JP2013010871A - Modified dienic rubber, method for producing the same, and rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the viscoelasticity, and improve the low fuel consumption and the wet skid property particularly in the case of being used for a tire.SOLUTION: The modified dienic rubber is obtained by reducing at least a part of epoxy groups of an epoxidized natural rubber with a diimide or its derivative in a latex to hydoxylate the part, and has a structural unit represented by formula (1) and/or formula (2).

Description

  The present invention relates to a modified diene rubber having a hydroxyl group introduced therein, a production method thereof, a rubber composition containing the modified diene rubber, and a pneumatic tire using the rubber composition.

  Among diene rubbers having a rubber-like structure and structures having double bonds such as unsaturated fatty acids, some or all of them have an epoxy group. Among them, diene rubbers having an epoxy group generated by oxidation of the double bond portion of the main chain, particularly epoxidized natural rubber, are generally used as a rubber component in a tire rubber composition.

  A pneumatic tire is required to have low fuel consumption (rolling resistance performance) and be hard to slip on a wet road surface, that is, to improve wet skid property. However, in general, both performances are in a trade-off relationship, and it is difficult to satisfy the two characteristics of low fuel consumption and wet skid at the same time. For example, the epoxidized natural rubber has a large hysteresis loss and is excellent in wet skid properties, but has a disadvantage that fuel efficiency is insufficient.

  In order to eliminate such drawbacks, the following Patent Documents 1 and 2 disclose that an epoxy group of a tire tread rubber composition is reacted with a Lewis acid, an amine compound, a thiol compound, an amide compound or an imidazole compound to react with an epoxy group. The use of modified natural rubber obtained by ring opening is disclosed. As the modified natural rubber, specifically, a modified natural rubber in which an epoxy group is opened using phenol as a Lewis acid is disclosed. In this case, a phenoxy group together with a hydroxyl group is included in the main chain of the natural rubber. Will be introduced. Thus, the introduction | transduction of the substituent derived from a Lewis acid etc. has a possibility that a coupling | bonding or reactivity with fillers, such as a silica, may be impaired.

  Patent Documents 3 and 4 below disclose that a modified natural rubber having a hydroxyl group directly bonded to a main chain of a natural rubber is used in a rubber composition used for a tire. In this document, natural rubber or epoxidized natural rubber is dissolved in an organic solvent, and then a predetermined amount of an acid catalyst and water is added to introduce a hydroxyl group into the epoxy group. And has a diol structure in which two hydroxyl groups are introduced. In such a diol structure, the effect of improving the binding or reactivity with a filler such as silica is not necessarily sufficient, and further improvements in fuel economy and wet skid properties are required. Further, there are problems such as a decrease in molecular weight, a decrease in molecular entanglement, and a troublesome time for taking out rubber due to dissolution in an organic solvent, and it is difficult to maintain the original physical properties of natural rubber.

JP 2004-359773 A JP-A-2005-041960 JP 2010-106250 A Japanese Patent No. 4538533 JP 2004-359716 A

  This invention is made | formed in view of the above point, and aims at improving the low fuel consumption property and wet skid property at the time of using for a tire. Another object of the present invention is to provide a method for producing a modified diene rubber that can improve properties by hydroxylation without impairing the original properties of the original diene rubber such as natural rubber.

  In the method for producing a modified diene rubber according to the first aspect of the present invention, at least a part of the epoxy group is contained in the latex with respect to the diene rubber having an epoxy group generated by oxidation of the double bond portion of the main chain. And then hydroxylated by reduction with diimide or a derivative thereof.

  In the first aspect, the double bond portion of the main chain of the diene rubber is epoxidized in the latex, and at least a part of the generated epoxy group is further reduced in the latex with the diimide or derivative thereof. It may be hydroxylated. The diene rubber is preferably natural rubber and / or synthetic isoprene rubber.

