JP2007284554A - Rubber composition for base tread - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for base treads, improving all of steering stability, rolling resistance and cord adhesion without impairing cut resistance and crack growth resistance. <P>SOLUTION: The rubber composition for base treads comprises 100 pts.wt. of a rubber component comprising (a) 20-60 wt.% of a polybutadiene rubber containing 2.5-20 wt.% of 1,2-syndiotactic polybutadiene crystal, (b) 5-80 wt.% of a tin-modified polybutadiene rubber made by using a lithium initiator, 50-3,000 ppm in tin atom content, 5-50 wt.% in vinyl linkage and 2 or less in molecular weight distribution index(Mw/Mn) and (c) 10-75 wt.% of a rubber other than the rubbers(a) and (b), and 2.5-3.5 pts.wt. of sulfur. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rubber composition for a base tread.

  In recent years, various means have been taken up in order to reduce the rolling resistance of a tire (improve the rolling resistance characteristic) or improve the steering stability of a vehicle for the purpose of energy saving. As a means for this, the tread of the tire has a double structure (inner surface layer and surface layer), and a rubber composition exhibiting excellent rolling resistance characteristics and steering stability is used for the base tread as the inner surface layer. It is done.

  Patent Document 1 discloses a rubber composition for a tire containing a polybutadiene rubber having 1 to 25% of 1,2-syndiotactic polybutadiene crystals as a rubber component, but when it is used as a base tread However, there is a problem that it is impossible to satisfy both the maneuverability mainly related to the rigidity and the tan δ related to the rolling resistance.

Japanese Patent Laid-Open No. 11-349732

  An object of the present invention is to provide a rubber composition for a base tread capable of improving all of handling stability, rolling resistance characteristics and cord adhesion without reducing cut resistance and crack growth resistance. .

  In the present invention, (a) 20 to 60% by weight of polybutadiene rubber containing 2.5 to 20% by weight of 1,2-syndiotactic polybutadiene crystals, (b) polymerized by a lithium initiator, and the content of tin atoms is 5 to 80% by weight of tin-modified polybutadiene rubber having 50 to 3000 ppm, vinyl bond content of 5 to 50% by weight, and molecular weight distribution (Mw / Mn) of 2 or less, and (c) Other than (a) and (b) The present invention relates to a rubber composition for a base tread containing 2.5 to 3.5 parts by weight of sulfur with respect to 100 parts by weight of a rubber component containing 10 to 75% by weight of rubber.

  The rubber composition for base tread preferably has a swelling degree (Swell) of 240 to 270%.

  According to the present invention, by containing a predetermined amount of a predetermined rubber component and sulfur, all of steering stability, rolling resistance characteristics, and cord adhesion can be improved without reducing cut resistance and crack growth resistance. It is possible to provide a rubber composition for a base tread that can be used.

  The rubber composition for base treads of the present invention contains a rubber component and sulfur.

  The rubber component includes (a) a polybutadiene rubber containing 1,2-syndiotactic polybutadiene crystals (BR (a)), (b) a tin-modified polybutadiene rubber (BR (b)) and (c) (a) and ( Contains rubber other than b) (rubber (c)).

  In BR (a), 1,2-syndiotactic polybutadiene crystal (SPB) is not simply dispersed in BR (a), but is chemically bonded to BR (a) and dispersed non-oriented. It is preferable. When the crystals are chemically bonded to the rubber component and then dispersed, the generation and propagation of cracks tend to be suppressed.

  The melting point of SPB is preferably 180 ° C. or higher, and more preferably 190 ° C. or higher. When the melting point of SPB is less than 180 ° C., crystals melt during vulcanization of the tire by pressing, and the hardness tends to decrease. The melting point of SPB is preferably 220 ° C. or lower, and more preferably 210 ° C. or lower. When the melting point of SPB exceeds 220 ° C., the molecular weight of BR (a) increases, so that dispersibility tends to deteriorate in the rubber composition.

  The content of the boiling n-hexane insoluble matter in BR (a) is preferably 2.5% by weight or more, and more preferably 8% by weight or more. When the content of the boiling n-hexane insoluble matter is less than 2.5% by weight, there is a tendency that sufficient hardness of the rubber composition cannot be obtained. Further, the content of boiling n-hexane insolubles is preferably 22% by weight or less, more preferably 20% by weight or less, and further preferably 18% by weight or less. When the content of boiling n-hexane insolubles exceeds 22% by weight, the viscosity of BR (a) itself is high, and the dispersibility of BR (a) and filler in the rubber composition tends to deteriorate. Here, the boiling n-hexane insoluble means 1,2-syndiotactic polybutadiene (SPBD) in BR (a).

