JP6904212B2 - Pneumatic tires and cross-linked rubber compositions - Google Patents

Description

The present invention relates to pneumatic tires and crosslinked rubber compositions.

It is considered that the crosslinked rubber composition generally used for a tire tread is excellent in fracture characteristics and wear resistance as the filler is excellent in dispersibility. This is because if the dispersibility of the filler is poor, the filler aggregates and the aggregated filler becomes the starting point of fracture, resulting in deterioration of fracture characteristics and wear resistance.

Therefore, various techniques for improving the dispersibility of the filler in the crosslinked rubber composition have been proposed (Patent Document 1 and the like). However, better filler dispersibility does not necessarily mean better fracture characteristics and wear resistance, and there are exceptions. That is, although the filler dispersibility in the crosslinked rubber composition is excellent, it has been confirmed that excellent results cannot be obtained when the wear resistance of the crosslinked rubber composition or the rubber product is measured.

So far, rubber fracture and friction phenomena have been observed by various methods to elucidate the mechanism by which such exceptions occur, but they have not been completely elucidated.

On the other hand, an X-ray CT (Computed Tomography) imaging technique is known as a technique for analyzing a material constituting a solid sample and a low-density region contained therein. For example, Patent Document 2 describes an analysis method for visually analyzing a material constituting a friction material and a low-density region existing inside, but a state in which external energy such as elongation is added to a sample object. And the analysis of the density of the sample are not described.

Japanese Unexamined Patent Publication No. 2008-274017 Japanese Unexamined Patent Publication No. 2009-85732

An object of the present invention is to provide a pneumatic tire and a crosslinked rubber composition having excellent wear resistance.

As a result of diligent studies, the present inventors reduced the number of voids during elongation due to the applied stress of 3.0 MPa and increased the dispersibility of the filler, so that the growth of cracks generated inside the crosslinked rubber composition was increased. We have found that it can be suppressed and the wear resistance can be further improved, and have completed the present invention.

That is, in the present invention, the bead cores provided in the pair of left and right bead portions are used.
A carcass ply extending from the crown portion through both sidewall portions to both bead portions and moored to the bead core, an inner liner arranged inside the carcass ply in the tire radial direction, and a tire radial outside the carcass ply. The tread is provided in the above, and the volume of the void portion at the time of elongation due to the applied stress of 3.0 MPa is 7.5% or less, and the filler dispersibility index ΔG ^* represented by the following formula (I) is 3 or less. The present invention relates to a pneumatic tire characterized by being provided with.
ΔG ^* = (G ^* (4%) -G ^* (256%)) / G ^* (256%) (I)
In formula (I), G ^* (n%) represents the shear modulus when n% strain is applied.

Further, in the present invention, the volume of the void portion at the time of elongation due to the applied stress of 3.0 MPa is 7.5% or less, and the index ΔG ^* of the filler dispersibility represented by the following formula (I) is 3 or less. Regarding rubber compositions.
ΔG ^* = (G ^* (4%) -G ^* (256%)) / G ^* (256%) (I)
In formula (I), G ^* (n%) represents the shear modulus when n% strain is applied.

It is preferable that the rubber component is a rubber component containing at least one rubber component containing a conjugated diene compound.

It is preferable that the void portion is a region where the density is 0 to 0.1 times that of the crosslinked rubber composition before elongation.

It is preferable that the volume evaluation method of the void portion is X-ray CT imaging.

The decay time of the phosphor for converting X-rays into visible light is preferably 100 ms or less.

It is preferable that the brightness of the X-ray is 10 ¹⁰ photons / s / mrad ² / mm ² / 0.1% bw or more.

The pneumatic tire of the present invention having a tread with a high dispersibility of the filler and a small number of voids during elongation due to an applied stress of 3.0 MPa, and a small number of voids during elongation due to an applied stress of 3.0 MPa and a dispersion of the filler. According to the crosslinked rubber composition of the present invention having high properties, it is possible to provide a pneumatic tire and a crosslinked rubber composition having excellent wear resistance.

It is a perspective view which shows typically an example of the evaluation apparatus which evaluates the density distribution at the time of elongation of a crosslinked rubber composition. It is a flowchart which shows the processing procedure of the evaluation method of the density distribution of the crosslinked rubber composition at the time of elongation.

The crosslinked rubber composition of the present invention is a crosslinked rubber composition having few voids during elongation due to an applied stress of 3.0 MPa and high dispersibility of the filler. The crosslinked rubber composition in the present specification is a rubber composition that has been crosslinked with a vulcanizing agent, an organic peroxide, or the like.

Rubber component The rubber component is not particularly limited, and isoprene-based rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), styrene isoprene butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile butadiene rubber (NBR). From the rubber components used in the conventional rubber industry such as diene-based rubber and butyl-based rubber, one can be used alone or two or more kinds can be appropriately selected and used. Among them, it is preferable to contain one or more rubber components containing a conjugated diene compound, and it is preferable to contain SBR and BR from the viewpoint of balance of fuel efficiency, wear resistance, durability and wet grip performance.

The SBR is not particularly limited, and examples thereof include emulsion polymerization SBR (E-SBR) and solution polymerization SBR (S-SBR), which may or may not be oil-expanded. In addition, end-modified S-SBR having enhanced interaction with the filler and main chain-modified S-SBR can also be used. One type of these SBRs may be used, or two or more types may be used in combination.

From the viewpoint of grip performance, the styrene content of SBR is preferably 16% by mass or more, more preferably 20% by mass or more, further preferably 25% by mass or more, and particularly preferably 30% by mass or more. Further, if the styrene content is too high, the styrene groups are adjacent to each other, the polymer becomes too hard, the cross-linking tends to be non-uniform, the blow property during high temperature running may be deteriorated, and the temperature dependence is increased. 60% by mass or less is preferable, 50% by mass or less is more preferable, and 40% by mass or less is preferable, because the performance change with respect to the temperature change becomes large and stable grip performance during running / late stage tends not to be obtained well. The following is more preferable. In this specification, the styrene content of SBR is ^{calculated by 1 1} H-NMR measurement.

The vinyl content of SBR is preferably 10% or more, more preferably 15% or more, from the viewpoint of Hs and grip performance of the crosslinked rubber composition. Further, from the viewpoint of grip performance, EB (durability), and wear resistance, 90% or less is preferable, 80% or less is more preferable, 70% or less is further preferable, and 60% or less is particularly preferable. In the present specification, the vinyl content of SBR (1,2-bonded butadiene unit amount) can be measured by infrared absorption spectroscopy.

For SBR, the glass transition temperature (Tg) is preferably −45 ° C. or higher, and more preferably −40 ° C. or higher. The Tg is preferably 10 ° C. or lower, and more preferably 5 ° C. or lower from the viewpoint of preventing embrittlement cracks in the temperate winter season. In the present specification, the glass transition temperature of SBR is a value measured by differential scanning calorimetry (DSC) under the condition of a heating rate of 10 ° C./min according to JIS K 7121.

