JP2012236933A - Rubber composition for tire tread and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for tire treads capable of reducing rolling resistance by improving a high modulus of elasticity, cut and chipping resistance, fracture resistance, and abrasion resistance in a good balance and enhancing low heat build-up properties; and to provide a pneumatic tire.SOLUTION: The rubber composition for tire treads includes: 100 pts.mass of a rubber component comprising 50-100 pts.mass of a natural rubber or polyisoprene rubber and 0-50 pts.mass of a polybutadiene rubber; and 0.5-30 pts.mass of an inorganic filler wherein an angle of repose is ≥40 degrees, the Mohs hardness is ≤2.0, the BET specific surface area (BET5) (m/g) is ≥10 m/g, and a ratio (DBP)/(BET5) of the dibutyl phthalate (DBP) absorption number (mL/100 g) to the BET specific surface area (BET5) (m/g) is ≥2.0.

Description

  The present invention relates to a rubber composition for a tire tread and a pneumatic tire containing at least a rubber component and an inorganic filler, and has a high elastic modulus, cut / chipping resistance, fracture resistance and wear resistance in a well-balanced manner. In addition, the present invention relates to a rubber composition for a tire tread and a pneumatic tire that can reduce rolling resistance by improving low heat buildup.

  In general, special carbon black is used as a technique to improve the elastic modulus (hardness) and fracture resistance (breaking strength and tear strength) of vulcanized rubber reinforced with reinforcing fillers such as carbon black and silica. And a method of substituting a part of carbon black with silica. Although these methods have an effect of improving the elastic modulus and fracture resistance, there is a problem that the processability is inferior, for example, the viscosity of the rubber composition when not vulcanized is increased. In addition, as a method for improving the processability of rubber compositions and the tear resistance of vulcanized rubber, methods of adding processing aids and rosin resins have also been proposed. As a result, tire durability and rolling resistance tended to increase (deteriorate).

  In the following Patent Document 1, in the vulcanized rubber of the rubber composition for an inner liner of a tire, in order to improve tear strength and fatigue resistance while maintaining good airtightness, in the rubber composition, A method of blending talc with a high flatness together with predetermined carbon black is described. However, in this method, the airtightness is improved, but the improvement in tear strength and fatigue resistance is insufficient, and there is room for further improvement in this respect. Also, in Patent Documents 2 and 3 below, a rubber composition containing a porous inorganic filler or a layered viscosity mineral is described, but specific characteristics such as the shape of the porous inorganic filler or the layered viscosity mineral are described. It has not been.

Special table 2008-528739 gazette JP 2000-79807 A JP 2008-189725 A

  The present invention has been made in view of the above circumstances, and its purpose is to improve the high elastic modulus, cut / chipping resistance, fracture resistance, and wear resistance in a well-balanced manner, and to improve the low heat generation. An object of the present invention is to provide a tire tread rubber composition and a pneumatic tire capable of reducing rolling resistance.

The above object can be achieved by the present invention as described below. That is, the rubber composition for a tire tread according to the present invention is a rubber composition for a tire tread containing at least a rubber component and an inorganic filler, and the rubber component is a natural rubber in 100 parts by mass of the rubber component. Alternatively, it contains 50 to 100 parts by mass of polyisoprene rubber and 0 to 50 parts by mass of polybutadiene rubber, and the inorganic filler has an angle of repose of 40 degrees or more, a Mohs hardness of 2.0 or less, and a BET ratio. The surface area (BET5) (m ² / g) is 10 m ² / g or more, and the ratio (DBP) / dibutyl phthalate (DBP) absorption (ml / 100 g) to BET specific surface area (BET5) (m ² / g) / (BET5) is 2.0 or more, and the content of the inorganic filler with respect to 100 parts by mass of the rubber component is 0.5 to 30 parts by mass.

  According to the tire tread rubber composition, the specific flatness (repose angle), specific specific surface area (BET5), specific structure development ((DBP) / (BET5)), and specific Mohs hardness Since the inorganic filler is contained in an amount of 0.5 to 30 parts by mass, the high elastic modulus, the cut / chipping resistance, the fracture resistance and the wear resistance are improved in a well-balanced manner, and the low heat build-up is improved. In addition, with the improvement in low heat build-up, in a pneumatic tire using such a rubber composition, it becomes possible to reduce rolling resistance.

