Rubber composition for coating steel cord and tire

Abstract

To provide a rubber composition for coating a steel cord having excellent adhesion performance and aging adhesion performance and exhibiting high breaking strength and a tire using the same.SOLUTION: There is provided a rubber composition for coating a steel cord which comprises a diene-based rubber including a natural rubber satisfying the following condition A and a cobalt compound, wherein the content of the cobalt compound is 0.1 to 0.3 pt.mass as a cobalt element content based on 100 pts.mass of the diene-based rubber. Condition A: 2 g of a natural rubber and 12 mL of water are placed in a 50-mL autoclave under an environment at 25°C and 1 atmospheric pressure, followed by sealing and heating at 120°C for 2 hours. The autoclave is returned to 25°C and 1 atmospheric pressure to obtain an extract. The pH of the extract measured under an environment at 25°C and 1 atmospheric pressure is 6 or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a rubber composition for coating steel cords and a tire.

Background Art

[0002] Since a tire is subjected to strong impacts and large loads, it usually has a belt layer composed of a plurality of steel cords coated with a rubber composition. Examples of the rubber composition for coating steel cords (rubber composition for coating steel cords) include those described in Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Recently, as the demand for safety has increased, further improvement in the adhesiveness to steel cords (hereinafter, also referred to as "adhesion performance") and breaking strength of the rubber composition for coating steel cords has been desired. In particular, further improvement in the adhesion performance after aging (hereinafter, also referred to as "aged adhesion performance") has been desired. Under such circumstances, when the inventor examined the rubber composition described in Patent Document 1, it became clear that further improvement in the adhesion performance (particularly the aged adhesion performance) and breaking strength is desirable in consideration of the requirements that will further increase in the future.

[0005] Therefore, in view of the above circumstances, an object of the present invention is to provide a rubber composition for coating steel cords that is excellent in adhesion performance and aged adhesion performance and exhibits high breaking strength, and a tire using the same.

Means for Solving the Problems

[0006] As a result of intensive studies on the above problems, the present inventor has found that the above problems can be solved by using a specific natural rubber, and thus has reached the present invention. That is, the present inventor has found that the above problems can be solved by the following configuration.

[0007] (1) A diene rubber containing a natural rubber satisfying the following condition A and a cobalt compound, A rubber composition for coating a steel cord, wherein the content of the cobalt compound is 0.1 to 0.3 parts by mass in terms of cobalt element content with respect to 100 parts by mass of the diene rubber. Condition A: Put 2 g of natural rubber and 12 mL of water into a 50 mL autoclave in an environment of 25 °C and 1 atm, seal it, and heat it at 120 °C for 2 hours. Return the autoclave to 25 °C and 1 atm to obtain an extract. The pH of the extract measured in an environment of 25 °C and 1 atm is 6 or more. (2) The rubber composition for coating a steel cord according to (1) above, wherein the pH is 6.5 or more. (3) A tire using the rubber composition for coating a steel cord according to (1) or (2) above for coating a steel cord.

Advantages of the Invention

[0008] As shown below, according to the present invention, it is possible to provide a rubber composition for coating a steel cord that is excellent in adhesion performance and aged adhesion performance and exhibits high breaking strength, and a tire using the same.

Brief Description of the Drawings

[0009]

Figure 1

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the rubber composition for coating a steel cord of the present invention and the tire of the present invention will be described. In addition, the numerical range represented by "~" in this specification means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. Also, each component may be used alone or in combination of two or more. Here, when two or more of each component are used in combination, the content of that component refers to the total content unless otherwise specified. Also, showing high breaking strength is also referred to as "excellent breaking strength". Also, excellent adhesion performance, aging adhesion performance, and breaking strength are collectively referred to as "excellent effects of the present invention".

