Fluororubber composition for hot air crosslinking and preparation method of crosslinked fluororubber

Abstract

The invention provides a fluororubber composition, which comprises a fluorine-containing copolymer, a cross-linking agent and an optional cross-linking auxiliary agent, and the cross-linking agent comprises diacyl peroxide. The invention provides a preparation method of cross-linked fluororubber, which comprises the following steps: (1) mixing a fluorine-containing copolymer, a cross-linking agent and an optional cross-linking auxiliary agent, the cross-linking agent comprising diacyl peroxide; and (2) heating the fluororubber composition provided by the invention in the presence of air so as to realize crosslinking. The invention also provides a cross-linked fluororubber which is obtained by cross-linking the fluororubber composition provided by the invention.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of fluoroelastomer, and particularly relates to a fluoroelastomer composition for hot air crosslinking and a manufacturing method of crosslinked fluoroelastomer. BACKGROUND

[0002] Crosslinked fluoroelastomer is a material prepared by crosslinking a fluorine-containing elastomeric copolymer, and has excellent heat resistance, chemical resistance, oil resistance and weather resistance. These properties make it widely used as sealing materials such as O-rings, gaskets, oil seals and grommets in vehicles, ships, aircrafts, general machinery and construction industry, and also used as cushioning materials and covering materials for electric wires and cables.

[0003] In the prior art, such fluoroelastomer is usually crosslinked using alkyl and dialkyl organic peroxide compounds as crosslinking agents. As a widely used crosslinking agent in rubber, thermoplastic elastomer and resin, organic peroxide initiates the abstraction of hydrogen in rubber through the oxygen radicals generated by its decomposition, and then forms polymer radicals, which are then coupled with each other to achieve the crosslinking reaction of rubber. SUMMARY

[0004] Technical problems to be solved by the application

[0005] However, when alkyl and dialkyl organic peroxides are used to crosslink fluoroelastomer in air, the alkyl and dialkyl peroxides will undergo thermal decomposition, and there are volatile substances such as methane, tert-butyl alcohol and acetone in the thermal decomposition products, which will form bubbles in the fluoroelastomer, resulting in the decrease of the physical properties of the crosslinked fluoroelastomer. At the same time, the crosslinking reaction will be hindered on the surface of the fluoroelastomer due to the presence of oxygen in the air, resulting in the tackiness of the surface of the crosslinked fluoroelastomer. In order to solve these problems, the process usually adopted is to pressurize the fluoroelastomer and heat it while excluding oxygen molecules, for example, crosslinking in a steam pipe, molten salt bath, steam autoclave or exhaust sealed metal mold. However, this requires the use of special equipment to maintain the crosslinking conditions, resulting in high time and cost overheads.

[0006] Therefore, the present application aims to provide a fluoroelastomer composition for crosslinking, which can achieve crosslinking under normal pressure hot air conditions without the need for special equipment to achieve pressurization and exclusion of oxygen molecules, and the crosslinked fluoroelastomer product has no bubbles and the surface is not tacky.

[0007] In addition, the present application aims to provide a manufacturing method of crosslinked fluoroelastomer, which can achieve crosslinking under normal pressure hot air conditions without the need for special equipment to achieve pressurization and exclusion of oxygen molecules, and the crosslinked fluoroelastomer product has no bubbles and the surface is not tacky.

[0008] Technical means adopted to solve the problems

[0009] According to a first aspect of the present application, there is provided a fluororubber composition comprising a fluorine-containing copolymer, a crosslinking agent, and optionally a crosslinking aid, wherein the crosslinking agent comprises a diacyl peroxide.

[0010] According to a second aspect of the present application, there is provided a method for producing a crosslinked fluororubber, comprising the steps of:

[0011] (1) mixing a fluorine-containing copolymer, a crosslinking agent, and optionally a crosslinking aid, wherein the crosslinking agent comprises a diacyl peroxide;

[0012] (2) heating the fluororubber composition of the present application in the presence of air, thereby effecting crosslinking.

[0013] According to a third aspect of the present application, there is provided a crosslinked fluororubber obtained by crosslinking the fluororubber composition of the present application.

[0014] Effects of the Invention

[0015] According to the present application, a crosslinking fluororubber composition can be provided, which can effect crosslinking under normal pressure and hot air conditions, without the need for special equipment for pressurization and oxygen molecule removal, and without the generation of bubbles in the crosslinked fluororubber product and the surface becoming tacky.

[0016] According to the production method of the present application, crosslinking can be effected under normal pressure and hot air conditions, without the need for special equipment for pressurization and oxygen molecule removal, and without the generation of bubbles in the crosslinked fluororubber product and the surface becoming tacky. DETAILED DESCRIPTION

[0017] The ranges disclosed herein are defined by their lower and upper endpoints, given that a range is defined by selecting a lower endpoint and an upper endpoint, the selected lower and upper endpoints define the boundaries of the particular range. Ranges defined by endpoints can be inclusive or exclusive without specific recitation, and can be arbitrarily combined, i.e., any lower endpoint can be combined with any upper endpoint to form a range. For example, if ranges of 60-120 and 80-110 are listed, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, a numerical range "a-b" indicates a shorthand way of describing each and every number that is an integer within the given range of a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand way of describing each and every number that is an integer within the given range of 0 and 5. Also, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0018] In this application, all the embodiments and preferred embodiments mentioned herein can be combined with each other to form new technical solutions, unless otherwise specified.

[0019] In this application, all the technical features and preferred features mentioned herein can be combined with each other to form new technical solutions, unless otherwise specified.

[0020] In this application, all the steps mentioned herein can be performed in sequence or randomly, but preferably in sequence, unless otherwise specified. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0021] In this application, "including" and "containing" mentioned herein means open or closed, for example, "including" and "containing" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0022] In the description herein, it is to be understood that, unless otherwise specified, "above" and "below" are inclusive of the number, and "several" means two or more.

[0023] In the description herein, the term "or" is inclusive, unless otherwise stated. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0024] In the present description, unless otherwise specified, percentages (%) or parts are weight percentages or weight parts relative to the composition.

[0025] In the present description, unless otherwise specified, the sum of the contents of the components in the composition is 100%.

[0026] In the present description, unless otherwise specified, "combination thereof" means a multi-component mixture of the elements described, such as two, three, four, and up to the maximum possible multi-component mixture.

[0027] In the present description, unless otherwise specified, the term "one" means "at least one".

[0028] According to a first aspect of the present application, there is provided a fluororubber composition comprising a fluorine-containing copolymer, a crosslinking agent, and optionally a crosslinking co-agent, wherein the crosslinking agent comprises a diacyl peroxide.

[0029] Fluorine-containing copolymer

[0030] The fluororubber composition of the present application comprises a fluorine-containing copolymer. Preferably, the above fluorine-containing copolymer is a fluorine-containing elastomeric copolymer.

