BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rubber composition and a thermoplastic resin composition, and a production method thereof.

The present application claims priority on the basis of Japanese Patent Application No. 2010-156668 filed in Japan on Jul. 9, 2010, the contents of which are incorporated herein by reference.

2. Description of Related Art

A method consisting of dispersing crosslinked rubber in a resin by dynamic crosslinking has been proposed in the past as a method of controlling the hardness (softness) of a resin.

For example, a fluorinated thermoplastic elastomer is disclosed in Japanese Unexamined Patent Application, First Publication No. S61-57641 that has a continuous phase and a dispersed phase, the continuous phase is essentially composed of a crystalline thermoplastic fluorocarbon, and the dispersed phase is composed of a crosslinked fluoroelastomer.

In addition, a method that uses a resin composition containing a polyamide-based resin and a rubber component is disclosed in, for example, Published Japanese Translation No. 117-503982 of PCT International Publication.

In addition, a method of incorporating a fluorinated terpolymer is disclosed in, for example, Japanese Unexamined Patent Application, First Publication No. H10-101880 in order to enhance tensile strength of a thermoplastic resin composition obtained by dynamic crosslinking.

SUMMARY OF THE INVENTION

The present invention employs the constitutions described below.

According to a first aspect of the present invention, a rubber composition contains a fluororubber, a radical initiator having a 1-minute half-life temperature of 280Â° C. or higher, and a crosslinking assistant having a melting point of 200Â° C. or higher and having two or more double bonds between carbon atoms.

In the aforementioned rubber composition according to the first aspect, the radical initiator is preferably 2,3-dimethyl-2,3-diphenylbutane or fluorinated pitch.

In addition, in the aforementioned rubber composition according to the first aspect, the crosslinking assistant is preferably N,Nâ€²-m-phenylene bismaleimide.

In addition, a second aspect of the present invention is a thermoplastic resin composition containing a fluororesin and the aforementioned rubber composition of the present invention.

In the aforementioned thermoplastic resin composition of the second aspect, the rubber composition in the fluororesin is preferably crosslinked.

In addition, in the aforementioned thermoplastic resin composition of the second aspect, the fluororesin is preferably tetrafluoroethylene-hexafluoropropylene copolymer (FEP), perfluoroalkoxy fluororesin (PFA) or ethylene-tetrafluoroethylene copolymer (ETFE).

In addition, a third aspect of the present invention is a production method of a thermoplastic resin composition comprising mixing a rubber composition containing a fluororubber, a radical initiator having a 1-minute half-life temperature of 280Â° C. or higher, and a crosslinking assistant having a melting point of 200Â° C. or higher and having two or more double bonds between carbon atoms, with a fluororesin at a temperature of 280Â° C. or higher, and crosslinking the rubber composition in the molten fluororesin.

In the aforementioned production method according to the third aspect, the radical initiator is preferably 2,3-dimethyl-2,3-diphenylbutane or fluorinated pitch.

In addition, in the aforementioned production method of the third aspect, the crosslinking assistant is preferably N,Nâ€²-m-phenylene bismaleimide.

In addition, in the aforementioned production method of the third aspect, the fluororesin is preferably tetrafluoroethylene-hexafluoropropylene copolymer (FEP), perfluoroalkoxy fluororesin (PFA) or ethylene-tetrafluoroethylene copolymer (ETFE).

DETAILED DESCRIPTION OF THE INVENTION

A rubber composition of the present embodiment contains a fluororubber, a radical initiator having a 1-minute half-life temperature of 280Â° C. or higher, and a crosslinking assistant having a melting point of 200Â° C. or higher and having two or more double bonds between carbon atoms.

(Fluororubber)

The fluororubber in the present embodiment may be a rubber having a fluorine atom within a molecule thereof, preferable examples of which include fluorine-containing elastic copolymers of vinylidene fluoride and at least one type of another ethylenic unsaturated monomer copolymerizable therewith, such as vinylene fluoride-ethylene tetrafluoride-propylene copolymer, vinylidene fluoride-ethylene tetrafluoride-propylene hexafluoride copolymer or vinylene fluoride-propylene hexafluoride copolymer. In particular, tetrafluoroethylene-propylene copolymers are preferable since they further improve heat resistance and chemical resistance.

