DE102013220522A1 - RUBBER COMPOSITION FOR STEEL CORD GUMMING, BREAKER BORDER STRIPES, BREAKER PADS, OR A STRIPE AND AIR TIRE ADJUSTABLE TO A CORD - Google Patents

Abstract

There is provided a rubber composition for a steel cord rubber lining, a breaker edge strip, a breaker pad or a strip adjacent to cords, which can improve drivability stability, fuel economy, elongation at break, adhesion to steel cords, processability and tire durability in a balanced manner even if the ratio of Zinc oxide content to sulfur content is a specific value or less, and a pneumatic tire using them is provided. The rubber composition contains a specific insoluble sulfur, has a predetermined ratio of zinc oxide content to sulfur content, and has a predetermined sulfur content, a predetermined cobalt content, a predetermined sum of (A) stearic acid and (B) cobalt stearate calculated as stearic acid and the amount of (C) a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid.

Description

TECHNICAL AREA

The present invention relates to a rubber composition for a steel cord gum, a breaker edge strip, a breaker pad or a strip adjacent to cords and a pneumatic tire using the same.

TECHNICAL BACKGROUND

Rubber cord rubber gumming compositions, a breaker edge strip, a breaker pad, cords adjacent to cords (particularly rubber compositions for steel cord gumming) are required to provide well-balanced performance enhancements such as stability in ride performance, fuel economy, elongation at break, adhesion to steel cords, and processability to reach.

As a method for improving such properties, z. For example, a method is proposed in which natural rubber having excellent elongation properties is blended with a synthetic rubber such as modified butadiene rubber and a butadiene rubber containing 1,2-syndiotactic polybutadiene crystals. In this method, however, if the dispersity of the polymers is poor, the elongation at break and adhesion to the steel cords may decrease.

Moreover, Patent Literature 1 discloses the use of phenolic resin and the like. In this case, good stability in driving behavior can be achieved; however, adhesion to the steel cords and workability still needs to be improved. As described, there remains a need to improve stability in drivability, fuel economy, elongation at break, adhesion to steel cords, processability and tire life in a balanced manner.

Meanwhile, rubber compositions for a steel cord gum, a break edge tape, a breaker pad, or a strip adjacent to cords (in particular rubber composition for a steel cord gum) generally contain a greater amount of sulfur in the form of insoluble sulfur than can be dissolved as soluble sulfur. Of the insoluble sulfur contained, 80% by mass or more are not converted into soluble sulfur after the rubber kneading process, and form particles which float in the rubber, or e.g. B. on zinc oxide particles, soot or silica absorb. However, if the amount of sulfur to be converted into soluble sulfur is large before vulcanization, sulfur flowers are formed on the surface of the steel cord gum rubber, and thereby the adhesion in processing is deteriorated, resulting in poor processability (extrusion processability) and poor adhesion Steel cords (in the fresh state and after hydrothermal aging) and may cause buckling or separation, resulting in the problem of reducing tire durability. Therefore, it is important to improve the properties in a balanced manner to suppress the formation of flowers of flowers. It should be noted that the term "flower" as used herein refers to a phenomenon in which sulfur is precipitated on the surface of the rubber composition in a flower-like manner.

As an approach to prevent the formation of such sulfur flowers, the addition of a large amount of zinc oxide has been widely used (to satisfy a ratio of zinc oxide content to sulfur content of 1.79 or more). However, in recent years, zinc oxide contained in rubber compositions for tires has become a topic of environmental pollution (in particular growth inhibition of plants), and it is therefore desired to reduce the amount of zinc oxide. Under these circumstances, it has been desired to develop a technique which improves stability in drivability, fuel economy, elongation at break, adhesion to steel cords, workability and tire life in a balanced manner, without large quantities to require zinc oxide.

QUOTE LIST

Patent Literature

• Patent Literature 1: JP 2008-156418A

SUMMARY OF THE INVENTION

TECHNICAL PROBLEM

An object of the present invention is to provide a rubber composition for a steel cord gum, a breaker edge strip, a breaker pad, or a strip adjacent to cords, which can solve the aforementioned problems and stability in handling, fuel economy, elongation at break, adhesion to steel cords Improves processability and tire life in a balanced manner, even if the ratio of zinc oxide content to sulfur content does not exceed a specific value, and to provide a pneumatic tire using them.

THE SOLUTION OF THE PROBLEM

The present inventor has intensively studied means for obtaining a rubber composition for a steel cord gum, a break edge tape, a breaker pad, or a strip adjacent to cords (particularly a rubber composition for a steel cord gum) which has good properties without the need to increase the amount of zinc oxide (in other words, even if the ratio of the zinc oxide content to the sulfur content is not more than a specific value). As a result, the present inventor has found that the total amount of (A) stearic acid, (B) cobalt stearate and (C) a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, the cobalt content and other factors have the aforementioned properties influence. In addition, the present inventor has found that the effect of added cobalt can be better achieved by adding an insoluble sulfur having a low iron content. Based on these findings, the present invention has been accomplished.

Specifically, the present invention relates to a rubber composition for a steel cord gum, a breaker edge strip, a breaker pad, or a strip adjacent to cords containing insoluble sulfur having an iron content of 30 ppm or less, a ratio of zinc oxide content to sulfur content of 1.45 Having a sulfur content of 3.0 to 6.0 parts by mass, a cobalt content of 0.05 to 0.15 mass parts, and a sum of stearic acid component content calculated from (A) stearic acid and (B) stearic acid calculated cobalt stearate , and the amount of (C) a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid of 0.5 to 1.5 parts by mass, each based on 100 parts by mass of the rubber component of the rubber composition.

Preferably, the rubber composition for a steel cord gum, a breaker edge strip, a breaker pad, or a strip adjacent to cords, based on 100 parts by mass of the rubber component, contains 30 to 70 parts by mass of carbon black having a nitrogen adsorption specific surface area of 60 to 120 m ² / g and a ratio of (specific surface area measured by nitrogen adsorption) / (dibutyl phthalate absorption) of> 0.95.

Preferably, the rubber composition for a steel cord gum, a break edge tape, a breaker pad or a strip adjacent to cords contains 2.5 parts by mass or less of the process oil relative to 100 parts by mass of the rubber component.

Preferably, the rubber composition for a steel cord gum, a break edge tape, a breaker pad, or a strip adjacent to cords, based on 100 parts by mass of the rubber component, contains 0.5 to 3 parts by mass of a quinoline antioxidant containing a primary amine content of 0.7 mass%. % or less.

Preferably, the rubber composition for a steel cord gum, a breaker edge strip, a breaker pad or a strip adjacent to cords contains silica.

The present invention also relates to a pneumatic tire containing a steel cord rubberization formed from the above-mentioned rubber composition, breaker edge strip, breaker pad or strips adjacent to cords.

ADVANTAGEOUS EFFECTS OF THE INVENTION

According to the present invention, the rubber composition for a steel cord gum, a break edge tape, a breaker pad, or a strip adjacent to cords contains insoluble sulfur having an iron content of 30 ppm or less; has a zinc oxide to sulfur ratio of 1.45 to 1.78; and has a sulfur content of 3.0 to 6.0 parts by mass, a cobalt content of 0.05 to 0.15 parts by mass and a sum of stearic acid component content calculated from (A) stearic acid and (B) stearic acid calculated as cobalt stearate, and the amount of (C) a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid of 0.5 to 1.5 parts by mass, based in each case on 100 parts by mass of the rubber component of the rubber composition. This rubber composition can smoothly improve the stability in driving performance, fuel economy, elongation at break, adhesion to steel cords, processability and tire durability even if the ratio of zinc oxide content to sulfur content does not exceed a specific value, and therefore a pneumatic tire can be provided which has improved stability in handling, fuel economy, elongation at break, adhesion to steel cords and tire life in a balanced manner.

BRIEF DESCRIPTION OF THE DRAWINGS

1 shows an exemplary fragmentary cross-sectional view of a pneumatic tire.

2 shows an exemplary fragmentary cross-sectional view of a pneumatic tire.

3 shows an exemplary fragmentary cross-sectional view of a pneumatic tire.