The weight average molecular weight (Mw) of SBR is preferably 700,000 or more, more preferably 900,000 or more, still more preferably 1 million or more, from the viewpoint of grip performance and blowability. From the viewpoint of blowability, the weight average molecular weight is preferably 2 million or less, more preferably 1.8 million or less. In the present specification, the weight average molecular weight of SBR is gel permeation chromatography (GPC) (GPC-8000 series manufactured by Toso Co., Ltd., detector: differential refractometer, column: TSKGEL SUPERMALTPORE manufactured by Toso Co., Ltd.). It can be obtained by standard polystyrene conversion based on the measured value by HZ-M).

The content of SBR in the rubber component is preferably 30% by mass or more, more preferably 40% by mass or more, because sufficient grip performance can be obtained. The SBR content is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less, from the viewpoints of wear resistance, grip performance, and fuel efficiency.

Among them, it is preferable to contain 40% by mass or more of SBR having a styrene content of 16 to 60% by mass, and SBR having a styrene content of 25 to 55% by mass, because it can exhibit higher grip performance and blowability. Is more preferably contained in an amount of 50% by mass or more.

The BR is not particularly limited, and is, for example, BR1220 manufactured by ZEON CORPORATION, BR130B manufactured by Ube Industries, Ltd., BR150B manufactured by BR150B, and the like, BR (HISIS BR) having a high cis content, and ZEON CORPORATION. Modified BR such as BR1250H, BR containing syndiotactic polybutadiene crystals such as VCR412 and VCR617 manufactured by Ube Industries, Ltd., and BR synthesized using rare earth element catalysts such as BUNA-CB25 manufactured by Lanxess Corporation. (Rare earth BR) etc. can be used. One type of these BRs may be used, or two or more types may be used in combination. Among them, Hisys BR and rare earth BR are preferable from the viewpoint of excellent workability, wear resistance and fracture characteristics.

When BR is contained, the content of BR in the rubber component is preferably 10% by mass or more, more preferably 15% by mass or more, and 20% by mass or more from the viewpoint of wear resistance, grip performance, and fuel efficiency. Is even more preferable. The content is preferably 70% by mass or less, more preferably 60% by mass or less, from the viewpoint of wear resistance, grip performance, and fuel efficiency.

As the filler, carbon black or silica is mainly preferable, although it can be arbitrarily selected and used from those conventionally used in a crosslinked rubber composition.

Examples of carbon black include furnace black, acetylene black, thermal black, channel black, graphite, and the like, and these carbon blacks may be used alone or in combination of two or more. Of these, furnace black is preferable because it can improve low temperature characteristics and wear performance in a well-balanced manner.

The nitrogen adsorption specific surface area (N ₂ ^{SA) of carbon black is preferably 70 m 2} / g or more, and more preferably 90 m ² / g or more, from the viewpoint of obtaining sufficient reinforcing properties and wear resistance. Also, N ₂ SA of carbon black is excellent in dispersibility, from the viewpoint that it is difficult to heat generation, preferably 300 meters ² / g or less, more preferably 250m ² / g. _{The N 2} SA of carbon black in the present specification is measured according to JIS K 6217-2 "Basic characteristics of carbon black for rubber-Part 2: How to obtain specific surface area-Nitrogen adsorption method-Single point method". It is the value that was set.

When carbon black is contained, the content of the rubber component with respect to 100 parts by mass is preferably 3 parts by mass or more, and more preferably 4 parts by mass or more. If it is less than 3 parts by mass, sufficient reinforcing properties tend not to be obtained. The carbon black content is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 60 parts by mass or less. If it exceeds 200 parts by mass, the workability tends to deteriorate, heat generation tends to occur easily, and wear resistance tends to decrease.

The silica is not particularly limited, and examples thereof include dry silica (silicic anhydride) and wet silica (hydrous silicic acid), but wet silica is preferable because it has a large number of silanol groups.

The nitrogen adsorption specific surface area (N ₂ ^{SA) of silica is preferably 80 m 2} / g or more, and more preferably 100 m ² / g or more, from the viewpoint of durability and elongation at break. The N ₂ SA of the silica, from the viewpoint of fuel economy and workability, preferably 250 meters ² / g or less, more preferably 220 m ² / g. _{The N 2} SA of silica in the present specification is a value measured according to ASTM D3037-93.

When silica is contained, the content of the rubber component with respect to 100 parts by mass is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, from the viewpoint of durability and elongation at break. The silica content is 200 parts by mass from the viewpoint of improving dispersibility during kneading and from the viewpoint of suppressing the reaggregation of silica during heating during rolling and storage after rolling to reduce processability. The following is preferable, and 150 parts by mass or less is more preferable.

When silica is contained, it is preferable to use a silane coupling agent in combination. As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, Si75 and Si266 (bis (3-triethoxysilyl) manufactured by Ebonic Degussa) can be used. Propyl) disulfide), sulfides such as Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by the same company, 3-mercaptopropyltrimethoxysilane, NXT-Z100, NXT-Z45, NXT manufactured by Momentive, etc. Mercapto-based (silane coupling agent having a mercapto group), vinyl-based such as vinyltriethoxysilane, amino-based such as 3-aminopropyltriethoxysilane, glycidoxy-based such as γ-glycidoxypropyltriethoxysilane, 3- Examples thereof include nitro type such as nitropropyltrimethoxysilane and chloro type such as 3-chloropropyltrimethoxysilane. These may be used alone or in combination of two or more. Of these, sulfide-based and mercapto-based are preferable because they have a strong binding force to silica and are excellent in low heat generation.

When the silane coupling agent is contained, the content with respect to 100 parts by mass of silica is preferably 2 parts by mass or more, and more preferably 3 parts by mass or more. When the content of the silane coupling agent is less than 2 parts by mass, the effect of improving the filler dispersibility tends not to be sufficiently obtained. The content of the silane coupling agent is preferably 25 parts by mass or less, more preferably 20 parts by mass or less. When the content of the silane coupling agent exceeds 25 parts by mass, the effect commensurate with the cost tends not to be obtained.

In addition to the above components, the crosslinked rubber composition of the present invention includes compounding agents generally used in the production of crosslinked rubber compositions, such as resin components, oils, zinc oxide, stearic acid, antiaging agents, and waxes. , Sulfur donor, vulcanizing agent, vulcanization accelerator and the like can be appropriately blended.

In the crosslinked rubber composition of the present invention, the volume of the void portion at the time of elongation due to the applied stress of 3.0 MPa is 7.5% or less, and the filler dispersibility index ΔG ^* represented by the formula (I) is 3 or less. It is characterized by being.

The crosslinked rubber composition having few regions where voids are generated is excellent in durability against external stress such as fracture characteristics and wear resistance. Further, the crosslinked rubber composition having a high dispersibility of the filler has less agglomerates of the filler and can suppress the concentration of stress. The crosslinked rubber composition of the present invention can realize high wear resistance because there are few voids during elongation due to an applied stress of 3.0 MPa and the dispersibility of the filler is high. The volume of the void portion at the time of elongation due to the applied stress of 3.0 MPa is preferably 7.0% or less.

In order to realize a state in which the volume of the void portion at the time of elongation due to the applied stress of 3.0 MPa is 7.5% or less, it is necessary to make the crosslinked state in the rubber composition uniform. Examples of the means for homogenizing the crosslinked state include uniforming the dispersed state of the vulcanizing agent and / or the vulcanization accelerator by lengthening the kneading time or increasing the number of kneading times. Be done.

