JP6297152B2 - Rubber composition for tire sidewall - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a rubber composition for a tire sidewall that improves the appearance of a tire to a conventional level or more while ensuring excellent ozone resistance.

  Conventionally, it is known that a rubber composition containing natural rubber or conjugated diene rubber undergoes oxidative degradation in the presence of ozone, causing cracks (ozone cracks) on the surface or lowering physical properties. In particular, ozone degradation is a major problem in the sidewalls of pneumatic tires.

  In order to prevent oxidative deterioration due to ozone, a rubber or an amine-based antioxidant is added to the rubber composition forming the sidewall portion. Thereby, generation | occurrence | production and progress of an ozone crack can be suppressed. However, if the wax migrates to the surface of the sidewall part and crystallizes, it may cause poor appearance such as whitening, and if the amine-based anti-aging agent migrates to the surface, problems such as browning will occur. There was a problem of getting worse.

  On the other hand, Patent Document 1 improves the tire appearance by suppressing whitening and browning by blending a specific nonionic surfactant with a rubber component made of natural rubber and a conjugated diene-olefin copolymer. Propose to be. However, the demands of consumers on the appearance of pneumatic tires are increasing in recent years, and there is a further demand for making the tire appearance more excellent without whitening or browning.

Japanese Unexamined Patent Publication No. 2013-170233

  An object of the present invention is to provide a rubber composition for a tire side wall that improves the tire appearance to a conventional level or more while ensuring excellent ozone resistance.

（式中、Ｒ¹は炭素数５〜２１の炭化水素基、Ｒ²はエチレン基および／またはプロピレン基、Ｒ³はメチル基またはエチル基を表し、ｎは１〜８の整数である。）The rubber composition for a tire sidewall according to the present invention that achieves the above-described object is obtained by adding 0.5% paraffin wax to 100 parts by weight of a diene rubber containing at least 20 to 80% by weight of natural rubber and 20 to 80% by weight of butadiene rubber. 10 to 10 parts by weight, 0.5 to 10 parts by weight of an amine-based antioxidant, and 0.2 to 5 parts by weight of a polyalkylene glycol carboxylic acid alkyl ester represented by the following general formula (I) .

(In the formula, R ¹ represents a hydrocarbon group having 5 to 21 carbon atoms, R ² represents an ethylene group and / or a propylene group, R ³ represents a methyl group or an ethyl group, and n is an integer of 1 to 8.)

In the general formula (I), R ² is preferably an ethylene group, and n is preferably an integer of 2 to 6.

  The rubber composition for tire sidewall according to the present invention has excellent ozone resistance because a specific amount of paraffin wax and an amine anti-aging agent are blended with a diene rubber including natural rubber and butadiene rubber. Can do. In addition, since a specific polyalkylene glycol carboxylic acid alkyl ester is blended, whitening caused by wax and browning caused by amine-based anti-aging agent can be suppressed, and the tire appearance can be improved.

By making R ² described in the general formula (I) an ethylene group, whitening can be more efficiently suppressed. Moreover, the effect which suppresses whitening and browning can be made more excellent by making n into an integer of 2-6.

FIG. 1 is a partial cross-sectional view in the tire meridian direction showing an example of an embodiment of a pneumatic tire using the rubber composition for a tire sidewall of the present invention.

  FIG. 1 shows an example of an embodiment of a pneumatic tire using a rubber composition for a tire sidewall. The pneumatic tire includes a tread portion 1, a sidewall portion 2, and a bead portion 3.

  In FIG. 1, the pneumatic tire has two carcass layers 4 in which reinforcing cords extending in the tire radial direction are arranged between the left and right bead portions 3 at predetermined intervals in the tire circumferential direction and embedded in a rubber layer. The both ends are folded back from the inner side in the tire axial direction so as to sandwich the bead filler 6 around the bead core 5 embedded in the bead part 3. An inner liner layer 7 is disposed inside the carcass layer 4. On the outer peripheral side of the carcass layer 4 of the tread portion 1, there are arranged two belt layers 8 in which reinforcing cords inclined and extending in the tire circumferential direction are arranged at predetermined intervals in the tire axial direction and embedded in the rubber layer. It is installed. The reinforcing cords of the two belt layers 8 intersect each other with the inclination directions with respect to the tire circumferential direction being opposite to each other. A belt cover layer 9 is disposed on the outer peripheral side of the belt layer 8. A tread portion 1 is formed of a tread rubber layer 10 on the outer peripheral side of the belt cover layer 9. A side rubber layer 11 is disposed outside the carcass layer 4 of each sidewall portion 2, and a rim cushion rubber layer 12 is provided outside the folded portion of the carcass layer 4 of each bead portion 3. The side rubber layer 11 is preferably composed of the rubber composition for a tire sidewall of the present application.

  In the rubber composition for a tire sidewall according to the present invention, the rubber component is a diene rubber, which necessarily includes natural rubber and butadiene rubber, and contains these as main components. The phrase “consisting mainly of natural rubber and butadiene rubber” means that the total content of natural rubber and butadiene rubber is 50% by weight or more with respect to 100% by weight of diene rubber. The total of natural rubber and butadiene rubber is preferably 50 to 100% by weight, more preferably 65 to 100% by weight.

  In the present invention, the content of the natural rubber is 20 to 80% by weight, preferably 25 to 70% by weight, and more preferably 30 to 65% by weight in 100% by weight of the diene rubber. The content of butadiene rubber is 10 to 80% by weight, preferably 15 to 75% by weight, and more preferably 35 to 70% by weight in 100% by weight of diene rubber. By making the contents of natural rubber and butadiene rubber within the above-mentioned ranges and using them as the main component of the diene rubber, it is possible to make the rubber composition excellent in ozone resistance and bending fatigue.

  In the present invention, other diene rubbers other than natural rubber and butadiene rubber can be contained. Examples of other diene rubbers include isoprene rubber, styrene butadiene rubber, acrylonitrile butadiene rubber, butyl rubber, halogenated butyl rubber, ethylene-propylene-diene rubber, and chloroprene rubber. Of these, styrene butadiene rubber, ethylene-propylene-diene rubber, and halogenated butyl rubber are preferable. The content of the other diene rubber is preferably 0 to 50% by weight, more preferably 0 to 35% by weight in 100% by weight of the diene rubber.

  The rubber composition for a tire sidewall of the present invention can suppress the occurrence and progress of ozone cracks by blending paraffin wax.

  The paraffin wax is not particularly limited, and is preferably an aliphatic saturated hydrocarbon having 15 to 55 carbon atoms, more preferably 23 to 45 carbon atoms, still more preferably a linear aliphatic having 32 to 45 carbon atoms. It is good that it is a saturated hydrocarbon. The branched aliphatic saturated hydrocarbon may be included in part.

  The blending amount of the paraffin wax is 0.5 to 10 parts by weight, preferably 1.0 to 6.0 parts by weight with respect to 100 parts by weight of the diene rubber. Generation | occurrence | production and progress of an ozone crack cannot fully be suppressed as the compounding quantity of paraffin wax is less than 0.5 weight part. Moreover, when the compounding quantity of paraffin wax exceeds 10 weight part, precipitation and crystallization on the surface of a rubber composition will become remarkable, and the whitening resulting from paraffin wax cannot be suppressed.

  The rubber composition for a tire sidewall of the present invention can suppress the occurrence and progress of ozone cracks particularly during dynamic use by incorporating an amine-based anti-aging agent.

  Examples of the amine-based antiaging agent include alkylated diphenylamine, 4,4′-bis (α, α-dimethylbenzyl) diphenylamine, N, N′-diphenyl-p-phenylenediamine, N-phenyl-N′-isopropyl- p-phenylenediamine, N-phenyl-N'-1,3-dimethylbutyl-p-phenylenediamine, p- (p-toluenesulfonylamido) diphenylamine, N-phenyl-N '-(3-methacryloyloxy-2 -Hydroxypropyl) -p-phenylenediamine and the like, among which N-phenyl-N'-1,3-dimethylbutyl-p-phenylediamine is particularly preferable.

  The compounding amount of the amine antioxidant is 0.5 to 10 parts by weight, preferably 1.0 to 5.0 parts by weight, based on 100 parts by weight of the diene rubber. Generation | occurrence | production and progress of the ozone crack in the tire which started use as the compounding quantity of an amine type anti-aging agent being less than 0.5 weight part cannot fully be suppressed. Moreover, when the compounding quantity of an amine type anti-aging agent exceeds 10 weight part, the bloom to the surface of a rubber composition will become remarkable and the browning of a surface external appearance cannot be suppressed.

（式中、Ｒ¹は炭素数５〜２１の炭化水素基、Ｒ²はエチレン基および／またはプロピレン基、Ｒ³はメチル基またはエチル基を表し、ｎは１〜８の整数である。）The rubber composition for a tire sidewall of the present invention can suppress whitening and browning of the tire appearance by blending a polyalkylene glycol carboxylic acid alkyl ester represented by the following general formula (I). The polyalkylene glycol carboxylic acid alkyl ester represented by the general formula (I) balances the molecular weight close to that of the wax and the appropriate hydrophilicity and hydrophobicity. When mixed with the above-mentioned paraffin wax, the paraffin wax Compatible with. For this reason, it is suppressed that the paraffin wax transferred to the surface of the rubber composition is cured (crystallized) and imparts flexibility to the paraffin wax. For this reason, when the rubber surface is rubbed, paraffin wax crystals are rolled up, and the occurrence of irregular reflection of light and whitening can be reduced as much as possible. Moreover, since the protective action of paraffin wax is maintained, ozone resistance is ensured. Since the polyalkylene glycol carboxylic acid alkyl ester migrates to the surface of the rubber composition together with the paraffin wax earlier than the amine-based anti-aging agent, the surface appearance is brown to suppress the migration of the amine-based anti-aging agent to the outermost surface. It can also be prevented from changing.

(In the formula, R ¹ represents a hydrocarbon group having 5 to 21 carbon atoms, R ² represents an ethylene group and / or a propylene group, R ³ represents a methyl group or an ethyl group, and n is an integer of 1 to 8.)

R ¹ is a hydrocarbon group having 5 to 21 carbon atoms, and may be either a saturated hydrocarbon group or an unsaturated hydrocarbon group. R ¹ is preferably a saturated or unsaturated hydrocarbon group having 5 to 19 carbon atoms, more preferably 9 to 19 carbon atoms. When R ^{1 has} a carbon number of 5 or more, more preferably 9 or more, transpiration during rubber kneading is less likely to occur, and when the carbon number is 21 or less, more preferably 19 or less, bleed with the wax and whitening derived from the wax. Can be suppressed.

Specific examples of the fatty acid corresponding to the fatty acid part (R ¹ CO part) of the general formula (I) include caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, myristic acid, palmitic acid, and palmitolein. Acid, stearic acid, oleic acid, linoleic acid, linolenic acid, palm-derived C18 mixed fatty acid, rapeseed-derived C18 mixed fatty acid, palm-derived C8-C14 mixed fatty acid, palm kernel-derived C8-C18 mixed fatty acid, arachidic acid, behenic acid, etc. Can be mentioned.

R ² is an ethylene group (—CH ₂ CH ₂ —) and / or a propylene group (—CH ₂ CH ₂ CH ₂ —). R ² is preferably an ethylene group from the viewpoint of suppressing the whitening of the tire appearance.

The oxyalkylene group (R ² O) may be any one of an ethylene oxide group and a propylene oxide group, or two types of an ethylene oxide group and a propylene oxide group may be included. Only an ethylene oxide group is preferable in terms of suppressing whitening of the tire appearance. When there are two oxyalkylene groups, the ethylene oxide group and the propylene oxide group may be random addition or block addition.

R ³ is a methyl group or an ethyl group.

n is the added mole number of the oxyalkylene group (R ² O), and is an integer of 1 to 8. When R ² O is an oxyethylene group and n exceeds 8, the hydrophilicity of the polyalkylene glycol carboxylic acid alkyl ester becomes strong, so that it is not compatible with the wax and whitening cannot be suppressed. In addition, tea changes caused by amine-based anti-aging agents also occur. Furthermore, since it is easily dissolved in water, there is a concern that it may be washed away by water such as rain. When R ² O is an propylene group and n exceeds 8, the reason is not known, but whitening cannot be suppressed. When n is less than 1, the hydrophobicity of the polyalkylene glycol carboxylic acid alkyl ester becomes strong, and the effect of suppressing the curing (crystallization) of the paraffin wax cannot be obtained, so that the whitening caused by the paraffin wax is suppressed. I can't. Therefore, n is an integer of 1 to 8, preferably an integer of 1 to 6, more preferably an integer of 2 to 6, from the viewpoint of having an appropriate balance between hydrophobicity and hydrophilicity and suppressing whitening. Good. The polyalkylene glycol carboxylic acid alkyl ester used in the present invention acts on paraffin wax by appropriately adjusting the balance between hydrophobicity and hydrophilicity, that is, precipitates on the tire surface while being compatible with paraffin wax. Appearance defects due to whitening can be reduced by suppressing crystallization and softening.

The HLB value of the polyalkylene glycol carboxylic acid alkyl ester represented by the general formula (I) is not particularly limited, but is preferably 2.0 to 13.0, more preferably 4.0 to 10. 0 is good. If the HLB value is less than 2.0, the hydrophobicity becomes too strong and whitening cannot be suppressed. On the other hand, if the HLB value exceeds 13.0, the hydrophilicity becomes too strong, whitening cannot be suppressed, and browning also occurs. In this specification, an HLB value shall be defined by the Griffin method, and is calculated | required by the following general formula.
HLB = 20 × total formula weight of hydrophilic part / molecular weight The HLB value takes a value from 0 to 20, and the closer to 0, the higher the hydrophobicity, and the closer to 20, the higher the hydrophilicity.

Examples of such polyalkylene glycol carboxylic acid alkyl esters include C ₇ H ₁₅ —COO— (C ₂ H ₄ O) ₃ —CH ₃ , C ₇ H ₁₅ —COO— (C ₂ H ₄ O) ₅ —CH. ₃ , C ₇ H ₁₅ —COO— (C ₃ H ₆ O) ₃ —CH ₃ , C ₉ H ₁₉ —COO— (C ₂ H ₄ O) ₃ —CH ₃ , C ₁₁ H ₂₃ —COO— (C _{2 H 4 O) 3 -CH 3,} C 11 H 23 -COO- (C 2 H 4 O) 5 -CH 3, C 11 H 23 -COO- (C 2 H 4 O) 7 -CH 3, C 11 H _{23 -COO- (C 3 H 6 O} ) 3 -CH 3, C 11 H 23 -COO- (C 3 H 6 O) 5 -CH 3, C 11 H 23 -COO- (C 2 H 4 O) 3 — (C ₃ H ₆ O) ₂ —CH ₃ , C ₁₁ H ₂₃ —COO— (C ₂ H ₄ O) ₃ —C ₂ H ₅ , C ₁₃ H ₂₇ —COO— (C ₂ H ₄ O) ₃ — _{CH 3, C 15 H 31 -COO-} (C 2 H 4 O) ₃ —CH ₃ , C ₁₇ H ₃₃ —COO— (C ₂ H ₄ O) ₃ —CH ₃ , C ₁₇ H ₃₃ —COO— (C ₂ H ₄ O) ₅ —CH ₃ , C18-derived fatty acid remainder— _{O- (C 2 H 4 O)} 3 -CH 3, C18 -derived fatty acid remainder _{-O- (C 2 H 4 O)} 5 -CH 3, C18 -derived fatty acid remainder _{-O- (C 2 H 4 O)} 7 -CH ₃ , C18-derived fatty acid remainder —O— (C ₃ H ₆ O) ₃ —CH ₃ , C ₁₉ H ₃₉ —COO— (C ₂ H ₄ O) ₃ —CH _{3, and the} like. These may be one kind or a mixture of two or more kinds. Further, the C18-derived fatty acid part is (R ¹ CO), and indicates a mixed fatty acid derived from animals and plants whose main component is that having 18 carbon atoms.

  The compounding amount of the polyalkylene glycol carboxylic acid alkyl ester is 0.2 to 5 parts by weight, preferably 1.0 to 3.0 parts by weight, per 100 parts by weight of the diene rubber. When the blending amount of the polyalkylene glycol carboxylic acid alkyl ester is less than 0.2 parts by weight, whitening and browning of the surface of the rubber composition cannot be sufficiently suppressed. If the blending amount of the polyalkylene glycol carboxylic acid alkyl ester exceeds 5 parts by weight, the whitening of the surface cannot be suppressed.

  The polyalkylene glycol carboxylic acid alkyl ester is not particularly limited and can be produced by a conventionally known method according to the purpose. For example, a method by transesterification of fats and oils and polyalkylene glycol alkyl ether, It can be produced by a method of esterification with a glycol alkyl ether, a method of transesterification of a fatty acid alkyl ester and a polyalkylene glycol alkyl ether, a method of directly inserting an alkylene oxide into a fatty acid alkyl ester, and the above production method Can also be manufactured.

  The rubber composition for tire sidewall of the present invention is within the range not impairing the achievement of the object of the present invention, for example, carbon black, silica, clay, mica, talc, calcium carbonate, aluminum hydroxide, aluminum oxide, titanium oxide. A reinforcing filler such as can be blended.

  For tire sidewall rubber compositions, vulcanization or crosslinking agents, vulcanization accelerators, anti-aging agents, plasticizers, processing aids, liquid polymers, thermosetting resins, etc. are generally used for tire sidewall rubber compositions. Various kinds of compounding agents that are commonly used can be blended. Such a compounding agent can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or crosslinking. The compounding amounts of these compounding agents can be conventional conventional compounding amounts as long as the object of the present invention is not violated. The rubber composition for a tire sidewall can be produced by kneading and mixing the above components using a known rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

  20 kinds of rubber compositions for tire sidewalls (Examples 1 to 12, Comparative Examples 1 to 8) having the compounding agents shown in Table 3 as common compounding and the compositions shown in Tables 1 and 2 are accelerated with sulfur and vulcanization. The master batch which knead | mixed the component except an agent for 5 minutes with a 1.7-liter closed Banbury mixer was discharge | released, and it was made to cool at room temperature. The master batch was returned to a 1.7 L closed Banbury mixer, and sulfur and a vulcanization accelerator were added and mixed to prepare a rubber composition for a tire sidewall. In addition, the compounding quantity of the compounding agent described in Table 3 was shown by the weight part with respect to 100 weight part of diene rubber described in Table 1,2.

  Twenty kinds of obtained rubber compositions were press vulcanized at 170 ° C. for 10 minutes in a predetermined mold to prepare test pieces made of a rubber composition for a tire sidewall. The test specimens were evaluated for whitening resistance, tea denaturation resistance and ozone resistance by the following methods.

Whitening Resistance After the obtained test piece was allowed to stand for 1 week for condition adjustment, the surface of the test piece was visually observed, and the whitening state was evaluated in five stages based on the following criteria. The obtained results are shown in the “whitening resistance” column of Tables 1 and 2. A larger index means better whitening resistance and less whitening.
5: No whitening is observed on the surface of the test piece.
4: Almost no whitening is observed on the surface of the test piece.
3: No whitening is observed on the surface of the test piece.
2: Whitening is observed partially or slightly on the surface of the test piece.
1: Overall whitening is observed on the surface of the test piece.

Tea-resistant denaturation After the obtained test piece was allowed to stand at 40 ° C. for 2 weeks for conditioning, the color tone (L ^* a ^* b ^* ) of the test piece was measured according to JIS Z8729 according to CIE 1976 (L ^* , a ^* , b ^* ) The b ^* values of the yellow and blue axes in the color space (positive values are closer to yellow) are shown in the “Browning resistance” column of Tables 1 and 2. A smaller index of 3 or less means better tea resistance.

Ozone resistance A JIS No. 3 dumbbell-shaped test piece based on JIS K6251 was cut out from the obtained test piece. The test piece was elongated by 20% and ozone-degraded for 24 hours at an ozone concentration of 50 pphm and 40 ° C., and then the presence or absence of cracks (ozone cracks) on the surface of the test piece was visually evaluated. The obtained results indicate the presence or absence of ozone cracks in the column of “Ozone resistance” in Table 1.

The types of raw materials used in Tables 1 and 2 are shown below.
NR: natural rubber, SIR-20
-BR: Butadiene rubber, Nipol BR1220 manufactured by Nippon Synthetic Rubber
EPDM: ethylene propylene diene rubber, Esprene 505A manufactured by Sumitomo Chemical Co., Ltd.
Amine-based anti-aging agent: N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine, Ozonon 6C manufactured by Seiko Chemical Co., Ltd.
Paraffin wax: Paraffin wax having 20 to 50 carbon atoms, Sunnock N manufactured by Ouchi Shinsei Chemical Co., Ltd.

Polyalkylene glycol carboxylic acid alkyl esters (esters 1 to 11 described in Tables 1 and 2) were prepared by the following production methods, respectively.
Ester _{1: C 5 H 11 -COO- (} C 2 H 4 O) 3 -CH 3, HLB = 10.1
In a 5 L four-necked flask, 1432 g of methyl caproate (manufactured by Junsei Kagaku), 1724 g of triethylene glycol monomethyl ether (trade name “MTG”, manufactured by Nippon Emulsifier Co., Ltd.), tetraisopropoxy titanate (TPT) catalyst 5 g was charged and nitrogen substitution was performed. Then, while circulating nitrogen at a flow rate of 1 mL / min, the liquid temperature was raised to 140 ° C. to conduct a transesterification reaction, and methanol produced by the reaction was removed by distillation. After removing methanol, the temperature was further increased to 160 ° C. while gradually reducing the pressure to 1.0 kPa to obtain crude product (1A) with unreacted methyl caproate and triethylene glycol monomethyl ether being 3% or less. .
Next, 30 g of KYOWARD 500SH was added to 1500 g of the crude product (1A), and the mixture was stirred for 1 hour while maintaining the liquid temperature at 100 ° C. to perform the catalyst adsorption treatment. Thereafter, 7.5 g of Hyflo Supercell was further added as a filter aid, stirred for 10 minutes and uniformly dispersed, and then subjected to pressure filtration at 80 ° C. to obtain ester 1.

Ester 2: C ₁₁ H ₂₃ —COO— (C ₂ H ₄ O) ₃ —CH ₃ , HLB = 7.6
In place of methyl caproate, the amount of methyl laurate (trade name “Pastel M12”, manufactured by Lion Corporation) was changed to 1714 g, the amount of triethylene glycol monomethyl ether was changed to 1313 g, and the transesterification reaction temperature was set to 190 ° C. The ester 2 was obtained in the same manner as the ester 1 except that the temperature was raised to 200 ° C. while gradually reducing the pressure to 1.0 kPa after removing the methanol.

Ester 3: C ₁₉ H ₃₉ —COO— (C ₂ H ₄ O) ₃ —CH ₃ , HLB = 5.8
Instead of methyl caproate, the amount of methyl arachidate (manufactured by Tokyo Chemical Industry Co., Ltd.) was 2128 g, the amount of triethylene glycol monomethyl ether was 985 g, the transesterification temperature was 190 ° C., and methanol Ester 3 was obtained in the same manner as Ester 1 except that the temperature was raised to 200 ° C. while gradually reducing the pressure to 1.0 kPa.

Ester 4: C ₁₁ H ₂₃ —COO— (C ₂ H ₄ O) ₇ —CH ₃ , HLB = 11.8
Alumina hydroxide and magnesia (Kyowa Chemical Industry Kyoward 300SN) having a chemical formula of 2.5 MgO, Al ₂ O ₃ and nH ₂ O were calcined at 750 ° C. for 3 hours in a nitrogen stream, and calcined alumina hydroxide and magnesium ( Al / Mg molar ratio = 0.44 / 0.56) A catalyst was obtained. A 4 L autoclave was charged with 535.7 g of methyl laurate and 7.2 g of the obtained catalyst, and nitrogen substitution was performed. Next, the temperature was raised to 180 ° C., the inside of the reaction vessel was returned to normal pressure with nitrogen, and 770 g of ethylene oxide (equivalent to 7 moles per 1 mole of methyl laurate) was gradually introduced into the container. Immediately after the introduction, the pressure of 0.34 MPa decreased with the progress of the reaction, and after 2 hours, the EO addition reaction was continued until the pressure became constant at 0.29 MPa. 19.6 g of Hyflo Supercell (manufactured by Celite: diatomaceous earth) (1.5% with respect to the crude product 1B) was added to 1305 g of the obtained crude product 1B and dispersed uniformly, and then pressure filtration was performed at 80 ° C. To give ester 4.

Ester 5: C ₁₁ H ₂₃ —COO— (C ₃ H ₇ O) ₃ —CH ₃
1105 g of methyl laurate was charged instead of methyl caproate, and 1032 g of tripropylene glycol methyl ether (trade name “MFTG”, manufactured by Nippon Emulsifier Co., Ltd.) was used instead of triethylene glycol monomethyl ether. The ester 5 was obtained in the same manner as the ester 1 except that the ester exchange reaction was performed by heating and the temperature was raised to 185 ° C. while gradually reducing the pressure to 1.0 kPa after removing methanol.

Ester 6: C ₃ H ₇ —COO— (C ₂ H ₄ O) ₃ —CH ₃ , HLB = 11.3
The ester 6 was obtained in the same manner as the ester 4 except that the amount of methyl butyrate (manufactured by Tokyo Chemical Industry Co., Ltd.) was changed to 613 g and the amount of ethylene oxide was changed to 792 g instead of methyl laurate.

Ester 7: C ₁₁ H ₂₃ —COO— (C ₂ H ₄ O) _10.6 —CH ₃ , HLB = 13.7
Using 900 g of methyl laurate instead of methyl caproate and using 2100 g of polyethylene glycol monomethyl ether (trade name “Pluriol A 500E”, manufactured by BASF) having an average molecular weight of 500 instead of triethylene glycol monomethyl ether, 170 Ester 7 was carried out in the same manner as in ester 1, except that the ester exchange reaction was carried out by raising the temperature to 185 ° C. and that the temperature was raised to 185 ° C. while gradually reducing the pressure to 1.0 kPa after removing methanol. Got.

Ester 8: C ₁₁ H ₂₃ —COO—CH ₃
Methyl laurate was used as ester 8.

Ester 9: C ₁₁ H ₂₃ —COO— (C ₂ H ₄ O) ₃ —C ₂ H ₅ , HLB = 7.3
1714 g of methyl laurate was charged instead of methyl caproate, and 1426 g of triethylene glycol ethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of triethylene glycol monomethyl ether. The ester 9 was obtained in the same manner as the ester 1 except that the reaction was performed and the temperature was raised to 185 ° C. while gradually reducing the pressure to 1.0 kPa after removing the ethanol.

Ester 10: C ₁₇ H ₂₂ —COO— (C ₂ H ₄ O) ₅ —CH ₃ , HLB = 8.5
The ester 10 was obtained in the same manner as the ester 4 except that the amount of methyl oleate (trade name “Pastel M182”, manufactured by Lion Corporation) was changed to 771 g and the amount of ethylene oxide was changed to 572 g instead of methyl laurate.

