Rubber composition for tires and pneumatic tires

Abstract

To improve tearing resistance, wear resistance and flexural fatigue resistance.SOLUTION: A rubber composition for tires comprises: a diene rubber; a filler; and a fatty acid ester of polyoxyalkylene glyceryl ether, with 50 mass % or more of the filler being carbon black. The fatty acid ester of polyoxyalkylene glyceryl ether preferably has an HLB of 13 or less. There is also provided a tire that contains the rubber composition for tires.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] It is known that a surfactant is blended into a rubber composition for tires. For example, Patent Document 1 discloses that in a rubber composition blended with silica, a novel silane coupling agent is used to improve fuel economy, abrasion resistance, wet performance, and steering stability in a well-balanced manner, and a surfactant such as a polyoxyalkylene derivative is blended to promote dispersion of the filler and prevent discoloration due to deterioration over time.

[0003] Patent Document 2 discloses that in order to obtain excellent fracture resistance, abrasion resistance, and performance on ice, a surfactant such as a nonionic ester-type surfactant is blended into a diene rubber component together with short fibers, and that blending the surfactant improves the dispersibility of the short fibers.

[0004] Patent Document 3 discloses that a monoester and / or diester of a polyoxyalkylene glycerin fatty acid ester is compounded in a rubber composition containing silica in order to improve the processability and abrasion resistance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-151018 A [Patent Document 2] International Publication No. 2017 / 069273 [Patent Document 3] JP 2019-131696 A Summary of the Invention [Problem to be solved by the invention]

[0006] Generally, surfactants are blended into rubber compositions to improve the dispersibility of highly hydrophilic fillers such as silica, but it was not known that their use in blends in which carbon black, which has good dispersibility, is the main filler, would improve performance.

[0007] The present inventors have found that the use of a specific surfactant, a fatty acid ester of polyoxyalkylene glyceryl ether, in a compound containing carbon black as a main filler improves tear resistance, abrasion resistance, and flex fatigue resistance. That is, an object of the present invention is to provide a rubber composition for tires that can improve tear resistance, abrasion resistance, and flex fatigue resistance in a compound containing carbon black as a main filler, and a tire using the same. [Means for solving the problem]

[0008] A rubber composition for a tire according to an embodiment of the present invention contains a diene rubber, a filler, and a fatty acid ester of a polyoxyalkylene glyceryl ether, and 50% by mass or more of the filler is carbon black.

[0009] A tire according to an embodiment of the present invention contains the above-mentioned rubber composition for tires. Effect of the Invention

[0010] According to an embodiment of the present invention, in a rubber composition containing carbon black as a main filler, the tear resistance, abrasion resistance, and flexural fatigue resistance can be improved by compounding the fatty acid ester of the polyoxyalkylene glyceryl ether. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The rubber composition for tires (hereinafter also referred to as rubber composition) according to this embodiment is obtained by blending a diene rubber with a filler and a fatty acid ester of polyoxyalkylene glyceryl ether.

[0012] The diene rubber as the rubber component is not particularly limited, and examples thereof include various diene rubbers that are usually used in rubber compositions, such as natural rubber (NR), synthetic isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, etc. These diene rubbers may be used alone or in combination of two or more.

[0013] The diene rubber according to a preferred embodiment includes at least one selected from the group consisting of natural rubber, butadiene rubber, and styrene-butadiene rubber, and more preferably includes at least natural rubber. For example, 100 parts by mass of the diene rubber may include 60 parts by mass to 100 parts by mass of natural rubber and 0 parts by mass to 40 parts by mass of butadiene rubber.

[0014] In this embodiment, the filler is mainly composed of carbon black. That is, the ratio of carbon black to 100% by mass of the filler is 50% by mass or more. When the ratio of carbon black is 50% by mass or more, excellent improvement effects are obtained in tear resistance, abrasion resistance, and flex fatigue resistance by using it in combination with a fatty acid ester of polyoxyalkylene glyceryl ether. The ratio of carbon black is preferably more than 50% by mass, more preferably 60% by mass or more, and even more preferably 70% by mass or more, and may be 100% by mass.

[0015] The carbon black is not particularly limited, and various known types can be used. For example, SAF grade (N100 series), ISAF grade (N200 series), HAF grade (N300 series), and FEF grade (N500 series) (all ASTM grades) are preferably used. These grades of carbon black can be used alone or in combination of two or more.

[0016] The nitrogen adsorption specific surface area (NSA) (JIS K6217-2) of carbon black is not particularly limited and is, for example, 30 to 200 m 2 / g is also acceptable, and 70 to 150m 2 / g is also acceptable, 100-130m 2 / g is also acceptable.

[0017] The amount of the filler is not particularly limited, and may be 20 to 100 parts by mass, 25 to 80 parts by mass, or 30 to 60 parts by mass, relative to 100 parts by mass of the diene rubber. The amount of the carbon black is not particularly limited as long as it is 50% by mass or more of the total filler, and may be, for example, 15 to 100 parts by mass, 15 to 70 parts by mass, or 20 to 50 parts by mass, relative to 100 parts by mass of the diene rubber.

[0018] The filler may be carbon black alone, or may be silica mixed with carbon black. The amount of silica mixed is not particularly limited, and may be 30 parts by mass or less, 25 parts by mass or less, or 5 to 20 parts by mass, based on 100 parts of diene rubber.

[0019] The rubber composition according to the present embodiment contains a fatty acid ester of polyoxyalkylene glyceryl ether (hereinafter, sometimes referred to as ether ester). By adding the ether ester to the carbon black, the hydrophilic and hydrophobic parts of the ether ester interact with the diene rubber and the carbon black, improving the tear resistance, abrasion resistance, and flex fatigue resistance.

