JP2012111888A - Rubber composition for tire cord topping and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for tire cord toppings which can improve breaking energy and heat resistance, and to provide a pneumatic tire using the same.SOLUTION: This rubber composition for tire cord toppings comprises natural rubber and a wet masterbatch (1), wherein the wet masterbatch (1) is obtained by mixing a styrene-butadiene rubber latex, a carbon black dispersion liquid, and a liquid styrene-butadiene copolymer emulsion or a liquid butadiene polymer emulsion. Alternatively the rubber composition for tire cord toppings comprises styrene-butadiene rubber and a wet masterbatch (2), wherein the wet masterbatch (2) is obtained by mixing a natural rubber latex, the carbon black dispersion liquid, and a liquid isoprene polymer emulsion or the liquid butadiene polymer emulsion.

Description

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

Durability is required for tire cord topping (covering) rubber such as carcass, breaker, and band. In order to improve durability, it is necessary to improve fracture energy (fracture characteristics) and heat resistance. For example, carbon black having reinforcing properties is used together with natural rubber and styrene butadiene rubber.

However, if high-reinforcing carbon black such as that used in treads is used, heat will be generated during rubber kneading and topping on the cord material, and workability will deteriorate. Is difficult. Moreover, it is possible to improve heat resistance by reducing the blending ratio of natural rubber and increasing the blending ratio of styrene-butadiene rubber, but the breaking energy is lowered. Thus, with tire cord topping rubber, it has been difficult to achieve both high fracture energy and heat resistance.

Patent Document 1 describes the use of a hydrogenated liquid polymer, but there is room for improvement in terms of achieving both fracture energy and heat resistance.

JP 2005-225946 A

An object of the present invention is to solve the above-mentioned problems and to provide a rubber composition for tire cord topping that can improve fracture energy and heat resistance, and a pneumatic tire using the same.

1st this invention contains natural rubber and wet masterbatch (1), This wet masterbatch (1) is styrene butadiene rubber latex, carbon black dispersion liquid, liquid styrene butadiene copolymer emulsion, or liquid butadiene polymer. The present invention relates to a rubber composition for tire cord topping obtained by mixing with an emulsion.

The second invention includes a styrene butadiene rubber and a wet masterbatch (2), the wet masterbatch (2) comprising a natural rubber latex, a carbon black dispersion, a liquid isoprene polymer emulsion or a liquid butadiene polymer emulsion. It is related with the rubber composition for tire cord toppings obtained by mixing these.

3rd this invention relates to the rubber composition for tire cord toppings containing the said wet masterbatch (1) and (2).

In the rubber composition, the wet master batches (1) and (2) are composed of 40 to 100 parts by mass of carbon black and 10 to 50 parts of liquid diene polymer with respect to 100 parts by mass of the rubber component in the rubber latex. It is preferable to include parts by mass. Here, the weight average molecular weight of the liquid diene polymer is preferably 1000 to 50000.

In the rubber composition, the compound 1 represented by the following formula (1), the compound 2 having a structure represented by the following formula (2), the compound 3 represented by the following formula (3), and the compound 3 It is preferable to include at least one selected from the group consisting of hydrates.
R ¹ —S—S— (CH ₂ ) _p —S—S—R ² (1)
(In formula (1), p represents an integer of 2 to 12. R ¹ and R ² are the same or different and each represents a monovalent organic group containing a nitrogen atom.)
_{^{- (R 3 -S x) n}} - (2)
(In Formula (2), R ³ represents — (CH ₂ —CH ₂ —O) _m —CH ₂ —CH ₂ —, m represents an integer of 2 to 5, and x represents an integer of 2 to 6). N represents an integer of 10 to 400.)
_{MO 3 S-S- (CH 2} ) q -S-SO 3 M (3)
(In Formula (3), q represents an integer of 3 to 10. M is the same or different and represents lithium, potassium, sodium, magnesium, calcium, barium, zinc, nickel, or cobalt.)

The present invention also relates to a pneumatic tire produced using the rubber composition.

According to the present invention, (A) a natural rubber, and a wet masterbatch (1) obtained by mixing a styrene butadiene rubber latex, a carbon black dispersion, and a liquid styrene butadiene copolymer emulsion or a liquid butadiene polymer emulsion, (B) Styrene butadiene rubber, and wet master batch (2) obtained by mixing natural rubber latex, carbon black dispersion, and liquid isoprene polymer emulsion or liquid butadiene polymer emulsion, or (C) the wet master batch Since it is a rubber composition for tire cord toppings including (1) and (2), it is possible to achieve both fracture energy and heat resistance at high levels. Therefore, a pneumatic tire having excellent durability can be provided.

The rubber composition for tire cord topping of the present invention is any one of the following (A) to (C).
(A) Natural rubber, and wet masterbatch (1) obtained by mixing styrene butadiene rubber latex, carbon black dispersion, and liquid styrene butadiene copolymer emulsion or liquid butadiene polymer emulsion.
(B) The wet masterbatch (2) obtained by mixing a styrene butadiene rubber and a natural rubber latex, a carbon black dispersion, and a liquid isoprene polymer emulsion or a liquid butadiene polymer emulsion.
(C) The wet master batches (1) and (2) are included.

