JP2011021085A - Rubber composition for pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a pneumatic tire that has processability, elongation at break, elastic modulus, low-heat build-up property, flexural fatigue resistance and the like well-balancedly improved and is suitably employable for a rim cushion part and the like of a tire. <P>SOLUTION: The rubber composition for a pneumatic tire comprises 100 pts.wt. of a modified diene rubber comprising (A) 95-99 wt.% of a diene rubber and (B) 5-1 wt.% of a hydrogen-bonding thermoplastic elastomer that has a main chain comprised of a diene rubber, bears a carbonyl-containing group and a nitrogen-containing heterocycle in the molecule and has a weight-average molecular weight Mw of at most 50,000 and, incorporated therewith, 75-110 pts.wt. of carbon black and a vulcanizing ingredient having a vulcanization accelerator/sulfur weight ratio of 0.9-1.8. <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 vulcanization molding of a rim cushion portion of a pneumatic tire.

  2. Description of the Related Art Conventionally, a pneumatic tire in which a rim cushion rubber is disposed on the inner peripheral side of a bead portion that comes into contact with a rim has been used in order to improve the fit between the pneumatic tire and the rim in an automobile vehicle. By adopting such a structure, the rebound resilience of the rim cushion rubber that is compressed and deformed when the rim is assembled improves the adhesion to the rim, thereby improving the rim fitting property and the rim slip resistance.

  The rim cushion portion is not only subjected to physical stress from the road surface but also directly subjected to stress such as rotational torque. Accordingly, the rim cushion portion is subjected to stress from the road surface and stress from the rim in the opposite direction, so that durability tends to be impaired compared to other portions of the tire. It is also susceptible to deformation and heat aging due to heat generated by high speed running.

  For this reason, the processability, elongation at break, elastic modulus, low heat build-up, resistance to bending fatigue, etc. of the rubber of the rim cushion are very important in relation to maintaining the tire internal pressure. Deformation due to various stresses, and tire deflection due to a decrease in air pressure due to breakage increase, leading to phenomena such as accelerated failure.

  Also, in automobile vehicles, pneumatic tires are mounted via the rubber of the rim and rim cushion, and if the rubber of this part is soft, the fitting will deteriorate and rim displacement will occur, so it must be high hardness Is required. As a countermeasure, there is a method of increasing the hardness by increasing the amount of carbon black or increasing the amount of the vulcanizing compounding agent.

  However, in such a method, there are problems such as cracking due to a decrease in the breaking strength of rubber, and since heat aging tends to proceed when heat generation is large, it is required to have low heat generation properties. As a countermeasure for this, it is generally known that silica is blended. However, the blending of silica brings about an increase in viscosity, and it is inevitable that the factory processability deteriorates.

  The present applicant has previously described natural rubber and / or polyisoprene rubber 18 to 55 parts by weight, polybutadiene rubber 43 to 80 parts by weight, styrene-butadiene copolymer rubber 2 as a rubber composition suitably used for a rim cushion part and the like. A rubber composition comprising a rubber composed of at least part by weight and less than 10 parts by weight, wherein the styrene content in the styrene-butadiene copolymer rubber is 35% by weight or less based on 100% by weight of the styrene-butadiene copolymer rubber Is proposed in Patent Document 1. Although the rim cushion part obtained from such a rubber composition is excellent in compression set resistance, further improvement is desired in terms of heat aging resistance and durability.

JP 2007-302715 A 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 is suitably used for a rim cushion portion of a tire, improving workability, elongation at break, elastic modulus, low heat buildup, bending fatigue resistance and the like in a balanced manner. There is to do.

  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. Is a vulcanization system in which 75 to 110 parts by weight of carbon black and a vulcanization accelerator / sulfur weight ratio of 0.9 to 1.8 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 This is achieved by a rubber composition for a pneumatic tire obtained by blending a compounding agent. 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.

  Since the diene rubber composition according to the present invention improves the workability, elongation at break, elastic modulus, low heat build-up, bending fatigue resistance, etc. in a well-balanced manner, it can be used as a vulcanization molding material for rim cushion parts of pneumatic tires. Preferably used.

