JP5443072B2 - Rubber composition for pneumatic tread and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition for a base tread and a pneumatic tire using the same.

In recent years, in response to social demands for energy saving, fuel efficiency of automobiles has been reduced by reducing tire rolling resistance and suppressing heat generation. In particular, an excellent low heat generation property is required for a tread having a high occupation ratio in a tire among tire members. One technique for reducing rolling resistance is to employ a tread having a two-layer structure of cap tread / base tread and a rubber compound having low heat build-up as the base tread.

As a low exothermic rubber compound for the purpose of reducing rolling resistance, it is conceivable to suppress the amount of carbon black filling. However, since the hardness (rigidity) decreases, the steering stability tends to deteriorate. It is done. On the other hand, the hardness (rigidity) can be improved by increasing the filling amount of carbon black in the base tread, but the rolling resistance is deteriorated. Therefore, it is desired to increase the hardness (rigidity) and improve the steering stability without deteriorating the rolling resistance.

Patent Document 1 discloses a pneumatic tire that uses a rubber composition containing acetylene black, carbon fiber, and the like to improve productivity, but carbon fiber has not been studied in detail. Patent Document 2 discloses a studless tire using carbon fiber precursor short fibers for a tread, but its application to a base tread is not studied. There is also room for improvement in the above performance.

JP 2004-330822 A JP 2004-34743 A

The present invention provides a rubber composition for a base tread that solves the above-mentioned problems and can achieve a good balance between steering stability and rolling resistance characteristics, and a pneumatic tire having a base tread produced using the composition (particularly a passenger car) It is an object to provide a pneumatic tire for use.

The present invention relates to a rubber composition for a base tread containing 4 to 55 parts by mass of coal pitch-based carbon fiber with respect to 100 parts by mass of a rubber component.
It is preferable to contain 10 to 70 parts by mass of a reinforcing filler with respect to 100 parts by mass of the rubber component. The coal pitch-based carbon fibers preferably have an average fiber diameter of 1 to 80 μm and an average fiber length of 0.1 to 30 mm.

The present invention relates to a pneumatic tire having a base tread produced using the rubber composition.
The present invention also includes a tread having a two-layer structure composed of two layers of a cap tread and a base tread produced using the rubber composition, and the volume ratio of the cap tread and the base tread [cap tread (%) / The present invention relates to a pneumatic tire for passenger cars having a base tread (%) of 60/40 to 90/10.

According to the present invention, since it is a rubber composition in which a coal pitch-based carbon fiber is blended with a rubber component, by applying the rubber composition to a base tread, steering stability and rolling resistance characteristics are well balanced. A compatible pneumatic tire can be provided.

The rubber composition for base treads of the present invention contains a rubber component and coal pitch-based carbon fiber. For this reason, high hardness (E ^* ) can be obtained while maintaining low tan δ, and high rubber strength can also be obtained. Therefore, by using the rubber composition for the base tread, it is possible to produce a pneumatic tire that can achieve both steering stability and rolling resistance characteristics and is well balanced in both performances.

Examples of rubber components include natural rubber (NR), epoxidized natural rubber (ENR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), butyl rubber (IIR), and acrylonitrile butadiene rubber (NBR). ), Diene rubbers such as chloroprene rubber (CR), styrene isoprene butadiene rubber (SIBR), styrene isoprene rubber, and isoprene butadiene rubber. These may be used alone or in combination of two or more. Of these, NR, BR, ENR, and SBR are preferable from the viewpoint of steering stability and rolling resistance characteristics, and NR and BR are more preferably used in combination.

The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20, and the like can be used. It is not particularly limited as BR, for example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B having high cis content such as BR150B, VCR412 manufactured by Ube Industries, Ltd., VCR617, etc. BR containing syndiotactic polybutadiene crystals can be used.

The content of NR is preferably 20% by mass or more, more preferably 30% by mass or more, and still more preferably 40% by mass or more, in 100% by mass of the rubber component. If it is less than 20% by mass, the workability tends to deteriorate. The NR content is preferably 80% by mass or less, more preferably 70% by mass or less, and still more preferably 60% by mass or less. When it exceeds 80 mass%, it exists in the tendency for rolling resistance to become disadvantageous compared with BR.

The content of BR is preferably 20% by mass or more, more preferably 30% by mass or more, and still more preferably 40% by mass or more, in 100% by mass of the rubber component. If it is less than 20% by mass, rolling resistance tends to be disadvantageous. The BR content is preferably 80% by mass or less, more preferably 70% by mass or less, and still more preferably 60% by mass or less. When it exceeds 80 mass%, workability tends to deteriorate.