In the present invention, since the wet masterbatch is used, not only the process oil but also a liquid diene polymer is used to improve the breaking energy, as well as carbon black and liquid diene in the rubber component (polymer). By increasing the dispersibility of the polymer, the fracture energy can be remarkably improved, and at the same time, the heat resistance can be improved. Therefore, these performances can be achieved at a high level, and high durability can be obtained.

[Wet masterbatch (1), (2)]
The wet masterbatch (WMB) can be prepared, for example, by mixing a rubber latex, a carbon black dispersion, and a liquid diene polymer emulsion, and then coagulating and drying.

(Rubber latex)
The styrene butadiene rubber latex (SBR latex) and natural rubber latex (NR latex) in the above (A) to (C) are not particularly limited, and commercially available products such as commercially available products can be used.

The SBR in the SBR latex is not particularly limited, and those commonly used in the tire industry such as emulsion-polymerized styrene butadiene rubber (E-SBR) can be used. Among these, E-SBR is preferable because the effects of the present invention can be obtained satisfactorily.

The vinyl content of the SBR is preferably 5% by mass or more, more preferably 15% by mass or more. When the vinyl content is less than 5% by mass, the heat resistance tends to decrease. The vinyl content is preferably 50% by mass or less, more preferably 25% by mass or less. When the vinyl content exceeds 50% by mass, the fracture energy tends to decrease.
The vinyl content of SBR can be measured by infrared absorption spectrum analysis.

The styrene content of the SBR is preferably 20% by mass or more, more preferably 30% by mass or more. When the styrene content is less than 20% by mass, the fracture energy tends to decrease. The styrene content is preferably 60% by mass or less, more preferably 45% by mass or less. When the styrene content exceeds 60% by mass, it tends to be hard at low temperatures, tends to cause brittle fracture, and heat generation tends to increase.
Incidentally, styrene content of the SBR ^is calculated by H 1 -NMR measurement.

Specifically, raw latex produced by tapping heavy trees or purified latex concentrated by centrifugation can be used as the NR latex. Furthermore, high ammonia latex to which ammonia is added by a conventional method may be used to prevent the progress of decay due to bacteria present in the raw rubber latex and to avoid coagulation of the latex. Deproteinized natural rubber latex and high-purity natural rubber latex can also be used.

The concentration of the rubber component (rubber solid content) in the SBR latex and NR latex is not particularly limited, but is preferably 20 to 80% by mass, more preferably from the viewpoint of uniform dispersibility in the rubber latex (100% by mass). 30 to 60% by mass.

(Carbon black dispersion)
In the above (A) to (C), examples of the carbon black dispersion include those obtained by dispersing carbon black in an aqueous medium. By using the dispersion, the polymer (rubber molecule) and carbon black can be mixed in a liquid state, and good filler dispersibility can be obtained.

The carbon black dispersion can be produced by a known method, for example, using a high-pressure homogenizer, an ultrasonic homogenizer, a colloid mill, or the like. Specifically, the dispersion can be prepared by placing an aqueous medium in a colloid mill, adding a filler while stirring, and then circulating with a surfactant as necessary using a homogenizer. The concentration of carbon black in the dispersion is not particularly limited, but is preferably 0.5 to 10% by mass, more preferably 3 to 7 from the viewpoint of uniform dispersibility in the dispersion (100% by mass). % By mass.

As described in the method for producing a dispersion liquid, a surfactant may be added to the carbon black dispersion liquid from the viewpoint of dispersibility. The surfactant is not particularly limited, and known anionic surfactants, nonionic surfactants, amphoteric surfactants, and the like can be appropriately used. In the above dispersion, the addition amount of the surfactant is not particularly limited, but is preferably 0.01 to 3% by mass, more preferably from the viewpoint of uniform dispersibility of the carbon black in the dispersion (100% by mass). Is 0.05-1 mass%.

Examples of the carbon black that can be used include GPF, FEF, HAF, ISAF, and SAF. In the present invention, the carbon black having low reinforcing properties can be used to ensure workability and improve the fracture energy. Durability.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 20 m ² / g or more, more preferably 60 m ² / g or more. If it is less than 20 m < ² > / g, there exists a possibility that reinforcement may be low and sufficient durability may not be acquired. Further, the N ₂ SA of the carbon black is preferably 130 m ² / g or less, more preferably 90 m ² / g or less. When it exceeds 130 m < ² > / g, there exists a possibility that workability may fall.
In addition, the nitrogen adsorption specific surface area of carbon black is calculated | required by A method of JISK6217.

The iodine adsorption amount (IA) of carbon black is preferably 50 mg / g or more, more preferably 80 mg / g or more. When the iodine adsorption amount is less than 50 mg / g, the reinforcing effect is small, and there is a tendency that sufficient fracture energy cannot be obtained. On the other hand, the upper limit of the IA is preferably 120 mg / g or less, more preferably 90 mg / g or less. If it exceeds 120 mg / g, the workability may be reduced.
The iodine adsorption amount of carbon black can be measured by a method based on ASTM-D-1510.

