Rubber composition and tires

Abstract

This product uses naturally derived waxes as a sustainable material while simultaneously achieving both ozone resistance and suppression of whitening. [Solution] The rubber composition according to the embodiment contains a rubber component and a naturally derived wax with an acid value of 50 mgKOH / g or more.

Description

Technical Field

[0001] The present invention relates to a rubber composition and a tire using the same.

Background Art

[0002] In rubber compositions such as rubber compositions for tires, wax is blended to improve ozone resistance. Wax exhibits ozone resistance by blooming on the surface of the rubber after vulcanization to form a film. Generally, petroleum-derived waxes such as paraffin wax are used as the wax.

[0003] Recently, efforts to move away from oil dependence and promote the sustainable use of natural resources have been active, and sustainable raw materials such as raw materials derived from biomass resources and recycled resources have attracted attention. From such a sustainable perspective, the use of natural-derived waxes is being studied as a substitute for petroleum-derived waxes even in waxes.

[0004] For example, Patent Document 1 discloses that in a rubber composition for tires, a natural wax having a softening point of less than 40°C and a polar natural wax having a softening point of 40°C or higher are blended together with carbon black and silica.

[0005] Patent Document 2 discloses that in a rubber composition for tires, a natural-derived wax having an ester component content of 40 to 98% by mass, a phenylenediamine-based and / or quinone-based antioxidant, and a nonionic surfactant are blended.

[0006] Patent Document 3 discloses that in a rubber composition for tires, a mixed wax obtained by mixing three kinds of waxes, namely, a hydrolyzate of a plant-derived wax, paraffin wax, and microcrystalline wax, is blended.

Prior Art Documents

Patent Documents

[0007] [Patent Document 1] Japanese Patent Publication No. 2015-017273 [Patent Document 2] Japanese Patent Publication No. 2015-013955 [Patent Document 3] Japanese Patent Publication No. 2022-156284 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] As mentioned above, the use of naturally derived waxes is desirable from a sustainability perspective, but a problem specific to waxes is that they cause whitening of the rubber surface, which significantly deteriorates the appearance of the product.

[0009] In view of the above, embodiments of the present invention aim to provide a rubber composition that can achieve both ozone resistance and suppression of whitening while using naturally derived wax as a sustainable material, and a tire using the same. [Means for solving the problem]

[0010] The present invention includes embodiments shown below. [1] A rubber composition comprising a rubber component and a naturally derived wax with an acid value of 50 mgKOH / g or more. [2] The rubber composition according to [1], which does not contain petroleum-derived waxes. [3] The rubber composition according to [1] or [2], wherein the content of the natural wax per 100 parts by mass of the rubber component is 0.5 to 7.0 parts by mass. [4] The rubber composition according to any one of [1] to [3], wherein the natural wax comprises a plant-derived wax. [5] A tire having a rubber portion made using any one of the rubber compositions described in [1] to [4]. [Effects of the Invention]

[0011] According to embodiments of the present invention, it is possible to achieve both ozone resistance and suppression of whitening while using naturally derived wax as a sustainable material. [Modes for carrying out the invention]

[0012] The inventors have found that there is a correlation between the whitening of the rubber surface in naturally derived waxes and the acid value of the wax, and that by using a naturally derived wax with a specific acid value, whitening can be suppressed while ensuring ozone resistance. The rubber composition according to this embodiment comprises a rubber component and a naturally derived wax with an acid value of 50 mgKOH / g or more.

[0013] The rubber component is not particularly limited, and various diene rubbers commonly used in rubber compositions can be used. A diene rubber is a rubber having repeating units corresponding to a diene monomer with a conjugated double bond, and the main chain of the polymer contains a carbon-carbon double bond. The content of diene rubber in the rubber component is preferably 80% by mass or more, more preferably 90% by mass or more, and may be 100% by mass.

[0014] Specific examples of diene rubbers include natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber. Any one of these may be used, or two or more may be used in combination. These diene rubbers also include those that have been modified by introducing functional groups to the ends or main chain, or those that have been modified to impart desired properties. Among these, at least one selected from the group consisting of natural rubber, butadiene rubber, and styrene-butadiene rubber is preferred as the diene rubber.

