JP2014218629A - Rubber composition for sidewalls and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for sidewalls which, while considering the influence on environment and health, can reduce an odor, can inhibit deterioration in appearance such as brown discoloration (browning) due to the bloom of an age resister and whitening due to the bloom of wax and also improve weather resistance, and further improve tire performance such as fuel economy and flexing crack-growth resistance, and a pneumatic tire having a sidewall prepared using the same.SOLUTION: A rubber composition for sidewalls comprises a rubber component and wax derived from citrus.

Description

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

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 car, the rubber composition for the sidewall has more weather resistance and appearance than other tire members. It is required to have excellent properties.

Conventionally, paraffin wax has been mainly used as a wax compounded in a rubber composition. However, paraffin wax is a petroleum 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 weather resistance and flex crack growth 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 recent fuel-efficient blending systems such as silica blending, there is also a problem that if a large amount of petroleum-based wax is blended, fuel economy is inferior.

Therefore, in recent years, as disclosed in Patent Documents 1 and 2, blending examples using naturally derived waxes such as carnauba wax and candelilla wax have been disclosed, but appearance, low fuel consumption, flex crack growth resistance, etc. There is room for improvement.

On the other hand, as another method of improving the weather resistance, there is a method of blending an anti-aging agent. However, when a large amount of the anti-aging agent is blended, the appearance of the rubber surface is deteriorated due to the browning of the rubber surface due to bloom. There was a problem that the effect decreased with the moon. In addition, chemically synthesized anti-aging agents have problems such as toxicity and environmental impact of the product itself, and odors during kneading.

On the other hand, Patent Document 3 discloses a technique for blending a citrus fragrance into a rubber composition for a base tread to reduce odor, but the citrus fragrance is an oil component that is liquid at room temperature. Therefore, there is room for improvement in improving weather resistance and rubber properties.

In this way, while taking into consideration the impact on the environment and health, it is possible to reduce odors, while suppressing deterioration in appearance such as tea discoloration (browning) due to bloom of the anti-aging agent and whitening due to wax bloom There is a demand for development of a technology that can improve weather resistance and also improve tire performance such as low fuel consumption and flex crack growth resistance.

JP 2008-297392 A JP 2008-303249 A JP 2007-8225 A

The present invention solves the above-mentioned problems and can reduce the odor while taking into consideration the influence on the environment and health, and the appearance such as tea discoloration (browning) due to bloom of anti-aging agent and whitening due to bloom of wax Rubber composition for sidewall capable of improving weather resistance while suppressing deterioration of tire and improving tire performance such as low fuel consumption and flex crack growth resistance, and pneumatic tire having a sidewall produced using the rubber composition The purpose is to provide.

As a result of diligent study, the present inventors have been able to reduce odor while considering the impact on the environment and health by blending citrus-derived wax, and tea discoloration (browning) due to bloom of the anti-aging agent The first invention was completed by finding that weather resistance can be improved while suppressing deterioration in appearance such as whitening due to wax bloom, and tire performance such as low fuel consumption and flex crack growth resistance can also be improved. I let you.
That is, the first present invention relates to a rubber composition for a sidewall containing a rubber component and a citrus-derived wax.

The wax preferably has a total content of flavonoids and carotenoids of 0.2% by mass or more.

The wax preferably has a phytosterol content of 1% by mass or more.

The softening point of the wax is preferably 35 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).

It is preferable that the wax is extracted from citrus flowers and / or peels.

It is preferable that butadiene rubber is included.

It is preferable to contain isoprene-based rubber.

It is preferable to contain silica.

Furthermore, the present inventors have scrutinized the components contained in the citrus wax and found that the total content of flavonoids and carotenoids is important, and completed the second invention.
That is, the second aspect of the present invention relates to a rubber composition for a sidewall containing a rubber component and a naturally-derived wax having a total content of flavonoids and carotenoids of 0.2% by mass or more.

Furthermore, the present inventors have scrutinized the components contained in the citrus wax and found that the content of phytosterols is important, and completed the third invention.
That is, the third aspect of the present invention relates to a rubber composition for a sidewall containing a rubber component and a naturally derived wax having a phytosterol content of 1% by mass or more.

