RUBBER COMPOSITION FOR SIDE RUNNING SURFACE

Abstract

A rubber composition for a sidewall tread is provided that can provide satisfactorily maintained hardness and tensile strength, as well as improved low heat buildup (tan δ (60°C)), while suppressing a decrease in elongation at break over time of the rubber composition stored in the unvulcanized state, and that can provide these performances in a fairly balanced and highly compatible manner. The composition contains a diene-based rubber comprising 35 to 55 mass% of an isoprene rubber and 45 to 65 mass% of a butadiene rubber, silica with a specific CTAB adsorption surface area of ​​60 m². 2 / g up to 100 m 2 / g, carbon black with a specific CTAB adsorption surface of 30 m 2 / g up to 100 m 2 / g, a sulfur-containing silane coupling agent, and a guanidine-based vulcanization accelerator. The blended amount of silica is 5 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the diene-based rubber, and the sum of the blended amounts of silica and carbon black is less than 55 parts by mass per 100 parts by mass of the diene-based rubber. The ratio Ma / Ms of the blended amount of the guanidine-based vulcanization accelerator Ma to the blended amount Ms of the silica is 0.02 to 0.08.

Description

Technical area

[0001] The present invention relates to a rubber composition for a side tread intended mainly for use in a side tread of a tire. State of the art

[0002] To reduce environmental impact, there is still hope for improving the fuel efficiency of pneumatic tires during driving. To this end, heat generation in the rubber composition that makes up the individual parts of the pneumatic tire is suppressed. To further reduce fuel consumption, for example, in recent years, research has been conducted into suppressing heat generation in a rubber composition that forms the side tread rubber layer of the pneumatic tire (side tread rubber composition).

[0003] As an indicator of the heat generation of a rubber composition, tan δ at 60°C (hereinafter referred to as "tan δ (60°C)") obtained from dynamic viscoelasticity measurement is typically used. A smaller tan δ (60°C) of the rubber composition indicates lower heat generation. Examples of methods for reducing tan δ (60°C) of a rubber composition include reducing the blended amount of a filler such as carbon black and increasing the particle size of the carbon black. Alternatively, blending silica with a large particle size has also been proposed (see, for example, Patent Document 1). However, these methods cannot always provide sufficient rubber hardness, and there is also concern about an impact on the tensile strength required for a rubber composition for a sidewall tread.Furthermore, there is a risk of deterioration of the rubber composition over time (especially a decrease in elongation at break). Therefore, further measures to improve low heat generation (tan δ (60°C)) were expected for a rubber composition for a sidewall tread, which satisfactorily maintains hardness and tensile strength, and suppresses the decrease in elongation at break over time. Literature listPatent literature

[0004] Patent Document 1: JP 2013-001889 A Brief description of the inventionTechnical problem

[0005] An object of the present invention is to provide a rubber composition for a sidewall tread which offers satisfactorily maintained hardness and tensile strength and improved low heat build-up (tan δ (60°C)) while suppressing a decrease in elongation at break with time of the rubber composition stored in the unvulcanized state, and which can provide these performances in a balanced and highly compatible manner. Solution to the problem

[0006] A rubber composition for a sidewall tread according to an embodiment of the present invention for achieving the above-described object is a rubber composition for a sidewall tread comprising a diene-based rubber containing 35 mass% to 55 mass% of an isoprene-based rubber and 45 mass% to 65 mass% of a butadiene rubber; silica having a CTAB specific adsorption surface area of ​​60 m 2 / g up to 100 m 2 / G; carbon black with a specific CTAB adsorption surface of 30 to 100 m 2 / g; a sulfur-containing silane coupling agent; and a guanidine-based vulcanization accelerator, wherein the blended amount of the silica is 5 parts by mass or more and 50 parts by mass or less, and the total amount of the blended amounts of the silica and the carbon black is less than 55 parts by mass per 100 parts by mass of the diene-based rubber, and the ratio Ma / Ms of the blended amount Ma of the guanidine-based vulcanization accelerator to the blended amount Ms of the silica is 0.02 to 0.08. Advantageous effects of the invention

[0007] The rubber composition for a sidewall tread according to one embodiment of the present invention has the above-described formulation and can thus provide satisfactorily maintained hardness and tensile strength, as well as improved low heat buildup, while suppressing a decrease in elongation at break over time, and can provide these performances in a balanced and highly compatible manner. Specifically, tan δ (60°C) can be reduced and low heat buildup can be improved by using large-particle silica with a CTAB specific adsorption surface area of ​​60 m². 2 / g up to 100 m 2 / g is used. Furthermore, the reduction of tan δ (60°C) (improvement of low heat generation) is also expected from the viewpoint that the blending ratio of the large-particle silica and carbon black is adjusted as described above. On the other hand, if the guanidine-based vulcanization accelerator is blended as a vulcanization accelerator in an appropriate amount relative to the silica, it is possible to ensure satisfactory maintenance of hardness and tensile strength and suppress a decrease in elongation at break over time.Through the interaction of these factors, it is possible to ensure satisfactory maintenance of hardness and tensile strength and improved low heat generation while suppressing a reduction in elongation at break over time, thereby advantageously achieving the physical properties required for a side tread rubber layer.

[0008] In the present invention, it is preferable that the butadiene rubber contains a butadiene rubber synthesized with a neodymium-based catalyst and optionally a terminal-modified butadiene rubber for silica. At this time, it is preferable that the proportion of the butadiene rubber synthesized with the neodymium-based catalyst contained in the butadiene rubber is 69 to 100 mass%, the proportion of the terminal-modified butadiene rubber for silica is 0 to 31 mass%, and the proportion of the blended amount of the terminal-modified butadiene rubber for silica per 100 mass% of the diene-based rubber is less than 20 mass%.When the butadiene rubber synthesized with the neodymium-based catalyst and the terminal-modified butadiene rubber for silica are contained in this manner, it is advantageous to provide satisfactorily maintained hardness and tensile strength and improved low heat build-up while suppressing a decrease in elongation at break with time.

