JP2010254791A - Rubber composition for rubber crawler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a rubber crawler capable of giving a white rubber crawler which causes no poor adhesion with a core grid during vulcanization adhesion, is excellent in machinery physical properties, and leaves no traveling traces by friction between a tread surface and a contact area. <P>SOLUTION: The rubber composition for a rubber crawler, including, as rubber constituents, an unvulcanized diene-based solid rubber and a conjugated diene-based polymer or a conjugated diene-aromatic vinyl copolymer that has a weight average molecular weight (Mw) of 5,000-40,000 and a molecular weight distribution of 3.0 or less and contains hydroxyl groups on both ends of a molecular chain, is characterized in that the mixing rate of the conjugated diene-based polymer or the conjugated diene-aromatic vinyl copolymer that contains the hydroxyl groups on both ends of the molecular chain is 15-30 phr and the rubber composition includes a white filler as a reinforcer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rubber composition for a rubber crawler to be mounted around a suspension such as a small aerial work vehicle for indoor use, a mini crane, and a transport vehicle. More specifically, the present invention relates to a rubber composition for a white rubber crawler that does not leave running marks due to friction between the tread surface of the rubber crawler and the ground contact surface and does not stain the ground contact surface.

  A rubber crawler is usually an endless rubber elastic body that is reinforced by embedding and reinforcing a core bar that engages with a drive wheel (sprocket) and transmits power, and a steel cord that holds tension. Combines and tractors that are required to run on soft ground that is difficult to drive with ordinary tires such as wet fields, fields, and muddy areas. It is mounted on the undercarriage of industrial machines such as various agricultural machines such as mini excavators and civil engineering machines, and small work vehicles such as small indoor work vehicles, mini cranes, and transport vehicles.

  In the rubber forming this rubber crawler, a black rubber material containing carbon black as a reinforcing material is frequently used from the viewpoint of reinforcing properties and the like. The rubber crawler formed of this black rubber material has a problem that the black rubber material has an effect on the running surface when traveling on soil, gravel, rocks, etc., such as civil engineering sites such as forests or farmland. It is rarely said. However, if the running surface of the rubber crawler is cobblestone, tiled, bricked or colored concrete, such as a floor surface in a commercial facility or warehouse, a white concrete surface in a cemetery cemetery, etc. The friction between the tread surface of the crawler and the floor surface may leave a black running mark on the floor surface. If the running mark is noticeable, the aesthetic appearance of the floor surface may be impaired. In addition, the visibility of lane markings and safety signs drawn on the floor surface may be reduced in the warehouse, which may hinder the workability and safety of work in the warehouse. In particular, if the running trace remains strongly due to strong friction when the aircraft is turning and the aesthetics of the floor surface are significantly impaired, the floor surface may be cleaned, repainted, or repainted. Therefore, usually in such a work vehicle used in the field, as a countermeasure against the running trace, a part of or all of the reinforcing material is replaced with white filler such as silica or white or light gray. A rubber crawler (hereinafter sometimes referred to as “white rubber crawler”) is attached.

  However, white fillers such as silica are generally less compatible with rubber than the carbon black and are difficult to disperse, so that it is difficult to obtain a sufficient reinforcing effect by itself. In particular, since rubber materials used for applications such as rubber crawlers are required to have high mechanical properties, it is difficult to obtain required characteristics simply by replacing carbon black with a white filler such as silica. Therefore, when preparing white rubber using a white filler such as silica as a reinforcing material, a silane coupling agent such as bis (3-triethoxypropyl) tetrasulfane is usually added to improve dispersibility. In addition, it is common practice to improve the rubber reinforcing effect by increasing the surface activity of the particles to facilitate the formation of chemical bonds between the white filler and the polymer.

  On the other hand, steel cords and metal cores are embedded in the rubber crawler as described above, and it is necessary to firmly bond these to rubber. In particular, the cored bar is firmly bonded to rubber, so that vulcanization bonding is performed after applying an adhesive. However, when the rubber to be bonded to the core metal is a white rubber in which a white filler and a silane coupling agent are blended, a blister-like non-bonded portion (blister) may occur on the bonding surface.

