JP2008013609A - Rubber composition for base tread of heavy load tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a base tread of a heavy load tire, having a small rolling resistance, and excellent in abrasion resistance and vulcanizing property. <P>SOLUTION: This rubber composition for the base tread of the heavy load tire is provided by containing a diene-based rubber, carbon black having 80 to 135 m<SP>2</SP>/g nitrogen adsorption specific surface area (N<SB>2</SB>SA) and 100 to 140 mL/100 g DBP oil absorption amount, a sulfenamide-based vulcanization accelerator, 0.1 to 1 pt.wt. tetrabenzylthiuram disulfide based on 100 pts.wt. diene-based rubber and 1.6 to 2.0 pts.wt. sulfur based on 100 pts.wt. diene-based rubber, and having 3 to 5 MPa storage elastic modulus E' (80°C) of its vulcanized material at 80°C and 0.03 to 0.08 tanδ (80°C). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rubber composition for a base tread of a heavy duty tire, a heavy duty pneumatic tire using the rubber composition, and a method for producing a heavy duty pneumatic tire, and further has a small rolling resistance. The present invention relates to a rubber composition for a base tread having excellent wear resistance and vulcanizability.

  Conventionally, in order to reduce the fuel consumption of automobiles in heavy-duty tires used for trucks and buses, development studies have been conducted on the base tread rubber compound as part of the reduction of hysteresis loss in the tread rubber part. Examples of such a rubber composition for base tread include those containing silica and a silane coupling agent.

  However, although the rubber composition containing silica can achieve improvement in rolling resistance and heat generation, wear resistance is lowered. In heavy-duty tires, it is generally used even after the base tread is exposed on the tread surface, so the wear resistance of the base tread is also important for extending the tire life. It will lead to deterioration of life.

  Further, the rubber composition containing silica generally has a slow vulcanization rate, and there is a problem that the scorch resistance deteriorates when trying to improve the vulcanization rate with a general-purpose vulcanization accelerator. Improvement is difficult. In particular, the base tread located on the inner side in the radial direction compared to the cap tread is difficult to vulcanize because it is far from the heat source at the time of vulcanization molding. Therefore, when a rubber composition containing silica is used for the base tread, it is produced. It is difficult to ensure sex.

  By the way, although it is known to mix | blend tetrabenzyl thiuram disulfide in the rubber composition for tires (refer the following patent documents 1-3), the said subject cannot be solved only by this prior art.

  For example, in the following Patent Document 1, in a dread rubber composition for a heavy duty tire, sulfur, a sulfenamide vulcanization accelerator, and tetrabenzyl thiuram disulfide may be blended in a predetermined ratio with a diene rubber. It is disclosed. However, this document improves the elongation at break after aging of rubber, suppresses an increase in heat generation, and suppresses a decrease in elongation at break at high temperatures. Tetrabenzylthiuram disulfide together with specific carbon black It is not disclosed that blending can improve vulcanization speed and scorch resistance without impairing not only low heat build-up but also wear resistance. In addition, there is no disclosure regarding the specific blending with the base tread.

Patent Document 2 below discloses that diene rubber is compounded with sulfur and tetrabenzylthiuram disulfide. This document mainly describes tread rubber for passenger car tires, and grip performance and steering stability. It is only intended to improve wear and wear.
JP 2002-206035 A JP 2002-226629 A JP 11-49897 A JP 2005-344064 A

  An object of the present invention is to provide a rubber composition for a base tread of a heavy-duty tire that has low rolling resistance and excellent wear resistance and vulcanizability.

  As a result of diligent investigations in view of the above problems, the present inventor has found that a blend containing a specific carbon black and tetrabenzylthiuram disulfide in a diene rubber has rolling resistance and heat generation without impairing wear resistance and vulcanizability. As a result, the present invention was completed.