The gap portion will be described. First, when the stress applied to the crosslinked rubber composition exceeds the critical value peculiar to the crosslinked rubber composition, the density of the crosslinked rubber composition is biased, and a low density region is generated inside. This low density region has a reversible portion and an irreversible portion.

The reversible portion is a low-density region that occurs when the applied stress is small (1.5 MPa), disappears when the stress is released, and the density distribution recovers to the original uniform state. Here, the low density region generated when the applied stress is small is a region in which the density is 0.1 times or more and 0.8 times or less the average density of the crosslinked rubber composition before elongation. By evaluating the distribution of the reversible portion, the rubber test piece can be evaluated with high accuracy.

The irreversible portion is a low-density region generated when the applied stress is large (3.0 MPa), and the stress partially destroys the internal structure (bonding of molecular chains) of the crosslinked rubber composition to reduce the stress. It is a low-density region that remains without recovering to its original state even after it is released. Here, among the irreversible portions, the region where the internal structure is extremely destroyed and the density is 0 times or more and 0.1 times or less the average density of the crosslinked rubber composition before elongation is defined as the void portion. The rubber test piece can be evaluated with high accuracy by evaluating the distribution of the voids.

The method for evaluating the volume of the gap during elongation due to the applied stress of 3.0 MPa is not particularly limited as long as the density distribution of the crosslinked rubber composition during elongation can be evaluated, but X-ray CT imaging was used. The evaluation method is preferable.

A method for evaluating the density distribution of the crosslinked rubber composition during elongation using X-ray CT imaging will be described with reference to the attached drawings. FIG. 1 is a perspective view schematically showing an example of an evaluation device used in the evaluation method. The evaluation device 1 shown in FIG. 1 includes a stress applying means 2, an imaging means 3, and an evaluation means 4.

The stress applying means 2 applies a stress for extending the rubber test piece 10 to generate a low density region inside the rubber test piece 10.

The stress applying means 2 includes a pair of jigs 21 and 22 to which the test piece 10 is fixed, and a driving means 23 for applying stress to the test piece 10 by relatively moving the jig 21 and the jig 22. It is preferable to have it. The driving means 23 moves the other jig 22 in the axial direction of the test piece 10 with one jig 21 fixed. As a result, a stress that extends the rubber test piece 10 in the axial direction is applied.

The stress applied to the test piece 10 is detected by a load cell (not shown) or the like. The position and format of the load cell is arbitrary. A predetermined stress is applied to the rubber test piece 10 by the stress applying means 2. The drive means 23 is configured so that the test piece 10 and the jigs 21 and 22 can rotate around the axis of the rubber test piece 10.

The photographing means 3 irradiates the test piece 10 with X-rays and photographs a projected image. The photographing means 3 includes an X-ray tube 31 for irradiating X-rays and a detector 32 for detecting X-rays and converting them into an electric signal. By rotating the test piece 10 and the jigs 21 and 22 around the axis of the test piece 10 and taking a plurality of projected images by the photographing means 5, it is possible to obtain a projected image of the test piece 10 over the entire circumference.

The detector 52 has a phosphor 32a for converting X-rays into visible light. The decay time of the phosphor 32a is preferably 100 ms or less. When the attenuation time of the phosphor 32a exceeds 100 ms, when a plurality of projected images are continuously photographed while rotating the test piece 10 or the like around the axis of the test piece 10, the afterimage of the previously captured projected image is generated. It may affect the projected image taken later. From this point of view, the more desirable decay time of the phosphor 32a is 50 ms or less, and the more desirable decay time is 10 ms or less.

The evaluation means 4 evaluates the performance of the crosslinked rubber composition based on the density distribution measured from the projected image. For example, a computer 40 is applied to the evaluation means 4. The computer 40 includes a main body 41, a keyboard 42, and a display device 43. The main body 41 is provided with, for example, a storage device such as an arithmetic processing unit (CPU), a ROM, a working memory, and a hard disk. The storage device stores in advance a processing procedure (program) for executing the simulation method of the present embodiment.

FIG. 2 is a flowchart showing a processing procedure of a method for evaluating the density distribution of the crosslinked rubber composition during stretching using the evaluation device 1. The density distribution evaluation method includes steps S1 and S2 in which stress is applied to the test piece 10 to generate a density bias (low density region) inside the rubber test piece 10, and the rubber test piece 10 is irradiated with X-rays. The imaging steps S3 and S4 for photographing the projected image and the evaluation steps S5 and S6 for evaluating the density distribution of the crosslinked rubber composition based on the density distribution measured from the projected image are included.

In step S1, the rubber test piece 10 is fixed to the jigs 21 and 22.

The shape of the rubber test piece 10 is not particularly limited, but a columnar shape and a rectangular parallelepiped are preferable, and a columnar shape is more preferable, because the rubber test piece 10 has symmetry and highly reproducible measurement results can be easily obtained.

The rubber test piece 10 preferably has a diameter of 5 times or more the axial length thereof, more preferably 10 times or more, still more preferably 20 times or more. According to such a test piece 10, when stress is applied to the rubber test piece 10, the deformation of the side surface of the rubber test piece 10 is limited. As a result, the volume of the rubber test piece 10 increases, and a very large stress is applied to the inside. Therefore, a low density region is likely to be generated inside the test piece 10, and the performance evaluation of the elastic material can be performed quickly and easily.

The rubber test piece 10 is fixed to both jigs 21 and 22 in a state of being sandwiched between the jigs 21 and 22. The upper end surface of the rubber test piece 10 is fixed to the lower end surface of the jig 21, and the lower end surface of the test piece 10 is fixed to the upper end surface of the jig 22. The fixing method can be appropriately selected depending on the test environment and the like. For example, fixing by an adhesive or fixing by vulcanization adhesion of an elastic material constituting the test piece 10 can be applied. Further, the test piece 10 and the jigs 21 and 22 are fixed to each other by providing corresponding engaging portions on the upper end surface, the lower end surface, the lower end surface, and the upper end surface and engaging the respective engaging portions. You may be.

In step S2, as shown in FIG. 1, the jig 21 and the jig 22 are moved by the driving means 23 in the axial direction of the rubber test piece 10, that is, in the direction in which the jig 22 is separated from the jig 21, and the rubber is formed. Extend the test piece 10. When the stress exceeds the critical value peculiar to the crosslinked rubber composition, the rubber test piece 10 has a density bias, and a low density region is generated inside.

In the present invention, even in the low density region generated when the applied stress is large, the stress for extending the rubber test piece 10 when measuring the distribution of the void portion, which is the region where the internal structure is extremely destroyed, is 3. It is 0 MPa.

In step S3, the rubber test piece 10 is irradiated with X-rays from the X-ray tube 31. X-rays pass through the rubber test piece 10 and are detected by the detector 32. The detector 32 converts the detected X-rays into an electric signal and outputs the detected X-rays to the computer 40.

The brightness of the X-rays emitted from the X-ray tube 31 to the rubber test piece 10 is greatly related to the S / N ratio of the X-ray scattering data. When the brightness of X-rays is small, the signal intensity tends to be weaker than the statistical error of X-rays, and even if the measurement time is lengthened, it may be difficult to obtain data with a sufficiently good S / N ratio. .. From this point of view, the brightness of X-rays ^{is preferably 10 10} photons / s / mrad ² / mm ² / 0.1% bw or more.