In addition, examples of the aqueous medium include water and alcohol. Among them, water is preferably used.

(Liquid diene polymer emulsion)
In the above (A) to (C), as the liquid diene polymer emulsion, liquid styrene butadiene copolymer (liquid SBR) emulsion, liquid butadiene polymer (liquid BR) emulsion, liquid isoprene polymer (liquid IR) emulsion are available. used. Examples of these emulsions include those obtained by emulsifying a liquid diene polymer using a surfactant, and the oil-in-water solution can be further improved in compatibility between the rubber component and the liquid diene polymer. Drop emulsions are preferred.

Each liquid diene polymer emulsion can be prepared by a known emulsification method. A predetermined amount of a surfactant and water are added to a liquid diene polymer (liquid SBR, liquid BR, liquid IR), a homomixer, a colloid mill. An oil-in-water emulsion can be prepared by applying a shear stress using an emulsifier or mixer such as a line mill, a homogenizer, a planetary mixer, or a trimix mixer.

The weight average molecular weight (Mw) of the liquid diene polymer is preferably 1000 or more, more preferably 1500 or more. If Mw is less than 1000, the fracture energy may not be sufficiently improved. The Mw of the liquid diene polymer is preferably 50000 or less, more preferably 30000 or less. When Mw exceeds 50000, the difference in molecular weight from the rubber component becomes small, and the effect as a plasticizer tends to be hardly exhibited. In addition, in this specification, a weight average molecular weight (Mw) is measured by the method as described in the below-mentioned Example.

The weight average molecular weight (Mw) of the liquid SBR is preferably 2000 or more, more preferably 3000 or more. The Mw of the liquid SBR is preferably 50000 or less, more preferably 40000 or less, and still more preferably 15000 or less.

The weight average molecular weight (Mw) of the liquid IR is preferably 10,000 or more, more preferably 20,000 or more. Moreover, Mw of liquid IR becomes like this. Preferably it is 50000 or less, More preferably, it is 40000 or less.

The weight average molecular weight (Mw) of the liquid BR is preferably 5000 or more, more preferably 6000 or more. The Mw of the liquid BR is preferably 50000 or less, more preferably 30000 or less, and still more preferably 20000 or less.
In addition, when Mw of liquid SBR, liquid IR, and liquid BR is outside the above range, the same tendency as in the case of the liquid diene polymer is obtained.

The vinyl content of the liquid SBR is preferably 10% by mass or more, more preferably 20% by mass or more. When the vinyl content is less than 10% by mass, the heat resistance tends to decrease.
The vinyl content is preferably 90% by mass or less, more preferably 75% by mass or less. When the vinyl content exceeds 90% by mass, the fracture energy tends to decrease.
The vinyl content of the liquid SBR can be measured by infrared absorption spectrum analysis.

The styrene content of the liquid SBR is preferably 10% by mass or more, more preferably 15% by mass or more. If the styrene content is less than 10% by mass, the fracture energy tends to decrease. The styrene content is preferably 60% by mass or less, more preferably 50% by mass or less. When the styrene content exceeds 60% by mass, it tends to be hard at low temperatures and the heat generation tends to be high.
Incidentally, styrene content of the liquid SBR ^is calculated by H 1 -NMR measurement.

The concentration of the liquid diene polymer in the emulsion is not particularly limited.

As the surfactant, a known surfactant can be used, but a nonionic surfactant is preferably used from the viewpoint that the liquid diene polymer can be favorably dispersed. Of these, polyoxyalkylene alkyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene hydrogenated castor oil and the like are preferable.

Further, in the nonionic surfactant, the hydrophilic part preferably has 2 to 40 repeating units of oxyethylene, and the lipophilic part preferably has an alkyl ether or alkenyl ether structure.

In the above emulsion, the addition amount of the surfactant is not particularly limited, but from the viewpoint of uniform dispersibility of the liquid diene polymer in the emulsion (100% by mass), preferably 0.1 to 10% by mass, More preferably, it is 1-5 mass%.

(mixture)
The mixing method of the rubber latex, the carbon black dispersion, and the liquid diene polymer emulsion is not particularly limited. For example, the rubber latex is placed in a blender mill and stirred, and the carbon black dispersion and the liquid diene system are mixed. A method of dropping a polymer emulsion, a method of adding a rubber latex and a liquid diene polymer emulsion to this while stirring a carbon black dispersion, and a stirring of a liquid diene polymer emulsion. Examples thereof include a method of dropping rubber latex and a carbon black dispersion. Alternatively, a method of mixing a rubber latex stream, a carbon black dispersion liquid stream, and a liquid diene polymer emulsion stream having a constant flow rate ratio under vigorous hydraulic stirring conditions may be used.