The modified diene rubber according to the second aspect of the present invention is a modified diene rubber obtained by modifying a diene rubber composed of natural rubber and / or synthetic isoprene rubber, and is a diene rubber in the main chain of the diene rubber. It has at least one of the structural unit represented by the following formula (1) and the structural unit represented by the following formula (2) obtained by reducing at least a part of the epoxy group generated by oxidation of the heavy bond portion. Is.

The modified diene rubber according to the second embodiment may further have a structural unit represented by the following formula (3).

  The rubber composition according to the third aspect of the present invention contains any one of the above-mentioned modified diene rubbers. In this case, it is preferable to contain 10 to 120 parts by mass of silica with respect to 100 parts by mass of the rubber component containing the modified diene rubber. Furthermore, you may contain 2-12 mass parts of silane coupling agents with respect to 100 mass parts of said silica.

  A pneumatic tire according to a fourth aspect of the present invention includes a tread formed using any one of the above rubber compositions.

  According to the present invention, a hydroxyl group is formed by reducing the epoxy group on a diene rubber having an epoxy group in the main chain, so that one hydroxyl group is introduced into the double bond portion of the main chain. A modified diene rubber having a monool structure is obtained. By introducing a hydroxyl group in this way, it is possible to control viscoelasticity by changing the glass transition temperature, and particularly when used in tires, it is possible to improve the binding or reactivity with fillers, etc., and low fuel consumption (Rolling resistance performance) and wet skid property can be improved.

  Further, when the epoxy group of the diene rubber is reduced to introduce a hydroxyl group in the latex, the properties can be improved by hydroxylation without impairing the original characteristics of the original diene rubber.

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

  In the method for producing a modified diene rubber according to this embodiment, at least a part of the epoxy group is diimide in the latex or the diene rubber having an epoxy group generated by oxidation of the double bond portion of the main chain. It is hydroxylated by reduction with a derivative.

  Examples of the diene rubber to be modified include natural rubber, synthetic isoprene rubber, butadiene rubber, styrene butadiene rubber, styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer. Although rubber | gum etc. are mentioned, What has an isoprene unit is preferable, More preferably, they are a natural rubber and / or a synthetic isoprene rubber. The natural rubber is not particularly limited, and examples include RSS No. 3 and TSR20. As the synthetic isoprene rubber, 1,4-cis-polyisoprene generally used as a substitute for natural rubber (that is, polyisoprene having 90% or more of cis 1,4-bond) can be used. Hereinafter, natural rubber and / or synthetic isoprene rubber, particularly natural rubber will be mainly described as a preferred embodiment.

  The method for epoxidizing the diene rubber is not particularly limited. For example, it may be performed using various known methods such as a chlorohydrin method, a direct oxidation method, a hydrogen peroxide method, an alkyl hydroperoxy method, and a peracid method. Can do. Preferably, the double bond portion of the main chain of the diene rubber is epoxidized in the latex. As an example, an epoxidized natural rubber can be obtained by reacting a natural rubber latex with a peroxide and an acid. Commercially available epoxidized natural rubber may also be used.

  In the obtained epoxidized diene rubber, the content of epoxy groups is not particularly limited, but diene units (isoprene units in the case of natural rubber or synthetic isoprene rubber. Hereinafter referred to as “isoprene units”, natural rubber or synthetic rubber) In the case other than isoprene rubber, it means a diene unit.) It is preferably 5 to 50 mol%, more preferably 10 to 30 mol%. Here, the content (epoxidation rate) of the epoxy group is the ratio of the number of moles of the epoxy group to the number of moles of the isoprene unit. Therefore, 10 mol% is when the total number of isoprene units is 100, It means that the number of isoprene units into which epoxy groups are introduced is ten.

  Next, part or all of the epoxy group is reduced with diimide or a derivative thereof in the latex of the obtained epoxidized diene rubber. Reduction in latex reduces the possibility of damaging the original properties of the original diene rubber, such as lowering the molecular weight, as compared with the conventional case of hydroxylating an epoxidized natural rubber in an organic solvent. be able to. In particular, it is preferable to carry out hydroxylation by reduction in the latex as it is after epoxidation in the latex as described above. By performing a series of reactions such as epoxidation and hydroxylation in the latex in this way, the modification with improved properties while further reducing the risk of impairing the original properties of the original diene rubber (especially natural rubber) Diene rubber can be obtained.