[0015] In one embodiment, the rubber component preferably includes natural rubber and butadiene rubber. For example, 100 parts by mass of the rubber component may include 30 to 70 parts by mass of natural rubber and 30 to 70 parts by mass of butadiene rubber, or may include 40 to 60 parts by mass of natural rubber and 40 to 60 parts by mass of butadiene rubber.

[0016] The rubber composition according to this embodiment is blended with a natural-derived wax having an acid value of 50 mg KOH / g or more. By using such a natural-derived wax having a high acid value, it is possible to achieve both ozone resistance and suppression of whitening. Note that a natural-derived wax having a high acid value can be obtained, for example, by increasing the content rate of free fatty acids.

[0017] The acid value of the natural-derived wax is more preferably 55 mg KOH / g or more. The upper limit of the acid value is not particularly limited. For example, the acid value may be 150 mg KOH / g or less, 100 mg KOH / g or less, or 70 mg KOH / g or less.

[0018] Here, the acid value is the number of milligrams of potassium hydroxide required to neutralize free fatty acids and the like contained in 1 g of the sample, and is measured by a neutral titration method conforming to JIS K0070-1992.

[0019] The natural-derived wax is a wax derived from non-petroleum resources and is also referred to as a natural wax. Examples of the natural-derived wax include those derived from animals and plants, that is, plant-derived waxes and / or animal-derived waxes, but do not include petroleum-derived waxes.

[0020] The plant-derived wax is a wax extracted from plants and is also referred to as a plant wax. Examples of the plant-derived wax include rice wax, candelilla wax, carnauba wax, wood wax, jojoba wax, and the like. These may also be derivatives obtained by performing modifications such as purification, oxidation, esterification, and saponification.

[0021] Animal-derived wax is wax extracted from animals and is also referred to as animal-based wax. Examples of animal-derived waxes include beeswax, lanolin wax, and whale wax. These may also be derivatives that have undergone modifications such as purification, oxidation, esterification, and saponification.

[0022] In this embodiment, among these naturally derived waxes, those with an acid value of 50 mgKOH / g or more are used. Any one of such naturally derived waxes with a high acid value may be used, or two or more may be used in combination. Note that the naturally derived wax incorporated into the rubber composition preferably consists only of one or more naturally derived waxes with an acid value of 50 mgKOH / g or more, but a naturally derived wax with a low acid value may be additionally incorporated within the range where the desired effect is maintained.

[0023] In one embodiment, the naturally derived wax with an acid value of 50 mgKOH / g or more preferably contains plant-derived wax, and more preferably contains rice wax. The naturally derived wax preferably has plant-derived wax as the main component. That is, the naturally derived wax with an acid value of 50 mgKOH / g or more preferably contains 50 mass% or more, more preferably 70 mass% or more, still more preferably 90 mass% or more, and may be 100 mass% of plant-derived wax (more preferably rice wax) with an acid value of 50 mgKOH / g or more.

[0024] The content of the naturally derived wax with an acid value of 50 mgKOH / g or more is preferably 0.5 to 7.0 parts by mass, more preferably 1.0 to 5.0 parts by mass, based on 100 parts by mass of the rubber component.

[0025] From the perspective of sustainability, the rubber composition according to this embodiment preferably does not contain petroleum-derived wax. Here, petroleum-derived wax is wax extracted from petroleum, and examples include paraffin wax, microcrystalline wax, and petrolatum.

[0026] In addition to the above-mentioned components, the rubber composition according to this embodiment may also contain various additives commonly used in rubber compositions, such as fillers, oils, zinc oxide, stearic acid, antioxidants, vulcanization accelerators, and vulcanizing agents.

[0027] Examples of fillers include carbon black and / or silica. The carbon black is not particularly limited, and various known varieties can be used. The silica is also not particularly limited, and examples include wet silica such as wet sedimentation silica and wet gelation silica. The content of the filler is not particularly limited; for example, it may be 30 to 200 parts by mass, 40 to 150 parts by mass, or 50 to 100 parts by mass per 100 parts by mass of rubber component.

[0028] Examples of oils include mineral oils such as paraffinic, naphthenic, and aromatic oils, as well as vegetable oils, animal oils, and pyrolytic oils. The oil content is not particularly limited; for example, it may be 0 to 40 parts by mass, 3 to 30 parts by mass, or 5 to 25 parts by mass per 100 parts by mass of rubber components.

