JP7301470B2 - Fluoro-rubber composition for open cross-linking and method for cross-linking fluoro-rubber composition - Google Patents

Description

The present invention relates to a fluororubber composition. In particular, it relates to a fluororubber composition capable of open cross-linking in air and a cross-linking method.

Fluororubber has excellent heat resistance, chemical resistance, and oil resistance, and is used in a wide variety of applications. For example, fluororubber is used in semiconductor manufacturing processes, automobile parts manufacturing processes, and electronic device manufacturing processes. Fluororubber may be foamed by chemical foaming or physical foaming and used as a sealing member.

For example, Patent Document 1 discloses a technique for obtaining a crosslinked foamed fluororubber by blending a tetrafluoroethylene-based fluororubber with a pyrolytic foaming agent and a peroxide-based cross-linking agent. Fluororubber is disclosed to improve chemical resistance in particular.

JP 2015-174927 A

Peroxide cross-linking does not require the addition of metal oxides, and is suitable for preventing elution and improving chemical resistance. On the other hand, peroxide cross-linking is known to be prone to cross-linking inhibition. For example, acyl peroxides are inhibited from cross-linking when carbonaceous matter is contained in the rubber composition. Also, alkyl peroxides cannot undergo open cross-linking in the air. In addition, Patent Document 1 describes Permyl D, Perhexine 25B, etc. as organic peroxides for peroxide crosslinking of fluororubber, but these peroxides cannot be open-crosslinked, so they can be obtained by using a mold. It needs to be press-crosslinked.

When fluororubber is extruded and peroxide-crosslinked, oxygen is removed by cross-linking in a nitrogen gas atmosphere, or by passing the extruded fluororubber through a tank of polyethylene glycol (PEG) heated to a predetermined temperature. Crosslinking is carried out in the closed state to obtain a crosslinked product. In particular, when PEG is used, it is necessary to wash the outer surface of the molded article after the completion of cross-linking, and the treatment is complicated. Therefore, when string-like sealing materials, packings, tubes, hollow rods, etc. are produced from fluororubber, it is desired to be capable of open cross-linking. A peroxide cross-linking system capable of open cross-linking fluororubbers is not known.

An object of the present invention is to provide an open-crosslinkable fluororubber composition.

As a result of intensive studies, the inventors found that a fluororubber composition can be open-crosslinked by including a specific organic peroxide in an organic peroxide-based cross-linking system and also including a thermally expandable microcapsule foaming agent. The inventors have found that and completed the present invention.

The present invention relates to a fluororubber composition capable of open cross-linking in air in the presence of oxygen, comprising 0.1 to 5 parts by weight of unexpanded thermally expandable microcapsules per 100 parts by weight of uncrosslinked fluororubber, Contains 0.1 to 8 parts by weight of an organic peroxide, and the uncrosslinked fluororubber is vinylidene fluoride fluororubber, tetrafluoroethylene-propylene fluororubber, tetrafluoroethylene-perfluorovinyl ether fluororubber, or A mixture thereof, or a vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer ternary fluororubber, wherein the organic peroxide is t-butyl peroxybenzoate, α,α'-di A fluororubber composition for open cross-linking containing (t-butylperoxy)diisopropylbenzene or dicumyl peroxide (first invention).
Here, open cross-linking refers to obtaining a cross-linked fluororubber composition by heating a fluororubber composition in air, particularly in air in which oxygen is present, to cause a cross-linking reaction.

In the first invention, preferably, the thermally expandable microcapsules have a thermoplastic acrylic resin as a shell and encapsulate a hydrocarbon compound (second invention). In addition, in the first invention, preferably, 0.1 to 200 parts by weight of carbonaceous matter is further included (third invention).

The present invention also provides a fluororubber composition for open cross-linking according to any one of the first to third inventions, which is subjected to open cross-linking in air in the presence of oxygen to obtain a cross-linked foamed fluororubber composition. A method for cross-linking a rubber composition (fourth invention).

According to the fluororubber composition of the present invention (first invention) and the method for crosslinking a fluororubber composition of the present invention (fourth invention), the fluororubber composition is a peroxide-based crosslinking system (organic peroxide-based crosslinking system). System) provides the effect of enabling open cross-linking in air in the presence of oxygen .

