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: None

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 studied so far. For example, Patent Document 1 discloses a rubber composition for tires containing a diene rubber (A) containing a specific amount of a specific conjugated diene rubber represented by a specific formula, silica having a CTAB adsorption specific surface area within a specific range, and a silane coupling agent represented by a specific formula, and a pneumatic tire using the same in the tire tread. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-141405 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, since wet grip performance and abrasion resistance are fundamentally mutually exclusive, it is difficult to improve both at the same time, and further improvements are required to achieve a balance between these performances.

[0005] An object of the present invention is to provide a tire which 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 composed 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 styrene content in the rubber component is 25% by mass or less, The content (mass%) of the butadiene rubber in the rubber component is A BR , where L is the land ratio (%) of the tread surface of the tread portion, A BR A pneumatic tire in which and L satisfy the following formula: (1) A BR ×L>3000 Effect 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 description of the drawings]

[0008] [Figure 1] 1 is a diagram showing a schematic representation of the total contact area of ​​a tread surface. [Diagram 2] 1 is an exploded view of a portion of a tire tread having a perforation in a shoulder region. [Diagram 3] FIG. 2 is a development view of a portion of a tread of a tire having circumferential narrow grooves in shoulder regions. [Figure 4] FIG. 2 is a development view of a portion of a tread of a tire having widened circumferential grooves in the land portion closest to the tire centerline. [Diagram 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 PREFERRED EMBODIMENTS

[0009] A tire according to an embodiment of the present invention is a pneumatic tire having a tread portion, The tread portion is composed 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 styrene content in the rubber component is 25% by mass or less, The content (mass%) of the butadiene rubber in the rubber component is A BR , where L is the land ratio (%) of the tread surface of the tread portion, A BR and L satisfy the following formula: (1) A BR ×L>3000

[0010] Without intending to be bound by theory, the following is believed 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] That is, (1) in the rubber composition constituting the tread portion, by making the main polymer of the rubber component be butadiene rubber (BR), wear resistance is improved, (2) by containing a certain amount or more of silica, the road surface following ability of the tread portion is improved, thereby improving wet grip performance, (3) by further containing styrene-butadiene rubber (SBR) in the rubber component and keeping the total styrene content of the rubber component below a certain value, SBR becomes more compatible with BR, and SBR domains, where silica is likely to be unevenly distributed, are dispersed in the BR phase, effectively reinforcing BR, maintaining wear resistance and improving wet grip performance, (4) since a rubber composition containing such a rubber component with a low total styrene content has a lower glass transition temperature, temperature dependency is reduced, and grip performance when the tire heats up due to high-speed driving and wear resistance in cold weather are less likely to decrease, and (5) by keeping the land ratio of the tread surface large, the contact area is increased, which disperses the wear energy input from the road surface to the tread surface, and it is considered that tread wear is suppressed. 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 Then, 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 becomes larger, L becomes larger, and A STY Since there are constraints on the direction of decreasing the wet grip performance during high-speed driving and the wear resistance at low temperatures, it is considered that this will be advantageous for both the wet grip performance during high-speed driving and the wear resistance at low temperatures.

[0014] The rubber composition preferably contains at least one type of 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 SBR domains, so by combining a certain amount or more of hydrocarbon resin, the SBR domains, which tend to have concentrated hydrocarbon resins, are dispersed into the BR phase, which is thought to be advantageous in terms of 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 formula (1) is preferably 3,250, and more preferably 3,500.

[0021] It is believed that 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 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 that is generally considered to contribute to wet grip (0°C tan δ) also decreases, destroying the balance with wet grip performance during high-speed driving. Therefore, it is considered necessary to keep the butadiene rubber content below 70% by mass in order to achieve both performances.

[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 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 a tire circumferential direction and a land portion 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 substrate 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 the land portions located at the outermost sides in the tire width direction among the land portions is 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 believed to improve drainage in the shoulder regions and thus wet grip performance.

