JP2017081545A - Pneumatic tire and cross-linking rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire and a cross-linking rubber composition excellent in abrasion resistance.SOLUTION: A pneumatic tire comprises: bead cores respectively provided for a pair of right/left bead parts; a carcass ply extending from a crown part through both sidewalls to both bead parts and moored by the bead cores; an inner liner disposed at the inner side in the tire radial direction in comparison with the carcass ply; and a tread disposed at the outer side in the tire radial direction in comparison with the carcass ply in which volume of a low density region is 35% or more and rigidity is 65 or more when elongated by applied stress of 1.5 MPa. A cross-linking rubber composition is given in which volume of a low density region is 35% or more and rigidity is 65 or more when elongated by applied stress of 1.5 MPa.SELECTED DRAWING: Figure 2

Description

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

  In general, it is known that a crosslinked rubber composition used for a tire tread has a higher steering stability as the hardness thereof is higher (for example, Patent Document 1). Furthermore, it is known that the rigidity of the tire tread part can bend a curve with a small steering angle, so that the lateral force applied to the tread part is reduced, and the fracture characteristics and wear resistance of the tire are improved. Yes.

  However, higher hardness is not necessarily superior in fracture characteristics and wear resistance, and there are exceptions. That is, although the hardness in the crosslinked rubber composition is high, it has been confirmed that excellent results cannot be obtained when the abrasion resistance of the crosslinked rubber composition or rubber product is measured.

  Until now, the destruction and friction phenomena of rubber have been observed by various methods to elucidate the mechanism that causes such an exception, but it has 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 included 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 extension is added to a sample object It is not described until the analysis of the sample and the analysis of the density of the sample.

JP 2011-246527 A JP 2009-85732 A

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

  As a result of intensive studies, the inventors have increased the low-density region when stretched by an applied stress of 1.5 MPa and increased the hardness, thereby suppressing the growth of cracks generated inside the crosslinked rubber composition. The present inventors have found that the wear resistance can be further improved and have completed the present invention.

  That is, the present invention includes a bead core provided in each of the pair of right and left bead portions, a carcass ply extending from the crown portion to both bead portions via both sidewall portions, and a tire diameter larger than the carcass ply. An inner liner disposed on the inner side in the direction, and on the outer side in the tire radial direction with respect to the carcass ply, the volume of the low density region when stretched by an applied stress of 1.5 MPa is 35% or more, and the hardness is 65 or more. A pneumatic tire characterized by comprising a tread.

  The present invention also relates to a crosslinked rubber composition having a low density region volume of 35% or more when stretched by an applied stress of 1.5 MPa and a hardness of 65 or more.

  The rubber component is preferably a rubber component including one or more rubber components including a conjugated diene compound.

  The low density region is preferably a region where the density is 0.1 to 0.8 times that of the crosslinked rubber composition before elongation.

  The volume evaluation method for the low density region is preferably X-ray CT imaging.

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

The X-ray luminance is preferably 10 ¹⁰ photons / s / mrad ² / mm ² /0.1% bw or more.

  The pneumatic tire of the present invention having a tread having a high hardness with many low density regions when stretched by an applied stress of 1.5 MPa, and a high hardness with many low density regions when stretched by an applied stress of 1.5 MPa. According to the crosslinked rubber composition of the present invention, a pneumatic tire and a crosslinked rubber composition excellent in wear resistance can be provided.

It is a perspective view which shows roughly an example of the evaluation apparatus which evaluates the density distribution at the time of the expansion | extension of a crosslinked rubber composition. It is a flowchart which shows the process sequence of the evaluation method of the density distribution of the crosslinked rubber composition at the time of expansion | extension.

  The cross-linked rubber composition of the present invention is a cross-linked rubber composition having a high hardness and a large number of low density regions when stretched by an applied stress of 1.5 MPa. In addition, the crosslinked rubber composition in this specification is a rubber composition that has been crosslinked with a vulcanizing agent or an organic peroxide.

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), acrylonitrile butadiene rubber (NBR). From rubber components conventionally used in the rubber industry such as diene rubbers and butyl rubbers, one or two or more can be appropriately selected and used. Especially, it is preferable to contain 1 or more types of rubber components containing a conjugated diene type compound, and it is preferable to contain SBR and BR from a viewpoint of the balance of low fuel consumption, abrasion resistance, durability, and wet grip performance.

  SBR is not particularly limited, and examples thereof include emulsion polymerization SBR (E-SBR), solution polymerization SBR (S-SBR), and the like, and may or may not be oil-extended. Further, terminal-modified S-SBR and main chain-modified S-SBR with enhanced interaction force with the filler can also be used. These SBRs may be used alone or in combination of two or more.

