JP6073689B2 - Rubber composition for sidewall and pneumatic tire - Google Patents

Description

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

Rubber compositions, particularly tire rubber compositions used in tires, are required to have weather resistance (ozone resistance), that is, to prevent cracking and deterioration of rubber due to ozone in the atmosphere. The rubber composition contains a wax. In particular, because the tire sidewall is a member that is in direct contact with the outside air and that is visible to the human eye when mounted on a vehicle, the rubber composition for the sidewall is more resistant to ozone and more than other tire members. It is required to have excellent appearance.

Conventionally, paraffin wax has been mainly used as a wax compounded in a rubber composition. However, paraffin wax is a petroleum-based wax synthesized from petroleum, which is a fossil-derived resource, and is not preferable from the viewpoint of the global environment. In addition, although the petroleum-based wax is excellent in ozone resistance, there is a problem that the appearance of the tire is impaired due to whitening by bloom. In addition, since petroleum-based wax has a small polarity, in a recent fuel-efficient blending system such as silica blending, there is a problem that blending a large amount of petroleum-based wax deteriorates fuel economy and flex crack resistance.

Therefore, in recent years, formulation examples using naturally derived waxes such as carnauba wax, jojoba wax, and rice wax have been presented (for example, Patent Documents 1 and 2), but there is room for improvement in improving ozone resistance. .

Patent Document 3 discloses a technique in which an oil component derived from sunflower is blended to improve environmental considerations and rubber physical properties. However, the oil component is an oil component having a melting point of room temperature or lower. It was necessary to add a wax component separately.

On the other hand, there is a method of blending an anti-aging agent as another method for improving ozone resistance. However, when a large amount of the anti-aging agent is added, there is a problem that the browning of the tire surface is caused and the appearance of the tire is impaired.

As described above, while preventing deterioration of tire appearance by suppressing browning (browning) due to bloom of anti-aging agent and whitening due to bloom of wax, good ozone resistance, low fuel consumption, and bending resistance A technique capable of imparting crack growth is desired.

JP 2008-297392 A JP 2008-303249 A JP 2012-131860 A

The present invention solves the above-mentioned problems and can reduce the deterioration of the appearance (discoloration) of the tire while considering the environment, and can improve the fuel efficiency, ozone resistance, and resistance to flex crack growth, and a rubber composition for a sidewall. And it aims at providing a pneumatic tire using the same.

The present invention relates to a rubber composition for a sidewall containing a rubber component and a wax derived from sunflower seeds.

The softening point of the wax is preferably 65 to 85 ° C. when measured as the peak top temperature of the maximum endothermic peak in an endothermic curve measured by differential scanning calorimetry (DSC).

The monoester component content of the wax is preferably 85% by mass or more.

The acid value of the wax is preferably 7 mgKOH / g or less.

The sidewall rubber composition preferably contains silica.

The present invention also relates to a pneumatic tire having a sidewall produced using the rubber composition.

According to the present invention, since it is a rubber composition for a sidewall containing a rubber component and a wax derived from sunflower seeds, deterioration of appearance (discoloration) of a tire can be reduced while considering the environment, and fuel efficiency and ozone resistance are reduced. And the resistance to flex crack growth can be improved, the deterioration of the appearance of the tire can be reduced while considering the environment, and a pneumatic tire excellent in fuel efficiency, ozone resistance, and flex crack growth resistance can be provided.

The rubber composition for a side wall of the present invention contains a rubber component and a wax derived from sunflower seeds (hereinafter also referred to as sunflower wax).

