JP4895833B2 - Rubber composition for tire tread and pneumatic tire using the same - Google Patents

Description

  The present invention relates to a rubber composition for a tire tread containing magnetic carbon black and a pneumatic tire using the same.

  In recent years, while the performance of automobiles has increased and the horsepower has increased, awareness of safety has increased, and the demand for grip performance on tires has increased. For example, various performances during high-speed traveling are listed as one of them. The tread portion of the pneumatic tire generates heat as the vehicle travels, and there is a problem that grip performance deteriorates due to high temperature.

  Conventionally, as a technique for improving grip performance, for example, in a rubber composition for tire treads, a basic anti-aging agent such as imidazoles and lactams and an organic metal compound are blended as in Patent Document 1, for example. A basic anti-aging agent having an ionic bond could be imparted, and as a result, grip performance could be improved. However, the organometallic compound used for imparting an ionic bond to the basic anti-aging agent has a problem that carboxylic acid, which is a strong acid, is generated and crosslinking is inhibited.

JP 2006-124423 A

  An object of this invention is to provide the rubber composition for tire treads which improved the grip performance over medium-high temperature, and a pneumatic tire using the same.

  The present invention relates to a rubber composition for a tire tread containing (B) 10 to 200 parts by weight of magnetic carbon black with respect to 100 parts by weight of (A) diene rubber.

  Further, (A) 0.1 to 30 parts by weight of at least one compound selected from the group consisting of piperidine derivatives, imidazoles and caprolactams with respect to 100 parts by weight of diene rubber, and (D) It is preferable to contain 0.1-30 weight part of 1 or more types of compounds chosen from the group which consists of organic carboxylic acid metal salt, thiocarboxylate, and phosphate.

  Moreover, this invention relates also to the pneumatic tire which has a tire tread using the said rubber composition for tire treads.

  ADVANTAGE OF THE INVENTION According to this invention, the rubber composition for tire tread which improved the grip performance of a wide temperature range by mix | blending magnetic carbon black, and a pneumatic tire using the same can be provided.

  The rubber composition of the present invention contains (B) magnetic carbon black in (A) diene rubber.

  Diene rubbers (A) include natural rubber (NR), styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), butyl rubber (IIR), acrylonitrile butadiene rubber (NBR), and ethylene propylene diene rubber. (EPDM), chloroprene rubber (CR) and the like, which are usually used in the rubber industry are mentioned, and these are not particularly limited and may be used alone or in combination of two or more. NR, SBR, or BR is preferably used, and SBR is more preferably used because it has sufficient strength as a tire tread rubber and exhibits excellent wear resistance.

  The amount of bound styrene of SBR is preferably 10% by weight or more, more preferably 20% by weight or more, further preferably 30% by weight or more, and particularly preferably 35% by weight or more. When the amount of bound styrene of SBR is less than 10% by weight, there is a tendency that a sufficient improvement effect of grip performance cannot be obtained under medium temperature and high temperature conditions. The amount of bound styrene in SBR is preferably 60% by weight or less, more preferably 50% by weight or less, and further preferably 45% by weight or less. When the amount of bound styrene in SBR exceeds 60% by weight, the rubber becomes hard, the contact area with the road surface decreases, and high grip performance tends to be not obtained.

  When SBR is contained in the diene rubber (A), a sufficient grip performance can be obtained, so that the SBR content is most preferably 100% by weight.

  Generally, when a magnetic material such as a ferrite magnet is blended as it is in a diene rubber, the rubber strength is lowered, so that it cannot be used as a rubber composition for treads. By blending the magnetic carbon black (B) contained in the magnetic carbon black, the magnetic carbon blacks can repeatedly be attracted and repelled in the diene rubber to generate high tan δ. As a result, grip performance in a wide temperature range can be improved.

  Magnetic carbon black (B) is a composite fine particle of carbon black and a decomposition product of a transition metal compound which is a magnetic fine particle. Specifically, the magnetic carbon black (B) can be obtained by the production methods described in JP-A-63-199272 and JP-A-63-205369.