In step S4, the electric signal output from the detector 32 is processed by the computer 40, and a projected image is acquired.

In step S5, the projected image is reconstructed by the computer 40, and a three-dimensional tomographic image of the rubber test piece 10 is acquired. Then, in step S6, the density distribution of the crosslinked rubber composition at the time of elongation can be evaluated from the tomographic image, and the volume of the void portion can be obtained.

As described above, the crosslinked rubber composition of the present invention has a filler dispersibility index ΔG ^* represented by the following formula (I) of 3 or less.
ΔG ^* = (G ^* (4%) -G ^* (256%)) / G ^* (256%) (I)
In formula (I), G ^* (n%) represents the shear modulus when n% strain is applied.

By using a crosslinked rubber composition having a filler dispersibility index ΔG ^* of 3 or less, the crosslinked rubber composition has excellent filler dispersibility, less filler agglomerates as a starting point of fracture, and excellent fracture characteristics and wear resistance. Can be a thing. ΔG ^* is preferably 2.5 or less. Further, ΔG ^* is preferably 0.1 or more.

As a means for realizing the state where the filler dispersibility index ΔG ^* is 3 or less, for example, increasing the kneading time after the filler is added can be mentioned. ^{For example, the value of the index ΔG *} can be reduced by lengthening the final kneading time in which the vulcanizing agent or the like is kneaded after the filler is added. Further, a filler surface-treated so as to have high dispersibility may be used, or a silane coupling agent or a carbon coupling agent which enhances the dispersibility of the filler may be used.

The crosslinked rubber composition of the present invention can be produced by a general method as long as the above-mentioned crosslinked rubber composition exhibiting the volume of voids and filler dispersibility during elongation can be obtained. For example, a known kneader used in the general rubber industry such as a Banbury mixer, a kneader, and an open roll is used to knead each of the above components other than the vulcanizing agent and the vulcanization accelerator, and then knead the components. It can be produced by adding a vulcanizing agent and a vulcanization accelerator to the mixture, further kneading the mixture, and then vulcanizing.

Since the crosslinked state of the crosslinked rubber composition can be made uniform and a rubber composition having a small volume of voids at the time of elongation can be easily obtained, before kneading the rubber component and the filler, the rubber component and the rubber component are mixed. A production method including a step of starting kneading the sulfur donor and the sulfur atom-containing vulcanization accelerator, then adding a filler to the obtained kneaded product, and kneading at a kneading temperature of 120 ° C. or higher is preferable.

The sulfur donor refers to, for example, elemental sulfur or a sulfur compound that releases active sulfur under vulcanization conditions (for example, 150 ° C., 1.5 MPa) or lower temperature and pressure. In other words, this sulfur compound is a compound that generally functions as a vulcanizing agent under vulcanization conditions (for example, 150 ° C., 1.5 MPa) or lower temperatures and pressures. The released active sulfur forms a part of the pendant type structure described later.

The sulfur atom-containing vulcanization accelerator refers to a vulcanization accelerator containing a sulfur atom that is single-bonded to another molecule. Some sulfur atom-containing vulcanization accelerators release active sulfur and some do not. However, from the viewpoint of suppressing the progress of the cross-linking reaction during kneading, sulfur atom-containing vulcanization accelerator that does not release active sulfur is promoted. Agents are preferred.

By starting kneading of the rubber component, the sulfur donor, and the sulfur atom-containing vulcanization accelerator before kneading the rubber component and the filler, the sulfur donor and the sulfur atom-containing vulcanization accelerator by the filler are kneaded. Since adsorption can be prevented, the sulfur donor and the sulfur atom-containing vulcanization accelerator in the rubber component can be efficiently dispersed. Then, in the production method, a filler is added to the kneaded product obtained by kneading the rubber component, the sulfur donor, and the sulfur atom-containing vulcanization accelerator, and the mixture is kneaded at a kneading temperature of 120 ° C. or higher. Active sulfur is released from the sulfur donor by a kneading temperature of 120 ° C. or higher and a mechanical shearing force during kneading. A state in which the active sulfur reacts with the sulfur atom-containing vulcanization accelerator and the rubber component, and all or part of the sulfur atom-containing vulcanization accelerator (hereinafter, "vulcanization accelerator residue") is bound to the rubber component. That is, a pendant-type structure in which "-S-vulcanization accelerator residue" is bound to the rubber component is formed. The mechanism of this reaction is that the released active sulfur reacts with the sulfur atom of the sulfur atom-containing vulcanization accelerator to form a structure in which two or more sulfur atoms are bonded, and the structure portion and the rubber component are double-bonded. It is presumed that the part is reacting. By performing kneading in the state where the pendant type structure is formed, the vulcanization accelerator residue moves together with the rubber component, so that the uniformity of the dispersed state of the vulcanization accelerator residue in the entire rubber composition is enhanced. Can be done. As a result, in the production method, it is possible to make the crosslink density uniform during vulcanization. The kneading temperature referred to here is the actual measured temperature of the rubber composition in the kneading machine, and the surface temperature of the rubber composition can be measured by a non-contact type temperature sensor or the like.

As described above, the characteristics of the production method are that the kneading of the rubber component, the sulfur donor and the sulfur atom-containing vulcanization accelerator is started before the filler is kneaded, and that the temperature is 120 ° C. or higher after the filler is added. The point is to knead at the kneading temperature of. Any material may be added in any step as long as the above requirements are satisfied. For example, when the kneading step consists of two steps including step X and step F, kneading of the rubber component, the sulfur donor, and the sulfur atom-containing vulcanization accelerator is started at the beginning of step X, and filling is performed in the middle of step X. The agent may be added and kneaded at a kneading temperature of 120 ° C. or higher, and then step F may be performed. Further, for example, when the kneading step consists of three steps including step X, step Y, and step F, kneading of the rubber component, the sulfur donor, and the sulfur atom-containing vulcanization accelerator is started in step X, and the subsequent steps. The filler may be added in Y and kneaded at a kneading temperature of 120 ° C. or higher, and the subsequent step F may be performed. As another example in the case of the three steps, kneading of the rubber component, the sulfur donor, and the sulfur atom-containing vulcanization accelerator is started at the beginning of the step X, and a filler is added in the middle of the step X to 120. Kneading may be performed at a kneading temperature of ° C. or higher, and then steps Y and F may be performed, or kneading of the rubber component, the sulfur donor, and the sulfur atom-containing vulcanization accelerator may be started at the initial stage of step X. , The filler may be added in the middle of the step X, the filler may be further added in the subsequent step Y, kneaded at a kneading temperature of 120 ° C. or higher, and then the step F may be performed. Remilling may be performed between each step.

The kneading temperature of the rubber component, the sulfur donor, and the sulfur atom-containing vulcanization accelerator is not particularly limited, but the cross-linking reaction by the sulfur donor and the sulfur atom-containing vulcanization accelerator proceeds. From the viewpoint of suppressing, the temperature is preferably less than 160 ° C, more preferably 150 ° C or lower.