DESCRIPTION OF EMBODIMENTS

The rubber composition for a steel cord gum, a breaker edge strip, a breaker pad, or a strip adjacent to cords of the present invention (hereinafter referred to as the rubber composition of the present invention) contains insoluble sulfur having an iron content of 30 ppm or less; has a zinc oxide to sulfur ratio of 1.45 to 1.78; and has a sulfur content of 3.0 to 6.0 parts by mass, a cobalt content of 0.05 to 0.15 parts by mass, and a sum of stearic acid component content calculated from (A) stearic acid and (B) stearic acid calculated as cobalt stearate, and An amount of (C) a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid of 0.5 to 1.5 parts by mass, based in each case on 100 parts by mass of the rubber component of the rubber composition.

In the present invention, since the aforementioned specific components are combined and mixed in specific proportions, and in addition insoluble sulfur having a low iron content is contained, the stability in drivability (E ^* ), fuel economy, elongation at break (in the fresh state and after ( oxidative) aging in dry heat, adhesion to steel cords (fresh and after hydrothermal aging), processability (extrusion processability) and tire life are improved in a balanced manner, even if the ratio of zinc oxide content to sulfur content does not exceed a specific value.

Cobalt (Co) in a rubber composition for a steel cord gum, a break edge tape, a breaker pad, or a strip adjacent to cords (especially in a rubber composition for a steel cord rubberization) migrates during vulcanization of rubber to the plating interface of the steel cord (about 1000 nm = 1 μm the plating). As a result of migration, the plating layer on the steel cord (for example, a thin film having an average thickness of 250 nm, having a composition of copper (Cu) / zinc (Zn) = 65% / 35%) becomes a ternary alloy layer made of Cu-Zn-Co, which provides excellent adhesion. Therefore, the adhesion between the cords and the rubber is likely to be maintained even during hydrothermal aging conditions. In addition, the effect of added cobalt is better achieved when insoluble low iron sulfur is added. This is presumably because, with a high iron content in the insoluble sulfur, the ionization and migration of Co in the rubber composition and the fixation of Co in the plated layer can be prevented. It should be noted that the break edge tape, the breaker pad, and the cords adjacent to cords are not rubber components for coating steel cords; however, these components are positioned around the steel cord rubberizing component. Indes is a plurality of steel cord rubberizing components are overlapped and connected (in other words, the steel cord rubberizing components are mutually fixed so that one steel cord rubberizing component is superimposed over an edge portion of another steel cord rubberizing component). In addition, steel cords are exposed in a peripheral portion of the steel cord rubberizing component (on a side cutout). Due to this structure, the breaker edge strip, the breaker pad, and the strip adjacent to cords may be in contact with the steel cords during vulcanization. Therefore, good adhesion to steel cords is needed. In addition, since these components are thin (for example, 0.5 to 1.00 mm), sulfur flowers easily form. In the case of flowers of flowers, the adhesion to neighboring components and ultimately the durability can be severely impaired. On the other hand, sulfur flowers in the present invention can be sufficiently suppressed. Therefore, when the present invention is applied to a break margin tape, a breaker pad, or a strip adjacent to cords, stability in driving performance (E ^* ), fuel economy, elongation at break (in the fresh state, and after (oxidative) aging in dry heat), Adhesion to steel cords (in the fresh state and after hydrothermal aging), processability (extrusion processability) and tire durability are improved in a balanced manner.

Exemplary materials which can be used as the rubber component in the present invention include diene rubbers such as isoprene-based rubbers, butadiene rubber (BR), styrene-butadiene rubber (SBR) and styrene-isoprene-butadiene rubber (SIBR). The rubber materials may be used alone or in combination of two or more. In particular, isoprene-based rubbers are preferred for the reason that then stability in drivability, fuel economy, elongation at break, adhesion to steel cords, processability and tire durability can be improved in a balanced manner.

Examples of isoprene-based rubber include isoprene rubber (IR), natural rubber (NR), and epoxidized natural rubber (ENR). In particular, NR is preferred for the reason that it is excellent in tire durability, adhesion to steel cords, and the like. Examples of NRs to be used include SIR20, RSS # 3 and TSR20 and others commonly used in the tire industry. Examples of IR include, but are not limited to, those commonly used in the tire industry.

The content of isoprene-based rubber in the rubber component (100 mass%) is preferably 60 mass% or more, more preferably 80 mass% or more, and may be 100 mass%. If the content is less than 60 mass%, sufficient elongation at break, adhesion to steel cords, workability and tire durability could not be achieved.

The rubber composition according to the present invention contains insoluble sulfur having an iron content of 30 ppm or less. This allows the effect of added cobalt to be better achieved, namely to provide good adhesion (especially after hydrothermal aging). Consequently, the effects of the present invention can be sufficiently obtained.

The iron content in the insoluble sulfur is 30 ppm or less, preferably 25 ppm or less, and more preferably 20 ppm or less. If the iron content exceeds 30 ppm, the effect of added cobalt can not be sufficiently obtained, with the result that the effect of the present invention (especially elongation at break (especially after dry heat aging), adhesion to steel cords and ultimately tire durability) is insufficient can be. It should be noted that the lower limit of the iron content is not particularly limited, and it is preferable that the iron content is lower.

It should be noted that the iron content in the insoluble sulfur when oil is contained in the insoluble sulfur (in the case of an oil-treated insoluble sulfur) refers to the iron content relative to the total mass, the insoluble sulfur and oil (in other words the mass of the oil-treated insoluble sulfur).

Furthermore, the iron content in the insoluble sulfur can be determined by an inductively coupled plasma (ICP) emission analyzer.

The sulfur content based on 100 parts by mass of the rubber component is 3.0 parts by mass or more, preferably 4.0 parts by mass or more, and particularly preferably 4.5 parts by mass or more. If the content is less than 3.0 parts by mass, the stability in drivability and adhesiveness decreases. Of Further, the sulfur content is 6.0 parts by mass or less, and preferably 5.5 parts by mass or less. If the content exceeds 6.0 parts by mass, sulfur flowers tend to form, with the result that the workability (extrusion processability), adhesion to steel cords, and ultimately tire durability decrease. Furthermore, the elongation at break (especially after aging under dry heat) decreases.

The sulfur content here refers to the amount of the sulfur component contained in the insoluble sulfur. If an oil-treated insoluble sulfur is used, the sulfur content refers to the amount of the sulfur component contained in the oil-treated insoluble sulfur (namely, the amount of oil-treated insoluble sulfur excluding oil).

The rubber composition according to the present invention contains zinc oxide. This makes it possible to improve the adhesion to steel cords, stability in handling, fuel economy and elongation at break. Further, zinc oxide temporarily absorbs sulfur (during kneading) in the clay slurry and serves as a storage for sulfur. Consequently, flowers of flowers can be reduced. Examples of zinc oxide include those conventionally used in the rubber industry, and especially zinc oxide # 1 and # 2 manufactured by MITSUI MINING & SMELTING CO., LTD.

The ratio of zinc oxide content to sulfur content is 1.45 or more, preferably 1.50 or more, and particularly preferably 1.55 or more. If the ratio is less than 1.45, sulfur flowers tend to be formed, with the result that the workability (extrusion processability), adhesion to steel cords (especially after hydrothermal aging), elongation at break (especially after aging under dry heat) and ultimately tire durability decrease.

The ratio is 1.78 or less, preferably 1.70 or less. If the ratio exceeds 1.78, sulfur flowers are better suppressed, as shown in the prior art, and hence excellent properties result; however, a reduction of the zinc oxide content can not be achieved. In addition, since zinc oxide, which has a high unit price and a high density, is contained in a large amount, the cost and weight for a tire increase.

Further, if the above ratio is maintained, the breakage nucleation of zinc oxide can be prevented, and a good elongation at break and tire durability can be obtained.

The rubber composition according to the present invention contains at least one member selected from the group consisting of (A) stearic acid, (B) cobalt stearate and (C) a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid. This makes it possible to advantageously carry out the vulcanization in order to synergistically improve the balance of the properties. Thereby, the effects of the present invention can be advantageously obtained.

The total amount of (A) stearic acid and (B) stearic acid-calculated cobalt stearate (the total amount of stearic acid and the amount of stearic acid calculated from the amount of cobalt stearate) based on 100 parts by mass of the rubber component is preferably 0.5 part by mass or more and more preferably 0.7 part by mass or more. If the total amount is less than 0.5 parts by mass, stability in drivability and fuel economy decrease. The total amount is preferably 1.5 parts by mass or less, and more preferably 1.2 parts by mass or less. If the total amount exceeds 1.5 parts by mass, the elongation at break (especially after aging under dry heat), adhesion to steel cords (especially after hydrothermal aging) and finally tire durability tend to decrease.

