JP2010111785A - Rubber composition for tire and run flat tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve low heat generation properties and reduce the weight in a rubber composition while maintaining reinforcing properties by combinedly using a specific polymer gel and a lignin derivative. <P>SOLUTION: In the rubber composition for tire, the polymer gel, which is crosslinked diene polymer particles modified by a compound having a hydroxy group and having -100 to 0°C glass transition temperature, and the lignin derivative are compounded in a rubber component comprising a diene rubber. In a run flat tire, a side pad formed by using the rubber composition is provided inside a carcass of a sidewall. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a tire rubber composition and a run flat tire using the rubber composition as a side pad.

  A run-flat tire is a pneumatic tire that can travel a certain distance even when the air pressure inside the tire decreases due to a failure such as puncture and the air pressure becomes zero. As one of tire structures for enabling such run-flat running, a tire structure in which an inner surface of a sidewall portion is reinforced by a reinforcing rubber layer called a side pad is known.

  Since the side pad is required to have durability during run flat running, it is required to have relatively high hardness and excellent fracture characteristics. In addition, as the side pad, a thick rubber layer having a substantially crescent-shaped cross section is generally used, so there is a demand for weight reduction. Also, if the side pad is made of a rubber composition that easily generates heat, not only will the tire rolling resistance increase during normal driving and fuel efficiency will deteriorate, but the side pad will be easily damaged by heat during run flat driving. Low exothermicity is also required to extend the flat travel distance.

  As a means to improve the durability of run-flat tires, it is known to increase sulfur and increase oil to increase the vulcanization density and increase the elastic modulus, and to improve workability. It has been. However, the low exothermic property is impaired by such means. On the other hand, in order to improve the exothermic property and reduce the weight of the rubber composition, it is generally only necessary to reduce the filler. In this case, however, the reinforcing property is lowered, which is not preferable as a rubber composition for a side pad of a run-flat tire. . Thus, as a rubber composition for a run flat tire, it is difficult to achieve both a low exothermic property, a fracture property (reinforcing property), and a weight reduction at a high level.

  Conventionally, as a rubber composition for run-flat tires, the following Patent Document 1 includes a rubber component containing natural rubber, which maintains processability and is excellent in fracture resistance and low heat build-up by blending transpolybutadiene. Compositions have been proposed. Further, in Patent Document 2 below, a rubber composition in which a specific organic sulfide compound is blended as a vulcanizing agent to improve the heat aging resistance and bending fatigue resistance of the vulcanized rubber while maintaining the necessary hardness. Has been proposed.

  Further, in Patent Document 3 below, in order to improve the low heat build-up, it is modified with a compound having a hydroxyl group and has a glass transition point of −100 to −65 ° C., a toluene swelling index Qi of 1 to 15 and an average. It has been proposed to use a rubber composition containing crosslinked rubber particles (polymer gel) having a particle diameter of 5 to 2000 nm for a side pad of a run-flat tire. However, there is a demerit that the reinforcing property is lowered simply by adding the polymer gel.

By the way, lignin is a main component of wood together with cellulose and hemicellulose, and is a substance that is abundant in nature and obtained by using a cooking eluate by-produced during pulp production as a raw material. It has been proposed to use such lignin and derivatives thereof as a tackifier for rubber compositions (see Patent Document 4 below). In addition, it has been proposed to improve grip properties on ice roads by blending cellulose fibers containing lignin into a rubber composition (see Patent Document 5 below). However, it is not known to use a lignin derivative in combination with a specific polymer gel.
JP 2008-106148 A JP 2008-1111071 A JP 2008-174606 A JP-A-5-98082 JP-A-11-157303

  The present invention provides a tire rubber composition which can improve the low heat buildup and reduce the weight while maintaining the reinforcing property by using a specific polymer gel and a lignin derivative in combination. Objective. Moreover, it aims at providing the run flat tire using this rubber composition.

  The rubber composition for a tire according to the present invention is a polymer gel which is a diene-based polymer particle modified with a compound having a hydroxyl group and a crosslinked diene-based polymer particle having a glass transition point of −100 to 0 ° C. And a lignin derivative.

