Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-12-03
2004-07-13
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S094000, C525S121000, C525S144000, C525S199000, C525S276000, C525S280000, C524S495000, C524S496000
Reexamination Certificate
active
06762245
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a fluoropolymer-based conductive composition. Fluoropolymers such as, for example, PVDF (polyvinylidene fluoride) are known for their resistance to numerous products and are thus used in applications in which they are in contact with chemically corrosive fluids such as solvents, motor fuels, acids and bases. Thus, plates, components, yarns, tubes, connectors, containers and coatings for distillation columns or for pumps which may be in contact with or immersed in these fluids are prepared. Since the circulation of certain fluids on contact with these fluoropolymer components can generate electrostatic charges, other components must be grounded, and it is thus necessary to make these components electrically conductive.
THE TECHNICAL PROBLEM
The friction of a solvent on a component made of PVDF may generate electrostatic charges, an accumulation of which may lead to an electric discharge (spark) capable of igniting the solvent, with catastrophic consequences (explosion). Thus, it is necessary to make these components conductive.
It is known practice to lower the surface resistivity of polymer materials or resins by incorporating conductive materials and/or semiconductors such as carbon black, steel fibres, carbon fibres and particles (fibres, plates, spheres) metallized with gold, silver or nickel. Among these materials, carbon black is most particularly used, for economic reasons and for its ease of use. Besides its particular electrical conductivity properties, carbon black behaves like a filler such as, for example, talc, chalk or kaolin. Thus, a person skilled in the art knows that when the content of fillers increases, the viscosity of the polymer/filler mixture increases. Similarly, when the content of filler increases, the flexural modulus of the filler-containing polymer increases and its impact strength decreases. These known and predictable phenomena are discussed in detail in “Handbook of Fillers and Reinforcements for Plastics” edited by H. S. Katz and J. V. Milewski—Van Nostrand Reinhold Company—ISBN 0-442-25372-9, see in particular chapter 2, section II for fillers in general and chapter 16, section VI for carbon black in particular.
As regards the electrical properties of carbon black, the technical report “Ketjenblack EC—BLACK 94/01” from the company AKZO NOBEL mentions that the resistivity of the formulation falls very abruptly when a critical content of carbon black, known as the percolation threshold, is reached. When the content of carbon black increases further, the resistivity decreases rapidly, until it reaches a stable level (plateau region). For a given resin, therefore, it is preferred to operate in the plateau region, in which an error in metering will only slightly affect the resistivity of the compound.
PVDF has fragile multiaxial impact behaviour. The addition of an agent to make it electrically conductive, such as a carbon black, makes it even more fragile. Various ways of improving the impact strength properties usually involve the incorporation of soft elastomeric phases which can present morphologies of “core-shell” types in a PVDF matrix. The major drawback of such a combination is a large decrease in chemical resistance.
The aim of the present invention is to obtain a fluoropolymer-based composition containing an agent to make it electrically conductive while at the same time substantially conserving the chemical resistance and also conserving a high modulus, and preferably having an impact strength at least equivalent to that of the PVDF matrix alone, and which may be used easily.
International patent application WO 99/29772 discloses the reinforcement of PVDF with a poly(styrene)-poly(butadiene)-poly (methyl methacrylate) triblock copolymer. The PVDF thus modified conserves its chemical resistance properties. Nothing is stated regarding the incorporation of carbon black to make this PVDF conductive.
It has now been found that by adding a triblock copolymer such as poly(styrene)-poly(butadiene)-poly(methyl methacrylate) and an electrically conductive product into a fluoropolymer, a conductive polymer is obtained which conserves the chemical resistance of the fluoropolymer, has a high modulus and very good impact strength, and may be used easily.
SUMMARY OF THE INVENTION
The present invention relates to a conductive composition comprising (i) a fluoropolymer, (ii) an electrically conductive product and (iii) a triblock copolymer ABC, the three blocks A, B and C being linked together in this order, each block being either a homopolymer or a copolymer obtained from two or more monomers, block A being linked to block B and block B to block C by means of a covalent bond or an intermediate molecule linked to one of these blocks via a covalent bond and to the other block via another covalent bond, and such that:
block A is compatible with the fluoropolymer,
block B is incompatible with the fluoropolymer and is incompatible with block A,
block C is incompatible with the fluoropolymer, block A and block B.
The invention also relates to the components manufactured with the above composition. These components may be—plates, films, tubes, rods, centrifugal pump components and containers.
As regards the fluoropolymer, this term thus denotes any polymer containing in its chain at least one monomer chosen from compounds containing a vinyl group capable of opening to polymerize and which contains, directly attached to this vinyl group, at least one fluorine atom, a fluoroalkyl group or a fluoroalkoxy group.
Examples of monomers which may be mentioned include vinyl fluoride; vinylidene fluoride (VF2); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers such as perfluoro(methyl vinyl)ether (PMVE), perfluoro(ethyl vinyl)ether (PEVE) and perfluoro(propyl vinyl)ether (PPVE); perfluoro(1,3-dioxole); perfluoro(2,2-dimethyl-1,3-dioxole) (PDD); the product of formula CF
2
═CFOCF
2
CF(CF
3
) OCF
2
CF
2
X in which X is SO
2
F, CO
2
H, CH
2OH, CH
2
OCN or CH
2
OPO
3
H; the product of formula CF
2
═CFOCF
2
CF
2
SO
2
F; the product of formula F(CF
2
)nCH
2
OCF═CF
2
in which n is 1, 2, 3, 4 or 5; the product of formula R,CH
2
OCF═CF
2
in which R
1
is hydrogen or F(CF
2
)z and z is 1, 2, 3 or 4; the product of formula R
3
OCF═CH
2
in which R
3
is F(CF
2
)z- and z is 1, 2, 3 or 4; perfluorobutylethylene (PFBE); 3,3,3-trifluoropropene and 2-trifluoromethyl-3,3,3-trifluoro-1-propene.
The fluoropolymer may be a homopolymer or a copolymer, and may also comprise non-fluoro monomers such as ethylene.
The fluoropolymer is advantageously chosen from:
vinylidene fluoride (VF2) homopolymers and copolymers preferably containing at least 50% by weight of VF2, the comonomer being chosen from chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF3) and tetrafluoroethylene (TFE),
trifluoroethylene (VF3) homopolymers and copolymers,
copolymers, and in particular terpolymers, combining residues of chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP) and/or ethylene units and optionally VF2 and/or VF3 units.
The fluoropolymer is preferably poly(vinylidene fluoride) (PVDF) homopolymer. Advantageously, the PVDF has a viscosity ranging from 100 Pa·s to 2000 Pa·s, the viscosity being measured at 230° C., at a shear rate of 100 s
−1
, using a capillary rheometer. Specifically, these PVDFs are particularly suitable for extrusion and injection. The PVDF preferably has a viscosity ranging from 300 Pa·s to 1200 Pa·s, the viscosity being measured at 230° C., at a shear rate of 100 s
−1
using a capillary rheometer.
Thus, the PVDFs sold under the brand name Kynar® 710 or 720 are entirely suitable for this formulation.
As regards the electrically conductive product, these are all conductors of electricity. Examples which may be mentioned include metals and carbon-based products. Examples of carbon-based products which may be mentioned includ
Bonnet Anthony
Court Francois
Leibler Ludwik
Asinovsky Olga
ATOFINA
Millen White Zelano & Branigan P.C.
Seidleck James J.
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