  This is because the volatile component (mainly alcohol) derived from the silane coupling agent concentrates on the slight non-adhesive and non-contact areas formed on the adhesive surface between the rubber and metal, and expands rapidly with the temperature rise immediately after vulcanization. It has been found that this is for spreading the non-adhered part and the non-contact part. Therefore, when a rubber crawler is formed with the above-mentioned white rubber, a large blister (blister) is generated on the bonding surface between the rubber and the core metal immediately after vulcanization, resulting in poor adhesion, and productivity may be greatly impaired. In addition, the rubber crawler with blisters is inferior in durability, and if it is accidentally put on the market, it may lead to early damage or even a serious accident.

  Therefore, conventionally, in order to maintain the mass production performance of the white rubber crawler, by reducing the blending amount of the silane coupling agent, it is difficult to cause the above-mentioned adhesion failure while sacrificing the reinforcing property (mechanical property of rubber). Although measures have been taken in the direction, it has been difficult to efficiently produce rubber crawlers with sufficient mechanical properties. Accordingly, there is a demand for a method capable of easily and reliably obtaining a white rubber crawler without causing poor adhesion to the core metal while sufficiently securing the mechanical properties of the rubber.

  As conventional techniques of the present invention, Japanese Patent Application Laid-Open No. 2000-273240 (Patent Document 1) and International Publication No. 2004/072173 (Patent Document 2) disclose a specific hydroxyl-terminated liquid diene system for a rubber component. Disclosed is a rubber composition for tires that improves dispersibility in a rubber compound without using a silane coupling agent by blending rubber, has excellent processability, and exhibits good physical properties after crosslinking. Has been.

JP 2000-273240 A International Publication No. 2004/072173 Pamphlet

  The present invention has been made in view of the above circumstances, does not cause poor adhesion to the core during vulcanization adhesion, has excellent mechanical properties, and leaves running marks due to friction between the tread surface and the ground contact surface. It is an object of the present invention to provide a rubber composition for a rubber crawler which can obtain a white rubber crawler free of water.

  As a result of intensive studies to solve the above problems, the present inventors have found that when preparing a white rubber composition for a rubber crawler using a white filler such as silica as a reinforcing material, an unvulcanized diene is used. A conjugated diene polymer or a conjugated diene-aromatic vinyl copolymer having a specific molecular weight and molecular weight distribution and having a hydroxyl group (OH group) at the end of the molecular chain is added to the solid rubber. Therefore, the dispersibility of the filler is improved, and the hydroxyl group forms a strong bond with the particle surface of the white filler, so that sufficient reinforcement can be obtained without the addition of a silane coupling agent. And no silane coupling agent is required, so that it is possible to prevent poor adhesion between the rubber and the core metal (occurrence of blistering) due to volatile components derived from the silane coupling agent. Reached

That is, the present invention provides the following rubber compositions for rubber crawlers (1) to (4).
(1) As a rubber component, an unvulcanized diene solid rubber and a conjugated diene polymer or conjugated diene having hydroxyl groups at both ends of a molecular chain having a weight average molecular weight (Mw) of 5000 to 40000 and a molecular weight distribution of 3.0 or less. A blending ratio of a conjugated diene polymer or a conjugated diene-aromatic vinyl copolymer having a hydroxyl group at both ends of the molecular chain is 15 to 30 phr, and a reinforcing material. A rubber composition for a rubber crawler containing a white filler as

(2) The rubber composition for a rubber crawler of the present invention, wherein the conjugated diene polymer or conjugated diene-aromatic vinyl copolymer is styrene-butadiene rubber (SBR) or isoprene rubber (IR).
(3) The rubber composition for a rubber crawler of the present invention, wherein the white filler is one or more selected from silicon dioxide (silica), clay, talc and calcium carbonate.
(4) The rubber composition for a rubber crawler according to the present invention, wherein the blending amount of the white filler is 50 to 80 phr.

  The rubber composition for a rubber crawler according to the present invention can improve the mechanical properties of rubber without adding a silane coupling agent when a white filler such as silica is used as a reinforcing material. Since it is possible to prevent poor adhesion caused by volatile components derived from the silane coupling agent, a white rubber crawler rubber having excellent mechanical properties can be obtained efficiently.

  The rubber composition for a rubber crawler of the present invention includes, as a rubber component, an unvulcanized diene solid rubber, a conjugated diene polymer having a specific molecular weight and molecular weight distribution, and having hydroxyl groups at both ends of the molecular chain. It contains a conjugated diene-aromatic vinyl copolymer, and further contains a white filler such as silica as a reinforcing material.