The kneading time of the rubber component, the sulfur donor, and the sulfur atom-containing vulcanization accelerator before adding the filler to the rubber component is not particularly limited, but from the viewpoint of improving the dispersibility, for example, 10 More than a second.

The kneading temperature after adding the filler is preferably 170 ° C. or lower from the viewpoint of suppressing the excessive progress of the crosslinking reaction.

The kneading time after the filler is added to the rubber component and the kneading temperature reaches 120 ° C. is not particularly limited, but is, for example, 2 minutes or more from the viewpoint of improving the dispersibility. The kneading time referred to here is the time from the time when the filler is added to the rubber component and the kneading temperature reaches 120 ° C. to the time when the entire kneading step is completed. For example, in step X, the rubber component is used. When the kneading temperature reaches 120 ° C. by adding the filler to the mixture, it is the time from that point to the time when the step F is completed.

As described above, as the sulfur donor, an elemental sulfur and / or a sulfur compound that releases the above-mentioned active sulfur can be used. Examples of the elemental sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, and insoluble sulfur.

If elemental sulfur is added too much as a sulfur donor, the vulcanization reaction may proceed excessively in the kneading step. Therefore, when elemental sulfur is used as the sulfur donor, the content with respect to 100 parts by mass of the rubber component is preferably 0.1 part by mass or less. The content of the elemental sulfur is preferably 0.05 parts by mass or more from the viewpoint of breaking strength.

Examples of the sulfur compound that functions as a sulfur donor include _{a high molecular weight polysulfide represented by − (−MS—C−) n− and a structure −S n} − (in which two or more sulfur atoms are single-bonded). Examples thereof include compounds having n ≧ 2) and releasing active sulfur. Examples of this compound include alkylphenol disulfide, morpholin disulfide, _{and thiuram-based sulfide accelerating agents having −S n} − (n ≧ 2) (tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD), tetrabutyltiuram disulfide). (TBTD), dipentamethylene thiuram tetrasulfide (DPTT), etc.), sulfide accelerator 2- (4'-morpholinodithio) benzothiazole (MDB), and polysulfide type silane coupling agent (for example, Si69 manufactured by Degusa). Bis (3-triethoxysilylpropyl) tetrasulfide)), sulfide compounds represented by the following formulas (1), (2) or (3) can be mentioned.

（式中、Ｒ¹は、同一または異なって、置換基を有してもよい炭素数３〜１５の１価の炭化水素基を表す。ｎは、２〜６の整数を表す。）

(In the formula, R ¹ represents a monovalent hydrocarbon group having 3 to 15 carbon atoms which is the same or different and may have a substituent. N represents an integer of 2 to 6.)

^{R 1} in the formula (1) is a monovalent hydrocarbon group having 3 to 15 carbon atoms which may have a substituent, and the carbon number is preferably 5 to 12, more preferably 6 to 10. preferable. The ^{monovalent hydrocarbon group of R 1} may be linear, branched or cyclic, and may be a saturated or unsaturated hydrocarbon group (aliphatic, alicyclic, aromatic hydrocarbon group, etc.). It may be. Of these, an aromatic hydrocarbon group which may have a substituent is preferable.

Examples of R ¹ include an alkyl group having 3 to 15 carbon atoms, a substituted alkyl group, a cycloalkyl group, a substituted cycloalkyl group, an aralkyl group, a substituted aralkyl group, and the like, among which the aralkyl group and the substituted aralkyl group are used. preferable. Here, examples of the alkyl group include a butyl group and an octyl group; examples of the cycloalkyl group include a cyclohexyl group; examples of the aralkyl group include a benzyl group and a phenethyl group; and examples of the substituent include an oxo group (= O). , Hydroxyl group, carboxyl group, carbonyl group, amino group, acetyl group, amide group, polar group such as imide group and the like.

Further, n in the formula (1) is an integer of 2 to 6, preferably 2 to 3.

（式中、Ｒ²は、同一または異なって、置換基を有してもよい炭素数３〜１５の２価の炭化水素基を表す。ｍは、２〜６の整数を表す。）

(In the formula, R ² represents a divalent hydrocarbon group having 3 to 15 carbon atoms which is the same or different and may have a substituent. M represents an integer of 2 to 6.)

^{R 2} in the above formula (2) is a divalent hydrocarbon group having 3 to 15 carbon atoms which may have a substituent, and the carbon number is preferably 3 to 10 and 4 to 8 is preferable. More preferred. The ^{divalent hydrocarbon group of R 2} may be linear, branched or cyclic, and may be a saturated or unsaturated hydrocarbon group (aliphatic, alicyclic, aromatic hydrocarbon group, etc.). It may be. Among them, an aliphatic hydrocarbon group which may have a substituent is preferable, and a linear aliphatic hydrocarbon group is more preferable.

Examples of R ² include an alkylene group having 3 to 15 carbon atoms and a substituted alkylene group. Here, examples of the alkylene group include a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group and the like, and examples of the substituent include those similar to those ^{of the R 1 substituent.}

Further, m in the above formula (2) is an integer of 2 to 6, preferably 2 to 3.

Specific examples of the sulfide compounds represented by the above formulas (1) and (2) include N, N'-di (γ-butyrolactam) disulfide and N, N'-di (5-methyl-γ-butyrolactam). ) Disulfide, N, N'-di (5-ethyl-γ-butyrolactam) disulfide, N, N'-di (5-isopropyl-γ-butyrolactam) disulfide, N, N'-di (5-methoxy-γ-) Butyloractum) disulfide, N, N'-di (5-ethoxy-γ-butyrolactam) disulfide, N, N'-di (5-chloro-γ-butyrolactam) disulfide, N, N'-di (5-nitro-γ) -Butylolactum) disulfide, N, N'-di (5-amino-γ-butyrolactam) disulfide, N, N'-di (δ-valerolactam) disulfide, N, N'-di (δ-caprolactam) disulfide, N , N'-di (ε-caprolactam) disulfide, N, N'-di (3-methyl-δ-caprolactam) disulfide, N, N'-di (3-ethyl-ε-caprolactam) disulfide, N, N' -Di (3-isopropyl-ε-caprolactam) disulfide, N, N'-di (δ-methoxy-ε-caprolactam) disulfide, N, N'-di (3-ethoxy-ε-caprolactam) disulfide, N, N ′ -Di (3-chloro-ε-caprolactam) disulfide, N, N'-di (δ-nitro-ε-caprolactam) disulfide, N, N'-di (3-amino-ε-caprolactam) disulfide, N, N'-di (ω-heptalactum) disulfide, N, N'-di (ω-octalactum) disulfide, dithiodicaprolactam, morpholin disulfide, N-benzyl-N-[(dibenzylamino) disulfide] phenylmethanamine (N, N'-dithiobis (dibenzylamine)) and the like. These sulfide compounds may be used alone or in combination of two or more.

（式中、Ｒ³は、同一または異なって、アルキル基、ベンゾチアゾリル基、アミノ基、モルホリノ基、ジアルキルチオカルバモイル基、または下記式（４）で表される基を表す。ｋは、２〜６の整数を表す。

(In the formula, R ³ is the same or different and represents an alkyl group, a benzothiazolyl group, an amino group, a morpholino group, a dialkylthiocarbamoyl group, or a group represented by the following formula (4). K represents 2 to 6 Represents an integer of.

