JP5478809B2 - Rubber composition and pneumatic tire - Google Patents

Description

  The present invention relates to a rubber composition and a pneumatic tire using the same.

  Conventionally, as a filler for rubber reinforcement, by replacing part of carbon black with silica, the hydrogen bonding of silanol groups present on the silica surface improves the reinforcement and improves the wetness and fuel efficiency of the tire. It is known to do. However, silica is prone to agglomerate due to the influence of its silanol group and has poor dispersibility, so that there is a problem that the above performance cannot be exhibited sufficiently. For this reason, various proposals have been made to improve the dispersibility of silica.

  For example, Patent Document 1 listed below uses a blend of general-purpose silica having a large amount of silanol groups and silica having a small amount of silanol groups, thereby reducing aggregation due to hydrogen bonding of the silanol groups, and elasticity during microdeformation. It is disclosed that the rate E ′ is decreased to improve the wet performance and reduce the rolling resistance. However, if silica having a small amount of silanol groups is simply used, there is a concern that the reinforcing property is lowered.

Patent Document 2 below discloses that the dispersibility is improved by using silica having a specific particle size distribution and surface reactivity and / or porosity, and the physical properties of silica are 50 to 300 m. The relationship between the BET specific surface area of ² / g, the amount of silanol groups and the CTAB specific surface area is specified, and the pH of the reaction system in the silica production method is specified. However, the pH of the obtained silica is not specified, and those used in the examples are also outside the scope of the present invention.
JP 10-36559 A JP 2005-500420 A

  The present inventor has intensively studied for the purpose of improving the dispersibility of silica, and defines the silanol group amount of silica within a predetermined range smaller than that of general-purpose silica, and the silica pH is relatively low. By defining it within a low predetermined range, the dispersibility of silica can be dramatically improved, thereby improving the tensile product at the time of breaking the rubber composition and improving the adhesion to the steel cord. I found out.

  That is, an object of the present invention is to provide a rubber composition capable of improving the rubber breaking property and improving the adhesiveness with a steel cord by improving the dispersibility of silica.

The rubber composition according to the present invention has a BET specific surface area of 50 to 300 m ² / g, a silanol group amount per unit surface area of 5 to 11 per nm ² per 100 parts by weight of diene rubber, and JIS. It contains 5 to 100 parts by weight of silica having a pH of 4.5 to 6.0 measured by K6220 method B.
In the present invention, the amount of silanol groups per unit surface area (units / nm ² ) is calculated from the BET specific surface area and Qactual by the following formula (X). Here, Qactual is the amount of silanol groups per unit weight (mmol / g), and is calculated by Si-NMR described in "Journal of the American Chemical Society", 114, 6412 (1992).
Silanol group amount [units / nm ² ] = (Qactual [mmol / g] × N _A ) / S [m ² / g] (X)
Wherein, N _A is the Avogadro constant, S is a BET specific surface area.

  The pneumatic tire according to the first embodiment of the present invention has a tread made of the rubber composition. A pneumatic tire according to a second embodiment of the present invention includes a rubber-steel cord composite made of the rubber composition and a steel cord.

  According to the present invention, by blending the above specific silica, the dispersibility of the silica is improved, and it becomes possible to improve the breaking characteristics of the rubber and improve the adhesion with the steel cord. .

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

  In the rubber composition of the present invention, the diene rubber is not particularly limited, but natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, styrene-isoprene rubber, butadiene-isoprene rubber, nitrile rubber, ethylene-propylene- A diene terpolymer etc. are mentioned, These can be used individually or in mixture of 2 or more types, respectively.

  Preferably, in the case of a rubber composition for a tire tread, one or a combination of two or more of natural rubber, butadiene rubber, and styrene-butadiene rubber is used. More specifically, a blend of natural rubber and butadiene rubber Styrene-butadiene rubber alone or a blend of styrene-butadiene rubber and butadiene rubber is preferred. In the case of a steel cord bonding rubber composition, natural rubber alone is preferable.

Silica used in the rubber composition of the present invention is
(1) BET specific surface area: 50 to 300 m ² / g,
(2) Silanol group (SiOH) amount per unit surface area: 5 to 11 / nm ² , and
(3) pH measured by JIS K6220 B method: 4.5 to 6.0,
It has the characteristic of.

