tire

Abstract

To provide a tire capable of achieving both wet grip performance during high-speed traveling and abrasion resistance performance at a low temperature.SOLUTION: A pneumatic tire comprises a tread part. The tread part is composed of a rubber composition comprising 50 pts.mass or more of silica based on 100 pts.mass of a rubber component. The rubber component comprises more than 50 mass% of butadiene rubber, and styrene-butadiene rubber. A total styrene amount in the rubber component is 25 mass% or less. When a content (mass%) of the butadiene rubber in the rubber component is ABR, and a land ratio (%) of a tread surface of the tread part is L, ABR and L satisfy the following expression: (1) ABR×L>3000.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tire. [Background technology]

[0002] Various methods for improving wet grip performance and abrasion resistance have been investigated. For example, Patent Document 1 discloses a rubber composition for tires containing a diene rubber (A) containing a predetermined amount of a specific conjugated diene rubber represented by a predetermined formula, silica having a CTAB adsorption specific surface area within a predetermined range, and a silane coupling agent represented by the predetermined formula, and a pneumatic tire using the same in the tire tread. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-141405 Summary of the Invention [Problem to be solved by the invention]

[0004] However, wet grip performance and abrasion resistance are fundamentally mutually exclusive, making it difficult to improve both simultaneously, and further improvements are required to achieve both of these properties.

[0005] An object of the present invention is to provide a tire that can achieve both wet grip performance during high-speed driving and wear resistance at low temperatures. [Means for solving the problem]

[0006] The present invention relates to the following tire. A pneumatic tire having a tread portion, the tread portion is made of a rubber composition containing 50 parts by mass or more of silica per 100 parts by mass of a rubber component, The rubber component contains more than 50% by mass of butadiene rubber and styrene-butadiene rubber, The total amount of styrene in the rubber component is 25% by mass or less, The content (mass%) of the butadiene rubber in the rubber component is A BR , when the land ratio (%) of the tread surface of the tread portion is L, A BR A pneumatic tire where and L satisfy the following formula: (1) A BR ×L>3000 [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a tire that can achieve both wet grip performance during high-speed driving and wear resistance at low temperatures. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram schematically showing the total contact area of ​​a tread surface. [Figure 2] 1 is an exploded view of a portion of a tire tread having perforations in the shoulder regions. [Figure 3] 1 is a development view of a portion of a tread of a tire having narrow circumferential grooves in shoulder regions. [Figure 4] FIG. 1 is a development view of a portion of a tread of a tire having widened circumferential grooves in a land portion closest to the tire centerline. [Figure 5] 5 is a diagram showing a cross section of the widened circumferential groove of FIG. 4 taken along a plane passing through the tire rotation axis. DETAILED DESCRIPTION OF THE INVENTION

[0009] A tire according to one embodiment of the present invention is a pneumatic tire having a tread portion, the tread portion is made of a rubber composition containing 50 parts by mass or more of silica per 100 parts by mass of a rubber component, The rubber component contains more than 50% by mass of butadiene rubber and styrene-butadiene rubber, The total amount of styrene in the rubber component is 25% by mass or less, The content (mass%) of the butadiene rubber in the rubber component is A BR , when the land ratio (%) of the tread surface of the tread portion is L, A BR and L satisfy the following formula: (1) A BR ×L>3000

[0010] Although not intending to be bound by theory, the following is thought to be the mechanism by which the present invention can achieve both wet grip performance during high-speed driving and wear resistance at low temperatures.

[0011] (1) In the rubber composition constituting the tread, using butadiene rubber (BR) as the main polymer of the rubber component improves abrasion resistance; (2) By incorporating a certain amount of silica or more, the road-following ability of the tread is improved, thereby improving wet grip performance; (3) By further incorporating styrene-butadiene rubber (SBR) into the rubber component and keeping the total styrene content of the rubber component below a certain value, SBR becomes more compatible with BR, and the SBR domains, where silica tends to be unevenly distributed, are dispersed into the BR phase, effectively reinforcing the BR and maintaining abrasion resistance and improving wet grip performance; (4) A rubber composition containing such a rubber component with a low total styrene content has a lower glass transition temperature, which reduces temperature dependency and reduces the deterioration of grip performance when the tire heats up due to high-speed driving and abrasion resistance in cold weather; and (5) By maintaining a large land ratio on the tread surface, the contact area increases, which disperses the abrasion energy input from the road surface to the tread surface, thereby suppressing tread wear. It is believed that the cooperation of (1) to (5) makes it possible to achieve both wet grip performance during high-speed driving and wear resistance at low temperatures.

[0012] The total styrene amount (% by mass) is A STY When A BR , L and A STY It is preferable that the following formula is satisfied: (2) (A BR / A STY )×L>130

[0013] A BR is getting bigger, L is getting bigger, and A STY Since there are constraints on the direction of decreasing the axial length, it is thought that this will be advantageous for both wet grip performance during high-speed driving and wear resistance at low temperatures.

[0014] The rubber composition preferably contains at least one hydrocarbon resin, and the content of the hydrocarbon resin in the rubber composition is preferably 5% by mass or more.

[0015] Like silica, hydrocarbon resins tend to be concentrated in the SBR domains. Therefore, by combining a certain amount of hydrocarbon resin or more, the SBR domains, which tend to concentrate hydrocarbon resins, are dispersed into the BR phase, which is thought to be beneficial for both wet grip performance and abrasion resistance.

[0016] The content of the silica per 100 parts by mass of the rubber component is preferably 100 parts by mass or more.

[0017] It is believed that the silica further improves the road-following ability of the tread, resulting in improved wet grip performance.

[0018] The rubber composition preferably has a glass transition temperature of less than -30°C.

[0019] This is because it is believed that the temperature dependency of the rubber composition is reduced, and the grip performance when the tire heats up due to high-speed driving and the wear resistance in cold weather are less likely to decrease.

[0020] The right side of the formula (1) is preferably 3250, and more preferably 3500.

[0021] It is believed that an improvement in abrasion resistance can be expected by increasing the product of the butadiene rubber content and the land ratio.

[0022] The content A of the butadiene rubber in the rubber component BR is preferably less than 70% by mass.

[0023] Increasing the butadiene rubber content in the rubber component tends to improve wear resistance at low temperatures, but as the Tg decreases, the loss in the temperature range (0°C tanδ) that is generally considered to contribute to wet grip also decreases, disrupting the balance with wet grip performance at high speeds. Therefore, it is thought that a content of less than 70% by mass is necessary to achieve both performance.

[0024] The glass transition temperature of the styrene butadiene rubber is preferably less than -30°C.

[0025] It is believed that the glass transition temperature of the rubber composition is lowered, and that the grip performance when the tire heats up during high-speed driving and the wear resistance in cold weather are less likely to deteriorate.

[0026] The tread surface has two or more circumferential main grooves extending in the tire circumferential direction and land portions defined by the circumferential main grooves, When a pair of land portions located at the outermost sides in the tire width direction among the land portions are defined as shoulder land portions, the shoulder land portions have an opening area of ​​more than 0.1 mm and less than 15 mm 2 It is preferable that the porous body has one or more small holes.

[0027] The small holes contribute to improved drainage, which is thought to improve drainage in the shoulder area and improve wet grip performance.

[0028] The tread surface has two or more circumferential main grooves extending in the tire circumferential direction and land portions defined by the circumferential main grooves, and when a pair of land portions located at the outermost sides in the tire width direction among the land portions are defined as shoulder land portions, it is preferable that the shoulder land portions have at least one or more circumferential narrow grooves.

[0029] The circumferential narrow grooves contribute to improving drainage, which is thought to improve drainage in the shoulder regions and improve wet grip performance.

[0030] The tread surface preferably has widening circumferential grooves whose groove width widens on the inner side in the tire radial direction.

[0031] The widened circumferential grooves increase in width as the tread wears, which is thought to improve drainage after tire wear and improve wet grip performance.

[0032] The widened circumferential groove is preferably present in a land portion located on the tire centerline, or in a land portion closest to the tire centerline when a circumferential main groove is present on the tire centerline.

[0033] It is believed that this improves drainage after tire wear in the central portion in the tire width direction, thereby improving wet grip performance.

[0034] [Definition] "Normal condition" refers to a condition in which the tire is mounted on a normal rim, filled to normal internal pressure, and is unloaded.

[0035] Unless otherwise specified, the "dimensions of each part of the tire" are values ​​that are specified when the tire appears on the outer surface and is in its normal state, while the "dimensions of each part of the tire" are values ​​that are specified when the tire is cut along a plane that includes the tire rotation axis and the cut tire piece is maintained within the rim width of a normal rim and is in its normal state when it appears on the outer surface and is in its normal state when it appears on the inner surface of the tire ...

