JP5638966B2 - Rubber composition for tire and tire for truck and bus - Google Patents

Description

The present invention relates to a tire rubber composition and a truck / bus tire using the same.

Tires are known to be deteriorated by heat generated during running, ozone in the air, oxygen, ultraviolet rays, and the like, and in recent years, the amount of ozone has been increasing due to industrialization. Therefore, it is required to further improve the ozone resistance, suppress the deterioration of the rubber, and extend the life of the tire.

As a method for improving ozone resistance, a method of blending an anti-aging agent, a wax or the like is known. However, in such a method, the anti-aging agent and the wax migrate to the tire surface, and the appearance of the tire is impaired. Such deterioration of aesthetics is a problem particularly in the sidewall, but it is also a problem in vehicles and the like that are less frequent in the tread.

Patent Document 1 discloses a rubber composition using an amine-based anti-aging agent and a thiourea-based anti-aging agent in combination to improve ozone resistance and appearance (discoloration resistance). However, there is still room for improvement in terms of improving these performances. In addition, tires used for trucks and buses also emphasize destructive properties such as chip cut resistance, but such performance has not been studied.

JP-A-7-62156

The present invention provides a rubber composition for a tire that can solve the above-mentioned problems, can improve ozone resistance, and can suppress discoloration (whitening, browning) of a rubber surface, and a truck / bus tire using the same. For the purpose.

The present invention relates to a tire rubber comprising a rubber component and a nonionic surfactant of a fatty acid polyhydric alcohol ester (1) having a melting point of 45 to 60 ° C. and a fatty acid polyhydric alcohol ester (2) having a melting point of 65 to 75 ° C. Relates to the composition. Here, the content of natural rubber in 100% by mass of the rubber component is preferably 55% by mass or more.

The rubber component includes natural rubber or a diene synthetic rubber, and the total content of the fatty acid polyhydric alcohol esters (1) and (2) is 0.1 to 10 parts by mass with respect to 100 parts by mass of the rubber component. Preferably there is.

The fatty acid polyhydric alcohol esters (1) and (2) are sorbitol fatty acid ester, sorbitan fatty acid ester, glycerin fatty acid ester, polyglycerin fatty acid ester, polyethylene glycol fatty acid ester, polypropylene glycol fatty acid ester, pentaerythritol fatty acid ester or trimethylolpropane. A fatty acid ester is preferred.

The rubber composition is preferably used as a tread rubber composition.

The present invention also relates to a truck / bus tire produced using the rubber composition.

Since the present invention is a tire rubber composition containing the nonionic surfactants of fatty acid polyhydric alcohol esters (1) and (2) each having a specific melting point, ozone resistance can be improved, and the rubber surface Discoloration (whitening, browning) can be suppressed.

The rubber composition for tires of the present invention is a nonionic surfactant comprising a rubber component, a fatty acid polyhydric alcohol ester (1) having a melting point of 45 to 60 ° C., and a fatty acid polyhydric alcohol ester (2) having a melting point of 65 to 75 ° C. Including. When the fatty acid polyhydric alcohol esters (1) and (2) having different melting points are used in combination, ozone transfer resistance can be synergistically improved because the moving speed of the polymer substrate such as the rubber component is different. Furthermore, by using these in combination, a nonionic surfactant film is formed on the rubber surface, thereby shielding the anti-aging agent and wax and reducing the effects of exposure to the atmosphere. Even in this case, discoloration (whitening, browning) of the rubber surface can be remarkably suppressed.

Although melting | fusing point of fatty-acid polyhydric alcohol ester (1) is 45-60 degreeC, it is preferable that a minimum is 46 degreeC or more and an upper limit is 55 degrees C or less. When the temperature is lower than 45 ° C., the speed of moving the polymer substrate is high, the remaining amount of the polymer substrate is small, and ozone resistance and discoloration resistance tend not to be sufficiently improved. When the temperature exceeds 60 ° C., the melting point difference from the ester (2) becomes small, and therefore ozone resistance and discoloration resistance tend not to be sufficiently improved.

The melting point of the fatty acid polyhydric alcohol ester (2) is 65 to 75 ° C, but the lower limit is preferably 68 ° C or higher and the upper limit is preferably 73 ° C or lower. When the temperature is lower than 65 ° C., the difference in melting point from the ester (1) becomes small, and therefore ozone resistance and discoloration resistance tend not to be sufficiently improved. If it exceeds 75 ° C., the moving speed of the polymer substrate is slow, and it becomes difficult to form a film on the rubber surface, and there is a tendency that ozone resistance and discoloration resistance cannot be sufficiently improved.