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

According to the first aspect of the present invention, since it is a rubber composition for tires containing a rubber component and a citrus wax, it is possible to reduce odor while taking into consideration the impact on the environment and health, and by the bloom of the anti-aging agent Providing pneumatic tires with improved weather resistance, improved fuel efficiency and flex crack growth resistance, while suppressing deterioration in appearance such as browning (browning) and whitening due to wax bloom it can.
Further, according to the second aspect of the present invention, since it is a rubber composition for a tire containing a rubber component and a naturally-derived wax having a total content of flavonoid and carotenoid of 0.2% by mass or more, Odor can be reduced while considering the impact on health, and weather resistance is improved while suppressing deterioration of appearance such as tea discoloration (browning) due to bloom of anti-aging agent and whitening due to bloom of wax In addition, it is possible to provide a pneumatic tire with improved fuel efficiency and improved resistance to flex crack growth.
Moreover, according to the third aspect of the present invention, since the rubber composition for tires contains a rubber component and a naturally-derived wax having a content of phytosterols of 1% by mass or more, it has an impact on the environment and health. The odor can be reduced while taking into consideration, and weather resistance is improved while suppressing deterioration in appearance such as browning (browning) due to bloom of the anti-aging agent, and whitening due to blooming of wax, and low fuel consumption. And a pneumatic tire with improved flex crack growth resistance can be provided.

(Rubber composition for tire of first invention)
The rubber composition for a side wall of the present invention contains a rubber component and a citrus-derived wax.

By blending citrus wax, the odor can be reduced while taking into consideration the impact on the environment and health. Appearance such as tea discoloration (browning) due to bloom of the anti-aging agent and whitening due to wax bloom In addition to improving the weather resistance, the tire performance such as low fuel consumption and resistance to flex crack growth can be improved.
This is because the components such as flavonoids and carotenoids contained in citrus-derived waxes act as natural anti-aging agents, and in particular, weather resistance and odor can be improved. Furthermore, phytosterols contained in citrus-derived waxes and As phytosterols such as phytosterol esters act as natural surfactants, in particular, compatibility with other compounding components can be improved, fuel efficiency and flex crack growth resistance can be improved, and citrus-derived It is presumed that the bloom of wax and anti-aging agent can also be suppressed and the appearance of whitening and browning can be improved. Moreover, since the citrus-derived wax is a natural (plant) -derived wax, the influence on the environment and health can be reduced.

The first aspect of the present invention will be described below.

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, diene-based synthetic 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), halogenated butyl rubber (X-IIR) and the like. A rubber component may be used independently and may use 2 or more types together. These rubber components may be those in which the main chain and / or ends of the rubber are modified with a modifying agent, and a part thereof is coupled with a multifunctional modifying agent such as tin tetrachloride or silicon tetrachloride. Also, it may have a branched structure.

As the rubber component, BR and isoprene-based rubber are preferable, BR is more preferable, and BR and isoprene-based rubber are particularly preferably used in terms of obtaining good flex crack growth resistance and low fuel consumption.

The BR is not particularly limited. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd. Commonly used in the tire industry such as BR containing syndiotactic polybutadiene crystals can be used. These BRs may be used alone or in combination of two or more.

The cis content of BR is preferably 95% by mass or more. By using 95% by mass or more, the wear resistance is further improved. The cis content can be measured by infrared absorption spectrum analysis.

The toluene solution viscosity of BR is preferably 200 cps or less, more preferably 150 cps or less, and still more preferably 100 cps or less. If it exceeds 200 cps, the viscosity tends to be too high, and the processability tends to be reduced, or it tends to be difficult to mix with other rubber components. In addition, the toluene solution viscosity of BR can be calculated from the flow time of a 5% by weight toluene solution of a kinematic viscometer measured using a Cannon-Fenske type kinematic viscometer (# 400). The 5 mass% toluene solution means a toluene solution having a BR content of 5 mass%.

The molecular weight distribution (Mw / Mn) of BR is preferably 3.0 to 3.4. Within this range, both improvement in workability and improvement in wear resistance can be achieved. In the present specification, the number average molecular weight (Mn) and the weight average molecular weight (Mw) are gel permeation chromatograph (GPC) (GPC-8000 series manufactured by Tosoh Corporation), detector: differential refractometer, column: It is determined by standard polystyrene conversion based on the measured value by TSKGEL SUPERMALTPORE HZ-M manufactured by Tosoh Corporation.

