JP5634914B2 - Rubber composition, method for producing the same, and pneumatic tire - Google Patents

Description

  The present invention relates to a rubber composition and a method for producing the same, and more particularly to a rubber composition that can be suitably used as a tire tread as an example, and a pneumatic tire using the rubber composition. is there. In particular, a rubber composition that can improve braking performance (wet grip properties) and wear resistance on wet road surfaces while maintaining low fuel consumption by using the tire tread, a method for producing the same, and the method The present invention relates to a pneumatic tire using the composition in a tread.

  In recent years, the demand for lower fuel consumption of automobiles has been increasing, and there is a strong demand for reducing the rolling resistance of tires. Since the rolling resistance is related to the heat build-up of the rubber composition after vulcanization, in order to reduce fuel consumption, it is generally necessary to reduce the hysteresis loss of the rubber composition after vulcanization, that is, loss factor. It is required to keep (tan δ) low. On the other hand, there is a high demand for safety of automobiles, and the performance requirements for the rubber composition of tire treads are not limited to merely reducing rolling resistance, but need to have both high fuel efficiency and braking performance. Has been.

  In order to meet such demands, attempts have been made to achieve braking performance and low fuel consumption on wet road surfaces by blending a large amount of silica as a reinforcing filler.

  In particular, in Patent Document 1 below, “when mixing a silica-containing rubber composition containing natural rubber and / or other diene rubber such as IR and SBR, a diene rubber such as SBR and silica are mixed in advance. After making the masterbatch, by adding NR and / or IR, the incompatibility is promoted and the bipolarization of tan δ temperature dispersion can be increased ”, so that the embrittlement temperature can be kept low. (Paragraph 0007).

  Further, in Patent Document 2 below, “as a first-stage mixing, in a closed mixer, a part of a predetermined amount of rubber, silica and other fillers, silane coupling agents, and other rubber drugs are mixed. In advance, the mixture is homogeneously mixed in a short time at a predetermined temperature, and after that, as the second stage mixing, the remaining rubber is continuously put into the mixture (without being discharged from the mixer), and further at the predetermined temperature. Mixing for a short time "(paragraph 0008) has been proposed. As a result, “a silica-containing rubber composition masterbatch having excellent properties excellent in dispersibility can be obtained very efficiently and without reducing productivity” (paragraph 0008).

  On the other hand, in Patent Document 3 below, “dispersion of silica in rubber is improved”, thereby “viscosity is reduced without using a processing aid and processability is improved”, and “ In order to improve the chipping resistance "(paragraph 0005)," Firstly, in the first stage mixing, a master batch of silica is obtained from all or a part of the predetermined rubber component and silica and a silane coupling agent; In the second stage mixing, the remaining rubber and the compounding agent excluding the required vulcanizing compounding agent are added and mixed, and finally the final mixing is performed and the vulcanizing compounding agent is added and mixed "(paragraph 0008) Has been. Here, in the “second stage mixing”, carbon black is added (claim 1 and all examples in Tables 1 and 2).

On the other hand, in the following Patent Document 4, “the grip performance and the overall running performance can be improved without impairing other physical properties such as wear resistance and blowout resistance” (paragraph 0004), “Identify a wet-process styrene-butadiene carbon black masterbatch in which a petroleum aromatic hydrocarbon resin with a specific kinematic viscosity and carbon black with a nitrogen adsorption specific surface area (N ₂ SA) of at least 140 m ² / g are dispersed in advance. "Mixing amount" (paragraph 0005) has been proposed.

JP 2008-138086 A JP 2006-036918 A JP 2008-138081 A Japanese Patent Laid-Open No. 10-101849

  All of the above Patent Documents 2 to 4 are considered to be intended to efficiently and uniformly disperse a reinforcing filler such as silica. That is, it is considered that the premise is that the desired low fuel consumption can be obtained by mixing the rubber material as uniformly as possible and making maximum contact with the rubber. Patent Document 1 is also considered to realize a reduction in embrittlement temperature due to incompatibility of rubber components, on the premise that reinforcing fillers such as silica are uniformly dispersed. That is, in Patent Documents 1 to 4, the reinforcing filler such as silica is more uniformly dispersed, or the compatible state of rubber materials (polymers) is controlled on the premise of uniform dispersion of the filler. It can be said that

  In addition, any of the above-described conventional methods cannot always satisfy the requirements of low fuel consumption and wet surface braking, which have become increasingly severe in recent years, and the required degree of wear resistance. Note that Patent Documents 3 to 4 do not mention low fuel consumption, and it is obvious that the methods disclosed therein are not very suitable for realizing low fuel consumption.

