Note: Descriptions are shown in the official language in which they were submitted.
CA 02324954 2000-09-20
WO 99/48939 PCT/US99/03490
PERFLUOROELASTOMER COMPOSITIONS
FIELD OF THE INVENTION
This invention relates to peroxide-curable perfluoroelastomer compositions
which
have excellent processability, and which when cured, have excellent physical
properties.
io BACKGROUND OF THE INVENTION
Perfluoroelastomers (elastomeric perfluoropolymers) are polymeric materials
which exhibit outstanding high temperature tolerance and chemical resistance.
Consequently, such compositions are particularly adapted for use as seals and
gaskets in
15 systems in which elevated temperatures and/or corrosive chemicals are
encountered. They
are useful in industries such as, chemical processing, semiconductor,
aerospace,
petroleum, etc.
The outstanding properties of perfluoropolymers are largely attributable to
the
stability and inertness of the copolymerized perfluorinated monomer units
which make up
2o the major portion of the polymer backbone, e.g., tetrafluoroethylene and
perfluoro(alkyl
vinyl) ethers. In order to completely develop elastomeric properties,
perfluoropolymers
are typically crosslinked, i.e. vulcanized. To this end, a small percentage of
a cure site
monomer is copolymerized with the perfluorinated monomer units. Cure site
monomers
containing at least one bromo or iodo group are known. Such cure site
monomers, when
25 combined with a peroxide and a coagent, will provide a suitably cured
composition.
Perfluoroelastomers are very expensive materials, and therefore are only used
in
situations where no other material will do the job. In view of the very high
raw material
costs, scrap rates during the molding operation must be kept to a minimum.
Unfortunately,
perfluoroelastomers are known to be very difficult to process with respect to
30 compounding, flow characteristics and mold release. When conventional
initiators are
used to produce the polymers (e.g., persulfates) the polymeric end groups are
typically of
an ionic and/or acidic nature. These ionizable polymer end-groups, that are
normally
present, are prone to undesirable reactions with some commonly used additives,
(e.g., acid
CA 02324954 2000-09-20
_::.::.::::::: '~_":''": _:::>:T:.:.::'::-..::.-.::~:.:.>.:::::_:
::::::::::::::::::~..<:::::::::::::::
:.. ...~I~.:.2. .~7. ::. :~:..~~.~3.....~~'..:: :L~l:_~ '..:::~::::::::::::
.:1.~....:::::::::::~.:::Q.: ::
::.:::::.~:..::.::::::.~::::::::::::::.~::.~.::::. ::::: : ~~.::::::::. :. ::.
:::::;:::::<...:....:::.:>:;:::...:...,::...>.-.
.:.:..:..~.::.::.~.:...........:..::.::.....:;:.....::.>::::..:....:.::: VO I
"~..':..:.::....:;:::..:.:...;...:::;:;::...;:...<
SS lr5 t~ r~ktNtF
'~efc~a~ ~ perfluoroelastomer is sut~tas~alIy free~fiddizablgtmd~oups ~ai~~
~~~m ~e group PATENTANWALTE
~ ~ ~ ~~~ ~ ~ ~ s . SIEBERTSTR. 4
consisting of carboxylate or carboxyl ~c ac~ end-gr~ i~psan~
sul~on~~e~,sulfQni:d end ~ groupss~ 675 M U N C H E t~
E-
acceptors). Examples of commonly used acid acceptors are zinc oxide, calcium i
~' ~~~1 ~~~~J
0
M U i hydroxide, calcium carbonate, magnesium oxide, etc. They are used in the
compound
formulation to bind any HF or other acids that might be generated at the high
temperatures
~ ~O ~ where perfluoroeIas~omers must functio~ ~ ~~~ ZA~ f
V ~ ~ PerfluoroeIastomer compounds that show very good processing
characte~stics are
a G'O
much desired. Because many applications for these polymers also iequire good
sealing
capabilities, the steps to improve processability are preferrably not
detrimental to critical
physical properties such as compression set resistance.
to SUMMARY OF THE INVENTION ,.
