JP2670793B2 - Fluorine-containing elastomer composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a fluorine-containing elastomer composition. More specifically, it relates to a perfluoro type fluorine-containing elastomer composition having improved low temperature properties.

[Conventional technology]

As perfluoro-type fluoroelastomer,
For example, the following are known, but improvement in low temperature characteristics is desired.

U.S. Patent No. 4,281,092: a copolymer of tetrafluoroethylene and perfluoro (lower alkyl vinyl _{ether), CF 2 = CF [OCF} 2 CF (CF 3)] as an oxidizing site monomer _{1 to 2} O (CF ₂₎ obtained by introducing _{1 to 4} CN. However, in this copolymer, the glass transition temperature Tg, which is a measure of low temperature characteristics, is not sufficiently lowered even if the content of perfluoro (lower alkyl vinyl ether) is increased as much as possible.

JP 58-71906 JP: formula _{Rf (OCFRCF 2) nOCF = CF} 2 [Rf: perfluoroalkyl group, R: .omega.-hydroxy perfluoroalkyl radical
A copolymer obtained by copolymerizing 15 to 50 mol% of vinyl ether represented by with tetrafluoroethylene, trifluoroethylene, and the like. This copolymer has a sufficiently low glass transition temperature Tg and is excellent in low temperature resistance, but in the copolymerization reaction carried out by the solution polymerization method, the solution viscosity increases and stirring of the polymerization system becomes difficult. , It is difficult to control the heat of polymerization and uniform heating, and in the emulsion polymerization method,
In addition to having to carry out the polymerization reaction at a relatively high temperature, the resulting copolymer often has unstable terminal groups, which causes foaming during vulcanization. However, it is difficult to obtain a stable copolymer having excellent low temperature resistance.

Unlike these types of copolymers, it has been attempted to synthesize perfluoropolyether having an ether bond in the main chain by ionic polymerization of perfluoroolefin oxide, etc. Although it is possible to obtain a polymer having a considerably low glass transition temperature Tg by increasing it, it is generally difficult to obtain an elastomeric polymer material.

[Problems to be solved by the invention]

It is an object of the present invention to overcome these problems found in the prior art, and to provide a perfluoro type fluorine-containing elastomer having no problem in terms of polymerizability and excellent in low temperature resistance in the form of a composition. I do.

[Means for solving the problem]

The fluorine-containing elastomer composition of the present invention which achieves such an object is a tetrafluoroethylene-perfluoro (lower alkyl vinyl ether) copolymer or tetrafluoroethylene-perfluoro (alkoxy lower alkyl vinyl ether) having a peroxide crosslinkable group. It comprises a copolymer, a perfluoropolyether compound having an average molecular weight of about 200 to 25,000 or its terminal iodine group and / or bromine group substituent and an organic peroxide.

The copolymerization of tetrafluoroethylene and perfluoro (lower alkyl vinyl ether) represented by perfluoro (methyl vinyl ether) or perfluoro (alkoxy lower alkyl vinyl ether) is generally about 10-70 mol% of the former in the copolymer, The latter is about 90-30
The copolymerization reaction itself is carried out in such a proportion that it accounts for mol% and the copolymerization reaction itself is carried out easily and stably, so there is no problem in terms of polymerizability.

During this copolymerization reaction, a peroxide crosslinkable group is introduced into the copolymer. The introduction of the peroxide crosslinkable group is represented by the general formula RB
A method of carrying out a copolymerization reaction in the presence of an iodine-containing bromine compound represented by rnIm (R: fluorohydrocarbon group, chlorofluorohydrocarbon group, chlorohydrocarbon group or hydrocarbon group, n, m = 1 or 2) ( Japanese Patent Publication No. 1-57125).

Examples of the perfluoropolyether compound added to the peroxide-crosslinkable group-containing copolymer include the following.

RfO (CFXCF ₂ O) _{3 to 50} CF ₂ X [I] Rf: perfluoro lower alkyl group X: CF ₃ group or F atom A method described in US Pat. Nos. 3,250,807 and 3,250,808 In the presence of a cesium fluoride catalyst, hexafluoropropene oxide or tetrafluoroethylene oxide is anionically polymerized to obtain an acid fluoride compound having a terminal -CFXCOF group, which is described in JP-B-62-10490. According to the method, about 1
By treating with fluorine gas, generally nitrogen gas diluted fluorine gas, at a temperature of 00 to 350 ° C., the compound of the above formula [I] is obtained.