  In the tire tread rubber composition, the inorganic filler is preferably talc. When talc is used, the elastic modulus, fracture resistance, and low heat buildup of vulcanized rubber are improved in a balanced manner. Further, talc is a natural mineral and is low in cost, and is preferable from both the environmental and cost aspects.

  The tire tread rubber composition preferably further contains a reinforcing filler composed of at least one of carbon black and silica. The rubber composition contains a reinforcing filler made of at least one of carbon black and silica, together with an inorganic filler having a specific flatness, a specific degree of structure development, a specific specific surface area, and a specific Mohs hardness. In this case, due to the influence of the inorganic filler, the dispersibility of the reinforcing filler in the rubber composition is improved as compared with the case where the reinforcing filler is contained alone. For this reason, the elastic modulus, cut / chipping resistance, fracture resistance, and low heat build-up of vulcanized rubber are particularly improved in a well-balanced manner. The reason why the dispersibility of the reinforcing filler is improved when used in combination with the inorganic filler is not clear, but when the inorganic filler and the reinforcing filler are kneaded together with the rubber component, the inorganic filler is Since it slips in the polymer, it can be considered that it functions to assist the dispersion of the reinforcing filler in the polymer. In order to improve the elastic modulus, cut / chipping resistance, fracture resistance, and low heat buildup of the vulcanized rubber in a well-balanced manner, the content of the reinforcing filler is 35 with respect to 100 parts by mass of the rubber component. It is preferable that it is -60 mass parts.

  The present invention relates to a pneumatic tire using the rubber composition for a tire tread described above. In such a pneumatic tire, the tread resistance to cut and chipping is improved, the wear life is improved, and the low heat generation property is also improved. For this reason, the fracture resistance of the pneumatic tire is improved and the rolling resistance can be reduced.

Side view showing instrument and method for measuring angle of repose and height (H) of inorganic filler Tire meridian cross-sectional view showing an example of a pneumatic tire according to the present invention

  The tire tread rubber composition according to the present invention contains at least a rubber component and an inorganic filler. In the present invention, the rubber component contains 50 to 100 parts by mass of natural rubber or polyisoprene rubber and 0 to 50 parts by mass of polybutadiene rubber in 100 parts by mass of the rubber component. In order to improve the elastic modulus, cut / chipping resistance, fracture resistance, and low heat build-up property of vulcanized rubber in a well-balanced manner, as a rubber component, natural rubber or polyisoprene rubber is used in 60 to 100 parts by mass of rubber component. It is preferable that 80 mass parts and 20-40 mass parts of polybutadiene rubbers are contained. As natural rubber (NR), polyisoprene rubber (IR), and polybutadiene rubber (BR), those having a terminal modified (for example, terminal tin-modified BR, etc.) or desired properties should be imparted as necessary. Those modified (for example, modified NR) can also be used suitably. Regarding polybutadiene rubber (BR), in addition to those synthesized using a cobalt (Co) catalyst, a neodymium (Nd) catalyst, a nickel (Ni) catalyst, a titanium (Ti) catalyst, and a lithium (Li) catalyst, WO2007 What was synthesize | combined using the polymerization catalyst composition containing the metallocene complex as described in -129670 can also be used. When using polybutadiene rubber (BR), in order to improve the wear resistance, processability, tear resistance and low heat build-up of the vulcanized rubber in a balanced manner, the mass average molecular weight is 350,000 to 1,000,000, And it is preferable to use polybutadiene rubber (BR) whose cis-1,4 minutes is 95% or more.