The perfluoroelastomers compounds of this invention employ a
perfluoroelastomer
that is prepared using an initiator combination of an oxidizer and a
perfluoroalkyl sulfinate
of type RfSOzNa. The copolymers prepared in this manner surprisingly can be
processed
15 like other elastomer gums. They are easy to process on conventional 2 roll
mills, or
mixing devices, i.e. the mills or mixing devices need not be heated above room
temperature. Their compound viscosity does not increase when acid acceptors,
such as
Ca(OH~, are added. The perfluoroelastomers also show improved physical
properties
(e.g. compression set resistance).
2o One embodiment of the invention provides a peroxide curable
perfluoroelastomer
~~>
compound that is easily processable and is essentially free of ionizable end
groups. rBy
"essentially free" of such groups it is meant that less than IO%.of these end
groups are
ionizable groups. The compound of this embodiment comprises:
A) a perfluoroelastomer containing interpolymerized units derived from 1) a
25 perfluoroolefin, 2) a perfluorovinyl ether selected from the group
consisting
ofperfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers, and
mixtures thereof, and 3) a cure site component containing a halogen group
capable of participation in a peroxide cure reaction, selected from the group
consisting of fluorinated olefins having at least one such halogen group,
30 fluorinated vinyl ethers having at least one such halogen group, chain
transfer agents containing at least one such halogen group, and initiators
containing at least one such halogen group, and mixtures thereof; with~the
t
AMENDED SHEET
.....
:: :.....
::::::.
::: .::
:.
::: .
_.
CA 02324954 2000-09-20
- WO-A-97/02300 describes a process for the preparation of a fluorine-
containing
polymer, comprising polymerizing, in an aqueous emulsion or suspension, a
fluorine-containing olefin, wherein the initiator is a combination of a
fluoroaliphatic
sulfinate or sulfinic acid and an oxidizing agent selected from the group
consisting
of chorate ion, bromate ion and hypochorite ion, and provided that said
fluoroaliphatic sulfinate or fluoroaliphatic sulfinic acid and said oxidizing
agent are
water-soluble.
FR-A-2 305 462 discloses fluoropolymers made by copolymerizing a small amount
of bromotrifluoroethylene or bromotetrafluorobutene with certain combinations
of
monomers comprising selected fluorine-containing compounds. A fluoropolymer
composition useful in the manufacture of cured fluoropolymer articles can be
made by mixing the resulting fluoropolymer or a closely related fluoropolymer
with
an organic peroxide such as dialkyl peroxide, and preferably also adding a
divalent metal oxide andlor hydroxide and a suitable co-agent such as triallyl
isocyanorate.
US-A-5,285,002 describes a method for the preparation of a fluorine-containing
polymer comprising polymerizing, under free radical conditions, an aqueous
emulsion or suspension of a polymerizable mixture comprising a fluoroaliphatic-
. _.
radical containing sulfinate, and an oxidizing agent capable of oxidizing said
sulfinate to a sulfonyl radical.
AMENDED SHEET
..;...::.
....
..
:2::
::v. v
CA 02324954 2000-09-20
WO 99/48939 PCT/US99/03490
proviso that the cure site component contains substantially no nitrile
groups, and
B) a peroxide curative.
In another embodiment, the invention provides a peroxide curable
perftuoroelastomer compound that is easily processable comprising:
A) a perfluoroelastomer substantially free of ionizable end groups, wherein
the .
perfluoroelastomer contains interpolymerized units derived from I) a
perfluoroolefin, 2) a perfluorovinyl ether selected from the group consisting
of perfluoro(alkyl vinyl) ethers, perfluoro(alkoxy vinyl) ethers, and
to mixtures thereof, and 3) a cure site component containing a bromine or
iodine atom capable of participation in a peroxide cure reaction, selected
from the group consisting of brominated or iodinated olefins having at least
one such atom, brominated or iodinated vinyl ethers having at least one
such atom, brominated or iodinated chain transfer agents, brominated or
iodinated initiators, and mixtures thereof; and
B) a peroxide curative.
The present invention also provides a method for improving the processability
of
perfluoroelastomers, comprising: polymerizing, under free-radical conditions,
an aqueous
emulsion or suspension of a polymerizable mixture comprising a perfluoroolefin
and a
2o perfluoroalkyl vinyl ether or a perfluoroalkoxy vinyl ether and mixtures
thereof, a
halogen-containing cure-site component capable of participation in a peroxide
cure
reaction, a fluoroaliphatic-radical containing sulfinate, and an oxidizing
agent capable of
oxidizing said sulfinate to a sulfonyl radical, with the proviso that the cure
site component
contains substantially no nitrile groups.