  As the unvulcanized diene-based solid rubber, known rubbers can be used and are not particularly limited. Specifically, known natural rubbers, butadiene rubbers, styrene-butadiene rubbers, isoprene rubbers are used. Synthetic rubbers such as ethylene-propylene-diene rubber, butyl rubber, halogenated butyl rubber, chloroprene rubber, isobutylene-isoprene rubber, acrylonitrile-butadiene rubber, epoxidized natural rubber, acrylate butadiene rubber, and molecular chains of these natural rubber or synthetic rubber One having a modified end can be used, and one of these can be used alone, or two or more can be mixed and used. In the present invention, natural rubber, styrene-butadiene rubber, and ethylene-propylene-diene rubber can be preferably used.

A conjugated diene polymer or a conjugated diene-aromatic vinyl copolymer having a hydroxyl group (OH group) at both ends of a molecular chain used in combination with the diene solid rubber is disclosed in, for example, Japanese Patent Application Laid-Open No. 2007-145949. As stated,
(A) In a saturated hydrocarbon solvent, a conjugated diene monomer, or a conjugated diene monomer and an aromatic vinyl monomer are polymerized with a dilithium initiator to obtain a weight average molecular weight of 5000 to 40000 and a molecular weight. Producing a conjugated diene polymer or a conjugated diene-aromatic vinyl copolymer having a distribution of 3.0 or less;
(B) The conjugated diene polymer or conjugated diene-aromatic vinyl copolymer is reacted with an alkylene oxide to produce a conjugated diene polymer polyol or a conjugated diene-aromatic vinyl copolymer polyol. It is a liquid polymer obtained by going through the steps.
Details thereof will be described below.

First, as a first step (A), a conjugated diene monomer, or a conjugated diene monomer and an aromatic vinyl monomer are polymerized with a dilithium initiator in a saturated hydrocarbon solvent, A conjugated diene polymer or a conjugated diene-aromatic vinyl copolymer (hereinafter sometimes referred to as “(co) polymer”) is produced. Since the main polymerization is living anionic polymerization, the polymerization can be performed while controlling the molecular weight and molecular weight distribution. The molecular weight can polymerize a polymer having a predetermined molecular weight depending on the amount of the dilithium initiator and the above monomer, and in particular, when the weight average molecular weight (Mw) is 5000 or more, a narrow polymer having a molecular weight distribution of 2 or less. Easy to get. If desired, anionic polymerization may be carried out in the presence of a randomizer.
Next, as a second step (B), a conjugated diene polymer polyol having hydroxyl groups at both ends by reacting the polymer end which is a living anion with an alkylene oxide in an equivalent manner in the above (co) polymer. Alternatively, a conjugated diene-aromatic vinyl copolymer polyol can be obtained.

Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 2-phenyl-1,3-butadiene, 1,3-hexadiene, and the like. Can be mentioned. These may be used alone or in combination of two or more. In the present invention, 1,3-butadiene and isoprene can be suitably used.
Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, paramethylstyrene, and the like. These may be used alone or in combination of two or more.
Furthermore, you may combine other monomers, such as isobutylene and acrylonitrile, as needed.

  The dilithium initiator is not particularly limited, and known ones can be used. For example, Japanese Patent Publication No. 1-53681 discloses a method for producing a dilithium initiator by reacting a monolithium compound with a disubstituted vinyl or an alkenyl group-containing aromatic hydrocarbon in the presence of a tertiary amine. ing.

  Monolithium compounds used when producing a dilithium initiator include ethyl lithium, n-propyl lithium, isopropyl lithium, n-butyl lithium, sec-butyl lithium, tert-butyl lithium, tert-octyl lithium, and n-decyl. Examples of the lithium include phenyl lithium, 2-naphthyl lithium, 2-butyl-phenyl lithium, 4-phenyl-butyl lithium, cyclohexyl lithium, and cyclopentyl lithium. Among these, sec-butyl lithium is preferable.

Examples of the tertiary amine used when producing the dilithium initiator include lower aliphatic amines such as trimethylamine and triethylamine, N, N-diphenylmethylamine, and the like, and triethylamine is particularly preferable.
Examples of the disubstituted vinyl or alkenyl group-containing aromatic hydrocarbon include 1,3- (diisopropenyl) benzene, 1,4- (diisopropenyl) benzene, 1,3-bis (1-ethylethenyl). ) Benzene, 1,4-bis (1-ethylethenyl) benzene and the like are preferred.