  The present invention has been made in view of the above-mentioned problems of the prior art, and maintains a low fuel consumption and wear resistance while improving braking performance on a wet road surface, and a method for producing the same, And it aims at providing the pneumatic tire which used this composition for the tread.

  The present inventor has intensively studied in view of the above problems, and in order to obtain a rubber composition used for tire treads and others, the reinforcing filler mainly composed of silica is not uniformly dispersed throughout, but silica is used. A surprising idea has been obtained that a silica unevenly distributed phase containing a large amount and a silica non-uniformly distributed phase having an extremely low silica content are formed. In other words, a high glass transition point (Tg) polymer phase that is highly exothermic and advantageous for braking performance but is disadvantageous for low fuel consumption and wear resistance can be effectively added to a silica non-uniformly distributed phase with a smaller amount of addition. An attempt was made to efficiently improve the braking performance on wet road surfaces without deteriorating fuel efficiency and wear resistance. Specifically, it was performed as follows. First, 85% by mass or more of the rubber component containing at least a part of a modified polymer having a good compatibility with the reinforcing filler and all of the reinforcing filler mainly composed of silica are mixed in the first kneading step. The first master batch was obtained by taking out from the kneading apparatus. Subsequently, only a high Tg / high molecular weight styrene butadiene rubber having a glass transition point (Tg) of −10 to 10 ° C. and a mass average molecular weight of 900,000 or more is added in the second kneading stage and again kneaded. To obtain a second master batch. Then, at the final kneading stage, sulfur and other vulcanizing chemicals were added to obtain an unvulcanized rubber composition. As a result, it has been found that excellent braking performance (wet grip performance) and wear resistance on wet road surfaces can be obtained while maintaining low fuel consumption, and the present invention has been completed.

  That is, in a preferred embodiment, the rubber composition according to the present invention has a modified styrene butadiene rubber (hereinafter referred to as “hetero-modified SBR”) 20% by mass or more introduced with a functional group containing a hetero atom, a glass transition point ( Filling for reinforcement with respect to 100 parts by mass of a diene rubber component containing 5 to 15% by mass of styrene butadiene rubber (hereinafter referred to as “high TgSBR”) having a Tg) of −10 to 10 ° C. and a weight average molecular weight of 900,000 or more A rubber composition comprising 30 to 110 parts by mass of silica as an agent and 3 to 15% by mass of a silane coupling agent based on the amount of silica, which is substantially high in TgSBR at the first kneading stage. All the diene rubber components other than the above, substantially all the reinforcing fillers, and substantially all the rubber compounding agents other than the vulcanizing agent and the vulcanizing aid are mixed in the kneader. Once taken out from the kneading apparatus to form a master batch, in the second kneading stage, substantially only the master batch and the high TgSBR are kneaded. As a result, the phase in which the reinforcing filler is unevenly distributed and the reinforcement And a non-uniformly distributed phase with a low filler content.

  The method for producing a rubber composition according to the present invention comprises 30 to 110 parts by mass of silica as a reinforcing filler and 3 to 15% by mass of a silica compounding amount based on 100 parts by mass of a diene rubber component. In order to obtain a rubber composition to which is added, as a diene rubber component, a hetero-modified SBR having 20% by mass or more of a functional group containing a hetero atom as a diene rubber component, and a glass transition point (Tg) of −10 to 10 ° C. Including a high TgSBR having a mass average molecular weight of 900,000 or more and 25 to 25% by mass, and substantially all the diene rubber components other than the high TgSBR to be added later, and substantially all the reinforcing fillers, A first kneading step in which the first master batch is once taken out from the kneading apparatus, and the first master batch in the kneading apparatus has a substantially high Tg. It is intended to include a second kneading step of adding the BR only.

  According to the present invention, braking performance on a wet road surface can be improved while maintaining low fuel consumption and wear resistance.

