WO2000018832A1

WO2000018832A1 - Fluororubber mixtures made fast crosslinkable fluororubbers

Info

Publication number: WO2000018832A1
Application number: PCT/EP1999/006837
Authority: WO
Inventors: Ralf KRÜGER; David B. Harrison
Original assignee: Bayer Aktiengesellschaft
Priority date: 1998-09-28
Filing date: 1999-09-15
Publication date: 2000-04-06
Also published as: CA2345460A1; AU5978699A; DE19844338A1; JP2002525411A; EP1124894A1

Abstract

The present invention relates to fluororubber mixtures containing at least one fluororubber having exclusively hydrogen, alkyl and/or alkoxy groups in addition to vinylic end groups. The invention also relates to the use of said mixtures in the production of all sorts of shaped articles.

Description

Fluororubber mixtures made of quickly usable fluororubbers

The present invention relates to fluororubber mixtures containing at least one fluororubber which, in addition to vinyl end groups, exclusively

Has hydrogen, alkyl and / or alkoxy end groups, and their use for the production of moldings of all kinds.

Fluororubbers are the polymer of choice for high-temperature applications such as O-rings and seals, in which leaks must be prevented even after prolonged compression deformation. Injection molding technology is becoming increasingly popular for the mass production of these parts. It combines low production costs through shorter cycle times and a higher degree of automation with low error tolerances in the dimensions of the individual parts compared to the compression molding technology.

Many conventional fluororubbers cannot be used in injection molding technology due to their lack of scorch resistance, the early onset of crosslinking at higher temperatures and / or higher strainer. As a result, the bisphenolic crosslinkable fluororubbers are preferred in the

Injection molding technology is used because this crosslinking system combines better scorch resistance with a quick and flexible crosslinking reaction. The parts crosslinked in this way also have a better compression set than the peroxidically or aninically crosslinked parts (S. Bowers in: Kautschuk Gummi Kunststoffe, 9/1997, p. 618 ff).

A reduction in the molecular weight of the fluororubbers leads to a reduction in the viscosity, which permits shorter cycle times and work with lower pressures in the injection molding process, but generally leads to significantly poorer compression set residues in the parts produced therefrom. The bisphenolic crosslinking requires a certain minimum molecular weight of the fluororubber polymers in order to guarantee at least two bisphenolic crosslinking points per fluororubber chain. Unfortunately, fluororubbers with this molecular weight of 25,000 g / mol and higher have only very limited flowability.

There is a general desire in the rubber industry for better processability of the rubbers used. In particular, this affects the flow properties. The lower the viscosity of the raw rubber, the easier the processing technology, the greater the productivity and the less waste. The aspects mentioned are of great relevance, in particular, in the case of fluororubbers, since these are expensive rubbers which cannot be processed continuously on injection molding machines in the rubber industry.

According to the prior art, fluoroelastomers are preferably produced by aqueous emulsion or suspension polymerization (Ulimann's Encyclopedia of

Industrial Chemistry, Vol. A-l l, VCH Verlagsgesellschaft, Weinheim 1988, p. 417 ff). In general, inorganic water-soluble peroxides, such as Persulfates, used as initiators and emulsifiers or suspension stabilizers. The addition of chain transfer agents, such as carbon tetrachloride, acetone, diethyl malonate and methanol, is customary for setting the desired molecular weights. In this way, ionic or polar end groups are introduced into the polymer chain, e.g. -COF, -COOH, -COOR or OH groups. On the one hand, these impair processing behavior by increasing the mixture viscosity through intermolecular interactions, on the other hand, crosslinking by means of bisnucleophiles in the presence of an onium salt as catalyst is also hindered, see e.g. US 4524197 (Khan).

The task therefore was to provide fluororubber mixtures which at least partially do not have the disadvantages mentioned above. The invention relates to fluororubber mixtures containing a fluororubber which, in addition to vinylic end groups, have exclusively hydrogen, alkyl and / or alkoxy end groups, and an ionic crosslinking system consisting of at least one organic polyhydroxy compound, an onium salt and at least one acid acceptor. ~

The fluororubbers which can be used according to the invention are prepared in a process, characterized in that at least one fluoromonomer is polymerized in the presence of organic peroxides as initiators in at least one inert fluorine-containing solvent in the absence of water and molecular weight regulators, the solvent being selected so that the monomers are soluble are, but the polymers with a molecular weight above 25 kg / mol can no longer be dissolved.

