JP2014015585A - Rubber composition for tire bead filler, and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tire bead filler, capable of improving high hardness, workability and low heat build up performance in a good balance.SOLUTION: A rubber composition for a tire bead filler contains 1 to 25 pts.mass of a modified liquid polybutadiene having functional groups including a heteroatom, obtained by hydrogenation of polybutadiene having 50 mol% or more of 1,2-vinyl bound amount, and 1 to 40 pts.mass of at least one kind of phenolic composition selected from a group containing a phenolic resin and a phenol compound, based on 100 pts.mass of the rubber component containing diene rubber. A pneumatic tire having a bead filler (7) made of the rubber composition is also provided.

Description

  The present invention relates to a bead filler rubber composition used for a bead filler of a pneumatic tire.

  As a measure for increasing the hardness of the bead filler disposed in the bead portion of the pneumatic tire, there is a method of blending a large amount of reinforcing filler or a phenolic resin. However, these measures have a problem that workability and low heat generation performance deteriorate.

  Patent Document 1 listed below discloses diene rubber, functional group-modified liquid polybutadiene, and a mass as a cross-linking agent or chain extender for improving hardness while increasing processability. A rubber composition for bead filler obtained by blending kud polyisocyanate and a novolac-type phenolic resin has been proposed. However, this document does not disclose the use of hydrogenated (hereinafter sometimes simply referred to as hydrogenated) polybutadiene as the functional group-modified liquid polybutadiene, and the 1,2-vinyl bond is not disclosed. It is also silent about the use of hydrogenated high vinyl liquid polybutadiene.

  In Patent Document 2 below, a hydrogenated liquid polybutadiene is blended with a diene rubber as a rubber composition for a bead apex having high rubber strength, excellent steering stability, and good rolling resistance and processability. Are disclosed. However, this document does not disclose the use of a functional group-modified hydrogenated liquid polybutadiene, and also points to the use of hydrogenated high vinyl liquid polybutadiene having a high 1,2-vinyl bond content. The liquid polybutadiene used in the examples is also a low vinyl product having a 1,2-vinyl bond content of about 35 mol%.

JP 57-212239 A JP 2010-174102 A

  An object of the present invention is to provide a rubber composition for a tire bead filler that can improve the hardness, workability, and low heat generation performance in a well-balanced manner, and a pneumatic tire using the rubber composition.

  The rubber composition for a tire bead filler according to the present invention is a hydrogenated product obtained by hydrogenating polybutadiene having a 1,2-vinyl bond content of 50 mol% or more with respect to 100 parts by mass of a rubber component made of a diene rubber. 1 to 25 parts by mass of a modified liquid polybutadiene having a functional group containing a heteroatom that is polybutadiene, and 1 to 40 parts by mass of at least one phenolic component selected from the group consisting of phenolic resins and phenolic compounds To do.

  In addition, a pneumatic tire according to a preferred embodiment of the present invention is provided with a bead filler made of the rubber composition.

  According to the present invention, by blending a phenolic component such as a phenolic resin with a functional group-modified liquid polybutadiene obtained by hydrogenating high vinyl liquid polybutadiene, the bead filler is processed with a reduced viscosity while increasing the hardness of the bead filler. Can be improved, and heat generation can be reduced. Therefore, it is possible to achieve both the steering stability performance and the low fuel consumption performance of the pneumatic tire without impairing the workability.

It is a half sectional view showing an example of a pneumatic tire concerning an embodiment.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  In the rubber composition according to the embodiment, a diene rubber is used as a rubber component. As the diene rubber, natural rubber (NR) and / or diene synthetic rubber can be used. Examples of the diene-based synthetic rubber include isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), chloroprene rubber (CR), and nitrile rubber (NBR). These diene rubbers can be used alone or in a blend of two or more.

  The rubber component is preferably composed mainly of natural rubber having excellent fracture characteristics. Therefore, the rubber component is preferably composed of natural rubber alone or a blend of natural rubber and another diene rubber, and in the case of blend, the natural rubber is preferably 50% by mass or more in the rubber component. More preferably, it is 80% by mass or more.

