JP2010111789A - Fluorine-containing elastomer and crosslinkable composition thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluorine-containing elastomer that produces a crosslinked product having improved compression set resistance properties while maintaining excellent ordinary state physical properties, especially elongation properties and a crosslinkable composition thereof. <P>SOLUTION: The fluorine-containing elastomer has a copolymerization composition of (a) 50-85 mol% of vinylidene fluoride, (b) 7-20 mol% of perfluoro(methyl vinyl ether), (c) 3-15 mol% of perfluorovinyl ether represented by general formula CF<SB>2</SB>=CFO[CF<SB>2</SB>CF(CF<SB>3</SB>)O]<SB>n</SB>CF<SB>3</SB>(wherein n is an integer of 2-6) and (d) 0.1-2 mol% of a terminally brominated perfluorovinyl ether represented by general formula CF<SB>2</SB>=CFO[CF<SB>2</SB>CF(CF<SB>3</SB>)O]<SB>m</SB>CF<SB>2</SB>CF<SB>2</SB>Br (wherein m is an integer of 3-5). The crosslinkable fluorine-containing elastomer composition is obtained by adding an organic peroxide, a polyfunctional unsaturated compound and an acid acceptor to the fluorine-containing elastomer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fluorine-containing elastomer and a crosslinkable composition thereof. More specifically, the present invention relates to a fluorine-containing elastomer and a crosslinkable composition thereof capable of providing a crosslinked product having improved compression set properties while maintaining good normal physical properties, particularly elongation properties.

The present applicant has previously used a fluorine-containing elastomer capable of providing a vulcanizate having excellent low-temperature characteristics and solvent resistance without impairing the molding processability and compression set resistance inherent to the fluorine-containing elastomer. As a composition with excellent properties and fuel oil resistance, its copolymer composition is
(a) Vinylidene fluoride 50-85 mol%
(b) Tetrafluoroethylene 0-25 mol%
(c) Perfluoro (methyl vinyl ether) 7-20 mol%
(d) CF ₂ = CFO [CF ₂ CF (CF ₃ ) O] nCF ₃ 3-15 mol%
(Where n is an integer from 2 to 6)
(e) RfX (Rf is an unsaturated fluorohydrocarbon group having 2 to 8 carbon atoms, 0.1 to 2 mol%
The group may have one or more ether bonds,
X is bromine or iodine)
Containing 100 to 10 parts by weight of the peroxide-crosslinkable fluorine-containing elastomer, 0.1 to 10 parts by weight of an organic peroxide, 0.1 to 10 parts by weight of a polyfunctional unsaturated compound, and 3 to 20 parts by weight of an acid acceptor. A fluoroelastomer composition is proposed.
JP 2004-346087 A

  Since this fluorine-containing elastomer composition gives a crosslinked product excellent in cold resistance and fuel oil resistance, this crosslinked product is suitably used as a sealing material for automobile fuels, but aims to further improve compression set resistance properties. In this case, if a general method for increasing the crosslink density is adopted, the normal state physical property value, particularly the elongation property is lowered, and a cross-linked product having a balance between the normal state physical property value and the compression set resistance property cannot be obtained. This is a new problem.

  An object of the present invention is to provide a fluorine-containing elastomer and a crosslinkable composition thereof capable of providing a crosslinked product having improved compression set properties while maintaining good normal physical properties, particularly elongation properties.

The object of the present invention is that the copolymer composition is
(a) Vinylidene fluoride 50-85 mol%
(b) Perfluoro (methyl vinyl ether) 7-20 mol%
(c) General formula CF ₂ = CFO [CF ₂ CF (CF ₃ ) O] _n CF ₃ 3-15 mol%
(Where n is an integer of 2 to 6)
(d) General formula CF ₂ = CFO [CF ₂ CF (CF ₃ ) O] _m CF ₂ CF ₂ Br 0.1 to ₂ mol%
(Wherein m is an integer of 3 to 5) represented by a fluorine-containing elastomer which is a terminally brominated perfluorovinyl ether and per 100 parts by weight of the fluorine-containing elastomer,
Organic peroxide 0.1 to 10 parts by weight Polyfunctional unsaturated compound 0.1 to 10 parts by weight This is achieved by a crosslinkable fluorine-containing elastomer composition comprising 3 to 20 parts by weight of an acid acceptor.

