JP2015218280A - Rubber composition for coating of steel cord - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for coating of a steel cord which is improved in mixing processability at a higher level while improving the adhesiveness to a steel cord.SOLUTION: A rubber composition for coating of a steel cord comprises 40-80 pts. wt. of carbon black of a nitrogen adsorption specific surface area NSA or 60-120 m/g, 0.3-2 pts. wt. of a farnesene polymer and 0.5-2 pts. wt. of an organic acid cobalt salt to 100 pts. wt. of a diene rubber containing 90 wt.% or more of natural rubber, and the combined blend ratio of the farnesene and the organic acid cobalt salt is 1-3 pts. wt.

Description

  The present invention relates to a rubber composition for coating a steel cord that improves the mixing processability to a conventional level while improving the adhesion to the steel cord.

  In recent years, from the viewpoint of consideration for the global environment and effective use of resources, there is a demand for extending the life of pneumatic tires, that is, improving tire durability. For this reason, while improving the durability of the member which comprises a tire, improving the adhesiveness between each member and preventing structural destruction is requested | required.

  In general, when steel cords are used for the belt layer and carcass layer of heavy duty pneumatic tires for trucks, buses, etc. and large pneumatic tires for construction vehicles, the rubber composition for coating the steel cords has an adhesion to the steel cords. In order to make it high, what mix | blended organic acid cobalt salt is used (for example, refer patent document 1). When the organic acid cobalt salt is blended, the mixing processability of the rubber composition may be improved.

  However, when the compounding amount of the organic acid cobalt salt is large, the adhesiveness to the steel cord may be lowered, and it is difficult to achieve both the adhesiveness and the mixed processability of the steel cord coating rubber composition. For example, reducing the blending amount of the organic acid cobalt salt to improve the adhesiveness deteriorates the mixing processability. To compensate for this, there is a problem that the adhesiveness and rubber strength are reduced when oils and plasticizers are blended. It was.

JP 2005-53953 A

  An object of the present invention is to provide a rubber composition for coating a steel cord which improves the mixing processability to a conventional level while improving the adhesion to the steel cord.

The rubber composition for coating a steel cord of the present invention that achieves the above object has a nitrogen adsorption specific surface area N ₂ SA of 60 to 120 m ² / g with respect to 100 parts by weight of a diene rubber containing 90% by weight or more of natural rubber. 40 to 80 parts by weight of carbon black, 0.3 to 2 parts by weight of farnesene polymer, 0.5 to 2 parts by weight of organic acid cobalt salt, and the total amount of the farnesene and organic acid cobalt salt It is characterized by being 1 to 3 parts by weight.

  The rubber composition for coating a steel cord of the present invention is such that a farnesene polymer and an organic acid cobalt salt are blended with a diene rubber mainly composed of natural rubber to limit the total of the farnesene polymer and the organic acid cobalt salt. As a result, the adhesion to the steel cord can be improved and the mixing processability can be maintained and improved.

  The diene rubber may contain 10% by weight or less of at least one selected from butadiene rubber and styrene butadiene rubber.

  The pneumatic tire using the steel cord coating rubber composition of the present invention for the belt layer improves the adhesion to the steel cord, improves the tire durability, and uses a rubber composition excellent in mixing processability. Therefore, a high quality pneumatic tire can be manufactured stably.

  In the rubber composition for coating a steel cord of the present invention, the rubber component is made of a diene rubber and contains 90% by weight or more of natural rubber as the diene rubber. By containing 90% by weight or more of natural rubber, the adhesion to the steel cord can be increased and the rubber strength can be increased. The content of natural rubber is preferably 92 to 100% by weight, more preferably 95 to 100% by weight.

  In the rubber composition for coating a steel cord of the present invention, the diene rubber other than natural rubber is 10% by weight or less, preferably 8% by weight or less, more preferably 5% by weight or less in 100% by weight of the diene rubber. Can be contained. If the content of other diene rubber exceeds 10% by weight, the adhesion to the steel cord and the rubber strength are lowered.

  Examples of other diene rubbers include isoprene rubber, butadiene rubber, styrene butadiene rubber, acrylonitrile-butadiene rubber, chloroprene rubber, butyl rubber, and nitrile rubber. These other diene rubbers can be used alone or as any blend. The other diene rubber is preferably at least one selected from butadiene rubber and styrene butadiene rubber.

  In the rubber composition for coating a steel cord of the present invention, the rubber strength can be increased by blending carbon black. The compounding amount of the carbon black is 40 to 80 parts by weight, preferably 50 to 70 parts by weight with respect to 100 parts by weight of the diene rubber. If the blending amount of carbon black is less than 40 parts by weight, the rubber composition cannot be sufficiently reinforced and the rubber strength is lowered. On the other hand, when the blending amount of carbon black exceeds 80 parts by weight, the mixing processability decreases.