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

[0031] Since the groove width of the widened circumferential groove increases as the tread portion wears, it is believed that drainage after tire wear improves and wet grip performance improves.

[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 the tire has worn in the center portion in the tire width direction, thereby improving wet grip performance.

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

[0035] Unless otherwise specified, the "dimensions of each part of the tire" that appear on the outer surface of the tire are values ​​specified in a normal state, while those present inside the tire are values ​​specified when the tire is cut along a plane including the tire rotation axis and the cut tire piece is kept within the rim width of a normal rim.

[0036] "Genuine rim" refers to the rim that is specified for each tire by the standard system including the standard on which the tire is based, for example, "Standard rim" in the applicable size described in the "Jatma Year Book" for JATMA (Japan Automobile Tire Manufacturers Association), "Measuring Rim" in the "STANDARDS MANUAL" for ETRTO (The European Tire and Rim Technical Organisation), and "Design Rim" in the "YEAR BOOK" for TRA (The Tire and Rim Association, Inc.). 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 rim that can be assembled with the rim and can hold internal pressure, that is, the rim with the smallest rim diameter and the next narrowest rim width among the rims that do not leak air from between the rim and tire.

[0037] "Regular internal pressure" refers to the air pressure specified for each tire by the standard system including the standard on which the tire is based, for example, "Maximum Air Pressure" for JATMA, "INFLATION PRESSURE" for ETRTO, and the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA. 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 regular internal pressure (250kPa or more) of another tire size (defined in the standard) that is specified with the regular rim as the standard rim, and if multiple regular internal pressures of 250kPa or more are specified, it refers to the smallest value among them.

[0038] "Normal load" refers to the load that is set for each tire in the standard system that includes the standard on which the tire is based. For example, for JATMA, it is "Maximum Load Capacity", for ETRTO, it is "LOAD CAPACITY", and for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES". As with normal rims and normal internal pressures, refer to JATMA, ETRTO, and TRA in that order, and follow the standard if there is an applicable size at the time of reference. 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. TIFF0007670202000001.tif1484V: Virtual volume of tire (mm 3 ) Dt: Tire outer diameter Dt (mm) Ht: Section height of the tire (mm) Wt: tire section width (mm)

[0039] "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 contact area / total contact area) x 100

[0040] "Total contact area" is the area of ​​the tread region obtained from the outline when the tire is pressed against the ground. The total contact area is obtained by mounting a tire to a standard rim, applying standard internal pressure, leaving it at rest for 24 hours at 25°C, 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 is 0°) to transfer the ink. The above transfer process is performed on a total of five places by rotating the tire 72 degrees each time, and the total contact area is calculated by averaging the five areas obtained.

[0041] "Effective contact area" is the area of ​​the tread region where the tire comes into contact with the ground when pressed against it. The effective contact area is measured by mounting a tire to a standard rim, applying standard internal pressure, and leaving it at rest for 24 hours at 25°C, then applying standard load (maximum load capacity) to the tire and pressing it vertically against cardboard (camber angle is 0°) to transfer the ink. The above transfer process is performed on a total of five locations by rotating the tire 72° each time, and the effective contact area is calculated by averaging 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, in a 100% rubber component, when styrene butadiene rubber with a styrene content of 40% by mass is 85% by mass, styrene butadiene rubber with a styrene content of 25% by mass is 5% by mass, and butadiene rubber with a styrene content of 0% by mass is 10% 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 type of 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 in the oil-extended rubber.

[0045] The term "circumferential main 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 4 mm or more. The circumferential main groove may extend linearly in the circumferential direction, or may extend in a wavy, sinusoidal, or zigzag shape in the circumferential direction. However, this does not include the widening circumferential groove described below.

[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. A pair of land portions located on the outermost sides in the tire width direction are called shoulder land portions, and a land portion that exists in the area between the shoulder land portions is called a center land portion. When there is a single circumferential main groove, only shoulder land portions exist, and no center land portion exists.