In this embodiment, diimide (H—N═N—H) or a derivative thereof is used as a reducing agent for reducing an epoxy group to form a hydroxyl group. By reducing the epoxy group by diimide reduction using diimide or its derivative, unlike the diol structure in the case of water addition to the epoxy group by conventional acid, one hydroxyl group is added to the double bond part of the main chain. (Monool structure). More specifically, in the reaction of diimide and epoxy group, two hydrogen atoms at both ends of diimide (N—N═N—H) attack the epoxy group to cause hydrogenation, and the remaining two nitrogen atoms. Atoms are liberated as nitrogen gas (N ₂ ). Therefore, a monool structure is obtained by adding two hydrogen atoms to the structural unit containing the epoxy group represented by the above formula (3). Therefore, other substituents such as a phenoxy group are not introduced as in Patent Documents 1 and 2 above. By forming a monool structure in this way, even if the amount of hydroxyl groups in one molecule is the same as that of the diol structure, the number of isoprene units having hydroxyl groups is twice that of the diol structure. Thus, the hydroxyl groups can be uniformly dispersed. In addition, the reduction method using diimide or a derivative thereof can reduce the double bond of the main chain of the diene rubber as a side reaction, so that the deterioration resistance is improved as long as the properties of the rubber are not impaired. be able to.

As the diimide derivative, a diimide precursor capable of forming a diimide upon reaction in latex is used, and examples thereof include hydrazine hydrate (H ₂ NNH ₂ .H ₂ O), hydrazide compounds, and the like. . Hydrazine hydrate can generate a diimide by reacting with oxygen (eg, peracid). A hydrazide compound is a compound having a structure in which a hydroxyl group (hydroxyl group) of an oxo acid is substituted with a hydrazino group (—NH—NH ₂ ), and a diimide can be generated by decomposition. Examples of the hydrazide compound include p-toluenesulfonyl hydrazide (to produce p-toluenesulfonic acid and diimide by thermal decomposition), triisopropylbenzenesulfonic acid hydrazide, benzenesulfonic acid hydrazide, 3-fluoro-3-oxo-1 A sulfonic acid hydrazide such as propanesulfonic acid hydrazide (RSO ₂ NHNH ₂ , where R is preferably an alkyl or aryl group having 1 to 12 carbon atoms and may have a substituent), acetic acid hydrazide Carbohydrazides such as benzoic hydrazide, pentanoic hydrazide, cyclohexanecarboxylic acid hydrazide, hydrazinecarboxylic acid (RCONHNH ₂ , where R is preferably an alkyl group or aryl group having 1 to 12 carbon atoms and has a substituent. Ben) Nkarubochio acid hydrazide thioacid hydrazide, such as (RCSNHNH _2, wherein, R represents preferably may have a substituent an alkyl group or an aryl group having 1 to 12 carbon atoms.), Such as pentanoate polyhydrazidoimide Hydrazide imide (R (= NH) NHNH ₂ , wherein R is preferably an alkyl group or aryl group having 1 to 12 carbon atoms and may have a substituent), benzenecarbohydrazone hydrazide, etc. And hydrazide hydrazone (R (= NNH ₂ ) NHNH ₂ , where R is preferably an alkyl group or aryl group having 1 to 12 carbon atoms and may have a substituent). These diimides and their derivatives may be used alone or in combination of two or more.

  The method of reducing in latex using diimide or its derivative is not particularly limited. For example, diene or its derivative is added to latex of epoxidized diene rubber and stirred while heating to diene type. The epoxy group of rubber can be reduced.