  The compounding quantity of magnetic carbon black (B) is 10 weight part or more with respect to 100 weight part of diene rubber (A), and 20 weight part or more is preferable. When the content of magnetic carbon black (B) is less than 10 parts by weight, tan δ tends not to be improved. The content of magnetic carbon black (B) is 200 parts by weight or less, preferably 150 parts by weight or less. When the content of magnetic carbon black (B) exceeds 200 parts by weight, the dispersibility tends to deteriorate.

  The magnetic flux density of the magnetic carbon black (B) is preferably 100 to 1000 mT.

The specific surface area of the magnetic carbon black (B) is preferably 80 m ² / g or more, and more preferably 100 m ² / g or more. When the specific surface area is less than 80 m ² / g, grip performance tends to be lowered. Further, the specific surface area of the magnetic carbon black (B) is preferably 280 m ² / g or less, and more preferably 200 m ² / g or less. When the specific surface area exceeds 280 m ² / g, the workability tends to decrease.

  The average particle size of the magnetic carbon black (B) is preferably 30 nm or more, and more preferably 200 nm or more. If the average particle size is less than 30 nm, the dispersibility tends to be poor. Further, the average particle size of the magnetic carbon black (B) is preferably 200 nm or less, and more preferably 180 nm or less. When the average particle diameter exceeds 200 nm, the wear resistance tends to decrease.

  The average primary particle diameter of carbon black in the magnetic carbon black (B) is preferably 10 nm or more, and more preferably 15 nm or more. When the average primary particle diameter is less than 10 nm, the produced magnetic carbon black becomes small, and thus the dispersibility tends to be deteriorated. Moreover, the average primary particle diameter of carbon black in the magnetic carbon black (B) is preferably 200 nm or less, and more preferably 180 nm or less. When the average primary particle diameter exceeds 200 nm, the produced magnetic carbon black becomes large, so that the wear resistance tends to decrease. The average primary particle diameter of the magnetic fine particles in the magnetic carbon black (B) is preferably 20 nm or more, and more preferably 30 nm or more. When the average primary particle diameter is less than 20 nm, the magnetism tends to be small. The average primary particle size of the magnetic fine particles in the magnetic carbon black is preferably 200 nm or less, more preferably 100 nm or less, and particularly preferably 90 nm or less. When the magnetic carbon black (B) exceeds 200 nm, the wear resistance tends to decrease. The average primary particle diameter of the magnetic fine particles in the magnetic carbon black is preferably larger than the average primary particle diameter of the carbon black in the magnetic carbon black from the viewpoint of imparting ferromagnetism.

  Specific examples of the transition metal compound used as a raw material for the magnetic fine particles include metallocene of at least one metal selected from Fe, Co, and Ni, a carbonyl complex compound, an inorganic salt, or an organic acid salt. . Among these, ferrocene using Fe as a transition metal is preferable because it is easily available.

  The content of the magnetic fine particles is preferably 1% by weight or more, more preferably 5% by weight or more, and still more preferably 10% by weight or more in the magnetic carbon black (B). When the content of the magnetic fine particles is less than 1% by weight, tan δ is not improved and grip performance tends not to be improved. The content of the magnetic fine particles is preferably 50% by weight or less, more preferably 30% by weight or less, and still more preferably 20% by weight or less in the magnetic carbon black (B). When the content of the magnetic fine particles exceeds 50% by weight, the magnetic fine particles cannot be fused and bonded to the carbon black particles.

  The compound (C) contains a hydrogen bond, and can be improved in grip performance under intermediate temperature conditions (30 to 50 ° C.) by blending in the rubber composition.