The total content of NR and BR is preferably 80% by mass or more, more preferably 90% by mass or more, and may be 100% by mass in 100% by mass of the rubber component. If it is less than 80% by mass, other rubber components such as SBR are blended, and rolling resistance tends to be disadvantageous.

In the present invention, coal pitch-based carbon fiber is used. By blending the coal pitch-based carbon fiber, heat conductivity can be increased, and heat generation can be suppressed by releasing heat to the whole rubber. For this reason, high hardness can be obtained while maintaining low tan δ, and excellent rubber strength can be obtained. Therefore, both steering stability and rolling resistance characteristics can be achieved in a balanced manner.

The coal pitch-based carbon fiber preferably has an average fiber diameter of 1 to 80 μm from the viewpoint of dispersion in rubber and improvement in low heat build-up. The lower limit of the average fiber diameter is more preferably 3 μm or more, and further preferably 5 μm or more. Further, the upper limit of the average fiber diameter is more preferably 30 μm or less, and still more preferably 20 μm or less.

Moreover, it is preferable that an average fiber length is 0.1-30 mm from a viewpoint of the dispersion | distribution in rubber | gum, and a low exothermic improvement, as for a coal pitch-type carbon fiber. The lower limit of the average fiber length is more preferably 1 mm or more, and further preferably 4 mm or more. Moreover, the upper limit of average fiber length becomes like this. More preferably, it is 15 mm or less, More preferably, it is 10 mm or less.
In addition, the said average fiber diameter and average fiber length can be measured by observing with an electron microscope, for example.

Although it does not specifically limit as a coal pitch-type carbon fiber in this invention, For example, what is obtained by the manufacturing method as described in Unexamined-Japanese-Patent No. 7-331536 is used suitably. Specifically, the pitch fiber is infusible according to a conventional method, and carbonized and / or graphitized at a desired temperature to obtain “carbon fiber as a raw material”. A coal pitch-based carbon fiber can be produced by placing it in a graphite crucible together with the graphitized packing coke and performing a graphitization treatment.

In addition, as pitch fiber (spinning pitch) used by the said manufacturing method, carbonaceous raw materials (40% or more, preferably 70% or more, more preferably 90%) such as coal-based coal tar, coal tar pitch, and coal liquefaction. And those obtained by spinning using an optically anisotropic structure of at least%). Moreover, a sizing agent (such as an epoxy compound or a water-soluble polyamide compound) may be attached to the “carbon fiber as a raw material”.

By the manufacturing method, the thermal conductivity in the fiber axis direction is 500 to 1500 W / m · K, the tensile modulus is 85 ton / mm ² or more, the compressive strength is 35 kg / mm ² or more, and the graphite crystal lamination thickness Lc is 30 to 30. Coal pitch-based carbon fibers having a ratio (La / Lc) with a spread La in the layer plane direction of 50 nm and a graphite crystal of 1.5 times or more and a domain size in a cross section in the fiber axis direction of 500 nm or less can be produced, It can be suitably used in the present invention. The thermal conductivity, tensile elastic modulus, compressive strength, Lc, La, domain size, and optically anisotropic texture ratio can be measured by the method described in the above publication.

The coal pitch-based carbon fiber produced by the above production method uses a liquid crystal (mesophase) whose molecular orientation is regulated in one direction as a raw material, and therefore has a very high degree of crystallinity, a high elastic modulus and a high thermal conductivity.
The coal pitch-based carbon fiber in the present invention preferably has a structure in which polycyclic aromatic molecular skeletons are stacked in layers. As a commercial product of coal pitch-based carbon fiber, “K6331T” manufactured by Mitsubishi Plastics, Inc., and the like can be given.

Content of the said coal pitch-type carbon fiber is 4 mass parts or more with respect to 100 mass parts of rubber components, Preferably it is 5 mass parts or more, More preferably, it is 7 mass parts or more. Moreover, this content is 55 mass parts or less, Preferably it is 52 mass parts or less, More preferably, it is 50 mass parts or less. When the amount is less than 4 parts by mass, improvement in handling stability cannot be expected, and when it exceeds 55 parts by mass, the strength of the rubber is lowered and the cost is also increased, which is not preferable.

The rubber composition of the present invention preferably contains a reinforcing filler. Thereby, a reinforcement effect is acquired and rigidity can be improved. As the reinforcing filler, those generally used in the tire industry can be used without particular limitation, and examples thereof include carbon black, silica, clay, talc, and magnesium carbonate. Of these, carbon black is preferably used.

