JP5146314B2 - Method for producing fluororubber - Google Patents

Description

The present invention relates to a method for producing fluororubber.

In general, fluororubber is produced by preparing a compound after heat-drying a coagulated product obtained by coagulating an emulsion after emulsion polymerization. Coagulation is usually performed using a coagulant. As a coagulant, aluminum sulfate has recently been used in place of conventionally used magnesium chloride. However, when aluminum sulfate is used, there is a problem that the obtained fluororubber is colored.

In the past, fluororubbers were often used in a mixture of carbon, and coloring was not regarded as a problem, but for white or colored fluororubber products that have recently been in demand, there is a problem that coloring affects. is there.

For the purpose of whitening, a method of melt extrusion in the presence of an alkali metal nitrate has been proposed (see, for example, Patent Document 1). However, this technique is intended only for fluororesins that can be melt processed.
Japanese Patent Laid-Open No. 10-292054

An object of the present invention is to provide a method for producing a fluororubber in which coloring is prevented in view of the above situation.

The present invention is a method for producing a fluororubber comprising a step of heat drying a coagulated product of a fluorine-containing elastomer aqueous dispersion in the presence of an alkali metal nitrate.
The present invention is described in detail below.

The fluorine-containing elastomer aqueous dispersion is obtained by dispersing a fluorine-containing elastomer in an aqueous medium.
The fluorine-containing elastomer is an amorphous fluorine-containing polymer having rubber elasticity.
The fluorine-containing elastomer generally has 30 to 80% by mass of copolymerized units of the first monomer.

In the present specification, the “first monomer” means a monomer that constitutes a copolymer unit occupying the largest mass among all copolymer units in the molecular structure of the fluorine-containing elastomer. .

In the present specification, the copolymer unit means a part of the molecular structure of the fluorine-containing elastomer and derived from the corresponding monomer. For example, the vinylidene fluoride [VDF] unit is a part of the molecular structure of the VDF copolymer and is a part derived from VDF, and is represented by — (CH ₂ —CF ₂ ) —. The above-mentioned “all copolymerized units” are all parts derived from the monomer in the molecular structure of the fluorine-containing elastomer.
The content of the copolymerized unit is obtained by measuring ¹⁹ F-NMR.

In the fluorine-containing elastomer of the present invention, the copolymer unit derived from a monomer other than the first monomer is derived from only one of the monomers copolymerizable with the first monomer. May be derived from two or more monomers that are copolymerizable with the first monomer.

Examples of the monomer copolymerizable with the first monomer include a fluorine-containing olefin, a fluorine-containing vinyl ether, and a hydrocarbon olefin.

Although it does not specifically limit as said fluorine-containing olefin, For example, VDF, tetrafluoroethylene [TFE], hexafluoropropylene [HFP], 1,2,3,3,3-pentafluoropropene, chlorotrifluoroethylene [CTFE] ], Vinyl fluoride [VF], etc. are mentioned.

As said fluorine-containing vinyl ether, perfluoro (vinyl ether) is mentioned, for example.
As said perfluoro (vinyl ether), perfluoro (alkyl vinyl ether) [PAVE] etc. are mentioned, for example.

As the PAVE, for example,
General formula (1): CF ₂ = CFO (RfaO) _n (RfbO) _m Rfc [wherein Rfa and Rfb are different and are perfluoroalkylene groups having 2 to 6 carbon atoms which are linear or branched. , M and n are each independently an integer of 0 to 10, and Rfc is a perfluoroalkyl group having 1 to 6 carbon atoms. A compound represented by
Formula _{(2): CF 2 = CFO} (CF 2 CFXO) r Rfd (X is -F or -CF _3, r is an integer from 0 to 5, Rfd has 1 to 6 carbon atoms A perfluoroalkyl group).
Formula _{(3): CF} 2 = _CFO in _{[(CF 2) u CF 2} CFZO] v Rfe ( wherein, RFE is a perfluoroalkyl group having 1 to 6 carbon atoms, u is an integer of 0 or 1 , v is an integer from 0 to 5, Z is -F or -CF _3.) the compound represented by,
General formula (4): CF ₂ = CFO [(CF ₂ CF (CF ₃ ) O) _m (CF ₂ CF ₂ CF ₂ O) _n (CF ₂ ) _y ] C _z F _{2z + 1} [wherein m and n are And independently represents an integer of 0 to 10, y is an integer of 0 to 3, and z is an integer of 1 to 5 carbon atoms. A compound represented by
Formula _{(5): CF 2 = CFOCF} 2 CF (CF 3) O (CF 3 O) in w _{C x F 2x + 1} [formula, w is an integer of 1 to 5, x is is an integer from 1 to 3 . And the like.

The compound represented by the general formula (2) is preferably perfluoro (methyl vinyl ether) [PMVE], perfluoro (ethyl vinyl ether) [PEVE], perfluoro (propyl vinyl ether) [PPVE] or the like.

