U.S. patent application number 09/727793 was filed with the patent office on 2001-04-19 for fluoroelastomer composition having excellent processability and low temperature properties.
Invention is credited to Bowers, Stephen.
Application Number | 20010000343 09/727793 |
Document ID | / |
Family ID | 46149909 |
Filed Date | 2001-04-19 |
United States Patent
Application |
20010000343 |
Kind Code |
A1 |
Bowers, Stephen |
April 19, 2001 |
Fluoroelastomer composition having excellent processability and low
temperature properties
Abstract
Fluoroelastomers containing copolymerized units of vinylidene
fluoride, perfluoro(alkyl vinyl) ether, 2-hydropentafluoropropene,
and, optionally, tetrafluoroethylene, and having an iodine atom
present at some polymer chain ends, exhibit excellent low
temperature properties and processability when dual cured with both
polyhydroxy compounds and organic peroxides.
Inventors: |
Bowers, Stephen; (St.
Cergue, CH) |
Correspondence
Address: |
DUPONT DOW ELASTOMERS, LLC
LEGAL DEPARTMENT -- PATENTS
1007 MARKET STREET
WILMINGTON
DE
19898
US
|
Family ID: |
46149909 |
Appl. No.: |
09/727793 |
Filed: |
December 1, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09727793 |
Dec 1, 2000 |
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09378365 |
Aug 20, 1999 |
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60097387 |
Aug 21, 1998 |
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Current U.S.
Class: |
526/255 ;
525/248; 525/250; 525/264 |
Current CPC
Class: |
C08K 3/22 20130101; C08K
5/36 20130101; C08K 5/0025 20130101; C08F 214/222 20130101; C08F
8/00 20130101; C08F 216/1408 20130101; C08K 5/5317 20130101; C08F
8/00 20130101; C08K 5/17 20130101; C08K 5/0025 20130101; C08K
5/5317 20130101; C08K 5/17 20130101; C08K 5/13 20130101; C08L 27/12
20130101; C08L 27/12 20130101; C08L 27/12 20130101; C08L 27/12
20130101; C08L 27/12 20130101; C08F 214/18 20130101; C08K 5/13
20130101; C08K 5/36 20130101 |
Class at
Publication: |
526/255 ;
525/248; 525/250; 525/264 |
International
Class: |
C08F 251/00; C08F
255/00 |
Claims
What is claimed is:
1. A curable composition comprising: A. a fluoroelastomer copolymer
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; said fluoroelastomer
having between 0.05 and 1 weight percent iodine chemically bound at
copolymer chain ends; B. a polyhydroxy crosslinking agent; C. a
cure accelerator; D. an acid acceptor selected from the group
consisting of metal oxides, metal hydroxides, and mixtures thereof;
E. an organic peroxide; and F. a coagent.
2. A composition of claim 1 wherein the polyhydroxy crosslinking
agent is selected from the group consisting of i) dihydroxy-,
trihydroxy-, and tetrahydroxy- benzenes, -naphthalenes, and
-anthracenes; ii) bisphenols of the formula 2where A is a stable
divalent radical; x is 0 or 1; and n is 1 or 2; iii) dialkali salts
of said bisphenols, iv) quaternary ammonium and phosphonium salts
of said bisphenols, v) tertiary sulfonium salts of said bisphenols,
and vi) esters of phenols.
3. A curable composition of claim 1 wherein said cure accelerator
is chosen from the group consisting of quaternary ammonium salts,
tertiary sulfonium salts and quaternary phosphonium salts.
4. A curable composition of claim 1 wherein said organic peroxide
is selected from the group consisting of
2,5-dimethyl-2,5-di(tertiarybutylpe- roxy)hexyne-3;
2,5-dimethyl-2,5-di(tertiarybutylperoxy)-hexane; dicumylperoxide;
dibenzoylperoxide; tertiarybutylperbenzoate; and
di[1,3-dimethyl-3-(t-butylperoxy)butyl]carbonate.
5. A curable composition of claim 1 wherein said coagent is
selected from the group consisting of triallyl cyanurate; triallyl
isocyanurate; tri(methallyl)isocyanurate;
tris(diallylamine)-s-triazine; triallyl phosphite; N,N-diallyl
acrylamide; hexaallyl phosphoramide; N,N,N',N'-tetraalkyl
tetraphthalamide; N,N,N',N'-tetraallyl malonamide; trivinyl
isocyanurate; 2,4,6-trivinyl methyltrisiloxane; and
tri(5-norbornene-2-methylene)cyanurate.
6. A composition of claim 1 further comprising a zeolite.
7. A composition of claim 1 further comprising a modified silane
coated mineral filler.
8. A composition of claim 7 wherein the modified silane coated
mineral filler is selected from the group consisting of epoxysilane
coated wollastonites and aminosilane coated wollastonites.
9. A composition of claim 1 further comprising a molecular
sieve.
