JP5812155B1 - Rubber composition for tire rim cushion or gum finishing and pneumatic tire - Google Patents

Abstract

Provided are a tire rim cushion or a rubber composition for gum finishing which is excellent in low heat buildup and ozone resistance when made into a tire, and a pneumatic tire using the rubber composition. SOLUTION: A diene rubber and carbon black, wherein the diene rubber comprises a natural rubber and a modified polymer obtained by reacting a nitrone compound with a double bond of a conjugated diene polymer. And the content of the natural rubber in the diene rubber is 30 to 60% by mass, the content of the modified polymer in the diene rubber is 8 to 70% by mass, and the content of the carbon black A rubber composition for a tire rim cushion or a gum finishing, which is 67 to 90 parts by mass with respect to 100 parts by mass of the diene rubber, and the nitrogen adsorption specific surface area of the carbon black is 60 to 150 m 2 / g. [Selection figure] None

Description

  The present invention relates to a tire rim cushion or rubber composition for gum finishing and a pneumatic tire.

A rim cushion is provided on the outer surface of the bead portion of the pneumatic tire so as to be in close contact with the rim when the tire is assembled on the wheel.
Also, for finishing pneumatic tires, rubber sheets that do not use fibers (so-called gum finishing) are used for reasons such as weight reduction of tires and cost reduction.

For example, Patent Document 1 discloses that “blocked isocyanate group is used with respect to 100 parts by mass of a rubber component comprising 40 to 60 parts by mass of natural rubber and 60 to 40 parts by mass of a diene rubber having a modifying group capable of reacting with an isocyanate group. And a polyrotaxane compound having blocking groups arranged at both ends of the linear molecule so that the cyclic molecule is not detached from the linear molecule. A rubber composition for a tire rim cushion or gum finishing, characterized by blending 1 to 30 parts by mass and 70 to 90 parts by mass of carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 90 to 130 m ² / g. ” ([Claim 1]).

Patent Document 2 states that “the cis-1,4 bond content is 97% or more, the Mooney viscosity at 100 ° C. (ML1 + 4) is 45 or more, and the Mooney viscosity is 5 at 25 ° C. 30% to 70% by mass of butadiene rubber having a ratio of mass% toluene solution viscosity (T-cp) [cps] of (T-cp) / (ML1 + 4) of 2.0 or more, and other diene rubbers 30 to 70 55 to 75 parts by mass of carbon black (1) having a nitrogen adsorption specific surface area of 35 m ² / g or more and less than 50 m ² / g and a nitrogen adsorption specific surface area of 50 m ² with respect to 100 parts by mass of the rubber component composed of mass%. / g or more ^{95 m} 2 / g or less of carbon black (2) 5 to 20 parts by mass, the sum of the carbon black (1) and (2), characterized in that 60 to 95 parts by weight Taiyarimuku Deployment or gums finishing rubber composition. "Is described.

JP 2014-34623 A JP, 2014-31425, A

  When the present inventors prepared the rubber composition described in Patent Documents 1 and 2 and manufactured a tire, the ozone resistance needs to be further improved in consideration of the improvement in the required level for future durability. It became clear that there is. It was also clarified that the low heat buildup of the obtained tire does not necessarily satisfy the level required recently.

  Accordingly, an object of the present invention is to provide a tire rim cushion or a rubber composition for gum finishing that is excellent in low heat buildup and ozone resistance when made into a tire, and a pneumatic tire using the rubber composition. .

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] containing a diene rubber and carbon black,
The diene rubber includes natural rubber and a modified polymer obtained by reacting a nitrone compound having a carboxy group with a double bond of a conjugated diene polymer,
The content of the natural rubber in the diene rubber is 30 to 60% by mass,
The content of the modified polymer in the diene rubber is 8 to 70% by mass,
The carbon black content is 67 to 90 parts by mass with respect to 100 parts by mass of the diene rubber.
A rubber composition for a tire rim cushion or gum finishing, wherein the carbon black has a nitrogen adsorption specific surface area of 60 to 150 m ² / g.
[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 tire rim cushion or gum finishing according to [1].
[3] The rubber composition for a tire rim cushion or gum finishing according to [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. 3] The rubber composition for a tire rim cushion or gum finishing according to any one of [3].
[5] The tire rim cushion or gum finishing 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. Rubber composition.
[6] A pneumatic tire using the rubber composition according to any one of [1] to [5] for a tire rim cushion or gum finishing.

  As described below, according to the present invention, a tire rim cushion or a rubber composition for gum finishing that is excellent in low heat buildup and ozone resistance when made into a tire, and a pneumatic tire using the rubber composition are provided. can do.

