JP5612427B2 - Rubber composition for tread and pneumatic tire - Google Patents

Description

The present invention relates to a rubber composition for a tread and a pneumatic tire having a tread produced using the rubber composition.

The rubber composition for a tread of a pneumatic tire is usually blended with a filler such as silica or carbon black. It is known that silica can reduce rolling resistance as compared with carbon black. In the case of a rubber composition for a tread containing silica, 1 to 2 parts by mass of sulfur and 0.5 to 3 parts by mass of zinc white (zinc oxide) are added to 100 parts by mass of the rubber component, and TBBS, Generally, a vulcanization accelerator such as CBS or DPG is appropriately blended.

The zinc white is a hardly dispersible inorganic substance and impairs wear resistance, so it is desirable to reduce the amount. However, when the amount of zinc white is reduced, the complex elastic modulus E ^* decreases and the steering stability tends to deteriorate, so it was practically difficult to reduce the content of zinc white to 0 part by mass.

Generally as said sulfur, powdered S8 sulfur, insoluble sulfur, etc. are used. These are more polar than tire polymers (rubber components) such as styrene butadiene rubber, natural rubber, and butadiene rubber, and are self-aggregating, making them difficult to disperse in the polymer and uniform cross-polymer crosslinking. There was a problem that it was difficult to form. In order to solve this problem, hybrid crosslinking aids such as KA9188 manufactured by Bayer, PK900 manufactured by Flexis, and Si69 manufactured by Degussa are used in place of a part of sulfur. Further, Patent Document 1 uses Tachyroll V200 manufactured by Taoka Chemical Co., Ltd. as a hybrid crosslinking aid.

As described above, replacing sulfur with a hybrid crosslinking aid having a large molecular weight and excellent dispersibility is effective to some extent in forming uniform crosslinking. However, with conventional hybrid crosslinking aids, it has been difficult to ensure sufficient E ^* when the amount of zinc white or sulfur is reduced.

Moreover, when butadiene rubber is replaced with natural rubber, wet grip performance and elongation at break EB are improved, but wear resistance tends to deteriorate.

JP 2009-114427 A

The present invention solves the above-mentioned problems and provides a rubber composition for a tread which can improve rolling resistance characteristics and wear resistance while ensuring wet grip performance, handling stability and elongation at break, and a tread produced using the same. It aims at providing the pneumatic tire which has.

（式中、ｘは１以上の数である。Ｒ^１〜Ｒ^４はそれぞれ独立に炭素数１〜１８の直鎖若しくは分岐鎖アルキル基、又は炭素数５〜１２のシクロアルキル基を表す。） 1st this invention relates to the rubber composition for treads whose content of the compound (1) represented by a following formula (I) is 0.2-15 mass parts with respect to 100 mass parts of rubber components.

(In the formula, x is a number of 1 or more. R ^{1 to} R ⁴ each independently represents a linear or branched alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 5 to 12 carbon atoms.)

The rubber composition of the first invention preferably contains 1.0 part by mass or less of zinc oxide with respect to 100 parts by mass of the rubber component.

（式中、Ｒ^５〜Ｒ^８はそれぞれ独立に炭素数１〜１８の直鎖若しくは分岐鎖アルキル基、又は炭素数５〜１２のシクロアルキル基を表す。） In the second aspect of the present invention, the content of the compound (2) represented by the following formula (II) is 0.2 to 15 parts by mass with respect to 100 parts by mass of the rubber component, and the sulfur content is 1. It is related with the rubber composition for treads which is 1 mass part or less.

^(Wherein, represents a cycloalkyl group of R 5 to R ⁸ straight or branched chain alkyl group having 1 to 18 carbon atoms are each independently, or 5 to 12 carbon atoms.)

In the third aspect of the present invention, the content of the compound (1) is 0.2 to 15 parts by mass and the content of the compound (2) is 0.2 to 15 parts by mass with respect to 100 parts by mass of the rubber component. It is related with the rubber composition for tread which is a part.

The rubber composition of the third aspect of the present invention has a zinc oxide content of 1.0 parts by mass or less and a diphenylguanidine content of 0.5 parts by mass or less with respect to 100 parts by mass of the rubber component. It is preferable.

The present invention also relates to a pneumatic tire having a tread produced using the rubber composition.