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

  In the rubber composition of the present invention, the diene rubber component contains 20 to 95% by mass, preferably 20 to 85% by mass, of a modified styrene butadiene rubber modified to improve dispersibility with a filler such as silica. Preferably it contains 30-70 mass%, More preferably, it contains 40-60 mass%. The modified SBR here is a heteroatom group-introduced SBR (hetero-modified SBR) in which a functional group containing a heteroatom is introduced in order to impart affinity or chemical reactivity to an silanol group of an inorganic filler such as silica. Here, the functional group containing a hetero atom is preferably at least one selected from the group consisting of a hydroxyl group, an amino group, a carboxyl group, an alkoxyl group, an epoxy group, a cyano group, and a halogen group. Modified SBR itself having such a functional group is known, and its production method and the like are not limited. For example, the functional group may be introduced by modifying SBR synthesized by anionic polymerization with a modifier. Alternatively, the monomer having the functional group may be replaced with a monomer constituting the base polymer. You may introduce | transduce into a polymer chain by copolymerizing with a certain styrene and butadiene. Specifically, for example, the above hetero-modified SBR can be produced by a method described in Japanese Patent Publication No. 3488926 and the like, Nipol NS616, NS530 manufactured by Nippon Zeon Co., Ltd. A commercially available product can also be used. When the content of the hetero-modified SBR is lower than the above range, the formation of the non-uniformly distributed phase of the filler such as silica is insufficient, and the filler such as silica cannot be sufficiently dispersed in the unevenly distributed phase, and the desired wet road surface Brake performance (wet grip performance) and low fuel consumption cannot be obtained.

  The glass transition point (Tg) of the hetero-modified SBR is preferably −10 ° C. or lower, more preferably −20 ° C. to −120 ° C. A glass transition point higher than this is disadvantageous in obtaining low fuel consumption. Here, the glass transition point is a value (temperature increase rate 20 ° C./min) measured using differential scanning calorimetry (DSC) in accordance with JIS K7121. The hetero-modified SBR is solution-polymerized styrene butadiene rubber (S-SBR) in a preferred embodiment. S-SBR is generally a copolymer rubber obtained by copolymerization of 1,3-butadiene and styrene using an organolithium compound as an initiator. Further, those having a styrene content (St) of 10 to 40% by mass and a vinyl content (Vi) in the butadiene part of 5 to 70% by mass are preferably used. The molecular weight of the hetero-modified SBR is not particularly limited, but for example, those having a mass average molecular weight (Mw) of 400,000 to 1,500,000 can be suitably used.

  In the rubber composition of the present invention, the diene rubber component contains 5 to 25% by mass, preferably 5 to 20% by mass, more preferably 5 to 15% by mass, and further preferably 7 to 13% by mass, high TgSBR. However, the high TgSBR additionally blended in the second kneading step is preferably 5 to 15% by mass, more preferably 7 to 13% by mass, based on the total amount of the diene rubber component. High TgSBR has a glass transition point (Tg) measured by the above measurement method of preferably −10 to 10 ° C., more preferably −10 ° C. to 0 ° C., and a mass average molecular weight (Mw) of preferably 900,000 or more, more preferably Is 1 million or more, more preferably 1.1 million or more. On the other hand, the upper limit of Mw is not particularly limited, but is usually 2 million or less, more preferably 1.5 million or less. Mw is a value measured by gel permeation chromatography (GPC, “HCL-8220” manufactured by Tosoh Corporation, measuring temperature 40 ° C.) using tetrohydrofuran (THF) as a developing solvent. When the Tg of the high TgSBR is less than −10 ° C., it is difficult to obtain the effect of improving wet grip properties. On the other hand, when it exceeds 10 ° C., it is difficult to ensure low temperature performance and wear resistance. On the other hand, by using a high molecular weight as described above while having a high Tg, it is difficult for a filler component such as silica to be mixed into the high TgSBR in the second kneading stage. By doing in this way, the braking property (wet grip property) on a wet road surface can be exhibited more effectively. As high TgSBR, only 1 type may be used or it may be used in combination of 2 or more types.

A styrene-butadiene rubber having a high glass transition point can be obtained by adjusting the styrene content and the vinyl content in the butadiene portion. Specifically, the styrene-butadiene rubber can be obtained by increasing both the styrene content and the vinyl content. Although not particularly limited, the styrene content (St) is 35 to 50% by mass, and the vinyl content in the butadiene part (Vi, content of 1,2-vinyl structure when the entire butadiene part is 100% by mass). ) Is preferably from 55 to 80% by mass. The styrene content and the vinyl content in the butadiene part are values calculated from the integral ratio of the ¹ HNMR spectrum. High TgSBR is also solution-polymerized styrene butadiene rubber (S-SBR) in a preferred embodiment. S-SBR is generally a copolymer rubber obtained by copolymerization of 1,3-butadiene and styrene using an organolithium compound as an initiator.