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 from the viewpoint of grip performance. Also, if the styrene content is too high, the styrene group is adjacent, the polymer becomes too hard, the cross-linking tends to be uneven, the blowability at high temperature running may be deteriorated, and the temperature dependency increases, The performance change with respect to the temperature change becomes large, and there is a tendency that the stable grip performance in the running / late period cannot be obtained well, so 60 mass% or less is preferable, 50 mass% or less is more preferable, 40 mass% More preferred are: In the present specification, the styrene content of SBR is calculated by 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. Moreover, from a viewpoint of grip performance, EB (durability), and abrasion resistance, 90% or less is preferable, 80% or less is more preferable, 70% or less is further more preferable, and 60% or less is especially preferable. In addition, in this specification, the vinyl content (1,2-bond butadiene unit amount) of SBR can be measured by an infrared absorption spectrum analysis method.

  SBR has a glass transition temperature (Tg) of 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 performing differential scanning calorimetry (DSC) in accordance with JIS K 7121 under the condition of a heating rate of 10 ° C./min.

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

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

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

  The BR is not particularly limited. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B, etc., high cis content BR (Hisys BR), manufactured by Nippon Zeon Co., Ltd. BR synthesized using a modified BR such as BR1250H, a BR containing syndiotactic polybutadiene crystals such as VCR412 and VCR617 manufactured by Ube Industries, Ltd., and a rare earth element catalyst such as BUNA-CB25 manufactured by LANXESS (Rare earth BR) or the like can be used. These BR may use 1 type and may use 2 or more types together. Of these, high cis BR and rare earth BR are preferred because they are excellent in 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 more preferably 20% by mass or more from the viewpoints of wear resistance, grip performance, and fuel efficiency. Is more preferable. The content is preferably 70% by mass or less, and more preferably 60% by mass or less from the viewpoint of wear resistance, grip performance, and low fuel consumption.

  The filler can be arbitrarily selected from those conventionally used in cross-linked rubber compositions, but carbon black and silica are mainly preferred.

  Examples of carbon black include furnace black, acetylene black, thermal black, channel black, graphite, and the like. These carbon blacks may be used alone or in combination of two or more. Among these, furnace black is preferable because it can improve the 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, more preferably 90 m ² / g or more, from the viewpoint that sufficient reinforcement and wear resistance can be obtained. 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. In this specification, N ₂ SA of carbon black is measured according to JIS K 6217-2 “Basic characteristics of carbon black for rubber—Part 2: Determination of specific surface area—Nitrogen adsorption method—Single point method” Value.

  In the case of containing carbon black, the content with respect to 100 parts by mass of the rubber component is preferably 3 parts by mass or more, and more preferably 4 parts by mass or more. When the amount 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 still more preferably 60 parts by mass or less. When it exceeds 200 mass parts, there exists a tendency for workability to deteriorate, the tendency to generate | occur | produce heat easily, and a tendency for abrasion resistance to fall.

  The silica is not particularly limited, and examples thereof include dry process silica (anhydrous silicic acid), wet process silica (hydrous silicic acid), and the like, but wet process silica is preferable because of its large number of silanol groups.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 80 m ² / g or more, 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. In this specification, N ₂ SA of silica is a value measured according to ASTM D3037-93.

  The content with respect to 100 parts by mass of the rubber component in the case of containing silica 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. Further, the content of silica is 200 parts by mass from the viewpoint of improving dispersibility at the time of kneading, and suppressing reduction of workability due to re-aggregation of silica during heating during rolling and storage after rolling. 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, Si266 (bis (3-triethoxysilyl) manufactured by Evonik Degussa Co., Ltd. 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- Nitropropi Nitro-based, such as trimethoxysilane, 3-chloropropyl-chloro system such as trimethoxysilane. These may be used alone or in combination of two or more. Of these, sulfide type and mercapto type are preferable from the viewpoints of strong bonding strength with silica and excellent low heat build-up.

  In the case of containing a silane coupling agent, 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 content of a silane coupling agent is less than 2 mass parts, there exists a tendency for the silica dispersibility improvement effect not to be fully acquired. Further, the content of the silane coupling agent is preferably 25 parts by mass or less, and more preferably 20 parts by mass or less. When content of a silane coupling agent exceeds 25 mass parts, there exists a tendency for the effect corresponding to cost not to be acquired.

  In addition to the above components, the crosslinked rubber composition of the present invention contains compounding agents generally used in the production of crosslinked rubber compositions, such as resin components, oil, zinc oxide, stearic acid, anti-aging agents, waxes. , A sulfur donor, a vulcanizing agent, a vulcanization accelerator and the like can be appropriately blended.

  The crosslinked rubber composition of the present invention is characterized in that the volume of a low density region when stretched by an applied stress of 1.5 MPa is 35% or more and the hardness measured by a type A durometer is 65 or more. The hardness is a hardness measured using a type A durometer in accordance with a test method of “Hardness test method of vulcanized rubber and thermoplastic rubber” of JIS K6253.