RfO (CF ₂ CF ₂ O) a (CF ₂ O) b (O) cCF ₃ [II] Rf: perfluoro lower alkyl group CF ₂ CF ₂ O group, CF ₂ O group, O group: randomly distributed a, It can be c: 0 instead of b: 0.

a + b + c: about 200 or less, preferably about 40 or less As described in JP-B-49-45719 and JP-A-50-50052, it can be obtained by reacting tetrafluoroethylene with oxygen under irradiation of ultraviolet rays. Terminal-COF
By treating the acid fluoride compound having a group with fluorine gas, generally nitrogen gas diluted fluorine gas, at a temperature of about 100 to 300 ° C., a compound of the above formula [II] can be obtained. Prior to the fluorine gas treatment of the acid fluoride compound, heating to about 50 to 400 ° C. in a nitrogen gas stream gives a compound from which the peroxy bond has been removed.

RfO (CF ₂ CF ₂ CF ₂ O) _{2 to 200} CF ₂ CF ₃ [III] Rf: perfluoro lower alkyl group According to the method described in JP-A-60-202122, in the presence of a cesium fluoride catalyst, 2 Fluorine-containing polyether obtained by anionic polymerization of 1,2,3,3-tetrafluorooxetane- (CH ₂ CF ₂ CF ₂ O) n-160 to 300 ° C., fluorine gas, preferably fluorine gas under UV irradiation. The compound of the above formula [III] is obtained by treatment with This perfluoropolyether is commercially available as Daikin Product Demnum.

In addition, the terminal groups of these perfluoropolyether compounds substituted with iodine and / or bromine groups are synthesized as follows.

(A) When synthesizing the compound of the above formula [I], BrCF ₂ COF is allowed to coexist to obtain an acid fluoride compound having a terminal Rf group of BrCF ₂ CF ₂ group, and then (a) a terminal —COF group is replaced with a —COCl group. after hydrolyzed, after being converted to carboxylic acid silver salt is reacted with iodine or bromine under light irradiation to obtain a _{BrCF 2 CF 2 O (CFXCF 2} O) nCFXBr BrCF 2 CF 2 O (CFXCF 2 O) nCFXI Method (J. Am. Chem. Soc. Vol. 73, page 2461, 1951) or (b) by reacting with tetrafluoroethylene and iodine or iodine bromide, and then ICF ₂ CF ₂ O (CFXCF ₂ O) nCFXCF ₂ OCF ₂ CF ₂ I BrCF ₂ CF ₂ O (CFXCF ₂ O) nCFXCF ₂ OCP ₂ CF ₂ I Method (US Pat. No. 4,594,458) (B) US Pat. No. 3,600,315 Both methods obtained according to the method described in US Pat. the terminal -COF group perfluoropolyether compound _{FCOCFX (OCF 2 CFX) nO (} CF 2) lO (CFXCF 2 O) mCFXCOF, apply the method of the (a) (a) or (b) In the composition according to the present invention, the perfluoropolyether compound or its terminal iodine-substituted compound is tetrafluoroethylene-perfluoro (lower alkyl vinyl ether). About 5 to 100 parts by weight, preferably about 5 to 50 parts by weight, and about 10 to 100 parts by weight, preferably about 10 to 10 parts by weight of the terminal bromine or iodine and bromine-substituted product thereof, relative to 100 parts by weight of the copolymer. Each is used in a proportion of 50 parts by weight. If the addition ratio is less than this, the desired improvement in the low temperature characteristics cannot be achieved, while if it is used more than this, the decrease in the normal state physical properties cannot be ignored.

In the composition, organic peroxides as vulcanizing agents, such as benzoyl peroxide, dicumyl peroxide, 2,5
-Dimethyl-2,5-di (tertiary butylperoxy) hexane, α, α'-bis (tertiary butylperoxy) diisopropylbenzene, aliphatic or alicyclic bisperoxycarbonate, etc. are copolymers. About 0.5 to 5 per 100 parts by weight
In addition to the essential parts added by weight, polyfunctional unsaturated compounds such as triallyl cyanurate, triaryl isocyanurate, trimethacryl isocyanurate, xylylene bis (diallyl isocyanurate), divinylbenzene, and m-phenylene bismaleimide are added. As a vulcanization aid, carbon black, silica, etc. as a reinforcing agent,
Further, oxides such as lead, zinc, magnesium and calcium are appropriately added as acid acceptors.

