Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-09-20
2002-08-06
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C525S248000, C525S250000, C525S264000, C526S247000, C526S253000
Reexamination Certificate
active
06429271
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to fluoroelastomers that are capable of being crosslinked with polyhydroxy compounds to produce cured compositions having excellent processability and low temperature properties.
BACKGROUND OF THE INVENTION
Elastomeric fluoropolymers (i.e. fluoroelastomers) exhibit excellent resistance to the effects of heat, weather, oil, solvents and chemicals. Such materials are commercially available and are most commonly either dipolymers of vinylidene fluoride (VF
2
) with hexafluoropropylene (HFP) or terpolymers of VF
2
, HFP, and tetrafluoroethylene (TFE). While these di- and terpolymers have many desirable properties, including low compression set and excellent processability, their low temperature flexibility is not adequate for all applications.
It is known that incorporation of perfluorinated ether monomer units into vinylidene fluoride elastomers improves low temperature properties. For example, Carlson, in U.S. Pat. No. 5,214,106 discloses that when perfluoro(methyl vinyl) ether (PMVE) is substituted for HFP, the resultant VF
2
/PMVE/TFE copolymers have glass transition temperature (T
g
) values which are 10°-20° C. lower than those of the corresponding VF
2
/HFP/TFE copolymers. T
g
is often used as an indicator of low temperature flexibility because polymers having low glass transition temperatures maintain elastomeric properties at low temperatures.
Kruger, in U.S. Pat. No. 5,696,216, discloses PMVE-containing fluoroelastomers that are similar to those disclosed by Carlson. Those disclosed by Kruger contain copolymerized units of VF
2
; at least one fluorinated propene and or fluorinated methyl vinyl ether; TFE; at least one perfluoro(polyoxyalkyl vinyl) ether, and a crosslinking site.
The compositions of Carlson and Kruger are most effectively crosslinked through use of peroxide cure systems. However, when compression molding equipment is used with peroxide curable VF
2
/PMVE copolymers the compositions generally exhibit a tendency to stick to and foul the mold.
Tetrapolymers of VF
2
, HFP, TFE and perfluoro(alkyl vinyl) ethers (PAVE) other than PMVE are also known to exhibit improved low temperature properties compared to terpolymers of VF
2
, HFP and TFE. For example, Arcella, et al. in U.S. Pat. No. 5,260,393 disclose a tetrapolymer comprising copolymerized units of 48-65 wt. % VF
2
, 21-36 wt. % HFP, 3-9 wt. % PAVE, and 0-17 wt. % TFE. The compositions can be cured using a bisphenol curing system and do not exhibit the mold fouling problems associated with peroxide cures of VF
2
/PMVE copolymers. Similarly, British Patent 1,296,084 discloses fluoroelastomeric tetrapolymers containing copolymerized units of 48-65 wt. % VF
2
, 8-23 wt. % HFP, 4-15 wt. % TFE, and 17-30 wt. % PAVE. Such compositions have good low temperature properties and are curable with bisphenols or amines. Although these tetrapolymers exhibit good low temperature properties, many applications require improved low temperature and processability performance.
Merely raising the PAVE content while lowering the HFP content is not a solution to the problem of improving low temperature performance of VF
2
/HFP/PAVE/TFE terpolymers. This is because polymers wherein the level of HFP is below about 8-10 mole percent do not contain sufficient copolymerized monomer sequences consisting of HFP units flanked by VF
2
units to permit efficient crosslinking with bisphenols. As is well known in the art, efficient curing of VF
2
/HFP-containing fluoroelastomers with a bisphenol/accelerator system is possible only when a —CH
2
— group in the polymer backbone is flanked by two perfluorinated carbons (e.g. CF
2
CF(CF
3
)CH
2
CF
2
CF
2
), rendering the hydrogens acidic enough to be abstracted by base. The dehydrofluorinated polymers are easily crosslinked by bisphenols. Furthermore, as discussed by W. W. Schmiegel, in
Angewandte Makromolekylare Chemie,
76/77, 39 (1979), completely eliminating HFP to form VF
2
/TFE/PMVE terpolymers results in formation of monomer sequences consisting of TFE/VF
2
/TFE; TFE/VF
2
/PMVE; PMVE/VF
2
/PMVE; and PMVE/VF
2
/TFE. Although such sites readily undergo elimination of HF or HOCF
3
in the presence of base, the double bonds thus formed are not easily crosslinked by bisphenols or any other traditional crosslinking agents.
