JP2011021162A - Rubber composition for pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for pneumatic tires which is improved in both modulus and low-heat generation performance through preparing its own simple composition, and is suitably used as a rubber composition or the like for covering steel cords of tires. <P>SOLUTION: The rubber composition for pneumatic tires is prepared by compounding 30-70 pts.wt. of carbon black and 0.05-0.5 pt.wt., on a metal basis, of an organometal salt in 100 pts.wt. of a modified diene rubber comprising (A) 95-99 wt.% of a diene rubber and (B) 5-1 wt.% of such a thermoplastic elastomer with hydrogen bond-forming performance that the main chain consists of a diene rubber and there are carbonyl-containing groups and nitrogen-containing heterocyclic rings intramolecularly and the weight-average molecular weight Mw is 50,000 or lower. In the rubber composition, the thermoplastic elastomer with hydrogen bond-forming performance to be used is preferably a diene polymer that is prepared by successively reacting a carbonyl group-containing unsaturated compound and a nitrogen-containing heterocyclic compound substituted with functional groups reactive to the carbonyl groups with the polymer main chain consisting of the diene rubber. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rubber composition for a pneumatic tire. More specifically, the present invention relates to a rubber composition for a pneumatic tire that is suitably used as a rubber material for covering a steel cord of a tire.

  Steel cords are used as reinforcing materials because automobile tires are subjected to strong impacts and large loads. The rubber covering the steel cord causes deterioration of the tire due to heat generation during running and deterioration due to impact or load, causing the rubber and the steel cord to peel off, resulting in a tire failure. Therefore, it is necessary to prevent the rubber used for coating the steel cord from being deteriorated by heat and to reduce the deformation amount of the rubber product due to impact, etc. Is required.

  Conventionally, as a method of increasing the elasticity of a rubber composition, a method of increasing the crosslinking density by increasing the amount of a vulcanizing agent such as carbon black or sulfur or a vulcanization accelerator has been used. However, although these methods make it possible to increase the elasticity of the rubber composition, when the amount of carbon black is increased, the calorific value is increased and the workability is deteriorated due to an increase in viscosity when not vulcanized. When the amount was increased, deterioration due to thermal oxidation was observed, and the life of the rubber product was sometimes shortened.

  Here, for the purpose of achieving high elasticity and low heat build-up of the rubber composition, xylenol (A), phenol, cresol with respect to 100 parts by weight of rubber composed of natural rubber, synthetic rubber or a mixed rubber thereof. Alternatively, phenols (B) made of a mixture of these are co-condensed with an aldehyde compound at a molar ratio (A / B) in the range of 25/75 to 75/25, and the softening point is 90 to 150 ° C. Patent Document 1 proposes a rubber composition comprising 0.5 to 10 parts by weight of the novolak resin and 0.5 to 10 parts by weight of a compound capable of donating a methylene group upon heating. However, since such a composition requires a special resin as an essential requirement, the preparation of the composition has been complicated.

JP-A-5-156091 Japanese Patent No. 3,998,690 Japanese Patent No. 4,011,057 Japanese Patent No. 4,037,016 EP 0 933 381 A1

  An object of the present invention is to provide a rubber composition for a pneumatic tire that can be suitably used as a rubber composition for covering a steel cord of a tire by improving the elastic modulus and low heat build-up by preparing a simple composition. It is in.

  The object of the present invention is to provide a weight average molecular weight Mw having (A) 95 to 99% by weight of a diene rubber and (B) a main chain comprising a diene rubber and having a carbonyl-containing group and a nitrogen-containing heterocycle in the molecule. Per 100 parts by weight of a modified diene rubber composed of 5 to 1% by weight of a hydrogen-bonding thermoplastic elastomer having a weight of 50,000 or less, and 30 to 70 parts by weight of carbon black and 0.05 to 0.5 parts by weight of an organic metal salt as a metal content This is achieved by the rubber composition for a pneumatic tire. As such a hydrogen bondable thermoplastic elastomer, a polymer main chain composed of a diene rubber is preferably reacted sequentially with a carbonyl group-containing unsaturated compound and a nitrogen-containing heterocyclic compound substituted with a functional group capable of reacting with the carbonyl group. The diene polymer obtained by making it use is used.