[0009] In the present invention, it is preferable that an additional vulcanization accelerator other than a guanidine-based vulcanization accelerator be blended, and that the ratio Ma / Mt of the blended amount Ma of the guanidine-based vulcanization accelerator to a total amount Mt of the vulcanization accelerators including the guanidine-based vulcanization accelerator and the additional vulcanization accelerator be 0.2 to 0.5. The blended amount Ma of the guanidine-based vulcanization accelerator is preferably 0.5 parts by mass or more per 100 parts by mass of the diene-based rubber.By blending an appropriate amount of the guanidine-based vulcanization accelerator in this way, it is possible to achieve improved low heat build-up while suppressing a reduction in elongation at break over time of the rubber composition stored in the unvulcanized state and to provide these performances quite balanced.

[0010] The tread rubber composition according to an embodiment of the present invention can be suitably used in a side tread rubber layer of a tire. A tire having a side tread rubber layer made of the side tread rubber composition according to an embodiment of the present invention can satisfactorily maintain the hardness and tensile strength required for the side tread rubber layer, and exhibits reduced rolling resistance and improved fuel efficiency, while suppressing a decrease in elongation at break over time due to the excellent physical properties of the side tread rubber composition according to an embodiment of the present invention. Brief description of the drawings Fig.1 is a meridian cross-sectional view illustrating an example of a pneumatic tire using a rubber composition for a side tread according to an embodiment of the present invention. Description of embodiments

[0011] Configurations of embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0012] As in Fig. 1, a pneumatic tire using the rubber composition for a side tread according to an embodiment of the present invention includes a tread portion 1, a pair of sidewall portions 2 each disposed on both sides of the tread portion 1, and a pair of bead portions 3 each disposed on an inner side of the pair of sidewall portions 2 in a tire radial direction. "CL" in Fig.1 denotes a tire equator. Although in Fig. 1, which is a meridian cross-sectional view, not illustrated, the tread portion 1, the sidewall portions 2, and the bead portions 3 each extend in the tire circumferential direction and form an annular shape. This forms an annular basic structure of the pneumatic tire. Although the description using Fig. 1 is essentially based on the illustrated meridian cross-section, all tire components subsequently extend in the tire circumferential direction and form the ring shape.

[0013] A carcass layer 4 is arranged between the pair of left and right bead portions 3. The carcass layer 4 has a plurality of reinforcing cords extending in the tire radial direction and is folded back from the inside to the outside in the tire width direction around a bead core 5 arranged in each of the bead portions 3. A bead filler 6 is arranged on the circumference of the bead core 5, and the bead filler 6 is enclosed by a body portion and a folded-back portion of the carcass layer 4. On the other hand, on an outer peripheral side of the carcass layer 4, a plurality of belt layers 7 (two layers in Fig.1) is embedded in the tread portion 1. The belt layers 7 each include a plurality of reinforcing cords inclined with respect to the tire circumferential direction and arranged such that the reinforcing cords of the different layers intersect each other. In these belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set in a range of, for example, 10° to 40°. Further, a belt reinforcing layer 8 (two layers including a full cover 8a covering an entire width of the belt layer 7 and an edge cover 8b covering one end of the belt layer 7) is arranged on an outer peripheral side of the belt layer 7. The belt reinforcing layer 8 includes organic fiber cords oriented in the tire circumferential direction.In the belt reinforcing layer 8, the angle with respect to the tire circumferential direction in the organic fiber cord is set to, for example, 0° to 5°.

[0014] A tread rubber layer 10 is disposed on the outer peripheral side of the carcass layer 4 in the tread portion 1. A side tread rubber layer 20 is disposed on the outer peripheral side (outer in the tire width direction) of the carcass layer 4 in each of the sidewall portions 2. A rim cushion rubber layer 30 is disposed on the outer peripheral side (outer in the tire width direction) of the carcass layer 4 in each of the bead portions 3. The rubber composition for a side tread according to an embodiment of the present invention is used for the side tread rubber layer 11 of the tire as described above. Accordingly, the basic structure of other portions is not limited to the structure described above.It should be noted that, unlike the tread rubber layer 10, which comes into contact with the road surface, and the rim cushion rubber layer 30, which comes into contact with the rim (not shown), the side tread rubber layer 20 is the part of the tire subjected to the greatest flexion during driving and therefore must have excellent elongation at break (flexion fatigue resistance). Furthermore, the side tread rubber layer must have excellent cut resistance because the layer is frequently exposed to external damage.

[0015] The tire using the sidewall tread rubber composition according to an embodiment of the present invention is preferably a pneumatic tire (a tire inflated with air, an inert gas such as nitrogen, or another gas in its inner region), but may also be a non-inflatable tire. In the case of a non-inflatable tire, the sidewall tread rubber composition according to an embodiment of the present invention may be used in a portion located between a portion in contact with the road surface (portion corresponding to the tread rubber layer 10 in a pneumatic tire) and a portion in contact with a rim when the tire is mounted on the rim without air inflation (portion corresponding to the rim cushion rubber layer 30 in a pneumatic tire).

[0016] In the rubber composition for a sidewall tread according to one embodiment of the present invention, the rubber component is diene-based rubber and always contains isoprene-based rubber and butadiene rubber. As the butadiene rubber, butadiene rubber polymerized using a neodymium-based catalyst (hereinafter sometimes referred to as Nd-BR) is suitable. Alternatively, Nd-BR and a terminal-modified butadiene rubber for silica described below are preferably used in combination. The use of isoprene-based rubber and butadiene rubber (especially Nd-BR and terminal-modified butadiene rubber for silica) in this way is advantageous for improving tensile strength, low heat buildup, and fatigue resistance.

[0017] Examples of isoprene-based rubbers include various natural rubbers, epoxidized natural rubbers, and various synthetic polyisoprene rubbers. Of these isoprene-based rubbers, natural rubber is particularly well-suited. The blended amount of the isoprene-based rubber is in the range of 35 to 55 mass%, preferably 37.5 to 52.5 mass%, and more preferably 40 to 50 mass%, per 100 mass% of the diene-based rubber. When such an amount of the isoprene-based rubber is blended, tensile strength and fatigue resistance can be improved in a balanced manner. If the blended amount of the isoprene rubber is less than 35 mass%, the tensile strength decreases. If the blended amount of the isoprene-based rubber is more than 55 mass%, the fatigue resistance deteriorates.