  In the run flat tire according to the present invention, a side pad provided on the inner side of the carcass of the sidewall portion is formed of the rubber composition.

  According to the present invention, by using a polymer gel having a specific glass transition point having a hydroxyl group and a lignin derivative in combination, the dispersibility of the polymer gel can be improved and the low heat build-up can be improved while maintaining the reinforcing property. At the same time, the weight of rubber can be reduced. Therefore, when used for a side pad of a run flat tire, it is possible to contribute to a reduction in tire rolling resistance while maintaining durability during run flat running.

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

  The rubber composition according to the present invention contains (A) a rubber component made of a diene rubber, (B) a polymer gel, and (C) a lignin derivative.

  The diene rubber as the component (A) is not particularly limited. For example, natural rubber (NR), polyisoprene rubber (IR), styrene-butadiene rubber (SBR), polybutadiene rubber (BR), styrene-isoprene rubber. , Butadiene-isoprene rubber, styrene-isoprene-butadiene copolymer rubber, nitrile rubber, and the like. These may be used alone or in combination of two or more. When the rubber composition is used for a side pad of a run-flat tire, it is preferable to use a blend of natural rubber and / or polyisoprene rubber and polybutadiene rubber.

  As the polymer gel of the component (B), cross-linked diene polymer particles (rubber particles) modified with a compound having a hydroxyl group and having a glass transition point (Tg) of −100 to 0 ° C. are used. it can. Thus, by using a polymer gel having a low glass transition point, the loss factor (tan δ) can be lowered and the low heat generation property can be improved. Moreover, the dispersibility of a polymer gel improves because the hydroxyl group which exists in the particle | grain surface interacts with the hydroxyl group of the lignin derivative mentioned later, and this can further improve low exothermic property.

  Such a polymer gel can be produced by crosslinking a rubber dispersion. Examples of the rubber dispersion include rubber latex produced by emulsion polymerization, rubber dispersion obtained by emulsifying solution-polymerized rubber in water, and examples of the crosslinking agent include organic peroxides and organic azo compounds. And sulfur-based crosslinking agents. The rubber particles can also be crosslinked by copolymerization with a polyfunctional compound having a crosslinking action during the emulsion polymerization of the rubber. Specifically, methods disclosed in JP-A-10-204225, JP-T 2004-504465, JP-T 2004-506058, JP-T 2004-530760, and the like can be used.

  Examples of the diene polymer constituting the polymer gel include the various diene rubbers described above, and these can be used alone or in combination of two or more. Preferably, the main component is polybutadiene rubber or styrene butadiene rubber, and more preferably the main component is polybutadiene rubber.

  As the polymer gel, one having a glass transition point (Tg) of −100 to 0 ° C. is used. By using a material having a low glass transition point, tan δ can be lowered. The glass transition point is more preferably −30 ° C. or lower, and further preferably −60 ° C. or lower. In addition, the glass transition point of a polymer gel can be adjusted with the kind of diene polymer used as a base, and its crosslinking degree. The glass transition point is a value (temperature increase rate 20 ° C./min) measured using differential scanning calorimetry (DSC) in accordance with JIS K7121.

  As the polymer gel, one modified with a compound having an OH (hydroxyl) group is used. The polymer gel is composed of a diene polymer and has a C═C double bond on the particle surface. Therefore, by using a compound having an OH group and a reactivity with respect to the C═C double bond, Can incorporate OH groups.

  Examples of such compounds (modifiers) include hydroxyalkyl (such as hydroxybutyl acrylate or methacrylate, hydroxyethyl acrylate or methacrylate, hydroxypropyl acrylate or methacrylate, as described in JP-T-2004-506058. And (meth) acrylate.

  Since the polymer gel is composed of a diene polymer, it has a double bond on the surface. Therefore, when silica is used as the filler and a silane coupling agent is blended, the polymer gel and silica can be bonded via the silane coupling agent by the reaction of the silane coupling agent with the double bond. . Further, the OH group on the surface of the polymer gel reacts with the silane coupling agent, and the polymer gel and the rubber component can be bonded via the silane coupling agent. Alternatively, the polymer gel can be cross-linked by the reaction of the silane coupling agent between the double bond of the polymer gel and the OH group. As a result, the performance can be further improved.