[0047] The "small hole" is a small hole on the tread surface that extends from the inside of the tread and opens to the tread surface. The small holes exist independently and are 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 shape in the circumferential direction. However, it does not include the widened circumferential groove described below.

[0049] The "widening circumferential groove" is 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 is configured to widen on the inner side in the tire radial direction. The widening circumferential groove may extend linearly in the circumferential direction, or may extend in a wavy, sinusoidal, or zigzag shape 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] "Cis content (cis-1,4-bonded butadiene unit amount) (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 a temperature (tan δ peak temperature) corresponding to a maximum value in the range of -60°C to 40°C on a temperature distribution curve of tan δ measured using a dynamic viscoelasticity measuring device (e.g., Iplexer series manufactured by GABO) under conditions of a frequency of 10Hz, an initial strain of 10%, a dynamic strain of ±0.5%, and a temperature rise rate of 2°C / min. In addition, 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 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 point with the lowest temperature is taken as the glass transition temperature.

[0055] The "weight average molecular weight (Mw)" can be determined based on a measurement value obtained by gel permeation chromatography (GPC) (e.g., GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation) in terms of standard polystyrene.

[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 average 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 short diameter is used as the particle size, and 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 is applied 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] Hereinafter, the pneumatic tire of the present invention will be described with reference to the drawings as appropriate. However, the drawings are merely examples, and the present invention should not be interpreted as being limited based on 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 , where L is the land ratio (%) of the tread surface in the tread portion, 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 and calculated as described above from the total contact area and the effective contact area of ​​the tire.

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

[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, even more preferably 65% ​​or more. The land ratio is preferably 80% or less, more preferably 75% or less, 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 may be, for example, 6,500, 6,000, or 5,000.

[0066] <Formula (2)> In the pneumatic tire of the present invention, the total styrene content (mass%) in the rubber component contained in the rubber composition is A STY Then, 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 xL, but it may be, for example, 750, 700, or 650.

[0068] <Glass transition temperature of rubber composition> In the rubber composition constituting the tread portion of the pneumatic tire of the present invention, the glass transition temperature (°C) of the rubber composition is preferably lower 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 appropriately adjusted by 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 substrate has one or more small holes.

[0072] FIG. 2 shows an embodiment of the pneumatic tire of the present invention having the small hole. In FIG. 2, a small hole 4 is formed on a pair of land portions 3 present in the shoulder region of the tread surface. The small hole contributes to improving drainage, which improves drainage in the shoulder region and contributes to improving wet grip performance. For example, even if one side of the shoulder land portion or the center land portion wears preferentially in actual use and the remaining shoulder land portion hardens over time, it is believed that the small hole ensures drainage and makes it easier to improve wet grip performance after wear. The opening area of ​​the small hole on the tread surface is 0.1 mm 2 More than 0.5mm is preferable 2 More than 1.0mm is more preferable.2 More preferably, 1.5 mm 2 The opening area of ​​the small holes on the tread surface is preferably 15 mm or less. 2 Less than 10mm is preferable 2 Less than 7.0mm is preferable. 2 Less than 5.0 mm is more preferable. 2 It is particularly preferable that the depth of the deepest portion of the small hole is 3% or more, and more preferably 5% or more, of the depth of the deepest portion of the circumferential main groove. Also, it is preferable that the depth of the deepest portion of the small hole is 80% or less, and 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 circumferential narrow groove.

[0074] Fig. 3 shows an embodiment of the 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 region of the tread surface. The circumferential narrow groove contributes to improving drainage, which improves drainage in the shoulder region and contributes to improving wet grip performance.