Furthermore, in the case of the second invention, the foamed state of the fluororubber composition after cross-linking is improved. Further, when the third invention is used, a foamed fluororubber composition having excellent strength can be obtained.

Embodiments of the present invention will be described below. The present invention is an open-crosslinkable fluororubber composition comprising an uncrosslinked fluororubber blended with an organic peroxide and unexpanded thermally expandable microcapsules. The fluororubber composition may contain a carbonaceous material. Hereinafter, each component will be described in order.

The open-crosslinkable fluororubber composition is crosslinked to become a crosslinked foamed fluororubber composition, for example, a member such as a string-like sealing member, a tube, a cylindrical cover, or a sheet. The use of the rubber composition is not particularly limited.

(Uncrosslinked fluororubber)
The type of uncrosslinked fluororubber is not particularly limited, and examples thereof include vinylidene fluoride fluororubber (FKM), tetrafluoroethylene-propylene fluororubber (FEPM, TFE-P), and tetrafluoroethylene-perfluorovinyl ether fluororubber. (FFKM) or a mixture thereof. Among them, tetrafluoroethylene-propylene fluororubber is preferable. As the fluororubber mainly composed of tetrafluoroethylene-propylene fluororubber, a fluororubber sold by AGC Co., Ltd. under the trade name of "AFLAS" can be exemplified. Further, the fluororubber may be a ternary fluororubber of vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer. This fluororubber is sold by Daikin Co., Ltd. under the trade name of "DAIEL".

(organic peroxide)
The organic peroxide of the organic peroxide-based cross-linking system blended in the fluororubber composition is t-butyl peroxybenzoate, α,α'-di(t-butylperoxy)diisopropylbenzene, or dicumylper Contains oxide. t-Butyl peroxybenzoate is an organic peroxide sold by NOF Corporation under the trade name of "PERBUTYL Z" and has a CAS-No of 614-45-9. α,α'-di(t-butylperoxy)diisopropylbenzene is an organic peroxide sold by NOF Corporation under the trade name of "Perbutyl P", and CAS-No is 25155-25-3. is. Dicumyl peroxide is an organic peroxide sold by NOF Corporation under the trade name of "Percumyl D" and has a CAS-No of 80-43-3.

The organic peroxide-based cross-linking system may contain the above organic peroxides alone or in combination. Although the organic peroxide-based cross-linking system may contain other organic peroxides, the above-mentioned organic peroxide is the main organic peroxide component of the cross-linking system, and the organic peroxide-based Preferably, a crosslinked system is constructed. The amount of the organic peroxide compounded is preferably 0.1 to 8 parts by weight, more preferably 0.2 to 6 parts by weight, per 100 parts by weight of the uncrosslinked fluororubber.

(Crosslinking component)
Moreover, it is preferable that the organic peroxide cross-linking system further contains a polyfunctional unsaturated compound (polyfunctional monomer) or the like as a cross-linking component. A cross-linking component intervening between fluororubber polymers facilitates the progress of the cross-linking reaction and improves the flexibility of the rubber. Examples of the cross-linking component include triallyl isocyanurate (TAIC, manufactured by Mitsubishi Chemical) and trimethallyl isocyanurate (TMAIC, manufactured by Mitsubishi Chemical). The amount of the cross-linking component in the organic peroxide-based cross-linking system is preferably 1-15 parts by weight, more preferably 2-10 parts by weight, per 100 parts by weight of the uncrosslinked fluororubber.

(Thermal expandable microcapsules)
The unexpanded thermally expandable microcapsules blended in the fluororubber composition are microcapsules in which a hydrocarbon compound is encapsulated in a thermoplastic resin shell. When the microcapsules are heated, the shell softens and the hydrocarbons inside evaporate, expanding in volume. The thermally expandable microcapsules are selected so that the expansion peak temperature of the microcapsules is lower than the processing temperature at which the fluororubber composition is crosslinked. The unexpanded thermally expandable microcapsules are sold, for example, by Matsumoto Yushi Co., Ltd. under the trade name of "Matsumoto Microspheres".