The present invention also provides a method for improving the processability
of
perfluoroelastomers, comprising: polymerizing, under free-radical conditions,
an aqueous
emulsion or suspension of a polymerizable mixture comprising a perfluoroolefin
and a
perfluoroalkyl vinyl ether or a perfluoroalkoxy vinyl ether and mixtures
thereof, a
bromine- or iodine-containing cure-site component, a fluoroaliphatic-radical
containing
3o sulfinate, and an oxidizing agent capable of oxidizing said sulfinate to a
sulfonyl radical.
The invention further relates to cured and uncured articles made from such
curable
compounds.
CA 02324954 2000-09-20
WO 99/48939 PCT/US99/03490
DETAILED DESCRIPTION
The compositions of the present invention comprise peroxide curable
perfluoroelastomers which are characterized by improved processability and
less reactivity
to bases. These compositions comprise a) a perfluoroelastomer having
copolymerized
units of a perfluoroolefin, a perfluorovinyl ether and a cure site component
having at least
one bromine- or iodine-containing moiety, and b) a compound which acts as a
curative for
the perfluoroelastomer. The perfluoroelastomers are substantially free of
ionizable end
1o groups, such as those reactive with bases. This does not preclude the
presence of cure
sites in the perfluoroelastomers needed for crosslinking.
Examples of suitable perfluorinated olefins useful in the invention include
tetrafluoroethylene and hexafluoropropylene.
Examples of suitable perfluorinated vinyl ethers are those of the formula
CF2=CFO(Rt0)n (R' f0),nR f (I)
where R f and R'g are different linear or branched perfluoroalkylene groups of
Z-6 carbon
atoms, m and n are independently 0-10, and Rg is a perfluoroalkyl group of 1-6
carbon
atoms.
A preferred class of perfluoro(alkyl vinyl) ethers includes compositions of
the
2o formula CF2=CFO(CF2CFX0)nRf (II)
where X is F or CF3, n is 0-5, and Rg is a perfluoroalkyl group of I-6 carbon
atoms.
Most preferred perfluoro(alkyl vinyl) ethers are those wherein n is 0 or 1 and
Rf
contains 1-3 carbon atoms. Examples of such perfluorinated ethers include
perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, and
perfluoro(propyl vinyl)
ether. Other useful monomers include compounds of the formula
CF2=CFO[(CF2)mCF2CFZ0]nRp (III)
where Rg is a perfluoroalkyl group having 1-6 carbon atoms, m=0 or 1, n=0-5,
and Z=F or
CF3.
Preferred members of this class are those in which Rf is C3F~, m=0, and n=1.
3o Additional perfluoro(alkyl vinyl) ether monomers useful in the invention
include
compounds of the formula
4
CA 02324954 2000-09-20
WO 99/48939 PCT/US99/03490
CF2=CFO[(CF2CFCF30)n(CF2CF2CF20),n(CF2)p]CXF2x+1 (
where m and n=1-10, p=0-3, and x=1-5 .
Preferred members ofthis class include compounds where n=0-1, m=0-I, and x=1.
Examples of perfluoro(alkoxy vinyl) ethers useful in the invention include
CF2=CFOCF2CF(CFg)O(CF20),nCnF2n+1 (
where n=1-5, m=1-3, and where, preferably, n=1.
Specific examples of useful perfluorovinyl ethers useful in the invention
include
CF2=CFOCFZOCF2CF2CF3, CF2=CFOCF2CF3, CF2=CFO(CF2)30CF3, and
CF2=CFOCF2CFzOCF3.
1o Mixtures of perfluoro(alkyl vinyl) ethers and perfluoro(alkoxy vinyl)
ethers may
also be used.
Preferred copolymers 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
15 monomer units in the polymer.
The cure site component used in the present invention is a halogen containing
material that is capable of participation in a peroxide cure reaction.
