JP2011168638A - Rubber composition for tire inner liner, and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a tire inner liner, the composition capable of improving flexure fatigue resistance without decreasing resistance against air permeation. <P>SOLUTION: The rubber composition for the tire inner liner contains 0.5 to 5 pts.mass of zinc borate based on 100 pts.mass of a butyl rubber component containing a halogenated butyl rubber and/or a butyl rubber. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rubber composition used as an inner liner of a pneumatic tire, and a pneumatic tire using the rubber composition.

  In a tubeless pneumatic tire, in order to ensure airtightness, a rubber layer having a low air permeability called an inner liner is provided on the inner surface of the tire. For such an inner liner, a halogenated butyl rubber having a low air permeability as compared with a normal rubber layer constituting a tread, a sidewall or the like is used (for example, see Patent Document 1 below).

  By the way, in order to improve the durability of the tire, the inner liner is required to have excellent bending fatigue resistance. As a method for improving the bending fatigue resistance, there is generally a method of blending oil, but when oil is blended, the air permeation resistance deteriorates. Therefore, it is required to improve the bending fatigue resistance without impairing the air permeation resistance.

  Patent Document 2 below discloses a rubber composition containing zinc borate. However, this document is mainly intended for tire treads, and therefore, diene rubber such as styrene butadiene rubber is mainly used as a rubber component. In addition, this document improves the reaction efficiency of the silane coupling agent by adding silica, a silane coupling agent, and zinc borate to the rubber component, and suppresses the generation of bubbles, while at the same time improving the wear resistance. It is intended to improve and reduce rolling resistance. That is, zinc borate is blended to improve the reaction efficiency of the silane coupling agent and suppress the generation of bubbles, and does not disclose any effects of the present invention.

  Patent Document 3 below discloses a rubber composition for coating a steel cord, which contains silica having a specific nitrogen adsorption specific surface area in a diene rubber, a silane coupling agent, and zinc borate. This document also improves the reactivity of the silane coupling agent by adding zinc borate and suppresses the generation of blisters (bubbles), and does not suggest any effect of the present invention. .

Japanese Patent Laid-Open No. 10-130442 JP 2007-084756 A JP 2008-156448 A

  An object of this invention is to provide the rubber composition for tire inner liners which can improve bending fatigue resistance, without impairing air permeation resistance.

  The rubber composition for a tire inner liner according to the present invention contains 0.5 to 5 parts by mass of zinc borate with respect to 100 parts by mass of a butyl rubber component composed of halogenated butyl rubber and / or butyl rubber.

  The pneumatic tire according to the present invention includes an inner liner made of such a rubber composition.

  According to the present invention, by adding zinc borate to the halogenated butyl rubber and / or butyl rubber, the bending fatigue resistance can be improved without impairing the air permeation resistance. Durability can be improved while ensuring airtightness.

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

  The butyl rubber component used in the rubber composition of the present invention comprises halogenated butyl rubber and / or butyl rubber (IIR). Examples of the halogenated butyl rubber include brominated butyl rubber (BIIR) and chlorinated butyl rubber (CIIR). By using these, the air permeability of the inner liner can be improved. More preferably, the butyl rubber component is composed of a halogenated butyl rubber alone or a blend rubber of a halogenated butyl rubber and a butyl rubber, and the proportion of the halogenated butyl rubber in the butyl rubber component is 60% by weight or more. preferable.

  Zinc borate is blended in the rubber composition according to the present invention. By blending zinc borate, the bending fatigue resistance can be improved without impairing the air permeation resistance. The reason is not necessarily clear, but zinc borate contains zinc atoms, while zinc borate particles dispersed in the rubber matrix maintain air permeation resistance by interfering with air permeation. It is presumed that the bending fatigue resistance is improved by participating in the cross-linking reaction of the halogenated butyl rubber by white (however, the present invention is not limited thereby).

The zinc borate, zinc borate 3.5 hydrate _{(2ZnO · 3B 2 O 3 ·} 3.5H 2 O), tetraborate zinc _{(ZnB 4 O} 7), zinc metaborate (Zn _(BO 2) ₂ ), basic zinc borate (ZnB ₄ O ₇ · 2ZnO) and the like, and these can be used alone or in combination of two or more. Among these, zinc borate 3.5 hydrate (2ZnO · 3B ₂ O ₃ · 3.5H ₂ O) is particularly preferably used.

  The particle size of zinc borate is not particularly limited, but as the particle size increases, the air permeability resistance tends to improve. On the other hand, if the particle size becomes too large, the effect of improving bending fatigue resistance decreases, and on the contrary, Since there is a possibility that the bending fatigue property may be impaired, the average particle diameter is preferably 0.1 to 200 μm, more preferably 0.5 to 50 μm. Here, the average particle diameter is a value measured by a laser diffraction scattering method.