Examples of the thermoplastic resin forming the shell of the thermally expandable microcapsules include vinylidene chloride resins, acrylic resins, and olefin resins. Among them, it is preferable to use thermally expandable microcapsules whose shells are made of acrylic resin.

The unexpanded thermally expandable microcapsules are blended in an amount of 0.1 to 5 parts by weight, preferably 0.2 to 4 parts by weight, per 100 parts by weight of the uncrosslinked fluororubber.

(carbonaceous)
Although not essential, the fluororubber composition may contain a carbonaceous material. As the carbonaceous material, carbon black or graphite can be blended singly or in combination. The carbonaceous material is preferably blended in an amount of 0.1 to 200 parts by weight, preferably 1 to 150 parts by weight, per 100 parts by weight of the uncrosslinked fluororubber.

Carbon black generally available on the market for the rubber industry can be used as the carbon black. For example, the carbon black may be channel black, furnace black, thermal black, or the like. Among thermal blacks, it is particularly preferable to blend MT carbon. Carbon black is preferably blended in an amount of 0.1 to 120 parts by weight, preferably 0.5 to 100 parts by weight, per 100 parts by weight of the uncrosslinked fluororubber.

As the graphite, flake graphite, earthy graphite, expanded graphite, expanded graphite, and the like can be used. As the graphite, unexpanded expandable graphite may be blended. Graphite is preferably blended in an amount of 0.1 to 200 parts by weight, preferably 0.5 to 150 parts by weight, per 100 parts by weight of the uncrosslinked fluororubber.

(Other compounding materials)
The fluororubber composition may contain optional ingredients such as other compounding materials such as fillers (silica-based reinforcing fillers, inorganic fillers such as barium sulfate, etc.), plasticizers (ester-based, especially DOS), Metal oxides (zinc oxide, etc.), lubricants, processing aids, pigments, and the like can be blended as needed.

The fluororubber composition can be produced by blending each component in an arbitrary order and sufficiently mixing them. Mixing of the rubber composition containing these agents can be carried out using a twin roll, a kneader, a Banbury, a twin-screw kneading extruder, various mixers, and other kneaders, and the agents are uniformly dispersed. An unvulcanized rubber composition can be obtained.

When the fluororubber composition obtained in the unvulcanized state by the above steps is crosslinked, it becomes a crosslinked foamed fluororubber composition. As a method for crosslinking, conventionally known thermal crosslinking methods can be widely adopted. . By heating the uncrosslinked fluororubber composition, the organic peroxide is decomposed to generate oxygen radicals, and the fluororubber is crosslinked. In addition, foaming of the microcapsules proceeds along with the cross-linking reaction, and the fluororubber composition becomes a foamed fluororubber composition.

In particular, the fluororubber composition is capable of open cross-linking, and can be cross-linked even in an air environment in which oxygen is present. For example, an uncrosslinked fluororubber composition extruded into a specific cross-sectional shape from the nozzle of an extruder is subjected to open crosslinking in hot air to obtain a string-like crosslinked foamed fluororubber composition. can be used as a sealing material. When extrusion molding is used, the extruded uncrosslinked fluororubber composition can be passed through a heating furnace for continuous crosslinking to obtain a long strip-shaped rubber composition. Heating can be carried out in two or more stages, and the heating method may be any open cross-linking method such as hot air vulcanization, nitrogen atmosphere vulcanization, UHF vulcanization, far infrared rays, and direct steam vulcanization. can.
The fluororubber composition does not necessarily have to be open-crosslinked, and can be press-crosslinked with a heated mold.

The effects of the fluororubber composition will be described.
The fluororubber composition contains t-butyl peroxybenzoate, α,α'-di(t-butylperoxy)diisopropylbenzene, or dicumylper as the organic peroxide constituting the organic peroxide cross-linking system. Since it contains an oxide and also contains a predetermined amount of unexpanded thermally expandable microcapsules, open cross-linking is possible.