Organic or fluoroorganic dialkyl peroxides, diacyl peroxides, dialkyl peroxydicarbonates, alkyl peresters and / or perketals are used as initiators, for example tert-butyl peroxipivalate, tert-butyl peroxy-2-ethyl-hexanoate, dicyclohexyl peroxydicarbonate, bis (trifluoroacetyl desoxydoxydoxydoxydoxydluidoxydioxide) or the meren {CF ₃ CF ₂ CF ₂ OCF (CF ₂ ) COO} ₂ .

The above Inert, fluorinated solvents used in the process are characterized in that under the reaction conditions there are no significant transfer reactions, that the resulting rubber no longer dissolves homogeneously above a molecular weight of 25 kg / mol and has no ozone damage potential. As such, certain fluorocarbon or fluorocarbon compounds containing fluorocarbon or heteroatoms are suitable, such as 1,1,1,3,3-pentafluoropropane, perfluorobutanesulfofluoride or 1,1,1,2,3,3-hexafluoropropane.

Suitable monomers for the fluororubbers which can be used according to the invention are fluorinated, optionally substituted ethylenes which, in addition to fluorine, are hydrogen and / or chlorine, such as vinylidene fluoride, tetrafluoroethylene and chlorotrifluoroethylene, fluorinated 1-alkenes with 2-8 carbon atoms, such as hexafluoropropene, 3,3,3-trifluoropropene, chloropentafluoropropene, hexafluoroisobutene and / or perfluorinated vinyl ethers of the formula

CF ₂ = CF-OX

With

X = C, -C ₃ -perfluoroalkyl or - (CF ₂ -CF YO) nR _F ,

where n = 1-4,

Y = F or CF ₃ and

Rp = C _j -C -perfluoroalkyl, are used.

The combination of vinylidene fluoride, hexafluoropropene and optionally tetrafluoroethylene and / or perfluorinated vinyl ethers, such as e.g.

Perfluoro (methyl vinyl ether) used.

The following composition is particularly preferred for the fluororubbers which can be used according to the invention: 40 to 90 mol% of vinylidene fluoride,

10 to 15 mol% of hexafluoropropylene 0 to 25 mol% of tetrafluoroethylene 0 to 25 mol% of perfluorinated vinyl ether

Formula CF = CF-OX X = C 1 -C 3 perfluoroalkyl or - (CF ₂ -CF YO) nR _F ,

in which

n = 1-4,

Y = F or CF ₃ and

R _F = -C-C ₃ perfluoroalkyl.

It is decisive for the fluororubbers which can be used according to the invention that the end groups, in addition to vinyl end groups, are exclusively hydrogen, alkyl or alkoxy groups, preferably methyl groups in addition to other alkyl groups

Depending on the organic peroxide used, e.g. 2-ethyl-pentyl or isobutyl radicals and the t-butoxy radical.

The fluororubbers which can be used according to the invention preferably contain no chlorine, bromine or iodine groups, no carbonyl (-COF, -COOH, -COOR, -COR) and no hydroxyl end groups.

The vinyl end groups are preferably -CH = CF ₂ .

The number average molecular weights of the fluororubbers which can be used according to the invention are in the range from 25 to 100 kg / mol, preferably from 40 to 80 kg / mol, with molecular weight distributions, defined as M _w / M _n , in the range from 1.5 to 3.5. The Mooney viscosities MLι ₊ ι ₀ are at 120 ° C values in the range from 1 to 40, preferably from 4 to 20. The Mooney viscosity is determined according to DIN 53 523. The organic polyhydroxy compound serves as a co-crosslinker in the fluororubber mixture according to the invention. Organic polyhydroxy compounds are state of the art, for example US 4,259,463 (Moggi et al.), US 4,912,171 (Grootaert et al.), US 5,384,374 (Guerra et al.) Or US 5,654,375 ( Jing et al.). Aromatic polyhydroxy compounds, such as 2,2-bis (4-hydroxyphenyl) ~ hexafluoropropane (“bisphenol AF”), 4,4′-dihydroxydiphenyl sulfone or fluoroaliphatic diols, such as 1,1,6,6-tetrahydrooctafluorohexanediol, are suitable for the purposes of the invention , and other compounds mentioned in U.S. 4,259,463, U.S. 4,912,171, U.S. 5,384,374 or U.S. 5,654,375, bisphenols are preferred.