The carbon black used in the present invention has a nitrogen adsorption specific surface area N ₂ SA of 60 to 120 m ² / g, preferably 70 to 100 m ² / g. When N ₂ SA is less than 60 m ² / g, mechanical properties such as rubber strength and dynamic elastic modulus of the rubber composition are lowered. When N ₂ SA exceeds 120 m ² / g, the adhesion to the steel cord and the mixing processability deteriorate. N ₂ SA shall be measured according to JIS K6217-2. Such carbon black can be appropriately selected from HAF grade to ISAF grade and used.

  The steel cord covering rubber composition may contain a reinforcing filler other than carbon black. Examples of other reinforcing fillers include silica, clay, mica, talc, calcium carbonate, aluminum oxide, titanium oxide, activated zinc white and the like. Of these, silica and clay are preferable.

  The rubber composition for coating a steel cord of the present invention increases adhesion to the steel cord by blending an organic acid cobalt salt. The compounding amount of the organic acid cobalt salt is 0.5 to 2 parts by weight, preferably 0.7 to 1.8 parts by weight with respect to 100 parts by weight of the diene rubber. When the blending amount of the organic acid cobalt salt is less than 0.5 parts by weight, the adhesion to the steel cord cannot be sufficiently improved, and the mixing processability is lowered. When the compounding amount of the organic acid cobalt salt exceeds 2 parts by weight, the adhesiveness to the steel cord is deteriorated.

  Examples of the organic acid cobalt salt include cobalt naphthenate, cobalt neodecanoate, cobalt stearate, cobalt rosinate, cobalt versatate, cobalt tall oil, cobalt borate neodecanoate, cobalt acetylacetonate and the like. . The organic acid cobalt salt is preferably an organic acid cobalt salt containing boron. For example, the organic acid cobalt salt may be a composite salt in which a part of the organic acid is replaced with boric acid or the like. The organic acid cobalt salt containing boron has a cobalt content of 20 Cobalt orthoborate that is ˜23 wt% is preferred.

  Examples of organic acid cobalt salts include DIC Cobalt Naphthenate 10% (Co content 10%), DIC Co. DICnate NBC-2 (Co content 22%), Nippon Kagaku Sangyo Co., Ltd. Nursem Cobalt Co (Co Content rate 16.54%), Rhodia Manobond C22.5 and Manobond 680C, Jhepherd CoMend A and CoMend B, Dainippon Ink and Chemicals YYNBC-II, and the like can be exemplified.

  By blending the farnesene polymer, the rubber composition for coating a steel cord of the present invention can improve the mixing processability while maintaining and improving the adhesion to the steel cord. The farnesene polymer has high affinity with natural rubber and is liquid and excellent in permeability from normal temperature to the processing temperature of the coating rubber composition, so that the mixing processability of the coating rubber composition can be improved. . Further, since the farnesene polymer has a relatively high molecular weight and a crosslinkable structure, the adhesion and rubber strength of the coating rubber composition after vulcanization can be made higher than conventional levels.

  The farnesene polymer is a polymer of α-farnesene, a polymer of β-farnesene or a copolymer of α-farnesene and β-farnesene, and preferably a polymer of β-farnesene. Further, the polymer of farnesene has a constitutional unit derived from α-farnesene and / or β-farnesene, preferably 90% by weight or more, more preferably 95% by weight or more, more preferably 100% by weight, butadiene, A structural unit derived from another monomer such as isoprene may be included.

  The blending amount of the farnesene polymer is 0.3 to 2 parts by weight, preferably 0.7 to 1.4 parts by weight with respect to 100 parts by weight of the diene rubber. If the blending amount of the farnesene polymer is less than 0.3 parts by weight, the effect of improving the mixing processability cannot be sufficiently obtained. On the other hand, when the blending amount of the farnesene polymer exceeds 2 parts by weight, the adhesion to the steel cord and the rubber strength are lowered.

  In the present invention, the total amount of the farnesene polymer and the organic acid cobalt salt is 1 to 3 parts by weight, preferably 1.5 to 2.5 parts by weight. When the total amount of the farnesene polymer and the organic acid cobalt salt is less than 1 part by weight, the mixing processability is lowered. On the other hand, when the total amount of the farnesene polymer and the organic acid cobalt salt exceeds 3 parts by weight, the adhesion to the steel cord cannot be sufficiently increased, and the rubber strength is lowered.

  The weight average molecular weight of the farnesene polymer is not particularly limited, but is preferably 2000 to 25000, more preferably 2500 to 20000. When the weight average molecular weight of the farnesene polymer is less than 2,000, the rubber strength of the rubber composition is lowered, and further, bleeding out from the rubber composition is likely to occur. On the other hand, when the weight average molecular weight of the farnesene polymer exceeds 25,000, the mixing processability is lowered.