[0036] "Genuine rim" refers to the rim specified for each tire in the standard system that includes the standard on which the tire is based. For example, for JATMA (Japan Automobile Tire Manufacturers Association), it refers to the "standard rim" for the applicable size listed in the "Jatma Year Book," for ETRTO (The European Tyre and Rim Technical Organization), it refers to the "Measuring Rim" listed in the "STANDARDS MANUAL," and for TRA (The Tire and Rim Association, Inc.), it refers to the "Design Rim" listed in the "YEAR BOOK." JATMA, ETRTO, and TRA are referenced in that order, and if there is an applicable size at the time of reference, that standard is followed. In the case of tires not specified in the standard, it refers to the rim that can be mounted on a rim and can maintain internal pressure, i.e., the rim with the smallest rim diameter and the next narrowest rim width, among rims that do not leak air from between the rim and tire.

[0037] "Normal internal pressure" refers to the air pressure specified for each tire in the standard system that includes the standard on which the tire is based. For example, for JATMA, it refers to "Maximum Air Pressure," for ETRTO, it refers to "INFLATION PRESSURE," and for TRA, it refers to the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." As with regular rims, refer to JATMA, ETRTO, and TRA in that order, and follow the standard if there is an applicable size at the time of reference. In the case of tires not specified in the standard, it refers to the normal internal pressure (250kPa or more) of another tire size (defined in the standard) that is specified using the regular rim as the standard rim. If multiple normal internal pressures of 250kPa or more are listed, it refers to the smallest value among them.

[0038] "Normal load" is the load specified for each tire in the standard system that includes the standard on which the tire is based, for example, "Maximum Load Capacity" for JATMA, "Load Capacity" for ETRTO, and the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA. As with normal rims and normal internal pressures, JATMA, ETRTO, and TRA should be referenced in that order, and if there is an applicable size at the time of reference, that standard should be followed. For tires not specified in the standard, the normal load W is calculated as follows: L In this specification, the term "maximum load capacity" is synonymous with the normal load. TIFF0007803443000001.tif1484V: Virtual volume of tire (mm 3 ) Dt: Tire outer diameter Dt (mm) Ht: tire section height (mm) Wt: tire cross-sectional width (mm)

[0039] The "land ratio L (%)" is calculated from the total contact area and effective contact area of ​​the tire using the following formula. Land ratio L (%) = (effective ground contact area / total ground contact area) x 100

[0040] "Total contact area" is the area of ​​the tread region obtained from the outline of the tire when pressed against the ground. The total contact area is obtained by mounting the tire on a standard rim, applying standard internal pressure, and leaving it at 25°C for 24 hours, then applying ink to the tire tread surface, applying a standard load (maximum load capacity) to the tire, and pressing it vertically against cardboard (camber angle 0°) to transfer the ink. The above transfer process is performed in a total of five places by rotating the tire 72 degrees each time, and the total contact area is calculated as the average of the five areas obtained.

[0041] "Effective contact area" is the area of ​​the tread that comes into contact with the tire when pressed against the ground. The effective contact area is measured by mounting a tire to a standard rim, applying standard internal pressure, and leaving it at 25°C for 24 hours, then applying ink to the tire tread surface, and then applying a standard load (maximum load capacity) to the tire and pressing it vertically against cardboard (camber angle 0°) to transfer the ink. The above transfer process is performed in a total of five places by rotating the tire 72 degrees each time, and the effective contact area is calculated as the average of the five areas obtained.

[0042] "Total styrene content (mass%)" refers to the total content of styrene moieties contained in the entire rubber component, and can be calculated by Σ(styrene content (mass%) in each rubber component × content (mass%) of each rubber component in the entire rubber component / 100). For example, if 100% by mass of rubber component contains 85% by mass of styrene-butadiene rubber with a styrene content of 40% by mass, 5% by mass of styrene-butadiene rubber with a styrene content of 25% by mass, and 10% by mass of butadiene rubber with a styrene content of 0% by mass, the total styrene content in the rubber component is 35.25% by mass (= 40 × 85 / 100 + 25 × 5 / 100 + 0 × 10 / 100).

[0043] The "content of hydrocarbon resin" refers to the total content of at least one hydrocarbon resin contained in the rubber composition.

[0044] The "plasticizer content" includes the amount of plasticizer in the rubber component extended by the plasticizer. Similarly, the "oil content" includes the amount of oil contained in the oil-extended rubber.

[0045] "Circumferential main groove" refers to a circumferential groove that extends continuously around the tire circumferentially and has a groove width in the tire width direction on the tread surface of 4 mm or more. The circumferential main groove may extend linearly along the circumferential direction, or may extend in a wavy, sinusoidal, or zigzag pattern along the circumferential direction. However, this does not include widened circumferential grooves, which will be described later.

[0046] A "land portion" is an area on the tread surface defined by circumferential main grooves, which is the portion of the tire that comes into contact with the road surface. Among the land portions, a pair of land portions located on the outermost sides in the tire width direction are called shoulder land portions, and the land portion that exists in the area sandwiched between the shoulder land portions is called a center land portion. When there is only one circumferential main groove, only shoulder land portions exist, and no center land portion exists.

[0047] "Small holes" are small holes on the tread surface that extend from the inside of the tread and open to the tread surface. Each small hole exists independently and is not connected to the circumferential grooves, lateral grooves, etc.

[0048] "Circumferential narrow groove" refers to a circumferential groove that extends continuously in the circumferential direction of the tire and has a groove width in the tire width direction on the tread surface of less than 4 mm. The circumferential narrow groove may extend linearly in the circumferential direction, or may extend in a wavy, sinusoidal, or zigzag pattern in the circumferential direction. However, this does not include widened circumferential grooves, which will be described later.

[0049] The "widening circumferential groove" refers to a circumferential groove that extends continuously in the tire circumferential direction and has a groove width in the tire width direction that is smallest on the tread surface and widens toward the tire radially inward. The widening circumferential groove may extend linearly in the circumferential direction, or may extend in a wavy, sinusoidal, or zigzag pattern in the circumferential direction.

[0050] [Measurement method] "Styrene content (mass%)" is 1 It is calculated by H-NMR measurement.

[0051] "Vinyl content (amount of 1,2-bonded butadiene units) (mol %)" is calculated by infrared absorption spectrum analysis in accordance with JIS K 6239-2:2017.

[0052] The "cis content (amount of cis-1,4-bonded butadiene units) (mol %)" is calculated by infrared absorption spectrum analysis in accordance with JIS K 6239-2:2017.

[0053] The "glass transition temperature (Tg) (°C)" is measured in accordance with JIS K 7121 using a differential scanning calorimeter (Q200) manufactured by TA Instruments Japan, Inc., while increasing the temperature at a rate of 10°C / min. In the present invention, the Tg of styrene-butadiene rubber, butadiene rubber, etc. is particularly measured.

[0054] The "glass transition temperature (Tg) of a rubber composition" is the temperature (tan δ peak temperature) corresponding to the maximum value in the range of -60°C to 40°C in the temperature distribution curve obtained by measuring the tan δ temperature distribution curve using a dynamic viscoelasticity measuring device (e.g., an Iplexer series manufactured by GABO) under conditions of a frequency of 10 Hz, an initial strain of 10%, a dynamic strain of ±0.5%, and a heating rate of 2°C / min. In the measurement in the range of -60 to 40°C, if the tan δ value continues to gradually increase or decrease with increasing temperature, the glass transition temperature of the rubber composition is taken to be 40°C or -60°C, respectively. In addition, if there are two or more points showing maximum values ​​in the range of -60°C to 40°C, the lowest temperature point is taken to be the glass transition temperature.

[0055] The "weight average molecular weight (Mw)" can be determined by converting the value into standard polystyrene based on the measurement value obtained by gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation).

[0056] "N2SA of carbon black" is measured in accordance with JIS K 6217-2:2017.

[0057] "N2SA of silica" is measured by the BET method in accordance with ASTM D3037-93.

[0058] The "average primary particle size" is calculated by photographing particles with a transmission or scanning electron microscope and taking the arithmetic mean of the particle sizes of 400 particles. If the particle shape is nearly circular, the diameter of the circle is used as the particle size; if it is needle-like or rod-like, the minor axis is used as the particle size; in other cases, the equivalent circle diameter is calculated from the electron microscope image. The equivalent circle diameter is calculated as "4 x (particle area) / positive square root of π." The average primary particle size applies to silica, carbon black, etc.

[0059] The "softening point" is defined as the temperature at which the ball drops when the softening point specified in JIS K 6220-1:2001 is measured using a ring and ball softening point measuring apparatus.

[0060] [tire] The pneumatic tire of the present invention will be described below with reference to the drawings as appropriate. However, the drawings are merely examples, and the present invention should not be construed as being limited by the drawings.