According to the present invention, a rubber composition (first invention) containing a predetermined amount of the above compound (1), a predetermined amount of the above compound (2), and a rubber having a sulfur content of a specific value or less. Since it is a rubber composition (third invention) containing a predetermined amount of the composition (second invention) or the above-mentioned compounds (1) and (2), by using this in a tread, wet A pneumatic tire having an excellent balance of grip performance, handling stability, elongation at break, rolling resistance characteristics, and wear resistance can be provided.

The rubber composition of the first aspect of the present invention contains a predetermined amount of the compound (1) represented by the above formula (I). Compound (1) exhibits a very effective crosslinking promoting action due to the synergistic effect of phosphorus atoms and sulfur atoms. This makes it possible to reduce the amount of zinc white as a crosslinking aid. As the compound (1), for example, SDT-50 and SDT / S manufactured by Rhein Chemie, and compounds similar to these (for example, those in which R ^{1 to} R ⁴ are n-butyl groups) can be used. .

The rubber composition of the second aspect of the present invention contains a predetermined amount of the compound (2) represented by the above formula (II), and the sulfur content is not more than a specific value. Compound (2) retains a zinc atom at the center of its structure, and exhibits a cross-linking promoting action superior to that of Compound (1). Thereby, not only zinc white but also sulfur as a crosslinking agent can be reduced. Examples of the compound (2) include TP-50, ZBOP-S, ZBOP-50 manufactured by Rhein Chemie, and compounds similar thereto (for example, R ^{5 to} R ⁸ are an n-propyl group, an iso-propyl group, n-octyl group) and the like can be used.

Thus, according to the first and second rubber compositions of the present invention, it becomes possible to reduce the amount of zinc white, sulfur, etc., which adversely affects performance, so that wet grip performance, steering stability and breaking The rolling resistance characteristics and wear resistance can be improved while securing the elongation.

Although the mechanism by which the crosslinking promoting action by the compounds (1) and (2) is exhibited is not clear, the following mechanisms a) to c) are considered.
a) Compound (1) or (2) binds to the silane coupling agent and mediates the bond between the silane coupling agent and silica.
b) Compound (1) or (2) binds to the vulcanization (crosslinking) accelerator and mediates the bond between the vulcanization accelerator and the rubber component.
c) Both a) and b) above.

It is known that DPG as a vulcanization accelerator exerts the action of the above a), and when the compound (1) or (2) is substituted with DPG, the performance exceeds DPG. It is highly possible that the mechanism is a). Further, when compound (1) or (2) is blended, the same level of E ^* can be secured even if the amount of the vulcanization accelerator is reduced. Since the compounds (1) and (2) have a molecular chain of an appropriate length and have a low polarity, they have a structure that is easily accessible to a silane coupling agent and a vulcanization accelerator. The above effect is presumed to be due to such structures of the compounds (1) and (2).

The compound (2) has a cross-linking promoting action superior to that of the compound (1). However, just using the compound (2) has room for improvement in terms of securing a good vulcanization rate while reducing the amount of diphenylguanidine (DPG), which has a large environmental load, along with zinc white and sulfur. It is presumed that the compound (2) takes in sulfur in the rubber and forms a structure similar to the compound (1). Thus, it is considered that the slow generation of the intermediate formed by the reaction of sulfur or zinc with the compound (1) or (2) is a factor for slowing the vulcanization rate. Further, it is speculated that the compound (1) takes in zinc in the rubber to form a structure similar to the compound (2). However, it is considered that this process cannot proceed efficiently only by using the compound (1). It is done.

On the other hand, the rubber composition of the third aspect of the present invention is formulated with a predetermined amount of the compounds (1) and (2), so that the crosslinking promoting action of the compounds (1) and (2) is synergistically exhibited. A good vulcanization rate can be obtained. Thereby, even if it reduces DPG with zinc white and sulfur, it becomes possible to ensure a favorable vulcanization speed. Moreover, the improvement effect of each performance can be heightened compared with the rubber composition of 1st and 2nd this invention.

(Compound (1))
In the above formula (I), R ^{1 to} R ⁴ each independently represents a linear or branched alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 5 to 12 carbon atoms. Examples of the linear or branched alkyl group represented by R ^{1 to} R ⁴ include a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, a 4-methylpentyl group, a 2-ethylhexyl group, and an octyl group. Group, octadecyl group, and the like. On the other hand, examples of the cycloalkyl group include a cyclopentyl group, a cyclohexyl group, and a cyclooctyl group. Of these, easily dispersed in the rubber composition, and from the viewpoint of easy manufacturing, R ¹ to R ⁴ is preferably a straight or branched chain alkyl group having 2 to 8 carbon atoms, 2- More preferred are an ethylhexyl group, an n-butyl group, an n-propyl group, an iso-propyl group, and an n-octyl group.

