JP7151595B2 - Rubber composition for tire and pneumatic tire using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rubber composition for tires and a pneumatic tire using the same. More specifically, the present invention relates to a rubber composition for tires having excellent filler dispersibility, excellent abrasion resistance and electrical conductivity, and a rubber composition containing the same. It relates to the pneumatic tire used.

A pneumatic tire is mainly composed of a pair of left and right bead portions and sidewall portions, and a tread portion connected to both sidewall portions and composed of a cap tread and an undertread. A carcass layer is provided inside the tire, and both ends of the carcass layer are folded back so as to wrap the bead core from the inside to the outside of the tire.

Tire cap tread compounds containing high silica are now widely used to improve wet performance and low rolling performance.
On the other hand, compounds for tire cap treads containing high silica are required to have the following properties.
(1) Excellent wear resistance.
(2) to improve electrical conductivity;

However, in (1) above, in order to improve wear resistance, techniques such as adjusting the particle size and specific surface area of silica have been investigated, but sufficient wear resistance has not yet been obtained.
In addition, in (2) above, an earth tread structure may be employed to improve electrical conductivity. The ground tread is a conductive rubber that is embedded in the tread rubber and exposed to the ground contact surface of the tire. However, installing the ground tread on the tire has the problem of increasing the number of man-hours for manufacturing the tire.

Patent Documents 1 to 3 disclose tire rubber compositions using carbon nanotubes, but neither disclose nor suggest the carbon nanotube-polymer composite of the present invention described below.

Japanese Patent No. 5367966 JP 2009-179809 A JP 2011-126529 A

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a rubber composition for tires having excellent filler dispersibility, wear resistance and electrical conductivity, and a pneumatic tire using the same.

As a result of intensive research, the present inventor found that the above-mentioned problems can be solved by blending specific amounts of silica and a specific carbon nanotube-polymer composite with a diene rubber, and completed the present invention. was made.
That is, the present invention is as follows.

1. 40 to 150 parts by mass of silica and 0.1 to 10 parts by mass of a carbon nanotube-polymer composite in which a polymer is attached to at least one part of carbon nanotubes are blended with 100 parts by mass of diene rubber. A rubber composition for tires characterized by:
2. 2. The rubber composition for tires as described in 1 above, wherein the polymer is attached in an amount of 5 to 20% by mass in the carbon nanotube-polymer composite.
3. 3. The rubber composition for tires as described in 1 or 2 above, wherein the carbon nanotube-polymer composite has an average particle size of 0.1 mm to 3 mm.
4. 4. The rubber composition for tires as described in any one of 1 to 3 above, wherein the rubber composition for tires has an average glass transition temperature (Tg) of −20° C. or lower.
5. 5. The rubber composition for tires as described in any one of 1 to 4 above, wherein the silica has a CTAB specific surface area (N ₂ SA) of 100 to 300 m ² /g.
6. A pneumatic tire using the tire rubber composition according to any one of the above 1 to 5 for a cap tread.

The composition of the present invention comprises 100 parts by mass of diene rubber, 40 to 150 parts by mass of silica, and 0.1 to 10 parts by mass of a carbon nanotube-polymer composite in which at least part of the carbon nanotube is attached with a polymer. Since it is characterized by being blended, it is possible to provide a rubber composition for tires having excellent filler dispersibility, excellent wear resistance and electrical conductivity, and a pneumatic tire having these properties.

The present invention will now be described in more detail.
(Diene rubber)
As the diene rubber used in the present invention, any diene rubber that can be blended in a normal rubber composition can be used. Examples include natural rubber (NR), isoprene rubber (IR), butadiene rubber ( BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), and the like. These may be used alone or in combination of two or more. Further, its molecular weight and microstructure are not particularly limited, and it may be terminally modified with an amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl group or the like, or epoxidized.

(silica)
The silica used in the present invention is not particularly limited, and for example, any conventionally known silica compounded in rubber compositions for use in tires can be used.
Specific examples of silica include wet silica, dry silica, and fumed silica. As for silica, one type of silica may be used alone, or two or more types of silica may be used in combination.
From the viewpoint of improving the effects of the present invention, particularly from the viewpoint of improving wear resistance, the CTAB specific surface area of silica is preferably 100 to 300 m ² /g, more preferably 150 to 260 m ² /g. . The CTAB specific surface area of silica is measured according to ISO5794/1.

(Carbon nanotube-polymer composite)
The carbon nanotube-polymer composite used in the present invention is obtained by attaching a polymer to at least a portion of the carbon nanotube.

