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
1999-05-14
2001-02-20
Niland, Patrick D. (Department: 1714)
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...
C524S492000, C524S493000, C524S544000
Reexamination Certificate
active
06191208
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to perfluoroelastomer compositions having a reduced tendency to generate hydrogen fluoride on heating.
BACKGROUND OF THE INVENTION
Perfluoroelastomers have achieved outstanding commercial success and are used in a wide variety of applications in which severe environments are encountered, in particular those end uses where exposure to high temperatures and aggressive chemicals occurs. These polymers are often used in seals for aircraft engines, in oil-well drilling devices, and in sealing elements for industrial equipment used at high temperatures.
Sealing components used in equipment for manufacture of electronic components, for example semi-conductor devices, must meet unusually stringent property requirements. Specifically, the seals are often exposed to reactive plasmas, corrosive cleaning gases and high temperatures, often up to about 300° C., that cause rapid deterioration of physical properties. In addition, polymer degradation can occur under the high temperature conditions encountered, leading to production of hydrogen fluoride (HF) which is a highly corrosive compound. A particular problem associated with HF is that its presence causes corrosion of any steel and quartz materials present in the semi-conductor manufacturing equipment.
Although conventional perfluoroelastomers are satisfactory for most uses, it would be desirable to have available a more resistant perfluoroelastomer composition. That is, an unmet need exists for perfluoroelastomer compositions that will function satisfactorily in the unusual and demanding process conditions found in electronics manufacturing, and, in addition will evolve only minimal amounts of HF when heated at temperatures of about 300° C.
SUMMARY OF THE INVENTION
The present invention is directed to a curable perfluoroelastomer composition that has a reduced tendency to generate HF on heating to high temperatures. More specifically, the present invention is directed to a curable composition comprising
A. a perfluoroelastomer comprising copolymerized units of (1) tetrafluoroethylene, (2) a perfluorovinyl ether selected from the group consisting of perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers, and mixtures thereof, and (3) a cure site monomer selected from the group consisting of nitrile-containing fluorinated olefins and nitrile-containing fluorinated vinyl ethers;
B. 1-25 parts per hundred parts perfluoroelastomer of an anhydrous silica; and
C. a curative for the perfluoroelastomer.
In a preferred embodiment of the invention the curative comprises diaminobisphenol AF. Such compositions exhibit accelerated cure response.
DETAILED DESCRIPTION OF THE INVENTION
The compositions of the present invention are based on elastomeric perfluoropolymers (hereinafter “perfluoroelastomers”), that is, substantially fully fluorinated fluoropolymers which, when cured, exhibit an elastomeric character. The perfluoroelastomers contain nitrile groups which render the polymers crosslinkable.
Perfluoroelastomers are polymeric compositions having copolymerized units of at least two principal perfluorinated monomers. Generally, one of the principal comonomers is a perfluoroolefin, while the other is a perfluorovinyl ether. Representative perfluorinated olefins include tetrafluoroethylene and hexafluoropropylene. Suitable perfluorinated vinyl ethers are 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 of perfluoro(alkyl vinyl) ethers includes those ethers wherein n is 0 or 1 and R
f
contains 1-3 carbon atoms. Examples of such perfluorinated ethers include perfluoro(methyl vinyl) ether and perfluoro(propyl vinyl) ether. Other useful monomers include compounds of the formula
CF
2
═CFO[(CF
2
)
m
CF
2
CFZO]
n
R
f
(III)
where R
f
is a perfluoroalkyl group having 1-6 carbon atoms,
m=0 or 1, n=0-5, and Z=F or CF
3
.
Preferred members of this class are those in which R
f
is C
3
F
7
, m=0, and n=1.
Additional perfluoro(alkyl vinyl) ether monomers include compounds of the formula
CF
2
═CFO[(CF
2
CFCF
3
O)
n
(CF
2
CF
2
CF
2
O)
m
(CF
2
)
p
]C
x
F
2x+1
(IV)
where m and n=1-10, p=0-3, and x=1-5.
Preferred members of this class include compounds where n=0-1, m=0-1, and x=1.
Examples of useful perfluoro(alkoxy vinyl) ethers include
CF
2
═CFOCF
2
CF(CF
3
)O(CF
2
O)
m
C
n
F
2n+1
(V)
where n=1-5, m=1-3, and where, preferably, n=1.
Mixtures of perfluoro(alkyl vinyl) ethers and perfluoro(alkoxy vinyl) ethers may also be used.
Preferred perfluoroelastomers are composed of tetrafluoroethylene and at least one perfluoro(alkyl vinyl) ether as principal monomer units. In such copolymers, the copolymerized perfluorinated ether units constitute from about 15-50 mole percent of total monomer units in the polymer.
The perfluoropolymer further contains copolymerized units of at least one cure site monomer, generally in amounts of from 0. 1-5 mole percent. The range is preferably between 0.3-1.5 mole percent. Although more than one type of cure site monomer may be present, most commonly one cure site monomer is used and it contains at least one nitrile substituent group. Suitable cure site monomers include nitrile-containing fluorinated olefins and nitrile-containing fluorinated vinyl ethers. Useful nitrile-containing cure site monomers include those of the formulas shown below.
CF
2
═CF—O(CF
2
)
n
—CN (VI)
where n=2-12, preferably 2-6;
CF
2
═CF—O[CF
2
—CFCF
3
—O]
n
—CF
2
—CFCF
3
—CN (VII)
where n=0-4, preferably 0-2;
CF
2
═CF—[OCF
2
CF(CF
3
)]
x
—O—(CF
2
)
n
—CN (VIII)
where x=1-2, and n=1-4; and
CF
2
═CF—O—(CF
2
)
n
—O—CF(CF
3
)CN (IX)
where n=2-4.
Those of formula (VIII) are preferred. Especially preferred cure site monomers are perfluorinated polyethers having a nitrile group and a trifluorovinyl ether group. A most preferred cure site monomer is
CF
2
═CFOCF
2
CF(CF
3
)OCF
2
CF
2
CN (X)
i.e. perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene) or 8-CNVE.
The second component of the curable compositions of the invention is an anhydrous silica (generally an acidic silica having a pH less than 7, preferably a pH of 4-5, or fumed silica). Such silicas are available from Degussa Aktiengesellschaft (Frankfurt, Germany) under the Aerosil® trademark. A particularly useful type is Aerosil® 200 silica. Other suitable silicas include Reolosil® silicas, available from Tokuyama KK (Tokyo, Japan), for example Reolosil® QS13, Reolosil® QS102, and Reolosil® QS30. Amounts of 1-25 parts per hundred parts perfluoroelastomer (phr) are effective to reduce HF generation. However, it is preferable to use no more than 1-7 phr because at higher concentrations of silica the compression set resistance of cured perfluoroelastomer seals deteriorates (i.e. increases). If less than 1 phr anhydrous silica is used, the degree of corrosion becomes unacceptable for many applications.
The third component of the curable compositions of the invention is a compound which is capable of crosslinking the perfluoroelastomer, for example an organotin compound or certain amino group-containing benzene compounds. Suitable organotin compounds include allyl-, propargyl-, triphenyl- and allenyl tin curatives. Tetraalkyltin compounds or tetraaryltin compounds are the preferred curing agents for use in conjunction with nitrile-substituted cure sites. The amount of curing agent employed will necessarily depend on t
Dupont Dow Elastomers L.L.S.
Niland Patrick D.
LandOfFree
Thermally stable perfluoroelastomer 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 Thermally stable perfluoroelastomer composition, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermally stable perfluoroelastomer composition will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2582817