  The content of SPB in BR (a) is 2.5% by weight or more, preferably 10% by weight or more. When the SPB content is less than 2.5% by weight, the hardness is insufficient. The content of SPB in BR (a) is 20% by weight or less, preferably 18% by weight or less. If the SPB content exceeds 20% by weight, BR (a) is difficult to disperse in the rubber composition, and processability deteriorates.

  The content of BR (a) in the rubber component is 20% by weight or more, preferably 30% by weight or more. When the content of BR (a) is less than 20% by weight, the cut resistance and crack growth are inferior. The BR (a) content is 60% by weight or less, preferably 50% by weight or less. If the BR (a) content exceeds 60% by weight, the tensile fracture characteristics of the rubber composition deteriorate, leading to a decrease in the BR (b) content in the rubber composition, and tan δ increases. .

  BR (b) is obtained by polymerizing 1,3-butadiene with a lithium initiator and then adding a tin compound, and the end of the BR (b) molecule is bound by a tin-carbon bond. It is preferable.

  Examples of the lithium initiator include lithium and lithium compounds such as alkyl lithium, aryl lithium, allyl lithium, vinyl lithium, organic tin lithium, and organic nitrogen lithium compounds. By using lithium or a lithium compound as an initiator for BR (b), BR (b) having a high vinyl content and a low cis content can be produced.

  Examples of tin compounds include tin tetrachloride, butyltin trichloride, dibutyltin dichloride, dioctyltin dichloride, tributyltin chloride, triphenyltin chloride, diphenyldibutyltin, triphenyltin ethoxide, diphenyldimethyltin, ditolyltin chloride, diphenyltin dichloride. Examples include octanoate, divinyldiethyltin, tetrabenzyltin, dibutyltin distearate, tetraallyltin, and p-tributyltin styrene, which may be used alone or in combination of two or more.

  The content of tin atoms in BR (b) is 50 ppm or more, preferably 60 ppm or more. If the tin atom content is less than 50 ppm, the effect of promoting the dispersion of carbon black in BR (b) is small, and tan δ increases. Moreover, the content rate of a tin atom is 3000 ppm or less, Preferably it is 2500 ppm or less, More preferably, it is 250 ppm or less. If the content of tin atoms exceeds 3000 ppm, the kneaded material is not well-organized and the edges are not aligned, so that the extrudability of the kneaded material is deteriorated.

  The molecular weight distribution (Mw / Mn) of BR (b) is 2 or less, preferably 1.5 or less. When Mw / Mn of BR (b) exceeds 2, the dispersibility of carbon black deteriorates and tan δ increases.

  The vinyl bond content of BR (b) is 5% by weight or more, preferably 7% by weight or more. When the vinyl bond content of BR (b) is less than 5% by weight, it is difficult to polymerize (manufacture) BR (b). The vinyl bond content of BR (b) is 50% by weight or less, preferably 20% by weight or less. When the vinyl bond amount of BR (b) exceeds 50% by weight, the dispersibility of carbon black tends to be poor and the tensile strength tends to be weak.

  The content of BR (b) in the rubber component is 5% by weight or more, preferably 10% by weight or more. When the content of BR (b) is less than 5% by weight, the effect of reducing tan δ cannot be sufficiently obtained. The content of BR (b) is 80% by weight or less, preferably 40% by weight or less. When the content of BR (b) exceeds 80% by weight, the effect of reducing tan δ is not improved, the total content of rubber (c) and BR (a) is 20% by weight or less, and the tensile strength and hardness are descend.

  The rubber (c) is a rubber other than BR (a) and BR (b). Specific examples include high-cis 1,4-polybutadiene rubber other than natural rubber (NR), isoprene rubber (IR), styrene butadiene rubber (SBR), BR (a), and BR (b). Of these, NR is preferred because of its excellent tensile strength. Further, as rubber (c), it is also preferable to use a combination of NR and IR, or a high-cis 1,4-polybutadiene rubber other than NR and BR (a) and BR (b).

  The content of rubber (c) in the rubber component is 10% by weight or more, preferably 20% by weight or more, more preferably 30% by weight or more. When the content of the rubber (c) is less than 10% by weight, sufficient tensile strength and cut resistance cannot be obtained. The content of BR (c) in the rubber component is 75% by weight or less, preferably 60% by weight or less. When the content of BR (c) exceeds 75% by weight, the total content of BR (a) and BR (b) becomes 25% by weight or less, and reduction of tan δ and improvement of hardness cannot be achieved.

