JP2018119079A - Rubber composition for tire outer layers and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for tire outer layers that can improve ozone resistance, discoloration resistance, and chipping resistance in a balanced manner, and a pneumatic tire prepared therewith.SOLUTION: A rubber composition for tire outer layers contains, based on a rubber component 100 pts.mass containing natural rubber and butadiene rubber, aliphatic polybasic acid ester with a freezing point of -50 to -10°C of 0.5-10 pts.mass.SELECTED DRAWING: None

Description

The present invention relates to a rubber composition for a tire outer layer and a pneumatic tire produced using the rubber composition.

In general, a wax is blended in a tire outer layer member such as a sidewall in order to prevent rubber cracks and the like. Since such a wax is eluted on the rubber surface after long-term use, there is a problem that the rubber surface is whitened and the appearance is deteriorated (see Patent Document 1).

Therefore, for the purpose of achieving both ozone resistance and appearance performance, optimization of the carbon number of the wax, optimization of the blending amount, and the like have been attempted. In addition to these performances, the outer layer member is also required to have performances such as chipping resistance and fracture resistance. And nowadays, since the demand for improving tire quality is further increased, further improvements in performance such as ozone resistance, discoloration resistance, and chipping resistance are desired.

JP 2011-068732 A

An object of the present invention is to solve the above problems and provide a rubber composition for a tire outer layer that can improve ozone resistance, discoloration resistance, and chipping resistance in a well-balanced manner, and a pneumatic tire using the same.

The present invention provides a rubber composition for a tire outer layer containing 0.5 to 10 parts by mass of an aliphatic polybasic acid ester having a freezing point of −50 to −10 ° C. with respect to 100 parts by mass of a rubber component containing natural rubber and butadiene rubber. About.

In 100% by mass of the rubber component, the content of the natural rubber is preferably 15 to 75% by mass, and the content of the butadiene rubber is preferably 25 to 85% by mass.
It is preferable to contain 20 to 70 parts by mass of carbon black with respect to 100 parts by mass of the rubber component.

The carbon black preferably has a nitrogen adsorption specific surface area of 120 to 170 m ² / g.

The rubber composition is preferably a sidewall rubber composition.
The present invention also relates to a pneumatic tire produced using the rubber composition described above.

According to the present invention, a tire outer layer rubber containing 0.5 to 10 parts by mass of an aliphatic polybasic acid ester having a freezing point of −50 to −10 ° C. with respect to 100 parts by mass of a rubber component containing natural rubber and butadiene rubber. Since it is a composition, ozone resistance, discoloration resistance, and chipping resistance can be improved in a well-balanced manner.

The rubber composition for a tire outer layer of the present invention contains a predetermined amount of an aliphatic polybasic acid ester having a specific freezing point with respect to a rubber component including natural rubber and butadiene rubber.

By adding an aliphatic polybasic acid ester having a specific freezing point to a blend rubber containing natural rubber and butadiene rubber, the performance balance of ozone resistance, discoloration resistance, and chipping resistance is improved. In particular, when the aliphatic polybasic acid ester is added to a blend containing a predetermined amount of natural rubber and a blend rubber containing butadiene rubber, for example, compared to a case where it is added to a blend using another rubber component as a rubber component, The performance balance is significantly (synergistically) improved.

Similarly, when the aliphatic polybasic acid ester is added to a formulation containing carbon black having a predetermined amount or a specific surface area, for example, it is added to a formulation using carbon black having another amount or another specific surface area. Compared to the case, the performance balance is significantly (synergistically) improved.
Further, among the outer layer members, the performance balance is remarkably improved (synergistically) particularly by applying to the side wall composition.

The rubber composition of the present invention contains natural rubber (NR) and butadiene rubber (BR) as rubber components. Thereby, good chipping resistance is obtained, and the performance balance of ozone resistance, discoloration resistance, and chipping resistance is remarkably improved.

The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20, deproteinized natural rubber (DPNR), and high-purity natural rubber (HPNR) can be used.

The BR is not particularly limited. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd. BR containing syndiotactic polybutadiene crystals can be used. Among them, it is preferable to use BR having a cis content of 90% by mass or more because it has good cut chipping resistance.
The cis content of BR can be measured by infrared absorption spectrum analysis.