[0075] <Wide circumferential groove> The pneumatic tire of the present invention preferably has a tread surface having widening 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 passing on the tire centerline. The widened circumferential groove may extend, for example, in a wavy, sinusoidal, or zigzag shape along the circumferential direction. There is no particular restriction on the land portion in which the widened circumferential groove is formed, but it is preferable that the widened circumferential groove is formed on a land portion located on the tire centerline, or, when a circumferential main groove exists on the tire centerline, it is preferable that the widened circumferential groove is formed on a land portion closest to the tire centerline, as in the widened circumferential groove 6 in FIG. 4. The land portion closest to the tire centerline is a land portion in which the distance between the tire width direction inner end of the land portion and the tire centerline is the smallest.

[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 the groove width is not limited to this, and may increase while repeating small increases and decreases in a curved or stepped manner, for example.

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

[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 other rubber components besides BR and SBR, such as isoprene-based rubber (IR-based rubber). Furthermore, the rubber component may be composed of more than 50% by mass of BR and only SBR.

[0081] (SBR) There is no particular limitation on the SBR, 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), etc. can also be used. SBR may be used alone or in combination of two or more types.

[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 mass%, more preferably less than 30 mass%, more preferably 20 mass% or less, and even more preferably 15 mass% or less. There is no particular restriction on the lower limit of the styrene content, but it is usually more than 1 mass%, or more than 3 mass%, or more than 5 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. Also, 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, breaking elongation, and abrasion resistance. The vinyl content of SBR (amount of 1,2-bonded butadiene units) is measured by the above-mentioned measurement method.

[0085] From the viewpoint of suppressing the temperature dependency of the rubber composition, the glass transition temperature (Tg) of SBR is preferably less than -30°C. The Tg of SBR is preferably less than -40°C, more preferably less than -50°C, and further preferably less than -55°C. The Tg is usually greater than -80°C, or 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 crosslinking 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 mass%, more preferably more than 30 mass%, and even more preferably 35 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 mass% or less, more preferably less than 48 mass%, and even more preferably 45 mass% or less.

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

[0089] As the high cis BR, for example, those commercially available from Zeon Corporation, Ube Industries, Ltd., JSR Corporation, etc. can be used. By containing high cis BR, low temperature properties and wear resistance can be improved. 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 spectrum analysis.

[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% 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 LTD. 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 an SPB-containing BR, commercially available products from Ube Industries, Ltd. can be used.

[0092] As the modified BR, a modified butadiene rubber (modified BR) in which the terminals and / or the 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 modified BRs include those obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and further having the terminals of the modified BR molecule bonded with tin-carbon bonds (tin-modified BR), etc. The 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 crosslinking 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 mass% of BR. BR From the viewpoint of wear resistance, A is preferably more than 51% by mass, more preferably more than 53% by mass, and even more preferably 55% by mass or more. 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 a rubber component other than SBR and BR. As the other rubber component, a crosslinkable rubber component generally used in the tire industry can be used, and examples thereof include 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] As the IR rubber, for example, isoprene rubber (IR) and natural rubber, which are common in the tire industry, can be used. In addition to unmodified natural rubber (NR), natural rubber also includes modified natural rubber such as epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), high-purity natural rubber, and grafted natural rubber. One type of isoprene rubber may be used alone, or two or more types may be used in combination.

[0098] The NR is not particularly limited, and any NR 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% by mass, more than 2% by mass, or more than 3% by mass.

[0100] (Total styrene content) Total styrene content (A STY ) is the total content (mass%) of styrene moieties contained in the total amount of the rubber component, as defined above. In the present invention, the total styrene amount in the rubber component is 25 mass% or less. The total styrene amount is preferably less than 20 mass%, more preferably less than 15 mass%, and further preferably less than 10 mass%. The total styrene amount is usually about 3 mass% or more, or 4 mass% or more, or 5 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 may be, for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrated silica), or other silica commonly used in the tire industry. From the viewpoint of environmental load, silica made from biomass materials (for example, amorphous silica purified from rice husks) may be used. Among them, 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 to produce a precipitate of silicon dioxide, which can be obtained by filtering, washing with water, drying, and pulverizing. When silica crystallizes, it does not dissolve in water, and its component silicic acid cannot be used. By controlling the combustion temperature and combustion time, the crystallization of silica in rice husk ash can be suppressed (see JP 2009-2594 A, Akita Prefectural University Web Journal B / 2019, vol. 6, p. 216-222, etc.). Amorphous silica extracted from rice husks can be commercially available from Wilmar Co., Ltd., etc.

