JP2009007408A - Rubber composition for adhesion of steel cord and pneumatic tire using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for adhesion of a steel cord, in which the use amount of source material from petroleum resource is decreased, good adhesiveness with the steel cord can be maintained, working property during preparation is satisfactory and a hysteresis loss is reduced, and to provide a pneumatic tire having a ply using the above composition. <P>SOLUTION: The rubber composition for adhesion of the steel cord comprises 100 parts by mass of a rubber component, to which 40 to 80 parts by mass of silica having a BET specific surface area of not more than 150 m<SP>2</SP>/g and not more than 5 parts by mass of carbon black are blended, wherein the rubber component comprises at least both of natural rubber and modified natural rubber. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rubber composition for bonding a steel cord and a pneumatic tire including a ply using the rubber composition.

In recent years, environmental issues have become more important and regulations on CO ₂ emissions have been strengthened. In addition, oil resources are limited, and in the future, it may become difficult to supply raw materials derived from petroleum resources such as carbon black, and oil prices are expected to rise due to a decrease in supply volume year after year. Is done. Therefore, it is required to replace raw materials derived from petroleum resources with raw materials derived from resources other than petroleum.

  Currently, commercially available tires are composed of raw materials in which more than half of the total weight is petroleum resources. For example, a general tire for a passenger car contains about 20% by mass of synthetic rubber, about 20% by mass of carbon black, a softener, a synthetic fiber, etc., so that about 50% by mass or more of the entire tire is a raw material derived from petroleum resources. It is composed of Therefore, development of rubber for tires using raw materials derived from natural resources is desired. However, for example, a rubber composition for tire steel cord adhesion requires a good adhesion between the steel cord and the rubber composition, and even when a raw material derived from natural resources is used, the rubber composition for tires is used. The basic performance required for the object is required for the object.

Patent Document 1 discloses a rubber for an inner liner containing 30 parts by mass or more of silica having a BET specific surface area of less than 150 m ² / g and 5 parts by mass or less of carbon black with respect to 100 parts by mass of a rubber component made of natural rubber. Compositions have been proposed. However, the technique of Patent Document 1 does not consider a rubber composition that satisfies the required performance for bonding steel cords.

Patent Document 2 includes at least one of a carcass, a bead reinforcing layer, a side portion reinforcing layer, and a belt as a reinforcing layer in which a steel cord is covered with a coating rubber, and the coating rubber is 100 of a diene rubber. Containing 30 parts by mass of silica, 30 to 80 parts by mass of silica having a nitrogen adsorption specific surface area of 70 m ² / g or more and 150 m ² / g or less, 1 to 15 parts by mass of a silane coupling agent, and cobalt organic acid. A pneumatic tire made of a rubber composition has been proposed. However, with the technique of Patent Document 2, it is difficult to achieve both improvement in workability and reduction in hysteresis loss while reducing the amount of raw material derived from petroleum resources.

On the other hand, when silica is compounded in the rubber composition, for example, the Mooney viscosity tends to be higher and the processability tends to be inferior compared with the case where carbon is compounded. An agent may be used. However, processing aids are generally derived from petroleum resources, and in order to reduce the amount of raw materials derived from petroleum resources, it is desirable to reduce the amount of processing aid used.
JP 2006-249147 A JP 2006-143821 A

  The present invention solves the above-mentioned problems, reduces the amount of petroleum-derived raw materials used, can maintain good adhesion with steel cords, has good workability during preparation, and hysteresis An object of the present invention is to provide a rubber composition for bonding a steel cord with reduced loss and a pneumatic tire including a ply using the rubber composition.

The present invention is, relative to 100 parts by mass of the rubber component, silica 40-80 parts by weight BET specific surface area of not more than 150 meters ² / g, carbon black 5 parts by weight or less and is formulated, the rubber component, natural rubber and modified A rubber composition for bonding a steel cord, comprising at least one of natural rubber.

  In the rubber composition for bonding steel cords of the present invention, the rubber component is preferably composed of at least one of natural rubber and epoxidized natural rubber.

  The present invention also provides a pneumatic tire provided with a ply using the rubber composition for bonding a steel cord described above.

  According to the present invention, the amount of the raw material derived from petroleum resources is reduced, the adhesiveness with the steel cord can be maintained well, the workability at the time of preparation is good, and the hysteresis loss is reduced. It is possible to provide a rubber composition for bonding a steel cord and a pneumatic tire including a ply using the rubber composition.