It is preferable to satisfy the relationship of melting point of fatty acid polyhydric alcohol ester (2) −melting point of fatty acid polyhydric alcohol ester (1) ≧ 10 ° C., and more preferably satisfy the relationship of ≧ 15 ° C. Moreover, it is preferable to satisfy | fill the relationship of melting | fusing point of fatty acid polyhydric alcohol ester (2)-melting | fusing point of fatty acid polyhydric alcohol ester (1) <= 50 degreeC, and it is more preferable to satisfy | fill the relationship of <35 degreeC. By satisfying the above relationship, ozone resistance and discoloration resistance can be improved.

In the present specification, the melting point is the peak top temperature when measured using a differential scanning calorimeter (DSC). For example, using a differential scanning calorimeter (Thermo plus DSC8230, manufactured by Rigaku), the temperature is raised at 5 ° C./min.

The fatty acid polyhydric alcohol esters (1) and (2) are preferably higher fatty acid polyhydric alcohol esters having 8 to 22 carbon atoms. Moreover, monoester, diester, triester, tetraester, etc. can be used. Examples of fatty acids constituting the esters (1) and (2) include stearic acid, oleic acid, linoleic acid, palmitic acid, myristic acid, lauric acid, capric acid, caprylic acid, and behenic acid. Can be mentioned. In addition, the polyhydric alcohols that are configured include ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, trimethylene glycol, butanediol, pentanediol, hexylenediol, octylenediol, glycerin, polyglycerin. And saturated aliphatic polyols such as trimethylolpropane, pentaerythritol, dipentaerythritol, 1,3-butylene glycol, sorbitol, sorbitan, and neopentyl glycol, and unsaturated aliphatic polyols.

The carbon number of the fatty acid constituting the fatty acid polyhydric alcohol ester (1) is preferably 14-22, more preferably 16-20, and the carbon number of the polyhydric alcohol constituting is preferably 3-9, more preferably. Is 5-7. On the other hand, the carbon number of the fatty acid constituting the fatty acid polyhydric alcohol ester (2) is preferably 12-20, more preferably 14-18, and the carbon number of the polyhydric alcohol constituting is preferably 2-8, More preferably, it is 4-6. In the above case, good ozone resistance and discoloration resistance can be obtained.

Examples of the fatty acid polyhydric alcohol esters (1) and (2) include sorbitol fatty acid ester, sorbitan fatty acid ester, glycerin fatty acid ester, polyglycerin fatty acid ester, polyethylene glycol fatty acid ester, polypropylene glycol fatty acid ester, pentaerythritol fatty acid ester or triglyceride. Examples include methylolpropane fatty acid ester. Specific compounds include mono-, di-, tri-, tetra- and higher polyesters of the aforementioned fatty acids such as sorbitol, sorbitan, glycerin, polyglycerin, polyethylene glycol, polypropylene glycol, pentaerythritol, trimethylolpropane.

In terms of obtaining good ozone resistance and discoloration resistance, the fatty acid polyhydric alcohol ester (1) is preferably sorbitan fatty acid ester, more preferably sorbitan monofatty acid ester or sorbitan difatty acid ester, and sorbitan monopalmitate. Sorbitan monostearate, sorbitan dipalmitate, and sorbitan distearate are more preferable.

The fatty acid polyhydric alcohol ester (2) is preferably pentaerythritol fatty acid ester, more preferably pentaerythritol difatty acid ester, pentaerythritol trifatty acid ester, pentaerythritol tetrafatty acid ester, pentaerythritol dipalmitate, pentaerythritol triacetate. More preferred are palmitate, pentaerythritol tetrapalmitate, pentaerythritol distearate, pentaerythritol tristearate, pentaerythritol tetrastearate.

The content of the fatty acid polyhydric alcohol ester (1) with respect to 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more. If the amount is less than 0.1 parts by mass, the effects of the present invention may not be sufficiently obtained. The content is preferably 5 parts by mass or less, more preferably 3.5 parts by mass or less. If it exceeds 5 parts by mass, discoloration of the rubber surface may not be sufficiently suppressed.

The content of the fatty acid polyhydric alcohol ester (2) with respect to 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more. If the amount is less than 0.1 parts by mass, the effects of the present invention may not be sufficiently obtained. The content is preferably 5 parts by mass or less, more preferably 3.5 parts by mass or less. If it exceeds 5 parts by mass, discoloration of the rubber surface may not be sufficiently suppressed.