  Examples of piperidine derivatives in compound (C) include 2,2,6,6-tetramethylpiperidine, bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, and bis (1,2,2). , 6,6-pentamethyl-4-piperidyl) sebacate, 1- [2- {3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy} ethyl] -4- {3- (3 , 5-di-t-butyl-4-hydroxyphenyl) propionyloxy} -2,2,6,6-tetramethylpiperidine, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, 8-acetyl -3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro [4,5] decane-2,4-dione, poly [{6- (1,1,3,3- Tetramethi Butyl) amino-1,3,5-triazine-2,4-diyl} {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetra Methyl-2-piperidyl) imino}], 1,2,2,6,6-tetramethyl-4-piperidyl-methacrylate, 2,2,6,6-tetramethyl-4-piperidyl-methacrylate, etc. 2,6,6-tetramethylpiperidine and derivatives thereof, among which 2,2,6,6-tetramethylpiperidine or a derivative thereof is preferable, and a derivative of 2,2,6,6-tetramethylpiperidine is preferable. More preferred.

  Examples of imidazoles in the compound (C) include imidazole, 1-methylimidazole, 2-methylimidazole, N-acetylimidazole, 2-mercapto-1-methylimidazole, benzimidazole, 2-mercaptobenzimidazole, and 2-phenyl. Examples include imidazole and 1-benzyl-2-methylimidazole. Among them, since the structure is simple, an acid approaches nitrogen, and a hydrogen bond is easily formed, so that 2-methylimidazole, imidazole, or 1-methylimidazole is formed. Is preferred.

  Examples of caprolactams in compound (C) include ε-caprolactam.

  As the compound (C), among at least one compound selected from the group consisting of piperidine derivatives, imidazoles and caprolactams, there is no steric hindrance and it is easy to form a bond with an acid. -Methylimidazole is more preferred. The above compounds may be used singly or in combination of two or more, but when used in combination of two or more, the effect of combining two or more compounds having hydrogen bonds may be used. Is difficult to obtain, and the rubber strength is lowered, which is not preferred.

  Content of a compound (C) is 0.1 weight part or more with respect to 100 weight part of diene rubber (A), Preferably it is 2 weight part or more. When the content of the compound (C) is less than 0.1 parts by weight, it is difficult to obtain the effect of improving the grip performance by the compound (C). Further, the content of the compound (C) is 30 parts by weight or less, preferably 20 parts by weight or less. Even if the content of the compound (C) exceeds 30 parts by weight, it is difficult to obtain the effect of adding the compound (C), and only the cost is increased.

  Compound (D) is at least one selected from the group consisting of organic carboxylic acid metal salts, thiocarboxylates, and phosphates.

  The compound (D) includes an ionic bond, and can be improved in grip performance under a high temperature condition (around 100 ° C.) by blending in the rubber composition.

  When an organic carboxylic acid metal salt is used as the compound (D), an aromatic carboxylic acid metal salt such as a benzoic acid metal salt or a naphthoic acid metal salt, or an acetic acid metal salt, a propionic acid metal salt, an acrylic acid metal salt, or methacrylic acid. Carboxylic acid metal salts that do not contain an aromatic ring, such as metal salts and metal oxalates.

  Examples of carboxylic acid metal salts that do not contain an aromatic ring include carboxylic acid metal salts that do not contain multiple bonds, such as acetic acid metal salts, propionic acid metal salts, and oxalic acid metal salts, or acrylic acid metal salts and methacrylic acid metal salts. Carboxylic acid metal salts containing multiple bonds can be mentioned, but carboxylic acid metal salts containing no multiple bonds are more preferred because variations in crosslinking can be suppressed and crosslinking density can be improved.

  Examples of the carboxylic acid metal salt not containing multiple bonds include organic monocarboxylic acid metal salts such as acetic acid metal salt and propionic acid metal salt, and organic dicarboxylic acid metal salts such as oxalic acid metal salt. More preferred are monocarboxylic acid metal salts not containing.

  Moreover, when using thiocarboxylate as a compound (D), thioacetate, thiopropionate, etc. are mention | raise | lifted.