  The crosslinked rubber composition having a large number of low density regions is dispersed without causing stress to concentrate on a specific region because the crosslinked structure of the crosslinked rubber composition is extremely uniform. Moreover, the crosslinked rubber composition having high hardness can suppress rapid deformation when stress is generated. The crosslinked rubber composition of the present invention has many low density regions when stretched by an applied stress of 1.5 MPa, and has high hardness, so that high wear resistance can be realized. The volume of the low density region when stretched by an applied stress of 1.5 MPa is preferably 40% or more. Further, the volume of the low density region at the time of elongation due to an applied stress of 1.5 MPa is preferably 95% or less.

  In order to realize a state in which the volume of the low density region when stretched by an applied stress of 1.5 MPa is 35% or more, it is necessary to make the crosslinked state in the rubber composition uniform. Examples of means for homogenizing the cross-linked state include, for example, homogenizing the dispersion state of the vulcanizing agent and / or vulcanization accelerator by increasing the kneading time or increasing the number of kneading. It is done.

  The low density region will be described. First, when the stress applied to the crosslinked rubber composition exceeds a critical value specific to the crosslinked rubber composition, density deviation occurs in the crosslinked rubber composition, and a low density region is generated inside. This low density region has a reversible part and an irreversible part.

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

  The irreversible part is a low-density region that occurs when the applied stress is large (3.0 MPa), and the internal structure (bonding of molecular chains) of the crosslinked rubber composition is partially broken by the stress. Even after the release, the low density region remains without being restored to the original state. Here, among the irreversible portion, the region where the internal structure is extremely destroyed and the region where the density is 0 to 0.1 times the average density of the crosslinked rubber composition before elongation is defined as the void. 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 low density region when stretched by an applied stress of 1.5 MPa is not particularly limited as long as the density distribution of the crosslinked rubber composition during stretching can be evaluated, but X-ray CT imaging is used. The evaluation method was preferable.

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

  The stress applying means 2 applies a stress that elongates 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 a stress to the test piece 10 by relatively moving the jig 21 and the jig 22. It is preferable to have. The driving unit 23 moves the other jig 22 in the axial direction of the test piece 10 while the one jig 21 is fixed. Thereby, the stress which expands 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 are arbitrary. A predetermined stress is applied to the rubber test piece 10 by the stress applying means 2. The driving means 23 is configured to rotate the test piece 10 and the jigs 21 and 22 around the axis of the rubber test piece 10.

  The imaging means 3 irradiates the test piece 10 with X-rays to capture a projected image. The imaging unit 3 includes an X-ray tube 31 that emits X-rays, and a detector 32 that detects X-rays and converts them into electrical signals. While the test piece 10 and the jigs 21 and 22 are rotated around the axis of the test piece 10, the imaging means 5 takes a plurality of projection images, whereby a projection image of the test piece 10 over the entire circumference can be obtained.

  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 decay time of the phosphor 32a exceeds 100 ms, when a plurality of projection images are continuously photographed while rotating the test piece 10 or the like around the axis of the test piece 10, an afterimage of the projection image previously taken is obtained. There is a risk of affecting a projected image to be taken later. From such a viewpoint, the more desirable decay time of the phosphor 32a is 50 ms or less, and the still more preferred 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 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 processing procedures (programs) for executing the simulation method of the present embodiment.

  FIG. 2 is a flowchart showing the processing procedure of the evaluation method of the density distribution of the crosslinked rubber composition during elongation using the evaluation apparatus 1. The evaluation method of the density distribution includes steps S1 and S2 in which stress is applied to the test piece 10 to generate a density deviation (low density region) inside the rubber test piece 10, and the rubber test piece 10 is irradiated with X-rays. Thus, it includes photographing steps S3 and S4 for photographing the projected image, and 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.

  In step S <b> 1, the rubber test piece 10 is fixed to the jigs 21 and 22.

  Although the shape of the rubber test piece 10 is not particularly limited, a cylindrical shape and a rectangular parallelepiped are preferable, and a cylindrical shape is more preferable because it has symmetry and can easily obtain a highly reproducible measurement result.

  The rubber test piece 10 preferably has a diameter that is 5 times or more the axial length, more preferably 10 times or more, and even more preferably 20 times or more. According to such a test piece 10, when stress is applied to the rubber test piece 10, deformation of the side surface of the rubber test piece 10 is limited. As a result, the volume of the rubber test piece 10 is increased, 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 while 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, fixation by an adhesive or fixation by vulcanization adhesion of an elastic material constituting the test piece 10 can be applied. Moreover, the test piece 10 and the jig | tool 21 and 22 are fixed by providing a corresponding engaging part in an upper end surface, a lower end surface, a lower end surface, and an upper end surface, respectively, and engaging each engaging part. It may be.