The total content of fatty acid polyhydric alcohol esters (1) and (2) with respect to 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 2 parts by mass or more. If the amount is less than 0.1 parts by mass, the effects of the present invention may not be sufficiently obtained. The content is preferably 10 parts by mass or less, more preferably 7 parts by mass or less. If it exceeds 10 parts by mass, discoloration of the rubber surface may not be sufficiently suppressed.

The rubber composition of the present invention usually contains a diene rubber such as natural rubber or diene synthetic rubber as a rubber component. Diene-based synthetic rubbers include isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and butyl rubber (IIR). ) And the like. Among these, NR is preferable because of excellent chip cut resistance, and the combined use of NR and BR is more preferable.

As the NR, for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20 can be used.

The content of NR in 100% by mass of the rubber component is preferably 55% by mass or more, more preferably 70% by mass or more. If it is less than 55% by mass, the chip cut resistance tends to decrease. The content may be 100% by mass, preferably 90% by mass or less, more preferably 80% by mass or less. When it exceeds 90% by mass, ozone resistance tends to deteriorate.

The content of BR in 100% by mass of the rubber component is preferably 10% by mass or more, more preferably 20% by mass or more. If it is less than 10% by mass, ozone resistance tends to deteriorate. The content is preferably 45% by mass or less, more preferably 30% by mass or less. If it exceeds 45 mass%, sufficient chip cut resistance may not be obtained.

When NR and BR are used in combination, the total content of NR and BR in 100% by mass of the rubber component is preferably 70% by mass or more, more preferably 90% by mass or more, and may be 100% by mass. If it is less than 70% by mass, sufficient chip cut resistance and low heat build-up may not be obtained.

The rubber composition of the present invention usually contains carbon black. Thereby, the intensity | strength of rubber | gum can be improved.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 20 m ² / g or more, more preferably 30 m ² / g or more. If it is less than 20 m ² / g, there is a tendency that sufficient reinforcing properties cannot be obtained. Also, _N 2 SA of carbon black is preferably 180 m ² / g, more preferably at most 160 m ² / g. When it exceeds 180 m ² / g, heat generation increases and rolling resistance tends to deteriorate.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by JISK6217-2: 2001.

The content of carbon black is preferably 10 parts by mass or more, more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 10 parts by mass, the fracture strength is lowered, and sufficient chip cut resistance may not be obtained. The content is preferably 100 parts by mass or less, more preferably 70 parts by mass or less. When it exceeds 100 mass parts, there exists a tendency for rolling resistance to deteriorate.

The rubber composition of the present invention usually contains an antioxidant. The anti-aging agent is not particularly limited. For example, naphthylamine, quinoline, diphenylamine, p-phenylenediamine, hydroquinone derivatives, phenol (monophenol, bisphenol, trisphenol, polyphenol), thiobisphenol Series, benzimidazole series, thiourea series, phosphorous acid series, and organic thioacid series antioxidants.

Examples of the naphthylamine anti-aging agent include phenyl-α-naphthylamine, phenyl-β-naphthylamine, aldol-α-trimethyl1,2-naphthylamine and the like.

Examples of the quinoline antioxidant include 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline.

Examples of the diphenylamine antioxidant include p-isopropoxydiphenylamine, p- (p-toluenesulfonylamide) -diphenylamine, N, N-diphenylethylenediamine, octylated diphenylamine and the like.

Examples of p-phenylenediamine-based antioxidants include N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine, N-isopropyl-N′-phenyl-p-phenylenediamine, and N, N ′. -Diphenyl-p-phenylenediamine, N, N'-di-2-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, N, N'-bis (1-methylheptyl) -P-phenylenediamine, N, N'-bis (1,4-dimethylpentyl) -p-phenylenediamine, N, N'-bis (1-ethyl-3-methylpentyl) -p-phenylenediamine, N- 4-methyl-2-pentyl-N′-phenyl-p-phenylenediamine, N, N′-diaryl-p-phenylenediamine, hindered dia Lumpur -p- phenylenediamine, phenyl hexyl -p- phenylenediamine, and the like phenyloctyl -p- phenylenediamine.

Examples of the hydroquinone derivative antioxidant include 2,5-di- (tert-amyl) hydroquinone and 2,5-di-tert-butylhydroquinone.