[0031] The fluorine-containing elastomeric copolymer of the present application is a fluorine-containing elastomeric copolymer obtained by copolymerizing tetrafluoroethylene (hereinafter referred to as TFE), propylene (hereinafter referred to as P), and perfluoro(alkyl vinyl ether) (hereinafter referred to as PAVE) as necessary.

[0032] As to the copolymerization ratio of TFE and P, the monomer ratio present in the polymerization system is determined under the condition that the repeating unit based on TFE / repeating unit based on P in the obtained fluorine-containing elastomeric copolymer is 30 / 70 to 70 / 30 (molar ratio). Preferably, the ratio of the repeating unit based on TFE and the repeating unit based on P is 45 / 55 to 65 / 35, more preferably 50 / 50 to 60 / 40 (molar ratio).

[0033] As the proportion of the monomers present in the polymerization system for obtaining the above-mentioned copolymerization ratio, it is preferable that TFE / P = 5 / 95 to 98 / 2 (molar ratio), more preferable that 40 / 60 to 95 / 5 (molar ratio), and most preferable that 50 / 50 to 93 / 7 (molar ratio).

[0034] Further, in the case where PAVE is copolymerized, the proportion of the repeating units based on TFE / repeating units based on P / repeating units based on PAVE in the obtained fluorine-containing elastomer copolymer is preferably 30 to 60 / 10 to 40 / 10 to 40 (molar ratio).

[0035] In addition, the fluorine-containing elastomer copolymer of the present application can copolymerize other monomers in addition to TFE, P, and PAVE, within a range not impairing the effects of the present application.

[0036] As the other monomers, fluorinated olefins such as monofluoroethylene, trifluoroethylene, trifluoropropylene, pentafluoropropylene, hexafluoropropylene, hexafluoroisobutylene, dichlorodifluoroethylene, hydrocarbon olefins such as ethylene, 1-butene, isobutylene, alkyl vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether, cyclohexyl vinyl ether, vinyl esters such as vinyl acetate, vinyl propionate, and the like can be exemplified.

[0037] The fluorine-containing elastomer copolymer of the present application has iodine atoms, and the content of the iodine atoms is 0.01 to 5.0 mass %.

[0038] The fluorine-containing elastomer copolymer of the present application can be produced by a production method in which tetrafluoroethylene, propylene, and, as necessary, perfluoro(alkyl vinyl ether) are copolymerized in the presence of a radical polymerization initiator and an iodine compound represented by the general formula Rl2, wherein R is an alkylene group or a perfluoroalkylene group having a carbon number of 3 or more, at a polymerization temperature in the range of 0°C to 50°C.

[0039] The iodine compound represented by the general formula Rl2 in the production method of the fluorine-containing elastomer copolymer of the present application is an iodine compound in which iodine atoms are bonded to both terminals of an alkylene group or a perfluoroalkylene group having a carbon number of 3 or more.

[0040] As specific examples, 1,3-diiodopropane, 1,4-diiodobutane, 1,6-diiodohexane, 1,8-diiodooctane, 1,3-diiodoperfluoropropane, 1,4-diiodoperfluorobutane, 1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane, and the like can be exemplified. The carbon number of the iodine compound represented by the general formula Rl2 is preferably 3 to 8. As the iodine compound represented by the general formula Rl2, more preferably is an iodine compound having a perfluoroalkylene group, and most preferably is 1,4-diiodoperfluorobutane.

[0041] In the present application, the iodine compound represented by the general formula RI2 is preferably added so that the iodine atom content in the fluorine-containing elastomer copolymer is 0.01 to 5.0 mass%. Particularly preferably, it is added so that the iodine atom content is 0.1 to 1.0 mass%.

[0042] In the production method of the fluorine-containing elastomer copolymer of the present application, as the polymerization method, there can be mentioned emulsion polymerization, solution polymerization, suspension polymerization, bulk polymerization, and the like. From the viewpoint of easiness in adjusting the molecular weight and copolymerization composition and good productivity, particularly preferably, the emulsion polymerization in which TFE and P or the like are polymerized in an aqueous medium in the presence of an emulsifier.

[0043] As the aqueous medium, preferably, there is water or water containing a water-soluble organic solvent, more preferably, water containing a water-soluble organic solvent.

[0044] As the water-soluble organic solvent, there can be mentioned t-butanol, propylene glycol, dipropylene glycol, monomethyl ether of dipropylene glycol, tripropylene glycol, and the like.

[0045] As the water-soluble organic solvent, preferably, there is t-butanol, propylene glycol, monomethyl ether of dipropylene glycol, more preferably, t-butanol.

[0046] The content of the water-soluble organic solvent in the aqueous medium is preferably 1 to 50 mass parts, more preferably 3 to 20 mass parts, with respect to 100 mass parts of water.

[0047] In the emulsion polymerization, the pH of the aqueous medium is preferably 7 to 14, more preferably 7 to 11, still more preferably 7.5 to 11, most preferably 8 to 10.5. When the pH is lower than 7, the stability of the iodine compound decreases, and the crosslinking reactivity of the resulting fluorine-containing elastomer copolymer can decrease.

[0048] It is desirable that the pH of the aqueous medium is within the above-mentioned range during the entire polymerization period from the start of the polymerization to the end of the polymerization in the emulsion polymerization, but it can not be during the entire polymerization period. It is preferred that it is during 80% or more of the entire polymerization period, more preferably 90% or more, still more preferably 95% or more.

[0049] The adjustment of the pH is preferably performed using a pH buffer. As the pH buffer, there can be mentioned inorganic salts and the like. As the inorganic salts, there can be mentioned disodium hydrogen phosphate, sodium dihydrogen phosphate, carbonates such as sodium hydrogen carbonate and sodium carbonate, and the like. As more preferable specific examples of the inorganic salts, there can be mentioned disodium hydrogen phosphate dihydrate, disodium hydrogen phosphate dodecahydrate, and the like.

[0050] As the emulsifier, because the mechanical stability and chemical stability of the latex of the resulting fluorine-containing elastomer copolymer are good, preferably, it is an ionic emulsifier, more preferably, an anionic emulsifier.

[0051] As the anionic emulsifier, known agents can be used, and as specific examples, hydrocarbon emulsifiers such as sodium lauryl sulfate, sodium dodecylbenzenesulfonate, fluorine-containing alkanoates such as ammonium perfluorooctanoate, ammonium perfluorohexanoate, and the like can be listed. As the fluorine-containing ether carboxylic acid compound represented by general formula (1) : R f1 OR f2 COOA f1 is a perfluoroalkyl group having a carbon number of 1 to 8, R f2 is a straight-chain fluorine-containing alkylene group which can contain an etheric oxygen atom and which can have a side chain of a perfluoroalkyl group having a carbon number of 1 to 3, and A is a hydrogen atom, an alkali metal, or NH4. Also, the carbon number of R f2 is preferably 1 to 12, and more preferably 1 to 8.

