Fluororubber compositions

Details Fluororubber compositions Fluororubber compositions

2000-12-06

2003-06-10

Harlan, Robert D. (Department: 1713)

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...

C524S544000, C524S588000

Reexamination Certificate

active

06576701

ABSTRACT:

This invention relates to fluororubber compositions which can be readily loaded with fillers and effectively roll milled and cure into products having excellent heat resistance as well as satisfactory solvent resistance, chemical resistance, low-temperature properties and mechanical strength.
BACKGROUND OF THE INVENTION
Prior art vinylidene fluoride base fluororubbers are used in a variety of applications mainly in the automobile and mechanical industries since they produce elastomers having good heat resistance and mechanical strength.
These fluororubbers, however, are not satisfactory in chemical resistance. They are readily swollen in polar solvents such as ketone, lower alcohol, carbonyl and organic acid solvents. They are deteriorated by amine-containing chemicals so that their rubber strength and elongation may substantially decline. With respect to low-temperature properties, the fluororubbers lose rubber elasticity at temperatures below −20° C. to such an extent that they cannot be used as sealants. This generally imposes a limit on the use of fluororubbers in cold areas.
In order to eliminate these drawbacks, curable fluorine-containing compositions comprising a perfluoro compound and a fluorinated organohydrogenpolysiloxane as main components were proposed. These compositions, however, are liquid because they are based on liquid perfluoro compounds having a low degree of polymerization. Then the compositions are suitable in the FIPG process and LIMS molding, but less effective in compression molding conventionally employed for rubber molding.
In particular, the curable fluorine-containing compositions often prohibit the use of conventional two-plate molds for rubber because of the difficulty of molding and the frequent occurrence of defects by air entrainment. Steady production is difficult unless a special LIMS mold is newly fabricated. The LIMS mold, however, has the problems that it is generally more expensive than the conventional two-plate molds for rubber, the mounting of the mold in a LIMS molding machine is cumbersome, and the molding machine requires time-consuming adjustment after mold mounting. The LIMS mold does not lend itself to the manufacture of a variety of parts in small quantities.
Under the circumstances, we previously proposed in U.S. Ser. No. 09/336,716 a method for preparing a rubber composition of the type that can be roll milled and molded in a compression molding rubber mold, referred to as millable type composition, from a fluorinated curable composition comprising a perfluoro compound, a fluorinated organohydropolysiloxane, a filler and a surface treating agent.
This composition has a good profile of properties including roll working, heat resistance, solvent resistance, chemical resistance, low-temperature properties and mechanical strength. However, the composition was found to be still short in the long-term heat resistance at high temperature as required in the application in a hot environment such as a sealant used in proximity to the automobile engine
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to provide a fluororubber composition of the millable type which can be effectively roll milled and cure into products having outstanding heat resistance as well as satisfactory solvent resistance, chemical resistance, low-temperature properties and mechanical strength.
The invention provides a crosslinkable fluororubber composition comprising
(A) 100 parts by weight of a perfluoro compound having at least two alkenyl groups in the molecule and a divalent perfluoroalkylene or divalent perfluoropolyether structure in the backbone or a polymer obtained by adding a compound having at least two hydrosilyl groups in the molecule and capable of addition reaction with alkenyl groups to some alkenyl groups on said perfluoro compound,
(B) 1 to 100 parts by weight of a reinforcing filler,
(C) a sufficient amount to induce reaction of the alkenyl groups in component (A) of a crosslinking agent having a hydrosilyl group in the molecule and capable of addition reaction or a peroxide crosslinking agent,
(D) 0.01 to 30 parts by weight of a surface treating agent having at least one fluoroalkyl or fluoropolyalkyl ether group and silanol groups in the molecule, and
(E) 0.01 to 10 parts by weight of at least one heat resistance modifier selected from carbon black, metal oxides and metal hydroxides.
We have found that the above formulation achieves a significant improvement in heat resistance over a long term and an improvement in roll milling operation.
DETAILED DESCRIPTION OF THE INVENTION
Component (A)
Component (A) of the crosslinkable fluororubber composition is (I) a perfluoro compound having at least two alkenyl groups in the molecule and a divalent perfluoroalkylene or divalent perfluoropolyether structure in the backbone or a polymer obtained by adding (II) a compound having at least two hydrosilyl groups in the molecule and capable of addition reaction with alkenyl groups to some alkenyl groups on the perfluoro compound (I).
The perfluoro compound as component (I) is technically difficult to synthesize into a high molecular weight polymer as typified by a resin or rubber. The perfluoro compound should have at least two alkenyl groups in the molecule and a divalent perfluoroalkylene or divalent perfluoropolyether structure in the backbone. It is preferably a linear perfluoro compound having a viscosity of about 25 to about 1,000,000 centistokes at 25° C.
The perfluoro compound is typically of the following general formula (1).
CH
2
═CH—(X)
p
—(Rf-Q)
a
-Rf-(X)
p
—CH═CH
2
  (1)
Herein, X is independently —CH
2
—, —CH
2
O—, —CH
2
OCH
2
—, —Y—NR
1
—SO
2
— or —Y—NR
1
—CO—wherein Y is —CH
2
— or —Si(CH
3
)
2
—Ph—,
and R
1
is hydrogen or a substituted or unsubstituted monovalent hydrocarbon group. Rf is a divalent perfluoroalkylene group or divalent perfluoropolyether group. Letter p is independently equal to 0 or 1, and
a
is an integer inclusive of 0.
Q is a group of the following general formula (2), (3) or (4).
X, p, and R
1
are as defined above; R
3
is a substituted or unsubstituted divalent hydrocarbon group; and R
4
is a substituted or unsubstituted divalent hydrocarbon group which may be separated by at least one intervening atom selected from oxygen, nitrogen, silicon and sulfur atoms, or a group of the following general formula (5) or (6).
R
5
is a substituted or unsubstituted monovalent hydrocarbon group and R
6
is a group containing in its backbone structure at least one atom selected from carbon, oxygen, nitrogen, silicon and sulfur atoms.
Specifically, Rf is a divalent perfluoroalkylene group or divalent perfluoropolyether group. The divalent perfluoroalkylene group is preferably represented by the formula: —C
m
F
2m
— wherein m is from 1 to 10, preferably 2 to 6. The divalent perfluoropolyether group is preferably represented by the formula:
wherein X is F or CF
3
, p, q and r are integers satisfying p≧1, q≧1,2≧p+q≦200, especially 2≦p+q≦110, and 0≦r≦6,
wherein r, s and t are integers satisfying 0≦r≦6, s≧0, t≧0, 0≦s+t≦200, especially 2≦s+t≦110,
wherein X is F or CF
3
, u is an integer of 1 to 100 and v is an integer of 1 to 50, or
—CF
2
CF
2
&Parenopenst;OCF
2
CF
2
CF
2
&Parenclosest;
W
OCF
2
CF
2
—
wherein w is an integer of 1 to 100.
Illustrative examples of Rf are given below.
Q is a group of the following general formula (2), (3) or (4).
R
1
is hydrogen or a substituted or unsubstituted monovalent hydrocarbon group. The substituted or unsubstituted monovalent hydrocarbon groups are preferably those of 1 to 12 carbon atoms, for example, alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, octyl, nonyl and decyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl; aryl groups such as phenyl, tolyl, xylyl and naphthyl; aralkyl groups such as benzyl, phenylethyl and phenylpropyl; and substituted ones of these groups in which some or al

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