  By reducing the epoxy group of the natural rubber and / or synthetic isoprene rubber epoxidized as described above, at least one of the structural unit represented by the above formula (1) and the structural unit represented by the formula (2) is obtained. A modified diene rubber having the same is obtained. By introducing these structural units in place of structural units having an epoxy group, it becomes possible to control viscoelasticity by changing the glass transition temperature, especially when used in tires, improving fuel economy and wet skidability. can do. In addition, having hydroxyl groups is thought to improve compatibility from intermolecular interactions due to hydrogen bonding and hydroxyl reactivity, and to improve the reactivity between polymers and between polymers and fillers, improving physical properties. This can contribute to improvements in fuel economy and wet skid. In addition, the modified diene rubber has a monool structure in which one hydroxyl group is added to the double bond portion of natural rubber or synthetic isoprene rubber. When the monool structure is used as described above, even if the amount of hydroxyl groups in one molecule is the same as that of the diol structure, the hydroxyl groups can be uniformly dispersed in the molecular chain. Therefore, the bond or reactivity with a filler such as silica can be improved, and further improvement in fuel efficiency and wet skid property can be achieved. In general, the structural unit of the formula (1) is mainly formed by the above reduction, but the structural unit of the formula (1) and the structural unit of the formula (2) have no practical difference in relation to these effects. Therefore, even if it has only the structural unit of formula (1) or only the structural unit of formula (2), the structural unit of formula (1) is equal to the structural unit of formula (2). It may be mixed in the molecule.

The modified diene rubber may further have a structural unit including an epoxy group generated by oxidation of the double bond portion of the main chain represented by the above formula (3). That is, all the epoxy groups contained in the epoxidized diene rubber may be reduced, but preferably a part thereof is reduced. Therefore, the modified diene rubber is directly bonded to the main chain. It is preferable to have an epoxy group together with a hydroxyl group. In the case of natural rubber and / or synthetic isoprene rubber, an unmodified structural unit represented by the following formula (4) is also included.

  In the modified diene rubber, the content (hydroxylation rate) of the structural unit containing a hydroxyl group represented by the formula (1) and / or the formula (2) is not particularly limited, but is 1 to 20 with respect to the isoprene unit. It is preferable that it is mol%, More preferably, it is 2-15 mol%, More preferably, it is 5-10 mol%. By making the hydroxylation rate 1 mol% or more, the effect of improving fuel economy can be enhanced by improving the reactivity between polymers and fillers. On the other hand, if the hydroxylation rate exceeds 20 mol%, the glass transition temperature of the modified diene rubber will rise, and the effect of improving fuel economy will be reduced. Here, the hydroxylation rate is the ratio of the number of moles of isoprene units into which hydroxyl groups have been introduced to the number of moles of all isoprene units.

  In the modified diene rubber, the content (epoxidation rate) of the structural unit containing an epoxy group represented by the formula (3) is not particularly limited, but may be 2 to 40 mol% with respect to the isoprene unit. More preferably, it is 3-20 mol%, More preferably, it is 5-15 mol%. By setting the epoxidation rate to 2 mol% or more, the glass transition temperature of the modified diene rubber can be increased, and the wet skid improvement effect can be enhanced. On the other hand, if the epoxidation rate exceeds 40 mol%, the glass transition temperature of the modified diene rubber becomes too high, and the effect of improving fuel economy may be reduced.

  The rubber composition according to this embodiment contains the modified diene rubber as a rubber component. As the rubber component, the above-mentioned modified diene rubber may be used alone, or may be used by blending with other diene rubber. Other diene rubbers to be blended are not particularly limited. For example, unmodified natural rubber (NR), unmodified synthetic isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), styrene -Isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, nitrile rubber (NBR), ethylene propylene diene copolymer rubber (EPDM), etc. You may combine 1 type, or 2 or more types. When blended with another diene rubber, the rubber component preferably contains 5% by mass or more of the modified diene rubber, and therefore 100 parts by mass of the rubber component contains 5 to 100 parts by mass of the modified diene rubber. It is preferable that More preferably, the rubber component contains 30% by mass or more, more preferably 50% by mass or more of the modified diene rubber.