  The polymer gel preferably has an average particle size (DVN value according to DIN 53 206) of 40 to 200 nm. By using a polymer gel having such an average particle diameter, the processability and the reinforcing effect of the rubber composition can be maintained, and the low heat build-up can be further improved.

  The polymer gel preferably has a toluene swelling index Qi of less than 16. The toluene swelling index is more preferably 1 to 15, and further preferably 3 to 8. If the toluene swelling index Qi is too large, the particles become soft and the reinforcing effect is lost. The polymer gel preferably has a gel content of 94% by weight or more. When the gel content is smaller than this, the elastic modulus of the rubber particles tends to be lowered, and the rubber composition containing the rubber particles is also affected.

  Here, the toluene swelling index and the gel content are measured by swelling a polymer gel in toluene and then drying it. That is, 250 mg of polymer gel was swollen in 25 mL of toluene under shaking for 24 hours, centrifuged at 20000 rpm, weighed, then dried to a constant mass at 70 ° C., and then dried mass Weigh. The gel content is the weight ratio (%) of the polymer gel after drying to the polymer gel used. The toluene swelling index is obtained by Qi = (wet mass of gel) / (dry mass of gel).

  The blending amount of the polymer gel is preferably 3 to 70 parts by weight, more preferably 5 to 50 parts by weight, and still more preferably 5 to 30 parts by weight with respect to 100 parts by weight of the rubber component. If the blending amount of the polymer gel is too small, it becomes difficult to obtain the effect of improving the low heat build-up property. Conversely, if the blending amount is too large, the reinforcing property tends to be impaired.

  Since the polymer gel has a low glass transition point, it becomes a relatively soft filler, and therefore the hardness of the rubber composition is lowered. Therefore, in the present invention, by blending the lignin derivative of the component (C), the hardness reduction due to the polymer gel can be compensated by the reinforcing effect. Moreover, the dispersibility of a polymer gel can be improved because the hydroxyl group which a lignin derivative has interacts with the hydroxyl group of the particle | grain surface of a polymer gel. Therefore, by blending the lignin derivative with the polymer gel, the heat build-up can be improved while maintaining the reinforcing property, and the rubber weight can be reduced.

  As the lignin derivative, lignin sulfonic acid or lignin sulfonic acid derivative is preferably used. Since lignin sulfonic acid and its derivatives are polymer electrolytes having functional groups such as phenolic hydroxyl groups and sulfonic acid groups, they are chemically or physically adsorbed on fillers such as carbon black and silica in rubber compositions. In addition, the dispersibility can be improved. The lignin derivative may be obtained by the sulfite pulp method, or may be obtained by the kraft pulp method.

  The lignin sulfonic acid derivative is preferably a lignin sulfonate. Examples of the lignin sulfonate include alkali metal salts, alkaline earth metal salts, ammonium salts, alcohol amine salts, ester salts, and the like of lignin sulfonic acid, and at least one of these can be used. Preferably, it is an alkali metal salt or alkaline earth metal salt of lignin sulfonic acid, for example, potassium salt, sodium salt, calcium salt, magnesium salt, lithium salt, barium salt and the like, and a mixed salt thereof may be used.

  The lignin sulfonate may contain saccharides such as monosaccharides or polysaccharides. As the saccharide, cellulose as a wood component, glucose which is a structural unit of cellulose, or a polymer of glucose, such as hexose, pentose, mannose, galactose, ribose, xylose, arabinose, lyxose, ribose, talose, altrose, allose , Growth, idose, starch, starch hydrolyzate, dextran, dextrin, hemicellulose and the like.

  It is preferable that the compounding quantity of this lignin derivative is 1-30 weight part with respect to 100 weight part of said rubber components. When the blending amount of the lignin derivative is too small, the polymer gel dispersibility improving effect and the reinforcing effect are insufficient.