  In step S2, as shown in FIG. 1, the driving means 23 causes the jig 21 and the jig 22 to move in the axial direction of the rubber test piece 10, that is, the direction in which the jig 22 moves away from the jig 21, and the rubber The test piece 10 is extended. When the stress exceeds the critical value inherent to the crosslinked rubber composition, density deviation occurs in the rubber test piece 10 and a low density region is generated inside.

  In the present invention, the stress for stretching the rubber test piece 10 when measuring the distribution of the low density region generated when the applied stress is small is 1.5 MPa.

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

The brightness of X-rays irradiated 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 luminance of X-ray is small, the signal intensity tends to be weaker than the statistical error of X-ray, and it may be difficult to obtain data having a sufficiently good S / N ratio even if the measurement time is extended. . From such a viewpoint, the luminance of the X-ray is preferably 10 ¹⁰ photons / s / mrad ² / mm ² /0.1% bw or more.

  In step S4, the electrical signal output from the detector 32 is processed by the computer 40 to obtain a projection image.

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

  As described above, the crosslinked rubber composition of the present invention has a hardness measured by a type A durometer of 65 or more.

  The hardness is preferably 68 or more, and more preferably 70 or more. The preferable upper limit of the hardness is 80. By setting the hardness to 80 or less, the rubber can easily follow the road surface and the wet grip performance can be maintained.

  Examples of means for realizing the state where the hardness is 65 or more include adjustment of the amount of sulfur, the amount of plasticizer such as oil, and the amount of filler. Hardness can be increased by increasing the amount of sulfur and filler, and hardness can be decreased by increasing the amount of plasticizer.

  The crosslinked rubber composition of the present invention can be produced by a general method as long as the crosslinked rubber composition showing the volume and hardness of the low density region at the time of elongation described above can be obtained. For example, after kneading ingredients other than the vulcanizing agent and vulcanization accelerator among the above-mentioned components in a known kneader used in a general rubber industry such as a Banbury mixer, a kneader, and an open roll, In addition, a vulcanizing agent and a vulcanization accelerator can be added and further kneaded and then vulcanized.

  Before the rubber component and the filler are kneaded, the rubber component and sulfur can be made uniform because the cross-linked state of the cross-linked rubber composition can be made uniform, and a rubber composition having a large number of low-density regions when stretched is easily obtained. A production method including a step of starting kneading of the donor and the sulfur atom-containing vulcanization accelerator, then adding a filler to the obtained kneaded material, 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 a temperature and pressure of vulcanization conditions (for example, 150 ° C., 1.5 MPa) or lower. In other words, this sulfur compound generally exhibits a function as a vulcanizing agent, for example, under vulcanization conditions (for example, 150 ° C., 1.5 MPa) or lower temperature and pressure. The released active sulfur forms a part of a pendant structure described later.

  The said sulfur atom containing vulcanization accelerator refers to the vulcanization accelerator containing the sulfur atom couple | bonded with the other molecule | numerator with the single bond. Although sulfur atom-containing vulcanization accelerators may or may not release active sulfur, sulfur atom-containing vulcanization acceleration that does not release active sulfur from the viewpoint of suppressing the progress of the crosslinking reaction during kneading. Agents are preferred.

  Before kneading the rubber component and the filler, by starting the kneading of the rubber component, the sulfur donor and the sulfur atom-containing vulcanization accelerator, the sulfur donor and sulfur atom-containing vulcanization accelerator of the filler Since adsorption can be prevented, the sulfur donor and sulfur atom-containing vulcanization accelerator in the rubber component can be efficiently dispersed. In the production method, a filler is added to a kneaded product obtained by kneading a rubber component, a sulfur donor, and a sulfur atom-containing vulcanization accelerator, and 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. The activated sulfur, the sulfur atom-containing vulcanization accelerator and the rubber component react, and the rubber component contains all or part of the sulfur atom-containing vulcanization accelerator (hereinafter referred to as “vulcanization accelerator residue”). That is, a pendant structure in which “-S-vulcanization accelerator residue” is bonded 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 part and the double bond of the rubber component It is presumed that the part is reacting. By kneading in a state where the pendant structure is formed, the vulcanization accelerator residue moves together with the rubber component, so that the uniformity of the dispersion state of the vulcanization accelerator residue in the entire rubber composition is improved. Can do. Thereby, in this manufacturing method, the crosslink density at the time of vulcanization can be made uniform. Here, the kneading temperature is an actual measurement temperature of the rubber composition in the kneader, and the surface temperature of the rubber composition can be measured with a non-contact 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 120 ° C. or higher after the filler is added. It is the point which knead | mixes at this kneading | mixing temperature. Any material may be added in any step as long as the above requirements are satisfied. For example, when the kneading process is a two-step process consisting of a process X and a process F, the kneading of the rubber component, the sulfur donor and the sulfur atom-containing vulcanization accelerator is started in the initial stage of the process X, and filling is performed in the middle of the process X. An agent may be added and kneaded at a kneading temperature of 120 ° C. or higher, and the subsequent step F may be performed. Also, for example, when the kneading step is a three-step process consisting of step X, step Y and step F, kneading of the rubber component, sulfur donor and sulfur atom-containing vulcanization accelerator is started in step X, and the subsequent steps The filler may be added at Y and kneaded at a kneading temperature of 120 ° C. or higher, and the subsequent step F may be performed. As another example of the case of three steps, kneading of a rubber component, a sulfur donor, and a sulfur atom-containing vulcanization accelerator is started at the beginning of step X, and a filler is added in the middle of step X to 120 Kneading may be carried out at a kneading temperature of not less than 0 ° C., and then the subsequent step Y and step F may be carried out. Further, a filler may be added during the process X, a filler may be further added in the subsequent process Y, and the mixture may be kneaded at a kneading temperature of 120 ° C. or higher, and the subsequent process F may be performed. In addition, you may perform a remill between each process.

