JP2011074309A - Polymer composition for inner liner, and pneumatic tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer composition for an inner liner with the excellent air permeation resistance and adhesion to an adjacent rubber, and a pneumatic tire using the same for an inner liner. <P>SOLUTION: The polymer composition for an inner liner includes a polymer component including 99.5-60 mass% of a styrene-isobutylene-styrene triblock copolymer, and 0.5-40 mass% of a styrene-maleic anhydride copolymer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polymer composition for an inner liner and a pneumatic tire using the same.

  In recent years, tires have been made lighter due to the strong social demand for low fuel consumption of vehicles, and among the tire members, the amount of air leakage from the inside of the pneumatic tire to the outside is arranged inside the tire. Even in an inner liner having a function of improving the air permeation resistance by reducing (air permeation amount), weight reduction and the like have been performed.

  Currently, the rubber composition for an inner liner uses a butyl rubber containing 70 to 100% by mass of butyl rubber and 30 to 0% by mass of natural rubber to improve the air permeation resistance of the tire. . In addition to butylene, the butyl rubber contains about 1% by mass of isoprene, which, together with sulfur, vulcanization accelerator, and zinc white, enables co-crosslinking with adjacent rubber. The butyl rubber usually requires a thickness of about 0.6 to 1.0 mm for passenger car tires and about 1.0 to 2.0 mm for truck and bus tires. Therefore, there has been proposed a polymer that is more excellent in air permeation resistance than butyl rubber and can make the inner liner layer thinner.

  In Patent Document 1, as a pneumatic tire capable of simultaneously suppressing air pressure reduction, improving durability, and improving fuel consumption, 100 parts by mass of a rubber component made of natural rubber and / or synthetic rubber is used. , The following general formula (I),

  (Wherein m and n are each independently 1 to 100 and x is 1 to 1000). The ethylene-vinyl alcohol copolymer represented by the formula is at least within a range of 15 to 30 parts by mass. There has been proposed a pneumatic tire using the contained rubber composition for an inner liner as an inner liner layer. However, in the technique of Patent Document 1, the thickness of the rubber sheet using the rubber composition is 1 mm, and there is room for improvement in terms of weight reduction of the tire.

  Patent Document 2 proposes a pneumatic tire in which an inner liner layer is formed using nylon having a low air permeability, and adhesion with a tire inner surface or a carcass layer, which is a rubber composition, can be improved. ing. However, in the technique of Patent Document 2, in order to form a nylon film layer, after the nylon film is RFL-treated, it is necessary to bond a rubber paste made of a rubber composition, which causes a problem that the process becomes complicated. .

JP 2007-291256 A JP-A-9-165469

  An object of the present invention is to provide a polymer composition for an inner liner excellent in air permeation resistance and adhesion to an adjacent rubber, and a pneumatic tire using the same for the inner liner.

  The present invention provides a polymer for an inner liner in which the polymer component contains 99.5 to 60% by mass of a styrene-isobutylene-styrene triblock copolymer and 0.5 to 40% by mass of a styrene-maleic anhydride copolymer. It is a composition.

  In the polymer composition for an inner liner according to the present invention, the styrene-isobutylene-styrene triblock copolymer preferably contains a styrene component in the range of 10 to 30% by mass.

  In the polymer composition for an inner liner according to the present invention, the styrene-maleic anhydride copolymer preferably has a styrene component / maleic anhydride component molar ratio of 50/50 to 90/10 and a weight average molecular weight of 4,000. And a styrene-maleic anhydride copolymer base resin having a maleic anhydride component acid value of 50 to 600.

  In the polymer composition for an inner liner according to the present invention, preferably, the styrene-maleic anhydride copolymer is a monoester group and a monocarboxylic acid obtained by esterifying a styrene-maleic anhydride copolymer base resin. A styrene-maleic anhydride copolymer ester resin having a group.

  In the polymer composition for an inner liner according to the present invention, preferably, the styrene-maleic anhydride copolymer is a styrene-maleic anhydride copolymer ammonium in which a styrene-maleic anhydride copolymer base resin is dissolved in an ammonium salt. Contains saline solution.

  The present invention is a pneumatic tire using the polymer composition for an inner liner as an inner liner.

  ADVANTAGE OF THE INVENTION According to this invention, the polymer composition for inner liners excellent in air permeation resistance and adhesiveness with adjacent rubber, and a pneumatic tire using the same for an inner liner can be obtained.