Typically the halogen
is bromine or iodine. Suitable cure-site components include terminally
unsaturated
monoolefins of 2 to 4 carbon atoms such as bromodifluoroethylene,
2o bromotrifluoroethylene, iodotrifluoraethylene, and
4-bromo-3,3,4,4-tetrafluorobutene-1. Examples of other suitable cure site
components
include CFz=CFOCFZCFZBr, CF2=CFOCF2CFZCFzBr, and
CF2=CFOCFZCF2CF20CFZCFZBr. Preferably, all or essentially all of these
components
are ethylenically unsaturated monomers.
25 Other useful cure-site components are brominated or iodinated chain
transfer
agents and initiators. Examples of useful chain transfer agents include
perfluoroalkyl
bromides or iodides. Examples of useful initiators include
Na02SC2F40F4X (where X is Br or I).
Suitable peroxide curatives for use in the invention are those which generate
free
3o radicals at curing temperatures. A dialkyl peroxide or a bis(dialkyl
peroxide) which
decomposes at a temperature above 50° C is especially preferred. In
many cases it is
preferred to use a di-tertiarybutyl peroxide having a tertiary carbon atom
attached to
CA 02324954 2000-09-20
WO 99/48939 PCT/US99/03490
peroxy oxygen. Among the most useful peroxides of this type are 2,S-dimethyl-
2,S-
di(tertiarybutylperoxy)hexyne-3 and 2,S-dimethyl-2,S-
di(tertiarybutylperoxy)hexane.
Other peroxides can be selected from such compounds as dicumyl peroxide,
dibenzoyl
peroxide, tertiarybutyl
S perbenzoate, a,a'-bis(t-butylperoxy-diisopropylbenzene), and di[1,3-dimethyl-
3-(t-
butylperoxy)-butyl]carbonate. Generally, about 1-3 parts of peroxide per 100
parts of
perfluoroelastomer is used.
Another material which is usually blended with the composition as a part of
the
curative system is a coagent composed of a polyunsaturated compound which is
capable of
1o 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 perfluoroelastomer,
preferably between
2-S parts per hundred parts perfluoroelastomer. Examples of useful coagents
include
triallyl cyanurate; triallyl isocyanurate; tri(methylallyl isocyanurate;
tris(diallylamine)-s-
triazine; triallyl phosphite; N,N-diallyl acrylamide; hexaallyl phosphoramide;
N,N,N',N'-
15 tetraalkyl tetraphthalamide; N,N,N',N'- tetraally( malonamide; trivinyl
isocyanurate; 2,4,6
trivinyl methyltrisiloxane; and tri(S-norbornene-2-methylene)cyanurate.
Particularly
useful is triallyl isocyanurate.
Other useful coagents include the bis-olefins disclosed in EPA 0 661 304 Al,
EPA
0 784 064 A1 and EPA 0 769 S21 A1.
2o Additives, such as carbon black, stabilizers, plasticizers, lubricants,
fillers, and
processing aids typically utilized in perfluoroelastomer compounding can be
incorporated
into the compositions of the present invention, provided they have adequate
stability for
the intended service conditions. In particular, low temperature performance
can be
enhanced by incorporation of perfluoropolyethers (cf.U.S. Pat No. 5,268,405).
25 Carbon black fillers are used in elastomers as a means to balance modulus,
tensile
strength, elongation, hardness, abrasion resistance, conductivity, and
processability of the
compositions. Suitable examples include MT blacks (medium thermal black)
designated
N-991, N-990, N-908, and N-907, and large particle size furnace blacks. When
used, 1-70
phr of large size particle black sS generally sufficient.
30 In addition, fluoropoiymer fillers may also be present in the composition.
Generally, from 1 to SO parts per hundred perfluoroelastomer of a
fluoropolymer filler is
used. The fluoropolymer filler can be finely divided, easily dispersed plastic
CA 02324954 2000-09-20
WO 99/48939 PCT/US99/03490
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
temperatures) of the perfluoroelastomer(s). Such finely divided, easily
dispersed
fluoroplastics are commonly called micropowders or fluoroadditives.
Micropowders are
ordinarily partially crystalline polymers.
