Rubber composition for covering steel cords, and pneumatic tires

Abstract

To provide a rubber composition for coating a steel cord capable of obtaining excellent processability and excellent peel force resistance under heat aging resistance conditions.SOLUTION: There is provided a rubber composition for coating a steel cord which comprises 1 to 5 pts.mass of sodium 1,6-hexamethylenediamine-dithiosulfate dihydrate and 0.1 to 1 pt.mass of 1,3,5-triazine-2,4,6-trithiol based on 100 pts.mass of a diene-based rubber, wherein the content ratio (sodium 1,6-hexamethylenediamine-dithiosulfate dihydrate / 1,3,5-triazine-2,4,6-trithiol) of sodium 1,6-hexamethylenediamine-dithiosulfate dihydrate to 1,3,5-triazine-2,4,6-trithiol is 1.6 or more by mass ratio.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] In pneumatic tires, particularly radial tires, steel cords are widely used as reinforcing materials for the belt layer of passenger car tires, the belts of large tires such as those for trucks and buses, the carcass, and the chafer layer. As the service life of tires lengthens, it is important to enhance the reinforcing effect of steel cords and maintain durability over a long period, and the rubber composition for coating steel cords is required to have excellent adhesion to steel cords.

[0003] Conventionally, for improving adhesion, as described in Patent Documents 1 and 2, triazine trithiols monoalkali metal salts have been used. However, in the case of triazine thiols or di- or trialkali metal salts of triazine trithiols, the hygroscopicity (deliquescence) of the chemicals becomes high, and there is a risk of deterioration of adhesion.

[0004] Also, conventionally, cobalt salts of organic acids have sometimes been used to improve processability. However, from the perspective of environmental protection, it is desirable not to use cobalt salts of organic acids, and a rubber composition excellent in processability without blending cobalt salts of organic acids is required.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In view of the above, the present invention aims to provide a rubber composition for coating steel cords that exhibits excellent processability and excellent peel resistance under heat aging conditions, as well as a pneumatic tire.

[0007] Furthermore, Patent Documents 1 and 2 contain: 1,6-Hexamethylene-dithiosulfate sodium dihydrate Furthermore, there is no description of examples in which 1,3,5-triazine-2,4,6-trithiol is used in combination. [Means for solving the problem]

[0008] The present invention includes embodiments shown below. [1] Per 100 parts by mass of diene rubber, 1,6-Hexamethylene-dithiosulfate sodium dihydrate It contains 1 to 5 parts by mass of and 0.1 to 1 part by mass of 1,3,5-triazine-2,4,6-trithiol. 1,6-Hexamethylene-dithiosulfate sodium dihydrate The content ratio of 1,3,5-triazine-2,4,6-trithiol ( 1,6-Hexamethylene-dithiosulfate sodium dihydrate A rubber composition for covering steel cords, wherein the mass ratio of (1,3,5-triazine-2,4,6-trithiol) is 1.6 or more. [2] The steel cord coating rubber composition according to [1], wherein the diene rubber contains natural rubber (NR) and / or isoprene rubber (IR). [3] A rubber composition for covering steel cords according to [1] or [2], which does not contain cobalt organic acid. [4] A pneumatic tire made using the rubber composition for steel cord coating described in any one of items [1] to [3]. [Effects of the Invention]

[0009] The rubber composition for coating steel cords of the present invention provides excellent processability and excellent peel resistance under heat aging conditions. [Modes for carrying out the invention]

[0010] The following describes in detail matters related to the implementation of the present invention.

[0011] The rubber composition for covering steel cords according to this embodiment is, with 100 parts by mass of diene rubber, 1,6-Hexamethylene-dithiosulfate sodium dihydrate It contains 1 to 5 parts by mass of and 0.1 to 1 part by mass of 1,3,5-triazine-2,4,6-trithiol. 1,6-Hexamethylene-dithiosulfate sodium dihydrate The content ratio of 1,3,5-triazine-2,4,6-trithiol ( 1,6-Hexamethylene-dithiosulfate sodium dihydrate The mass ratio of (1,3,5-triazine-2,4,6-trithiol) is 1.6 or higher.