[0052] As the emulsifier in the present application, a fluorine-containing emulsifier is preferable, and a fluorine-containing carboxylate or a compound of general formula (1) is more preferable.

[0053] Further, the emulsifier is preferably a fluorine-containing ether carboxylic acid compound represented by general formula (2) : F(CF2) p O(CF(X)CF2O) q CF(X)COOA (hereinafter referred to as a compound of general formula (2) ) ; in general formula (2), X represents a fluorine atom or a perfluoroalkyl group having a carbon number of 1 to 3, A represents a hydrogen atom, an alkali metal, or NH4, p represents an integer of 1 to 10, and q represents an integer of 0 to 3.

[0054] As the compound represented by general formula (1) or the compound represented by general formula (2), if a compound in which A is NH4 is exemplified, the following compounds can be listed:

[0055] C2F5OCF2COONH4, C3F7OCF2COONH4, C4F9OCF2COONH4, C5F 11 OCF2COONH4, C6F 13 OCF2COONH4, CF3OCF2CF2OCF2COONH4, C2F5OCF2CF2OCF2COONH4, C3F7OCF2CF2OCF2COONH4, C4F9OCF2CF2OCF2COONH4, C5F 11 OCF2CF2OCF2COONH4, C6F 13 OCF2CF2OCF2COONH4, C2F5O(CF2CF2O)2CF2COONH4, C3F7O(CF2CF2O)2CF2COONH4, C4F9O(CF2CF2O)2CF2COONH4, C5F 11O(CF2CF2O)2CF2COONH4, C6F 13 O(CF2CF2O)2CF2COONH4, C2F5O(CF2CF2O)3CF2COONH4, C3F7O(CF2CF2O)3CF2COONH4, C4F9O(CF2CF2O)3CF2COONH4, C5F 11 O(CF2CF2O)2CF2COONH4, C2F5O(CF2CF2O)3CF2COONH4, C3F7O(CF2CF2O)3CF2COONH4, C4F9O(CF2CF2O)3CF2COONH4, C5F 13 O(CF2CF2O)2CF2COONH4, C2F5O(CF2CF2O)3CF2COONH4, C3F7O(CF2CF2O)3CF2COONH4, C4F9O(CF2CF2O)3CF2COONH4, C5F

[0056] As more preferable compounds of the general formula (2), there can be mentioned F(CF2)2OCF2CF2OCF2COONH4, F(CF2)2O(CF2CF2O)2CF2COONH4, F(CF2)3O(CF(CF3)CF2O)2CF(CF3)COONH4, F(CF2)3OCF2CF2OCF2COONH4, F(CF2)3O(CF2CF2O)2CF2COONH4, F(CF2)4OCF2CF2OCF2COONH4, F(CF2)4O(CF2CF2O)2CF2COONH4, F(CF2)2OCF(CF3)CF2OCF(CF3)COONH4, and the like.

[0057] The content of the emulsifier is preferably 0.01 to 15 parts by mass, more preferably 0.1 to 10 parts by mass, and most preferably 0.1 to 3 parts by mass, relative to 100 parts by mass of the aqueous medium.

[0058] The polymerization temperature in the production method of the fluorine-containing elastomeric copolymer of the present application is 0°C to 50°C, preferably 10°C to 40°C, more preferably 20°C to 30°C. If the polymerization temperature exceeds 50°C, the cross-linking reactivity of the resulting fluorine-containing elastomeric copolymer is significantly decreased, which is undesirable. If the polymerization temperature is within the range, the cross-linking reactivity of the resulting fluorine-containing elastomeric copolymer is good, and the mechanical properties of the cross-linked rubber are good.

[0059] As the radical polymerization initiator in the production method of the present application, a water-soluble initiator and a redox polymerization initiator are preferable. The content of the radical polymerization initiator is preferably 0.0001 to 3 mass% relative to the total mass of the monomers, more preferably 0.001 to 1 mass%.

[0060] As the water-soluble initiator, ammonium persulfate, sodium persulfate, potassium persulfate and the like, and organic initiators such as dibenzoyl peroxide, azobis isobutylamidine dihydrochloride and the like can be exemplified, and ammonium persulfate and the like are preferable. Ammonium persulfate is most preferable.

[0061] As the redox initiator, a combination of a persulfate and a reducing agent can be exemplified, and it is necessary to be a polymerization initiator which can polymerize TFE and P and the like at a polymerization temperature of 0°C to 50°C. As specific examples of the persulfate, ammonium persulfate, sodium persulfate, potassium persulfate and the like can be exemplified, and ammonium persulfate is particularly preferable. On the other hand, as the reducing agent, thiosulfate, sulfite, bisulfite, metabisulfite, hydroxymethanesulfinate and the like can be exemplified, and hydroxymethanesulfinate is preferable, and sodium hydroxymethanesulfinate is most preferable.

[0062] In addition, it is preferable to coexist with a small amount of iron salts such as iron, ferrous salts, silver sulfate and the like as the third component, and it is particularly preferable to coexist with a water-soluble iron salt. As specific examples of the water-soluble iron salt, ferrous sulfate, ferric sulfate, ferrous nitrate, ferric nitrate, ferrous chloride, ferric chloride, ferrous ammonium sulfate, ferric ammonium sulfate and the like can be exemplified.

[0063] In addition to the redox initiator system, it is preferable to further add a chelating agent. As the chelating agent, disodium ethylenediaminetetraacetate is most preferable.

[0064] The use amount of the persulfate relative to the aqueous medium (100 mass%) is preferably 0.001 to 3 mass%, more preferably 0.01 to 1 mass%, and particularly preferably 0.05 to 0.5 mass%.

[0065] The use amount of the reducing agent relative to the aqueous medium (100 mass%) is preferably 0.001 to 3 mass%, more preferably 0.01 to 1 mass%, and particularly preferably 0.05 to 0.5 mass%.

[0066] Further, the amount of the iron salt such as iron, ferrous salt, the third component such as silver sulfate, is preferably 0.0001 to 0.3 mass% with respect to the aqueous medium (100 mass%), more preferably 0.001 to 0.1 mass%, and particularly preferably 0.01 to 0.1 mass%.

[0067] The amount of the chelating agent is preferably 0.0001 to 0.3 mass% with respect to the aqueous medium (100 mass%), more preferably 0.001 to 0.1 mass%, and particularly preferably 0.01 to 0.1 mass%.