[0011] [Rubber composition for steel cord coating] The rubber composition for steel cord coating of the present invention (hereinafter, also referred to as "the composition of the present invention") contains a diene rubber containing natural rubber (hereinafter, also referred to as "specific NR") that satisfies the following condition A and a cobalt compound, and the content of the above cobalt compound is 0.1 to 0.3 parts by mass in terms of cobalt element content with respect to 100 parts by mass of the above diene rubber, a rubber composition for steel cord coating. Condition A: Put 2 g of natural rubber and 12 mL of water into a 50 mL autoclave in an environment of 25°C and 1 atm, seal it, and heat it at 120°C for 2 hours. Return the autoclave to 25°C and 1 atm to obtain an extract. The pH of the extract measured in an environment of 25°C and 1 atm (hereinafter, also referred to as "specific pH") is 6 or more.

[0012] It is considered that the composition of the present invention solves the above-mentioned problems because of such a configuration. The reason is not clear, but it is presumably as follows.

[0013] It is known that microorganisms are mixed into natural rubber latex (hereinafter, also simply referred to as "latex"). The inventor has found that among the non-rubber components present in latex, the components necessary for the expression of the strength of natural rubber are decomposed by the above microorganisms, and that the adhesion performance and breaking strength are reduced by such decomposition. The inventor has also found that the pH when natural rubber (raw rubber) obtained from latex is extracted with hot water under specific conditions correlates with the amount of the above microorganisms. This is presumably due to the production of organic acids by the microorganisms. The present invention is based on these findings and the like. That is, since specific NR sufficiently contains the non-rubber components necessary for the expression of strength, it is presumed that the composition of the present invention containing such specific NR exhibits excellent adhesion performance and breaking strength.

[0014] Hereinafter, each component contained in the composition of the present invention will be described.

[0015] 〔Diene rubber〕 The diene rubber contained in the composition of the present invention is not particularly limited as long as it is a diene rubber containing specific NR. The above diene rubber may contain a diene rubber other than specific NR (other diene rubbers).

[0016] <Specific NR> As described above, the diene rubber contained in the composition of the present invention contains a natural rubber (specific NR) that satisfies the following condition A. Condition A: Put 2 g of natural rubber and 12 mL of water into a 50 mL autoclave under an environment of 25°C and 1 atm, seal it, and heat it at 120°C for 2 hours. Return the autoclave to 25°C and 1 atm to obtain an extract. The pH (specific pH) of the extract measured under an environment of 25°C and 1 atm is 6 or more. The above natural rubber is raw rubber obtained by coagulating and drying natural rubber latex, and is before vulcanization.

[0017] The specific pH is preferably 6.3 or higher, more preferably 6.5 or higher, for the reason that the effects of the present invention are more excellent. The upper limit of the specific pH is not particularly limited, but is preferably 10 or lower, more preferably 8 or lower, and even more preferably 7 or lower, for the reason that the effects of the present invention are more excellent.

[0018] The method for obtaining the specific NR is not particularly limited. For example, as shown in the Examples section described later, natural rubber with a specific pH of 6 or higher can be obtained by adjusting the type and concentration of the acid used when coagulating natural rubber latex. Also, natural rubber with a specific pH of 6 or higher can be selected by evaluating the specific pH of commercially available natural rubber.

[0019] (Content) The content of the specific NR in the diene rubber is not particularly limited, but is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, particularly preferably 70% by mass or more, and most preferably 90% by mass or more, for the reason that the effects of the present invention are more excellent. The upper limit of the content of the specific NR in the diene rubber is not particularly limited and is 100% by mass.

[0020] <Other diene rubbers> Examples of other diene rubbers include natural rubbers (NR) other than the specific NR, butadiene rubber (BR), aromatic vinyl-conjugated diene copolymer rubbers, isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR), and the like. Examples of the aromatic vinyl-conjugated diene copolymer rubbers include styrene-butadiene rubber (SBR), styrene-isoprene copolymer rubber, and the like.

[0021] (Content) The content of other diene rubbers in the diene rubber is not particularly limited, but it is preferably 90% by mass or less, more preferably 70% by mass or less, still more preferably 50% by mass or less, particularly preferably 30% by mass or less, and most preferably 10% by mass or less. The lower limit of the content of other diene rubbers in the diene rubber is not particularly limited and is 0% by mass.

