JP7151563B2 - 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. The present invention relates to a tire rubber composition having excellent conductivity and a pneumatic tire using the same.

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.

Compounds for tire undertread are required to have the following properties.
(1) To improve the durability by increasing the strength while maintaining the tire manufacturability.
(2) To reduce tire rolling resistance by reducing heat generation.
(3) To improve the steering stability of the tire by increasing the modulus of elasticity.

However, in the above (1), in order to increase the strength, there are methods such as increasing the amount of natural rubber compounded and using carbon black with a high specific surface area, but there is a problem in compatibility with low heat generation. be.
In addition, in (2) above, in order to reduce the heat generation, there are methods such as blending a filler such as silica or using low specific surface area carbon black, but there is a problem in compatibility with high strength. . Moreover, there is a difficulty in the dispersibility of the filler.
In addition, in (3) above, in order to increase the elastic modulus, there are methods such as using carbon black with a high specific surface area and using a high Tg polymer, but there is a problem in coexisting with low heat generation. be.

On the other hand, tires with high silica content may use earth tread 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 causes an increase in tire manufacturing man-hours, so an undertread is sometimes used as a substitute for the ground tread. In such a form, the undertread compound needs to maintain a certain level of electrical conductivity.

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

Accordingly, an object of the present invention is to provide a rubber composition for tires which has excellent filler dispersibility, achieves high strength, low heat generation and high elastic modulus, and has excellent electrical conductivity, and a pneumatic tire using the same. is to provide

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

1. 1 to 150 parts by mass of carbon black and 0.1 to 10 parts by mass of a carbon nanotube-polymer composite in which a polymer is attached to at least part of the carbon nanotubes, per 100 parts by mass of the 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 carbon black has a nitrogen adsorption specific surface area (N ₂ SA) of 30 to 140 m ² /g.
5. A pneumatic tire using the tire rubber composition according to any one of the above 1 to 4 for an undertread.
6. 5. A method of use, wherein the rubber composition for tires according to any one of 1 to 4 is used as a tire cap tread ground.

The composition of the present invention comprises 1 to 150 parts by mass of carbon black and 0.1 to 10 parts by mass of a carbon nanotube-polymer composite in which a polymer is attached to at least part of the carbon nanotubes, based on 100 parts by mass of the diene rubber. A rubber composition for tires that is characterized by being blended in parts, so that it has excellent filler dispersibility, achieves high strength, low heat generation, and high elastic modulus, and has excellent electrical conductivity, and its characteristics It is possible to provide a pneumatic tire that combines

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.
When the diene rubber of the present invention is used for the undertread, it is preferable that natural rubber is 40 parts by mass or more and styrene-butadiene copolymer rubber is 50 parts by mass or less per 100 parts by mass of the diene rubber.

(Carbon black)
Carbon black used in the present invention preferably has a nitrogen adsorption specific surface area (N ₂ SA) of 30 to 140 m ² /g. When the nitrogen adsorption specific surface area (N ₂ SA) is 30 m ² /g or more, high strength can be achieved. Further, when the nitrogen adsorption specific surface area (N ₂ SA) is 140 m ² /g or less, good dispersibility of the filler and low heat generation can be achieved. Further, from the viewpoint of improving the effects of the present invention, the nitrogen adsorption specific surface area (N ₂ SA) is preferably 30 to 100 m ² /g. The nitrogen adsorption specific surface area (N ₂ SA) is a value obtained according to JIS K6217-2.

(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.

The carbon nanotube-polymer composite used in the present invention has both high electrical conductivity and high strength. In addition, the dispersibility in diene rubber is also good, and from these reasons, the rubber composition has excellent filler dispersibility, achieves high strength, low heat generation and high elastic modulus, and has excellent electrical conductivity. can provide

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 mixed solution 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”).

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, 1 to 150 parts by mass of carbon black, and 0.1 to 10 parts by mass of the carbon nanotube-polymer composite. It is characterized by
When the amount of carbon black is less than 1 part by mass, the reinforcing performance is not exhibited, and when it exceeds 150 parts by mass, the rolling resistance deteriorates.
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 it exceeds 10 parts by mass, the filler dispersibility, strength and heat build-up deteriorate.

A more preferable blending amount of the carbon black is 30 to 100 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 rubber composition for tires of the present invention has excellent filler dispersibility, achieves high strength, low heat generation and high elastic modulus, and has excellent electrical conductivity, so it is particularly suitable for undertreads. preferably used. In this embodiment, the composition of the diene rubber is 10 to 100 parts by mass, preferably 40 to 80 parts by mass, of natural rubber, and 0 to 70 parts by mass of styrene-butadiene rubber, when the entire diene rubber is 100 parts by mass. , preferably 20 to 50 parts by mass, and 0 to 40 parts by mass, preferably 5 to 30 parts by mass, of butadiene rubber. Moreover, when silica is used, it is preferably less than 40 parts by mass with respect to 100 parts by mass of the diene rubber. It is also a preferred embodiment to use the rubber composition for a tire of the present invention as a tire cap tread ground in which part of the underdread is penetrated through the cap tread and exposed on the outer surface of the cap tread.

