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
2002-05-02
2004-03-09
Wilson, D. R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S326400, C525S359300, C525S340000, C525S343000, C525S345000, C525S366000, C525S374000, C525S386000, C525S281000
Reexamination Certificate
active
06703450
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polyhydroxy curable fluoroelastomer compositions wherein the fluoroelastomer comprises copolymerized units of tetrafluoroethylene, propylene, and a cure site monomer selected from the group consisting of i) trifluoroethylene, ii) 3,3,3-trifluoropropene-1, iii) 1,2,3,3,3-pentafluoropropylene, iv) 1,1,3,3,3-pentafluoropropylene, and v) 2,3,3,3-tetrafluoropropene.
BACKGROUND OF THE INVENTION
Specialty fluoroelastomers made from copolymers of tetrafluoroethylene (TFE), propylene (P), and optionally vinylidene fluoride (VF
2
) (i.e. TFE/P dipolymers or VF
2
/TFE/P terpolymers) are often utilized in applications wherein resistance to alkaline fluids and other high pH chemicals is critical. The TFE/P dipolymers have the best resistance to alkaline fluids. Terpolymers containing more than about 10 wt. % vinylidene fluoride units generally do not have significantly better alkaline fluid resistance than do conventional fluoroelastomers made from copolymers of vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene.
In order to fully develop physical properties such as tensile strength, elongation, and compression set, elastomers must be cured, i.e. crosslinked. In the case of fluoroelastomers, this is generally accomplished by mixing uncured polymer (i.e. fluoroelastomer gum) with a polyfunctional curing agent and heating the resultant mixture under pressure, thereby promoting chemical reaction of the curing agent with active sites along the polymer backbone or side chains. Interchain linkages produced as a result of these chemical reactions cause formation of a crosslinked polymer composition having a three-dimensional network structure. Commonly used curing agents for fluoroelastomers include difunctional nucleophilic reactants, such as polyhydroxy compounds. Alternatively, peroxidic curing systems containing organic peroxides and unsaturated coagents, such as polyfunctional isocyanurates, may be employed.
In many cases, polyhydroxy and peroxide cure processes or curing agent formulations are unsatisfactory when used to crosslink these specialty fluoroelastomers. For example, it is known to cure elastomeric VF
2
/TFE/P terpolymers with either peroxide (U.S. Pat. No. 4,910,260) or polyhydroxy (U.S. Pat. Nos. 4,882,390 and 4,912,171) cure systems. However, when such compositions are cured using a polyhydroxy compound, the cured products may exhibit undesirably high compression set. In fact, such specialty fluoroelastomers which contain less than about 10 wt. % copolymerized units of vinylidene fluoride show little to no cure response with polyhydroxy cure formulations.
The peroxide cures disclosed in U.S. Pat. No. 4,910,260 are undesirable because the curable compositions which are initially formed are extremely scorchy and would therefore be unsuitable for many commercial processes.
It would be particularly desirable to have an improved specialty fluoroelastomer that is resistant to alkaline fluids and which readily crosslinks with polyhydroxy cure systems to form cured articles having good tensile properties and compression set resistance.
SUMMARY OF THE INVENTION
It has been surprisingly found that the incorporation of a cure site monomer selected from the group consisting of i) trifluoroethylene, ii) 3,3,3-trifluoropropene-1, iii) 1,2,3,3,3-pentafluoropropylene, iv) 1,1,3,3,3-pentafluoropropylene, and v) 2,3,3,3-tetrafluoropropene into TFE/P dipolymers or into VF
2
/TFE/P terpolymers improves the polyhydroxy curing of these specialty fluoroelastomers without significantly diminishing the resistance of these fluoroelastomers to alkaline fluids. The resulting cured fluoroelastomer articles have excellent compression set resistance and tensile properties.
Accordingly, an aspect of this invention is a curable fluoroelastomer composition comprising
A) a specialty fluoroelastomer comprising copolymerized units of 45 to 80 weight percent tetrafluoroethylene; 10 to 40 weight percent propylene; and 0.1 to 15 weight percent of a cure site monomer selected from the group consisting of i) trifluoroethylene, ii) 3,3,3-trifluoropropene-1, iii) 1,2,3,3,3-pentafluoropropylene, iv) 1,1,3,3,3-pentafluoropropylene, and v) 2,3,3,3-tetrafluoropropene;
B) 0.1 to 20 parts by weight per 100 parts fluoroelastomer of a polyhydroxy curing agent;
C) 1 to 30 parts by weight per 100 parts fluoroelastomer of an acid acceptor; and
D) 0.1 to 20 parts by weight per 100 parts fluoroelastomer of a vulcanization accelerator.