10. A curable composition consisting essentially of A) a
fluoroelastomer copolymer 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; said fluoroelastomer having between 0.05
and 1 weight percent iodine chemically bound to copolymer chain
ends; and B) a compound selected from the group consisting of i)
quaternary ammonium salts of a bisphenol, ii) quaternary
phosphonium salts of a bisphenol and iii) tertiary sulfonium salts
of a bisphenol; C) an acid acceptor selected from the group
consisting of metal oxides, metal hydroxides, and mixtures thereof;
D) an organic peroxide; and E) a coagent.
11. A curable composition of claim 10 wherein said organic peroxide
is selected from the group consisting of
2,5-dimethyl-2,5-di(tertiarybutylpe- roxy)hexyne-3;
2,5-dimethyl-2,5-di(tertiarybutylperoxy)-hexane; dicumylperoxide;
dibenzoylperoxide; tertiarybutylperbenzoate; and
di[1,3-dimethyl-3-(t-butylperoxy)butyl]carbonate.
12. A curable composition of claim 10 wherein said coagent is
selected from the group consisting of triallyl cyanurate; triallyl
isocyanurate; tri(methallyl)isocyanurate;
tris(diallylamine)-s-triazine; triallyl phosphite; N,N-diallyl
acrylamide; hexaallyl phosphoramide; N,N,N',N'-tetraalkyl
tetraphthalamide; N,N,N',N'-tetraallyl malonamide; trivinyl
isocyanurate; 2,4,6-trivinyl methyltrisiloxane; and
tri(5-norbomene-2-methylene)cyanurate.
13. A composition of claim 10 further comprising a zeolite.
14. A composition of claim 10 further comprising a modified silane
coated mineral filler.
15. A composition of claim 14 wherein the modified silane coated
mineral filler is selected from the group consisting of epoxysilane
coated wollastonite and aminosilane coated wollastonite.
16. A composition of claim 10 further comprising a molecular sieve.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
1. This application is a continuation-in-part of U.S. application
Ser. No. 09/378,365, filed Aug. 20, 1999 which claims the benefit
of U.S. Provisional Application 60/097,387, filed Aug. 21,
1998.
FIELD OF THE INVENTION
2. This invention relates to fluoroelastomers that are capable of
being crosslinked with both polyhydroxy compounds and organic
peroxides to produce cured compositions having excellent
processability and low temperature properties.
BACKGROUND OF THE INVENTION
3. 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.sub.2)
with hexafluoropropylene (HFP) or terpolymers of VF.sub.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.
4. 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.sub.2/PMVE/TFE copolymers
have glass transition temperature (T.sub.g) values which are
10.degree.-20.degree. C. lower than those of the corresponding
VF.sub.2/HFP/TFE copolymers. T.sub.g is often used as an indicator
of low temperature flexibility because polymers having low glass
transition temperatures maintain elastomeric properties at low
temperatures.
5. 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.sub.2;
at least one fluorinated propene and or fluorinated methyl vinyl
ether; TFE; at least one perfluoro(polyoxyalkyl vinyl) ether, and a
crosslinking site.
6. 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.sub.2/PMVE copolymers the compositions generally exhibit a
tendency to stick to and foul the mold.
7. Tetrapolymers of VF.sub.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.sub.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.sub.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.sub.2/PMVE copolymers. Similarly, British Patent
1,296,084 discloses fluoroelastomeric tetrapolymers containing
copolymerized units of 48-65 wt. % VF.sub.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.
8. Merely raising the PAVE content while lowering the HFP content
is not a solution to the problem of improving low temperature
performance of VF.sub.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.sub.2 units to permit
efficient crosslinking with bisphenols. As is well known in the
art, efficient curing of VF.sub.2/HFP-containing fluoroelastomers
with a bisphenol/accelerator system is possible only when a
--CH.sub.2-- group in the polymer backbone is flanked by two
perfluorinated carbons (e.g.
CF.sub.2CF(CF.sub.3)CH.sub.2CF.sub.2CF.sub.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
Makromolekulare Chemie, 76/77, 39 (1979), completely eliminating
HFP to form VF.sub.2/TFE/PMVE terpolymers results in formation of
monomer sequences consisting of TFE/VF.sub.2/TFE;
TFE/VF.sub.2/PMVE; PMVE/VF.sub.2/PMVE; and PMVE/VF.sub.2/TFE.
Although such sites readily undergo elimination of HF or HOCF.sub.3
in the presence of base, the double bonds thus formed are not
easily crosslinked by bisphenols or any other traditional
crosslinking agents.
9. There thus exists an unfulfilled need in the art for a method of
providing copolymers of VF.sub.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
10. The present invention is directed to a curable composition
comprising
11. A. a fluoroelastomer copolymer 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; said fluoroelastomer copolymer having
between 0.05 and 1 weight percent iodine chemically bound at
copolymer chain ends;
12. B. a polyhydroxy crosslinking agent;
13. C. a cure accelerator;
14. D. an acid acceptor selected from the group consisting of metal
oxides, metal hydroxides, and mixtures thereof,
15. E. an organic peroxide; and
16. F. a coagent.
17. A preferred embodiment of the curable compositions of the
invention additionally comprises a modified silane coated mineral
filler.
