JP5248211B2 - Heavy duty tire tread rubber composition and heavy duty pneumatic tire - Google Patents

Description

  The present invention relates to a rubber composition used for a tread of a heavy load tire such as a truck or a bus, and a heavy load pneumatic tire using the rubber composition.

  In heavy-duty pneumatic tires used for large vehicles such as trucks and buses, the wear resistance of the tread portion is extremely important. Conventionally, in order to improve the wear resistance, a high cis type butadiene rubber having a high cis-1,4 bond content is used as a rubber component of a rubber composition used for a tread, or as a filler. There have been proposed measures such as using carbon black having a small particle diameter, having a high structure, or increasing the amount of carbon black (see, for example, Patent Document 1).

  Although these measures are expected to improve wear resistance, the workability in the kneading process is deteriorated, and the low heat generation characteristics necessary for tread rubber of heavy-duty tires, cut resistance and chip resistance are adversely affected. There is a drawback of affecting.

  In order to solve the above processability problem, generally, by adding a processing aid, the viscosity of the rubber composition is reduced to improve the processability. It has been proposed to add a fatty acid metal salt containing potassium or calcium, a fatty acid amide, a fatty acid ester, or the like to the rubber composition (see, for example, Patent Documents 2 and 3).

However, when the above fatty acid metal salt is simply used as a processing aid, the effect of improving the workability by reducing the viscosity is recognized, but the low heat build-up is impaired.
JP 2006-2045 A JP 2005-206673 A JP 2001-233997 A

  The present invention has been made in view of the above points, and a tire tread rubber composition for heavy loads that can satisfy the three aspects of wear resistance, low heat build-up and processability, and for heavy loads using the same. An object is to provide a pneumatic tire.

The tire tread rubber composition for heavy loads according to the present invention has a CTAB adsorption specific surface area of 115 to 150 m ² / g and a compressed DBP oil absorption (24M4DBP) of 100 to 120 ml / 100 g with respect to 100 parts by weight of the diene rubber. And the ratio of the nitrogen adsorption specific surface area (N ₂ SA) to the iodine adsorption amount (IA) N ₂ SA (m ² / g) / IA (g / kg) is 0.95 to 1.30 Processing aid for fatty acid metal salt containing 40-60 parts by weight of black and a peptizer consisting of 2,2′-dibenzamide diphenyl disulfide, zinc salt of 2-benzamidothiophenol, xylyl mercaptan or β-naphthyl mercaptan 0.5 to 5.0 parts by weight of the agent is blended.

  The heavy duty pneumatic tire according to the present invention includes a tread made of a rubber composition.

  According to the present invention, by using a specific processing aid having an effect of promoting kneading together with the specific carbon black, it is possible to simultaneously satisfy the three aspects of wear resistance, low heat generation and workability. Excellent performance as a tread rubber for heavy duty tires can be imparted.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  In the rubber composition of the present invention, examples of the diene rubber used as a rubber component include natural rubber, and diene synthetic rubbers such as isoprene rubber, butadiene rubber, and styrene-butadiene rubber. You may use, and you may blend and use 2 or more types.

  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 60 to 90% by weight, The butadiene rubber is 10 to 40% 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).

  The butadiene rubber preferably has a toluene solution viscosity (T-cp) of 100 or more at 25 ° C. When T-cp is less than 100, workability is improved, but wear resistance and low heat build-up tend to be deteriorated, and tire performance is deteriorated. Here, T-cp is the value of the viscosity of a toluene solution at 25 ° C. and 10 wt% measured by a Brookfield (BL) viscometer (value indicated in centipoise (cp)).

  The carbon black used in the rubber composition of the present invention satisfies the following requirements (1) to (3).

(1) CTAB adsorption specific surface area is 115 to 150 m ² / g,
(2) The compressed DBP oil absorption (24M4DBP) is 100 to 120 ml / 100 g, and
(3) nitrogen adsorption specific surface area _(N 2 SA) / iodine adsorption (IA) is from 0.95 to 1.30.

  By using carbon black that satisfies all of these requirements, it is possible to further strengthen the network with the rubber polymer and improve the wear resistance while suppressing the deterioration of low heat build-up.

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. If CTAB is less than 115 m ² / g, good wear resistance cannot be obtained as a tread rubber for heavy duty tires. If it exceeds 150 m ² / g, wear resistance is improved, but dispersibility is reduced. The performance of carbon black cannot be fully exhibited. As the carbon black having a CTAB of 115 to 150 m ² / g, those of SAF class and ISAF class (ASTM grade) can be used. A more preferable lower limit of CTAB is 125 m ² / g, and a more preferable upper limit is 140 m ² / g.

