JP6134556B2 - Rubber composition and method for producing rubber composition - Google Patents

Description

  The present invention relates to a rubber composition containing silica and a method for producing the rubber composition.

  In recent years, in connection with the growing interest in environmental issues, there are increasing demands for reducing fuel consumption of automobiles and durability of tires. In order to meet such demands, both reduction of rolling resistance (low heat generation) and improvement of wear resistance are required for tire performance.

  As a technique for reducing the rolling resistance of the tire, a technique for optimizing the tire structure has been studied, but it is now common to use a rubber composition having a lower energy loss as a rubber composition applied to the tire. It is done as a method. In order to reduce the energy loss of the rubber composition, it is necessary to reduce the energy loss derived from the rubber component and / or the energy loss derived from the filler. The most effective means to reduce the former is to shift the glass transition point of the rubber component to the low temperature side to reduce energy loss. However, the shift of the glass transition point to the low temperature side is also accompanied by wear on the wet road surface. There is a problem that the characteristics are also degraded. The most effective means to reduce the latter is to reduce the amount of filler used, but easy reduction of the filler is not easy because it causes a significant deterioration in tire wear. That is, it can be said that “reduction of rolling resistance”, “improvement of wear resistance” and “improvement of wear characteristics on wet road surface” are contradictory functions.

  As a technique for reducing the rolling resistance of a tire while achieving both wear characteristics and wear resistance on a wet road surface, there is a polymer modification technique. The polymer modification technique leads to an increase in a strong rubber layer called a bound rubber existing on the surface of the filler by forming a chemical bond between the polymer and the filler, and also improves the rubber wear resistance. This technique is advantageous both environmentally and economically because a great effect can be obtained with a small amount of chemical modification. The tire rolling resistance reduction mechanism by the polymer modification technology is that the modified functional group reacts with the filler surface, so that the filler that normally agglomerates is separated, and the dispersibility is improved, thereby reducing energy loss. It is believed that. However, it has been reported that when the interaction between the modified functional group and the filler is strengthened by the molecular design of the modified functional group, the energy loss reducing effect and the wear resistance improving effect reach a peak (Non-Patent Document 1). From the above points, it is considered that the energy loss reduction and wear resistance improving effects obtained only by the modification technique are limited.

Morikawa, A., Sonw, T., Shibata, M., Tadaki, T., International Rubebr Conference 2005 Yokohama, 26-S1-I-01 (2005) Keizo Ninagawa “Nanoscale Mechanical Simulation Technology of Rubber by Finite Element Method”, Journal of Japan Rubber Association Vol. 82, No. 5, p. 227-232 (2009)

  The subject of this invention is providing the rubber composition which can implement | achieve the low heat_generation | fever property of a tire, and the improvement of abrasion resistance. Another object of the present invention is to provide a method for producing a rubber composition capable of realizing low heat build-up and improved wear resistance of a tire.

The rubber composition of the present invention contains more than 0 parts by weight and 100 parts by weight or less of silica with respect to a total of 100 parts by weight of rubber components including two or more kinds of diene rubbers, and the diene rubbers have different glass transition temperatures. It is divided into two or more phases, of which at least one phase has a continuous structure, and at least one phase has a glass transition point of −50 ° C. or more, and at least one of the two or more phases of glass. The transition point is less than −50 ° C., and the phase contains at least one member selected from the group consisting of isoprene rubber, natural rubber, butadiene rubber, silicone rubber, butyl rubber, and styrene-butadiene rubber. more than 80 weight percent silica the total amount is included in one or more phases having a glass transition temperature above -50 ° C., the silica contained in said phase, the cutting surface of the rubber composition Kicking, average aggregate aggregate area is 2000 nm ² or less, wherein the.
The “average aggregate aggregate area” in the present invention refers to an area measured by the following method. That is, after cutting the upper surface of the rubber composition sample after vulcanization in a direction forming an angle of 38 ° with respect to the upper surface of the sample using a focused ion beam, the smooth surface of the sample formed by cutting is The image is taken at an acceleration voltage of 5 kV using a scanning electron microscope from a direction perpendicular to the smooth surface. Based on the binarized image obtained by converting the obtained image into a binarized image of the rubber part of the sample and the silica part as the filler by the Otsu method, the aggregated aggregate area of the silica part is obtained. From the total surface area of the silica portion and the number of aggregates, the average aggregate aggregate area of the silica portion per unit area (3 μm × 3 μm) is calculated by number average (arithmetic average). In the calculation, particles in contact with the edge (side) of the image are not counted, and particles of 20 pixels or less are regarded as noise and are not counted.
The rubber composition in the present invention is divided into two or more phases having different glass transition points, and silica is unevenly distributed in a phase having a high glass transition point of −50 ° C. or more (hereinafter referred to as “high Tg phase”). . In general, a high Tg phase increases its hardness in a state in which a high-speed tensile force is applied, compared with a phase having a low glass transition point of less than −50 ° C. (hereinafter referred to as “low Tg phase”). It has a property that wear resistance is easily improved. In the present invention, silica is further unevenly distributed in the high Tg phase, so that the phase has a higher wear resistance. On the other hand, the low Tg phase is more flexible than the high Tg phase and has the property of reducing its rolling resistance when used in a tire.
As described above, the rubber composition of the present invention is constituted by blending the high Tg phase and the low Tg phase without impairing the respective characteristics. The improvement of wear and low heat generation is achieved at the same time. In particular, when at least one phase has a continuous structure, the characteristics of the phase are efficiently exhibited.
However, it has been found that when the silica is unevenly distributed in the high Tg phase in this way, there is a problem that strain is concentrated in the high Tg phase. With respect to this problem, by reducing the silica agglomerates existing in this region, that is, by making the average aggregate aggregate area of the silica portion 2000 nm ² or less, the distortion is reduced and the rubber composition is used. It was found that the wear resistance and low heat build-up of the tires improved significantly.

  ADVANTAGE OF THE INVENTION According to this invention, the rubber composition which can implement | achieve the low heat generation property of a tire and the improvement of abrasion resistance can be provided.

It is the analysis image which calculated the strain distribution of the rubber composition by the nanoscale finite element method. (A) Silica average aggregate aggregate area is more than 2000 nm ² and (B) Silica average aggregate aggregate area is 2000 nm ² or less.