  The rubber composition according to this embodiment is mixed with modified liquid polybutadiene. The modified liquid polybutadiene is a polymer that is liquid at normal temperature (23 ° C.) and is not included in the rubber component that is solid at normal temperature. The modified liquid polybutadiene has a number average molecular weight (Mn) of usually 1,000 to 100,000, and is clearly distinguished from the diene rubber of the rubber component, which has a number average molecular weight of usually 200,000 or more. The number average molecular weight of the modified liquid polybutadiene is preferably 1,500 to 50,000, more preferably 1,500 to 10,000, still more preferably 2,000 to 5,000. The number average molecular weight is a value measured at 40 ° C. by GPC (gel permeation chromatography), solvent: THF (tetrohydrofuran).

  In this embodiment, hydrogenated polybutadiene obtained by hydrogenating polybutadiene having a 1,2-vinyl bond content of 50 mol% or more is used as the modified liquid polybutadiene. By using liquid polybutadiene having such a high vinyl microstructure, bleed to the rubber surface can be suppressed and processability and hardness can be increased. Moreover, high hardness can be achieved by using hydrogenated liquid polybutadiene.

The 1,2-vinyl bond content is the content of 1,2-vinyl bond units relative to the content of butadiene units contained in the polymer of polybutadiene before hydrogenation, and is calculated by the integration ratio of ¹ HNMR spectrum. The The 1,2-vinyl bond unit is converted into an ethyl group by hydrogenation, but the 1,2-bond form itself having a side chain of a hydrocarbon group having 2 carbon atoms is retained. If the hydrogenated and unhydrogenated 1,2-vinyl bond units are combined to form a 1,2-bond component, the hydrogenated polybutadiene contains 50 mol% or more of the 1,2-bond component. The amount of 1,2-vinyl bonds before hydrogenation is preferably 70 mol% or more, more preferably 80 to 95 mol%.

The hydrogenation rate of the modified liquid polybutadiene (the ratio of hydrogenated double bonds to the double bonds of polybutadiene before hydrogenation) is not particularly limited, but is preferably 20 mol% or more, more preferably 50 It is more than mol%, More preferably, it is 80-95 mol%. The hydrogenation rate is calculated from the spectrum reduction rate of the unsaturated bond portion in the ¹ HNMR spectrum. The hydrogenation can be performed by a known method using a catalyst such as palladium, and is not particularly limited.

  In the present embodiment, a functional group-modified liquid polybutadiene having a functional group containing a hetero atom is used as the modified liquid polybutadiene. As the functional group, those containing an oxygen atom as a hetero atom are preferable, and examples thereof include a hydroxyl group (—OH), a carboxyl group (—COOH), a carboxylic acid derivative group, and an epoxy group, each of which is one kind. May be introduced alone, or may be introduced in combination of two or more. These functional groups interact with a hydroxyl group that is a polar part of a phenolic component such as a phenolic resin, that is, have a reactivity such as a chemical bond with a hydroxyl group or an affinity such as a hydrogen bond. It is what you have. Therefore, it is considered that the dispersibility of the phenol-based component can be improved, and that it contributes to the improvement of the hardness, workability, and low heat generation performance of the bead filler.

Here, examples of the carboxyl group include maleic acid, phthalic acid, acrylic acid, and methacrylic acid. Examples of the carboxylic acid derivative group include ester groups derived from these carboxylic acids (carboxylic acid ester groups) and acid anhydride groups composed of anhydrides of dicarboxylic acids such as maleic acid and phthalic acid. Examples of the carboxylic acid ester group include an acrylate group (—O—CO—CH═CH ₂ ) and / or a methacrylate group (—O—CO—C (CH ₃ ) ═CH ₂ ). ) Acrylate group) is a preferred example.

  Such a functional group-modified liquid polybutadiene is obtained by, for example, reacting a hydrogenated polybutadiene obtained by hydrogenating liquid polybutadiene with a compound having a functional group to chemically modify the liquid polybutadiene having the functional group at the molecular end. Can be obtained. However, the manufacturing method is not particularly limited.

