JP5802569B2 - Rubber composition for tire and pneumatic tire - Google Patents

Description

  The present invention relates to a tire rubber composition and a pneumatic tire using the rubber composition.

  In general, diene rubber is used as a rubber component in a rubber composition, and a filler such as carbon black or silica is blended therein. In order to improve the physical properties of such a rubber composition, it is desirable to improve the compatibility or dispersibility of the filler with respect to the rubber component.

  In order to improve the dispersibility of the filler, a technique for modifying a diene rubber is known. Conventionally, a terminal structure modification to a synthetic rubber such as a styrene butadiene rubber, an addition modification on a main chain, or a polymerization stage. Have been proposed (see Patent Documents 1 to 6 below). In addition, since natural rubber is a natural product, techniques for changing its properties include techniques such as adding a functional group directly to a side chain or grafting a polymer to add a functional group (see below). Patent References 7 to 9). However, these modified diene rubbers according to the prior art may not always provide a sufficiently satisfactory level of physical properties, particularly in tire compounding.

JP 2009-138157 A JP-A-11-209517 JP 2007-217562 A JP 2010-275386 A WO2009 / 072650 JP 2011-173986 A JP 2004-359773 A JP-A-2005-041960 JP 2004-359716 A

  An object of this invention is to provide the rubber composition for tires which can improve the physical property of a tire by using a novel modified diene rubber.

The rubber composition for a tire according to the present invention has at least one linking group in the molecule among the linking groups represented by the following formulas (1) to (4), and the diene polymer chain is the linking group. Ri Na are connected via a, with respect to 100 parts by mass of the rubber component number average molecular weight comprising a solid form modified diene rubber in which 23 ° C. 6 10,000 or more, in which the filler contains 5 to 150 parts by weight .

  The pneumatic tire according to the present invention is formed using the rubber composition.

  According to the present invention, by using the specific modified diene rubber as the rubber component, the compatibility of the filler with the rubber component can be improved, and the physical properties of the tire rubber composition can be improved.

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

In the tire rubber composition according to the present embodiment, the modified diene rubber used as the rubber component contains at least one linking group of the linking groups represented by the following formulas (1) to (4) in the molecule. And having a diene polymer chain linked through the linking group.

  Such a modified diene rubber is not particularly limited, but the diene rubber polymer is decomposed by oxidative cleavage of a carbon-carbon double bond existing in the main chain to reduce the molecular weight, and the decomposition. It can be obtained by recombination by making the system containing the polymer polymer acidic or basic.

  Examples of the diene rubber polymer to be modified include conjugated diene compounds such as butadiene, isoprene, chloroprene, 2,3-dimethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, and 1,3-hexadiene. Examples thereof include polymers obtained using at least a part of the monomer. These conjugated diene compounds may be used alone or in combination of two or more.

  Examples of the diene rubber polymer include a copolymer of a conjugated diene compound and a monomer other than the conjugated diene compound. Other monomers include aromatic vinyl compounds such as styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, and 2,4-diisopropylstyrene, and various vinyls such as acrylonitrile and acrylate esters. Compounds. These vinyl compounds may be used alone or in combination of two or more.

  More specifically, as the diene rubber polymer, various rubber polymers having isoprene units and / or butadiene units in the molecule are preferable. For example, natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR). Styrene butadiene rubber (SBR), nitrile rubber (NBR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, and the like. Among these, styrene butadiene rubber, natural rubber, and synthetic isoprene rubber are preferably used.

  As the diene rubber polymer to be modified, those having a number average molecular weight of 60,000 or more are preferable because they are solid at room temperature (23 ° C.). When the modified diene rubber is used alone as a rubber component, if the number average molecular weight is less than 60,000, the viscosity is low and it becomes difficult to form a tire member. The number average molecular weight is preferably 60,000 to 1,000,000, more preferably 80,000 to 800,000, and still more preferably 100,000 to 500,000.

  The diene rubber polymer to be modified is not particularly limited as long as it is dissolved in a solvent, but it is preferable to use an aqueous emulsion, that is, a latex, which is in a micellar form in water, which is a protic solvent. By using an aqueous emulsion, after decomposing the polymer, a recombination reaction can be caused by changing the acid-basicity of the reaction field in that state. Although the density | concentration (solid content concentration of a polymer) of an aqueous emulsion is not specifically limited, It is preferable that it is 5-70 mass%, More preferably, it is 10-50 mass%. If the solid content concentration is too high, the emulsion stability is lowered, and the micelles are easily broken against pH fluctuations in the reaction field, which is not suitable for the reaction. On the other hand, when the solid content concentration is too small, the reaction rate becomes slow and lacks practicality.