Carnauba wax, jojoba wax, rice wax, candelilla wax, beeswax, etc., which have been used as natural waxes, have a high content of free fatty acids and alcohols. As a wax having a relatively high acid value (for example, exceeding 7 mgKOH / g). On the other hand, since the sunflower wax has a low content of free fatty acids and alcohols, the content of the ester component is high, and as a result, the acid value is relatively low (for example, 7 mgKOH / g or less). In addition, the sunflower wax contains a large amount of unbranched linear components (linear ester components) as the ester component. Therefore, when the said sunflower wax is mix | blended with the rubber composition for sidewalls, blooming of a sunflower wax is controlled moderately and ozone resistance can be improved, reducing the appearance deterioration (discoloration (whitening)) of a tire. In addition, since the sunflower wax has a high ester component content, the affinity for a relatively polar compound contained in the rubber composition, such as silica or an antioxidant, is improved, and as a result, these components It is presumed that the improvement in fuel dispersibility and the resistance to flex crack growth can be improved. Further, by blending the sunflower wax, the affinity between the sunflower wax and the anti-aging agent is good, so that bloom of the anti-aging agent can be suppressed, and deterioration of the appearance of the tire (discoloration (browning)) can be reduced. . Moreover, since the said sunflower wax is a natural origin component, it can consider an environment.

The rubber component that can be used in the rubber composition for a sidewall of the present invention is not particularly limited, and isoprene-based rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber ( CR), acrylonitrile butadiene rubber (NBR), ethylene propylene diene rubber (EPDM), butyl rubber (IIR), and halogenated butyl rubber (X-IIR). A rubber component may be used independently and may use 2 or more types together. These rubbers may be those in which the main chain and / or ends of the rubber are modified with a modifying agent, and some of them are coupled with a polyfunctional modifying agent such as tin tetrachloride or silicon tetrachloride, and branched. It may have a structure.

As the rubber component, isoprene-based rubber and BR are preferable, and isoprene-based rubber and BR are more preferably used in combination because good fuel economy and bending crack growth resistance can be obtained.

Examples of the isoprene-based rubber include isoprene rubber (IR), natural rubber (NR), and modified natural rubber. By blending isoprene-based rubber, fuel economy and flex crack growth resistance can be improved in a well-balanced manner.

NR includes deproteinized natural rubber (DPNR) and high-purity natural rubber (HPNR). Modified natural rubber includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), and grafted natural rubber. Etc. Moreover, as NR, what is common in tire industry, such as SIR20, RSS # 3, TSR20, can be used, for example. Among isoprene-based rubbers, NR is preferable because low fuel consumption and flex crack growth resistance can be obtained in a well-balanced manner.

When the rubber composition contains isoprene-based rubber, the content of isoprene-based rubber in 100% by weight of the rubber component is preferably 10% by weight or more, more preferably 30% by weight or more, and further preferably 40% by weight or more. Especially preferably, it is 50 mass% or more. If it is less than 10% by mass, sufficient fuel economy and bending crack growth resistance may not be obtained. The content of the isoprene-based rubber is preferably 90% by mass or less, more preferably 70% by mass or less. If it exceeds 90% by mass, sufficient flex crack growth resistance may not be obtained.

It is not particularly limited as BR, for example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B having high cis content such as BR150B, VCR412 manufactured by Ube Industries, Ltd., VCR617, etc. BR containing syndiotactic polybutadiene crystals can be used. Among them, the BR cis content is preferably 90% by mass or more because it has good wear resistance, flex crack growth resistance, and low fuel consumption. The toluene solution viscosity is preferably 200 cps or less, and more preferably 150 cps or less. If it exceeds 200 cps, the viscosity will be too high, the processability will be lowered, or it will be difficult to mix with other rubber components, and the fuel economy will tend to deteriorate.

Moreover, you may use the butadiene rubber whose molecular weight distribution (Mw / Mn) of butadiene rubber is 3.0-3.4. By using such butadiene rubber, it is possible to achieve both improvement in workability and improvement in wear resistance.

In addition, when it is assumed that petroleum resources will be depleted in the future, it is preferable to use a butadiene rubber obtained by not using a fossil fuel-derived monomer or using a renewable bio-derived raw material as a monomer. The butadiene rubber produced from such a bio-derived raw material can be obtained, for example, by a method of polymerizing the butadiene by causing a catalyst to act on bioethanol.