[0018] As the butadiene rubber, a rubber generally used in rubber compositions for tires, such as unmodified butadiene rubber and modified butadiene rubber, can be used. However, from the viewpoint of improving heat build-up, the use of butadiene rubber (Nd-BR) polymerized with a neodymium-based catalyst as described above is suitable. The blended amount of the butadiene rubber is in the range of 45 to 65 mass%, preferably 47.5 to 62.5 mass%, and more preferably 50 to 60 mass%, per 100 mass% of the diene-based rubber. When such an amount of the butadiene rubber is blended, tensile strength and fatigue resistance can be improved in a balanced manner. If the blended amount of the polybutadiene rubber is less than 45 mass%, fatigue resistance decreases.If the blended amount of polybutadiene rubber is more than 65 mass%, the tensile strength deteriorates.

[0019] Nd-BR, which is suitably used in the present invention, is a known material and is butadiene rubber polymerized using a neodymium-based catalyst such as a simple neodymium substance, a compound of neodymium and another metal, or an organic neodymium compound. The butadiene rubber synthesized with these neodymium-based catalysts has properties such as a high molecular weight and a sharp molecular weight distribution. A commercially available product can be used as the Nd-BR, and examples include Buna CB22 and Buna CB24 available from ARLANXEO. When the butadiene rubber is polymerized using a neodymium-based catalyst as described above, the low heat generation can be improved more effectively than with butadiene rubber polymerized using another catalyst (e.g., nickel or cobalt).

[0020] When Nd-BR is used as the butadiene rubber, the specific type of Nd-BR is not particularly limited, but one having a vinyl content of preferably 0 mass% to 1 mass%, more preferably 0 mass% to 0.8 mass%, and even more preferably 0 mass% to 0.5 mass% can be used. Suppressing the vinyl content to a low level in this way advantageously improves low heat generation. If the vinyl content in Nd-BR exceeds 1 mass%, the effect of improving low heat generation cannot be sufficiently expected. Note that the vinyl content of the butadiene rubber (Nd-BR) is measured by infrared spectroscopy (Hampton method). The increase or decrease of the vinyl content in the butadiene rubber can be appropriately adjusted by a conventional method such as changing the catalyst type (specific type of neodymium-based catalyst).

[0021] When Nd-BR is used as the butadiene rubber, the blended amount thereof is from 69 mass% to 100 mass%, preferably from 73 mass% to 100 mass%, and more preferably from 77 mass% to 100 mass%, per 100 mass% of the butadiene rubber. For example, when the blended amount of the butadiene rubber is 65 mass% in 100 mass% of the diene-based rubber, the blended amount of Nd-BR is from 45 mass% to 65 mass%, preferably from 47.5 mass% to 65 mass%, and more preferably from 50 mass% to 65 mass%, per 100 mass% of the diene-based rubber. When such an amount of Nd-BR is blended, low heat generation can be effectively improved. When the blended amount of Nd-BR is less than 69 mass% per 100 mass% of butadiene rubber, the fatigue resistance decreases.

[0022] In the present invention, terminal-modified butadiene rubber for silica can be used in combination with the above-described Nd-BR as the butadiene rubber. The terminal-modified butadiene rubber for silica is a butadiene rubber in which both or one molecular terminals are modified with a functional group having reactivity with a silanol group on a surface of the silica. Examples of the functional group that reacts with a silanol group preferably include at least one type selected from a polyorganosiloxane group, a hydroxyl group-containing polyorganosiloxane structure, an alkoxysilyl group, a hydroxyl group, an aldehyde group, a carboxyl group, an amino group, an imino group, an epoxy group, an amide group, a thiol group, and an ether group.Of these, the polyorganosiloxane group, the hydroxyl group-containing polyorganosiloxane structure, the alkoxysilyl group, the hydroxyl group, and the amino group are preferred. A combination of several of these functional groups (e.g., two types including the amino group and the alkoxysilyl group) may be used. When at least one type of terminal-modified butadiene rubber for silica is included as the butadiene rubber, the affinity for silica with the large particle size described below becomes good, and it is advantageous to improve low heat generation while satisfactorily maintaining hardness and tensile strength and suppressing the decrease in elongation at break over time.

[0023] When a terminal-modified butadiene rubber for silica is used as the butadiene rubber, the blended amount thereof is from 0 mass% to 31 mass%, preferably from 0 mass% to 27 mass%, and more preferably from 0 mass% to 23 mass%, per 100 mass% of the butadiene rubber. However, the blended amount of the terminal-modified butadiene rubber for silica is set to less than 20 mass% per 100 mass% of the diene-based rubber. For example, when the blended amount of the butadiene rubber is 65 mass% in 100 mass% of the diene-based rubber, the blended amount of the terminal-modified butadiene rubber for silica is from 0 mass% or more and less than 20 mass%, preferably from 0 mass% to 17.5 mass%, and more preferably from 0 mass% to 15 mass% per 100 mass% of the diene-based rubber.When such an amount of terminal-modified butadiene rubber is blended for silica, the affinity for silica with a large particle size can be sufficiently ensured as described below, and it is advantageous to improve low heat generation while satisfactorily maintaining hardness and tensile strength and suppressing a decrease in elongation at break over time. If the blended amount of terminal-modified butadiene rubber for silica is more than 31 mass% per 100 mass% of the butadiene rubber, the elongation at break deteriorates.

[0024] The rubber composition for a sidewall tread according to one embodiment of the present invention may contain, in addition to the isoprene-based rubber and the above-described butadiene rubber (Nd-BR, terminal-modified butadiene rubber for silica), another diene-based rubber. As such another diene-based rubber, a rubber generally used in rubber compositions for tires can be used. Examples include styrene-butadiene rubber. These other diene-based rubbers can be used alone or as a blend.