（式中、Ｒ⁴は、同一または異なって、アルキル基、ベンゾチアゾリルスルフィド基、シクロアルキル基または水素原子を表す。）

(In the formula, R ⁴ represents the same or different alkyl group, benzothiazolyl sulfide group, cycloalkyl group or hydrogen atom.)

^{R 3} in the above formula (3) represents the same or different alkyl group, benzothiazolyl group, amino group, morpholino group, dialkylthiocarbamoyl group, or group represented by the above formula (4). Alkyl groups having 1 to 10 carbon atoms, benzothiazolyl groups, amino groups, morpholino groups, or dialkylthiocarbamoyl groups (alkyl groups are the same or different alkyl groups having 1 to 10 carbon atoms) are preferable.

Examples of the alkyl group having 1 to 10 carbon atoms and the alkyl group having 1 to 10 carbon atoms in the dialkylthiocarbamoyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group and an n-butyl group. Examples thereof include iso-butyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, 2-ethylhexyl group, octyl group and nonyl group.

^{More preferably, the R 3} in the above formula (3) is the same or different, a benzothiazolyl group, a morpholino group, or a dialkylthiocarbamoyl group (the alkyl group is the same or different alkyl group having 1 to 5 carbon atoms. ). More preferably, it is the same or different benzothiazolyl group or dialkylthiocarbamoyl group (the alkyl group is the same or different alkyl group having 1 to 5 carbon atoms).

K in the above formula (3) is an integer of 2 to 6, and 2 to 3 is more preferable.

^{R 4} in the formula (4) is the same or different, an alkyl group, a benzothiazolyl sulfide group, a cycloalkyl group or a hydrogen atom. The alkyl group is preferably an alkyl group having 1 to 10 carbon atoms, and the cycloalkyl group is preferably a cycloalkyl group having 5 to 8 carbon atoms.

Examples of the sulfide compound represented by the above formula (3) include tetramethylthium disulfide, tetraethyl thiuram disulfide, tetrabutyl thiuram disulfide, 2- (morpholinodithio) benzothiazole, dibenzothiazolyl disulfide, and N-cyclohexyl-2. -Benzothiazolyl sulfeneamide and the like can be mentioned, and in particular, dibenzothiazolyl disulfide can be preferably used. These may be used alone or in combination of two or more.

When the sulfur compound functioning as a sulfur donor is used, the content of the rubber component with respect to 100 parts by mass is preferably 0.1 part by mass or more, preferably 0.2 parts by mass or more, because it promotes the formation of a pendant type structure. More preferred. The content of the compound is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and further preferably 2 parts by mass or less from the viewpoint of suppressing gelation during kneading.

As a vulcanization accelerator that functions as a sulfur donor, there is a vulcanization accelerator that contains a sulfur atom that is single-bonded to another molecule. Therefore, the sulfur atom-containing vulcanization accelerator that functions as a sulfur donor has the functions of both the sulfur donor and the sulfur atom-containing vulcanization accelerator, and the sulfur atom-containing vulcanization accelerator that functions as a sulfur donor. It is also possible to form a pendant type structure by blending a large amount of the agent alone or by using two or more kinds in combination. However, if a large amount of a sulfur atom-containing vulcanization accelerator that functions as a sulfur donor is added, the cross-linking reaction may proceed excessively during kneading, and if a small amount is added, the effect of homogenizing the cross-linking density may be difficult to obtain. Therefore, as the sulfur donor and the sulfur atom-containing vulcanization accelerator to be kneaded before adding the filler, the sulfur donor (sulfur atom-containing vulcanization accelerator that functions as a sulfur donor and / or other sulfur donors) Body) and a sulfur non-releasing sulfur atom-containing vulcanization accelerator are preferable.

The sulfur non-releasing sulfur atom-containing vulcanization accelerator is, for example, a sulfur atom-containing vulcanization accelerator that does not release active sulfur under vulcanization conditions (for example, 150 ° C., 1.5 MPa) or lower. Refers to the agent. In other words, this sulfur non-releasing sulfur atom-containing vulcanization accelerator functions as a vulcanizer under vulcanization conditions (for example, 150 ° C., 1.5 MPa) or lower temperatures and pressures. It is a sulfur atom-containing vulcanization accelerator that does not.

As the sulfur non-releasing sulfur atom-containing sulfur atom-containing sulfide accelerator, a thiazole-based sulfide accelerator (2-mercaptobenzothiazole (MBT), 2-mercaptobenzothiazole) which does not have _{−S n − (n ≧ 2)} Zinc salt (ZnMBT), cyclohexylamine salt of 2-mercaptobenzothiazole (CMBT), etc.), sulfur amide-based sulfurization accelerator (N-cyclohexyl-2-benzothiazolyl sulphenamide (CBS), N- (Tart-butyl) -2-benzothiazolesulfurene amide (TBBS), N, N-dicyclohexyl-2-benzothiazolysulfurphenamide, etc.), sulfide accelerator tetramethylthium monosulfide (TMTM), dithiocarbamine Acidate-based vulfurization accelerator (piperidinium pentamethylene dithiocarbamate (PPDC), zinc dimethyldithiocarbamate (ZnMDC), zinc diethyldithiocarbamate (ZnEDC), zinc dibutyldithiocarbamate (ZnBDC), N-ethyl-N-phenyl) Zinc dithiocarbamate (ZnEPDC), N-pentamethylene dithiocarbamate zinc (ZnPDC), sodium dibutyldithiocarbamate (NaBDC), copper dimethyldithiocarbamate (CuMDC), iron dimethyldithiocarbamate (FeMDC), tellurium diethyldithiocarbamate (TeEDC), etc. ) And so on. Di-2-benzothiazolyl disulfide (MBTS), which is a thiazole-based vulcanization accelerator, has −S _n − (n ≧ 2) and is a vulcanization accelerator that releases sulfur. Since it does not function as a vulcanizing agent for natural rubber and butadiene rubber at a general blending amount, it can be used in the same manner as a sulfur non-releasing sulfur atom-containing vulcanization accelerator.

The content of the sulfur atom-containing vulcanization accelerator with respect to 100 parts by mass of the rubber component is preferably 1.0 part by mass or more, preferably 1.5 parts by mass or more, because the vulcanization reaction proceeds efficiently in the vulcanization step. More preferred. Further, the content is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, from the viewpoint of scorch property and suppression of precipitation on the surface.

In the production method, it is preferable to add a filler to the rubber component and knead it at a kneading temperature of 120 ° C. or higher, and then knead an additional sulfur donor. By adding an additional sulfur donor, it is possible to sufficiently proceed the cross-linking reaction during vulcanization while suppressing the progress of the cross-linking reaction excessively during kneading.

The additional sulfur donor is added in step F, for example, after adding a filler to the rubber component and kneading at a kneading temperature of 120 ° C. or higher. The additional sulfur donor may be of the same type as that kneaded before adding the filler to the rubber component, or may be of a different type, for example powdered sulfur, precipitated sulfur, colloidal sulfur, etc. Elemental sulfur such as surface-treated sulfur and insoluble sulfur can be mentioned.

