersion will be obtained wherein fine particles of PTFE having an average particle size of from 0.1 to 0.5 &mgr;m are dispersed at a concentration of about 30 wt % or lower.
This aqueous dispersion is very unstable by itself, and it has been common that a nonionic surfactant such as a polyoxyethylene alkyl phenyl ether, e.g. Triton X 100, manufactured by Union Carbide having a molecular structure of C
8
H
17
C
6
H
4
O(C
2
H
4
O)
10
H, is added for primary stabilization, followed by concentration to a PTFE solid content of from 40 to 65 wt % by a known method such as an electrical concentration method or a phase separation method. Thereafter, in order to obtain a liquid physical property such as a viscosity suitable for various applications or stabilization during storage for a long period of time, water, an antiseptic such as ammonia, a surfactant, etc., are added to obtain an aqueous dispersion composition having a PTFE concentration of from 30 to 65 wt %.
However, there has been a problem that if a frictional action or a shearing action is exerted to the conventional PTFE aqueous dispersion composition, PTFE particles tend to be fibrous and agglomerate, whereby the uniformity of the dispersion tends to be impaired.
Specifically, when a PTFE aqueous dispersion composition is transported or circulated by a pump, if the operation time prolongs, agglomerates of PTFE are likely to be formed in the PTFE aqueous dispersion composition by a frictional action or a shearing action, whereby there has been a problem that the pump is likely to be clogged, the valve operation is likely to be impaired, or the filter is likely to be clogged.
Further, there has been a problem that when an excess PTFE aqueous dispersion composition coated on a substrate such as a glass fiber cloth or a metal foil, is to be removed by a doctor bar, agglomerates of PTFE formed by a frictional action, tend to deposit on the substrate, thus leading to drawbacks such as irregularity in thickness or foreign matters to deteriorate the yield of the product.
JP-B-53-6993 proposes a method of incorporating at least 1 wt % of an alkylene oxide polymer to PTFE for the purpose of preventing sedimentation of fine particles of PTFE, but discloses nothing about stability against the frictional action or the shearing action of the liquid. The polyethylene glycol having a relatively low molecular weight i.e. a molecular weight of from 1300 to 15000 disclosed in Examples of this specification was not one having an adequate effect for improving the frictional stability.
Further, a film prepared from a PTFE aqueous dispersion composition employing a conventional polyoxyethylene alkyl phenyl ether type surfactant, has had a problem that it is likely to be colored, and the electrical characteristic such as an insulating property tends to deteriorate.
JP-A-8-269285 discloses that a film prepared from an aqueous dispersion composition employing a polyoxyethylene alkyl ether type surfactant having a cloud point of from 48 to 85° C. and a content of ethylene oxide groups of from 65 to 70 wt %, such as RO(C
2
H
4
O)
n
H (wherein R is a C
8-18
linear alkyl group, and n is from 5 to 20), has coloration suppressed. However, this aqueous dispersion composition has the following problem. Namely, foams formed by stirring are hardly extinguishable, and if such foams will attach, traces of foams will bring about irregularities in the thickness of the PTFE film, and the strength, etc. of the film may deteriorate, thus leading to non-uniformity, and when the aqueous dispersion composition is subjected to multi-coating to prepare a thick film, the sintered PTFE surface has a low surface tension and is repelling, whereby multi-coating tends to be difficult.
DISCLOSURE OF THE INVENTION
The present invention has an object to improve a PTFE aqueous dispersion composition excellent in friction stability or shearing stability.
The present invention has an object to provide a PTFE aqueous dispersion composition whereby foams formed by stirring are readily extinguishable and multi-coating is possible, and a sintered PTFE film is free from coloration.
The present invention is a polytetrafluoroethylene aqueous dispersion composition, which comprises from 30 to 65 wt % of fine particles of polytetrafluoroethylene obtainable by emulsion polymerization, from 2 to 12 wt %, based on the polytetrafluoroethylene, of a nonionic surfactant, and at least 0.01 wt % and less than 1 wt %, based on the polytetrafluoroethylene, of at least one member selected from a polyethylene oxide having an average molecular weight of from 100,000 to 2,000,000 and an association type thickener based on a water-soluble polyurethane as essential components.
The present invention is the polytetrafluoroethylene aqueous dispersion composition, wherein the nonionic surfactant is at least one member selected from nonionic surfactants having molecular structures represented by the Formulae (1) and (2):
R—O—A—H (1)
(wherein R is an alkyl group having a straight chain or a branched chain represented by C
x
H
2x+1
where x=8 to 18, and A is a polyoxyalkylene chain constituted by from 5 to 20 oxyethylene groups and from 0 to 2 oxypropylene groups)
R′—C
6
H
4
—O—A′—H (2)
(wherein R′ is an alkyl group having a straight chain or a branched chain represented by C
x′
H
2x′+1
where x′=4 to 12, and A′ is a polyoxyethylene chain constituted by from 5 to 20 oxyethylene groups).
Further, the present invention is the PTFE aqueous dispersion composition, wherein the nonionic surfactant is a nonionic surfactant having a molecular structure represented by the Formula (1) wherein x is from 10 to 16, and A is a polyoxyalkylene chain constituted by from 7 to 12 oxyethylene groups and from 0 to 2 oxypropylene groups.
Further, the present invention is the PTFE aqueous dispersion composition, wherein the nonionic surfactant is a nonionic surfactant having a molecular structure represented by the Formula (2) wherein x′ is from 10 to 16, and A′ is a polyoxyalkylene chain constituted by from 7 to 12 oxyethylene groups.
The present invention is a polytetrafluoroethylene aqueous dispersion composition, which comprises from 30 to 65 wt % of fine particles of polytetrafluoroethylene obtainable by emulsion polymerization, and from 2 to 12 wt %, based on the polytetrafluoroethylene, of a nonionic surfactant having a molecular structure represented by the Formula (3):
R—O—B—H (3)
(wherein R is an alkyl group having a straight chain or a branched chain represented by C
x
H
2x+1
where x=8 to 18, and B is a polyoxyalkylene chain constituted by from 5 to 20 oxyethylene groups and from 1 to 2 oxypropylene groups).
Further, the present invention is the PTFE aqueous dispersion composition, wherein the nonionic surfactant is a nonionic surfactant having a molecular structure represented by the Formula (3) wherein x is from 10 to 16, and B is a polyoxyalkylene chain constituted by from 7 to 12 oxyethylene groups and from 1 to 2 oxypropylene groups.
BEST MODE FOR CARRYING OUT THE INVENTION
The fine particles of PTFE in the PTFE aqueous dispersion composition of the present invention are those obtainable by emulsion polymerization, and they can be produced by a conventional emulsion polymerization method.
The average particle size of the fine particles of PTFE is usually within a range of from 0.1 to 0.5 &mgr;m, particularly preferably within a range of from 0.15 to 0.3
Hoshikawa Jun
Kobayashi Shigeki
Asahi Glass Fluoropolymers Co. Ltd.
Lee Rip A
Wu David W.
LandOfFree
Aqueous polytetrafluoroethylene dispersion composition does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Aqueous polytetrafluoroethylene dispersion composition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aqueous polytetrafluoroethylene dispersion composition will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2995812