  The solvent used in the preparation of the above dilithium initiator and the production of the (co) polymer may be any organic solvent inert to the reaction, and hydrocarbons such as aliphatic, alicyclic and aromatic hydrocarbon compounds. System solvents are used, such as n-butane, l-butane, n-pentane, l-pentane, cis-2-butene, trans-2-butene, l-butene, n-hexane, n-heptane, n- One or two selected from octane, l-octane, methylcyclopentane, cyclopentane, cyclohexane, 1-hexene, 2-hexene, 1-pentene, 2-pentene, benzene, toluene, xylene, ethylbenzene, etc. . Of these, n-hexane and cyclohexane are usually used.

  Moreover, as an alkylene oxide used for the polyol-ized reaction which reacts with the terminal which is a living anion of said (co) polymer and produces | generates a hydroxyl group at both terminals, ethylene oxide, propylene oxide, butylene oxide etc. are mentioned, for example. This polyol reaction is preferably performed immediately after the polymerization reaction.

  Specific examples of the conjugated diene polymer having a hydroxyl group at both ends of the molecular chain or the conjugated diene-aromatic vinyl copolymer obtained by the above method include a styrene-butadiene rubber having a hydroxyl group at both ends of the molecular chain ( SBR), butadiene rubber (BR), isoprene rubber (IR), acrylonitrile-butadiene rubber (NBR), and isobutylene-isoprene rubber (IIR). Particularly preferred are SBR and IR having hydroxyl groups at both ends of the molecular chain. Can be used. The weight average molecular weight (Mw) of the (co) polymer having hydroxyl groups at both ends of the molecular chain is 5,000 to 40,000, preferably 10,000 to 30,000. When the weight average molecular weight is less than 5,000, the effect as a plasticizer is strongly exerted, and there is a possibility that the physical requirement characteristic that the solid rubber component is expressed cannot be expressed. Therefore, the number of terminal hydroxyl groups required for obtaining reinforcement with the white filler may be relatively reduced, and sufficient reinforcement may not be obtained. The molecular weight distribution is 3.0 or less, preferably 2.5 or less. When the molecular weight distribution exceeds 3.0, the rubber crawler properties may be adversely affected, such as variations in reinforcing properties between the rubber component and the white filler, and bleeding out of low molecular weight components.

  The present invention uses a diene solid rubber as a rubber component and a (co) polymer having hydroxyl groups at both ends of the molecular chain. In this case, the (co) polymer having hydroxyl groups at both ends of the molecular chain is used. The blending ratio is set to 15 to 30 phr, preferably 20 to 30 phr. In this case, if the blending ratio is less than 15 phr, the absolute amount of terminal hydroxyl groups necessary for reinforcement with the white filler is insufficient, so that the required reinforcement may not be achieved. Since the solid rubber component is relatively decreased, a sufficient elastic modulus may not be obtained, which is not preferable. Further, the plasticizing effect becomes too great, and there is a possibility that the moldability is impaired.

  In addition, since the (co) polymer having hydroxyl groups at both ends of the molecular chain has a low molecular weight as compared with the diene solid rubber, the viscosity increase when a white filler such as silica is blended during kneading. It also has the effect of acting as a plasticizer, and good processability can be obtained during kneading.

  The method for producing the (co) polymer having hydroxyl groups at both ends of the molecular chain is not particularly limited, and a known method can be applied. For example, it can manufacture by knead | mixing each component and the additive component used depending on necessity using the kneading machine which can adjust temperature, for example, a planetary mixer, a biaxial mixer, a high shear mixer, etc.

  In some cases, an appropriate amount of non-diene rubber may be blended in the rubber component with respect to the rubber component containing the diene solid rubber and the (co) polymer having hydroxyl groups at both ends of the molecular chain. it can. Examples of the non-diene rubber include silicone rubber and acrylic rubber.

  As the white filler, known materials can be used, and are not particularly limited. Examples thereof include silicon dioxide (silica), clay, talc and calcium carbonate. Can be used alone or in admixture of two or more. In the present invention, silica can be particularly preferably used. The amount of the white filler is 50 to 80 phr, preferably 55 to 70 phr. If the blending amount is less than 50 phr, there is a possibility that sufficient elastic modulus cannot be obtained as rubber for rubber crawlers. On the other hand, if it exceeds 80 phr, the elastic modulus may be too high as rubber for rubber crawlers. In addition, there is a possibility that the kneading processability is lowered.