The BET specific surface area of the above (1) is measured according to ASTM D4820. BET specific surface area is preferably 100 to 250 m ² / g, more preferably 150 to 200 m ² / g. When the BET specific surface area is too small, the total silanol groups are reduced, and it becomes difficult to ensure the breaking characteristics and the adhesiveness to the steel cord. Conversely, if the BET specific surface area is too large, it becomes difficult to ensure workability.

The amount of silanol groups per unit surface area (number / nm ² ) in ( ² ) is calculated from the following formula (X) from the BET specific surface area and Qactual. Qactual is the amount of silanol groups per unit weight (mmol / g), and is calculated by Si-NMR described in "Journal of the American Chemical Society", 114, 6412 (1992).
Silanol group amount [units / nm ² ] = (Qactual [mmol / g] × N _A ) / S [m ² / g] (X)
Wherein, N _A is the Avogadro constant, S is a BET specific surface area.

The regulation of the amount of silanol groups is to use silica having a smaller amount of silanol groups than conventional general-purpose silica. By prescribing the amount of silanol groups within the above-mentioned predetermined range, which is smaller than conventional ones, it is possible to improve the dispersibility of silica while securing the amount of silanol groups that can contribute to the improvement of fracture characteristics and adhesiveness. When the amount of silanol groups is more than 11 / nm ² , the dispersibility is impaired, the elongation at break is low, and the breaking properties are deteriorated. On the other hand, if the amount of silanol groups is less than 5 / nm ² , the breaking strength is lowered, the breaking properties are deteriorated, and the adhesiveness to the steel cord is also lowered. The amount of the silanol group is more preferably 5 to 10 / nm ² , and further preferably 6 to 8 / nm ² .

  The pH of the above (3) is the pH of the silica slurry measured by JIS K6220 7.3.4.2 method B (glass electrode type tabletop pH meter (type I)) (measurement temperature: 20 ° C.). . Thus, the improvement effect of a fracture | rupture characteristic and adhesiveness can be heightened by using the silica whose pH in a slurry state is lower than the conventional general purpose silica. If the pH is higher than 6.0, the amount of silanol groups increases and the elongation at break becomes low. On the other hand, if the pH is lower than 4.5, the amount of silanol groups is reduced and the breaking strength is lowered. The pH of such silica is more preferably 5 to 5.5.

  Conventionally, silica having few silanol groups has been generally produced by a dry method, but in the present invention, it is produced by a wet method and uses wet silica having the above characteristics (1) to (3). It is preferable. Cost can also be reduced by using wet silica. Examples of such silica include “Siloa 72X” manufactured by Rhodia, and its use is recommended.

  In the present invention, the silica is blended in an amount of 5 to 100 parts by weight with respect to 100 parts by weight of the diene rubber. When the blending amount of the silica is less than 5 parts by weight, the above-described effects of the present invention cannot be sufficiently exhibited. The amount of silica is more preferably 5 to 50 parts by weight.

  The rubber composition of the present invention may contain carbon black as a filler together with silica, although it is not essential, and the carbon black may be added in an amount of 0 to 100 parts by weight with respect to 100 parts by weight of the rubber component. preferable. Silica and carbon black are preferably blended in a total amount of 20 to 150 parts by weight.

  The rubber composition of the present invention includes various additives such as a silane coupling agent, a vulcanizing agent, a vulcanization accelerator, an anti-aging agent, a softening agent, a plasticizer, an activator, and a lubricant in addition to the above-described components. Can be added as needed.

  In particular, in the case of a steel cord bonding rubber composition, an organic acid metal salt such as an organic acid cobalt salt as an adhesion interface layer formation accelerator may be blended. Examples of the organic acid forming the organic acid metal salt include stearic acid, naphthenic acid, octylic acid, oleic acid, maleic acid, and boron-containing organic acids.

  In the case of a rubber composition for bonding steel cords, hexamethylenetetramine or a melamine derivative as a methylene donor may be blended. Examples of the melamine derivative include hexamethoxymethyl melamine obtained by reacting melamine and formaldehyde, hexamethylol melamine pentamethyl ether, and polyvalent methylol melamine.

  In the case of a steel cord bonding rubber composition, a phenolic component composed of a novolac type phenol resin, resorcin, or a resorcin derivative may be blended. Such a phenol-based component is interposed between the silica in the rubber and the plating on the surface of the steel cord so as to bond the two, so that the adhesion between the rubber and the steel cord can be improved. Examples of the novolak type phenol resin include an unmodified phenol resin obtained by condensing phenol and formaldehyde (straight phenol resin), an alkyl-substituted phenol resin such as cresol / formaldehyde resin, and an oil-modified phenol resin modified with an oil such as cashew nut oil. Etc. Examples of the resorcin derivative include a resorcin / formaldehyde resin initial condensate and a resorcin / formaldehyde condensate condensate such as resorcin / alkylphenol co-condensed formaldehyde resin.