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

  Further, 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. From the viewpoint of improving 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 crosslinking reaction from proceeding excessively.

  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 dispersibility. The kneading time referred to here is the time from when the filler is added to the rubber component and the kneading temperature reaches 120 ° C. until when all the steps of the kneading process are completed. When the kneading temperature reaches 120 ° C. by adding a filler, the time from that point to the point when the process F ends.

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

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

Examples of the sulfur compound that functions as a sulfur donor include a polymer polysulfide represented by-(-MS-C-) _n- , or a structure -S _n- (wherein two or more sulfur atoms are single-bonded. and compounds that have n ≧ 2) and release active sulfur. As the compounds, alkylphenol disulfide, morpholine _{disulfide, -S n - (n ≧ 2} ) thiuram vulcanization accelerator having a (tetramethylthiuram disulfide (TMTD), tetraethyl thiuram disulfide (TETD), tetrabutyl thiuram disulfide (TBTD), dipentamethylene thiuram tetrasulfide (DPTT), etc.), vulcanization accelerator 2- (4'-morpholinodithio) benzothiazole (MDB), polysulfide silane coupling agent (for example, Si69 (manufactured by Degussa) Bis (3-triethoxysilylpropyl) tetrasulfide)), sulfide compounds represented by the following formula (1), (2) or (3).

（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, same or different, .n representing a monovalent hydrocarbon group which may having 3 to 15 carbon atoms have a substituent, represents an integer from 2 to 6.)

R ¹ in formula (1) is a monovalent hydrocarbon group having 3 to 15 carbon atoms which may have a substituent, and the number of carbon atoms is preferably 5 to 12, more preferably 6 to 10. preferable. The monovalent hydrocarbon group for R ¹ may be linear, branched or cyclic, and any of saturated and unsaturated hydrocarbon groups (aliphatic, alicyclic, aromatic hydrocarbon groups, etc.) But you can. 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, and a substituted aralkyl group. Among these, an aralkyl group and a substituted aralkyl group are exemplified. 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). And polar groups such as hydroxy group, carboxyl group, carbonyl group, amino group, acetyl group, amide group and imide group.

  Moreover, n in Formula (1) is an integer of 2-6, and 2-3 are preferable.

（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。）

(Wherein, R ² are the same or different, .m representing a divalent hydrocarbon group which may having 3 to 15 carbon atoms have a substituent, represents an integer from 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 preferably 4 to 8 More preferred. The divalent hydrocarbon group for R ² may be linear, branched or cyclic, and any of saturated and unsaturated hydrocarbon groups (aliphatic, alicyclic, aromatic hydrocarbon groups, etc.) But you can. Especially, the 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, and a nonylene group, and examples of the substituent include those similar to the substituent for R ¹ .

  Moreover, m in the said Formula (2) is an integer of 2-6, and 2-3 are preferable.

  Specific examples of the sulfide compounds represented by the above formulas (1) and (2) include N, N′-di (γ-butyrolactam) disulfide, 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-) Butyrolactam) disulfide, N, N′-di (5-ethoxy-γ-butyrolactam) disulfide, N, N′-di (5-chloro-γ-butyrolactam) disulfide, N, N′-di (5-nitro-γ) -Butyrolactam) 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-heptalactam) disulfide, N, N'-di (ω-octalactam) disulfide, dithiodi Caprolactam, morpholine disulfide, N-benzyl-N - [(dibenzylamino) disulfanyl] phenylmethanamine (N, N'- dithiobis (dibenzyl amine)), 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 is 2-6. Represents an integer.

（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 s} are the same or different and each represents an alkyl group, a benzothiazolyl sulfide group, a cycloalkyl group or a hydrogen atom.)