In the fluorine-containing elastomer according to the present invention, a terminal brominated perfluorovinyl ether represented by the general formula CF ₂ = CFO [CF ₂ CF (CF ₃ ) O] _m CF ₂ CF ₂ Br is used as a bromine group-containing unsaturated compound. By using a polymerized fluorine-containing elastomer, good normal physical properties, especially elongation characteristics, are maintained compared to the case of using a fluorine-containing elastomer copolymerized with an equimolar amount of CF ₂ = CFOCF ₂ CF ₂ Br. On the other hand, a cross-linked product with improved compression set resistance can be provided.

This is because the bromine group-containing unsaturated compound used in the present invention has a longer chain, so that the cold-resistant monomer CF ₂ = CFO [CF ₂ CF (CF ₃ ) O] _n CF, which is one of the polymer compositions _The steric hindrance due to ₃ can be avoided, so that the cross-linking efficiency is improved, the compression set resistance is improved, while the molecular weight between cross-linking points is extended from the structure, so it is assumed that the stretch characteristics are maintained. The

  The copolymer composition ratio of the fluorine-containing elastomer is (a) vinylidene fluoride is 50 to 85 mol%, preferably 60 to 85 mol%, (b) perfluoro (methyl vinyl ether) is 7 to 20 mol%, preferably 7 to 15 mol%, (c) 3 to 15 mol%, preferably 3 to 10 mol% of the perfluorovinyl ether represented by the above general formula, (d) 0.1% of the terminal brominated perfluorovinyl ether represented by the above general formula ˜2 mol%, preferably 0.3 to 1.5 mol%, and these composition ratios were selected as a range capable of providing a desired normal state property, in particular, a cross-linked product having an excellent balance between elongation property and compression set property. Is.

The following components (b) to (d), preferably the components (b) to (e) are copolymerized with the vinylidene fluoride as the component (a).
The component (b), perfluoro (methyl vinyl ether), is an essential component for imparting flexibility to the resulting copolymer and improving the low temperature characteristics, particularly the TR ₇₀ value in the TR test.
When the tetrafluoroethylene component (e) is further copolymerized, the solvent resistance can be remarkably improved. However, if the composition ratio of the component (e) is too large, the low temperature characteristics are impaired, so the ratio is 25 mol% or less, preferably 20 mol% or less. Further, the copolymerization of the component (e) remarkably improves resistance to oxygen-containing compound mixed fuels such as methanol / gasoline mixed fuel and ethanol / gasoline mixed fuel, and alcohol fuels such as methanol and ethanol.
As the perfluorovinyl ether of component (c), a single component of the compound represented by the general formula may be used, or a mixture of two or more having various n values may be used. The perfluorovinyl ether represented by the above general formula is obtained by reacting CF ₃ OCF (CF ₃ ) COF with hexafluoropropene oxide in the presence of a cesium fluoride catalyst, diglyme solvent, etc., and then reacting with anhydrous potassium carbonate and heat. The product is obtained by carrying out a decomposition reaction, and the product is a mixture of n = 2 to 6, but by separating it, perfluorovinyl ethers having various n values can be separated and used alone. it can. Alternatively, they can be used as a mixture without separating them.
The terminal brominated perfluorovinyl ether of component (d) is obtained by reacting BrCF ₂ COF with hexafluoropropene oxide in the presence of a cesium fluoride catalyst, diglyme solvent, etc., and terminal brominated perfluoropolyether acid fluoride.
BrCF ₂ [OCF (CF ₃ ) CF ₂ ] _m OCF (CF ₃ ) COF
Then, it is reacted with sodium carbonate in a diglyme solvent, converted to the corresponding sodium perfluoropolyether carboxylic acid sodium salt, and then obtained by performing a decarboxylation reaction by thermal decomposition, and the product is m = 3 to 5 However, by fractionating it, products having various m values can be separated and used alone. Alternatively, they can be used as a mixture without separating them.