The content of fluorine atoms in the fluororubber is preferably within the range of 0.1 to 40% by weight, more preferably within the range of 1 to 40% by weight. If the content of fluorine atoms is equal to or greater than the lower limit value, heat resistance, chemical resistance and slidability (effects produced by fluorine atoms) become favorable, while if the content of fluorine atoms is less than the upper limit value, crosslinking efficiency (crosslinking becomes difficult if the fluororubber is composed entirely of fluorine atoms) becomes favorable.

Specific examples of fluororubber include AFLAS100s (trade name) manufactured by Asahi Glass, Viton (trade name) manufactured by DuPont, and Dai-El manufactured by Daikin Industries.

One type of fluororubber may be used alone or two or more types may be used in combination.

(Radical Initiator)

A radical initiator having a 1-minute half-life temperature of 280Â° C. or higher is used in the present embodiment. A radical initiator having a 1-minute half-life temperature of 280Â° C. or higher is resistant to thermal degradation and can be used for dynamic crosslinking at high temperatures in the case of using a resin having a high melting point such as a fluororesin.

A radical initiator in which the upper limit value of the 1-minute half-life temperature is substantially 350Â° C. or lower is used from the viewpoint of inhibiting deterioration of a fluororubber or fluororesin used in combination therewith.

The â€œ1-minute half-life temperatureâ€ of the radical initiator indicates the temperature when the amount of radical generated as a result of decomposition of the radical initiator falls to one-half the original value in 1 minute.

The 1-minute half-life temperature indicates a value determined in the following manner. Namely, a radical initiator solution having a concentration of 0.1 mol/L is prepared by using benzene for the main solvent, and the resulting solution is sealed in a glass tube in which the atmosphere inside has been replaced with nitrogen. The glass tube is then immersed in a constant-temperature bath adjusted to a prescribed temperature to induce thermal decomposition. The 1-minute half-life temperature can then be determined according to a method complying with, for example, a relational expression during decomposition of organic peroxide in dilute solution.

[Relational Expression During Decomposition of Organic Peroxide in Dilute Solution]

In general, since decomposition of organic peroxide in a dilute solution can be approximately treated as a first-order reaction, this decomposition can be represented as indicated below by defining the amount of decomposed peroxide (PO) as x, defining the decomposition rate constant as k, defining time as t, and defining the PO initial concentration as a.

dx/dt=k(aâˆ’x)â€ƒâ€ƒFormula (1)

ln a/(aâˆ’x)=ktâ€ƒâ€ƒFormula (2)

Here, since half-life is the time until the concentration of PO decreases to half the initial concentration, formula (3) is obtained by representing half-life with t_1/2and substituting a/2 for x in formula (2).

kt_1/2=ln 2â€ƒâ€ƒFormula (3)

Thus, half-life t_1/2, at a certain constant temperature can be determined by inducing thermal decomposition at that temperature, plotting the relationship between time (t) and ln a/(aâˆ’x), determining k from the slope of the resulting straight line, and substituting the value of k into formula (3).

A decomposition temperature that yields an arbitrary half-life can be obtained from a straight line obtained by measuring t_1/2for several prescribed temperatures and plotting the relationship between In t_1/2, and 1/T (absolute temperature, K). The decomposition temperature for a 1-minute half-life (1-minute half-life temperature) is determined by using this method.

Among radical initiators, 2,3-dimethyl-2,3-diphenylbutane (1-minute half-life temperature: 285Â° C.) and fluorinated pitch (1-minute half-life temperature: 300Â° C.) are examples of preferable radical initiators since they further enhance the crosslinking efficiency of fluororubber.

Specific examples of radical initiators that can be used include Nofmer BC (trade name) manufactured by NOF Corp., and fluorinated pitch (trade name) manufactured by Osaka Gas.

One type of radical initiator may be used alone or two or more types may be used in combination.