18. A further preferred embodiment of the curable compositions of
the invention additionally comprises a molecular sieve.
DETAILED DESCRIPTION OF THE INVENTION
19. The copolymers employed in the compositions of the present
invention are capable of undergoing crosslinking reactions with
both polyhydroxy compounds and organic peroxides to form
elastomeric compositions that exhibit unusually good low
temperature properties and low mold sticking characteristics.
20. The polymer backbones of the copolymers consist essentially of
copolymerized units of VF.sub.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.sub.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. %.
21. In addition, the fluoroelastomer copolymers used in this
invention contain between 0.05 and 1 wt. % (preferably between 0.08
and 0.3 wt. %) iodine which is bound to copolymer chain ends, the
iodine being introduced via use of an iodine-containing chain
transfer agent during polymerization.
22. The fluoroelastomers employed in the curable compositions 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.
23. Perfluoro(alkyl vinyl) ethers (PAVE) suitable for use as
comonomers include those of the formula
CF.sub.2.dbd.CFO(R.sub.f'O).sub.n(R.sub.f"O).sub.mR.sub.f (I)
24. where R.sub.f and R.sub.f"are different linear or branched
perfluoroalkylene groups of 2-6 carbon atoms, m and n are
independently 0-10, and R.sub.f is a perfluoroalkyl group of 1-6
carbon atoms.
25. A preferred class of perfluoro(alkyl vinyl) ethers includes
compositions of the formula
CF.sub.2.dbd.CFO(CF.sub.2CFXO).sub.nR.sub.f (II)
26. where X is F or CF.sub.3, n is 0-5, and R.sub.f is a
perfluoroalkyl group of 1-6 carbon atoms.
27. A most preferred class of perfluoro(alkyl vinyl) ethers
includes those ethers wherein n is 0 or 1 and R.sub.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.sub.2.dbd.CFO[(CF.sub.2).sub.mCF.sub.2CFZO].sub.nR.sub.f
(III)
28. where R.sub.f is a perfluoroalkyl group having 1-6 carbon
atoms,
29. m=0 or 1, n=0-5, and Z=F or CF.sub.3.
30. Preferred members of this class are those in which R.sub.f is
C.sub.3F.sub.7, m=0, and n= 1.
31. Additional perfluoro(alkyl vinyl) ether monomers include
compounds of the formula
CF.sub.2.dbd.CFO[(CF.sub.2CFCF.sub.3O).sub.n(CF.sub.2CF.sub.2CF.sub.2O).su-
b.m(CF.sub.2).sub.p]C.sub.xF.sub.2x+1 (IV)
32. where m and n independently=1-10, p=0-3, and x=1-5.
33. Preferred members of this class include compounds where n=0-1,
m=0-1, and x=1.
34. Examples of useful perfluoro(alkoxy vinyl) ethers include
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)O(CF.sub.2O).sub.mC.sub.nF.sub.2n+1
(V)
35. where n=1-5, m=1-3, and where, preferably, n=1.
36. Mixtures of perfluoro(alkyl vinyl) ethers and perfluoro(alkoxy
vinyl) ethers may also be used.
37. The perfluoro(alkyl vinyl) ether content of the
fluoroelastomers of the invention ranges from 25-75 wt. %. If
perfluoro(methyl vinyl) ether is used, then the fluoroelastomer
preferably contains between 30-44 wt. % copolymerized
perfluoroether units. If less than 25 wt. % perfluoro(alkyl vinyl)
ether is present, the low temperature properties of the
fluoroelastomers are adversely affected.
38. Copolymerized units of tetrafluoroethylene may also be present
in the fluoroelastomers used in the invention at levels up to 30
wt. %. The presence of copolymerized units of TFE is desirable for
the purpose of increasing fluorine content without unduly
compromising low temperature flexibility. High fluorine content
promotes good fluid resistance. If TFE is present as a comonomer,
it is preferably copolymerized in amounts of at least 3 wt. %.
Levels of 3 wt. % or greater TFE lead to improved fluid resistance
in some end use applications. TFE levels above 30 wt. % result in
some polymer crystallinity which affects low temperature
compression set and flexibility.