Preparation of the composition, using a cooling roll, first knead the copolymer as a fluorine-containing elastomer and the perfluoropolyether compounds dispersed in the reinforcing agent, then other compounding agent stepping on the vulcanizing agent It is performed by adding and kneading.

〔The invention's effect〕

Tetrafluoroethylene and perfluoro (lower alkyl vinyl ether) have excellent polymerizability, and the obtained peroxide crosslinkable group-containing group polymer is a perfluoropolyether compound or its terminal iodine and / or bromine group substitution product. Is added as an additive, the low-temperature characteristics of the fluoroelastomer made of this copolymer are remarkably improved, and applications requiring elasticity and chemical resistance in a wide low-temperature range, such as rockets and fuel tanks. Provided are effective molding materials for sealing materials such as oil seals, packings and gaskets used in petrochemical plants.

In particular, when a terminal iodine and / or bromine group-substituted perfluoropolyether compound is used, these additives chemically bond with the fluorine-containing elastomer during vulcanization, so that the vulcanized product has solvent resistance. It is excellent and in fact if the additive which is extracted as a mixture is extracted with CFCl ₂ CF ₂ Cl after vulcanization, no more extraction with this solvent takes place. Further, the vulcanized product retains an excellent surface appearance for a long time and does not show a sticky phenomenon.

Further, in the case of perfluoro (alkoxy lower alkyl vinyl ether) copolymerized with tetrafluoroethylene, the obtained copolymer is generally extremely inferior in mold releasability. Thus, a significant improvement in releasability is achieved by adding a small amount of perfluoropolyether compound.

〔Example〕

 Next, effects of the present invention will be described with reference to examples.

Examples Fluorine-containing elastomer: A copolymer obtained by copolymerizing tetrafluoroethylene and perfluoro (methyl vinyl ether) in the presence of an iodine-containing bromine compound (1-iodo-2-bromotetrafluoroethane) (copolymerization molar ratio). 55/45, iodine and bromine content 0.5% by weight) Reinforcing agent: MT carbon black Vulcanizing agent: 2,5-dimethyl-2,5-di (tertiary butylperoxy) hexane (concentration 60% by weight) Vulcanization aid Agent: Triallyl isocyanurate (concentration 60% by weight) Acid acceptor: Lead oxide Additive I: Hexafluoropropene oxide polymer Average molecular weight 7300 Viscosity 408Cst (40 ° C) Additive II: Tetrafluoroethylene oxide polymer Average molecular weight Approx. 18000 Viscosity 400Cst (40 ° C) CF ₃ O (CF ₂ CF ₂ O) ₅₅ (CF ₂ O) ₁₇₀ CF ₃ Additive III: Polymer synthesized by the following method Average Molecular weight about 5700 Viscosity 280Cst (40 ℃), m + n = 31 Perfluoropolyether 560 with COF groups at both ends of the above formula obtained by the method described in U.S. Pat. No. 3,600,315
g was hydrolyzed by stirring with 3000 ml of R-113 and 1000 ml of water at room temperature for 8 hours, 20 g of sodium fluoride was added to the separated lower layer, and the mixture was stirred for about 10 minutes and filtered. Put molecular sieve 3A in the solution, leave it overnight, separate it, and add 200m to the solution.
16.8 g of potassium hydroxide dissolved in l of ethanol is added and stirred for 1 hour. The reaction solution is decolorized with activated carbon, the activated carbon is filtered off, R-113 and ethanol are distilled off under reduced pressure, and the residue powder is further dried under reduced pressure of 0.1 mmHg. The powder is extracted 3 times with 100 ml of ethanol and filtered.
After adding 500 ml of dehydrated benzene to the filtrate, benzene is distilled off under reduced pressure. The residue powder was dried under reduced pressure at 100 ° C,
700 ml of dehydrated R-113, 300 ml of dehydrated acetonitrile and 25 ml of phosphorus oxychloride are added to this powder, and the mixture is refluxed for 24 hours. The reaction product was filtered, and R-113 and the like were distilled off from the filtrate under reduced pressure to obtain 420 g of an oily COCl-terminated perfluoropolyether at both ends. 57 g of this oil, 5.0 g of silver oxide and 100 ml of Freon E-3 (product of DuPont) were mixed,
After refluxing for 5.5 hours, 5 g of bromine is added, and the mixture is refluxed for another 2 hours. After filtering it, the filtrate was washed with a 5% sodium sulfite aqueous solution, dehydrated with magnesium sulfate, and distilled under reduced pressure to give oily Br-terminated perfluoropolyether (Br content: 2.67%; calculated value: 2.81%). ) Obtained 47 g.

