JP2008285506A - Rubber composition for tire tread - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for tire tread capable of improving the rolling resistance, heat deterioration resistance and suppression to heat generation of tire, while maintaining its abrasion resistance and processability. <P>SOLUTION: The rubber composition contains (A) sulfur, (B) 1,6-bis(N,N-dibenzyl thiocarbamoyl dithio)hexane, (C) at least one vulcanization promoter selected from sulfenamide-based vulcanization promoters and (D) at least one vulcanization promoter selected from thiuram-based vulcanization promoters. In this rubber composition, the compounding amounts of the components (A) to (D) are 0.1-2 pts.wt., based on 100 pts.wt. of a diene rubber component, respectively, preferably meeting all of the following relationships (1) to (5): (1) (A)≥(B), (2) (C)≥(D), (3) 1.0≤(A)+(B)≤2.0, (4) 1.0≤(C)+(D)≤2.0, and (5) 0.5≤[(A)+(B)]/[(C)+(D)]≤1.5. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rubber composition for a tire tread, and particularly relates to a rubber composition excellent in rolling resistance and durability that is suitably used for a tread of a large pneumatic tire.

  In recent years, there has been an increasing demand for lower fuel consumption of automobiles, and there is a demand for reducing rolling resistance of tires even for large pneumatic tires used in large vehicles such as trucks and buses. At the same time, tire durability performance such as wear resistance, heat aging resistance, and heat generation durability of the tread portion is important for large tires.

  Conventionally, it has been known that the rolling resistance is related to the hysteresis loss of the rubber composition, and when the hysteresis loss is reduced, the rolling resistance is improved, but the wear resistance tends to be deteriorated. Was in contradiction, and it was difficult to improve both in a balanced manner.

  For example, in order to improve the wear resistance, a high cis type butadiene rubber having a high cis-1,4 content is used as the rubber component of the rubber composition used in the tread, or carbon black as a filler is used. As such, measures such as using a small particle size, using a high structure, improving surface activity, and increasing the amount added have been proposed (for example, Patent Documents 1 to 3). Such).

  According to the above measures, although improvement in wear resistance can be expected, wear resistance and heat aging required for large tires, reduced heat durability, workability in kneading and extrusion processes deteriorated, rolling resistance and The updateability is also adversely affected.

In addition, tread rubber compositions for large tires with a large amount of natural rubber components must be vulcanized for a long time at a relatively low temperature, and are prone to reversion (reversion) and are used under heavy load conditions. There was a problem that tire performance deteriorated over time due to severe heat aging due to.
Japanese Patent Laid-Open No. 11-60984 Japanese Patent Laid-Open No. 11-60985 JP 2000-80302 A

  The present invention has been made in view of the above points, and while maintaining the wear resistance and processability of the rubber composition, the rolling resistance, heat aging property, and heat generation property are improved, and the fuel efficiency of the pneumatic tire is improved. An object of the present invention is to provide a tire tread rubber composition that can improve durability.

  The inventor uses a diene rubber composition together with a specific vulcanizing agent capable of forming a sulfur and a long-chain cross-linked structure as a vulcanizing agent, and a sulfenamide vulcanizing accelerator as a vulcanizing accelerator and It has been found that the above problems can be solved by using a thiuram vulcanization accelerator in combination. In addition, by using carbon black with a specific particle size and structure index, a strong network structure is formed by promoting the bond between carbon black and rubber component polymer, thereby improving heat generation and wear resistance. It has been found to improve.

  That is, the tire tread rubber composition according to the present invention is selected from sulfur, 1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane, and sulfenamide vulcanization accelerator as the diene rubber component. And at least one vulcanization accelerator selected from thiuram vulcanization accelerators.

In the present invention, the sulfur (A), 1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane (B), sulfenamide-based vulcanization acceleration is based on 100 parts by weight of the diene rubber component. 0.1 to 2 parts by weight of at least one vulcanization accelerator (C) selected from the agents and at least one vulcanization accelerator (D) selected from the thiuram vulcanization accelerators, It is preferable that the blending parts by weight of A) to (D) satisfy all the relationships of the following formulas (1) to (5).
(A) ≧ (B) (1)
(C) ≧ (D) (2)
1.0 ≦ (A) + (B) ≦ 2.0 (3)
1.0 ≦ (C) + (D) ≦ 2.0 (4)
0.5 ≦ {(A) + (B)} / {(C) + (D)} ≦ 1.5 (5)

Furthermore, the rubber composition for a tire tread of the present invention has a CTAB adsorption specific surface area (CTAB) of 110 to 150 m ² / g and a compressed DBP absorption amount (24M4DBP) of 100 ml / 100 parts by weight of the diene rubber component. It is preferable to blend 40 to 60 parts by weight of carbon black that is 100 g or more.