In the rubber composition according to this embodiment, silica is preferably blended as a filler. Examples of silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), and wet silica is preferable. Although it does not specifically limit as a colloidal characteristic of a silica, For example, it is preferable that a nitrogen adsorption specific surface area (BET) is 100-300 m < ² > / g. The BET of silica is measured according to the method described in the BET method described in ISO 5794. The compounding amount of silica is preferably 10 to 120 parts by mass with respect to 100 parts by mass of the rubber component, more preferably the lower limit is 20 parts by mass or more, still more preferably 30 parts by mass or more, and the upper limit is The amount is preferably 100 parts by mass or less.

  You may mix | blend carbon black as a filler with the rubber composition which concerns on this embodiment. The carbon black is not particularly limited, and is used as a rubber reinforcing agent, such as SAF (N100 series), ISAF (N200 series), HAF (N300 series), FEF (N500 series), GPF (N600 series), etc. Various carbon blacks can be used. The compounding amount of carbon black is preferably 5 to 100 parts by mass with respect to 100 parts by mass of the rubber component.

  Moreover, as a filler, you may mix | blend titanium oxide, clay, talc, calcium carbonate, etc. other than the said silica and carbon black. Preferably, silica and / or carbon black is blended, and more preferably, silica is used alone. In addition, when using a silica and carbon black together, it is preferable that the total compounding quantity is 15-150 mass parts with respect to 100 mass parts of said rubber components, More preferably, it is 30-120 mass parts.

  In the rubber composition according to this embodiment, when silica is blended as a filler, it is preferable to blend a silane coupling agent. As the silane coupling agent, various known silane coupling agents can be used and are not particularly limited. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilyl) Propyl) disulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) disulfide, etc. Sulfide silane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyldimethylmethoxysilane, mercaptoethyltriethoxysilane Protected mercaptosilanes such as mercaptosilane such as 3-octanoylthio-1-propyltriethoxysilane, 3-propionylthiopropyltrimethoxysilane, etc., and these may be used alone or in combination of two or more. Can be used. It is preferable that the compounding quantity of a silane coupling agent is 2-12 mass parts with respect to 100 mass parts of silica, More preferably, it is 2-10 mass parts.

  In addition to the above-described components, the rubber composition according to this embodiment is generally used in rubber compositions such as softeners, plasticizers, anti-aging agents, zinc white, stearic acid, vulcanizing agents, and vulcanization accelerators. Various additives can be blended. Examples of the vulcanizing agent include sulfur, a sulfur-containing compound, and the like. Although not particularly limited, the blending amount is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the rubber component, More preferably, it is 0.5-5 mass parts. Moreover, as a compounding quantity of a vulcanization accelerator, it is preferable that it is 0.1-7 mass parts with respect to 100 mass parts of said rubber components, More preferably, it is 0.5-5 mass parts.

  The rubber composition according to the present embodiment is prepared by kneading according to a conventional method using a rubber kneader such as a normal Banbury mixer or kneader. The rubber composition thus obtained can be used for various applications such as treads and sidewalls, belts and ply topping rubbers, bead fillers, tires such as rim strips, conveyor belts, and anti-vibration rubbers. Preferably, it is used for a pneumatic tire. In particular, it is suitably used for a tread rubber constituting the ground contact surface of a pneumatic tire, and the tread portion can be formed by vulcanization molding at, for example, 140 to 200 ° C. according to a conventional method. In the tread portion of the pneumatic tire, there are a two-layer structure of a cap rubber and a base rubber, and a single-layer structure in which both are integrated. In the case of a single layer structure, the entire tread portion is preferably made of the rubber composition, and in the case of a double layer structure, the cap rubber is preferably made of the rubber composition.

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

[Synthesis of modified diene rubber]
Synthesis Example 1: Modified diene rubber A (comparative example)
Emulsifier: Sodium Dodecyl Sulfate (SDS) 0.9g is added to 100g of natural rubber latex ("LA-NR" manufactured by Residex, Inc.) adjusted to 30% by mass of DRC (Dry Rubber Content), and the emulsified state is stabilized at 100 rpm. While stirring, 10.6 g of 30% by mass hydrogen peroxide and 4.06 g of formic acid were added dropwise and reacted at 50 ° C. for 24 hours. Then, epoxidized natural rubber was obtained as the modified diene rubber A by adding ethanol and solidifying and drying. Epoxidation rate of the obtained modified diene rubber A was 20 mol%.