In the general formula (3), Rfe is preferably —C ₃ F ₇ , u is an integer of 0, and v is preferably an integer of 1.

In the general formula (4), m and n are preferably independently an integer of 0 or 1, and z is preferably an integer of 1.

In the general formula (5), x is preferably an integer of 1.

When the said fluorine-containing elastomer has a PAVE unit, it is preferable that a PAVE unit is 20-70 mass%.
When the said fluorine-containing elastomer has a PMVE unit, it is preferable that a PMVE unit is 30-55 mass%.

Although it does not specifically limit as said hydrocarbon olefin, For example, although ethylene, propene, etc. are mentioned, propene is preferable.
When the fluorine-containing elastomer of the present invention has hydrocarbon olefin units, the hydrocarbon olefin units are preferably 4 to 20% by mass of the total copolymer units.

Examples of the fluorine-containing elastomer include a TFE / perfluoro (vinyl ether) copolymer, a VDF / HFP copolymer, a VDF / CTFE copolymer, a VDF / HFP / TFE copolymer, and a VDF / CTFE. / TFE copolymer, TFE / propylene copolymer, TFE / propylene / VDF copolymer, fluorine-containing copolymer such as ethylene / HFP copolymer, and the like. It is preferable that the monomer is a VDF copolymer in which VDF is VDF or a TFE copolymer in which the first monomer is TFE.

Examples of the TFE copolymer include a TFE / propylene copolymer and a TFE / PAVE copolymer.

Examples of the VDF copolymer include VDF / HFP copolymer, VDF / HFP / TFE copolymer, general formula: ICH ₂ CF ₂ CF ₂ O [CF (CF ₃ ) CF ₂ O] _y CF = Examples thereof include a VDF copolymer having an iodine compound represented by CF ₃ (y = 0 to 3) as a copolymer unit.

The fluorine-containing elastomer preferably has a number average molecular weight of 1,000 to 300,000. When the number average molecular weight is less than 1000, the viscosity is too low and the handleability tends to deteriorate. When it exceeds 300,000, the viscosity rises and the handleability tends to deteriorate.

The number average molecular weight (Mn) was measured by performing gel permeation chromatography [GPC] using the following apparatus and conditions.
・ Device: HLC-8000 (manufactured by Tosoh Corporation)
-Column used: GPC KF-806M 2
1 GPC KF-801
2 GPC KF-801 detectors: differential refractometer, developing solvent: tetrahydrofuran, temperature: 35 ° C
Sample concentration: 0.1% by weight
Standard samples: various monodispersed polystyrenes (weight average molecular weight [Mw] /Mn=1.14 (Max)), TSK standard POLYSTYRENE (manufactured by Tosoh Corporation)

The average primary particle size of the fluorine-containing elastomer is usually 10 to 500 nm, preferably 50 to 300 nm.
The average primary particle size of the fluorine-containing elastomer is measured using Microtrack 9340UPA (manufactured by HONEYWELL).

In the fluorine-containing elastomer aqueous dispersion in the invention, the concentration of the fluorine-containing elastomer is preferably 10 to 80% by mass, and more preferably 20 to 50% by mass.

The aqueous medium in the aqueous fluorine-containing elastomer dispersion may be water or a mixed solvent of water and a water-soluble organic solvent such as alcohol.
The fluorine-containing elastomer aqueous dispersion is generally obtained by dispersing a fluorine-containing elastomer in the presence of a surfactant.

The surfactant is not particularly limited as long as it is conventionally known as a surfactant for a fluorine-containing polymer, and for example, a fluorine-containing surfactant having 8 to 20 carbon atoms or a fluorine-free surfactant. Agents and the like.

Examples of the fluorine-containing elastomer aqueous dispersion in the present invention include emulsions, slurries, suspensions and the like. The emulsion may be an emulsion obtained by emulsion polymerization. The slurry may be the one before heat drying in which an emulsion obtained by emulsion polymerization is coagulated.

The fluorine-containing elastomer aqueous dispersion can be obtained by polymerizing a fluorine-containing monomer and optionally a fluorine-free monomer in an aqueous medium in the presence of the above-mentioned surfactant. In addition, a fluorine-containing elastomer aqueous dispersion can also be obtained by using the generated oligomer in the same manner as an emulsifier without using a surfactant. This polymerization method is also a kind of emulsion polymerization method.

In the system using the above surfactant, for example, fluorine-based anionic surfactants such as ammonium perfluorooctanoate and the following fluorine-containing vinyl group-containing surfactants are preferable.