That is, the rubber composition for base treads of heavy duty tires according to the present invention has a diene rubber, a nitrogen adsorption specific surface area (N ₂ SA) of 80 to 135 m ² / g and a DBP oil absorption of 100 to 140 ml / 100 g. A carbon black, a sulfenamide vulcanization accelerator, 0.1 to 1 part by weight of tetrabenzylthiuram disulfide with respect to 100 parts by weight of the diene rubber, and 1 with respect to 100 parts by weight of the diene rubber. 6 to 2.0 parts by weight of sulfur, and the vulcanizate has a storage elastic modulus E ′ (80 ° C.) at 80 ° C. of 3 to 5 MPa and a tan δ (80 ° C.) of 0.03. It is -0.08, It is characterized by the above-mentioned.

  Moreover, the heavy-duty pneumatic tire according to the present invention has a base tread made of the rubber composition at a ratio of 20 to 70% with respect to the total capacity of the tread rubber portion.

  The present invention also provides a method for producing a heavy duty pneumatic tire comprising a tread rubber portion composed of a cap tread and a base tread, and the method comprises a rubber containing tetrabenzyl thiuram disulfide in the base tread. A rubber composition not containing tetrabenzyl thiuram disulfide is used for the cap tread, and the cap tread is vulcanized and molded in a state where the cap tread is laminated on the outer side in the radial direction of the base tread. is there.

  When the rubber composition of the present invention is used as a base tread for a heavy duty tire, the rolling resistance is small, heat generation can be suppressed, the wear resistance is excellent, and the vulcanization speed is increased while the scorch resistance is increased. Deterioration is suppressed and vulcanizability is excellent, and thus productivity can be improved.

  Further, according to the method for producing a heavy-duty pneumatic tire of the present invention, with respect to a base tread that is far from a heat source during vulcanization molding and has poor heat resistance, by adding tetrabenzylthiuram disulfide to the rubber composition, the scorch resistance is improved. The productivity can be improved by improving the vulcanization speed without deteriorating the temperature. In addition, for cap treads that are close to the heat source during vulcanization molding and have good heat resistance, by not adding tetrabenzylthiuram disulfide to the rubber composition, it is possible to reduce costs and suppress overvulcanization.

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

  Examples of the diene rubber in the rubber composition of the present invention 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. 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.

The carbon black used in the rubber composition of the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of 80 to 135 m ² / g and a DBP oil absorption of 100 to 140 ml / 100 g. Both are specified in order to achieve both heat generation and wear resistance. When the N ₂ SA or DBP oil absorption is smaller than the above range, the wear resistance is inferior. Sex worsens.

Here, the nitrogen adsorption specific surface area (N ₂ SA) is a value measured according to JIS K6217-2, and the DBP (dibutyl phthalate) oil absorption is a value measured according to JIS K6217-4. .

  The compounding amount of the carbon black is preferably 30 to 40 parts by weight with respect to 100 parts by weight of the diene rubber. If the blending amount of carbon black is less than 30 parts by weight, it will be difficult to ensure wear resistance, and if it exceeds 40 parts by weight, it will be difficult to ensure rolling resistance and heat generation.

  Examples of the sulfenamide-based vulcanization accelerator compounded in the rubber composition of the present invention include N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N-tert-butyl-2-benzothiazoli. Rusulfenamide (BBS), N-oxydiethylene-2-benzothiazolylsulfenamide (OBS), N, N-diisopropyl-2-benzothiazolylsulfenamide (DPBS), N, N-dicyclohexyl-2- Examples thereof include benzothiazolylsulfenamide, and these may be used alone or in combination of two or more. The blending amount of the sulfenamide vulcanization accelerator is preferably 0.5 to 2 parts by weight with respect to 100 parts by weight of the diene rubber.

  A small amount of tetrabenzyl thiuram disulfide (TBzTD) is blended with the sulfenamide vulcanization accelerator in the rubber composition of the present invention. Although the sulfenamide vulcanization accelerator alone can improve the vulcanization speed, it has a drawback of short scorch, but by adding a small amount of tetrabenzylthiuram disulfide, the vulcanization speed is improved. The scorch can be lengthened and has excellent vulcanizability.

  Tetrabenzyl thiuram disulfide is blended at 0.1 to 1 part by weight with respect to 100 parts by weight of the diene rubber. If the blending amount is too small, the effect of addition cannot be obtained, and if it is too large, there arises a problem that the scorch resistance deteriorates or the wear resistance deteriorates.