  The molecular weight distribution of the farnesene polymer (Mw / Mn; Mw is the weight average molecular weight, Mn is the number average molecular weight) is preferably 1.0 to 2.0, more preferably 1.0 to 1.5, and even more preferably 1. It is good that it is .0 to 1.3. When the molecular weight distribution of the farnesene polymer is within such a range, variation in viscosity is reduced. In the present specification, the weight average molecular weight Mw and the number average molecular weight Mn of the farnesene polymer are measured by GPC (gel permeation chromatography) and determined by standard polystyrene conversion.

  The melt viscosity of the farnesene polymer is preferably 0.1 to 3.5 Pa · s, more preferably 0.1 to 2 Pa · s, and still more preferably 0.1 to 1.5 Pa · s. When the melt viscosity of the farnesene polymer is in such a range, the rubber composition is easily kneaded and the mixing processability is improved. In this specification, the melt viscosity of the farnesene polymer is a melt viscosity at 38 ° C. measured by a Brookfield viscometer.

  The farnesene polymer can be synthesized by an ordinary method, and examples thereof include an emulsion polymerization method and a solution polymerization method, and preferably a synthesis by a solution polymerization method.

  The rubber composition for coating a steel cord of the present invention includes various vulcanization or cross-linking agents, vulcanization accelerators, various oils, anti-aging agents, plasticizers and the like that are generally used for rubber compositions for coating a steel cord. An additive can be blended, and the additive can be kneaded by a general method to obtain a rubber composition, which can be vulcanized or crosslinked. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. The rubber composition for coating a steel cord of the present invention can be produced by mixing the above components using a normal rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for covering a steel cord of the present invention can be suitably used for a component having a steel cord such as a carcass layer and a belt layer in a pneumatic tire. In particular, the pneumatic tire using the rubber composition of the present invention for the belt layer can improve the durability beyond the conventional level because the adhesiveness of the steel cord is improved. In addition, since a rubber composition whose mixed processability is maintained / improved is used, a high-quality pneumatic tire can be stably obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

Preparation of rubber composition for coating steel cord and evaluation of mixing processability 11 kinds of rubber compositions (Examples 1 to 6, Comparative Examples 1 to 6) having the compounding ingredients shown in Table 2 as common ingredients and the composition shown in Table 1 In preparing 5), the components excluding sulfur and vulcanization accelerator were weighed and kneaded for 5 minutes in a 1.8 L closed mixer, and then the master batch was discharged and cooled at room temperature. At that time, the weight of the rubber piece which did not become a lump was measured. The smaller the rubber piece weight, the better the mass of rubber and the better the mixing processability. The obtained results were used as an index for setting the reciprocal of the rubber piece amount of Comparative Example 1 to 100, and are shown in the column of “Mixing processability” in Table 1. A larger index means better mixed processability.

  The master batch obtained above was subjected to a 1.8 L closed mixer, and sulfur and a vulcanization accelerator were added and mixed to obtain a rubber composition for steel cord coating. The adhesion (wire adhesion) to the steel cord and rubber strength of the 11 types of rubber compositions obtained were evaluated by the methods shown below.

Steel cord adhesion (wire adhesion)
A plurality of steel cords were arranged in parallel with each other at intervals of 13 mm, embedded in an unvulcanized steel cord coating rubber composition, and vulcanized at 170 ° C. for 15 minutes to prepare test samples. Using the test sample, a peel test was performed in accordance with JIS L1017, and the rubber coverage (with rubber [%]) on the steel cord was measured visually. The obtained results are shown in the “wire adhesion” column of Tables 1 and 2 as an index with the value of Comparative Example 1 being 100. The larger this index is, the greater the adhesion strength to the steel cord.

Rubber Strength The 11 types of rubber compositions obtained were press vulcanized in a predetermined mold at 170 ° C. for 10 minutes to prepare a vulcanized rubber test piece comprising a steel cord coating rubber composition. A JIS No. 3 dumbbell-shaped test piece was cut out from the obtained vulcanized rubber test piece in accordance with JIS K6251. In accordance with JIS K6251, a tensile test was performed at 25 ° C. and a tensile speed of 500 mm / min, and the tensile strength at break was measured. The obtained results are listed in the “Rubber Strength” column of Table 1 as an index with the value of Comparative Example 1 being 100. A larger index means higher rubber strength.

