JP6068951B2 - Rubber composition for tire, pneumatic tire and method for preventing tire discoloration - Google Patents

Description

The present invention relates to a tire rubber composition, a pneumatic tire using the same, and a method for preventing tire discoloration.

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 enhancing ozone resistance, a method of blending an anti-aging agent or a wax is known, but in such a method, the anti-aging agent and the wax migrate to the tire surface, and yellowing, browning, whitening There is concern that discoloration of the tire will occur, such as discoloration. In particular, when discoloration occurs in sidewalls, treads, etc., the appearance of black tires containing carbon black is impaired, and there are many problems such as being noticed by consumers when storing products at stores.

Patent Document 1 discloses a method of suppressing the migration of the anti-aging agent to the sidewall surface by blending a polyethylene glycol having a specific molecular weight. However, provision of other methods is also desired. .

Japanese Patent Laid-Open No. 5-179067

The present invention provides a rubber composition for a tire capable of suppressing the discoloration of the tire surface while solving the above-mentioned problems and obtaining good ozone resistance, a pneumatic tire using the same, and a tire discoloration preventing method. Objective.

The present invention relates to a tire rubber composition in which a fluorescent whitening agent is blended with a rubber component.

（式（Ｉ）中、Ｒ^１〜Ｒ^４は、同一若しくは異なって、水素、又は置換されてもよい炭化水素基を表す。） The fluorescent brightening agent is preferably a compound represented by the following formula (I).

(In formula (I), R ^{1 to} R ⁴ are the same or different and represent hydrogen or an optionally substituted hydrocarbon group.)

It is preferable that the optical brightener is 2,5-bis (5-tert-butyl-2-benzoxazolyl) thiophene.

The compounding amount of the fluorescent whitening agent with respect to 100 parts by mass of the rubber component is preferably 0.05 to 2.0 parts by mass.

It is preferable to contain an anti-aging agent and / or a wax.

The rubber component preferably contains at least one selected from the group consisting of natural rubber, isoprene rubber, butadiene rubber and styrene butadiene rubber.

The present invention relates to a pneumatic tire having a sidewall and / or a tread produced using the rubber composition.
The present invention also relates to a method for preventing tire discoloration by adding a fluorescent brightening agent to a rubber component.

According to the present invention, since it is a tire rubber composition and a tire discoloration prevention method characterized by blending a fluorescent whitening agent with respect to a rubber component, discoloration of the tire surface while obtaining good ozone resistance. Can also be suppressed.

The rubber composition for tires and the method for preventing tire discoloration according to the present invention are characterized in that a fluorescent whitening agent is blended with a rubber component.

The principle of feeling the color is to feel the color due to the difference in the state of the reflected light radiated to the object with the sunbeam. If the wavelength of 400 to 700 nm is uniformly included, the color is achromatic, and if the wavelength is biased, the color is chromatic. I feel. For example, it is considered that an amine-based anti-aging agent that is prominent in yellow discoloration has a yellow discoloration that is a complementary color due to absorption of a blue-violet spectrum of a specific wavelength (400 to 435 nm) by the substance. . Therefore, the present invention blends a fluorescent brightening agent such as 2,5-bis (5-tert-butyl-2-benzoxazolyl) thiophene, which is particularly effective in suppressing yellowing, and absorbs ultraviolet rays. By emitting fluorescence in the vicinity of 400 to 450 nm, the yellow component becomes inconspicuous, and as a result, discoloration (yellow or red) can be suppressed. In addition, even when a fluorescent brightening agent is blended, a decrease in ozone resistance is not observed, so that good ozone resistance can be obtained.

In the present invention, the fluorescent whitening agent has absorption in the near-ultraviolet region (light having a wavelength in the vicinity of 300 to 450 nm, which is visible in the ultraviolet to short wave), and has a violet-blue to blue fluorescence (having a wavelength in the vicinity of 400 to 500 nm). It is a colorless or lightly colored compound that emits fluorescence.

Optical brighteners include thiophene, diaminobenzene sulfonic acid, benzoxazole, coumarin, pyrazoline, pyrene, oxazole, thiazole, imidazole, benzimidazole, imidazolone, benzidine, stilbene Conventionally known compounds such as these compounds can be mentioned, and for example, thiophene compounds can be preferably used.