When the said rubber composition contains BR, content of BR in 100 mass% of rubber components becomes like this. Preferably it is 20 mass% or more, More preferably, it is 30 mass% or more. If it is less than 20% by mass, the resistance to flex crack growth tends to decrease. The BR content is preferably 60% by mass or less, more preferably 50% by mass or less. When it exceeds 60% by mass, fuel efficiency tends to deteriorate.

In the present invention, sunflower wax is used. As a result, deterioration of the appearance of the tire can be reduced while considering the environment, and low fuel consumption, ozone resistance, and flex crack growth resistance can be improved.

Sunflower wax is a wax derived from sunflower seeds. The method for collecting wax from sunflower seeds is not particularly limited. For example, sunflower wax can be obtained by wintering (dewaxing) sunflower oil collected by seed pressing or solvent extraction, solvent washing of the seed shell surface, and the like. Moreover, you may use what is marketed for cosmetics use etc. In addition, the sunflower wax may be subjected to a purification treatment such as solvent extraction, distillation, adsorption, hydrogenation, and filtration as necessary.

The content of the monoester component of the sunflower wax is 100% by mass of the sunflower wax, preferably 85% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and the upper limit is not particularly limited. . When the content of the monoester component is 85% by mass or more, compatibility with other components contained in the rubber composition is improved, fuel efficiency, ozone resistance, tire appearance (brown resistance), The bending crack growth resistance can be improved more suitably.

The content of the linear monoester component of the sunflower wax is preferably 50% by mass or more in 100% by mass of the sunflower wax, and the upper limit is not particularly limited. When the content of the linear monoester component is 50% by mass or more, compatibility with other components contained in the rubber composition is improved, resulting in low fuel consumption, ozone resistance, tire appearance (brown resistance) ) And flex crack growth resistance (especially ozone resistance) can be improved more suitably.

The content of free fatty acid in the sunflower wax is preferably 10% by mass or less, more preferably 5% by mass or less, still more preferably 2% by mass or less, and particularly preferably 0.5% by mass in 100% by mass of the sunflower wax. The lower limit is not particularly limited. When the content of free fatty acid is 10% by mass or less, compatibility with other components contained in the rubber composition is improved, resulting in low fuel consumption, ozone resistance, tire appearance (browning resistance), and bending resistance. The crack growth property (especially ozone resistance) can be improved more suitably.

In the present specification, the content of various components such as a monoester component, a linear monoester component, and a free fatty acid contained in the wax can be measured by gas chromatography.

The sunflower wax preferably has an acid value of 7 mgKOH / g or less, more preferably 6 mgKOH / g or less, still more preferably 4 mgKOH / g or less, particularly preferably 3 mgKOH / g or less, and most preferably 2 mgKOH / g or less. Is not particularly limited. When the acid value is 7 mgKOH / g or less, there are few free fatty acids, and the effects of the present invention can be more suitably obtained.
In this specification, the acid value can be measured by a titration method based on JIS K2501.

The softening point of the sunflower wax is preferably 65 to 85 ° C., 68 to 83 ° C. when measured as the peak top temperature of the maximum endothermic peak in the endothermic curve measured by differential scanning calorimetry (DSC). Is more preferable, and it is still more preferable that it is 70-80 degreeC. If it is less than 65 degreeC, there exists a possibility that ozone resistance in a high temperature range may fall, and if it exceeds 85 degreeC, there exists a possibility that ozone resistance in a low temperature range may fall.
In the present specification, the softening point distribution (peak top temperature of the maximum endothermic peak) of the wax is a temperature increase rate of 5 ° C./min from −30 ° C. to 100 ° C. using a differential scanning calorimetry (DSC) apparatus. To measure the heat flow (mW / g).

The content of the sunflower wax with respect to 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, still more preferably 1 part by mass or more, particularly preferably 2 parts by mass. As mentioned above, Most preferably, it is 3 mass parts 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 sunflower wax content is preferably 100 parts by mass or less, more preferably 30 parts by mass or less, still more preferably 20 parts by mass or less, particularly preferably 12 parts by mass or less, and most preferably 8 parts by mass or less. . If it exceeds 100 parts by mass, the fuel efficiency and the flex crack growth resistance may be reduced.