[0029] The zinc oxide content is not particularly limited; for example, it may be 0 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 4 parts by mass per 100 parts by mass of rubber component.

[0030] The amount of stearic acid is not particularly limited; for example, it may be 0 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 4 parts by mass per 100 parts by mass of rubber component.

[0031] Examples of anti-aging agents include amine-ketone, aromatic secondary amine, monophenol, bisphenol, and benzimidazole types, and any one or more of these can be used in combination. Preferably, an amine-ketone anti-aging agent and an aromatic secondary amine anti-aging agent are used in combination, and the mass ratio of the two (amine-ketone / aromatic secondary amine) may be, for example, 0.1 to 10 or 0.2 to 5. The content of the anti-aging agent is not particularly limited and may be, for example, 0 to 10 parts by mass, 1 to 8 parts by mass, or 2 to 5 parts by mass per 100 parts by mass of rubber component.

[0032] Examples of vulcanization accelerators include sulfenamide-based, thiuram-based, thiazole-based, and guanidine-based vulcanization accelerators, which can be used individually or in combination of two or more. The content of the vulcanization accelerator is not particularly limited and may be 0 to 10 parts by mass, 0.1 to 5 parts by mass, or 0.5 to 3 parts by mass per 100 parts by mass of rubber component.

[0033] Sulfur is preferably used as the vulcanizing agent, and examples include powdered sulfur, precipitated sulfur, insoluble sulfur, and highly dispersible sulfur. The content of the vulcanizing agent is not particularly limited, and may be 0 to 10 parts by mass, 0.5 to 5 parts by mass, or 1 to 4 parts by mass per 100 parts by mass of rubber component.

[0034] The rubber composition according to this embodiment can be prepared by kneading in accordance with conventional methods using a commonly used mixer such as a Banbury mixer, kneader, or roll. That is, for example, in the first mixing stage, other additives excluding the vulcanizing agent and vulcanization accelerator can be added and mixed with the rubber component, and then, in the final mixing stage, the vulcanizing agent and vulcanization accelerator can be added and mixed with the resulting mixture to prepare an unvulcanized rubber composition.

[0035] The rubber composition according to this embodiment can be used in various rubber components such as tires, vibration-damping rubber, and conveyor belts. Preferably, it is for tires. Examples of tires include passenger car tires, large tires for trucks and buses, and pneumatic tires of various sizes and applications.

[0036] A tire according to one embodiment has a rubber portion made using the above-mentioned rubber composition. Examples of application areas for the tire include the tread, sidewall, and bead portion, with the sidewall being preferred.

[0037] In one embodiment, a tire is manufactured as follows: A rubber composition is molded into a predetermined shape by conventional methods, for example by extrusion, to obtain unvulcanized rubber components (e.g., tread rubber, sidewall rubber, etc.). A green tire is produced by combining these rubber components with other tire components. The tire can be manufactured by vulcanizing the green tire at, for example, 140-180°C. [Examples]

[0038] The following are examples of the present invention, but the present invention is not limited to these examples.

[0039] The raw materials used in the examples and comparative examples are as follows: • BR: "UBEPOL BR 150B" manufactured by UBE Elastomer Co., Ltd. ·NR:RSS No.3 • Carbon Black: "Seast 3" manufactured by Tokai Carbon Co., Ltd. • Oil: ENEOS Corporation's "Process NC-140" • Zinc oxide: "Zinc Oxide Type 2" manufactured by Mitsui Mining & Smelting Co., Ltd. • Stearic acid: "Lunaq S-20" manufactured by Kao Corporation • Anti-aging agent 1: Aromatic secondary amine type, "Antigen 6C" manufactured by Sumitomo Chemical Co., Ltd. • Anti-aging agent 2: Amine-ketone type, "Antigen RD-G" manufactured by Sumitomo Chemical Co., Ltd. • Vulcanization accelerator: "Noxellar NS-P" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. • Sulfur: "5% Oil-containing Powdered Sulfur" manufactured by Tsurumi Chemical Industries Co., Ltd.