Hereinafter, the present invention will be described in detail based on an embodiment thereof.
<Rubber composition>
The rubber composition of the present invention comprises the rubber composition of the present invention containing more than 0 parts by weight and 100 parts by weight or less of silica with respect to a total of 100 parts by weight of rubber components including two or more kinds of diene rubbers The rubber is divided into two or more phases each having a different glass transition temperature, of which at least one phase has a continuous structure and at least one phase has a glass transition point of −50 ° C. or more. At least one of the above phases has a glass transition point of less than −50 ° C., and the phase is at least one selected from the group consisting of isoprene rubber, natural rubber, butadiene rubber, silicone rubber, butyl rubber, and styrene-butadiene rubber. wherein, more than 80% by weight of the formulation silica are included in one phase of one or more phases having a glass transition temperature above -50 ° C., the silica contained in said phase, the rubber composition In the cutting surface, average aggregate aggregate area is 2000 nm ² or less, and wherein.

  Here, the method for measuring the average aggregate aggregate area is as described above, and a direction in which the upper surface of the vulcanized rubber composition sample is formed at an angle of 38 ° with respect to the upper surface of the sample by using a focused ion beam. Then, the smooth surface of the sample formed by cutting is photographed at an acceleration voltage of 5 kV using a scanning electron microscope from a direction perpendicular to the smooth surface. Based on the binarized image obtained by converting the obtained image into a binarized image of the rubber part of the sample and the silica part as the filler by the Otsu method, the aggregated aggregate area of the silica part is obtained. From the total surface area of the silica part and the number of aggregates, the average aggregate aggregate area of the silica part per unit area (3 μm × 3 μm) is calculated by number average (arithmetic average). However, in the calculation, particles in contact with the edge (side) of the image are not counted, and particles of 20 pixels or less are regarded as noise and are not counted.

In measuring the average aggregate aggregate area according to the present invention, it is preferable to use a FIB-SEM in which a focused ion beam processing observation apparatus (FIB) and a scanning electron microscope (SEM) are combined into one apparatus. Moreover, it is preferable to use a very low acceleration voltage scanning electron microscope as a scanning electron microscope (SEM).
Examples of the FIB-SEM include FEI, trade name “NOVA200” (registered trademark), SII Nano Technology Inc., trade name “SMI-3050MS2” (registered trademark), and the like. NOVA200 "(registered trademark) is preferred.
An image processing apparatus based on the Otsu method is used for conversion to a binary image.

In the measurement of the average aggregate aggregate area according to the present invention, the top surface of the rubber composition sample after vulcanization is cut using a focused ion beam in a direction that forms an angle of 38 ° with respect to the top surface of the sample. The smooth surface of the sample formed by the above is photographed at an acceleration voltage of 5 kV using a scanning electron microscope from a direction perpendicular to the smooth surface. In this method, a high-accuracy image including only the surface information of the cross section can be obtained for a flat cross section of the sample without being affected by the difference in brightness or the focus shift. As a result, based on the high-accuracy image obtained, the dispersion state of the filler in the polymer material is quantified, and the average aggregate aggregate area of the rubber composition after vulcanization containing silica is quantitatively evaluated. It became possible to do. When the sample is cut with FIB, the cut surface formed in the direction parallel to the FIB irradiation direction is a smooth surface without unevenness, and the cutting surface formed in the direction perpendicular to the FIB irradiation direction is rough surface with unevenness. It becomes. Accordingly, the smooth surface used for photographing in the present invention means a cutting surface formed in a direction parallel to the FIB irradiation direction.
Next, a threshold value for binarization of the obtained image is determined using the Otsu method. Based on the binarized image obtained by converting the rubber portion of the sample and the silica portion serving as the filler, the aggregated aggregate area of the silica portion is obtained, and the total surface area of the silica portion is calculated. From the number of aggregates, the average aggregate aggregate area of the silica portion per unit area (3 μm × 3 μm) is calculated by number average (arithmetic average). In the calculation, particles in contact with the edge (side) of the image are not counted, and particles of 20 pixels or less are regarded as noise and are not counted.

The aggregated aggregate of silica in the rubber composition of the present invention refers to an aggregate of one or a plurality of aggregates, and includes a single aggregate. Here, the aggregate (primary agglomerate) refers to a complex agglomerated form in which silica basic particles are fused together and branched into a chain or irregular chain shape. The size of the meter.
Aggregate aggregates in the present invention are much smaller than agglomerates (secondary aggregates) that are usually considered to be tens to hundreds of microns in size, and they are completely different concepts.

Average aggregate aggregate area of the silica, and 2000 nm ² or less, in particular, 1950 nm ² or less, or more 1900 nm ² or less. When the average aggregate aggregate area of silica is 2000 nm ² or less, the rubber composition is imparted with good wear resistance and low heat build-up without strain being concentrated on the high Tg phase in which silica is unevenly distributed. The average aggregate aggregate area is preferably as small as possible.

FIG. 1 is a photograph showing an analysis image obtained by calculating a strain distribution of a rubber composition by a nanoscale finite element method. (A) Silica average aggregate aggregate area is an example exceeding 2000 nm ² and (B) Silica average aggregate aggregate area is an example of 2000 nm ² or less. In the example of (A), a large strain concentration occurs in the two-phase discontinuous phase, and the low heat buildup and the fracture resistance are likely to deteriorate. On the other hand, as shown in (B), when the two phases have a co-continuous structure and the average aggregate aggregate area of silica is 2000 nm ² or less, the concentration of strain is reduced, and low heat buildup and resistance Destructibility is improved.

[Rubber component]
The rubber composition of the present invention contains two or more types of diene rubber as a whole as a rubber component, and is divided into two or more rubber phases having different glass transition points. In the present specification, a rubber phase having a glass transition point of −50 ° C. or higher is referred to as a high Tg phase, and a phase lower than −50 ° C. is referred to as a low Tg phase.

  The rubber component contained in the high Tg phase preferably contains at least one of unmodified and terminal-modified styrene-butadiene copolymer (SBR). In particular, terminal-modified SBR can be preferably used. The term “terminal modification” as used herein means amino group, imino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group, hydroxyl group, carboxyl group, carbonyl group, epoxy group, oxy group. Polar group containing at least one polar group selected from the group consisting of carbonyl group, sulfide group, disulfide group, sulfonyl group, sulfinyl group, thiocarbonyl group, nitrogen-containing heterocyclic group, oxygen-containing heterocyclic group and alkoxysilyl group This is the addition of the containing monomer and bonding the polar group-containing monomer to the end of the polymer, or terminal tin modification, which increases the affinity with the silica to be blended. By using such a terminal-modified polymer, it is possible to obtain an effect that the silica to be blended is likely to be unevenly distributed in a high Tg phase.