It is typical sectional drawing which shows the right half of the pneumatic tire in one embodiment of this invention.

<Polymer composition for inner liner>
In one embodiment of the present invention, the polymer composition for the inner liner has a polymer component of 99.5 to 60% by mass of a styrene-isobutylene-styrene triblock copolymer (hereinafter also referred to as SIBS), styrene-anhydrous Maleic acid copolymer (hereinafter also referred to as SMA) 0.5 to 40% by mass.

<Styrene-isobutylene-styrene triblock copolymer>
Due to the isobutylene block of SIBS, the polymer composition containing SIBS has excellent air permeation resistance. Therefore, when a polymer composition containing SIBS is used for the inner liner, a pneumatic tire excellent in air permeation resistance can be obtained.

  Further, SIBS has excellent durability because its molecular structure other than aromatic is completely saturated, thereby preventing deterioration and hardening. Therefore, when a polymer composition made of SIBS is used for the inner liner, a pneumatic tire having excellent durability can be obtained.

  When a pneumatic tire is manufactured by applying a polymer composition comprising SIBS to an inner liner, conventional air permeation resistance, such as halogenated butyl rubber, is provided to ensure air permeation resistance by incorporating SIBS. Therefore, it is possible to reduce the amount of use even if the high specific gravity halogenated rubber that has been used for this purpose is not used. As a result, the weight of the tire can be reduced, and the effect of improving fuel consumption can be obtained.

  In the polymer component of the polymer composition for an inner liner in one embodiment of the present invention, the SIBS content is 99.5 to 60% by mass. When the SIBS content is 60% by mass or more, an inner liner having excellent air permeation resistance and durability can be obtained. Moreover, when the content of SIBS is 99.5% by mass or less, an inner liner excellent in adhesiveness with adjacent rubber can be obtained. The content is preferably 98 to 70% by mass in terms of better air permeation resistance and durability.

  The molecular weight of SIBS is not particularly limited, but the weight average molecular weight by GPC measurement is preferably 50,000 to 400,000 from the viewpoint of fluidity, molding processability, rubber elasticity and the like. If the weight average molecular weight is less than 50,000, rubber elasticity may be lowered, and if it exceeds 400,000, fluidity and molding processability are lowered, which is not preferable.

  SIBS generally contains 10 to 40% by mass of a styrene component. It is preferable that content of the styrene component in SIBS is 10-30 mass% at the point from which air permeation resistance and durability become more favorable.

  The SIBS preferably has a molar ratio of isobutylene component to styrene component (isobutylene component / styrene component) of 40/60 to 95/5 from the viewpoint of rubber elasticity of the copolymer. In SIBS, the degree of polymerization of each block is about 10,000-150,000 for isobutylene and 5,000-30,000 for styrene from the viewpoint of rubber elasticity and handling (becomes liquid when the degree of polymerization is less than 10,000). It is preferably about 000.

  SIBS can be obtained by a general vinyl compound polymerization method, for example, a living cationic polymerization method.

  For example, JP-A-62-48704 and JP-A-64-62308 disclose that living cationic polymerization of isobutylene and other vinyl compounds is possible. By using isobutylene and other compounds as vinyl compounds, It is disclosed that a polyisobutylene-based block copolymer can be produced. In addition, methods for producing vinyl compound polymers by the living cationic polymerization method are disclosed in, for example, U.S. Pat. No. 4,946,899, U.S. Pat. No. 5,219,948, and JP-A-3-174403. Are listed.

  Since the SIBS has no double bond other than aromatic in the molecule, it is more stable to ultraviolet rays than a polymer having a double bond in the molecule, such as polybutadiene, and therefore has a weather resistance. Good properties. Furthermore, although it has no double bond in the molecule and is a saturated rubber-like polymer, the refractive index (nD) at 20 ° C. of light with a wavelength of 589 nm is the Polymer Handbook (1989: Wiley). -(Polymer Handbook, Willy, 1989)). This is significantly higher than other saturated rubbery polymers such as ethylene-butene copolymers.

<Styrene-maleic anhydride copolymer>
In this specification, the styrene-maleic anhydride copolymer is an esterification of a styrene-maleic anhydride copolymer base resin (hereinafter also referred to as SMA base resin) or a styrene-maleic anhydride copolymer base resin. The styrene-maleic anhydride copolymer ester resin (hereinafter also referred to as SMA ester resin) and the styrene-maleic anhydride copolymer-based resin having a monoester group and a monocarboxylic acid group are converted into ammonium salts. It describes as a concept containing the melt | dissolved styrene-maleic anhydride copolymer ammonium salt aqueous solution (henceforth SMA resin ammonium salt aqueous solution).