[0061] The pneumatic tire of the present invention is a tire having a tread portion, the tread portion being made of a predetermined rubber composition, and in the rubber composition, the content (mass%) of butadiene rubber in the rubber component is A BR , when the land ratio (%) of the tread surface in the tread portion is L, A BR and L satisfy the following formula: (1) A BR ×L>3000

[0062] <Formula (1)> In the pneumatic tire of the present invention, the land ratio L (%) of the tread surface is defined as above and calculated from the total contact area and effective contact area of ​​the tire.

[0063] Figure 1 shows the tread area obtained from the outline of the tire when pressed against the ground when calculating the total contact area. As mentioned above, this outline is obtained by mounting the tire on a standard rim, applying standard internal pressure, and leaving it at 25°C for 24 hours, then applying ink to the tire tread surface, applying a standard load (maximum load capacity) to the tire, and pressing it perpendicularly against cardboard (camber angle 0°) to transfer the ink. In Figure 1, CL is the tire centerline.

[0064] The land ratio is preferably 60% or more, more preferably 61% or more, even more preferably 62% or more, even more preferably 63% or more, even more preferably 64% or more, and even more preferably 65% ​​or more. The land ratio is also preferably 80% or less, even more preferably 75% or less, and even more preferably 70% or less.

[0065] The right side of formula (1) is preferably 3250, more preferably 3500, even more preferably 3750, and even more preferably 4000. BR There is no particular upper limit to the value of ×L, but it can be, for example, 6500, 6000, or 5000.

[0066] <Formula (2)> The pneumatic tire of the present invention is characterized in that the total amount of styrene (mass%) in the rubber component contained in the rubber composition is A STY When A BR , L and A STY It is preferable that satisfies the following formula: (2) (A BR / A STY )×L>130

[0067] The right side of formula (2) is preferably 200, more preferably 300, even more preferably 360, even more preferably 450, even more preferably 550, and even more preferably 600. BR / A STY There is no particular upper limit to the value of )×L, but it may be, for example, 750, 700, or 650.

[0068] <Glass transition temperature of rubber composition> The rubber composition constituting the tread portion of the pneumatic tire of the present invention preferably has a glass transition temperature (°C) of less than -30°C.

[0069] From the viewpoint of reducing the temperature dependency of the rubber composition, the glass transition temperature is preferably less than −33° C., more preferably less than −37° C., even more preferably less than −40° C., and still more preferably less than −42° C. On the other hand, the lower limit of the glass transition temperature is not particularly limited, and may be, for example, more than −50° C., more than −47° C., or more than −45° C.

[0070] The glass transition temperature can be adjusted appropriately by changing the type and amount of the rubber component constituting the rubber composition, and the type and amount of additives other than the rubber component.

[0071] <Small hole> The pneumatic tire of the present invention has a tread surface having two or more circumferential main grooves extending in the tire circumferential direction and land portions defined by the circumferential main grooves, and when a pair of land portions located on the outermost sides in the tire width direction among the land portions are defined as shoulder land portions, the shoulder land portions have an opening area of ​​more than 0.1 mm but less than 15 mm 2 It is preferable that the porous body has one or more small holes.

[0072] FIG. 2 shows one embodiment of the pneumatic tire of the present invention having the small holes. In FIG. 2, small holes 4 are formed above a pair of land portions 3 present in the shoulder regions of the tread surface. The small holes contribute to improving drainage, thereby improving drainage in the shoulder regions and contributing to improved wet grip performance. For example, even if, in actual use, one of the shoulder land portions or the center land portion wears preferentially and the remaining shoulder land portion hardens over time, the small holes are thought to ensure drainage and make it easier to improve wet grip performance after wear. The opening area of ​​the small holes on the tread surface is 0.1 mm 2 More than 0.5mm is preferred 2 Ultra-low is more preferable, 1.0 mm2 More than 1.5mm is more preferable 2 The opening area of ​​the small holes on the tread surface is preferably 15 mm or more. 2 Less than 10mm is preferable 2 Less than 7.0 mm is preferable. 2 Less than 5.0 mm is more preferable. 2 The depth of the deepest portion of the small holes is preferably 3% or more, more preferably 5% or more, of the depth of the deepest portion of the circumferential main groove. The depth of the deepest portion of the small holes is preferably 80% or less, more preferably 60% or less, and even more preferably 40% or less, of the depth of the deepest portion of the circumferential main groove.

[0073] <Circumferential narrow groove> The pneumatic tire of the present invention has a tread surface having two or more circumferential main grooves extending in the tire circumferential direction and land portions defined by the circumferential main grooves, and when a pair of land portions located on the outermost sides in the tire width direction among the land portions are defined as shoulder land portions, it is preferable that the shoulder land portions have at least one or more circumferential narrow grooves.

[0074] Fig. 3 shows an embodiment of a pneumatic tire of the present invention having the circumferential narrow groove. In Fig. 3, a circumferential narrow groove 5 is formed on a pair of land portions 3 present in the shoulder regions of the tread surface. The circumferential narrow groove contributes to improving drainage, thereby improving drainage in the shoulder regions and contributing to improving wet grip performance.

[0075] <Wide circumferential groove> The pneumatic tire of the present invention preferably has a tread surface having widened circumferential grooves whose groove width is wider on the inner side in the tire radial direction.

[0076] FIG. 4 shows an embodiment of the pneumatic tire of the present invention having the widened circumferential groove. In FIG. 4, a linear widened circumferential groove 6 is formed on each of two land portions 3 adjacent to a circumferential main groove 2 that runs along the tire centerline. The widened circumferential groove may extend, for example, in a wavy, sinusoidal, or zigzag pattern along the circumferential direction. There are no particular restrictions on the land portions in which the widened circumferential grooves are formed. However, they are preferably formed on land portions located on the tire centerline. Alternatively, if a circumferential main groove is located on the tire centerline, they are preferably formed on land portions closest to the tire centerline, as in the widened circumferential groove 6 in FIG. 4. The land portion closest to the tire centerline is the land portion with the shortest distance between the tire centerline and the tire widthwise inner end of the land portion.

[0077] Fig. 5 shows a cross section of the widened circumferential groove 6. In Fig. 5, the groove width of the widened circumferential groove increases uniformly toward the inside in the tire radial direction, but the increase in groove width is not limited to this, and may be, for example, an increase in the groove width repeating small increases and decreases in a curved or stepped manner.

[0078] [Rubber composition] The rubber composition constituting the tread portion of the pneumatic tire of the present invention will be described below.

[0079] The rubber composition according to the present invention contains 50 parts by mass or more of silica per 100 parts by mass of the rubber component.

[0080] <Rubber component> The rubber component contains more than 50% by mass of butadiene rubber (BR) and styrene-butadiene rubber (SBR). The rubber component may also contain rubber components other than BR and SBR, such as isoprene-based rubber (IR-based rubber). Furthermore, the rubber component may consist solely of more than 50% by mass of BR and SBR.

[0081] (SBR) The SBR is not particularly limited, and examples thereof include solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), and modified SBRs thereof (modified S-SBR, modified E-SBR). Modified SBRs include SBRs whose ends and / or main chains are modified, and modified SBRs (condensates, those having a branched structure, etc.) coupled with tin, silicon compounds, etc. Among these, S-SBR and modified SBR are preferred. Furthermore, hydrogenated products of these SBRs (hydrogenated SBR) can also be used. One type of SBR may be used alone, or two or more types may be used in combination.

[0082] Examples of S-SBR that can be used in the present invention include S-SBR manufactured and sold by JSR Corporation, Sumitomo Chemical Co., Ltd., Ube Industries, Ltd., Asahi Kasei Corporation, ZS Elastomers Co., Ltd., and the like.

[0083] The styrene content of SBR is preferably low from the viewpoint of suppressing the temperature dependency of the rubber composition, for example, preferably less than 40% by mass, more preferably less than 30% by mass, more preferably 20% by mass or less, and even more preferably 15% by mass or less. There is no particular restriction on the lower limit of the styrene content, but it is usually more than 1% by mass, more than 3% by mass, or more than 5% by mass. The styrene content of SBR is measured by the above-mentioned measurement method.

[0084] The vinyl content of SBR is preferably more than 10 mol%, more preferably more than 13 mol%, and even more preferably more than 15 mol%, from the viewpoints of ensuring reactivity with silica, wet grip performance, rubber strength, and abrasion resistance. Furthermore, the vinyl content of SBR is preferably less than 50 mol%, more preferably less than 40 mol%, and even more preferably 30 mol% or less, from the viewpoints of preventing an increase in temperature dependency, elongation at break, and abrasion resistance. The vinyl content (amount of 1,2-bonded butadiene units) of SBR is measured by the above-mentioned measurement method.