Further, for the purpose of adjusting the molecular weight of the fluorine-containing elastomer copolymer used in the composition of the present invention or for the purpose of suppressing molding processability, particularly foaming in the curing stage, the general formula R (Br) n (I) It is very effective to carry out the copolymerization reaction in the presence of a bromine-containing and / or iodine compound represented by m. Such compounds, for example, _{ICF 2 CF 2 CF 2 CF 2} I, ICF 2 CF 2 CF 2 CF 2 Br, ICF 2 CF 2 Br and the like are used, in particular _{ICF 2 CF 2 CF 2 CF 2} I curing characteristics From the viewpoint of the above, it is preferable.
Japanese Patent Publication No.54-1585 Japanese Patent Publication No.58-4728

  These compounds act as chain transfer agents and serve to control the molecular weight of the copolymer produced. As a result of the chain transfer reaction, a copolymer having bromine and / or iodine atoms bonded to the molecular ends is obtained, and these sites serve as curing sites in the vulcanization molding stage. However, since the mechanical strength of the final molded product is lowered when the proportion used in the polymerization step is large, the proportion used is about 1% by weight or less, preferably about 0.5 to less than the total monomer weight. 0.01% by weight.

Further, in order to improve the compression set resistance of the vulcanized molded product, perfluorodivinyl ether as described below may be copolymerized. The proportion of use is about 1% by weight or less, preferably about 0.5 to 0.1% by weight, based on the total monomer weight, from the viewpoint of the mechanical properties of the molded product.
CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ OCF = CF ₂

  In addition, other monomers such as fluorinated monomers such as trifluoroethylene, hexafluoropropene, and chlorotrifluoroethylene are further copolymerized within a range that does not impair the desired properties required for the fluorinated elastomer. You may let them.

  Such a fluorine-containing elastomer can be produced by an aqueous emulsion polymerization method or an aqueous suspension polymerization method. In the aqueous emulsion polymerization method, either a water-soluble peroxide alone or a redox system in combination with a water-soluble reducing substance can be used as a reaction initiator system. Examples of water-soluble peroxides include ammonium persulfate, potassium persulfate, and sodium persulfate. Examples of water-soluble reducing substances include sodium sulfite and sodium hydrogen sulfite. At this time, a pH regulator (relaxation agent) such as sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium monohydrogen phosphate, potassium dihydrogen phosphate and the like is also used as a stabilizer for the aqueous emulsion.

As the emulsifier used in the emulsion polymerization method, a fluorinated carboxylate is generally used, preferably
CF ₃ CF ₂ CF ₂ O [CF (CF ₃ ) CF ₂ O] nCF (CF ₃ ) COONH ₄ (n: 1 or 2)
Is used. These emulsifiers are used as an aqueous solution of about 1 to 30% by weight, preferably about 5 to 20% by weight. If the amount of the emulsifier is less than this, the monomer and the produced copolymer cannot be uniformly dispersed in the aqueous medium, and if it is too much, it is economically disadvantageous.
Japanese Patent Publication No.5-139661

  The copolymerization reaction is performed at a temperature of about 20-80 ° C, preferably about 25-60 ° C. If the polymerization temperature is too high, problems such as foaming occur during the molding process, and the compression set resistance of the crosslinked molded article also deteriorates. The polymerization pressure is generally performed at about 5 MPa or less.

  The fluorine-containing elastomer thus obtained has a solution viscosity ηsp / c (35 ° C., 1 wt% methyl ethyl ketone solution) as an index of molecular weight of about 0.1 to 2 dl / g, preferably about 0.2 to 1 dl / g. It is desirable to be.

  This fluorine-containing elastomer can be cured by various conventionally known vulcanization methods such as peroxide crosslinking method, polyamine vulcanization method, polyol vulcanization method or irradiation methods such as radiation and electron beam. The peroxide cross-linking method using a product provides a cross-linked product with excellent mechanical strength and excellent chemical resistance, wear resistance, solvent resistance, etc. because the structure of the cross-linking point forms a stable carbon-carbon bond. Therefore, it is particularly preferably used.