The organic polyhydroxy compound is used in amounts in the range from 0.1 to 15 phr, preferably from 0.3 to 10 phr. It is of course also possible to use mixtures of different organic polyhydroxy compounds.

The onium salt serves as a catalyst or accelerator for crosslinking and is known in principle. Quaternary phosphonium, ammonium, aminophosphonium, sulfonium, arsenium or antimonium compounds are substituted with alkyl and or aryl radicals, where the alkyl and / or aryl radicals can optionally contain heteroatoms such as O, N, Si etc. For example, its called benzyltriphenylphosphonium chloride, benzyltributylphosphonium chloride, bis (benzyldiphenylphosphine) iminium chloride and other compounds mentioned in US Pat. Nos. 4,259,463, 4,912,171, 5,384,374 or 5,654,375. Benzyl tributylphosphonium chloride is preferred.

The onium salt is used in amounts ranging from 0.1 to 15 phr, preferably from 0.1 to

8 phr added.

The covemeters and accelerators can of course each be contained individually or in mixtures. In addition, it is possible to condense the polyol and the onium salt before adding them to the fluororubber mixture, for example a phosphonium phenolate being formed, cf. U.S. 4,912,171. Metal oxides or hydroxides, such as Ca (OH) ₂ , CaO, MgO, ZnO, and basic metal salts of organic acids, such as sodium stearate or magnesium oxalate, can be used as acid acceptors. These are described in more detail in US 4,912,171. The acid acceptor is used in amounts in the range from 1 to 10, preferably 2 to 8 phr.

The fluororubber mixtures according to the invention can be compounded and crosslinked by conventional methods, cf. Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, 1993, Vol. A 23, Chapter 2.6, p. 265-S. 269.

Screws, kneaders or two-roller rubber mixers can be used for compounding.

Before further processing into rubber-elastic molded articles, fillers, processing aids, further accelerators and other modifying agents can be added to the fluororubber mixture according to the invention.

Because of the low Mooney viscosity of the rubbers, the mixture is particularly advantageous for further processing into elastic molded articles

Extrusion or injection molding technology. The vulcanizable mixtures are injected into commercially available thermoplastic injection molding machines in hot molds at 160 to 230 ° C and, depending on the mixture formulation and mold temperature, held in the mold for 30 to 300 s and vulcanized in the process.

The fluororubber mixtures according to the invention are outstandingly suitable for the production of moldings of all kinds, in particular seals, hoses and profiles. Examples

Standards / conditions / information

example 1

620 ml of perfluorobutanesulfofluoride (PFBSF) were placed in a 4-1-1 autoclave. The closed autoclave was evacuated twice with cooling, then pressurized with 3 bar nitrogen pressure and slowly stirred for 10 minutes each. 440 g of vinylidene fluoride (VDF) and 880 g of hexafluoropropene (HFP) were added to the evacuated autoclave and the reaction mixture was heated to 60 ° C. with stirring. After reaching this temperature, the internal pressure in the autoclave was 27 bar. The polymerization was initiated by adding 4.25 g of TBPPI-75-AL (= tert-butyl peroxypivalate as a 75% solution in aliphates, from Peroxid-

Chemie GmbH, peroxide content 47.1%) dissolved in 20 g PFBSF. The polymerisation started after a few minutes. During the polymerization, a monomer mixture of 60% by weight vinylidene fluoride and 40% by weight hexafluoropropen was pressed in such a way that the interior of the autoclave pressure was kept constant at 26.8 + 0.2 bar. In this way, a total of 300 g of vinylidene fluoride and 200 g of hexafluoropropene were replenished within a reaction time of 14 h. After the end of the polymerization, the reaction mixture was cooled and the unreacted monomer mixture was removed from the reactor by expansion and evacuation. The remaining reactor contents were heated to 80 ° C. with stirring. 15 minutes after the stirrer was switched off, the contents of the reactor were discharged via a bottom drain valve into a second pressure vessel underneath.