[0068] The polymerization pressure in the production method of the fluorine-containing elastomer copolymer of the present application is preferably 1.0 to 10 MPaG, more preferably 1.5 to 5.0 MPaG, and most preferably 2.0 to 4.0 MPaG. If the polymerization pressure is lower than 1.0 MPaG, the polymerization rate is extremely low and is not desirable. If it is within the range, the polymerization rate is appropriate, easy to control, and the productivity is good.

[0069] If the production method of the fluorine-containing elastomer copolymer of the present application is employed, the polymerization rate can be 10 to 100 g / L•hour. The polymerization rate is preferably 5 to 70 g / L•hour, and more preferably 30 to 50 g / L•hour. If the polymerization rate is lower than the above range, the productivity is low and is not desirable in terms of practicality. On the other hand, if it is higher than the above range, the molecular weight is low and the crosslinking property is decreased, and thus is not desirable.

[0070] The latex of the fluorine-containing elastomer copolymer obtained by the above emulsion polymerization method is coagulated by a known method, and the fluorine-containing elastomer copolymer is separated. As the coagulation method, a method of adding a metal salt to perform salting-out, a method of adding an inorganic acid such as hydrochloric acid, a method of using mechanical shearing, a method of using freezing / thawing, and the like can be exemplified.

[0071] The Mooney viscosity of the fluorine-containing elastomer copolymer of the present application is preferably 5 to 200, more preferably 10 to 170, and most preferably 20 to 100.

[0072] The Mooney viscosity is a basis of the molecular weight of rubber, and is measured as follows: according to JIS K6300, using an L-type rotor having a diameter of 38.1 mm and a thickness of 5.54 mm, at 100°C, with a preheating time set to 1 minute and a rotor rotation time set to 10 minutes. If it is within the range, the balance between the flowability and the crosslinking property is good.

[0073] The glass transition temperature of the fluorine-containing elastomer copolymer of the present application is preferably -40 to 20°C, and more preferably -20 to 10°C.

[0074] The specific gravity of the fluorine-containing elastomer copolymer of the present application is preferably 1.20 to 1.70, and more preferably 1.40 to 1.65.

[0075] Crosslinking agent

[0076] In the present invention, the crosslinking agent for crosslinking the fluororubber composition comprises a diacyl peroxide compound. The diacyl peroxide compound refers to a compound comprising a structure of Formula I.

[0077]

[0078] In the above-mentioned diacyl peroxide compounds, the two carbonyl carbon atoms may be connected to the same substituent or different substituents. Examples of the above-mentioned substituents include alkyl, alkylphenyl, chlorophenyl, bromophenyl, acylphenyl and the like.

[0079] In the present invention, the decomposition half-life of the diacyl peroxide compound is preferably 40-100°C, more preferably 50-90°C, and particularly preferably 50-80°C for a 10-hour half-life. Furthermore, the temperature for a 1-minute half-life is preferably 80-140°C, more preferably 80-130°C, and particularly preferably 100-130°C. Using a diacyl peroxide compound with a decomposition half-life within this range allows for easy decomposition under normal pressure hot air conditions, enabling crosslinking of the fluororubber composition. Furthermore, the crosslinked fluororubber product is free of bubbles and a non-sticky surface.

[0080] As the above-mentioned diacyl peroxide compound, one or a combination of two or more of benzoyl peroxide, 4-methylbenzoyl peroxide, 3,5-dimethylbenzoyl peroxide, 2,4,6-trimethylbenzoyl peroxide, 4-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 2,6-dichlorobenzoyl peroxide, 2,4,6-trichlorobenzoyl peroxide, etc. can be used, preferably benzoyl peroxide and 2,4-dichlorobenzoyl peroxide, and most preferably 2,4-dichlorobenzoyl peroxide.

[0081] If the above crosslinking agent is used, the fluororubber composition of the present invention can be crosslinked under normal pressure hot air conditions without the need for special equipment for pressurization and oxygen molecule removal. In addition, no bubbles are generated in the crosslinked fluororubber product and the surface is not sticky.

[0082] The crosslinking agent may consist solely of the diacyl peroxide compound, or may contain other crosslinking agent compounds in addition to the diacyl peroxide compound. There are no particular limitations on the other crosslinking agent compounds as long as they do not affect the practice of the present invention.

[0083] The content of the crosslinking agent described above is preferably 0.1 to 50 parts by mass, more preferably 0.2 to 40 parts by mass, more preferably 0.3 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, more preferably 1 to 10 parts by mass, and most preferably 1.5 to 7.0 parts by mass, relative to 100 parts by mass of the fluorine-containing copolymer. If the amount of the crosslinking agent used is within this range, the crosslinking speed is appropriate, the balance between the tensile strength and the elongation of the resulting crosslinked rubber is good, and further, the production of air bubbles in the crosslinked fluororubber product and the tackiness of the surface can be further achieved.

[0084] Crosslinking coagent

[0085] Optionally, the fluororubber composition of the present application contains a crosslinking aid. The crosslinking aid described above is used in order to improve the crosslinking reactivity of the fluorine-containing copolymer.

[0086] As the crosslinking aid, there is no particular limitation to the structure as long as it can improve the crosslinking reactivity of the fluorine-containing copolymer, and isopropyl isocyanate compounds, cyanuric acid ester compounds, isocyanuric acid ester compounds, and the like can be exemplified. As specific examples of the crosslinking aid, one or a combination of two or more of triallyl cyanurate, triallyl isocyanurate, trimethallyl isocyanate, and the like can be used, and triallyl cyanurate is preferred.

[0087] The content of the crosslinking aid described above is preferably 0.1 to 25 parts by mass, more preferably 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, and most preferably 5 to 10 parts by mass, relative to 100 parts by mass of the fluorine-containing copolymer. If the amount of the crosslinking aid added is within this range, the crosslinking speed is appropriate, and the balance between the strength and the elongation of the resulting crosslinked rubber is good.

[0088] Other ingredients

[0089] The fluororubber composition described above can contain other components than those described above as needed within a range not impairing the effects of the present application.

[0090] As the other components, processing aids, fillers and reinforcing agents, metal oxides, pigments, and the like can be exemplified.

[0091] As the processing aid, acid absorbers such as fatty acid esters, fatty acid metal salts, and the like can be exemplified. As specific examples, magnesium stearate, calcium stearate, and the like can be exemplified. The amount of the processing aid added is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 8 parts by mass, more preferably 0.5 to 5 parts by mass, and particularly preferably 1 to 3 parts by mass, relative to 100 parts by mass of the fluorine-containing elastomer copolymer.

[0092] As the filler and the reinforcing agent, white carbon, barium sulfate, calcium metasilicate, calcium carbonate, clay, talc, and the like can be exemplified. The amount of the filler and the reinforcing agent to be added is preferably 1 to 40 parts by mass, more preferably 2 to 30 parts by mass, more preferably 2 to 20 parts by mass, and particularly preferably 3 to 10 parts by mass, relative to 100 parts by mass of the fluorine-containing elastomeric copolymer.

