JP2008189896A - Rubber composition for use in steel cord adhesion, and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide such a rubber composition for use in steel cord adhesion as is improved in the adhesion to a steel cord and in the failure characteristics therewith without impairing the processability. <P>SOLUTION: The rubber composition for use in the steel cord adhesion comprises a silica master batch which is obtained by mixing a silica that has a specific surface area in the CATB adsorption of 165-210 m<SP>2</SP>/g and a natural rubber latex in a solution state. The pneumatic tire uses a rubber/steel cord composite body comprising the above rubber composition and the steel cord. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rubber composition for bonding a steel cord and a pneumatic tire using a rubber-steel cord composite in which a steel cord is coated with the rubber composition.

  Conventionally, steel cords plated with brass, bronze, zinc, etc. have been used as reinforcing materials for rubber products such as pneumatic tires and belt conveyors. It is important to improve the adhesive strength with rubber. Therefore, for example, in a rubber composition for bonding steel cords, an amount of sulfur that promotes formation of an adhesive interface layer or a compound containing cobalt organic acid is used. There is also a technique of using resorcinol or a phenolic resin in combination with a methylene group donor to increase elasticity and improve adhesion.

  By the way, in the rubber composition for tires, a part of carbon black which is a filler for rubber reinforcement may be substituted with silica. Conventionally, such substitution with silica has been performed in order to achieve both low heat generation (low fuel consumption) and grip on wet road surfaces, but silica is prone to agglomerate due to the influence of silanol groups on the surface and is dispersed. There is a disadvantage that the nature is bad. For this reason, it has been proposed to improve dispersibility by making silica a master batch with rubber latex in advance.

  For example, Patent Document 1 below proposes a method for producing a silica masterbatch in which silica mixed in a large amount in a rubber latex is well dispersed.

  Patent Document 2 listed below proposes a rubber composition that is excellent in workability, natural rolling latex, carbon black, and silica as a master batch, and that is excellent in low rolling property and wear resistance.

  Patent Document 3 below proposes a rubber composition for a tire carcass in which a master batch of styrene-butadiene rubber latex and silica is used to reduce heat generation and to reduce fuel consumption of the tire, and to improve steering stability. Has been.

Patent Document 4 below proposes a rubber composition in which heat resistance is greatly improved by mixing a water-based silica colloid solution and a rubber latex to form a master batch.
JP 2001-213971 A JP 2005-220187 A JP-A-2005-247985 JP 2006-083256 A

  However, all of the above prior arts are intended to reduce the heat generation of the rubber composition by making silica and rubber latex into a master batch, and of course the effect of improving the adhesion between the steel cord and rubber. In addition, there is no disclosure of use as a steel cord bonding rubber composition.

  An object of the present invention is to provide a rubber composition for bonding a steel cord and a pneumatic tire using the same, which have improved adhesiveness to steel cord and fracture characteristics without impairing workability.

  As a result of diligent studies to solve the above-mentioned problems, the present inventor has formulated a silica masterbatch obtained by mixing a small particle size silica with natural rubber latex in a solution state, thereby providing a rubber composition for bonding steel cords. As a result, it was found that adhesiveness and fracture characteristics could be improved without impairing workability, and the present invention was completed.

That is, the steel cord bonding rubber composition according to the present invention contains a silica masterbatch obtained by mixing silica having a CTAB adsorption specific surface area of 165 to 210 m ² / g and natural rubber latex in a solution state. It is.

  The pneumatic tire according to the present invention is formed by using a rubber-steel cord composite made of the steel cord bonding rubber composition and a steel cord.

  According to the present invention, a specific small particle size silica is mixed with a natural rubber latex in advance and blended into a master batch, so that there is no increase in viscosity when mixing the unvulcanized rubber composition, that is, Without impairing the workability, the adhesion to the steel cord can be improved, in particular the adhesion after aging can be improved, and the fracture characteristics can be improved.

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

  The silica masterbatch used in the rubber composition of the present invention is obtained by mixing small particle size silica and natural rubber latex in a solution state.