  In the rubber composition of the present invention, sulfur is added as a vulcanizing agent in an amount of 1.6 to 2.0 parts by weight with respect to 100 parts by weight of the diene rubber. If the amount of sulfur is small, the vulcanization rate is slow and the rolling resistance is poor, and conversely if too much sulfur, the scorch resistance is deteriorated and the wear resistance is poor.

  In addition to the components described above, the rubber composition for base treads of the present invention is generally used in rubber compositions for base treads of heavy duty tires such as softeners, plasticizers, anti-aging agents, zinc white, and stearic acid. Various additives can be blended.

  The rubber composition for base tread of the present invention has a vulcanized product having the following physical properties. That is, the storage elastic modulus E ′ (80 ° C.) of the vulcanized product is 3 to 5 MPa, and the loss coefficient tan δ (80 ° C.) satisfies 0.03 to 0.08. If these physical properties are not satisfied, the wear resistance, rolling resistance, and low heat build-up cannot be achieved as a base tread. More specifically, if E ′ (80 ° C.) is smaller than the above range, the exothermic property of the base tread is impaired, and conversely, if it is larger, the wear resistance of the cap tread is impaired. Further, if tan δ (80 ° C.) is larger than the above range, rolling resistance is impaired, and conversely, it is substantially difficult to make it smaller than the above range due to the type of carbon black, the blending amount, and the regulation of E ′. It is.

  Here, the storage elastic modulus E ′ and tan δ are values measured using a viscoelastic spectrometer under measurement conditions of initial strain: 5%, dynamic strain: ± 2%, frequency: 10 Hz, and temperature of 80 ° C. is there.

  A heavy-duty pneumatic tire according to the present invention includes a tread rubber portion including a base tread on an inner layer side provided on a radially outer side of a belt and a cap tread on a ground contact surface side provided on a radially outer side of the belt. . The base tread rubber composition is used as the base tread, and the ratio of the base tread to the total capacity of the tread rubber portion, that is, the base tread / tread rubber as a whole is provided at a ratio of 20 to 70%. If the capacity ratio of the base tread is less than 20%, the effect of reducing the rolling resistance as a tire becomes insufficient. Conversely, if it exceeds 70%, the wear resistance is poor.

  In the method for producing a heavy duty pneumatic tire according to the present invention, more specifically, a rubber composition is prepared by blending a base tread with a diene rubber and tetrabenzylthiuram disulfide, and a cap tread with a diene. A rubber composition was prepared without adding tetrabenzylthiuram disulfide to the rubber, the rubber composition layer of the base tread was provided on an unvulcanized belt, and the rubber composition layer of the cap tread was provided thereon. A green tire is produced, and the obtained green tire is vulcanized in a mold.

  As the base tread rubber composition, the above base tread rubber composition containing carbon black, sulfenamide vulcanization accelerator, tetrabenzyl thiuram disulfide, and sulfur is used as the diene rubber. Is preferred.

On the other hand, the rubber composition of the cap tread is not particularly limited as long as it does not contain tetrabenzyl thiuram disulfide, but it is usually a diene composed of natural rubber and / or isoprene rubber, or a blend of these with butadiene rubber. Carbon black, a sulfenamide vulcanization accelerator, sulfur, and other various additives are blended with the rubber. The carbon black preferably has a nitrogen adsorption specific surface area (N ₂ SA) equal to or greater than that of the carbon black compounded in the base tread rubber composition. Moreover, it is preferable that the compounding quantity is larger than the compounding quantity of the carbon black in the rubber composition of a base tread. Thus, in a cap tread, the wear resistance can be improved by blending a large amount of carbon black having a high activity equal to or higher than that of the base tread. Moreover, in the rubber composition of a cap tread, it is preferable from the point of abrasion resistance to mix | blend a small amount of sulfur rather than a base tread.

  Such a rubber composition can be prepared using various mixers such as a Banbury mixer, a roll, a kneader, or a sheet-shaped rubber composition kneaded with a cap tread and a base tread, respectively, Alternatively, a tread rubber portion having a two-layer structure can be formed by extruding into a two-layer structure with an extruder. The green tire having the tread rubber portion is vulcanized and molded in a mold according to a conventional method, and thus vulcanized and molded in a state in which a cap tread is laminated on the outer side in the radial direction of the base tread.