  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 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 75 to 110 parts by weight of carbon black and a vulcanization accelerator / sulfur per 100 parts by weight of the rubber. A vulcanizing compounding agent having a weight ratio of 0.9 to 1.8 is blended and used.

  As carbon black, grades of carbon black such as HAF, FEF, GPF, etc. are used in a proportion of 75 to 110 parts by weight, preferably 75 to 105 parts by weight, per 100 parts by weight of the modified diene rubber. If the carbon black content is used more than this, the elastic modulus will deteriorate.

  Further, in the diene rubber composition, as a rubber vulcanizing compound, 1.0 to 2.3 parts by weight of sulfur as a vulcanizing agent, preferably 1.1 to 2.0 parts by weight 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.), 0.9 to 4.14 parts by weight, preferably 1.1 to 3.2 parts by weight of a vulcanization accelerator such as xanthate (ZnBX etc.) is used, and these have a vulcanization accelerator / sulfur weight ratio of 0.9 to 1.8, preferably 1.0 to It is added at a rate such that 1.6. When the vulcanization accelerator / sulfur weight ratio is smaller than this, the bending fatigue resistance is inferior, whereas when it is larger, the elastic modulus is inferior.

  In the diene rubber composition containing the above components as essential components, a compounding agent generally used as a compounding agent for rubber, for example, reinforcing agents or fillers such as talc, clay, graphite, calcium silicate, etc. Further, processing aids such as stearic acid, paraffin wax and aroma oil, zinc oxide, anti-aging agent, plasticizer and the like are appropriately blended and used as necessary.

  The composition was 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 was vulcanized according to the diene rubber used. Vulcanized at temperature to form a rim cushion.

  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)
Natural rubber (RSS # 3) 50 parts by weight Butadiene rubber (Nippon Zeon product NIPOL BR1220) 50 〃
HAF carbon black (Tokai carbon product seast 300) 80 〃
Stearic acid (Japanese oil and fat product beads stearic acid) 1 〃
Zinc oxide (Zondox Chemical Products Zinc Oxide 3 types) 5 〃
Sulfur (Akzo Nobel product HS OT 20, sulfur content 80%) 1.9 〃
Vulcanization accelerator (Ouchi Emerging Chemical Industry Noxeller NS) 2 〃

  Among the above components, the components other than the vulcanization accelerator and sulfur were kneaded for 8 minutes in a 16 L closed mixer, and released when the temperature reached 160 ° 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 (vulcanization accelerator / sulfur weight ratio = 1.316).

Comparative Example 2
In Comparative Example 1, the amount of HAF carbon black was changed to 60 parts by weight.

Comparative Example 3
In Comparative Example 1, the amount of HAF carbon black was changed to 120 parts by weight.

Comparative Example 4
In Comparative Example 1, the sulfur content was changed to 3 parts by weight to obtain a diene rubber composition (vulcanization accelerator / sulfur weight ratio = 0.833).

Comparative Example 5
In Comparative Example 1, 10 parts by weight of silica (Degussa Ultrasil VN3GR) and 0.8 parts by weight of a silane coupling agent (Si69) were additionally used.

Comparative Example 6
In Comparative Example 1, the amount of natural rubber [NR] was changed to 49.5 parts by weight, and 0.5 part by weight of the hydrogen bonding thermoplastic elastomer [TPE] obtained in the above Reference Example was used.

Example 1
In Comparative Example 1, the amount of NR was changed to 49 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 47 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 45 parts by weight, and 5 parts by weight of TPE was used.

Comparative Example 7
In Comparative Example 1, the amount of NR was changed to 40 parts by weight, and 10 parts by weight of TPE was used.

Comparative Example 8
In Example 2, the sulfur content was changed to 1.3 parts by weight to obtain a diene rubber composition (vulcanization accelerator / sulfur weight ratio = 1.923).