39. The fourth copolymerized monomer unit in the copolymers
employed in the invention is 2-hydropentafluoropropene (HPFP). A
particular characteristic of the HPFP monomer is that it acts as an
independent cure site monomer that takes part in crosslinking
reactions with polyhydroxylic curing agents. Polymers that contain
copolymerized HPFP monomer units do not require the presence of
copolymerized monomer sequences of VF.sub.2 flanked by
perfluoromonomers (e.g. HFP/NVF.sub.2/HFP) for initiation of
dehydrofluorination. Introduction of copolymerized HPFP units into
the VF.sub.2/HFP copolymer chain creates sites that exceed the
reactivity of HFP/VF.sub.2/HFP sequences. HFP is a perfluorinated
monomer and thus contains no hydrogens. It cannot function as an
independent cure site monomer because it is incapable of undergoing
dehydrofluorination. In fact, HFP-containing VF.sub.2 copolymers of
PMVE must contain at least about 8-10 wt. % HFP in order to provide
a sufficient concentration of
--CF.sub.2CF(CF.sub.3)CH.sub.2CF.sub.2CF.sub.- 2-- sequences for
effective cure by polyhydroxylic compounds.
40. HPFP/TFE/PMVE terpolymers are disclosed in U.S. Pat. Nos.
5,478,902 and 5,719,245. In addition, HPFP/TFE/PMVE tetrapolyrners
containing not more than about 20 mole percent of an additional
monomer are disclosed therein. Compositions containing high levels
of VF.sub.2 comonomer are not disclosed. In addition, U.S. Pat. No.
5,874,506 discloses VF.sub.2/TFE/HFP/HPFP tetrapolymers. The
polymers must contain 16-30 mol % HFP. Pentapolymers containing up
to 5 mol % of additional comonomers are also disclosed therein. The
tetrapolymers and pentapolymers disclosed in this reference do not
exhibit good low temperature properties and have very different
fluids resistance from the polymers of the present invention.
41. Because of the ease of hydrogen abstraction in HPFP-containing
VF.sub.2 fluoroelastomers, the polymers employed in the present
invention require only low levels of HPFP, i.e. 0.3-5 wt. %, to
promote efficient polyhydroxylic cures. This permits adjustment of
other comonomer levels to maximize particular physical properties.
Thus, the copolymers used in the present invention exhibit
excellent cure characteristics with only low levels of HPFP. They
maintain the high temperature compression set resistance properties
and excellent cure response characteristic of polymers having
significant amounts of copolymerized VF.sub.2. Further, they
exhibit a combination of excellent low temperature properties and
processability not found in prior art fluoroelastomers. Preferably
levels of HPFP will be between 0.7 and 3.0 wt. %.
42. The polymers employed in this invention may be prepared using
free radical batch or semi-batch, or continuous free radical
emulsion polymerization processes. They may also be prepared by
free radical suspension polymerization processes.
43. For example, if a continuous emulsion process is utilized, the
polymers are generally prepared in a continuous stirred tank
reactor. Polymerization temperatures may be in the range of
40.degree. to 145.degree. C., preferably 100.degree. to 135.degree.
C. at pressures of 2 to 8 MPa. Residence times of 20 to 60 minutes
are preferred. Free radical generation may be effected through use
of a water-soluble initiator such as ammonium persulfate, either by
thermal decomposition or by reaction with a reducing agent such as
sodium sulfite. An inert surface-active agent such as ammonium
perfluorooctanoate may be utilized to stabilize the dispersion,
usually in conjunction with addition of a base such as sodium
hydroxide or a buffer such as disodium phosphate to control pH in
the range 3 to 7. Unreacted monomer is removed from the reactor
effluent latex by vaporization at reduced pressure. Polymer is
recovered from the stripped latex by coagulation. For example,
coagulation may be effected by reducing latex pH to about 3 by
addition of acid, then adding a salt solution, such as an aqueous
solution of calcium nitrate, magnesium sulfate, or potassium
aluminum sulfate, to the acidified latex. The polymer is separated
from the serum, then washed with water and subsequently dried.
After drying, the product may be cured.
44. Chain transfer agents may be used in the polymerization in
order to control the molecular weight distribution of the resulting
polymers. Examples of chain transfer agents include isopropanol;
methyl ethyl ketone; ethyl acetate; diethyl malonate;
isopentane;1,3-diiodoperfluoropr- opane; 1,4-diiodoperfluorobutane;
1,6-diiodoperfluorohexane; 1,8-diiodoperfluorooctane; methylene
iodide; trifluoromethyl iodide; perfluoro(isopropyl) iodide; and
perfluoro(n-heptyl) iodide.
45. Polymerization in the presence of iodine-containing chain
transfer agents results in a copolymer with one or two iodine atoms
per fluoroelastomer copolymer chain, bound at the chain ends (see
for example U.S. Pat. No. 4,243,770 and U.S. Pat. No. 4,361,678).
Such polymers are also curable with an organic peroxide and they
may have improved flow and processability compared to polymers made
in the absence of a chain transfer agent.
46. An aspect of the present invention is a curable composition
that comprises the above-described copolymers, a polyhydroxylic
curing agent and an organic peroxide curing agent.