  The compressed DBP (dibutyl phthalate) oil absorption amount of (2) is a 24M4DBP oil absorption amount measured in accordance with JIS K6217-4 (hereinafter sometimes abbreviated as “24M4DBP”), and has a carbon black structure. It is an indicator of In the present invention, a high structure product having 24M4DBP of 100 to 120 ml / 100 g is used. If it is less than 100 ml / 100 g, the effect of improving the wear resistance is inferior. , Workability decreases. A more preferable lower limit of 24M4DBP is 105 ml / 100 g, and a more preferable upper limit is 110 ml / 100 g.

The nitrogen adsorption specific surface area (N ₂ SA) / iodine adsorption amount (IA) in (3) is an index of the surface activity of carbon black. N ₂ SA (m ² / g) is a value measured according to JIS K6217-2, and IA (g / kg) is a value measured according to JIS K6217-5. When N ₂ SA / IA is less than 0.95, a balanced effect cannot be obtained in wear resistance and low heat build-up. If N ₂ SA / IA exceeds 1.30, the dispersibility of the carbon black is deteriorated and the processability is lowered. A more preferred lower limit of N ₂ SA / IA is 1.10, and a more preferred lower limit is 1.20.

  The compounding amount of the carbon black is 40 to 60 parts by weight with respect to 100 parts by weight of the diene rubber. When the blending amount of the carbon black is less than 40 parts by weight, the wear resistance is deteriorated. On the other hand, when it exceeds 60 parts by weight, the low heat build-up is deteriorated.

  The rubber composition of the present invention contains a processing aid of a fatty acid metal salt containing a peptizer along with the carbon black. By using a specific processing aid having such a kneading promoting effect, it is possible to improve low heat buildup and workability while maintaining or improving wear resistance, as shown in the examples described later. . That is, when a processing aid for a simple fatty acid metal salt was used, the processability was improved, but the tendency to deteriorate the low heat build-up was seen. However, by containing a peptizer, the rubber component polymer As a result of appropriately cutting the molecular chain, the uniformity of the rubber composition can be improved and a low heat generation effect can be exhibited.

  The amount of the processing aid is 0.5 to 5.0 parts by weight with respect to 100 parts by weight of the diene rubber component. If the blending amount is less than 0.5 parts by weight, the effects of the present invention are hardly obtained. Conversely, if the blending amount exceeds 5.0 parts by weight, the processability is excellent but the molecular chain scission of the rubber component polymer is large. As a result, the modulus decreases and the low heat build-up deteriorates.

  The fatty acid of the fatty acid metal salt is a saturated or unsaturated fatty acid having 6 to 28 carbon atoms, such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, arachidic acid, behenic acid. And nervonic acid. These may be used alone or in combination of two or more. Preferably, a saturated fatty acid having 14 to 20 carbon atoms is used. Examples of the metal forming the salt of these fatty acids include alkali metals such as potassium and sodium, alkaline earth metals such as magnesium, calcium and barium, zinc, nickel and molybdenum, and zinc is particularly preferable. These fatty acid metal salts may be used alone or in combination of two or more.

  The peptizer can be used as long as it can react with the molecular chain radical of the cut rubber component polymer to suppress recombination. For example, 2,2′-dibenzamide diphenyl disulfide (DBD) , Zinc salt of 2-benzamidothiophenol, xylyl mercaptan, β-naphthyl mercaptan and the like, and DBD is particularly preferable.

  The processing aid preferably contains 5 to 10% by weight of a peptizer. If the content of the peptizer is less than 5% by weight, the uniformity of the rubber composition is insufficient and it is difficult to exert a low exothermic effect, and if it exceeds 10% by weight, the molecular chain breakage of the rubber component polymer This is disadvantageous in terms of low exothermicity.

  As a processing aid for the fatty acid zinc salt containing 5 to 10% by weight of DBD, “Actiplast MS” manufactured by Rhein Chemie is exemplified as a suitable one.

  In addition to the above components, the rubber composition of the present invention includes a rubber composition for tire treads such as zinc white, stearic acid, anti-aging agent, softener such as oil, vulcanizing agent such as sulfur, and vulcanization accelerator. Various additives generally used in products can be blended. The rubber composition is prepared by kneading according to a conventional method using a rubber kneader such as a normal Banbury mixer or kneader.