It should be noted that the rubber component according to the present invention may contain cobalt stearate as described above; however, other cobalt salts of organic acids may be included. In this case, the adhesion of rubber to steel cords can be improved. Examples of cobalt salts of organic salts include cobalt naphthenate, cobalt abietate, cobalt neodecanoate and cobalt boron-3-neodecanoate. In particular, boron-containing cobalt salts of organic acids are preferred for the reason that the adhesion to steel cords is better.

The cobalt content (the total amount of cobalt derived from cobalt stearate and other cobalt salts of organic compounds and the like) here is, based on 100 parts by mass of the rubber component, 0.05 part by mass or more, and preferably 0.08 part by mass or more. The content is 0.15 mass parts or less, and preferably 0.12 mass parts or less. If the salary in this area falls, good adhesion to steel cords (especially after hydrothermal aging), elongation at break (especially after aging under dry heat) and tire durability can be achieved.

With respect to (C) the mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, examples of the aliphatic carboxylic acid in the zinc salt of an aliphatic carboxylic acid include aliphatic carboxylic acids derived from vegetable oils such as coconut oil, palm kernel oil, camellia oil, olive oil, Almond oil, canola oil, peanut oil, rice oil, cocoa butter, palm oil, soybean oil, cottonseed oil, sesame oil, linseed oil, castor oil and rapeseed oil, aliphatic carboxylic acids derived from animal oils such as beef tallow, and aliphatic carboxylic acids derived from petroleum or the like; were chemically synthesized. Aliphatic carboxylic acids derived from vegetable oils are preferred, and aliphatic carboxylic acids from coconut oil, palm kernel oil or palm oil are particularly preferred since excellent stability in drivability can then be achieved.

The number of carbon atoms of the aliphatic carboxylic acid is preferably 4 or more, and more preferably 6 or more. The number of carbon atoms of the aliphatic carboxylic acid is preferably 16 or less, and more preferably 12 or less. If the number of carbon atoms falls within this range, excellent stability in driveability can be achieved.

It should be noted that the aliphatic group in the aliphatic carboxylic acid may have an acyclic structure such as an alkyl group or a cyclic structure such as a cycloalkyl group.

With respect to (C) the mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid, examples of the aromatic carboxylic acid of the zinc salt include an aromatic carboxylic acid, benzoic acid, phthalic acid, mellitic acid, hemimellitic acid, trimellitic acid, diphenic acid, toluic acid and naphthoic acid. In particular, benzoic acid, phthalic acid or naphthoic acid are preferred, since then excellent stability in handling can be achieved.

The ratio of the amount of the zinc salt of an aliphatic carboxylic acid to the amount of the zinc salt of an aromatic carboxylic acid (the molar ratio (the zinc salt of an aliphatic carboxylic acid) / (the zinc salt of an aromatic carboxylic acid), hereinafter referred to as the quantitative ratio) in the mixture is preferable 1/20 or more, and more preferably 1/10 or more. If the amount ratio is less than 1/20, there is a tendency that the dispersibility and stability of the mixture deteriorate. In addition, the amount ratio is preferably 20/1 or less, and more preferably 10/1 or less. If the amount ratio exceeds 20/1, the effect of improved stability in driving behavior tends to be insufficiently maintained.

The zinc content in (C) of the mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid is preferably 3% by mass or more, and more preferably 10% by mass or more. Also, the zinc content in the mixture is preferably 30% by mass or less, and more preferably 25% by mass or less. If the zinc content falls within this range, favorable processability and stability in driveability can be achieved.

The amount of (C) the mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid based on 100 parts by mass of the rubber component is preferably 0.2 part by mass or more, and more preferably 0.5 part by mass or more. If the amount is less than 0.2 mass parts, the effect of improved stability in handling and adhesion to steel cords may not be sufficiently achieved. The amount of the mixture is preferably 1.5 parts by mass or less, and more preferably 1 part by mass or less. If the amount exceeds 1.5 parts by mass, the fuel economy tends to deteriorate.

The sum of stearic acid component content calculated from (A) stearic acid and (B) stearic acid-calculated cobalt stearate and the amount of (C) a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid based on 100 parts by mass of a rubber component is 0.5 part by mass or more, and preferably 0.7 part by mass or more. The sum is 1.5 parts by mass or less, and preferably 1.2 parts by mass or less. When the sum falls within this range, favorable stability in drivability, elongation at break (especially after aging of underneath heat), adhesion to steel cords (especially after hydrothermal aging) and tire durability can be obtained.

Preferably, the rubber composition of the present invention contains carbon black. This provides a good reinforcement, so that the balance of the properties improves synergistically. Therefore, the effects of the present invention can be advantageously obtained.

The carbon black is not particularly limited and is preferably carbon black having a nitrogen adsorption specific surface area (BET specific surface area (N ₂ SA)) of 60 to 120 m ² / g and a ratio of nitrogen adsorption-specific surface area (N ₂ SA )) / (Dibutyl phthalate absorption (DBP)) of> 0.95, as it easily adsorbs sulfur and thereby suitably suppresses sulfur flowers, so that the effects of the present invention (in particular, tire durability) can more suitably be obtained.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 60 m ² / g or more, and more preferably 70 m ² / g or more. If the N ₂ SA is less than 60 m ² / g, sufficient elongation at break and stability in handling performance could not be obtained. The N ₂ SA is preferably 120 m ² / g or less, and more preferably 100 m ² / g or less. If the N ₂ SA exceeds 120 m ² / g, a satisfactory fuel economy could not be achieved.

It should be noted that the N ₂ SA of carbon black in the description in accordance with the JIS K 6217-2: 2001 is measured.

The carbon black preferably has a ratio of (nitrogen adsorption-measured specific surface area (N ₂ SA)) / (dibutyl phthalate absorption (DBP)) of more than 0.95, more preferably 1.0 or more, and most preferably 1.1 or more. If the ratio is 0.95 or less, the heat build-up tends to increase, and hence the fuel economy tends to be poor. In addition, the processability tends to be bad. The ratio is preferably 1.6 or less, more preferably 1.5 or less, and most preferably 1.2 or less. If the ratio exceeds 1.6, the complex elastic modulus E ^* tends to become low, and hence the stability in drivability tends to decrease.

It should be noted that the DBP of carbon black is in accordance with the JIS K6217-4: 2001 is measured.

The amount of carbon black (preferably having a nitrogen adsorption specific surface area of 60 to 120 m ² / g and a ratio of (nitrogen adsorption measured specific surface area) / (dibutal phthalate absorption) of> 0.95) is, relative to 100 parts by mass Rubber component, preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and most preferably 50 parts by mass or more. Also, the amount of carbon black is preferably 70 parts by mass or less, and more preferably 65 parts by mass or less. If the amount falls within this range, the aforementioned properties can be advantageously obtained.

Preferably, the rubber composition of the present invention contains silica. This provides a good reinforcement. In addition, silica adsorbs sulfur, thereby suitably suppressing flowers of flowers, so that the balance of properties (especially stability in driving performance, fuel economy, adhesion to steel cords and processability) can be synergistically improved. As a result, the effects of the present invention can be better achieved.

Examples of silica include, but are not limited to, dry process silica (silica anhydride) and wet process silica (hydrogenated silica). Wet Process Silica is preferred for the reason that a large number of silanol groups are present.

The nitrogen adsorption specific surface area (N ₂ SA) of silica is preferably 100 m ² / g or more, and more preferably 110 m ² / g or more. If the N ₂ SA is less than 100 m ² / g, the elongation at break tends to decrease. The N ₂ SA is preferably 250 m ² / g or less, and more preferably 230 m ² / g or less. If the N ₂ SA exceeds 250 m ² / g, fuel economy and processability tend to decrease.

It should be noted that the N ₂ SA of silica is a value determined by the BET method in accordance with the ASTM D3037-93 is measured.

The silica content based on 100 parts by mass of the rubber component is preferably 3 parts by mass or more. If the content is less than 3 parts by mass or more, the adhesion to steel cords (especially after hydrothermal aging) may decrease. Also, the silica content is preferably 15 parts by mass or less, and more preferably 10 parts by mass or less. If the content exceeds 15 parts by mass, the stability in driving performance may decrease.

The carbon black content based on the total amount of silica and carbon black is preferably 50% by mass or more, more preferably 60% by mass or more, and most preferably 80% by mass or more. Also, the upper limit of the carbon black content is not particularly limited, and the carbon black content may be 100 mass%, and is preferably 95 mass% or less. When the content falls within this range, a rubber composition having excellent balanced properties can be obtained.