Synthesis example 2: Modified diene rubber B (comparative example)
100 g of the modified diene rubber A obtained in Synthesis Example 1 was dissolved in 2250 ml of THF (tetrahydrofuran). While stirring at 200 rpm, 11.7 ml of 6N sulfuric acid and 2.52 g of water were added dropwise and reacted at room temperature for 2 hours. After that, a large amount of water was added to make a rubber as a poor solvent. This was dried to obtain an epoxy-hydroxylated natural rubber having a epoxidation rate of 15 mol% and a hydroxylation rate of 5 mol% as a modified diene rubber B.

Synthesis Example 3: Modified diene rubber C (Example)
600 g of water was added to 200 g of the latex before coagulating the modified diene rubber A obtained in Synthesis Example 1 to adjust DRC to 7.5% by mass, and 7.82 g of paratoluenesulfonyl hydrazide was added while stirring at 100 rpm. And reacted at 80 ° C. for 24 hours. Thereafter, ethanol was added, and the mixture was solidified and dried to obtain an epoxy-hydroxylated natural rubber having a epoxidation rate of 15 mol% and a hydroxylation rate of 5 mol% as modified diene rubber C. The spectrum was compared with the modified diene rubber A of Synthesis Example 1 by the following ¹ H-NMR, and it was confirmed that no functional group other than a hydroxyl group was introduced.

Synthesis Example 4: Modified diene rubber D (Example)
The amount of added paratoluenesulfonyl hydrazide was changed to 15.6 g, and the others were the same as in Synthesis Example 3, and the modified diene rubber D was an epoxy hydroxylated natural rubber having an epoxidation rate of 10 mol% and a hydroxylation rate of 10 mol%. Got.

Synthesis Example 5: Modified diene rubber E (Example)
In the same manner as in Synthesis Example 1, epoxidized natural rubber whose epoxidation rate is adjusted to 10 mol% is adjusted by adding 600 g of water to 200 g of latex before coagulation to adjust DRC to 7.5 mass% and stirring at 100 rpm. Then, 8.03 g of paratoluenesulfonyl hydrazide was added and reacted at 80 ° C. for 24 hours. Thereafter, ethanol was added to solidify and dry to obtain an epoxy hydroxylated natural rubber having a epoxidation rate of 5 mol% and a hydroxylation rate of 5 mol% as a modified diene rubber E.

Synthesis Example 6: Modified diene rubber F (Example)
In the same manner as in Synthesis Example 1, epoxidized natural rubber whose epoxidation rate was adjusted to 15 mol% was added to 600 g of water before coagulation, 600 g of water was added to adjust DRC to 7.5 mass%, and the mixture was stirred at 100 rpm. Then, 7.96 g of paratoluenesulfonyl hydrazide was added and reacted at 80 ° C. for 24 hours. Thereafter, ethanol was added, solidified and dried to obtain an epoxy hydroxylated natural rubber having a epoxidation rate of 10 mol% and a hydroxylation rate of 5 mol% as a modified diene rubber F.

Synthesis Example 7: Modified diene rubber G (Example)
In the same manner as in Synthesis Example 1, epoxidized natural rubber whose epoxidation rate was adjusted to 25 mol% was adjusted by adding 600 g of water to 200 g of latex before coagulation to adjust DRC to 7.5 mass% and stirring at 100 rpm. Then, 15.5 g of paratoluenesulfonyl hydrazide was added and reacted at 80 ° C. for 24 hours. Thereafter, ethanol was added and solidified and dried to obtain an epoxy-hydroxylated natural rubber having a epoxidation rate of 15 mol% and a hydroxylation rate of 10 mol% as a modified diene rubber G.