  Further, the white filler can be improved in its reinforcing properties and dispersibility by surface treatment with a known silane coupling agent in advance before kneading with the rubber component. This surface treatment is more effective when clay, talc and calcium carbonate other than silica are used as the white filler. The amount of coupling agent used for the surface treatment and the surface treatment method are not particularly limited, but in order not to generate blisters during vulcanization, the volatile components are finally sufficiently removed. It is preferable.

  Here, in the present invention, “phr” is a case where a diene solid rubber and a conjugated diene polymer or conjugated diene-aromatic vinyl copolymer having a hydroxyl group at both ends of the molecular chain are blended with another rubber. Is the number of blended parts relative to 100 parts by weight of the total amount of rubber components including other rubbers (however, the (co) polymer having hydroxyl groups at both ends of the molecular chain represents the number of blended parts in the rubber component). The same applies to “phr” for other compounding components thereafter.

  As the anti-aging agent, known ones can be used and are not particularly limited, and examples thereof include phenol-based anti-aging agents, imidazole-based anti-aging agents, and amine-based anti-aging agents. In the invention, from the viewpoint of maintaining the color of the white rubber crawler to be produced, it is preferable to use a non-fouling phenolic anti-aging agent. The blending amount of the anti-aging agent is not particularly limited, but may be about 0.5 to 4 phr.

  As the plasticizer, known ones can be used, and are not particularly limited. Specific examples thereof include process oils such as aromatic oils, naphthenic oils and paraffin oils, vegetable oils such as palm oil, and alkylbenzenes. Synthetic oils such as oil can be used, and one or more of them may be appropriately selected and used from these. The blending amount of the plasticizer is not particularly limited, but may be about 3 to 20 phr.

  Although not particularly limited, in the present invention, sulfur is usually used as a vulcanizing agent, and the blending amount is not particularly limited, but may be about 0.5 to 3 phr. .

  As the vulcanization accelerator, known ones can be used, and are not particularly limited. For example, CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (Nt-butyl) -2-benzothiazylsulfenamide), TBSI (Nt-butyl-2-benzothiazylsulfenimide) and other sulfenamide vulcanization accelerators, DPG (diphenylguanidine) and other guanidine series Examples thereof include vulcanization accelerators, thiuram vulcanization accelerators such as tetraoctyl thiuram disulfide and tetrabenzyl thiuram disulfide, and vulcanization accelerators such as zinc dialkyldithiophosphate. The blending amount of the vulcanization accelerator is not particularly limited, but may be about 1 to 3 phr.

  The vulcanization acceleration aid is blended from the viewpoint of promoting vulcanization, and known zinc white (ZnO) or the like can be blended. Although the compounding quantity of the said vulcanization | cure acceleration | stimulation adjuvant is not restrict | limited in particular, What is necessary is just to be about 2-10phr.

  Also, for the diene solid rubber, vulcanizing agents other than the above components, vulcanization accelerators, anti-aging agents, waxes, antioxidants, fillers, plasticizers, oils, lubricants, tackifiers, petroleum Additives such as system resins, ultraviolet absorbers, dispersants, compatibilizing agents, and homogenizing agents can be appropriately blended depending on the purpose and purpose.

  When obtaining the rubber composition of the present invention, there is no particular limitation on the blending method of each of the above components, and all the component raw materials may be blended and kneaded at once, and each component may be divided into two or three stages. You may mix | blend and knead | mix. In the kneading, a kneader such as a roll, an internal mixer, a Banbury rotor or the like can be used. In addition, the conditions at the time of vulcanizing the obtained composition can employ | adopt normal conditions, Although it does not restrict | limit in particular, It can be set as the conditions of 100-180 degreeC and 3 to 30 minutes.

  The rubber composition for a rubber crawler of the present invention can be suitably used for a rubber crawler used for traveling at a work site where it is not preferable to soil a floor surface of an indoor work vehicle or the like. And when manufacturing a rubber crawler using the rubber composition of this invention, a conventionally well-known manufacturing method can be employ | adopted.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not restrict | limited to the following Example.