  The rubber composition for a pneumatic tire according to the present invention has an improved elastic modulus and low heat build-up compared to conventional products, and its preparation is simple, so that a belt, a steel carcass, an edge tape, and a belt edge cushion are prepared. It is suitably used as a rubber composition used for a rubber for covering a steel cord of a tire or a rubber member adjacent to the steel cord-covered rubber.

  Diene rubbers include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), chloroprene rubber (CR), butyl rubber (IIR), nitrile rubber (NBR), styrene butadiene rubber (SBR), etc. Or as a blend rubber, preferably NR, BR or a blend rubber thereof. As BR, cis-1,4-polybutadiene (vinyl cis rubber: VCR) modified with syndiotactic-1,2-polybutadiene can be used in addition to butadiene rubber. Syndiotactic used here The cis-1,4-polybutadiene modified with -1,2-polybutadiene is available as a commercial product, and more specifically, “VCR” (registered trademark) series such as VCR412, VCR617 from Ube Industries, Ltd. , VCR450, VCR800 and the like, and any of these can be used in the present invention. As the SBR, either emulsion polymerization SBR (E-SBR) or solution polymerization SBR (S-SBR) can be used.

  The hydrogen-bonding thermoplastic elastomer added to these diene rubbers has a main chain made of a diene rubber, has a carbonyl-containing group and a nitrogen-containing heterocyclic ring in the molecule, and has a weight average molecular weight Mw (by the GP method). (Measurement) is 50,000 or less, preferably 10,000 to 40,000. Such hydrogen-bonding thermoplastic elastomers are described in Patent Documents 2 to 4 describing patent inventions related to the applicant's application.

  As the hydrogen-bonding thermoplastic elastomer, a polymer main chain composed of a diene rubber is preferably reacted successively with a carbonyl group-containing unsaturated compound and a nitrogen-containing heterocyclic compound substituted with a functional group capable of reacting with the carbonyl group. The diene polymer obtained in this way is used.

  Natural rubber, isoprene rubber, butadiene rubber, chloroprene rubber, nitrile rubber, styrene butadiene rubber, etc. are used as the diene rubber molecule of the hydrogen bondable thermoplastic elastomer whose main chain is composed of a diene rubber molecule, preferably isoprene rubber. Is used.

  Examples of the carbonyl group-containing unsaturated compound that undergoes an addition reaction to the polymer main chain of these diene rubber molecules include maleic anhydride and maleic acid, and maleic anhydride is preferably used. The modification rate of maleic anhydride is generally set to about 0.1 to 10% by weight based on the weight of the polymer molecule to be modified.

  The addition reaction of maleic anhydride to the polymer main chain is preferably carried out by an ene reaction. As described in Patent Document 5, maleic anhydride is ring-opened in the usual addition reaction, and many are added as maleic acid. However, according to the ene reaction, maleic anhydride has almost no acid anhydride structure. It is added while holding

  As such a maleic anhydride-added diene rubber, a commercially available product can be used as it is. Examples of maleic anhydride-modified liquid polyisoprene rubber include Kuraray product LIR-410A.

  The maleic anhydride group thus added includes a nitrogen-containing heterocyclic compound in which the nitrogen-containing heterocyclic ring is a 5-membered ring or a 6-membered ring and is substituted with a functional group capable of reacting with maleic acid, for example. 4H-3-amino-1,2,4-triazole, 4-aminopyridine and the like in which the substituted functional group is an amino group, 4-hydroxypyridine in which the substituted functional group is a hydroxyl group, 4- The addition reaction is further carried out by heating at about 120 to 200 ° C. using a small excess of methylolpyridine and the like.

  Here, as a thermoplastic elastomer, an addition reaction of maleic anhydride to a diene rubber and further reaction with a functional group-substituted nitrogen-containing heterocyclic compound is a carbonyl group derived from a carbonyl group-containing unsaturated compound, and A hydrogen bond consisting of a donor-H-acceptor as shown by OH… O, NH… O, OH… N, NH… N is formed with the reacted nitrogen-containing heterocyclic compound to enable self-crosslinking. In addition, it dissociates during heating (120 ° C.), and forms hydrogen bonds again at around room temperature.

  A hydrogen-bonding thermoplastic elastomer obtained by sequentially reacting a carbonyl group-containing unsaturated compound and a nitrogen-containing heterocyclic compound substituted with a functional group capable of reacting with the polymer main chain obtained by such a series of reactions, The diene rubber is used at a ratio of 5 to 1 part by weight with respect to 95 to 99 parts by weight of the diene rubber. When used in a smaller proportion, no significant improvement is observed in various properties, while when used in a proportion higher than this, the exothermic property is improved, but the elongation at break is significantly reduced.

  A modified diene rubber comprising 95 to 99% by weight of a diene rubber and 5 to 1% by weight of a hydrogen-bonding thermoplastic elastomer has 30 to 70 parts by weight of carbon black and an organic metal salt as a metal per 100 parts by weight of the rubber. 0.05 to 0.5 part by weight is used in combination.

  As the carbon black, grades of carbon black such as HAF, FEF, and GPF are used in a proportion of 30 to 70 parts by weight, preferably 40 to 60 parts by weight per 100 parts by weight of the modified diene rubber. If carbon black is used in a smaller proportion, the elastic modulus will decrease, while if it is used in a proportion higher than this, the calorific value will increase, which is not preferable.

  In addition, as an organic metal salt, an organic metal salt containing cobalt, nickel or the like as a metal, such as naphthenic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, palmitic acid, neodecanoic acid, rosin acid, tall oil acid, An organic acid cobalt salt or nickel salt such as boric acid trineodecanoic acid is used in a proportion of 0.05 to 0.5 parts by weight, preferably 0.1 to 0.3 parts by weight, per 100 parts by weight of the modified diene rubber. If the organic metal salt is used in a proportion other than the above, the effect of improving the elastic modulus and low heat build-up will not be seen.

  In the rubber composition containing the above components as essential components, sulfur and thiazole (MBT, MBTS, ZnMBT, etc.), sulfenamide (CBS, DCBS, BBS, etc.), guanidine ( DPG, DOTG, OTBG, etc.), thiuram (TMTD, TMTM, TBzTD, TETD, TBTD, etc.), dithiocarbamate (ZTC, NaBDC, etc.), xanthate (ZnBX, etc.), etc. One or more types are blended and used. Furthermore, other compounding agents generally used as rubber compounding agents, for example, reinforcing agents or fillers such as talc, clay, graphite, calcium silicate, processing aids such as stearic acid, zinc oxide, softening agents, A plasticizer, an antiaging agent, and the like are appropriately blended and used as necessary.

  The composition is prepared by kneading by a general method using a kneader such as a kneader or a Banbury mixer and an open roll, and the obtained composition is pressure-bonded to the surface of the steel cord by a calender roll. Thus, a steel-rubber composite as a band-shaped member is formed. Such a rubber composition for tires is adjacent to a portion in a pneumatic tire where high elasticity and low heat generation are required, such as a steel cord covering rubber, in addition to a steel cord covering rubber used for a member such as a carcass or a belt. It can also be used to form members, specifically belt edge tapes, belt edge cushions, and the like.

  Next, the present invention will be described with reference to examples.

Reference Example Maleic anhydride-modified liquid isoprene rubber (Kuraray product LIR-410A; Mw 25,000, maleic anhydride modification rate 3.9% by weight) 200.00 g (79.6 mmol in terms of maleic anhydride skeleton), 4H-3-amino-1, 6.97 g (82.9 mmol) of 2,4-triazole was added and stirred at 160 ° C. for 3 hours. After confirming that the solution was uniform, the solution was allowed to stand overnight to obtain 202.8 g of a gel-like hydrogen-bonding thermoplastic elastomer (yield 98%).

または

The gel-like hydrogen-bonding thermoplastic elastomer that is the reaction product is considered to have an amic acid bond [I], an imide bond [II], or both, and the main product is [II 〕it is conceivable that.

Or

Comparative example 1 (standard example)
100 parts by weight of natural rubber (RSS # 3)
HAF carbon black (Tokai carbon product seast 300) 60 〃
Cobalt orthoborate neodecanoate 1 〃
(Rhodia product Manobond: Cobalt content 22%)
Zinc oxide (Zinc oxide, Zodo Chemical Industrial products) 7 〃
Sulfur (Akzo Nobel product Christex HS OT 20; sulfur content 80%) 5 〃
Vulcanization accelerator (Ouchi Emerging Chemical Industry Noxeller DS) 1 1

  Of the above components, the components other than the vulcanization accelerator and sulfur were kneaded for 6 minutes with a 16 L closed mixer, and released when the temperature reached 110 ° C. to obtain a master batch. A vulcanization accelerator and sulfur were added to this master batch and kneaded with an open roll to obtain a diene rubber composition.