In the above formula (I), x is a number of 1 or more. From the viewpoint that sufficient sulfur can be supplied into the rubber composition and the thermal stability is excellent, x is preferably 2 or more, and more preferably 3 or more. Moreover, although the upper limit of x is not specifically limited, Preferably it is about 10 or less.

In the rubber composition of the first aspect of the present invention, the content of the compound (1) (the content of the active ingredient) is 0.2 parts by mass or more, preferably 0.5 parts by mass with respect to 100 parts by mass of the rubber component. As mentioned above, More preferably, it is 1.0 mass part or more. When the amount is less than 0.2 parts by mass, the effect of compounding compound (1) tends to be insufficient. Moreover, this content is 15 mass parts or less, Preferably it is 6 mass parts or less, More preferably, it is 5 mass parts or less. When it exceeds 15 parts by mass, the scorch time is shortened and the workability tends to deteriorate.

In the rubber composition of the third aspect of the present invention, the content of the compound (1) (the content of the active ingredient) is 0.2 parts by mass or more, preferably 0.3 parts by mass with respect to 100 parts by mass of the rubber component. As mentioned above, More preferably, it is 0.4 mass part or more. When the amount is less than 0.2 parts by mass, the effect of compounding compound (1) tends to be insufficient. Moreover, this content is 15 mass parts or less, Preferably it is 6 mass parts or less, More preferably, it is 2 mass parts or less. When it exceeds 15 parts by mass, the scorch time is shortened and the workability tends to deteriorate.

(Compound (2))
In the above formula (II), R ^{5 to} R ⁸ each independently represents a linear or branched alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 5 to 12 carbon atoms. Specific examples of the linear or branched alkyl group or cycloalkyl group represented by R ^{5 to} R ⁸ include the same as in R ^{1 to} R ⁴ . Of these, easily dispersed in the rubber component, and from the viewpoint of easy manufacturing, R ⁵ to R ⁸ is preferably a straight or branched chain alkyl group having 2 to 8 carbon atoms, n- butyl A group, an n-propyl group, an iso-propyl group, and an n-octyl group are more preferable.

In the rubber composition of the second invention, the content of the compound (2) (the content of the active ingredient) is 0.2 parts by mass or more, preferably 0.5 parts by mass with respect to 100 parts by mass of the rubber component. As mentioned above, More preferably, it is 1.0 mass part or more. When the amount is less than 0.2 parts by mass, the effect of compounding the compound (2) tends to be insufficient. Moreover, this content is 15 mass parts or less, Preferably it is 8 mass parts or less, More preferably, it is 6 mass parts or less. When it exceeds 15 parts by mass, the scorch time is shortened and the workability tends to deteriorate.

In the rubber composition of the third aspect of the present invention, the content of the compound (2) (the content of the active ingredient) is 0.2 parts by mass or more, preferably 0.5 parts by mass with respect to 100 parts by mass of the rubber component. As mentioned above, More preferably, it is 1.0 mass part or more. When the amount is less than 0.2 parts by mass, the effect of compounding the compound (2) tends to be insufficient. Moreover, this content becomes like this. Preferably it is 15 mass parts or less, More preferably, it is 4 mass parts or less, More preferably, it is 2.5 mass parts or less. When it exceeds 15 parts by mass, the scorch time is shortened and the workability tends to deteriorate.

In the rubber composition of the third aspect of the present invention, the total content of compounds (1) and (2) (total content of active ingredients) is preferably 0.4 parts by mass or more with respect to 100 parts by mass of the rubber component. More preferably, it is 1.0 mass part or more, More preferably, it is 1.5 mass part or more. When the amount is less than 0.4 parts by mass, the effect of the combined use of the compounds (1) and (2) tends to be insufficient. The total content is preferably 30 parts by mass or less, more preferably 12 parts by mass or less, and still more preferably 8 parts by mass or less. When it exceeds 30 parts by mass, the scorch time is shortened and the workability tends to deteriorate.