[Synthesis Example 1]
After adding 1 mol of 1,3- (diisopropenyl) benzene to a fully dehydrated and purified cyclohexane solvent, 2 mol of triethylamine and 2 mol of sec-butyllithium are sequentially added and stirred at 50 ° C. for 2 hours. A dilithium polymerization initiator was prepared.
In a 7 liter polymerization reactor purged with argon, 1.50 kg of dehydrated purified cyclohexane, 2.00 kg of a hexane solution of 22.9% by mass of 1,3-butadiene monomer, and a cyclohexane solution of 20.0% by mass of styrene monomer were added. After adding 209.4 ml of hexane solution of 765 kg, 1.6 mol / liter OOPS (2-2'-di (tetrahydrofuryl) propane), 223.5 ml of 0.5 mol / liter dilithium polymerization initiator was added. The polymerization was started.
Polymerization was performed for 1.5 hours while raising the temperature of the polymerization reactor to 50 ° C., then 220.4 ml of a 1 mol / liter ethylene oxide cyclohexane solution was added, and the mixture was further stirred for 2 hours, and then 50 ml of isopropyl alcohol was added. did. A hexane solution of the polymer was precipitated in isopropyl alcohol and sufficiently dried to obtain SBR-1 having hydroxyl groups at both ends of a molecular chain having a styrene content of 25% by mass, a weight average molecular weight of 7100, and a molecular weight distribution of 1.25.

[Synthesis Example 2]
After adding 1 mol of 1,3- (diisopropenyl) benzene to a fully dehydrated and purified cyclohexane solvent, 2 mol of triethylamine and 2 mol of sec-butyllithium are sequentially added and stirred at 50 ° C. for 2 hours. A dilithium polymerization initiator was prepared.
In a 7-liter polymerization reactor purged with argon, 1.90 kg of dehydrated and purified cyclohexane, 2.00 kg of a hexane solution of 22.9% by mass of 1,3-butadiene monomer, and a cyclohexane solution of 20.0% by mass of styrene monomer were added. After adding 130.4 ml of hexane solution of 765 kg, 1.6 mol / liter OOPS (2-2'-di (tetrahydrofuryl) propane), 108.0 ml of 0.5 mol / liter dilithium polymerization initiator was added. The polymerization was started.
Polymerization was carried out for 1.5 hours while raising the temperature of the polymerization reactor to 50 ° C., then 108.0 ml of a 1 mol / liter ethylene oxide cyclohexane solution was added, and the mixture was further stirred for 2 hours, and then 50 ml of isopropyl alcohol was added. did. A hexane solution of the polymer was precipitated in isopropyl alcohol and sufficiently dried to obtain SBR-2 having hydroxyl groups at both ends of a molecular chain having a styrene content of 25% by mass, a weight average molecular weight of 14500, and a molecular weight distribution of 1.20.

[Synthesis Example 3]
After adding 1 mol of 1,3- (diisopropenyl) benzene to a fully dehydrated and purified cyclohexane solvent, 2 mol of triethylamine and 2 mol of sec-butyllithium are sequentially added and stirred at 50 ° C. for 2 hours. A dilithium polymerization initiator was prepared.
In a 7 liter polymerization reactor purged with argon, 2.50 kg of dehydrated and purified cyclohexane, 2.00 kg of a hexane solution of 22.9% by mass of 1,3-butadiene monomer, and a cyclohexane solution of 20.0% by mass of styrene monomer were added. After adding 130.4 ml of hexane solution of 765 kg, 1.6 mol / liter OOPS (2-2′-di (tetrahydrofuryl) propane), 54.0 ml of 0.5 mol / liter dilithium polymerization initiator was added. The polymerization was started.
Polymerization was carried out for 1.5 hours while raising the temperature of the polymerization reactor to 50 ° C., 53.8 ml of a 1 mol / liter ethylene oxide cyclohexane solution was added, and the mixture was further stirred for 2 hours, and then 50 ml of isopropyl alcohol was added. did. A hexane solution of the polymer was precipitated in isopropyl alcohol and sufficiently dried to obtain SBR-3 having hydroxyl groups at both ends of a molecular chain having a styrene content of 25% by mass, a weight average molecular weight of 25300, and a molecular weight distribution of 1.86.

[Examples 1 to 4, Comparative Examples 1 to 5]
The rubber composition shown in Table 1 was kneaded according to a conventional method. About this rubber composition, the target test piece was produced by the following method, and the following characteristic was evaluated.