The method of this invention comprises the use of perfluorosulfinate and an
oxidizing agent in a free-radical polymerization process. The polymerization
process
includes free-radical polymerization of monomers alone or as solutions,
emulsions, or
to dispersions in an organic solvent or water. Polymerization in an aqueous
emulsion or
suspension is often preferred because of the rapid and nearly complete
conversion of
monomers, easy removal of the heat of polymerization, and ready isolation of
the polymer.
Emulsion or suspension polymerization typically involves polymerizing monomers
in an
aqueous medium in the presence of an inorganic free-radical initiator system
and
15 surfactant or suspending agent.
Aqueous emulsion polymerization can be carried out continuously under steady-
state conditions in which, for example, monomers, water, surfactants, buffers
and catalysts
are fed continuously to a stirred reactor under optimum pressure and
temperature
conditions while the resulting emulsion or suspension is removed continuously.
An
2o alternative technique is batch or semibatch polymerization by feeding the
ingredients into
a stirred reactor and allowing them to react at a set temperature for a
specified length of
time or by charging ingredients into the reactor and feeding the monomer into
the reactor
to maintain a constant pressure until a desired amount of polymer is formed.
A class of the fluoroaliphatic sulfinates useful in this invention are found
in U.S.
25 patent No. 5,285,002 incorporated herein by reference and can be
represented bythe
following general formulae
R3fs~2M1/x (VI)
or
R2f~S02M1/x~n (VII)
3o wherein R3 f represents a monovalent fluoroaliphatic radical having, for
example, from 1 to
20 carbon atoms, preferably 4 to 10 carbon atoms, R2p represents a polyvalent,
preferably
CA 02324954 2000-09-20
WO 99/48939 PCT/US99/03490
divalent, fluoroaliphatic radical having, for example, from 1 to 20 carbon
atoms,
preferably from 2 to 10 carbon atoms, M represents a hydrogen atom or cation
with
valence x, which is 1 to 2, and is preferably l, and n is 1 to 4, preferably 1
or 2.
The monovalent fluoroaliphatic radical, R3 f is a fluorinated, stable, inert,
non-
polar, saturated moiety. It can be straight chain, branched chain, and, if
sufficiently large,
cyclic, or combinations thereof, such as alkyl cycloaliphatic radicals.
Generally, R3 f will
have 1 to 20 carbon atoms, preferably 4 to 10, and will contain 40 to 83
weight percent,
preferably 50 to 78 weight percent fluorine. The preferred compounds are those
in which
the R3 f group is fully or substantially
1o completely fluorinated, as in the case where R3 f is perfluoroalkyl,
CnF2n+1, where n is 1 to
20.
The polyvalent, preferably divalent, fluoroaliphatic radical, R2 f is a
fluorinated,
stable, inert, non-polar, saturated moiety. It can be straight chain, branched
chain, and, if
sufficiently large, cyclic or combinations thereof, such as
alkylcycloaliphatic diradicals.
Generally, R2 f will have 1 to 20 carbon atoms, preferably 2 to I 0. The
preferred
compounds are those in which the R2f group is perfluoroalkylene, CnF2n, where
n is 1 to
20, or perfluorocycloalkyl, CnF2n, where n is 5 to 20.
With respect to either R3f or R2g the skeletal chain of carbon atoms can be
interrupted by divalent oxygen, hexavalent sulfur or trivalent nitrogen hetero
atoms, each
ofwhich is bonded only to carbon atoms, but preferably where such hetero atoms
are
present, such skeletal chain does not contain more than one said hetero atom
for every two
carbon atoms. An occasional carbon-bonded hydrogen atom, iodine, bromine, or
chlorine
atom may be present; where present, however, they preferably are present not
more than
one for every two carbon atoms in the chain. Where R3g or R2 f is or contains
a cyclic
structure, such structure preferably has 6 ring member atoms, 1 or 2 of which
can be said
hetero atoms, e.g., oxygen and/or nitrogen. Examples of R3 f radicals are
fluorinated alkyl,
e.g., C4F9--, C6F13--, CgFI~--, alkoxyalkyl, e.g., C3F~OCF2--. Examples
ofR2fare
fluorinated alkylene, e.g., --C4Fg--, --CgFl6--. Where R3p is designated as a
specific
radical, e.g., CgF~~--, it should be understood that this radical can
represent an average
s
CA 02324954 2000-09-20
WO 99/48939 PCT/US99/03490
structure of a mixture, e.g., C6F13-- to C~oF21--, which mixture can also
include branched
structures.