  In order to oxidatively cleave the carbon-carbon double bond of the diene rubber polymer, an oxidant can be used. For example, an oxidant is added to the water-based emulsion of the rubber polymer and stirred to oxidatively cleave. it can. Examples of the oxidizing agent include manganese compounds such as potassium permanganate and manganese oxide, chromium compounds such as chromic acid and chromium trioxide, peroxides such as hydrogen peroxide, perhalogen acids such as periodic acid, ozone, Examples thereof include oxygens such as oxygen. Among these, it is preferable to use periodic acid. For oxidative cleavage, a metal-based oxidation catalyst such as a salt or complex with a metal chloride or organic compound such as cobalt, copper, or iron may be used in combination. For example, air oxidation in the presence of the metal-based oxidation catalyst. May be.

The diene rubber polymer is decomposed by the oxidative cleavage, and a polymer having a carbonyl group (> C═O) or a formyl group (—CHO) at the terminal is obtained. Specifically, a polymer having a structure represented by the following formula (5) at the end is generated.

In the formula, R ¹ is a hydrogen atom or a methyl group, and when the isoprene unit is cleaved, R ¹ becomes a methyl group at one cleavage end, and R ¹ becomes a hydrogen atom at the other cleavage end, and the butadiene unit is cleaved. In this case, R ¹ is a hydrogen atom at both cleavage ends. More specifically, the decomposed polymer has a structure represented by the above formula (5) at at least one end of its molecular chain, that is, as shown in the following formulas (6) and (7), A polymer in which a group represented by the formula (5) is directly bonded to one or both ends of the polymer chain is produced.

In the formulas (6) and (7), R ¹ is a hydrogen atom or a methyl group, and a portion represented by a wavy line is a diene polymer chain. For example, when natural rubber is decomposed, the portion represented by the wavy line is a polyisoprene chain composed of a repeating structure of isoprene units, and when styrene butadiene rubber is decomposed, the portion represented by the wavy line is a random containing styrene units and butadiene units. Copolymer chain.

  By decomposing the polymer by the oxidative cleavage, the molecular weight is decreased. Although the number average molecular weight of the polymer after decomposition is not particularly limited, it is preferably 3 to 500,000, more preferably 5 to 100,000, and still more preferably 1,000 to 50,000. The amount of the functional group after recombination can be adjusted by the size of the molecular weight after decomposition, but if the molecular weight at the time of decomposition is too small, a binding reaction within the same molecule tends to occur.

  After decomposing the polymer as described above, it is recombined by making the reaction system containing the decomposed polymer acidic or basic. That is, by changing the acid-basicity of the reaction field in this state after decomposition, a binding reaction that is a reverse reaction to cleavage proceeds preferentially. At that time, the structure of the above formula (5) has two types of tautomerism and is bonded to the original carbon-carbon double bond structure, and the linking group represented by the above formulas (1) to (4). It is divided into what forms. Here, by controlling the pH of the reaction field, the aldol condensation reaction is prioritized to produce a polymer containing a linking group represented by formulas (1) to (4). In detail, some reaction systems, especially aqueous emulsions, have pH adjusted for stabilization. Depending on the method used for decomposition and the type and concentration of the chemical, the pH during decomposition is either acidic or basic. Stop by either. Therefore, when the reaction system at the time of decomposition is acidic, it is preferable to make the reaction system basic. Conversely, when the reaction system at the time of decomposition is basic, the reaction system is made acidic. It is preferable to do.

Here, when polymers having a terminal structure in which R ¹ is a hydrogen atom are bonded to each other, an aldol condensation reaction results in a linking group represented by the formula (3). It becomes the linking group represented. When a polymer having a terminal structure in which R ¹ is a hydrogen atom and a polymer having a terminal structure in which R ¹ is a methyl group are bonded to each other, an aldol condensation reaction results in a linking group represented by the formula (2). By separating, it becomes a linking group represented by the formula (1). In addition, for example, when a polymer having a terminal structure in which R ¹ is a methyl group is bonded, a linking group other than the above formulas (1) to (4) may be generated. The linking groups of formulas (1) to (4) are mainly produced in a small amount.