  Furthermore, when using a phosphate as a compound (D), a metaphosphate etc. are mention | raise | lifted.

  Examples of the metal in the compound (D) include alkali metals such as sodium and potassium, alkaline earth metals such as magnesium and calcium, transition metals such as zinc and nickel, and alkaline earth metals are preferable.

  Examples of the organic carboxylic acid metal salt (D) satisfying the above conditions include magnesium acetate, calcium propionate, calcium acetate, magnesium propionate, and the like, but since they are generally commercially available and easily available, magnesium acetate or propion Calcium acid is preferred. As the organic carboxylic acid metal salt (D), the above compounds may be used alone or in combination of two or more. When two or more of them are used in combination, two types of compounds having an ionic bond are used. Even if they are used in combination, it is difficult to obtain the effect of the combination, and further, the rubber strength is lowered, which is not preferable.

  The content of the organic carboxylic acid metal salt (D) is 0.1 parts by weight or more, preferably 1 part by weight or more with respect to 100 parts by weight of the diene rubber (A). When the content of the organic carboxylic acid metal salt (D) is less than 0.1 parts by weight, it is difficult to obtain the effect of improving the grip performance by blending the organic carboxylic acid metal salt (D). The content of the organic carboxylic acid metal salt (D) is 30 parts by weight or less, preferably 20 parts by weight or less. When the content of the organic carboxylic acid metal salt (D) exceeds 30 parts by weight, the tackiness increases.

  The rubber composition of the present invention contains an organic carboxylic acid metal salt (D) by stimulating heat, strain or the like by blending a compound (C) having a hydrogen bond and an organic carboxylic acid metal salt (D) having an ionic bond. The organic carboxylic acid liberated from the compound can hydrogen bond with the compound (C) to cause more bond energy loss, and is larger than when the compound (C) and the organic carboxylic acid metal salt (D) are blended. The grip performance can be improved in the temperature range (30 to 100 ° C.).

  The rubber composition for a tire tread of the present invention preferably further contains an anti-aging agent. The anti-aging agent is not particularly limited, and N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine, 2,2,4-trimethyl-1,2-dihydroquinoline polymer, N -Phenyl-N'-isopropyl-p-phenylenediamine, N, N'-diphenyl-p-phenylenediamine, and the like. These antioxidants may be used alone or in combination of two or more. It may be used.

  0.1 weight part or more is preferable with respect to 100 weight part of diene rubber (A), and, as for content of an antioxidant, 1 weight part or more is more preferable. When the content of the anti-aging agent is less than 0.1 parts by weight, the anti-aging effect tends to be small. Moreover, 20 weight part or less is preferable and, as for content of an anti-aging agent, 10 weight part or less is more preferable. When the content of the anti-aging agent exceeds 20 parts by weight, the tire performance tends to be affected.

  The rubber composition for a tire tread of the present invention preferably further contains a filler.

  Examples of the filler include carbon black, silica, calcium carbonate, magnesium oxide and the like, and carbon black is preferable because of its large reinforcing effect.

The nitrogen adsorption specific surface area of carbon black is preferably 80 m ² / g or more, and more preferably 100 m ² / g or more. When the nitrogen adsorption specific surface area of carbon black is less than 80 m ² / g, grip performance and wear resistance tend to be lowered. Moreover, the nitrogen adsorption specific surface area of carbon black is preferably 280 m ² / g or less, and more preferably 200 m ² / g or less. When the nitrogen adsorption specific surface area of carbon black exceeds 280 m ² / g, the workability tends to be lowered.

  The content of carbon black (including the amount of carbon black contained in magnetic carbon black (B)) is preferably 10 parts by weight or more, and 20 parts by weight or more with respect to 100 parts by weight of diene rubber (A). More preferred. When the content of carbon black is less than 10 parts by weight, the wear resistance tends to decrease. The carbon black content is preferably 200 parts by weight or less, and more preferably 150 parts by weight or less. When the content of carbon black exceeds 200 parts by weight, processability tends to be lowered.