Hereinafter, the production method of the terminal-modified SBR will be exemplified. The SBR before terminal modification is obtained by anionic polymerization or coordination polymerization, but is preferably produced by anionic polymerization.
The polymerization initiator used for the anionic polymerization is an alkali metal compound, but a lithium compound is preferable. As the lithium compound, hydrocarbyl lithium is preferable. By using hydrocarbyllithium, an SBR having a hydrocarbyl group at the polymerization initiation terminal can be obtained.
As the hydrocarbyl lithium, those having a hydrocarbyl group having 2 to 20 carbon atoms are preferable, for example, ethyl lithium, n-propyl lithium, isopropyl lithium, n-butyl lithium, sec-butyl lithium, tert-butyl lithium, tert-octyl. Lithium, n-decyl lithium, phenyl lithium, 2-naphthyl lithium, 2-butyl-phenyl lithium, 4-phenyl-butyl lithium, cyclohexyl lithium, cyclopentyl lithium, reaction products of diisopropenyl benzene and butyl lithium, etc. Can be mentioned.
Further, if desired, any randomizer can be appropriately selected from known compounds that are generally used. Specifically, dimethoxybenzene, tetrahydrofuran, dimethoxyethane, diethylene glycol dibutyl ether, diethylene glycol dimethyl ether, 2,2-bis (2-tetrahydrofuryl) -propane, triethylamine, pyridine, N-methylmorpholine, N, N, N ′, Examples thereof include ethers such as N′-tetramethylethylenediamine and 1,2-dipiperidinoethane, and tertiary amines. Further, potassium salts such as potassium tert-amylate and potassium tert-butoxide, and sodium salts such as sodium tert-amylate can also be used.

  There is no restriction | limiting in particular as a manufacturing method of SBR by anionic polymerization, A conventionally well-known method can be used. Specifically, in the organic solvent inert to the reaction, for example, hydrocarbon solvents such as aliphatic, alicyclic, and aromatic hydrocarbon compounds, the above-mentioned randomizer may be used as an organic lithium compound as a polymerization initiator. In the presence of styrene, the target SBR is obtained by anionic polymerization of styrene and 1,3-butadiene. The temperature in this polymerization reaction is usually selected in the range of -80 to 150 ° C, preferably -20 to 100 ° C. The polymerization reaction can be carried out under generated pressure, but it is usually desirable to operate at a sufficient pressure to keep the monomer in a substantially liquid phase. Higher pressures can be used, and such pressures can be obtained by any suitable method, such as pressurizing the reactor with a gas that is inert with respect to the polymerization reaction.

The terminal-modified SBR is obtained, for example, by bonding a polar group-containing monomer to the polymerization active terminal of the SBR after completion of the polymerization reaction of the unmodified SBR obtained as described above, before the polymerization is terminated, by graft polymerization or the like. can get. As the polar group-containing monomer, those having an interaction with silica are preferable, and amino group, imino group, nitrile group, ammonium group, imide group, amide group, hydrazo group, azo group, diazo group, hydroxyl group. , Carboxyl group, carbonyl group, epoxy group, oxycarbonyl group, sulfide group, disulfide group, sulfonyl group, sulfinyl group, thiocarbonyl group, nitrogen-containing heterocyclic group, oxygen-containing heterocyclic group and alkoxysilyl group. And a polar group-containing monomer containing at least one polar group. In particular, a monomer containing an amino group or an alkoxysilyl group is preferably used.
Terminal-modified SBR can also be obtained by using an organolithium compound having the above polar group as an anionic polymerization initiator.

The terminal tin-modified SBR is obtained by reacting a tin compound as a modifier with the polymerization active terminal of SBR after completion of the polymerization reaction of the unmodified SBR obtained as described above. Examples of the tin compound include tin tetrachloride, tributyltin chloride, trioctyltin chloride, dioctyltin dichloride, dibutyltin dichloride, and triphenyltin chloride.
The terminal tin-modified SBR can also be obtained by using a lithium compound having a tin atom as an initiator for anionic polymerization. Examples of the lithium compound having a tin atom include triorganotin lithium compounds such as tributyltin lithium and trioctyltin lithium.

  The terminal-modified SBR preferably contains a styrene component in a range of 5 to 50% by weight, more preferably in a range of 10 to 40% by weight, and further in a range of 15 to 35% by weight. preferable. Moreover, it is preferable that the vinyl content of a butadiene part is 70 weight% or less.

The rubber component contained in the low Tg phase contains at least one of the group consisting of isoprene rubber, natural rubber, butadiene rubber, silicone rubber, butyl rubber, and styrene-butadiene rubber . These rubber components have a low Tg and can improve the low heat buildup of the tire. In addition, since it is desired that the compounded silica is not present in the low Tg phase as much as possible, it is preferable to use an unmodified rubber component.

  The amount of the high Tg phase in the rubber composition of the present invention is preferably 30 to 90% by weight, particularly 30 to 75% by weight, and more preferably 30 to 65% by weight. Sufficient wear resistance can be imparted by adjusting the blending amount of the high Tg phase to 30% by weight or more. On the other hand, when the blending amount of the high Tg phase is 90% by weight or less, it is possible to maintain low exothermic properties.

[silica]
As the silica used in the rubber composition of the present invention, any commercially available silica can be used, among which wet silica, dry silica and colloidal silica are preferably used, and wet silica is more preferably used. Wet silica is classified into precipitated silica and gel silica. Precipitated silica is particularly preferable because it is easily dispersed in the rubber composition by kneading shear and has excellent reinforcing properties due to surface reaction after dispersion.
As the CTAB adsorption specific surface area of the silica (measured according to JIS K6217 method), and more preferably preferably less than 140 m ² / g, less than 60 m ² / g or more and 140 m ² / g.
Precipitated silica with a CTAB adsorption specific surface area within this range includes Rhodia Co., Ltd., trade name “Zeosil 1115” (registered trademark) (CTAB adsorption specific surface area = 110 m ² / g), trade name “Zeosil 115”. (Registered trademark) (CTAB adsorption specific surface area = 110 m ² / g), trade name “Zeosil 125” (registered trademark) (CTAB adsorption specific surface area = 115 m ² / g) and the like are preferable.