  Examples of the organic peroxide used in the peroxide crosslinking method include 2,5-dimethyl-2,5-bis (tertiary butyl peroxy) hexane, 2,5-dimethyl-2,5-bis (tertiary butyl). Peroxy) hexyne-3, benzoyl peroxide, bis (2,4-dichlorobenzoyl) peroxide, dicumyl peroxide, di-tert-butyl peroxide, tert-butyl cumyl peroxide, tert-butyl peroxybenzene, 1 , 1-Bis (tert-butylperoxy) -3,5,5-trimethylcyclohexane, 2,5-dimethylhexane-2,5-dihydroxyperoxide, α, α'-bis (tert-butylperoxy)- Examples thereof include p-diisopropylbenzene, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, and tertiary butyl peroxyisopropyl carbonate.

  In the peroxide crosslinking method in which these organic peroxides are used, polyfunctional unsaturated compounds such as tri (meth) allyl isocyanurate, tri (meth) allyl cyanurate, triallyl trimellitate, N N′-m-phenylenebismaleimide, diallyl phthalate, tris (diallylamine) -s-triazine, triallyl phosphite, 1,2-polybutadiene, ethylene glycol diacrylate, diethylene glycol diacrylate, and the like are preferably used in combination. By using these co-crosslinking agents in combination, a crosslinked product having superior vulcanization characteristics, mechanical strength, compression set resistance, and the like can be obtained.

  Furthermore, hydrotalcite compounds and divalent metal oxides or hydroxides such as oxides or hydroxides of Ca, Mg, Pb, Zn and the like can also be used as the acid acceptor.

  Each of the above components to be blended in the peroxide crosslinking system is about 0.1 to 10 parts by weight, preferably about 0.5 to 5 parts by weight of organic peroxide per 100 parts by weight of the fluorine-containing elastomer, and if necessary The co-crosslinking agent is used in an amount of about 0.1 to 10 parts by weight, preferably about 0.5 to 5 parts by weight, and the acid acceptor is used in an amount of about 2 parts by weight or more, preferably about 3 to 20 parts by weight. If the proportion of the acid acceptor used is less than this, the corrosion resistance to the metal is impaired.

A composition formed by adding an organic peroxide, a polyfunctional unsaturated compound and an acid acceptor to a fluorine-containing elastomer gives a crosslinked product exhibiting the low-temperature characteristics shown below after the organic peroxide crosslinking.
-43 ℃ ≦ TR ₁₀ <-30 ℃ <TR ₇₀ ≦ -20 ℃
Here, the TR ₁₀ and TR ₇₀ values are 50% elongation of the sample in the TR test, and after vitrification with the glass transition temperature Tg or less, the strain gradually relaxes as the temperature is gradually raised, and the initial elongation is reduced. Shows 10% or 70% recovered temperature.

In order to satisfy the conditions for the TR ₁₀ and TR ₇₀ , the total composition amount of the perfluoro (methyl vinyl ether) of the component (b) and the perfluorovinyl ether of the component (c) is 10 mol% or more, Preferably it is 15 mol% or more. When the total amount of these component compositions is 10 mol% or less, the resulting copolymer becomes a semi-resin or the low temperature characteristics, particularly TR ₇₀ value, deteriorates.

  In crosslinking, conventionally known fillers, reinforcing agents, plasticizers, lubricants, processing aids, pigments, and the like can be appropriately blended in addition to the above components. When carbon black is used as a filler or reinforcing agent, it is generally used at a ratio of about 10 to 50 parts by weight per 100 parts by weight of the fluorine-containing elastomer.

  Each of the above components is kneaded by a commonly used mixing method such as roll mixing, kneader mixing, Banbury mixing, solution mixing, etc., and the kneaded kneaded material is generally pressed at about 100 to 250 ° C. for about 1 to 60 minutes. Vulcanization is performed by vulcanization, and oven vulcanization (secondary vulcanization) is performed at about 150 to 250 ° C. within about 30 hours.