[0022] <Molecular weight> The weight average molecular weight (Mw) of the diene rubber is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 100,000 to 5,000,000, more preferably 200,000 to 3,000,000, and still more preferably 300,000 to 2,000,000.

[0023] In addition, in this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are values in terms of standard polystyrene obtained by gel permeation chromatography (GPC) measurement.

[0024] [Cobalt compound] The composition of the present invention contains a cobalt compound (a compound containing a cobalt element). The cobalt compound is preferably a cobalt organic acid salt for the reason that the effects of the present invention are more excellent. Specific examples of the cobalt organic acid salt include cobalt acetate, cobalt octylate, cobalt naphthenate, cobalt malonate, cobalt neodecanoate, cobalt stearate, cobalt propionate, cobalt benzoate, cobalt p-hydroxybenzoate, fatty acid cobalt-boron compounds [for example, commercially available products such as Manobond CCP420 (manufactured by Mankem), Manobond CC680 (manufactured by Mankem)], cobalt rosinate, cobalt versatic acid, cobalt tall oil acid, and the like. The cobalt salt of an organic acid is preferably a compound selected from the group consisting of cobalt naphthenate, cobalt oleate, cobalt linoleate, cobalt stearate, cobalt linolenate, cobalt paltiminic acid, cobalt neodecanoate, cobalt rosinate, cobalt tall oilate, and a cobalt salt of an organic acid containing boron. The cobalt salt of an organic acid containing boron is preferably a complex salt in which a part of the organic acid is replaced with boric acid, and more preferably cobalt trisneodecanoate borate, because the effects of the present invention are more excellent.

[0025] <Content> In the composition of the present invention, the content of the cobalt compound is 0.1 to 0.3 parts by mass in terms of cobalt element content with respect to 100 parts by mass of the above-mentioned diene rubber. Hereinafter, the content of the cobalt compound as the cobalt element content with respect to 100 parts by mass of the diene rubber is also simply referred to as the "cobalt element content".

[0026] In the composition of the present invention, the content of the cobalt compound is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass with respect to 100 parts by mass of the above-mentioned diene rubber, because the effects of the present invention are more excellent.

[0027] 〔Optional component〕 The composition of the present invention can further contain other components (optional components) as necessary within a range that does not impair the effects and purposes thereof. Examples of the above optional components include various additives generally used in rubber compositions such as fillers (e.g., silica, carbon black), silane coupling agents, terpene resins (e.g., aromatic-modified terpene resins), thermally expandable microcapsules, zinc oxide (zinc white), stearic acid, antioxidants, waxes, processing aids, oils, liquid polymers, thermosetting resins, vulcanizing agents (e.g., sulfur), and vulcanization accelerators.

[0028] <Carbon black> The composition of the present invention preferably contains carbon black because the effects of the present invention are more excellent. The above carbon black is not particularly limited, and for example, various grades such as SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS, HAF, HAF-LS, FEF, etc. can be used. The nitrogen adsorption specific surface area (N2SA) of the above carbon black is not particularly limited, but for the reason that the effects of the present invention are more excellent, it is preferably 20 to 150 m 2 / g, and more preferably 40 to 140 m 2 / g. The nitrogen adsorption specific surface area (N2SA) is measured in accordance with JIS K6217-7.

[0029] (Content) When the rubber composition of the present invention contains carbon black, its content is preferably 10 to 100 parts by mass, and more preferably 30 to 70 parts by mass, based on 100 parts by mass of the above-mentioned diene rubber, because the effects of the present invention are more excellent.

[0030] (Zinc Oxide) The composition of the present invention preferably contains zinc oxide because the effects of the present invention are more excellent.

[0031] (Content) When the rubber composition of the present invention contains zinc oxide, its content is preferably 1 to 20 parts by mass, and more preferably 5 to 12 parts by mass, based on 100 parts by mass of the above-mentioned diene rubber, because the effects of the present invention are more excellent.

[0032] (Sulfur) The composition of the present invention preferably contains sulfur because the effects of the present invention are more excellent.