[0085] The glass transition temperature (Tg) of SBR is preferably less than -30°C from the viewpoint of suppressing the temperature dependency of the rubber composition. The Tg of SBR is preferably less than -40°C, more preferably less than -50°C, and even more preferably less than -55°C. The Tg is usually greater than -80°C, greater than -70°C, or greater than -65°C. The Tg of SBR is measured by the above-mentioned measurement method.

[0086] From the viewpoint of wet grip performance, the weight average molecular weight (Mw) of SBR is preferably more than 200,000, more preferably more than 250,000, and even more preferably more than 300,000. From the viewpoint of crosslink uniformity, the weight average molecular weight is preferably less than 2,000,000, more preferably less than 1,800,000, and even more preferably less than 1,500,000. The weight average molecular weight of SBR is measured by the above-mentioned measurement method.

[0087] From the viewpoint of wet grip performance, the content of SBR in the rubber component is preferably more than 25% by mass, more preferably more than 30% by mass, and even more preferably 35% by mass or more. On the other hand, from the viewpoint of the effects of the invention, the content of SBR in the rubber component is preferably 50% by mass or less, more preferably less than 48% by mass, and even more preferably 45% by mass or less.

[0088] (BR) The BR is not particularly limited, and examples thereof include BR having a cis content of less than 50 mol% (low-cis BR), BR having a cis content of more than 90 mol% (high-cis BR), rare earth butadiene rubber synthesized using a rare earth catalyst (rare earth BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), and modified BR (high-cis modified BR, low-cis modified BR), which are commonly used in the tire industry. Modified BRs include BRs modified with functional groups similar to those described above for SBR. Among these, modified BRs are preferred. BRs may be used alone or in combination of two or more.

[0089] As the high-cis BR, for example, commercially available products from Zeon Corporation, Ube Industries, Ltd., JSR Corporation, etc. can be used. The inclusion of high-cis BR can improve low-temperature properties and wear resistance. The cis content is preferably more than 95 mol%, more preferably more than 96 mol%, and even more preferably 97 mol% or more. In this specification, the cis content (amount of cis-1,4-bonded butadiene units) is a value calculated by infrared absorption spectroscopy.

[0090] The rare earth BR is synthesized using a rare earth catalyst and has a vinyl content of preferably less than 1.8 mol%, more preferably less than 1.6 mol%, and even more preferably 1.5 mol% or less, and a cis content of preferably more than 95 mol%, more preferably more than 96 mol%, and even more preferably 97 mol% or more. As the rare earth BR, for example, commercially available products from LANXESS K.K. can be used.

[0091] The SPB-containing BR is not one in which 1,2-syndiotactic polybutadiene crystals are simply dispersed in the BR, but one in which the 1,2-syndiotactic polybutadiene crystals are dispersed after being chemically bonded to the BR. As such SPB-containing BR, commercially available products from Ube Industries, Ltd. and the like can be used.

[0092] As the modified BR, a modified butadiene rubber (modified BR) whose terminals and / or main chain are modified with a functional group containing at least one element selected from the group consisting of silicon, nitrogen, and oxygen is preferably used.

[0093] Other examples of modified BR include tin-modified BR, which is obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and in which the terminals of the modified BR molecule are further bonded with a tin-carbon bond (tin-modified BR).Modified BR may be either non-hydrogenated or hydrogenated.

[0094] From the viewpoint of abrasion resistance, the weight-average molecular weight (Mw) of BR is preferably more than 300,000, more preferably more than 350,000, and even more preferably more than 400,000. From the viewpoint of crosslink uniformity, etc., it is preferably less than 2,000,000, more preferably less than 1,000,000, and even more preferably less than 500,000. Mw can be determined by the above-mentioned measurement method.

[0095] The rubber component according to the present invention contains more than 50% by mass of BR. BR ) is preferably more than 51% by mass, more preferably more than 53% by mass, and even more preferably 55% by mass or more, from the viewpoint of abrasion resistance. BR In one embodiment, from the viewpoint of wet grip performance, A is preferably less than 90% by mass, more preferably less than 85% by mass, even more preferably less than 80% by mass, and even more preferably less than 75% by mass. BR In another embodiment, it is preferably less than 70% by mass, more preferably less than 65% by mass, and even more preferably less than 60% by mass.

[0096] (Other rubber components) The rubber component according to the present invention may contain rubber components other than SBR and BR. Examples of other rubber components that can be used include crosslinkable rubber components commonly used in the tire industry, such as isoprene-based rubber (IR-based rubber), styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer (SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber. The other rubber components may be used alone or in combination of two or more.

[0097] Examples of IR rubbers that can be used include isoprene rubber (IR) and natural rubber, which are commonly used in the tire industry. Natural rubber includes unmodified natural rubber (NR), as well as modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), highly purified natural rubber, and grafted natural rubber. Isoprene rubbers may be used alone or in combination of two or more.

[0098] The NR is not particularly limited, and those commonly used in the tire industry can be used, such as SIR20, RSS#3, and TSR20.

[0099] When other rubber components are contained, the content in the rubber component is preferably less than 15% by mass, more preferably 10% by mass or less, and even more preferably less than 5% by mass, from the viewpoint of the effects of the present invention. On the other hand, the lower limit of the content of other rubber components in the rubber component is not particularly limited and may be 0% by mass, but may also be, for example, more than 1%, more than 2%, or more than 3% by mass.

[0100] (Total styrene content) Total styrene content (A STY As defined above, styrene content (mass%) is the total content (mass%) of styrene moieties contained in the total amount of the rubber component. In the present invention, the total styrene content in the rubber component is 25% by mass or less. The total styrene content is preferably less than 20% by mass, more preferably less than 15% by mass, and even more preferably less than 10% by mass. The total styrene content is usually about 3% by mass or more, or 4% by mass or more, or 5% by mass or more.

[0101] <Filler> The rubber composition according to the present invention contains silica as a filler in an amount of 50 parts by mass or more per 100 parts by mass of the rubber component.

[0102] The rubber composition according to the present invention may contain carbon black as a filler in addition to silica. The filler preferably contains silica and carbon black, and may be a filler consisting of only silica and carbon black.

[0103] (silica) The silica is not particularly limited, and silica commonly used in the tire industry, such as silica prepared by a dry method (anhydrous silica) or silica prepared by a wet method (hydrated silica), can be used. From the viewpoint of environmental impact, silica made from biomass materials (e.g., amorphous silica purified from rice husks) may also be used. Among these, hydrated silica prepared by a wet method is preferred because it contains a large number of silanol groups. Silica may be used alone or in combination of two or more types.

[0104] Silica made from biomass materials can be obtained, for example, by extracting silicate from rice husk ash obtained by burning rice husks using a sodium hydroxide solution, and then reacting the silicate with sulfuric acid in the same manner as conventional wet silica processing to produce a silicon dioxide precipitate. The resulting precipitate is then filtered, washed with water, dried, and pulverized. Crystallized silica is insoluble in water, and its component, silicic acid, cannot be utilized. Controlling the combustion temperature and duration can suppress the crystallization of silica in rice husk ash (see, for example, JP 2009-2594 A, Akita Prefectural University Web Journal B / 2019, vol. 6, pp. 216-222). Amorphous silica extracted from rice husks can be commercially available from Wilmar, Inc.

[0105] The nitrogen adsorption specific surface area (N2SA) of silica is 140m from the viewpoint of fuel efficiency and wear resistance. 2 / g or more is preferable, and 150m 2 / g is more preferable, and 160m 2 / g or more is more preferable, and 175m 2 / g or more is more preferable. From the viewpoint of fuel efficiency and processability, 2 / g or less is preferable, and 300m 2 / g is more preferable, and 250m 2 / g or less is more preferable. The N2SA of silica is measured by the above-mentioned measuring method.

[0106] The average primary particle size of silica is preferably greater than 10 nm, more preferably greater than 12 nm, and even more preferably greater than 14 nm. The average primary particle size is preferably less than 26 nm, more preferably less than 24 nm, and even more preferably 22 nm or less. The average primary particle size of silica is measured by the above-mentioned measurement method.

[0107] From the viewpoint of wet grip performance, the content of silica per 100 parts by mass of the rubber component is preferably more than 70 parts by mass, more preferably 80 parts by mass or more, even more preferably more than 90 parts by mass, and still more preferably 100 parts by mass or more, and from the viewpoint of abrasion resistance, it is preferably less than 200 parts by mass, more preferably less than 150 parts by mass, and still more preferably less than 130 parts by mass.

[0108] (carbon black) Carbon black commonly used in the tire industry can be used as appropriate, and examples include GPF, FEF, HAF, ISAF, and SAF. From the perspective of life cycle assessment, in addition to the above-mentioned carbon black, carbon black made from lignin or recycled carbon black obtained by pyrolysis or the like from products containing carbon black, such as tires, may also be used. One type of carbon black may be used alone, or two or more types may be used in combination.