If desired, the rubber composition of the present invention may contain carbon black in addition to the above-described silica. By containing carbon black, it is possible to enjoy the effect of reducing electrical resistance and suppressing charging. The carbon black is not particularly limited. For example, high, medium or low structure SAF, ISAF, IISAF, N339, HAF, FEF, GPF, SRF grade carbon black, particularly SAF, ISAF, IISAF, N339, HAF, Preferably, FEF grade carbon black is used. The nitrogen adsorption specific surface area (N ₂ SA, measured in accordance with JIS K 6217-2: 2001) is preferably 30 to 250 m ² / g. This carbon black may be used individually by 1 type, and may be used in combination of 2 or more type.

  The rubber composition of the present invention contains more than 0 parts by weight and 200 parts by weight or less of silica with respect to 100 parts by weight of the total rubber components. Preferably, it contains 40 to 150 parts by weight, more preferably 50 to 100 parts by weight of silica. By providing more than 0 part of silica, the wear resistance of the rubber composition can be improved. By making the silica 100 parts by weight or less, the low heat build-up property is hardly inhibited.

Further, in the rubber composition of the present invention, it is preferable to contain 40 to 200 parts by weight of a filler composed of silica and optionally added carbon black with respect to 100 parts by weight of the rubber component. If it is 40 parts by weight or more, it is preferable from the viewpoint of improving the reinforcing property of the rubber composition, and if it is 200 parts by weight or less, it is preferable from the viewpoint of low heat generation.
In the filler, silica is preferably 40% by weight or more from the viewpoint of achieving both wear resistance and low heat build-up, and more preferably 50% by weight or more.

  In the rubber composition of the present invention, 80% by weight or more, preferably 85% by weight or more, more preferably 90% by weight or more of the silica to be blended is contained in one or more high Tg phases. The uneven distribution of silica in the high Tg phase increases the wear resistance of the high Tg phase, while maintaining a low heat generation effect of the low Tg phase because the amount of silica contained in the low Tg phase is small. . A rubber composition in which silica is unevenly distributed in the high Tg phase is obtained by using modified SBR as the rubber component of the high Tg phase, using an unmodified polymer as the rubber component of the low Tg phase, and kneading silica by the method described later. Can be realized. Note that the higher the proportion of silica contained in the high Tg phase, the better.

  Here, the distribution ratio of silica in the high Tg phase and the low Tg phase can be measured by the following method. That is, after cutting the upper surface of the rubber composition sample after vulcanization in a direction forming an angle of 38 ° with respect to the upper surface of the sample using a focused ion beam, the smooth surface of the sample formed by cutting is The image is taken at an acceleration voltage of 5 kV using a scanning electron microscope from a direction perpendicular to the smooth surface. Based on the binarized image obtained by converting the obtained image into a binarized image of the two-phase rubber part of the sample and the silica part as the filler by the Otsu method, each phase for the entire silica area is obtained. The ratio of the silica area contained in is obtained.

[Silane coupling agent]
As the silane coupling agent used in the rubber composition of the present invention, any known silane coupling agent can be used, but it should be at least one selected from polysulfide compounds and thioester compounds. preferable. Polysulfide compounds and thioester compounds are preferred because they are less likely to be burned (scorched) during kneading and can have good processability. A silane coupling agent may be used individually by 1 type, and may be used in combination of 2 or more type.
It is preferable that the compounding quantity of the silane coupling agent of the rubber composition of this invention is 1 to 20 weight% of a silica. If the amount is less than 1% by weight, the effect of improving the low heat build-up of the rubber composition is hardly exhibited. If the amount exceeds 20% by weight, the cost of the rubber composition becomes excessive and the economic efficiency is lowered. Furthermore, 5 to 15% by weight of silica is more preferable, and 5 to 10% by weight of silica is particularly preferable.

[Vulcanization accelerator]
Examples of the vulcanization accelerator suitably used in the rubber composition of the present invention include guanidines, sulfenamides, thiazoles, thiurams, dithiocarbamates, thioureas and xanthates.
Examples of guanidines used in the rubber composition of the present invention include 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, and di-o-tolylguanidine salt of dicatechol borate. 1,3-di-o-cumenyl guanidine, 1,3-di-o-biphenyl guanidine, 1,3-di-o-cumenyl-2-propionyl guanidine, and the like may be mentioned, 1,3-diphenyl guanidine, 1,3-di-o-tolylguanidine and 1-o-tolylbiguanide are preferable because of high reactivity.

  Examples of the sulfenamides used in the rubber composition of the present invention include N-cyclohexyl-2-benzothiazolylsulfenamide, N, N-dicyclohexyl-2-benzothiazolylsulfenamide, N-tert-butyl- 2-benzothiazolylsulfenamide, N-oxydiethylene-2-benzothiazolylsulfenamide, N-methyl-2-benzothiazolylsulfenamide, N-ethyl-2-benzothiazolylsulfenamide, N -Propyl-2-benzothiazolylsulfenamide, N-butyl-2-benzothiazolylsulfenamide, N-pentyl-2-benzothiazolylsulfenamide, N-hexyl-2-benzothiazolylsulfenamide N-pentyl-2-benzothiazolylsulfenamide, N-oct Ru-2-benzothiazolylsulfenamide, N-2-ethylhexyl-2-benzothiazolylsulfenamide, N-decyl-2-benzothiazolylsulfenamide, N-dodecyl-2-benzothiazolylsulfen Amides, N-stearyl-2-benzothiazolylsulfenamide, N, N-dimethyl-2-benzothiazolylsulfenamide, N, N-diethyl-2-benzothiazolylsulfenamide, N, N-dipropyl 2-benzothiazolylsulfenamide, N, N-dibutyl-2-benzothiazolylsulfenamide, N, N-dipentyl-2-benzothiazolylsulfenamide, N, N-dihexyl-2-benzothia Zolylsulfenamide, N, N-dipentyl-2-benzothiazolylsulfenamide, N, -Dioctyl-2-benzothiazolylsulfenamide, N, N-di-2-ethylhexylbenzothiazolylsulfenamide, N-decyl-2-benzothiazolylsulfenamide, N, N-didodecyl-2-benzo Examples include thiazolylsulfenamide, N, N-distearyl-2-benzothiazolylsulfenamide, and the like. Of these, N-cyclohexyl-2-benzothiazolylsulfenamide and N-tert-butyl-2-benzothiazolylsulfenamide are preferable because of their high reactivity.