R ³ in the above formula (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 above formula (4). An alkyl group having 1 to 10 carbon atoms, a benzothiazolyl group, an amino group, a morpholino group, or a dialkylthiocarbamoyl group (the alkyl groups are the same or different and are 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, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, Examples include iso-butyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, 2-ethylhexyl group, octyl group, nonyl group and the like.

More preferably, R ³ in the above formula (3) is the same or different and is a benzothiazolyl group, a morpholino group, or a dialkylthiocarbamoyl group (the alkyl groups are the same or different and are alkyl groups having 1 to 5 carbon atoms). ). More preferably, they are the same or different and are a benzothiazolyl group or a dialkylthiocarbamoyl group (the alkyl group is the same or different and is an alkyl group having 1 to 5 carbon atoms).

  K in the said Formula (3) is an integer of 2-6, and 2-3 are still more preferable.

R ⁴ in formula (4) is the same or different and is 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 tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, 2- (morpholinodithio) benzothiazole, dibenzothiazolyl disulfide, N-cyclohexyl-2. -A benzothiazolylsulfenamide etc. are mentioned, Dibenzothiazolyl disulfide can be used conveniently especially. These may be used alone or in combination of two or more.

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

  Vulcanization accelerators that function as sulfur donors include vulcanization accelerators containing sulfur atoms that are bonded to other molecules by single bonds. 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. A pendant structure can also be formed by blending a large number of agents alone or using two or more agents in combination. However, if a large amount of sulfur atom-containing vulcanization accelerator that functions as a sulfur donor is blended, the crosslinking reaction may proceed excessively during kneading, and if it is blended in a small amount, the effect of uniformizing the crosslinking density may not be obtained. Therefore, sulfur donors and sulfur atom-containing vulcanization accelerators to be kneaded before adding the filler include sulfur donors (sulfur atom-containing vulcanization accelerators functioning as sulfur donors and / or other sulfur donors). And a sulfur non-releasing sulfur atom-containing vulcanization accelerator.

  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 (eg, 150 ° C., 1.5 MPa) or lower temperature and pressure. Refers to an agent. In other words, this sulfur non-releasing sulfur atom-containing vulcanization accelerator exhibits a function as a vulcanizing agent, for example, under vulcanization conditions (for example, 150 ° C., 1.5 MPa) or lower temperature and pressure. Sulfur atom-containing vulcanization accelerator.

The sulfur-releasing of the sulfur-containing vulcanization _{accelerators, -S n - (n ≧ 2} ) no, thiazole vulcanization accelerator (2-mercaptobenzothiazole (MBT), 2-mercaptobenzothiazole Zinc salt (ZnMBT), 2-mercaptobenzothiazole cyclohexylamine salt (CMBT), etc.), sulfenamide vulcanization accelerators (N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N- (Tert-butyl) -2-benzothiazolesulfenamide (TBBS), N, N-dicyclohexyl-2-benzothiazolylsulfenamide), vulcanization accelerator tetramethylthiuram monosulfide (TMTM), dithiocarbamine Acid salt vulcanization accelerator (piperidinium pentamethylene dithiocarbamate (PPDC) Zinc dimethyldithiocarbamate (ZnMDC), zinc diethyldithiocarbamate (ZnEDC), zinc dibutyldithiocarbamate (ZnBDC), zinc N-ethyl-N-phenyldithiocarbamate (ZnEPDC), zinc N-pentamethylenedithiocarbamate (ZnPDC), dibutyl And sodium dithiocarbamate (NaBDC), copper dimethyldithiocarbamate (CuMDC), iron dimethyldithiocarbamate (FeMDC), tellurium diethyldithiocarbamate (TeEDC) and the like. Note that di-2-benzothiazolyl disulfide (MBTS), which is a thiazole vulcanization accelerator, has -S _n- (n ≧ 2) and is a vulcanization accelerator that releases sulfur. In general, the compounding amount does not exhibit a function as a vulcanizing agent with respect to natural rubber or butadiene rubber, so that 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, and more preferably 1.5 parts by mass or more, because the vulcanization reaction proceeds efficiently in the vulcanization process. More preferred. In addition, the content is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less from the viewpoint of scorch properties and suppression of precipitation on the surface.

  In the production method, it is preferable to add a filler to the rubber component and knead 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 advance the crosslinking reaction during vulcanization while suppressing excessive progress of the crosslinking reaction during kneading.

  The additional sulfur donor is added, for example, in Step F 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 the same as that kneaded before adding the filler to the rubber component, or may be a different one, such as powdered sulfur, precipitated sulfur, colloidal sulfur, Elemental sulfur such as surface-treated sulfur and insoluble sulfur can be used.

  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, because the vulcanization reaction proceeds efficiently in the vulcanization step. More than mass part is more preferable. In addition, the content of the additional sulfur donor is preferably 3.0 parts by mass or less, and 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 disulfides and polysulfides that are sulfur atom-containing vulcanization accelerators, guanidine-based, aldehyde-amine-based, and aldehydes that are vulcanization accelerators that do not have sulfur atoms. -Ammonia-based and imidazoline-based vulcanization accelerators are included.