[0025] In one embodiment of the present invention, silica and carbon black are always blended as fillers into the diene-based rubber described above. As the silica used in one embodiment of the present invention, silica typically used for rubber compositions for tires, such as wet silica, dry silica, or surface-treated silica, can be used. However, silica with a specific CTAB adsorption surface area of ​​60 m² is always used. 2 / g up to 100 m 2 / g, preferably 65 m 2 / g up to 95 m 2 / g and more preferably 70 m 2 / g up to 90 m 2 / g is used. When silica with a large particle size is used in this way, the tan δ (60°C) can be reduced and the low heat generation can be improved. If the specific CTAB adsorption surface of silica is less than 60 m 2 / g, the tensile strength decreases. If the specific CTAB adsorption surface of the silica is more than 100 m 2 / g, the low heat generation deteriorates. As long as the silica meets the conditions described above, silica can be appropriately selected and used from commercially available products, or silica obtained through a conventional manufacturing process can be used.

[0026] The blended amount Ms of silica is 5 parts by mass or more and 50 parts by mass or less, preferably from 10 parts by mass to 45 parts by mass, and more preferably from 15 parts by mass to 40 parts by mass, per 100 parts by mass of the diene-based rubber. When silica is blended in an appropriate amount in this way, low heat buildup can be effectively improved. A blended amount Ms of silica of less than 5 parts by mass reduces the tensile strength. A blended amount Ms of silica exceeding 50 parts by mass deteriorates the low heat buildup.

[0027] As the carbon black used in one embodiment of the present invention, among carbon black commonly used in rubber compositions for tires, carbon black having a CTAB specific adsorption surface area of ​​30 m 2 / g up to 100 m 2 / g, preferably 30 m 2 / g up to 85 m 2 / g, and more preferably 30 m2 / g up to 70 m 2 / g. The use of such carbon black is advantageous in improving low heat generation, while advantageously maintaining hardness and tensile strength and suppressing a decrease in elongation at break over time. If the specific CTAB adsorption surface of carbon black is less than 30 m 2 / g, the tensile strength decreases. If the specific CTAB adsorption surface of the carbon black is more than 100 m 2 / g, the low heat development decreases.

[0028] In one embodiment of the present invention, silica and carbon black are always used as described above. The sum (Ms + Mc) of the blended amount Ms of silica and the blended amount Ms of carbon black is preferably less than 55, preferably 20 parts by mass or more, and less than 55 parts by mass, and more preferably from 25 parts by mass to 50 parts by mass, per 100 parts by mass of the diene-based rubber described above. When silica and carbon black are blended in appropriate amounts in this way, it is possible to improve low heat generation while advantageously maintaining hardness and tensile strength and suppressing a decrease in elongation at break with time. When the sum of the blended amounts of silica and carbon black is 55 parts by mass or more, low heat generation decreases.It should be noted, however, that the blended amount of the carbon black alone is not particularly limited, but is preferably from 5 parts by mass to 30 parts by mass, and more preferably from 5 parts by mass to 25 parts by mass per 100 parts by mass of the diene-based rubber.

[0029] The rubber composition according to one embodiment of the present invention may also include inorganic fillers other than silica and carbon black. Examples of the additional filler include materials typically used for rubber compositions for tires, such as clay, talc, calcium carbonate, mica, and aluminum hydroxide.

[0030] In the rubber composition for a sidewall tread according to an embodiment of the present invention, a sulfur-containing silane coupling agent is always blended when blending the above-described silica. When blending the sulfur-containing silane coupling agent, the dispersibility of the silica in the diene-based rubber can be improved. Examples of the sulfur-containing silane coupling agent include bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, 3-trimethoxysilylpropylbenzothiazoletetrasulfide, γ-mercaptopropyltriethoxysilane, and 3-octanoylthiopropyltriethoxysilane. Of these, those having a tetrasulfide bond in the molecule can be used particularly suitably. The blended amount of the silane coupling agent is preferably in the range of less than 10 mass% and more preferably from 3 mass% to 9 mass% with respect to the blended amount of the silica.If the blended amount of the silane coupling agent is 10 mass% or more per blended amount of the silica, the silane coupling agent condenses, and thus the desired hardness and strength of the rubber composition cannot be achieved.

[0031] A vulcanization accelerator is always blended into the rubber composition for a tread according to one embodiment of the present invention. A vulcanization accelerator typically used for rubber compositions for tires can be used as the vulcanization accelerator, and examples include a guanidine-based vulcanization accelerator, a sulfenamide-based vulcanization accelerator, and a thiuram-based vulcanization accelerator. However, since the large particle size silica is blended as described above in the present invention, the guanidine-based vulcanization accelerator is always blended therein.That is, although the vulcanization rate tends to decrease by blending silica with a large particle size, vulcanization can be accelerated by blending the guanidine-based vulcanization accelerator, which is beneficial for achieving desired rubber physical properties. Furthermore, in the present invention, by blending the guanidine-based vulcanization accelerator, it is possible to suppress the deterioration of the rubber composition in the unvulcanized state over time during storage (decrease in elongation at break over time). Note that vulcanization accelerators other than the guanidine-based vulcanization accelerator can optionally be used in combination.In a case where two kinds of vulcanization accelerators are used, examples of the vulcanization accelerator that can be combined with the guanidine-based vulcanization accelerator include a sulfenamide-based vulcanization accelerator and a thiuram-based vulcanization accelerator, and of these, the sulfenamide-based vulcanization accelerator can be suitably used.

[0032] Examples of guanidine-based vulcanization accelerators include diphenylguanidine and di-ortho-tolylguanidine. Examples of sulfenamide-based vulcanization accelerators include N,N-dicyclohexyl-1,3-benzothiazole-2-sulfenamide (DZ), N-cyclohexyl-2-benzothiazole-sulfenamide (CZ), N-oxydiethylene-2-benzothiazole-sulfenamide (OBS), and N-(tert-butyl)benzothiazole-2-sulfenamide (NS). Examples of thiuram-based vulcanization accelerators include tetramethylthiuram monosulfide and tetramethylthiuram disulfide.

[0033] When the guanidine-based vulcanization accelerator is blended, the ratio Ma / Ms of the blended amount Ma of the guanidine-based vulcanization accelerator to the blended amount Ms of the silica is set to 0.02 to 0.08, preferably 0.02 to 0.07, and more preferably 0.03 to 0.06. Therefore, blending an appropriate amount of the guanidine-based vulcanization accelerator with the above-described large particle size silica is advantageous for suppressing a decrease in the elongation at break of the rubber composition in the unvulcanized state over time. If the ratio Ma / Ms of the blended amount Ma of the guanidine-based vulcanization accelerator to the blended amount Ms of the silica is less than 0.02, elongation at break may occur over time when the rubber composition is stored in the unvulcanized state.If the ratio Ma / Ms of the blended amount Ma of the guanidine-based vulcanization accelerator to the blended amount Ms of the silica exceeds 0.08, the hardness cannot be maintained optimally and the low heat generation also deteriorates.