  The rubber composition comprising the above is suitable for a tread portion, particularly a tread cap portion of a heavy duty pneumatic tire such as a truck or a bus. And the pneumatic radial tire provided with this tread part can be produced by carrying out 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.

  80 parts by weight of natural rubber (RSS # 3) and 100 parts by weight of a diene rubber component in which 20 parts by weight of the following butadiene rubber (BR1,2) are blended, 50 parts by weight of carbon black (CB1-4) having the following characteristics, In addition, the following processing aids 1 and 2 are blended in the blending amounts shown in Table 1, respectively, and, as other components, 3 parts by weight of zinc white (Mitsui Metal Mining Co., Ltd. “Zinc Flower 1”), stearin 3 parts by weight of acid (“Beadstearic acid” manufactured by NOF Corporation), 1 part by weight of anti-aging agent (“6PPD” manufactured by Monsanto), 2 parts by weight of sulfur (“5% oil-treated powdered sulfur” manufactured by Tsurumi Chemical Co., Ltd.) Parts, 1 part by weight of a vulcanization accelerator (“SOC SEAL CZ” manufactured by Sumitomo Chemical Co., Ltd.) was added and kneaded with a Banbury mixer to prepare a heavy load tire tread rubber composition.

[Butadiene rubber]
BR1: “BR150L” manufactured by Ube Industries, Ltd. (cis-1,4 bond content = 98%, T-cp = 105),
BR2: “CB24” manufactured by LANXESS (cis-1,4 bond content = 95%, T-cp = 147).

[Carbon black]
CB1: “Seast 9” manufactured by Tokai Carbon Co., Ltd. (CTAB = 132 m ² / g, 24M4DBP = 97 ml / 100 g, N ₂ SA / IA = 0.99),
CB2: test carbon (CTAB = 137 m ² / g, 24M4DBP = 97 ml / 100 g, N ₂ SA / IA = 1.16),
CB3: test carbon (CTAB = 137 m ² / g, 24M4DBP = 109 ml / 100 g, N ₂ SA / IA = 1.25),
CB4: “Seast 6” manufactured by Tokai Carbon Co., Ltd. (CTAB = 119 m ² / g, 24M4DBP = 102 ml / 100 g, N ₂ SA / IA = 0.99),
Note that the test carbons (CB2, CB3) are produced in the production of carbon black, a combustion chamber having a tangential air supply port on the furnace head and a combustion burner mounted in the furnace axial direction, and coaxial with the combustion chamber. Using an oil furnace configured by a multistage narrow-diameter reaction chamber and a wide-diameter reaction chamber having a continuous feed oil injection nozzle, the split feed conditions for feedstock oil, the supply amount of fuel oil and air, oxygen gas It was obtained by adjusting the addition conditions.

[Processing aid]
Processing aid 1: Fatty acid zinc salt containing 5 to 10% by weight of DBD as a peptizer (constituent fatty acid is a saturated fatty acid having 18 carbon atoms as a main component), “Actiplast MS” manufactured by Rhein Chemie,
Processing aid 2: Saturated fatty acid zinc salt, “Actinplast PP” manufactured by Rhein Chemie.

  Each rubber composition obtained was measured and evaluated for processability, 300% modulus, abrasion resistance, low heat build-up, carbon black dispersity, and bound rubber amount. Each measurement / evaluation method is as follows.

Processability: The Mooney viscosity at 100 ° C. was measured according to JIS K6300, and displayed as an index with the value of Comparative Example 1 being 100. It shows that it is excellent in workability, so that an index | exponent is small.

300% modulus: Using a test piece obtained by vulcanizing each rubber composition, a tensile test (dumbbell-shaped No. 3) was performed in accordance with JIS K6251, the 300% modulus was measured, and the value of Comparative Example 1 was 100. It was expressed as an index.

Abrasion resistance: Abrasion amount was measured by a lambone test in accordance with JIS K6264 using a test piece obtained by vulcanizing each rubber composition. Standard conditions were shown as an index with a slip rate of 30%, a load of 40 N, a sandfall amount of 20 g / min, and the value of Comparative Example 1 as 100. It shows that it is excellent in abrasion resistance, so that an index | exponent is large.

Low exothermic property: Viscoelastic properties (tan δ at 60 ° C.) were evaluated using test pieces obtained by vulcanizing each rubber composition. 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. The smaller the index, the less heat is generated and the lower the exothermic property.