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

When the rubber composition of the first invention contains BR, the content of BR is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 20% by mass in 100% by mass of the rubber component. That's it. Moreover, this content becomes like this. Preferably it is 70 mass% or less, More preferably, it is 60 mass% or less, More preferably, it is 50 mass% or less. When the amount is less than 5% by mass, the weather resistance tends to decrease, and when it exceeds 70% by mass, the rubber strength tends to decrease.

Examples of the isoprene-based rubber include isoprene rubber (IR), natural rubber (NR), and modified natural rubber. By blending isoprene-based rubber, the rubber strength can be improved.

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 of the first invention contains isoprene-based rubber (preferably NR), the content of isoprene-based rubber (preferably NR) is preferably 30% by mass or more in 100% by mass of the rubber component. More preferably, it is 40 mass% or more, More preferably, it is 50 mass% or more. Moreover, this content becomes like this. Preferably it is 70 mass% or less, More preferably, it is 65 mass% or less. If it is less than 30% by mass, the strength of the rubber may be reduced, or the rubber may not be tightly kneaded at the time of kneading and the productivity may be deteriorated. If it exceeds 70% by mass, the weather resistance may be deteriorated. .

When BR and isoprene-based rubber (preferably NR) are used in combination, the total content of BR and isoprene-based rubber (preferably NR) is preferably 70% by mass or more, more preferably 80% by mass in 100% by mass of the rubber component. % Or more, more preferably 90% by mass or more, and most preferably 100% by mass. By setting the content to 70% by mass or more, good flex crack growth resistance and fracture resistance can be achieved, and the effect of vulcanization resistance can be increased.

The rubber composition of the first present invention contains a citrus wax. This makes it possible to reduce odors while taking into consideration the impact on the environment and health, and withstands the deterioration of appearance such as tea discoloration (browning) due to the bloom of the anti-aging agent and whitening due to wax bloom. The tire performance such as fuel efficiency and bending crack growth resistance can be improved.

Citrus fruits include oranges (Valencia Orange, Navel Orange, Blood Orange, Bergamot, etc.); Grapefruits (Grapefruit, Orangero, etc.); (Natsumikan, Hassaku, Hyuganatsu, Sweety, etc.); Tangors (Iyokan, Kiyomi, Harumi, Tankan, etc.); Tanzeros (Seminor, Tangero, etc.); Unshu mikan, Ponkan, Tachibana, Kishu mandarin, etc.); Karatachi (Karatachi, Hiryu, Unryu, etc.); Kumquat (Kumquat, etc.) and the like. Among these, oranges, grapefruits, and mandarin oranges are preferable, and oranges are more preferable because they are easily available and the effects of the present invention can be more suitably obtained.

The method for collecting wax from citrus fruits is not particularly limited, but wintering (dewaxing) of oil collected by squeezing citrus flowers, seeds, fruits, fruit peels (fruit peels), solvent extraction, etc., and the fruit surface It can be obtained by solvent washing. Moreover, what is marketed for cosmetics use etc. can also be used.

Examples of the citrus wax are those extracted from citrus flowers by the above method (for example, orange flower wax) and those extracted from the skin of the fruit (fruit skin) by the above method (for example, orange peel wax). Among them, a wax extracted from the pericarp by the above-described method is more preferable, an orange peel wax is more preferable because it is easily available and the effects of the present invention can be obtained more suitably.

The above orange peel wax is a soft wax obtained after separating essential oil and orange terpene from orange oil obtained from orange peel, a complex mixture of special esters, free alcohols, free sterols, free fatty acids, hydrocarbons Consists of. In addition, it contains small amounts of flavonoids, carotenoids, glycolipids and phospholipids, and phytosterols. Free fatty acids are conventionally blended into tire rubber compositions, but generally blended alone or in polar blends such as silica when included in large amounts in normal natural waxes. While bringing about effects such as improved affinity with products and improved processability, it may lead to aging deterioration of the wax and weather resistance of the rubber composition, but when it is contained in citrus wax, It has also been found that there is no adverse effect as described above. This is presumably because the citrus-derived wax contains flavonoids, carotenoids, phytosterols, and the like.