The small particle size silica has a CTAB (cetyltrimethylammonium bromide) adsorption specific surface area in the range of 165 to 210 m ² / g. By using silica having such a high CTAB, the amount of silanol groups on the surface of the silica can be increased, and the hydrogen bond can improve the fracture characteristics and the adhesion to the steel cord. By making the diameter silica into a master batch with natural rubber latex, the effect of improving the fracture characteristics and adhesiveness due to hydrogen bonding can be enhanced. Moreover, it is excellent also in the adhesive improvement effect after aging. On the other hand, when small particle size silica is used, there is a concern about an increase in viscosity due to aggregation due to an increase in the amount of silanol groups on the surface. Thus, it is possible to obtain a rubber composition having improved fracture characteristics, reinforcing properties and adhesiveness without suppressing an increase in viscosity and impairing processability.

The CTAB adsorption specific surface area is obtained by adsorbing CTAB according to ASTM D4820 and measuring the adsorption amount. A more preferable range of the CTAB adsorption specific surface area is 180 to 210 m ² / g.

  The natural rubber latex is a latex in which a natural rubber having excellent fatigue resistance compared to other diene rubbers is dispersed in an aqueous solvent such as water, and various known natural rubber latexes can be used.

  The method for mixing the small particle size silica and the natural rubber latex in a solution state is not particularly limited, and various known methods disclosed in Japanese Patent Application Laid-Open No. 2001-213971 can be used. For example, a method of dropping the natural rubber latex while stirring the silica aqueous dispersion, or a method of dropping the silica water dispersion while stirring the natural rubber latex can be used. The mixed small particle size silica and natural rubber latex are usually coagulated and then washed with water, dehydrated and dried to obtain a silica masterbatch. Also for these methods, known methods can be employed.

  The silica masterbatch preferably contains 5 to 60 parts by weight of silica, more preferably 10 to 30 parts by weight of silica with respect to 100 parts by weight of natural rubber derived from natural rubber latex. When the silica content is less than 5 parts by weight, it is difficult to obtain a sufficient improvement effect of adhesiveness and fracture characteristics. Conversely, when the silica content exceeds 60 parts by weight, the Mooney viscosity of the silica masterbatch increases and the mixing processability deteriorates. Sometimes.

  The rubber composition of the present invention may contain a diene rubber other than the natural rubber derived from the silica master batch together with the silica master batch. That is, in the rubber composition of the present invention, the rubber component may be composed only of the natural rubber derived from the silica masterbatch, but other diene rubbers may be blended. Examples of such a diene rubber include natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, and more preferably natural rubber and / or isoprene rubber, which are used alone or in combination of two or more. Can be used.

  Specifically, the rubber component in the rubber composition of the present invention is preferably composed of 100 to 10% by weight of the natural rubber derived from the silica masterbatch and 0 to 90% by weight of another diene rubber. More preferably, it is comprised with 70-30 weight% of natural rubbers derived from a silica masterbatch, and 30-70 weight% of other diene rubbers. When the composition ratio of the natural rubber derived from the silica masterbatch is less than 10% by weight, the effect obtained by making the masterbatch in advance becomes insufficient.

  In the rubber composition of the present invention, 0 to 195 parts by weight of carbon black and 5 to 50 parts by weight of silica are blended in a total amount of 20 to 200 parts by weight with respect to 100 parts by weight of the rubber component. It is preferable. The compounding amount of silica is the total amount of silica including silica in the silica masterbatch. If the amount is less than 5 parts by weight, the effect of improving adhesiveness and fracture characteristics is small. Getting worse. The more preferable amount of silica is 5 to 30 parts by weight. Moreover, although carbon black is not essential, when mix | blending, it is preferable to mix | blend with 195 weight part or less. Here, if the total amount of silica and carbon black is less than 20 parts by weight, the reinforcing property is insufficient, while if it exceeds 200 parts by weight, the workability is impaired.

  In the rubber composition of this invention, it is preferable to mix | blend 3-6 weight part of sulfur with respect to 100 weight part of said rubber components. Thus, by increasing the compounding amount of sulfur, the adhesion interface layer between the rubber and the steel cord can be sufficiently formed.

  You may mix | blend organic acid metal salts, such as organic acid cobalt salt, as a formation promoter of an adhesion interface layer with the rubber composition of this invention. Examples of the organic acid that forms the organic acid metal salt include stearic acid, naphthenic acid, octylic acid, oleic acid, maleic acid, and boron-containing organic acids, and are not particularly limited.