  In the rubber composition for bonding steel cords of the present invention, a relatively small amount of carbon black is blended and a predetermined amount of silica having a small BET specific surface area is used together to maintain good adhesion to the steel cord. The processability during preparation is good and the hysteresis loss is reduced. Reduction of the hysteresis loss of the steel cord bonding rubber composition contributes to reduction of rolling resistance of the pneumatic tire.

  Further, in the present invention, the amount of the raw material derived from petroleum resources can be reduced by using a rubber component composed of at least one of natural rubber and modified natural rubber and reducing the amount of carbon black used.

<Rubber component>
The rubber component used in the present invention comprises at least one of natural rubber and modified natural rubber. As the natural rubber, those conventionally used in the rubber industry can be used singly or in combination of two or more, and examples thereof include natural rubber of grades such as RSS # 3 and TSR. Examples of the modified natural rubber include one or a combination of two or more such as epoxidized natural rubber and hydrogenated natural rubber. The rubber component is particularly preferably composed of at least one of natural rubber and epoxidized natural rubber.

  Epoxidized natural rubber is a kind of modified natural rubber in which unsaturated double bonds of natural rubber are epoxidized, and molecular cohesion is increased by epoxy groups that are polar groups. Therefore, the glass transition temperature (Tg) is higher than that of natural rubber, and the mechanical strength and wear resistance are excellent. In particular, when silica is compounded in the rubber composition, due to the reaction between the silanol group on the silica surface and the epoxy group of the epoxidized natural rubber, the same degree as when carbon black is compounded in the rubber composition. The mechanical strength and wear resistance can be obtained.

  The epoxidation rate of the epoxidized natural rubber is preferably 5% or more, more preferably 15% or more, and further preferably 20% or more. This is because when the epoxidation rate is less than 5%, the glass transition temperature of the rubber component is low, and the rigidity and hardness of the rubber composition for bonding a steel cord tend to be low, so that the mechanical strength tends to be low. On the other hand, the epoxidation rate of the epoxidized natural rubber is preferably 70% or less, more preferably 60% or less, and further 55% or less. This is because when the epoxidation rate exceeds 70%, the rubber composition for bonding steel cords becomes hard and mechanical strength tends to decrease.

  The epoxidation rate means the ratio of the number of epoxidized out of the total number of carbon-carbon double bonds in the natural rubber before epoxidation, and is obtained by, for example, titration analysis or nuclear magnetic resonance (NMR) analysis. It is done.

  As the epoxidized natural rubber, a commercially available product may be used, or a natural rubber epoxidized product may be used. The method for epoxidizing natural rubber is not particularly limited, and examples thereof include a chlorohydrin method, a direct oxidation method, a hydrogen peroxide method, an alkyl hydroperoxide method, and a peracid method. Examples of the peracid method include a method of reacting an organic peracid such as peracetic acid or performic acid as an epoxidizing agent with an emulsion of natural rubber.

  More typical examples of the epoxidized natural rubber include an epoxidized natural rubber having an epoxidation rate of 25% and an epoxidized natural rubber having an epoxidation rate of 50%.

  Part or all of the natural rubber may be deproteinized natural rubber (DPNR), and part or all of the modified natural rubber may be modified rubber of the deproteinized natural rubber (DPNR).

<Silica>
In the rubber composition for bonding a steel cord of the present invention, silica having a BET specific surface area of 150 m ² / g or less is blended. When the BET specific surface area of silica exceeds 150 m ² / g, the viscosity increases during the preparation of the steel cord bonding rubber composition, and the processability deteriorates. More preferably, the BET specific surface area of silica is 130 m ² / g or less. On the other hand, if the BET specific surface area of silica is less than 90m ² / g, the hardness of the steel cord adhesion rubber composition tends to mechanical strength decreases becomes lower, the BET specific surface area, 90m ² / g Preferably, it is more than 100 m ² / g, more preferably 110 m ² / g or more.

In the present invention, when two or more types of silica having different BET specific surface areas are used in combination, the number average value of the BET specific surface area of the entire silica is set to 150 m ² / g or less.

Silica may be prepared by a wet method or may be prepared by a dry method. Moreover, as a preferable commercial item, "Ultrasil VN2" (BET specific surface area 125m < ² > / g) made from Degussa etc. can be illustrated, for example.