Representative fluoroaliphatic sulfinate compounds useful in the method of
this
invention include the following:
CF3S02Na
C4F9S02H
CgFZ~S02Na
CF3C(Cl)2CF2S02K
CI(CF2)gOC2F4S02Na
1o CI(CF2)XCF2S02Na, where x is 0,1,3,4,7,9
Na02SCgF16S02Na
Na02SC6F12S02Na
Na02SC2F40C2F4S02Na
Na02SC2F40C2F4X, where X is Br or I
Na02S[C4Fg0]~C3F6S02Na
Na02SCF20(CF2CF20)In(CF20)nCF2S02Na
(CF3)2NCF2CF2S02Na
(C2F5)2NCF2CF2S02Na
N(C2F4S02Na)3
2o Na02SCgF~6S02F
Na02SCF2CF2-~.F V-CF2CF2S02Na
0 F~~l~i - CF2CF2S02Na
Na02SC3F60(C4Fg0)"C3F6S02Na where n is 4 to 8.
Combinations of monosulfinates, disulfinates, and trisulfinates can be used,
depending on whether it is desired to use sulfinate as an initiator, a
monomer, or both.
When polyvalent sulfinates, such as those represented by Formula VII, are
used, the
sulfinate is a monomer and the fluorinated moiety is incorporated into the
polymer
backbone. When monosulfinates are used the fluorinated moiety is incorporated
as a
polymer end group.
9
CA 02324954 2000-09-20
WO 99/48939 PCT/US99/03490
The amount of fluoroaliphatic sulfinate used in the methods) of the invention
can
vary, depending, for example, on the molecular weight of polymer desired.
Preferably the
amount of fluoroaliphatic sulfinate is from 0.01 to 50 mole %, and most
preferably from
0.05 to 10 mole %, of sulfinate compound based on total quantity of monomers.
In addition to the sulfinate, other reducing agents can be present, such
as sodium, potassium or ammonium sulfites, bisulfate, metabisulfite,
hyposulfite,
thiosulfite, phosphate, sodium or potassium formaldehyde sulfoxylate or
hypophosphite.
Activators such as ferrous, cuprous, and silver salts, may also be present.
The oxidizing agent used in the method of the invention is water soluble and
is
capable of converting the sulfinate to a sulfonyl moiety. The sulfonyl radical
produced in
the method of the invention is believed to eliminate S02 and form a
fluorinated radical
that initiates the polymerization of the ethylenically unsaturated monomers.
A number of useful oxidizing agents are known as taught in U.S. Patent
5,285,002.
Representative examples of such useful oxidizing agents are sodium, potassium,
and
1s ammonium persulfates, perphosphates, perborates, percarbonates, bromates,
chlorates and
hypochlorites. Other useful oxidizing agents include cerium IV compounds such
as
~4)2Ce~03)6. It is understood that this list of oxidizing agents is exemplary
only.
One of ordinary skill in the art will recognize that there are other oxidizing
agents useful
in the invention based upon this disclosure.
2o The amount of oxidizing agent used can vary depending on the particular
oxidizing
agent and sulfinate employed. Typically an equimolar amount or less (based on
the
amount of sulfinate) is used.
The curable compositions of the present invention may be prepared by mixing a
perfluoroelastomer, a peroxide curative, and other additives in conventional
rubber
2s processing equipment. Such equipment includes rubber mills, internal
mixers, such as
Banbury mixers, and mixing extruders.
Prior to the present invention, it was difficult to prepare compositions
containing
perfluoroelastomer. Typically the compositions required the use of heated
processing
equipment to keep the compositions from forming crumbly masses. The
3o perfluoroelastomer compounds of this invention do not require the use of
heated rolls or
processing equipment during compounding. They can be prepared at ambient
temperatures without forming a crumbly mass. The substantial lack of reactive
end groups
CA 02324954 2000-09-20
WO 99/48939 PCT/US99/03490
on the perfluoroelastomers is at least partially responsible for this. The
substantial lack of
these groups minimizes reactive problems, such as exotherm or significant
viscosity
increase during addition of acid acceptors. The lack of compound viscosity
increase
prevents problems with flow and filling of mold cavities. The ability to
compound at lower
temperatures minimizes the problem of premature onset of the cure or
crosslinking
reaction.