The content of NR is preferably 15% by mass or more, more preferably 30% by mass or more, and further preferably 40% by mass or more, in 100% by mass of the rubber component. Further, the content is preferably 75% by mass or less, more preferably 60% by mass or less, and still more preferably 50% by mass or less. By setting it within the above range, good chipping resistance can be obtained and the performance balance can be improved.

The content of BR is preferably 25% by mass or more, more preferably 40% by mass or more, and still more preferably 50% by mass or more, in 100% by mass of the rubber component. Moreover, this content becomes like this. Preferably it is 85 mass% or less, More preferably, it is 70 mass% or less, More preferably, it is 60 mass% or less. By setting it within the above range, good chipping resistance is obtained, and the performance balance is improved.

In the rubber composition, the content ratio of NR and BR (NR / BR (mass ratio)) is preferably 30/70 to 70/30, more preferably 35/65 to 60/40, from the viewpoint of the performance balance. 40 / 60-50 / 50 is still more preferable.

The total content of NR and BR is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass in 100% by mass of the rubber component. If it is less than 50% by mass, sufficient chipping resistance may not be obtained.

The rubber composition of the present invention may contain other rubber components in addition to NR and BR. Other rubber components include isoprene rubber (IR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR), and butyl rubber. (IIR), halogenated butyl rubber (X-IIR) and the like.

In the present invention, an aliphatic polybasic acid ester having a freezing point of −50 to −10 ° C. is included. When the aliphatic polybasic acid ester is used as a plasticizer, discoloration resistance and chipping resistance are improved while obtaining good ozone resistance, and the performance balance is remarkably improved.

The freezing point of the aliphatic polybasic acid ester is preferably −40 ° C. or higher, more preferably −30 ° C. or higher. The freezing point is preferably −15 ° C. or lower. Within the above range, the effects of the present invention can be obtained satisfactorily.
In the present invention, the freezing point is a value measured by the following method.
The sample was sealed in an aluminum cell, and the aluminum cell was inserted into a sample holder of a differential scanning calorimeter (manufactured by Shimadzu Corporation, DSC-60A), and then the sample holder was placed at 10 ° C./min in a nitrogen atmosphere. The endothermic peak was observed while heating to 150 ° C., and the obtained endothermic peak was taken as the freezing point.

The SP value of the aliphatic polybasic acid ester is preferably 8.4 or more, and more preferably 8.6 or more. The SP value is preferably 9.5 or less, more preferably 9.0 or less, and even more preferably 8.8 or less. By setting the SP value within the above range, compatibility with NR and BR is ensured, appearance defects are improved, and as a result, a good performance balance is obtained.
In the present invention, the SP value means a solubility parameter calculated using a Hansen formula.

The flash point of the aliphatic polybasic acid ester is preferably 100 ° C. or higher, more preferably 150 ° C. or higher, and further preferably 200 ° C. or higher. When the temperature is lower than 100 ° C., the volatility is high, and the weight is reduced during vulcanization from rubber kneading, and the planned physical properties tend to be difficult to obtain. Although an upper limit is not specifically limited, Usually, it is 250 degrees C or less. In addition, in this invention, flash point is the value measured by the Cleveland open method based on JISK2265-4: 2007.

The theoretical molecular weight (Mw) of the aliphatic polybasic acid ester is preferably 150 or more, more preferably 250 or more, and still more preferably 350 or more. When it is less than 150, the aliphatic polybasic acid ester tends to be unable to sufficiently exhibit the effect of the aliphatic polybasic acid ester due to migration to the adjacent member or volatilization. The Mw is preferably 1000 or less, more preferably 750 or less, and even more preferably 500 or less. If it exceeds 1000, the plasticizing effect may be reduced.

Examples of the aliphatic polybasic acid ester include aliphatic dibasic acid esters and aliphatic tribasic acid esters. Among these, aliphatic dibasic acid esters such as adipic acid ester, azelaic acid ester, sebacic acid ester, maleic acid ester, and fumaric acid ester are preferable because the effects of the present invention can be obtained more favorably.