(Rubber component)
Examples of rubber components blended in the first to third inventions include natural rubber (NR), epoxidized natural rubber (ENR), isoprene rubber (IR), butadiene rubber (BR), and styrene butadiene rubber (SBR). Styrene isoprene butadiene rubber (SIBR), ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), acrylonitrile butadiene rubber (NBR) and the like can be used. These may be used alone or in combination of two or more. Among these, SBR and BR are preferable, and SBR is more preferable because carbon black, silica, oil, and a crosslinking agent are easily dispersed and fatigue resistance and wet grip performance are excellent.

The SBR is not particularly limited, and for example, those commonly used in the tire industry such as emulsion polymerization styrene butadiene rubber (E-SBR), solution polymerization styrene butadiene rubber (S-SBR) can be used. Moreover, SBR (modified SBR) whose terminal is modified with a modifying agent can be suitably used because of excellent wet grip performance and rolling resistance characteristics.

Examples of the modifying agent used for modifying SBR include 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylethyldimethoxysilane, and 3-aminopropyltrimethoxysilane. These may be used alone or in combination of two or more. Of these, 3-aminopropyltrimethoxysilane is preferred because it has good binding properties with polymers and high affinity with fillers.

As a method for modifying SBR with a modifier, conventionally known methods such as those described in JP-B-6-53768 and JP-B-6-57767 can be used. For example, SBR may be brought into contact with a modifying agent, and examples include a method of adding a modifying agent to an SBR solution and reacting them.

The styrene content of the modified SBR is preferably 5% by mass or more, more preferably 15% by mass or more. When it is less than 5% by mass, the wear resistance tends to deteriorate. Moreover, this styrene content becomes like this. Preferably it is 45 mass% or less, More preferably, it is 40 mass% or less. When it exceeds 45 mass%, there exists a tendency for rolling resistance characteristics to deteriorate.
In the present specification, the styrene content is calculated by ¹ H-NMR measurement.

The content of the modified SBR in 100% by mass of the rubber component is preferably 40% by mass or more, more preferably 50% by mass or more, and further preferably 60% by mass or more. If it is less than 40% by mass, the effect of blending modified SBR tends to be insufficient. Further, the content may be 100% by mass, but is preferably 95% by mass or less, more preferably 85% by mass or less in order to improve each performance in a well-balanced manner by using together with other rubber components. .

The BR is not particularly limited. For example, BR1220 manufactured by Nippon Zeon Co., Ltd., BR130B manufactured by Ube Industries, Ltd., BR150B having a high cis content such as BR150B, VCR412 manufactured by Ube Industries, Ltd. BR containing syndiotactic polybutadiene crystals can be used.

The content of BR in 100% by mass of the rubber component is preferably 5% by mass or more, more preferably 15% by mass or more, and further preferably 20% by mass or more. If it is less than 5% by mass, the effect of blending BR tends to be insufficient. Moreover, this content becomes like this. Preferably it is 60 mass% or less, More preferably, it is 40 mass% or less, More preferably, it is 30 mass% or less. If it exceeds 60% by mass, the content of the modified SBR is relatively reduced, which is not preferable.

(Zinc flower)
Compound (1) can enhance the cross-linking promoting action when used in combination with zinc white. This is because the compound (1) and zinc white in the production process are kneaded to bond the compound (1) and zinc in the zinc white to form a structure similar to the compound (2). I guess it is not.

In the rubber composition of the first aspect of the present invention, the content of zinc white is preferably 0.05 parts by mass or more, more preferably 0.08 parts by mass or more, and still more preferably 0 with respect to 100 parts by mass of the rubber component. .1 part by mass or more. When the amount is less than 0.05 parts by mass, the crosslinking promoting action of the compound (1) tends not to be sufficiently increased. The content is preferably 1.0 part by mass or less, more preferably 0.5 part by mass or less, still more preferably 0.4 part by mass or less, and particularly preferably 0.3 part by mass or less. When it exceeds 1.0 mass part, there exists a tendency for abrasion resistance to deteriorate.

Since compound (2) has a cross-linking accelerating action superior to that of compound (1), it is not particularly necessary to use it together with zinc white. Accordingly, in the rubber compositions of the second and third inventions, the content of zinc white is preferably 1.0 parts by mass or less, more preferably 0.5 parts by mass or less, with respect to 100 parts by mass of the rubber component. More preferably, it is 0.3 parts by mass or less, particularly preferably 0.1 parts by mass or less, and most preferably 0 part by mass (not contained). Thereby, abrasion resistance can be improved more.