Comparative Example 9
In Example 2, the sulfur content was changed to 3 parts by weight to obtain a diene rubber composition (vulcanization accelerator / sulfur weight ratio = 0.833).

The diene rubber composition obtained in each of the above Examples and Comparative Examples and the rubber composition were vulcanized at 160 ° C. for 20 minutes to obtain a predetermined vulcanized rubber test piece, and the following items were measured for these. . The measured value is indicated by an index with a standard value of 100.
Viscosity: JIS K6300 compliant, measured at 100 ° C using a large rotor
(The larger the index, the lower the viscosity and the better the workability)
Elongation at break [Tb]: Measured under room temperature conditions according to JIS K6251
(The larger the index, the better the elongation at break)
Elastic modulus (E ′), tanδ: JIS K6394 compliant, initial strain 10%, amplitude 2%, frequency 20Hz, 20 ° C
Measured under conditions
(E ′ has a higher modulus of elasticity as the index increases, and tanδ has a higher index.
(It is hard to generate fever.)
Bending fatigue resistance: JIS K6260-1999 compliant, times until sample breaks under 40mm strain
Measure number
(The larger this index, the better the bending fatigue resistance)

The measurement results obtained are the amount of natural rubber [NR] used in the composition preparation (parts by weight), the amount of thermoplastic elastomer [TPE] (parts by weight), the amount of carbon black [CB] (parts by weight) and the vulcanization. The accelerator / sulfur weight ratio [A / S ratio] is shown in the following table.
table
Composition measurement results
Example NR TPE CB A / S Specific viscosity Tb E ′ tanδ Bending fatigue Comparative example 1 50 − 80 1.316 100 100 100 100 100
〃 2 50 − 60 1.316 121 126 79 130 129
３ 3 50 − 120 1.316 81 79 129 78 76
４ 4 50 −80 0.833 97 90 120 98 132
〃 5 50 − 80 1.316 90 100 100 109 100
６ 6 49.5 0.5 80 1.316 99 99 100 101 100
Example 1 49 1 80 1.316 99 99 100 105 121
〃 2 47 3 80 1.316 99 98 100 107 111
〃 3 45 5 80 1.316 98 96 100 108 100
Comparative Example 7 40 10 80 1.316 97 90 100 116 78
47 8 47 3 80 1.923 102 105 92 101 140
９ 9 47 3 80 0.833 96 98 120 104 90

From the above results, the following can be said.
(1) Each of the examples is good for each measured item, and is particularly excellent in terms of heat generation and bending fatigue resistance.
(2) If the amount of carbon black is less than the specified amount, the value of E ′ (Comparative Example 2) decreases.
(3) When the vulcanization accelerator / sulfur weight ratio is less than the specified amount, the Tb value decreases (Comparative Example 4).
(4) When silica is used in combination, the viscosity increases and processability decreases (Comparative Example 5).
(5) If the blend ratio of the thermoplastic elastomer is less than the specified amount, no particular property improving effect is observed (Comparative Example 6), and if it is too much, the Tb value is greatly reduced (Comparative Example 7).
(6) Even when an appropriate amount of thermoplastic elastomer is used, if the vulcanization accelerator / sulfur weight ratio is less than the specified amount, the bending fatigue resistance is particularly poor (Comparative Example 9), and too much. The value of E ′ decreases (Comparative Example 8).

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 Carbon black 75-110 parts by weight and vulcanization accelerator / sulfur weight ratio 0.9-1.8 vulcanization compounding agent is blended per 100 parts by weight of modified diene rubber 100% by weight of thermoplastic elastomer A rubber composition for a pneumatic tire.   (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 a vulcanizing compound comprising 1.0 to 2.3 parts by weight of sulfur and 0.9 to 4.14 parts by weight of a vulcanization accelerator is used.   The rubber composition for a pneumatic tire according to claim 1, which is used as a rubber material for vulcanization molding of a rim cushion portion.   A pneumatic tire having a rim cushion portion vulcanized and molded from the rubber composition for a pneumatic tire according to claim 5.