In the rubber composition of the present invention, the process oil content based on 100 parts by mass of the rubber component is preferably 2.5 parts by mass or less, more preferably 2.0 parts by mass or less, and still more preferably 1.5 parts by mass or less. If the content exceeds 2.5 parts by mass, the plated surface of the steel cords is coated with oil, with the result that the adhesion to steel cords tends to deteriorate. In addition, the stability in driving behavior could decrease. Furthermore, sulfur flowers could be induced. It should be noted that the lower limit for the process oil content is not particularly limited.

Here, the process oil refers to a mineral oil which has been added separately from the rubber component and the like in order to improve the processability of the rubber (for example, the plasticizer effect, the component dispersion effect, the lubricating effect), and includes none which have been previously added to other components such as HMMPME (described later), insoluble sulfur and oil-drawn rubber. Examples of the process oil include paraffinic oils, naphthenic oils and aromatic ones, but do not include coumarone-indene resin (described later), C5 petroleum resin, resorcinol resin, phenolic resin, alkylphenol resin and C9 petroleum resin.

In addition, the total oil content in the rubber composition of the present invention (the total amount of process oil, oils previously contained in other components, and the like) is preferably 4.0 parts by mass or less, more preferably 3.5 parts by mass or less, and most preferably 3 , 0 parts by mass or less. If the total amount exceeds 4.0 parts by mass, the plated surface of the steel cords is coated with oil, with the result that the adhesion of the steel cords tends to decrease. The lower limit of the total amount is not particularly limited, and the amount of the oil other than the process oil previously supplied as a component of other components is preferably about 1.0 to 1.5 parts by mass.

Preferably, the rubber composition of the present invention contains a C5 petroleum resin. This can improve the tackiness, processability and elongation at break. As examples of the C5 petroleum resin, aliphatic petroleum resins mainly composed of olefins and diolefins of the C5 fraction obtained by cracking naphtha are mentioned.

The softening point for the C5 petroleum resin is preferably 50 ° C or more, and more preferably 80 ° C or more. Also, the softening point is preferably 150 ° C or less, and more preferably 130 ° C or less. When the softening point falls within this range, the aforementioned properties can be advantageously obtained.

The C5 petroleum resin content based on 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, and more preferably 1.5 parts by mass or more. Also, the content is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less. When the content falls within this range, tackiness, processability and elongation at break can be advantageously obtained.

Preferably, the rubber composition of the present invention contains a coumarone-indene resin. This contributes to good adhesion to steel cords, elongation at break and tire life, thereby synergistically improving the balance of properties. In particular, coumarone-indene resins (liquid coumarone-indene resins) having a softening point satisfying the following range contribute to a good fuel economy. This is presumably due to the fact that the dispersion of sulfur and vulcanization accelerator is due to the appropriate polarity and mobility of the coumarone Inden resin is accelerated, with the result that the formation of uniform sulfur crosslinks is accelerated. In addition, the coumarone-indene resin does not cause sulfur flowers and also serves as a surface tension reducing agent, thereby improving the compatibility between the plated layer of the steel cords and the rubber rubbers.

The softening point of the coumarone-indene resin is preferably -20 ° C or higher, and more preferably 0 ° C or higher. In addition, the softening point is preferably 60 ° C or lower, more preferably 35 ° C or lower, and most preferably 15 ° C or lower. When the softening point falls within this range, the aforementioned properties can be favorably obtained.

The coumarone-indene resin content based on 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, and more preferably 1.5 parts by mass or more. Also, the content is preferably 6 parts by mass or less, and more preferably 3.5 parts by mass or less. If the content falls within this range, then the effects of the present invention can be advantageously obtained.

Preferably, the rubber composition of the present invention contains an antioxidant. This makes it possible to suppress the decomposition of the polymer due to oxygen or ozone on the rubber rubber surface. In addition, the reaction of insoluble sulfur in soluble sulfur can be inhibited to suppress sulfur flowers.

The antioxidant is not particularly limited, and is preferably a quinoline antioxidant, for the reason that the effects of the present invention can be better achieved. In addition, as a result of its investigations, the present inventor has found that a primary amine contained in a quinoline antioxidant causes flowers of flowers and thereby reduces the adhesion to steel cords, processability and tire durability. Therefore, the primary amine content in the quinoline antioxidant (100 mass%) is preferably 0.7 mass% or less, and more preferably 0.65 mass% or less. The lower limit of the content is not particularly limited, and is preferably 0.2% by mass or more, and more preferably 0.4% by mass or more.

The primary amine content in an antioxidant can be determined by the following method.

Aniline solutions of different concentrations are added to a p-dimethylaminobenzaldehyde (DAB) solution (10 g / l). After 30 minutes or later, absorbances of the solution mixtures are measured at 440 nm. It should be noted that corrections are made in the measurements based on the absorbance of a blank. Thereafter, the absorbance values (corrected extinctions) obtained from the measurements are plotted against the aniline concentrations in a graph to obtain a calibration curve.

Subsequently, to an antioxidant (0.20 g) are added chloroform (50 ml) and 7% hydrochloric acid (50 ml). The mixture is shaken for 10 minutes and allowed to stand alone for one hour. Subsequently, the upper liquid phase (7% hydrochloric acid) is separated, and a DAB solution is added to the obtained liquid. After 30 minutes or later, the absorbance of the mixed solutions is measured at 440 nm. It should be noted that corrections were made in the measurements based on the absorbance of a blank. Thereafter, the content of primary amine is calculated from the corrected absorbance based on the calibration curve.

The antioxidant content (preferably quinoline antioxidant content) based on 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, and more preferably 1.0 part by mass or more. Also, the content is preferably 3.0 parts by mass or less, and more preferably 2.5 parts by mass or less. When the content is in this range, the effects of the present invention can be advantageously obtained.

It is preferable that the rubber composition of the present invention contains at least one member selected from the group consisting of resorcinol resin, phenolic resin and alkylphenol resin. These contribute to a high degree of stability in handling, breaking elongation and adhesion to steel cords.

For example, resorcinol-formaldehyde condensates may be mentioned as resorcinol resin. Specific examples thereof include Sumitomo Chemical Co., Ltd. prepared resorcinol. Moreover, that is Resorcinol resin preferably a modified resorcinol resin. Resorcinol resin which has partially alkylated repeat units is mentioned, for example, as the modified resorcinol resin. Specific examples thereof include Penacolit Resin B-18-S and B-20 manufactured by INDSPEC Chemical Corporation; SUMIKANOL 620 manufactured by Taoka Chemical Co., Ltd .; R-6, manufactured by Uniroyal; SRF1501, manufactured by Schenectady Chemicals, Inc .; and Arofene 7209, manufactured by Ashland Inc.

Examples of the phenolic resin include those obtained by the reaction of a phenol with an aldehyde such as formaldehyde, acetaldehyde and furfural in the presence of an acid or lawn catalyst. Especially preferred are those obtained from the reaction in the presence of an acid catalyst (eg novolak type phenolic resins).

The softening point for the phenol resin is preferably 70 ° C or higher, and more preferably 85 ° C or higher. Also, the softening point is preferably 140 ° C or lower, and more preferably 110 ° C or lower.

The weight-average molecular weight (Mw) of the phenol resin is preferably 1,000 or more, and more preferably 4,000 or more. The Mw is preferably 10,000 or less, and more preferably 7,000 or less. If the Mw is in this range, the effects of the present invention can be better obtained.

The phenolic resin may be an unmodified phenolic resin and may more preferably be a modified phenolic resin modified with cashew oil, tall oil, linseed oil or other animal or vegetable oils or with a compound such as unsaturated fatty acid, rosin, alkylbenzene resin, aniline and melamine.

The modified phenolic resin may suitably be a cashew oil-modified phenolic resin. In particular, modified phenolic resins represented by the following formula (1) are preferably used because the balance of properties is improved synergistically.

In this formula, p is an integer of 1 to 9, and preferably an integer of 5 to 6, for the reason that the reactivity is so good that the dispersibility can be improved.

The alkylphenol resin may suitably be alkylphenol resin formed from formaldehyde and at least one compound selected from the group consisting of 2-alkylphenol, 3-alkylphenol and 4-alkylphenol. In this case, excellent fuel economy and tire durability can be obtained. The alkylphenol resin is particularly preferably a novolak-type alkylphenol resin, for the reason that the balance of the property can be synergistically improved and therefore the effects of the present invention can be advantageously achieved.