[0034] In a case where a vulcanization accelerator includes the guanidine-based vulcanization accelerator and an additional vulcanization accelerator other than the guanidine-based vulcanization accelerator (other vulcanization accelerator), a ratio Ma / Mt of the blended amount Ma of the guanidine-based vulcanization accelerator to a total amount Mt of the vulcanization accelerators (sum of the blended amount Ma of the guanidine-based vulcanization accelerator and a blended amount of the additional vulcanization accelerator per 100 parts by mass of the diene-based rubber) is preferably 0.2 to 0.5, more preferably 0.25 to 0.5, and even more preferably 0.3 to 0.5. In order to improve low heat generation, it is advantageous to blend an appropriate amount of the guanidine-based vulcanization accelerator with respect to the total amount of the vulcanization accelerators.If the Ma / Mt ratio is less than 0.2, the elongation at break may decrease when the rubber composition is stored in the unvulcanized state. If the Ma / Mt ratio exceeds 0.5, tan δ (60°C) deteriorates, and the effect of improving low heat buildup is limited.

[0035] Furthermore, when blending the guanidine-based vulcanization accelerator, the blended amount Ma thereof is preferably 0.5 parts by mass or more, more preferably in the range of 0.5 parts by mass to 2 parts by mass, and even more preferably in the range of 0.5 parts by mass to 1.5 parts by mass, per 100 parts by mass of the diene-based rubber. Blending such an appropriate amount of the guanidine-based vulcanization accelerator is advantageous for suppressing a decrease in the elongation at break of the rubber composition in the unvulcanized state over time. If the blended amount Ma of the guanidine-based vulcanization accelerator is less than 0.5 parts by mass, the elongation at break may decrease when the rubber composition is stored in the unvulcanized state.

[0036] In the rubber composition for a sidewall tread according to an embodiment of the present invention, an additional compounding agent other than the above may be added. Examples of the additional compounding agent include various compounding agents typically used in rubber compositions for tires, such as vulcanizing or crosslinking agents, antiaging agents, and liquid polymers. These compounding agents can be blended in conventional blending amounts in the prior art, as long as the objects of the present invention are not hindered. As the kneading device, a typical kneading device for a rubber, such as a Banbury mixer, a kneader, or a roller, can be used.

[0037] The present invention will be further described below by way of examples, but the scope of the present invention is not limited to these examples. Example

[0038] To prepare 16 types of side tread rubber compositions (Comparative Examples 1 to 6 and Examples 1 to 10) in the blending ratios shown in Table 1, the blending ingredients other than a vulcanization accelerator and sulfur were weighed and kneaded for 5 minutes in a 1.8-liter sealed Banbury mixer. A masterbatch was then dispensed and cooled at room temperature. The masterbatch was then charged into the 1.8-liter sealed Banbury mixer, the vulcanization accelerator and sulfur were added, and mixed for 2 minutes. Thus, each side tread rubber composition was obtained.

[0039] Please note that the "Mc + Ms" line in Table 1 represents the sum of the blended amount of carbon black and the blended amount of silica. The "Ma / Ms" line in Table 1 indicates the ratio of the blended amount of vulcanization accelerator 2 (guanidine-based vulcanization accelerator) to the blended amount of silica. The "Ma / Mt" line in Table 1 indicates the ratio of the blended amount of vulcanization accelerator 2 (guanidine-based vulcanization accelerator) to the total amount of vulcanization accelerators (the sum of vulcanization accelerators 1 and 2).

[0040] The obtained side tread rubber compositions were evaluated for hardness, tensile strength, tan δ at 60°C, and elongation at break retention using the methods described below. hardness

[0041] Each sidewall rubber composition was vulcanized in a mold with a predetermined shape at 160°C for 20 minutes to prepare a vulcanized rubber test piece. The hardness of each of the vulcanized rubber test pieces was measured at a temperature of 20°C using a Type A hardness tester in accordance with JIS K 6253. The results obtained are shown in the "Hardness" row in Table 1, with the value of Comparative Example 1 expressed as an index of 100. A larger index value indicates higher strength. Tensile strength

[0042] Each rubber composition for a sidewall tread was vulcanized in a mold of a predetermined shape at 160°C for 20 minutes to prepare a vulcanized rubber test piece. A dumbbell-shaped test piece conforming to JIS No. 3 was cut from each of the vulcanized rubber test pieces in accordance with JIS K 6251. Tensile testing was performed at a pulling speed of 500 mm / minute at room temperature (20°C), and the stress at the time of failure (rupture strength TB, unit: MPa) was measured. The results obtained are shown in the "Tensile Strength" row in Table 1, with the value of Comparative Example 1 expressed as an index of 100. A larger index value indicates a greater tensile strength. Tan δ at 60 °C

[0043] Each rubber composition for a sidewall tread was vulcanized in a mold with a predetermined shape at 160°C for 20 minutes, thus preparing a vulcanized rubber test piece. Using a viscoelasticity spectrometer available from Toyo Seiki Seisaku-sho, Ltd., the tan δ at 60°C of each of these vulcanized rubber test pieces was measured under the following conditions: initial strain of 10%, amplitude of ±2%, frequency of 20 Hz, and temperature of 60°C. The results obtained are shown in the "tan δ (60°C)" row in Table 1, where the value of Comparative Example 1 is expressed as an index of 100. A smaller value indicates superior, i.e., low heat buildup. Maintaining elongation at break