The content of the radical initiator in the rubber composition is preferably within the range of 0.1 to 10 parts by weight, preferably within the range of 1 to 5 parts by weight by weight based on 100 parts by weight of the fluororubber. If the content of the radical initiator is equal to or greater than the lower limit value, crosslinking efficiency of the fluororubber is further enhanced, while if the content of the radical initiator is less than the upper limit value, decomposition reactions by the radical initiator are inhibited.

(Crosslinking Assistant)

A crosslinking assistant is used in the present embodiment that has a melting point of 200Â° C. or higher and has two or more double bonds (>Câ• C<) between carbon atoms.

In the present embodiment, â€œmelting pointâ€ refers to a value measured by thermal analysis.

The melting point of the crosslinking assistant in the present embodiment is 200Â° C. or higher, preferably within the range of 200 to 320Â° C. If the melting point of the crosslinking assistant is 200Â° C. or higher, it is resistant to thermal degradation and can be used for dynamic crosslinking at high temperatures in the case of using a resin having a high melting point such as a fluororesin. On the other hand, if the melting point of the crosslinking assistant is 320Â° C. or lower, the crosslinking reaction can be allowed to proceed more effectively as a result of melting during crosslinking.

The crosslinking assistant preferably has 2 or more double bonds, and more preferably has 2 to 6 double bonds. A crosslinked structure is formed by connecting fluororubber molecules as a result of having 2 or more double bonds. On the other hand, if the crosslinking assistant has 6 or fewer double bonds, crosslinking density is adequately enhanced. In addition, heat resistance properties are also favorable.

Examples of crosslinking assistants include N,Nâ€²-m-phenylene bismaleimide (melting point: 202Â° C.), 2,2-bis(4-maleimidophenyl)hexafluoromethane and 2-trifluoromethyl-4-maleimidophenyl biphenyl.

In particular, N,Nâ€²-m-phenylene bismaleimide is preferable as a crosslinking agent since it greatly enhances crosslinking density of fluororubber.

Specific examples of crosslinking assistants that can be used include Actor PBM (trade name) manufactured by Kawaguchi Chemical Industry.

One type of crosslinking assistant may be used alone or two or more types may be used in combination.

The content of crosslinking assistant in the rubber composition is preferably within the range of 3 to 30 parts by weight, more preferably within the range of 5 to 20 parts by weight by weight based on 100 parts by weight of fluororubber. If the content of crosslinking agent is equal to greater than the lower limit value, crosslinking density of the fluororubber is enhanced, while if the content of crosslinking agent is equal to or less than the upper limit value, softness properties can be maintained.

(Other Components)

The rubber composition of the present embodiment may also contain other components in addition to the aforementioned fluororubber, radical initiator and crosslinking assistant.

Examples of other components include metal powder, inorganic powder, inorganic oxides, inorganic compounds, antioxidants, colorants and anti-photodegradation agents.

Crosslinking of a rubber composition containing fluororubber can be favorably carried out even at high temperatures (temperatures equal to or higher than the melting point of fluororesin such as roughly 280Â° C. or higher), which was previously difficult, by using the previously described combination of fluororubber, specific radical initiator resistant to thermal degradation and crosslinking assistant in the rubber composition of the present embodiment.

The resulting crosslinked fluororubber has high crosslinking density, favorable tensile strength and softness, and superior heat resistance.

The crosslinked fluororubber is introduced into a resin such as a fluororesin in a uniformly dispersed state by carrying out dynamic crosslinking using this rubber composition. As a result, hardness can be controlled even in the case of a fluororesin and the like having a high melting point.

The thermoplastic resin composition of the present embodiment contains a fluororesin and the previously described rubber composition of the present invention.

(Fluororesin)

The fluororesin in the present embodiment is a resin that has a fluorine atom in a molecule thereof, and preferable examples include tetrafluoroethylene-hexafluoropropylene copolymer (FEP), perfluoroalkoxy fluororesin (PFA) and ethylene-tetrafluoroethylene copolymer (ETFE) since these fluororesins enable a high degree of softness to be easily obtained.

Specific examples of fluororesins that can be used include 130J (trade name) manufactured by DuPont-Mitsui, P-63PT (trade name) manufactured by Asahi Glass, and C-88AP (trade name) manufactured by Asahi Glass.