In addition to the rubber component, the rubber composition for a tire tread according to the present invention has an angle of repose of 40 degrees or more, a Mohs hardness of 2.0 or less, a BET specific surface area (BET5) of 10 m ² / g or more, and dibutyl phthalate ( DBP) contains an inorganic filler having a ratio (DBP) / (BET5) of 2.0 or more of the absorption amount (ml / 100 g) and the BET specific surface area (BET5) (m ² / g). When the angle of repose of the inorganic filler is less than 40 degrees, the flatness is too high or the particle diameter is too large, so that the fracture resistance of the vulcanized rubber is deteriorated. On the other hand, if the Mohs hardness of the inorganic filler exceeds 2, it causes a decrease in dispersibility and stress concentration in the rubber, resulting in deterioration of fracture resistance and low heat buildup. Furthermore, when (DBP) / (BET5) is less than 2, a sufficient reinforcing effect cannot be obtained, and the elastic modulus decreases. In order to improve the elastic modulus and puncture resistance of the vulcanized rubber in a well-balanced manner and to improve the low heat build-up, the angle of repose is 42 degrees or more, the Mohs hardness is 1 or less, the BET 5 is 10 m ² / g or more, and Preferably, (DBP) / (BET5) is 3.0 or more. The upper limit of the angle of repose is 50 degrees or less, the upper limit of BET5 is 30 m ² / g or less, and / or the upper limit of (DBP) / (BET5) is 10 or less.

  The angle of repose of the inorganic filler can be measured by the following method.

(Apparatus and method for measuring angle of repose and height (H) of inorganic filler)
As shown in FIG. 1, a 10 g powder sample 1, a tempered glass funnel 2 (bore diameter 45 mm, leg inner diameter 5 mm, total length 90 mm, leg length 45 mm), funnel mount 3 that supports and fixes the funnel 2, and the funnel A rubber stopper is used to block the discharge port 21 at the lower end of the leg 2. The height from the horizontal base plate 4 to the discharge port 21 of the funnel 2 is adjusted to 4 cm by adjusting the height of the funnel mount 3. A 10 g powder sample is poured into a glass funnel with the outlet 21 of the funnel 2 closed with a rubber stopper, and then the rubber stopper is gently pulled out. After confirming that the powder sample 1 has formed a substantially accurate cone-shaped peak on the horizontal base plate 4, the height (H) and diameter (D) of this cone-shaped peak are measured. Further, based on this measurement, the following formula (1):
tan (angle of repose) = H / (D / 2) (1)
To find the angle of repose.

  The inorganic filler used in the present invention has a higher degree of flatness (high flatness) as the angle of repose measured by the above method is smaller. When an inorganic filler that is highly flat is blended in the rubber composition, the fracture resistance is particularly deteriorated. Similarly, the lower the height (H) measured by the above method, the higher the flatness of the inorganic filler (higher flatness). For this reason, when the low flat inorganic filler whose height (H) measured by the said method is 30 mm or more is mix | blended in a rubber composition, since the fracture-resistance characteristic of vulcanized rubber improves especially, it is preferable.

  The content of the inorganic filler in the rubber composition for a tire tread according to the present invention is set to 0.5 to 30 parts by mass with respect to 100 parts by mass of the rubber component. By setting the content of the inorganic filler within such a range, the elastic modulus, cut / chipping resistance, fracture resistance, and low heat build-up of the vulcanized rubber can be improved in a balanced manner. In order to improve the physical properties of the vulcanized rubber with better balance, the content of the inorganic filler with respect to 100 parts by mass of the rubber component is preferably 2 to 20 parts by mass.

  An example of the inorganic filler is talc. When talc is used as an inorganic filler, the elastic modulus, fracture resistance, and low heat buildup of vulcanized rubber are improved in a well-balanced manner.

Talc is an inorganic powder obtained by pulverizing an ore called natural talc, and contains hydrous magnesium silicate [Mg ₃ Si ₄ O ₁₀ (OH) ₂ ] as a main component. In the present invention, commercially available talc can also be used preferably. For example, “MISTOR VAPOR RE” (Mittron VAPOR RE, manufactured by Nippon Mytron Co., Ltd., angle of repose 44 °, Mohs hardness 1, (BET5) 13.4 m ² / g, (DBP ) / (BET5) 3.7), “P-6” manufactured by Nippon Talc Co., Ltd. (repose angle 44 degrees, Mohs hardness 1, (BET5) 10.5 m ² / g, (DBP) / (BET5) 4.3) Etc.) can be suitably used.