[0012] In the rubber composition according to this embodiment, examples of diene rubbers used as rubber components include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, acrylonitrile butadiene rubber (NBR), chloroprene rubber (CR), and butyl rubber (IIR). These diene rubbers can be used individually or in blends of two or more.

[0013] The above rubber component preferably contains natural rubber and / or isoprene rubber, and the content of natural rubber and isoprene rubber in 100 parts by mass of diene rubber is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, and even more preferably 95 parts by mass or more.

[0014] The rubber composition according to this embodiment, 1,6-Hexamethylene-dithiosulfate sodium dihydrate The material contains 1 to 5 parts by mass, preferably 1 to 3 parts by mass, and more preferably 1 to 2 parts by mass, per 100 parts by mass of diene rubber. When the content is within the above range, excellent processability and excellent peel resistance under heat aging conditions are easily obtained.

[0015] The rubber composition according to this embodiment contains 1,3,5-triazine-2,4,6-trithiol, and the content thereof is 0.1 to 1 part by mass with respect to 100 parts by mass of the diene rubber, preferably 0.1 to 0.8 part by mass, and more preferably 0.1 to 0.5 part by mass. Since 1,3,5-triazine-2,4,6-trithiol has highly reactive thiol groups, if the content is 超过 0.1 part by mass, a high effect can be exerted, and excellent processability and peel resistance under heat aging conditions can be easily obtained. When the content is 1 part by mass or less, it is easy to suppress the scorch time from becoming fast and rubber burning from occurring.

[0016] 1,6-Hexamethylene-dithiosulfate sodium dihydrate The content ratio of 1,6-Hexamethylene-dithiosulfate sodium dihydrate / 1,3,5-triazine-2,4,6-trithiol) is 1.6 or more in terms of mass ratio, preferably 1.6 to 50, more preferably 2 to 30, and even more preferably 3 to 15. When the content ratio is within the above range, excellent processability and excellent peel resistance under heat aging conditions can be easily obtained.

[0017] The rubber composition for steel cord coating according to this embodiment 1,6-Hexamethylene-dithiosulfate sodium dihydrate By using 1,6-Hexamethylene-dithiosulfate sodium dihydrate and 1,3,5-triazine-2,4,6-trithiol in a predetermined ratio, excellent processability and excellent peel resistance under heat aging conditions can be obtained. This mechanism is not clear, but it can be speculated as follows. First, 1,6-Hexamethylene-dithiosulfate sodium dihydrate cracks, and the radicals generated thereby react with the metal surface of the steel cord and the double bonds in the polymer to form a crosslinked structure. And the crosslinked structure formed by 1,6-Hexamethylene-dithiosulfate sodium dihydrate is thermally more stable than the crosslinked structure formed by sulfur, so it can be speculated that the peel resistance under heat aging conditions is improved. Here, the 1,3,5-triazine-2,4,6-trithiol used in combination 1,6-Hexamethylene-dithiosulfate sodium dihydrateIt is considered that radicals are more likely to be generated compared to 1,6-Hexamethylene-dithiosulfate sodium dihydrate . The radical generation of 1,6-Hexamethylene-dithiosulfate sodium dihydrate is promoted by the radicals generated from 1,3,5-triazine-2,4,6-trithiol, and the reaction with the metal surface of the steel cord and the double bonds in the polymer is promoted. That is,

[0018] It can be presumed that a synergistic effect is obtained for improving the peel resistance by using

[0019] and 1,3,5-triazine-2,4,6-trithiol in a predetermined ratio. Furthermore, it can be presumed that the scorch time is prolonged by limiting the content of highly reactive 1,3,5-triazine-2,4,6-trithiol to a small amount, and an unexpected effect of improving the processability is obtained.

[0020] The reinforcing filler can be incorporated into the rubber composition according to this embodiment.