  The styrene-maleic anhydride copolymer is used as a polymer surfactant and a highly functional cross-linking agent in dispersion and emulsification, and has excellent vulcanization adhesiveness with rubber. Moreover, since the wettability is given to rubber, the adhesive effect is also excellent.

  In one embodiment of the present invention, the polymer composition for an inner liner can improve vulcanization adhesion with rubber while maintaining air barrier properties by blending SMA with SIBS.

  In the polymer component of the polymer composition for the inner liner, the SMA content is 0.5 to 40% by mass. When the content of SMA is 0.5% by mass or more, an inner liner excellent in adhesiveness with adjacent rubber can be obtained. Moreover, when the SMA content is 40% by mass or less, an inner liner having excellent air permeation resistance and durability can be obtained. The content of SMA in the polymer component is more preferably 2 to 30% by mass.

(Styrene-maleic anhydride copolymer-based resin)
In one embodiment of the present invention, the SMA preferably contains a styrene-maleic anhydride copolymer base resin from the viewpoints of unvulcanized tackiness and post-vulcanized adhesion.

  The SMA base resin preferably has a styrene component / maleic anhydride component molar ratio of 50/50 to 90/10 from the viewpoints of a high softening point and high thermal stability.

  The SMA base resin preferably has a weight average molecular weight of 4,000 to 20,000 from the viewpoint of adhesion after vulcanization and fluidity. Furthermore, the weight average molecular weight is more preferably 5,000 to 15,000.

  In the SMA base resin, the maleic anhydride component in the styrene-maleic anhydride copolymer preferably has an acid value of 50 to 600 from the viewpoint of unvulcanized adhesiveness. Furthermore, the acid value of the maleic anhydride component is more preferably 95 to 500.

(Ester resin of styrene-maleic anhydride copolymer)
In one embodiment of the present invention, the styrene-maleic anhydride copolymer is a styrene-maleic anhydride copolymer having a monoester group and a monocarboxylic acid group obtained by esterifying an SMA base resin. It is preferable that the ester resin (hereinafter also referred to as SMA ester resin) is included.

  The SMA ester resin has the property of being excellent in vulcanization adhesion. Therefore, the polymer composition for inner liners excellent in vulcanization adhesiveness with the rubber layer can be obtained by blending SMA ester resin with SIBS.

  The SMA ester resin preferably has a styrene component / maleic anhydride component molar ratio of 50/50 to 90/10 from the viewpoint of vulcanization adhesion.

  The SMA ester resin preferably has a weight average molecular weight of 5,000 to 12,000 from the viewpoint of adhesion after vulcanization and fluidity. Furthermore, the weight average molecular weight is more preferably 6,000 to 11,000.

  In the SMA ester resin, the maleic anhydride component preferably has an acid value of 50 to 400 from the viewpoint of adhesion to unvulcanized rubber. Furthermore, the acid value of the maleic anhydride component is more preferably 95 to 290.

  The SMA ester resin can be produced, for example, by introducing a base resin and alcohol into a reaction vessel and heating and stirring in an inert gas atmosphere.

(Styrene-maleic anhydride copolymer ammonium salt aqueous solution)
In one embodiment of the present invention, the styrene-maleic anhydride copolymer is a styrene-maleic anhydride copolymer aqueous ammonium salt solution (hereinafter also referred to as an SMA ammonium salt aqueous solution) in which an SMA base resin is dissolved in an ammonium salt. ) Is preferably included.

  The SMA ammonium salt aqueous solution has a property of excellent wettability. Therefore, the polymer composition for inner liners excellent in adhesiveness can be obtained by mix | blending SMA ammonium salt aqueous solution with SIBS.

  The SMA ammonium salt aqueous solution preferably has a solid content of 10.0 to 45.0% from the viewpoint of adhesion to unvulcanized rubber and molding processability.

  The aqueous SMA ammonium salt solution preferably has a pH of 8.0 to 9.5 from the viewpoint of tackiness.