  In the rubber composition of the present invention, the diene rubber component may contain other diene rubber different from hetero-modified SBR and high TgSBR in a range of 75% by mass or less. As such another diene rubber component, a rubber component having a glass transition point of −120 ° C. to −20 ° C. (that is, −120 ° C. ≦ Tg ≦ −20 ° C.) is preferably blended, preferably 5 -70 mass%, More preferably, it is 10-60 mass%, More preferably, 20-50 mass% is mix | blended. A glass transition point higher than this is disadvantageous in obtaining low fuel consumption. Such other diene rubber is not particularly limited, and for example, other styrene butadiene rubber (SBR) such as solution polymerization styrene butadiene rubber (S-SBR) and emulsion polymerization styrene butadiene rubber (E-SBR), Examples include polybutadiene rubber (BR), natural rubber (NR), and polyisoprene rubber (IR). The molecular weight of the diene rubber is not particularly limited. For example, a rubber having a mass average molecular weight (Mw) of 400,000 to 1,500,000 can be suitably used.

In the rubber composition of the present invention, 30 to 110 parts by mass, preferably 40 to 100 parts by mass of silica is added to 100 parts by mass of the diene rubber component. When the amount of silica is less than 30 phr, even if the silica non-uniformly distributed phase is formed, there is almost no influence on the silica network structure in the rubber, and no improvement effect on braking performance and low fuel consumption on wet road surfaces is observed. Moreover, when the compounding amount of silica exceeds 110 phr, the amount of silica with respect to the diene rubber component becomes excessive in the phase in which the silica is unevenly distributed, excessive increase in viscosity during processing, and the obtained vulcanized rubber The loss coefficient (tan δ) of the member increases. Therefore, processability and fuel efficiency are deteriorated. On the other hand, the silica to be blended in the rubber composition is not particularly limited, and examples thereof include wet silica, dry silica, colloidal silica, and precipitated silica. It is particularly preferable to use wet silica containing hydrous silicic acid as a main component. The BET specific surface area (one-point method of JIS Z8830) reflecting the average particle diameter of silica is preferably 90 to 250 m ² / g, more preferably 150 to 230 m ² / g.

  Further, the silane coupling agent is added in an amount of 3 to 15% by mass, preferably 5 to 10% by mass, based on the amount of the silica. Examples of coupling agents that can be used include bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) tetrasulfide, and 3-mercaptopropyl. Examples include trimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-nitropropyltrimethoxysilane, and γ-aminopropyltriethoxysilane.

In the rubber composition of the present invention, 5 to 20 parts by mass of carbon black is preferably blended with 100 parts by mass of the diene rubber component. Abrasion resistance etc. can be improved by mix | blending carbon black further. From the viewpoint of wear resistance of the rubber member after vulcanization, the nitrogen adsorption specific surface area (N ₂ SA) (JIS K6217-2) is 70 to 150 m ² / g, and the DBP oil absorption (JIS K6217-4) Is preferably 100 to 150 ml / 100 g. Specifically, SAF, ISAF, and HAF grade carbon black are exemplified.

  In the method for producing a rubber composition of the present invention, in the first kneading stage, diene rubber components 75 to 95 containing 20 parts by mass or more of the above hetero-modified SBR out of 100 parts by mass of the total charged amount of diene rubber components. Part by mass and all reinforcing fillers mainly composed of silica are mixed in a kneading apparatus. Under the present circumstances, high TgSBR can also be mix | blended in the range of preferably 10 mass parts or less, More preferably, 8 mass parts or less. After the completion of the first kneading step, the rubber composition obtained from the kneading apparatus is once taken out as a first master batch and charged again into the kneading apparatus. Thereafter, in the subsequent second kneading stage, substantially only the high TgSBR is added to the first master batch in the kneading apparatus. In addition, in rubber compositions containing silica, two or more kneading stages are generally employed in order to improve the dispersibility of the silica and promote the reaction between the silica and the coupling agent. There are also many. Therefore, it is considered that the productivity of the rubber composition is equivalent to the conventional one.

  In the first kneading stage, it is considered that silica is uniformly dispersed in the hetero-modified SBR. Even when a diene rubber component other than the hetero-modified SBR is blended in the first kneading step, the hetero-modified SBR is mixed with the other diene rubber component as long as it has compatibility with the hetero-modified SBR. By mixing uniformly, it is considered that silica or silica and other fillers are uniformly dispersed throughout the rubber composition.