The citrus wax may be subjected to purification treatment such as solvent extraction, distillation, adsorption, hydrogenation, and filtration as necessary.

In addition, natural wax such as beeswax or carnauba wax diluted with orange oil may be marketed as orange wax. In this specification, natural oils other than those derived from citrus are added to these citrus-derived oils. The mixed wax obtained by mixing the wax is not included in the citrus wax.

As described above, it is preferable that the citrus-derived wax contains a flavonoid and / or a carotenoid. Thereby, a weather resistance and an odor can be improved more suitably.

The citrus-derived wax has a total content of flavonoids and carotenoids in 100% by mass of citrus-derived wax, preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and further preferably 1% by mass. That's it. The upper limit of the content is not particularly limited, but is preferably 30% by mass or less, more preferably 20% by mass or less, still more preferably 10% by mass or less, and particularly preferably 5% by mass or less. Since flavonoids and carotenoids function as natural anti-aging agents, the effects of the present invention (particularly, weather resistance and odor improvement effects) can be obtained more suitably when the total content of flavonoids and carotenoids is within the above range. It is done.

As described above, the citrus-derived wax preferably contains phytosterols. Thereby, compatibility with other compounding components is further improved, fuel efficiency and flex crack growth resistance can be improved more suitably, and citrus-derived wax and anti-aging bloom are also more preferably suppressed, Appearance deterioration due to whitening and browning can be improved more suitably.

Examples of phytosterols include phytosterols, phytosterol esters, hydrogenated phytosterols, and the like, among which phytosterols and phytosterol esters are preferable.

In the citrus wax, the content of phytosterols (preferably the total content of phytosterols and phytosterol esters) is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, in particular. Preferably it is 15 mass% or more. The upper limit of the content is not particularly limited, but is preferably 50% by mass or less, more preferably 40% by mass or less, and still more preferably 30% by mass or less. Since phytosterols function as natural surfactants, if the content of phytosterols is within the above range, the effects of the present invention (particularly, deterioration in appearance due to whitening and browning, low fuel consumption, and resistance to The effect of improving the bending crack growth property is more suitably obtained.

The content of free fatty acids in the citrus wax is preferably 1% by mass or more, more preferably 3% by mass or more, and still more preferably 5% by mass or more in 100% by mass of the citrus wax. The content is preferably 30% by mass or less, more preferably 20% by mass or less, and still more preferably 15% by mass or less. If the amount is less than 1% by mass, the affinity with silica may decrease, and the workability, fuel efficiency, and resistance to flex crack growth may deteriorate. If the amount exceeds 30% by mass, the weather resistance tends to decrease.

In the present specification, the content of various components contained in the wax can be measured by gas chromatography.

The softening point of the citrus wax is preferably 35 to 85 ° C., more preferably 40 when measured as the peak top temperature of the maximum endothermic peak in an endothermic curve measured with a differential scanning calorimeter (DSC). It is -80 degreeC, More preferably, it is 45-75 degreeC. If it is less than 35 degreeC, the effect as a wax which blooms on the surface cannot fully be expressed, and there exists a tendency for a weather resistance to be inferior, and when it exceeds 85 degreeC, there exists a possibility that the weather 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 citrus wax 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 per 100 parts by mass of the rubber component. More than part by mass. The 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, and particularly preferably 12 parts by mass or less. If the amount is less than 0.1 parts by mass, the effects of the present invention may not be sufficiently obtained. If the amount exceeds 100 parts by mass, the rubber stiffness and the resistance to flex crack growth decrease, and the wax tends to bloom, resulting in whitening. There is a tendency to cause deterioration of the appearance due to.

The rubber composition according to the first aspect of the present invention may contain other waxes together with the citrus wax. For the purpose of maximizing the effects of the present invention, the wax used in combination is preferably an ester wax having a strong polarity, particularly a naturally derived wax such as beeswax, carnauba wax or rice wax.

In the rubber composition according to the first aspect of the present invention, in addition to the rubber component and the wax component, softeners such as oils commonly used in the tire industry, anti-aging agents, stearic acid, fillers, and coupling agents In addition, additives such as zinc oxide, vulcanizing agents such as sulfur, vulcanization accelerators, and the like can be appropriately blended.