(sulfur)
Since the compound (2) has a cross-linking accelerating action superior to that of the compound (1), the amount of sulfur as a cross-linking agent can be reduced, and the wear resistance and elongation at break can be further improved. In the rubber composition of the second invention, the sulfur content is 1.1 parts by mass or less, preferably 0.8 parts by mass or less, more preferably 0.1 parts by mass with respect to 100 parts by mass of the rubber component. Hereinafter, it is more preferably 0 part by mass (not contained). Similarly, in the rubber composition of the third invention, the sulfur content is preferably 1.4 parts by mass or less, more preferably 1.2 parts by mass or less, particularly preferably 100 parts by mass of the rubber component. Is 1.0 part by mass or less.

In the rubber composition according to the first aspect of the present invention, the sulfur content may be about the same as before (about 1 to 2 parts by mass with respect to 100 parts by mass of the rubber component).

(Vulcanization accelerator)
The rubber compositions of the first to third inventions may contain a general vulcanization accelerator (TBBS, CBS, DPG, TBZTD). However, since the compounds (1) and (2) have high activity, when they are blended, rubber burn (discoloration) is likely to occur in the kneading step, and the crosslinking density tends to increase. Accordingly, the rubber compositions of the first to third inventions preferably reduce the amount of a general vulcanization accelerator. Specifically, in the rubber compositions of the first to third inventions, the content of a general vulcanization accelerator is preferably 5 parts by mass or less, more preferably 100 parts by mass of the rubber component. 3 parts by mass or less, more preferably 1 part by mass or less. Further, since the rubber compositions of the second and third inventions contain the compound (2) having higher activity than the compound (1), it is only necessary to contain a small amount of a general vulcanization accelerator.

Research institutes have pointed out the carcinogenicity of animal experiments in DPG, and there is a need to reduce the amount used. Conventionally, it has been difficult to reduce the amount of DPG while ensuring a good vulcanization rate. It was. On the other hand, since the rubber composition of the third aspect of the present invention uses the compounds (1) and (2) in combination, a good vulcanization rate can be ensured even if the amount of DPG is reduced. In the rubber composition of the third invention, the DPG content is preferably 0.5 parts by mass or less, more preferably 0.2 parts by mass or less, still more preferably 0.1 parts by mass or less, and particularly preferably 0. Parts by mass (not contained).

(silica)
The rubber compositions of the first to third inventions preferably contain silica. Thereby, rolling resistance characteristic can be improved more, improving reinforcing property. Examples of the silica include silica produced by a wet method, silica produced by a dry method, and the like, but there is no particular limitation.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 80 m ² / g or more, more preferably 120 m ² / g or more, and further preferably 150 m ² / g or more. If it is less than 80 m ² / g, there is a possibility that sufficient reinforcing properties cannot be obtained. Further, N ₂ SA of silica is preferably 280 m ² / g or less, more preferably 260 m ² / g or less, and still more preferably 250 m ² / g or less. When it exceeds 280 m < ² > / g, the viscosity of an unvulcanized rubber composition will become high and there exists a tendency for workability to deteriorate.
The _N 2 SA of silica is a value measured by the BET method in accordance with ASTM D3037-81.

The content of silica is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and still more preferably 50 parts by mass or more with respect to 100 parts by mass of the rubber component. When the amount is less than 30 parts by mass, there is a possibility that sufficient reinforcement cannot be obtained. Moreover, this content becomes like this. Preferably it is 150 mass parts or less, More preferably, it is 120 mass parts or less, More preferably, it is 110 mass parts or less. When it exceeds 150 parts by mass, silica is difficult to disperse and rolling resistance characteristics tend to deteriorate.

The rubber compositions of the first to third inventions preferably contain a silane coupling agent together with silica. As the silane coupling agent, any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-tri Ethoxysilylethyl) tetrasulfide, bis (3-triethoxysilylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) ) Sulfide vulcanization accelerators such as disulfide. Of these, bis (3-triethoxysilylpropyl) disulfide is preferable because it is inexpensive and easily available. These silane coupling agents may be used alone or in combination of two or more.

The content of the silane coupling agent is preferably 1 part by mass or more, more preferably 2 parts by mass or more with respect to 100 parts by mass of silica. If it is less than 1 part by mass, the viscosity of the unvulcanized rubber composition tends to be high, and the processability tends to deteriorate. Moreover, this content becomes like this. Preferably it is 20 mass parts or less, More preferably, it is 15 mass parts or less. When it exceeds 20 parts by mass, there is a tendency that an effect commensurate with the increase in cost cannot be obtained.