In conventional fluororubber compositions, in order to perform peroxide crosslinking using an organic peroxide, it is necessary to block oxygen. Cross-linking had to be done with a heating bath filled with glycol. This is because if peroxide cross-linking is carried out in air in the presence of oxygen, poor cross-linking (typically under-cross-linking) occurs and the surface of the rubber composition becomes sticky like uncross-linked rubber. .

The inventor has constructed an organic peroxide-based cross-linking system to include t-butyl peroxybenzoate, α,α'-di(t-butylperoxy)diisopropylbenzene, or dicumyl peroxide, and It was found that when thermally expandable microcapsules are combined, even a peroxide-crosslinked fluororubber composition can be open-crosslinked in an environment where air exists, preventing the occurrence of stickiness on the rubber surface and under-crosslinking.

Although the mechanism of why open cross-linking becomes possible when a specific organic peroxide-based cross-linking agent is combined with thermally expandable microcapsules is not clear, it is presumed to be based on the following mechanism.
Since the surface of the rubber composition is heated by hot air, far infrared rays, or the like during open cross-linking, the temperature rises quickly on the surface of the rubber composition, and the timing of softening and foaming of the microcapsules is also early. Therefore, in the vicinity of the surface of the rubber composition, the expanded microcapsules are considered to be in a semi-molten state and partially cover the surface of the rubber composition. Vaporized hydrocarbon compounds leak out from the inside of the heated and expanded microcapsules, and the gas of such hydrocarbon compounds flows from the inside of the rubber composition toward the surface and into the air. These actions make it difficult for oxygen in the air to enter the interior of the rubber composition. Hydrocarbon compounds released from the microcapsules are also thought to affect the behavior of the organic peroxide-based crosslinked system.

The presence of thermoplastic resin components and hydrocarbon compounds in these capsules and their interaction with specific organic peroxides enables open cross-linking even with peroxide cross-linking, resulting in sufficiently cross-linked foamed fluororubber. It is believed that a composition is obtained.

When the heat-expandable microcapsules have a thermoplastic acrylic resin as a shell and contain a hydrocarbon compound, the timing of expansion of the microcapsules and decomposition of the organic peroxide cross-linking agent can be easily adjusted. Both the crosslinked state and the foamed state of the crosslinked foamed fluororubber obtained are likely to be good.

In addition, when the uncrosslinked fluororubber composition further contains 0.1 to 200 parts by weight of carbonaceous matter with respect to 100 parts by weight of fluororubber, such carbonaceous matter increases the strength of the crosslinked fluororubber composition. improvement can be achieved. In peroxide cross-linking technology, carbonaceous substances are known to inhibit peroxide cross-linking and tend to cause poor cross-linking, especially when an acyl organic peroxide is used as a cross-linking agent. In the above fluororubber composition, a specific organic peroxide is included as a component of the cross-linking agent, and by using thermally expandable microcapsules in combination, even if the uncrosslinked fluororubber composition contains carbonaceous , it is possible to obtain a fluororubber composition that is satisfactorily crosslinked by open cross-linking without causing poor cross-linking.

Then, if the above-described fluororubber composition for open crosslinking is open-crosslinked to obtain a crosslinked fluororubber composition, for example, an extruded string-shaped or tubular uncrosslinked fluororubber composition can be efficiently crosslinked to efficiently produce crosslinked fluororubber string-like sealing members and tubes.

The open crosslinkable fluororubber composition of the present invention will be described in more detail below with reference to examples. In the following description, "parts" means "parts by weight". The formulations and test results of Examples and Comparative Examples are shown in Table 1. In the examples and comparative examples, carbonaceous materials, processing aids, lubricants, etc. are blended. These components are not essential components of the present invention.

(Example 1)
100 parts of AFLAS 400E from AGC Co., Ltd. as a fluororubber component, and 2 parts of Matsumoto Microsphere FD-230D (manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) as a thermally expandable microcapsule, included in the organic peroxide cross-linking system. As an organic peroxide, 1 part of Perbutyl Z (manufactured by NOF Corporation) containing t-butyl peroxybenzoate, and as a cross-linking component contained in the organic peroxide-based cross-linking system, triallyl isocyanurate (TAIC, Nikka Trading Co., Ltd.), 5 parts of carbonaceous (MT carbon), 20 parts of N990 (manufactured by Tokai Carbon Co., Ltd.), 1 part of Suclactol WS-280 (manufactured by S&S Co., Ltd.) as a lubricant, and stearin as a processing aid. An uncrosslinked fluororubber composition (Example 1) was obtained using a pressure kneader or an open roll so that sodium phosphate (manufactured by Showa Kagaku Co., Ltd.) was blended at a rate of 1.5 parts and kneaded uniformly. rice field.