  In the present invention, at least one of carbon black and silica is used as the reinforcing filler. As carbon black, for example, conductive carbon black such as acetylene black and ketjen black can be used in addition to carbon black used in ordinary rubber industry such as SAF, ISAF, HAF, FEF, and GPF. Examples of the silica include wet silica, dry silica, colloidal silica, precipitated silica, and the like. It is particularly preferable to use wet silica containing hydrous silicic acid as a main component. In order to improve the elastic modulus, cut / chipping resistance, fracture resistance, and low heat buildup of the vulcanized rubber in a balanced manner, the reinforcing filler content is 35-60 with respect to 100 parts by mass of the rubber component. It is preferable that it is a mass part, and it is more preferable that it is 45-55 mass parts. When producing a cap tread on the ground contact side of a pneumatic tire using the rubber composition according to the present invention, hard carbon (HAF or higher carbon black) having wear resistance is used as a reinforcing filler. In addition, the amount of silica is preferably 0 to 15 parts by mass. Furthermore, when using silica, it is preferable to mix | blend a silane coupling agent 5-15 mass% with respect to content of a silica.

  The rubber composition according to the present invention comprises the above rubber component, inorganic filler, reinforcing filler, sulfur, silane coupling agent, zinc white, stearic acid, vulcanization accelerator, vulcanization accelerator, vulcanization A compounding agent usually used in the rubber industry such as a retarder, an anti-aging agent, a softening agent such as wax or oil, or a processing aid can be appropriately blended and used within a range not impairing the effects of the present invention.

  Sulfur should just be normal sulfur for rubber | gum, For example, powder sulfur, precipitated sulfur, insoluble sulfur, highly dispersible sulfur etc. can be used. When the rubber physical properties and durability after vulcanization are taken into consideration, the sulfur content relative to 100 parts by mass of the rubber component is preferably 0.5 to 5.0 parts by mass in terms of sulfur content.

  As the vulcanization accelerator, sulfenamide vulcanization accelerator, thiuram vulcanization accelerator, thiazole vulcanization accelerator, thiourea vulcanization accelerator, guanidine vulcanization, which are usually used for rubber vulcanization. Vulcanization accelerators such as accelerators and dithiocarbamate vulcanization accelerators may be used alone or in admixture as appropriate. When the rubber physical properties and durability after vulcanization are taken into consideration, the blending amount of the vulcanization accelerator with respect to 100 parts by mass of the rubber component is preferably 0.1 to 5.0 parts by mass.

  As an anti-aging agent, an aromatic amine-based anti-aging agent, an amine-ketone-based anti-aging agent, a monophenol-based anti-aging agent, a bisphenol-based anti-aging agent, a polyphenol-based anti-aging agent, dithiocarbamic acid, which are usually used for rubber Anti-aging agents such as a salt-based anti-aging agent and a thiourea-based anti-aging agent may be used alone or in an appropriate mixture. In consideration of rubber physical properties and durability, the blending amount of the anti-aging agent with respect to 100 parts by mass of the rubber component is preferably 0.0 to 5.0 parts by mass.

  The rubber composition according to the present invention comprises the above rubber component, inorganic filler, reinforcing filler, and optionally sulfur, silane coupling agent, zinc white, stearic acid, vulcanization accelerator, and vulcanization accelerator. Additives usually used in the rubber industry such as vulcanization retarders, anti-aging agents, softeners such as waxes and oils, processing aids, etc. are used in the normal rubber industry such as Banbury mixers, kneaders, rolls, etc. It can be obtained by kneading using a kneader.

  In addition, the blending method of each of the above components is not particularly limited, and a blending component other than a vulcanizing component such as sulfur and a vulcanization accelerator is previously kneaded to obtain a master batch, and the remaining components are added and further kneaded. , Rubber component and carbon black only in advance as a kneading masterbatch, the remaining components are added and further kneaded, each component is added in any order and kneaded, all components are added simultaneously and kneaded, etc. Either of these may be used. In addition, when making a rubber component and carbon black into a masterbatch beforehand, you may use the wet masterbatch obtained by mixing carbon black in rubber latex.