  The rubber composition for tires of the present invention preferably further contains a softening agent.

  Examples of the softening agent include oils such as aroma oil, naphthene oil, paraffin oil, and vegetable oil, and resins such as coumarone resin, petroleum resin, phenol resin, terpene resin, and xylene resin.

  When oil is blended, the oil content is preferably 10 parts by weight or more, more preferably 20 parts by weight or more, including oil-extended oil, with respect to 100 parts by weight of the diene rubber (A). If the oil content is less than 10 parts by weight, the wet grip performance tends to be insufficient.

  The oil content is preferably 200 parts by weight or less, and more preferably 150 parts by weight or less. When the amount of oil exceeds 200 parts by weight, the wear resistance tends to be remarkably lowered.

  The softening point of the resin is preferably 40 ° C. or higher, and more preferably 60 ° C. or higher. If the softening point of the resin is less than 40 ° C., the grip performance under high temperature conditions tends to decrease. Further, the softening point of the resin is preferably 200 ° C. or lower, and more preferably 180 ° C. or lower. When the softening point of the resin exceeds 200 ° C., the dispersibility during kneading tends to decrease.

  When the resin is blended, the content of the resin is preferably 1 part by weight or more and more preferably 5 parts by weight or more with respect to 100 parts by weight of the diene rubber (A). If the resin content is less than 1 part by weight, sufficient grip performance tends not to be obtained. The resin content is preferably 50 parts by weight or less, more preferably 30 parts by weight or less, based on 100 parts by weight of the diene rubber (A). If the resin content exceeds 50 parts by weight, excessive tackiness is exhibited, which tends to make processing difficult.

  The rubber composition for a tire tread of the present invention includes the diene rubber (A), magnetic carbon black (B), compound (C), organic carboxylic acid metal salt (D), anti-aging agent, filler and softener. In addition, additives generally used in the rubber industry, such as vulcanizing agents such as stearic acid, zinc oxide, and sulfur, and vulcanization accelerators can be appropriately blended.

  The pneumatic tire of the present invention is produced by a normal method using a tire tread rubber composition for a tire tread. That is, the rubber composition is extruded into the shape of a tread portion of a tire at an unvulcanized stage, and bonded together by a normal method on a tire molding machine to form an unvulcanized tire. The unvulcanized tire can be heated and pressurized in a vulcanizer to obtain a pneumatic tire.

  Pneumatic tires include passenger car tires and competition tires, but competition tires are preferred because particularly excellent grip performance is required.

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

Next, various chemicals used in Examples and Comparative Examples will be described in detail.
SBR: Toughden 4350 manufactured by Asahi Kasei Corporation (bound styrene content: 39%, containing 50 parts by weight of oil with respect to 100 parts by weight of rubber solids)
Carbon black: Diamond Black A (N110, nitrogen adsorption specific surface area: 130 m ² / g) manufactured by Mitsubishi Chemical Corporation
Magnetic carbon: magnetic carbon black (average particle size 30 nm, magnetic flux density 100 to 1000 mT (magnetic fine particles (Fe), average primary particle size: 40 nm), carbon black, average primary particle size: 15 nm, manufactured by Mitsubishi Chemical Corporation) Blending amount: 10% by weight))
Ferrite magnet: FH801 manufactured by Toda Kogyo Co., Ltd.
Anti-aging agent 6C: Santoflex 13 (N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine) manufactured by Flexis Co., Ltd.
Anti-aging agent 224: Nocrack 224 (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Flexis Co., Ltd.
Stearic acid: Nippon Oil & Fats Co., Ltd. Zinc Oxide: Mitsui Metal Mining Co., Ltd. Zinc Oxide Type 2 Aroma Oil: Japan Energy Co., Ltd. Process X-260
Nitrogen compound 1: Epicure MI-2 manufactured by Yuka Shell Epoxy Co., Ltd.
Acid: Noxeller NS30 (4,4'-butylidenebis- (3-methyl-6-tert-butylphenol)) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Magnesium acetate: Sulfur manufactured by Kishida Chemical Co., Ltd .: Vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd. NS: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide manufactured by Ouchi Shinsei Chemical Co., Ltd.) )