[0033] (Content) When the rubber composition of the present invention contains sulfur, its content is preferably 1 to 20 parts by mass, more preferably 4 to 9 parts by mass, based on 100 parts by mass of the diene rubber described above, for the reason that the effects of the present invention are more excellent.

[0034] [Method for producing rubber composition for steel cord coating] The production method of the composition of the present invention is not particularly limited. Specific examples thereof include, for example, a method of kneading the above-described respective components using a known method and apparatus (for example, Banbury mixer, kneader, roll, etc.). When the composition of the present invention contains sulfur or a vulcanization accelerator, it is preferable to first mix the components other than these components at a high temperature (preferably 130 to 190 ° C), cool them, and then mix sulfur and the vulcanization accelerator. In addition, the composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions.

[0035] [Use] The composition of the present invention is suitably used for coating steel cords. Among them, it is suitable for coating steel cords of pneumatic tires, and particularly suitable for coating steel cords in the belt layer, carcass layer, and bead portion.

[0036] [Tire] The tire of the present invention is a tire using the composition of the present invention described above for coating a steel cord. The tire of the present invention is preferably a pneumatic tire, and can be filled with an inert gas such as air, nitrogen, and other gases.

[0037] FIG. 1 shows a schematic partial cross-sectional view of a tire representing an example of an embodiment of the tire of the present invention, but the tire of the present invention is not limited to the embodiment shown in FIG. 1.

[0038] In FIG. 1, reference numeral 1 represents a bead portion, reference numeral 2 represents a sidewall portion, and reference numeral 3 represents a tire tread portion. Also, between a pair of left and right bead portions 1, a carcass layer 4 in which fiber cords are embedded is mounted, and the end portion of this carcass layer 4 is folded back from the inside of the tire to the outside around the bead core 5 and the bead filler 6 and wound up. Also, in the tire tread portion 3, a belt layer 7 is disposed over the entire circumference of the tire outside the carcass layer 4. Here, the belt layer 7 is a layer composed of a plurality of steel cords coated with the composition of the present invention. Also, in the bead portion 1, a rim cushion 8 is disposed at a portion in contact with the rim.

[0039] The tire of the present invention can be manufactured, for example, according to a conventionally known method. Further, as the gas filled in the tire, in addition to normal air or air with adjusted oxygen partial pressure, inert gases such as nitrogen, argon, and helium can be used.

Example

[0040] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[0041] [Manufacture of natural rubber] Natural rubber (raw rubber) was produced by adding an acid to natural rubber latex to coagulate it and then drying it. Here, three types of natural rubbers (NR1 to 3) were obtained by changing the type of acid and the concentration of the acid (mass% with respect to the entire natural rubber latex) as shown in Table 1 below.

[0042]

Table 1

[0043] The specific pH of each natural rubber is shown in Table 1. Since NR1 to 2 have a specific pH of 6 or more, they correspond to specific NR. On the other hand, since NR3 has a specific pH of less than 6, it does not correspond to specific NR.

[0044] [Manufacture of rubber composition] The components shown in Table 2 below were mixed at the ratios (parts by mass) shown in the same table. Specifically, first, the components excluding sulfur and vulcanization accelerator among the components shown in Table 2 below were mixed for 5 minutes using a 1.7-liter sealed Banbury mixer, discharged at about 160 °C, cooled to room temperature to obtain a masterbatch. Further, using the above Banbury mixing roll, sulfur and vulcanization accelerator were mixed into the obtained masterbatch to obtain a rubber composition.

[0045] [Evaluation] The following evaluations were performed on the obtained rubber composition.

[0046] [Adhesion performance] Using the obtained rubber composition, brass-plated steel cords arranged in parallel at an interval of 12.7 mm were coated, embedded with an embedding length of 12.7 mm, and vulcanization-bonded under vulcanization conditions of 160 °C × 20 minutes to prepare a rubber-coated evaluation sample. In accordance with ASTM D-2229, the steel cord was pulled out from the obtained rubber-coated evaluation sample, and the rubber adhesion amount (%) covering the surface thereof was evaluated. The results are shown in Table 2. The results are expressed as an index with the value of Example 1 being 100. The larger the index, the better the adhesion performance. Practically, the index is preferably 95 or more.