[0109] The nitrogen adsorption specific surface area (N2SA) of carbon black is 10m from the viewpoint of reinforcement. 2 / g or more is preferable, and 30m 2 / g is more preferable, and 50m 2 From the viewpoint of fuel economy and processability, it is more preferable that the tensile strength is more than 200 m / g. 2 / g or less is preferred, and 175m 2 / g is more preferable, and 150m 2The N2SA of carbon black is measured by the above-mentioned measurement method.

[0110] The average primary particle size of carbon black is preferably greater than 10 nm, more preferably greater than 12 nm, and even more preferably greater than 14 nm. The average primary particle size is preferably less than 26 nm, more preferably less than 24 nm, and even more preferably 22 nm or less. The average primary particle size of carbon black is measured by the above-mentioned measurement method.

[0111] When carbon black is contained, the content per 100 parts by mass of the rubber component is preferably more than 1 part by mass, more preferably more than 3 parts by mass, and even more preferably 5 parts by mass or more, from the viewpoint of abrasion resistance and wet grip performance, and is preferably less than 50 parts by mass, more preferably less than 30 parts by mass, and even more preferably less than 10 parts by mass, from the viewpoint of fuel economy.

[0112] When both silica and carbon black are contained, the content of silica is preferably greater than the content of carbon black from the viewpoint of the balance of fuel economy, wet grip performance, and abrasion resistance. The proportion of silica to the total content of silica and carbon black is preferably more than 80 mass%, more preferably more than 90 mass%, and even more preferably more than 95 mass%.

[0113] (Other fillers) As the filler, in addition to carbon black and silica, other fillers may also be used. Such fillers are not particularly limited, and any fillers conventionally commonly used in the tire industry, such as aluminum hydroxide, alumina (aluminum oxide), calcium carbonate, magnesium sulfate, talc, clay, and biochar (BIO CHAR), may be used. The other fillers may be used alone or in combination of two or more.

[0114] The total content of the filler per 100 parts by mass of the rubber component is preferably more than 40 parts by mass, more preferably more than 60 parts by mass, and even more preferably more than 80 parts by mass from the viewpoint of abrasion resistance, and is preferably less than 250 parts by mass, more preferably less than 200 parts by mass, and even more preferably less than 150 parts by mass from the viewpoint of fuel economy and elongation at break.

[0115] (Silane coupling agent) Silica is preferably used in combination with silane coupling agent.Silane coupling agent is not particularly limited, and can use any silane coupling agent that is conventionally used in combination with silica in tire industry, for example, thioester-based silane coupling agent such as 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane; mercapto-based silane coupling agent such as the one shown in the following chemical formula; sulfide-based silane coupling agent such as bis(3-triethoxysilylpropyl) disulfide, bis(3-triethoxysilylpropyl) tetrasulfide; vinyltriethoxysilane; Examples of suitable silane coupling agents include vinyl-based silane coupling agents such as vinyltrimethoxysilane; amino-based silane coupling agents such as 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, and 3-(2-aminoethyl)aminopropyltriethoxysilane; glycidoxy-based silane coupling agents such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based silane coupling agents such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. Among these, thioester-based silane coupling agents and / or sulfide-based silane coupling agents are preferred. Silane coupling agents may be used alone or in combination.

[0116] The mercapto-based silane coupling agent is preferably a compound represented by the following chemical formula (1) and / or a compound containing a bonding unit A represented by the following chemical formula (2) and a bonding unit B represented by the following chemical formula (3). [ka] (In the formula, R 101 , R 102 , and R 103 are each independently an alkyl having 1 to 12 carbon atoms, an alkoxy having 1 to 12 carbon atoms, or -O-(R 111 -O) z -R 112 (z R 111 each independently represents a divalent hydrocarbon group having 1 to 30 carbon atoms; R 112 represents an alkyl having 1 to 30 carbon atoms, an alkenyl having 2 to 30 carbon atoms, an aryl having 6 to 30 carbon atoms, or an aralkyl having 7 to 30 carbon atoms; z represents an integer of 1 to 30; 104 represents an alkylene having 1 to 6 carbon atoms. [ka] [ka] (wherein x represents an integer of 0 or more; y represents an integer of 1 or more; R 201 represents a hydrogen atom, a halogen atom, an alkyl having 1 to 30 carbon atoms, an alkenyl having 2 to 30 carbon atoms, or an alkynyl having 2 to 30 carbon atoms, which may be substituted with a hydroxyl or carboxyl; R 202 represents an alkylene having 1 to 30 carbon atoms, an alkenylene having 2 to 30 carbon atoms, or an alkynylene having 2 to 30 carbon atoms; 201 and R 202 may form a ring structure with

[0117] Examples of the compound represented by formula (1) include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, and the compound represented by the following chemical formula (4) (Si363 manufactured by Evonik Degussa GmbH), and the compound represented by the following chemical formula (4) can be preferably used. These may be used alone or in combination of two or more. [ka]

[0118] Examples of compounds containing a bonding unit A represented by chemical formula (2) and a bonding unit B represented by chemical formula (3) include those manufactured and sold by Momentive, Inc.

[0119] When a silane coupling agent is contained, the content (total amount when multiple silane coupling agents are used) per 100 parts by mass of the rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 part by mass, even more preferably more than 2.0 parts by mass, and even more preferably more than 4.0 parts by mass from the viewpoint of improving the dispersibility of silica. Also, from the viewpoint of preventing a decrease in abrasion resistance, the content is preferably less than 20 parts by mass, more preferably less than 12 parts by mass, even more preferably less than 10 parts by mass, and even more preferably less than 9.0 parts by mass.

[0120] The content of the silane coupling agent relative to 100 parts by mass of silica is preferably more than 1.0 part by mass, more preferably more than 3.0 parts by mass, and even more preferably more than 5.0 parts by mass, from the viewpoint of improving the dispersibility of silica. Also, from the viewpoint of cost and processability, it is preferably less than 20 parts by mass, more preferably less than 15 parts by mass, and even more preferably less than 12 parts by mass.

[0121] <Plasticizer> The rubber composition according to the present invention preferably contains a plasticizer, such as hydrocarbon resin, oil, liquid rubber, or ester-based plasticizer.

[0122] (hydrocarbon resin) A hydrocarbon resin refers to a polymer having a skeleton formed from hydrocarbons and that is solid at 25°C. Hydrocarbon resins may generally contain oxygen elements derived from carboxyl groups, hydroxyl groups, coumarone, or the like. Examples of hydrocarbon resins include, but are not limited to, petroleum resins commonly used in the tire industry, terpene resins, rosin resins, and phenolic resins. Examples of hydrocarbon resins that can be used include those commercially available from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Kraton, Eastman Chemical Company, Nitto Chemical Co., Ltd., LUHUA, Nippon Shokubai Co., Ltd., ENEOS Corporation, Arakawa Chemical Industries, Ltd., and Taoka Chemical Co., Ltd. One type of hydrocarbon resin may be used alone, or two or more types may be used in combination.

[0123] <Petroleum resin> As the petroleum resin, C5 petroleum resin, aromatic petroleum resin, C5C9 petroleum resin, etc. The petroleum resin may be used alone or in combination of two or more kinds.

[0124] C5 petroleum resin refers to a resin obtained by polymerizing a C5 fraction. Examples of C5 fractions include petroleum fractions having 4 to 5 carbon atoms, such as cyclopentadiene, pentene, pentadiene, and isoprene, and these may be hydrogenated or modified. Dicyclopentadiene resin (DCPD resin) is preferably used as the C5 petroleum resin.

[0125] Aromatic petroleum resins refer to resins obtained by polymerizing C9 fractions, and may be hydrogenated or modified. Examples of C9 fractions include petroleum fractions having 8 to 10 carbon atoms, such as vinyltoluene, alkylstyrene, indene, and methylindene. Specific examples of aromatic petroleum resins that are preferably used include coumarone-indene resins, coumarone resins, indene resins, and aromatic vinyl resins.

[0126] As the aromatic vinyl resin, a homopolymer of α-methylstyrene or styrene, or a copolymer of α-methylstyrene and styrene is preferred, and a copolymer of α-methylstyrene and styrene is more preferred, because they are economical, easy to process, and have excellent heat generation properties.

[0127] The C5C9 petroleum resin refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be a hydrogenated or modified resin. Examples of the C5 fraction and the C9 fraction include the petroleum fractions described above.

[0128] <Terpene resin> Examples of terpene resins include polyterpene resins composed of at least one terpene compound selected from α-pinene, β-pinene, limonene, dipentene, and the like; aromatic modified terpene resins made from the terpene compound and an aromatic compound; terpene phenolic resins made from a terpene compound and a phenolic compound; and those obtained by subjecting these terpene resins to hydrogenation treatment (hydrogenated terpene resins). Examples of aromatic compounds used as raw materials for aromatic modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds used as raw materials for terpene phenolic resins include phenol, bisphenol A, cresol, and xylenol. Terpene resins may be used alone or in combination of two or more.