  The rubber composition of the present invention may also contain hexamethylenetetramine or a melamine derivative as a methylene donor. Examples of the melamine derivative include hexamethoxymethyl melamine obtained by reacting melamine and formaldehyde, hexamethylol melamine pentamethyl ether, and polyvalent methylol melamine. The blending amount of these methylene donors is preferably 0.5 to 5.0 parts by weight with respect to 100 parts by weight of the rubber component.

  The rubber composition of the present invention may contain a phenolic component composed of a novolac type phenol resin, resorcin, or a resorcin derivative. 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. The phenolic component is preferably blended in an amount of 0.5 to 5.0 parts by weight with respect to 100 parts by weight of the rubber component.

  Examples of the novolac type phenol resin include unmodified phenol resin (straight phenol resin) obtained by condensing phenol and formaldehyde, alkyl-substituted phenol resin, and oil-modified phenol resin. Examples of the alkyl-substituted phenol resin include a cresol-formaldehyde resin using cresol instead of phenol, and an alkyl phenol resin using another alkyl phenol such as xylenol or octylphenol instead of phenol. Examples of the oil-modified phenol resin include novolak-type modified phenol resins modified with various oils such as cashew nut oil, tall oil, and rosin oil.

  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.

  When the amount of sulfur is increased as described above, or when an adhesive resin such as a methylene donor and a phenolic component is blended, generally, there is a concern about an increase in viscosity of the unvulcanized rubber composition. By adding the silica masterbatch, it is possible to suppress the increase in viscosity and maintain the workability.

  In addition to the above-described components, the rubber composition of the present invention may be appropriately added with a processing aid such as a vulcanization accelerator, a silane coupling agent, an anti-aging agent, zinc white, stearic acid, and process oil. it can.

  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. A rubber-steel cord composite composed of such a rubber composition and a steel cord is formed by coating a steel cord with the above rubber composition, and is used as a reinforcing material for a belt or a carcass of a pneumatic radial tire. Alternatively, it can be used as a reinforcing material for various belt conveyors.

  Specifically, using the above rubber composition and steel cord, a steel cord topping material 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 used as a tire reinforcing member. The pneumatic tire of the present invention can be manufactured by forming and vulcanizing a green tire together with other members. The pneumatic tire of the present invention is preferably a heavy duty pneumatic tire such as a truck or a bus.

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

  Details of silicas 1 to 5 used in Examples and Comparative Examples are as follows.

Silica 1: CTAB adsorption specific surface area = 106 m ² / g large particle size silica,
-Silica 2: CTAB adsorption specific surface area = 160 m ² / g medium particle size silica (Degussa “Ultrasil 7000GR”),
Silica 3: CTAB adsorption specific surface area = 168 m ² / g small particle size silica (“Nipsil AQ” manufactured by Nippon Silica),
Silica 4: CTAB adsorption specific surface area = 189 m ² / g small particle size silica (“1205MP” manufactured by Rhodia),
Silica 5: CTAB adsorption specific surface area = 198 m ² / g small particle size silica (“PR” manufactured by Tokuyama Corporation).

  The details of the silica master batches MB1 to MB5 are as follows.

MB1: 20 g of silica 5 was mixed with 80 g of distilled water to prepare a silica water dispersion. While stirring 167g of natural rubber latex ("NR-LATEX" manufactured by Residex Co., Ltd.), the silica aqueous dispersion is added dropwise to mix the two, and then the pH is lowered to 4.5 with formic acid. Obtained. The obtained solidified product was washed with water, dehydrated with a roll, and dried with a vacuum dryer at 50 ° C. for 24 hours to obtain a silica master batch MB1.

MB2: The silica masterbatch MB2 was prepared in the same manner as MB1 except that the amount of silica 5 was 10 parts by weight with respect to 100 parts by weight of natural rubber.

MB3: Silica master batch MB3 was prepared in the same manner as MB1 except that silica 4 was used instead of silica 5.

MB4: Silica masterbatch MB4 was prepared in the same manner as MB1 except that silica 3 was used instead of silica 5.

MB5: Silica masterbatch MB5 was prepared in the same manner as MB1 except that silica 2 was used instead of silica 5.