In the present invention, other waxes may be blended together with the sunflower wax. The other wax is desirably an ester wax having a relatively high polarity, particularly a natural wax such as beeswax, carnauba wax, rice wax, etc. for the purpose of maximizing the effects of the present invention.

The rubber composition of the present invention preferably contains a filler. Any filler can be used without limitation as long as it is commonly used in tires. Examples of the filler include, but are not limited to, silica, carbon black, aluminum hydroxide, clay, calcium carbonate, montmorillonite, cellulose, glass balloon, and various short fibers. As the filler, silica, carbon black, and aluminum hydroxide are preferable in terms of tire physical properties. These may be used alone or in combination of two or more.

When the rubber composition contains a filler, the blending amount of the filler is preferably 10 to 250 parts by mass, more preferably 20 to 200 parts by mass, and still more preferably 30 to 100 parts by mass of the rubber component. ~ 180 parts by mass. If the amount is less than 10 parts by mass, the strength of the rubber composition may be insufficient. If the amount exceeds 250 parts by mass, the filler is not sufficiently dispersed in the rubber and the physical properties of the rubber tend to deteriorate.

Among the fillers, it is more preferable to contain silica from the viewpoint of low fuel consumption. Examples of the silica include, but are not limited to, dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and wet process silica is preferable because of its large number of silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 50 m ² / g or more, more preferably 100 m ² / g or more, and further preferably 150 m ² / g or more. If it is less than 50 m ² / g, the rubber strength and the flex crack growth resistance tend to decrease. The N ₂ SA is preferably 250 m ² / g or less, more preferably 210 m ² / g or less. If it exceeds 250 m ² / g, fuel economy and processability tend to be reduced.
The _N 2 SA of silica is a value determined by the BET method in accordance with ASTM D3037-93.

When the rubber composition contains silica, the content of silica is preferably 5 parts by mass or more, more preferably 10 parts by mass or more with respect to 100 parts by mass of the rubber component. The silica content is preferably 100 parts by mass or less, more preferably 85 parts by mass or less, still more preferably 65 parts by mass or less, particularly preferably 40 parts by mass or less, and most preferably 30 parts by mass or less. By making the content of silica within the above range, good fuel efficiency can be obtained and a reinforcing effect (flexible crack growth resistance) can be obtained.

The rubber composition of the present invention preferably contains a silane coupling agent together with silica.
As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, sulfide systems such as bis (3-triethoxysilylpropyl) tetrasulfide, 3 -Mercaptopropyltrimethoxysilane, Mercapto type such as NXT and NXT-Z manufactured by Momentive, vinyl type such as vinyltriethoxysilane, amino type such as 3-aminopropyltriethoxysilane, γ-glycidoxypropyltriethoxy Examples include glycidoxy series of silane, nitro series such as 3-nitropropyltrimethoxysilane, and chloro series such as 3-chloropropyltrimethoxysilane. Among these, sulfide type is preferable, and bis (3-triethoxysilylpropyl) tetrasulfide is more preferable.

When the said rubber composition contains a silane coupling agent, Preferably content of a silane coupling agent is 2 mass parts or more with respect to 100 mass parts of silica, More preferably, it is 5 mass parts or more. If it is less than 2 parts by mass, the rubber strength and the flex crack growth resistance tend to decrease. Further, the content of the silane coupling agent is preferably 20 parts by mass or less, more preferably 12 parts by mass or less. When it exceeds 20 parts by mass, there is a tendency that an effect commensurate with the increase in cost cannot be obtained.

As a filler, the rubber composition of the present invention preferably contains carbon black. Thereby, while being able to obtain a favorable reinforcing effect, it is possible to enhance the effect of preventing the whitening of the tire. Examples of carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF, but are not particularly limited. Carbon black may be used alone or in combination of two or more. Furthermore, when assuming that there will be a future depletion of petroleum resources, it is preferable to use carbon black that uses renewable biological materials.