Examples 1-3 and Comparative Examples 1-4
According to the blending content of step (1) in Table 1, the mixture was kneaded for 3 minutes at 150 ° C. in a BP Banbury mixer. Further, sulfur and vulcanization accelerator NS were added to step (2) in Table 1. And kneaded for 5 minutes at 50 ° C. with an open roll to prepare an unvulcanized rubber sheet.

  Furthermore, the unvulcanized rubber sheet was press vulcanized for 12 minutes under the condition of 170 ° C., and the vulcanized rubber sheets of Examples 1-2 and Comparative Examples 1-4 were prepared.

(Degree of crosslinking (SWELL))
The vulcanized rubber sheet was immersed in toluene at 25 ° C. for 24 hours, and the volume change rate (SWELL) before and after immersion was measured. The larger the measured value, the greater the variation in cross-linking, which is not preferable.

(Viscoelasticity test)
Using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., physical properties (complex elastic modulus E) of vulcanized rubber sheets at 40 ° C. and 100 ° C. under conditions of initial strain 10%, dynamic strain 2%, and vibration frequency 10 Hz. 'And loss tanD) were measured. The larger the value of tanD, the higher the grip and the better the grip performance.

(Tensile test)
Based on JIS K 6251 “Vulcanized Rubber and Thermoplastic Rubber—How to Obtain Tensile Properties”, a test was conducted with a dumbbell No. 3 sample, and a 300% elongation stress (M300) was measured. The M300 of Comparative Example 1 was set to 100, and each index was displayed by the following calculation formula. The larger the tensile strength index, the better the abrasion wear resistance.
(Tensile strength index) = (M300 of each formulation) / (M300 of Comparative Example 1) × 100

(Actual vehicle evaluation)
An unvulcanized rubber sheet is molded into a tread shape, pasted with other tire members, and press vulcanized at 170 ° C for 12 minutes to produce an 11 x 7.10-5 size cart tire did.

  The tire produced in the cart was mounted, and the test course of 1 lap 2 km was run for 8 weeks. The grip performance of the tire of Comparative Example 1 was set to 3 points, and the test driver made a sensory evaluation with a maximum score of 5 points. The initial grip performance indicates the grip performance of the first to fourth laps, and the second half grip performance indicates the grip performance of the fifth to eighth laps. Furthermore, the appearance of the tire of Comparative Example 1 after running was given 3 points, and the wear appearance of each formulation was relatively evaluated with a maximum of 5 points.

  Each evaluation result is shown in Table 1.

  As is apparent from Table 1, with respect to grip performance in the rubber composition containing the magnetic material, Examples 1 to 3 using magnetic carbon black are more resistant to wear than Comparative Example 4 using ferrite magnets. It turns out that it is excellent in. Moreover, it turns out that Examples 1-3 are excellent in grip performance compared with Comparative Examples 1-3 which do not contain a magnetic body.

Claims (3)

(A) A rubber composition for a tire tread containing (B) 10 to 200 parts by weight of magnetic carbon black with respect to 100 parts by weight of a diene rubber. Further, (A) 0.1 to 30 parts by weight of at least one compound selected from the group consisting of piperidine derivatives, imidazoles and caprolactams with respect to 100 parts by weight of diene rubber, and (D) The rubber composition for tire treads of Claim 1 containing 0.1-30 weight part of 1 or more types of compounds chosen from the group which consists of organic carboxylic acid metal salt, thiocarboxylate, and phosphate. A pneumatic tire having a tire tread using the rubber composition for a tire tread according to claim 1.