  As shown in FIG. 2, the pneumatic tire according to the present invention includes a pair of bead wires 101, a bead filler 102 disposed on the outer side in the tire radial direction of the bead wires 101, and a bead wire 101 and a bead filler 102. A sidewall 103 extending radially outward; a tread 104 connected to each tire radial outer end of the sidewall 103; and a carcass ply 105 having a pair of bead wires 101 wound up from the inner side to the outer side in the tire width direction; And a belt 106 made of a plurality of belt plies arranged on the outer peripheral side (outer side in the tire radial direction) of the carcass ply 105. The tread 104 may be composed of a single rubber part, or may be composed of two layers of a cap tread on the ground contact surface side and a base tread on the inner side in the tire radial direction.

  On the inner side in the tire radial direction of the bead wire 101 and the bead filler 102, a chacher 107 and a rim strip 108 are arranged via a carcass ply 105, and the rim strip 108 is seated so as to be in contact with a tire rim (not shown). On the outer side of the bead filler 102 in the tire radial direction, a chacher pad 109 is disposed so as to sandwich the chacher 107. On the other hand, an inner liner 110 for maintaining air pressure is disposed on the inner peripheral side of the carcass ply 105. Further, a shoulder pad 111 is disposed on the end side of the belt 106 on the inner side in the tire radial direction, and a belt edge filler 112 is disposed between a plurality of belt ply end portions.

  Using the rubber composition for a tire tread according to the present invention, the tread 104 is manufactured by a known facility such as a rubber extruder, an unvulcanized tire including the same is molded, and then vulcanized according to a known method. By doing so, a pneumatic tire can be manufactured. As described above, the vulcanized rubber of the tire tread rubber composition according to the present invention is excellent in high elastic modulus, cut / chipping resistance, fracture resistance, and low heat build-up. Useful as. When used as a cap tread, for example, the rolling resistance of a pneumatic tire is reduced, and D.B. G. (Differential groove) and / or sipe and other tearing forces are improved, and the wear resistance of the land is improved. For this reason, the rubber composition for tire treads according to the present invention is useful for an all-weather (all weather) tire.

  Hereinafter, examples and the like specifically showing the configuration and effects of the present invention will be described. The evaluation items in Examples and the like were evaluated based on the following evaluation conditions for rubber samples obtained by heating and vulcanizing each rubber composition at 150 ° C. for 30 minutes.

(1) Breaking strength (breaking resistance)
In accordance with JIS K6251, a sample was prepared using dumbbell No. 3 and subjected to a tensile test, and the breaking strength (MPa) at the time of breaking the sample was measured. The measured value of Comparative Example 1 is set to 100 and displayed by index evaluation, and the larger the value, the better the fracture resistance.

(2) Elongation at break (%) (cut and chipping resistance)
In accordance with JIS K6251, a sample was prepared using dumbbell No. 3, a tensile test was performed, and the elongation at break (%) at the time of sample breakage was measured. The measured value of Comparative Example 1 is set to 100 and displayed by index evaluation. The larger the value, the better the cut and chipping resistance.

(3) Abrasion resistance Based on JIS K6264, it evaluated based on the result measured by the slip rate 30%, the load load 40N, and the amount of sandfall 20g / min. The measured value of Comparative Example 1 is set to 100 and displayed by index evaluation, and the larger the value, the better the wear resistance.

(4) tan δ (low exothermic property)
Evaluation was performed based on tan δ values measured at an initial strain of 15%, a dynamic strain of ± 2.5%, a frequency of 10 Hz, and a temperature of 60 ° C. using a viscoelastic spectrometer manufactured by UBM. It means that it is excellent in low exothermic property, so that a numerical value is small.