The nitrogen adsorption specific surface area _(N 2 SA) of carbon black is preferably 10~280m ² / g, more preferably 20~250m ² / g, and further preferably from 30 to 150 m ² / g. The upper limit is particularly preferably ^{100m 2 / g, 60m 2 /} g being most preferred. When N ₂ SA of carbon black is less than 10 m ² / g, sufficient flex crack growth resistance cannot be obtained, and wear resistance tends to be lowered. On the other hand, when it exceeds 280 m ² / g, the dispersibility is inferior, and the wear resistance and fuel efficiency tend to be lowered.
Incidentally, _N 2 SA of carbon black, JIS K 6217-2: determined by 2001.

When the said rubber composition contains carbon black, 1-150 mass parts is preferable with respect to 100 mass parts of rubber components, 3-100 mass parts is more preferable, and 10-80 mass parts is preferable. Further preferred. The upper limit is more preferably 60 parts by weight, particularly preferably 40 parts by weight, and most preferably 30 parts by weight. If the content of carbon black is within the above range, the mechanical strength of rubber (flexible crack growth resistance) can be ensured, and good ozone resistance and good compatibility with the sunflower wax can be obtained.

The rubber composition of the present invention may contain oil. By blending oil, processability can be improved and the strength of rubber and resistance to flex crack growth can be increased. As the oil, for example, process oil, vegetable oil, or a mixture thereof can be used. As the process oil, for example, a paraffin process oil, an aroma process oil, a naphthenic process oil, or the like can be used. Specific examples of the paraffinic process oil include PW-32, PW-90, PW-150, and PS-32 manufactured by Idemitsu Kosan Co., Ltd. Specific examples of the aroma-based process oil include AC-12, AC-460, AH-16, AH-24, and AH-58 manufactured by Idemitsu Kosan Co., Ltd. As vegetable oils and fats, castor oil, cottonseed oil, sesame oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut hot water, rosin, pine oil, pineapple, tall oil, corn oil, rice bran oil, beet flower oil, sesame oil, Examples include olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. Among these, vegetable oils and fats are preferable, and sunflower oil is more preferable because of its good compatibility with the sunflower wax and the maximum effect of the present invention. In the present invention, the oil is preferably liquid at normal temperature (25 ° C.).

In the sunflower oil, the content of oleic acid in 100% by mass of the constituent fatty acid is preferably 45% by mass or more, more preferably 50% by mass or more, still more preferably 70% by mass or more, and particularly preferably 75% by mass or more. . The upper limit of the content of the oleic acid is not particularly limited, but is preferably 98% by mass or less, more preferably 95% by mass or less in consideration of availability and cost. When the content of oleic acid is within the above range, the effect of the present invention can be more suitably obtained. The fatty acid composition (oleic acid content) can be measured by GLC (gas-liquid chromatography) according to the method described in JP-T-2009-543561.

When the rubber composition contains oil, the content of oil is preferably 1 part by mass or more, more preferably 3 parts by mass or more with respect to 100 parts by mass of the rubber component. The oil content is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, still more preferably 50 parts by mass or less, particularly preferably 30 parts by mass or less, and most preferably 15 parts by mass or less. When the oil content is within the above range, the effects of the present invention can be more suitably obtained.

The rubber composition of the present invention preferably contains an antiaging agent. 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. Especially, since the effect of this invention is acquired more suitably, p-phenylenediamine type | system | group is preferable.

When the rubber composition contains an anti-aging agent, the content of the anti-aging agent 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 parts by mass, sufficient ozone resistance may not be obtained. The content of the anti-aging agent is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and still more preferably 6 parts by mass or less. If it exceeds 10 parts by mass, the anti-aging agent blooms, and the appearance (brown resistance) of the tire may be deteriorated.

The rubber composition of the present invention preferably contains a vulcanization accelerator. Examples of the vulcanization accelerator include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. Etc. These vulcanization accelerators may be used alone or in combination of two or more. Of these, sulfenamide-based vulcanization accelerators are preferable because the effects of the present invention can be obtained more suitably.