Examples of the fluorovinyl group-containing surfactant include the following general formula (I):
_{CF 2 = CF- (CF 2)} a -Y (I)
[Wherein, a represents an integer of 1 to 10, Y represents —SO ₃ M or —COOM, and M represents H, NH ₄ or an alkali metal. A fluorine-containing vinyl group-containing compound (I) represented by the following general formula (II)
_{CF 2 = CF- (CF 2 C} (CF 3) F) b -Y (II)
[Wherein, b represents an integer of 1 to 5, Y represents —SO ₃ M or —COOM, and M represents H, NH ₄ or an alkali metal. A fluorine-containing vinyl group-containing compound (II) represented by the following general formula (III)
_{CF 2 = CFO- (CF 2)} c -Y (III)
[Wherein, c represents an integer of 1 to 10, Y represents —SO ₃ M or —COOM, and M represents H, NH ₄ or an alkali metal. A fluorine-containing vinyl group-containing compound (III) represented by the following general formula (IV)
_{CF 2 = CF (CF 2)} d -O- (CF 2 CFXO) e - (CF 2) f -Y (IV)
[Wherein, X represents F or —CF ₃ , d represents an integer of 0 to 2, e represents an integer of 1 to 10, f represents an integer of 1 to 3, and Y represents represents -SO ₃ M or -COOM, M represents H, an NH ₄ or an alkali metal. And a fluorine-containing vinyl group-containing compound (IV) represented by the following general formula (V)
CH ₂ = CFCF ₂ O (CF (CF ₃ ) CF ₂ O) _g CF (CF ₃ ) Y (V)
[Wherein, g represents an integer of 0 to 10, Y represents —SO ₃ M or —COOM, and M represents H, NH ₄ or an alkali metal. A fluorine-containing vinyl group-containing compound (V) represented by the following general formula (VI)
_{CF 2 = CF (CF 2)} h O- (CF (CF 3) CF 2 O) i -CF (CF 3) -Y (VI)
[Wherein, h represents an integer of 1 to 6, i represents an integer of 1 to 10, Y represents —SO ₃ M or —COOM, and M represents H, NH ₄ or an alkali metal. Represent. A fluorine-containing vinyl group-containing compound (VI) represented by the following general formula (VII)
_{CH 2 = CH (CF 2)} p1 -Y (VII)
[Wherein, p1 represents an integer of 1 to 10, Y represents —SO ₃ M or —COOM, and M represents H, NH ₄ or an alkali metal. ] The fluorine-containing vinyl group containing compound (VII) represented by these, and / or following General formula (VIII)
_{CF 2 = CFO- (CH 2)} q - (CF 2) p2 -Y (VIII)
[Wherein q represents an integer of 1 to 4, p2 represents an integer of 1 to 10, Y represents —SO ₃ M or —COOM, and M represents H, NH ₄ or an alkali metal. Represent. And a compound comprising a fluorine-containing vinyl group-containing compound (VIII) represented by the formula:

The surfactant is preferably added in an amount corresponding to 50 to 5000 ppm of the aqueous medium.
The surfactant concentration is obtained by adding an equal amount of methanol to the aqueous dispersion to be measured and performing Soxhlet extraction or performing centrifugation and then measuring by HPLC.

As said fluorine-containing monomer, the above-mentioned fluorine-containing olefin, fluorine-containing vinyl ether, etc. are mentioned, for example.
Examples of the fluorine-free monomer include the above-described hydrocarbon olefins.
The total supply amount of the fluorine-containing monomer and the non-fluorine-containing monomer is preferably 10 parts by mass with respect to 100 parts by mass of the aqueous medium, and more preferably 20 masses in terms of dispersion stability of the resulting fluorine-containing elastomer. In terms of the yield of the fluorine-containing elastomer, a preferable upper limit is 80 parts by mass with respect to 100 parts by mass of the aqueous medium, and a more preferable upper limit is 50 parts by mass.

The total supply amount of the fluorine-containing monomer and the fluorine-free monomer is a total amount of the initial charge amount at the start of the polymerization reaction and the continuous charge amount added during the polymerization reaction.
Among these, the supply amount of the non-fluorine-containing monomer can be appropriately set according to the desired composition of the fluorine-containing elastomer.

The polymerization may be carried out by adding a radical polymerization initiator to an aqueous medium, if desired, in addition to the surfactant, the fluorine-containing monomer, and a fluorine-free monomer that is optionally added.

Examples of the radical polymerization initiator include water-insoluble organic peroxides (for example, diisopropyl peroxydicarbonate), azo compounds, and the like. These water-insoluble organic peroxides and azo compounds can be used alone or in combination of two or more, and can also be used together with peroxides of water-soluble inorganic compounds or water-soluble organic compounds.

The addition amount of the radical polymerization initiator can be appropriately set according to the composition and yield of the fluorine-containing elastomer polymer to be produced, the use amount of the fluorine-containing monomer, the fluorine-free monomer, and the like. The radical polymerization initiator is preferably added in an amount of 0.01 to 0.4 parts by mass, and in an amount of 0.05 to 0.3 parts by mass with respect to 100 parts by mass of the resulting fluorine-containing elastomer. Is more preferable.