With respect to the phenolic anti-aging agent, the monophenolic anti-aging agent includes 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,6- Di-tert-butylphenol, 1-oxy-3-methyl-4-isopropylbenzene, butylhydroxyanisole, 2,4-dimethyl-6-tert-butylphenol, n-octadecyl-3- (4′-hydroxy-3 ′, 5'-di-tert-butylphenyl) propionate, styrenated phenol and the like. Examples of the bisphenol-based, trisphenol-based, and polyphenol-based antiaging agents include 2,2′-methylene-bis- (4-methyl-6-tert-butylphenol), 2,2′-methylene-bis- (4-ethyl- 6-tert-butylphenol), 4,4′-butylidene-bis- (3-methyl-6-tert-butylphenol), 1,1′-bis- (4-hydroxyphenyl) -cyclohexane, tetrakis- [methylene-3 -(3 ', 5'-di-tert-butyl-4'-hydroxyphenyl) propionate] methane and the like.

Examples of the thiobisphenol antioxidant include 4,4′-thiobis- (6-tert-butyl-3-methylphenol) and 2,2′-thiobis- (6-tert-butyl-4-methylphenol). Can be mentioned. Examples of the benzimidazole antioxidant include 2-mercaptomethylbenzimidazole. Examples of the thiourea antioxidant include tributylthiourea. Examples of the phosphite antioxidant include tris (nonylphenyl) phosphite. Examples of the organic thioacid-based anti-aging agent include dilauryl thiodipropionate.

Among these, a p-phenylenediamine-based antiaging agent is preferable, and N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine is more preferable because ozone resistance can be remarkably improved.

The content of the anti-aging agent is preferably 0.2 parts by mass or more, more preferably 1 part by mass or more with respect to 100 parts by mass of the rubber component. The content is preferably 7 parts by mass or less, more preferably 4 parts by mass or less. When the content is within the above range, the effect of the present invention can be obtained satisfactorily.

The rubber composition of the present invention preferably contains a wax. Thereby, ozone resistance can be improved.

Examples of the wax include petroleum waxes such as paraffin wax, and vegetable waxes such as carnauba wax, rice wax, candelilla wax, Japan wax, urushi wax, sugar cane wax, and palm wax. Among these, petroleum wax is preferable and paraffin wax is more preferable because excellent ozone resistance can be obtained.

The content of the wax is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more with respect to 100 parts by mass of the rubber component. If the amount is less than 0.1 part by mass, the content of the wax is too small and an effective film may not be formed. The content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less. If it exceeds 5 parts by mass, discoloration of the rubber surface may not be sufficiently suppressed.

In addition to the above-mentioned components, the rubber composition of the present invention contains, as appropriate, compounding agents generally used in the production of rubber compositions, such as oil, zinc oxide, stearic acid, vulcanizing agents, vulcanization accelerators, and the like. it can.

The oil content is preferably 3 parts by mass or less, more preferably 1 part by mass or less, with respect to 100 parts by mass of the rubber component, and the oil may not be contained. Thereby, sufficient rubber strength is obtained and the effects of the present invention can be obtained satisfactorily.

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 components with a kneader such as a Banbury mixer, a kneader, or an open roll, and then vulcanizing. The rubber composition of the present invention can be used for tire members such as treads, and can be suitably used for treads for truck and bus tires.

The tire for trucks and buses of the present invention is produced by an ordinary method using the rubber composition. That is, if necessary, a rubber composition containing various additives is extruded in accordance with the shape of a tread or the like at an unvulcanized stage, molded by a normal method on a tire molding machine, Bonding together with the tire member forms an unvulcanized tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to produce a tire.

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

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR: TSR20
BR: BR150B manufactured by Ube Industries, Ltd.
Carbon black: Dia Black E (N550) manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 41 m ² / g)
Anti-aging agent: Antigen 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Zinc oxide: Mitsui Metal Mining Co., Ltd. Stearic acid: NOF Co., Ltd. Koji Surfactant A: Tokyo Chemical Industry Co., Ltd. sorbitan monostearate (melting point: 52 ° C.)
Surfactant B: Pentaerythritol tetrapalmitate (melting point: 67-72 ° C.) manufactured by Kao Corporation
Surfactant C: Pentaerythritol distearate (melting point: 72 ° C.) manufactured by Tokyo Chemical Industry Co., Ltd.
Surfactant D: sorbitan monopalmitate (melting point: 46 ° C.) manufactured by Kao Corporation
Wax: Ozoace 0355 (paraffin type) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Sulfur (insoluble sulfur): Seimisulfur manufactured by Nippon Kiboshi Kogyo Co., Ltd. (60% insoluble matter due to carbon disulfide, 10% oil content)
Vulcanization accelerator: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfanamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Examples and Comparative Examples>
According to the formulation shown in Table 1, using a 1.7 L Banbury mixer, materials other than sulfur and a vulcanization accelerator were kneaded for 5 minutes at 150 ° C. to obtain a kneaded product ( Step 1). Next, sulfur and a vulcanization accelerator were added to the obtained kneaded material, and kneaded for 3 minutes under the condition of 80 ° C. using an open roll to obtain an unvulcanized rubber composition (step 2). The obtained unvulcanized rubber composition was press vulcanized with a 2 mm thick mold at 150 ° C. for 30 minutes to obtain a vulcanized rubber composition (test piece).