  In the rubber composition according to this embodiment, the modified liquid polybutadiene can be blended at 1 to 25 parts by mass with respect to 100 parts by mass of the rubber component. By using a modified liquid polybutadiene obtained by hydrogenating a high vinyl product as described above and chemically modified with a functional group in such a blending amount, the hardness, workability and low heat generation performance are improved in a balanced manner. be able to. The blending amount of the modified liquid polybutadiene is preferably 5 to 20 parts by mass with respect to 100 parts by mass of the rubber component.

  The rubber composition according to the present embodiment is blended with at least one phenolic component selected from the group consisting of phenolic resins and phenolic compounds in order to increase hardness. A phenol type component can be mix | blended in 1-40 mass parts with respect to 100 mass parts of rubber components, More preferably, it is 5-30 mass parts, More preferably, it is 10-25 mass parts.

  Phenol compounds include phenol, resorcin, or alkyl derivatives thereof. Alkyl derivatives include derivatives of relatively long-chain alkyl groups such as nonylphenol and octylphenol, as well as methyl group derivatives such as cresol and xylenol. These phenol compounds may be used in combination. Among these, it is preferable to use resorcin when using one not condensed with an aldehyde.

  The phenolic resin is a thermosetting resin obtained by condensing the above phenolic compound with an aldehyde such as formaldehyde. A plurality of the above phenol compounds may be used and condensed with an aldehyde. Therefore, phenolic resins include unmodified phenolic resin (straight phenolic resin) obtained by condensing phenol and formaldehyde, alkyl-substituted phenolic resin obtained by condensing alkylphenol such as cresol, xylenol and octylphenol with formaldehyde, resorcin and formaldehyde. Various novolak type phenol resins such as resorcinol-formaldehyde resin obtained by condensation, resorcinol-alkylphenol co-condensation formaldehyde resin obtained by condensation of resorcin, alkylphenol and formaldehyde are exemplified. In addition, an oil-modified novolak type phenol resin modified with various oils such as cashew nut oil, tall oil, and rosin oil can also be used.

  In the rubber composition according to this embodiment, hexamethylenetetramine or a melamine derivative as a methylene donor may be used in combination with a phenol component. Examples of the melamine derivative include hexamethoxymethyl melamine obtained by reacting melamine and formaldehyde, hexamethylol melamine pentamethyl ether, and polyvalent methylol melamine. It is preferable that the compounding quantity of these methylene donors is 30-200 weight part with respect to 100 mass parts of said phenolic components.

  Carbon black can be blended as a filler in the rubber composition according to this embodiment. The carbon black is not particularly limited, and grades generally used for bead fillers such as ISAF, HAF, FEF, and GPF can be used. Although the compounding quantity of carbon black is not specifically limited, It is preferable that it is 30-100 mass parts with respect to 100 mass parts of rubber components, More preferably, it is 50-90 mass parts.

  In the rubber composition according to the present embodiment, in addition to the above-described components, other fillers such as silica, oil, zinc white, stearic acid, anti-aging agent, vulcanizing agent, vulcanization accelerator, and the like tire Various additives generally used in the rubber composition for bead filler can be blended. Examples of the vulcanizing agent include sulfur and sulfur-containing compounds, and are not particularly limited, but the blending amount is preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the rubber component. More preferably, it is 1-5 mass parts. Moreover, as a compounding quantity of a vulcanization accelerator, it is preferable that it is 0.1-7 mass parts with respect to 100 mass parts of said rubber components, More preferably, it is 0.5-5 mass parts.

  The rubber composition can be prepared by kneading according to a conventional method using a commonly used Banbury mixer, kneader, roll, or other mixer. That is, in the first mixing stage, to the rubber component, together with the modified liquid polybutadiene and the phenol component, other additives except for the vulcanizing agent and the vulcanization accelerator are added and mixed, and then the resulting mixture is A rubber composition can be prepared by adding and mixing a vulcanizing agent and a vulcanization accelerator in the final mixing stage.

  The rubber composition of the above embodiment is used as a rubber composition for constituting a bead filler of a pneumatic tire, and forms a bead filler by vulcanization molding at 140 to 180 ° C., for example, according to a conventional method. can do.