  The thiazoles used in the rubber composition of the present invention include 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, zinc salt of 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, 2 -(N, N-diethylthiocarbamoylthio) benzothiazole, 2- (4'-morpholinodithio) benzothiazole, 4-methyl-2-mercaptobenzothiazole, di- (4-methyl-2-benzothiazolyl) disulfide, 5 -Chloro-2-mercaptobenzothiazole, 2-mercaptobenzothiazole sodium, 2-mercapto-6-nitrobenzothiazole, 2-mercapto-naphtho [1,2-d] thiazole, 2-mercapto-5-methoxybenzothiazole, 6-amino-2-mer Hept benzothiazole and the like. Of these, 2-mercaptobenzothiazole and di-2-benzothiazolyl disulfide are preferred because of their high reactivity.

  The thiurams used in the rubber composition of the present invention include tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrapropylthiuram disulfide, tetraisopropylthiuram disulfide, tetrabutylthiuram disulfide, tetrapentylthiuram disulfide, tetrahexylthiuram disulfide, tetraheptyl Thiuram disulfide, tetraoctyl thiuram disulfide, tetranonyl thiuram disulfide, tetradecyl thiuram disulfide, tetradodecyl thiuram disulfide, tetrastearyl thiuram disulfide, tetrabenzyl thiuram disulfide, tetrakis (2-ethylhexyl) thiuram disulfide, tetramethyl thiuram monosulfide, tetraethyl thiuram Monos Fido, tetrapropyl thiuram monosulfide, tetraisopropyl thiuram monosulfide, tetrabutyl thiuram monosulfide, tetrapentyl thiuram monosulfide, tetrahexyl thiuram monosulfide, tetraheptyl thiuram monosulfide, tetraoctyl thiuram monosulfide, tetranonyl thiuram monosulfide, Examples include tetradecyl thiuram monosulfide, tetradodecyl thiuram monosulfide, tetrastearyl thiuram monosulfide, tetrabenzyl thiuram monosulfide, dipentamethylene thiuram tetrasulfide and the like. Of these, tetrakis (2-ethylhexyl) thiuram disulfide and tetrabenzylthiuram disulfide are preferred because of their high reactivity.

  Examples of the dithiocarbamate used in the rubber composition of the present invention include zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dipropyldithiocarbamate, zinc diisopropyldithiocarbamate, zinc dibutyldithiocarbamate, zinc dipentyldithiocarbamate, and zinc dihexyldithiocarbamate. , Zinc diheptyldithiocarbamate, zinc dioctyldithiocarbamate, zinc di (2-ethylhexyl) dithiocarbamate, zinc didecyldithiocarbamate, zinc didodecyldithiocarbamate, zinc N-pentamethylenedithiocarbamate, N-ethyl-N-phenyldithiocarbamine Zinc oxide, zinc dibenzyldithiocarbamate, copper dimethyldithiocarbamate, copper diethyldithiocarbamate, di Copper Lopyldithiocarbamate, Copper diisopropyldithiocarbamate, Copper dibutyldithiocarbamate, Copper dipentyldithiocarbamate, Copper dihexyldithiocarbamate, Copper diheptyldithiocarbamate, Copper dioctyldithiocarbamate, Copper di (2-ethylhexyl) dithiocarbamate, Didecyldithiocarbamine Copper acid, copper didodecyl dithiocarbamate, copper N-pentamethylenedithiocarbamate, copper dibenzyldithiocarbamate, sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, sodium dipropyldithiocarbamate, sodium diisopropyldithiocarbamate, sodium dibutyldithiocarbamate, dipentyl Sodium dithiocarbamate, dihexyl dithiocarbamate Sodium, sodium diheptyldithiocarbamate, sodium dioctyldithiocarbamate, sodium di (2-ethylhexyl) dithiocarbamate, sodium didecyldithiocarbamate, sodium didodecyldithiocarbamate, sodium N-pentamethylenedithiocarbamate, sodium dibenzyldithiocarbamate, dimethyl Ferric dithiocarbamate, ferric diethyldithiocarbamate, ferric dipropyldithiocarbamate, ferric diisopropyldithiocarbamate, ferric dibutyldithiocarbamate, ferric dipentyldithiocarbamate, ferric dihexyldithiocarbamate, di Ferric heptyldithiocarbamate, ferric dioctyldithiocarbamate, di (2-ethylhexyl) dithioca Ferric vammin acid, ferric didecyl dithiocarbamate, ferric didodecyl dithiocarbamate, N- ferric pentamethylene dithiocarbamate, ferric dibenzyldithiocarbamate acid. Of these, zinc dibenzyldithiocarbamate, zinc N-ethyl-N-phenyldithiocarbamate, zinc dimethyldithiocarbamate and copper dimethyldithiocarbamate are preferred because of their high reactivity.

  Examples of thioureas used in the rubber composition of the present invention include N, N′-diphenylthiourea, trimethylthiourea, N, N′-diethylthiourea, N, N′-dimethylthiourea, N, N′-dibutylthiourea. , Ethylenethiourea, N, N′-diisopropylthiourea, N, N′-dicyclohexylthiourea, 1,3-di (o-tolyl) thiourea, 1,3-di (p-tolyl) thiourea, 1, 1-diphenyl-2-thiourea, 2,5-dithiobiurea, guanylthiourea, 1- (1-naphthyl) -2-thiourea, 1-phenyl-2-thiourea, p-tolylthiourea, o-tolylthiourea Etc. Of these, N, N'-diethylthiourea, trimethylthiourea, N, N'-diphenylthiourea and N, N'-dimethylthiourea are preferred because of their high reactivity.