  As sulfur, insoluble sulfur generally used in the rubber industry can be suitably used.

  The sulfur content is at least 2.5 parts by weight, preferably at least 2.7 parts by weight, based on 100 parts by weight of the rubber component. If the sulfur content is less than 2.5 parts by weight, sufficient hardness cannot be obtained. In addition, in this case, sulfur flows from the rubber composition for cord coating adjacent to the base tread, and the sulfur around the cord is insufficient. As a result, the code adhesion deteriorates. The sulfur content is 3.5 parts by weight or less, preferably 3.3 parts by weight or less. If the sulfur content exceeds 3.5 parts by weight, in this case, sulfur will flow out to the cap tread adjacent to the base tread, and the cap tread will harden, causing tread cracking and groove cracking. Performance decreases, or rolling resistance increases.

  The rubber composition for a base tread of the present invention contains a predetermined rubber component and sulfur in a predetermined amount, so that steering stability, rolling resistance characteristics, and cord adhesion are not deteriorated without reducing cut resistance and crack growth resistance. Can be improved in a balanced manner.

  The rubber composition for a base tread of the present invention may further contain a reinforcing filler.

  Examples of the reinforcing filler include carbon black, silica, calcium carbonate, clay, alumina, aluminum hydroxide, talc and the like, and carbon black is preferable because sufficient hardness and reinforcing properties are easily obtained.

  When the reinforcing filler is contained, the content of the reinforcing filler is preferably 25 parts by weight or more and more preferably 30 parts by weight or more with respect to 100 parts by weight of the rubber component. When the content of the reinforcing filler is less than 25 parts by weight, the hardness tends to decrease and the reinforcing property tends to be insufficient. Further, the content of the reinforcing filler is preferably 50 parts by weight or less, and more preferably 45 parts by weight or less. When the content of the reinforcing filler exceeds 50 parts by weight, the heat generation tends to be high.

  In addition to the rubber component, sulfur and reinforcing filler, the rubber composition for base tread of the present invention includes compounding agents conventionally used in the rubber industry, such as softeners such as aroma oil, waxes, and various anti-aging agents. An agent, stearic acid, zinc oxide, various vulcanization accelerators and the like can be appropriately blended as necessary.

  The swelling degree (SWELL) of the rubber composition for a base tread of the present invention is preferably 240% or more, and more preferably 245% or more. When the SWELL of the rubber composition for a base tread of the present invention is less than 240%, the crosslinking density is too high and the crack growth resistance tends to be inferior. The SWELL of the rubber composition for a base tread of the present invention is preferably 270% or less, and more preferably 265% or less. When the SWELL of the rubber composition for a base tread of the present invention exceeds 270%, sufficient hardness cannot be obtained, and the cut resistance and cord adhesion tend to be inferior.

  The JIS-A hardness of the rubber composition for a base tread of the present invention is preferably 60 or more, and more preferably 62 or more. If the rubber composition for base treads of the present invention has a JIS-A hardness of less than 60, steering stability and cut resistance tend to be reduced. The JIS-A hardness of the rubber composition for a base tread of the present invention is preferably 75 or less, more preferably 70 or less. When the JIS-A hardness of the rubber composition for a base tread of the present invention exceeds 75, the crack growth resistance tends to decrease.

  The rubber composition for a base tread of the present invention is blended with the above-mentioned compounding agents as necessary, kneaded, extruded in accordance with the shape of the base tread of the tire at an unvulcanized stage, and placed on a tire molding machine. By bonding together with other tire members, an unvulcanized tire is formed, and further, the tire can be obtained by heating and pressing the unvulcanized tire in a vulcanizer.

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

Next, various chemicals used in Examples and Comparative Examples will be described together.
Butadiene rubber (a) (BR (a)): VCR617 (polybutadiene rubber containing 1,2-syndiotactic polybutadiene crystal, 1,2-syndiotactic polybutadiene crystal (SPB), manufactured by Ube Industries, Ltd. : 17% by weight, melting point of SPB: 200 ° C., content of boiling n-hexane insoluble matter: 15 to 18% by weight)
Butadiene rubber (b) (BR (b)): BR1250 (tin-modified polybutadiene rubber (modified BR) manufactured by Nippon Zeon Co., Ltd., polymerization using lithium as an initiator, vinyl bond amount: 10 to 13% by weight, Mw / Mn: 1.5, tin atom content: 250 ppm)
Rubber (c): Natural rubber (NR, RSS # 3)
Carbon Black: Show Black (N330) manufactured by Cabot Japan
Aroma oil: Diana Process AH-24 manufactured by Idemitsu Kosan Co., Ltd.
Wax: Sunnock anti-aging agent manufactured by Ouchi Shinsei Chemical Co., Ltd .: NOCRACK 6C (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shin Chemical Co., Ltd. )
Stearic acid: Zinc stearate oxide manufactured by Nippon Oil & Fats Co., Ltd .: Zinc Hua No. 1 insoluble sulfur manufactured by Mitsui Mining & Smelting Co., Ltd. Insoluble matter: 60% or more)
Vulcanization accelerator: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