After separating the product from the PFBSF, it was dried, resulting in 450 g of a rubbery copolymer.

The following copolymer composition was determined by ¹⁹ F-NMR analyzes (solvent: acetone; standard: CFC1 ₃ ): 20.5 mol% hexafluoropropene, 79.5 mol% vinylidene fluoride.

The number average molecular weight (membrane osmosis) was 68,900 g / mol. The M _w / M _n determined by GPC tests was 2.3. A value of 16 was determined at 120 ° C. for the Mooney viscosity ML _{j +} ιo (Table 1).

Example 2

To prepare a crosslinkable mixture, 100 parts by weight of the fluororubber from Example 1 were used on a well-cooled two-roll mixer

30 parts of carbon black MT N 990, 6 parts of calcium hydroxide, 3 parts of magnesium oxide (Maglite D) and 4 parts of a mixture of bisphenol AF and Viton A® (50/50 parts by weight) and 2 parts of a mixture of benzyltriphenylphosphonium chloride with Viton A® (33/66 parts by weight) incorporated. To determine the crosslinking behavior, the mixture prepared in this way was examined in a Monsanto rheometer of the type MDR 2000 E at 170 ° C. (measuring time 30 min).

The mixture was pressure-vulcanized at 170 ° C and 200 bar in molds for 1x10x10 mm plates and 6x70 mm cylinders for 30 min and then vulcanized in a convection oven (1 h at 160 ° C, 1 h at 170 ° C, 2 h at 180 ° C and 20 h at 230 ° C). The tensile / elongation properties of the vulcanized molded bodies before and after hot air aging (72 h / 275 ° C) and the compression set (cylinder, 70 h / 200 ° C) were determined. The results are in

Table 3 listed.

Example 3

The polymerization was carried out in a manner analogous to that in Example 1, using 1,1,1-pentafluoropropane instead of the PFBSF and 2.5 g of tert-butyl per-2-ethylhexanoate as the initiator instead of the TBPPI-75-AL have been used, the polymerization temperature has been increased to 78 ° C. and an initial pressure of 33.6 bar has been established accordingly.

After a running time of 15 h, 541 g of rubber were isolated. The analysis values are shown in Table 1.

Example 4

A crosslinkable rubber mixture was produced from the product from Example 3 analogously to Example 2 (Table 3). Example 5

The polymerization was carried out in a manner analogous to that in Example 1, replacing the PFBSF with 620 ml of 1,1,1,3,3-pentafluoropropane as the polymerization medium and increasing the amount of HFP to 1 026 g and correspondingly an initial pressure set from 29 bar. After a running time of 25 h, 518 g of rubber were isolated (Table 1).

Example 6

The fluororubber from Example 5 was processed and investigated analogously to Example 2 to form a crosslinkable mixture. The results are shown in Table 3.

Comparative Example 1

25.2 kg of deionized water and 30.2 g of lithium perfluorooctyl sulfonate and 29.3 g of oxalic acid dihydrate were placed in a 36-1 autoclave, a pH of 3 being established in the entire aqueous receiver. The closed autoclave was evacuated four times, then pressurized with 3 bar nitrogen pressure and slowly stirred for 10 minutes each. 269 g of vinylidene fluoride and 366 g of hexafluorophore were added to the evacuated autoclave and the reaction mixture was heated to 35 ° C. with stirring. After reaching this temperature, the internal pressure in the autoclave was 10.5 bar. The polymerization was initiated by adding 53 ml of an aqueous solution containing 20 g / 1 potassium permanganate. Immediately after the single addition, said solution was continuously metered in at a rate of 39 ml / h. The polymerization started after 20 min. During the polymerization, a monomer mixture of 60% by weight vinylidene fluoride and 40% by weight hexafluoropropene was pressed in such a way that the internal pressure in the autoclave was kept constant at 10.3 + 0.2 bar. After 250 g of monomer conversion, a total of 80 ml of diethyl malonate were added at a metering rate of 20 ml / h.