  Xanthates used in the rubber composition of the present invention include zinc methylxanthate, zinc ethylxanthate, zinc propylxanthate, zinc isopropylxanthate, zinc butylxanthate, zinc pentylxanthate, zinc hexylxanthate, Zinc heptylxanthate, zinc octylxanthate, zinc 2-ethylhexylxanthate, zinc decylxanthate, zinc dodecylxanthate, potassium methylxanthate, potassium ethylxanthate, potassium propylxanthate, potassium isopropylxanthate, butylxanthate Potassium, potassium pentylxanthate, potassium hexylxanthate, potassium heptylxanthate, octylxa Potassium tomate, potassium 2-ethylhexylxanthate, potassium decylxanthate, potassium dodecylxanthate, sodium methylxanthate, sodium ethylxanthate, sodium propylxanthate, sodium isopropylxanthate, sodium butylxanthate, sodium pentylxanthate Sodium hexyl xanthate, sodium heptyl xanthate, sodium octyl xanthate, sodium 2-ethylhexyl xanthate, sodium decyl xanthate, sodium dodecyl xanthate, and the like. Of these, zinc isopropylxanthate is preferable because of its high reactivity.

  The rubber composition of the present invention preferably contains 0.1 to 10 parts by weight, more preferably 0.2 to 5 parts by weight, of the vulcanization accelerator with respect to 100 parts by weight of the rubber component.

[Organic acid compound]
The rubber composition of the present invention may contain an organic acid compound. Organic acid compounds to be blended include stearic acid, palmitic acid, myristic acid, lauric acid, arachidic acid, behenic acid, lignoceric acid, capric acid, pelargonic acid, caprylic acid, enanthic acid, caproic acid, oleic acid, vaccenic acid Organic acids selected from saturated fatty acids such as linoleic acid, linolenic acid, nervonic acid and the like, and resin acids such as rosin acid and modified rosin acid, metal salts or esters of the organic acids, phenol derivatives, etc. .
In the present invention, 50 mol% or more in the organic acid compound is preferably stearic acid because it is necessary to sufficiently exhibit the function as a vulcanization acceleration aid.

[Multiphase structure of rubber component]
The rubber component having two or more phases in the rubber composition of the present invention requires that at least one phase has a continuous structure. For example, the continuous structure refers to a continuous arrangement when rubber samples measuring several μm square are measured. The rubber component having two or more phases preferably has a two-phase structure having one high Tg phase and one low Tg phase. In particular, the high Tg phase preferably has a continuous structure. By continuously disposing the high Tg phase throughout the composition, it becomes possible to efficiently improve the wear resistance of the entire rubber composition.
Furthermore, it is more preferable that the low Tg phase has a continuous structure in addition to the high Tg phase. Since both phases have a continuous structure, the characteristics of both phases (abrasion resistance, low exothermic property) are more easily exhibited.

<Method for producing rubber composition>
In the rubber composition of the present invention, with respect to a total of 100 parts by weight of two or more kinds of diene rubbers, the silica composition contains more than 0 parts by weight and 100 parts by weight or less of silica, and each of the diene rubbers has two or more phases having different glass transition temperatures. And at least one phase has a continuous structure, and 80% by weight or more of the blended silica is contained in one or more phases having a glass transition point of −50 ° C. or more, and the silica contained in the phase There is no limitation on the method for producing a rubber composition having an average aggregate aggregate area of 2000 nm ² or less, and any kneading method may be used. However, the following production method is effective for the rubber composition. Is preferable.

As a first step, a rubber composition (composition A) having a rubber component that forms a high Tg phase and a rubber composition (composition B) having a rubber component that forms a low Tg phase are formed separately. All or part of the terminal-modified SBR and silica, all or part of the silane coupling agent, and a vulcanization accelerator are added and kneaded (Composition A). Separately, a rubber component such as isoprene rubber and a vulcanization accelerator are added and kneaded (composition B). Next, as a second step, the remaining silane coupling agent, vulcanization accelerator and organic acid compound are added as necessary, and composition A and composition B are kneaded.
Alternatively, the vulcanization accelerator may be added in the first stage or in the second stage depending on the type used.
Usually, various compounding agents such as vulcanization activator such as zinc white and anti-aging agent blended in the rubber composition are mixed in the first or second stage of kneading, or the first and second stages as required. Kneading in an intermediate stage.

  In the manufacturing method described above, the first and second kneading steps are steps of blending and kneading raw materials other than the vulcanizing agent, such as rubber components, fillers, and coupling agents. This is a process for reinforcing the rubber component by dispersing in the composition.

  As the kneading apparatus in the present invention, any known kneading apparatus such as a twin screw extruder, a roll, and an intensive mixer can be used.

The maximum temperature of the rubber composition in the first and second kneading steps is preferably 120 to 190 ° C, more preferably 130 to 175 ° C, and further preferably 140 to 170 ° C. The kneading time is preferably 1 to 20 minutes, more preferably 1 to 15 minutes, and further preferably 1 to 10 minutes.
Further, the maximum temperature of the rubber composition in the vulcanization process in which a chemical relating to crosslinking (vulcanizing agent, vulcanization accelerator) is mixed and kneaded is preferably 60 to 140 ° C, and preferably 70 to 140 ° C. Is more preferable, and it is more preferable that it is 70-120 degreeC. The kneading time is preferably 0.5 to 15 minutes, more preferably 0.5 to 10 minutes, and further preferably 0.5 to 5 minutes.
The rubber composition of the present invention can be produced by appropriately combining the above kneading conditions and vulcanizing conditions.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.
In addition, the average aggregation aggregate area and low exothermic property (tan δ index) of the vulcanized rubber composition were evaluated by the following methods.

<Average Aggregated Aggregate Area of Silica of Vulcanized Rubber Composition>
A rubber composition sample after vulcanization was prepared by cutting a vulcanized rubber sheet with a razor. The shape was 5 mm × 5 mm × thickness 1 mm.
Using FIB-SEM (manufactured by FEI, NOVA200), the upper surface of the sample was cut in a direction forming an angle of 38 ° with respect to the upper surface of the sample using a focused ion beam under the condition of a voltage of 30 kV. The smooth surface of the sample formed by cutting was photographed at an acceleration voltage of 5 kV using a SEM from a direction perpendicular to the smooth surface. Based on the binarized image obtained by converting the obtained image into a binarized image of the rubber part of the sample and the silica part as the filler by the Otsu method, the aggregated aggregate area of the silica part is obtained. From the total surface area of the silica part and the number of aggregates, the average aggregate aggregate area of the silica part per unit area (3 μm × 3 μm) was calculated by number average (arithmetic mean). In the calculation, particles in contact with the edge (side) of the image were not counted, and particles of 20 pixels or less were regarded as noise and were not counted.