  FIG. 1 is a half sectional view showing an example of a pneumatic radial tire according to the embodiment. The tire includes a pair of left and right bead portions (1) and sidewall portions (2), and a tread portion (3) extending between both sidewall portions (2). The bead portion (1) is provided with an annular bead core (4) formed by winding a steel wire a plurality of times. Between the pair of left and right bead cores (4), a carcass ply (5) is provided in which a large number of cords arranged at right angles to the tire circumferential direction extend. And both ends of the carcass ply (5) are folded and locked so as to wrap the bead core (4) from the inner side in the tire axial direction to the outer side. A belt (6) formed by superposing at least two belt plies is disposed outside the carcass ply (5) in the tread portion (3) in the radial direction.

  And the rubber bead filler (7) is arrange | positioned by the tire outer peripheral side of the bead core (4). The bead filler (7) is composed of a rolled-up portion (5A) formed when the end portion of the carcass ply (5) is folded back and locked along the bead core (4), the carcass ply body, and the bead core (4). It fills the enclosed space. Therefore, the bead filler (7) is an annular rubber member disposed along the outer periphery of the bead core (4), and is generally formed in a triangular shape with a taper toward the outer side in the radial direction. What consists of such a structure WHEREIN: The whole bead filler (7) is formed with the said rubber composition.

  The configuration of the pneumatic tire shown in FIG. 1 is merely an example, and the present invention is not limited to this. The pneumatic tire may be used for passenger cars or heavy loads such as trucks and buses, and can be applied to bead fillers of various pneumatic tires.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  Using a Banbury mixer, according to the composition (parts by mass) shown in Table 1 below, first, in the first mixing stage, components other than sulfur and vulcanization accelerator are added and mixed (discharge temperature = 160 ° C.), and then obtained. In the final mixing stage, sulfur and a vulcanization accelerator were added to and mixed with the resulting mixture (discharge temperature = 90 ° C.) to prepare a rubber composition for tire bead filler. The details of each component in Table 1 are as follows.

[Rubber component]
・ Natural rubber: RSS # 3
[Liquid polybutadiene]
Liquid polybutadiene 1: “BI-3000” manufactured by Nippon Soda Co., Ltd. (unmodified hydrogenated liquid polybutadiene, Mn = 3,300, 1,2-vinyl bond amount (Vi) before hydrogenation = 90 mol%, hydrogen (Addition rate = 90 mol% or more)
Liquid polybutadiene 2: “GI-3000” manufactured by Nippon Soda Co., Ltd. (OH-terminated hydrogenated liquid polybutadiene, Mn = 3,100, Vi before hydrogenation = 90 mol%, hydrogenation rate = 90 mol% or more)
Liquid polybutadiene 3: “TEAI-1000” manufactured by Nippon Soda Co., Ltd. (acrylate-terminated modified hydrogenated liquid polybutadiene, Mn = 2,000, Vi prior to hydrogenation = 90 mol%, hydrogenation rate = 90 mol% or more)
Liquid polybutadiene 4: “L-1502” manufactured by Kuraray Co., Ltd. (OH-modified hydrogenated liquid polybutadiene, Mn = 7,000, Vi before hydrogenation = 40 mol% or less, hydrogenation rate = 90 mol% or more)
Liquid polybutadiene 5: “Poly pbR45HT” manufactured by Idemitsu Kosan Co., Ltd. (OH-modified liquid polybutadiene, Mn = 2,500, non-hydrogenated, Vi = 20 mol% or less)
[Other ingredients]
Carbon black: N550 (FEF), “Seast SO” manufactured by Tokai Carbon Co., Ltd.
-Oil: "Extract No. 4 S" manufactured by Showa Shell Sekiyu KK
・ Zinc flower: “Zinc flower No. 1” manufactured by Mitsui Mining & Smelting Co., Ltd.
Anti-aging agent: “Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.
・ Stearic acid: “Lunac S-20” manufactured by Kao Corporation
・ Phenolic resin: Oil-modified novolak type phenolic resin, “Sumilite Resin PR13349” manufactured by Sumitomo Bakelite Co., Ltd.
Melamine derivative: Hexamethoxymethyl melamine, “Cyretz 963L” manufactured by Mitsui Cytec Co., Ltd.
・ Sulfur: “5% oil-filled fine powder sulfur” manufactured by Tsurumi Chemical
・ Vulcanization accelerator: “Noxeller NS-P” manufactured by Ouchi Shinsei Chemical Co., Ltd.