  At the time of this vulcanization molding, for the base tread that is far from the heat source and bad around the heat, the rubber composition contains tetrabenzyl thiuram disulfide, so the vulcanization rate can be improved without deteriorating the scorch resistance. And productivity can be improved. For cap treads that are close to the heat source and have good heat resistance, even if tetrabenzylthiuram disulfide is not blended, there is no shortage of vulcanization, but rather it can be used to reduce costs. Further, over-vulcanization can be suppressed as much as possible.

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

  Using a Banbury mixer, a rubber composition for base tread was prepared according to the composition shown in Table 2 below. Details of each compound in Table 2 are as follows.

・ Natural rubber: RSS No. 3,
・ Butadiene rubber: “BR150L” manufactured by Ube Industries,
・ Silica: Nippon Silica “Nip Seal AQ”
Silane coupling agent: “Si69” manufactured by Degussa
Accelerator CZ: Sulfenamide vulcanization accelerator “Soccinol CZ” (N-cyclohexyl-2-benzothiazolylsulfenamide (CBS)) manufactured by Sumitomo Chemical,
TBzTD: “Tetrabenzylthiuram disulfide” manufactured by Flexis,
・ Sulfur: “5% oil-treated powdered sulfur” manufactured by Tsurumi Chemical.

The carbon blacks CB1 to CB6 are as shown in Table 1 below.

  In each rubber composition, as a common formulation, 100 parts by weight of diene rubber, 1 part by weight of aroma oil ("Process X140" manufactured by JOMO), 1 part by weight of wax ("OZOACE0355" manufactured by Nippon Seiki), zinc white 3 parts by weight (Mitsui Kinzoku "Zinc Hana 1"), 1 part by weight of stearic acid (manufactured by Nippon Oil & Fats), and 1 part by weight of an antioxidant ("6PPD" manufactured by Monsanto) were blended.

  About each rubber composition, the storage elastic modulus E 'and tan-delta of the vulcanizate were measured. The measurement was performed using a viscoelastic spectrometer for a test piece (length × width × thickness = 20 mm × 5 mm × 1 mm) vulcanized at 150 ° C. × 30 minutes. The measurement conditions were as follows: at a temperature of 80 ° C., vibrations with an initial strain of 5%, a dynamic strain of ± 2%, and a frequency of 10 Hz were applied in the length direction. The results are shown in Table 2.

  Each rubber composition was measured and evaluated for vulcanization speed and scorch resistance. The results are shown in Table 2. The measurement method is as follows.

Vulcanization rate: For each unvulcanized rubber composition, a test in accordance with JIS K6300-2 was performed using a rheometer, and the t90 value at the time of measurement at a temperature of 150 ° C. was displayed as an index with Comparative Example 1 being 100. did. The smaller the index, the faster and better the vulcanization rate.

・ Scorch resistance: For each unvulcanized rubber composition, Mooney scorch test in accordance with JIS K6300-1 was performed using a Mooney viscosity tester (using an L-shaped rotor), preheating for 1 minute, at a temperature of 125 ° C The t5 value was expressed as an index with Comparative Example 1 taken as 100. A larger index indicates better scorch resistance.

  In addition, a radial tire for a truck having a tire size of 11R22.5 14PR was produced according to a conventional method using each of the rubber compositions described above as a base tread. The volume ratio of the base tread to the entire tread rubber portion is as shown in Table 2. The rubber composition of cap tread is 100 parts by weight of natural rubber (RSS3), 50 parts by weight of carbon black (CB1), 3 parts by weight of zinc white (Mitsui Metals "Zinc Hana 1"), stearic acid (Japan) 2 parts by weight of oil and fat, 3 parts by weight of aroma oil ("Process X140" manufactured by JOMO), 2 parts by weight of anti-aging agent ("6PPD" manufactured by Monsanto), 2 parts by weight of wax ("OZOACE0355" manufactured by Nippon Seiki), sulfur (Tsurumi Chemical "5% oil-treated powder sulfur") 1.2 parts by weight, vulcanization accelerator (Sumitomo Chemical "Soxinol CZ") 1.2 parts by weight.