  When making the reaction system basic, the pH of the reaction system for the binding reaction is preferably 7.5 to 13, and more preferably 8 to 10. On the other hand, when making a reaction system acidic, it is preferable that it is 4-6.8, More preferably, it is 5-6. In addition, when making it into acidic conditions, there exists a possibility of destroying the micelle of latex if acidity is raised too much. The pH can be adjusted by adding an acid or base to the reaction system, and is not particularly limited. Examples of the acid include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and the base includes hydroxylated. Sodium, potassium hydroxide, sodium carbonate, sodium hydrogen carbonate, etc. are mentioned.

  In the binding reaction, an acid or a base for adjusting the pH serves as a catalyst for the binding reaction, and pyrrolidine-2-carboxylic acid may be used as a catalyst for controlling the reaction.

After the binding reaction as described above, the water-based emulsion is coagulated and dried to obtain a modified diene rubber that is solid at room temperature. In the resulting modified diene rubber, the linking group represented by the above formulas (1) to (4) is introduced into the main chain by a recombination reaction, and the main chain structure is modified. That is, the modified diene rubber used in the embodiment has in the molecule at least one of the linking groups represented by the above formulas (1) to (4), and the diene polymer chain directly passes through the linking group. It has a linked structure. The diene polymer chain is a part of the molecular chain of the diene rubber polymer to be modified, and, for example, in the case of a homopolymer of a conjugated diene compound, a structural unit comprising the conjugated diene compound as the ^{a 1,} - ^(a _{1) n} - is a repeating structure of ^{a 1,} represented by (n is an integer of 1 or more, preferably 10 to 10000, more preferably from 50 to 1,000). Further, in the case of a binary copolymer, the diene polymer chain has each constituent unit as A ¹ and A ² (at least one of A ¹ and A ² is a unit composed of a conjugated diene compound, and other units include And a unit composed of the above vinyl compound.), A repeating structure of A ¹ and A ² represented _by- (A ¹ ) _n- (A ² ) _m- (these may be random type or block type). n and m are each an integer of 1 or more, preferably 10 to 10,000, and more preferably 50 to 1,000. In the case of a terpolymer, the diene-based polymer chain is composed of A ¹ , A ² and A ³ as constituent units (at least one of A ¹ , A ² and A ³ is a unit composed of a conjugated diene compound. And other units include units composed of the above vinyl compounds.), A ¹ , A ² and A ³ represented _by- (A ¹ ) _n- (A ² ) _m- (A ³ ) _p- (These may be random type or block type. N, m, and p are each an integer of 1 or more, preferably 10 to 10,000, more preferably 50 to 1000). The same applies to quaternary copolymers or more.

In one embodiment, the modified diene rubber has at least one linking group in the molecule among the linking groups represented by the above formulas (1) to (4), and is represented by the following formula (8). It may be a modified isoprene rubber in which polyisoprene chains are linked via the linking group.

  The modified isoprene rubber is a case where natural rubber and / or synthetic isoprene rubber is used as a modification target, and has the polyisoprene chain composed of a repeating structure of isoprene units as a diene polymer chain. In formula (8), n is an integer greater than or equal to 1, Preferably it is 10-10000, More preferably, it is 50-1000.

In one embodiment, the modified diene rubber has at least one linking group in the molecule among the linking groups represented by the above formulas (3) and (4), and is represented by the following formula (9). It may be a modified styrene butadiene rubber in which random copolymer chains are linked via the linking group.

  The modified styrene butadiene rubber is a case where styrene butadiene rubber is used as a modification target, and has a styrene butadiene copolymer chain represented by the formula (9) as a diene polymer chain. In formula (9), n and m are each independently an integer of 1 or more, preferably 10 to 10000, more preferably 50 to 1000.

The diene polymer chain contained in the modified diene rubber may be a polybutadiene chain represented by the following formula (10) in addition to the polyisoprene chain and the styrene butadiene copolymer chain. That is, when polybutadiene rubber is used as the modification target, it has at least one linking group of the linking groups represented by the above formulas (3) and (4) in the molecule, and the polybutadiene chain is the linking group. A modified butadiene rubber is obtained which is linked via the.

  In formula (10), n is an integer greater than or equal to 1, Preferably it is 10-10000, More preferably, it is 50-1000.