[0105] The nitrogen adsorption specific surface area (N2SA) of silica is set at 140m from the viewpoints of fuel efficiency and wear resistance. 2 / g or more is preferable, and 150m 2 / g is more preferable, and 160m 2 More preferably, 175m 2 From the viewpoints of fuel efficiency and processability, it is more preferable that the tensile strength is 350 m 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 more than 10 nm, more preferably more than 12 nm, and even more preferably more 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] 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 even more preferably 100 parts by mass or more, from the viewpoint of wet grip performance, and is preferably less than 200 parts by mass, more preferably less than 150 parts by mass, and even more preferably less than 130 parts by mass, from the viewpoint of abrasion resistance.

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

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

[0110] The average primary particle size of carbon black is preferably more than 10 nm, more preferably more than 12 nm, and even more preferably more 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] In the case where both silica and carbon black are contained, the content of silica is preferably higher than the content of carbon black from the viewpoint of the balance of fuel economy performance, wet grip performance, and abrasion resistance performance. The ratio 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 be used. Such fillers are not particularly limited, and any fillers that have been conventionally and generally 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 viewpoints of fuel economy and elongation at break.

[0115] (Silane coupling agent) Silica is preferably used in combination with a silane coupling agent.Silane coupling agent is not particularly limited, and can be used any silane coupling agent that is conventionally used in combination with silica in the tire industry, such as thioester-based silane coupling agents such as 3-octanoylthio-1-propyltriethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, 3-octanoylthio-1-propyltrimethoxysilane; mercapto-based silane coupling agents such as those shown in the following chemical formula; sulfide-based silane coupling agents such as bis(3-triethoxysilylpropyl) disulfide, bis(3-triethoxysilylpropyl) tetrasulfide; vinyltriethoxysilane, Examples of the silane coupling agents include vinyl trimethoxysilane and the like; amino silane coupling agents such as 3-aminopropyl triethoxysilane, 3-aminopropyl trimethoxysilane, and 3-(2-aminoethyl) aminopropyl triethoxysilane; glycidoxy silane coupling agents such as γ-glycidoxypropyl triethoxysilane and γ-glycidoxypropyl trimethoxysilane; nitro silane coupling agents such as 3-nitropropyl trimethoxysilane and 3-nitropropyl triethoxysilane; chloro silane coupling agents such as 3-chloropropyl trimethoxysilane and 3-chloropropyl triethoxysilane. Among these, thioester silane coupling agents and / or sulfide silane coupling agents are preferred. The silane coupling agents may be used alone or in combination of two or more.

[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 group having 1 to 12 carbon atoms, an alkoxy group 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 group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, an aryl group having 6 to 30 carbon atoms, or an aralkyl group 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 group having 1 to 30 carbon atoms, an alkenyl group having 2 to 30 carbon atoms, or an alkynyl group having 2 to 30 carbon atoms, which may be substituted by a hydroxyl or carboxyl group; 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.)

[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), 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 the compound 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 parts 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 with respect to 100 parts by mass of silica is preferably more than 1.0 parts 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 increasing the dispersibility of silica.Furthermore, 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 a hydrocarbon resin, oil, liquid rubber, or an ester-based plasticizer.