  In the second kneading stage, substantially only a relatively small amount of high TgSBR is blended into the first masterbatch containing a relatively high concentration of filler. Moreover, the first master batch is once taken out from the kneading apparatus, and cooled to, for example, 50 ° C. or less, and then charged into the kneading apparatus. Therefore, if the vulcanizing agent is not added, the diene rubber portion not containing the filler is not easily mixed. In particular, under conditions where a relatively small amount of high TgSBR having a high molecular weight is added, the portion derived from the first masterbatch and the additional blended portion are difficult to mix. Further, since the modified SBR contained in the first master batch has already reacted to some extent with a filler such as silica to form a bond, it is difficult to distribute the filler such as silica to the diene rubber added additionally. Therefore, if the kneading conditions for a normal rubber composition for producing a rubber member of a tire are adopted, a filler unevenly distributed portion such as silica derived from the first master batch and a filler are not included. The non-distributed portion of the filler such as silica derived from the diene rubber added additionally forms a different phase. Since the portion derived from the first masterbatch is large in quantity, it generally forms a continuous phase, and the additional blended portion that does not contain a filler or the like becomes island-like or another continuous phase, Or it seems to form a partially continuous phase. In the second kneading stage, even if the portion derived from the first masterbatch and the additional blending portion are partially mixed, the entire phase is almost unevenly distributed with a silica-based filler. It is thought that another phase having no or low concentration is retained in the rubber composition after kneading.

  Preferably, after the end of the second kneading step, the second master batch is taken out again from the kneading apparatus. Then, in the third kneading stage, sulfur and a vulcanization accelerator are added. In the third kneading step, the kneading operation is finished when the sulfur and the vulcanization accelerator are uniformly mixed throughout. Therefore, the phase in which silica and other fillers are unevenly distributed and the silica non-uniformly distributed phase can be kept separated. The unvulcanized rubber composition obtained in the third kneading step is supplied into a vulcanization mold to produce a vulcanized rubber product.

  As a kneading apparatus that can be used in the first to third kneading steps, those generally used for mixing rubber compositions can be used without particular limitation, and examples thereof include a Banbury mixer, a roll, an extruder, and a kneader. Can be mentioned. In addition, since it is necessary to make a silane coupling agent fully react, in the 1st kneading | mixing stage, the temperature of a rubber composition needs to reach 140-170 degreeC, for example. However, if a sealable mixing device such as a Banbury mixer is used, the temperature is naturally raised to a temperature of 140 to 170 ° C. at the end of kneading due to natural heat generation during kneading. That is, it is preferable to use a Banbury mixer or the like because a separate heating mechanism is unnecessary and the entire temperature can be increased uniformly. The second to third kneading stages can be realized by the same kneading apparatus as used in the first kneading stage or by a separate kneading apparatus. For example, a Banbury mixer may be used in the first kneading stage, and a twin screw extruder may be used in the second to third kneading stages.

  The amount of the hetero-modified SBR charged in the first kneading step is preferably 30 parts by mass or more, more preferably 40 to 70 parts by mass, and still more preferably, of 100 parts by mass of the total amount of diene rubber component. 50-60 parts by mass. This is because, in order to form a silica unevenly dispersed phase in which silica is well dispersed, it is desirable that the amount of hetero-modified SBR is large to some extent. When 40 to 70 parts by mass of hetero-modified SBR is blended, 15 to 55 parts by mass of other diene rubber is blended, and when 50 to 60 parts by mass of hetero-modified SBR is blended, 25 to 25 parts of other diene rubber is blended. 45 parts by mass is blended.

  On the other hand, in a 2nd kneading | mixing stage, high TgSBR which occupies 5-15 mass parts among 100 mass parts of total preparation amounts of a diene-type rubber component is added and charged.

  The rubber composition of the present invention obtained by the second kneading step is preferably once taken out from the kneading apparatus and appropriately stored as a second master batch. Before obtaining a rubber member as a rubber product, a vulcanizing agent such as sulfur and a vulcanization accelerator (for example, guanidine-based, thiazole-based, sulfenamide-based, thiuram-based, etc.) are added. 3. Subject to kneading stage. By providing the third kneading step for adding the vulcanizing agent and the vulcanization accelerator, the silica, the silane coupling agent and the functional group of the modified polymer are sufficiently reacted even in the second kneading step. It can be discharged at temperatures such as 170 ° C.