[0021] As the reinforcing filler, it is preferable to use carbon black and / or silica. That is, the reinforcing filler may be carbon black alone, silica alone, or a combination of carbon black and silica. Preferably, it is carbon black or a combination of carbon black and silica. The content of the reinforcing filler is not particularly limited, and for example, it is preferably 10 to 140 parts by mass, more preferably 20 to 100 parts by mass, and still more preferably 30 to 80 parts by mass with respect to 100 parts by mass of the above diene rubber.

[0022] The rubber composition according to this embodiment may contain a methylene acceptor and a methylene donor. The hydroxyl group of the methylene acceptor reacts with the methylene group of the methylene donor to enhance the adhesion between the rubber and the steel cord, thereby suppressing deterioration of adhesion due to load and heat generated during tire operation.

[0023] As methylene acceptors, phenolic compounds or phenolic resins obtained by condensing phenolic compounds with formaldehyde are used. These phenolic compounds include phenol, resorcinol, or their alkyl derivatives. Alkyl derivatives include methyl group derivatives such as cresol and xylenol, as well as derivatives with relatively long-chain alkyl groups such as nonylphenol and octylphenol. The phenolic compounds may also contain acyl groups, such as acetyl groups, as substituents.

[0024] Furthermore, phenolic resins obtained by condensing phenolic compounds with formaldehyde include resorcinol-formaldehyde resins, phenolic resins (i.e., phenol-formaldehyde resins), cresol resins (i.e., cresol-formaldehyde resins), and formaldehyde resins composed of multiple phenolic compounds. These are uncured resins that are liquid or have thermal fluidity.

[0025] Among these, from the viewpoint of compatibility with rubber components and other components, density of the resin after curing, and reliability, resorcinol or a resorcinol derivative is preferred as the methylene acceptor, and in particular, resorcinol or resorcinol-alkylphenol-formaldehyde resin is preferred.

[0026] The content of these methylene acceptors is not particularly limited, but is preferably 1 to 10 parts by mass, and more preferably 1 to 4 parts by mass, per 100 parts by mass of diene rubber.

[0027] As the methylene donor, hexamethylenetetramine or a melamine derivative can be used. Examples of melamine derivatives include methylolmelamine, a partially etherified methylolmelamine, and a condensate of melamine, formaldehyde, and methanol, among which hexamethoxymethylmelamine is particularly preferred.

[0028] The content of the methylene donor is not particularly limited, but is preferably 0.5 to 10 parts by mass, and more preferably 0.5 to 4 parts by mass, per 100 parts by mass of diene rubber.

[0029] In the rubber composition according to this embodiment, organic cobalt acid salts may be added as adhesion enhancers to steel cords, provided that the effects of the present invention are not impaired. However, from the viewpoint of environmental protection, it is preferable not to include them. Examples of organic cobalt acid salts include cobalt naphthenate, cobalt stearate, cobalt oleate, cobalt neodecanoate, cobalt rosinate, cobalt borate, and cobalt maleate.

[0030] In addition to the components described above, the rubber composition according to this embodiment may contain, within a normal range, various compounding agents commonly used in the rubber industry, such as process oil, zinc oxide, stearic acid, softeners, plasticizers, waxes, antioxidants, vulcanizing agents, and vulcanization accelerators.

[0031] Examples of the above-mentioned vulcanizing agent include sulfur components such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur, and are not particularly limited, but the content is preferably 1 to 10 parts by mass, and more preferably 2 to 8 parts by mass, per 100 parts by mass of diene rubber. Furthermore, the content of the vulcanization accelerator is preferably 0.1 to 3 parts by mass, and more preferably 0.2 to 2 parts by mass, per 100 parts by mass of diene rubber.

[0032] As a vulcanization accelerator, sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, guanidine-based vulcanization accelerators, and dithiocarbamate-based vulcanization accelerators may be used individually or in appropriate mixtures. Among these, sulfenamide-based vulcanization accelerators are preferred, and N-(tert-butyl)-2-benzothiazole sulfenamide (TBBS) is more preferred.

[0033] The rubber composition according to this embodiment can be prepared by kneading in accordance with conventional methods using a commonly used mixing machine such as a Banbury mixer, kneader, or roll.