（式（Ｉ）中、Ｒ^１〜Ｒ^４は、同一若しくは異なって、水素、又は置換されてもよい炭化水素基を表す。） Examples of the thiophene fluorescent brightening agent (thiophene compound) include benzoxazolylthiophene derivatives, and examples include compounds represented by the following formula (I).

(In formula (I), R ^{1 to} R ⁴ are the same or different and represent hydrogen or an optionally substituted hydrocarbon group.)

The carbon number of the hydrocarbon group which may be substituted for R ^{1 to} R ⁴ is preferably 1 to 15, more preferably 1 to 8. The hydrocarbon group may be linear, cyclic or branched. For example, an alkyl group (methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group) Butyl group etc.), alkenyl group (vinyl group, allyl group, 1-propenyl group, 1-methylethenyl group etc., aryl group etc.), aryl group (phenyl group, methylphenyl group, ethylphenyl group etc.) etc. are mentioned. The substituent in R ^{1 to} R ⁴ is not particularly limited, and examples thereof include a halogen group and an alkoxy group.

Preferable examples of the compound represented by the formula (I) include compounds in which each of R ^{1 to} R ⁴ is a group represented by the following.

Among these, a compound represented by (I-6), that is, 2,5-bis (5-tert-butyl-2-benzoxazolyl) thiophene represented by the following formula is particularly preferable.

The content of the optical brightener is preferably 0.05 to 2.0 parts by mass with respect to 100 parts by mass of the rubber component. When the amount is 0.05 parts by mass or more, discoloration due to the amine-based anti-aging agent can be made inconspicuous. . The lower limit is more preferably 0.1 parts by mass or more, still more preferably 0.4 parts by mass or more, and the upper limit is more preferably 1.0 parts by mass or less, still more preferably 0.8 parts by mass or less.

Examples of the rubber component that can be used in the rubber composition and the method for preventing discoloration according to the present invention include natural rubber and diene rubber such as diene synthetic rubber. 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. Especially, when using as a rubber composition for sidewalls, it is preferable to use BR from the viewpoint of mechanical fatigue resistance, and it is more preferable to use NR and / or IR and BR. When used as a rubber composition for a tread, SBR is preferably used from the viewpoint of wear resistance, and may be used in combination with BR, NR, IR, and the like.

In the case of the rubber composition for a sidewall, the content of NR 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, the mechanical fatigue resistance may be inferior. The content is preferably 70% by mass or less, more preferably 50% by mass or less. When it exceeds 70 mass%, there exists a possibility that it may be inferior to a weather resistance.

In the case of the rubber composition for a sidewall, the BR content in 100% by mass of the rubber component is preferably 30% by mass or more, more preferably 50% by mass or more. There exists a possibility that it may be inferior to a weather resistance in it being less than 30 mass%. The content is preferably 90% by mass or less, more preferably 80% by mass or less. If it exceeds 90% by mass, the flex resistance may be inferior.

In the case of a rubber composition for a tread, the content of SBR in 100% by mass of the rubber component is preferably 50% by mass or more, more preferably 75% by mass or more, still more preferably 90% by mass or more, and particularly preferably 100% by mass. It is. If it is less than 50% by mass, good abrasion resistance may not be obtained.

The rubber composition and the method for preventing discoloration of the present invention can be suitably applied to a black tire, and any carbon black is usually used as a reinforcing filler. Thereby, the intensity | strength of rubber | gum can be improved.

In the case of a rubber composition for a sidewall, 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. Further, N ₂ SA of carbon black is preferably 150 m ² / g or less, more preferably 100 m ² / g or less, and further preferably 60 m ² / g or less. When it exceeds 150 m ² / g, heat generation increases and rolling resistance tends to deteriorate.

In the case of a rubber composition for a tread, the nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 80 m ² / g or more, more preferably 100 m ² / g or more. If it is less than 80 m < ² > / g, there exists a tendency for grip performance and abrasion resistance to fall. Also, _N 2 SA is preferably at most 280 meters ² / g of carbon black, more preferably not more than 200 meters ² / g, more preferably 175 m ² / g or less. When it exceeds 280 m ² / g, the dispersibility of carbon black tends to be lowered, and the wear resistance tends to be lowered.
Incidentally, _N 2 SA of carbon black is, JIS K6217-2: determined by 2001.