[0044] Each of the sidewall rubber compositions was vulcanized immediately after preparation by the above method in a mold having a predetermined shape at 160°C for 20 minutes, and thus a vulcanized rubber test piece A was prepared. Each of the sidewall rubber compositions prepared by the above method and left in an unvulcanized state for 30 days was vulcanized in a mold having a predetermined shape at 160°C for 20 minutes, and thus a vulcanized rubber test piece B was prepared. A dumbbell-shaped test piece according to JIS No. 3 was cut out from each of the vulcanized rubber test piece A and the vulcanized rubber test piece B according to JIS K 6251, the tensile strength test was carried out at a tensile speed of 500 mm / minute at room temperature (20°C), and the elongation at the time of failure (elongation at failure EB, unit: %) was measured.Then, for each of the rubber compositions for a side tread, a ratio (unit: %) of the elongation at break measured for the vulcanized rubber test piece B to the elongation at break measured for the vulcanized rubber test piece A was calculated, used as an index of elongation at break maintenance, and displayed in the "Elongation at Break Maintenance" row in Table 1. When this value is closer to 100%, it means that the decrease in elongation at break over time is smaller. [Table 1-I] Comparison example 1 Comparison example 2 NR Mass-produced parts 45 45 BR1 Mass-produced parts 55 55 BR2 Mass-produced parts BR3 Mass-produced parts CB1 Mass-produced parts 15 15 CB2 Mass-produced parts Silica 1 Mass-produced parts 20 Silica 2 Mass-produced parts 20 Silica 3 Mass-produced parts Silane coupling agent Mass-produced parts 0,8 0,8 Aroma oil Mass-produced parts 5 5 Anti-aging agent 1 Mass-produced parts 3 3 Anti-aging agent 2 Mass-produced parts 1 1 wax Mass-produced parts 1 1 Stearic acid Mass-produced parts 2 2 zinc oxide Mass-produced parts 3 3 sulfur Mass-produced parts 1,5 1,5 Vulcanization accelerator 1 Mass-produced parts 2,4 2,4 Vulcanization accelerator 2 Mass-produced parts Mc + Ms Mass-produced parts 35 35 Ma / Ms 0 0 Ma / Mt 0 0 hardness Index value 100 100 Tensile strength Index value 100 101 Tan δ (60 °C) Index value 100 127 Maintaining elongation at break % 90 85 [Table 1-II] Comparison example 3 Comparison Example 4 NR Mass-produced parts 45 45 BR1 Mass-produced parts BR2 Mass-produced parts 55 55 BR3 Mass-produced parts CB1 Mass-produced parts 15 15 CB2 Mass-produced parts Silica 1 Mass-produced parts Silica 2 Mass-produced parts Silica 3 Mass-produced parts 20 20 Silane coupling agent Mass-produced parts 0,8 0,8 Aroma oil Mass-produced parts 5 5 Anti-aging agent 1 Mass-produced parts 3 3 Anti-aging agent 2 Mass-produced parts 1 1 wax Mass-produced parts 1 1 Stearic acid Mass-produced parts 2 2 zinc oxide Mass-produced parts 3 3 sulfur Mass-produced parts 1,5 1,5 Vulcanization accelerator 1 Mass-produced parts 2,4 1,2 Vulcanization accelerator 2 Mass-produced parts 1,8 Mc + Ms Mass-produced parts 35 35 Ma / Ms 0 0,09 Ma / Mt 0 0,6 hardness Index value 95 98 Tensile strength Index value 92 107 Tan δ (60 °C) Index value 78 105 Maintaining elongation at break % 78 101 [Table 1-III] Example 1 Example 2 Example 3 NR Mass-produced parts 45 45 45 BR1 Mass-produced parts BR2 Mass-produced parts 55 55 40 BR3 Mass-produced parts 15 CB1 Mass-produced parts 15 20 15 CB2 Mass-produced parts Silica 1 Mass-produced parts Silica 2 Mass-produced parts Silica 3 Mass-produced parts 20 15 20 Silane coupling agent Mass-produced parts 0,8 0,8 0,8 Aroma oil Mass-produced parts 5 5 5 Anti-aging agent 1 Mass-produced parts 3 3 3 Anti-aging agent 2 Mass-produced parts 1 1 1 wax Mass-produced parts 1 1 1 Stearic acid Mass-produced parts 2 2 2 zinc oxide Mass-produced parts 3 3 3 sulfur Mass-produced parts 1,5 1,5 1,5 Vulcanization accelerator 1 Mass-produced parts 1,4 1,4 1,4 Vulcanization accelerator 2 Mass-produced parts 1 1 1 Mc + Ms Mass-produced parts 35 35 35 Ma / Ms 0,05 0,067 0,05 Ma / Mt 0,42 0,42 0,42 hardness Index value 99 100 100 Tensile strength Index value 108 112 100 Tan δ (60 °C) Index value 82 81 72 Maintaining elongation at break % 102 99 100 [Table 1-IV] Example 4 Example 5 Example6 NR Mass-produced parts 45 45 45 BR1 Mass-produced parts 55 BR2 Mass-produced parts 55 55 BR3 Mass-produced parts CB1 Mass-produced parts 15 15 15 CB2 Mass-produced parts Silica 1 Mass-produced parts Silica 2 Mass-produced parts Silica 3 Mass-produced parts 20 20 20 Silane coupling agent Mass-produced parts 0,8 0,8 0,8 Aroma oil Mass-produced parts 5 5 5 Anti-aging agent 1 Mass-produced parts 3 3 3 Anti-aging agent 2 Mass-produced parts 1 1 1 wax Mass-produced parts 1 1 1 Stearic acid Mass-produced parts 2 2 2 zinc oxide Mass-produced parts 3 3 3 sulfur Mass-produced parts 1,5 1,5 1,5 Vulcanization accelerator 1 Mass-produced parts 2 1,2 1,4 Vulcanization accelerator 2 Mass-produced parts 0,5 1,2 1 Mc + Ms Mass-produced parts 35 35 35 Ma / Ms 0,025 0,06 0,05 Ma / Mt 0,2 0,5 0,42 hardness Index value 99 99 98 Tensile strength Index value 114 107 110 Tan δ (60 °C) Index value 78 85 92 Maintaining elongation at break % 95 100 98 [Table 1-V] Example7 Example8 Example9 NR Mass-produced parts 55 35 45 BR1 Mass-produced parts BR2 Mass-produced parts 45 65 55 BR3 Mass-produced parts CB1 Mass-produced parts 15 15 5 CB2 Mass-produced parts Silica 1 Mass-produced parts Silica 2 Mass-produced parts Silica 3 Mass-produced parts 20 20 45 Silane coupling agent Mass-produced parts 0,8 0,8 0,8 Aroma oil Mass-produced parts 5 5 5 Anti-aging agent 1 Mass-produced parts 3 3 3 Anti-aging agent 2 Mass-produced parts 1 1 1 wax Mass-produced parts 1 1 1 Stearic acid Mass-produced parts 2 2 2 zinc oxide Mass-produced parts 3 3 3 sulfur Mass-produced parts 1,5 1,5 1,5 Vulcanization accelerator 1 Mass-produced parts 1,4 1,4 1,4 Vulcanization accelerator 2 Mass-produced parts 1 1 1 Mc + Ms Mass-produced parts 35 35 50 Ma / Ms 0,05 0,05 0,022 Ma / Mt 0,42 0,42 0,42 hardness Index value 99 100 110 Tensile strength Index value 126 99 134 Tan δ (60 °C) Index value 82 82 96 Maintaining elongation at break % 100 103 97 [Table 1-VI] Comparison example 5 NR Mass-produced parts 45 BR1 Mass-produced parts BR2 Mass-produced parts 55 BR3 Mass-produced parts CB1 Mass-produced parts 5 CB2 Mass-produced parts Silica 1 Mass-produced parts Silica 2 Mass-produced parts Silica 3 Mass-produced parts 55 Silane coupling agent Mass-produced parts 0,8 Aroma oil Mass-produced parts 5 Anti-aging agent 1 Mass-produced parts 3 Anti-aging agent 2 Mass-produced parts 1 wax Mass-produced parts 1 Stearic acid Mass-produced parts 2 zinc oxide Mass-produced parts 3 sulfur Mass-produced parts 1,5 Vulcanization accelerator 1 Mass-produced parts 1,4 Vulcanization accelerator 2 Mass-produced parts 1 Mc + Ms Mass-produced parts 60 Ma / Ms 0,018 Ma / Mt 0,42 hardness Index value 118 Tensile strength Index value 151 Tan δ (60 °C) Index value 105 Maintaining elongation at break % 94 [Table 1-VII] Comparison example 6 NR Mass-produced parts 45 BR1 Mass-produced parts BR2 Mass-produced parts 55 BR3 Mass-produced parts CB1 Mass-produced parts CB2 Mass-produced parts 15 Silica 1 Mass-produced parts Silica 2 Mass-produced parts Silica 3 Mass-produced parts 20 Silane coupling agent Mass-produced parts 0,8 Aroma oil Mass-produced parts 5 Anti-aging agent 1 Mass-produced parts 3 Anti-aging agent 2 Mass-produced parts 1 wax Mass-produced parts 1 Stearic acid Mass-produced parts 2 zinc oxide Mass-produced parts 3 sulfur Mass-produced parts 1,5 Vulcanization accelerator 1 Mass-produced parts 1,4 Vulcanization accelerator 2 Mass-produced parts 1 Mc + Ms Mass-produced parts 35 Ma / Ms 0,05 Ma / Mt 0,42 hardness Index value 101 Tensile strength Index value 112 Tan δ (60 °C) Index value 99 Maintaining elongation at break % 101 [Table 1-VIII] Example 10 NR Mass-produced parts 45 BR1 Mass-produced parts 40 BR2 Mass-produced parts BR3 Mass-produced parts 15 CB1 Mass-produced parts 15 CB2 Mass-produced parts Silica 1 Mass-produced parts Silica 2 Mass-produced parts Silica 3 Mass-produced parts 20 Silane coupling agent Mass-produced parts 0,8 Aroma oil Mass-produced parts 5 Anti-aging agent 1 Mass-produced parts 3 Anti-aging agent 2 Mass-produced parts 1 wax Mass-produced parts 1 Stearic acid Mass-produced parts 2 zinc oxide Mass-produced parts 3 sulfur Mass-produced parts 1,5 Vulcanization accelerator 1 Mass-produced parts 1,4 Vulcanization accelerator 2 Mass-produced parts 1 Mc + Ms Mass-produced parts 35 Ma / Ms 0,05 Ma / Mt 0,42 hardness Index value 98 Tensile strength Index value 100 Tan δ (60 °C) Index value 84 Maintaining elongation at break % 98