Examples of the alkylphenol (monomer component) include 2-alkylphenols, 3-alkylphenols and 4-alkylphenols. It is preferable to use at least two compounds selected from the group consisting of 2-alkylphenol, 3-alkylphenol and 4-alkylphenol, and more preferably to use the three compounds 2-alkylphenol, 3-alkylphenol and 4-alkylphenol the reason that then the effects of the present invention can be suitably achieved.

The number of carbon atoms of the alkyl group of the alkylphenol is not particularly limited and is preferably 1 to 10, more preferably 1 to 5, even more preferably 1 to 3, and most preferably 1, for the reason that then the effects of the present invention can be suitably obtained. The alkylphenol may be a mixture of alkyl groups differing in the number of carbon atoms.

In particular, it is most preferable to use o-cresol, m-cresol and p-cresol as the 2-alkylphenol, 3-alkylphenol and 4-alkylphenol, in other words, to use a cresol resin as the alkylphenol resin. In this case, the balance of properties can be synergistically improved, and thus the effects of the present invention can be suitably achieved.

The alkylphenol resin can be obtained, for example, by reacting formaldehyde with at least one component selected from the group consisting of 2-alkylphenol, 3-alkylphenol and 4-alkylphenol in the presence of an acid catalyst.

The acid catalyst is not particularly limited. Examples include boron trifluoride-ether complexes, boron trifluoride-phenol complexes, boron trifluoride-water complexes, boron trifluoride-alcohol complexes and boron trifluoride-amine complexes, and mixtures of these. The method of reacting formaldehyde with an alkylphenol in the presence of an acid catalyst is not particularly limited, and a known method can be used.

The softening point for the alkylphenol resin is preferably 90 ° C or more, more preferably 120 ° C or more, and most preferably 125 ° C or more. Also, the softening point is preferably 140 ° C or less, and more preferably 135 ° C or less. If the softening point is in this range, stability in drivability, fuel economy, tire durability, ride quality and adhesion to steel cords can be advantageously obtained.

The weight-average molecular weight (Mw) of the alkylphenol resin is preferably 1,000 or more, and more preferably 1,500 or more. The Mw is preferably 3000 or less, more preferably 2500 or less, and most preferably 1900 or less. When the Mw falls within this range, advantageous stability in drivability, fuel economy, tire durability, ride quality and adhesion to steel cords can be obtained.

The total amount of free 2-alkylphenol, 3-alkylphenol and 4-alkylphenol (total amount of free alkylphenol) in the alkylphenol resin is preferably 3 mass% or less, more preferably 2 mass% or less and most preferably 1 mass% or fewer. If the total amount exceeds 3 mass%, the hardness may decrease.

Here, in order to adjust the total content of free alkylphenol in the alkylphenol resin to a specific value or less, any method can be adopted. For example, after the alkylphenol resin is dissolved in a solvent, a purification step such as recrystallization, column chromatography, and distillation may be conducted until the total content of free alkylphenol in the alkylphenol resin falls to or below a specific value. The distillation method may suitably be a method which, for example, in the JP 2011-74205 A (which is incorporated by reference in its entirety).

It should be noted that the weight average molecular weight (Mw) of a phenolic resin or an alkylphenol resin can be measured by gel permeation chromatography (GPC) relative to polystyrene standards. In addition, the total content of free alkylphenol is a value measured by gel permeation chromatography (GPC).

• (1) Apparatur: HLC-8020, hergestellt von Tosoh Corporation
• (2) Trennsäulen: GMH-XL (2 Säulen in Serie), hergestellt von Tosoh Corporation
• (3) Messtemperatur: 40°C
• (4) Träger: Tetrahydrofuran
• (5) Flussrate: 0,6 ml/Minute
• (6) Injektionsvolumen: 5 μl
• (7) Detektor: Differentialrefraktometer
• (8) Molekulargewichtsstandards: Polystyrolstandards

In the specification, the GPC is carried out on a phenol resin or an alkylphenol resin under the following conditions (1) to (8).

• (1) Apparatus: HLC-8020 manufactured by Tosoh Corporation
• (2) Separation columns: GMH-XL (2 columns in series) manufactured by Tosoh Corporation
• (3) Measurement temperature: 40 ° C
• (4) Carrier: tetrahydrofuran
• (5) Flow rate: 0.6 ml / minute
• (6) Injection volume: 5 μl
• (7) Detector: differential refractometer
• (8) Molecular weight standards: polystyrene standards

It should be noted that in the specification, the softening point of a resin (C5 petroleum resin, coumarone-indene resin, phenol resin, alkylphenol resin) refers to a temperature at which, during the measurement of the softening point in FIG JIS K6220-1: 2001 with a ring and ball softening point apparatus a ball falls.

The total amount of the resorcinol resin, the phenol resin and the alkylphenol resin based on 100 parts by mass of the rubber component is preferably 0.5 part by mass or more, and more preferably 1.5 parts by mass or more. If the total amount is less than 0.5 part by mass, a satisfactory stability in driving performance and a satisfactory adhesion to steel cords can not be obtained. The total amount is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less. If the total amount exceeds 10 parts by mass, the elongation at break may decrease, with the result that a satisfactory tire durability can not be obtained.

Preferably, the rubber composition of the present invention contains a partial condensate of hexamethoxymethylol melamine (HMMM) and / or a partial condensate of hexamethylol melamine pentamethyl ether (HMMPME). This can reinforce the cord / rubber adhesive layer so that the balance of properties can be synergistically improved. In particular, it is preferred to include a partial condensate of HMMPME, because then excellent adhesion to steel cords can be obtained. Here, the use of a resorcinol resin, a phenolic resin or an alkylphenol resin in admixture with a partial condensate of HMMPME can provide better stability in drivability, fuel economy, elongation at break, adhesion to steel cords, processability and tire durability.

The total amount of the partial condensate HMMM and the partial condensate HMMPME based on 100 parts by mass of the rubber component is 0.5 part by mass or more, and preferably 1 part by mass or more. If the total amount is less than 0.5 part by mass, the amount of methylene supply may be small, and therefore the stability in drivability may decrease. Also, the total amount is 5 parts by mass or less, and preferably 2 parts by mass or less. If the total amount exceeds 5 parts by mass, the tire durability tends to decrease.

Preferably, the rubber composition in the present invention contains an organic thiosulfate compound. This contributes to good adhesion to steel cords (especially after hydrothermal aging), so that the balance of properties can be synergistically improved. The organic thiosulfate compound is preferred, but not limited to, a compound represented by the following formula (2) and / or a hydrate thereof: MO ₃ SS- (CH ₂ ) _q -S-SO ₃ M (2), where q is an integer from 3 to 10 and the Ms, which may be the same or different, are each lithium, potassium, sodium, magnesium, calcium, barium, zinc, nickel or cobalt.

In the formula (2), q is an integer of 3 to 10, and is preferably an integer of 3 to 6. If q is less than 3, then the elongation at break could not be sufficiently improved. If q exceeds 10, the effect of improving the elongation at break and the like tends to be small as compared to the increase in molecular weight.

In the formula (2), M is preferably lithium, potassium, sodium, magnesium, calcium, barium, zinc, nickel or cobalt, and particularly preferably potassium or sodium. In addition, the hydrate of the compound represented by the formula (2) may be, for example, a sodium salt monohydrate or a sodium salt dihydrate.

The compound represented by formula (2) or a hydrate thereof is preferably a derivative derived from sodium thiosulfate, e.g. For example, sodium 1,6-hexamethylenedithiosulfate dihydrate.

The content of the organic thiosulfate compound is, based on 100 parts by mass of the rubber component, preferably 0.1 part by mass or more and particularly preferably 0.25 part by mass or more. If the content is less than 0.1 part by mass, the effect of improved adhesion to steel cords (especially after hydrothermal aging) may not be sufficiently obtained. The content is preferably 2 parts by mass or less, and more preferably 1 part by mass or less. If the content exceeds 2 parts by mass, the effect of improved adhesion to steel cords and the like tends to be in proportion to the amount added.

Preferably, the rubber composition of the present invention contains a vulcanization accelerator. Examples of the vulcanization accelerator include guanidine, aldehyde amine, aldehyde ammonia, thiazole, sulfenamide, thiourea, thiriram, dithiocarbamate and xanthate compounds. In particular, vulcanization accelerators containing a group represented by the following formula (benzothiazolylsulfide group) are preferred for the reason that the effects of the present invention can be suitably obtained.