The polymerization may be performed by adding an additive such as a chain transfer agent.
The chain transfer agent is not particularly limited as long as it is used for the production of a fluorine-containing polymer, and for example, an alcohol having 1 to 12 carbon atoms, an ester having 1 to 12 carbon atoms, or an alkyl having 1 to 12 carbon atoms. Alkane, a C1-C12 ketone, or a C1-C12 mercaptan. Each of the above compounds may be partially substituted with fluorine, iodine and / or chlorine.

As the chain transfer agent, for example, the general formula: iodine compound represented by Rf · I _x and the like.
In the above general formula, Rf is a saturated or unsaturated fluorohydrocarbon group or chlorofluorohydrocarbon group having 1 to 16 carbon atoms, and preferably a perfluoroalkyl group having 4 to 8 carbon atoms. When the carbon number exceeds 16, the reactivity tends to decrease.

In the above general formula, x is the number of bonds of Rf, is an integer of 1 or more and 4 or less, and preferably 2 or more and 3 or less. Although it can be used even when x exceeds 4, it is not preferable in terms of synthesis cost. X is most preferably 2 in terms of few polymer branches.

Examples of the iodine compound include monoiodoperfluoromethane, monoiodoperfluoroethane, monoiodoperfluoropropane, and monoiodoperfluorobutane [for example, 2-iodoperfluorobutane, 1-iodoperfluoro (1,1 -Dimethylethane)], monoiodoperfluoropentane [for example, 1-iodoperfluoro (4-methylbutane)], 1-iodoperfluoro-n-octane, monoiodoperfluorocyclobutane, 2-iodoperfluoro (1- Cyclobutylethane) cyclohexane, monoiodoperfluorocyclohexane, monoiodotrifluorocyclobutane, monoiododifluoromethane, monoiodomonofluoromethane, 2-iodo-1-hydroperfluoroethane, 3-iodo-1-hydride Perfluoropropane, monoiodomonochlorodifluoromethane, monoiododichloromonofluoromethane, 2-iodo-1,2-dichloro-1,1,2-trifluoroethane, 4-iodo-1,2-dichloroperfluorobutane, 6-iodo-1,2-dichloroperfluorohexane, 4-iodo-1,2,4-trichloroperfluorobutane, 1-iodo-2,2-dihydroperfluoropropane, 1-iodo-2-hydroper Fluoropropane, monoiodotrifluoroethylene, 3-iodoperfluoropropene-1,4-iodoperfluoropentene-1,4-iodo-5-chloroperfluoropentene-1,2-iodoperfluoro (1-cyclobu Tenenylethane), 1,3-diiodoperfluoropropane, 1,4-diyo Doperfluoro-n-butane, 1,3-diiodo-2-chloroperfluoropropane, 1,5-diiodo-2,4-dichloroperfluoro-n-pentane, 1,7-diiodoperfluoro-n-octane, 1,2-di (iododifluoromethyl) perfluorocyclobutane, 2-iodo-1,1,1-trifluoroethane, 1-iodo-1-hydroperfluoro (2-methylethane), 2-iodo-2,2 -Dichloro-1,1,1-trifluoroethane, 2-iodo-2-chloro-1,1,1-trifluoroethane, 2-iodoperfluoroethyl perfluorovinyl ether, 2-iodoperfluoroethyl perfluoroisopropyl Ether, 3-iodo-2-chloroperfluorobutylperfluoromethylthioether, 3-iodo Examples include -4-chloroperfluorobutyric acid.

Among these, 1,4-diiodoperfluoro-n-butane is preferable from the viewpoint of ease of synthesis, reactivity, economy, and stability.
The additives such as the chain transfer agent can be appropriately selected according to the type of fluorine-containing monomer used, the composition of the desired fluorine-containing elastomer, and the like.

The polymerization may be carried out by any of batch operation, semi-batch operation and continuous operation, but it is preferable to carry out by semi-batch operation.
In the above polymerization, the above-mentioned fluorine-containing monomer, non-fluorine-containing monomer, surfactant polymerization initiator and chain transfer additive are appropriately added during the polymerization reaction depending on the composition and yield of the desired fluorine-containing elastomer. can do.

The polymerization is usually carried out while maintaining a temperature in the range of 10 to 120 ° C. If the temperature is less than 10 ° C, the reaction rate cannot be increased to an effective size on an industrial scale. If the temperature exceeds 120 ° C, the reaction pressure required for maintaining the polymerization reaction increases, It cannot be maintained.

The above polymerization can be generally performed while maintaining the pressure in the range of 0.5 to 10 MPa in terms of reaction rate and cost. A preferable lower limit of the pressure is 1.0 MPa, and a preferable upper limit is 6.2 MPa.