The mixing ratio of fluororesin and the aforementioned rubber composition in the thermoplastic resin composition in terms of the weight ratio of fluororubber in the rubber composition to the fluororesin is preferably within the range 0.5/99.5 to 50/50, more preferably within the range of 10/90 to 40/60. Softness increases if the weight ratio is equal to or greater than the lower limit value thereof (if the ratio of the content of fluororubber increases). On the other hand, hardness increases if the weight ratio is equal to or less than the upper limit value thereof (if the ratio of the content of fluororubber decreases).

(Other Components)

The thermoplastic resin composition of the present embodiment may contain other components in addition to the aforementioned fluororesin and rubber composition.

Examples of other components include metal powder, inorganic powder, inorganic oxides, inorganic compounds, antioxidants, colorants and anti-photodegradation agents.

In the thermoplastic resin composition of the present embodiment, the rubber composition is preferably crosslinked in the fluororesin since in addition to demonstrating superior heat resistance and oil resistance, a higher degree of softness is obtained or hardness is easily controlled.

There are no particular limitations on the method used to produce the thermoplastic resin composition of the present invention, and a preferable example thereof is the â€œThermoplastic Resin Composition Production Methodâ€ subsequently described as an example since it enables a thermoplastic resin composition in which the rubber composition is crosslinked in the fluororesin to be easily prepared.

The production method of the thermoplastic resin composition of the present embodiment consists of mixing a rubber composition containing a fluororubber, a radical initiator having a 1-minute half-life temperature of 280Â° C. or higher and a crosslinking assistant having a melting point of 200Â° C. or higher and two or more double bonds between carbon atoms, with a fluororesin at a temperature of 280Â° C. or higher, and crosslinking the rubber composition in the molten fluororesin.

Examples of the fluororubber, radical initiator, crosslinking assistant and fluororesin used in the production method of the present invention respectively include the same fluororubber, radical initiator, crosslinking agent and fluororesin as previously described.

In particular, the radical initiator is preferably 2,3-dimethyl-2,3-diphenylmethane or fluorinate pitch, the crosslinking assistant is preferably N,Nâ€²-m-phenylene bismaleimide, and the fluororesin is preferably tetrafluoroethylene-hexafluoropropylene copolymer (FEP), perfluoroalkoxy fluororesin (PFA) or ethylene-tetrafluoroethylene copolymer (ETFE).

Temperature conditions when mixing the fluororesin and the rubber composition are such that the temperature during mixing is at least 280Â° C., preferably 300Â° C. or higher, more preferably within the range of 300 to 350Â° C. If the temperature during mixing is 280Â° C. or higher, dynamic crosslinking can be carried out in the molten fluororesin. If the temperature during mixing is equal to or lower than the upper limit temperature, thermal degradation of components contained in the rubber composition is inhibited.

The duration of mixing of the fluororesin and the rubber composition is preferably 5 minutes or longer, more preferably within the range of 5 to 10 minutes. If the mixing time is within the aforementioned ranges, the fluororesin and the rubber composition can be adequately melted and kneaded. The duration of mixing can be varied according to the aforementioned temperature conditions during mixing. In addition, in the case of not carrying out melting and kneading for 5 minutes or longer, the total heating time preferably exceeds 5 minutes under the same temperature conditions as the temperature during melting and kneading.

There are no particular limitations on the method used to mix the fluororesin and the rubber composition, and a conventionally known mixing method can be used.

In the production method of the present embodiment, as a result of mixing the fluororesin and the rubber composition at a temperature of 280Â° C. or higher, in addition to melting the fluororesin, the radical initiator generates radicals during thermal decomposition, and carbon atoms of the crosslinking assistant at allylic positions are radicalized. Next, the radicals generated as a result of radicalization radicalize carbon atoms of hydrocarbon moieties of the fluororubber, thereby allowing the crosslinking reaction to proceed. As a result of this crosslinking reaction within the molten fluororesin, a crosslinked fluororubber having superior heat resistance is formed from the rubber composition, and a fluororesin is produced in which the crosslinked fluororubber is uniformly dispersed in the fluororesin.