47. Any of the known polyhydroxylic aromatic crosslinking agents
that require accelerators for satisfactory cure rates are suitable
for use with the fluoroelastomers of the present invention. The
crosslinking agent is usually added in amounts of from about 0.5-4
parts by weight per hundred parts by weight fluoroelastomer (phr),
usually 1-2.5 phr. Preferred crosslinking agents are di- tri-,
tetrahydroxybenzenes, naphthalenes, anthracenes and bisphenols of
the formula 1
48. where A is a stable divalent radical, such as a difunctional
aliphatic, cycloaliphatic, or aromatic radical of 1-13 carbon
atoms, or a thio, oxy, carbonyl, sulfinyl, or sulfonyl radical; A
is optionally substituted with at least one chlorine or fluorine
atom; x is 0 or 1; n is 1 or 2 and any aromatic ring of the
polyhydroxylic compound is optionally substituted with at least one
atom of chlorine, fluorine, or bromine, a --CHO group, or a
carboxyl or acyl radical (e.g. a --COR where R is OH or a
C.sub.1-C.sub.8 alkyl, aryl, or cycloalkyl group). It will be
understood from the above formula describing bisphenols that the
--OH groups can be attached in any position (other than number one)
in either ring. Blends of two or more such compounds can also be
used.
49. Referring to the bisphenol formula shown in the previous
paragraph, when A is alkylene, it can be, for example, methylene,
ethylene, chloroethylene, fluoroethylene, difluoroethylene,
1,3-propylene, 1,2-propylene, tetramethylene, chlorotetramethylene,
fluorotetramethylene, trifluorotetramethylene,
2-methyl-1,3-propylene, 2-methyl-1,2-propylene, pentamethylene, and
hexamethylene. When A is alkylidene, it can be for example
ethylidene, dichloroethylidene, difluoroethylidene, propylidene,
isopropylidene, trifluoroisopropylidene, hexafluoroisopropylidene,
butylidene, heptachlorobutylidene, heptafluorobutylidene,
pentylidene, hexylidene, and 1,1-cyclohexylidene. When A is a
cycloalkylene radical, it can be for example 1,4-cyclohexylene,
2-chloro-1,4-cyclohexylene, 2-fluoro-1,4-cyclohexylene- ,
1,3-cyclohexylene, cyclopentylene, chlorocyclopentylene,
fluorocyclopentylene, and cycloheptylene. Further, A can be an
arylene radical such as m-phenylene, p-phenylene,
2-chloro-1,4-phenylene, 2-fluoro-1,4-phenylene, o-phenylene,
methylphenylene, dimethylphenylene, trimethylphenylene,
tetramethylphenylene, 1,4-naphthylene, 3-fluoro-1 ,4-naphthylene,
5-chloro-1,4-naphthylene, 1,5-naphthylene, and 2,6-naphthylene.
Bisphenol AF (sometimes referred to as
4,4'-(hexafluoroisopropylidene)diphenol or as
4,4'-(2,2,2-trifluoro-1-(tr- ifluoromethyl)ethylidene)bisphenol) is
a preferred polyhydroxylic curing agent.
50. Other useful crosslinking agents include hydroquinone,
dihydroxybenzenes such as catechol, resorcinol, 2-methyl
resorcinol, 5-methyl resorcinol, 2-methyl hydroquinone,
2,5-dimethyl hydroquinone; 2-t-butyl hydroquinone; and
1,5-dihydroxynaphthalene.
51. Additional polyhydroxy curing agents include alkali metal salts
of bisphenol anions, quaternary ammonium salts of bisphenol anions
and quaternary phosphonium salts of bisphenol anions. For example,
the salts of bisphenol A and bisphenol AF. Specific examples
include the disodium salt of bisphenol AF, the dipotassium salt of
bisphenol AF, the monosodium monopotassium salt of bisphenol AF and
the benzyltriphenylphosphonium salt of bisphenol AF. Quaternary
ammonium and phosphonium salts of bisphenol anions and their
preparation are discussed in U.S. Pat. Nos. 4,957,975 and
5,648,429.
52. In addition, derivatized polyhydroxy compounds, such as
diesters, are useful crosslinking agents. Examples of such
compositions include diesters of phenols, such as the diacetate of
bisphenol AF, the diacetate of sulfonyl diphenol, and the diacetate
of hydroquinone.
53. The curable compositions of the present invention also
generally include a cure accelerator. The most useful accelerators
are quaternary phosphonium salts, quaternary alkylammonium salts,
or tertiary sulfonium salts. Particularly preferred accelerators
are n-tetrabutylammonium hydrogen sulfate, tributylallylphosphonium
chloride, benzyltriphenylphosphonium chloride,
methyltributylammonium hydrogen sulfate, and tripropylammonium
bromide. Other useful accelerators include those described in U.S.