[0122] (Hydrocarbon resin) The term "hydrocarbon resin" refers to a polymer having a skeleton formed by hydrocarbons, which is solid at 25°C. The hydrocarbon resin may generally contain an oxygen element derived from a carboxyl group, a hydroxyl group, coumarone, or the like. The hydrocarbon resin is not particularly limited, but examples thereof include petroleum resins, terpene resins, rosin resins, and phenol resins commonly used in the tire industry. As the hydrocarbon resin, for example, commercially available products from Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Tosoh Corporation, Rutgers Chemicals, BASF, Clayton, Eastman Chemical Co., Nitto Chemical Co., Ltd., LUHUA, Nippon Shokubai Co., Ltd., ENEOS Corporation, Arakawa Chemical Industries Co., Ltd., Taoka Chemical Co., Ltd., and the like can be used. The hydrocarbon resin may be used alone or in combination of two or more types.

[0123] <Petroleum resin> As the petroleum resin, C5 petroleum resin, aromatic petroleum resin, C5C9 petroleum resin, etc. can be used. 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 may be hydrogenated or modified. As a C5 petroleum resin, dicyclopentadiene resin (DCPD resin) is preferably used.

[0125] Aromatic petroleum resin refers to a resin obtained by polymerizing a C9 fraction, and may be a hydrogenated or modified resin. 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 the terpene resin include polyterpene resins consisting of at least one selected from terpene compounds such as α-pinene, β-pinene, limonene, and dipentene; aromatic modified terpene resins made from the terpene compounds and aromatic compounds; terpene phenolic resins made from terpene compounds and phenolic compounds; and those obtained by subjecting these terpene resins to hydrogenation treatment (hydrogenated terpene resins). Examples of aromatic compounds that are raw materials for aromatic modified terpene resins include styrene, α-methylstyrene, vinyltoluene, and divinyltoluene. Examples of phenolic compounds that are raw materials for terpene phenolic resins include phenol, bisphenol A, cresol, and xylenol. The 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 natural resin rosin through hydrogenation, disproportionation, dimerization, esterification, etc. The rosin-based resins may be used alone or in combination of two or more kinds.

[0130] <Phenol-based resin> The phenol-based 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 phenol-based resin may be used alone or in combination of two or more kinds.

[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. 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. Moreover, 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 measuring method using a differential scanning calorimeter.

[0133] ≪Weight average molecular weight (Mw)≫ The Mw of the hydrocarbon resin is preferably more than 500, more preferably more than 600, and even more preferably more than 650, from the viewpoint of being less likely to volatilize and having good grip. In addition, 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 being easily entangled with the polymer and less likely to come off, and therefore having excellent dry grip. By having the Mw within the above range, the rubber composition obtained has excellent processability, and the heat build-up and elongation at break can be improved. The Mw is measured by the above-mentioned measurement method.

[0134] ≪Content≫ From the viewpoint of wet grip performance, the rubber composition according to the present invention preferably contains at least one type of 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, 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 the oil include process oil, vegetable oil, and animal oil. Examples of the process oil include paraffin-based process oil, naphthenic process oil, and aromatic process oil. In addition, as an environmental measure, process oil with a low content of polycyclic aromatic compound (PCA) compounds can be used. Examples of the low PCA content process oil include light 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. Also, 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 content of oil 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. The liquid rubber may be used alone or in combination of two or more kinds.

[0138] When the 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 even more preferably more than 5 parts by mass. The content of the liquid rubber is preferably less than 50 parts by mass, more preferably less than 40 parts by mass, and even 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 appropriately contain compounding agents 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 the processing aid include fatty acid metal salts, fatty acid amides, amide esters, silica surfactants, fatty acid esters, mixtures of fatty acid metal salts and amide esters, mixtures of fatty acid metal salts and fatty acid amides, etc. The processing aids may be used alone or in combination of two or more. Examples of the processing aids that can be used include those commercially available from Schill+Seilacher, Performance Additives, etc.

[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 parts 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 speed.