  The compounding amount of the silica with respect to 100 parts by mass of the rubber component is in the range of 40 to 80 parts by mass. When the blending amount of silica is less than 40 parts by mass, the reinforcing effect of the rubber composition for bonding a steel cord cannot be obtained sufficiently, and when it exceeds 80 parts by mass, the processability at the time of preparing the rubber composition for bonding a steel cord As hysteresis decreases, hysteresis loss increases. The compounding amount of silica is preferably 45 parts by mass or more, more preferably 50 parts by mass or more, more preferably 70 parts by mass or less, and further preferably 65 parts by mass or less.

<Carbon black>
The compounding quantity of carbon black with respect to 100 mass parts of rubber components shall be 5 mass parts or less. When the blending amount of the carbon black exceeds 5 parts by mass, the effect of reducing the amount of raw material derived from petroleum resources and the effect of reducing hysteresis loss cannot be sufficiently obtained. The blending amount of carbon black is more preferably 3 parts by mass or less. In addition, when the blending amount of the carbon book is less than 3 parts by mass, it is necessary to blend more silica, for example, in order to ensure the mechanical strength of the rubber composition for bonding a steel cord. Since there exists a tendency for adhesiveness with a steel cord to fall, it is preferable that this compounding quantity is 3 mass parts or more.

  The DBP oil absorption of carbon black is preferably in the range of 70 to 120 ml / 100 g. When the DBP oil absorption of carbon black is less than 70 ml / 100 g, the mechanical strength of the steel cord bonding rubber composition tends to decrease, and when it exceeds 120 ml / 100 g, There is a tendency for workability to decrease. The DBP oil absorption of carbon black is more preferably 75 ml / 100 g or more, more preferably 80 ml / 100 g or more, more preferably 115 ml / 100 g or less, and even more preferably 100 ml / 100 g or less.

  Examples of preferable commercially available carbon black include “Show Black N550”, “Show Black N330”, “Show Black N220”, and “Show Black N110” manufactured by Cabonet Japan.

<Silane coupling agent>
In the present invention, it is preferable to use a silane coupling agent in combination. Thereby, the reinforcement effect which was more excellent with respect to the rubber composition for steel cord adhesion | attachment is provided. The compounding amount of the silane coupling agent is preferably in the range of 1 to 20% by mass when the compounding amount of silica is 100% by mass. When the amount of the silane coupling agent is less than 1% by mass, the reinforcing effect tends to be low. When the amount exceeds 20% by mass, a significant improvement in the reinforcing effect cannot be expected even if the amount is increased, while the cost is high. There is a tendency to become less economical because of the rise. From the viewpoint of dispersibility and coupling effect, the amount of the silane coupling agent is further 4% by mass or more, more preferably 6% by mass or more, and 12% by mass or less, further 10% by mass or less. It is more preferable that

  As the silane coupling agent, a conventionally known silane coupling agent can be used. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4- Triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilylbutyl) tetrasulfide, bis (3-triethoxy Silylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) trisulfide, bis (2-trimethoxysilylethyl) ) Resulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4-triethoxysilylbutyl) disulfide, bis (3 -Trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyltetrasulfide, 3-tri Ethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N, N-dimethylthio Sulfide systems such as rubamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-trimethoxysilylpropyl methacrylate monosulfide; 3-mercaptopropyltrimethoxysilane Mercapto series such as 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane; Vinyl series such as vinyltriethoxysilane and vinyltrimethoxysilane; 3-aminopropyltriethoxysilane 3-aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltriethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxy Amino systems such as silane; glycidoxy systems such as γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane Nitro compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, 2-chloroethyltri Chloro-based compounds such as ethoxysilane; These silane coupling agents may be used alone or in combination of two or more.

  Of these, Si69 (bis (3-triethoxysilylpropyl) tetrasulfide), Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa are preferably used because of their good processability. It is done.

<Other ingredients>
In addition to the components described above, the rubber composition for bonding steel cords of the present invention includes other compounding agents conventionally used in the rubber industry, such as vulcanizing agents, stearic acid, vulcanization accelerators, and vulcanization acceleration aids. Oils, curable resins, waxes, anti-aging agents, etc. may be blended.

