CA2324954A1 - Perfluoroelastomer compositions - Google Patents
Perfluoroelastomer compositions Download PDFInfo
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- CA2324954A1 CA2324954A1 CA002324954A CA2324954A CA2324954A1 CA 2324954 A1 CA2324954 A1 CA 2324954A1 CA 002324954 A CA002324954 A CA 002324954A CA 2324954 A CA2324954 A CA 2324954A CA 2324954 A1 CA2324954 A1 CA 2324954A1
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- cure
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F214/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
- C08F214/18—Monomers containing fluorine
- C08F214/26—Tetrafluoroethene
- C08F214/262—Tetrafluoroethene with fluorinated vinyl ethers
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K5/00—Use of organic ingredients
- C08K5/04—Oxygen-containing compounds
- C08K5/14—Peroxides
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L27/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers
- C08L27/02—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment
- C08L27/12—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
Abstract
A perfluoroelastomer compound having improved processability comprising a perfluoroolefin, a perfluorovinyl ether and a halogen-containing cure site, where the polymer contains substantially no ionizable moieties; and processes for making such copolymers; and articles made therefrom.
Description
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 _::.::.::::::: '~_":''": _:::>:T:.:.::'::-..::.-.::~:.:.>.:::::_:
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'~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
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
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- 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
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....
..
:2::
::v. v 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.
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 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 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 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 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 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 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.
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 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 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 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 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 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.
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 _::.::.::::::: '~_":''": _:::>: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
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
.....
:: :.....
::::::.
::: .::
:.
::: .
_.
- 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 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.
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 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 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 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 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 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 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.
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 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 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 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 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 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.
Claims (10)
1. A peroxide curable perfluoroelastomer compound that is easily processable comprising:
A) a perfluoroelastomer substantially free of ionizable end groups, said perfluoroelastomer containing interpolymerized units derived from 1) a perfluoroolefin, 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 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, 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 proviso that the cure site component contains substantially no nitrite groups, and B) a peroxide curative.
A) a perfluoroelastomer substantially free of ionizable end groups, said perfluoroelastomer containing interpolymerized units derived from 1) a perfluoroolefin, 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 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, 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 proviso that the cure site component contains substantially no nitrite groups, and B) a peroxide curative.
2. A peroxide curable perfluoroelastomer compound according to Claim 1, wherein the perfluorovinyl ether is selected from the group consisting of perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether.
3. A peroxide curable perfluoroelastomer compound according to Claim 1, wherein the halogen of the cure site component is bromine or iodine.
4. A peroxide curable perfluoroelastomer according to Claim 1, wherein the perfluoroelastomer is substantially free of ionizable end groups selected from the group consisting of carboxylate or carboxylic acid end-groups and sulfonate or sulfonic acid end groups.
5. 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 halogen-containing cure-site component that is 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 nitrite groups.
6. The method of claim 5, wherein the halogen-containing cure-site component is a bromine-containing or iodine-containing cure-site component,
7. A shaped article comprising the peroxide curable perfluoroelastomer compound of Claim 1.
8. A peroxide curable perfluoroelastomer compound according to Claim 1 wherein the perfluoroolefin is tetrafluoroethylene, the perfluoro vinyl ether is perfluoromethyl vinyl ether.
9. A peroxide curable perfluoroelastomer compound according to Claim 1 wherein the cure-site component is said chain transfer agent.
10. A peroxide curable perfluoroelastomer compound according to Claim 1 wherein the cure site component is said chain transfer initiator.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US7906198P | 1998-03-23 | 1998-03-23 | |