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

Reference Example In a 500 ml stainless steel autoclave, 6.0 g of cesium fluoride and 90 g of diglyme were charged and stirred, and then 56 g of BrCF ₂ COF and 221 g of hexafluoropropene oxide were sequentially injected. When the reaction was terminated after stirring overnight, 250 g of terminal brominated perfluoropolyether acid fluoride having a purity of about 80% was obtained.
BrCF ₂ [OCF (CF ₃ ) CF ₂ ] _m OCF (CF ₃ ) COF

This terminal brominated perfluoropolyether acid fluoride was gradually dropped into a flask charged with 70 g of sodium carbonate and 100 g of diglyme while stirring to convert it into the corresponding sodium salt of polyether carboxylic acid, and then heated to 120 ° C. A decarboxylation reaction was performed to obtain a crude product having a purity of about 70%. This crude product was subjected to fractional distillation to obtain 67 g of terminal brominated perfluorovinyl ether having a boiling point of 80 to 82 ° C./267 Pa represented by the following formula (yield 22.5% based on BrCF ₂ COF).
CF ₂ = CFO (CF ₂ CF (CF ₃ ) O) ₄ (CF ₂ ) Br (FBrPr ₄ VE)

Example 1
(1) The inside of a 500 ml stainless steel autoclave was replaced with nitrogen gas, and after deaeration, the following reaction medium was charged.
Surfactant CF ₃ CF ₂ CF ₂ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COONH ₄ 30g
Na ₂ HPO ₄・ 12H ₂ 0 0.5g
Ion exchange water 250ml

The inside of the autoclave was again replaced with nitrogen gas, and after deaeration, the following reaction raw materials were charged.
Vinylidene fluoride [VdF] 40 g (74.7%)
Perfluoro (methyl vinyl ether) [FMVE] 24g (17.3%)
CF ₂ = CFO (CF ₂ CF (CF ₃ ) O) ₃ CF ₃ (MPr ₃ VE) 40 g (7.2%)
CF ₂ = CFO (CF ₂ CF (CF ₃ ) O) ₄ (CF ₂ ) ₂ Br (FBrPr ₄ VE) 6.8 g (0.8%)
ICF ₂ CF ₂ CF ₂ CF ₂ I (DIOFB) 0.5g
The percentage in parentheses is mol%.

Next, the temperature inside the autoclave was set to 50 ° C., and 0.01 g of sodium hydrogen sulfite and 0.05 g of ammonium persulfate were added as 0.3 wt% aqueous solutions to start the polymerization reaction. After reacting for 20 hours, cooling, discharging the residual gas, taking out the emulsion, adding 5 wt% calcium chloride aqueous solution to this, coagulating the polymer, washing with water, drying, solution viscosity ηsp / c 103 g of an elastomeric copolymer having a following composition (by ¹⁹ F-NMR) at 0.56 dl / g (35 ° C., 1 wt% methyl ethyl ketone solution) was obtained.
VdF 77 mol%
FMVE 15 mol%
MPr ₃ VE 7.2 mol%
FBrPr ₄ VE 0.8 mol%

(2) To 100 parts of the elastomeric copolymer obtained in (1) above (weight, the same shall apply hereinafter)
MT carbon black (Cancab product Thermax N990) 30 parts Triallyl isocyanurate (Nippon Kasei products TAIC M60) 6 parts Organic peroxide (Nippon Yushi Co., Ltd. Perhexa 25B-40) 1.4 parts
Add 4 parts of ZnO, mix with a two-roll mill, and compress the resulting crosslinkable composition at 180 ° C for 10 minutes to obtain a sheet and O-ring (P24) with a thickness of 2 mm, and further at 200 ° C for 10 hours Secondary vulcanization (oven vulcanization) was performed.