[0034] The rubber composition according to this embodiment is used as a coating (topping) rubber for steel cords used as reinforcing material in the belt layer and carcass layer of a pneumatic tire. That is, it is used as a coating rubber composition for belt cords and / or carcass cords. The rubber composition can be used to produce steel cord topping sheets using a topping device such as a steel calender according to a conventional method, and these sheets can be used as the belt layer and / or carcass layer to produce an unvulcanized tire, which can then be vulcanized and molded according to a conventional method to produce a pneumatic tire.

[0035] The pneumatic tire can be a passenger car tire or a heavy-duty tire, and is not particularly limited. The structure of the pneumatic tire itself is well known and is not particularly limited. Generally, a pneumatic tire comprises a pair of left and right beads and sidewalls, a tread provided between the two sidewalls so as to connect the radially outward ends of the left and right sidewalls, and at least one carcass layer extending across the pair of left and right beads. The carcass layer extends from the tread through the sidewalls, with both ends locked to the beads, and reinforces the above parts. In addition, a belt layer is usually provided in two or more layers between the tread rubber on the outer circumference side of the carcass layer on the tread, and reinforces the tread on the outer circumference of the carcass layer. In this embodiment, when the above rubber composition is used as the coating rubber for steel cords, it may be applied to either the belt layer or the carcass layer, or to both. [Examples]

[0036] The following are examples of the present invention, but the present invention is not limited to these examples.

[0037] Using a Banbury mixer, the rubber composition was prepared according to the formulation (parts by mass) shown in Table 1 below. First, in the first mixing stage, the components excluding sulfur and vulcanization accelerator were added and mixed (discharge temperature = 160°C). Then, in the final mixing stage, sulfur and vulcanization accelerator were added and mixed into the resulting mixture (discharge temperature = 90°C).

[0038] The details of each component in Table 1 are as follows: • Natural rubber: RSS#3 • Carbon black: HAF, manufactured by Tokai Carbon Co., Ltd. "Seast 300" • Silica: Evonik "Ultrasil VN3" • Zinc oxide: "3 types of zinc oxide" manufactured by Mitsui Mining & Smelting Co., Ltd. • Stearic acid: "Bead Stearic Acid" manufactured by NOF Corporation • Anti-aging agent: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Resorcinol derivatives: "Sumikanol 620" manufactured by Sumitomo Chemical Co., Ltd., and resorcinol-alkylphenol-formaldehyde resin • Melamine derivatives: "Sailets 963L" manufactured by Ornex Japan Co., Ltd., hexamethoxymethylmelamine • Cobalt stearate: "Corebond CS-9.5" manufactured by Taiko Precision Chemicals Co., Ltd. • Crosslinking agent 1: Duralink HTS manufactured by Flexis 1,6-Hexamethylene-dithiosulfate sodium dihydrate • Crosslinking agent 2: "Thiocyanuric Acid" and 1,3,5-triazine-2,4,6-trithiol, manufactured by Tokyo Chemical Industry Co., Ltd. • Sulfur: "Mucron OT-20" manufactured by Shikoku Chemicals Co., Ltd. • Vulcanization accelerator: "Sunceller NS-G" manufactured by Sanshin Chemical Industry Co., Ltd., N-(tert-butyl)-2-benzothiazole sulfenamide (TBBS)

[0039] Each of the obtained rubber compositions was evaluated for processability, scorch resistance, and peel resistance under heat aging conditions. The evaluation method was as follows.

[0040] • Processability: In accordance with JIS K6300, a rotaryless Mooney torque measuring instrument manufactured by Toyo Seiki Co., Ltd. was used to preheat unvulcanized rubber at 100°C for 1 minute, and then measure the torque value in Mooney units after 4 minutes. The torque value of Comparative Example 1 is shown as an index with 100. A higher value indicates a higher torque value and superior processability.

[0041] • Scorching: In accordance with JIS K6300, using a rotaryless Mooney measuring instrument manufactured by Toyo Seiki, the unvulcanized rubber composition was preheated at 125°C for 1 minute. The time t5 required for the viscosity to increase by 5 Mooney units from the minimum viscosity Vm was measured and expressed as an index with the value of Comparative Example 1 set to 100. A higher value indicates a longer Mooney scorching time.