In the rubber composition of the present invention, 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 it is less than 10 parts by mass, the durability tends to be inferior. The content is preferably 100 parts by mass or less, more preferably 70 parts by mass or less. When it exceeds 100 parts by mass, heat generation increases and rolling resistance tends to deteriorate.

Moreover, you may mix | blend a silica with the rubber composition of this invention as a reinforcing filler. Silica is not particularly limited, and any commercially available product can be used. Of these, wet silica, dry silica, and colloidal silica are preferable, and wet silica is particularly preferable. Here, the compounding amount of the reinforcing filler is preferably 30 to 120 parts by mass with respect to 100 parts by mass of the rubber component. In addition, when using silica, it is preferable to mix | blend a silane coupling agent from a viewpoint of reinforcing property, and the compounding quantity is preferably 1-20 mass parts with respect to 100 mass parts of silica from a heat generating viewpoint. 6 to 12 parts by mass is more preferable.

In the present invention, an antiaging agent is usually used. Although it does not specifically limit as an anti-aging agent, Amine-type anti-aging agents, such as p-phenylenediamine type | system | group, a naphthylamine type | system | group, a diphenylamine type | system | group, can be used conveniently.

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

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

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 amine-based antioxidant is preferably 1.0 parts by mass or more, more preferably 2.0 parts by mass or more, and still more preferably 3.0 parts by mass or more with respect to 100 parts by mass of the rubber component. If it is less than 1.0 part by mass, ozone resistance may be reduced. The content is preferably 7.0 parts by mass or less, more preferably 5.5 parts by mass or less, and still more preferably 4.5 parts by mass or less. If it exceeds 7.0 parts by mass, discoloration may occur.

Anti-aging agents other than amine-based anti-aging agents may be blended, and 2,2,4-trimethyl-1,2-dihydroquinoline polymer, 6-ethoxy-2,2,4-trimethyl-1,2- A quinoline anti-aging agent such as dihydroquinoline can be preferably used.

In the present invention, the total content of the anti-aging agent is preferably 2.0 parts by mass or more, more preferably 3.5 parts by mass or more, and further preferably 4.5 parts by mass or more with respect to 100 parts by mass of the rubber component. It is. There exists a possibility that ozone resistance may fall that it is less than 2.0 mass parts. The total content is preferably 10.0 parts by mass or less, more preferably 8.0 parts by mass or less, and still more preferably 7.0 parts by mass or less. If it exceeds 10.0 parts by mass, discoloration may occur.

In the present invention, a wax is preferably used. 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 the present invention, in addition to the above components, compounding agents generally used in the production of rubber compositions such as oil, zinc oxide, stearic acid, vulcanizing agents, vulcanization accelerators and the like can be used as appropriate.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading each component with a kneader such as a Banbury mixer, a kneader, or an open roll, and then vulcanizing. The rubber composition and the method for preventing discoloration of the present invention are particularly suitable for sidewalls and treads because they are excellent in ozone resistance and discoloration resistance.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, a rubber composition containing various additives as necessary is extruded in accordance with the shape of sidewalls, treads, etc. at an unvulcanized stage, and molded by a normal method on a tire molding machine. Then, they are bonded together with other tire members to form an unvulcanized tire. This unvulcanized tire can be heated and pressurized in a vulcanizer to produce a tire. Since the tire is blended with the fluorescent brightening agent, discoloration that occurs when an anti-aging agent such as an amine anti-aging agent migrates to the tire surface is prevented, and the appearance is good over a long period of time. Moreover, it is excellent in ozone resistance.