Examples of the sulfenamide vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N -Dicyclohexyl-2-benzothiazolylsulfenamide (DCBS) and the like. Among these, TBBS is preferable because the effects of the present invention can be obtained more suitably.

When the rubber composition contains a vulcanization accelerator, the content of the vulcanization accelerator is preferably 0.3 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. It is. The content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less. When the content of the vulcanization accelerator is within the above range, the effect of the present invention can be more suitably obtained.

In addition to the above components, the rubber composition of the present invention contains a compounding agent generally used in the production of rubber compositions, such as zinc oxide, stearic acid, tackifiers, vulcanizing agents such as wax and sulfur. It can mix | blend suitably.

As a method for producing the rubber composition of the present invention, a known method can be used. For example, the above components are kneaded using a rubber kneader such as an open roll or a Banbury mixer, and then vulcanized. Can be manufactured.

The rubber composition of the present invention constitutes the surface (outer surface) of a tire and can be suitably used for a tire sidewall requiring good ozone resistance.

The pneumatic tire of the present invention can be produced by a usual method using the rubber composition.
That is, by extruding the rubber composition containing the above components in accordance with the shape of the sidewall and the like at the unvulcanized stage, and molding the tire composition together with other tire members by a normal method on a tire molding machine. An unvulcanized tire can be formed. A tire is obtained by heating and pressurizing the unvulcanized tire in a vulcanizer.

The pneumatic tire of the present invention is used as an “eco-tire” that is friendly to the global environment, for example, as a tire for passenger cars, a tire for trucks and buses, a tire for motorcycles, a high-performance tire, and the like. In addition, the high-performance tire in this specification is a tire that is particularly excellent in grip performance, and is a concept that includes a competition tire used in a competition vehicle.

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: RSS # 3
BR: Polybutadiene rubber UBEPOL BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass, ML _{1 + 4} (100 ° C.): 40, Mw / Mn: 3.3)
Carbon black: Seast N550 manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 41 m ² / g)
Silica: Ultrasil VN3 (N ₂ SA: 175 m ² / g) manufactured by EVONIK-DEGUSSA
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by EVONIK-DEGUSSA
Sunflower wax: Sunflower wax manufactured by Koster Keunen (wax derived from sunflower seeds, softening point: 77 ° C., monoester component content: 99% by mass, linear monoester component content: 50% by mass or more, Free fatty acid content: 0.2% by mass, acid value: 1.0 mgKOH / g)
Petroleum wax: Ozoace 0355 manufactured by Nippon Seiwa Co., Ltd.
Carnauba wax: Carnauba wax manufactured by Toa Kasei Co., Ltd. (softening point: about 82 ° C., content of ester component: 79% by mass, content of monoester component: 50% by mass, acid value: 8 mgKOH / g)
Anti-aging agent: Nocrack 6C (N- (1,3-dimethylbutyl) -N-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Oil: High oleic sunflower oil manufactured by Orisoi (content of oleic acid in 100% by mass of constituent fatty acid: 82% by mass, polyunsaturated fatty acid ratio 9% by mass, saturated fatty acid ratio 9% by mass)
Stearic acid: Stearic acid “paulownia” manufactured by NOF Corporation
Zinc oxide: Zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Sulfur powder vulcanization accelerator manufactured by Tsurumi Chemical Co., Ltd .: Noxeller NS (N-tert-butyl-2-benzothiazoli manufactured by Ouchi Shinsei Chemical Rusulfenamide)

In accordance with the formulation shown in Table 1, chemicals other than sulfur and a vulcanization accelerator were kneaded using a 1.7 L Banbury mixer. Next, using an open roll, sulfur and a vulcanization accelerator were added to the kneaded product and kneaded to obtain an unvulcanized rubber composition. Next, the obtained unvulcanized rubber composition was press vulcanized with a 2 mm thick mold at 170 ° C. for 15 minutes to obtain a vulcanized rubber composition (vulcanized rubber sheet).
Moreover, the tire for a test was produced by shape | molding the obtained unvulcanized rubber composition in a side wall shape, bonding together with another tire member, and vulcanizing for 15 minutes at 170 degreeC.