As the filler, those generally used in the tire industry can be used, and examples thereof include silica, carbon black, aluminum hydroxide, clay, calcium carbonate, montmorillonite, cellulose, glass balloon, and various short fibers. Among these, 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.

As the filler, it is particularly 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. Examples of the wet process silica include Ultrasil VN3 manufactured by Degussa Co., Ltd. and Nip Seal VN3 AQ manufactured by Nippon Silica Industry Co., Ltd. Silica may be used alone or in combination of two or more.

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. Further, the _N 2 SA is preferably 250 meters ² / g or less, 210 m ² / g or less is more preferable. If it is less than 50 m ² / g, the rubber strength tends to decrease. If it exceeds 250 m ² / g, the processability tends to deteriorate.
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 200 parts by mass or less, more preferably 180 parts by mass or less, still more preferably 150 parts by mass or less, particularly preferably 100 parts by mass or less, and most preferably 50 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 can be obtained.

The rubber composition of the first aspect 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 -Mercapto type such as mercaptopropyltrimethoxysilane, vinyl type such as vinyltriethoxysilane, amino type such as 3-aminopropyltriethoxysilane, glycidoxy type of γ-glycidoxypropyltriethoxysilane, 3-nitropropyltri Examples thereof include nitro compounds such as methoxysilane and chloro compounds such as 3-chloropropyltrimethoxysilane. These may be used alone or in combination of two or more. 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 1 mass part or more with respect to 100 mass parts of silica, More preferably, it is 2 mass parts or more. Further, the content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less with respect to 100 parts by mass of silica. If the amount is less than 1 part by mass, the effect of containing a silane coupling agent may not be sufficiently obtained. If the amount exceeds 20 parts by mass, the coupling effect cannot be improved for an increase in cost, and the reinforcing property is increased. If it decreases or unreacted silane coupling agent remains, there is a risk of rubber burning during processing.

As a filler, the rubber composition of the first 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 80~150m ² / g. If the N ₂ SA of the carbon black is less than 10 m ² / g, sufficient wet grip performance cannot be obtained, and the flex crack growth resistance tends to decrease. On the other hand, when it exceeds 280 m ² / g, the dispersibility is inferior, and the flex crack growth resistance and the low fuel consumption 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, and 3-100 mass parts is more preferable. The upper limit is more preferably 50 parts by mass, and particularly preferably 30 parts by mass. If the carbon black content is within the above range, the mechanical strength of the rubber can be ensured, and good weather resistance and good compatibility with the citrus wax can be obtained.

The rubber composition of the first present invention may contain oil. By blending oil, processability can be improved and the strength of the rubber 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. Of these, vegetable oils and fats are preferred, and sunflower oil is more preferred because it is compatible with the above-mentioned citrus-derived wax and exhibits the effects of the present invention to the maximum. In the first aspect of 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 2 parts by mass or more, and further 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 90 parts by mass or less, still more preferably 80 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 first present invention preferably contains an anti-aging 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 it is less than 0.1 part by mass, sufficient weather resistance may not be obtained. The content of the anti-aging agent is preferably 10 parts by mass or less, more preferably 6 parts by mass or less, still more preferably 4 parts by mass or less, and particularly preferably 3 parts by mass or less. If it exceeds 10 parts by mass, the anti-aging agent will bloom, and the appearance of the tire may be deteriorated or the odor may be deteriorated. In the present invention, by blending the citrus wax, the weather resistance can be improved without increasing the amount of the antioxidant, so that the amount of the antioxidant can be adjusted to the above amount. And since the deterioration of the external appearance attributed to an anti-aging agent and generation | occurrence | production of an odor can be suppressed by making the amount of anti-aging agent into the said amount, the effect of this invention is acquired more suitably.

The rubber composition of the first 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.

The rubber composition of the first present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, a kneader, an open roll or the like and then vulcanizing. The rubber composition can be suitably used for a sidewall located on the tire surface and requiring weather resistance.

(Rubber composition for sidewall of the second invention)
The rubber composition for a sidewall according to the second aspect of the present invention contains a rubber component and a naturally derived wax having a total content of flavonoids and carotenoids of 0.2% by mass or more.