  In the rubber composition according to the present invention, silica and / or carbon black is usually blended as a filler. Although the compounding quantity of a filler is not specifically limited, It is preferable that it is 30-100 weight part with respect to 100 weight part of said rubber components. When the rubber composition is used for a side pad of a run flat tire, the filler is preferably composed mainly of carbon black, that is, carbon black alone or a blend of carbon black and silica.

As carbon black, various carbon blacks used as a reinforcing filler for rubber can be used, and are not particularly limited. For example, carbon black having colloidal characteristics with a nitrogen adsorption specific surface area (N ₂ SA, measured according to JIS K6217-2) of 20 to 150 m ² / g is preferably used. When the rubber composition is used for a side pad of a run flat tire, it is preferable to use carbon black having a nitrogen adsorption specific surface area of 20 to 100 m ² / g, that is, a GPF, FEF, or HAF grade.

  Examples of the silica include wet silica, dry silica, colloidal silica, precipitated silica and the like, and it is particularly preferable to use wet silica containing hydrous silicic acid as a main component.

  When silica is blended, it is preferable to blend a silane coupling agent. The silane coupling agent is, for example, an organic silane compound having an organic part capable of reacting with a polymer such as sulfide, amino group, mercapto group, vinyl group, methacryl group or epoxy group, and a halogen or alkoxy group. Various silane coupling agents can be used. Preferably, a sulfide silane represented by the following general formula (1) or a protected mercaptosilane represented by the following general formula (2) is used.

_{(C 2 H 5 O) 3} Si-C y H 2y -S x -C y H 2y -Si (OC 2 H 5) 3 ... (1)
_{(C n H 2n + 1 O} ) 3 Si-C m H 2m -S-CO-C k H 2k + 1 ... (2)
In said formula (1), y is an integer of 1-9, Preferably it is 2-5, x is 1-4, Preferably it is 2-4. Specifically, x has a normal distribution, that is, it is generally marketed as a mixture of different numbers of sulfur chain bonds, and x represents an average value thereof. Specific examples of the preferred sulfide silane represented by the formula (1) include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, and bis (2-triethoxysilylethyl) tetra. And sulfides.

  In said formula (2), n is an integer of 1-3, m is an integer of 1-5, k is an integer of 5-9. Examples of the protected mercaptosilane represented by the formula (2) include 3-octanoylthio-1-propyltriethoxysilane in which n = 2, m = 3, and k = 7, and n = 1, m = 3, k. Preferred examples include 3-propionylthiopropyltrimethoxysilane where = 2.

  The amount of the silane coupling agent is preferably 2 to 25 parts by weight, more preferably 5 to 15 parts by weight, based on 100 parts by weight of silica.

  In addition to the components described above, the rubber composition according to the present invention is generally used in tire rubber compositions such as softeners, plasticizers, anti-aging agents, zinc white, stearic acid, vulcanizing agents, and vulcanization accelerators. Various additives used can be blended. The rubber composition can be prepared by kneading using a usual mixer such as a Banbury mixer or a kneader.

  The rubber composition can constitute rubber parts of various pneumatic tires by vulcanization molding at 140 to 200 ° C., for example, according to a conventional method. Examples of the rubber portion include tread rubber, sidewall rubber, topping rubber for belts and plies, bead fillers, rim strips, and side pads for run-flat tires. Among these, in particular, the rubber composition is preferably used for a side pad, a side wall rubber, and a rim strip of a run flat tire, and more preferably used for a side pad.

  FIG. 1 is a half cross-sectional view showing a run-flat tire (10) according to one embodiment. The tire (10) includes a pair of left and right bead portions (1) to be rim assembled, a pair of left and right sidewall portions (2) extending outward in the tire radial direction from the bead portion (1), and the pair of sidewall portions. (2) It is comprised from the tread part (3) earth | grounded on the road surface provided in between.

  A ring-shaped bead core (4) is embedded in the pair of bead portions (1). A carcass (5) made of a carcass ply using an organic fiber cord is folded around the bead core (4) and locked, and is provided so as to span between the left and right bead portions (1). Further, on the outer peripheral side of the tread portion (3) of the carcass (5), a belt (6) composed of two cross belt plies using a rigid tire cord such as a steel cord or an aramid fiber is provided.