[0129] <Rosin-based resin> The rosin-based resin is not particularly limited, but examples thereof include natural resin rosin and rosin-modified resins obtained by modifying rosin by hydrogenation, disproportionation, dimerization, esterification, etc. The rosin-based resins may be used alone or in combination of two or more.

[0130] <Phenol-based resin> The phenolic resin is not particularly limited, but examples thereof include phenol formaldehyde resin, alkylphenol formaldehyde resin, alkylphenol acetylene resin, oil-modified phenol formaldehyde resin, etc. The phenolic resin may be used alone or in combination of two or more.

[0131] ≪Softening point≫ From the viewpoint of wet grip performance, the softening point of the hydrocarbon resin is preferably above 60° C., more preferably above 70° C., and even more preferably above 80° C. Furthermore, from the viewpoint of processability and improving the dispersibility of the rubber component and the filler, the softening point is preferably below 150° C., more preferably below 140° C., and even more preferably below 130° C. The softening point is measured by the above-mentioned measurement method.

[0132] <Glass transition temperature (Tg)> The Tg of the hydrocarbon resin is preferably 110°C or lower, more preferably 105°C or lower, and even more preferably 100°C or lower, from the viewpoint of excellent compatibility with the rubber component. Furthermore, the Tg is preferably -35°C or higher, more preferably 0°C or higher, and even more preferably 30°C or higher, from the viewpoint of excellent compatibility with the rubber component. The Tg is measured by the above-mentioned measurement method using a differential scanning calorimeter.

[0133] ≪Weight average molecular weight (Mw)≫ The Mw of the hydrocarbon resin is preferably greater than 500, more preferably greater than 600, and even more preferably greater than 650, from the viewpoints of resistance to volatilization and good gripping properties. Furthermore, the Mw is preferably less than 15,000, more preferably less than 13,000, and even more preferably less than 11,000, from the viewpoint of excellent dry gripping properties due to the resin's tendency to easily entangle with the polymer and resist release. By having the Mw within the above range, the resulting rubber composition can have excellent processability and improved heat buildup and elongation at break. The Mw is measured by the above-mentioned measurement method.

[0134] ≪Content≫ From the viewpoint of wet grip performance, etc., the rubber composition according to the present invention preferably contains at least one hydrocarbon resin, and the content of the hydrocarbon resin in the rubber composition of the present invention is preferably 5% by mass or more. The content of the resin in the rubber composition is more preferably more than 6% by mass, even more preferably more than 7% by mass, even more preferably more than 10% by mass, and even more preferably more than 12% by mass. From the viewpoint of suppressing heat buildup, etc., the content of the hydrocarbon resin in the rubber composition is preferably less than 100% by mass, more preferably less than 80% by mass, even more preferably less than 60% by mass, particularly preferably less than 50% by mass, even more particularly preferably less than 35% by mass, and most preferably less than 25% by mass.

[0135] (oil) Examples of oils include process oil, vegetable oils and fats, and animal fats and oils. Examples of the process oil include paraffinic process oil, naphthenic process oil, and aromatic process oil. Furthermore, as an environmental measure, process oil with a low content of polycyclic aromatic compounds (PCA) can also be used. Examples of the low PCA content process oil include mild extract solvate (MES), treated distillate aromatic extract (TDAE), and heavy naphthenic oil. One type of oil may be used alone, or two or more types may be used in combination.

[0136] When oil is contained, the content per 100 parts by mass of the rubber component is preferably more than 5 parts by mass, more preferably more than 10 parts by mass, and even more preferably more than 15 parts by mass from the viewpoint of processability. Furthermore, from the viewpoint of abrasion resistance, the content is preferably less than 120 parts by mass, more preferably less than 80 parts by mass, and even more preferably less than 40 parts by mass. In this specification, the oil content includes the amount of oil contained in the oil-extended rubber.

[0137] (liquid rubber) The liquid rubber is not particularly limited as long as it is a polymer that is in a liquid state at room temperature (25°C), and examples thereof include liquid butadiene rubber (liquid BR), liquid styrene butadiene rubber (liquid SBR), liquid isoprene rubber (liquid IR), liquid styrene isoprene rubber (liquid SIR), liquid farnesene rubber, etc. One type of liquid rubber may be used alone, or two or more types may be used in combination.

[0138] When a liquid rubber is contained, the content per 100 parts by mass of the rubber component is preferably more than 1 part by mass, more preferably more than 2 parts by mass, even more preferably more than 3 parts by mass, and still more preferably more than 5 parts by mass. The content of the liquid rubber is also preferably less than 50 parts by mass, more preferably less than 40 parts by mass, and still more preferably less than 20 parts by mass.

[0139] (ester plasticizer) Examples of ester-based plasticizers include dibutyl adipate (DBA), diisobutyl adipate (DIBA), dioctyl adipate (DOA), di-2-ethylhexyl azelate (DOZ), dibutyl sebacate (DBS), diisononyl adipate (DINA), diethyl phthalate (DEP), dioctyl phthalate (DOP), diundecyl phthalate (DUP), dibutyl phthalate (DBP), dioctyl sebacate (DOS), tributyl phosphate (TBP), trioctyl phosphate (TOP), triethyl phosphate (TEP), trimethyl phosphate (TMP), thymidine triphosphate (TTP), tricresyl phosphate (TCP), trixylenyl phosphate (TXP), etc. Ester-based plasticizers may be used alone or in combination of two or more.

[0140] (Plasticizer content) The content of the plasticizer per 100 parts by mass of the rubber component is preferably more than 5 parts by mass, more preferably more than 10 parts by mass, and even more preferably more than 15 parts by mass from the viewpoint of wet grip performance, and is preferably less than 120 parts by mass, more preferably less than 80 parts by mass, and even more preferably less than 60 parts by mass from the viewpoint of processability.

[0141] <Other compounding agents> In addition to the above-mentioned components, the rubber composition according to the present invention may contain, as appropriate, compounding agents that are generally used in the tire industry, such as processing aids, zinc oxide, stearic acid, wax, antioxidants, vulcanizing agents, and vulcanization accelerators.

[0142] (processing aids) Examples of processing aids include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, and mixtures of fatty acid metal salts and fatty acid amides. These processing aids may be used alone or in combination. Examples of processing aids that can be used include those commercially available from Schill + Seilacher, Performance Additives, and the like.

[0143] When a processing aid is contained, the content thereof per 100 parts by mass of the rubber component is preferably more than 0.5 parts by mass, more preferably more than 1 part by mass, and even more preferably more than 1.5 parts by mass from the viewpoint of improving processability, and is preferably less than 10 parts by mass, more preferably less than 8.0 parts by mass, and even more preferably less than 5.0 parts by mass from the viewpoints of abrasion resistance and breaking strength.

[0144] (zinc oxide) When zinc oxide is contained, the content per 100 parts by mass of the rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 part by mass, and even more preferably more than 1.5 parts by mass from the viewpoint of processability, and is preferably less than 10 parts by mass, more preferably less than 7 parts by mass, and even more preferably less than 5 parts by mass from the viewpoint of abrasion resistance.

[0145] (stearic acid) When stearic acid is contained, the content per 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, and even more preferably 1.5 parts by mass or more from the viewpoint of processability, and is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less from the viewpoint of vulcanization rate.

[0146] (wax) When wax is contained, the content per 100 parts by mass of the rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 part by mass, and even more preferably more than 1.3 parts by mass from the viewpoint of weather resistance of the rubber, and is preferably less than 10 parts by mass, more preferably less than 7.0 parts by mass, and even more preferably less than 5.0 parts by mass from the viewpoint of preventing whitening of the tire due to bloom.

[0147] (anti-aging agent) The antioxidant is not particularly limited, but examples include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, as well as metal carbamates. Preferred are phenylenediamine-based antioxidants such as N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, and N-cyclohexyl-N'-phenyl-p-phenylenediamine, and quinoline-based antioxidants such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline. Antiaging agents may be used alone or in combination of two or more.

[0148] When an antioxidant is contained, the content per 100 parts by mass of the rubber component is preferably more than 0.5 parts by mass, more preferably more than 1.0 part by mass, and even more preferably more than 1.5 parts by mass from the viewpoint of ozone crack resistance of the rubber, and is preferably less than 10 parts by mass, more preferably less than 7 parts by mass, and even more preferably less than 5 parts by mass from the viewpoint of abrasion resistance and wet grip performance.

[0149] (vulcanizing agent) Sulfur is preferably used as the vulcanizing agent. Examples of sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur. The vulcanizing agent may be used alone or in combination of two or more.