[0093] As the metal oxide, the oxide of a divalent metal is preferable. As the oxide of a divalent metal, magnesium oxide, calcium oxide, zinc oxide, lead oxide, and the like can be exemplified. The amount of the metal oxide to be added is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, relative to 100 parts by mass of the fluorine-containing elastomeric copolymer.

[0094] The content of the above-mentioned other components is preferably 0.1 to 40 parts by mass, more preferably 0.5 to 30 parts by mass, and particularly preferably 1 to 20 parts by mass, relative to 100 parts by mass of the above-mentioned fluorine-containing copolymer.

[0095] According to a second aspect of the present application, there is provided a method for producing a crosslinked fluororubber, comprising the steps of:

[0096] (1) mixing a fluorine-containing copolymer, a crosslinking agent, and an optional crosslinking aid, wherein the crosslinking agent comprises a diacyl peroxide;

[0097] (2) heating the fluororubber composition of the present application in the presence of air, thereby effecting crosslinking.

[0098] In step (1), the mixing of the components can be performed using various mixing devices, including but not limited to rolls, kneaders, Banbury mixers, or rubber-extruding machines. Double roll mixing is preferable. The above-mentioned mixing process can be performed at room temperature or under heating. The above-mentioned mixing process can be performed under atmospheric pressure or under pressurized conditions.

[0099] As some specific embodiments of the above-mentioned mixing, a double roll mixer is used, the temperature of the rolls is set to 35°C to 45°C, the rotation speed of the rolls is set to 20 to 50 rpm / min, and the mixing is performed by first mixing the raw rubber (i.e., the fluorine-containing copolymer), adding the reinforcing material and the acid absorber as needed, and finally adding the crosslinking agent and the optional crosslinking aid, and passing the mixture through the rolls 10 to 20 times, with a mixing time of 30 to 40 minutes. The rotation speed of the rolls is preferably 30 to 50 rpm / min, and the number of passes is preferably 10.

[0100] In step (2), after the above-mentioned components are mixed, the mixture is subjected to hot air crosslinking, i.e., the fluororubber composition of the present application is heated in the presence of air, thereby effecting crosslinking.

[0101] The heating temperature is preferably higher than the decomposition temperature at which the half-life of the above-mentioned diacyl peroxide is 10 hours, for example, the heating temperature is preferably from 70°C to 300°C, more preferably from 90°C to 240°C, and even more preferably from 100°C to 230°C. If the heating temperature is within this range, the fluorine-containing copolymer is easily crosslinked, so that the surface does not become tacky, and no bubbles are generated in the crosslinked fluororubber product.

[0102] The heating time is preferably from 0.5 minutes to 480 minutes, more preferably from 1 minute to 60 minutes, even more preferably from 5 to 40 minutes, and most preferably from 10 to 30 minutes.

[0103] According to a third aspect of the present application, there is provided a crosslinked fluororubber obtained by crosslinking the fluororubber composition of the present application.

[0104] Examples

[0105] The present application will be described in detail below by way of examples, but the present application is not limited to these examples.

[0106] <Stretching properties>

[0107] For the crosslinked rubber sheet obtained in each of the following examples and comparative examples, a test sample was prepared by cutting with a No. 3 dumbbell, and the stretching properties (tensile strength, elongation) were measured at 25°C based on JIS K6251 using an AGS universal tester manufactured by Shimadzu Corporation.

[0108] <Hardness>

[0109] The Shore A hardness was measured based on JIS K6253 using a GS-719N hardness tester manufactured by TECLOCK Corporation.

[0110] <Surface tackiness>

[0111] For the crosslinked rubber sheet obtained in each of the following examples and comparative examples, the crosslinked rubber sheet was immediately taken out after hot air crosslinking, and the surface of the test piece was scraped with an HB pencil within 30 seconds. If the surface crosslinking was not complete, the pencil would scrape off the uncrosslinked surface. The surface crosslinking state was judged by the scraping state of the surface.

[0112] If the test piece surface was scraped and damaged, it indicated that the crosslinking was not complete, and the surface state was recorded as X.

[0113] If the test piece surface was not scraped and damaged, it indicated that the crosslinking was complete, and the surface state was recorded as O.

[0114] <Bubbles>

[0115] For the crosslinked rubber sheet obtained in each of the following examples and comparative examples, the crosslinked rubber sheet was immediately taken out after hot air crosslinking, and the presence or absence of bubbles in the test piece was confirmed with the naked eye.

[0116] If there is a bubble, mark X.

[0117] If there is no bubble, mark O.

[0118] <Fluoropolymer>

[0119] Fluoropolymer 1

[0120] After degassing the inside of a stainless steel pressure-resistant reactor having a content volume of 3200 mL equipped with an anchor blade for stirring, 1500 g of ion exchange water, 60 g of disodium hydrogen phosphate dodecahydrate, 0.9 g of sodium hydroxide, 198 g of t-butyl alcohol, 9 g of C2F5OCF2CF2OCF2COONH4 as a fluorine-containing emulsifier, and 3.8 g of ammonium persulfate were added to the reactor. Then, an aqueous solution obtained by dissolving 0.4 g of ethylenediaminetetraacetic acid disodium salt dihydrate (hereinafter referred to as EDTA) and 0.3 g of ferrous sulfate heptahydrate in 200 g of ion exchange water was added to the reactor. At this time, the pH of the aqueous medium in the reactor was 9.5.

[0121] Next, a monomer mixture gas of TFE / P = 88 / 12 (molar ratio) was pressurized at 24°C under the condition that the internal pressure of the reactor reached 2.50 MPaG. The anchor blade was rotated at 300 rpm, and 6.4 g of 1,4-diiodoperfluorobutane was added. Then, a 2.5 mass% aqueous solution of sodium hydroxymethanesulfinate dihydrate (hereinafter referred to as TINUVIN®) adjusted to pH 10.0 with sodium hydroxide (hereinafter referred to as TINUVIN® 2.5 mass% aqueous solution) was added to the reactor, and the polymerization reaction was started. Thereafter, the TINUVIN® 2.5 mass% aqueous solution was continuously added to the reactor using a high-pressure pump.

[0122] The polymerization was carried out while maintaining the polymerization temperature at 24°C, and as the polymerization proceeded, the pressure in the reactor decreased, so that when the internal pressure of the reactor decreased to 2.49 MPaG, a monomer mixture gas of TFE / P = 56 / 44 (molar ratio) was pressurized, and the internal pressure of the reactor was increased to 2.51 MPaG. This operation was repeated, and the internal pressure of the reactor was maintained at 2.49 to 2.51 MPaG, and the polymerization reaction was continuously carried out. When the total amount of the pressurized monomer mixture gas of TFE / P reached 900 g, the addition of the TINUVIN® 2.5 mass% aqueous solution was stopped, the internal temperature of the reactor was cooled to 10°C, and the polymerization reaction was stopped, and a latex of a fluoropolymer was obtained. The pH of the obtained latex was 8.0. The amount of the added TINUVIN® 2.5 mass% aqueous solution was 88 g. The polymerization time was about 7 hours.