By blending the above natural-derived waxes, the odor can be reduced while taking into consideration the impact on the environment and health. Appearance such as tea discoloration (browning) due to bloom of the anti-aging agent and whitening due to wax bloom In addition to improving the weather resistance while suppressing the deterioration of the property, it is also possible to improve tire performance such as low fuel consumption and flex crack growth resistance. As described above, since components such as flavonoids and carotenoids act as natural anti-aging agents, particularly weather resistance and odor can be improved, weather resistance and odor can be improved more suitably. Moreover, since the said natural origin wax is a natural (plant) origin wax, the influence on an environment or health can be reduced.

The second aspect of the present invention is basically the same as the first aspect of the present invention except that the above-mentioned naturally-derived wax is blended, and therefore only the naturally-derived wax will be described below.

The naturally-derived wax is not particularly limited as long as the total content of flavonoids and carotenoids is 0.2% by mass or more, and preferably the same wax as the citrus-derived wax used in the first invention. Can be used. The only difference between the natural wax and the citrus wax is that the natural wax is not limited to citrus.

The origin of the natural wax is not limited to citrus fruits. For example, those derived from fruits and seeds other than citrus fruits such as grape and cacao, and leaves of trees such as teas can be used.

In the second aspect of the present invention, the naturally-derived wax preferably has a total content of flavonoids and carotenoids of 0.2% by mass or more and a content of phytosterols of 1% by mass or more. Thereby, the effect of this invention is acquired more suitably.

(Rubber composition for sidewall of the third invention)
The rubber composition for a sidewall of the third aspect of the present invention contains a natural wax having a rubber component and a phytosterol content of 1% by mass or more.

By blending the above natural-derived waxes, the odor can be reduced while taking into consideration the impact on the environment and health. Appearance such as tea discoloration (browning) due to bloom of the anti-aging agent and whitening due to wax bloom In addition to improving the weather resistance while suppressing the deterioration of the property, it is also possible to improve tire performance such as low fuel consumption and flex crack growth resistance. As mentioned above, phytosterols such as phytosterols and phytosterol esters act as natural surfactants, and in particular, improve compatibility with other ingredients, resulting in low fuel consumption and flex crack growth resistance. In addition to being able to improve more, the citrus-derived wax and anti-aging blooms are also more suitably suppressed, and the deterioration of appearance due to whitening and browning can be further improved. Further, it is possible to more suitably improve the low fuel consumption and the bending crack growth resistance. Moreover, since the said natural origin wax is a natural (plant) origin wax, the influence on an environment or health can be reduced.

The third aspect of the present invention is basically the same as the first aspect of the present invention except that the above-mentioned naturally-derived wax is blended, and therefore only the naturally-derived wax will be described below.

The naturally-derived wax is not particularly limited as long as the content of phytosterols is 1% by mass or more, and the same wax as the citrus-derived wax used in the first aspect of the present invention can be suitably used. The only difference between the natural wax and the citrus wax is that the natural wax is not limited to citrus. The origin of the natural wax is not limited to citrus, for example, as in the second aspect of the present invention.

In the third aspect of the present invention, the naturally derived wax preferably has a phytosterol content of 1% by mass or more and a total content of flavonoids and carotenoids of 0.2% by mass or more. Thereby, the effect of this invention is acquired more suitably.

The pneumatic tire of the present invention is produced by a usual method using the rubber composition. That is, the rubber composition blended with the above components is extruded in accordance with the shape of each tire member such as a sidewall at an unvulcanized stage, and along with other tire members, on a tire molding machine by a normal method. An unvulcanized tire is formed by molding. A tire can be manufactured by heat-pressing this unvulcanized tire in a vulcanizer.

(Pneumatic tire of the present invention)
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.