  In the first kneading step, in addition to silica and carbon black, various rubber additives that are generally blended into a rubber composition can be blended as appropriate. However, vulcanizing agents and vulcanization accelerators are excluded. For example, compounding chemicals such as anti-aging agents (amine-ketone series, aromatic secondary amine series, phenol series, imidazole series, etc.), zinc white, oil, wax, stearic acid, plasticizer, resins, etc. are in the normal range. It can mix | blend suitably within. Moreover, hard granular materials, such as a vegetable granular material, can also be further mix | blended as fillers other than a silica and carbon black.

  A predetermined rubber member or rubber product is obtained from the rubber composition of the present invention after the third stage through a vulcanization molding step. The pneumatic tire of the present invention is prepared, for example, by forming a tread portion of a tire with a rubber extruder using the rubber composition after undergoing the above-described third stage and molding an unvulcanized tire according to a conventional method. It can be manufactured through a vulcanization process. When applied to a tire having a cap base structure, the rubber composition of the present invention may be applied only to the cap tread on the contact surface side.

  Examples of the present invention will be described below, but the present invention is not limited to these examples. In addition, the unit of the compounding quantity of each component in each mixing step in the following table is part by mass. Further, when simply referred to as “parts by mass”, it is a value when the total amount of the diene rubber component is 100 parts by mass.

  The above-described first to third kneading steps were performed using the Banbury mixer having a capacity of 1.7 liters according to the formulation shown in Table 1 for the formulation components shown in Table 1 below. In the first and second kneading stages, mixing was performed until the temperature reached 160 ° C., and the mixture was taken out immediately after the kneading. In the third kneading stage, it was discharged at 90 ° C. or lower. That is, according to the formulation of Table 1 below, the first masterbatch is prepared and removed once in the first kneading step (silica uneven phase generation step), and added to the first masterbatch in the second kneading step. After adding only the rubber component and taking out again to obtain the second master batch, only the vulcanizing agent and the vulcanization accelerator were added in the third kneading step. Thus, the unvulcanized rubber composition of each Example and each comparative example shown in Table 1 was obtained. In addition, in the display of the blending prescription in Table 1 below, for the oil-extended SBR, the blending amount (part by mass) including the oil component is described, and the blending amount based on the polymer component excluding the oil component is shown in parentheses. .

Details of each component in the table are as follows.
Modified S-SBR: “Nipol NS616” (solution-polymerized styrene / butadiene rubber, glass transition point Tg = −25 ° C., bonded styrene content = 21% by mass, hydroxyl group introduced at the terminal), manufactured by Nippon Zeon Co., Ltd.
High TgS-SBR (1): “SE6529” manufactured by Sumitomo Chemical Co., Ltd. (solution-polymerized styrene-butadiene rubber. Glass transition temperature Tg = −4 ° C., bound styrene content = 43 mass%, mass average molecular weight Mw = 1.200,000. , 44.0 phr oil exhibition),
High TgS-SBR (2): “SE6233” manufactured by Sumitomo Chemical Co., Ltd. (solution-polymerized styrene-butadiene rubber. Glass transition point Tg = −2 ° C., bound styrene content = 40 mass%, mass average molecular weight Mw = 1.16 million 37.5 phr oil exhibition),
-Butadiene rubber (BR): “BR01” (glass transition point Tg = −102 ° C.) manufactured by JSR Corporation,
Unmodified E-SBR: “SBR0122” manufactured by JSR Corporation (emulsion polymerized styrene / butadiene rubber. Glass transition temperature Tg = −40 ° C., amount of bonded styrene = 37% by mass, 34.0 phr oil).
Silica: “Nippal Seal AQ” manufactured by Tosoh Corporation (nitrogen adsorption specific surface area BET = about 205 m ² / g),
Carbon black: “N339 Seest KH” manufactured by Tokai Carbon Co., Ltd. (HAF-HS grade, nitrogen adsorption specific surface area BET = about 90 m ² / g),
Silane coupling agent: “Si69” manufactured by Degussa;
・ Oil: "Process NC140" manufactured by Japan Energy Co., Ltd.
・ Stearic acid: “Lunac S-20” manufactured by Kao Corporation
・ Zinc flower: “Zinc flower No. 1” manufactured by Mitsui Mining & Smelting Co., Ltd.
Anti-aging agent: “Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.
・ Wax: “Sunnock N” manufactured by Ouchi Shinsei Chemical Co., Ltd.
・ Vulcanization accelerator (1): dibenzothiazolyl disulfide (“Sanseller DM-G” manufactured by Sanshin Chemical Industry Co., Ltd.)
-Vulcanization accelerator (2): N-cyclohexyl-2-benzothiazolylsulfenamide ("Soccinol CZ" manufactured by Sumitomo Chemical Co., Ltd.)
Sulfur: “5% oil-treated powder sulfur” manufactured by Tsurumi Chemical Co., Ltd.