  An aqueous SMA ammonium salt solution causes exothermic reaction when water is added to a reaction vessel, base resin is added with vigorous stirring, and ammonium hydroxide is gradually added. Then, it can manufacture by heating to predetermined temperature and continuing stirring until melt | dissolution is completed.

<Other ingredients>
The polymer composition for the inner liner includes other reinforcing agents, vulcanizing agents, vulcanization accelerators, various oils, anti-aging agents, softeners, plasticizers, coupling agents, etc. for tires or general polymer compositions. Various compounding agents and additives blended in can be blended. Moreover, the content of these compounding agents and additives can also be set to general amounts.

<Method for producing polymer composition for inner liner>
The unvulcanized product of the polymer composition for the inner liner can be produced by a conventionally known method. For example, after weighing each of the above materials to a predetermined blending ratio, rubber such as an open roll, a Banbury mixer, etc. There is a method of kneading at 100 to 250 ° C. for 5 to 60 minutes using a kneading apparatus.

<Pneumatic tire structure>
A pneumatic tire 1 according to an embodiment of the present invention will be described with reference to FIG.

  The pneumatic tire 1 can be used for passenger cars, trucks / buses, heavy machinery and the like. The pneumatic tire 1 has a tread portion 2, a sidewall portion 3, and a bead portion 4. Further, a bead core 5 is embedded in the bead portion 4. Further, a carcass 6 provided from one bead portion 4 to the other bead portion, folded back at both ends to lock the bead core 5, and a belt layer 7 formed of two plies outside the crown portion of the carcass 6, Is arranged. An inner liner 9 extending from one bead portion 4 to the other bead portion 4 is disposed on the inner side in the tire radial direction of the carcass 6. The belt layer 7 is formed so that two plies made of a cord such as a steel cord or an aramid fiber intersect each other so that the cord is usually at an angle of 5 to 30 ° with respect to the tire circumferential direction. Placed in. The carcass has organic fiber cords such as polyester, nylon, and aramid arranged at approximately 90 ° in the circumferential direction of the tire. In the region surrounded by the carcass and its folded portion, the side wall extends from the upper end of the bead core 5. A bead apex 8 extending in the direction is arranged.

  The thickness of the inner liner 9 is preferably 0.05 to 0.5 mm from the viewpoint of good air permeation resistance and improvement in fuel consumption performance by reducing the weight of the tire.

<Examples 1-9, Comparative Examples 1-4>
(Production of polymer composition)
In accordance with the formulation shown in Table 1, various compounding agents were put into a twin-screw extruder (screw diameter: φ50 mm, L / D: 30, cylinder temperature: 220 ° C.) and pelletized, and then a T-die extruder (screw). A polymer sheet for an inner liner made of a polymer composition for an unvulcanized inner liner was prepared with a diameter: φ80 mm, L / D: 50, die lip width: 500 mm, cylinder temperature: 220 ° C., film gauge: 0.3 mm). . The following tests were conducted using the polymer sheet.

<Peel test>
A peel test was conducted according to JIS K 6256 “Vulcanized Rubber and Thermoplastic Rubber—How to Determine Adhesiveness”. First, the polymer sheet having a thickness of 0.3 mm, the rubber sheet having a thickness of 2 mm (formulation: NR / BR / SBR = 40/30/30) and the reinforced canvas fabric were stacked in the order described above under the condition of 170 ° C. A test specimen for peeling was produced by heating under pressure for 12 minutes. Using the obtained test piece, a peel test was performed to measure the adhesive force between the polymer sheet for the inner liner and the rubber sheet. The size of the test piece was 25 mm wide, and it was performed under a room temperature condition of 23 ° C. The peel strength index was calculated by the following calculation formula using the obtained numerical value as a reference (100) as Comparative Example 1. The larger the value, the better the adhesion.

(Peeling strength index) = (Adhesive strength of each formulation) / (Adhesive strength of Comparative Example 1) × 100
The results are shown in Table 1.

<JIS-A hardness>
Test pieces were prepared according to JIS K 6253 “How to obtain hardness of vulcanized rubber and thermoplastic rubber”, and JIS-A hardness was measured at room temperature of 23 ° C. The results are shown in Table 1.

(Production of tire)
The polymer sheet for the inner liner was applied to the inner liner portion of the tire and press molded at 170 ° C. for 20 minutes to produce a 195 / 65R15 size tire. A static air drop rate test and a bending crack growth test were performed using the tire.