The thermoplastic resin composition of the present embodiment obtained according to the production method of the present embodiment is a novel material that has superior heat resistance and oil resistance in addition to softness.

EXAMPLES

Although the following provides a more detailed explanation of the present invention using examples thereof, the present invention is not limited to these examples.

Components used in the examples are indicated below.

(Fluororubber)

Trade name: AFLAS100s, Asahi Glass, specific gravity: 1.55, fluorine atom content: 57% by weight

(Radical Initiators)

2,3-dimethyl-2,3-diphenylmethane, trade name: Nofmer BC, NOF Corp., molecular weight: 238.38, 1-minute half-life temperature: 285Â° C.

Fluorinated hydrocarbon, trade name: Fluorinated Pitch, Osaka Gas, 1-minute half-life temperature: 300Â° C.

(Comparative Radical Initiator Component)

2,5-dimethyl-2,5-di(t-butylperoxy)hexane, trade name: Perhexyne 25B, NOF Corp., molecular weight: 290.45, 1-minute half-life temperature: 194.3Â° C.

(Crosslinking Assistants)

N,Nâ€²-m-phenylene bismaleimide, trade name: Actor PBM, Kawaguchi Chemical Industry, molecular weight: 268, melting point: 202Â° C.

2-trifluoromethyl-4-maleimidophenyl biphenyl, synthesized in-house, molecular weight: 420

Synthesis method: 2,2-bis(trifluoromethyl)benzidine was dissolved in tetrahydrofuran followed by the addition of maleic anhydride and allowing to react for 30 minutes while heating at 60Â° C. Subsequently, pyridine and acetic anhydride were added followed by additionally reacting for 1 hour. The solvent was removed from the resulting reaction solution with an evaporator and the resulting solid was recrystallized with acetic anhydride to obtain a pure product of 2-trifluoromethyl-4-maleimidophenyl biphenyl.

(Comparative Crosslinking Assistant Component)

Triallylisocyanurate, trade name: TAIC M-60, Nippon Kasei Chemical, melting point: 23 to 27Â° C.

(Fluororesins)

FEP, trade name: 130J, DuPont-Mitsui, specific gravity: 2.16, MFR: 0.8 to 35 g/10 min., tensile strength: 20 MPa, melting point: 270Â° C.

PFA, trade name: P-63PT, Asahi Glass, specific gravity: 2.12, MFR: 7 to 18 g/10 min., tensile strength: 30 MPa, melting point: 310Â° C.

ETFE, trade name: C-88AP, Asahi Glass, specific gravity: 1.74, MFR: 4.5 to 6.7 g/10 min., tensile strength: 48 MPa, melting point: 260Â° C.

Each component was mixed under the kneading conditions indicated below using a batch kneader (twin screw extruder) in accordance with the compositions shown in Table 1, followed by molding under the hot pressing conditions indicated below to produce a crosslinked fluororubber sheet.

Kneading conditions: screw rotating speed: 50 rpm, kneader temperature: 150Â° C., kneading time: 5 minutes

Hot pressing conditions: pressure: 25 MPa, temperature: 300Â° C., pressing time: 5 minutes

Fluororubber, radical initiator and crosslinking assistant were mixed in accordance with the compositions shown in Table 2 to prepare a rubber composition, followed by mixing the rubber composition with fluororesin under the following kneading conditions using a batch kneader (twin screw extruder), crosslinking the fluororubber in the molten fluororesin under the hot pressing conditions indicated below and extruding to produce a crosslinked sheet of a thermoplastic resin composition.

Kneading conditions: screw rotating speed: 50 rpm, kneader temperature in case of using FEP and EFTE and fluororesins: 280Â° C., kneader temperature in the case of using PFA: 320Â° C., kneading time: 5 minutes

Hot pressing conditions: pressure: 25 MPa, temperature in case of using FEP and ETFE as fluororesins: 300Â° C., temperature in case of using PFA: 320Â° C., pressing time: 5 minutes

The crosslinking density of the resulting crosslinked fluororubber sheets was measured.