[Measurement of epoxidation rate and hydroxylation rate]
The rubber obtained by synthesis was dissolved in CDCl ₃ (deuterated chloroform), and from the spectrum of ¹ H-NMR (“400 ULTRASHIELD” manufactured by BRUKER), the proton peak of the double bond portion of the isoprene unit was 5.2 ppm, and the epoxy The epoxidation rate and the hydroxylation rate were calculated from the area intensity of the proton peak of 2.7 ppm at the group bond portion and the proton peak at 3.4 ppm or 1.4 to 1.6 ppm at the hydroxyl bond portion. Each of the proton peaks is a peak of H bonded to carbon on the opposite side to carbon bonded with a methyl group. In the case of a hydroxyl group, in the case of a 2-mol adduct or a 1-mol adduct in which a hydroxyl group is bonded to the opposite carbon, the proton peak is 3.4 ppm, and the hydroxyl group is bonded to the carbon to which the methyl group is bonded. In the case of 1 mol adduct, the proton peak is 1.4 to 1.6 ppm. For isoprene units hydrogenated in the double bond, a peak corresponding to hydrogenation appears in the proton bonded to the carbon adjacent to the double bond, so the isoprene unit hydrogenated from the area strength. The ratio was calculated and taken into account when calculating the total number of isoprene units.

[Measurement of viscosity average molecular weight]
Viscosity measurement was performed using "Viscosity measuring device PVS1" manufactured by LAUDA. As a standard sample 1,4-polyisoprene (molecular weight: 600,1500,7500,21000,80000,210000,750000,1000000 eight) using the coefficients of [η] = KM ^α by viscosity method K, calculated alpha Using the coefficient, the viscosity average molecular weight M of each sample was determined from the equation.

[Measurement of glass transition temperature]
Using Mettler Toledo Co., Ltd. The "Differential Scanning Calorimetry DSC822 ^e" was measured by DSC.

  As shown in Table 1, in the modified diene rubber B, water was added using an acid catalyst in an organic solvent system, and thus a decrease in molecular weight was observed. On the other hand, in the modified diene rubbers C to G, there was almost no decrease in molecular weight, and the glass transition temperature could be changed by hydroxylation.

[Preparation of rubber composition]
Using a Banbury mixer, a rubber composition for a tire tread was prepared according to a conventional method according to the formulation (parts by mass) shown in Table 2 below. Specifically, first, in the first mixing stage, other compounding agents excluding sulfur and a vulcanization accelerator are added to the rubber component and kneaded, and then the obtained kneaded product is subjected to sulfur in the final mixing stage. And a vulcanization accelerator were added and kneaded to prepare a rubber composition. Details of each component in Table 2 excluding the rubber are as follows.

・ Natural rubber: Natural rubber obtained by coagulating and drying “LA-NR” (DRC (Dry = 60% by mass)) manufactured by Resitex Corporation ・ Silica: “Nip seal AQ” (BET = 200 m) manufactured by Tosoh Silica ² / g)
Silane coupling agent: bis (3-triethoxysilylpropyl) tetrasulfide, “Si69” manufactured by Evonik Degussa
・ Zinc flower: “Zinc flower 1” manufactured by Mitsui Mining & Smelting Co., Ltd.
Anti-aging agent: “NOCRACK 6C” manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
・ Stearic acid: “Lunac S-20” manufactured by Kao Corporation
・ Process oil: “X-140” manufactured by Japan Energy Co., Ltd.
・ Sulfur: Hosoi Chemical Co., Ltd. “Powder sulfur for rubber 150 mesh”
・ Vulcanization accelerator: “Noxeller CZ” manufactured by Ouchi Shinsei Chemical Co., Ltd.

  For each rubber composition, unvulcanized rubber is vulcanized at 160 ° C. for 20 minutes to produce a vulcanized rubber piece. Each vulcanized rubber piece has low fuel consumption, wet skid performance, deterioration resistance, and tensile strength. evaluated. The results are shown in Table 2. The evaluation method is as follows.