  One or more linking groups are included in one molecule of the modified diene rubber, and usually a plurality of linking groups are included in one molecule. When two or more types are included, a plurality of any one of the linking groups represented by the above formulas (1) to (4) may be included, or two or more types may be included. Although the content rate of a coupling group is not specifically limited, It is preferable that it is 0.001-25 mol% with the sum total of the coupling group of Formula (1)-(4), More preferably, it is 0.1-15 mol%. More preferably, it is 0.5 to 10 mol%. Here, the content (modification rate) of the linking group is a ratio of the number of moles of the linking group to the number of moles of all the structural units constituting the modified diene rubber. For example, in the case of natural rubber, the total isoprene of the modified polymer. The ratio of the number of moles of linking groups to the total number of moles of units and linking groups. In the case of styrene butadiene rubber, the ratio of the number of moles of linking groups to the total number of moles of butadiene units, styrene units and linking groups in the modified polymer. It is.

  Although the content rate of each coupling group represented by Formula (1)-(4) is not specifically limited, It is preferable that it is 25 mol% or less (namely, 0-25 mol%), respectively. For example, in the case of natural rubber or synthetic isoprene rubber (that is, when the diene polymer chain has an isoprene unit), all of the linking groups represented by the formulas (1) to (4) are usually included. In this case, the content of the linking group represented by the formula (1) is preferably 0.001 to 20 mol%, more preferably 0.05 to 10%. It is mol%, More preferably, it is 0.5-5 mol%. In the case of styrene butadiene rubber (that is, when the diene polymer chain contains only a butadiene unit as a conjugated diene compound), the linking group represented by the formulas (3) and (4) is usually included. 4) is mainly included, and in this case, the content of the linking group represented by the formula (4) is preferably 0.001 to 20 mol%, more preferably 0.05 to It is preferable that it is 10 mol%, More preferably, it is 0.5-5 mol%.

  The number average molecular weight of the modified diene rubber is preferably 60,000 or more, more preferably 60,000 to 1,000,000, still more preferably 80,000 to 800,000, still more preferably 100,000 to 500,000. . Thus, the molecular weight of the modified diene rubber is preferably set to be equivalent to that of the original polymer by recombination as described above, thereby preventing the molecular weight from being lowered and thus avoiding adverse effects on physical properties. A functional group can be introduced into the main chain of the polymer. Of course, a polymer having a molecular weight smaller than that of the original polymer may be obtained. The weight average molecular weight of the modified diene rubber is not particularly limited, but is preferably 70,000 or more, more preferably 100,000 to 1,500,000, still more preferably 300,000 to 1,000,000.

  According to the present embodiment, as described above, the double bond of the main chain is oxidatively cleaved to decompose the polymer to reduce the molecular weight, and then recombine by changing the acid basicity of the reaction system. As a result, a modified diene rubber is produced, so that it can be converged to a more uniform structure by monodispersing the polymer. That is, the molecular weight distribution of the modified diene rubber can be made smaller than the molecular weight distribution of the original polymer. This is because the shorter the polymer decomposed by oxidative cleavage, the higher the reactivity and the easier the recombination, so it is considered that the molecular weight is made uniform by reducing the number of short polymers.

  Further, according to the present embodiment, the reaction for oxidative cleavage is controlled by adjusting the type and amount of the oxidizing agent that is a drug that dissociates the double bond, the reaction time, and the pH at the time of recombination. The coupling reaction can be controlled by adjusting the catalyst, reaction time, etc., and the molecular weight of the modified diene rubber can be controlled by these controls. Therefore, the number average molecular weight of the modified diene rubber can be set equal to that of the original polymer, and can be set lower than that of the original polymer.

  Further, when the polymer main chain is decomposed and recombined, the linking group is inserted as a structure different from the main chain, and the bonding point of the segment of the main chain structure is functionalized. That is, a highly reactive structure is introduced into the molecular main chain, and the characteristics of the original polymer can be changed. As described above, this embodiment is neither a graft nor direct addition nor ring-opening, but changes the main chain structure of the diene rubber, which is clearly different from the conventional modification method, and the main chain structure is simple. Functional groups can be introduced. In addition, a modified natural rubber having a novel structure can be produced by rearranging the main chain structure of natural rubber, and the characteristics of the diene rubber can be changed.

  Specifically, in the case of the above-described modified diene rubber, the filler may change due to a change in the interaction (intermolecular force, polarity or reactivity) between the polymer and the filler, or a change in the composition of the polymer. Compatibility and dispersibility are improved. Due to this effect, improvement in fuel economy and improvement in elastic modulus can be seen, and it becomes possible to achieve both high hardness, wet skid performance, and rolling resistance performance, both of which are particularly important in tire tread formulations.