[0123] The fluorine-containing polymer latex was added to a 5 mass% aqueous solution of calcium chloride, and the fluorine-containing polymer latex was coagulated by salting-out to precipitate the fluorine-containing polymer. The fluorine-containing copolymer was recovered by filtration. Next, the fluorine-containing copolymer was washed with ion-exchange water and dried in an oven at 100°C for 15 hours to obtain 880 g of white fluorine-containing polymer 1.

[0124] The ratio of the TFE-based repeating unit to the P-based repeating unit in the fluorine-containing polymer 1 was 56 / 44 (molar ratio). In addition, the fluorine-containing polymer 1 had a Mooney viscosity of 80, a specific gravity of 1.55, and a glass transition temperature of -3°C.

[0125] Fluorine-containing polymer 2

[0126] The fluorine-containing polymer 2 was "AFLAS 150E" manufactured by AGC Inc., which is a tetrafluoroethylene-propylene copolymer having a molar ratio of TFE-based repeating unit to P-based repeating unit of 56 / 44.

[0127] Example 1

[0128] To 100 parts by mass of the fluorine-containing polymer 1 prepared above, 1.5 parts by mass of 2,4-dichlorobenzoyl peroxide (DCBP), 1 part by mass of calcium stearate, 10 parts by mass of white carbon, and 13.5 parts by mass of powder TAIC WH-60 (a mixture of TAIC and silica, in which the purity of TAIC is 60%) were added, and the fluorine-containing polymer 1 was masticated using an 8-inch roll mill with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min. After the mastication, the white carbon as a reinforcing material and the calcium stearate as an acid acceptor were added, and finally the DCBP as a crosslinking agent and the powder TAIC WH-60 as a crosslinking aid were added. The mixture was mixed by passing through the roll 10 times, and the mixing time was 35 min. Then, the crosslinking was performed by heating under hot air at 160°C for 20 min to obtain a crosslinked fluorine resin 1. The crosslinked fluorine resin 1 had no significant bubbles in the rubber sheet, and the surface was not tacky.

[0129] Example 2

[0130] To 100 parts by mass of the fluoropolymer 1 prepared above, 2 parts by mass of DCPB, 1 part by mass of calcium stearate, 10 parts by mass of white carbon, and 13.5 parts by mass of powder TAIC WH-60 were added, and an 8-inch roll mill was used with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min. The fluoropolymer 1 was first masticated, and then the white carbon as a reinforcing material and the calcium stearate as an acid acceptor were added, and finally the DCPB as a crosslinking agent and the powder TAIC WH-60 as a crosslinking co-agent were added. The mixture was mixed by 10 thin passes, and the mixing time was 35 min. Then, crosslinking was performed by heating under hot air at 160°C for 20 min, and a crosslinked fluororesin 2 was prepared. The rubber sheet of the crosslinked fluororesin 2 had no obvious bubbles and the surface was not tacky.

[0131] Example 3

[0132] To 100 parts by mass of the fluoropolymer 1 prepared above, 2 parts by mass of DCPB, 1 part by mass of calcium stearate, 10 parts by mass of white carbon, and 13.5 parts by mass of powder TAIC WH-60 were added, and an 8-inch roll mill was used with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min. The fluoropolymer 1 was first masticated, and then the white carbon as a reinforcing material and the calcium stearate as an acid acceptor were added, and finally the DCPB as a crosslinking agent and the powder TAIC WH-60 as a crosslinking co-agent were added. The mixture was mixed by 10 thin passes, and the mixing time was 35 min. Then, crosslinking was performed by heating under hot air at 160°C for 20 min, and a crosslinked fluororesin 2 was prepared. The rubber sheet of the crosslinked fluororesin 2 had no obvious bubbles and the surface was not tacky.

[0133] Example 4

[0134] To 100 parts by mass of the fluoropolymer 1 prepared above, 2 parts by mass of DCPB, 1 part by mass of calcium stearate, 10 parts by mass of white carbon, and 13.5 parts by mass of powder TAIC WH-60 were added, and an 8-inch roll mill was used with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min. The fluoropolymer 1 was first masticated, and then the white carbon as a reinforcing material and the calcium stearate as an acid acceptor were added, and finally the DCPB as a crosslinking agent and the powder TAIC WH-60 as a crosslinking co-agent were added. The mixture was mixed by 10 thin passes, and the mixing time was 35 min. Then, crosslinking was performed by heating under hot air at 160°C for 20 min, and a crosslinked fluororesin 2 was prepared. The rubber sheet of the crosslinked fluororesin 2 had no obvious bubbles and the surface was not tacky.

[0135] Example 5

[0136] To 100 parts by mass of the fluoropolymer 1 prepared above, 5 parts by mass of DCBP, 1 part by mass of calcium stearate, 10 parts by mass of white carbon, and 13.5 parts by mass of powder TAIC WH-60 were added, and an 8-inch roll mill was used with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min. The fluoropolymer 1 was first masticated, and then the white carbon as a reinforcing material and the calcium stearate as an acid acceptor were added, and finally the DCBP as a crosslinking agent and the powder TAIC WH-60 as a crosslinking co-agent were added. The mixture was mixed by 10 thin passes, and the mixing time was 35 min. Then, crosslinking was performed by heating under hot air at 160°C for 20 min, and crosslinked fluororesin 5 was prepared. The rubber sheet of the crosslinked fluororesin 5 had no obvious bubbles and the surface was not tacky.

[0137] Example 6

[0138] To 100 parts by mass of the fluoropolymer 1 prepared above, 7 parts by mass of DCBP, 1 part by mass of calcium stearate, 10 parts by mass of white carbon, and 13.5 parts by mass of powder TAIC WH-60 were added, and an 8-inch roll mill was used with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min. The fluoropolymer 1 was first masticated, and then the white carbon as a reinforcing material and the calcium stearate as an acid acceptor were added, and finally the DCBP as a crosslinking agent and the powder TAIC WH-60 as a crosslinking co-agent were added. The mixture was mixed by 10 thin passes, and the mixing time was 35 min. Then, crosslinking was performed by heating under hot air at 160°C for 20 min, and crosslinked fluororesin 6 was prepared. The rubber sheet of the crosslinked fluororesin 6 had no obvious bubbles and the surface was not tacky.