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 Examples 1-2, Examples 1-6, Comparative Examples 1-2
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 or 2 as 100. A smaller index indicates better dispersibility of the filler (carbon black, carbon nanotube-polymer composite, silica).
Tensile strength (TB): Based on JIS K6251 (JIS No. 3 dumbbell), a tensile test was carried out at 100°C. The results were indexed with the value of Standard Example 1 or 2 as 100. A higher index indicates higher strength.
Storage elastic modulus E': Storage elastic modulus (E') at 20°C under the conditions of 10% initial strain, ±2% amplitude, and 20 Hz frequency using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho in accordance with JIS K6394. asked for The results were indexed with the value of Standard Example 1 or 2 as 100. A larger index indicates a higher elastic modulus.
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.
Tan δ (60°C): Using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd., tan δ (60°C) was measured under conditions of initial strain of 10%, amplitude of ±2%, frequency of 20 Hz, and temperature of 60°C. The results were indexed with the value of Standard Example 1 or 2 as 100. A smaller index indicates a lower heat build-up.
The results are also shown in Table 1. The results of Examples 1-4 and Comparative Examples 1-2 are compared with the results of Standard Example 1, and the results of Examples 5-6 are compared with the results of Standard Example 2.

*1: NR (SIR20 made by PT. KIRANA SAPTA)
*2: SBR (Nipol 1502 manufactured by Nippon Zeon Co., Ltd.)
*3: BR (Nipol BR 1220 manufactured by Nippon Zeon Co., Ltd.)
*4: Carbon black (Cabot Japan's use black N339, N ₂ SA = 90 m ² /g)
*5: 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 )
*6: Carbon nanotube-polymer composite 1 (Mitsubishi Corporation Durobeads, product number = DP2210, polymer used = liquid paraffin oil)
* 7: Carbon nanotube-polymer composite 2 (Mitsubishi Corporation Durobeads, product number = DP4210, polymer used = SBR)
* 8: Carbon nanotube-polymer composite 3 (Mitsubishi Corporation Durobeads, product number = DP5210, polymer used = NR)
*9: Zinc oxide (Type 3 zinc oxide manufactured by Seido Chemical Industry Co., Ltd.)
* 10: Stearic acid (bead stearic acid YR manufactured by NOF Corporation)
*11: Anti-aging agent (6PPD manufactured by EASTMAN)
*12: Oil (Extract No. 4S manufactured by Showa Shell Co., Ltd.)
*13: Sulfur (Mucron OT-20 manufactured by Shikoku Chemical Industry Co., Ltd.)
*14: Vulcanization accelerator (Suncellar CM-G manufactured by Sanshin Chemical Industry Co., Ltd.)
*15: Silica (ULTRASIL VN3GR manufactured by EVONIK)
*16: Silane coupling agent (Si69 manufactured by EVONIK)

As is clear from Table 1 above, the rubber compositions prepared in Examples 1 to 6 contained 1 to 150 parts by mass of carbon black and at least 1 part by mass of carbon nanotubes per 100 parts by mass of diene rubber. Since 0.1 to 10 parts by mass of a carbon nanotube-polymer composite with a polymer attached to it is blended, it has excellent filler dispersibility, high strength, low heat generation, and high elasticity compared to standard examples 1 or 2. Achieving efficiency and excellent electrical conductivity.
Since Comparative Example 1 does not contain carbon nanotubes or carbon nanotube-polymer composites, it is inferior to Standard Example 1 in breaking strength, storage modulus and electrical conductivity.
In Comparative Example 2, the blending amount of the carbon nanotube-polymer composite exceeded the upper limit specified in the present invention, so compared with Standard Example 1, the filler dispersibility, breaking strength, and tan δ (60°C) were deteriorated.

Claims (5)

1 to 150 parts by mass of carbon black 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 the carbon nanotubes are blended with 100 parts by mass of the 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. 3. The rubber composition for a tire according to claim 1, wherein the carbon black has a nitrogen adsorption specific surface area (N ₂ SA) of 30 to 140 m ² /g. A pneumatic tire using the tire rubber composition according to any one of claims 1 to 3 for an undertread. A method of using the tire rubber composition according to any one of claims 1 to 3 as a tire cap tread earth.