[0150] When sulfur is contained as a vulcanizing agent, the content per 100 parts by mass of the rubber component is preferably more than 0.1 parts by mass, more preferably more than 0.3 parts by mass, and even more preferably more than 0.5 parts by mass, from the viewpoint of ensuring a sufficient vulcanization reaction. Furthermore, from the viewpoint of preventing deterioration, the content is preferably less than 5.0 parts by mass, more preferably less than 4.0 parts by mass, and even more preferably less than 3.0 parts by mass. When oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is the total content of pure sulfur contained in the oil-containing sulfur.

[0151] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensate, sodium 1,6-hexamethylene-dithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, etc. These vulcanizing agents other than sulfur can be commercially available from Taoka Chemical Co., Ltd., Lanxess K.K., Flexis, etc.

[0152] (Vulcanization accelerator) Examples of the vulcanization accelerator include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, and xanthate-based vulcanization accelerators, etc. One type of vulcanization accelerator may be used alone, or two or more types may be used in combination.

[0153] Among these, it is preferable that the rubber composition contains one or more vulcanization accelerators selected from the group consisting of sulfenamide-based, guanidine-based, and thiazole-based vulcanization accelerators, and it is more preferable that the rubber composition contains a sulfenamide-based vulcanization accelerator and a guanidine-based vulcanization accelerator.

[0154] Examples of sulfenamide vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), etc. Among these, N-cyclohexyl-2-benzothiazolylsulfenamide (CBS) is preferred.

[0155] Examples of guanidine vulcanization accelerators include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatechol borate, 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine, etc. Among these, 1,3-diphenylguanidine (DPG) is preferred.

[0156] Examples of the thiazole vulcanization accelerator include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, etc. Among these, 2-mercaptobenzothiazole is preferred.

[0157] When a vulcanization accelerator is contained, the content thereof per 100 parts by mass of the rubber component is preferably more than 1 part by mass, more preferably more than 1.5 parts by mass, and even more preferably more than 2 parts by mass. The content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably less than 8 parts by mass, more preferably less than 7 parts by mass, and even more preferably less than 6 parts by mass. By setting the content of the vulcanization accelerator within the above range, breaking strength and elongation tend to be ensured.

[0158] [Manufacturing] The rubber compositions according to the present invention can be produced by any known method, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or an internal kneader (such as a Banbury mixer or kneader).

[0159] The kneading step includes, for example, a base kneading step in which compounding ingredients and additives other than the vulcanizing agent and vulcanization accelerator are kneaded, and a final kneading (F kneading) step in which the vulcanizing agent and vulcanization accelerator are added to the kneaded product obtained in the base kneading step and kneaded. Furthermore, the base kneading step can be divided into multiple steps as desired.

[0160] The kneading conditions are not particularly limited, but examples include a method in which the base kneading step involves kneading for 3 to 10 minutes at a discharge temperature of 150 to 170°C, and in the final kneading step, kneading for 1 to 5 minutes at 70 to 110°C.

[0161] The pneumatic tire of the present invention can be manufactured by a conventional method using the unvulcanized rubber composition. That is, the pneumatic tire of the present invention can be manufactured by extruding the unvulcanized rubber composition into a predetermined tread shape using an extruder equipped with a die of a predetermined shape, laminating it together with other tire components on a tire building machine, molding it by a conventional method to form an unvulcanized tire, and heating and pressurizing this unvulcanized tire in a vulcanizer. The vulcanization conditions are not particularly limited, and examples include a method of vulcanizing at 150 to 200°C for 10 to 30 minutes.

[0162] [Application] The pneumatic tire of the present invention can be used for any purpose, for example, as a passenger car tire, a large passenger car tire, a light truck tire, a large SUV tire, a racing tire, or a motorcycle tire. Among these, passenger car tires and light truck tires are preferred. Here, passenger car tires are tires designed to be mounted on four-wheeled vehicles, and refer to tires with a maximum load capacity of 1000 kg or less according to the JATMA standard, while light truck tires refer to tires with a maximum load capacity of less than 1400 kg according to the JATMA standard.

[0163] The tire of the present invention can be used as a summer tire, a winter tire, or a studless tire, among the above-mentioned tires. Among these, winter tires and studless tires, which are used at low temperatures, are preferred. [Example]

[0164] The present invention will be described based on examples, but the present invention is not limited to only the examples.

[0165] [Various medicines] The various chemicals used in the examples and comparative examples are listed below. NR:TSR20 SBR1: SLR6430 manufactured by TRINSEO (S-SBR, styrene content: 40% by mass, vinyl bond content: 24 mol%, Tg: -30°C, Mw: 1,010,000, oil-extended product containing 37.5 parts by weight of oil per 100 parts by weight of rubber component) SBR2: Styrene-butadiene rubber synthesized in Production Example 1 below (modified S-SBR, styrene content: 20% by mass, vinyl content: 20% by mole, Tg: -60°C, Mw: 800,000) SBR3: Styrene-butadiene rubber synthesized in Production Example 2 below (modified S-SBR, styrene content: 15% by mass, vinyl content: 30% by mole, Tg: -60°C, Mw: 800,000) BR1: UBEPOL BR (registered trademark) 150B manufactured by Ube Industries, Ltd. (vinyl content: 1.5 mol%, cis content: 97 mol%, Tg: -108°C, Mw: 440,000) BR2: ASAPRENE N103 manufactured by Asahi Kasei Corporation (modified BR whose terminals are modified with a mixture of tetraglycidyl-1,3-bisaminomethylcyclohexane and its oligomer component, vinyl content: 12 mol%, cis content: 36 mass%, Tg: -90°C, Mw: 550,000) CB (carbon black): Cabot Japan Co., Ltd.'s Show Black N134 (N2SA: 148m 2 / g, average primary particle diameter: 18nm) Silica: ULTRASIL® VN3 (N2SA: 175 ml) manufactured by Evonik Degussa 2 / g, average primary particle diameter: 18nm) Coupling agent (silane coupling agent): Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa Oil: H&R VivaTec 500 (TDAE oil) Hydrocarbon resin 1: Sylvatraxx 4401 (aromatic vinyl resin (copolymer of styrene and α-methylstyrene), Mw: 700, softening point: 85°C, Tg: 34°C) manufactured by Kraton Hydrocarbon resin 2: Exxon Mobil PR395 (C5C9 resin, Mw: 880, softening point: 117.8°C, Tg: 68°C) Zinc oxide: Zinc oxide type 2 manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Camellia stearic acid beads manufactured by NOF Corporation Wax: Sunnock N manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Antioxidant 1: Antigen 6C (6PPD, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd. Antioxidant 2: Nocrac 224 (TMQ, 2,2,4-trimethyl-1,2-dihydroquinoline polymer) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Sulfur: Powdered sulfur manufactured by Karuizawa Sulfur Co., Ltd. Vulcanization accelerator 1: Noccela CZ (CBS, N-cyclohexyl-2-benzothiazolyl sulfenamide) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noccela D (DPG, 1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0166] [Manufacturing example] Production Example 1: Synthesis of SBR2 The ratio of styrene to 1,3-butadiene is adjusted so that the styrene content in the final product is 20% by mass. Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene are charged into a nitrogen-purged autoclave reactor. After adjusting the temperature of the reactor contents to 20°C, n-butyllithium is added to initiate polymerization. Polymerization is carried out under adiabatic conditions, and when the polymerization conversion rate reaches 99%, 1,3-butadiene is added and further polymerization is carried out. After further polymerization, methyltriethoxysilane is added as a modifier to carry out a modification reaction. After the reaction is complete, 2,6-di-tert-butyl-p-cresol is added. The solvent is then removed by steam stripping, and the resulting mixture is dried on a heated roll heated to 110°C to obtain SBR2.

[0167] Production Example 2: Synthesis of SBR3 The ratio of styrene to 1,3-butadiene is adjusted so that the styrene content in the final product is 15% by mass. Cyclohexane, tetrahydrofuran, styrene, and 1,3-butadiene are charged into a nitrogen-purged autoclave reactor. After adjusting the temperature of the reactor contents to 20°C, n-butyllithium is added to initiate polymerization. Polymerization is carried out under adiabatic conditions, and when the polymerization conversion rate reaches 99%, additional 1,3-butadiene is added. After further polymerization, 3-[bis(trimethylsilyl)amino]propyltriethoxysilane is added as a modifier to carry out a modification reaction. After the reaction is complete, 2,6-di-tert-butyl-p-cresol is added. The solvent is then removed by steam stripping, and the mixture is dried on a heated roll heated to 110°C to obtain SBR3.