The vulcanized rubber composition and the test tire were evaluated as follows, and the results are shown in Table 1.

(Viscoelasticity test (low fuel consumption))
Measurement of loss tangent (tan δ) of vulcanized rubber slab sheet using viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho Co., Ltd. under conditions of temperature 70 ° C., initial strain 10%, dynamic strain 2% and frequency 10 Hz. Then, the rolling resistance index of Comparative Example 1 was set to 100, and the rolling resistance was indicated by an index according to the following calculation formula. The larger the rolling resistance index, the lower the rolling resistance and the better the fuel efficiency.
(Rolling resistance index) = (tan δ of Comparative Example 1) / (tan δ of each formulation) × 100

(Ozone resistance test)
Based on JIS K 6259 “Vulcanized Rubber and Thermoplastic Rubber-Determination of Ozone Resistance”, ozone concentration 50 ± 5 pphm, each temperature (low temperature: 0 ° C., medium temperature: 25 ° C., high temperature: 50 ° C.), elongation strain 20 The ozone resistance was evaluated by observing the state of cracks after testing for 48 hours under the condition of ± 2%. In addition, the evaluation method represented the number and the magnitude | size of the crack according to the system as described in JIS. The alphabet (A, B and C) indicates that A is a small number of cracks and C is a large number of cracks, and the numbers (1-5) indicate that the larger the number, the larger the crack size, “No crack” indicates that no crack occurred.

(Tire appearance (anti-white))
A wheel was attached to the test tire, air of 2.2 atm was sealed, and the tire was left outdoors (Kobe city) for 3 months, and the degree of discoloration thereafter was visually evaluated. ○ and Δ were judged to be good.
○: No discoloration △: Slightly whitening ×: Whitening intensely

(Appearance of tire (brown resistance))
The test tire was left outdoors in sunlight (Kobe city) for 6 months and exposed to sunlight, and the degree of browning was visually evaluated on a five-point scale. Larger values indicate better brown discoloration. If it was 3 or more, it judged that it was favorable.

(Flexible crack growth resistance)
Using the obtained vulcanized rubber composition, a sample was prepared based on JIS-K-6260 “Vulcanized Rubber and Thermoplastic Rubber—Dematcher Bending Crack Test Method”, a bending crack growth test was conducted, and 70% elongation was obtained. After the sample was bent 1,000,000 times, the length of the generated crack was measured.
And the measured value (length) of the comparative example 1 was set to 100, and it displayed by the index | exponent by the following formula. The larger the index is, the more the crack growth is suppressed and the resistance to flex crack growth is excellent.
(Bending crack growth resistance index) = (Measured value of Comparative Example 1) / (Measured value of each formulation) × 100

The example containing the rubber component and the wax derived from sunflower seeds was able to reduce deterioration in appearance (discoloration) of the tire while considering the environment, and improved fuel economy, ozone resistance, and flex crack growth resistance.

Claims (9)

A rubber composition for a sidewall, comprising a rubber component and a wax derived from sunflower seeds. The sidewall rubber according to claim 1, wherein the softening point of the wax is 65 to 85 ° C when measured as a peak top temperature of a maximum endothermic peak in an endothermic curve measured by differential scanning calorimetry (DSC). Composition. The rubber composition for a sidewall according to claim 1 or 2, wherein the wax has a monoester component content of 85% by mass or more. The rubber composition for a sidewall according to any one of claims 1 to 3, wherein the wax has an acid value of 7 mgKOH / g or less. The rubber composition for a side wall according to any one of claims 1 to 4, comprising silica. The rubber composition for a sidewall according to any one of claims 1 to 5, comprising isoprene-based rubber and butadiene rubber as the rubber component. Nitrogen adsorption specific surface area of 10-100m ² The rubber composition for a sidewall according to any one of claims 1 to 6, comprising / g of carbon black. The rubber composition for a sidewall according to any one of claims 1 to 7, comprising an oil. Pneumatic tire having a sidewall prepared using the rubber composition according to any one of claims 1-8.