・ Low fuel consumption: tan δ at 60 ° C. was measured at a static strain of 2%, dynamic strain of 5%, and a frequency of 10 Hz using “Viscoelasticity tester VR-7110” manufactured by Ueshima Seisakusho Co., Ltd. About the reciprocal number, it represented by the index | exponent which set the value of the comparative example 1 to 100. The larger the index, the smaller the tan δ and the less heat generation, that is, the better the fuel efficiency.

Wet skid performance: tan δ at 0 ° C. was measured at a static strain of 2%, a dynamic strain of 5%, and a frequency of 10 Hz using “Viscoelasticity testing machine VR-7110” manufactured by Ueshima Seisakusho Co., Ltd. It was displayed as an index with the value of 100 as 100. The larger the index, the larger the tan δ, which means that the wet skid performance is excellent.

Deterioration resistance: The heat deterioration resistance was evaluated by the rate of change in tensile strength before and after 168 hours passed at 100 ° C. by an air heating aging test (normal oven method) based on JIS K6257-1993. The reciprocal of the rate of change was expressed as an index with the value of Comparative Example 1 as 100. The larger the index, the smaller the rate of change and the better the deterioration resistance.

-Tensile strength: Measured by a tensile test based on JIS K6251 (dumbbell-shaped No. 3 type), and displayed as an index with the value of Comparative Example 1 as 100. A larger index means a higher tensile strength.

  The results are as shown in Table 2, and in Comparative Example 2 using epoxidized natural rubber instead of the unmodified natural rubber according to Comparative Example 1, the wet skid property was greatly improved, but the low fuel consumption was It was getting worse and the balance of both performances was insufficient. In Comparative Example 3, although a part of the epoxy group of the epoxidized natural rubber was hydroxylated, since it had a diol structure, the effect of improving fuel economy and wet skid performance was insufficient. In addition, the tensile strength was reduced due to a decrease in the molecular weight of the polymer.

  On the other hand, when it is Examples 1-5, viscoelasticity control by the change of glass transition temperature became possible by reducing a part of epoxy group and introducing the structural unit containing the hydroxyl group of monool structure, In addition, the balance between the low fuel consumption and the wet skid property is remarkably improved due to the improvement of the binding property with silica, and an improvement effect was also observed for Comparative Example 3. Moreover, the improvement effect of deterioration resistance was recognized because the double bond in the natural rubber molecular chain was reduced by side reaction by the reducing agent. Furthermore, the physical property (tensile strength) was not lowered.

  The modified diene rubber according to the present invention can be suitably used as a compound in a rubber composition for a pneumatic tire, and more specifically, particularly suitable for a rubber composition constituting a tread rubber of a pneumatic tire. Can be used.

Claims (10)

  A diene rubber having an epoxy group generated by oxidation of a double bond portion of a main chain is characterized in that at least a part of the epoxy group is hydroxylated by reduction with diimide or a derivative thereof in latex. A method for producing a modified diene rubber.   The double bond portion of the main chain of the diene rubber is epoxidized in latex, and at least a part of the generated epoxy group is further hydroxylated by reduction with the diimide or derivative thereof in the latex. The method for producing a modified diene rubber according to claim 1.   The method for producing a modified diene rubber according to claim 1 or 2, wherein the diene rubber is natural rubber and / or synthetic isoprene rubber.   A modified diene rubber obtained by the method according to any one of claims 1 to 3. A modified diene rubber obtained by modifying a diene rubber composed of natural rubber and / or synthetic isoprene rubber, wherein at least part of the epoxy group generated by oxidation of a double bond portion in the main chain of the diene rubber A modified diene rubber having at least one of a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2) obtained by reduction.

The modified diene rubber according to claim 5, further comprising a structural unit represented by the following formula (3).

  A rubber composition comprising the modified diene rubber according to any one of claims 4 to 6.   The rubber composition according to claim 7, comprising 10 to 120 parts by mass of silica with respect to 100 parts by mass of the rubber component containing the modified diene rubber.   Furthermore, the rubber composition of Claim 8 which contains 2-12 mass parts of silane coupling agents with respect to 100 mass parts of said silica.   The pneumatic tire provided with the tread which uses the rubber composition of any one of Claims 7-9.