(Production method)
The rubber compositions of the first to third inventions are produced by a general method. That is, it can be produced by a method of kneading each of the above components with a kneader such as a Banbury mixer, a kneader, or an open roll, and then vulcanizing.

The rubber compositions of the first to third inventions are used as treads for pneumatic tires. In particular, it can be suitably used for a cap tread which is a surface layer of a tread having a multilayer structure. For example, it is suitable for a surface layer of a tread having a two-layer structure [a surface layer (cap tread) and an inner surface layer (base tread)].

The pneumatic tire of the present invention is produced by a usual method using the rubber composition.
That is, the rubber composition containing the above components is extruded in accordance with the shape of the tread at an unvulcanized stage and molded together with other tire members on a tire molding machine by a normal method. Form a vulcanized tire. The pneumatic tire of the present invention can be manufactured by heating and pressurizing this unvulcanized tire in a vulcanizer.

The pneumatic tire of the present invention can be suitably used for passenger cars, trucks, buses and the like.

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

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
BR: BR150B manufactured by Ube Industries, Ltd.
Modified S-SBR: HPR355 manufactured by JSR Corporation (modified with 3-aminopropyltrimethoxysilane, styrene content: 27% by mass)
NR: TSR20
Silica: Ultrasil VN3 manufactured by Degussa (N ₂ SA: 175 m ² / g)
Carbon Black: Show Black N220 manufactured by Cabot Japan
Oil: TDAE oil wax manufactured by Japan Energy Co., Ltd .: Sunnock N manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Anti-aging agent 6PPD: Antigen 6C manufactured by Sumitomo Chemical Co., Ltd.
Anti-aging agent TMQ: FLECTOL TMQ manufactured by FLEXSYS
Stearate: Zinc Hana manufactured by NOF Corporation: Zinc Hana No. 1 silane coupling agent manufactured by Mitsui Mining & Smelting Co., Ltd .: Si266 (bis- (3-triethoxysilylpropyl) disulfide) manufactured by Degussa
Sulfur: 5% oil-containing powder sulfur manufactured by Tsurumi Chemical Co., Ltd. (In Tables 1 to 3 shown below, the mass of only the sulfur content is described.)
Vulcanization accelerator TBBS: Noxeller NS (N-tert-butyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Vulcanization accelerator DPG: Noxeller D (N, N-diphenylguanidine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Crosslinking aid SDT-50: SDT-50 manufactured by Rhein Chemie (compound (1) represented by formula (I), R ^{1 to} R ⁴ : 2-ethylhexyl group, x: 1 or more, active ingredient 50% by mass)
Crosslinking aid SDT-50 analog: prototype (compound (1) represented by formula (I), R ^{1 to} R ⁴ : n-butyl group, x: 1 or more, active ingredient 50% by mass)
Crosslinking assistant TP-50: TP-50 manufactured by Rhein Chemie (compound (2) represented by formula (II), R ^{5 to} R ⁸ : n-butyl group, active ingredient 50% by mass)
Crosslinking assistant ZBOP-50: ZBOP-50 manufactured by Rhein Chemie (compound (2) represented by formula (II), R ^{5 to} R ⁸ : alkyl group, active ingredient 50% by mass)

Examples 1-22 and Comparative Examples 1-12
According to the formulation of Tables 1 to 3, using a Banbury mixer, 2/3 of the compounding amount of silica and chemicals other than sulfur, vulcanization accelerator and crosslinking aid were kneaded at a discharge temperature of 150 ° C. Thereafter, the remainder of the silica was added and further kneaded under the condition of a discharge temperature of 150 ° C. to obtain a kneaded product. Next, using a biaxial open roll, sulfur, a vulcanization accelerator, and a crosslinking aid are added to the obtained kneaded product, and kneaded for 5 minutes at 100 ° C. to obtain an unvulcanized rubber composition. Obtained.
The obtained unvulcanized rubber composition was press vulcanized at 170 ° C. for 12 minutes to obtain a vulcanized rubber composition.
Further, the obtained unvulcanized rubber composition is processed into a tread shape, bonded to another tire member, and vulcanized for 12 minutes at 170 ° C. (tire size: 195 / 65R15). Got.
The amount of the vulcanization accelerator was adjusted so that the hardness (Hs) was the same in each formulation.