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

The tire rim cushion or rubber composition for gum finishing of the present invention and the pneumatic tire of the present invention will be described below.
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 tire rim cushion or gum finishing]
The rubber composition for a tire rim cushion or gum finishing of the present invention (hereinafter also referred to as “the rubber composition of the present invention”) contains a diene rubber and carbon black.
Here, the diene rubber includes a natural rubber and a modified polymer obtained by reacting a nitrone compound with a double bond of a conjugated diene polymer, and contains the natural rubber in the diene rubber. The amount is 30 to 60% by mass, and the content of the modified polymer in the diene rubber is 8 to 70% by mass.
The carbon black content is 67 to 90 parts by mass with respect to 100 parts by mass of the diene rubber, and the nitrogen adsorption specific surface area of the carbon black is 60 to 150 m ² / g.
Since the rubber composition of the present invention has such a configuration, it is considered that the rubber composition is excellent in low heat generation and ozone resistance.

As described above, the rubber composition of the present invention contains a modified polymer obtained by modifying a conjugated diene polymer with a nitrone compound. Therefore, the nitrone modification site 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), increasing the dispersibility of the carbon black (composition When the product 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 where the modified polymer is contained (Example) is superior to the case where the modified polymer is not contained (Comparative Example 1). Also guessed.
Hereinafter, each component contained in the rubber composition of the present invention will be described in detail.

[Diene rubber]
The diene rubber contained in the rubber composition of the present invention includes natural rubber and a modified polymer obtained by modifying a conjugated diene polymer with a nitrone compound. Here, the content of the natural rubber in the diene rubber is 30 to 60% by mass, and the content of the modified polymer in the diene rubber is 8 to 70% by mass.
The diene rubber may contain a rubber component other than the natural rubber and the modified polymer. The rubber component is not particularly limited, but isoprene rubber (IR), butadiene rubber (BR), aromatic vinyl-conjugated diene copolymer rubber (for example, styrene butadiene rubber (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.

<Natural rubber>
As described above, the diene rubber contained in the rubber 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 it is 30 to 60% by mass, but it is preferably 35 to 55% by mass from the viewpoint of wear resistance and weather resistance.

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

(Conjugated diene polymer)
The conjugated diene polymer used for the production of the modified polymer is not particularly limited. Specific examples thereof include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), and aromatic vinyl-conjugated diene copolymer. Examples thereof include 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 reacted with respect to 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. 5 parts by mass is more preferable.

(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%.
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, and more specifically, the nitrone compound. The ratio (mol%) by which the structure of the said Formula (4) or the said Formula (5) was formed by modification | denaturation by is represented. 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 not particularly limited as long as it is 8 to 70% by mass, but it is 20 to 60% by mass for the reason that the low heat build-up becomes better when the tire is formed. Preferably, it is 40-60 mass parts%.

〔Carbon black〕
The carbon black contained in the rubber composition of the present invention is not particularly limited as long as the nitrogen adsorption specific surface area is 60 to 150 m ² / g.
Further, the nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably at 60 m ² / g or less super 145m ² / g, more preferably 70~145m ² / g.
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 is 67 to 90 parts by mass with respect to 100 parts by mass of the diene rubber, preferably more than 67 parts by mass and 90 parts by mass or less, and more preferably 70 to 85 parts by mass. preferable.

[Optional ingredients]
The rubber composition of the present invention can contain other additives as necessary within a range not impairing the object of the present invention.
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. .
Of these additives, it is preferable to use wax.
Since the pneumatic tire manufactured using the rubber composition of the present invention has a nitrone-modified site, the polarity changes. Therefore, the transition of the wax to the surface is promoted, and the crack resistance is further improved. As a result, the pneumatic tire manufactured using the rubber composition of the present invention is more excellent in ozone resistance.
In the rubber composition of the present invention, the content in the case of containing a 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]
The method for producing the rubber 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 of doing is 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 40 to 160 ° C.) and cooled, and then sulfur or It is preferable to mix a vulcanization accelerator.
The rubber composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions.

[Use]
The rubber composition of the present invention is used for manufacturing a pneumatic tire. Especially, it is used suitably for the tire rim cushion or gum finishing of a pneumatic tire.

[Pneumatic tire]
The pneumatic tire of the present invention is a pneumatic tire manufactured using the above-described rubber composition of the present invention. Especially, it is preferable that it is a pneumatic tire which used the rubber composition of this invention for the tire rim cushion or the gum finishing.
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 rim cushion 8 shown in FIG. 1 is a member having a finishing function in a part thereof, and the part having this function can also be called a gum finishing.