  The rubber composition of the present invention can be prepared by kneading using a commonly used mixer such as a Banbury mixer or a kneader. The use of the rubber composition is not particularly limited, but the rubber composition is suitably used as a tire rubber composition for tire treads and steel cord adhesion.

  In the case of a rubber composition for a tire tread, the tread of a pneumatic tire can be formed by vulcanizing and molding the tire according to a conventional method.

  Steel cord adhesive rubber composition is used to coat the surface of steel cords plated with brass, bronze, zinc, etc. used as reinforcing materials in rubber products such as pneumatic tires and belt conveyors. It is a rubber composition used. That is, a rubber-steel cord composite as a reinforcing material can be obtained by coating the steel cord with a rubber composition.

  Specifically, using the rubber composition and steel cord, a steel cord topping fabric as a rubber-steel cord composite is manufactured by a topping device such as a steel calender according to a conventional method, and this is then used for a belt or carcass. The pneumatic tire according to the embodiment can be manufactured by molding and vulcanizing a green tire together with other members using the tire reinforcing member.

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

Example 1
Using a Banbury mixer, a tire tread rubber composition was prepared according to the formulation shown in Table 1 below. The detail of each component of Table 1 is as follows.

SSBR: styrene-butadiene rubber, “VSL5025-OHM” manufactured by Bayer,
-BR: butadiene rubber, "BR150B" manufactured by Ube Industries,
・ Silica 1: “Nip seal AQ” made by Tosoh silica,
-Silica 2: "Zeosil 1165MP" manufactured by Rhodia,
Silica 3: “Siloa 72X” manufactured by Rhodia,
Carbon black: “Diamond Black” manufactured by Mitsubishi Chemical.

  For each rubber composition, 5.6 parts by weight of a silane coupling agent (“De75” “Si75”) and an anti-aging agent (“Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.) with respect to 100 parts by weight of diene rubber as a common compound 2 parts by weight, 2 parts by weight of stearic acid ("Lunac S-20" manufactured by Kao), 3 parts by weight of zinc flower ("Zinc Flower No. 1" manufactured by Mitsui Mining & Mining), process oil ("Process Oil X-140" manufactured by JOMO) ) 40 parts by weight, 2 parts by weight of wax (“OZOACE0355” manufactured by Nippon Seiki), 1.5 parts by weight of vulcanization accelerator (“Soccinol CZ” manufactured by Sumitomo Chemical), vulcanization accelerator (“Noxeller manufactured by Ouchi Shinsei Chemical) D ") 2.0 parts by weight and 1.0 part by weight of sulfur (" 5% oil-filled fine powdered sulfur "manufactured by Tsurumi Chemical Co., Ltd.).

  About each obtained rubber composition, the sample vulcanized | cured on the conditions of 160 degreeC x 30 minutes is produced, the tension test based on JISK6251 is done, 300% modulus as a reinforcement property, and the resistance as a fracture | rupture property The tension product (TB (tensile strength) × EB (elongation at break)) was determined and displayed as an index with the value of Comparative Example 1 taken as 100. It shows that it is excellent in a reinforcement property and a fracture | rupture characteristic, so that a numerical value is large.

As a result, as shown in Table 1, Example 1 according to the present invention has a lower amount of silanol groups in the silica used and a lower pH than Comparative Example 1, so that the reinforcement (modulus) is equivalent. However, the breaking characteristics were greatly improved. On the other hand, in Comparative Example 2, although the total specific surface area of the blended silica was the same as that in Example 1, the effect of improving the breaking properties was insufficient because of the large amount of silanol groups. Further, in Comparative Example 3, although the total amount of silanol groups of silica is the same as that of Example 1, since the silica filling amount (total specific surface area) is small, the reinforcing property is inferior and the effect of improving the breaking property is also obtained. It was insufficient.

(Example 2)
A rubber composition for bonding steel cords was prepared using a Banbury mixer according to the formulation shown in Table 2 below. Details of each component in Table 2 are as follows.