| US60/079,061 | 1998-03-23 | ||
| PCT/US1999/003490 WO1999048939A1 (en) | 1998-03-23 | 1999-02-18 | Perfluoroelastomer compositions |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2324954A1 true CA2324954A1 (en) | 1999-09-30 |
Family
ID=22148172
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002324954A Abandoned CA2324954A1 (en) | 1998-03-23 | 1999-02-18 | Perfluoroelastomer compositions |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP1068248A1 (en) |
| JP (1) | JP2002507640A (en) |
| KR (1) | KR100612706B1 (en) |
| CN (1) | CN100441605C (en) |
| BR (1) | BR9908975A (en) |
| CA (1) | CA2324954A1 (en) |
| WO (1) | WO1999048939A1 (en) |
Families Citing this family (31)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1194462A1 (en) | 1999-07-02 | 2002-04-10 | Dyneon LLC | Fluoroelastomer compositions and articles made therefrom |
| US6255536B1 (en) † | 1999-12-22 | 2001-07-03 | Dyneon Llc | Fluorine containing vinyl ethers |
| US6593416B2 (en) | 2000-02-01 | 2003-07-15 | 3M Innovative Properties Company | Fluoropolymers |
| US6720360B1 (en) | 2000-02-01 | 2004-04-13 | 3M Innovative Properties Company | Ultra-clean fluoropolymers |
| IT1318487B1 (en) * | 2000-04-21 | 2003-08-25 | Ausimont Spa | FLUORO-ELASTOMERS. |
| IT1318488B1 (en) * | 2000-04-21 | 2003-08-25 | Ausimont Spa | FLUOROVINYLETERS AND POLYMERS THAT CAN BE OBTAINED. |
| US6916855B2 (en) | 2000-11-22 | 2005-07-12 | Dsm Ip Assets B.V. | Radiation curable compositions |
| US7706659B2 (en) | 2000-11-22 | 2010-04-27 | Dsm Ip Assets B.V. | Coated optical fibers |
| US7067564B2 (en) | 2000-11-22 | 2006-06-27 | Dsm Ip Assets B.V. | Coated optical fibers |
| US6730760B2 (en) | 2001-01-31 | 2004-05-04 | 3M Innovative Properties Company | Perfluoroelastomers having a low glass transition temperature and method of making them |
| US6890995B2 (en) | 2001-01-31 | 2005-05-10 | 3M Innovative Properties Company | Fluoropolymer compositions |
| US6844388B2 (en) | 2001-04-12 | 2005-01-18 | 3M Innovative Properties Company | Fluoropolymer compositions containing a nitrogen cure site monomer |
| US6803425B2 (en) | 2001-04-12 | 2004-10-12 | 3M Innovative Properties Company | Fluoropolymers having pendant imidate structures |
| US6794457B2 (en) | 2001-04-30 | 2004-09-21 | 3M Innovative Properties Company | Fluoropolymer curing system containing a nitrogen cure site monomer |
| US6916887B2 (en) * | 2002-05-02 | 2005-07-12 | Dupont Dow Elastomers Llc | Curable base-resistant fluoroelastomers |
| US6803435B2 (en) | 2002-07-18 | 2004-10-12 | 3M Innovative Properties Company | Curable fluoropolymers containing bromine groups having improved compression set |
| AU2003273314A1 (en) * | 2002-09-12 | 2004-04-30 | 3M Innovative Properties Company | Fluoroelastomers with improved permeation resistance and method for making the same |
| US6846880B2 (en) | 2002-10-11 | 2005-01-25 | 3M Innovative Properties Company | Fluoropolymer compositions |
| US6734254B1 (en) | 2003-01-13 | 2004-05-11 | 3M Innovative Properties Company | Co-curable blends featuring bromine-and iodine-containing fluoroplastic polymers |
| US6956085B2 (en) | 2003-02-14 | 2005-10-18 | 3M Innovative Properties Company | Fluoroelastomer compositions |
| ITMI20041571A1 (en) | 2004-07-30 | 2004-10-30 | Solvay Solexis Spa | perfluoroelastomers |
| ITMI20041573A1 (en) | 2004-07-30 | 2006-01-31 | Solvay Solexis Spa | FLUORO-ELASTOMERS |
| EP1630179B1 (en) * | 2004-08-25 | 2007-10-31 | Asahi Glass Company Ltd. | Fluorocopolymer |
| US7402630B2 (en) | 2004-12-16 | 2008-07-22 | 3M Innovative Properties Company | Curing compositions for fluoropolymers |
| JP2012505948A (en) | 2008-10-22 | 2012-03-08 | ダイキン工業株式会社 | Perfluoroelastomer composition |
| WO2010076876A1 (en) | 2008-12-29 | 2010-07-08 | Daikin Industries, Ltd. | Perfluoroelastomer composition and crosslinked molded article made by crosslinking and molding said perfluoroelastomer composition |
| WO2010151610A2 (en) | 2009-06-25 | 2010-12-29 | 3M Innovative Properties Company | Curing compositions for fluoropolymers |
| EP2651989B1 (en) * | 2010-12-17 | 2019-01-23 | 3M Innovative Properties Company | Microemulsions and fluoropolymers made using microemulsions |
| WO2012166578A2 (en) * | 2011-06-03 | 2012-12-06 | 3M Innovative Properties Company | Allyl ether-terminated fluoroalkyl sulfinic acids and salts thereof |
| CN103833874B (en) * | 2014-03-07 | 2016-08-17 | 中昊晨光化工研究院有限公司 | A kind of fluorubber and synthetic method thereof |
| CN114621383B (en) * | 2020-12-14 | 2023-12-12 | 中昊晨光化工研究院有限公司 | Perfluoroether elastomer emulsion, preparation method and perfluoroether elastomer |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4035565A (en) * | 1975-03-27 | 1977-07-12 | E. I. Du Pont De Nemours And Company | Fluoropolymer containing a small amount of bromine-containing olefin units |
| US5285002A (en) * | 1993-03-23 | 1994-02-08 | Minnesota Mining And Manufacturing Company | Fluorine-containing polymers and preparation and use thereof |
| US5639837A (en) * | 1996-06-04 | 1997-06-17 | E. I. Du Pont De Nemours And Company | Process for making fluoropolymers |
| JP3806941B2 (en) * | 1995-06-30 | 2006-08-09 | イー・アイ・デュポン・ドウ・ヌムール・アンド・カンパニー | Method for producing fluoropolymer |
-
1999
- 1999-02-18 BR BR9908975-0A patent/BR9908975A/en not_active Application Discontinuation
- 1999-02-18 JP JP2000537917A patent/JP2002507640A/en active Pending
- 1999-02-18 CN CNB998043354A patent/CN100441605C/en not_active Expired - Fee Related
- 1999-02-18 CA CA002324954A patent/CA2324954A1/en not_active Abandoned
- 1999-02-18 KR KR1020007010508A patent/KR100612706B1/en not_active IP Right Cessation
- 1999-02-18 WO PCT/US1999/003490 patent/WO1999048939A1/en not_active Application Discontinuation
- 1999-02-18 EP EP99908238A patent/EP1068248A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| JP2002507640A (en) | 2002-03-12 |
| WO1999048939A1 (en) | 1999-09-30 |
| KR100612706B1 (en) | 2006-08-16 |
| CN100441605C (en) | 2008-12-10 |
| KR20010034623A (en) | 2001-04-25 |
| BR9908975A (en) | 2000-12-05 |
| CN1294601A (en) | 2001-05-09 |
| EP1068248A1 (en) | 2001-01-17 |
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