〔式（１）中、Ｒ^１１は、２価の飽和又は不飽和炭化水素基を表す。Ｒ^１２及びＲ^１３は、同一又は異なって、分岐若しくは非分岐のアルキル基、又は−（Ｒ^１４−Ｏ）_ｎ−Ｒ^１５（ｎ個のＲ^１４は、同一又は異なって、分岐若しくは非分岐のアルキレン基を表す。Ｒ^１５は、分岐若しくは非分岐のアルキル基を表す。ｎは整数を表す。）で表される基を表す。〕 As such aliphatic dibasic acid ester, for example, a compound represented by the following formula (1) can be preferably used. When a compound having a high SP value is used, the Tg tends to be high and the fracture characteristics tend to be impaired. However, when a compound represented by the following formula (1) is used, since the flexibility of the rubber is not impaired, the characteristics required for the sidewalls It is possible to promote the dissolution of the wax without impairing the resistance.

[In formula (1), R ¹¹ represents a divalent saturated or unsaturated hydrocarbon group. R ¹² and R ¹³ are the same or different and are branched or unbranched alkyl groups, or — (R ¹⁴ —O) _n —R ¹⁵ (wherein n R ^{14 s} are the same or different and are branched or unbranched). Represents an alkylene group, R ¹⁵ represents a branched or unbranched alkyl group, and n represents an integer. ]

The divalent saturated or unsaturated hydrocarbon group for R ¹¹ may be branched or unbranched, and examples thereof include an alkylene group, an alkenylene group, and an arylene group. The saturated or unsaturated hydrocarbon group preferably has 1 to 10 carbon atoms, more preferably 2 to 6 carbon atoms. Specifically, as an alkylene group, a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, etc., an alkenylene group, a vinylene group, 1- Examples of arylene groups such as propenylene group and 2-propenylene group include phenylene group, tolylene group, and xylylene group.

About R < ¹² > and R < ¹³ >, carbon number of a branched or unbranched alkyl group becomes like this. Preferably it is 1-15, More preferably, it is 4-10. Specifically, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, iso-butyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, An octyl group, a nonyl group, a decyl group, etc. are mentioned.

Regarding the group represented by — (R ¹⁴ —O) _n —R ¹⁵ of R ¹² and R ¹³ , the branched or unbranched alkylene group of R ¹⁴ preferably has 1 to 3 carbon atoms. The carbon number of the branched or unbranched alkyl group of R ¹⁵ is preferably 1 to 10, more preferably 2 to 6. Specific examples of the alkylene group and the alkyl group include those described above. The integer n is preferably 1 to 10, more preferably 1 to 5, and still more preferably 1 to 3.

Among them, it is preferable that at least one of R ¹² and ¹³ is a group represented by — (R ¹⁴ —O) _n —R ¹⁵ from the viewpoint that the effects of the present invention can be obtained better. The group is more preferable.

Preferable examples of the aliphatic dibasic acid ester represented by the formula (1) include those represented by-(R ¹⁴ -O) _n -R ¹⁵ such as bis [2- (2-butoxyethoxy) ethyl] adipate. And bis (alkoxyalkoxyalkyl) adipate having the above group. Other examples include di-n-butyl adipate and diisobutyl adipate. These may be used alone or in combination of two or more.

Content of the said aliphatic polybasic acid ester is 0.5 mass part or more with respect to 100 mass parts of rubber components, Preferably it is 1 mass part or more, More preferably, it is 3 mass parts or more. There exists a possibility that the effect of this invention may not be acquired as it is less than 0.5 mass part. Moreover, this content is 10 mass parts or less, Preferably it is 8 mass parts or less, More preferably, it is 6 mass parts or less. When it exceeds 10 parts by mass, the discoloration resistance may be deteriorated.

The rubber composition of the present invention preferably contains carbon black from the viewpoint that good ozone resistance and chipping resistance are obtained and the balance is remarkably improved. Examples of carbon black include carbon black produced by an oil furnace method, and two or more types having different colloidal characteristics may be used in combination. Specific examples include GPF, HAF, ISAF, and SAF. Among these, SAF is preferable.

Nitrogen adsorption specific surface area _(N 2 SA) of carbon black is preferably not less than 120 m ² / g, more preferably at least 125m ² / g, more preferably more than 130m ² / g. The N ₂ SA is preferably 170 m ² / g or less, more preferably 160 m ² / g or less, and still more preferably 155 m ² / g or less. By setting it within the above range, good chipping resistance is obtained, and the performance balance is improved.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required based on JISK6217-2: 2001.