Examples of the vulcanization accelerators having a benzothiazolylsulfide group include sulfenamide vulcanization accelerators such as N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N, N-dicyclohexyl-2-benzothiazolylsulfenamide (DCBS), N, N-diisopropyl-2-benzothiazolyl sulfenamide, N, N -di (2-ethylhexyl) -2-benzothiazolyl sulfenamide (BENZ), N, N -di (2-methylhexyl) -2-benzothiazolyl sulfenamide (BMHZ), and N-ethyl-Nt- butylbenzothiazole-2-sulfenamide (ETZ) and N-tert-butyl-2-benzothiazolyl sulfenimide (TBSI) and di-2-benzothiazolyl disulfide (DM). Especially preferred are compounds which represent the following formula (3). In these cases, the stability in drivability, fuel economy, elongation at break (especially after dry heat aging) and tire durability can be advantageously obtained, and therefore the balance of properties can be synergistically improved.

In the formula, R ^{1 represents} an alkyl group having 2 to 16 carbon atoms, and R ^{2 represents} an alkyl group having 3 to 16 carbon atoms, a benzothiazolyl sulfide group or a cycloalkyl group.

The alkyl group denoted by R ¹ preferably has a branched structure for the reason that the effects of the present invention can be advantageously obtained. Preferably, the alkyl group having a branched structure is a (a linear alkyl group having a branched structure) obtained by substitution of at least one hydrogen atom contained in the carbon chain (CH ₂ ) _{k of} a linear alkyl group represented by - (CH ₂ ) _k -CH ₃ (wherein k is an integer ranging from 1 to 14) is represented by an alkyl group.

The number of carbon atoms in the alkyl group represented by R ¹ is preferably 3 to 16, more preferably 4 to 16, and most preferably 6 to 12. If the number of carbon atoms is 1, the vulcanization accelerator tends to be adsorbed. If the number of carbon atoms is 17 or more, the hardness tends to decrease.

Examples of preferred alkyl groups represented by R ¹ include an ethyl group, a t-butyl group, a 2-ethylhexyl group, a 2-methylhexyl group, a 3-ethylhexyl group, a 3-methylhexyl group, a 2-ethylpropyl group, a 2-ethylbutyl group , a 2-ethylpentyl group, a 2-ethylheptyl group and a 2-ethyloctyl group.

Preferably, the alkyl group represented by R ^{2 has} a branched structure for the reason that the effects of the present invention can then be advantageously obtained. The alkyl group having a branched structure is preferably the same as that of the above-mentioned R ¹ .

The number of carbon atoms in the alkyl group represented by R ² is preferably 4 to 16, and more preferably 6 to 12. If the number of carbon atoms is 2 or less, the vulcanization accelerator tends to be adsorbed. If the number of carbon atoms is 17 or more, the hardness tends to decrease.

Examples of preferred alkyl groups represented by R ² include a t-butyl group, a 2-ethylhexyl group, a 2-methylhexyl group, a 3-ethylhexyl group, a 3-methylhexyl group, a 2- Ethylpropyl group, a 2-ethylbutyl group, a 2-ethylpentyl group, a 2-ethylheptyl group and a 2-ethyloctyl group.

The benzothiazole sulfide group represented by R ^{2 is} represented by the following formula.

The number of carbon atoms of the cycloalkyl group represented by R ² is preferably 3 to 16. Examples of preferable cycloalkyl groups represented by R ² include a cyclohexyl group.

Here, R ^{2 is} preferably a benzothiazolyl sulfide group when R ^{1 is} a t-butyl group, for the reason that stability in drivability, fuel economy, tire durability, ride quality, and adhesion to steel cords can then be advantageously obtained.

Examples of the compound represented by the formula (3) include BENZ (N, N-di (2-ethylhexyl) -2-benzothiazolyl sulfenamide) manufactured by Kawaguchi Chemical Industry Co., LTD., BMHZ (N, N-di (2 -methylhexyl) -2-benzothiazolylsulfenamide), manufactured by Kawaguchi Chemical Industry Co., LTD., SantoCure TBSI (N-tert-butyl-2-benzothiazolylsulfenimide) manufactured by Flexsys, and ETZ (N-ethyl-Nt-butylbenzothiazole-2 -sulfenamide) manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.

The content of the vulcanization accelerator based on 100 parts by mass of the rubber component is preferably 0.3 part by mass or more, and more preferably 0.5 part by mass or more. If the content is less than 0.3 part by mass, the effect of improving driveability can not be sufficiently obtained. The content is preferably 4 parts by mass or less, and more preferably 3 parts by mass or less. If the content exceeds 4 parts by mass, the adhesion to steel cords tends to decrease (especially after hydrothermal aging).

The ratio of sulfur content to vulcanization accelerator content is preferably 2.5 to 15.0, more preferably 3.5 to 12.0 and most preferably 4.0 to 10.0. If the ratio is less than 2.5, adhesion to steel cords tends to decrease (especially after hydrothermal aging). Conversely, if the ratio exceeds 15.0, the elongation at break after (oxidative) aging under dry heat tends to decrease.

The sulfur content used herein refers to the amount of sulfur component contained in the insoluble sulfur. If an oil-treated insoluble sulfur is used, the sulfur content refers to the amount of sulfur content contained in the oil-treated insoluble sulfur (namely, the amount of the oil-treated insoluble sulfur excluding oil).

The rubber composition of the present invention may suitably contain, in addition to the aforementioned components, the compounding components generally used for the preparation of rubber compositions, e.g. For example, 1,3-bis (citraconimidomethyl) benzene.

As the method for producing the rubber composition of the present invention, known methods can be used. For example, the rubber composition may be prepared by kneading (kneading) the aforementioned components using a rubber kneader such as an open roll mill and a Banbury mixer, and then subjecting this mixture to vulcanization.

Preferably, the kneading step includes:

• (I) Basic kneading step 1: kneading the chemicals except insoluble sulfur, vulcanization accelerator, organic thiosulfate compound and cobalt salt of organic acid using a rubber kneader (kneading time: 3 to 7 minutes, leaving temperature: 140 to 160 ° C);
• (II) Basic kneading step 2: adding the cobalt salt of an organic acid to the kneading mass obtained in the base kneading step 1 and kneading the mixture using the rubber kneader (kneading time: 1 to 5 minutes, leaving temperature: 125 to 145 ° C); and
• (III) Final kneading step: adding the insoluble sulfur and the vulcanization accelerator (and optionally the organic thiosulfate component) to the kneading mass obtained in the base kneading step 2 and kneading the mixture using the rubber kneader (kneading time: 1 to 5 minutes, leaving temperature: 95 to 105 ° C), since then the effects of the present invention can be better obtained.

The rubber composition of the present invention can be used as a rubber component for coating steel cords (rubber composition for rubberization), and particularly suitably as a rubber composition for breaker rubberization.

The rubber composition of the present invention may be additionally used as a rubber composition for a break edge tape, a rubber composition for a breaker pad, or a rubber composition for a tape adjacent to cords. The 1 to 3 show exemplary partial cross-sectional views of a pneumatic tire of the present invention. 1 shows a case in which near the edge of the breaker 12 a breaker edge strip 16 between an inner layer 44 and an outer layer 46 the breaker 12 is arranged and a breaker pad 32 is between a carcass fabric 28 and a strip 31 on the breaker pad (or strip under a first breaker) and adjacent to a stripe layer (BP stripe layer) 30 provided, which is inserted between the breaker and the tissue. The 2 shows a case in which near the edge of a breaker 12 a breaker edge strip 16A is arranged to form a marginal section of an outer layer 46 the breaker 12 to cover; a breaker edge strip 16B is provided to a marginal section of an inner layer 44 the breaker 12 to cover; and a breaker pad 32 is between a carcass layer 28 , the inner layer 44 the breaker 12 and the breaker edge strip 16B and adjacent to a stripe layer (BP stripe layer) 30 , which is sandwiched between the breaker and the layer, arranged. In addition, shows 3 a case in which near the edge of the breaker 12 a breaker edge strip 16A between an outer layer 46 the breaker 12 and a band 15 is arranged; a breaker edge strip 16B is between an inner layer 44 and an outer layer 46 the breaker 12 arranged; and a breaker pad 32 is between a carcass ply 28 and a strip 31 on the breaker pad (or strip under a first breaker) and adjacent to a stripe layer (BP stripe layer) 30 , which is sandwiched between the breaker and the fabric, arranged.