A total of 4,641 g of vinylidene fluoride and 3,078 g of hexafluoropropenes were metered in in this way within a reaction time of 7.9 h. To terminate the polymerization, the permanganate metering was stopped, the unreacted monomer mixture was removed from the reactor by expansion and evacuation, and the remaining contents of the autoclave were cooled. The resulting latex was dropped into a well-stirred template consisting of 8,000 ml of a 2% CaCl solution, then washed with deionized water and washed for

Dried for 24 hours at 60 ° C in a vacuum drying cabinet. In this way, 7.5 kg of a rubbery copolymer was isolated.

The following copolymer composition was determined by ¹⁹ F-NMR analyzes: 21.4 mol% hexafluoropropene, 78.6 mol% vinylidene fluoride.

The number average molecular weight was 79,800 g / mol. The M _w / M _n determined by GPC tests was 1.97.

A value of 34 was determined at 120 ° C. for the Mooney viscosity MLι ₊ ι ₀

(Table 2).

Comparative Example 2

The raw rubber from comparative example 1 was processed and examined analogously to example 2 to form a crosslinkable mixture. The results are described in Table 3. Comparative Example 3

Viton A 200® - a copolymer from Du Pont Dow Elastomers produced by emulsion polymerization with the properties shown in Table 2 was processed and investigated as in Example 2 to form a crosslinkable mixture. The results are also shown in Table 3.

Table 1

1) by ¹⁹ F NMR

2) by elemental analysis

3) by IR analysis (High Polymers Vol. XXV: Fluoropolymers, ed. L. Wall, Wiley, New York, (1972), 336)

4) by -NMR (Balague et al, J. Fluorine Chem. 70, (1995), 215) Table 2

1) by ¹⁹ F NMR

2) by elemental analysis

3) by IR analysis

4) by Η NMR

Table 3

5) after press vulcanization (10 min / 170 ° C) and tempering 24h / 230 ^c

All examples and comparative examples have a similar VDF content in mole percent, no chlorine, bromine or iodine end groups and also no OH end groups. In addition to vinylic end groups, the fluororubbers which can be used according to the invention have exclusively H, alkyl and alkoxy end groups. Comparative example 2 also has only H and alkyl end groups, but no vinyl end groups, while comparative example 1 has only carbonyl end groups. The advantages of the fluororubber mixtures according to the invention are shown in Table 3.

The minimum viscosity of the vulcanization compound (s' _m j _n ) is significantly lower in Examples 2 and 4 and 6 compared to Comparative Example 2 and Comparative Example 3. The crosslinking takes place significantly faster in the fluororubber mixtures according to the invention (t ₉₀ and t _9Q -t _s ι) with comparable scorch resistance (t _sj ) and comparable to slightly better tensile / elongation behavior and hot air aging properties compared to the comparison mixtures.

Claims

claims

1. fluororubber mixture comprising a fluororubber which, in addition to vinyl end groups, has exclusively hydrogen, alkyl and / or alkoxy end groups, and an ionic crosslinking system consisting of at least one organic polyhydroxy compound, an onium salt and at least one acid acceptor.

2. fluororubber mixture according to claim 1, characterized in that the Mooney viscosity MLj ₊ ιo of the fluororubber measured at 120 ° C in

Range is 1 to 40.

3. fluororubber mixture according to claim 1, characterized in that a bisphenol is used as the organic polyhydroxyl compound.

4. fluororubber mixture according to claim 1, characterized in that one uses the organic polyhydroxyl compound in amounts in the range of 0.1 to 10 phr.

5. fluororubber mixture according to claim 1, characterized in that benzyltriphenylphosphonium chloride is used as the onium salt.

6. fluororubber mixture according to claim 1, characterized in that CaO and / or MgO is used as the acid acceptor.

7. Use of a fluororubber mixture according to claim 1 for processing by injection molding or extrusion molding technology.

8. Injection molded parts made from a fluororubber mixture according to claim 1. Use of a fluororubber mixture according to claim 1 for the production of all kinds of molded articles.