Pat. Nos. 5,591,804; 4,912,171; 4,882,390; 4,259,463 and 4,250,278
such as tributylbenzylammonium chloride, tetrabutylammonium
bromide, tetrabutylammonium chloride, benzyl
tris(dimethylamino)phosphonium chloride;
8-benzyl-1,8-diazabicyclo[5,4,0]- -7-undecenonium chloride,
[(C.sub.6H.sub.5).sub.2S.sup.+(C.sub.6H.sub.13)]- [Cl].sup.-, and
[(C.sub.6H.sub.13).sub.2S(C.sub.6H.sub.5)].sup.+[CH.sub.3C-
O.sub.2].sup.-. In general, about 0.2 phr accelerator is an
effective amount, and preferably about 0.35-1.5 phr is used.
54. If quaternary ammonium or phosphonium salts of bisphenols are
used as curing agents, then addition of a cure accelerator is not
necessary.
55. The curable compositions of the invention will also contain an
acid acceptor such as a metal compound composed of a divalent metal
oxide (e.g. magnesium oxide, zinc oxide, calcium oxide, or lead
oxide), or a divalent metal hydroxide; or a mixture of the oxide
and/or hydroxide with a metal salt of a weak acid, for example a
mixture containing about 1-70 percent by weight of the metal salt.
Among the useful metal salts of weak acids are barium, sodium,
potassium, lead, and calcium stearates, benzoates, carbonates,
oxalates, and phosphites. The amount of the metal compound added is
generally about 1-15 phr, about 2-10 parts being preferred.
56. The compositions of the present invention also contain an
organic peroxide curing agent. Compositions containing both
polyhydroxy and organic peroxide curatives may cure faster than
compositions which contain only a polyhydroxy compound or only an
organic peroxide. In addition, the resulting cured article may have
better physical properties (e.g. compression set) than articles
cured only with a polyhydroxy compound or an organic peroxide.
57. Useful organic peroxides are those which generate free radicals
at curing temperatures. A dialkyl peroxide or a bis(dialkyl
peroxide) which decomposes at a temperature above 50.degree. C. is
especially preferred. In many cases it is preferred to use a
ditertiarybutyl peroxide having a tertiary carbon atom attached to
a peroxy oxygen. Among the most useful peroxides of this type are
2,5-dimethyl-2,5-di(tertiarybutylperoxy)hexyne- -3 and
2,5-dimethyl-2,5-di(tertiarybutylperoxy)-hexane. Other peroxides
can be selected from such compounds as dicumyl peroxide, dibenzoyl
peroxide, tertiarybutyl perbenzoate, and
di[1,3-dimethyl-3-(t-butylperoxy- )butyl]carbonate. Generally,
about 1-3 parts of peroxide per 100 parts of fluoroelastomer is
used.
58. Another material which is contained in the composition of the
invention is a coagent composed of a polyunsaturated compound which
is capable of cooperating with the peroxide to provide a useful
cure. These coagents can be added in an amount equal to 0.1 and 10
parts per hundred parts fluoroelastomer, preferably between 2-5
parts per hundred parts fluoroelastomer. The coagent may be one or
more of the following compounds: triallyl cyanurate; triallyl
isocyanurate; tri(methallyl)isocyanurate;
tris(diallylamine)-s-triazine; triallyl phosphite; N,N-diallyl
acrylamide; hexaallyl phosphoramide; N,N,N',N'-tetraalkyl
tetraphthalamide; N,N,N',N'-tetraallyl malonamide; trivinyl
isocyanurate; 2,4,6-trivinyl methyltrisiloxane; and
tri(5-norbornene-2-methylene)cyanurate. Particularly useful is
triallyl isocyanurate (TAIC).
59. Other additives may be compounded into the fluoroelastomer to
optimize various physical properties. Such additives include carbon
black, stabilizers, plasticizers, lubricants, pigments, fillers,
and processing aids typically utilized in perfluoroelastomer
compounding. Any of these additives can be incorporated into the
compositions of the present invention, provided the additive has
adequate stability for the intended service conditions.
60. Carbon black is used in elastomers as a means to balance
modulus, tensile strength, elongation, hardness, abrasion
resistance, conductivity, and processability of the compositions.
Carbon black is generally useful in amounts of from 5-60 phr.
61. In addition, or in the alternative, fluoropolymer fillers may
be present in the composition. Generally from 1 to 50 phr of a
fluoropolymer filler is used, and preferably at least about 5 phr
is present. The fluoropolymer filler can be any finely divided,
easily dispersed plastic fluoropolymer that is solid at the highest
temperature utilized in fabrication and curing of the
perfluoroelastomer composition. By solid, it is meant that the
fluoroplastic, if partially crystalline, will have a crystalline
melting temperature above the processing temperature(s) of the
perfluoroelastomer(s). Such finely divided, easily dispersed
fluoroplastics are commonly called micropowders or fluoroadditives.
Micropowders are ordinarily partially crystalline polymers.