  In the rubber composition for a tire tread of the present invention, the diene rubber may comprise 100 to 50 parts by weight of natural rubber and / or isoprene rubber and 0 to 50 parts by weight of butadiene rubber.

  The butadiene rubber is preferably a high cis type having a cis-1,4 bond content of 95% or more.

  According to the rubber composition for a tire tread of the present invention, sulfur and a specific vulcanizing agent capable of forming a long-chain crosslinked structure are used in combination, and a sulfenamide-based vulcanization is used as a primary vulcanization accelerator. By using thiuram vulcanization accelerators as accelerators and secondary vulcanization accelerators, the cross-linking network structure between rubber molecules can be made appropriate, thereby rolling while maintaining wear resistance and workability. Resistance, heat generation, and heat aging can be improved to improve the fuel efficiency and durability of a pneumatic tire.

  Hereinafter, embodiments of the present invention will be described.

  The tire tread rubber composition according to the present invention is selected from diene rubber components, sulfur, 1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane, and sulfenamide vulcanization accelerators. All of at least one vulcanization accelerator and at least one vulcanization accelerator selected from thiuram vulcanization accelerators are contained.

  Examples of the diene rubber used as the rubber component include natural rubber and diene synthetic rubbers such as isoprene rubber, butadiene rubber, and styrene-butadiene rubber. These may be used alone or in combination of two kinds. You may blend and use above.

  Preferably, the diene rubber is composed of 100 to 50% by weight of natural rubber and / or isoprene rubber and 0 to 50% by weight of butadiene rubber. That is, natural rubber and / or isoprene rubber alone or a blend of this with butadiene rubber is preferable. When blended, the natural rubber and / or isoprene rubber is preferably 50% by weight or more and the butadiene rubber is preferably 50% by weight or less, more preferably, the natural rubber and / or isoprene rubber is 50 to 90% by weight, The butadiene rubber is 10 to 50% by weight.

  As the butadiene rubber, a high cis type rubber having a cis-1,4 bond content of 95% or more is preferable for improving wear resistance. Here, the cis-1,4 bond content is a value measured by an infrared absorption spectrum method (Morello method).

  In the rubber composition of the present invention, sulfur and 1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane are used in combination as a vulcanizing agent.

  Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and oil-treated sulfur. Two or more of these sulfurs may be used in combination.

1,6-Bis (N, N-dibenzylthiocarbamoyldithio) hexane has a —SS— (CH ₂ ) ₆ —SS— structure in the molecule, and is a polymer molecule when used in combination with sulfur. By forming a polysulfide bond between them to form a long-chain crosslinked structure appropriately, the exothermic property, heat aging property, and resistance to vulcanization can be improved, and in particular, the exothermic property and heat aging property can be improved.

  As the 1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane, Bayer Vulcuren KA9188 can be used as a commercial product.

  In addition, the rubber composition of the present invention includes at least one vulcanization accelerator selected from sulfenamide vulcanization accelerators as a primary vulcanization accelerator and thiuram vulcanization as a secondary vulcanization accelerator. At least one vulcanization accelerator selected from accelerators is used.

  The primary vulcanization accelerator is a component formulated to reduce the amount of sulfur as a vulcanizing agent, shorten the vulcanization time, and lower the vulcanization temperature. Can be demonstrated.

  As the primary vulcanization accelerator, at least one vulcanization accelerator selected from sulfenamide vulcanization accelerators is used.

  Examples of the sulfenamide vulcanization accelerator include N-cyclohexyl-2-benzothiazole sulfenamide (CBS (CZ)), N-tert-butylbenzothiazole-2-sulfenamide (BBS (NS)), N- Examples include oxydiethylene-2-benzothiazole sulfenamide (OBS), N, N-diisopropyl-2-benzothiazole sulfenamide (DPBS), N, N-dicyclohexyl-2-benzothiazole sulfenamide, and the like. These can be used alone or in combination of two or more.

  Although the secondary vulcanization accelerator itself does not exhibit a sufficient vulcanization acceleration effect, it exhibits an auxiliary effect on the primary vulcanization accelerator. As the secondary vulcanization accelerator, at least one vulcanization accelerator selected from thiuram vulcanization accelerators is used.