In addition, the show 1 to 3 Cases in which as a strip adjacent to cords, the stripe layer (BP stripe layer) 30 sandwiched between the breaker and the carcass ply, between the inner layer 44 the breaker 12 and the carcass layer 28 is arranged. In addition, the show 1 and 3 Cases in which, as another strip of adjacent stripes, the strip 31 on the breaker pad (or strip under a first breaker) between the inner layer 44 the breaker 12 and the breaker pad 32 is provided. The rubber composition for a steel cord gum, a break edge tape, a breaker pad or a cords-adjacent strip of the present invention is preferably used as a rubber composition for a steel cord rubberization.

The pneumatic tire of the present invention can be produced by a usual method using the aforementioned rubber composition.

More specifically, a rubber composition containing the aforementioned components is formed into a sheet before vulcanization. The plate is pressed and rolled on steel cords from above and below to form a fabric with cords (a steel cord gum component (total thickness: about 1.00 to 2.00 mm; the kind of cords, the end number, and the amount of rubber vary depending on the type of cords) Applications)), a break margin strip, a breaker pad, or a strip adjacent to cords. Each of these components is combined with other tire components and molded in a tire-making machine into an unvulcanized tire by a conventional method. The unvulcanized tire is pressed under heat into a vulcanizer to obtain a tire.

EXAMPLES

The present invention will be described in detail with reference to Examples. However, the present invention is not limited to these.

Various chemicals used in Examples and Comparative Examples are collectively described below.
<NR>: TSR20
<IR>: IR2200, manufactured by JSR Corporation
<Silica>: ULTRASIL VN3 (N ₂ SA (BET): 175 m ² / g), manufactured by Degussa
<Carbon black 1>: DIABLACK N219 (N ₂ SA (BET): 110 m ² / g, DBP: 76 ml / 100 g, N ₂ SA (BET) / DBP = 1.45) manufactured by Mitsubishi Chemical Corporation
<Carbon black>: DIABLACK N326 (N ₂ SA (BET): 84 m ² / g, DBP: 74 ml / 100 g, N ₂ SA (BET) / DBP = 1.14) manufactured by Mitsubishi Chemical Corporation
<Carbon black 3>: DIABLACK N220 (N ₂ SA (BET): 115 m ² / g, DBP: 114 ml / 100 g, N ₂ SA (BET) / DBP = 1.01) manufactured by Mitsubishi Chemical Corporation
<Carbon black 4>: ShoBlack N351H (N ₂ SA (BET): 64 m ² / g, DBP: 136 ml / 100 g, N ₂ SA (BET) / DBP = 0.47) manufactured by Cabot Japan
<Carbon black>: DIABLACK N330 (N ₂ SA (BET): 78 m ² / g, DBP: 102 ml / 100 g, N ₂ SA (BET) / DBP = 0.76) manufactured by Mitsubishi Chemical Corporation
<Carbon black 6>: DIABLACK N660 (N ₂ SA (BET): 28 m ² / g, DBP: 82 ml / 100 g, N ₂ SA (BET) / DBP = 0.34) manufactured by Mitsubishi Chemical Corporation
<Antioxidant 1>: Purified product of NOCRAC 224 (experimental product (quinoline antioxidant), primary amine content: 0.6 mass%) manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.
<Antioxidant 2>: NOCRAC 224 (2,2,4-trimethyl-1,2-dihydroquinoline polymer (quinoline antioxidant), primary amine content: 26.4 mass%), manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.
<C5 petroleum resin>: Marukarez T-100AS (C5 petroleum resin: aliphatic petroleum resin mainly composed of olefins and diolefins of C5 fraction obtained by cracking naphtha) (softening point: 100 ° C), manufactured by Maruzen Petrochemical CO., LTD.
<Mineral oil>: Process P-200 (process oil) manufactured by Japan Energy Corporation
<Liquid coumarone-indene resin>: NOVARES C10 (coumarone-indene resin, softening point: 5 to 15 ° C) manufactured by Rutgers Chemicals
<Zinc Oxide>: Zinc Oxide # 2 manufactured by MITSUI MINING & SMELTING CO., LTD.
<Stearic acid>: Tsubaki manufactured by NOF Corporation
<Activating agent (mixture of zinc salt of aliphatic carboxylic acid and zinc salt of aromatic carboxylic acid): Activator 73A ((i) Aliphatic carboxylic acid zinc salt: zinc salt of a coconut oil-derived fatty acid (carbon number: 8 to 12) and (ii) an aromatic carboxylic acid zinc salt: Zinc benzoate, molar ratio: 1/1, zinc content: 17 mass%) produced by STRUKTOL
<Cobalt Stearate>: Cost-F (cobalt content: 9.5 mass%, stearic acid content: 90.5 mass%) manufactured by DIC Corporation
<Cobalt boron neodecanoate>: Dicnate NBC-II (cobalt boro-3-neodecanoate, cobalt content: 22.0 mass%) manufactured by DIC Corporation
<HTS>: DURALINK HTS (sodium 1,6-hexamethylene dithiosulfate dihydrate (organic thiosulfate compound)) manufactured by Flexsys
<Insoluble Sulfur A>: Crystex HSOT 20 modified product (experimental product, insoluble sulfur containing sulfur (80 mass%) and oil (20 mass%), iron content: 15 ppm) manufactured by Flexsys
<Insoluble sulfur B>: IS-HS-7520 (insoluble sulfur containing sulfur (80 mass%) and oil (20 mass%), iron content: 50 ppm) manufactured by Shanghai Jinghai Chemical (China)
<Insoluble sulfur C>: IS-HS-7520 (other lot of insoluble sulfur B, insoluble sulfur containing sulfur (80 mass%) and oil (20 mass%), iron content: 200ppm) manufactured by Shanghai Jinghai Chemical (China)
<DCBS>: NOCCELER DZ (vulcanization accelerator, N, N'-dicyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.
<TBSI>: SantoCure TBSI (vulcanization accelerator, N-tert-butyl-2-benzothiazolyl sulfenimide) manufactured by Flexsys
<HMMPME>: Sumikanol 507A (modified etherified methylolmelamine resin (partial condensate of hexamethylolmelamine pentamethyl ether (HMMPME)) content of active ingredients: 65 mass%, silica: 32 mass%, paraffin oil: 3 mass%) manufactured by Sumitomo Chemical Co ., Ltd.
<High purity cresol resin>: PR-X11061 (o-cresol, m-cresol and p-cresol were used as the alkylphenol component (monomer component); total content of free alkylphenol content: 0.6 mass%; novolak type alkylphenol resin content: 99.4 masses Softening point: 128 ° C; Mw: 1800) manufactured by Sumitomo Bakelite Co., Ltd.
<Modified Phenolic Resin>: PR12686 (cashew oil modified phenolic resin, free phenol content: 0.2 mass%, novolak phenolic resin content: 99.8 mass%, softening point: 94 ° C, Mw: 5330) manufactured by Sumitomo Bakelite Co., Ltd.
<Modified resorcinol resin>: SUMIKANOL 620 (modified resorcinol resin (modified resorcinol / formaldehyde condensate)) manufactured by Taoka Chemical Co., Ltd.

In each of the formulations shown in Tables 1 and 2, the chemicals other than insoluble sulfur, vulcanization accelerator (s), HTS, cobalt stearate and cobalt boron neodecanoate were kneaded using a 1.7 L Banbury mixer (kneading time: 5 minutes, leaving temperature : 150 ° C) to obtain a plasticine. Then, cobalt stearate and cobalt boron neodecanoate were added to the obtained kneading material and kneaded using a 1.7 L Banbury mixer (kneading time: 3 minutes, leaving temperature: 135 ° C) to obtain a kneading material. Then, to the obtained putty, the insoluble sulfur, the vulcanization accelerator and HTS were added and kneaded using a roller (kneading time: 3 minutes, leaving temperature: 105 ° C) to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was subjected to press vulcanization at 170 ° C for 12 minutes to obtain a vulcanized rubber composition.

Steel cords were separately coated with the obtained unvulcanized rubber composition and then cut at a predetermined angle and subjected to compounding. Subsequently, the obtained product was compounded with a break edge tape, a breaker pad and a strip between a breaker and a fabric layer formed from the obtained unvulcanized rubber composition and other tire components to form an unvulcanized tire, and then was heated at 170 ° C Subjected to press vulcanization for 12 minutes to prepare a test tire (tire size: 195 / 65R15).