The curable compositions of the present invention are useful in production of
articles such as gaskets, tubing, and seals. Such articles are produced by
molding a
compounded formulation of the curable composition with various additives under
1o pressure, curing the part, and then subjecting it to a post cure cycle.
During the molding
step, the perfluoroelastomers of the invention demonstrate an additional
advantage. Lower
viscosity is evidenced by faster mold filling or the lower pressures required.
Improved
mold release is apparent when removing the press cured part or injection
molded part from
the mold. The cured compositions have excellent thermal stability and chemical
15 resistance. They are particularly useful in applications such as seals and
gaskets for
manufacturing semiconductor devices, and in seals for high temperature
automotive uses.
The following examples will further demonstrate the present invention. In
these
examples, the properties were tested as follows.
Mooney viscosity was determined by ASTM D 1646-96
(N>I,1+10@121°C).
2o Results are reported in Mooney units.
Cure Rheology Tests were run on compounded admixtures using a Monsanto Moving
Die Rheometer (MDR} Model 2000 in accordance with ASTM D 5289-95 at
177°C, no
preheat, 12 minute elapsed time (unless otherwise specified) and a 0.5°
arc. Values were
obtained for Minimum torque (ML), Maximum torque (MI-~, i.e., highest torque
attained
25 during specified period of time when no plateau or maximum was obtained,
were measured.
Also reported were: ts2 (time for torque to increase 2 units above ML), t'S0
(time for torque
to reach ML + 0.5{MH-ML]), and t'90 (time for torque to reach ML + 0.9[MFi-
MH]).
Torque is reported as deci Newton meters (dNm).
Press-cured samples (150 x 150 x 2.0 mm sheets, unless otherwise noted) were
3o prepared for physical property determination by pressing at about 6.9
MegaPascals (MPA)
for the indicated amount of time and temperature.
il
CA 02324954 2000-09-20
WO 99/48939 PCT/US99/03490
Post-cured samples were prepared by placing a press-cured sample in a
circulating air
oven. The oven was maintained at the indicated temperatures and the samples
treated for the
indicated amount of time.
Force per unit area is reported as Mega Pascals (MPa).
Physical properties were obtained according to ASTM D-412 and Hardness was
obtained according to ASTM D 2240.
Compression sets were determined by ASTM D 395-89 Method B with 0.139 inch
(3.5 mm) O-rings compressed for 70 hours at 200°C. Results are reported
as %.
1o EXAMPLE 1
Several fluoropolymers were prepared in a manner similar to Example 1 ofU.S.
Patent No. 5,285,002 except the monomers and other ingredients used are as
listed below
in gram weight quantities. The monomers used were tetrafluoroethylene (TFE),
perfluoromethyl vinyl ether (PMVE) and bromotrifluoroethylene (BTFE).
(NH4)2S20g
was identified as APS. The fluorochemical sulfinate (C4F9S02Na) was prepared
as
discussed in U.S. Patent
No. 5,285,002.
Comparative
Polymer A Polymer
A
Deionized (DI) water: 2,777 2,774
2o CAF 15COONH4: 15.9 15.9
IC21IP04: 10 10
C4F9S02Na: _______ 4
Precharge monomers:
TFE: 142 140
PMVE: 342 331
BTFE: 3.9 3
APS injected: 2 3
Runtime monomer fed:
TFE: 662 664
3o PMVE: 496 497
BTFE: 9.7 9.9
12
CA 02324954 2000-09-20
WO 99/48939 PC'T/US99/03490
The polymerizations were run at 60° C for 651 minutes for Comparative
Polymer A and
71° C for 262 minutes for Polymer A. Both polymerizations were run at a
pressure of 16
bar.
In both cases a water clear transparent polymer latex was obtained. The latex
was
coagulated using 30 g Al2(S04)3~18H20 in 1000 mL DI water. The polymers were
filtered, washed several times with hot DI water and dried overnight in a
circulating air
oven at 100° C to form polymer gums.