Examples 1-4 and Comparative Examples 1-7
In accordance with the formulation of Table 1, various chemicals other than vulcanizing fillers such as sulfur and vulcanization accelerators are kneaded in a BR type Banbury, then sulfur and vulcanization accelerator are added, and 8 inches are added. It knead | mixed on 90 degreeC conditions using the roll, and obtained the unvulcanized rubber composition. This was vulcanized and molded at 170 ° C. for 12 minutes at a pressure of 25 kgf / cm ² to prepare vulcanized rubber compositions of Examples 1 to 4 and Comparative Examples 1 to 7.

(Swelling degree (SWELL))
The obtained vulcanized rubber composition was extracted with toluene, and the volume change rate (swelling degree, SWELL) before and after extraction was measured.

(Hardness measurement)
The hardness of the resulting vulcanized rubber composition was measured using a JIS-A hardness meter in accordance with JIS K 6253 “Method for testing hardness of vulcanized rubber and thermoplastic rubber”.

(Viscoelasticity test)
Using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd., loss tangent tan δ at 70 ° C. was measured under the conditions of a frequency of 10 Hz, an initial strain of 10% and a dynamic strain of 2%. In addition, it shows that rolling resistance is reduced and it is excellent, so that the value of tan-delta is small.

(Cut resistance)
Cut index With a pendulum type impact cutting tester, a 20 mm wide steel blade was used to load the scratches, the depth of the cut scratches was measured, and the cut resistance index of Example 1 was set to 100 using the following formula: And the depth of cut flaws of each formulation was displayed as an index. In addition, it shows that it is excellent in cut resistance, so that a cut resistance index is large.
(Cut resistance index) = (Depth of cut flaw of Example 1)
÷ (depth of cut flaws for each formulation) x 100

(Flexible crack growth resistance)
According to JIS K 6260 “Demach bending cracking test method for vulcanized rubber and thermoplastic rubber”, the length of the crack when it was repeatedly bent 120,000 times was measured. The growth index was set to 100, and the crack length of each formulation was displayed as an index. In addition, it shows that it is excellent in the bending crack growth resistance, so that a bending crack growth resistance index | exponent is large.
(Bending crack growth resistance index) = (crack length of Example 1)
÷ (length of crack in each formulation) x 100

(Adhesion peel test)
An unvulcanized rubber sheet having a thickness of 2 mm is cut out from the unvulcanized rubber composition, and the unvulcanized carcass having a thickness of 1.25 mm and coated with a cord, the unvulcanized rubber sheet, Unvulcanized cap treads with a thickness of 6 mm were laminated in order, and vulcanized and bonded for 18 minutes under the condition of 165 ° C. to prepare a vulcanized lab rubber sheet for an adhesion peel test. This was peeled at a tensile speed of 50 mm / min at room temperature, the peel strength (N / mm) was measured, the cord adhesion index of Example 1 was taken as 100, and the peel strength of each formulation was displayed as an index according to the following formula. did. In addition, it shows that it is excellent in code | cord adhesiveness, so that a code | cord adhesiveness index is large.
(Cord adhesion index) = (Peel strength of each formulation)
÷ (Peel strength of Example 1) × 100

  The evaluation results of the above test are shown in Table 1.

Claims (2)

(A) 20 to 60% by weight of polybutadiene rubber containing 2.5 to 20% by weight of 1,2-syndiotactic polybutadiene crystals;
(B) A tin-modified polybutadiene rubber polymerized by a lithium initiator and having a tin atom content of 50 to 3000 ppm, a vinyl bond content of 5 to 50% by weight, and a molecular weight distribution (Mw / Mn) of 2 or less is 5 to 5. 80 parts by weight and (c) 100 parts by weight of a rubber component containing 10 to 75% by weight of rubber other than (a) and (b)
A rubber composition for a base tread containing 2.5 to 3.5 parts by weight of sulfur. The rubber composition for a base tread according to claim 1, wherein the swelling degree (Swell) is 240 to 270%.