[0146] (wax) When the wax 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 1.0 parts 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 antiaging agent is not particularly limited, but examples thereof include amine-based, quinoline-based, quinone-based, phenol-based, and imidazole-based compounds, and carbamic acid metal salts, and the like. Phenylenediamine-based antiaging agents 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 antiaging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline are preferred. The antiaging agent 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 parts 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) As the vulcanizing agent, sulfur is preferably used. As the sulfur, powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur, etc. can be used. The vulcanizing agent may be used alone or in combination of two or more kinds.

[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 sufficient vulcanization reaction. Also, from the viewpoint of preventing deterioration, it 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. Note that, when oil-containing sulfur is used as a vulcanizing agent, the content of the vulcanizing agent is the total content of the pure sulfur contained in the oil-containing sulfur.

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

[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, or xanthate-based vulcanization accelerators, etc. The vulcanization accelerators may be used alone or in combination of two or more.

[0153] Among them, 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 them, N-cyclohexyl-2-benzothiazolylsulfenamide (CBS) is preferred.

[0155] Examples of the guanidine vulcanization accelerator 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 them, 1,3-diphenylguanidine (DPG) is preferable.

[0156] Examples of the thiazole-based 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 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 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 composition 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 (Banbury mixer, kneader, etc.).

[0159] The kneading step includes, for example, a base kneading step in which compounding ingredients and additives other than the vulcanizing agent and the vulcanization accelerator are kneaded, and a final kneading (F kneading) step in which the vulcanizing agent and the 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 a plurality of steps as desired.

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

[0161] The pneumatic tire of the present invention can be manufactured by a normal 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 normal method to form an unvulcanized tire, and heating and pressurizing the unvulcanized tire in a vulcanizer. The vulcanization conditions are not particularly limited, and examples thereof 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 that are intended to be mounted on automobiles that run on four wheels, and refer to tires with a maximum load capacity of 1000 kg or less according to the JATMA standard, and 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 which winter tires and studless tires used at low temperatures are preferred. EXAMPLES

[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 mass%, vinyl content: 20 mol%, Tg: -60°C, Mw: 800,000) SBR3: Styrene butadiene rubber synthesized in Production Example 2 below (modified S-SBR, styrene content: 15 mass%, vinyl content: 30 mol%, 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 ends are modified with a mixture of tetraglycidyl-1,3-bisaminomethylcyclohexane and its oligomer components, vinyl content: 12 mol%, cis content: 36 mass%, Tg: -90°C, Mw: 550,000) CB (Carbon Black): Show Black N134 (N2SA: 148m) manufactured by Cabot Japan Co., Ltd. 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 VivaTec500 (TDAE oil) Hydrocarbon resin 1: Sylvatraxx 4401 manufactured by Kraton (aromatic vinyl resin (copolymer of styrene and α-methylstyrene), Mw: 700, softening point: 85°C, Tg: 34°C) Hydrocarbon resin 2: ExxonMobil PR395 (C5C9 resin, Mw: 880, softening point: 117.8°C, Tg: 68°C) Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Beads of stearic acid camellia manufactured by NOF Corporation Wax: Sannock N manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Anti-aging agent 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: Noccelaer D (DPG, 1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

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

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

[0168] [Examples and Comparative Examples] According to the compounding recipe shown in each table, chemicals other than sulfur and vulcanization accelerator are kneaded for 1 to 10 minutes using a 1.7L closed type Banbury mixer until the discharge temperature reaches 150 to 160 ° C. to obtain a kneaded product. Next, sulfur and vulcanization accelerator are added to the kneaded product obtained using a two-axis open roll, and kneaded for 4 minutes until the temperature reaches 105 ° C. to obtain an unvulcanized rubber composition. Using the obtained unvulcanized rubber composition, it is molded according to the shape of a predetermined tread according to each table, and laminated together with other tire components to prepare an unvulcanized tire, which is press-vulcanized for 12 minutes under the condition of 170 ° C. to obtain each test tire (Tire 1: 225 / 60R16 98H, Tire 2: 275 / 55R20 117T XL).