The following tests were performed on these cross-linked products.
Normal physical properties: compliant with JIS K6250,6253 Compression set: 200 ° C for P24 O-ring, according to ASTM D395 Method B
Measure values for 70 hours Low temperature characteristics: Measure TR ₁₀ and TR ₇₀ values according to ASTM D1329

Example 2
In Example 1 (1), the amount of FBrPr ₄ VE charged was changed to 3.4 g, the solution viscosity ηsp / c (35 ° C., 1 wt% methyl ethyl ketone solution) was 0.58 dl / g, and the following composition ( ¹⁹ F-NMR 103 g of an elastomeric copolymer having
VdF 76 mol%
FMVE 16.6 mol%
MPr ₃ VE 7 mol%
FBrPr ₄ VE 0.4 mol%

  Preparation of a crosslinkable composition using this elastomeric copolymer, vulcanization, and a test on a cross-linked product were carried out in the same manner as in Example 1 (2).

Comparative Example In Example 1, CF ₂ = CFO (CF ₂ ) ₂ Br [FBrVE] 2 g was used instead of FBrPr ₄ VE, and the solution viscosity ηsp / c (35 ° C., 1 wt% methyl ethyl ketone solution) was 0.56 dl / 105 g of an elastomeric copolymer having the following composition (by ¹⁹ F-NMR) was obtained.
VdF 83mol%
FMVE 11 mol%
MPr ₃ VE 5.2 mol%
FBrVE 0.8 mol%

  Preparation of a crosslinkable composition using this elastomeric copolymer, vulcanization, and a test on a cross-linked product were carried out in the same manner as in Example 1 (2).

The measurement results in the above examples and comparative examples are shown in the following table.
table
Measurement item Example 1 Example 2 Comparative example
Normal physical properties
Hardness (Duro A) 66 65 67
Tensile strength (MPa) 10.5 8.9 10.7
Elongation (%) 180 230 150
Compression set
200 ° C, 70 hours (%) 28 34 33
Low temperature characteristics
TR ₁₀ (℃) -36.2 -35.8 -35.8
TR ₇₀ (℃) -25.5 -25.2 -24.7

Claims (8)

Its copolymer composition is
(a) Vinylidene fluoride 50-85 mol%
(b) Perfluoro (methyl vinyl ether) 7-20 mol%
(c) General formula CF ₂ = CFO [CF ₂ CF (CF ₃ ) O] _n CF ₃ 3-15 mol%
(Where n is an integer of 2 to 6)
(d) General formula CF ₂ = CFO [CF ₂ CF (CF ₃ ) O] _m CF ₂ CF ₂ Br 0.1 to ₂ mol%
(Wherein m is an integer of 3 to 5) A fluorine-containing elastomer which is a terminal brominated perfluorovinyl ether.   The fluorine-containing elastomer according to claim 1, wherein the total copolymerization amount of the component (b) and the component (c) is 10 mol% or more.   The fluorine-containing elastomer according to claim 1, further comprising 25 mol% or less of (e) tetrafluoroethylene copolymerized.   The fluorine-containing elastomer according to claim 1 or 3, wherein the solution viscosity ηsp / c (35 ° C, 1 wt% methyl ethyl ketone solution) is 0.1 to 2 dl / g.   General formula R (Br) n (I) m (wherein R is a saturated fluorohydrocarbon group or saturated chlorofluorohydrocarbon group having 2 to 6 carbon atoms, n and m are 0, 1 or 2, The fluorine-containing elastomer according to claim 1 or 3, which is obtained by a copolymerization reaction in the presence of a bromine-containing and / or iodine compound represented by m + n is 2. The fluorine-containing elastomer according to claim 5, wherein the bromine-containing and / or iodine compound is ICF ₂ CF ₂ CF ₂ CF ₂ I. Per 100 parts by weight of the fluorine-containing elastomer according to claim 1 or 3,
Organic peroxide 0.1-10 parts by weight Polyfunctional unsaturated compound 0.1-10 parts by weight A fluorine-containing elastomer composition comprising 3 to 20 parts by weight of an acid acceptor. After organic peroxide crosslinking,
-43 ℃ ≦ TR ₁₀ <-30 ℃ <TR ₇₀ ≦ -20 ℃
The fluorine-containing elastomer composition according to claim 7, which gives a cross-linked product exhibiting a low-temperature characteristic represented by the formula: