JP5812153B1 - Sidewall rubber composition and pneumatic tire - Google Patents

Abstract

The present invention provides a rubber composition for a sidewall which is excellent in low heat buildup and ozone resistance when used as a tire, and a pneumatic tire using the rubber composition. A modified polymer containing a diene rubber and carbon black, wherein the diene rubber is obtained by reacting a nitrone compound with a double bond of a conjugated diene polymer, and a natural rubber. In addition, the content of the modified polymer in the diene rubber is 8 to 65% by mass, the nitrogen adsorption specific surface area of the carbon black is 20 to 60 [? 103 m2 / kg], and the carbon black is contained. The rubber composition for side walls whose quantity is 30-67 mass parts with respect to 100 mass parts of said diene rubbers. [Selection figure] None

Description

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

In order to reduce the fuel consumption of automobiles, the sidewall portion of a pneumatic tire is required to be excellent in low heat generation when used as a tire.
Under such circumstances, Patent Document 1 discloses a rubber composition for a tire sidewall containing natural rubber, butadiene rubber, and carbon black having a specific nitrogen adsorption specific surface area (Claims, Examples). etc). Patent Document 1 describes that the structure disclosed in Patent Document 1 can reduce tan δ and reduce fuel consumption.

JP 2006-63284 A

On the other hand, since the sidewall portion of the pneumatic tire is exposed to sunlight, there is a case where a crack called an ozone crack occurs due to strong ultraviolet light. Therefore, the rubber composition for sidewalls is required to be excellent in ozone resistance when formed into a tire. Here, in order to improve the ozone resistance of the rubber composition for a sidewall, a method is known in which a large amount of wax is blended to form a wax thin film on the surface of the sidewall. However, when a large amount of wax is blended as described above, poor appearance tends to occur.
In addition, from the viewpoint of environmental problems and the like, further improvement in fuel efficiency has been demanded. Along with this, the rubber composition for sidewalls is required to further improve low heat buildup when used as a tire.

  Under these circumstances, the present inventors prepared a rubber composition for a sidewall with reference to Patent Document 1 and manufactured a tire, and considering the improvement in the required level for future durability, the ozone resistance is further increased. It became clear that there was a need for improvement. It has also been clarified that the low heat buildup of the obtained tire does not necessarily satisfy the level required recently.

  Therefore, in view of the above circumstances, the present invention provides a rubber composition for a sidewall that is excellent in low heat buildup and ozone resistance when made into a tire, and a pneumatic tire using the rubber composition. Objective.

As a result of diligent study on the above problems, the present inventors have used a natural rubber and a modified polymer obtained by modifying a conjugated diene polymer with a nitrone compound as a diene rubber, and a specific nitrogen adsorption. The present inventors have found that the above problems can be solved by using carbon black having a specific surface area, and have reached the present invention.
That is, the present inventors have found that the above problem can be solved by the following configuration.

(1) Contains a diene rubber and carbon black,
The diene rubber contains a modified polymer obtained by reacting a nitrone compound having a carboxy group with a double bond of a conjugated diene polymer, and a natural rubber, and the diene rubber contains the modified polymer in the diene rubber. The content is 8 to 65% by mass,
The carbon black has a nitrogen adsorption specific surface area of 20 to 60 [× 10 ³ m ² / kg],
The rubber composition for a sidewall, wherein the content of the carbon black is 30 to 67 parts by mass with respect to 100 parts by mass of the diene rubber.
(2) The nitrone compound is N-phenyl-α- (4-carboxyphenyl) nitrone, N-phenyl-α- (3-carboxyphenyl) nitrone, N-phenyl-α- (2-carboxyphenyl) nitrone, A compound selected from the group consisting of N- (4-carboxyphenyl) -α-phenylnitrone, N- (3-carboxyphenyl) -α-phenylnitrone and N- (2-carboxyphenyl) -α-phenylnitrone. The rubber composition for a side wall according to the above (1).
(3) The rubber composition for a sidewall according to the above (1) or (2), wherein the modification rate of the modified polymer is 0.02 to 4.0 mol%. Here, the modification rate represents the ratio (mol%) modified by the nitrone compound among all the double bonds derived from the conjugated diene of the conjugated diene polymer.
(4) The amount of the nitrone compound reacted with respect to the double bond of the conjugated diene polymer is 0.1 to 10 parts by mass with respect to 100 parts by mass of the diene rubber. The rubber composition for a side wall according to any one of (3).
(5) The rubber composition for a sidewall according to any one of (1) to (4), wherein the modified polymer is a modified polymer obtained by reacting a nitrone compound with a double bond of butadiene rubber. object.
(6) The rubber composition for a sidewall according to any one of (1) to (5), further comprising a wax.
(7) A pneumatic tire using the rubber composition for a sidewall according to any one of (1) to (6) as a sidewall portion.

  As shown below, according to the present invention, it is possible to provide a rubber composition for a sidewall that is excellent in low heat buildup and ozone resistance when made into a tire, and a pneumatic tire using the rubber composition. it can.

It is a partial section schematic diagram of the tire showing an example of the embodiment of the pneumatic tire of the present invention.

Below, the rubber composition for sidewalls of this invention and the pneumatic tire manufactured using the rubber composition for sidewalls of this invention are demonstrated.
In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Rubber composition for sidewall]
The rubber composition for side walls of the present invention (hereinafter also referred to as the composition of the present invention) contains a diene rubber and carbon black.
Here, the diene rubber includes a modified polymer obtained by reacting a nitrone compound with a double bond of a conjugated diene polymer, and a natural rubber, and contains the modified polymer in the diene rubber. The amount is 8 to 65% by mass. Moreover, the nitrogen adsorption specific surface area of the carbon black is 20 to 60 [× 10 ³ m ² / kg], and the content of the carbon black is 30 to 67 mass with respect to 100 parts by mass of the diene rubber. Part.
Since the composition of this invention takes such a structure, it is thought that it is excellent in low heat generation property and ozone resistance.

As described above, the composition of the present invention contains a modified polymer obtained by modifying a conjugated diene polymer with a nitrone compound. Therefore, the nitrone residue (modified nitrone group) in the modified polymer interacts with the carbon black in the composition (if the composition contains silica, it also interacts with the silica in the composition). (If the composition contains silica, the dispersibility of silica in the composition is also increased). As a result, the pain effect is reduced, and it is considered that the tire has excellent low heat generation when used as a tire.
This is because, as shown in Examples and Comparative Examples described later, the case of containing a modified polymer (Example of the present application) is superior to the case of containing no modified polymer (Comparative Example 1). It is guessed from.

  Hereinafter, each component contained in the composition of this invention is explained in full detail.

[Diene rubber]
The diene rubber contained in the composition of the present invention includes a modified polymer obtained by reacting a nitrone compound with a double bond of a conjugated diene polymer, and a natural rubber. Here, the content of the modified polymer in the diene rubber is 8 to 65% by mass.
The diene rubber may contain a rubber component other than the modified polymer and natural rubber. The rubber component is not particularly limited, but isoprene rubber (IR), butadiene rubber (BR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR). ), Chloroprene rubber (CR) and the like. Of these, butadiene rubber (BR) is preferable.

<Modified polymer>
As described above, the diene rubber contained in the composition of the present invention includes a modified polymer obtained by reacting a nitrone compound with a double bond of a conjugated diene polymer.

(Conjugated diene polymer)
The conjugated diene polymer used for producing the modified polymer is not particularly limited, and natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), aromatic vinyl-conjugated diene copolymer rubber (for example, SBR). ), Acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR) and the like. Of these, butadiene rubber (BR) is preferable. That is, the modified polymer is preferably a modified polymer obtained by reacting a nitrone compound with a double bond of butadiene rubber.

(Nitron compounds)
The nitrone compound used for the production of the modified polymer is not particularly limited as long as it is a compound having a nitrone group represented by the following formula (1).

  In the above formula (1), * represents a bonding position.

  The nitrone compound is preferably a compound represented by the following formula (2).

  In the above formula (2), X and Y each independently represent an aliphatic hydrocarbon group, an aromatic hydrocarbon group or an aromatic heterocyclic group which may have a substituent.

  Examples of the aliphatic hydrocarbon group represented by X or Y include an alkyl group, a cycloalkyl group, and an alkenyl group. Examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group, Examples thereof include a tert-pentyl group, 1-methylbutyl group, 2-methylbutyl group, 1,2-dimethylpropyl group, n-hexyl group, n-heptyl group, n-octyl group and the like. Of the alkyl group is preferable, and an alkyl group having 1 to 6 carbon atoms is more preferable. Examples of the cycloalkyl group include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Among them, a cycloalkyl group having 3 to 10 carbon atoms is preferable, and a cycloalkyl group having 3 to 6 carbon atoms is preferable. More preferred. Examples of the alkenyl group include a vinyl group, a 1-propenyl group, an allyl group, an isopropenyl group, a 1-butenyl group, a 2-butenyl group, and among them, an alkenyl group having 2 to 18 carbon atoms is preferable. An alkenyl group having 2 to 6 carbon atoms is more preferable.

Examples of the aromatic hydrocarbon group represented by X or Y include an aryl group and an aralkyl group.
Examples of the aryl group include a phenyl group, a naphthyl group, an anthryl group, a phenanthryl group, and a biphenyl group. Among them, an aryl group having 6 to 14 carbon atoms is preferable, and an aryl group having 6 to 10 carbon atoms is more preferable. A phenyl group and a naphthyl group are more preferable.
Examples of the aralkyl group include a benzyl group, a phenethyl group, and a phenylpropyl group. Among them, an aralkyl group having 7 to 13 carbon atoms is preferable, an aralkyl group having 7 to 11 carbon atoms is more preferable, and a benzyl group is preferable. Further preferred.

  Examples of the aromatic heterocyclic group represented by X or Y include, for example, pyrrolyl group, furyl group, thienyl group, pyrazolyl group, imidazolyl group (imidazole group), oxazolyl group, isoxazolyl group, thiazolyl group, isothiazolyl group, pyridyl group (Pyridine group), furan group, thiophene group, pyridazinyl group, pyrimidinyl group, pyrazinyl group and the like. Of these, a pyridyl group is preferable.

The substituent that the group represented by X or Y may have is not particularly limited, and examples thereof include an alkyl group having 1 to 4 carbon atoms, a hydroxy group, an amino group, a nitro group, a carboxy group, a sulfonyl group, An alkoxy group, a halogen atom, etc. are mentioned. Of these, a carboxy group is preferable.
Examples of the aromatic hydrocarbon group having such a substituent include an aryl group having a substituent such as a tolyl group and a xylyl group; and a substituent such as a methylbenzyl group, an ethylbenzyl group, and a methylphenethyl group. An aralkyl group; and the like.

  The compound represented by the above formula (2) is preferably a compound represented by the following formula (3).

In formula (3), m and n each independently represent an integer of 0 to 5, and the sum of m and n is 1 or more.
The integer represented by m is preferably an integer of 0 to 2, and more preferably an integer of 0 to 1, because the solubility in a solvent at the time of synthesizing a nitrone compound becomes good and the synthesis becomes easy.
The integer represented by n is preferably an integer of 0 to 2, and more preferably an integer of 0 to 1, because the solubility in a solvent at the time of synthesizing a nitrone compound is improved and the synthesis is facilitated.
Moreover, 1-4 are preferable and, as for the sum total (m + n) of m and n, 1-2 are more preferable.

  Although it does not restrict | limit especially as such carboxy nitrone represented by Formula (3), N-phenyl- (alpha)-(4-carboxyphenyl) nitrone represented by following formula (3-1), following formula (3- 2) N-phenyl-α- (3-carboxyphenyl) nitrone represented by the following formula (3-3), N-phenyl-α- (2-carboxyphenyl) nitrone represented by the following formula (3-3), 4) N- (4-carboxyphenyl) -α-phenylnitrone represented by the following formula (3-5), and N- (3-carboxyphenyl) -α-phenylnitrone represented by the following formula (3-5) A compound selected from the group consisting of N- (2-carboxyphenyl) -α-phenylnitrone represented by 3-6) is preferable.

  The method for synthesizing the nitrone compound is not particularly limited, and a conventionally known method can be used. For example, a compound having a hydroxyamino group (—NHOH) and a compound having an aldehyde group (—CHO) have a molar ratio of hydroxyamino group to aldehyde group (—NHOH / —CHO) of 1.0 to 1. By stirring in an amount of 5 in an organic solvent (for example, methanol, ethanol, tetrahydrofuran, etc.) at room temperature for 1 to 24 hours, both groups react to give a nitrone compound having a nitrone group.

(Method for producing modified polymer)
The method for producing the modified polymer by reacting the nitrone compound with the double bond of the conjugated diene polymer is not particularly limited. For example, the above-described conjugated diene polymer and the above-described nitrone compound are mixed at 100 to 200 ° C. And a method of mixing for 1 to 30 minutes.
At this time, as shown in the following formula (4) or the following formula (5), the cycloaddition reaction between the double bond derived from the conjugated diene of the conjugated diene polymer and the nitrone group of the nitrone compound Happens and gives a five-membered ring. The following formula (4) represents a reaction between a 1,4-bond and a nitrone compound, and the following formula (5) represents a reaction between a 1,2-vinyl bond and a nitrone compound. Formulas (4) and (5) represent reactions when the conjugated diene is butadiene (1,3-butadiene), but a similar reaction also gives a five-membered ring when the conjugated diene is other than butadiene. .

  The amount of the nitrone compound to be reacted with the double bond of the conjugated diene polymer is not particularly limited, but is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the conjugated diene polymer. Part by mass is more preferable. The amount of the nitrone compound reacted with respect to the double bond of the conjugated diene polymer is preferably more than 1 part by mass with respect to 100 parts by mass of the conjugated diene polymer.

(Modification rate)
The modification rate of the modified polymer is not particularly limited, but is preferably 0.02 to 4.0 mol%, and more preferably 0.10 to 2.0 mol%. The modification rate is preferably 0.20 mol% or more.
Here, the modification rate represents the ratio (mol%) modified by the nitrone compound among all the double bonds derived from the conjugated diene (conjugated diene diene unit) of the conjugated diene polymer. Is butadiene (1,3-butadiene), it represents a ratio (mol%) in which the structure of the above formula (4) or the above formula (5) is formed by modification with a nitrone compound. The modification rate can be determined, for example, by performing NMR measurement of the conjugated diene polymer and modified polymer (that is, the polymer before and after modification).
In the present specification, a modified polymer having a modification rate of 100 mol% also corresponds to a diene rubber.

The content of the modified polymer in the diene rubber is 8 to 65% by mass. Especially, it is preferable that it is 20-60 mass%, it is more preferable that it is 30-50 mass%, and it is further more preferable that it is 40 mass% or more.
When the content of the modified polymer in the diene rubber is less than 8% by mass or more than 65% by mass, the low heat buildup and / or ozone resistance of the obtained tire becomes insufficient.

<Natural rubber>
As described above, the diene rubber contained in the composition of the present invention includes natural rubber.
The content of the natural rubber in the diene rubber is not particularly limited as long as the content of the modified polymer in the diene rubber is 8 to 65% by mass, but is preferably 20 to 60% by mass, and preferably 30 to 50%. It is more preferable that it is mass%, and it is further more preferable that it is 30-40 mass%.

〔Carbon black〕
The carbon black contained in the composition of the present invention is not particularly limited as long as the nitrogen adsorption specific surface area (N ₂ SA) is 20 to 60 [× 10 ³ m ² / kg].
Here, the nitrogen adsorption specific surface area (N ₂ SA) is the nitrogen adsorption amount on the carbon black surface according to JIS K6217-2: 2001 “Part 2: Determination of specific surface area—nitrogen adsorption method—single point method”. It is a measured value.

The carbon black content in the composition of the present invention is 30 to 67 parts by mass with respect to 100 parts by mass of the diene rubber.
If the carbon black content is less than 30 parts by mass with respect to 100 parts by mass of the diene rubber, the resulting tire has insufficient cut resistance.
When the content of carbon black exceeds 67 parts by mass with respect to 100 parts by mass of the diene rubber, fatigue resistance becomes insufficient.

[Optional ingredients]
The composition of this invention can contain an additive further in the range which does not impair the effect and objective as needed.
Examples of the additive include fillers other than carbon black (for example, silica), silane coupling agents, zinc oxide (zinc white), stearic acid, adhesive resin, peptizer, anti-aging agent, wax, Various additives generally used in rubber compositions such as processing aids, aroma oils, liquid polymers, terpene resins, thermosetting resins, vulcanizing agents (for example, sulfur), and vulcanization accelerators can be mentioned. .
The composition of the present invention preferably contains a wax.
The wax is not particularly limited. For example, vegetable wax (rice wax, candelilla wax, carnauba wax, Japan wax, urushi wax, sugarcane wax, palm wax, etc.), ore wax (montane wax, ozokerite and ceresin, oil) And waxes obtained from shells), animal waxes (eg beeswax wax) and the like.
Since the tire manufactured using the composition of the present invention has a nitrone residue (modified nitrone group), the polarity changes. Therefore, when the composition of the present invention contains a wax, the migration of the wax to the tire surface is promoted, and the crack resistance is further improved. As a result, tires manufactured using the composition of the present invention are superior in ozone resistance.
In the composition of the present invention, the content of the wax is not particularly limited, but is preferably 1 to 2.5 parts by mass with respect to 100 parts by mass of the diene rubber from the viewpoint of appearance.

<Method for producing rubber composition for side wall>
The production method of the composition of the present invention is not particularly limited, and specific examples thereof include, for example, kneading the above-described components using a known method and apparatus (for example, a Banbury mixer, a kneader, a roll, etc.). The method etc. are mentioned. When the composition of the present invention contains sulfur or a vulcanization accelerator, components other than sulfur and the vulcanization accelerator are first mixed at a high temperature (preferably 80 to 140 ° C.) and cooled, and then sulfur or It is preferable to mix a vulcanization accelerator.
The composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions.

[Use]
The composition of this invention is used for manufacture of a pneumatic tire. Especially, it uses suitably for the side wall part of a pneumatic tire.

[Pneumatic tire]
The pneumatic tire of the present invention is a pneumatic tire manufactured using the composition of the present invention described above. Especially, it is preferable that it is a pneumatic tire which used the composition of this invention for the sidewall part.
FIG. 1 shows a schematic partial sectional view of a tire representing an example of an embodiment of the pneumatic tire of the present invention, but the pneumatic tire of the present invention is not limited to the embodiment shown in FIG.

In FIG. 1, reference numeral 1 represents a bead portion, reference numeral 2 represents a sidewall portion, and reference numeral 3 represents a tire tread portion.
Further, a carcass layer 4 in which fiber cords are embedded is mounted between the pair of left and right bead portions 1, and the end of the carcass layer 4 extends from the inside of the tire to the outside around the bead core 5 and the bead filler 6. Wrapped and rolled up.
In the tire tread 3, a belt layer 7 is disposed over the circumference of the tire on the outside of the carcass layer 4.
Moreover, in the bead part 1, the rim cushion 8 is arrange | positioned in the part which touches a rim | limb.
Note that the sidewall portion 2 is formed of the above-described composition of the present invention.

  The pneumatic tire of the present invention can be manufactured, for example, according to a conventionally known method. Moreover, as gas with which a tire is filled, inert gas, such as nitrogen, argon, helium other than the air which adjusted normal or oxygen partial pressure, can be used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.

<Synthesis of nitrone compounds>
Methanol (900 mL) warmed to 40 ° C. was placed in a 2 L eggplant flask, and terephthalaldehyde acid (30.0 g) represented by the following formula (b-1) was added and dissolved therein. To this solution was added phenylhydroxyamine (21.8 g) represented by the following formula (a-1) dissolved in methanol (100 mL), and the mixture was stirred at room temperature for 19 hours. After completion of stirring, nitrone compound (carboxynitrone) represented by the following formula (c-1) was obtained by recrystallization from methanol (41.7 g). The yield was 86%.

<Synthesis of Modified Polymer (Modified Polymer 1)>
Butadiene rubber (NIPOL BR1220 manufactured by Nippon Zeon Co., Ltd.) was put into a 120 ° C. Banbury mixer and masticated for 2 minutes. Thereafter, 0.67 parts by mass of the nitrone compound synthesized as described above was added to 100 parts by mass of butadiene rubber, and mixed at 150 ° C. for 5 minutes to modify the butadiene rubber with the nitrone compound. The resulting modified polymer is referred to as modified polymer 1.
The obtained modified polymer 1 was subjected to NMR measurement to obtain a modification rate. The modification rate of the modified polymer 1 was 0.16 mol%. Specifically, the modification rate was determined as follows. That is, for the polymer before and after modification, the peak area around 8.08 ppm (attributed to two protons adjacent to the carboxy group) was determined by ¹ H-NMR measurement (CDCl ₃ , 400 MHz, TMS) using CDCl ₃ as a solvent. The denaturation rate was determined by measurement. The ¹ H-NMR measurement of the modified polymer was carried out using a sample dried under reduced pressure after repeating the purification of dissolving the modified polymer in toluene and precipitating in methanol twice.

<Synthesis of Modified Polymer (Modified Polymer 2)>
Modified Polymer 1 except that the compounding amount of the nitrone compound was changed from 0.67 parts by mass to 1.67 parts by mass, the mixing temperature was changed from 150 ° C. to 160 ° C., and the mixing time was changed from 5 minutes to 2 minutes. The butadiene rubber was modified with a nitrone compound according to the same procedure as described above. The resulting modified polymer is referred to as modified polymer 2.
The obtained modified polymer 2 was subjected to NMR measurement to determine the modification rate. The modification rate of the modified polymer 2 was 0.37 mol%. The method for obtaining the modification rate is as described above.

<Preparation of rubber composition for sidewall>
The components shown in Table 1 below were blended in the proportions (parts by mass) shown in Table 1 below.
Specifically, first, components excluding sulfur and a vulcanization accelerator among the components shown in Table 1 below were mixed for 5 minutes with a Banbury mixer at 80 ° C. Next, using a roll, sulfur and a vulcanization accelerator are mixed to obtain rubber compositions for sidewall tires (hereinafter, “rubber compositions for sidewall tires” are also simply referred to as “rubber compositions”). It was.

<Preparation of vulcanized rubber sheet>
Each obtained rubber composition (unvulcanized) was press vulcanized at 160 ° C. for 15 minutes in a mold (15 cm × 15 cm × 0.2 cm) to produce a vulcanized rubber sheet.

<Evaluation of heat generation>
For each vulcanized rubber sheet obtained, loss tangent (tan δ (60 ° C.) was measured with a viscoelastic spectrometer (manufactured by Toyo Seiki Seisakusho) under the conditions of initial strain 10%, amplitude ± 2%, frequency 20 Hz, temperature 60 ° C. )) Was measured. The results are shown in Table 1 (exothermic property). The results were expressed as an index with tan δ (60 ° C.) of Comparative Example 1 as 100. The smaller the value, the better the low heat generation when the tire is made.

<Evaluation of ozone resistance>
Each obtained vulcanized rubber sheet was placed in an ozone tank (50 ° C., 100 pphm) and allowed to stand for 48 hours in a 40% stretched state. Thereafter, the vulcanized rubber sheet was observed, and the number of cracks having a length of 1 mm or more present on the surface was counted. And it evaluated by the following criteria. The results are shown in Table 1 (ozone resistance). Practically, it is preferably 3-5, more preferably 4-5.
1: The vulcanized rubber sheet breaks: 2 or more cracks of 1 mm or more 21 or more cracks of 3: 1 mm or more 10 or more and 20 or less 4 cracks of 1 mm or more: 1 or more and less than 10 cracks of 5: 1 mm or more There is no

<Appearance evaluation>
The obtained vulcanized rubber sheet was allowed to stand in an oven at 40 ° C. for 2 weeks, and then the appearance was visually observed and scored according to the following criteria (n = 3). The average of n = 3 (rounded off after the decimal point) is shown in Table 1. It is preferably 3-5, more preferably 4-5.
Score 1: Overall color changes to white. Score 2: About 30% of the area changes to white. Score 3: Overall is dull. Score 4: About 30% of area is dull. Score 5: Unchanged.

In Table 1, the CPN amount converted value represents the part by mass of the nitrone compound used for the synthesis of the modified polymer with respect to 100 parts by mass of the diene rubber.
In Table 1, the modification rate represents the modification rate of the modified polymer described above.

The detail of each component shown by the said Table 1 is as follows.
・ Natural rubber: TSR20
-Butadiene rubber: NIPOL BR 1220 (manufactured by Nippon Zeon)
Modified polymer 1: Modified polymer 1 synthesized as described above
Modified polymer 2: Modified polymer 2 synthesized as described above
Carbon black: Seast F (Nitrogen adsorption specific surface area: 42 [× 10 ³ m ² / kg], manufactured by Tokai Carbon Co., Ltd.)
・ Zinc flower: Zinc flower No. 3 (manufactured by Shodo Chemical Co., Ltd.)
・ Stearic acid: Stearic acid YR (manufactured by NOF Corporation)
Anti-aging agent: SANTOFLEX 6PPD (manufactured by Soltia Europe)
・ Wax: Sunnock (Ouchi Shinsei Chemical Co., Ltd.)
・ Oil: Extract No. 4 S (made by Showa Shell Sekiyu KK)
・ Vulcanization accelerator: Noxeller CZ-G (manufactured by Ouchi Shinsei Chemical Co., Ltd.)
・ Sulfur: Oil-treated sulfur (manufactured by Karuizawa Refinery)

As can be seen from Table 1, as compared with Comparative Example 1 which does not contain a modified polymer, all of the Examples of the present invention containing a modified polymer were excellent in low heat buildup and ozone resistance when made into tires. Further, Comparative Example 2 in which the amount of the wax was increased without containing the modified polymer was excellent in ozone resistance, but the low heat build-up was insufficient and the appearance was poor.
From a comparison between Examples 1 and 2, Example 2 in which the content of the modified polymer in the diene rubber was 40% by mass or more was excellent in heat generation when made into a tire, and was also excellent in appearance.

1 Bead part 2 Side wall part 3 Tire tread part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Rim cushion

Claims (7)

Contains diene rubber and carbon black,
The diene rubber includes a modified polymer obtained by reacting a nitrone compound having a carboxy group with a double bond of a conjugated diene polymer, and a natural rubber, and the diene rubber contains the modified polymer in the diene rubber. The content is 8 to 65% by mass,
The carbon black has a nitrogen adsorption specific surface area of 20 to 60 [× 10 ³ m ² / kg],
The rubber composition for sidewalls, wherein the content of the carbon black is 30 to 67 parts by mass with respect to 100 parts by mass of the diene rubber.   The nitrone compound is N-phenyl-α- (4-carboxyphenyl) nitrone, N-phenyl-α- (3-carboxyphenyl) nitrone, N-phenyl-α- (2-carboxyphenyl) nitrone, N- ( A compound selected from the group consisting of 4-carboxyphenyl) -α-phenylnitrone, N- (3-carboxyphenyl) -α-phenylnitrone and N- (2-carboxyphenyl) -α-phenylnitrone. Item 2. The rubber composition for a sidewall according to Item 1.   The rubber composition for a side wall according to claim 1 or 2, wherein the modification rate of the modified polymer is 0.02 to 4.0 mol%. Here, the modification rate represents the ratio (mol%) modified by the nitrone compound among all the double bonds derived from the conjugated diene of the conjugated diene polymer.   The amount of the nitrone compound reacted with respect to the double bond of the conjugated diene polymer is 0.1 to 10 parts by mass with respect to 100 parts by mass of the diene rubber. 2. The rubber composition for a sidewall according to item 1.   The rubber composition for a sidewall according to any one of claims 1 to 4, wherein the modified polymer is a modified polymer obtained by reacting a nitrone compound with a double bond of butadiene rubber.   Furthermore, the rubber composition for sidewalls of any one of Claims 1-5 containing a wax.   The pneumatic tire which used the rubber composition for sidewalls of any one of Claims 1-6 for the sidewall part.