Examples of the polymer include diene rubbers such as NR and SBR; olefin resins such as polyethylene and polyα-olefin; silicone resins; fluorine resins such as polyvinylidene fluoride; silicone resins; Vinyl chloride; polyvinyl acetate; polystyrene and the like.

From the viewpoint of improving the effects of the present invention, it is preferable that the amount of the polymer attached to the carbon nanotube-polymer composite is, for example, 5 to 20% by mass.
A more preferable attachment amount is 5 to 15% by mass.

In the carbon nanotube-polymer composite used in the present invention, a plurality of single carbon nanotubes (primary structure) are aggregated (secondary structure), and these secondary carbon nanotubes are further aggregated (tertiary structure), At least part or all of the tertiary-structured carbon nanotubes may be attached with the polymer to form beads. Here, the term “attachment” generally refers to a state in which the polymer is attached to at least a portion of the tertiary-structured carbon nanotube, or the entirety of the carbon nanotube is coated with the polymer. It is sufficient that the polymer is immobilized, and it does not matter whether the bond between them is a mechanical bond or a chemical bond. Moreover, the average particle size of the beads is, for example, 0.1 mm to 3 mm. The average particle diameter can be grasped, for example, by observing the carbon nanotube-polymer composite under a microscope and calculating the average particle diameter of 100 composites. Such a carbon nanotube-polymer composite can be produced by known means. For example, a single carbon nanotube (primary structure) is dispersed in water to prepare a dispersion, and the polymer is separately dissolved in a solvent. A carbon nanotube-polymer composite can be obtained by preparing a solution, stirring and granulating the dispersion and the solution in the same vessel, and drying. Such a carbon nanotube-polymer composite has an electrical conductivity equivalent to that of a single carbon nanotube (primary structure).

A method for producing a carbon nanotube-polymer composite will be described in more detail.
A carbon nanotube-polymer composite can be produced, for example, according to the methods disclosed in Japanese Patent No. 4787892 and Japanese Patent No. 5767466.

When the polymer is a thermoplastic resin other than rubber, (1) a dissolving step of dissolving the thermoplastic resin in a water-insoluble solvent to prepare a resin binder solution; A suspension step of adding carbon nanotubes corresponding to 100 to 1500 parts by mass with respect to 100 parts by mass of the thermoplastic resin to water and uniformly suspending to obtain a suspension; (4) a mixing step of adding the resin binder solution to the suspension obtained in the suspension step to prepare a mixed solution; and (4) stirring the mixed solution obtained in the mixing step. (5) separating and removing the aqueous phase and the resin phase from the mixture obtained in the stirring step, and drying the resin phase to increase the height of the carbon nanotubes; A carbon nanotube-polymer composite can be obtained through a separation/drying step of obtaining the compounded resin particles.

Carbon nanotubes (CNT) as a raw material are not particularly limited, but those having a fiber diameter of 1 to 200 nm and a fiber length of 1 to 100 μm, for example, can be used.

The (1) dissolving step is a step of dissolving the thermoplastic resin in a water-insoluble solvent. The solvent used here may be a non-aqueous solvent or a water-soluble solvent.
Any of various water-insoluble solvents capable of dissolving the thermoplastic resin can be used as the solvent. As a simple method to check the degree of dissolution, the extent to which all the liquid can be filtered with a round filter paper #5C manufactured by Advantech is a guideline, and if even a small amount of filtration residue is present, it is necessary to change the solvent.
Examples of water-insoluble solvents include organic solvents such as toluene, xylene, hexane, tetrahydrofuran, benzene and cyclohexane.

In the (2) suspension step, 100 to 1,500 parts by mass, preferably 200 to 1,000 parts by mass of CNTs are added to 100 parts by mass of the thermoplastic resin and uniformly suspended. The CNT concentration in the suspension is preferably 0.1-10% by mass, more preferably 0.5-5% by mass.
The degree of dispersion of the CNTs in water was determined by taking the suspension on a glass plate with a dropper, spreading it with a spatula, and examining the undispersed lumps visually and with a finger. Let By this treatment, the CNTs are sufficiently disentangled from the state of agglomeration.
The suspending method is preferably carried out by mechanically stirring the CNTs in a dispersion medium such as water. Moreover, you may use ultrasonic irradiation together.

In the mixing step (3), the resin-dissolving solvent should be added at a uniform rate of, for example, 60 cc/min. adversely affect final performance.
Dropping is performed by a tube pump, a diagram pump, a gear pump, or the like, and the temperature of the suspension of CNT and water is preferably 50° C. or less, preferably 25° C. or less.
Regarding the dripping condition, the droplet shape does not necessarily have to be granular. Depending on the stirring speed, a thin liquid column may be continuously dropped.
At this time, the temperature of the additive solution is not particularly limited, and may be within a temperature range around room temperature.