  Zinc borate is blended at 0.5 to 5 parts by mass with respect to 100 parts by mass of the butyl rubber component. When the blending amount of zinc borate is less than 0.5 parts by mass, the effect of improving the bending fatigue resistance cannot be obtained. On the other hand, if the blending amount exceeds 5 parts by mass, the bending fatigue resistance is impaired. A more preferable blending amount is 1 to 4 parts by mass with respect to 100 parts by mass of the butyl rubber component.

  The rubber composition of the present invention is usually blended with zinc white (ZnO). Zinc flower is blended as a vulcanizing agent (crosslinking agent) for halogenated butyl rubber, and the blending amount is preferably 1 to 5 parts by mass with respect to 100 parts by mass of the butyl rubber component, More preferably, it is 2-4 mass parts.

  The rubber composition of the present invention preferably contains a tackifier. The tackifier is an additive that imparts tackiness to the rubber composition, and is also referred to as a tackifier. By adding a tackifier, the adhesiveness at the joint part of the inner liner can be increased before the vulcanization after the green tire is molded, and the opening of the joint part can be suppressed. Adhesiveness can also be improved.

  As the tackifier, an alkylphenol-based resin, a hydrocarbon resin, or the like can be used, but a hydrocarbon resin is preferably used from the viewpoint of air permeability resistance. Examples of the hydrocarbon resin include aliphatic petroleum resins, aromatic petroleum resins, and aliphatic / aromatic copolymer petroleum resins. The aliphatic petroleum resin is a resin obtained by cationic polymerization of unsaturated monomers such as isoprene and cyclopentadiene, which are petroleum fractions corresponding to 4 to 5 carbon atoms (C5 fraction) (C5 petroleum resins). It may also be hydrogenated. An aromatic petroleum resin is a resin obtained by cationic polymerization of monomers such as vinyltoluene, alkylstyrene, and indene, which are petroleum fractions (C9 fraction) having 8 to 10 carbon atoms (C9 petroleum). It may also be referred to as a resin) and may be hydrogenated. The aliphatic / aromatic copolymer petroleum resin is a resin obtained by copolymerizing the C5 fraction and the C9 fraction (also referred to as C5 / C9 petroleum resin), and is hydrogenated. There may be. Particularly preferred is a petroleum resin mainly composed of a C5 component.

  The amount of the tackifier, preferably a hydrocarbon resin, is preferably 2 to 15 parts by mass, more preferably 3 to 10 parts by mass with respect to 100 parts by mass of the butyl rubber component.

  In the rubber composition of the present invention, carbon black can be blended as a filler, and the carbon black is preferably blended in an amount of 30 to 70 parts by mass with respect to 100 parts by mass of the butyl rubber component. Preferably it is 40-60 mass parts. When the blending amount of the carbon black is less than 30 parts by mass, the unvulcanized rubber composition has a large shrinkage and the workability may be impaired. On the other hand, if the blending amount exceeds 70 parts by mass, the viscosity of the unvulcanized rubber composition may increase and the processability may be impaired.

The carbon black is not particularly limited, and various grades can be appropriately selected and used. The iodine adsorption amount is 15 to 55 mg / g and the DBP (dibutyl phthalate) oil absorption amount is 75. What is -125cm < ³ > / 100g is used preferably. Specifically, it is preferable to use carbon black belonging to GPF class. If the iodine adsorption amount is too large, the adhesiveness is impaired. Here, the iodine adsorption amount (IA) is a value measured in accordance with JIS K6217-1, and the DBP oil absorption is a value measured in accordance with JIS K6217-4.

  In the rubber composition of the present invention, in addition to the components described above, vulcanization aids such as stearic acid, anti-aging agents, processing aids, fillers other than carbon black, vulcanization agents, vulcanization accelerators, etc. Various additives usually blended in the rubber composition of the inner liner can be blended.

  The rubber composition comprising the above is extruded into a sheet shape by a roll or an extruder according to a conventional method, and the extruded sheet material is vulcanized in a state where it is attached to the inside of the rubber constituting the tread, sidewall, etc. Thus, a tubeless pneumatic tire having an inner liner made of a thin rubber layer on the inner surface of the tire is formed. In addition, although the thickness of an inner liner changes with tire sizes etc., it is 0.5-3.0 mm normally.

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

  Using a Banbury mixer, rubber compositions for inner liners of Examples 1 to 4 and Comparative Examples 1 to 7 were prepared according to the composition shown in Table 1 below. The detail of each component of Table 1 is as follows.