[0168] [Examples and Comparative Examples] According to the formulation shown in each table, chemicals other than sulfur and vulcanization accelerators were mixed in a 1.7 L closed-type Banbury mixer for 1 to 10 minutes until the discharge temperature reached 150 to 160°C, yielding a kneaded mixture. Next, sulfur and vulcanization accelerators were added to the resulting mixture using a two-screw open roll mill, and the mixture was mixed for 4 minutes until the temperature reached 105°C, yielding an unvulcanized rubber composition. The resulting unvulcanized rubber composition was molded into the specified tread shape according to each table, and then bonded together with other tire components to produce an unvulcanized tire. The tire was then press-vulcanized at 170°C for 12 minutes to obtain test tires (Tire 1: 225 / 60R16 98H, Tire 2: 275 / 55R20 117T XL).

[0169] The tread surface of each test tire had at least a circumferential main groove and lateral grooves. There were three circumferential main grooves, one of which ran along the tire centerline, and the other two were positioned equidistantly outward in the tire width direction from the main groove running along the tire centerline. The test tires did not have small holes, narrow circumferential grooves, or widened circumferential grooves.

[0170] <Evaluation> The results of measurements for each test tire by the following methods are also recorded in the corresponding columns of the table below.

[0171] (Rand ratio) For each test tire, the total contact area and effective contact area as defined above are determined, and the land ratio (%) is calculated.

[0172] (High-speed wet grip performance) Each test tire was fitted to all wheels of a vehicle (Tire 1: Japanese-made FF vehicle, 2000cc displacement; Tire 2: Japanese-made 4WD vehicle, 3000cc displacement) and the vehicle was driven on a test course with a wet asphalt surface at a speed of 100km / h. The grip performance during the drive was evaluated by 20 test drivers on a scale of 1 to 5, and a total score was calculated. The results were expressed as an index, with the reference comparative example being 100. A higher index indicates better handling stability during driving and better high-speed wet grip performance.

[0173] (Low temperature wear resistance) Each test tire was fitted to all wheels of a vehicle (Tire 1: Japanese-made front-wheel drive vehicle, 2000cc displacement; Tire 2: Japanese-made 4WD vehicle, 3000cc displacement), and the vehicle was driven 20,000km on an asphalt test course at an outside temperature of 10°C or below, and the amount of tread thickness reduction from the start of the drive was measured. The results were expressed as an index, with the reference comparative example being set at 100. A higher index indicates less reduction and better low-temperature wear resistance.

[0174] [Table 1]

[0175] [Table 2]

[0176] [Embodiment] The following describes a preferred embodiment.

[0177] [1] A pneumatic tire having a tread portion, the tread portion is made of a rubber composition containing 50 parts by mass or more, preferably 70 parts by mass or more, more preferably 80 parts by mass or more, and even more preferably 90 parts by mass or more of silica per 100 parts by mass of the rubber component, The rubber component contains more than 50% by mass of butadiene rubber and styrene-butadiene rubber, The total amount of styrene in the rubber component is 25% by mass or less, The content (mass%) of the butadiene rubber in the rubber component is A BR , when the land ratio (%) of the tread surface of the tread portion is L, A BR A pneumatic tire where and L satisfy the following formula: (1) A BR ×L>3000 [2] The total styrene amount (mass%) is A STY When A BR , L and A STY A pneumatic tire according to [1], wherein the following formula is satisfied: (2) (A BR / A STY )×L>130 Here, the right side of formula (2) is preferably 200, more preferably 300, even more preferably 360, even more preferably 450, even more preferably 550, and even more preferably 600. [3] The pneumatic tire according to [1] or [2], wherein the rubber composition contains at least one hydrocarbon resin, and the content of the hydrocarbon resin in the rubber composition is 5% by mass or more, preferably more than 6% by mass, more preferably more than 7% by mass, even more preferably more than 10% by mass, and even more preferably more than 12% by mass. [4] The pneumatic tire according to any one of [1] to [3], wherein the content of the silica relative to 100 parts by mass of the rubber component is more than 70 parts by mass, preferably 80 parts by mass or more, more preferably more than 90 parts by mass, and even more preferably 100 parts by mass or more. [5] The pneumatic tire according to any one of [1] to [4], wherein the glass transition temperature of the rubber composition is less than -30°C, preferably less than -33°C, more preferably less than -37°C, even more preferably less than -40°C, and still more preferably less than -42°C. [6] The pneumatic tire according to any one of [1] to [5], wherein the right side of formula (1) is 3250. [7] The pneumatic tire according to any one of [1] to [5], wherein the right side of formula (1) is 3500, preferably 3750, and more preferably 4000. [8] The content A of the butadiene rubber in the rubber component BR The pneumatic tire according to any one of [1] to [7], wherein the content of the hydroxyl group is less than 70% by mass, preferably less than 65% by mass, and more preferably less than 60% by mass. [9] The pneumatic tire according to any one of [1] to [8], wherein the glass transition temperature of the styrene-butadiene rubber is less than -30°C, preferably less than -40°C, more preferably less than -50°C, and even more preferably less than -55°C.

[10] The tread surface has two or more circumferential main grooves extending in the tire circumferential direction and land portions defined by the circumferential main grooves, When a pair of land portions located at the outermost sides in the tire width direction among the land portions are defined as shoulder land portions, the shoulder land portions have an opening area of ​​more than 0.1 mm and less than 15 mm 2 , preferably more than 0.5 and less than 10 mm 2 , more preferably more than 0.5 and less than 7.0 mm 2 , more preferably more than 1.0 and less than 5.0 mm 2 The pneumatic tire according to any one of [1] to [9], having one or more small holes.

[11] The tread surface has two or more circumferential main grooves extending in the tire circumferential direction and land portions defined by the circumferential main grooves, The pneumatic tire according to any one of [1] to

[10] , wherein a pair of land portions located at the outermost sides in the tire width direction among the land portions are shoulder land portions, and the shoulder land portions have at least one circumferential narrow groove.

[12] The pneumatic tire according to any one of [1] to

[11] , wherein the tread surface has widened circumferential grooves whose groove width widens on the radially inner side of the tire.

[13] The pneumatic tire according to

[12] , wherein the widened circumferential groove is present in a land portion located on the tire center line, or in a case where a circumferential main groove is present on the tire center line, in a land portion closest to the tire center line. [Explanation of symbols]

[0178] CL··Tire centerline Te Tread Edge W: Tire width direction C Circumferential direction of the tire 1. Tire 2... Circumferential main groove 3... land department 4...Small hole 5... Circumferential narrow groove 6 Widened circumferential groove

Claims

1. A pneumatic tire having a tread portion, the tread portion is made of a rubber composition containing 50 parts by mass or more of silica per 100 parts by mass of a rubber component, the rubber component contains more than 50% by mass of butadiene rubber and styrene-butadiene rubber, the total amount of styrene in the rubber component is 25% by mass or less, The glass transition temperature of the rubber composition is less than −30° C., The content (mass%) of the butadiene rubber in the rubber component is A BR , when the land ratio (%) of the tread surface of the tread portion is L, A BR A pneumatic tire in which and L satisfy the following formula: (1) A BR ×L>3000

2. The total styrene amount (% by mass) is A STY When this is done, A BR , L and A STY The pneumatic tire according to claim 1, wherein: (2) (A BR / A STY )×L>130

3. The pneumatic tire according to claim 1 , wherein the rubber composition contains at least one hydrocarbon resin, and the content of the hydrocarbon resin in the rubber composition is 5% by mass or more.

4. The pneumatic tire according to claim 1, wherein the content of the silica per 100 parts by mass of the rubber component is 100 parts by mass or more.

5. The pneumatic tire according to claim 1, wherein the rubber composition has a glass transition temperature of less than -33°C.

6. The pneumatic tire according to claim 1, wherein the right side of formula (1) is 3250.

7. The pneumatic tire according to claim 6, wherein the right side of formula (1) is 3500.

8. The content A of the butadiene rubber in the rubber component BR The pneumatic tire according to claim 1, wherein the total mass of the tread is less than 70 mass %.

9. The pneumatic tire according to claim 1, wherein the styrene-butadiene rubber has a glass transition temperature of less than -30°C.

10. The tread surface has two or more circumferential main grooves extending in the tire circumferential direction and land portions defined by the circumferential main grooves, When a pair of land portions located at the outermost sides in the tire width direction among the land portions are defined as shoulder land portions, the shoulder land portions have an opening area of ​​more than 0.1 mm and less than 15 mm 2 2. The pneumatic tire according to claim 1, having one or more small holes.

11. The tread surface has two or more circumferential main grooves extending in the tire circumferential direction and land portions defined by the circumferential main grooves, The pneumatic tire according to claim 1 , wherein when a pair of the land portions located outermost in the tire width direction among the land portions are defined as shoulder land portions, the shoulder land portions have at least one circumferential narrow groove.

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