  In the sidewall portion (2), a sidewall rubber (7) that forms the sidewall outer surface is provided on the tire outer surface side of the carcass (5). A rim strip (8) made of a rubber layer is provided so as to cover a contact area with the rim flange in the bead portion (1), and a sidewall rubber (7) is formed on the upper end of the rim strip (8). The lower end of the is overlapping.

  In the side wall portion (2), a side pad (9) is provided on the inner surface side of the carcass (5) over the region from the vicinity of the rim line (RL) in contact with the upper end of the rim flange to the end portion of the belt (6). It has been. The side pad (9) has a substantially crescent shape in a cross section in the tire width direction including the tire shaft in order to reinforce the sidewall portion (2).

  This side pad (9) is formed of a rubber composition containing the polymer gel (B) and the lignin derivative (C). Since the side pad (9) occupies a large cross-sectional area in the side wall portion (2), the excellent low heat build-up of the rubber composition provides a great effect of contributing to a reduction in rolling resistance during normal internal pressure running. It becomes like this. Moreover, the reduction effect of rolling resistance is acquired also by the weight reduction effect which this rubber composition has. Furthermore, since the rubber composition can improve the low heat build-up while maintaining the reinforcing property, it can suppress the heat generation of the side pad (9) and improve the durability while ensuring the strength during run-flat running. it can.

  The rubber composition can also be applied to the sidewall rubber (7) and / or the rim strip (8). Thereby, the reduction effect of rolling resistance can be heightened more.

  In the above embodiment, an example in which the carcass is formed of one layer is shown. However, the side pad rubber may be divided into a plurality of layers, and a reinforcing fiber layer may be disposed therebetween. When the carcass is composed of two or more layers, a reinforcing pad rubber having a substantially crescent-shaped cross section may be disposed between the inner surface side of the carcass layer and the carcass layer.

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

  Using a Banbury mixer, a rubber composition for a side pad of a run flat tire was prepared according to the composition shown in Table 1 below. Each component in Table 1 is as follows.

NR: natural rubber, RSS # 3,
BR: butadiene rubber, “BR01” manufactured by JSR Corporation
Carbon black: GPF, “Seast V” manufactured by Tokai Carbon Co., Ltd. (nitrogen adsorption specific surface area = 27 m ² / g),
Polymer gel 1: “Micromov 1P” manufactured by Rhein Chemie (polymer gel based on SBR, Tg = 65 ° C., toluene swelling index Qi = 7, gel content = 96 wt%, average particle size = 60 nm, hydroxyl group modification Product),
Polymer gel 2: “Micromov 4B” manufactured by Rhein Chemie (SBR-based polymer gel, Tg = −15 ° C., toluene swelling index Qi = 6, gel content = 96 wt%, average particle size = 60 nm, hydroxyl group Modified product),
Polymer gel 3: “Micromov 30B” manufactured by Rhein Chemie (BR based polymer gel, Tg = −80 ° C., toluene swelling index Qi = 5.9, gel content = 97 wt%, average particle size = 130 nm, Hydroxyl group modified product),
Lignin derivative: sodium lignin sulfonate, “Vanilex N” manufactured by Nippon Paper Chemicals Co., Ltd.

  In each rubber composition, 2 parts by weight of stearic acid ("Lunac S-25" manufactured by Kao Corporation) and zinc white ("Zinc oxide" manufactured by Mitsui Mining & Smelting Co., Ltd.) are used as a common compound. "3 types") 5 parts by weight, anti-aging agent ("Santflex 6C" manufactured by Flexis) 2 parts by weight, vulcanization accelerator ("Noxeller NS" manufactured by Ouchi Shinsei Chemical Co., Ltd.) 3 parts by weight, and sulfur 3 parts by weight (“Powder sulfur 150 mesh” manufactured by Hosoi Chemical Co., Ltd.) was blended.