62. A preferred additive class includes molecular sieves,
particularly zeolites. Molecular sieve zeolites are crystalline
aluminosilicates of Group IA and Group IIA elements, such as
sodium, potassium, magnesium, and calcium. Chemically, they are
represented by the empirical formula: M.sub.2/nO.Al.sub.2O.sub.3.
ySiO.sub.2.wH.sub.2O where y is 2 or greater, n is the cation
valence, and w represents the water contained in the voids of the
zeolite. Commercially available examples of such compositions
include Molecular Sieve 3A, Molecular Sieve 4A, Molecular Sieve 5A,
and Molecular Sieve 13X, all available from Aldrich Chemical Co.,
Inc. Milwaukee, Wis. Use of this class of additives prevents
sponging and improves heat aging of vulcanizates upon press curing
in many instances. In general, use of about 1-5 phr is
sufficient.
63. Other preferred additives include modified silane coated
mineral fillers. By "modified silane" is meant that the silane
contains at least one reactive functional group such as an amino
group, or an epoxy group. The mineral fillers used in this
invention are preferably somewhat alkaline, such as calcium
metasilicates (CaSiO.sub.3), especially wollastonite. Wollastonite
coated with either an aminosilane or an epoxysilane is especially
preferred. These compounds are commercially available from
Quartzwerke GmbH of Freschen, Germany as Tremin.RTM.283 EST
(epoxysilane treated wollastonite) and Tremin.RTM.283 AST
(aminosilane treated wollastonite). These modified silane coated
mineral fillers prevent sponging of the fluoroelastomer composition
during press cure and also accelerate the cure rate. Generally,
about 5 to 80 phr modified silane coated mineral filler is useful
in the compositions of this invention, about 10 to 60 phr being
preferred.
64. Organotin hydrides are another class of additive that may be
employed. Tri-n-butyltin hydride (TBTH) is especially preferred.
These tin hydride fillers accelerate the cure rate of the
compositions of this invention and increase the modulus and improve
the compression set resistance of the cured compounds. Generally,
about 0.2 to 1.5 phr organotin hydride filler is useful, about 0.4
to 0.8 phr being preferred.
65. The crosslinking agents, coagent, accelerator, metal oxide, and
other additives are generally incorporated into the polymer by
means of an internal mixer or on a rubber mill. The resultant
composition is then cured, generally by means of heat and pressure,
for example by compression transfer or injection molding.
66. The curable compositions of the present invention are useful in
production of gaskets, tubing, seals and other molded components.
Such articles are generally produced by molding a compounded
formulation of the curable composition with various additives under
pressure, curing the part, and then subjecting it to a post cure
cycle. The cured compositions have excellent low temperature
flexibility and processability as well as excellent thermal
stability and chemical resistance. They are particularly useful in
applications such as seals and gaskets requiring a good combination
of oil resistance, fuel resistance and low temperature flexibility,
for example in fuel injection systems, fuel line connector systems
and in other seals for high and low temperature automotive
uses.
67. The invention is now illustrated by certain embodiments wherein
all parts and percentages are by weight unless otherwise
specified.
EXAMPLES
TEST METHODS
68. Cure Characteristics
69. Unless otherwise noted, cure characteristics were measured
using an Alpha Systems model MDR 2000E moving die rheometer (MDR),
under the following conditions:
70. Moving die frequency: 1.66 Hertz
71. Oscillation amplitude: .+-.0.5.degree.
72. Temperature: 180.degree. C.
73. Sample size: 7 to 8 g
74. Duration: 12 minutes
75. The following cure parameters were recorded:
76. M.sub.H: maximum torque level, in units of dN.m
77. M.sub.L: minimum torque level, in units of dN.m
78. Delta M: difference between maximum and minimum torque, in
units of dN.m
79. t.sub.s2: minutes to a 2.26 dNm rise above M.sub.L
80. tc50: minutes to 50% of maximum torque
81. tc90: minutes to 90% of maximum torque
82. Tensile Properties
83. Unless otherwise noted, stress/strain properties were measured
on test specimens that had been press cured at 180.degree. C. for
15 minutes and then post cured in a hot air oven for 24 hours at
232.degree. C. The following physical property parameters were
recorded; test methods are in parentheses:
84. M.sub.100: modulus at 100% elongation in units of MPa (ISO
37)
85. T.sub.B: tensile strength in units of MPa (ISO 37)
86. T.sub.S: tear strength in units of dN/m (ISO 34, Die B)
87. E.sub.B: elongation at break in units of % (ISO 37)
88. TR-10: temperature of retraction (ISO 2921)
89. According to the TR test method, a standard test piece of
length 50 mm is stretched at room temperature and then cooled in a
bath (usually filled with isopropanol) to a temperature of about
10.degree. C. less than the T.sub.g of the polymer. The test piece
is then allowed to retract freely while the test temperature is
raised at a rate of 1.degree. C. per minute. Readings of the
retracted length are taken every 2 minutes until the retraction
reaches 75%. TR-10 is the temperature at which a retraction of 10%
is achieved.