The fluorine-containing elastomer usually constitutes particles (sometimes referred to as “primary particles” in this specification) in the fluorine-containing elastomer aqueous dispersion. The agglomerated material described later is mainly composed of secondary particles obtained by agglomerating the primary particles by coagulation.

The average primary particle size of the fluorine-containing elastomer is usually 10 to 500 nm. The average primary particle size was measured using Microtrac 9340UPA (manufactured by HONEYWELL).

The aqueous fluorine-containing elastomer dispersion in the present invention can be prepared so that the concentration of the fluorine-containing elastomer falls within the above-mentioned range by appropriately concentrating and diluting after the polymerization.
The fluorine-containing elastomer aqueous dispersion may be further purified by a conventionally known method such as phase separation.

The aqueous fluorine-containing elastomer dispersion in the present invention can be made into a coagulated product by adding a coagulant, for example.
The coagulated product of the fluorine-containing elastomer aqueous dispersion generally contains the above-mentioned fluorine-containing elastomer and a coagulant.

Examples of the coagulant include aluminum salts such as aluminum sulfate and potassium alum; calcium salts such as calcium chloride; magnesium salts such as magnesium chloride; monovalent cation salts such as sodium chloride and potassium chloride;

The coagulant may be used alone or in combination of two or more, but even when it contains aluminum sulfate, by applying the present invention, Conventional coloring can be prevented in the obtained fluororubber.
The amount of the coagulant used and the conditions for addition can be appropriately selected according to the type and amount of the fluorine-containing elastomer in the fluorine-containing elastomer aqueous dispersion, the type of coagulant used, and the like.

For example, when the coagulant is aluminum sulfate, it is preferably 0.01 to 0.20 parts by mass per 100 parts by mass of the fluorine-containing elastomer in the obtained coagulated product. When the amount used is less than 0.01 parts by mass per 100 parts by mass of the fluorinated elastomer in the obtained coagulated product, it may take time to complete coagulation, and the efficiency may deteriorate. In the case of more than part, it may be excessively added and not economical.

The average particle diameter of the aggregate is not particularly limited as long as it can be handled.
The coagulated product may be an elastomer obtained by a method of directly heating and drying the emulsified dispersion, or may be obtained by adding, mixing and coagulating a coagulant.
When the coagulant and the emulsified dispersion are mixed for coagulation, the average particle size of the coagulated product is preferably 1 mm or more from the viewpoint of solid-liquid separation such as a draining process, and the piping during transfer From the viewpoint of occlusion, it is desirable that it is 20 mm or less.

The average particle size of the coagulated material is obtained by sampling the crumb after coagulation, taking a photograph with a standard scale, measuring the major axis and minor axis of the particle, and obtaining the average value.

The method for producing fluororubber of the present invention includes a step of heating and drying the coagulated product of the above-mentioned fluorine-containing elastomer aqueous dispersion in the presence of an alkali metal nitrate.
Examples of the alkali metal in the alkali metal nitrate include lithium, sodium, and potassium.
In the present invention, the alkali metal nitrate is preferably sodium nitrate and / or potassium nitrate.

In the present invention, heat drying of the coagulated product of the above-mentioned fluorine-containing elastomer aqueous dispersion is performed in the presence of an alkali metal nitrate.

The timing of the presence of the alkali metal nitrate is not particularly limited. For example, the alkali metal nitrate may be added during the polymerization to obtain a fluorine-containing elastomer, but the effect of adding an electrolyte to the aqueous dispersion is avoided. And, it is preferable to add after obtaining the coagulated product in the abundance (yield) in the obtained product with respect to the added amount. In addition, drying is performed until the weight loss when heated (for example, 200 ° C., 2 hours) in the absence of nitrate is 0.3% or less before heating, and the coloration can be visually observed. When solid is mixed, it may be difficult to suppress coloring, so it is desirable to add it before the coloring is visible.

The alkali metal nitrate may be added as a solid, but is preferably added in the form of an aqueous solution in terms of uniform dispersion.

The effect of the alkali metal nitrate in the method for producing fluororubber of the present invention can be seen even with a small amount, but the remarkable effect of suppressing coloring of the resulting fluororubber per 100 parts by mass of the fluoroelastomer in the coagulated product. Is preferably 0.04 parts by mass or more, and preferably 0.5 parts by mass or less in terms of preventing whitening of the obtained fluororubber, deterioration of compression set, and the like.

The method for heating and drying is not particularly limited, and for example, the drying may be performed in an extruder, or may be performed using an aeration drying apparatus or a box-type dryer (tray oven). It is preferable.

The extruder has a single or biaxial rotating shaft and a barrel (heating unit), and can be dried by kneading and heating in the extruder.
The temperature of the heat drying can be set according to the drying method, the physical properties of the product, and the production efficiency, but considering the heat resistance of the fluoroelastomer (decomposition start temperature), it is generally room temperature or higher, preferably 50 ° C. or higher. Moreover, it is desirable that it is 200 degrees C or less.