[0169] The tread surface of each test tire has at least a circumferential main groove and a lateral groove. There are three circumferential main grooves, one of which runs on the tire centerline, and the remaining two are installed at equal intervals on the outer side in the tire width direction from the main groove running on the tire centerline. There are no small holes, circumferential narrow grooves, or widened circumferential grooves.

[0170] <Evaluation> For each test tire, the results measured by the following methods are also given in the corresponding columns of the table below.

[0171] (Rand) For each test tire, the total contact area and the 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: domestic FF vehicle, 2000cc displacement; Tire 2: domestic 4WD vehicle, 3000cc displacement) and driven on a test course with a wet asphalt surface at a speed of 100km / h. The grip performance during the drive was evaluated on a scale of 1 to 5 by 20 test drivers, and a total score was calculated. The results were expressed as an index, with the standard comparative example being 100. A higher index indicates better driving 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 FF vehicle, 2000cc displacement; Tire 2: Japanese-made 4WD vehicle, 3000cc displacement) and driven 20,000km on an asphalt test course when the outside temperature was below 10°C, and the amount of reduction in tread thickness from the start of the drive was measured. The results were expressed as an index, with the reference comparative example being set at 100. The higher the index, the less the amount of reduction and the better the low-temperature wear resistance.

[0174] [Table 1]

[0175] [Table 2]

[0176] [Embodiment] The following are preferred embodiments.

[0177] [1] A pneumatic tire having a tread portion, the tread portion is composed 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 further preferably 90 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 styrene content in the rubber component is 25% by mass or less, The content (mass%) of the butadiene rubber in the rubber component is A BR , where L is the land ratio (%) of the tread surface of the tread portion, A BR A pneumatic tire in which and L satisfy the following formula: (1) A BR ×L>3000 [2] The total styrene content (% by mass) is A STY Then, 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 type of 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 per 100 parts by mass of the rubber component is more than 70 parts by mass, preferably not less than 80 parts by mass, more preferably not less than 90 parts by mass, and even more preferably not less than 100 parts by mass. [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 pores is less than 70 mass %, preferably less than 65 mass %, and more preferably less than 60 mass %. [9] The pneumatic tire according to any one of [1] to [8], wherein the styrene-butadiene rubber has a glass transition temperature of 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 , and 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 defined as shoulder land portions, the shoulder land portions having at least one circumferential narrow groove.

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

[11] , wherein the tread surface has a widening circumferential groove whose groove width is wider 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 centerline, or in the case where a circumferential main groove is present on the tire centerline, in the land portion closest to the tire centerline. [Explanation of symbols]

[0178] CL··Tire center line Te Tread edge W: Tire width direction C Tire circumferential direction 1. Tires 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 styrene content in the rubber component is 25% by mass or less, The tread surface of the tread portion has a widening circumferential groove whose groove width is wider on the inner side in the tire radial direction, The widened circumferential groove is present in a land portion located on a tire centerline, or in a case where a circumferential main groove is present on the tire centerline, in a land portion closest to the tire centerline, 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 Then, A BR , L and A STY The pneumatic tire according to claim 1 , wherein (2) (A BR / A STY )×L>130

3. 3. The pneumatic tire according to claim 1, wherein the rubber composition comprises 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 or 2, wherein a 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 or 2, wherein the rubber composition has a glass transition temperature of lower than -30°C.

6. The pneumatic tire according to claim 1 or 2, 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 3,500.

8. The content A of the butadiene rubber in the rubber component BR The pneumatic tire according to claim 1 or 2, wherein the content of the cyclic alkyl ether in the cyclic alkyl ether is less than 70 mass %.

9. The pneumatic tire according to claim 1 or 2, 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 a 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 3. 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 a tire circumferential direction and land portions defined by the circumferential main grooves, The pneumatic tire according to claim 1 or 2, wherein a pair of land portions located outermost in the tire width direction among the land portions are defined as shoulder land portions, and the shoulder land portions have at least one circumferential narrow groove.

Images