90. Hardness (Shore A, ISO 868)
91. Compression set of small pip samples (ISO 815)
Example 1
92. Polymer 1, a polymer of the invention, was prepared by
semi-batch emulsion polymerization carried out at 80.degree. C. in
a well-stirred reaction vessel. A 41.5 liter reactor was charged
with 63.25 grams of ammonium perfluorooctanoate and 27436.75 grams
of deionized, deoxygenated water. The reactor was heated to
80.degree. C. and then pressurized with 800 grams of a mixture of
42.3 mol % vinylidene fluoride, 29.1 mol % perfluoro(methyl vinyl
ether), 25.6 mol % 1,1,3,3,3-pentafluoropropene (HPFP), and 3.0 mol
% tetrafluoroethylene, bringing the reactor pressure to 1.48 MPa. A
16.0 ml aliquot of a mixture of 49.3 mol %
1,4-diiodoperfluorobutane, 34.8 mol % 1,6-diiodoperfluorohexane,
12.6 mol % 1,8-diiodoperfluorooctane, and 3.3 mol %
1,10-diiodoperfluorodecane was added to the reactor and the
resulting mixture agitated 15 minutes. Next, 50.0 ml of a solution
of 1% ammonium persulfate and 5% disodium phosphate heptahydrate
were added to the reactor. As the reactor pressure dropped, a
mixture of 51.4 mol % vinylidene fluoride, 22.6 mol %
perfluoro(methyl vinyl ether), 1.1 mol %
1,1,3,3,3-pentafluoropropene, and 24.9 mol % tetrafluoroethylene
was added to the reactor to maintain a 1.48 MPa pressure. After 155
grams of the 1% ammonium persulfate/5% disodium phosphate
heptahydrate mixture had been added to the reactor, corresponding
to the use of 9250 grams of monomer and an elapsed time of 24.0
hours, monomer feed to the reactor was halted and pressure reduced
to atmospheric. The pH of the resulting latex was reduced to 3.3
with sulfuric acid. Latex was coagulated with 400 grams of
potassium aluminum sulfate, washed with deionized water and then
dried at 70.degree. C. for two days. The polymer had a
copolymerized monomer unit composition of 32.30 wt. % VF.sub.2,
37.50 wt. % PMVE, 28.90 wt. % TFE, 1.20 wt. % HPFP and 0.13 wt. %
iodine. Mooney viscosity, ML(1+10) at 121.degree. C., was 93.
93. Polymer 1 was compounded on a two-roll rubber mill with the
additives shown in Table I. Sample 1B is a composition of this
invention. The other samples are controls of a similar composition
cured with i) bisphenol only (1A) and ii) peroxide only (1C).
Curing characteristics are reported in Table I. Compounds were
press molded at 170.degree. C. for 5 minutes and then post cured
for 24 hours at 230.degree. C. Physical properties of the cured
compositions were measured according to the Test Methods and are
also reported in Table I.
1 TABLE I 1A 1B 1C Polymer 1 100 100 100 MT Black.sup.1 2.5 2.5 2.5
Tremin 283 600 EST.sup.2 45 45 45 Calcium Oxide VG 6 6 6 Elastomag
170.sup.3 1 1 1 Molecular Sieves 13X 3 3 3 Bisphenol AF.sup.4 2 1 0
TBAHS.sup.5 0.5 0.25 0 VPA #2.sup.6 1 1 1 Peroxide.sup.7 0 1.9 3.75
Coagent.sup.8 0 1.35 2.70 M.sub.L, dNm 2.72 3.15 3.41 M.sub.H, dNm
32.75 42.18 34.09 Delta M, dNm 30.03 39.03 30.68 t.sub.s2, minutes
0.60 0.32 0.31 tc50, minutes 1.50 0.53 0.44 tc90, minutes 4.21 1.03
0.64 Peak Rate, dNm/min 17.7 98.3 120 T.sub.B, MPa 13.40 16.90
16.50 E.sub.B, % 144 135 195 M.sub.100, MPa 10.4 14.6 11.1 Hardness
(Shore A) 75.3 79.1 77.1 Compression Set (70 23.8 19.6 24.9 hours
at 200.degree. C.), % TR-10, .degree. C. -21 -22 -22 .sup.1Thermax
FF N 990 medium thermal carbon black (available from Lehmann &
Voss Co.) .sup.2Epoxysilane coated wollastonite .sup.3Magnesium
oxide (available from Morton Performance Chemicals, Inc.).
.sup.44,4'(Hexafluoroisopropylidene)diphenol (available from DuPont
Dow Elastomers L.L.C.) .sup.5Tetrabutylammonium hydrogen sulfate
(available from DuPont Dow Elastomers L.L.C.) .sup.6Rice Bran Wax
(available from DuPont Dow Elastomers L.L.C.) .sup.7Luperox 101 XL
45 (available from Atofina) .sup.8Diak #7 (TAIC)(available from
DuPont Dow Elastomers L.L.C.)
* * * * *