The drying in the heat drying is performed so that the weight loss rate when the dried fluororubber is heated at 200 ° C. for 2 hours is preferably 0.5% or less, more preferably 0.3% or less.

The above-mentioned heat drying can be generally carried out under a pressure of -1 to 20 MPa, preferably -1 to 10 MPa.
The heat drying is generally performed for 1 to 1500 minutes, preferably 3 to 1200 minutes.

The fluororubber production method of the present invention includes a step of heating and drying the above-mentioned coagulated product in the presence of an alkali metal nitrate, thereby not only preventing coloring of the resulting fluororubber but also increasing the vulcanization rate. Can be improved. Unlike thermoplastic resins, elastomers are usually used after being crosslinked, and an improvement in vulcanization speed is preferable from the viewpoint of shortening the production time.

The coloring of fluororubber is conventionally considered to be caused by the presence of added coagulant such as aluminum sulfate during heat drying. In the present invention, the heat drying is performed in the presence of an alkali metal nitrate. It is thought that it was possible to prevent coloring. With regard to the mechanism for improving the vulcanization rate, it is conceivable that at the same time as suppressing coloration, generation of a double bond due to HF removal from an unstable terminal, etc. is suppressed to facilitate crosslinking.

The fluororubber obtained by the present invention has a Mooney viscosity (ML _{1 + 10} ) at 100 ° C. of preferably _{10 to} 160, and a more preferred lower limit is 30 in terms of the vulcanizability of the obtained molded product, etc. A preferable upper limit is 140 in terms of moldability. The ML _{1 + 10} is measured under the condition of a rotor rotational speed of 2 rpm using a measuring device ALPHA TECHNOLOGIES MV2000E type in accordance with ASTM-D 1646 and JIS K6300.

The fluororubber obtained by the present invention can be formed into a molded body by adding a crosslinking agent to crosslink.
Examples of the crosslinking agent include polyols, polyamines, organic peroxides, organic tins, bis (aminophenol) tetraamines, and bis (thioaminophenol).

The crosslinking can be carried out by appropriately selecting the conditions by a conventionally known method according to the composition and amount of the fluororubber used and the type of the crosslinking agent.

A molded product obtained from the fluororubber is suppressed in coloration, has a low compression set, and is excellent in mechanical strength. Since the molded body is made of the above-described fluororubber, it is suitable as a seal, a wire covering material, a tube, a hose, a film, a laminated body, and the like, and particularly suitable for a semiconductor manufacturing apparatus part, an automobile part, etc. .

Since the fluororubber production method of the present invention has the above-described configuration, it is possible to obtain a fluororubber in which coloring is prevented.

The present invention will be described in more detail below with reference to experimental examples, but the present invention is not limited to these experimental examples.

Each data in the experimental example is obtained by the following measuring method.
1. A MINOLTA spectrophotometer CM-3500d was used as a coloring degree measuring instrument, and a yellowness index (YI) or a hunter whiteness (Z value) was measured.

In the above measurement, when the thickness of the sheet, such as extrusion drying, was constant, the sheet-like sample obtained by drying was placed in the measuring part of the spectrophotometer, and a standard dark box was placed over it to perform the measurement.

In the case of box-type drying or the like, the amount charged in the tray is the same for each sample, and the thickness after drying is the same.
About Z value, the sample was set | placed on the measurement part, the standard board (Tristimulus value X = 92.17, Y = 94.15, Z = 110.56) was set | placed on it, and it measured.

2. Mooney Viscosity Measurement Using ALPHA TECHNOLOGIES MOONY MV-2000, at 100 ° C., held for 1 minute as indicated as ML _{1 + 10} , measurement was performed for 10 minutes.

3. KNO ₃ concentration The potassium ion concentration in the fluorine-containing elastomer was measured by the following method, and the measured value was calculated.

(Potassium ion concentration measurement method)
Place 2.5 g of fluorine-containing elastomer in a platinum dish, heat in an oven heated to 600 ° C. for 15 minutes, take out the whole platinum dish and cool it, add 1 ml of 35% hydrochloric acid, and adjust the temperature to 85 to 95 ° C. The platinum dish was placed in a water bath and evaporated to dryness. To the platinum dish taken out from the water bath, 40 g of 0.1N (normal) hydrochloric acid was added, and ion exchange water was further added to make 50 g, and the potassium concentration was measured using an atomic absorption photometer. Air / acetylene was used as the combustion gas, and Hitachi Polarized Zeeman atomic absorption photometer Z-8100 was used as the apparatus.

(Conversion method)
Using the obtained potassium concentration measurement results, the potassium nitrate concentration was determined based on the molecular weight ratio between potassium and potassium nitrate (molecular weight potassium: 39.1, potassium nitrate: 101.1).

4). Vulcanization rate Measurement was carried out at a temperature of 170 ° C. using a JSR curaster meter type II.