The obtained uncrosslinked and unexpanded fluororubber composition was cut into a sheet having a thickness of 1 mm with an open roll. The resulting uncrosslinked and unfoamed fluororubber composition sheet was heated in a gear oven heated to 200° C. for 10 minutes to carry out open crosslinking (primary vulcanization). Further, secondary vulcanization was performed in a gear oven at 200° C. for 2 hours to obtain a crosslinked foamed fluororubber sheet.

Hereinafter, formulations of other examples and comparative examples will be described. In the following description, the points that are different from the preceding embodiment will be mainly described, and the description of the points that are the same will be omitted. The obtained uncrosslinked rubber compositions of Examples and Comparative Examples were separated and subjected to an open cross-linking treatment in the same manner as in Example 1.

(Example 2)
As the organic peroxide contained in the organic peroxide-based cross-linking system, 1 part of Perbutyl P (manufactured by NOF Corporation) containing α,α'-di(t-butylperoxy)diisopropylbenzene, The uncrosslinked fluororubber composition of Example 2 with the same formulation as in Example 1, except that 0.5 parts of Expancel DU-80 (manufactured by Nippon Philite Co., Ltd.) was included as a capsule. got

(Example 3)
The rubber component of the fluororubber is DAIEL G902 (100 parts) of Daikin Industries, Ltd., and the organic peroxide contained in the organic peroxide cross-linking system is Permil D (manufactured by NOF Corporation) containing dicumyl peroxide. 1 part of heat-expandable microcapsules, 0.2 parts of Matsumoto Microsphere FD-190D (manufactured by Matsumoto Yushi Seiyaku Co., Ltd.), triallyl isocyanurate as a cross-linking component contained in the organic peroxide-based cross-linking system (TAIC, Nikka Trading Co., Ltd.), except that sodium stearate (manufactured by Showa Kagaku Co., Ltd.) was not included. to obtain an uncrosslinked fluororubber composition.

(Comparative example 1)
An uncrosslinked fluororubber composition of Comparative Example 1 was obtained in the same formulation as in Example 1, except that the thermally expandable microcapsules were not included.

(Comparative example 2)
Example 3 except that the organic peroxide contained in the organic peroxide cross-linking system was 1 part of Perbutyl Z containing t-butyl peroxybenzoate and no thermally expandable microcapsules were contained. , and an uncrosslinked fluororubber composition of Comparative Example 2 was obtained.

(Comparative Example 3)
An uncrosslinked fluororubber composition of Comparative Example 3 was obtained in the same manner as in Example 2, except that the thermally expandable microcapsules were not included.

(Comparative Example 4)
Implemented except that the organic peroxide contained in the organic peroxide-based crosslinking system was 1 part of PerhexaHC (manufactured by NOF Corporation) containing 1,1-di(t-hexylperoxy)cyclohexane. Using the same formulation as in Example 1, an uncrosslinked fluororubber composition of Comparative Example 4 was obtained.

(Comparative Example 5)
Perhexa 25B-40 (manufactured by NOF Corporation) containing 2,5-dimethyl-2,5-di(t-butylperoxy)hexane was used as the organic peroxide contained in the organic peroxide-based cross-linking system. An uncrosslinked fluororubber composition of Comparative Example 5 was obtained in the same formulation as in Example 1, except that parts were used.

(Comparative Example 6)
The same formulation as in Example 1 except that the organic peroxide contained in the organic peroxide-based cross-linking system was 1 part of Nyper BW (manufactured by NOF Corporation) containing benzoyl peroxide, and Comparative Example An uncrosslinked fluororubber composition No. 6 was obtained.

