JP2011168666A - 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 resistance against air permeation and flexure fatigue resistance in a good balance. <P>SOLUTION: The rubber composition for a tire inner liner contains 0.5 to 5 pts.mass of zinc borate and 10 to 50 pts.mass of a planar filler such as pulverized coal 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 low air permeability as compared with a normal rubber layer constituting a tread, a sidewall or the like is used.

  Further, in order to further improve the air permeation resistance, there is a method of blending a pulverized bituminous coal having a layered structure and a flat filler such as talc having a plate-like structure (see Patent Documents 1 and 2 below). ).

  However, when such a flat filler as described above is blended, there is a drawback that the bending fatigue resistance is deteriorated. Therefore, it is required to improve the air permeation resistance and the bending fatigue resistance in a balanced manner.

  Patent Document 3 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 4 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 2002-088191 A JP 2007-084756 A JP 2008-156448 A

  An object of the present invention is to provide a rubber composition for a tire inner liner that can improve the air permeation resistance and the bending fatigue resistance in a balanced manner.

  The rubber composition for a tire inner liner according to the present invention includes 0.5 to 5 parts by mass of zinc borate and a flat filler 10 with respect to 100 parts by mass of a butyl rubber component composed of halogenated butyl rubber and / or butyl rubber. It contains ~ 50 parts by mass.

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

  According to the present invention, air permeation resistance can be improved without impairing bending fatigue resistance by blending halogenated butyl rubber and / or butyl rubber with zinc borate and a flat filler. Therefore, the air tightness can be improved without impairing the durability of the tubeless pneumatic tire.

  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.

  A flat filler is blended in the rubber composition according to the present invention. The flat filler is a filler whose main particle shape is flat, and improves air permeation resistance of the inner liner by inhibiting air permeation in the rubber layer. That is, an inner liner made of a thin rubber layer is generally formed by being extruded into a sheet shape with a roll or an extruder, etc., so that the flat filler is laid down substantially parallel to the layer surface in the rubber layer. Thus, the air that attempts to pass through the rubber layer in the thickness direction is blocked by the flat plate filler, and the air permeation is thus inhibited.

  The flat filler may be an inorganic filler such as a layered mineral (for example, talc, mica, clay) or an organic filler. Preferably, the compatibility with the rubber component is good, so that it is excellent in dispersibility with respect to the rubber component, so that an organic filler mainly composed of carbon is used. Specifically, coal pulverized by finely pulverizing coal Things. Since coal has a layered structure, flat particles can be obtained by crushing with a pulverizer such as a ball mill, and this can be used as a filler.

  The flat filler preferably has an average particle size of 0.5 to 100 μm, more preferably 1 to 30 μm. If it is less than 0.5 μm, the effect of improving the air permeation resistance may be insufficient, and if it exceeds 100 μm, the durability of the inner liner may be reduced. Here, the average particle diameter is measured by a laser diffraction scattering method.

  The aspect ratio of the flat filler is not particularly limited, but is preferably 5 to 30. Here, the aspect ratio is the ratio of the major axis (maximum dimension in the plane portion) to the thickness of the flat filler, and was randomly extracted using an image obtained with a transmission electron microscope (TEM). About each particle | grain, thickness and a major axis are measured, an aspect ratio is calculated, and it calculates | requires as the arithmetic mean.

  It is preferable that the compounding quantity of a flat filler is 10-50 mass parts with respect to 100 mass parts of the said butyl rubber components, More preferably, it is 10-40 mass parts. When the blending amount of the flat filler is less than 10 parts by mass, the effect of improving the air permeation resistance is insufficient. On the other hand, if the blending amount exceeds 50 parts by mass, the bending fatigue resistance may be impaired even if zinc borate is used in combination.

Carbon black can be blended as a reinforcing filler in the rubber composition of the present invention. 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 to What is 125 cm < 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.

  The compounding amount of carbon black is preferably 30 to 70 parts by mass, more preferably 40 to 60 parts by mass with respect to 100 parts by mass of the butyl rubber component. 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 total amount of carbon black and the flat filler (total filler amount) is preferably 40 to 120 parts by mass, more preferably 100 parts by mass with respect to 100 parts by mass of the butyl rubber component. 50 to 110 parts by mass. In addition, as a filler, you may mix | blend fillers other than a flat filler and carbon black in the range which does not impair the effect of this invention.

  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, in addition to the components described above, vulcanization aids such as stearic acid, anti-aging agents, processing aids, vulcanizing agents, vulcanization accelerators and the like can be used for the inner liner rubber composition. Various additives that are usually blended 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 6 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)
-Coal pulverized product: Bituminous coal pulverized product, “Austin Black 325” manufactured by Coal Fillers (average particle size = (measured using a particle size analyzer “Microtrac HRA” manufactured by Nikkiso Co., Ltd.) = 5 μm)
Flat talc: “HAR” (average particle size = 5.7 μm, aspect ratio = 4.7) manufactured by Nippon Mystron Co., Ltd.
- zinc _{borate: 2ZnO · 3B 2 O 3 ·} 3.5H 2 O, an 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. Larger values indicate better air permeation resistance.

  The results are as shown in Table 1. Compared to Comparative Example 1, which is a control, in Comparative Example 2, the air permeation resistance was greatly improved by adding a flat filler, but the flex fatigue resistance was improved. Deteriorated greatly.

  On the other hand, in Examples 1 to 6 according to the present invention, by blending a predetermined amount of zinc borate together with the flat plate filler for Comparative Example 1 as a control, the bending fatigue resistance is not impaired. The air permeation resistance has been remarkably improved, and thus the air tightness can be improved while ensuring the durability of the tubeless pneumatic tire.

  In Comparative Example 3, the amount of zinc borate was too small to improve the bending fatigue resistance. Even in Comparative Example 4 in which the amount of zinc borate was too large, the bending fatigue resistance could not be improved.

Further, Comparative Example 5 in which barium metaborate is blended instead of zinc borate, Comparative Example 6 in which aluminum borate is blended, and Comparative Example 7 in which magnesium borate is blended all improve the bending fatigue resistance. I couldn't. From this, it can be said that the bending fatigue resistance improving effect is a unique effect when zinc borate is used among borates.

  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 tire comprising 0.5 to 5 parts by mass of zinc borate and 10 to 50 parts by mass of a flat filler with respect to 100 parts by mass of a butyl rubber component comprising a halogenated butyl rubber and / or a butyl rubber. Rubber composition for inner liner.   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.