The carbon black dibutyl phthalate (DBP) oil absorption is preferably 90 ml / 100 g or more, more preferably 105 ml / 100 g or more, and even more preferably 110 ml / 100 g or more. The DBP is preferably 150 ml / 100 g or less, more preferably 135 ml / 100 g or less, and still more preferably 125 ml / 100 g or less. By setting it within the above range, good chipping resistance is obtained, and the performance balance is improved.
The DBP of carbon black is measured according to JIS K 6217-4: 2001.

The content of carbon black is preferably 20 parts by mass or more, more preferably 30 parts by mass or more with respect to 100 parts by mass of the rubber component. Moreover, this content becomes like this. Preferably it is 70 mass parts or less, More preferably, it is 60 mass parts or less. If it is less than 20 parts by mass, chipping resistance may be deteriorated, and if it exceeds 70 parts by mass, workability may be deteriorated.

In the rubber composition of the present invention, as a reinforcing filler, those conventionally used in rubber compositions for tires such as silica, calcium carbonate, alumina, clay and talc can be used in addition to carbon black.

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

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

The content of the wax is preferably 0.5 parts by mass or more, and more preferably 1.0 part by mass or more with respect to 100 parts by mass of the rubber component. Moreover, this content becomes like this. Preferably it is 6.0 mass parts or less, More preferably, it is 4.5 mass parts or less. If the amount is less than 0.5 parts by mass, the effect of ozone resistance may not be sufficiently exhibited. If the amount exceeds 6.0 parts by mass, bloom may occur.

In addition to the above components, the rubber composition of the present invention contains compounding agents generally used in the tire industry, such as zinc oxide, stearic acid, anti-aging agents, sulfur vulcanizing agents, vulcanization acceleration. You may mix | blend materials, such as an agent, suitably.

Examples of the vulcanization accelerator include sulfenamide-based, thiazole-based, thiuram-based, and guanidine-based vulcanization accelerators. Among them, thiazole-based and sulfenamide-based vulcanization accelerators can be preferably used.

Examples of the thiazole vulcanization accelerator include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, and the like. Among them, 2-mercaptobenzothiazole is preferable. Examples of the sulfenamide vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N Examples include '-dicyclohexyl-2-benzothiazolylsulfenamide (DZ), and TBBS is preferable because of its suitable scorch time and vulcanization rate.

The content of the vulcanization accelerator 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. Moreover, this content becomes like this. Preferably it is 10 mass parts or less, More preferably, it is 5 mass parts or less. If the amount is less than 0.1 parts by mass, sufficient vulcanization may not be achieved. If the amount exceeds 10 parts by mass, sufficient scorch time may not be ensured.

The rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading the above components with a Banbury mixer, kneader, open roll or the like and then vulcanizing. In particular, the rubber composition can be suitably used for a sidewall of a pneumatic tire.

The pneumatic tire of the present invention is 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. To form an unvulcanized tire. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

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

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
BR: Ubepol BR150B manufactured by Ube Industries, Ltd. (cis content: 97% by mass)
NR: TSR20
SBR: SBR1502 manufactured by JSR Corporation
Carbon Black 1: Seast 9 (SAF, N ₂ SA: 142 m ² / g, DBP oil absorption: 115 ml / 100 g) manufactured by Tokai Carbon Co., Ltd.
Carbon Black 2: Show Black N330 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 75 m ² / g, DBP oil absorption: 102 ml / 100 g)
Oil: Diana Process AH-24 manufactured by Idemitsu Kosan Co., Ltd.
Plasticizer TOP: manufactured by Daihachi Chemical Industry Co., Ltd., tris (2-ethylhexyl) phosphate (normal phosphate ester, freezing point: −70 ° C. or lower, flash point: 204 ° C., SP value: 8.20, Mw: 435)
Plasticizer BXA-N: manufactured by Daihachi Chemical Industry Co., Ltd., bis [2- (2-butoxyethoxy) ethyl] adipate (aliphatic dibasic acid ester, freezing point: -19 ° C, flash point: 207 ° C, SP value: 8 .70, Mw: 435)
Zinc oxide: Zinc oxide stearic acid manufactured by Mitsui Mining & Smelting Co., Ltd .: Stearic acid “Kashiwa” manufactured by NOF Corporation
Anti-aging agent: Antigen 6C (N-phenyl-N ′-(1,3-dimethyl) -p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Wax: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Sulfur: Powder sulfur vulcanization accelerator NS manufactured by Karuizawa Sulfur Co., Ltd. NS: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator M: Noxeller M (2-mercaptobenzothiazole) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