(coagulation)
After the mixing step, solidification is usually performed, but the solidification step is usually performed by adding an acidic compound such as formic acid and sulfuric acid and a coagulant such as a salt such as sodium chloride. In some cases, the mixture may be solidified. In this case, a coagulant may not be used.

(Dry)
After solidification, the obtained solidified product is usually recovered, dehydrated by centrifugation or the like, and further washed and dried to obtain the WMB. Examples of the dryer that can be used for drying include a vacuum dryer, an air dryer, a drum dryer, a band dryer, a hot air dryer, and a kiln type dryer.

(Composition of WMB (1), (2))
The content of carbon black in WMB is preferably 40 parts by mass or more and more preferably 45 parts by mass or more with respect to 100 parts by mass of the rubber component (rubber solid content) in the rubber latex. If it is less than 40 parts by mass, the reinforcing property is low and the durability may be lowered. Moreover, 100 mass parts or less are preferable and, as for content of this filler, 70 mass parts or less are more preferable. If it exceeds 100 parts by mass, the workability may be reduced.

The content of the liquid diene polymer in WMB is preferably 10 parts by mass or more, more preferably 15 parts by mass or more with respect to 100 parts by mass of the rubber component (rubber solid content) in the rubber latex. If it is less than 10 parts by mass, sufficient destruction energy may not be obtained. Moreover, this content becomes like this. Preferably it is 50 mass parts or less, More preferably, it is 30 mass parts or less. When it exceeds 50 parts by mass, the heat generation tends to be high, the fracture strength, and the heat resistance tend to decrease.
In the present specification, the liquid diene polymer is not included in the rubber component.
Moreover, WMB (1) and (2) may contain another component in the range which does not inhibit the effect of this invention.

The first rubber composition (A) contains natural rubber in addition to WMB (1), and the second rubber composition (B) contains styrene butadiene rubber in addition to WMB (2). Thereby, fracture energy and heat resistance are improved in a well-balanced manner.

The NR is not particularly limited, and for example, those commonly used in the tire industry such as SIR20, RSS # 3, TSR20, and the like can be used. In addition, modified natural rubber (HPNR) having a phosphorus content of 200 ppm or less as NR can be suitably used. Thereby, heat resistance can be improved.

As the modified natural rubber, those obtained by the production methods described in JP 2010-138359 A and JP 2010-174169 A are preferably used. For example, as a modified natural rubber, a process of obtaining a saponified natural rubber latex by saponifying natural rubber latex, and a phosphorus content in the obtained saponified natural rubber latex is 200 ppm or less. What was obtained by the manufacturing method including the process wash | cleaned until is suitable.

The modified natural rubber (HPNR) preferably has a phosphorus content of 150 ppm or less, more preferably 100 ppm or less. When the phosphorus content is within the above range, more excellent heat resistance can be obtained. Phosphorus is derived from phospholipids (phosphorus compounds).

The gel content in the modified natural rubber is preferably 20% by mass or less, and more preferably 7% by mass or less. The gel content means a value measured as an insoluble content with respect to toluene which is a nonpolar solvent, and may be simply referred to as “gel content” or “gel content” below.

In the modified natural rubber, the nitrogen content is preferably 0.3% by mass or less, and more preferably 0.15% by mass or less. Here, nitrogen is derived from protein.
In addition, in this specification, phosphorus content, the content rate of a gel part, and nitrogen content are measured by the method as described in the below-mentioned Example.

It does not specifically limit as SBR, The thing similar to SBR in the said SBR latex can be used conveniently.

The third rubber composition (C) contains WMB (1) and (2). Since WMB in which carbon black and a liquid diene polymer are well dispersed in NR or SBR are used in combination, fracture energy and heat resistance can be achieved at a high level.

The total content of NR in 100% by mass of the total amount of rubber components (NR, SBR, SBR contained in WMB (1), NR contained in WMB (2), etc.) contained in the first to third rubber compositions Is preferably 30% by mass or more, more preferably 50% by mass or more. If it is less than 30% by mass, sufficient destruction energy may not be obtained. The total content may be 100% by mass, but is preferably 85% by mass or less, more preferably 75% by mass or less. If it exceeds 80% by mass, the SBR blending ratio will be low, and the heat resistance may be reduced.

The total content of SBR is preferably 15% by mass or more, more preferably 25% by mass or more, in the total amount of 100% by mass of the rubber components contained in the first to third rubber compositions. If it is less than 15% by mass, the heat resistance may decrease. The total content is preferably 70% by mass or less, more preferably 50% by mass or less. If it exceeds 70% by mass, the SBR blending ratio will be low, and the heat resistance may be reduced.

The total content of NR and SBR is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 100% by mass in the total amount of 100% by mass of the rubber components contained in the first to third rubber compositions. %. Thereby, destruction energy and heat resistance can be obtained with a good balance.

In addition to carbon black contained in WMB, the rubber composition of the present invention may further contain carbon black as necessary. As carbon black, those similar to WMB can be used preferably.