Steel cords were separately coated with the obtained unvulcanized rubber composition and subjected to press vulcanization at 150 ° C for 30 minutes to obtain a peel test specimen.

In addition, the obtained vulcanized rubber compositions and peel test specimens were hydrothermally aged at a temperature of 80 ° C and a relative humidity of 95% for 150 hours to obtain the corresponding hydrothermally aged products.

The obtained vulcanized rubber compositions were separately aged under dry heat in a drying oven at a temperature of 80 ° C for 96 hours (decomposed by air oxidation) to obtain a dry-aged product.

Further, the non-rim mounted test tire was hydrothermally aged at a temperature of 80 ° C and a relative humidity of 95% for 4 weeks to obtain a hydrothermally aged tire.

The unvulcanized rubber compositions, cured rubber compositions (aged fresh, hydrothermally aged, aged under dry heat), peel test specimens (fresh, hydrothermally aged), and test tires (hydrothermally aged) were evaluated as follows. The results are shown in Tables 1 and 2.

(Viscoelasticity Test)

The complex elastic modulus E ^* (MPa) and loss tangent (tanδ) of the above vulcanized rubber compositions (as fresh) were measured at a temperature of 70 ° C, a frequency of 10 Hz, an initial elongation of 10% and a dynamic elongation of 2 % was measured using a viscoelasticity spectrometer VES manufactured by Iwamoto Seisakusho Co., Ltd. The higher the E ^* value, the higher the stiffness and, in turn, the better the stability in handling. The smaller the tanδ value, the lower the heat buildup and, in turn, the better the fuel economy.

(Zugdehnungsversuch)

From the vulcanized rubber composition described above (aged fresh, aged under dry heat), # 3 dumbbells were subjected to a tensile elongation test at room temperature according to the invention JIS K 6251 , "Rubber, vulcanized or thermoplastic - Determination of tensile stress properties", exposed to measure the elongation at break EB (%). The larger the EB value, the better the elongation at break.

(Hafffigkeitigkeitsprüfung (evaluation of rubber coverage after peeling): adhesion to steel cords)

An adhesion test was conducted using test specimens (peel test specimens (fresh, hydrothermally aged) to measure the rubber composition after peeling (the proportion of the peeled surface covered with rubber after the rubber was separated from the steel cords), and the results were rated on a scale of 1 to 5, with a value of 5 meaning that the entire surface is covered, and a value of 0 means the surface is not covered at all, the higher the value, the better the adhesion to steel cords.

(Workability (extrusion processability))

• (1) Klebrigkeit der Plattenoberfläche (bewertet während des Zeitraums zwischen unmittelbar nach dem Formen und einem Tag Ruhen bei Raumtemperatur)
• (2) Grad an weißem Ausblühung und Niederschlägen, wie Schwefel und Zinkstearat
• (3) Anvulkanisation der Zusammensetzung, wie vernetzte Flecken/Krumen
• (4) Ebenheit
• (5) Randzustand

Each of the unvulcanized rubber compositions was extruded and then formed into a breaker gumming cord fabric. The obtained tissue was evaluated by eye and by hand for the following five aspects. Here, the sensory evaluation was performed on a scale of 1 to 5. The higher the numerical value, the better the extrusion processability.

• (1) stickiness of the plate surface (evaluated during the period between immediately after molding and one day rest at room temperature)
• (2) Degree of white efflorescence and precipitation, such as sulfur and zinc stearate
• (3) vulcanization of the composition, such as crosslinked stains / crumbs
• (4) flatness
• (5) edge condition

It should be noted that with respect to the edge condition, the straightest and smoothest edges are considered to be "good". Concerning the scorching of the composition, a 2 mm thick 15 cm ² plate was cut from the above-formed product, which was evaluated as "good" if it had no irregularities due to vulcanized pieces. The flatness of the plate was rated "good" if it was flat enough to adhere firmly to a flat plate.

(Costs)

O Δ x XX TeuerThe unit price of a material decreases in the following order: a rare metal (Co), a high density metal (Zn), a complicated organic compound (HTS, modified resorcinol resin, HMMPME), a through a synthesis process consisting of 5 steps, synthesized organic compound (DCBS, activator, antioxidant)> an organic material (NR, SBR, C5 petroleum resin)>sulfur>silica> carbon black> oil. The cost of the formulation can be reduced by reducing the amount of materials with a high unit price. The formulation costs were evaluated as follows.

Cheap

O Δ x XX Expensive

(Tire durability (hydrothermal aging durability test))

The test tire (hydrothermally aged tire) was subjected to a running drum under overload conditions which are related to 140% of the maximum load defined by the JIS standard (maximum air pressure conditions). The running distance was measured until an abnormal phenomenon such as a tread on the tread or abnormal noise occurred. The running distance of Comparative Example 1 was defined as 100 and the running distances of the individual compositions were indicated by index numbers. The higher the index number, the better the tire life (tire durability in Southeast Asia and in the south and central areas of Japan).

In the examples in which insoluble sulfur having an iron content of 30 ppm or less was included, the ratio of zinc oxide content to sulfur content was 1.45 to 1.78; and the sulfur content is 3.0 to 6.0 parts by mass, the cobalt content is 0.05 to 0.15 parts by mass, and the sum of the stearic acid component content calculated from (A) stearic acid and (B) stearic acid calculated cobalt stearate and the amount of ( C) a mixture of a zinc salt of an aliphatic carboxylic acid and a zinc salt of an aromatic carboxylic acid 0.5 to 1.5 parts by mass, based in each case on 100 parts by mass of the rubber component, was the stability in handling, fuel economy, elongation at break, adhesion on steel cords, processability and tire durability in a balanced manner even though the ratio of zinc oxide content to sulfur content was not more than a specific value.

LIST OF REFERENCE NUMBERS

2

tire

4

tread

12

Breaker

14

Inner coat

15

tape

16

Breaker edge strip

16A

Breaker edge strip

16B

Breaker edge strip

28

carcass

30

Stripe layer between breaker and tissue

31

Strip on breaker pad

32

Breaker cushion

44

Inner layer

46

Outer layer

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 2011-74205 A [0092]

Cited non-patent literature

• JIS K 6217-2: 2001 [0050]
• JIS K6217-4: 2001 [0052]
• ASTM D3037-93 [0057]
• JIS K6220-1: 2001 [0095]
• IS-HS-7520 [0128]
• IS-HS-7520 [0128]
• JIS K 6251 [0137]

Claims (6)

A rubber composition for a steel cord gum, a breaker edge strip, a breaker pad, or a strip adjacent to cords, which comprises insoluble sulfur having an iron content of 30 ppm or less; has a zinc oxide to sulfur content of 1.45 to 1.78, and a sulfur content of 3.0 to 6.0 parts by mass, a cobalt content of 0.05 to 0.15 parts by mass, and a sum of stearic acid component content calculated from (A) stearic acid and (B) stearic acid calculated cobalt stearate, and the amount of (C) a mixture of a zinc salt of an aliphatic carboxylic acid with a zinc salt of an aromatic carboxylic acid of 0.5 to 1.5 parts by mass, each based on 100 parts by mass of the rubber component of the rubber composition. A rubber composition for a steel cord gum, a breaker edge strip, a breaker pad or a cords adjacent to cords according to claim 1, which comprises 30 to 70 parts by mass of carbon black having a nitrogen adsorption specific surface area of 60 to 120 m ² / g with respect to 100 parts by mass of the rubber component Ratio of specific surface area (measured by nitrogen adsorption) / (dibutyl phthalate absorption) of> 0.95. A rubber composition for a steel cord gum, a break edge tape, a breaker pad or a cords adjacent to cords according to claim 1 or 2, wherein the process oil content is 2.5 parts by mass or less based on 100 parts by mass of the rubber component. A rubber composition for a steel cord gum, a break edge tape, a breaker pad, or a cords according to any one of claims 1 to 3, which contains 0.5 to 3 parts by mass of a quinoline antioxidant having a primary amine content of 0, based on 100 parts by mass of the rubber component. 7 mass% or less. A rubber composition for a steel cord gum, a breaker edge strip, a breaker pad, or a strip adjacent to cords according to any one of claims 1 to 4, which contains silica. A pneumatic tire containing a steel cord rubberization formed from the rubber composition according to any one of claims 1 to 5, break margin tape, breaker pad or a strip adjacent to cords.

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