There thus exists an unfulfilled need in the art for a method of providing copolymers of VF
2
, TFE, and PAVE that maintain optimum low temperature properties, but which exhibit low mold sticking characteristics, improved processability and are easily curable.
SUMMARY OF THE INVENTION
The present invention is directed to a fluoroelastomer consisting essentially of copolymerized units of 23-65 weight percent vinylidene fluoride, 25-75 weight percent perfluoro(alkyl vinyl) ether, 0-30 weight percent tetrafluoroethylene, and 0.3-5 weight percent 2-hydropentafluoropropene.
In addition, the invention is directed to a curable composition comprising
A. a fluoroelastomer consisting essentially of copolymerized units of 23-65 weight percent vinylidene fluoride, 25-75 weight percent perfluoro(alkyl vinyl) ether, 0-30 weight percent tetrafluoroethylene, and 0.3-5 weight percent 2-hydropentafluoropropene;
B. a polyhydroxy crosslinking agent;
C. a cure accelerator; and
D. a metal oxide or metal hydroxide.
A preferred embodiment of the curable compositions of the invention additionally comprises a modified silane coated mineral filler.
A further preferred embodiment of the curable compositions of the invention additionally comprises a molecular sieve.
DETAILED DESCRIPTION OF THE INVENTION
The polymers of the present invention include both uncured (raw) and cured fluorinated copolymers. The copolymers are capable of undergoing crosslinking reactions with polyhydroxylic compounds to form elastomeric compositions that exhibit unusually good low temperature properties.
The polymer backbones of the copolymers consist essentially of copolymerized units of VF
2
, PAVE, 2-hydropentafluoropropene (i.e. 1,1,3,3,3-pentafluoropropene), referred to herein as HPFP, and, optionally, TFE. That is, each of the first three monomers (and optionally TFE) must be present in the polymer chain, but higher order polymers, i.e. those containing other additional monomer units, the addition of which does not affect the basic and novel characteristics of the polymer, are also within the scope of the present invention. For example, the tetrapolymer VF
2
/PAVE/TFE/HPFP can contain other copolymerized vinyl or olefin monomers such as vinyl fluoride, trifluoroethylene, trifluoropropene, chlorotrifluoroethylene, alkyl vinyl ether, vinyl acetate, vinyl chloride, ethylene, and propylene, generally in quantities of up to about 5 wt. %. In addition, the fluoroelastomer copolymers of this invention may contain up to about 1 wt. % iodine bound to polymer chain ends, the iodine being introduced via use of an iodine-containing chain transfer agent during polymerization.
The fluoroelastomers of the invention contain between 23-65 wt. % copolymerized vinylidene fluoride units, preferably between 33-55 wt. % of such units. If less than 23 wt. % vinylidene fluoride units are present, the polymerization rate is very slow. In addition, good low temperature flexibility cannot be achieved. Vinylidene fluoride levels above 65 wt. % result in polymers that contain crystalline domains and are characterized by poor low temperature compression set resistance and reduced fluids resistance.
Perfluoro(alkyl vinyl) ethers (PAVE) suitable for use as comonomers include those of the formula
CF
2
═CFO(R
f′
O)
n
(R
f″
O)
m
R
f
(I)
where R
f′
and R
f″
are different linear or branched perfluoroalkylene groups of 2-6 carbon atoms, m and n are independently 0-10, and R
f
is a perfluoroalkyl group of 1-6 carbon atoms.
A preferred class of perfluoro(alkyl vinyl) ethers includes compositions of the formula
CF
2
═CFO(CF
2
CFXO)
n
R
f
(II)
where X is F or CF
3
, n is 0-5, and R
f
is a perfluoroalkyl group of 1-6 carbon atoms.
A most preferred class
DuPont Dow Elastomers L.L.C.
Pezzuto Helen L.
LandOfFree
Fluoroelastomer composition having excellent processability... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fluoroelastomer composition having excellent processability..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fluoroelastomer composition having excellent processability... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2911902