  Thiuram-based vulcanization accelerators include tetramethylthiuram monosulfide (TMTM), tetramethylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD), tetrabutylthiuram disulfide (TBTD), tetrakis (2-ethylhexyl) thiuram disulfide ( TOT-N), thiuram compounds such as dipentamethylene thiuram disulfide, dipentamethylene thiuram monosulfide, dipentamethylene thiuram tetrasulfide, dipentamethylene thiuram hexasulfide, tetrabutyl thiuram disulfide, pentamethylene thiuram tetrasulfide These can be used alone or in combination of two or more.

  Sulfenamide vulcanization accelerators tend to produce many polysulfide bonds, and thiuram vulcanization accelerators tend to increase monosulfide bonds, and sulfur and 1,6-bis are used as vulcanizing agents. Using (N, N-dibenzylthiocarbamoyldithio) hexane to combine the sulfenamide and thiuram vulcanization accelerators as vulcanization accelerators to optimize the cross-linking structure and to provide the characteristics of polymers and carbon black Taking advantage of this, it is possible to reduce rolling resistance while maintaining wear resistance and workability, and improve heat generation and heat aging in a well-balanced manner.

In order for the rubber composition of the present invention to sufficiently exhibit the above effects, the sulfur (A), 1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane (B), sulfenamide-based additive, The sulfur accelerator (C) and the thiuram vulcanization accelerator (D) are each blended in an amount of 0.1 to 2 parts by weight with respect to 100 parts by weight of the diene rubber component, and each of (A) to (D) It is preferable that the blending part satisfies all the relationships of the following formulas (1) to (5).
(A) ≧ (B) (1)
(C) ≧ (D) (2)
1.0 ≦ (A) + (B) ≦ 2.0 (3)
1.0 ≦ (C) + (D) ≦ 2.0 (4)
0.5 ≦ {(A) + (B)} / {(C) + (D)} ≦ 1.5 (5)

  By configuring in this way, rubber suitable for tire treads that secures the initial physical properties of the rubber composition, reduces rolling resistance while maintaining wear resistance and workability, and balances heat generation and heat aging properties. A composition can be obtained.

  When each of the above compounding agents is less than 0.1 parts by weight, the effect of the present invention is not sufficiently obtained. When the amount exceeds 2 parts by weight, exothermic property and heat aging property can be improved, but rubber physical properties are lowered and wear resistance and rolling are reduced. Resistance deteriorates, vulcanization speed increases, and scorch properties deteriorate.

  The blended parts by weight of the vulcanizing agents (A) and (B), when the relationship of the formula (1) is not satisfied, the scorch property and the fatigue resistance are lowered, and when the relationship of the formula (3) is not satisfied, Abrasion is reduced.

  The weight parts of the vulcanization accelerators (C) and (D) are reduced in scorch and fatigue resistance if the relationship of the formula (2) is not satisfied, and the breaking strength if the relationship of the formula (4) is not satisfied. Abrasion resistance is reduced.

  Also, if the relationship of formula (5) is not satisfied and the amount of vulcanizing agent is too much or too little relative to the vulcanization accelerator, the rubber physical properties such as the breaking strength are lowered, and the wear resistance and fatigue resistance are deteriorated. Will be invited.

  In the rubber composition of the present invention, the carbon black used as the reinforcing agent preferably satisfies the following requirements (1) and (2).

(1) CTAB adsorption specific surface area (CTAB) is 110 to 150 m ² / g,
(2) The compressed DBP absorption amount (24M4DBP) is 100 ml / 100 g or more.

  By using carbon black having the above colloidal properties, a rubber composition having a highly improved rolling resistance and wear resistance can be obtained by further strengthening the network with the polymer without impairing heat generation and heat aging. Can do.

The CTAB (cetyltrimethylammonium bromide) adsorption specific surface area of (1) above is a value measured according to ASTM D3765 and serves as an index of the particle size of carbon black. When CTAB is less than 110 m ² / g, it is not possible to obtain good wear resistance particularly as a tread rubber for large tires, and when it exceeds 150 m ² / g, wear resistance is improved, but dispersibility is reduced, The performance of carbon black cannot be fully demonstrated.

  The compressed DBP (dibutyl phthalate) absorption amount of (2) above is a 24M4 DBP absorption amount measured in accordance with ASTM D3493 (hereinafter sometimes abbreviated as “24M4DBP”), and is an indicator of the structure of carbon black. It will be. In the present invention, a high structure product having 24M4DBP of 100 ml / 100 g is used, and if it is less than 110 ml / 100 g, the effect of improving the wear resistance is small. The upper limit of 24MDBP is not particularly limited, but if it exceeds 120 ml / 100 g, the dispersibility of carbon black deteriorates and the workability deteriorates. Therefore, the upper limit of 24MDBP is preferably about 120 ml / 100 g. As such carbon black, SAF and ISAF grade carbon black can be used.