  In the rubber composition according to this embodiment, the rubber component may be the above-mentioned modified diene rubber alone or a blend of the modified diene rubber and another rubber. Other rubbers are not particularly limited. For example, natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), nitrile rubber (NBR), butyl rubber (IIR), Various diene rubbers such as halogenated butyl rubber are exemplified. These can be used alone or in combination of two or more. The content of the modified diene rubber in the rubber component is not particularly limited, but is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and still more preferably 50 parts by mass in 100 parts by mass of the rubber component. More than a part.

  In the rubber composition according to the present embodiment, as the filler, for example, various inorganic fillers such as silica, carbon black, titanium oxide, aluminum silicate, clay, and talc can be used. It can be used in combination of more than one species. Among these, silica and / or carbon black is preferably used.

The silica is not particularly limited and includes wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), etc. Among them, wet silica is preferable. Colloidal properties of the silica are not particularly limited, those which are nitrogen adsorption specific surface area (BET) 150~250m ² / g by BET method is preferably used, more preferably 180~230m ² / g. The BET of silica is measured according to the BET method described in ISO 5794.

  The carbon black is not particularly limited, and various grades of furnace carbon black such as SAF, ISAF, HAF, and FEF, which are used as rubber reinforcing agents, can be used.

  The blending amount of the filler is 5 to 150 parts by mass, preferably 20 to 120 parts by mass, and more preferably 30 to 100 parts by mass with respect to 100 parts by mass of the rubber component.

  Although not particularly limited, when the modified isoprene rubber is used as the modified diene rubber, it is preferable to blend carbon black as a filler. In the case of the above modified isoprene rubber obtained by modifying natural rubber or synthetic isoprene rubber, the use of carbon black as a filler is more effective in improving compatibility than when silica is used. is there. Therefore, when a modified isoprene rubber is used, the filler is preferably carbon black alone or a combination of carbon black and silica, and the carbon black is blended in an amount of 5 to 80 parts by mass with respect to 100 parts by mass of the rubber component. It is preferable to blend 20 to 80 parts by mass.

  When the modified styrene butadiene rubber is used as the modified diene rubber, it is preferable to blend silica as a filler. This is because in the case of the modified styrene butadiene rubber, the use of silica as the filler exhibits a greater effect in terms of improving compatibility than when carbon black is used. Therefore, when a modified styrene butadiene rubber is used, the filler is preferably silica alone or a combination of silica and carbon black, and the silica is blended in an amount of 5 to 80 parts by mass with respect to 100 parts by mass of the rubber component. It is preferable to blend 20 to 80 parts by mass.

  In the rubber composition according to this embodiment, when silica is blended as a filler, a silane coupling agent such as sulfide silane or mercaptosilane may be blended in order to further improve the dispersibility of silica. Although the compounding quantity of a silane coupling agent is not specifically limited, It is preferable that it is 2-20 mass% with respect to a silica compounding quantity.

  The rubber composition according to the present embodiment is generally used in rubber compositions such as oil, zinc white, stearic acid, anti-aging agent, wax, vulcanizing agent, and vulcanization accelerator in addition to the above components. Various additives can be blended.

  Examples of the vulcanizing agent include sulfur and sulfur-containing compounds (for example, sulfur chloride, sulfur dichloride, polymer polysulfide, morpholine disulfide, and alkylphenol disulfide). Two or more types can be used in combination. Although the compounding quantity of a vulcanizing agent is not specifically limited, It is preferable that it is 0.1-10 mass parts with respect to 100 mass parts of said rubber components, More preferably, it is 0.5-5 mass parts. .

  As said vulcanization accelerator, various vulcanization accelerators, such as a sulfenamide type | system | group, a thiuram type | system | group, a thiazole type | system | group, and a guanidine type | system | group, can be used, for example, any 1 type is used individually or in combination of 2 or more types. be able to. Although the compounding quantity of a vulcanization accelerator is not specifically limited, 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. is there.

  The rubber composition according to the present embodiment can be prepared by kneading according to a conventional method using a commonly used Banbury mixer, kneader, roll, or other mixer. That is, in the first mixing stage, other additives except the vulcanizing agent and the vulcanization accelerator are added and mixed with the rubber component in the first mixing stage, and then the vulcanizing agent is added to the obtained mixture in the final mixing stage. And a rubber composition can be prepared by adding and mixing a vulcanization accelerator.