The chemicals used in the examples and comparative examples are summarized below.
NR: RSS # 3
BR: UBEPOL BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass, toluene solution viscosity (BR content is 5% by mass): 48 cps, Mw / Mn: 3.3)
Carbon black: Seast N220 manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 114 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
Wax 1: Orange peel wax manufactured by Koster Keunen (citrus-derived wax, softening point: 50 ° C.)
Wax 2: Ozoace 0355 manufactured by Nippon Seiwa Co., Ltd. (petroleum wax)
Wax 3: Carnauba wax manufactured by Toa Kasei Co., Ltd. (other naturally derived wax, softening point: about 82 ° C.)
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: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .: Noxeller NS (N-tert-butyl manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) -2-Benzothiazolylsulfenamide)

The following analysis was performed on the orange peel wax (wax 1) and carnauba wax (wax 3). The results are shown in Table 1.

(Content of each component)
The content of each component contained in the wax was measured by gas chromatography.

(Softening point)
The softening point (peak top temperature of the maximum endothermic peak) of the wax is a heat flow (mW / g) at a rate of temperature increase of 5 ° C./min from −30 ° C. to 100 ° C. using a differential scanning calorimetry (DSC) apparatus It was calculated | required by measuring.

From Table 1, the total content of flavonoids and carotenoids contained in the citrus wax is 0.2% by mass or more, and the content of phytosterols (total content of phytosterols and phytosterol esters) is 1% by mass or more. I understand that.

<Examples and Comparative Examples>
In accordance with the formulation shown in Table 2, 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 following evaluation was performed about the obtained vulcanized rubber sheet and the tire for a test.

<Rolling resistance index>
Using a viscoelastic spectrometer VES manufactured by Iwamoto Seisakusho, the loss tangent (tan δ) of the vulcanized rubber sheet was measured under conditions of a temperature of 70 ° C., an initial strain of 10%, a dynamic strain of 2%, and a frequency of 10 Hz. 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 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

<Weather resistance evaluation>
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.

<Outdoor exposure test (whitening resistance evaluation)>
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. If it was ◯, it was judged that the appearance was good.
Whitening evaluation: ○: No discoloration △: Slightly whitening ×: Vigorous whitening

<Brown discoloration test (brown resistance evaluation)>
The vulcanized rubber sheets of the examples and comparative examples were left in a place exposed to the sun for 6 months, exposed to sunlight, and the degree of browning was visually evaluated on a five-point scale. Larger numbers indicate less brown discoloration and better appearance.

<Odor evaluation>
The odor of the rubber sample after vulcanization was confirmed. The sample having an unpleasant pungent odor was rated as “X”, the sample having a slight odor as Δ, and the sample having no odor as “◯”. It was judged that it was good (the odor could be reduced) if it was O or Δ.

<Bending crack growth resistance index>
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 1 million. After bending the sample repeatedly, the length of the generated crack was measured. The measured value (length) of Comparative Example 1 was set to 100, and indexed 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

From Table 2, it contains citrus-derived wax (naturally-derived wax having a total content of flavonoids and carotenoids of 0.2% by mass or more, naturally-derived wax having a content of phytosterols of 1% by mass or more). The examples are able to reduce odors while taking into consideration the impact on the environment and health, while suppressing deterioration of the appearance such as browning due to bloom of the anti-aging agent and whitening due to bloom of wax. In addition to improving weather resistance, tire performance such as low fuel consumption and flex crack growth resistance was also improved.

Claims (11)

A rubber composition for a sidewall containing a rubber component and a wax derived from citrus fruits. The rubber composition for a sidewall according to claim 1, wherein the total content of the flavonoid and the carotenoid in the wax is 0.2% by mass or more. The rubber composition for a sidewall according to claim 1 or 2, wherein the content of the phytosterols in the wax is 1% by mass or more. The softening point of the wax is 35 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 rubber composition for side walls as described. The rubber composition for a side wall according to any one of claims 1 to 4, wherein the wax is extracted from a citrus flower and / or pericarp. The rubber composition for a sidewall according to any one of claims 1 to 5, comprising butadiene rubber. The rubber composition for a sidewall according to any one of claims 1 to 6, comprising isoprene-based rubber. The rubber composition for a sidewall according to any one of claims 1 to 7, comprising silica. A pneumatic tire having a sidewall produced using the rubber composition according to claim 1. A rubber composition for a sidewall containing a rubber component and a naturally derived wax having a total content of flavonoids and carotenoids of 0.2% by mass or more. A rubber composition for a sidewall containing a rubber component and a naturally-derived wax having a phytosterol content of 1% by mass or more.