  Each unvulcanized rubber composition obtained through the third kneading step is vulcanized at 160 ° C. for 30 minutes to prepare a test piece of a predetermined shape, and the obtained test piece is used on a wet road surface. The braking performance, low heat build-up (low fuel consumption) and wear resistance were evaluated. Each evaluation method is as follows. In addition, these evaluation results are shown by the index | exponent which sets the value of the comparative example 2 of Table 1-1, the comparative example 4 of Table 1-2, and the comparative example 6 of Table 1-3 to 100, respectively. For convenience of comparison, in Tables 1-2 and 1-3, an index in which the comparative example 2 of Table 1-1 is 100 is shown in parentheses.

-Wet surface braking property (wet index): Using a Lüpke-type rebound resilience tester, rebound resilience (%) was measured according to JIS K6255 under the condition of 23 ° C. The reciprocal of the rebound resilience was obtained and expressed as an index as described above. The higher the value, the better the wet surface braking performance.

Low fuel consumption index: Using a viscoelasticity tester manufactured by Toyo Seiki Co., Ltd., tan δ was measured in accordance with JIS K 6394 under conditions of a frequency of 10 Hz, dynamic strain of 1%, and 60 ° C. The reciprocal of tan δ was determined and expressed as an index as described above. The larger the value, the smaller the heat generation and the better.

-Abrasion resistance: Abrasion amount was measured by a lambone test in accordance with JIS K 6264 using a test piece obtained by vulcanizing each rubber composition. The standard conditions were a slip rate of 30%, an applied load of 40 N, and a sandfall amount of 20 g / min. It shows that it is excellent in abrasion resistance, so that an index | exponent is large.

  The results are as shown in Table 1. In Examples 1 and 2, in which a relatively large amount of OH-modified S-SBR was blended in the first kneading stage and an appropriate amount of high TgSBR was added in the second kneading stage, Compared with Comparative Examples 1 and 2 in which no additional blending is performed in the kneading stage, the wet surface braking performance can be remarkably improved while maintaining the low exothermic property directly related to the low fuel consumption. Abrasion was slightly improved. In Example 1 and Example 2, the high TgSBR used was similar, and there was no significant difference in the evaluation results.

  In Comparative Example 2, although high TgSBR was used, since it was blended in the first kneading stage, the wet surface braking performance was considerably improved as compared with Comparative Example 1 in which high TgSBR was not blended. , Not always enough. Moreover, it was judged that the low heat generation property was slightly lower than that of Example 1. This is presumably because filler such as silica was distributed in the high TgSBR, and the silica non-uniformly distributed phase was hardly formed.

  In Comparative Example 3, as a result of adding a relatively small amount (10% by mass) of BR in the second kneading stage without using high TgSBR, almost the same result as Comparative Example 1 in which no additional blending was performed in the second kneading stage. It became. This was thought to be because when the BR was added in the second kneading stage, a silica non-uniformly distributed phase sufficient to achieve the desired performance could not be obtained with a blending amount of 10% by mass.

  The part of Table 1-2 (Comparative Examples 4 to 5 and Example 3) shows Examples and Comparative Examples in which the blending amount of high TgSBR is 20% by mass of the total amount of diene rubber. In Comparative Example 4, the same formulation as in Comparative Example 2 was adopted except that the blending amount of high TgSBR was doubled. As a result, compared with Comparative Example 2, although the braking performance on the wet road surface was excellent, It was inferior in abrasion resistance. In Example 3, a part of high TgSBR was blended in the first kneading stage and less than 15% by mass of high TgSBR was blended in the second kneading stage. As a result, all the same amount of high TgSBR was blended in the first kneading stage. Compared with Comparative Example 4, the wet surface braking performance was remarkably improved and the wear resistance could be improved while maintaining low heat generation.