  About the obtained tire, rolling resistance and abrasion resistance were measured with the following method.

-Rolling resistance: Based on the force measurement method of the rolling resistance test method for JATMA truck and bus tires, it was expressed as an index with Comparative Example 1 as 100. It shows that rolling resistance is so small that a numerical value is small.

Abrasion resistance: The distance traveled to the tread was measured with an actual vehicle, and displayed as an index with Comparative Example 5 taken as 100. It shows that abrasion resistance is so favorable that a numerical value is large.

As shown in Table 2, in Comparative Example 1 of the control, since the amount of carbon black was large, tan δ was high and the rolling resistance was large. In Comparative Example 2, although TBzTD was blended, N ₂ SA of the carbon black to be used in combination was small, so that the wear resistance was inferior. Moreover, in Comparative Example 3, although TBzTD was blended, N ₂ SA of the carbon black used in combination was large, and almost no effect of improving rolling resistance was obtained. In Comparative Example 4, the amount of carbon black was too large, tan δ was high, and the rolling resistance improvement effect was hardly obtained.

  On the other hand, in the silica compound as in Comparative Example 5, the vulcanization rate was slow and the scorch resistance was poor. In addition, the scorch resistance was poor when TBzTD was not added as in Comparative Example 6. Further, when the amount of sulfur was small as in Comparative Example 7, the vulcanization rate was slow, and conversely, when the amount of sulfur was large as in Comparative Example 8, the wear resistance was deteriorated and the scorch resistance was also poor. In Comparative Example 9, since the amount of TBzTD was large, the scorch resistance was deteriorated. Moreover, in Comparative Example 10, the DBP oil absorption of carbon black was small, and therefore the wear resistance was deteriorated.

  Further, in Comparative Example 11, the ratio of the base tread was small, and therefore, the rolling resistance was inferior. In Comparative Example 12, the ratio of the base tread was too large and the wear resistance was deteriorated.

  On the other hand, when it is Examples 1-7, while being excellent in rolling resistance compared with the comparative example 1, compared with the comparative example 5 of a silica mixing | blending, the abrasion resistance which is the fault was improved. Moreover, compared with these comparative examples 1 and 5, the vulcanization speed and scorch resistance were improved.

  As described above, according to the present invention, it is possible to improve vulcanizability (productivity) as well as wear resistance and rolling resistance. Therefore, large tires used for trucks and buses, that is, heavy duty tires. Can be suitably used.

Claims (4)

A diene rubber, a carbon black having a nitrogen adsorption specific surface area (N ₂ SA) of 80 to 135 m ² / g and a DBP oil absorption of 100 to 140 ml / 100 g, a sulfenamide vulcanization accelerator, and the diene system 0.1 to 1 part by weight of tetrabenzylthiuram disulfide with respect to 100 parts by weight of rubber, and 1.6 to 2.0 parts by weight of sulfur with respect to 100 parts by weight of the diene rubber,
Base of heavy duty tire, characterized in that storage elastic modulus E ′ (80 ° C.) at 80 ° C. of vulcanizate is 3 to 5 MPa and tan δ (80 ° C.) is 0.03 to 0.08. Rubber composition for tread.   The rubber composition for base treads according to claim 1, wherein the carbon black is contained in an amount of 30 to 40 parts by weight based on 100 parts by weight of the diene rubber.   A heavy-duty pneumatic tire having a base tread made of the rubber composition according to claim 1 or 2 at a ratio of 20 to 70% with respect to the total capacity of the tread rubber portion. A method of manufacturing a heavy duty pneumatic tire having a tread rubber portion comprising a cap tread and a base tread, wherein a rubber composition containing tetrabenzyl thiuram disulfide is used for the base tread, and tetrabenzyl thiuram disulfide is used for the cap tread. A method for producing a heavy duty pneumatic tire, characterized in that a rubber composition containing no vulcanization is used to vulcanize the cap tread in a state of being laminated on the radially outer side of the base tread.