  The content of the vulcanization accelerator added in Step F with respect to 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more. Moreover, the mass ratio of the blending amount of the vulcanization accelerator added in Step F to the blending amount of the sulfur atom-containing vulcanization accelerator kneaded before adding the filler to the rubber component is greater than 0% and 80% or less. Preferably, it is 60% or less. By setting it to 80% or less, a crosslinked rubber composition excellent in scorch properties, fracture characteristics, and abrasion resistance can be obtained.

  The crosslinked rubber composition of the present invention can be used for tire members such as tire treads, undertreads, carcass, sidewalls and beads, as well as anti-vibration rubbers, belts, hoses, and other rubber industrial products. In particular, because of excellent abrasion resistance, a tire having a tread composed of the crosslinked rubber composition of the present invention is preferable.

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

  It does not specifically limit as a structure of the pneumatic tire of this invention, It can be set as the structure of the conventional pneumatic tire. That is, the pneumatic tire of the present invention can be obtained by using at least one of the tire members constituting the pneumatic tire having the conventional structure as a member using the crosslinked rubber composition of the present invention. Among them, a bead core provided in each of the pair of left and right bead parts, a carcass ply that extends from the crown part to both bead parts through both side wall parts, and is anchored to the bead core, and on the inner side in the tire radial direction than the carcass ply. An inner liner that is disposed, a tread that is provided on the outer side in the tire radial direction than the carcass ply, has a volume of a low density region of 35% or more when stretched by an applied stress of 1.5 MPa, and has a hardness of 65 or more. It is preferable to make it a pneumatic tire provided with. The tread here is a portion in contact with the road surface. 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. Then, it is a tire of the present invention.

  The present invention will be specifically described based on examples, but the present invention is not construed as being limited to these examples.

Hereinafter, various chemicals used in Examples and Comparative Examples are shown together.
SBR1: prepared by the method for producing modified SBR1 described later (S-SBR, styrene content: 26% by mass, vinyl content: 59%, Tg: -25 ° C., Mw: 4 × 10 ⁵ )
SBR2: Nipol 1502 manufactured by Nippon Zeon Co., Ltd. (E-SBR, styrene content: 23.5% by mass, vinyl content: less than 20%, Tg: −54 ° C., Mw: 5 × 10 ⁵ )
BR: BR150B manufactured by Ube Industries, Ltd.
Silica: Ultrasil VN3 manufactured by Evonik (N ₂ SA: 175 m ² / g)
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Evonik
Carbon black: Diamond Black I manufactured by Mitsubishi Chemical Corporation (N ₂ SA: 98 m ² / g, DBP oil absorption: 124 ml / 100 g)
Zinc oxide: 2 types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Beads stearic acid manufactured by NOF Co., Ltd.
Anti-aging agent: Ozonon 6C (N- (1,3-dimethylbutyl) -N-phenyl-p-phenylenediamine, 6PPD) manufactured by Seiko Chemical Co., Ltd.
Oil: Diana Process AH-24 manufactured by Idemitsu Kosan Co., Ltd.
Elemental sulfur: Powder sulfur vulcanization accelerator manufactured by Tsurumi Chemical Industry Co., Ltd. 1: Noxeller NS (TBBS, Nt-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Sulfur donor: Renogran CLD80 (caprolactam disulfide) manufactured by Rhein Chemie

Hereinafter, various chemicals used in the manufacturing method of SBR1 are shown together.
Cyclohexane: cyclohexanepyrrolidine manufactured by Kanto Chemical Co., Ltd .: pyrrolidine divinylbenzene manufactured by Kanto Chemical Co., Ltd .: 1.6M n-butyllithium hexane solution of divinylbenzene manufactured by Sigma-Aldrich Co., Ltd .: 1. manufactured by Kanto Chemical Co., Inc. 6M n-butyllithium hexane solution Isopropanol: Isopropanol styrene manufactured by Kanto Chemical Co., Ltd .: Styrene butadiene manufactured by Kanto Chemical Co., Ltd .: 1,3-butadiene tetramethylethylenediamine manufactured by Takachiho Chemical Co., Ltd .: Kanto Chemical Co., Ltd. N, N, N ′, N′-tetramethylethylenediamine modifier: 3- (N, N-dimethylaminopropyl) trimethoxysilane manufactured by AMAX Co., Ltd.

Production method of SBR1 To a 100 ml container sufficiently purged with nitrogen, add 50 ml of cyclohexane, 4.1 ml of pyrrolidine, and 8.9 ml of divinylbenzene, and then add 0.7 ml of 1.6 M n-butyllithium hexane solution at 0 ° C. and stir. did. After 1 hour, isopropanol was added to stop the reaction, and extraction / purification was performed 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 purged with nitrogen, and 1.6 M n- at 40 ° C. 0.2 ml of butyllithium hexane solution was added and stirred. After 3 hours, 0.5 ml of a denaturant was added and 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, reprecipitation treatment was performed with methanol, followed by heating and drying to obtain SBR1.