[0040] • Wax 1: Rice wax, acid value 59.5 mg KOH / g, manufactured by Toa Chemical Co., Ltd. "TOWAX-3F20" • Wax 2: Rice wax, acid value 3.8 mg KOH / g, manufactured by Toa Chemical Co., Ltd. "TOWAX-3P1" • Wax 3: Rice wax, acid value 6.5 mg KOH / g, manufactured by Toa Chemical Co., Ltd. "TOWAX-3F15" • Wax 4: Carnauba wax, acid value 6.8 mg KOH / g, manufactured by Toa Chemical Co., Ltd. "TOWAX-131" • Wax 5: Refined beeswax, acid value 17.0 mgKOH / g, manufactured by Yokozeki Oil & Fat Industry Co., Ltd. "CY100"

[0041] The evaluation methods for each comparative example and example are as follows. (1) Ozone resistance A static ozone degradation test was conducted in accordance with JIS K6259-1:2015. Specifically, the test specimens were left for 24 hours under conditions of 10°C or 50°C, an ozone concentration of 100 pphm, and elongation to 20%. The state of cracks on the rubber surface after the test was visually observed, and the number of cracks, their size, and depth were evaluated based on Table 1 below.

[0042] [Table 1]

[0043] (2) Appearance (whitening) Two-millimeter-thick test specimens were exposed to sunlight outdoors, and their surface was visually observed after 40 days to evaluate their appearance (whitening) according to the following criteria. A higher score indicates less whitening and better appearance. Score 5: Almost no discoloration to white. Score 4: Slightly discolored to white. Score 3: Less than half of the material has turned white. Score 2: More than half of the material has turned white. Score 1: The entire surface has turned white.

[0044] Rubber compositions for Comparative Examples 1-6 and Examples 1-2 were prepared using a Banbury mixer according to the formulations (parts by mass) listed in Table 2 below. Specifically, in the first mixing stage, all components except the vulcanization accelerator and sulfur were added to the rubber components and kneaded (discharge temperature = 160°C). In the final mixing stage, the vulcanization accelerator and sulfur were added to the resulting mixture and kneaded (discharge temperature = 100°C) to prepare the rubber composition. The obtained rubber composition was vulcanized at 160°C for 20 minutes to prepare test specimens made of vulcanized rubber. The ozone resistance and appearance of the obtained test specimens were evaluated.

[0045] [Table 2]

[0046] The results are shown in Table 2. In Comparative Example 1, no wax was added, and therefore, although there was no whitening and the appearance was excellent, it had poor ozone resistance. In Comparative Examples 2 and 3, rice wax with a low acid value was added, and although it had ozone resistance, the rubber surface was whitened and the appearance was poor. In Comparative Example 4, the amount of rice wax was increased compared to Comparative Example 3, and the whitening worsened further. In Comparative Example 5, carnauba wax with a similar acid value was added instead of the rice wax in Comparative Example 3, and although it had ozone resistance, similar to Comparative Example 3, the rubber surface was whitened and the appearance was poor. In Comparative Example 6, beeswax with an acid value of 17.0 mgKOH / g was added, and although it had ozone resistance, similar to Comparative Example 3, the rubber surface was whitened and the appearance was poor.

[0047] In contrast, Example 1 contained rice wax with an acid value of 59.5 mgKOH / g, which exhibited ozone resistance and excellent appearance without whitening. In Example 2, the amount of rice wax was increased compared to Example 1, and even in this case, no whitening was observed, and the appearance was excellent.

[0048] Furthermore, the various numerical ranges described in this specification can be any combination of their upper and lower limits, and all such combinations are described herein as preferred numerical ranges. Also, the description of a numerical range as "X~Y" means X or greater and Y or less.

Claims

1. A rubber composition containing rubber components and a naturally derived wax with an acid value of 50 mgKOH / g or more.

2. The rubber composition according to claim 1, which does not contain petroleum-derived wax.

3. The rubber composition according to claim 1, wherein the content of the naturally derived wax is 0.5 to 7.0 parts by mass per 100 parts by mass of the rubber component.

4. The rubber composition according to claim 1, wherein the natural wax includes a plant-derived wax.

5. A tire having a rubber portion made using the rubber composition described in any one of claims 1 to 4.

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