  As the vulcanizing agent, an organic peroxide or a sulfur-based vulcanizing agent can be used. Examples of the organic peroxide include benzoyl peroxide, dicumyl peroxide, and di-t-butyl peroxide. , T-butyl cumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (benzoyl) Peroxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3 or 1,3-bis (t-butylperoxypropyl) benzene, di-t-butylperoxy- Diisopropylbenzene, t-butylperoxybenzene, 2,4-dichlorobenzoyl peroxide, 1,1-di t- butyl peroxy-3,3,5-trimethyl siloxane, and the like can be used n- butyl-4,4-di -t- butyl peroxy valerate. Of these, dicumyl peroxide, t-butylperoxybenzene and di-t-butylperoxy-diisopropylbenzene are preferred. Moreover, as a sulfur type vulcanizing agent, sulfur, morpholine disulfide, etc. can be used, for example. Of these, sulfur is preferred. These vulcanizing agents may be used alone or in combination of two or more. Further, sulfur may be oil-treated.

  Vulcanization accelerators include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine, aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. Those containing at least one of them can be used. Examples of the sulfenamide system include CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (N-tert-butyl-2-benzothiazylsulfenamide), N, N-dicyclohexyl-2- Sulfenamide compounds such as benzothiazylsulfenamide, N-oxydiethylene-2-benzothiazylsulfenamide, and N, N-diisopropyl-2-benzothiazolesulfenamide can be used. Examples of the thiazole group include MBT (2-mercaptobenzothiazole), MBTS (dibenzothiazyl disulfide), sodium salt of 2-mercaptobenzothiazole, zinc salt, copper salt, cyclohexylamine salt, 2- (2,4-dinitro). Thiazole compounds such as phenyl) mercaptobenzothiazole and 2- (2,6-diethyl-4-morpholinothio) benzothiazole can be used. Examples of thiurams include TMTD (tetramethylthiuram disulfide), tetraethylthiuram disulfide, tetramethylthiuram monosulfide, dipentamethylenethiuram disulfide, dipentamethylenethiuram monosulfide, dipentamethylenethiuram tetrasulfide, dipentamethylenethiuram hexasulfide. Further, thiuram compounds such as tetrabutylthiuram disulfide and pentamethylenethiuram tetrasulfide can be used. As the thiourea series, for example, thiourea compounds such as thiacarbamide, diethylthiourea, dibutylthiourea, trimethylthiourea, diortolylthiourea and the like can be used. Examples of guanidine-based compounds include guanidine-based compounds such as diphenylguanidine, diortolylguanidine, triphenylguanidine, orthotolylbiguanide, and diphenylguanidine phthalate. Examples of dithiocarbamate include zinc ethylphenyldithiocarbamate, zinc butylphenyldithiocarbamate, sodium dimethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc diamyldithiocarbamate, zinc dipropyldithiocarbamate , Complex salt of zinc pentamethylenedithiocarbamate and piperidine, zinc hexadecyl (or octadecyl) isopropyldithiocarbamate, zinc dibenzyldithiocarbamate, sodium diethyldithiocarbamate, piperidine pentamethylenedithiocarbamate, selenium dimethyldithiocarbamate, tellurium diethyldithiocarbamate, diamyl Di, such as cadmium dithiocarbamate And the like can be used Okarubamin acid compound. As the aldehyde-amine system or aldehyde-ammonia system, for example, an aldehyde-amine system or aldehyde-ammonia system compound such as acetaldehyde-aniline reaction product, butyraldehyde-aniline condensate, hexamethylenetetramine, acetaldehyde-ammonia reaction product, etc. is used. can do. As the imidazoline-based compound, for example, an imidazoline-based compound such as 2-mercaptoimidazoline can be used. As the xanthate type, for example, a xanthate type compound such as zinc dibutylxanthate can be used. These vulcanization accelerators may be used alone or in combination of two or more.

Examples of the vulcanization acceleration aid include zinc oxide.
As the anti-aging agent, an amine-based, phenol-based or imidazole-based anti-aging agent, a carbamic acid metal salt, or the like can be appropriately selected and used.

  Examples of the oil include process oil, vegetable oil and fat, or a mixture thereof. Examples of the process oil include paraffinic process oil, naphthenic process oil, and aromatic process oil. Vegetable oils include castor oil, cottonseed oil, sesame oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice bran oil, beet flower oil, sesame oil, Examples include olive oil, sunflower oil, palm kernel oil, cocoon oil, jojoba oil, macadamia nut oil, safflower oil, tung oil, and the like.

  The rubber composition for bonding steel cords of the present invention preferably contains an adhesion-imparting agent such as cobalt acid stearate and organic acid cobalt such as cobalt naphthenate in order to improve adhesion to the steel cord. . The steel cord is generally made of a material in which, for example, brass plating is applied as a plating layer on the surface of the steel, and the steel cord and the rubber cord are mixed with the steel cord adhering rubber composition by containing the above-described adhesion imparting agent in the rubber composition. Adhesiveness with the rubber composition can be improved.

  For example, when organic acid cobalt is used as the adhesiveness-imparting agent, the content of the organic acid cobalt is 0.5 to 3.0 parts by mass as a 10 wt% cobalt-containing salt with respect to 100 parts by mass of the rubber component. It is preferable to be within the range. When the content is less than 0.5 parts by mass, the effect of improving the adhesion between the steel cord and the rubber composition for bonding steel cords tends to be low. This is because a remarkable improvement in adhesiveness due to an increase in the amount of cobalt acid cannot be expected, while the cost tends to increase due to an increase in the amount of organic acid cobalt. The content is more preferably in the range of 1.0 to 2.5 parts by mass, and still more preferably in the range of 1.0 to 2.0 parts by mass.

  The rubber hardness measured by a type A durometer according to JIS K6253 “Method for testing hardness of vulcanized rubber and thermoplastic rubber” of the rubber composition for bonding steel cords of the present invention is in the range of 45 to 65. It is preferable. When the rubber hardness is less than 45, the rigidity of the steel cord bonding rubber composition tends to be low and the mechanical strength tends to decrease. On the other hand, when the rubber hardness exceeds 65, the steel cord bonding rubber composition tends to be hard and the mechanical strength tends to decrease. The rubber hardness is more preferably 50 or more, and more preferably 60 or less.

<Pneumatic tire>
The present invention also provides a pneumatic tire including a ply using the rubber composition for bonding a steel cord as described above. FIG. 1 is a cross-sectional view illustrating the left half of a pneumatic tire according to the present invention. The pneumatic tire 1 includes a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both ends of the tread portion 2, and a bead portion 4 positioned at an inner end of each sidewall portion 3. It is common to have a structure with. A carcass 6 is bridged between the bead portions 4, and a belt layer 7 that reinforces the tread portion 2 with a tagging effect is disposed outside the carcass 6 and inside the tread portion 2. .

  The carcass 6 is formed of one or more carcass plies in which the carcass cord is arranged at an angle of, for example, 70 to 90 ° with respect to the tire equator CO. The carcass ply extends from the tread portion 2 to the sidewall portion 3. After that, the periphery of the bead core 5 of the bead portion 4 is folded back from the inner side in the tire axial direction to be locked.

  The belt layer 7 is composed of two or more belt plies in which the belt cords are arranged at an angle of, for example, 30 ° or less with respect to the tire equator CO, and the belt cords are placed in different directions so that the belt cords cross each other. is doing.

  Further, a bead apex rubber 8 extending radially outward from the bead core 5 is disposed in the bead portion 4, and an inner liner rubber 9 forming a tire lumen surface is adjacent to the inside of the carcass 6. The outside of the carcass 6 is protected by clinch rubber 4G and sidewall rubber 3G.

  The ply included in the pneumatic tire of the present invention can typically be at least one of the carcass ply and the belt ply described above. The ply can be formed by coating a steel cord with the rubber composition for bonding a steel cord of the present invention by a conventionally known method.

  By using the rubber composition for adhering steel cords of the present invention, it is possible to form a ply that is reduced in the amount of use of petroleum resource-derived raw materials and is reduced in hysteresis loss and rich in durability. Therefore, a pneumatic tire in which the ply is formed, for example, as a carcass ply or a belt ply is an eco-friendly eco tire by reducing the amount of raw material derived from petroleum resources, and at the same time, rolling resistance is reduced. And good durability.

  The pneumatic tire of the present invention can be manufactured by a conventionally known method using the rubber composition for bonding a steel cord of the present invention. That is, an unvulcanized rubber composition obtained by kneading the compounding ingredients for obtaining the steel cord bonding rubber composition of the present invention is processed into a thin film having a thickness of 1 mm or less with a calender roll, and the rubber composition A steel cord is covered with a material to make a ply. Note that if the Mooney viscosity of the rubber composition is excessively increased, heat generation of the rubber composition during processing may increase, so it is preferable to adjust the line speed as appropriate so as to suppress the increase in Mooney viscosity. This is applied to the part of the pneumatic tire, for example, between the tread rubber and the case in a predetermined shape, and is molded together with the other members of the tire by a normal method on a tire molding machine, thereby unvulcanized. Form a tire. The pneumatic tire of the present invention can be obtained by heating and pressurizing the unvulcanized tire in a vulcanizer.

  The pneumatic tire provided by the present invention can be suitably applied to various applications such as for passenger cars, trucks, buses, heavy vehicles, etc. as “eco-tires” that are friendly to the global environment.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to these.

<Examples 1 and 2 and Comparative Examples 1 to 3>
According to each compounding prescription shown in Table 1, using a 1.7L Banbury made by Kobe Steel, compounding components excluding sulfur and a vulcanization accelerator were kneaded at 120 ° C. for 3 minutes to obtain a kneaded product. To this was added sulfur and a vulcanization accelerator in the formulation shown in Table 1, and an open roll was used and further kneaded at 90 ° C. for 2 minutes to prepare an unvulcanized rubber composition.

  The unvulcanized rubber composition obtained above was extruded to produce an unvulcanized rubber sheet having a predetermined thickness. Further, the unvulcanized rubber sheet was vulcanized at 150 ° C. for 30 minutes to prepare a vulcanized rubber sheet having a predetermined thickness.

(Mooney viscosity index)
For the above unvulcanized rubber composition, the Mooney viscosity at 130 ° C. was measured according to JIS K6300, and the following formula:
Mooney viscosity index = (Mooney viscosity of Comparative Example 1) ÷ (Mooney viscosity of each Example or each Comparative Example) × 100
Thus, the Mooney viscosity index was determined with the Mooney viscosity of Comparative Example 1 as 100. The larger the index, the lower the Mooney viscosity and the better the workability.

(Appearance of unvulcanized rubber sheet)
An unvulcanized rubber sheet having a thickness of 1.0 mm was prepared by the above method, and the state of the fabric of the unvulcanized rubber sheet was confirmed visually. The case where the ear breakage did not occur and there was no problem in the background and the unvulcanized rubber sheet was satisfactorily processed was indicated as A, and the case where it was not indicated as B.

(E * index, tan δ index)
A sample having a thickness of 2 mm, a length of 40 mm, and a width of 4 mm was cut out from the vulcanized rubber sheet produced by the above method, and the temperature was 70 ° C. and the initial strain was 10 using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.). E * (complex modulus) and tan δ (loss tangent) were respectively measured under the conditions of% and dynamic strain of 2%. The following formula,
E * index = (E * of each Example or each Comparative Example) ÷ (E * of Comparative Example 1) × 100
tan δ index = (tan δ of Comparative Example 1) ÷ (tan δ of each Example or each Comparative Example) × 100
Thus, the E * index was determined with E * of Comparative Example 1 being 100, and the tan δ index was determined with tan δ of Comparative Example 1 being 100. The larger the E * index, the better the mechanical strength, and the larger the tan δ index, the smaller the hysteresis loss and the better the rolling resistance.

(Rubber coverage index)
The unvulcanized rubber composition prepared by the above method is processed into a thin film with a thickness of 1 mm or less with a calender roll, and a steel cord made of brass plated on the steel surface is coated with the unvulcanized rubber composition. Further, this was vulcanized to prepare a test ply.

An adhesion test was performed on the obtained test ply. That is, when the steel cord and the rubber composition for bonding the steel cord are peeled off and the area of the peeling surface on the steel cord side is 100%, the portion of the peeling surface covered with the rubber composition for bonding the steel cord Is calculated as the rubber coverage (%), and the following formula:
Rubber coverage index = (Rubber coverage of each example or comparative example) ÷ (Rubber coverage of comparative example 1) × 100
Thus, the rubber coverage index was obtained by setting the rubber coverage of Comparative Example 1 to 100.

  Here, the portion of the peeled surface covered with the steel cord bonding rubber composition is a portion where the steel cord and the steel cord bonding rubber composition are not peeled and the rubber itself cohesively breaks down, that is, the steel cord. This is the part where the adhesiveness with the steel cord bonding rubber composition was good. The case where the rubber coverage is 100% means that the release surface is entirely covered with the steel cord bonding rubber composition, that is, the steel cord and the steel cord bonding rubber composition are not peeled off. To do. The larger the rubber coverage index, the better the adhesion between the steel cord and the steel cord bonding rubber composition.

(Peeling resistance index)
The surface of the steel cord was coated with the unvulcanized rubber composition prepared by the above method to obtain an unvulcanized ply. This was applied as a ply for the breaker portion of the tire, combined with other members, molded into a tire, and vulcanized by a conventional method with a tire molding machine to prepare a test tire (size 195 / 65R15).

From the obtained test tire, the ply is cut as a sample for peeling, the tensile drag is measured using an Instron, the following formula:
Peel resistance index = (tensile drag of each example or each comparative example) ÷ (tensile drag of comparative example 1) × 100
From the above, the tensile resistance index of Comparative Example 1 was taken as 100, and the peel resistance index was determined. The larger the peel resistance index, the better the adhesion between the steel cord and the steel cord bonding rubber composition.

Note 1: Natural rubber is “RSS # 3”.
Note 2: Carbon black is “Show Black N550” (DBP oil absorption: 84 ml / 100 g) manufactured by Showa Cabonet Co., Ltd.
Note 3: Silica A is “Ultra Gil VN3” (BET specific surface area: 210 m ² / g) manufactured by Degussa.
Note 4: Silica B is “Ultrazil VN2” (BET specific surface area: 125 m ² / g) manufactured by Degussa.
Note 5: Silane coupling agent is “Si266” manufactured by Degussa.
Note 6: Anti-aging agent is “NOCRACK 6C” manufactured by Ouchi Shinsei Chemical Co., Ltd.
Note 7: Stearic acid is stearic acid manufactured by NOF Corporation.
Note 8: Zinc oxide is “Zinc Hana 1” manufactured by Mitsui Mining & Smelting Co., Ltd.
Note 9: Sulfur is “Cristex HSOT20” (sulfur content: 80 mass%) manufactured by Flexis.
Note 10: The vulcanization accelerator is “Noxeller DZ” manufactured by Ouchi Shinsei Chemical Co., Ltd.

  As shown in Table 1, the appearance of the unvulcanized rubber sheet is not good in Comparative Example 1 in which the blended silica has a large BET specific surface area, and the Mooney viscosity is large in Comparative Example 2 in which the silica is small but has a large blending amount. In Comparative Example 3 in which the index and tan δ index were not good, and the BET specific surface area of silica was small but the blending amount was small, the E * index, rubber coverage index, and peel resistance index were not good. On the other hand, in Examples 1 and 2 in which a predetermined amount of carbon black and silica were used together and the BET specific surface area of silica was reduced, Mooney viscosity index, appearance of unvulcanized rubber sheet, E * index, tan δ index, rubber coating The rate index and peel resistance index were both good.

  From the above results, according to the steel cord bonding rubber composition of the present invention, while reducing the amount of raw materials derived from petroleum resources, maintaining good adhesion with the steel cord, the workability during preparation is improved. It can be seen that the hysteresis loss can be reduced while being obtained well.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The rubber composition for bonding steel cords of the present invention is suitably applied to pneumatic tire plies for various uses such as passenger cars, trucks, buses, heavy vehicles, and the like. It can be suitably applied to the application.

It is sectional drawing which illustrated the left half of the pneumatic tire which concerns on this invention.

Explanation of symbols

  1 tire, 2 tread part, 3 side wall part, 4 bead part, 5 bead core, 6 carcass, 7 belt layer, 8 bead apex rubber, 9 inner liner rubber, 3G side wall rubber, 4G clinch rubber.

Claims (3)

40 to 80 parts by mass of silica having a BET specific surface area of 150 m ² / g or less and 5 parts by mass or less of carbon black are blended with respect to 100 parts by mass of the rubber component,
The rubber composition for bonding a steel cord, wherein the rubber component comprises at least one of natural rubber and modified natural rubber.   The rubber composition for bonding a steel cord according to claim 1, wherein the rubber component is made of at least one of natural rubber and epoxidized natural rubber.   A pneumatic tire provided with a ply formed using the rubber composition for bonding a steel cord according to claim 1.

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