Additive IV: 2,2,3,3-tetrafluorooxetane polymer Average molecular weight about 7,000 Viscosity 200 Cst (40 ° C) C ₃ F ₇ O (CF ₂ CF ₂ CF ₂ O) ₄₀ C ₂ F ₅ Additive V: Polymer synthesized by the following method Average molecular weight about 4800 Viscosity 190Cst (40 ℃) Into the autoclave, add 177 g (1.0 mol) of BrCF ₂ COF, 76 g of cesium fluoride and 300 ml of tetraglyme,
Stir vigorously at room temperature for 15 hours. This was immersed in a cooling tank at -30 ° C, and 4980 g of hexafluoropropene oxide was added.
Will be added in small quantities over 24 hours. After addition is complete, at -25 ° C
Stirring is continued for 24 hours to give an oil. From this oil,
The distillate up to 100 ° C. was removed under reduced pressure, and perfluoropolyether having a Br group at one end was obtained as a brown oil. For 466.5 g of this oil, Additive III
The terminal COCl group formation reaction is performed in the same manner as in (However, 10
7.0 g of potassium hydroxide dissolved in 0 ml of ethanol was used), and 403 g of oily perfluoropolyether having COCl groups (infrared absorption spectrum: 1800 cm ⁻¹ ) as the other terminal group was obtained. 47.4 g of this oily substance, 2.7 g of silver oxide and 100 ml of Freon E-3 (product of DuPont) were mixed,
After refluxing for 5.5 hours, 2.7 g of iodine was added, followed by Additive III
Oily perfluoropolyether having one end group being a Br group and the other end group being an I group.
g was obtained.

(Activation analysis value) I 1.7%, Br 2.7% (Elemental analysis value) Calculated value C: 20.76%, F: 65.75% Measured value C: 20.65%, F: 64.22% Fluorine-containing using the above components The elastomer composition was prepared as follows.

The fluorine-containing elastomer is put into the gap between the two rolls in which cooling water is flown, and after confirming that the elastomer is wrapped around the roll, the additive dispersed in the reinforcing agent is added.
The gap between the rolls at this time is preferably narrow so that the reinforcing agent and the additive do not drop in large amounts on the tray. After adding all the amount of reinforcing agents and additives, a roll knife is used to cut back to enhance dispersion. After that, each component other than this was added in a premixed state, and the mixture was cut back for 15 minutes to uniformly disperse each component in the elastomer.

The physical properties, compression set and low temperature characteristics of the obtained composition were measured as follows.

Normal physical properties: 1 after press vulcanizing the composition at 160 ° C for 10 minutes
Oven vulcanization at 75 ° C for 6 hours gave sheet-shaped and O-ring-shaped vulcanizates, and these vulcanizates were JIS K-630.
Measured according to 1. Compression set: 25% compression of P-24 O-ring with 3.5 mm wire diameter (20
Low temperature characteristics: TR-10 test was performed and TR-10 value and TR-70 value were measured in order to read crystallization tendency during low temperature storage. Is shown in No. 1 is a comparative example.

Claims (1)

(57) [Claims] 1. A general formula RBrnIm used in a copolymerization reaction (wherein R is a fluorohydrocarbon group, a chlorofluorohydrocarbon group, a chlorohydrocarbon group or a hydrocarbon group, and n, m
Is a 1 or 2) tetrafluoroethylene-perfluoro (lower alkyl vinyl ether) having a peroxide crosslinkable group derived from an iodine-containing bromine compound represented by
Copolymer or tetrafluoroethylene-perfluoro (alkoxy lower alkyl vinyl ether) copolymer 10
0 parts by weight, perfluoropolyether compound having an average molecular weight of 200 to 25,000 or its terminal iodine substituted product 5 to 100 parts by weight or its terminal bromine or iodine and bromine substituted product
A fluorine-containing elastomer composition containing 10 to 100 parts by weight and 0.5 to 5 parts by weight of an organic peroxide.