[0045] Specified types of raw materials used in Table 1 are described below. • NR: Natural rubber, STR 20 • BR1: Butadiene rubber synthesized with a cobalt catalyst, NIPOL BR 1220, available from Zeon Corporation • BR2: Butadiene rubber synthesized with a neodymium-based catalyst, Buna CB24, available from ARLANXEO • BR3: Terminally modified butadiene rubber for silica, BR511, available from JSR Corporation • CB1: Carbon black, Show Black N550, available from Cabot Japan KK (specific CTAB adsorption surface area: 40 m 2 / G) • CB2: Carbon black, Show Black N234, available from Cabot Japan KK (specific CTAB adsorption surface area: 115 m 2 / G) • Silica 1: 115GR, available from Solvay (specific CTAB adsorption surface area: 110 m 2 / G) • Silica 2: 1165MP, available from Solvay (specific CTAB adsorption surface area: 160 m 2 / G) • Silica 3: 1085GR, available from Solvay (specific CTAB adsorption surface area: 80 m 2 / G) • Silane coupling agent: Si69, available from Evonik Degussa Japan Co., Ltd. • Aroma oil: Extract No. 4S, available from Showa Shell Sekiyu KK • Anti-aging agent 1: Santoflex 6PPD, available from Flexsys • Antiaging agent 2: NOCRAC 224, available from Ouchi Shinko Chemical Industrial Co., Ltd. • Wax: Paraffin wax, available from Ouchi Shinko Chemical Industrial Co., Ltd. • Stearic acid: Stearic acid beads, available from NOF Corporation • Zinc oxide: Zinc oxide III, available from Seido Chemical Industry Co., Ltd. • Sulfur: MUCRON OT-20, available from Shikoku Chemicals Corporation • Vulcanization accelerator 1: Sulfenamide-based vulcanization accelerator, Nocceler CZ-G (available from Ouchi Shinko Chemical Industrial Co. Ltd.) • Vulcanization accelerator 2: Guanidine-based vulcanization accelerator, Perkacit DPG, available from Flexsys Inc.