Comparative Example 2
In Comparative Example 1, the amount of HAF carbon black was changed to 70 parts by weight.

Comparative Example 3
In Comparative Example 1, the amount of natural rubber [NR] was changed to 97 parts by weight, and the amount of organic acid Co salt was changed to 0.2 parts by weight (Co content 0.044 parts by weight). 3 parts by weight of thermoplastic elastomer [TPE] was used.

Comparative Example 4
In Comparative Example 3, the amount of organic acid Co salt was changed to 3 parts by weight (Co content 0.66 parts by weight).

Example 1
In Comparative Example 1, the amount of NR was changed to 99 parts by weight, and 1 part by weight of TPE was used.

Example 2
In Comparative Example 1, the amount of NR was changed to 97 parts by weight, and 3 parts by weight of TPE was used.

Example 3
In Comparative Example 1, the amount of NR was changed to 95 parts by weight, and 5 parts by weight of TPE was used.

Example 4
In Example 2, 10 parts by weight of 97 parts by weight of NR was changed to butadiene rubber (Nippon Zeon product Nipol BR 1220).

Example 5
In Example 2, cis-1,4-polybutadiene (vinyl cis-rubber) in which 10 parts by weight of NR amount was 97 parts by weight modified with syndiotactic-1,2-polybutadiene (Ube Industries UBEPOL-VCR412) 10 The weight was changed to be used.

The diene rubber composition obtained in each of the above Examples and Comparative Examples was vulcanized at 160 ° C. for 30 minutes to obtain a vulcanized rubber sheet (15 × 15 × 0.2 cm), and the obtained vulcanized rubber sheet Were measured for elastic modulus (100% modulus) and exothermic properties.
Elastic modulus: Conforms to JIS K6251, expressed as an index with the value obtained in the standard example as 100
(The larger the value, the higher the elastic modulus)
Exothermic property: Conforms to JIS K6255, expressed as an index with the value obtained in the standard example as 100
(The larger the value, the lower the heat generation.)

The results obtained are shown in the following table.
Table measurement comparisons example implementation example
Item 1 2 3 4 1 2 3 4 5
Elastic modulus 100 113 98 102 113 110 110 103 103 108
Exothermic 100 91 100 97 103 105 105 110 115 110

From the above results, the following can be said.
(1) In each example, both the elastic modulus and the low heat generation property are good.
(2) Even when appropriate amounts of diene rubber and hydrogen bonding thermoplastic elastomer are used, when the organometallic salt falls below the specified amount, no improvement in elastic modulus is observed (Comparative Example 3).
(3) Even when diene rubber and hydrogen-bonding thermoplastic elastomer are used in appropriate amounts, if the organometallic salt exceeds the specified amount, improvement in low heat build-up is not observed (Comparative Example 4).

Claims (6)

  (A) 95 to 99% by weight of diene rubber and (B) hydrogen bondability with a main chain made of diene rubber and having a carbonyl-containing group and a nitrogen-containing heterocycle in the molecule, and a weight average molecular weight Mw of 50,000 or less A rubber composition for a pneumatic tire comprising 30 to 70 parts by weight of carbon black and 0.05 to 0.5 parts by weight of an organic metal salt as a metal per 100 parts by weight of a modified diene rubber comprising 5 to 1% by weight of a thermoplastic elastomer. .   (B) Component Hydrogen-bonding thermoplastic elastomer reacts sequentially with polymer main chain made of diene rubber with carbonyl group-containing unsaturated compound and nitrogen-containing heterocyclic compound substituted with functional group capable of reacting with this carbonyl group The rubber composition for a pneumatic tire according to claim 1, wherein the rubber composition is a diene polymer obtained.   The rubber composition for a pneumatic tire according to claim 2, wherein the nitrogen-containing heterocyclic compound substituted with a functional group capable of reacting with a carbonyl group is an amino group-substituted or hydroxyl group-substituted nitrogen-containing heterocyclic compound.   The rubber composition for a pneumatic tire according to claim 1, wherein the organic metal salt is an organic acid cobalt salt or an organic acid nickel salt.   The rubber composition for a pneumatic tire according to claim 1, which is used as a rubber material for steel cord coating or a rubber molding material for a member adjacent to steel cord coating rubber.   A pneumatic tire having a steel cord covering portion coated with a vulcanizate of the rubber composition for a pneumatic tire according to claim 5 or a rubber member adjacent to the steel cord covering rubber.