<Silica partition ratio of two-phase rubber component>
The smooth surface of the sample cut by the microtome was measured in a measuring range of 2 μm × 2 μm using AFM (MFP-3D manufactured by ASYLUM RESEARCH). Based on the ternarized image obtained by converting the obtained image into a ternary image with two types of polymers and silica parts from the histogram, the silica area contained in each of the two types of polymers is obtained, and the silica is calculated from the total amount of silica. The distribution ratio was calculated. When it was at the boundary surface between the two types of polymer, the silica was included on the polymer side where more silica was in contact. In the calculation, particles in contact with the edge (side) of the image were not counted, and particles of 9 pixels or less were regarded as noise and were not counted.

<Low exothermic property (tan δ index)>
Using a viscoelasticity measuring device (Rheometrics), tan δ was measured at a temperature of 60 ° C., a dynamic strain of 5%, and a frequency of 15 Hz. The reciprocal of tan δ in Comparative Example 2 was taken as 100 and expressed as an index using the following formula. A larger index value indicates a lower exothermic property and a smaller hysteresis loss.
Low exothermic index = {(tan δ of vulcanized rubber composition of Comparative Example 1) / (tan δ of test vulcanized rubber composition)} × 100

<Abrasion resistance>
A DIN abrasion test was performed in accordance with JIS-K6264-2: 2005 using a test piece cut into a disc shape (diameter: 16.2 mm × thickness: 6 mm) from each prepared vulcanized rubber. The amount of wear (mm ³ ) when a DIN wear test was performed at room temperature was measured. The reciprocal of each amount of wear when the reciprocal of the amount of wear in Comparative Example 2 is 100 is shown as an index. It shows that abrasion resistance is so favorable that an index value is large.

The rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 8 were prepared using the formulations and production conditions shown in Tables 1 and 2. The compound names abbreviated in the table indicate the following compounds in detail.
(1) Isoprene rubber: product name “IR2200” manufactured by JSR Corporation
(2) Unmodified SBR: manufactured by JSR Corporation, solution polymerized styrene-butadiene copolymer rubber (SBR), trade name “SBR1500”
(3) Terminal-modified SBR: manufactured by JSR Corporation, trade name “HPR355”
(4) Silica: manufactured by Tosoh Silica Co., Ltd., trade name “AQ”, nitrogen adsorption specific surface area (N ₂ SA) by BET method = 220 m ² / g)
(5) Silane coupling agent: bis (3-triethoxysilylpropyl) disulfide), Daiso Co., Ltd. silane coupling agent, trade name “CABRUS”
(6) Aroma oil: Process oil, manufactured by Idemitsu Kosan Co., Ltd., trade name “Diana Process Oil”
(7) Anti-aging agent: N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine, manufactured by Ouchi Shinsei Chemical Co., Ltd., trade name “NOCRACK 6C”
(8) Vulcanization accelerator: di-2-benzothiazolyl disulfide, manufactured by Sanshin Chemical Industry Co., Ltd., trade name “Sunceller DM”

<Example 1>
As the first stage, the components other than sulfur and vulcanization accelerator in the blending table were kneaded with a soot Barry mixer, and then kneaded at 160 ° C. for 40 minutes as an intermediate stage between the first stage and the second stage. Furthermore, as a second stage, sulfur and a vulcanization accelerator were added to the above and kneaded. Then, the vulcanized rubber composition was obtained by kneading at 145 ° C. for 40 minutes.
The average flocculated aggregate area, silica distribution rate, tan δ index and abrasion resistance of the vulcanized rubber composition obtained from this rubber composition were evaluated by the above methods. The results are shown in Table 1.

<Example 2>
A rubber composition of Example 2 was obtained in the same manner as in Example 1 except that the blending amounts of isoprene rubber and terminal-modified SBR were changed to 50 parts by weight and 50 parts by weight, respectively. The average flocculated aggregate area, silica distribution rate, tan δ index and abrasion resistance of the vulcanized rubber composition obtained from this rubber composition were evaluated by the above methods. The results are shown in Table 1.

<Example 3>
A rubber composition of Example 3 was obtained in the same manner as in Example 1 except that the blending amounts of isoprene rubber and terminal-modified SBR were changed to 30 parts by weight and 70 parts by weight, respectively. The average flocculated aggregate area, silica distribution rate, tan δ index and abrasion resistance of the vulcanized rubber composition obtained from this rubber composition were evaluated by the above methods. The results are shown in Table 1.

<Example 4>
A rubber composition of Example 5 was obtained in the same manner as in Example 1 except that the blending amounts of isoprene rubber and terminal-modified SBR were changed to 20 parts by weight and 80 parts by weight, respectively. The average flocculated aggregate area, silica distribution rate, tan δ index and abrasion resistance of the vulcanized rubber composition obtained from this rubber composition were evaluated by the above methods. The results are shown in Table 1.

<Comparative Example 1>
The blending amounts of silica and silane coupling are changed to 40 parts by weight and 4.0 parts by weight, respectively, without kneading corresponding to the intermediate stage, sulfur and vulcanization accelerator are added to the above as the second stage, and A rubber composition of Comparative Example 1 was obtained in the same manner as in Example 1 except that the vulcanization condition was 190 ° C. for 10 minutes. The average flocculated aggregate area, silica distribution rate, tan δ index and abrasion resistance of the vulcanized rubber composition obtained from this rubber composition were evaluated by the above methods. The results are shown in Table 2.

<Comparative example 2>
A rubber composition of Comparative Example 2 was obtained in the same manner as in Example 1 except that the vulcanization condition was 190 ° C. for 10 minutes. The average flocculated aggregate area, silica distribution rate, tan δ index and abrasion resistance of the vulcanized rubber composition obtained from this rubber composition were evaluated by the above methods. The results are shown in Table 2.

<Comparative Example 3>
The rubber composition of Comparative Example 3 was the same as Example 1 except that kneading corresponding to the intermediate stage was not performed, sulfur and a vulcanization accelerator were added as the second stage, and the vulcanization conditions were 190 ° C. for 10 minutes. I got a thing. The average flocculated aggregate area, silica distribution rate, tan δ index and abrasion resistance of the vulcanized rubber composition obtained from this rubber composition were evaluated by the above methods. The results are shown in Table 2.