The Mooney Viscosity (ML1+10 @ 121 ° C) of Comparative Polymer A
was 76
and for Polymer A was 96.
to One hundred parts by weight of each polymer gum was compounded by adding 15
parts by weight (phr) N990 carbon black, 5 phr zinc oxide, 1.5 phr LupercoTM
101 XL,
organic peroxide from Atochem and 2 phr triallylisocyanate-Dry Liquid
Concentrate
(TAIC-DLC; 72% active), available from Harwick, to each polymer gum.
Polymer A was compounded in a conventional manner on a two-roll rubber mill.
is The Comparative Polymer A had to be compounded on a heated (50-70°
C} two-roll mill
because it was crumbly and turned powdery if it was compounded in a
conventional
manner (i.e., using standard or unheated conditions).
Table 1 shows the rheological data obtained from the MDR testing.
Table 1
20 MDR (177°C) Comparative
Compound A Compound A
ML (dNm): 5.1 3.0
MH (dNm): 26 20
ts2 (min.): 0.44 0.48
25 t'S0 (min.): 0.65 0.68
t'90 (min.): 1.51 1.76
As can be seen from the MDR data, Comparative Compound A showed a
significant increase in ML (a measure of compound viscosity) compared to the
Compound
A, even though the Mooney viscosity of Comparative Polymer A was lower than
that of
3o Polymer A. In other words, even though the raw polymer viscosity of
Comparative
Polymer A was lower than that of Polymer A, the addition of the fillers, acid
acceptors and
13
CA 02324954 2000-09-20
WO 99/48939 PCT/US99/03490
curatives made the compound viscosity of Comparative Compound A rise above
that of
Compound A.
The data shown in Table 2 was obtained after the compounds were cured.
Comparative Compound A was press cured at 150°C for 10 minutes followed
by post
curing for 16 hours at 150°C and further post curing for 8 hours at
200°C. Compound A
was press cured at 177°C for 10 minutes followed by post curing at
200°C for 20 hours.
Attempts to cure and post cure the Comparative Compound A in the same manner
as
Compound A failed due to warping and formation of fissures in the test sample.
Table 2
to Comparative
Compound A Compound
A
Tensile Strength (MPa): 24.5 19.6
Elongation at break (%): 165 136
100% modulus (MPa): 14.1 12.7
Hardness (shoreA): g7 g0
Compression set O-ripgs, 70 hrs@ 42% 30%
200 C:
The compression set resistance of Compound A was significantly better than
that
of Comparative Compound A. Comparative Compound A also required heated rolls
for
compounding, a lower press cure temperature and a two-stage postcuring.
2o EXAMPLE 2
These samples were made to demonstrate the reactivity of the polymer when
compounding with a base or acid acceptor.
Polymer B was prepared in a manner similar to Polymer A except that no BTFE
was used, 4 g of APS and 5.4 g C4F9S02Na were used, and the polymerization was
run at
2s 11.6 bar pressure.
Comparative Polymer B was prepared in a manner similar to that of Polymer B
except that no sulfinate was used, only 1 g of APS was used, and the
polymerization was
run at 11.0 bar pressure.
The Mooney Viscosity (Na,l+10 @ 121° C) ofPolymer B was 38 and
3o Comparative Polymer B was 73.
Comparative Polymer B was milled with 15 phr MT N990 carbon black and 6 phr
Ca(OH)2. The combiniation of ingredients started to exotherm and formed a
crumbly
14
CA 02324954 2000-09-20
WO 99/48939 PCT/US99/03490
compound during milling. When the resulting Comparative Compound B was
examined
by MDR at 177° C, the torque of the crumbly compound increased from the
initial 3.4
dNm to 17 dNm within 30 seconds and kept rising to 20 dNm in 10 minutes.
Polymer B was compounded with the same additives as was Comparative
Compound B. The combination of ingredients remained as a viscous sheet on the
mill and
showed less then 1.1 dNm torque rise over 8 minutes on the MDR at
177° C.
These results demonstrate the substantially lower reactivity of the compound
of the
invention when adding basic ingredients, such as acid acceptor. This
difference is
to apparent even in compounds where no cure site component is present.