なお、表１において使用した原材料の種類を下記に示す。
ＮＲ：天然ゴム、ＲＳＳ＃３
ＢＲ：ブタジエンゴム、日本ゼオン社製Ｎｉｐｏｌ ＢＲ１２２０
ＳＢＲ：スチレンブタジエンゴム、日本ゼオン社製Ｎｉｐｏｌ １５０２、非油展品
カーボンブラック１：キャボットジャパン社製ショウブラックＮ３２６、ＨＡＦ級、窒素吸着比表面積が８１ｍ²／ｇ
カーボンブラック２：キャボットジャパン社製ショウブラックＮ２２０、ＩＳＡＦ級、窒素吸着比表面積が１１１ｍ²／ｇ
有機酸Ｃｏ塩：有機酸コバルト塩、ＤＩＣ社製ＤＩＣＮＡＴＥ ＮＢＣ−II（Ｃｏ含有率２２％）
ステアリン酸：日油社製ビーズステアリン酸
アロマオイル：昭和シェル石油社製エキストラクト４号Ｓ
ファルネセン重合体：下記の合成例１により重合されたβ−ファルネセンの重合体、重量平均分子量が１４００００、分子量分布が１．２、溶融粘度が６９Ｐａ・ｓ

In addition, the kind of raw material used in Table 1 is shown below.
NR: natural rubber, RSS # 3
BR: butadiene rubber, Nipol BR1220 manufactured by Nippon Zeon
SBR: styrene butadiene rubber, Nipol 1502 manufactured by Nippon Zeon Co., Ltd., non-oil exhibition carbon black 1: Show Black N326 manufactured by Cabot Japan, HAF grade, nitrogen adsorption specific surface area of 81 m ² / g
Carbon black 2: Shown black N220 manufactured by Cabot Japan, ISAF grade, nitrogen adsorption specific surface area is 111 m ² / g
Organic acid Co salt: Organic acid cobalt salt, DICATE NBC-II manufactured by DIC (Co content 22%)
Stearic acid: NOF beads manufactured by NOF Co., Ltd .: Extract No. 4 S manufactured by Showa Shell Sekiyu KK
Farnesene polymer: β-farnesene polymer polymerized in Synthesis Example 1 below, weight average molecular weight 140000, molecular weight distribution 1.2, melt viscosity 69 Pa · s

Synthesis example (farnesene polymer polymerization)
In a pressure vessel that was purged with nitrogen and dried, 274 g of hexane and 1.2 g of n-butyllithium (17 wt% hexane solution) were charged, and the temperature was raised to 50 ° C., followed by addition of 272 g of β-farnesene and polymerization for 1 hour. . After adding methanol to the obtained polymerization reaction solution, the polymerization reaction solution was washed with water. Water was separated, and the polymerization reaction solution was dried at 70 ° C. for 12 hours to obtain a β-farnesene polymer (farnesene polymer).

In addition, the kind of raw material used in Table 2 is shown below.
Anti-aging agent 1: SANTOFLEX 6PPD manufactured by FLEXSYS
Anti-aging agent 2: Nocrack 224RD made by Ouchi Shinsei Chemical Co., Ltd.
Zinc oxide: Zinc oxide type 3 vulcanization accelerator manufactured by Shodo Chemical Industry Co., Ltd .: Nouchira DZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.
Insoluble sulfur: Kristex HS OT 20 (Sulfur content is 80% by weight) manufactured by FLEXSYS
Vulcanization retarder: SANTOGARD PVI manufactured by FLEXSYS

  As is apparent from Table 1, it was confirmed that the rubber compositions of Examples 1 to 6 were improved in steel cord adhesion (wire adhesion), mixing processability and rubber strength to the conventional level or more.

In the rubber composition of Comparative Example 2, since the organic acid cobalt salt was reduced with respect to the rubber composition of Comparative Example 1, the wire adhesion and rubber strength were improved, but the mixing processability was deteriorated.
In the rubber composition of Comparative Example 3, the aroma oil was added to the rubber composition of Comparative Example 2, so that the mixing processability was improved, but the wire adhesion and rubber strength were deteriorated.

In the rubber composition of Comparative Example 4, since stearic acid was added to the rubber composition of Comparative Example 2, the mixing processability was recovered, but the wire adhesiveness was deteriorated.
The rubber composition of Comparative Example 5 cannot improve the mixing processability because the total amount of the organic acid cobalt salt and farnesene polymer is less than 1.0 part by weight.

Claims (3)

40 to 80 parts by weight of carbon black having a nitrogen adsorption specific surface area N ₂ SA of 60 to 120 m ² / g, and 0.3 to 0.3 parts of farnesene polymer with respect to 100 parts by weight of diene rubber containing 90% by weight or more of natural rubber. 2 parts by weight, 0.5 to 2 parts by weight of organic acid cobalt salt, and 1 to 3 parts by weight of the total blended amount of the farnesene and organic acid cobalt salt Composition.   The rubber composition for coating a steel cord according to claim 1, wherein the diene rubber contains 10% by weight or less of at least one selected from butadiene rubber and styrene butadiene rubber.   A pneumatic tire comprising the rubber composition for covering a steel cord according to claim 1 or 2 as a belt layer.