(Preparation of rubber composition)
In accordance with the formulation of Table 1, the rubber compositions of Examples 1 to 8 and Comparative Examples 1 to 6 were blended and kneaded using an ordinary Banbury mixer to prepare a rubber composition. Each compounding agent described in Table 1 is shown below (in Table 1, the compounding amount of each compounding agent is shown in terms of parts by mass with respect to 100 parts by mass of the rubber component). In addition, the repose angle and height (H) of the following inorganic fillers (A) to (F) (the height (H) measured by the above-mentioned “method for measuring the repose angle and height (H) of the inorganic filler”) )), Specific surface area (BET5), structure development degree ((DBP) / (BET5)), and Mohs hardness are shown in Table 2.
a) Rubber component
Natural rubber (NR) "RSS # 3"
Polybutadiene rubber (BR- (1)) “BR150L (end unmodified product, cis-1,4 min 98% product)”, Ube Industries' polybutadiene rubber (BR- (2)) “BR1250H (terminal tin) Modified product) ”, manufactured by Nippon Zeon Co., Ltd. b) carbon black carbon black (ISAF)“ Seast 6 ”, manufactured by Tokai Carbon Co., Ltd. c) silica“ nip seal AQ ”, manufactured by Tosoh Silica Co. d) inorganic filler inorganic filler (A ) "MISTON VAPOR RE", Nippon Mistron inorganic filler (B) "P-6", Nippon Talc inorganic filler (C) "SW", Nippon Talc inorganic filler (D) "HAR" Inorganic filler (E) "Shiraka Hana CC" manufactured by Nippon Mystron Co., Ltd. Inorganic filler (F) "Hard clay" manufactured by Shiraishi Kogyo Co., Ltd. e) Zinc oxide "Zinc Hana 1" F) Stearic acid “Bead stearic acid” manufactured by Mitsui Kinzoku Mining Co., Ltd. g) Anti-aging agent “Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd. h) Vulcanization accelerator “Suncellor CM-G”, Sanshin Chemical Industry i) Sulfur Tsurumi Chemical Co., Ltd. j) Silane coupling agent "Si69", Degussa

  From the results shown in Table 1, the vulcanized rubbers of the rubber compositions according to Examples 1 to 8 have a high elastic modulus, and the cut / chipping resistance, the fracture resistance and the wear resistance are improved in a well-balanced manner and are low. It turns out that exothermic property improves. On the other hand, since the vulcanized rubber of the rubber composition according to Comparative Example 2 has a large amount of inorganic filler, it can be seen that the resistance to cut and chipping deteriorates. Further, in the vulcanized rubber of the rubber composition according to Comparative Example 3, since BET5 is small and large particle size talc is used, the cut and chipping resistance is deteriorated, and the rubber according to Comparative Example 4 using high flat talc. It can be seen that even the vulcanized rubber of the composition deteriorates the cut and chipping resistance and the fracture resistance. Further, since the vulcanized rubber of the rubber composition according to Comparative Example 5 uses calcium carbonate having high Mohs hardness, the cut and chipping resistance and the fracture resistance are deteriorated. Since vulcanized rubber uses highly flat clay, it can be seen that the cut and chipping resistance and the fracture resistance deteriorate.

Claims (5)

A rubber composition for a tire tread containing at least a rubber component and an inorganic filler,
The rubber component contains 50 to 100 parts by mass of natural rubber or polyisoprene rubber in 100 parts by mass of the rubber component, and 0 to 50 parts by mass of polybutadiene rubber.
The inorganic filler has an angle of repose of 40 degrees or more, a Mohs hardness of 2.0 or less, a BET specific surface area (BET5) (m ² / g) of 10 m ² / g or more, and a dibutyl phthalate (DBP) absorption amount ( ml / 100 g) and BET specific surface area ^{(BET5) (m 2 / g} ) and the ratio of (DBP) / (BET5) a is 2.0 or more, the content of the inorganic filler relative to 100 parts by mass of the rubber component Is a rubber composition for a tire tread, characterized by being 0.5 to 30 parts by mass.   The rubber composition for a tire tread according to claim 1, wherein the inorganic filler is talc.   Furthermore, the rubber composition for tire treads of Claim 1 or 2 containing the filler for reinforcement which consists of at least 1 sort (s) of carbon black and a silica.   The tire tread rubber composition according to any one of claims 1 to 3, wherein a content of the reinforcing filler is 35 to 60 parts by mass with respect to 100 parts by mass of the rubber component.   The pneumatic tire using the rubber composition for tire treads in any one of Claims 1-4.

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