  The blending amount of the carbon black is about 40 to 60 parts by weight with respect to 100 parts by weight of the rubber component. If the blending amount of the carbon black is less than 40 parts by weight, the wear resistance becomes insufficient. Exceeding parts by weight tends to deteriorate exothermic properties.

  In addition to the components described above, the rubber composition of the present invention includes various additives generally used in rubber compositions for tire treads such as anti-aging agents, zinc white, stearic acid, softeners, processing aids, and the like. Can be blended.

  The rubber composition for a tire tread of the present invention having the above-described method is prepared by a conventional method using a rubber kneader such as a Banbury mixer or a kneader. Workability at the time of kneading is improved, and it is suitable as a cap tread portion of heavy duty pneumatic tires such as trucks and buses. The tread portion can be formed by vulcanization molding according to a conventional method.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  To 100 parts by weight of a total rubber component in which natural rubber (NR) (RSS 3) and butadiene rubber (BR) (manufactured by JSR Corporation, BR01, cis-1,4 bond content = 96%) were blended, Carbon black, vulcanizing agent, and vulcanization accelerator are blended in the blending amounts shown in Tables 1 and 2, and 3 parts by weight of zinc white (Mitsui Metal Mining Co., Ltd., zinc white 1) , 3 parts by weight of stearic acid (manufactured by NOF Corporation) and 1.5 parts by weight of an anti-aging agent (manufactured by Monsanto, 6PPD) were added and kneaded in a 200 liter closed-type Banbury mixer for each rubber composition Was prepared.

[Carbon black (CB)]
CB1: “Seast 9” manufactured by Tokai Carbon Co., Ltd., CTAB = 126 m ² / g, 24M4DBP = 100 ml / 100 g
CB2: “Seast 6” manufactured by Tokai Carbon Co., Ltd., CTAB = 111 m ² / g, 24M4DBP = 100 ml / 100 g
CB3: “Seast KH” manufactured by Tokai Carbon Co., Ltd., CTAB = 95 m ² / g, 24M4DBP = 101 ml / 100 g

[Vulcanizing agent]
・ Sulfur: “5% oil-treated powder sulfur” manufactured by Tsurumi Chemical Co., Ltd.
1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane: “Vulcuren KA9188” manufactured by Bayer
[Vulcanization accelerator]
・ Vulcanization accelerator CZ (N-cyclohexyl-2-benzothiazolesulfenamide): “Soccinol CZ” manufactured by Sumitomo Chemical Co., Ltd.
・ Vulcanization accelerator NS (N-tert-butylbenzothiazole-2-sulfenamide): “Suncellor NS-G” manufactured by Sanshin Chemical Industry Co., Ltd.
・ Vulcanization accelerator TBzTD (tetrabenzylthiuram disulfide): “Oxeller TBzTD” manufactured by Ouchi Shinsei Chemical Co., Ltd.
・ Vulcanization accelerator TOT-N (tetrakis (2-ethylhexyl) thiuram disulfide): “Noxeller TOT-N” manufactured by Ouchi Shinsei Chemical Co., Ltd.

  Each rubber composition obtained was evaluated for processability, and initial rubber properties were prepared by vulcanization at 150 ° C. for 30 minutes to prepare a sample. 300% modulus, breaking strength, wear resistance, fatigue resistance The exothermic properties were evaluated according to the following test methods and are shown in Tables 1 and 2.

  Furthermore, the 300% modulus, breaking strength, and exothermicity were evaluated using the same test method for heat aging characteristics (aging conditions: 150 ° C., vulcanization for 60 minutes). The heat aging characteristics are shown in Tables 1 and 2 in terms of the retention rate with the test result of the initial characteristics as 100.

  Next, radial tires for trucks and buses of size 11R22.5 14PR in which each rubber composition was applied to a tire tread cap rubber were manufactured, and rolling resistance was measured.

-300% modulus, breaking strength: A tensile test (dumbbell shape No. 3) was performed according to JIS K6251, the 300% modulus and breaking strength were measured, and the value was expressed as an index with the value of Comparative Example 1 being 100.

Processability: Mooney viscosity was measured according to JIS K6300, and displayed as an index with the value of Comparative Example 1 being 100. The smaller the index, the better the workability.