<Static air drop rate test>
A 195 / 65R15 steel radial PC tire is assembled to a JIS standard rim 15 × 6 JJ, an initial air pressure of 300 Kpa is enclosed, and left at room temperature for 90 days, and the rate of decrease in air pressure is calculated. The results are shown in Table 1.

<Flexible crack growth test>
In accordance with JIS K 6260 "Dematcher bending crack test method for vulcanized rubber and thermoplastic rubber", a test piece is prepared, a bending crack growth test is performed, and 70% elongation is repeated 1,000,000 times to bend the rubber sheet. After that, the length of the generated crack was measured. Using the obtained numerical value as a reference (100) as Comparative Example 1, the resistance to flex crack growth of each formulation was indicated by an index according to the following formula. A larger value means that cracks are less likely to grow and can be said to be good.

(Bending crack growth resistance index) = (Crack length of each formulation) / (Crack length of Comparative Example 1) × 100
<Evaluation results>

(Note 1) IIR: “Exon Chlorobutyl 1068” manufactured by ExxonMobil Co., Ltd.
(Note 2) SIBS: SIBS: “Sibusta-SIBSTAR 102T” manufactured by Kaneka Corporation (Shore A hardness 25, styrene content 25% by mass)
(Note 3) SMA base resin: “SMA1000” manufactured by Sartomer (styrene component / maleic anhydride component: 50/50, weight average molecular weight: 5,500, acid value of maleic anhydride: 490)
(Note 4) SMA ester resin: “SMA1440” manufactured by Sartomer (styrene component / maleic anhydride component: 80/20, weight average molecular weight: 7,000, acid value of maleic anhydride: 200)
(Note 5) SMA ammonium salt aqueous solution: “SMA1000H” (pH 9.0) manufactured by Sartomer
(Note 6) Carbon: “Seast V” manufactured by Tokai Carbon Co., Ltd. (N660, N ₂ SA 27 m ² / g)
Examples 1 to 9 are a polymer composition for an inner liner containing 99.5 to 60% by mass of SIBS and 0.5 to 40% by mass of SMA, and a pneumatic tire using the same. Compared with the comparative example 2 which a polymer component consists of 100 mass% of SIBS, adhesiveness improved, maintaining air permeation resistance.

  Comparative Example 1 was a polymer composition for an inner liner whose polymer component was 100% by mass of IIR and a pneumatic tire using the same, and was used as a reference.

  Comparative Example 2 is a polymer composition for an inner liner whose polymer component is 100% by mass of SIBS and a pneumatic tire using the same. Air permeation resistance is excellent, but adhesion is poor.

  Comparative Examples 3 and 4 are a polymer composition for an inner liner in which polymer components are 50% by mass of SIBS and 50% by mass of SMA, and a pneumatic tire using the same. Although the adhesion was improved as compared with Comparative Example 2, the air permeation resistance was deteriorated.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 pneumatic tire, 2 tread part, 3 sidewall part, 4 bead part, 5 bead core, 6 carcass, 7 belt layer, 8 bead apex, 9 inner liner.

Claims (6)

  A polymer composition for an inner liner, wherein the polymer component contains 99.5 to 60% by mass of a styrene-isobutylene-styrene triblock copolymer and 0.5 to 40% by mass of a styrene-maleic anhydride copolymer.   The polymer composition for an inner liner according to claim 1, wherein the styrene-isobutylene-styrene triblock copolymer contains a styrene component in an amount of 10 to 30% by mass.   The styrene-maleic anhydride copolymer has a styrene component / maleic anhydride component molar ratio of 50/50 to 90/10 and a weight average molecular weight of 4,000 to 20,000. The polymer composition for an inner liner according to claim 1 or 2, comprising a styrene-maleic anhydride copolymer base resin having an acid value of 50 to 600.   The styrene-maleic anhydride copolymer is a styrene-maleic anhydride copolymer having a monoester group and a monocarboxylic acid group obtained by esterifying the styrene-maleic anhydride copolymer base resin. The polymer composition for an inner liner according to any one of claims 1 to 3, comprising an ester resin.   The styrene-maleic anhydride copolymer includes an aqueous styrene-maleic anhydride copolymer ammonium salt solution in which the styrene-maleic anhydride copolymer base resin is dissolved in an ammonium salt. A polymer composition for an inner liner according to claim 1.   A pneumatic tire using the polymer composition for an inner liner according to claim 1 as an inner liner.

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