NR: natural rubber, RSS # 3,
・ Silica 1: “Nip seal AQ” made by Tosoh silica,
-Silica 2: "Zeosil 1165MP" manufactured by Rhodia,
Silica 3: “Siloa 72X” manufactured by Rhodia,
Carbon black: “Carbon Black N326” manufactured by Showa Cabot.

  In each rubber composition, 2 parts by weight of anti-aging agent 6C (“Santflex 6PPD” manufactured by Monsanto) and zinc white (“Zinc Flower No. 3” manufactured by Mitsui Mining & Smelting Co., Ltd.) are added as a common compound to 100 parts by weight of diene rubber. ] 8 parts by weight, cobalt stearate (manufactured by Nippon Mining) 2 parts by weight, boron-containing organic acid cobalt (manufactured by OMG "Manobond C22.5, C680C) 0.8 part by weight, vulcanization accelerator DZ (Ouchi Shinsei Chemical) “Noxeller DZ-G” manufactured by Kogyo Co., Ltd. 1 part by weight, 2 parts by weight of resorcin / alkylphenol / formalin copolymer (“SUMIKANOL 620” manufactured by Sumitomo Chemical), 4 parts by weight of hexamethoxymethylmelamine (“CYRETS 963L” manufactured by Mitsui Cytec) Then, 4.5 parts by weight of insoluble sulfur (“Crytex OT-20” manufactured by Akzo) was blended.

  About each obtained rubber composition, the sample vulcanized | cured on the conditions of 160 degreeC x 30 minutes is produced, the tension test based on JISK6251 is done, 300% modulus as a reinforcement property, and the resistance as a fracture | rupture property The tension product (TB (tensile strength) × EB (elongation at break)) was determined and displayed as an index with the value of Comparative Example 4 taken as 100. It shows that it is excellent in a reinforcement property and a fracture | rupture characteristic, so that a numerical value is large.

  Further, in order to evaluate the adhesive properties, each rubber composition was sheeted to prepare a rubber sheet having a thickness of 1.0 mm. Steel cords with brass plating (structure: 3 + 8 × 0.22mm) are arranged at 12 / 25mm intervals, and two pieces sandwiched between the rubber sheets are stacked, vulcanized at 150 ° C for 30 minutes, and steel A rubber-steel cord composite having two layers of cords was obtained, and this was cut into a width of 25 mm to prepare a sample. About each sample, the initial stage adhesiveness and the adhesiveness after wet heat aging were measured as follows.

[Initial Adhesiveness] The peel strength of the two-layer steel cord was measured using an autograph (Instron "5655 type"), and displayed as an index with the value of Comparative Example 4 being 100. A larger value means better adhesion.

[Adhesiveness after wet heat aging] Each sample was aged in a steam atmosphere at 105 ° C for 96 hours, and then the peel strength of the two-layer steel cord was measured using an autograph. The value of Comparative Example 4 was 100. The index was displayed. A larger value means better adhesion.

As a result, as shown in Table 2, Example 2 according to the present invention has a lower amount of silanol groups in the silica used and a lower pH than Comparative Example 4, so that the reinforcement (modulus) is equivalent. However, the breaking properties and adhesiveness were greatly improved. In contrast, in Comparative Example 5, although the total specific surface area of the blended silica is equivalent to that of Example 2, the amount of silanol groups is large, so that the effect of improving the breaking properties is insufficient and the adhesiveness is also poor. It was a thing. Further, in Comparative Example 6, although the total amount of silanol groups of silica is the same as that of Example 2, since the silica filling amount (total specific surface area) is small, the reinforcing property and adhesiveness are inferior, and the fracture characteristics are low. The improvement effect was also insufficient.

  According to the present invention, the breaking property of the rubber composition and the adhesiveness to the steel cord can be improved. Therefore, as a rubber composition for various pneumatic tires including those for treads, and for bonding a steel cord. The rubber composition can be suitably used, and can be used for various other rubber compositions.

Claims (3)

A BET specific surface area of 50 to 300 m ² / g, a silanol group amount per unit surface area of 5 to 11 per nm ² with respect to 100 parts by weight of a diene rubber, and a pH measured by the B method of JIS K6220 A rubber composition containing 5 to 100 parts by weight of silica having a ratio of 4.5 to 6.0.   A pneumatic tire having a tread made of the rubber composition according to claim 1.   A pneumatic tire comprising a rubber-steel cord composite comprising the rubber composition according to claim 1 and a steel cord.