  About each rubber composition, while evaluating workability in the unvulcanized state, the low exothermic performance and hardness were evaluated using the test piece of the predetermined shape vulcanized for 30 minutes at 150 degreeC. Each evaluation method is as follows.

-Processability: Using a rotorless Mooney measuring machine manufactured by Toyo Seiki Co., Ltd. according to JIS K6300, after preheating the unvulcanized rubber at 100 ° C for 1 minute, measuring the torque value after 4 minutes in Mooney units, The value is shown as an index with the value of Comparative Example 1 being 100. The smaller the index, the smaller the viscosity and the better the workability.

・ Low heat generation performance: In accordance with JIS K6394, the loss coefficient tanδ was measured using a viscoelasticity tester manufactured by Toyo Seiki Co., Ltd. under conditions of temperature 60 ° C., frequency 10 Hz, initial strain 10%, dynamic strain 1%. The index of Comparative Example 1 was expressed as 100. Tan δ at 60 ° C. is generally used as an index of low heat generation performance in rubber compositions for tires. The smaller the index, the smaller tan δ, and thus less heat generation, that is, excellent low heat generation performance. , It shows excellent fuel efficiency performance as a tire.

Hardness: Hardness was measured at 23 ° C. using a type A durometer (A type) conforming to JIS K6253, and indicated as an index with the value of Comparative Example 1 being 100. The larger the index is, the higher the hardness is. Therefore, when used as a bead filler, it indicates that the steering stability performance is excellent.

  The results are as shown in Table 1. In Comparative Example 2 in which the amount of carbon black was increased relative to Comparative Example 1 and in Comparative Example 3 in which the amount of phenolic resin was increased, the hardness increased, but the workability and low heat generation performance were improved. It got worse.

  In Comparative Example 4 in which the unmodified hydrogenated liquid polybutadiene was blended, the processability was improved as compared with Comparative Example 1, but the low heat generation performance was impaired and the hardness could not be increased. This shows that even when hydrogenated liquid polybutadiene is used, if it is not modified with a functional group, neither improvement in hardness nor reduction in heat generation performance can be obtained.

  In Comparative Example 5, a functional group-modified hydrogenated polybutadiene is used as the liquid polybutadiene. However, since it is a hydrogenated low vinyl product, bleeding occurs on the rubber surface, which improves workability and hardness. The effect was not obtained. This is thought to be due to the fact that the liquid polybutadiene bleeds on the surface, thereby impairing the effect of the phenolic resin as a dispersant and the effect of reducing the viscosity due to being liquid.

  In Comparative Example 6, functional group-modified polybutadiene was used as the liquid polybutadiene, but since it was a low vinyl product and not hydrogenated, the effect of increasing the hardness could not be obtained.

  On the other hand, in Examples 1 to 5 in which a functional group-modified liquid polybutadiene hydrogenated with a high vinyl product is blended together with a phenolic resin, high hardness, workability, and low heat generation performance can be improved in a well-balanced manner. did it. That is, in Examples 1-5, compared with the comparative example 1, it was possible to achieve high hardness while improving these without impairing workability and low heat generation performance.

DESCRIPTION OF SYMBOLS 1 ... Bead part, 2 ... Side wall part, 3 ... Tread part, 4 ... Bead core, 5 ... Carcass ply, 6 ... Belt, 7 ... Bead filler

Claims (3)

For 100 parts by mass of rubber component made of diene rubber,
1 to 25 parts by mass of a modified liquid polybutadiene having a functional group containing a hetero atom, which is a hydrogenated polybutadiene obtained by hydrogenating polybutadiene having a 1,2-vinyl bond amount of 50 mol% or more;
1 to 40 parts by mass of at least one phenolic component selected from the group consisting of phenolic resins and phenolic compounds,
A rubber composition for tire bead fillers. The rubber composition for tire bead filler according to claim 1, wherein the functional group of the modified liquid polybutadiene is at least one selected from the group consisting of a hydroxyl group, a carboxyl group, a carboxylic acid derivative group, and an epoxy group. .   A pneumatic tire provided with a bead filler comprising the rubber composition according to claim 1.

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