The carbon black is not particularly limited, and for example, FEF, GPF, HAF, ISAF, SAF and the like can be used. By using carbon black, the strength of the rubber can be improved. Moreover, by using together with coal pitch-type carbon fiber, steering stability can be improved, maintaining both rolling resistance characteristics, and both performances can be balanced.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 50 m ² / g or more, and more preferably 70 m ² / g or more. When it is less than 50 m ² / g, the reinforcing property of the rubber tends to deteriorate. The N ₂ SA of the carbon black is preferably 120 m ² / g or less, more preferably 100 m ² / g or less, and still more preferably 90 m ² / g or less. When it exceeds 120 m ² / g, the rolling resistance tends to be disadvantageous.
The N ₂ SA of carbon black is determined by the A method of JIS K6217.

The content of carbon black is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, and still more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 20 parts by mass, the reinforcing property of the rubber tends to deteriorate. Also, it tends to be disadvantageous in terms of handling stability. The content is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and still more preferably 50 parts by mass or less. When it exceeds 70 mass parts, there exists a possibility that rolling resistance may deteriorate.

In the present invention, the total content of reinforcing fillers such as carbon black is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and still more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 10 parts by mass, the processability and reinforcement of rubber tend to deteriorate. The content is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and still more preferably 50 parts by mass or less. When it exceeds 70 mass parts, there exists a tendency for rolling resistance to deteriorate.

In addition to the above components, the rubber composition of the present invention includes compounding agents, softeners (oils such as paraffinic, aroma-based and naphthenic process oils, plasticizers, etc.), stearic acid Zinc oxide, various anti-aging agents, waxes, vulcanizing agents such as sulfur or sulfur compounds, vulcanization accelerators, vulcanization acceleration aids, and the like can be appropriately blended as necessary.

When sulfur is used as the vulcanizing agent, the sulfur content is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more with respect to 100 parts by mass of the rubber component. Moreover, this content becomes like this. Preferably it is 4.0 mass parts or less, More preferably, it is 3.0 mass parts or less. If the amount is less than 0.5 parts by mass, the vulcanization rate tends to be slow and vulcanization tends to be insufficient. If the amount exceeds 4.0 parts by mass, the vulcanization rate is conversely high and tends to be scorched.

Examples of the vulcanization accelerator include sulfenamide vulcanization accelerators [N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), N, N-diisopropyl-2-benzothiazolesulfenamide, etc.], guanidine vulcanization accelerators (diphenylguanidine (DPG), diorthotri Guanidine, triphenylguanidine, orthotolylbiguanide, diphenylguanidine phthalate, etc.) are preferred, and CBS is particularly preferred.

The compounding amount of the vulcanization accelerator is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more with respect to 100 parts by mass of the rubber component. Moreover, this compounding quantity becomes like this. Preferably it is 3.0 mass parts or less, More preferably, it is 2.0 mass parts or less. If the amount is less than 0.5 parts by mass, the vulcanization rate tends to be slow and vulcanization tends to be insufficient. If the amount exceeds 3.0 parts by mass, the vulcanization rate tends to increase and scorching tends to occur.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing.

The rubber composition of the present invention is used as a tire base tread. The base tread is an inner layer portion of a tread having a multilayer structure, and is an inner surface layer in a tread having a two-layer structure [a surface layer (cap tread) and an inner surface layer (base tread)].

A tread having a multilayer structure is produced by pasting a sheet into a predetermined shape, or by inserting it into two or more extruders and forming it into two or more layers at the head outlet of the extruder. Can do.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, a rubber composition blended with various additives as necessary is extruded according to the shape of the base tread of the tire at an unvulcanized stage, and molded by a normal method on a tire molding machine, Bonding together with other tire members forms an unvulcanized tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to produce a tire.

When the pneumatic tire has a tread having a two-layer structure consisting of a cap tread and a base tread produced using the rubber composition, the volume ratio of the cap tread and the base tread [cap tread (%) / base tread (%)]. Is preferably 60/40 to 90/10, more preferably 65/35 to 85/15. When the volume ratio of the base tread is less than 10% of the entire tread, the effect of suppressing heat generation and reducing rolling resistance tends to be insufficient. On the other hand, if it exceeds 40%, the steering stability tends to deteriorate.