  The rubber composition thus obtained can be used in various applications such as passenger cars, large tires for trucks and buses, tread parts, side wall parts, bead parts, tire cord covering rubbers, etc. Can be applied to the site. That is, according to a conventional method, the rubber composition is molded into a predetermined shape by, for example, extrusion, and combined with other parts, and then vulcanized and molded at, for example, 140 to 180 ° C. to produce a pneumatic tire. can do. Among these, it is particularly preferable to use as a tire tread formulation.

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

<Modified diene rubber>
Each measuring method regarding the modified diene rubber is as follows.

[Number average molecular weight (Mn), weight average molecular weight (Mw), molecular weight distribution (Mw / Mn)]
Mn, Mw and Mw / Mn in terms of polystyrene were determined by measurement with gel permeation chromatography (GPC). Specifically, the measurement sample used was 0.2 mg dissolved in 1 mL of THF. “LC-20DA” manufactured by Shimadzu Corporation was used, the sample was filtered, and passed through a column (“PL Gel 3 μm Guard × 2” manufactured by Polymer Laboratories) at a temperature of 40 ° C. and a flow rate of 0.7 mL / min. Detection was performed by “RI Detector” manufactured by System.

[Content of linking group]
The content of the linking group was measured by NMR. The NMR spectrum was measured using “400ULTRASHIELDTM PLUS” manufactured by BRUKER, with TMS as a standard. 1 g of the polymer was dissolved in 5 mL of deuterated chloroform, 87 mg of acetylacetone chromium salt was added as a relaxation reagent, and the measurement was performed with an NMR 10 mm tube.

For the linking group of formula (1), the peak of carbon with a ketone group is present at 195 ppm in ¹³ C-NMR. For the linking group of formula (2), the peak of carbon with a ketone group is present at 205 ppm in ¹³ C-NMR. For the linking group of formula (3), the peak of carbon with a ketone group is at 200 ppm in ¹³ C-NMR. For the linking group of formula (4), the peak of carbon with a ketone group is present at 185 ppm in ¹³ C-NMR. Therefore, the structural amount (number of moles) of each peak was determined by the ratio with the base polymer component. In addition, about Formula (3), when terminal ketone (structure of Formula (5)) appears, since it overlaps with the carbon peak (200 ppm) here, the amount of terminal ketone was quantified and removed by the following method. . That is, since the proton peak attached to the ketone group appears at 9.0 ppm by ¹ H-NMR, the residual amount was determined by the ratio with the base polymer component.

Regarding the number of moles of each unit in the base polymer component, in the isoprene unit, carbon on the opposite side of the methyl group across the double bond and the peak of hydrogen (= CH-) bonded thereto, that is, by ¹³ C-NMR. It was calculated based on 122 ppm, 5.2 ppm by ¹ H-NMR. For styrene butadiene rubber, 5 carbons excluding the carbon bonded to the main chain in the phenyl group of the styrene unit, and 5 hydrogen peaks bonded thereto, ie 125-130 ppm by ¹³ C-NMR, ¹ H-NMR It was calculated based on 7.2 ppm (however, it was divided by 5 because it was a peak for 5). In this example, since the styrene content of the styrene butadiene rubber latex to be modified was 21.76% by mass, the number of moles of the entire styrene butadiene rubber was calculated from the ratio of the styrene content calculated above.

[PH]
It was measured using a portable pH meter “HM-30P type” manufactured by Toa DKK Corporation.

[Synthesis Example 1: Synthesis of modified diene rubber A]
As the diene rubber to be modified, natural rubber latex (“LA-NR”, manufactured by Resex Corp., DRC = 60 mass%) was used. The molecular weight of the unmodified natural rubber contained in the natural rubber latex was measured, and it was found that the weight average molecular weight was 15.1 million, the number average molecular weight was 26.90,000, and the molecular weight distribution was 5.6.

Periodic acid (H ₅ IO ₆ ) 3.3 g was added to 100 g of the polymer mass in the natural rubber latex adjusted to 30% by mass of DRC (Dry Rubber Content), and the mixture was stirred at 23 ° C. for 3 hours. Thus, by adding periodic acid to the emulsion polymer and stirring, the double bond in the polymer chain was oxidatively decomposed, and a polymer having a structure represented by the above formula (5) was obtained. The obtained decomposition polymer had a weight average molecular weight of 5,200, a number average molecular weight of 2500, a molecular weight distribution of 2.1, and the pH of the reaction solution after decomposition was 6.2.