BIIR: Brominated butyl rubber “Bromobutyl 2222” manufactured by ExxonMobil
IIR: Butyl rubber “Butyl 268” manufactured by ExxonMobil
Carbon black: GPF (Tokai Carbon Co., Ltd. "SEAST V", iodine adsorption = 26mg / g, DBP oil absorption ⁼ 87cm 3 / 100g)
・ Oil: “JOMO Process P200” manufactured by Japan Energy Co., Ltd.
- zinc _{borate: 2ZnO · 3B 2 O 3 ·} 3.5H 2 O, ( measured using Nikkiso Co. particle size analyzer "Microtrac HRA") Average particle diameter = 2 [mu] m, Borax Inc. "Fuya ear Break ZB EF "
· Barium _{metaborate: n (BaO · B 2 O} 3 · H 2 O), manufactured by Sakai Chemical Industry Co., Ltd. "BUSAN 11-M1"
· Aluminum _{borate: 9Al 2 O 3 · 2B 2} O 3, manufactured by Shikoku Chemicals Co., Ltd. "arbovirus Light PF03"
・ Magnesium borate: 2MgO ・ 3B ₂ O ₃・ nH ₂ O, manufactured by Tomita Pharmaceutical Co., Ltd. ・ Zinc flower: “Zinc flower 3” manufactured by Mitsui Kinzoku Co., Ltd.
・ Stearic acid: “Stearic acid” manufactured by Kao Corporation
・ Hydrocarbon resin: “Escollet 1102” manufactured by ExxonMobil (petroleum resin mainly composed of C5 component)
・ Processing aid: “Stractol 40MSF” manufactured by Straktor

  About each obtained rubber composition, the bending fatigue resistance and the air permeation resistance were evaluated. The evaluation method is as follows.

Flexural fatigue resistance: The number of crack growth was measured for a test piece vulcanized at 160 ° C. for 30 minutes in accordance with JIS K6260 using a demachic bending tester. It displays with the index | exponent when the crack growth frequency of the comparative example 1 is set to 100, and it shows that it is excellent in bending fatigue resistance, so that a numerical value is large.

-Air permeability resistance: For a vulcanized rubber sheet having a thickness of 1 mm vulcanized at 160 ° C. for 30 minutes, the air permeability was measured using a gas permeability tester (“BT-3” manufactured by Toyo Seiki Seisakusho) It was displayed as an index with the value of Comparative Example 1 being 100. It shows that it is excellent in air permeation resistance, so that a numerical value is small.

  The results are as shown in Table 1. Compared to Comparative Example 1 as a control, in Comparative Example 2, the oil resistance was significantly deteriorated, although the bending fatigue resistance was improved by adding oil.

  On the other hand, in Examples 1 to 4 according to the present invention, by adding a predetermined amount of zinc borate to Comparative Example 1 as a control, the bending fatigue resistance is reduced without impairing the air permeability. Thus, the durability was improved while ensuring the airtightness of the tubeless pneumatic tire.

In Comparative Example 3, the compounding amount of zinc borate was too small, and the effect of improving the bending fatigue resistance was not obtained. On the contrary, in Comparative Example 7, the amount of zinc borate was too large, and the bending fatigue resistance was worsened. Further, in Comparative Example 4 in which barium metaborate was blended instead of zinc borate, Comparative Example 5 in which aluminum borate was blended, and Comparative Example 6 in which magnesium borate was blended, the bending fatigue resistance deteriorated. It was. From this, the improvement effect of bending fatigue resistance is an effect peculiar when zinc borate is used among borates, and is an advantageous effect of the present invention.

  The rubber composition for a tire inner liner of the present invention can be used for various tubeless pneumatic tires such as tires for passenger cars, large tires (heavy duty tires) used for trucks and buses, and tires for motorcycles.

Claims (5)

  A rubber composition for a tire inner liner, containing 0.5 to 5 parts by mass of zinc borate with respect to 100 parts by mass of a butyl rubber component comprising a halogenated butyl rubber and / or a butyl rubber.   The rubber composition for a tire inner liner according to claim 1, further comprising 1 to 5 parts by mass of zinc white with respect to 100 parts by mass of the butyl rubber component.   Furthermore, the rubber composition for tire inner liners of Claim 1 or 2 which contains 2-15 mass parts of hydrocarbon resins with respect to 100 mass parts of said butyl-type rubber components.   The rubber composition for a tire inner liner according to any one of claims 1 to 3, further comprising 30 to 70 parts by mass of carbon black with respect to 100 parts by mass of the butyl rubber component.   A pneumatic tire provided with the inner liner which consists of a rubber composition of any one of Claims 1-4.