In addition, measurement of tensile strength and elongation as well as evaluation of heat resistance were carried out for the resulting crosslinked sheets and crosslinked thermoplastic resin composition sheets. The results are shown in Tables 1 and 2.

The methods used to measured crosslinking density, tensile strength and elongation and the method used to evaluate heat resistance are indicated below.

[Crosslinking Density]

1 g of a crosslinked fluororubber sheet were immersed in 10 mL of a good solvent followed by continuing to shake and stir for 24 hours. After 24 hours had elapsed, the weight of the crosslinked sheet was measured and crosslinking density (wt %) was determined by measuring the change in weight before and after immersion.

[Tensile Strength and Elongation]

Tensile strength and elongation were respectively measured in compliance with the procedure for measuring tensile strength of rubber of JIS K6251.

[Heat Resistance]

The resulting crosslinked fluororubber sheets and crosslinked thermoplastic resin composition sheets were respectively stored in air for 500 hours at 275Â° C. followed by measurement of tensile strength in the same manner as described above.

The percentage of change in tensile strength before and after storage was then determined, and heat resistance was evaluated based on the criteria indicated below.

Percentage of change in tensile strength (%)=

Tensile strength after storage/tensile strength before storageÃ—100

â—¯: Percentage of change in tensile strength of 70% or more

X: Percentage of change in tensile strength of less than 70%

TABLE 1Comp.Comp.Comp.Comp.Comp.Ex. 1Ex. 2Ex. 3Ex. 4Ex. 1Ex. 2Ex. 3Ex. 4Ex. 5FluororubberAFLAS 100s100100100100100100100100100RadicalNofmer BC3333initiatorFluorinated pitch33Perhexyne 25B33CrosslinkingActor PBM5101055assistant2-trifluoromethyl-54-maleimidophenylbiphenylTAIC M-6055Crosslinking density (wt %)6571736030221800Tensile strength (MPa)7.89.510.66.75.85.15.44.55.3Elongation (%)1000<1000<1000<1000<700700400300500Heat resistanceâ—¯â—¯â—¯â—¯XXXXX

Based on the results of Table 1, the crosslinked fluororubber sheets of Examples 1 to 4 demonstrated higher crosslinking density and favorable tensile strength and elongation (softness) in comparison with the comparative examples, and were also determined to have superior heat resistance.

TABLE 2Comp.Comp. Comp.Comp.Ex. 5Ex. 6Ex. 7Ex. 8Ex. 9Ex. 6Ex. 7Ex. 8Ex. 9FluororesinFEP 130J7070707070PFA P-63PT70ETFE C-88AP707070FluororubberAFLAS 100s3030303030303030RadicalNofmer BC0.90.90.90.9initiatorFluorinated pitch0.90.9Perhexyne 25B0.90.9CrosslinkingActor PBM1.51.51.51.51.5assistant2-trifluoromethyl-1.54-maleimidophenylbiphenylTAIC M-601.51.5Tensile strength (MPa)10.28.613.511.312.110.58.212.648Elongation (%)300350250250250300300200400Heat resistanceâ—¯â—¯â—¯â—¯â—¯XXXX

Based on the results of Table 2, the crosslinked thermoplastic resin composition sheets of Examples 5 to 9 were determined to have softness as well as demonstrate superior heat resistance in comparison with the comparative examples.

In addition, based on a comparison of Example 5 and Example 8, in the case of using FEP as fluororesin, hardness of the fluororesin was determined to be able to be controlled by changing the composition of the rubber composition.

Moreover, the crosslinked thermoplastic resin composition sheets of Examples 5 to 9 can be said to also demonstrate superior oil resistance as a result of using fluororesin and fluororubber.

According to the rubber composition of the present invention, the hardness of fluororesins having a high melting point can be controlled. In addition, according to the present invention, a thermoplastic resin composition having superior heat resistance and oil resistance together with softness can be provided along with a production method thereof.

Although the above has provided an explanation of preferable examples of the present invention, the present invention is not limited to these examples. Additions, omissions, substitutions and other changes can be made to the composition of the present invention within a range that does not deviate from the purport thereof.