The following evaluation was performed about the obtained vulcanized rubber composition. The results are shown in Table 1.

(discoloration)
A test piece (length 150 mm × width 150 mm × thickness 2.0 mm) is placed in a gear oven whose temperature is adjusted to 60 ° C. and left for 30 days. Thereafter, the surface of the test piece is visually observed and the following criteria are used. Discoloration was evaluated.
5: No discoloration 4: Slight discoloration 3: Discolored part is less than half of the whole 2: Discolored part is more than half of the whole 1: Discolored entirely

(Ozone resistance)
In accordance with JIS K6259, a test piece (length 60 mm × width 10 mm × thickness 2.0 mm) was extended by 30%, and a static ozone deterioration test was performed by allowing it to stand at an ozone concentration of 50 pphm for 24 hours (atmosphere temperature 40 ° C.). . Further, in accordance with the JIS standard, a dynamic ozone deterioration test was performed by reciprocating and extending at 0 to 20% for 24 hours at an ozone concentration of 50 pphm and an ambient temperature of 40 ° C. The state of occurrence of cracks after the test was visually observed, and Comparative Example 1 was set to 100, and ozone resistance was indicated by an index. A larger index indicates better ozone resistance.

(Chip cut resistance)
Using the above vulcanized rubber composition, No. 3 dumbbell-shaped rubber test piece was prepared, and a tensile test was conducted in accordance with JIS K6251 “vulcanized rubber and thermoplastic rubber—determining tensile properties”. The elongation at break (EB) was measured, and the rubber strength (TB × EB) was calculated. The chip cut resistance of Comparative Example 1 was set to 100, and the chip cut resistance of each formulation was indicated by an index according to the following formula. The larger the index, the better the chip cut resistance.
(Chip cut resistance index) = (TB × EB of each formulation) / (TB × EB of Comparative Example 1) × 100

From Table 1, the Example which uses 2 types of fatty-acid polyhydric-alcohol ester from which melting | fusing point can differ can improve ozone resistance notably, and can suppress discoloration (whitening, browning) of the rubber surface. On the other hand, the performance of the comparative example was inferior to that of the example.

Claims (6)

A rubber component, a nonionic surfactant of the fatty acid polyhydric alcohol ester (1) and a melting point 65 to 75 ° C. fatty acid polyhydric alcohol ester of melting point 45 to 60 ° C. (2) seen including,
A rubber composition for tires, wherein the content of natural rubber in 100% by mass of the rubber component is 55% by mass or more . The rubber component includes natural rubber or diene synthetic rubber,
Per 100 parts by mass of the rubber component, said fatty acid polyhydric alcohol ester (1) and (2) the total content of tire rubber composition according to claim 1 Symbol placement is 0.1 to 10 parts by weight of. The fatty acid polyhydric alcohol esters (1) and (2) are sorbitol fatty acid ester, sorbitan fatty acid ester, glycerin fatty acid ester, polyglycerin fatty acid ester, polyethylene glycol fatty acid ester, polypropylene glycol fatty acid ester, pentaerythritol fatty acid ester or trimethylolpropane. the tire rubber composition according to claim 1 or 2 is a fatty acid ester. The tire rubber composition according to any one of claims 1 to 3 , which is used as a rubber composition for a tread. Trucks and bus tires produced using the rubber composition according to any one of claims 1-4. Use of a rubber composition for tires comprising a rubber component and a nonionic surfactant of a fatty acid polyhydric alcohol ester (1) having a melting point of 45 to 60 ° C. and a fatty acid polyhydric alcohol ester (2) having a melting point of 65 to 75 ° C. Truck and bus tires made in