  About each rubber composition obtained, vulcanized at 160 ° C. for 30 minutes to prepare a test piece of a predetermined shape, and using the obtained test piece, hardness and breaking strength as a reinforcement index, low Tan δ as an index of exothermic property and specific gravity as an index of rubber weight reduction effect were measured. Each measuring method is as follows.

Hardness: Hardness at 23 ° C. was measured with a durometer type A conforming to JIS K6253 and displayed as an index with the value of Comparative Example 1 being 100. The larger the index, the higher the hardness.

-Breaking strength: Using an automatic tensile testing machine manufactured by Ueshima Seisakusho, a tensile test was performed in accordance with JIS K6251, and the tensile strength at break was measured. The value of Comparative Example 1 is expressed as an index, and the larger the index, the higher the breaking strength.

Tan δ: Using a viscoelasticity tester manufactured by Toyo Seiki, the loss factor tan δ was measured under the conditions of a frequency of 10 Hz, a static strain of 10%, a dynamic strain of 1%, and a temperature of 60 ° C., and the value of Comparative Example 1 was set to 100 Expressed as an index. The smaller the index, the smaller the tan δ, and the less the heat is generated (that is, the low heat buildup is excellent).

Specific gravity: The specific gravity was measured in accordance with JIS K0061 and displayed as an index with the value of Comparative Example 1 being 100. The smaller the index, the smaller the specific gravity and the better the rubber weight reduction effect.

  The results are as shown in Table 1. Compared with Comparative Example 1 as a control, tan δ (low exothermic property) deteriorated in Comparative Example 2 in which a polymer gel having a high glass transition point was blended. Moreover, although the glass transition point was comparatively low, in Comparative Example 3 in which only the polymer gel was added, the effect of improving the low exothermic property was insufficient. Further, in Comparative Example 4 in which only the polymer gel 3 having a lower glass transition point was added, although the effect of improving the low exothermic property was obtained, the hardness was lowered and it was not possible to achieve both the reinforcement and the reinforcing property. In Comparative Example 5 in which the amount of carbon black was reduced with respect to Comparative Example 4, the additional effect of low exothermic property was obtained, but the reinforcing property was greatly deteriorated. On the other hand, in Comparative Example 6 in which the lignin derivative was blended without adding the polymer gel, although the hardness was increased, the effect of improving the low heat generation was insufficient. Further, even when the polymer gel and the lignin derivative were used in combination, in Comparative Example 7 where the glass transition point of the polymer gel was high, the effect of improving the low heat generation was not obtained.

  On the other hand, in an example in which a polymer gel having a low glass transition point and a lignin derivative were used in combination, an improvement effect excellent in low exothermic property was obtained while generally maintaining reinforcement. Moreover, the effect of reducing rubber weight was also observed. In particular, Examples 2 and 3 using the polymer gel 3 having a lower glass transition point were more excellent in the effect of improving the low heat generation.

It is a half sectional view of a run flat tire concerning an embodiment.

Explanation of symbols

2 ... side wall part, 5 ... carcass, 9 ... side pad, 10 ... run flat tire

Claims (7)

In rubber component consisting of diene rubber,
A polymer gel which is a crosslinked diene polymer particle modified with a compound having a hydroxyl group and having a glass transition point of -100 to 0 ° C;
Blended with lignin derivative,
Rubber composition for tires.   The tire rubber composition according to claim 1, wherein the lignin derivative is lignin sulfonic acid or a lignin sulfonic acid derivative.   The rubber composition for tires according to claim 2, wherein the lignin sulfonic acid derivative is a lignin sulfonate.   The rubber composition for tires according to any one of claims 1 to 3, wherein the polymer gel has a toluene swelling index Qi of less than 16.   The rubber composition for tires according to any one of claims 1 to 4, wherein the polymer gel has an average particle size of 40 to 200 nm.   The tire rubber composition according to any one of claims 1 to 5, comprising 3 to 70 parts by weight of the polymer gel and 1 to 30 parts by weight of the lignin derivative with respect to 100 parts by weight of the rubber component.   The run flat tire which has a side pad formed with the rubber composition of any one of Claims 1-6 inside the carcass of a sidewall part.

Images