The polyhydroxy curing agent and vulcanization accelerator may be present as separate components or as the salt of the curing agent and accelerator.
Another aspect of the present invention is a specialty fluoroelastomer comprising copolymerized units of 45 to 80 weight percent tetrafluoroethylene; 10 to 40 weight percent propylene; and 0.1 to 15 weight percent of 3,3,3-trifluoropropene-1 cure site monomer.
DETAILED DESCRIPTION OF THE INVENTION
Specialty fluoroelastomers which may be employed in the curable compositions of this invention include the terpolymer of tetrafluoroethylene (TFE), propylene (P) and a cure site monomer selected from the group consisting of i) trifluoroethylene (TrFE), ii) 3,3,3-trifluoropropene-1 (TFP), iii) 1,2,3,3,3-pentafluoropropylene (1-HPFP) iv) 1,1,3,3,3-pentafluoropropylene (2-HPFP), and v) 2,3,3,3-tetrafluoropropene. Minor amounts (i.e. less than about 20 weight percent total) of other copolymerizable monomers may be present in higher order copolymer fluoroelastomers of this invention. Examples of such monomers include, but are not limited to chlorotrifluoroethylene, vinyl fluoride, perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers, perfluoro(alkoxyalkyl vinyl) ethers, perfluoroalkyl- or perfluoroalkoxy-alkenyl ethers (such as those disclosed in U.S. Pat. No. 5,891,965), ethylene, isobutene, and bromine- or iodine-containing cure site monomers such as CF
2
═CFOCF
2
CF
2
CF
2
OCF
2
CF
2
Br; 1-bromo-2,2-difluoroethylene; bromo-trifluoroethylene; 4-bromo-3,3,4,4-tetrafluorobutene-1; 4-bromo-1,1,2-trifluorobutene-1; 2-bromoperfluoro(ethyl vinyl) ether; 3-bromoperfluoro(propyl vinyl) ether; and 4-iodo-3,3,4,4-tetrafluorobutene-1. Alternatively, bromine or iodine cure sites may be introduced onto the fluoroelastomer polymer chain ends by use of iodinated or brominated chain transfer agents such as methylene iodide or 1, 4-diiodoperfluoro-butane during polymerization. The presence of brominated or iodinated groups permits the fluoroelastomers of this invention to be cured by organic peroxides in addition to polyhydroxy curatives.
Generally the specialty fluoroelastomers used in the compositions of this invention contain between 45 to 80 (preferably between 50 to 78, most preferably 65 to 78) weight percent copolymerized units of tetrafluoroethylene, based on the total weight of the fluoroelastomer. Less TFE causes the polymerization to be slow, while more TFE causes the resulting polymer to be plastic, rather than elastomeric.
The fluoroelastomers employed in the compositions of this invention typically contain between 10 to 40 (preferably between 12 to 30, most preferably 15 to 25) weight percent copolymerized units of propylene, based on the total weight of the fluoroelastomer. Less propylene causes the polymer to become plastic, while more propylene causes the polymerization to become slow.
The specialty fluoroelastomers used in the compositions of this invention also contain 0.1 to 15 (preferably 2 to 10, most preferably 3-6) weight percent copolymerized units of a cure site monomer, based on the total weight of the fluoroelastomer. The cure site monomer is selected from the group consisting of i) trifluoroethylene, ii) 3,3,3-trifluoropropene-1, iii) 1,2,3,3,3-pentafluoropropylene, iv) 1,1,3,3,3-pentafluoropropylene, and v) 2,3,3,3-tetrafluoropropene. The monomer 3,3,3-trifluoropropene-1 is especially preferred.
It is believed that during the polyhydroxy curing process, some copolymerized units of cure site monomer, which are located adjacent to tetrafluoroethylene units in the fluoroelastomer
Bauerle John Gordon
Schmiegel Walter Werner
DuPont Dow Elastomer L.L.C.
Wilson D. R.
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