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

Various chemicals used in Examples and Comparative Examples will be described together.
Natural rubber (NR): TSR20
Butadiene rubber (BR): BR1220 manufactured by Nippon Zeon Co., Ltd.
Styrene butadiene rubber (SBR): SBR1502 manufactured by JSR Corporation
Carbon Black 1: Dia Black E (N550) manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 41 m ² / g)
Carbon Black 2: Show Black N220 (N ₂ SA: 111 m ² / g) manufactured by Cabot Japan
Wax: Ozoace 0355 manufactured by Nippon Seiwa Co., Ltd.
Anti-aging agent 6C: Nocrack 6C (N-phenyl-N ′-(1,3-dimethylbutyl) -p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Anti-aging agent RD: Anti-aging agent 224 (2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Stearic acid: Tsubaki made by NOF Corporation
Zinc oxide: Oil manufactured by Mitsui Mining & Smelting Co., Ltd .: Process X-140 (Aroma Oil) manufactured by Japan Energy Co., Ltd.
Optical brightener: Tinopal OB (2,5-bis (5-tert-butyl-2-benzoxazolyl) thiophene) manufactured by BASF
Sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Examples and Comparative Examples>
According to the formulation shown in Tables 2-3, using a Banbury mixer, chemicals other than sulfur and a vulcanization accelerator were added, and the mixture was kneaded for 5 minutes at a maximum temperature of 165 ° C. to obtain a kneaded product. . Thereafter, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and kneaded for 3 minutes under a condition of a maximum temperature of 97 ° C. using a biaxial open roll to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was rolled into a sheet with a mold and press vulcanized at 170 ° C. for 12 minutes to produce a vulcanized rubber sheet.

The following evaluation was performed about the obtained vulcanized rubber sheet. The results are shown in Tables 2-3.

(Measurement of L ^* value, b ^* value)
About the obtained vulcanized rubber sheet, L ^* and b ^* were measured using a color difference meter CR-400 (manufactured by Konica Minolta Co., Ltd.) in accordance with JIS Z-8729. The L ^* value indicates lightness, and the b ^* value indicates color. A b ^* value of 0 indicates colorless, a positive b ^* value indicates yellow, and a negative b ^* value indicates blue. Regarding the degree of discoloration, L after leaving the vulcanized rubber piece for one month under the environmental conditions of leaving it outdoors in the summer (under a roof where it is not exposed to rain and being exposed to direct sunlight for a specific time of the day). ^The evaluation was based on the ^* value, b ^* value, and the degree of visual discoloration. The degree of visual discoloration is evaluated on a five-point scale: 5 if discoloration is severely recognized, 4 if discoloration is observed in more than half of the whole, 3 if discoloration is observed in less than half of the whole, and slightly discoloration occurs. The case where the discoloration was not recognized was set to 1 when the case where it was recognized.

(Ozone resistance)
According to JIS K6259: 2004, a dynamic ozone deterioration test is performed on the vulcanized rubber sheet (test piece) under conditions of a temperature of 40 ° C., an ozone concentration of 50 pphm, and an elongation of 20%, and the deterioration state of the test piece after 24 hours is observed. The presence or absence of cracks was evaluated. The occurrence of cracks was evaluated on a five-point scale, with 1 being the least cracked and 5 being the most cracked.

Both the sidewalls in Table 2 and the treads in Table 3 have better ozone resistance and less discoloration in the examples containing the fluorescent whitening agent than in the comparative example in which no fluorescent whitening agent is added. It was revealed that a good appearance can be obtained over a long period of time.

Claims (6)

A rubber composition for a tire containing a fluorescent whitening agent , carbon black, and an anti-aging agent for a rubber component ,
The optical brightener is 2,5-bis (5-tert-butyl-2-benzoxazolyl) thiophene,
The rubber composition for tires whose content of the said carbon black is 10-100 mass parts with respect to 100 mass parts of said rubber components . The amount of the fluorescent whitening agent according to claim 1 tire rubber composition, wherein 0.05 to 2.0 parts by mass with respect to 100 parts by mass of the rubber component. Claim 1 or 2 tire rubber composition according comprising the word box. The tire rubber composition according to any one of claims 1 to 3 , wherein the rubber component includes at least one selected from the group consisting of natural rubber, isoprene rubber, butadiene rubber, and styrene butadiene rubber. Pneumatic tire having a sidewall and / or tread produced from the rubber composition according to any one of claims 1-4. A tire discoloration prevention method comprising blending a fluorescent whitening agent , carbon black, and an anti-aging agent with respect to a rubber component ,
The optical brightener is 2,5-bis (5-tert-butyl-2-benzoxazolyl) thiophene,
The tire discoloration preventing method, wherein a content of the carbon black is 10 to 100 parts by mass with respect to 100 parts by mass of the rubber component .