The content of the additional sulfur donor is not particularly limited, but is preferably 0.5 parts by mass or more with respect to 100 parts by mass of the rubber component, preferably 0.8 parts by mass, because the vulcanization reaction proceeds efficiently in the vulcanization step. More than parts by mass is more preferable. The content of the additional sulfur donor is preferably 3.0 parts by mass or less, more preferably 2.5 parts by mass or less, because it is excellent in wear resistance.

When adding an additional sulfur donor in the step F, a general vulcanization accelerator may be added. Examples of general vulcanization accelerators include thiuram-based disulfides and polysulfides, which are sulfur atom-containing vulcanization accelerators, and guanidine-based, aldehyde-amine-based, and aldehydes, which are sulfur atom-free vulcanization accelerators. -Ammonia-based, imidazoline-based vulcanization accelerators, etc. can be mentioned.

The content of the vulcanization accelerator added in the step F with respect to 100 parts by mass of the rubber component is preferably 0.1 part by mass or more. Further, the mass ratio of the blending amount of the vulcanization accelerator added in the step F to the blending amount of the sulfur atom-containing vulcanization accelerator kneaded before adding the filler to the rubber component is larger than 0% and 80% or less. It is preferable, and 60% or less is more preferable. When the content is 80% or less, a crosslinked rubber composition having excellent scorch property, fracture property and wear resistance can be obtained.

The crosslinked rubber composition of the present invention can be used not only for tire members such as tire treads, under treads, carcasses, sidewalls and beads, but also for anti-vibration rubbers, belts, hoses and other rubber industrial products. In particular, since it is excellent in wear resistance, it is preferable to use a tire having a tread composed of the crosslinked rubber composition of the present invention.

A tire using the crosslinked rubber composition of the present invention can be produced by a usual method using an uncrosslinked rubber composition. That is, the uncrosslinked rubber composition in which the above-mentioned compounding agent is blended with the diene rubber component as needed is extruded according to the shape of a tread or the like, and bonded together with other tire members on a tire molding machine. An unvulcanized tire is formed by molding by a usual method, and the tire can be manufactured by heating and pressurizing the unvulcanized tire in a vulcanizer.

The structure of the pneumatic tire of the present invention is not particularly limited, and a conventional pneumatic tire structure can be used. That is, the pneumatic tire of the present invention can be obtained by using at least one or more of the tire members constituting the pneumatic tire having the conventional structure as the members using the crosslinked rubber composition of the present invention. Among them, the bead cores provided on the pair of left and right bead portions, the carcass ply extending from the crown portion through both sidewall portions to both bead portions and moored to the bead core, and the carcass ply inside the tire radial direction from the carcass ply. The volume of the arranged inner liner and the gap portion provided outside the carcass ply in the tire radial direction and stretched by an applied stress of 3.0 MPa is 7.5% or less, and is represented by the above formula (I). It is preferable to use a pneumatic tire having a tread having a filler dispersibility index ΔG ^{* of 3 or less.} The tread referred to here is a portion in contact with the road surface, and when the tread is composed of two or more different crosslinked rubber compositions, at least one of the crosslinked rubber compositions is the crosslinked rubber composition of the present invention. If so, it is the tire of the present invention.

Although the present invention will be specifically described based on Examples, the present invention is not construed as being limited to these.

Hereinafter, various chemicals used in Examples and Comparative Examples are collectively shown.
SBR1: Preparation by the production method described later modified SBR1 (S-SBR, styrene content: 26 wt%, vinyl content: 59%, Tg: -25 ℃ , Mw: 4 × 10 5)
SBR2: Nippon Zeon's Nipol 1502 (E-SBR, styrene content: 23.5 wt%, vinyl content: less than 20%, Tg: -54 ℃, Mw: 5 × 10 5)
BR: BR150B manufactured by Ube Industries, Ltd.
Silica: Evonik Ultrasil VN3 (N ₂ SA: 175m ² / g)
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Evonik Industries, Inc.
Carbon black: Diamond black I manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 98m ² / g, DBP oil absorption: 124ml / 100g)
Zinc oxide: Zinc oxide type 2 stearic acid manufactured by Mitsui Metal Mining Co., Ltd .: Bead stearic acid "Tsubaki" manufactured by NOF CORPORATION
Anti-aging agent: Ozonone 6C (N- (1,3-dimethylbutyl) -N-phenyl-p-phenylenediamine, 6PPD) manufactured by Seiko Kagaku Co., Ltd.
Oil: Diana Process AH-24 manufactured by Idemitsu Kosan Co., Ltd.
Elemental sulfur: Powdered sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd .1: Noxeller NS (TBBS, Nt-butyl-2-benzothiazolyl sulfeneamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Sulfur donor: Lenogran CLD80 (caprolactam disulfide) manufactured by Rheinchemy

Hereinafter, various chemicals used in the method for producing SBR1 are collectively shown.
Cyclohexane: Cyclohexanepyrrolidine manufactured by Kanto Chemical Co., Ltd .: Pyrrolidine divinylbenzene manufactured by Kanto Chemical Co., Ltd .: n-Butyllithium hexane solution of 1.6M divinylbenzene manufactured by Sigma Aldrich Co., Ltd .: 1. 6M n-butyllithium hexane solution Isopropanol: Isopropanol styrene manufactured by Kanto Chemical Co., Ltd .: Stylium butadiene manufactured by Kanto Chemical Co., Ltd .: 1,3-butadiene tetramethylethylenediamine manufactured by Takachiho Chemical Industry Co., Ltd .: Kanto Chemical Co., Ltd. ) N, N, N', N'-tetramethylethylenediamine modifier: 3- (N, N-dimethylaminopropyl) trimethoxysilane manufactured by Azumax Co., Ltd.

Method for Producing SBR1 To a 100 ml container fully substituted with nitrogen, 50 ml of cyclohexane, 4.1 ml of pyrrolidine and 8.9 ml of divinylbenzene were added, 0.7 ml of a 1.6 M n-butyllithium hexane solution was added at 0 ° C., and the mixture was stirred. did. After 1 hour, isopropanol was added to stop the reaction, and extraction and purification were carried out to obtain Monomer A. Next, 600 ml of cyclohexane, 12.6 ml of styrene, 71.0 ml of butadiene, 0.06 g of monomer A, and 0.11 ml of tetramethylethylenediamine were added to a 1000 ml pressure-resistant container sufficiently substituted with nitrogen, and 1.6 M n- at 40 ° C. 0.2 ml of a butyllithium hexane solution was added and stirred. After 3 hours, 0.5 ml of a denaturing agent was added and the mixture was stirred. After 1 hour, 3 ml of isopropanol was added to terminate the polymerization. After adding 1 g of 2,6-tert-butyl-p-cresol to the reaction solution, it was reprecipitated with methanol and dried by heating to obtain SBR1.