  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 compound (carboxynitrone)>
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, Nippon Zeon) was charged into a Banbury mixer at 120 ° C. and masticated for 2 minutes. Thereafter, 1 part 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. In this way, a nitrone-modified butadiene rubber was obtained. The resulting modified polymer is referred to as modified polymer 1.
The obtained modified polymer 1 was subjected to NMR measurement to determine the modification rate. The modification rate of the modified polymer 1 was 0.19 mol%. Specifically, the modification rate was determined as follows. That is, for the butadiene rubber before and after modification, the peak area around 8.08 ppm (attributed to two protons adjacent to the carboxy group) by ¹ H-NMR measurement (CDCl ₃ , 400 MHz, TMS) using CDCl ₃ as a solvent. Was measured to determine the denaturation rate. In addition, ¹ H-NMR measurement of the modified polymer 1 was performed using a sample dried under reduced pressure after repeating purification twice by dissolving the modified polymer 1 in toluene and precipitating it in methanol.

<Synthesis of Modified Polymer (Modified Polymer 2)>
The butadiene rubber was modified with the nitrone compound according to the same procedure as in the modified polymer 1 except that the blending amount of the nitrone compound was changed from 1 part by mass to 2 parts by mass. The resulting modified polymer is referred to as modified polymer 2.
The obtained modified polymer 2 was subjected to NMR measurement to obtain a modification rate. The modification rate of the modified polymer 2 was 0.41 mol%. The method for obtaining the modification rate is as described above.

[Comparative Examples 1-3 and Examples 1-9]
<Preparation of rubber composition>
The components shown in Tables 1 to 3 below were blended in the proportions (parts by mass) shown in Tables 1 to 3 below.
Specifically, first, the components excluding sulfur and the vulcanization accelerator among the components shown in Tables 1 to 3 below were mixed for 5 minutes with a Banbury mixer at 80 ° C. Next, sulfur and a vulcanization accelerator were mixed using a roll to obtain a rubber composition.

<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 Tables 1 to 3 below (exothermic property). The results are expressed as an index with the tan δ (60 ° C.) of Comparative Example 1 as 100 for the following Table 1, and as an index with the tan δ (60 ° C.) of Comparative Example 2 as 100 for the following Table 2. Table 3 is an index with tan δ (60 ° C.) of Comparative Example 3 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 Tables 1 to 3 below (ozone resistance). Practically, it is preferably 3-5, more preferably 4-5.
There is no crack of 5: 1 mm or more 4 cracks of 1 mm or more are 1 or more and less than 10 3 cracks of 1 mm or more are 10 or more and 20 or less 2 cracks of 1 mm or more are 21 or more 1: Vulcanized rubber sheet Breaks

In Tables 1 to 3 below, the converted value of CPN represents the parts 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 Tables 1 to 3 below, the modification rate represents the modification rate of the modified polymer described above.

The detail of each component shown by the said Table 1-Table 3 is as follows.
・ Natural rubber: TSR20
・ Butadiene rubber: Nipol BR1220 (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 1: Seast 9 (nitrogen adsorption specific surface area: 142 m ² / g, manufactured by Tokai Carbon Co., Ltd.)
Carbon black 2: Seest 3 (nitrogen adsorption specific surface area: 79 m ² / g, manufactured by Tokai Carbon Co., Ltd.)
・ Zinc oxide: Zinc Hana 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.)
・ Process 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 Tables 1 to 3, in comparison with Comparative Examples 1 to 3 which do not contain a modified polymer, Examples 1 to 9 containing a modified polymer have low heat build-up and Excellent ozone resistance.
Moreover, it turned out that low exothermic property becomes more favorable when there is much introduction amount of a nitrone compound from the comparison of Examples 1-3. The same tendency was found from the comparison of Examples 4 to 6 and the comparison of Examples 7 to 9.
Furthermore, from a comparison between Example 2 and Example 3, it was found that ozone resistance was better when a modified polymer having a high modification rate was blended. The same tendency was found from the comparison between Example 5 and Example 6 and the comparison between Example 8 and Example 9.

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 (6)

Contains diene rubber and carbon black,
The diene rubber includes natural rubber and a modified polymer obtained by reacting a nitrone compound having a carboxy group with a double bond of a conjugated diene polymer,
The content of the natural rubber in the diene rubber is 30 to 60% by mass,
The content of the modified polymer in the diene rubber is 8 to 70% by mass,
The carbon black content is 67 to 90 parts by mass with respect to 100 parts by mass of the diene rubber.
A rubber composition for a tire rim cushion or gum finishing, wherein the carbon black has a nitrogen adsorption specific surface area of 60 to 150 m ² / g.   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 tire rim cushion or rubber composition for gum finishing according to Item 1. The rubber composition for a tire rim cushion or gum finishing according to claim 1 or 2, wherein a 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. The rubber composition for tire rim cushions or gum finishing described in 1.   The rubber composition for a tire rim cushion or gum finishing 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.   A pneumatic tire using the rubber composition according to any one of claims 1 to 5 for a tire rim cushion or gum finishing.