The following evaluation was performed using the obtained vulcanized rubber composition and the test tire. The results are shown in Tables 1-3.

(Viscoelasticity test)
Using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., the complex elastic modulus E ^* and loss tangent of the vulcanized rubber composition at 40 ° C. under conditions of initial strain of 10%, dynamic strain of 2% and frequency of 10 Hz. Tan δ was measured. In addition, it shows that it is excellent in steering stability, so that E ^* is large, and it shows that it is excellent in rolling resistance characteristics (rolling resistance is low), so that tan-delta is small.

(Wet grip performance test)
The test tire was mounted on all wheels of a vehicle (domestic FF2000cc), and the braking distance from the point where the brake was applied at a speed of 100 km / h on a wet asphalt road surface was measured. And the braking distance of the comparative example 1 was set to 100, and the wet grip performance of each formulation was displayed as an index by the following formula. The larger the wet grip performance index, the better the wet grip performance.
(Wet grip performance index) = (Brake distance of Comparative Example 1) / (Brake distance of each formulation) × 100

(Tensile test)
Using a No. 3 dumbbell-shaped test piece made of the above vulcanized rubber composition, a tensile test was carried out according to JIS K 6251 “Vulcanized Rubber and Thermoplastic Rubber-Determination of Tensile Properties”, and the elongation at break EB ( %). It shows that it is excellent in chip-cut resistance, so that EB is large.

(Abrasion resistance test)
The test tire was mounted on all the wheels of a vehicle (domestic FF2000cc), and the test course was run on an actual vehicle, and the reduction amount of the pattern groove depth after running about 30000 km was determined. And the reduction amount of the comparative example 1 was set to 100, and the index display was carried out with the following formula. It shows that abrasion resistance is so favorable that a numerical value is large.
(Abrasion resistance index) = (Reduction amount of Comparative Example 1) / (Reduction amount of each formulation) × 100

From Tables 1-3, the Example which mix | blended compound (1) or (2) compared with the comparative example 1, rolling resistance characteristic, and ensuring wet grip performance, steering stability, and chip-cut-proof property. Improved wear resistance.

On the other hand, the comparative example which did not mix | blend compounds (1) and (2) had the tendency for each performance to be inferior to an Example.

In Comparative Examples 8 to 10, the compound (2) was blended, but since the sulfur content was large, a non-uniform crosslinked structure was formed, and each performance tended to be inferior to that of the Examples. In Comparative Examples 8 and 9, since the content of zinc white was also large, the wear resistance tended to be slightly inferior. In Comparative Example 10, E ^* was too high and EB was low.

From Table 3, the Example which used compound (1) and (2) together had the tendency for the improvement effect of each performance to be large compared with the other Example.

Claims (7)

For 100 parts by mass of the rubber component,
The content of the compound (1) represented by the following formula (I) is 0.2 to 15 parts by mass,
A rubber composition for a tread, wherein the content of zinc oxide is 1.0 part by mass or less.

(In the formula, x is a number of 1 or more. R ^{1 to} R ⁴ each independently represents a linear or branched alkyl group having 1 to 18 carbon atoms or a cycloalkyl group having 5 to 12 carbon atoms.) The rubber composition for a tread of Claim 1 further comprising silica. The rubber composition for a tread according to claim 1 or 2 , wherein the rubber component contains a modified styrene butadiene rubber. For 100 parts by mass of the rubber component containing the modified styrene butadiene rubber ,
The content of the compound (2) represented by the following formula (II) is 0.2 to 15 parts by mass,
The sulfur content is 1.1 parts by mass or less,
A rubber composition for a tread having a zinc oxide content of 0.5 parts by mass or less.

^(Wherein, represents a cycloalkyl group of R 5 to R ⁸ straight or branched chain alkyl group having 1 to 18 carbon atoms are each independently, or 5 to 12 carbon atoms.) For 100 parts by mass of the rubber component,
The content of the compound (1) is 0.2 to 15 parts by mass,
A rubber composition for a tread, wherein the content of the compound (2) is 0.2 to 15 parts by mass. For 100 parts by mass of the rubber component,
The zinc oxide content is 1.0 part by mass or less,
The rubber composition for a tread according to claim 5 , wherein the content of diphenylguanidine is 0.5 parts by mass or less. The pneumatic tire which has a tread produced using the rubber composition in any one of Claims 1-6 .