  Thereafter, 0.1 g of pyrrolidine-2-carboxylic acid is added as a catalyst, 1N sodium hydroxide is added so that the pH of the reaction solution becomes 10, and the mixture is stirred at 23 ° C. for 12 hours. It was allowed to settle, washed with water, and then dried at 30 ° C. for 24 hours with a hot air circulating dryer to obtain a modified diene rubber A that was solid at room temperature.

  By adding sodium hydroxide to the reaction system oxidatively decomposed in this way, the reaction system was forcibly changed to basic, thereby neutralizing the effect of periodic acid added during oxidative cleavage. Thus, the recombination reaction could be prioritized, and a modified natural rubber (modified diene rubber A) containing a linking group represented by the above formulas (1) to (4) was obtained. Although pyrrolidine-2-carboxylic acid is used as a catalyst, it is for accelerating the reaction, and the reaction proceeds even without it.

  As shown in Table 1 below, the resulting modified diene rubber A has a weight average molecular weight Mw of 790,000, a number average molecular weight Mn of 304,000, a molecular weight distribution Mw / Mn of 2.6, The rate was 1.03 mol% in the formula (1), 0.26 mol% in the formula (2), and 0.03 mol% in the formula (4), and the total was 1.32 mol%. Thus, the modified diene rubber A had a number average molecular weight substantially equal to that of the unmodified natural rubber. Further, the molecular weight distribution was smaller than that of the unmodified natural rubber, and the uniformity was excellent.

[Synthesis Examples 2 to 4: Synthesis of Modified Diene Rubbers B to D]
The reaction time during oxidative decomposition, the amount of periodic acid added, the pH adjuster and pH added during the recombination reaction, and the amount of catalyst were changed as shown in Table 1 below, and the others were the same as in Synthesis Example 1, Solid modified diene rubbers B to D were synthesized. Table 1 shows the contents of Mw, Mn, Mw / Mn and each linking group of the obtained modified diene rubbers B to D. Also in the modified diene rubbers B to D, the linking group having a functional group was introduced into the main chain, the molecular weight distribution was smaller than that of the unmodified natural rubber, and the uniformity was excellent. In addition, the molecular weight could be controlled by changing the above conditions.

  The unmodified NR in the table is an unmodified natural rubber obtained by coagulating and drying the above-mentioned natural rubber latex (“LA-NR”, DRC = 60% by mass, manufactured by Regex Corp.) without modification. .

[Synthesis Examples 5 to 8: Synthesis of modified diene rubbers E to H]
As the diene rubber to be modified, styrene butadiene rubber latex (“SBR Latex LX110, DRC = 50% by mass” manufactured by Nippon Zeon Co., Ltd.) was used. As a result of measurement, the weight average molecular weight was 680,000, the number average molecular weight was 324,000, and the molecular weight distribution was 2.1 Using this styrene butadiene rubber latex, the other examples were synthesized according to the conditions described in Table 1. Solid modified diene rubbers E to H were synthesized in the same manner as in 1. The contents of Mw, Mn, Mw / Mn and each linking group of the obtained modified diene rubbers E to H are shown in Table 1. In the modified diene rubbers E to H, only the formulas (3) and (4) were introduced as linking groups. Also, the molecular weight distribution is smaller than the non-modified styrene-butadiene rubber, it was excellent in uniformity. Also, by changing the conditions, it was possible to control the molecular weight.

  The unmodified SBR in the table is an unmodified styrene butadiene rubber obtained by coagulating and drying the styrene butadiene rubber latex without modification.

[Synthesis Examples 9 to 13: Synthesis of Modified Diene Rubbers I to M]
As the diene rubber to be modified, synthetic isoprene rubber latex (“Sepolex IR-100” manufactured by Sumitomo Seika Co., Ltd., DRC = 65 mass%) was used. The molecular weight of the unmodified synthetic isoprene rubber contained in the rubber latex was measured. The weight average molecular weight was 83,000, the number average molecular weight was 66,000, and the molecular weight distribution was 1.3. Using this synthetic isoprene rubber latex, solid modified diene rubbers I to M were synthesized in the same manner as in Synthesis Example 1 under the conditions described in Table 1. Table 1 shows the contents of Mw, Mn, Mw / Mn and each linking group of the obtained modified diene rubbers I to M. For the modified diene rubbers I to M, a linking group having a functional group could be easily introduced into the main chain. In addition, the molecular weight could be controlled by changing the conditions.