Abrasion resistance: The amount of wear was measured by a lambone test in accordance with JIS K6264. (Standard conditions: slip rate 30%, applied load 40N, amount of falling sand 20 g / min), the value of Comparative Example 1 is represented by an index of 100. It shows that it is excellent in abrasion resistance, so that an index | exponent is large.

-Fatigue resistance: Evaluated by bending inferiority test according to JIS K6260. On the basis of Comparative Example 1, the equivalent case was displayed as “◯” and the inferior case as “x”.

Exothermic property: Evaluated by viscoelastic properties (tan δ at 60 ° C.). The tan δ at 60 ° C. was measured using a spectrometer manufactured by Toyo Seiki Co., Ltd., with a frequency of 10 Hz, an initial elongation of 10%, and a strain amplitude of 2%, and was expressed as an index with the value of Comparative Example 1 being 100. It shows that it is excellent in exothermic property, so that an index | exponent is small.

Rolling resistance: The rolling resistance was measured in accordance with the force measurement method of the rolling resistance test method for tires for trucks and buses of JATMA. It was displayed as an index with the value of Comparative Example 1 being 100. The smaller the index, the smaller the rolling resistance and the better the fuel economy.

  As is known from Tables 1 and 2, Examples 1 to 6 according to the present invention ensure the initial rubber physical properties by using a specific vulcanizing agent and a vulcanization accelerator, wear resistance and processing. It can be seen that the heat generation property, heat aging property and rolling resistance can be improved while maintaining the properties, and the fuel efficiency and durability performance of the pneumatic tire can be improved.

  On the other hand, Comparative Example 2 in which the colloidal characteristics of carbon black are not satisfied does not achieve wear resistance, and Comparative Example 3 in which the vulcanization accelerator is CZ alone has a small effect of improving heat generation and heat aging, In Comparative Example 4 in which the vulcanizing agent is only sulfur, the exothermic improvement effect is small, the breaking strength is lowered, and the heat aging property is not improved. Further, in Comparative Example 5 where the blending amount is sulfur <KA9188 and in Comparative Example 6 where the primary vulcanization accelerator is less than the secondary vulcanization accelerator, the scorch property and fatigue resistance are deteriorated. Further, in Comparative Examples 7 and 8 in which KA9188 or TBzTD is less than 0.1 parts by weight, no improvement was observed in heat generation and heat aging, and in Comparative Examples 9 and 10 in which KA9188 or TBzTD exceeds 2 parts by weight, Although heat aging property is improved, breaking strength, wear resistance, and fatigue resistance are deteriorated, and a well-balanced improvement cannot be obtained.

  The rubber composition for a tire tread of the present invention can be suitably used as a rubber composition for forming a tread portion of a large pneumatic tire such as for trucks and buses, particularly a heavy duty tire.

Claims (5)

In diene rubber component,
Selected from sulfur, 1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane, at least one vulcanization accelerator selected from sulfenamide vulcanization accelerators, and thiuram vulcanization accelerators A rubber composition for tire treads, comprising at least one vulcanization accelerator. For 100 parts by weight of the diene rubber component,
At least one vulcanization accelerator (C) selected from the sulfur (A), 1,6-bis (N, N-dibenzylthiocarbamoyldithio) hexane (B), and a sulfenamide-based vulcanization accelerator; And at least one vulcanization accelerator (D) selected from thiuram-based vulcanization accelerators is blended in an amount of 0.1 to 2 parts by weight, and each part by weight of (A) to (D) is represented by the following formula (1): The rubber composition for a tire tread according to claim 1, wherein all of the relations (1) to (5) are satisfied.
(A) ≧ (B) (1)
(C) ≧ (D) (2)
1.0 ≦ (A) + (B) ≦ 2.0 (3)
1.0 ≦ (C) + (D) ≦ 2.0 (4)
0.5 ≦ {(A) + (B)} / {(C) + (D)} ≦ 1.5 (5) Furthermore, 40 to 60 weight percent of carbon black having a CTAB adsorption specific surface area (CTAB) of 110 to 150 m ² / g and a compressed DBP absorption amount (24M4DBP) of 100 ml / 100 g or more with respect to 100 parts by weight of the diene rubber component. The rubber composition for a tire tread according to claim 1 or 2, wherein the rubber composition for tire tread is mixed.   The rubber for tire tread according to any one of claims 1 to 3, wherein the diene rubber comprises 100 to 50 parts by weight of natural rubber and / or isoprene rubber and 0 to 50 parts by weight of butadiene rubber. Composition. The rubber composition for a tire tread according to claim 4, wherein the butadiene rubber is a high cis type having a cis-1,4 bond content of 95% or more.