In the (4) stirring step, the stirring is preferably completed within 30 minutes, depending on the liquid temperature of the suspension solution. If the stirring is continued for 30 minutes or more, the produced resin particles tend to be crushed into a slurry.
When the resin binder solution is added in the form of droplets or fine liquid columns while the uniform suspension of CNTs and water is being stirred, two phases, a resin phase and an aqueous phase, are formed. Initially, the CNTs are mainly present in the water phase, but if the stirring is continued, the CNTs in the water phase migrate into the resin phase (flushing action). If a solvent is present at this time, resin granules composed of CNT and resin can be obtained under agitation.

In the (5) separation/drying step, the separation operation can be easily performed using a sieve. Drying can be performed by a method such as steam drying or vacuum drying. The temperature at this time is preferably 200° C. or less in the case of a steam dryer or 150° C. or less in the case of vacuum drying.

When the polymer is rubber, (A) a dissolving step of dissolving a solid rubber in a solvent to prepare a rubber binder solution; (C) a suspension step of adding carbon nanotubes corresponding to 100 to 1500 parts by mass to water and uniformly suspending them to obtain a suspension; (D) a transition step of transferring the carbon nanotubes from the water phase to the rubber phase by stirring the mixture; (E ) Thereafter, the aqueous phase and the rubber phase are separated and removed from the mixed solution, and the rubber phase is dried to obtain a carbon nanotube-rich rubber granule, thereby obtaining a carbon nanotube-polymer composite. can be obtained.

(A) In the dissolution step, any solvent capable of dissolving the solid rubber can be used. As a simple method to check the degree of dissolution, the extent to which all the liquid can be filtered with a round filter paper #5C manufactured by Advantech is a guideline, and if even a small amount of filtration residue is present, it is necessary to change the solvent.
Examples of solvents include toluene, xylene, hexane, tetrahydrofuran, benzene, cyclohexane, naphthylamine, isooctane, isopropyl ether, ethylbenzene, cresol, chlorosulfonic acid, chlorotoluene, chloronaphthalene, chloroform, diethyl ether, dioxane, cyclohexane, dichlorobenzene. , dibutyl phthalate, dibenzyl ether, dipentene, tetralin, terpineol, trichlorethylene, dichloromethane, dichloroethane, nitrobenzene, carbon disulfide, tetrachloroethylene, pinene, piperidine, pyridine, furan, benzine, thiol, monochlorobenzene, methyl methacrylate, tetrachloride There are organic solvents such as carbon, etc. The amount of the solvent to be added is preferably 0.8 to 1.5 times the absorption ratio of the carbon nanotube (CNT) to DBP. The DBP absorption amount of carbon nanotubes was measured by the JIS K 6221A method.

The (B) suspension step, the (C) separation/drying step, the (D) transfer step and the (E) separation/drying step are respectively the (2) suspension step and the (3) The mixing step, the (4) stirring step, and the (5) separation/drying step can be performed in the same manner (“resin” should be read as “rubber”).

Also, the carbon nanotube-polymer composite is well dispersed in the diene-based rubber and can improve the elongation at break and elastic modulus, thereby providing excellent wear resistance.

As the carbon nanotube-polymer composite used in the present invention, a commercially available one can be used. %, average particle size = 0.5 mm to 2 mm),
Durobeads manufactured by Mitsubishi Corporation, product number = DP4210 (polymer used = SBR, amount of polymer attached = 10% by mass, average particle size = 0.5 mm to 2 mm),
Durobeads manufactured by Mitsubishi Corporation, product number = DP1210 (polymer used = polyethylene, amount of polymer attached = 10% by mass, average particle size = 0.5 mm to 2 mm),
Durobeads manufactured by Mitsubishi Corporation, product number = DP7210 (polymer used = polyvinylidene fluoride, amount of polymer attached = 10% by mass, average particle size = 0.5 mm to 2 mm),
Durobeads manufactured by Mitsubishi Corporation, product number = DR3110 (polymer used = silicone resin, amount of polymer attached = 10% by mass, average particle size = 0.5 mm to 2 mm),
Durobeads manufactured by Mitsubishi Corporation, product number = DP2210 (polymer used = liquid paraffin oil, amount of polymer impregnated = 10% by mass, average particle size = 0.5 mm to 2 mm),
etc.