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

Each rubber test piece obtained by cutting out a cylindrical rubber test piece having a diameter of 10 mm and a height of 1 mm from the tread portion of the volume test tire in the low density region is fixed to the jig shown in FIG. Tertiary created by CT imaging with X-rays (luminance: 10 ¹⁶ photons / s / mrad ² / mm ² /0.1%bw) when stretched by an applied stress of 1.5 MPa, and reconstruction of the captured images From the original tomographic image, the volume ratio of the low density region in the rubber test piece at the time of elongation was calculated from the density distribution. X-ray CT imaging is performed at the beam line BL20B2 of the large synchrotron radiation facility SPring-8, the phosphor uses P43 (Gd ₂ O ₂ S: Tb) with an attenuation time of 1 ms, and the CT reconstruction is the Convection Back Projection. By this method, 200 tomographic images having a thickness of 10 μm were stacked. Moreover, the low density area | region was performed as an area | region where the density became 0.1-0.8, when the average density of the rubber test piece before extending | stretching was set to 1.

Hardness Each rubber test piece cut out from the tread portion of the test tire is vulcanized rubber composition using a type A durometer according to the test method of “Hardness test method of vulcanized rubber and thermoplastic rubber” of JIS K6253. The hardness of the object was measured.

Wear resistance The same test tire produced as described above is mounted on four wheels of a domestic FF vehicle, and the groove depth of the tire tread portion after a running distance of 8000 km is measured. From the arithmetic mean value, the mileage when the tire groove depth decreases by 1 mm was calculated, and the abrasion resistance index of Comparative Example 1 was set to 100, and the results of each formulation were displayed as an index according to the following formula (wear resistance) index). The larger the wear resistance index, the better the wear resistance.
Abrasion resistance index = (travel distance when 1 mm groove depth decreases) / (travel distance when tire groove of Comparative Example 1 decreases by 1 mm) × 100

Examples 14-16
Various chemicals shown in Step X were kneaded in a 1.7 L Banbury mixer according to the blending contents, discharge temperature and time shown in Table 3 (Step X). Next, the kneaded product of Step X and the various chemicals shown in Step Y were kneaded in 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). And the kneaded material of the process Y and the various chemicals shown in the process F were kneaded according to the discharge temperature and time shown in Table 3 using an open roll (process F) to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was extruded into a tread shape by an extruder equipped with a predetermined-shaped die, and bonded together with other tire members to form an unvulcanized tire, under the condition of 170 ° C. A test tire (tire size: 195 / 65R15) was produced by press vulcanization for 12 minutes. The following evaluation was performed about the obtained tire for a test. The results are shown in Table 3.

  From the results of Tables 1 to 3, the pneumatic tire of the present invention having a tread having a high hardness and a low density region at the time of elongation due to an applied stress of 1.5 MPa, and the low density at the time of elongation due to an applied stress of 1.5 MPa. It can be seen that the crosslinked rubber composition of the present invention having a large density region and high hardness is a pneumatic tire and a crosslinked rubber composition excellent in wear resistance.

DESCRIPTION OF SYMBOLS 1 Evaluation apparatus 2 Stress application means 3 Imaging | photography means 4 Evaluation means 10 Rubber test piece

Claims (7)

A bead core provided in each of the pair of left and right bead parts;
A carcass ply that extends from the crown portion to both bead portions via both sidewall portions and is moored to the bead core;
An inner liner disposed inside the tire radial direction from the carcass ply;
A tread that is provided on the outer side in the tire radial direction than the carcass ply and has a volume of a low density region of 35% or more when stretched by an applied stress of 1.5 MPa and a hardness of 65 or more. Pneumatic tires. The volume of the low density region when stretched by an applied stress of 1.5 MPa is 35% or more,
A crosslinked rubber composition having a hardness of 65 or more. The crosslinked rubber composition according to claim 2, wherein the rubber component is a rubber component containing at least one rubber component containing a conjugated diene compound. The crosslinked rubber composition according to claim 2 or 3, wherein the low density region is a region in which the density is 0.1 to 0.8 times that of the crosslinked rubber composition before elongation. The crosslinked rubber composition according to any one of claims 2 to 4, wherein the volume evaluation method for the low density region is X-ray CT imaging. The crosslinked rubber composition according to claim 5, wherein the decay time of the phosphor for converting X-rays into visible light is 100 ms or less. The crosslinked rubber composition according to claim 5 or 6, wherein the X-ray luminance is 10 ¹⁰ photons / s / mrad ² / mm ² /0.1% bw or more.

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