<Examples and Comparative Examples>
According to the compounding prescription shown in Tables 1-3, compounding materials other than sulfur and a vulcanization accelerator were kneaded using a 1.7 L Banbury manufactured by Kobe Steel. Sulfur and a vulcanization accelerator were added to the obtained kneaded product and kneaded using an open roll to obtain an unvulcanized rubber composition.
The obtained unvulcanized rubber composition was press vulcanized at 150 ° C. for 30 minutes to obtain a vulcanized rubber composition.
Further, the obtained unvulcanized rubber composition was molded into a sidewall shape, bonded together with other tire members on a tire molding machine, vulcanized at 150 ° C. for 30 minutes, and a test tire (tire Size: 195 / 65R15) was obtained.

The following evaluation was performed about the obtained vulcanized rubber composition and the tire for a test. The results are shown in Tables 1-3.

(Discoloration resistance test)
The test tire was allowed to stand in an oven at 40 ° C. for 2 weeks, and then visually evaluated according to the following criteria.
1: The color is changed to white as a whole.
2: About 30% of the whole has turned white.
3: It is dull overall.
4: About 30% is dull.
5: No discoloration.

(Tensile test (chipping resistance))
Based on JIS K6251: 2010, a dumbbell-shaped No. 3 test piece was prepared from the obtained vulcanized rubber composition, a tensile test was performed using each vulcanized rubber composition, and the breaking strength TB (MPa), The elongation at break EB (%) was measured. Then, TB × EB / 2 (MPa ·%) was calculated as the fracture characteristic, and the fracture characteristic of Comparative Example 1 was indicated as 100 as an index. It shows that it is excellent in chipping resistance, so that an index | exponent is large.

(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 test was performed for 48 hours under the condition of ± 2%, and visually evaluated according to the following criteria.
1: Cracks or cuts of 3 mm or more have occurred.
2: A crack with deep and large cracks (less than 1 to 3 mm) is observed.
3: A crack is deep and relatively large (less than 1 mm).
4: What cannot be seen with the naked eye but can be confirmed with a 10x magnifier.
5: There is no crack that can be confirmed with the naked eye and a 10x magnifier.

From Table 1, ozone resistance, discoloration resistance, and chipping resistance were improved in a well-balanced manner by adding a predetermined amount of the aliphatic polybasic acid ester to NR and BR. Furthermore, from Tables 2 and 3, compared to the case where the aliphatic polybasic acid ester is added to the SBR blend, the low N ₂ SA and the low DBP carbon black blend, the blend using NR, BR, and the predetermined carbon black However, it was also revealed that the performance balance of ozone resistance, discoloration resistance, and chipping resistance was remarkably improved (synergistically).

Claims (6)

A rubber composition for a tire outer layer containing 0.5 to 10 parts by mass of an aliphatic polybasic acid ester having a freezing point of −50 to −10 ° C. with respect to 100 parts by mass of a rubber component containing natural rubber and butadiene rubber. The rubber composition for a tire outer layer according to claim 1, wherein a content of the natural rubber is 15 to 75% by mass and a content of the butadiene rubber is 25 to 85% by mass in 100% by mass of the rubber component. The rubber composition for a tire outer layer according to claim 1 or 2, comprising 20 to 70 parts by mass of carbon black with respect to 100 parts by mass of the rubber component. The carbon black according to claim 3 tire outer layer rubber composition according nitrogen adsorption specific surface area of 120~170m ² / g. The rubber composition for a tire outer layer according to any one of claims 1 to 4, which is a rubber composition for a sidewall. The pneumatic tire produced using the rubber composition in any one of Claims 1-5.