Examples 1 to 13 and Comparative Examples 1 to 3
According to the formulation contents shown in Tables 1 and 2, the various chemicals shown in Step X were kneaded with a 1.7 L Banbury mixer at a discharge temperature of 100 ° C. for 5.0 minutes (Step X). Next, the kneaded product of step X and the various chemicals shown in step Y were kneaded with a 1.7 L Banbury mixer at 140 ° C. or higher for 30 seconds, and further kneaded at a discharge temperature of 150 ° C. for 3 minutes (step Y). .. Then, the kneaded product of step Y and various chemicals shown in step F were kneaded using an open roll at about 80 ° C. according to the kneading time shown in Table 1 (step F) to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition is extruded into a tread shape by an extruder equipped with a base having a predetermined shape, and bonded together with other tire members to form an unvulcanized tire under the conditions of 170 ° C. A test tire (tire size: 195 / 65R15) was manufactured by press vulcanization for 12 minutes. The following evaluations were performed on the obtained test tires. The results are shown in Tables 1 and 2.

Volume of voids Each rubber test piece obtained by cutting out a columnar rubber test piece having a diameter of 10 mm and a height of 1 mm from the tread part of the test tire was fixed to the jig shown in FIG. 1 to start stretching, and 3 Three-dimensional created by reconstructing the captured image by irradiating ^{X-rays (brightness: 10 16} photons / s / mrad ² / mm ² / 0.1% bw) and performing CT imaging during elongation due to the applied stress of 0.0 MPa. From the tomographic image of the image, the volume ratio of the voids in the rubber test piece during elongation was calculated from the density distribution. X-ray CT imaging was performed at the beamline BL20B2 of the large-scale radiation facility SPring-8, the phosphor used was P43 (Gd ₂ O ₂ S: Tb) with an attenuation time of 1 ms, and CT reconstruction was performed by Convention Back Projection. By the method, 200 tomographic images having a thickness of 10 μm were laminated. Further, the gap portion was set as a region where the density was 0 to 0.1 when the average density of the rubber test pieces before stretching was 1.

^{Filler Dispersibility The strain shear force G *} from 4% to 256% of strain of each rubber test piece cut out from the tread portion of the test tire was measured using RPA2000 manufactured by α Technology Co., Ltd. Then, the index ΔG ^* of the filler dispersibility was obtained by the following formula. The smaller this value is, the better the silica dispersibility is.
ΔG ^* = (G ^* (4%) -G ^* (256%)) / G ^* (256%)
G ^* (n%) represents the shear modulus when n% strain is applied.

Abrasion resistance The same test tires manufactured as described above were mounted on the four wheels of a domestic FF vehicle, and the groove depth of the tire tread after a mileage of 8000 km was measured, and the groove depth of the four wheels was measured. The mileage when the tire groove depth was reduced by 1 mm was calculated from the arithmetic mean value, the wear resistance index of Comparative Example 1 was set to 100, and the results of each combination were displayed as an index by the following formula (wear resistance). index). The larger the wear resistance index, the better the wear resistance.
Wear resistance index = (mileage when the groove depth is reduced by 1 mm) / (mileage when the tire groove in Comparative Example 1 is reduced by 1 mm) × 100

Examples 14-16
The various chemicals shown in step X were kneaded with a 1.7 L Banbury mixer according to the formulation contents, discharge temperature and time shown in Table 3 (step X). Next, the kneaded product of step X and various chemicals shown in step Y were kneaded with a 1.7 L Banbury mixer according to the discharge temperature and time shown in Table 3, and further kneaded at a discharge temperature of 150 ° C. for 3 minutes (). Step Y). Then, the kneaded product of step Y and various chemicals shown in step F were kneaded using an open roll according to the discharge temperature and time shown in Table 3 (step F) to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition is extruded into a tread shape by an extruder equipped with a base having a predetermined shape, and bonded together with other tire members to form an unvulcanized tire under the conditions of 170 ° C. A test tire (tire size: 195 / 65R15) was manufactured by press vulcanization for 12 minutes. The following evaluations were performed on the obtained test tires. The results are shown in Table 3.

From the results in Tables 1 to 3, the pneumatic tire of the present invention having a tread with few gaps during elongation due to applied stress of 3.0 MPa and high filler dispersibility, and voids during elongation due to applied stress of 3.0 MPa. It can be seen that the crosslinked rubber composition of the present invention having a small number of parts and high filler dispersibility is a pneumatic tire and a crosslinked rubber composition having excellent wear resistance.

1 Evaluation device 2 Stress application means 3 Imaging means 4 Evaluation means 10 Rubber test piece

Claims (15)

The volume of the void during elongation due to the applied stress of 3.0 MPa is 7.3% or less.
A crosslinked rubber composition having a filler dispersibility index ΔG ^{* represented by the following formula (I) of 3.0 or less.}
A crosslinked rubber composition in which the void portion is a region where the density is 0 to 0.1 times that of the crosslinked rubber composition before elongation.
ΔG ^* = (G ^* (4%) -G ^* (256%)) / G ^* (256%) (I)

In formula (I), G ^* (n%) represents the shear modulus when n% strain is applied. The crosslinked rubber composition according to claim 1, wherein the volume of the void portion at the time of elongation due to an applied stress of 3.0 MPa is 7.0% or less. The crosslinked rubber composition according to claim 1, wherein the volume of the void portion at the time of elongation due to an applied stress of 3.0 MPa is 6.8% or less. The crosslinked rubber composition according to claim 1, wherein the volume of the void portion at the time of elongation due to an applied stress of 3.0 MPa is 6.7% or less. The crosslinked rubber composition according to claim 1, wherein the volume of the void portion at the time of elongation due to an applied stress of 3.0 MPa is 6.2% or less. The crosslinked rubber composition according to any one of claims 1 to 5, wherein the filler dispersibility index ΔG ^{* is 2.5 or less.} The crosslinked rubber composition according to any one of claims 1 to 5, wherein the filler dispersibility index ΔG ^{* is 1.5 or less.} The crosslinked rubber composition according to any one of claims 1 to 5, wherein the filler dispersibility index ΔG ^{* is 1.4 or less.} The crosslinked rubber composition according to any one of claims 1 to 5, wherein the filler dispersibility index ΔG ^{* is 1.2 or less.} The crosslinked rubber composition according to any one of claims 1 to 5, wherein the filler dispersibility index ΔG ^{* is 1.0 or less.} The crosslinked rubber composition according to any one of claims 1 to 10, which comprises a rubber component containing a conjugated diene compound. Any one of claims 1 to 11, wherein the volume of the void portion during elongation due to an applied stress of 3.0 MPa is calculated from the density distribution of the crosslinked rubber composition during elongation using X-ray CT imaging. The crosslinked rubber composition according to. The X-ray CT imaging is performed by an imaging means having a detector that detects X-rays and converts them into an electric signal, and the detector has a phosphor for converting X-rays into visible light. The crosslinked rubber composition according to claim 12, wherein the decay time of the phosphor for converting the X-rays into visible light is 100 ms or less. The crosslinked rubber composition according to claim 12 or 13, wherein the brightness of the X-rays applied to the crosslinked rubber composition in the X-ray CT imaging ^{is 10 10} photons / s / mrad ² / mm ^{2 / 0.1% bw or more.} The bead cores provided on each of the pair of left and right bead parts,
A carcass ply that extends from the crown portion through both sidewall portions to both bead portions and is moored to the bead core.
An inner liner arranged inside the tire radial direction from the carcass ply,
A pneumatic tire provided on the outer side in the tire radial direction with respect to the carcass ply, and comprising a tread composed of the crosslinked rubber composition according to any one of claims 1 to 14.

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