(Ratio of rubber composition for tires)
The rubber composition for tires of the present invention comprises 100 parts by mass of the diene rubber, 40 to 150 parts by mass of silica, and 0.1 to 10 parts by mass of the carbon nanotube-polymer composite. characterized by
If the amount of silica is less than 40 parts by mass, the benefits of the silica compound system cannot be enjoyed (for example, deterioration of rolling resistance).
If the amount of the carbon nanotube-polymer composite compounded is less than 0.1 part by mass, the amount added is too small, and the effects of the present invention cannot be obtained. Conversely, if the content exceeds 10 parts by mass, the dispersibility of the filler will be deteriorated, and there is a concern that the rolling resistance will be deteriorated.

A more preferable amount of silica compounded is 60 to 130 parts by mass with respect to 100 parts by mass of the diene rubber.
A more preferable blending amount of the carbon nanotube-polymer composite is 0.5 to 7 parts by mass with respect to 100 parts by mass of the diene rubber.

In addition to the components described above, the rubber composition for tires of the present invention includes a vulcanizing or cross-linking agent, a vulcanization or cross-linking accelerator, various fillers, various oils, anti-aging agents, plasticizers, and other rubber compositions. Various additives that are generally blended can be blended, and such additives can be kneaded by a common method to form a composition and used for vulcanization or cross-linking. The blending amount of these additives can also be a conventional general blending amount as long as it does not contradict the object of the present invention.

Further, the tire rubber composition of the present invention preferably has an average glass transition temperature (average Tg) of -20°C or lower.
The average Tg referred to in this specification is the sum of products obtained by multiplying the glass transition temperature of each component by the weight fraction of each component, that is, the value calculated based on the weighted average. Note that the sum of the weight fractions of each component is assumed to be 1.0 when calculating. Further, the glass transition temperature is measured by differential scanning calorimetry (DSC) under the condition of a temperature increase rate of 20° C./min and measuring a thermogram, and taken as the temperature at the middle point of the transition region.
Further, each of the above components means diene rubber, oil and resin. Note that the oil and resin may not be included in the rubber composition.
A more preferred average Tg is, for example, -20°C to -80°C.

Further, the rubber composition for tires of the present invention is excellent in filler dispersibility, wear resistance and electrical conductivity, and is therefore particularly preferably used for cap treads. In this embodiment, the composition of the diene rubber is 30 to 100 parts by mass, preferably 50 to 80 parts by mass, of styrene-butadiene copolymer rubber, and 0 part by mass of butadiene rubber when the total diene rubber is 100 parts by mass. 60 parts by mass, preferably 10 to 50 parts by mass, and 0 to 100 parts by mass, preferably 0 to 50 parts by mass of natural rubber or isoprene rubber.

Moreover, the rubber composition for tires of the present invention can be used to produce a pneumatic tire according to a conventional method for producing a pneumatic tire.

The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Standard Example 1, Examples 1-7, Comparative Examples 1-3
In the formulation (parts by weight) shown in Table 1, the vulcanization accelerator and components other than sulfur were kneaded for 5 minutes in a 1.7-liter internal Banbury mixer, and the rubber was discharged out of the mixer and cooled to room temperature. Then, the rubber was placed in the same mixer again, a vulcanization accelerator and sulfur were added, and the mixture was further kneaded to obtain a rubber composition. Next, the obtained rubber composition is press-vulcanized in a predetermined mold at 160 ° C. for 20 minutes to obtain a vulcanized rubber test piece, and the unvulcanized rubber composition and the vulcanized rubber are tested by the following test methods. Physical properties of the test piece were measured.

Filler dispersibility ΔG': An unvulcanized rubber composition was vulcanized at 160°C for 20 minutes, and strain shear stress G' was measured at a strain rate of 0.28% to 30.0% (unit: MPa). A viscoelasticity measuring device RPA2000 (manufactured by Alpha Technologies) was used for the measurement. The difference between G'(G'0.28) when the strain rate is 0.28% and G'(G'30.0) when the strain is 30.0% ΔG' = (G'0.28 - G'30 .0) was calculated. The results were indexed with the value of Standard Example 1 set to 100. A smaller index indicates better dispersibility of the filler (carbon black, carbon nanotube-polymer composite, silica).
Abrasion resistance: The abrasion resistance of the vulcanized rubber test piece was evaluated using a Lambourn abrasion tester according to JIS K6264. The obtained results were expressed as indices with the value of Standard Example 1 being 100. A larger index indicates better wear resistance.
Electrical conductivity: Electrical resistance was measured according to JIS K6911. The results were indexed with the value of Standard Example 1 set to 100. A smaller index indicates higher electrical conductivity.
The results are also shown in Table 1.