[0042] • Peel resistance under heat-resistant aging conditions: Twelve brass-plated steel cords (3×0.20+6×0.35 structure, copper:zinc = 64:36%, plating adhesion amount = 6g / kg) were arranged in parallel at intervals of 25mm. A cord / rubber composite sheet was prepared by sandwiching both sides of the cords between 0.8mm thick sheets of each rubber composition listed in Table 1. These two sheets were superimposed so that the cord arrangement direction was parallel, and adhesion evaluation samples were prepared by press vulcanization at 150°C for 30 minutes. After leaving the obtained samples in a 100°C oven for 96 hours, a peel test was performed between the two layers of steel cords using an Autograph (Shimadzu DCS500) to determine the peel strength. The value for Comparative Example 1 is expressed as an index with the value set to 100. A higher value indicates better peel strength.

[0043] [Table 1]

[0044] The results are shown in Table 1, and Comparative Examples 1-3 were used as crosslinking agents. 1,6-Hexamethylene-dithiosulfate sodium dihydrate This is an example of using [the first agent] alone, while Comparative Example 4 is an example of using 1,3,5-triazine-2,4,6-trithiol alone as a crosslinking agent. Comparing Examples 1-4 with Comparative Examples 1-4, 1,6-Hexamethylene-dithiosulfate sodium dihydrate It was found that by using 1,3,5-triazine-2,4,6-trithiol in combination, excellent processability and superior peel resistance under heat aging conditions can be obtained.

[0045] Comparative Examples 5 and 6 are: 1,6-Hexamethylene-dithiosulfate sodium dihydrate This is an example where the mixture contains 1,3,5-triazine-2,4,6-trithiol in proportions deviating from the specified ratio, resulting in poor peel resistance under heat aging conditions.

[0046] A comparison of Comparative Examples 4-6 revealed that the higher the content of 1,3,5-triazine-2,4,6-trithiol, the shorter the scorching time and the worse the processability.

[0047] Comparative Example 7 is an example in which cobalt stearate was used instead of crosslinking agents 1 and 2. Compared to Comparative Example 1, no improvement in processability was obtained, and the peel resistance under heat aging conditions was also inferior to that of Examples 1 to 4.

[0048] Furthermore, comparing Examples 1 to 4, 1,6-Hexamethylene-dithiosulfate sodium dihydrate The content ratio of 1,3,5-triazine-2,4,6-trithiol ( 1,6-Hexamethylene-dithiosulfate sodium dihydrate It was found that the larger the amount of triazine (1,3,5-triazine-2,4,6-trithiol), the greater the improvement in processability and peel resistance under heat aging conditions. [Industrial applicability]

[0049] The rubber composition for covering steel cords of the present invention is useful as a coating rubber for steel cords, which are reinforcing materials for pneumatic tires. Steel cord-rubber composites using this rubber composition can be used in the belt layer of passenger car tires, and in the belts, carcasses, and chaff layers of large tires such as those for trucks and buses.

Claims

1. For 100 parts by mass of diene rubber, 1,6-Hexamethylene-dithiosulfate sodium dihydrate, 1 to 5 parts by mass, It contains 0.1 to 1 part by mass of 1,3,5-triazine-2,4,6-trithiol, A rubber composition for covering steel cords, wherein the content ratio of 1,6-hexamethylene-dithiosulfate sodium dihydrate to 1,3,5-triazine-2,4,6-trithiol (1,6-hexamethylene-dithiosulfate sodium dihydrate / 1,3,5-triazine-2,4,6-trithiol) is 3 to 15 by mass.

2. The rubber composition for covering steel cords according to claim 1, wherein the diene rubber contains natural rubber (NR) and / or isoprene rubber (IR).

3. A rubber composition for covering steel cords according to claim 1 or 2, which does not contain organic cobalt.

4. A pneumatic tire made using the rubber composition for covering steel cords described in claim 1 or 2.

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