[0046] As can be seen from Table 1, Examples 1 to 10 exhibit improved low heat buildup (tan δ at 60°C) compared to Comparative Example 1, while maintaining or improving hardness and tensile strength. Furthermore, in Examples 1 to 10, compared to Comparative Example 1, it was possible to maintain the elongation at break even after 30 days in the unvulcanized state.

[0047] In Comparative Example 2, however, the specific CTAB adsorption surface area of ​​the silica was large and no guanidine-based vulcanization accelerator was included, thus impairing low heat generation and elongation at break retention. In Comparative Example 3, the particle size of the silica was appropriate, but no guanidine-based vulcanization accelerator was included, thus decreasing hardness, tensile strength, and elongation at break retention. In Comparative Example 4, the blended amount of the guanidine-based vulcanization accelerator was large relative to the blended amount of silica and the total amount of the vulcanization accelerator, thus deteriorating low heat generation (tan δ (60°C)).In Comparative Example 5, the blended amount of silica was large, and the total amount of silica and carbon black was also large, thus deteriorating the low heat generation (tan δ (60°C)). In Comparative Example 6, the CTAB adsorption specific surface area of ​​the carbon black was large, and thus, it was impossible to improve the low heat generation (tan δ (60°C)).

[0048] The present disclosure includes the following inventions. Invention [1] A rubber composition for a sidewall tread, the rubber composition comprising a diene-based rubber containing 35 to 55 mass% of an isoprene-based rubber and 45 to 65 mass% of a butadiene rubber; silica having a CTAB adsorption specific surface area of ​​60 m 2 / g up to 100 m 2 / G; carbon black with a specific CTAB adsorption surface of 30 to 100 m 2 / g; a sulfur-containing silane coupling agent; and a guanidine-based vulcanization accelerator; wherein the blended amount of the silica is 5 parts by mass or more and 50 parts by mass or less, and the total amount of the blended amounts of the silica and the carbon black is less than 55 parts by mass per 100 parts by mass of the diene-based rubber, and the ratio Ma / Ms of the blended amount Ma of the guanidine-based vulcanization accelerator to the blended amount Ms of the silica is 0.02 to 0.08. Invention [2] The rubber composition for a sidewall tread according to invention [1], wherein the butadiene rubber contains a butadiene rubber synthesized with a neodymium-based catalyst and optionally contains a terminal-modified butadiene rubber for silica.Invention [3] The rubber composition for a sidewall tread according to invention [2], wherein the butadiene rubber contains the butadiene rubber synthesized with the neodymium-based catalyst in a proportion of 69 mass% to 100 mass% and the terminal-modified butadiene rubber for silica in a proportion of 0 mass% to 31 mass%, and a proportion of a blended amount of the terminal-modified butadiene rubber for silica is less than 20 mass% per 100 mass% of the diene-based rubber. Invention [4] The rubber composition for a sidewall tread according to any one of inventions [1] to [3], wherein the rubber composition additionally contains a vulcanization accelerator other than the.

[0049] Contains a guanidine-based vulcanization accelerator, and a ratio Ma / Mt of the blended amount Ma of the guanidine-based vulcanization accelerator to a total amount Mt of the vulcanization accelerators including the guanidine-based vulcanization accelerator and the additional vulcanization accelerator is 0.2 to 0.5. Invention [5] The rubber composition for a side tread according to any one of the inventions [1] to [4], wherein the blended amount of the guanidine-based vulcanization accelerator is 0.5 parts by mass or more per 100 parts by mass of the diene-based rubber. Invention [6] A tire including a side tread rubber layer made of the rubber composition for a side tread according to any one of the inventions [1] to [5]. List of reference symbols 1 tread section 2 side wall section 3 bead section 4 carcass layers 5 Bead core 6 bead fillers 7 belt layer 8 Belt cover layer 10 Tread rubber layer 20 Side tread rubber layer 30 rim cushion rubber layer CL Tire Equator QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2013-001889 A

[0004]

Claims

[1] A rubber composition for a side tread, the rubber composition comprising a diene-based rubber comprising 35 to 55 mass% of an isoprene-based rubber and 45 to 65 mass% of a butadiene rubber; silica having a CTAB specific adsorption surface area of ​​60 m 2 / g up to 100 m 2 / G; carbon black with a specific CTAB adsorption surface of 30 to 100 m 2 / g; a sulfur-containing silane coupling agent; and a guanidine-based vulcanization accelerator; wherein the blended amount of the silica is 5 parts by mass or more and 50 parts by mass or less, and the total amount of the blended amounts of the silica and the carbon black is less than 55 parts by mass per 100 parts by mass of the diene-based rubber, and the ratio Ma / Ms of the blended amount Ma of the guanidine-based vulcanization accelerator to the blended amount Ms of the silica is 0.02 to 0.

08. [2] The rubber composition for a sidewall tread according to claim 1, wherein the butadiene rubber comprises a butadiene rubber synthesized with a neodymium-based catalyst and optionally comprises a terminal-modified butadiene rubber for silica. [3] The rubber composition for a sidewall tread according to claim 2, wherein the butadiene rubber comprises the butadiene rubber synthesized with the neodymium-based catalyst in a proportion of 69 mass% to 100 mass% and the terminal-modified butadiene rubber for silica in a proportion of 0 mass% to 31 mass%, and a proportion of a blended amount of the terminal-modified butadiene rubber for silica is less than 20 mass% per 100 mass% of the diene-based rubber. [4] The rubber composition for a side tread according to any one of claims 1 to 3, wherein the rubber composition comprises an additional vulcanization accelerator other than the guanidine-based vulcanization accelerator, and a ratio Ma / Mt of the blended amount Ma of the guanidine-based vulcanization accelerator to a total amount Mt of the vulcanization accelerators comprising the guanidine-based vulcanization accelerator and the additional vulcanization accelerator is 0.2 to 0.

5. [5] The rubber composition for a side tread according to any one of claims 1 to 4, wherein the blended amount Ma of the guanidine-based vulcanization accelerator is 0.5 parts by mass or more per 100 parts by mass of the diene-based rubber. [6] A tire comprising a side tread rubber layer comprising the rubber composition for a side tread according to any one of claims 1 to 5.

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