Comparative Example 1
Deaeration was performed so that the oxygen concentration was 20 ppm or less, and 1500 L of degassed ion exchange water [IE water] was charged into 2500 L of a jacketed reaction tank provided with a stirring blade. After the reaction vessel is stabilized at 80 ° C., 10 kg of hexafluoropropene [HFP] is charged while stirring at 77 rpm, and then a mixed monomer having a vinylidene fluoride [VDF] / HFP ratio of 78/22 mol%. 28 kg was charged.
Next, 850 g of ammonium persulfate [APS] was charged as a polymerization initiator to initiate the reaction.

During the reaction, the above mixed monomer was continuously charged so as to maintain a tank pressure of 1.2 MPa, and a total amount of 46 g of APS and 233 g of a chain transfer agent isopentane were charged until the reaction was completed. When the total amount of mixed monomers reached 550 kg, the monomer supply was terminated and the reaction was terminated. Thereafter, the stirring rotation speed was set to 35 rpm, unreacted monomers were collected until the internal pressure of the tank reached 0.1 MPa, and further cooling was performed from 80 ° C. to 60 ° C.

The dispersion obtained by the polymerization reaction had a solid content concentration of 26.8% by mass, and the composition of the obtained fluorine-containing elastomer was VDF / HFP = 78/22 mol%. In the present specification, the composition is analyzed by NMR.

Subsequently, a coagulant (aluminum sulfate aqueous solution, aluminum sulfate concentration: 0.18% by mass of the aqueous solution) was charged into a mixer, and the dispersion obtained by the polymerization was further dispersed: dispersion: coagulant = about 3 The mixture was charged to a ratio of 1 and stirred and pulverized at a temperature of 30 ° C. for 2 minutes to obtain a coagulated crumb.
The obtained crumb was subjected to solid-liquid separation, and dried with an electric hot air dryer at a drying temperature of 150 ° C. and a drying time of 4 hours.

Comparative Example 2
The dispersion obtained by the same method as in Comparative Example 1 was used at a flow rate of 14 L / min, and the coagulant (aluminum sulfate aqueous solution, aluminum sulfate concentration: 0.12% by mass of coagulated water) was supplied at a flow rate of 38 L / min. A coagulation crumb was prepared by continuously charging into a mixer (FIG. 1).
The obtained coagulated crumb was solid-liquid separated and then continuously fed into an extrusion dryer and dried by passing through a barrel adjusted to 100 ° C. to 180 ° C.

Comparative Example 3
Deaeration was performed so that the oxygen concentration was 20 ppm or less, and 1460 kg of degassed IE water was charged into a 2794 L jacketed reaction tank provided with a stirring blade adjusted to 0.1 MPa by VDF.

After stabilizing the reaction vessel at 80 ° C., VDF was charged to 1.35 MPa while stirring at 74 rpm, and then HFP was charged to 2.0 MPa while keeping 80 ° C.

Next, 0.08 part of diethyl malonate [DEM] was charged as a chain transfer agent, and then 1.58 kg of ammonium persulfate [APS] 5% solution was charged as a polymerization initiator to initiate the polymerization reaction.

During the polymerization reaction, a mixed monomer of VDF and HFP (VDF / HFP = 78/22 mol% ratio) is continuously charged so that the tank pressure can be maintained at 2.0 MPa, and the additional VDF amount is 320 kg and the additional HFP is 213 kg. At that point, the monomer supply was terminated and the reaction was terminated. The reaction time was 129 minutes.

Unreacted monomer was recovered until the internal pressure of the tank reached 0.1 MPa, and then cooled to 80 ° C. to 40 ° C.
The dispersion obtained by the polymerization reaction had a solid content concentration of 27.4% by mass, and the composition of the obtained fluorine-containing elastomer was VDF / HFP = 78.6 / 21.4 mol%.

The dispersion obtained by the above polymerization was continuously charged into a mixer at a flow rate of 14 L / min and a coagulant (aluminum sulfate aqueous solution, aluminum sulfate concentration: 0.12% by mass of the aqueous solution) at a flow rate of 38 L / min. A coagulation crumb was created (Figure 1).

The obtained coagulated crumb was solid-liquid separated and then continuously fed into an extrusion dryer and dried by passing through a barrel adjusted to 110 ° C. to 190 ° C.

Experimental example 1
The same method as in Comparative Example 1 was performed except that KNO ₃ was charged into a mixer for coagulation. Samples were prepared by changing the amount of KNO ₃ charged into the mixer to 10.8 g, 18.0 g, 36.0 g, and 72.0 g.
Table 1 shows data relating to the samples of Comparative Example 1 and Experimental Example 1.