In this case, the detail of each compounding component in Table 1 is as follows.
SBR: SBR # 1502
SBR-1 having hydroxyl groups at both ends of the molecular chain: weight average molecular weight 7100, molecular weight distribution 1.25
SBR-2 having hydroxyl groups at both ends of the molecular chain: weight average molecular weight 14500, molecular weight distribution 1.20
SBR-3 having hydroxyl groups at both ends of the molecular chain: weight average molecular weight 25300, molecular weight distribution 1.86
Carbon black: HAF grade carbon black White filler: manufactured by Tosoh Silica Co., Ltd., Nipsil AQ
Non-polluting anti-aging agent: manufactured by Seiko Chemical Co., Ltd., Ozonon EX
Plasticizer: Paraffinic process oil, manufactured by Nippon Oil Corporation, Super Oil Y22
Silane coupling agent: manufactured by DEGUSSA, SI69
Diethylene glycol: manufactured by Mitsui Chemicals, diethylene glycol vulcanization accelerator D: manufactured by Ouchi Shinsei Chemical Co., Ltd., Noxeller D
Vulcanization accelerator NS: Ouchi Shinsei Chemical Co., Ltd., Noxeller NS

・ Hardness (JIS-A hardness)
A rubber composition having the composition shown in Table 1 was formed into a sheet having a length of 120 mm, a width of 120 mm, and a thickness of 2 mm, and vulcanized and cured at 155 ° C. for 30 minutes to produce a rubber sheet (test piece). . Next, the hardness was measured with a durometer A in accordance with JIS K6253. The results are shown in Table 1.
-Strength and elongation A rubber sheet was produced in the same manner as described above. Next, in accordance with JIS K6251, a dumbbell-shaped No. 3 test piece was prepared, and tensile strength and elongation at break were measured. The results are shown in Table 1.
・ Releasability substitution test during rubber crawler vulcanization First, a SS400 metal plate with a width of 25 mm, a length of 60 mm and a thickness of 1 mm was blasted and then thoroughly washed with toluene, and a φ15 mm seal on one side of the metal plate A part of it was masked. Next, a PC made by Toyo Kagaku Co., Ltd. is applied as an undercoat adhesive to a thickness of about 10 μm on the entire surface subjected to masking as described above, dried, and then further coated on the undercoat adhesive layer. As a load, Chemlock 6220 manufactured by Lord Far East Co. was applied to a thickness of about 10 μm and dried. Then, the said seal | sticker was peeled off and the test piece which a part of metal surface exposed was produced. The test piece was embedded in a rubber piece having a width of 60 mm, a length of 70 mm and a thickness of 30 mm formed of a rubber composition having the composition shown in Table 1, and mold vulcanized at 155 ° C. for 60 minutes. After the vulcanization is completed, the rubber piece is removed from the mold, the test piece is taken out from the rubber piece, the surface of the test piece is observed, and the adhesive peeled portion by the blister from the masking portion (exposed portion of the metal surface) is observed. The area was examined and evaluated according to the following criteria. The results are shown in Table 1.
○: Area of adhesive peeling due to swelling is less than 1 mm ² ×: Area of adhesive peeling due to swelling is 1 mm ² or more

Claims (4)

  As the rubber component, an unvulcanized diene solid rubber and a conjugated diene polymer or conjugated diene-aromatic having a hydroxyl group at both ends of a molecular chain having a weight average molecular weight (Mw) of 5000 to 40000 and a molecular weight distribution of 3.0 or less. The conjugated diene polymer or the conjugated diene-aromatic vinyl copolymer having a hydroxyl group at both ends of the molecular chain is 15 to 30 phr, and is filled with white as a reinforcing material. A rubber composition for a rubber crawler, comprising an agent.   The rubber composition for a rubber crawler according to claim 1, wherein the conjugated diene polymer or conjugated diene-aromatic vinyl copolymer is styrene-butadiene rubber (SBR) or isoprene rubber (IR).   The rubber composition for a rubber crawler according to claim 1 or 2, wherein the white filler is one or more selected from silicon dioxide (silica), clay, talc and calcium carbonate.   The rubber composition for a rubber crawler according to any one of claims 1 to 3, wherein a blending amount of the white filler is 50 to 80 phr.