[0139] Example 7

[0140] To 100 parts by mass of the fluoropolymer 1 prepared above, 2 parts by mass of benzoyl peroxide (BPO), 1 part by mass of calcium stearate, 10 parts by mass of white carbon, and 13.5 parts by mass of powder TAIC WH-60 were added, and an 8-inch roll mill was used with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min. The fluoropolymer 1 was first masticated, and then the white carbon as a reinforcing material and the calcium stearate as an acid acceptor were added, and finally the BPO as a crosslinking agent and the powder TAIC WH-60 as a crosslinking co-agent were added. The mixture was mixed by 10 thin passes, and the mixing time was 35 min. Then, crosslinking was performed by heating under hot air at 160°C for 20 min, and crosslinked fluororesin 7 was prepared. The rubber sheet of the crosslinked fluororesin 7 had no obvious bubbles and the surface was not tacky.

[0141] Example 8

[0142] To 100 parts by mass of the fluoropolymer 1 prepared above, 5 parts by mass of BPO, 1 part by mass of calcium stearate, 10 parts by mass of white carbon, and 13.5 parts by mass of TAIC WH-60 powder were added. Using an 8-inch open mill, with the roll temperature set at 40°C and the roll speed set at 30 rpm / min, the fluoropolymer 1 was first masticated. Then, the white carbon as a reinforcement and calcium stearate as an acid absorber were added. Finally, BPO as a crosslinking agent and TAIC WH-60 powder as a crosslinking aid were added. The mixture was mixed by passing it through the mill 10 times for 35 minutes. The mixture was then heated in hot air at 160°C for 20 minutes for crosslinking, producing crosslinked fluororesin 8. The rubber sheet of crosslinked fluororesin 8 had no visible bubbles and was non-sticky.

[0143] The component contents and physical property measurement results of Examples 1 to 8 are summarized in Table 1.

[0144] [Table 1]

[0145]

[0146] Comparative Example 1

[0147] To 100 parts by mass of the fluoropolymer 1 prepared above were added 3 parts by mass of 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane (3M), 1 part by mass of calcium stearate, 10 parts by mass of carbon black N990, and 3 parts by mass of high-purity liquid TAIC. Using an 8-inch open mill with the rolls set to 40°C and 30 rpm / min, the fluoropolymer 1 was first masticated. Carbon black N990 as a reinforcement and calcium stearate as an acid absorber were then added. Finally, 3M as a crosslinking agent and high-purity liquid TAIC as a crosslinking aid were added. The mixture was mixed by passing it through the mill 10 times for 35 minutes. The mixture was then heated in hot air at 170°C for 20 minutes for crosslinking, producing crosslinked fluororesin 9. The rubber sheet of crosslinked fluororesin 9 had noticeable bubbles within it and a sticky surface.

[0148] Comparative Example 2

[0149] To 100 parts by mass of the fluoropolymer 1 prepared above, 3 parts by mass of 3M, 1 part by mass of calcium stearate, 10 parts by mass of carbon black N990, and 13.5 parts by mass of powder TAIC WH-60 were added, and an 8-inch roll mill was used with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min. The fluoropolymer 1 was first masticated, and then the carbon black N990 as a reinforcing material and the calcium stearate as an acid absorber were added, and finally the 3M as a crosslinking agent and the powder TAIC WH-60 as a crosslinking co-agent were added. The mixture was mixed in a manner of passing 10 times, and the mixing time was 35 min. Crosslinking was performed by heating under hot air at 170°C for 20 min, and a crosslinked fluororesin 10 was prepared. The rubber sheet of the crosslinked fluororesin 10 had a significant bubble in the inside and the surface was tacky.

[0150] Comparative Example 3

[0151] To 100 parts by mass of the fluoropolymer 1 prepared above, 5 parts by mass of 3M, 1 part by mass of calcium stearate, 10 parts by mass of carbon black N990, and 13.5 parts by mass of powder TAIC WH-60 were added, and an 8-inch roll mill was used with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min. The fluoropolymer 1 was first masticated, and then the carbon black N990 as a reinforcing material and the calcium stearate as an acid absorber were added, and finally the 3M as a crosslinking agent and the powder TAIC WH-60 as a crosslinking co-agent were added. The mixture was mixed in a manner of passing 10 times, and the mixing time was 35 min. Crosslinking was performed by heating under hot air at 170°C for 20 min, and a crosslinked fluororesin 11 was prepared. The rubber sheet of the crosslinked fluororesin 11 had a significant bubble in the inside and the surface was tacky.

[0152] Comparative Example 4

[0153] To 100 parts by mass of the fluoropolymer 1 prepared above, 2 parts by mass of 1,4-bis(tert-butylperoxy isopropyl) benzene (PF), 1 part by mass of calcium stearate, 10 parts by mass of carbon black N990, and 8 parts by mass of powder TAIC WH-60 were added, and an 8-inch roll mill was used with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min. The fluoropolymer 1 was first masticated, and then the carbon black N990 as a reinforcing material and the calcium stearate as an acid absorber were added, and finally the PF as a crosslinking agent and the powder TAIC WH-60 as a crosslinking co-agent were added. The mixture was mixed in a manner of passing 10 times, and the mixing time was 35 min. Crosslinking was performed by heating under hot air at 170°C for 20 min, and a crosslinked fluororesin 12 was prepared. The rubber sheet of the crosslinked fluororesin 12 had a significant bubble in the inside and the surface was tacky.

[0154] Comparative Example 5

[0155] To 100 parts by mass of the fluoropolymer 1 prepared above, 2 parts by mass of PF, 1 part by mass of calcium stearate, 10 parts by mass of white carbon, and 3 parts by mass of high-purity liquid TAIC were added, and an 8-inch open mill was used with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min. The fluoropolymer 1 was first masticated, and then the white carbon as a reinforcing material and the calcium stearate as an acid acceptor were added, and finally the PF as a crosslinking agent and the high-purity liquid TAIC as a crosslinking co-agent were added. The mixing was performed in a manner of thin passing 10 times, and the mixing time was 35 min. Crosslinking was performed by heating under hot air at 170°C for 20 min, and a crosslinked fluororesin 13 was produced. The crosslinked fluororesin 13 had a significant bubble in the rubber sheet, and the surface was tacky.

[0156] Comparative Example 6

[0157] To 100 parts by mass of the fluoropolymer 1 prepared above, 2 parts by mass of PF, 1 part by mass of calcium stearate, 10 parts by mass of white carbon, and 3 parts by mass of high-purity liquid TAIC were added, and an 8-inch open mill was used with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min. The fluoropolymer 1 was first masticated, and then the white carbon as a reinforcing material and the calcium stearate as an acid acceptor were added, and finally the PF as a crosslinking agent and the high-purity liquid TAIC as a crosslinking co-agent were added. The mixing was performed in a manner of thin passing 10 times, and the mixing time was 35 min. Crosslinking was performed by heating under hot air at 170°C for 20 min, and a crosslinked fluororesin 13 was produced. The crosslinked fluororesin 13 had a significant bubble in the rubber sheet, and the surface was tacky.