When the K concentration of each sample was measured and the KNO ₃ content was calculated, it was an amount corresponding to 0 to 2590 ppm of the fluorine-containing elastomer.
As shown in Table 1, according to the amount of KNO ₃ added, the content of KNO ₃ also increased, and the color improvement as shown by the YI value indicating yellowness and the Z value indicating whiteness with increasing. It was observed.
Further, the Mooney viscosity also shows an increase in viscosity depending on the amount added, indicating that the viscosity can be controlled by controlling the amount added.

Experimental example 2
The dispersion and coagulant were used in a mixer as in Comparative Example 1, except that the dispersion (fluorine-containing elastomer aqueous dispersion) 200 g obtained by the polymerization method shown in Comparative Example 1 and the amount of coagulated water 600 g were used. Charged and coagulated, and the KNO ₃ aqueous solution was sprayed on the cake cut after dehydration, followed by drying in an oven at 150 ° C. for 4 hours. The amount of KNO ₃ aqueous solution to be sprayed was constant (12.5 g), and the concentration of KNO ₃ in the aqueous solution was changed from 0 to 12%.
The results of each test are shown in Table 2.

When the K concentration of the fluorine-containing elastomer after drying was measured and the KNO ₃ concentration was calculated, it was 0 to 1348 ppm. As shown by the YI values in Table 2, the color was determined according to the KNO ₃ concentration in the fluorine-containing elastomer. The improvement was confirmed.

Experimental example 3
As shown in FIG. 2, the method shown in Comparative Example 2 was carried out except that the KNO ₃ solution was continuously added to the extrusion dryer. By changing the concentration and amount of the added solution, the amount of KNO ₃ added was changed from 1.1 parts to 8.8 parts with respect to 100 parts of the fluorine-containing elastomer to obtain a sample.
A compound was prepared from the obtained fluorine-containing elastomer with the formulation shown in Table 3, and vulcanization evaluation was carried out with a curlastometer type II.

The results of each test are shown in Table 4.

As shown in Table 4, the YI value indicated an improvement in color according to the amount added as in Experimental Example 1. It was also confirmed that the Mooney viscosity of the obtained fluororubber could be adjusted according to the amount of KNO ₃ added.

Furthermore, it was possible to confirm the vulcanization rate improvement in the measurement of the vulcanization rate T ₉₀ by Curelastometer.
The time indicated by the _{T 90,} at 170 ° C., indicating the time reaching a value of 90 when the 100 equally dividing the measured maximum torque and minimum torque curastometer (JSR II type).

Experimental Example 4
The method shown in Comparative Example 3 was carried out except that a 20% KNO ₃ aqueous solution was continuously charged with a plunger pump in a 20% KNO ₃ aqueous solution by an extruder and a plunger pump.
By measuring the K concentration of the prepared sample, the concentration of KNO ₃ present in the fluorine-containing elastomer was calculated.
The results of each test are shown in Table 5.

When this sample was compared with the sample of Comparative Example 2, the YI value was improved from 32.7 to −26.8, indicating that the color could be improved.
The Mooney viscosity was 54.6 for the sample prepared in Comparative Example 2 and 59.6 for the sample prepared in Experimental Example 4, and the Mooney viscosity was adjusted according to the amount of KNO ₃ added. It was confirmed that it was possible.

Experimental Example 5
The method shown in Experimental Example 1 was carried out except that NaNO ₃ was added to the mixer instead of KNO ₃ .
NaNO ₃ was added in an amount of 0.83 parts to 100 parts of the fluorine-containing elastomer.
The results of each test are shown in Table 6.

When the YI values of the obtained samples were compared, it was changed from 36.5 to -5.5, and color improvement was confirmed.
Moreover, it was able to confirm similarly about adjustment of Mooney viscosity.

Since the fluororubber production method of the present invention has the above-described configuration, it is possible to obtain a fluororubber in which coloring is prevented.

The creation of the coagulation crumb performed in Comparative Example 2 and the like is schematically illustrated. The operation of Experimental Example 3 is schematically illustrated.

Explanation of symbols

21 Dispersion storage tank 22 Mixer 23 Aluminum sulfate tank 24 Drainer 25 Extrusion dryer 26 Ion exchange water 31 KNO ₃ tank

Claims (4)

The Analyte coagulation of the aqueous fluoroelastomer dispersion drying by heating in the presence of a nitrate of an alkali metal saw including,
The fluorine-containing elastomer is a vinylidene fluoride-based copolymer in which the first monomer is vinylidene fluoride.
The method for producing a fluororubber, wherein a heat drying temperature in the heat drying step is 50C or more and 200C or less . The method for producing a fluororubber according to claim 1, wherein the alkali metal nitrate is 0.04 to 0.5 parts by mass per 100 parts by mass of the fluorine-containing elastomer in the coagulated product. The method for producing a fluororubber according to claim 1 or 2, wherein the alkali metal nitrate is sodium nitrate and / or potassium nitrate. The method for producing a fluororubber according to claim 1, 2 or 3, wherein the coagulated product contains aluminum sulfate.

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