<Comparative example 4>
A rubber composition of Comparative Example 4 was obtained in the same manner as in Example 1 except that unmodified SBR was used in place of the terminal-modified SBR and the vulcanization condition was 190 ° C. for 10 minutes. The average flocculated aggregate area, silica distribution rate, tan δ index and abrasion resistance of the vulcanized rubber composition obtained from this rubber composition were evaluated by the above methods. The results are shown in Table 2.

<Comparative Example 5>
The blending amounts of isoprene rubber and terminal-modified SBR were changed to 50 parts by weight and 50 parts by weight, respectively, and kneading corresponding to the intermediate stage was not performed, and sulfur and a vulcanization accelerator were added to the above as the second stage, followed by vulcanization A rubber composition of Comparative Example 5 was obtained in the same manner as in Example 1 except that the conditions were 190 ° C. and 10 minutes. The average flocculated aggregate area, silica distribution rate, tan δ index and abrasion resistance of the vulcanized rubber composition obtained from this rubber composition were evaluated by the above methods. The results are shown in Table 2.

<Comparative Example 6>
The blending amounts of isoprene rubber and terminal-modified SBR are changed to 30 parts by weight and 70 parts by weight, respectively, and kneading corresponding to the intermediate stage is not performed, and sulfur and a vulcanization accelerator are added to the above as the second stage, and vulcanized A rubber composition of Comparative Example 6 was obtained in the same manner as in Example 1 except that the conditions were 190 ° C. and 10 minutes. The average flocculated aggregate area, silica distribution rate, tan δ index and abrasion resistance of the vulcanized rubber composition obtained from this rubber composition were evaluated by the above methods. The results are shown in Table 2.

  As is clear from Tables 1 and 2, the rubber compositions of Examples 1 to 3 have both wear resistance and low heat build-up (tan δ index) as compared with the rubber compositions of Comparative Examples 1 to 6. It was good. In Example 4 where the blending amount of isoprene rubber was low, the low heat build-up was slightly reduced compared to Comparative Example 2, but the effect of improving wear resistance was observed.

  Since the rubber composition of the present invention is excellent in wear resistance and low heat build-up, it is used for passenger cars, small trucks, light passenger cars, light trucks and large vehicles (for trucks, buses, construction vehicles, etc.). It is suitably used as a member for various pneumatic tires, particularly as a tread member for pneumatic radial tires.

Claims (7)

Including 100 parts by weight of silica more than 0 part by weight and 100 parts by weight or less of the total of 100 parts by weight of rubber components including two or more kinds of diene rubbers
The diene rubber is divided into two or more phases each having a different glass transition temperature, of which at least one phase has a continuous structure, and at least one phase has a glass transition point of −50 ° C. or more,
The glass transition point of at least one of the two or more phases is less than −50 ° C., and the phase is at least from the group consisting of isoprene rubber, natural rubber, butadiene rubber, silicone rubber, butyl rubber, and styrene-butadiene rubber. Including one,
80% by weight or more of the total amount of silica per unit volume of the compounded rubber is contained in at least one phase having a glass transition point of −50 ° C. or higher, and the rubber composition is cut by the silica contained in the phase. on the surface, average aggregate aggregate area Ri der 2000 nm ² or less,
The average aggregate aggregate area is formed by cutting the upper surface of the vulcanized rubber composition sample in a direction that forms an angle of 38 ° with the upper surface of the sample using a focused ion beam. A smooth surface of the sample was photographed at an accelerating voltage of 5 kV from a direction perpendicular to the smooth surface with a scanning electron microscope, and the obtained image was subjected to 2 steps between the rubber portion and the silica portion of the sample by the Otsu method. Based on the binarized image obtained by converting to a binarized image, the aggregated aggregate area of the silica part is obtained, and from the total surface area of the silica part and the number of aggregated aggregates, per unit area (3 μm × 3 μm) The average aggregate aggregate area of the silica part is calculated by the number average (arithmetic average), and in this calculation, the particle contacting the edge (side) of the image and the particle of 20 pixels or less are not counted. value der was , Rubber wherein the composition.   The rubber composition according to claim 1, wherein the phase containing 80% by weight or more of silica contains at least one of unmodified and terminal-modified styrene-butadiene copolymers.   The rubber composition according to claim 1, wherein the diene rubber has a co-continuous structure of two or more phases.   The rubber composition according to claim 1, wherein the blending amount of the phase having a glass transition point of −50 ° C. or more in the entire rubber composition is 30 to 75% by weight.   The rubber composition of Claim 4 whose compounding quantity of the phase which has the glass transition point of -50 degreeC or more which occupies for the whole rubber composition is 30 to 65 weight%.   The rubber composition according to claim 1, further comprising at least one silane coupling agent and vulcanization accelerator selected from a polysulfide compound and a thioester compound. More than 0 parts by weight and 100 parts by weight or less of silica are blended with respect to a total of 100 parts by weight of rubber components including two or more kinds of diene rubbers,
The diene rubber is divided into two or more phases each having a different glass transition temperature, of which at least one phase has a continuous structure and at least one phase has a glass transition point of −50 ° C. or more, The glass transition point of at least one of the two or more phases is less than −50 ° C., and the phase is at least from the group consisting of isoprene rubber, natural rubber, butadiene rubber, silicone rubber, butyl rubber, and styrene-butadiene rubber. Including one,
80% or more of the compounded silica is contained in one of the one or more phases having a glass transition point of −50 ° C. or more, and the average agglomerated aggregate of silica contained in the phase on the cutting surface of the rubber composition The gate area should be 2000 nm ² or less ,
The average aggregate aggregate area is formed by cutting the upper surface of the vulcanized rubber composition sample in a direction that forms an angle of 38 ° with the upper surface of the sample using a focused ion beam. A smooth surface of the sample was photographed at an accelerating voltage of 5 kV from a direction perpendicular to the smooth surface with a scanning electron microscope, and the obtained image was subjected to 2 steps between the rubber portion and the silica portion of the sample by the Otsu method. Based on the binarized image obtained by converting to a binarized image, the aggregated aggregate area of the silica part is obtained, and from the total surface area of the silica part and the number of aggregated aggregates, per unit area (3 μm × 3 μm) The average aggregate aggregate area of the silica part is calculated by the number average (arithmetic average), and in this calculation, the particle contacting the edge (side) of the image and the particle of 20 pixels or less are not counted. value der was The method of the rubber composition, characterized in that.