[0047] [Aging adhesion performance] A rubber-coated evaluation sample was prepared in the same manner as the evaluation of the adhesion performance described above, and an accelerated test of thermal deterioration at a temperature of 80 °C for 336 hours was performed. Using the thermally deteriorated sample, the steel cord was pulled out in the same manner as the evaluation of the adhesion performance described above, and the rubber adhesion amount (%) covering the surface thereof was evaluated. The results are shown in Table 2. The results are expressed as an index with the value of Example 1 being 100. The larger the index, the better the aging adhesion performance. Practically, the index is preferably 95 or more.

[0048] [Tensile strength] The obtained rubber composition was vulcanized in a mold of a predetermined shape at 170 °C for 10 minutes to prepare test pieces. Using the obtained test pieces, JIS No. 3 dumbbell-shaped test pieces (thickness 2 mm) were punched out in accordance with JIS K6251, and tests were conducted at a tensile speed of 500 mm / min to measure the breaking strength. The results are shown in Table 2. The results were expressed as an index with the value of Example 1 being 100. A larger index means better breaking strength. Practically, the index is preferably 95 or more.

[0049]

Table 2

[0050] The details of each component shown in Table 2 are as follows. · NR1 to 3: NR1 to 3 manufactured as described above · NR4: TSR20 with a specific pH of 5.8 made from raw rubber obtained by natural coagulation of natural rubber latex · BR: Nipol BR1220 (manufactured by Zeon Corporation, Japan) · Carbon black: Seast 300 (manufactured by Tokai Carbon Co., Ltd.) · Zinc oxide: Three types of zinc oxide (manufactured by Shodo Chemical Industry Co., Ltd.) · Stearic acid: Bead stearic acid (manufactured by NOF Corporation) · Antioxidant: Santoflex 6PPD (manufactured by Flexsys) · Cobalt compound: Cobalt tris(neodecanoate) (cobalt element content: 22% by mass) · Sulfur: Cristex HS OT 20 (manufactured by AkzoNobel) · Vulcanization accelerator: Nocceler DZ (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

[0051] As can be seen from Table 2, Examples 1 to 3 using specific NR as natural rubber all showed excellent adhesion performance, aged adhesion performance, and breaking strength. Among them, Examples 2 to 3 in which the specific pH of the specific NR is 6.5 or more showed more excellent adhesion performance and breaking strength. Among them, Example 2 in which the content of the specific NR in the diene rubber is 90% by mass or more showed even more excellent adhesion performance, aged adhesion performance, and breaking strength.

[0052] On the other hand, Comparative Examples 1 and 4 using natural rubber other than the specific NR had insufficient aged adhesion performance and breaking strength. Also, Comparative Example 2 not containing a cobalt compound had insufficient adhesion performance, aged adhesion performance, and breaking strength. Further, Comparative Example 3 in which the cobalt element content exceeded 0.3 parts by mass had insufficient breaking strength.

Explanation of symbols

[0053] 1 Bead part 2 Sidewall part 3 Tire tread part 4 Carcass layer 5 Bead core 6 Bead filler 7 Belt layer 8 Rim cushion

Claims

Claim 1 A diene rubber containing natural rubber satisfying the following Condition A and a cobalt compound, wherein the content of the cobalt compound is 0.1 to 0.3 parts by mass in terms of cobalt element content with respect to 100 parts by mass of the diene rubber, a rubber composition for coating a steel cord. Condition A: 2 g of natural rubber and 12 mL of water are placed in a 50 mL autoclave, sealed, and heated at 120°C for 2 hours in an environment of 25°C and 1 atm. The autoclave is returned to 25°C and 1 atm to obtain an extract. The pH of the extract measured in an environment of 25°C and 1 atm is 6 or more. Claim 2 The rubber composition for coating a steel cord according to claim 1, wherein the pH is 6.5 or more. Claim 3 A tire using the rubber composition for coating a steel cord according to claim 1 or 2 for coating a steel cord.

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