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
2003-12-16
Wilson, D. R. (Department: 1715)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S326300, C525S359300, C525S368000, C525S384000
Reexamination Certificate
active
06664339
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polyhydroxy curable fluoroelastomers comprising copolymerized units of 1) ethylene, 2) a perfluoro ether such as a perfluoro(alkyl vinyl ether) or a perfluoro(alkyl or alkoxy alkenyl ether), 3) tetrafluoroethylene, and 4) a cure site monomer selected from the group consisting of i) 3,3,3-trifluoropropene-1, ii) trifluoroethylene, 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
Base resistant specialty fluoroelastomers made from copolymers of ethylene (E), a perfluoro(alkyl vinyl ether) (PAVE), tetrafluoroethylene (TFE) and a cure site monomer are known in the art (U.S. Pat. No. 4,694,045). In addition to being resistant to attack by strong bases, these fluoroelastomers have good sealing properties at both low and high temperatures and exhibit low swell in oil.
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, 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 or diamines. Alternatively, peroxidic curing systems containing organic peroxides and unsaturated coagents, such as polyfunctional isocyanurates, may be employed.
U.S. Pat. No. 4,694,045 discloses several cure site monomers which may be incorporated into E/PAVE/TFE specialty fluoroelastomers. These include brominated or iodinated alpha-olefins, and various halogenated vinyl ethers. Such fluoroelastomers may be cured with peroxides or tin compounds, but not polyhydroxy curatives. However, in many end use applications, it would be beneficial to be able to cure E/PAVE/TFE fluoroelastomers with polyhydroxy compounds because of the improved mold release properties and superior resistance to compression set (i.e. lower compression set) that is imparted by this type of crosslinking system.
Thus, it would be particularly desirable to have an improved specialty E/PAVE/TFE fluoroelastomer that is resistant to alkaline fluids and oil swell 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 introduction of a cure site monomer selected from the group consisting of i) 3,3,3-trifluoropropene-1, ii) trifluoroethylene, iii) 1,2,3,3,3-pentafluoropropylene, iv) 1,1,3,3,3-pentafluoropropylene, and v) 2,3,3,3-tetrafluoropropene into ethylene/perfluoro ether/tetrafluoroethylene copolymers improves the polyhydroxy curing of these specialty fluoroelastomers without significantly diminishing the resistance of these fluoroelastomers to alkaline fluids or oil and without significantly altering the low and high temperature sealing capabilities of these fluoroelastomers. The resulting cured fluoroelastomer articles have excellent compression set resistance and tensile properties.
Accordingly, an aspect of the present invention is a specialty fluoroelastomer comprising copolymerized units of 10 to 40 mole percent ethylene; 20 to 40 mole percent of a perfluoro ether selected from the group consisting of perfluoro(alkyl vinyl ethers), perfluoro(alkyl alkenyl ethers) and perfluoro(alkoxy alkenyl ethers); 32-60 mole percent tetrafluoroethylene; and 0.1 to 15 mole percent of a cure site monomer selected from the group consisting of i) 3,3,3-trifluoropropene-1, ii) trifluoroethylene, iii) 1,2,3,3,3-pentafluoropropylene, iv) 1,1,3,3,3-pentafluoropropylene, and v) 2,3,3,3-tetrafluoropropene.
Another aspect of this invention is a curable fluoroelastomer composition comprising
A) a specialty fluoroelastomer comprising copolymerized units of 10 to 40 mole percent ethylene; 20 to 40 mole percent of a perfluoro ether selected from the group consisting of perfluoro(alkyl vinyl ethers), perfluoro(alkyl alkenyl ethers) and perfluoro(alkoxy alkenyl ethers); 32-60 mole percent tetrafluoroethylene; and 0.1 to 15 mole percent of a cure site monomer selected from the group consisting of i) 3,3,3-trifluoropropene-1, ii) trifluoroethylene, 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 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.
DETAILED DESCRIPTION OF THE INVENTION
Fluoroelastomers of this invention comprise copolymerized units of 1) ethylene (E), 2) a perfluoro ether selected from the group consisting of perfluoro(alkyl vinyl ethers) (PAVE), perfluoro(alkyl alkenyl ethers) and perfluoro(alkoxy alkenyl ethers), 3) tetrafluoroethylene (TFE), and 4) a cure site monomer selected from the group consisting of i) 3,3,3-trifluoropropene-1 (TFP), ii) trifluoroethylene (TrFE), 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 mole percent total) of other copolymerizable monomers may also be present in the fluoroelastomers of this invention. Examples of such monomers include, but are not limited to chlorotrifluoroethylene; vinyl fluoride; propylene; 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; bromotrifluoroethylene; 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 optionally 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 fluoroelastomers of this invention contain between 10 to 40 (preferably between 20 to 40) mole percent copolymerized units of ethylene, based on the total moles of copolymerized monomers. Less ethylene adversely effects the low temperature sealing performance of the fluoroelastomers, while more ethylene adversely effects the base resistance and oil swell resistance properties of the fluoroelastomers.
The fluoroelastomers of this invention typically contain between 20 to 40 (preferably between 20 to 30) mole percent copolymerized units of a perfluoro ether selected from the group consisting of perfluoro(alkyl vinyl ethers), perfluoro(alkyl alkenyl ethers) and perfluoro(alkoxy alkenyl ethers), based on the total moles of copolymerized monomers. Less perfluoro ether will negatively impact the low temperature sealing performance of the fluoroelastomers of the invention, while more perfluoro ether causes the polymer to be more expensive to produce.
Perfluoro(alkyl vinyl ethers) suitable for use as monomers 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 perfluo
Schmiegel Walter Werner
Tang Phan Linh
DuPont Dow Elastomers LLC
Wilson D. R.
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