* 1: SBR1 (Nipol 1739 manufactured by Nippon Zeon Co., Ltd., oil extension amount = 37.5 parts by mass per 100 parts by mass of SBR)
*2: SBR2 (HP755B manufactured by JSR Corporation, oil extension amount = 37.5 parts by mass per 100 parts by mass of SBR)
*3: BR (Nipol BR 1220 manufactured by Nippon Zeon Co., Ltd.)
*4: Silica 1 (ZEOSIL1165MP manufactured by Solvay, CTAB specific surface area = 155 m ² /g)
*5: Silica 2 (ZEOSIL1115MP manufactured by Solvay, CTAB specific surface area = 110 m ² /g)
*6: Silica 3 (ZEOSIL Premium 200MP manufactured by Solvay, CTAB specific surface area = 200 m ² /g)
* 7: Carbon nanotube (VGCF manufactured by Showa Denko K.K., vapor grown carbon fiber synthesized by CVD method (with graphitization treatment), fiber diameter = 150 nm, fiber length = 10 to 20 μm, bulk density = 0.04 g / ^cm3 )
*8: Carbon nanotube-polymer composite 1 (Mitsubishi Corporation Durobeads, product number = DP2210, polymer used = liquid paraffin oil)
* 9: Carbon nanotube-polymer composite 2 (Mitsubishi Corporation Durobeads, product number = DP4210, polymer used = SBR)
*10: Carbon nanotube-polymer composite 3 (Mitsubishi Corporation Durobeads, product number = DP5210, polymer used = NR)
*11: Carbon black (Use black N339 manufactured by Cabot Japan)
*12: Silane coupling agent (Si69 manufactured by Evonik)
*13: Zinc oxide (Type 3 zinc oxide manufactured by Seido Chemical Industry Co., Ltd.)
* 14: Stearic acid (bead stearic acid YR manufactured by NOF Corporation)
*15: Anti-aging agent (6PPD manufactured by EASTMAN)
*16: Wax (paraffin wax manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.)
*17: Oil (Extract No. 4S manufactured by Showa Shell Co., Ltd.)
*18: Sulfur (Hosoi Chemical Industry Co., Ltd. oil processing sulfur)
*19: Vulcanization accelerator CBS (Suncellar CM-G manufactured by Sanshin Chemical Industry Co., Ltd.)
*20: Vulcanization accelerator DPG (Sokusil DG manufactured by Sumitomo Chemical Co., Ltd.)

As is clear from Table 1 above, the rubber compositions prepared in Examples 1 to 7 contained 40 to 150 parts by mass of silica and at least 1 part of carbon nanotubes per 100 parts by mass of diene rubber. Since 0.1 to 10 parts by mass of the polymer-attached carbon nanotube-polymer composite is blended, compared to Standard Example 1, the filler is superior in dispersibility, abrasion resistance, and electrical conductivity.
Since Comparative Example 1 did not contain carbon nanotubes or carbon nanotube-polymer composites, it showed no improvement in wear resistance and inferior electrical conductivity compared to Standard Example 1.
In Comparative Example 2, the blending amount of the carbon nanotube-polymer composite exceeds the upper limit specified in the present invention, so compared to Standard Example 1, the dispersibility of the filler deteriorates, and there is concern about deterioration of rolling resistance. .
In Comparative Example 3, the amount of silica added is less than the lower limit specified in the present invention, so compared to Standard Example 1, the dispersibility of the filler deteriorates, and there is concern about deterioration in rolling resistance.
In Comparative Example 4, the amount of silica added exceeded the upper limit specified in the present invention, so compared to Standard Example 1, the dispersibility of the filler deteriorated, and the wear resistance deteriorated.

Claims (5)

40 to 150 parts by mass of silica and 0.1 to 10 parts by mass of a carbon nanotube-polymer composite in which a polymer is attached to at least one part of carbon nanotubes are blended with 100 parts by mass of diene rubber,
A rubber composition for a tire, wherein the polymer is attached in an amount of 5 to 20% by mass in the carbon nanotube-polymer composite. 2. The rubber composition for tires according to claim 1, wherein the carbon nanotube-polymer composite has an average particle size of 0.1 mm to 3 mm. The rubber composition for tires according to claim 1 or 2, wherein the rubber composition for tires has an average glass transition temperature (Tg) of -20°C or lower. The rubber composition for tires according to any one of claims 1 to 3, wherein the silica has a CTAB specific surface area (N ₂ SA) of 100 to 300 m ² /g. A pneumatic tire using the tire rubber composition according to any one of claims 1 to 4 for a cap tread.