A tire having a base tread produced using the rubber composition for a base tread of the present invention can be particularly suitably used for a tire for a passenger car.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

(material)
Natural rubber (NR): RSS # 3
Butadiene rubber (BR): BR150B manufactured by Ube Industries, Ltd.
Carbon black: Dia Black HAF (N330, 79 m ² / g) manufactured by Mitsubishi Chemical Corporation
Process oil: Process X-140 manufactured by Japan Energy Co., Ltd.
Wax: Sannoc Wax anti-aging agent manufactured by Ouchi Shinsei Chemical Industry Co., Ltd .: NOCRACK 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-product manufactured by Ouchi New Chemical Co., Ltd.) Phenylenediamine)
Stearic acid: Zinc oxide manufactured by NOF Corporation: Zinc oxide No. 1 manufactured by Mitsui Mining Co., Ltd. Coal pitch-based carbon fiber: K6331T (chopped fiber, average fiber diameter: 11 μm, manufactured by Mitsubishi Chemical Corporation) (Average fiber length: 6.3 mm)
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Examples 1-6 and Comparative Examples 1-6
According to the formulation shown in Tables 1 and 2, chemicals other than sulfur and a vulcanization accelerator were kneaded using a Banbury mixer to obtain a kneaded product. Next, using an open roll, sulfur and a vulcanization accelerator were added to the obtained kneaded material and kneaded to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was press vulcanized at 175 ° C. for 10 minutes to prepare each vulcanized rubber composition.

Further, the obtained unvulcanized rubber composition is molded into a base tread shape, bonded to another tire member, and vulcanized for 10 minutes under conditions of 180 ° C. and 21 kgf / cm ² , for passenger cars. A pneumatic tire (195 / 65R15 size, test tire) was produced. The tread of the test tire has a two-layer structure including a cap tread and a base tread, and the cap tread / base tread = 80/20 (volume ratio (%)).

(Viscoelasticity test)
For the vulcanized rubber composition, using a viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho Co., Ltd., under conditions of a measurement temperature of 60 ° C., an initial strain of 10%, a dynamic strain of ± 2%, and a frequency of 10 Hz, a complex elastic modulus ( E ^* ) and loss tangent (tan δ) were measured. Larger E ^* indicates higher rigidity and better steering stability, and smaller tan δ indicates lower rolling resistance and better low heat buildup.

(Tensile test)
In accordance with JIS K 6251 “Vulcanized Rubber and Thermoplastic Rubber-Determination of Tensile Properties”, a tensile test was conducted using a No. 3 dumbbell-shaped test piece made of the vulcanized rubber composition, and the breaking strength (TB) And the elongation at break (EB) was measured. A value of TB × EB was used as an index of rubber strength. Each unit is TB (MPa) and EB (%).

(Maneuvering stability)
A sensory test was conducted on a test course using a normal passenger car fitted with the produced test tire. In particular, the handle response was evaluated relative to Comparative Example 1 as 3 points. The higher the score, the better the steering stability.

From Table 1, in Examples 1 to 3 (NR / BR = 50/50) using coal pitch-based carbon fiber, E ^* value is compared with Comparative Example 1 (without adding coal pitch-based carbon fiber). The handling stability was improved. Further, the tan δ value was almost the same as that of Comparative Example 1, and the rolling resistance was not deteriorated. Further, the TB × EB value was improved and high rubber strength was exhibited. In Comparative Example 2 in which a small amount (3 parts by mass) of coal pitch-based carbon fiber was added, no improvement in steering stability was observed. In addition, in Comparative Example 3 in which 60 parts by mass of coal pitch-based carbon fiber was blended, the TB × EB value was lowered, and the desired rubber strength was not obtained.
Furthermore, the same tendency was seen also in Table 2 changed to NR / BR = 75/25.

Claims (7)

A rubber composition for a base tread containing 4 to 55 parts by mass of a coal pitch-based carbon fiber with respect to 100 parts by mass of a rubber component. The rubber composition for base treads of Claim 1 which contains 10-70 mass parts of reinforcing fillers with respect to 100 mass parts of said rubber components. The base tread rubber composition according to claim 1 or 2, wherein the coal pitch-based carbon fiber has an average fiber diameter of 1 to 80 µm and an average fiber length of 0.1 to 30 mm. The rubber composition for base tread according to any one of claims 1 to 3, wherein the coal pitch-based carbon fiber has a structure in which polycyclic aromatic molecular skeletons are stacked in layers. The rubber composition for base tread according to any one of claims 1 to 4, wherein a content of the coal pitch-based carbon fiber is 5 to 50 parts by mass with respect to 100 parts by mass of the rubber component. The pneumatic tire which has a base tread produced using the rubber composition in any one of Claims 1-5 . A tread having a two-layer structure comprising a cap tread and a base tread produced using the rubber composition according to any one of claims 1 to 5 , wherein the cap tread and the volume ratio of the base tread [cap tread (% ) / Base tread (%)] is 60/40 to 90/10.