(Comparative Example 7)
Perhexa 25B-40 (manufactured by NOF Corporation) containing 2,5-dimethyl-2,5-di(t-butylperoxy)hexane was used as the organic peroxide contained in the organic peroxide-based cross-linking system. The composition was the same as in Example 3 except that 2 parts of Matsumoto Microsphere FD-230D (manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) was included as a thermally expandable microcapsule. A fluororubber composition was obtained.

The state of cross-linking was evaluated for each example. In Examples 1, 2, and 3, foaming was performed while maintaining a smooth sheet shape, and crosslinked foamed fluororubber sheets were obtained. In any of the examples, the rubber hardness could be measured, an appropriate elongation was ensured as a physical property of the crosslinked rubber, and a sufficiently crosslinked fluororubber composition was obtained. In these crosslinked samples, the rubber did not scrape even when the rubber surface was scratched with a pencil. This point is indicated by "o" in the "crosslinked state" column of Table 1.

For Examples 1, 2 and 3, the rubber hardness, 100% modulus, tensile strength and elongation of the obtained crosslinked fluororubber compositions were measured. The hardness of the rubber was determined according to JIS K6253 (1997) "Hardness test method for vulcanized rubber and thermoplastic rubber". ) Measured according to "Determination of tensile properties of vulcanized rubber and thermoplastic rubber". The crosslinked fluororubber compositions of Examples 1, 2, and 3 have moderate strength and elongation characteristics as foamed fluororubber compositions foamed by open crosslinking.

On the other hand, in Comparative Examples 1 to 7, even after the primary crosslinking (200°C, 10 minutes) was completed, the rubber surface was rough and sticky, and the crosslinking was not completed. It was in an under state. Depending on the sample, cross-linking progressed slower than foaming, resulting in excessive foaming and a smooth sheet shape that could not be maintained in some samples. All samples had poor surface conditions after cross-linking treatment, and the rubber hardness could not be measured. Dumbbells could not be produced for any of the samples, and strength, elongation, etc. could not be measured. In addition, in the sample of the comparative example, the rubber surface was not sufficiently crosslinked, so when the rubber surface was scratched with a pencil, the surface was scraped. These points are indicated by "x" in the "crosslinked state" column of Table 1.

Comparing these examples with comparative examples, open cross-linking becomes possible when a specific organic peroxide and thermally expandable microcapsules are combined as in Examples 1 to 3. However, as in Comparative Examples 1 to 3, even if the same organic peroxide is used, cross-linking does not go well unless thermally expandable microcapsules are blended. Moreover, as in Comparative Examples 4 to 7, even if thermally expandable microcapsules are blended, cross-linking does not go well when different organic peroxides are used.

The open-crosslinkable fluororubber composition is crosslinked to form a foamed fluororubber composition, which can be used for sealing members and the like, and has a high industrial utility value.

Claims (4)

A fluororubber composition capable of being openly crosslinked in air in the presence of oxygen,
For 100 parts by weight of uncrosslinked fluororubber,
0.1 to 5 parts by weight of unexpanded thermally expandable microcapsules,
0.1 to 8 parts by weight of an organic peroxide,
The uncrosslinked fluororubber is
vinylidene fluoride fluororubber,
Tetrafluoroethylene-propylene fluororubber,
Tetrafluoroethylene-perfluorovinyl ether fluororubber,
or mixtures thereof,
or a vinylidene fluoride/tetrafluoroethylene/hexafluoropropylene copolymer ternary fluororubber ,
The organic peroxide is
t-butyl peroxybenzoate,
α,α'-di(t-butylperoxy)diisopropylbenzene, or
containing dicumyl peroxide,
A fluororubber composition for open cross-linking. 2. The fluororubber composition for open cross-linking according to claim 1, wherein the heat-expandable microcapsules have a thermoplastic acrylic resin as a shell and contain a hydrocarbon compound. The fluororubber composition for open cross-linking according to claim 1, further comprising 0.1 to 200 parts by weight of carbonaceous matter. The open-crosslinking fluororubber composition according to any one of claims 1 to 3,
open cross-linking in air in the presence of oxygen to obtain a cross-linked foamed fluororubber composition;
A method for cross-linking a fluororubber composition.