Ester 11: C ₁₁ H ₂₃ —COO— (C ₂ H ₄ O) ₃ —CH ₃ , HLB = 7.6
In place of methyl caproate, 1763 g of lauric acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 1445 g of triethylene glycol monomethyl ether and 5.0 g of p-toluenesulfonic acid as an esterification catalyst were charged, and then 170 ° C. with stirring. After removing water as a by-product, the ester 11 was obtained in the same manner as the ester 1 except that the pressure was reduced to 0.6 kPa while raising the temperature to 200 ° C.

The types of raw materials used in Table 3 are shown below.
・ Carbon Black, Cabot Japan Show Black, N550
Aroma oil: Showa Shell Sekiyu Extract No. 4 S
・ Zinc oxide: Zinc oxide 3 types manufactured by Shodo Chemical Co., Ltd.
・ Sulfur: Fine powder sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Industry Co., Ltd. ・ Vulcanization accelerator: Noxeller CZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.

  As is clear from Tables 1 and 2, it was confirmed that the rubber compositions for tire sidewalls of Examples 1 to 12 were excellent in whitening resistance and browning resistance while securing good ozone resistance.

  As is clear from Table 1, the rubber composition of Comparative Example 1 did not contain an ester compound, so that the whitening resistance and the browning resistance were inferior to those of Examples 1-12.

  In the rubber composition of Comparative Example 2, the blending amount of ester 1 (polyalkylene glycol carboxylic acid alkyl ester) was less than 0.2 parts by weight, and therefore, whitening resistance and tea resistance could not be improved.

  In the rubber composition of Comparative Example 3, since the blending amount of ester 1 (polyalkylene glycol carboxylic acid alkyl ester) exceeded 5 parts by weight, the whitening resistance cannot be sufficiently improved.

In the rubber composition of Comparative Example 4, the compound 6 (polyalkylene glycol carboxylic acid alkyl ester) has sufficient R ¹ carbon number of R ^{1 in} the general formula (I) to be less resistant to whitening and resistance to browning. Cannot be improved.

  In the rubber composition of Comparative Example 5, since n in the general formula (I) of the blended ester 7 (polyalkylene glycol carboxylic acid alkyl ester) exceeds 8, it is possible to sufficiently improve the whitening resistance and the browning resistance. Can not.

In the rubber composition of Comparative Example 6, n in the general formula (I) of the blended ester 8 (polyalkylene glycol carboxylic acid ester) is less than 1, that is, it does not have an oxyalkylene group (R ² O). And can not improve the resistance to browning.

  In the rubber composition of Comparative Example 7, the content of natural rubber in the diene rubber is less than 20% by weight and the content of butadiene rubber is more than 80% by weight. Can not.

  In the rubber composition of Comparative Example 8, the content of natural rubber in the diene rubber exceeds 80% by weight, and the content of butadiene rubber is less than 20% by weight.

2 Side wall part 11 Side rubber layer

Claims (3)

0.5 to 10 parts by weight of paraffin wax and 0.5 to 10 parts by weight of an amine anti-aging agent with respect to 100 parts by weight of diene rubber containing at least 20 to 80% by weight of natural rubber and 20 to 80% by weight of butadiene rubber A rubber composition for a tire sidewall, comprising 0.2 to 5 parts by weight of a polyalkylene glycol carboxylic acid alkyl ester represented by the following general formula (I).

(In the formula, R ¹ represents a hydrocarbon group having 5 to 21 carbon atoms, R ² represents an ethylene group and / or a propylene group, R ³ represents a methyl group or an ethyl group, and n is an integer of 1 to 8.) The rubber composition for a tire sidewall according to claim 1, wherein R ^{2 in the} general formula (I) is an ethylene group.   3. The rubber composition for a tire sidewall according to claim 1, wherein n in the general formula (I) is an integer of 2 to 6.