In the rubber composition of the present invention, the total content of carbon black (the total content of carbon black contained in WMB and further blended carbon black) is 100 parts by mass of the total amount of rubber components (rubber solids). The amount is preferably 10 parts by mass or more, more preferably 30 parts by mass or more. The total content is preferably 100 parts by mass or less, more preferably 70 parts by mass or less. By making the total content of the filler within the above range, the effect of the present invention can be obtained satisfactorily.

The proportion of carbon black contained in WMB is preferably 10% by mass or more, more preferably 50% by mass or more, and still more preferably 100% by mass in 100% by mass of carbon black blended in the rubber composition of the present invention. It is. When the proportion of the filler is in the above range, the effect of the present invention can be obtained satisfactorily.

The rubber composition of the present invention includes a compound 1 represented by the following formula (1), a compound 2 having a structure represented by the following formula (2), a compound 3 represented by the following formula (3), and the compound It is preferable to include at least one selected from the group consisting of 3 hydrates. By using the above WMB and these compounds in combination, the compatibility between the rubber component and the liquid diene polymer is improved, and the dispersibility of the liquid diene polymer is improved. By being formed satisfactorily, the effect of improving the heat resistance can be enhanced synergistically, and the breaking energy can also be improved. Of the hydrates of Compounds 1 to 3 and Compound 3, Compound 1 is preferable.
R ¹ —S—S— (CH ₂ ) _p —S—S—R ² (1)
(In formula (1), p represents an integer of 2 to 12. R ¹ and R ² are the same or different and each represents a monovalent organic group containing a nitrogen atom.)
_{^{- (R 3 -S x) n}} - (2)
(In Formula (2), R ³ represents — (CH ₂ —CH ₂ —O) _m —CH ₂ —CH ₂ —, m represents an integer of 2 to 5, and x represents an integer of 2 to 6). N represents an integer of 10 to 400.)
_{MO 3 S-S- (CH 2} ) q -S-SO 3 M (3)
(In Formula (3), q represents an integer of 3 to 10. M is the same or different and represents lithium, potassium, sodium, magnesium, calcium, barium, zinc, nickel, or cobalt.)

In formula (1), p is an integer of 2 to 12, preferably 3 to 10, more preferably 4 to 8. When p is 1, thermal stability is poor and the effect of having an alkylene group tends not to be obtained. When _p is 13 or more, it is represented by —SS— (CH ₂ ) _p —S—S—. It tends to be difficult to form a crosslinked chain.

Examples of the alkylene group satisfying the above conditions include ethylene group, trimethylene group, tetramethylene group, pentamethylene group, hexamethylene group, heptamethylene group, octamethylene group, decamethylene group and the like. Among these, a hexamethylene group is preferable because a bridge represented by —SS— (CH ₂ ) _p —S—S— is formed smoothly between the polymers and is thermally stable.

In formula (1), R ¹ and R ² are not particularly limited as long as they are monovalent organic groups containing a nitrogen atom, but those containing at least one aromatic ring are preferred, and a carbon atom is bonded to a dithio group. And those containing a linking group represented by N—C (═S) —. R ¹ and R ² may be the same or different, but are preferably the same for reasons such as ease of production.
For example, what has the following structure can be used suitably as R < ¹ >, R < ² >.

Examples of the compound 1 represented by the above formula (1) include 1,2-bis (N, N′-dibenzylthiocarbamoyldithio) ethane and 1,3-bis (N, N′-dibenzylthiocarbamoyl). Dithio) propane, 1,4-bis (N, N′-dibenzylthiocarbamoyldithio) butane, 1,5-bis (N, N′-dibenzylthiocarbamoyldithio) pentane, 1,6-bis (N, N′-dibenzylthiocarbamoyldithio) hexane, 1,7-bis (N, N′-dibenzylthiocarbamoyldithio) heptane, 1,8-bis (N, N′-dibenzylthiocarbamoyldithio) octane, , 9-bis (N, N′-dibenzylthiocarbamoyldithio) nonane, 1,10-bis (N, N′-dibenzylthiocarbamoyldithio) decane and the like. . Among these, 1,6-bis (N, N′-dibenzylthiocarbamoyldithio) hexane is preferable because it is thermally stable and has excellent polarizability.

In Formula (2), m is 2-5, Preferably it is 2-4.

In formula (2), x is 2-6, preferably 3-5. When x is less than 2, vulcanization is delayed. Moreover, when x exceeds 6, manufacture of a rubber composition will become difficult.

In formula (2), n is 10 to 400, preferably 50 to 300. If n is less than 10, the organic vulcanizing agent tends to volatilize and handling becomes difficult. On the other hand, if n exceeds 400, the compatibility with rubber deteriorates, and the performance improvement effect may not be sufficient.

As such compound 2, for example, poly-3,6-dioxaoctane-tetrasulfide (such as 2OS4 manufactured by Kawaguchi Chemical Industry Co., Ltd.) can be used.

In formula (3), q is an integer of 3 to 10, preferably 3 to 6. If it is less than 3, the rubber strength and wear resistance may not be sufficiently improved, and if it exceeds 10, the effect of improving the rubber strength and wear resistance tends to be small although the molecular weight increases.

In formula (3), M is preferably lithium, potassium, sodium, magnesium, calcium, barium, zinc, nickel or cobalt, more preferably potassium or sodium. Examples of the hydrate of the compound represented by the formula (3) include sodium salt monohydrate and sodium salt dihydrate.

As the compound 3 represented by the formula (3) and a hydrate thereof, a derivative derived from sodium thiosulfate, for example, 1,6-hexamethylene-sodium dithiosulfate dihydrate is preferable.

In the rubber composition of the present invention, the total content of Compound 1, Compound 2, Compound 3, and the hydrate of Compound 3 is preferably 0.6 with respect to 100 parts by mass of the rubber component (rubber solid content). It is 1 part by mass or more, more preferably 1 part by mass or more. The content is preferably 12 parts by mass or less, more preferably 6 parts by mass or less. If it is less than the lower limit, the improvement effect by these compounds may not be sufficient, and if it exceeds the upper limit, the fracture energy tends to decrease.

The rubber composition of the present invention usually contains sulfur. When the WMB, the compounds 1 to 3, the hydrate of the compound 3 and sulfur are used in combination, the above-described operational effects are exhibited, and the operational effects due to the introduction of different crosslinking forms are also exhibited and destroyed. A sufficient effect of improving energy and heat resistance can be obtained.

In the rubber composition of the present invention, the sulfur content is preferably 0.5 to 6.0 parts by mass, more preferably 1.0 to 3.0 with respect to 100 parts by mass of the rubber component (rubber solids). Part by mass. In particular, when compounds 1 to 3 and a hydrate of compound 3 are blended, the content of sulfur is preferably 0.5 to 3.0 parts by mass, more preferably 1.0 to 2.5 parts by mass. Part. When the content is within the above range, the above-mentioned effects can be obtained satisfactorily.

In addition to the above components, the rubber composition of the present invention contains, as appropriate, compounding agents generally used in the production of rubber compositions such as zinc oxide, stearic acid, various anti-aging agents, oils, vulcanization accelerators, and the like. Can be blended.

As a method for producing the rubber composition of the present invention, known methods can be used. For example, the above components are kneaded using a rubber kneader such as an open roll or a Banbury mixer, and then vulcanized. Can be manufactured. The rubber composition can be suitably used for carcass members such as a breaker (belt), a band, and a case.

[Pneumatic tire]
The pneumatic tire of the present invention is produced by a usual method using the rubber composition.
That is, a rubber composition containing the above components is topped with a tire cord material at an unvulcanized stage, and is molded together with other tire members by a normal method on a tire molding machine. Form. The unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire.

The pneumatic tire of the present invention is suitably used as a passenger car tire, motorcycle tire, commercial vehicle tire, competition tire, and the like.

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

The following evaluation was performed for liquid SBR (RICON 100 manufactured by Sartomer), liquid IR (LIR-30 manufactured by Kuraray Co., Ltd.), and liquid BR (RICON 142 manufactured by Sartomer). The results are shown in Table 1.

(Measurement of weight average molecular weight (Mw))
The weight average molecular weight (Mw) is measured by gel permeation chromatograph (GPC) (GPC-8000 series, manufactured by Tosoh Corp., detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M, manufactured by Tosoh Corp.). It calculated | required by standard polystyrene conversion based on the value.

Hereinafter, various chemicals used in Production Examples 1 to 3 will be described together.
SBR latex: LX110 manufactured by Nippon Zeon Co., Ltd. (E-SBR, styrene content: 37.5% by mass, vinyl content: 18% by mass, concentration of rubber component in rubber latex: 40.5% by mass)
Natural rubber latex: Field latex obtained from Taitex Co., Ltd. (concentration of rubber component (solid content) in rubber latex: 30% by mass)
Carbon Black: Show Black N330 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 75 m ² / g, IA: 81 mg / g)
Liquid SBR: RICON 100 manufactured by Sartomer (styrene content: 20% by mass, vinyl content: 70% by mass)
Liquid IR: LIR-30 manufactured by Kuraray Co., Ltd.
Liquid BR: RICON142 manufactured by Sartomer
Demol N: Surfactant Demol N manufactured by Kao Corporation (sodium salt of β-naphthalene sulfonic acid formalin condensate (anionic surfactant))
New Coal NT-15: New Coal NT-15 manufactured by Nippon Emulsifier Co., Ltd. (nonionic polyoxyethylene alkyl ether type surfactant)

(Production Example 1)
(Preparation of WMB (1-1))
(Preparation of carbon black dispersion)
A colloid mill with a rotor diameter of 30 mm was charged with 1900 g of deionized water and 100 g of carbon black, and stirred for 10 minutes at a rotor-stator interval of 1 mm and a rotational speed of 2000 rpm. Subsequently, demole N was added so that it might become a density | concentration of 0.05 mass%, and it circulated 3 times using the pressure type homogenizer, and prepared the filler dispersion liquid.

(Preparation of liquid diene polymer emulsion)
After heating 100 g of liquid SBR to 50 ° C., 300 g of a 5% by mass aqueous solution of New Coal NT-15 was added and stirred to prepare a liquid diene polymer emulsion (oil-in-water emulsion).

(Rubber latex, carbon black dispersion, liquid diene polymer emulsion mixing, coagulation, drying)
Rubber latex (SBR latex), carbon black dispersion, liquid diene polymer emulsion so that the solid content ratio (mass ratio) of rubber component: carbon black component: liquid diene polymer component is 100: 50: 15 After the solution became homogeneous, sulfuric acid was added while continuing stirring, and the pH was adjusted to 5 to solidify. The obtained solid was filtered to collect the rubber component, and the rubber component was washed with pure water until the washed liquid (washing water) had a pH of 7, and dried to obtain WMB (1-1).

(Production Example 2)
(Preparation of WMB (2-1))
WMB (2-1) was obtained under the same conditions as in Production Example 1 except that the SBR latex was changed to NR latex and the liquid SBR was changed to liquid IR.

(Production Example 3)
(Preparation of WMB (2-2))
WMB (2-2) was obtained under the same conditions as in Production Example 1 except that the SBR latex was changed to NR latex and the liquid SBR was changed to liquid BR.

Hereinafter, various chemicals used in Production Example 4 will be described together.
Natural rubber latex: Field latex obtained from Taitex Co., Ltd. Surfactant: Emal-E (Polyoxyethylene lauryl ether sodium sulfate) manufactured by Kao Corporation
NaOH: NaOH manufactured by Wako Pure Chemical Industries, Ltd.

(Production Example 4)
(Preparation of saponified natural rubber (NR (2)))
After adjusting the solid rubber latex solids concentration (DRC) to 30% (w / v), 1000 g of natural rubber latex was added with 10 g of Emal-E and 20 g of NaOH, followed by saponification at room temperature for 48 hours. Natural rubber latex was obtained. Water was added to the latex to dilute to DRC 15% (w / v), and then formic acid was added with slow stirring to adjust the pH to 4.0 to 4.5 to cause aggregation. The agglomerated rubber was pulverized, washed repeatedly with 1000 ml of water, and then dried at 110 ° C. for 2 hours to obtain a solid rubber (saponified natural rubber).

The solid rubber and TSR obtained in Production Example 4 were measured for nitrogen content, phosphorus content, and gel content by the methods described below. The results are shown in Table 2.

(Measurement of nitrogen content)
The nitrogen content was measured using CHN CORDER MT-5 (manufactured by Yanaco Analytical Co., Ltd.). For the measurement, first, a calibration curve for determining the nitrogen content was prepared using antipyrine as a standard substance. Next, about 10 mg of the saponified natural rubber or TSR sample obtained in the production example was weighed, and the average value was obtained from the measurement results of three times to obtain the nitrogen content of the sample.

(Measurement of phosphorus content)
The phosphorus content was determined using an ICP emission spectrometer (ICPS-8100, manufactured by Shimadzu Corporation).
In addition, ³¹ P-NMR measurement of phosphorus uses an NMR analyzer (400 MHz, AV400M, manufactured by Nippon Bruker Co., Ltd.), and uses a measurement peak of P atom in an 80% aqueous phosphoric acid solution as a reference point (0 ppm), and raw rubber with chloroform. More extracted components were purified, dissolved in CDCl ₃ and measured.

(Measurement of gel content)
A raw rubber sample 70.00 mg cut to 1 mm × 1 mm was weighed, 35 mL of toluene was added thereto, and the mixture was allowed to stand in a cool dark place for 1 week. Subsequently, centrifugation was performed to precipitate a gel component insoluble in toluene, the soluble component of the supernatant was removed, and only the gel component was solidified with methanol, and then dried and the mass was measured. The gel content (%) was determined by the following formula.
Gel content (mass%) = [mass mg after drying / mg of initial sample] × 100

Hereinafter, various chemicals used in Examples and Comparative Examples will be described together.
NR (1): TSR20
NR (2): Production Example 4
SBR: Nipol 1502 (Emulsion polymerization styrene butadiene rubber, styrene content: 23.5 mass%, vinyl content: 18 mass%) manufactured by Nippon Zeon Co., Ltd.
WMB (1-1): Production Example 1
WMB (2-1): Production Example 2
WMB (2-2): Production Example 3
Carbon Black: Show Black N330 manufactured by Cabot Japan Co., Ltd. (N ₂ SA: 75 m ² / g, IA: 81 mg / g)
Liquid SBR: RICON 100 manufactured by Sartomer (styrene content: 20% by mass, vinyl content: 70% by mass)
Process oil: Diana Process NH-80 manufactured by Idemitsu Kosan Co., Ltd.
Anti-aging agent: Antigen 6C manufactured by Sumitomo Chemical Co., Ltd.
Stearic acid: Stearic acid “椿” manufactured by NOF Corporation
Zinc oxide: Sulfur manufactured by Mitsui Mining & Smelting Co., Ltd .: Powder sulfur heat-resistant cross-linking agent manufactured by Karuizawa Sulfur Co., Ltd. Hexane)
Heat-resistant crosslinking agent (2): Actor 2OS4 (poly-3,6-dioxaoctane-tetrasulfide) manufactured by Kawaguchi Chemical Industry Co., Ltd.
[Formula: — (R ³ —S _x ) _n — (wherein R ³ = — (CH ₂ —CH ₂ —O) _m —CH ₂ —CH ₂ —, m = 2, x = 4, n = 200 ]]
Heat-resistant crosslinking agent (3): DURALINK HTS (1,6-hexamethylene-sodium dithiosulfate dihydrate) manufactured by Flexis
Vulcanization accelerator: Noxeller NS (Nt-butyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