  On the other hand, in Comparative Example 5 in which high TgSBR, which is 20% by mass of the total amount of diene rubber, was blended in the second kneading stage, the wet road surface braking property was excellent, but the low heat build-up was significantly lower than Comparative Example 4, Abrasion was also a little low. The difference between the result of Comparative Example 5 and the result of Example 3 was considered to be due to the following reason. When a high TgSBR as high as 20% by mass is blended in the second kneading stage as in Comparative Example 5, the silica non-uniformly distributed phase consisting of a high TgSBR becomes excessive, and the balance between braking performance, low fuel consumption and wear resistance on wet road surfaces is achieved. It was thought to have collapsed.

  The part of Table 1-3 (Comparative Examples 6-7) shows the case where hetero-modified SBR was not used. Here, non-modified E-SBR was used instead of hetero-modified SBR. In Comparative Example 7, although 10% by mass of high TgSBR was blended in the second kneading stage, the result was almost the same as that of Comparative Example 6 in which normal mixing was performed. When the hetero-modified SBR is not used, even if an appropriate amount of high TgSBR is additionally blended in the second kneading stage, the filler such as silica is not sufficiently unevenly distributed in one phase, resulting in normal mixing (Comparative Example 6). It is thought that it became the same rubber.

  As known from the results of the above Examples and Comparative Examples, a styrene butadiene rubber having a heteroatom group introduced therein and a styrene butadiene rubber having a high glass transition point are used as at least a part of the diene rubber component, and a vulcanizing agent is used. The wet surface braking performance could be improved while maintaining low heat build-up and wear resistance by carrying out two-stage kneading according to a specific formulation before the addition.

  The pneumatic tire of the present invention can be used by being mounted on vehicles for various purposes such as tires for passenger cars, large truck tires for light trucks, trucks and buses.

Claims (6)

30 to 70 % by mass of a modified styrene butadiene rubber into which at least one functional group selected from the group consisting of a hydroxyl group, an amino group, a carboxyl group, an alkoxyl group, an epoxy group, a cyano group, and a halogen group is introduced, and a glass transition point As a reinforcing filler for 100 parts by mass of a diene rubber component containing 5 to 25% by mass of a styrene butadiene rubber having a high glass transition point (Tg) of −10 to 10 ° C. and a mass average molecular weight of 900,000 or more. 30 to 110 parts by mass of silica and 3 to 15% by mass of a silane coupling agent of the silica content,
In the first kneading step, the the modified SBR with 30 to 70 parts by mass including diene rubber component from 85 to 95 parts by weight, and all the reinforcing filler are mixed in a kneader device, once removed from the kneading device In the second kneading stage after being added, as a result of substantially only adding 5 to 15 parts by mass of the styrene butadiene rubber having the high glass transition point, the phase in which the reinforcing filler is unevenly distributed, and the reinforcing A rubber composition comprising a non-uniformly distributed phase having a low filler content. In obtaining a rubber composition in which 30 to 110 parts by mass of silica as a reinforcing filler and 3 to 15% by mass of a silane coupling agent with respect to the amount of silica are added to 100 parts by mass of a diene rubber component. ,
As a diene rubber component, modified SBR having 30 to 70 % by mass of a hydroxyl group, amino group, carboxyl group, alkoxyl group, epoxy group, cyano group, and at least one functional group selected from the group consisting of a halogen group is introduced. And a glass transition point (Tg) containing -10 to 10 ° C. and 5 to 25% by mass of styrene butadiene rubber having a high glass transition point having a mass average molecular weight of 900,000 or more,
A first kneading step of mixing 85 to 95 parts by mass of the diene rubber component containing 30 to 70 parts by mass of the modified SBR and substantially all the reinforcing filler in a kneading apparatus;
Thereafter, a step of taking out the first master batch from the kneading apparatus,
And a second kneading step of adding only 5 to 15 parts by mass of the styrene butadiene rubber having the high glass transition point to the first master batch in a kneading apparatus. The method for producing a rubber composition according to claim 2, wherein the other diene rubber comprises another styrene-butadiene rubber (SBR), polybutadiene rubber (BR), natural rubber (NR), or polyisoprene rubber (IR). . The method for producing a rubber composition according to claim 2 or 3, wherein a glass transition point (Tg) of the high glass transition point styrene butadiene rubber is -10 ° C to 0 ° C. The glass transition point of the modified SBR is -20 ° C to -120 ° C,
When the diene rubber component contains another diene rubber different from the modified SBR and SBR having a high glass transition point, the glass transition point of the diene rubber is -20 ° C to -120 ° C. The manufacturing method of the rubber composition in any one of Claims 2-4 characterized by the above-mentioned. A pneumatic tire provided with a tread made of a rubber composition obtained by the method according to any one of claims 2 to 5 .