  The unmodified IR in the table is an unmodified synthetic isoprene rubber obtained by coagulating and drying the synthetic isoprene rubber latex as it is without modification.

<Rubber composition>
Among the modified diene rubbers synthesized above, the rubber compositions were evaluated using the modified diene rubbers A, B, E, and F. Specifically, using a Banbury mixer, according to the composition (parts by mass) shown in Tables 2 to 6 below, first, in the first mixing stage, other compounding agents are added to the rubber component excluding sulfur and a vulcanization accelerator. Then, in the final mixing stage, sulfur and a vulcanization accelerator were added to the obtained kneaded material and kneaded to prepare a rubber composition. Details of each component in Tables 2 to 6 excluding the rubber component are as follows.

Silica: “Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd. (BET = 200 m ² / g)
・ Carbon black: “Seast 3” manufactured by Tokai Carbon Co., Ltd.
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.

  Each rubber composition obtained was vulcanized at 160 ° C. for 20 minutes to prepare a test piece having a predetermined shape, and a dynamic viscoelasticity test was performed using the obtained test piece to obtain wet skid performance (tan δ (0 ° C.)) and low fuel consumption performance (tan δ (60 ° C.)) were evaluated, and a tensile test was performed to evaluate the elastic modulus M300 and the tensile strength. Each evaluation method is as follows.

Wet skid performance (tan δ (0 ° C.)): Using a rheometer E4000 manufactured by USM, the loss factor tan δ was measured under the conditions of a frequency of 50 Hz, a static strain of 10%, a dynamic strain of 2%, and a temperature of 0 ° C. The index of the comparative example was expressed as 100. Tan δ at 0 ° C. is generally used as an index of grip performance (wet skid performance) on wet road surfaces in tire rubber compositions. The larger the index, the larger tan δ and the better wet skid performance. It shows that.

・ Low fuel consumption performance (tan δ (60 ° C.)): The temperature was changed to 60 ° C., and tan δ was measured in the same manner as tan δ (0 ° C.). Displayed. Tan δ at 60 ° C. is generally used as an index of low heat buildup in tire rubber compositions. The larger the index, the smaller tan δ, and thus the less heat is generated, resulting in low fuel consumption performance as a tire. It is excellent in.

-Modulus of elasticity M300: A tensile test (dumbbell shape No. 3) in accordance with JIS K6251 was performed to measure a 300% modulus, and an index with the value of each comparative example as 100 was displayed. The larger the index, the larger M300 and the higher the rigidity.

-Tensile strength: Tensile test (dumbbell shape No. 3 type) based on JIS K6251 was performed to measure the strength at break, and the value was expressed as an index with the value of each comparative example as 100. The larger the index, the higher the tensile strength and the better.

  The results are as shown in Tables 2 to 6, and in comparison with comparative examples using unmodified natural rubber and styrene butadiene rubber as controls, respectively, in the rubber compositions of the examples using modified diene rubbers. The wet skid performance and fuel efficiency performance were improved, and the elastic modulus was high and the reinforcement was excellent. That is, hardness, wet skid performance, and rolling resistance performance were compatible at a high level.

Claims (7)

The following formulas (1) to (4) Ri Na diene polymer chains have in the molecule at least one linking group of the linking group represented is connected via the linking group, the number average A rubber composition for tires containing 5 to 150 parts by mass of a filler with respect to 100 parts by mass of a rubber component containing a modified diene rubber solid at 23 ° C. having a molecular weight of 60,000 or more .

The modified diene rubber has at least one linking group among the linking groups represented by the above formulas (1) to (4) in the molecule, and is a polyisoprene chain represented by the following formula (8). The rubber composition for tires according to claim 1, wherein the rubber composition is a modified isoprene rubber that is connected through the connecting group.

(In the formula, n is an integer of 1 or more.)   The tire rubber composition according to claim 2, wherein the filler contains 5 to 80 parts by mass of carbon black. The modified diene rubber has at least one linking group of the linking groups represented by the above formulas (3) and (4) in the molecule, and is a random copolymer represented by the following formula (9) 2. The rubber composition for tires according to claim 1, which is a modified styrene butadiene rubber in which a coalesced chain is linked through the linking group.

(In the formula, n and m are each independently an integer of 1 or more.)   The rubber composition for tires according to claim 4, wherein the filler contains 5 to 80 parts by mass of silica.   A pneumatic tire using the rubber composition according to claim 1.   The pneumatic tire according to claim 6, wherein the rubber composition is used for a tread.