(Examples and Comparative Examples)
In accordance with the formulation shown in Tables 3 and 4, materials other than sulfur, heat-resistant crosslinking agent and vulcanization accelerator were kneaded for 4 minutes at 150 ° C. using a 1.7 L Banbury mixer to obtain a kneaded product. It was. Next, sulfur, a heat-resistant cross-linking agent, and a vulcanization accelerator were added to the kneaded material obtained, and kneaded for 3 minutes at 80 ° C. using an open roll to obtain an unvulcanized rubber composition.
The obtained unvulcanized rubber composition was vulcanized at 175 ° C. for 30 minutes to obtain a vulcanized rubber composition (rubber test piece).

The following evaluation was performed about the obtained vulcanized rubber composition. The results are shown in Tables 3 and 4.

(Destructive energy)
In accordance with JIS K6251 “Vulcanized rubber and thermoplastic rubber-Determination of tensile properties”, a tensile test was carried out using a No. 3 dumbbell-shaped test piece made of a vulcanized rubber composition to determine the breaking strength (TB) The time elongation (EB) was measured and the fracture energy (TB × EB / 2) was calculated. The strength index of Comparative Example 1 was set to 100, and the breaking energy of each formulation was displayed as an index according to the following calculation formula. In addition, it shows that it is excellent in fracture energy, so that an intensity | strength index | exponent is large.
(Destruction energy) = (Destruction energy of each formulation) / (Destruction energy of Comparative Example 1) × 100

(Heat-resistant)
The rubber test piece was repeatedly compressed and deformed with a flexo testing machine (test conditions: repeated compressive deformation strain 20%, frequency 10 Hz), and the time until blowout was measured by causing the rubber to self-heat. The heat resistance of each formulation was indicated by an index with the index of Comparative Example 1 being 100. In addition, it shows that it is excellent in heat resistance, so that an index | exponent is large.

The example using WMB obtained by mixing rubber latex, carbon black dispersion, and liquid diene polymer emulsion was able to achieve both higher fracture energy and heat resistance than the comparative example. In particular, in the examples in which WMB and the heat-resistant crosslinking agents (1) to (3) were used in combination, the heat resistance was remarkably improved.

Claims (7)

Including natural rubber and wet masterbatch (1),
The wet masterbatch (1) is a rubber composition for tire cord topping obtained by mixing a styrene butadiene rubber latex, a carbon black dispersion, and a liquid styrene butadiene copolymer emulsion or a liquid butadiene polymer emulsion. Including styrene butadiene rubber and wet masterbatch (2),
The wet masterbatch (2) is a rubber composition for tire cord topping obtained by mixing a natural rubber latex, a carbon black dispersion, and a liquid isoprene polymer emulsion or a liquid butadiene polymer emulsion. A rubber composition for tire cord topping comprising the wet masterbatch (1) and (2). The wet master batches (1) and (2) contain 40 to 100 parts by mass of carbon black and 10 to 50 parts by mass of a liquid diene polymer with respect to 100 parts by mass of the rubber component in the rubber latex. The rubber composition for tire cord toppings according to any one of to 3. The rubber composition for tire cord topping according to claim 4, wherein the liquid diene polymer has a weight average molecular weight of 1,000 to 50,000. The group consisting of the compound 1 represented by the following formula (1), the compound 2 having the structure represented by the following formula (2), the compound 3 represented by the following formula (3), and a hydrate of the compound 3 The rubber composition for tire cord topping according to any one of claims 1 to 5, comprising at least one selected from the above.
R ¹ —S—S— (CH ₂ ) _p —S—S—R ² (1)
(In formula (1), p represents an integer of 2 to 12. R ¹ and R ² are the same or different and each represents a monovalent organic group containing a nitrogen atom.)
_{^{- (R 3 -S x) n}} - (2)
(In Formula (2), R ³ represents — (CH ₂ —CH ₂ —O) _m —CH ₂ —CH ₂ —, m represents an integer of 2 to 5, and x represents an integer of 2 to 6). N represents an integer of 10 to 400.)
_{MO 3 S-S- (CH 2} ) q -S-SO 3 M (3)
(In Formula (3), q represents an integer of 3 to 10. M is the same or different and represents lithium, potassium, sodium, magnesium, calcium, barium, zinc, nickel, or cobalt.) The pneumatic tire produced using the rubber composition in any one of Claims 1-6.