  Using a Banbury mixer, rubber compositions of Examples 1 to 4 and Comparative Examples 1 to 4 were prepared according to the composition shown in Table 1 below. “Natural rubber” in Table 1 is RSS # 3 and “Natural rubber latex” is “NR-LATEX” manufactured by Residex Co. (however, formic acid is added and the pH is set to 4.5 to coagulate the coagulum with a roll. After dehydration, it is dried with a vacuum dryer).

  In each rubber composition, carbon black N326 (manufactured by Showa Cabot) 60 parts by weight, anti-aging agent 6C (“Santoflex 6PPD” manufactured by Monsanto) 2 parts by weight with respect to 100 parts by weight of the rubber component as a common compound. Zinc flower (Mitsui Kinzoku Co., Ltd. “Zinc flower No. 3”) 8 parts by weight, cobalt stearate (Nihon Mining Co., Ltd.) 2 parts by weight, boron-containing organic acid cobalt (OMG “Manobond C22.5, C680C”) 0 8 parts by weight, 1 part by weight of vulcanization accelerator DZ (“Noxeller DZ-G” manufactured by Ouchi Shinsei Chemical Co., Ltd.), 2 parts by weight of resorcin / alkylphenol / formalin copolymer (“SUMIKANOL 620” manufactured by Sumitomo Chemical Co., Ltd.) Part, 4 parts by weight of hexamethoxymethylmelamine (“Cyretz 963L” manufactured by Mitsui Cytec), insoluble sulfur (“Crytex OT-20” manufactured by Akzo) 5 parts by weight were blended.

  Each rubber composition was measured and evaluated for processability, adhesion and fracture characteristics. Each measuring method is as follows.

Processability: In accordance with JIS K6300-1, pre-heating for 1 minute, measurement for 4 minutes, temperature of 100 ° C., Mooney viscosity of unvulcanized rubber was measured, and displayed as an index with the value of Comparative Example 1 as 100 did. The smaller the value, the lower the viscosity and the better the workability.

Adhesiveness: 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 adhesiveness and the adhesiveness after 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 Comparative Example 1 taken as 100. A larger value means better adhesion.

[Adhesiveness after 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. displayed. A larger value means better adhesion.

・ Fracture characteristics: Tensile product based on JIS K6251 was obtained for samples obtained by vulcanizing each rubber composition at 150 ° C. for 30 minutes, and the tensile product was obtained. displayed. It shows that it is excellent in a fracture characteristic, so that a numerical value is large.

  As shown in Table 1, in Comparative Example 3 in which the small particle size silica was kneaded as it was, the adhesiveness and fracture characteristics were improved, but the viscosity of the unvulcanized rubber was high and the processability was poor. On the other hand, in Examples 1 to 4, which were formulated after master batch of small particle size silica and natural rubber latex, the adhesiveness and fracture characteristics were improved without substantially impairing the workability. In contrast to Comparative Example 3, a significant improvement effect was observed in the adhesiveness after aging. In addition, even when it mix | blends as a silica masterbatch, in the comparative example 4 using a medium particle size silica, it was a thing which is not much different from the comparative example 3 kneaded as it is.

  INDUSTRIAL APPLICABILITY The present invention can be particularly suitably used as a rubber for covering a steel cord in a reinforcing material such as a belt or a carcass of a pneumatic tire, but is not limited to this, and can also be used for a rubber covering various steel cords. Can do.

Claims (5)

A rubber composition for bonding steel cords, comprising a silica masterbatch obtained by mixing silica having a CTAB adsorption specific surface area of 165 to 210 m ² / g and natural rubber latex in a solution state.   The rubber composition for bonding steel cords according to claim 1, wherein the silica masterbatch contains 5 to 60 parts by weight of silica with respect to 100 parts by weight of natural rubber.   From 100 to 10 parts by weight of a rubber component composed of 100 to 10% by weight of natural rubber derived from the silica masterbatch and 0 to 90% by weight of another diene rubber, 0 to 195 parts by weight of carbon black, The rubber composition for bonding steel cords according to claim 1 or 2, wherein 50 parts by weight is contained in a total amount of 20 to 200 parts by weight.   The rubber composition for bonding steel cords according to claim 3, wherein 3 to 6 parts by weight of sulfur is contained with respect to 100 parts by weight of the rubber component.   A pneumatic tire using a rubber-steel cord composite comprising the rubber composition according to any one of claims 1 to 4 and a steel cord.