-Carbon black dispersion degree: The dispersion ratio per unit area of carbon black in the rubber cross section when unvulcanized rubber was vulcanized and cut was measured. The carbon black is all dispersed, and the state where aggregation cannot be confirmed is represented by an index of 100. The larger the value, the better the carbon black is dispersed in the rubber composition.

Bound rubber amount: 1 g of unvulcanized rubber cut into 2 mm square and the mass of the mesh basket are individually weighed individually, and the sample rubber is put in the mesh basket and put in a solvent bottle. Add 200 ml of toluene to the solvent bottle and leave at 30 ± 2 ° C. for 45 hours. Take out the mesh cage, dry it in the draft chamber until there is no odor of toluene, leave it for 2 hours using a vacuum dryer, weigh it precisely, subtract the mass of the mesh cage from that value, and extract the sample after extraction Find the mass. And the bound rubber amount (mass%) as a rubber | gum quantity couple | bonded with carbon black was computed from the following formula, and displayed with the index | exponent which set the value of the comparative example 1 to 100. The larger the index, the more bound rubber and the better the wear resistance.
Bound rubber amount (% by mass) = {A− (B × C / D)} / (B × E / D) × 100
Here, A = sample weight after extraction, B = sample weight before extraction, C = total number of parts of toluene insoluble compounding agent, D = total number of compounding parts, E = number of rubber component compounding parts.

  The results are as shown in Table 1. In Comparative Examples 1 and 2 using carbon blacks CB1 and CB2 in which 24M4DBP is outside the specified value, the effect of achieving both wear resistance and low heat build-up was insufficient. In Comparative Example 2 using carbon black CB2, the workability was greatly deteriorated. In Comparative Example 3 in which the processing aid 1 of a fatty acid metal salt containing a peptizer was combined with the carbon black CB2, the processability was improved, but the improvement effect of wear resistance and low heat build-up was insufficient. there were.

  Further, in Comparative Example 4 using carbon black CB3 having a small particle size and a structure and surface activity both within the specified values, although the wear resistance was improved, the workability was greatly deteriorated. Dispersibility was poor and the performance of the original carbon black could not be fully exhibited. In Comparative Example 5, the processability was improved by blending the processing aid 2 made of a fatty acid metal salt, but the low heat build-up was deteriorated.

  On the other hand, when it is Examples 1-6 which mix | blended the processing aid 1 of the fatty acid metal salt containing a peptizer with the carbon black with the said specific colloidal characteristic, the particle size reduction of carbon black, high Suppression of processability due to surface activation is suppressed, and the dispersibility of carbon black is improved, so that the interaction between the rubber polymer and carbon black increases, and the amount of bound rubber increases, resulting in further wear resistance. It was possible to improve. In addition, the low heat build-up was greatly improved as compared with the case of using a simple fatty acid metal salt processing aid.

  In Comparative Example 6 in which the blending amount of processing aid 1 is too small, the effect of improving processability is insufficient. Conversely, in Comparative Example 7 in which the blending amount of processing aid 1 is too large, 300% modulus is obtained. The temperature decreased and the exothermicity deteriorated.

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

Claims (5)

For 100 parts by weight of diene rubber,
CTAB adsorption specific surface area is 115 to 150 m ² / g, compressed DBP oil absorption (24M4DBP) is 100 to 120 ml / 100 g, and nitrogen adsorption specific surface area (N ₂ SA) ratio relative to iodine adsorption amount (IA) N ₂ 40 to 60 parts by weight of carbon black having a value of SA (m ² / g) / IA (g / kg) of 0.95 to 1.30,
2,2′-dibenzamide diphenyl disulfide, zinc salt of 2-benzamidothiophenol , processing aid for fatty acid metal salt containing a peptizer comprising xylyl mercaptan or β-naphthyl mercaptan 0.5 to 5.0 weight A heavy-duty tire tread rubber composition characterized by comprising a part.   The tire tread rubber composition for heavy loads according to claim 1, 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.   3. The heavy load according to claim 2, wherein the butadiene rubber has a cis-1,4 bond content of 95% or more and a toluene solution viscosity (T-cp) at 25 ° C. of 100 or more. Tire tread rubber composition.   The said peptizer is 2,2'- dibenzamide diphenyl disulfide, The said processing aid contains 5-10 weight% of this peptizer, The any one of Claims 1-3. Tire tread rubber composition for heavy loads.   The heavy duty pneumatic tire provided with the tread which uses the rubber composition of any one of Claims 1-4.