[0158] Comparative Example 7

[0159] To 100 parts by mass of the fluoropolymer 1 prepared above, 2 parts by mass of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (25B), 1 part by mass of calcium stearate, 10 parts by mass of carbon black N990, and 3 parts by mass of high-purity liquid TAIC were added, and an 8-inch open mill was used with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min. The fluoropolymer 1 was first masticated, and then the carbon black N990 as a reinforcing material and the calcium stearate as an acid acceptor were added, and finally the 25B as a crosslinking agent and the high-purity liquid TAIC as a crosslinking co-agent were added. The mixing was performed in a manner of thin passing 10 times, and the mixing time was 35 min. Crosslinking was performed by heating under hot air at 170°C for 20 min, and a crosslinked fluororesin 15 was produced. The crosslinked fluororesin 15 had a significant bubble in the rubber sheet, and the surface was tacky.

[0160] The component contents and the physical property measurement results of Comparative Examples 1 to 7 are summarized in Table 2.

[0161] [Table 2]

[0162]

[0163] Comparative Example 8

[0164] To 100 parts by mass of the fluoropolymer 1 prepared above, 2 parts by mass of DCPB, 1 part by mass of calcium stearate, 10 parts by mass of carbon black N990, and 13.5 parts by mass of the powder TAIC WH-60 were added, and the fluoropolymer 1 was first masticated using an 8-inch open mill with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min, and then the carbon black N990 as a reinforcing material and the calcium stearate as an acid acceptor were added, and finally the DCPB as a crosslinking agent and the powder TAIC WH-60 as a crosslinking co-agent were added, and the mixture was mixed by 10 thin passes, with the mixing time being 35 min. Then, crosslinking was performed by heating under hot air at 160°C for 20 min, and it was found that crosslinking could not be completed.

[0165] Comparative Example 9

[0166] To 100 parts by mass of the fluoropolymer 2 prepared above, 2 parts by mass of DCPB, 1 part by mass of calcium stearate, 10 parts by mass of white carbon black, and 13.5 parts by mass of the powder TAIC WH-60 were added, and the fluoropolymer 2 was first masticated using an 8-inch open mill with the roll temperature set to 40°C and the roll rotation speed set to 30 rpm / min, and then the white carbon black as a reinforcing material and the calcium stearate as an acid acceptor were added, and finally the DCPB as a crosslinking agent and the powder TAIC WH-60 as a crosslinking co-agent were added, and the mixture was mixed by 10 thin passes, with the mixing time being 35 min. Then, crosslinking was performed by heating under hot air at 160°C for 20 min, and it was found that crosslinking could not be completed.

[0167] The component contents and the physical property measurement results of Comparative Examples 8 and 9 are summarized in Table 3.

[0168] [Table 3]

[0169]

[0170] The present application is explained by the above examples, but the present application is not limited to the above detailed constitution, i.e. it does not mean that the present application must depend on the above detailed constitution to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of the components selected by the present application, addition of auxiliary components, selection of specific modes, etc. all fall within the protection scope and disclosure scope of the present application.

[0171] Possibility of industrial utilization

[0172] The cross-linking fluororubber composition of the present application can be cross-linked under normal pressure and hot air conditions without the need for special equipment for pressurization and oxygen molecule removal, and no bubbles are generated in the cross-linked fluororubber product and the surface is not tacky. The cross-linked fluororubber produced has excellent heat resistance, chemical resistance, oil resistance and weather resistance, and is widely used as a sealing material and a cushioning material in vehicles, ships, aircraft, general machinery and the construction industry, and as a coating material for electric wires and cables.

Claims

1. A fluoroelastomer composition comprising a fluorine-containing copolymer, a crosslinking agent, and optionally a crosslinking co-agent, wherein, The crosslinking agent contains a diacyl peroxide.

2. The fluoroelastomer composition of claim 1, wherein, The fluorine-containing copolymer is a fluorine-containing copolymer having a unit based on tetrafluoroethylene and a unit based on propylene.

3. The fluoroelastomer composition of claim 1, wherein, The fluorine-containing copolymer has an iodine atom.

4. The fluoroelastomer composition of claim 1, wherein, The diacyl peroxide-based compound contains one or a combination of two or more selected from the group consisting of benzoyl peroxide, 4-methylbenzoyl peroxide, 3,5-dimethylbenzoyl peroxide, 2,4,6-trimethylbenzoyl peroxide, 4-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 2,6-dichlorobenzoyl peroxide, 2,4,6-trichlorobenzoyl peroxide, preferably benzoyl peroxide and 2,4-dichlorobenzoyl peroxide, and most preferably 2,4-dichlorobenzoyl peroxide.

5. The fluoroelastomer composition of claim 1, wherein, The content of the crosslinking agent is preferably 0.1 to 50 parts by mass, more preferably 0.2 to 40 parts by mass, more preferably 0.3 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, more preferably 1 to 10 parts by mass, and most preferably 1.5 to 7.0 parts by mass, relative to 100 parts by mass of the fluorine-containing copolymer.

6. The fluoroelastomer composition of claim 1, wherein, The crosslinking coagent contains one or a combination of two or more selected from the group consisting of triallyl cyanurate, triallyl isocyanurate, and trimethallyl isocyanurate, preferably triallyl cyanurate.

7. The fluoroelastomer composition of claim 1, wherein, The content of the crosslinking coagent is preferably 0.1 to 25 parts by mass, more preferably 0.5 to 20 parts by mass, more preferably 1 to 15 parts by mass, and most preferably 5 to 10 parts by mass, relative to 100 parts by mass of the fluorine-containing copolymer.

8. The fluororubber composition according to claim 1, further comprising one or a combination of two or more selected from the group consisting of a processing aid, a filler and a reinforcing agent, and a metal oxide.

9. A production method of a crosslinked fluororubber, comprising the steps of: (1) mixing the fluorine-containing copolymer, the crosslinking agent, and the optional crosslinking co-agent, wherein The crosslinking agent contains a diacyl peroxide; (2) heating the fluororubber composition of the present application in the presence of air, thereby effecting crosslinking.

10. The method of producing a crosslinked fluororubber according to claim 9, wherein, In step (2), the temperature is preferably 70°C to 300°C, more preferably 90°C to 240°C, and more preferably 100°C to 230°C, and the heating time is preferably 0.5 minutes to 480 minutes, more preferably 1 minute to 60 minutes, more preferably 5 to 40 minutes, and most preferably 10 to 30 minutes.

11. A crosslinked fluororubber obtained by crosslinking the fluororubber composition according to any one of claims 1 to 8 or by the production method according to claim 9 or 10.

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