[0020] As the ether ester, one represented by the following general formula (1) is preferably used. [ka]

[0021] In formula (1), R 1 , R 2 and R 3 each independently represents a hydrogen atom or an aliphatic acyl group having 6 to 30 carbon atoms (i.e., -COR where R is an aliphatic hydrocarbon group), R4 , R 5 and R 6 each independently represents an alkylene group having 2 to 4 carbon atoms, and a, b, and c represent the average number of moles of alkylene oxide added.

[0022] R 1 , R 2 and R 3 Regarding the aliphatic hydrocarbon group of the aliphatic acyl group, it may be saturated or unsaturated, and may be linear or branched. 1 , R 2 and R 3 contains an aliphatic acyl group having an unsaturated aliphatic hydrocarbon group, i.e., the ether ester contains an unsaturated fatty acid in its constituent fatty acid, and the content of unsaturated fatty acid in the constituent fatty acid is preferably 50 mol % or more, more preferably 70 mol % or more. The number of carbon atoms in the aliphatic acyl group is more preferably 8 to 25, further preferably 10 to 22, and may be 12 to 20.

[0023] The ether ester is preferably a monoester or diester of polyoxyalkylene glycerin fatty acid ester. For example, in the ether ester represented by formula (1), the monoester is R 1 , R 2 and R 3 The main components of these are those in which one is an aliphatic acyl group and two are hydrogen atoms. Diesters are R 1 , R 2 and R 3 The main component is one in which two of the acyl groups are aliphatic and one is a hydrogen atom. Here, the main component refers to the component with the largest molar ratio.

[0024] The ether ester may have a distribution of esterification degrees. 1 , R 2 and R 3 At least one of the groups can be said to be an aliphatic acyl group. However, when the degree of esterification is distributed in this way, even if it is a monoester, R 1 , R 2and R 3 are all hydrogen atoms, and such embodiments are also included. The average degree of esterification of the ether ester is not particularly limited and may be, for example, 0.5 to 2.5, but since monoesters or diesters are preferred, the average degree of esterification is preferably 0.8 to 2.2, more preferably 0.9 to 2.1, and even more preferably 1.0 to 2.0. Here, the average degree of esterification is the arithmetic average of the number of hydrogen atoms of three hydroxyl groups of the polyoxyalkylene glyceryl ether substituted with aliphatic acyl groups (degree of esterification), that is, the ratio of the number of moles of esterified fatty acid to 1 mole of polyoxyalkylene glyceryl ether, and is a maximum of 3. Here, the average degree of esterification is 13 It is calculated using C-NMR.

[0025] In formula (1), R 4 , R 5 and R 6 R each independently represents an alkylene group having 2 to 4 carbon atoms, and a, b, and c each independently represent the average number of moles of alkylene oxide added. 4 , R 5 and R 6 More preferably, each independently represents an alkylene group having 2 or 3 carbon atoms. 4 , R 5 and R 6 The alkylene group of R may be linear or branched. 4 O, R 5 O and R 6 Examples of the oxyalkylene group represented by O include an oxyethylene group, an oxypropylene group, and an oxybutylene group.

[0026] (R 4 O) a , (R 5 O) b and (R 6 O) care polyoxyalkylene chains obtained by addition polymerization of alkylene oxides having 2 to 4 carbon atoms (e.g., ethylene oxide, propylene oxide, butylene oxide, etc.). The polymerization form of the alkylene oxide, etc. is not particularly limited, and may be a homopolymer, a random copolymer, or a block copolymer.

[0027] (R 4 O) a , (R 5 O) b and (R 6 O) c is preferably composed mainly of oxyethylene groups, (R 4 O) a , (R 5 O) b and (R 6 O) c It is preferable that 60 mass % or more of (R 4 O) a and a polyoxyalkylene chain represented by (R 5 O) b and a polyoxyalkylene chain represented by (R 6 O) c The polyoxyalkylene chain represented by the formula (R) preferably contains 60% by mass or more of oxyethylene groups in total, more preferably 80% by mass or more, and particularly preferably 100% by mass, i.e., consists of only oxyethylene groups as represented by the following general formula (2). 4 O) a , (R 5 O) b and (R 6 O) c Each of these preferably comprises 60 mass % or more of oxyethylene groups.

[0028] [ka] R in Equation (2) 1 , R 2 , R 3 , a, b and c are R in formula (1). 1 , R2 , R 3 , a, b and c.

[0029] Each of a, b, and c, which represent the average number of moles of oxyalkylene groups added, is preferably at least 1. The total of a, b, and c, i.e., a+b+c, is preferably 3 to 60, more preferably 3 to 50, and may be 3 to 30 or 4 to 20.

[0030] The HLB (hydrophilic-lipophilic balance) of the ether ester is preferably 13 or less. below This improves the balance of the interaction between the hydrophobic portion of the compound and the diene rubber and carbon black, thereby enhancing the effect of improving tear resistance, abrasion resistance, and flex fatigue resistance when carbon black is blended. The HLB of the ether ester is preferably 3 to 13, more preferably 5 to 12, and further preferably 7 to 10.

[0031] Here, HLB is a value calculated by the following Griffin's formula, and the larger the value, the higher the proportion of hydrophilic parts in the entire molecule, indicating higher hydrophilicity. HLB = 20 x (molecular weight of hydrophilic part) / (total molecular weight) The molecular weight of the hydrophilic part in the formula is (R 4 O) a , (R 5 O) b and (R 6 O) c is the molecular weight of the polyoxyalkylene chain represented by the formula:

[0032] The amount of the ether ester to be blended is not particularly limited, but is preferably 0.5 to 10 parts by mass, and more preferably 1 to 8 parts by mass, based on 100 parts by mass of the diene rubber.

[0033] In addition to the above components, the rubber composition according to the present embodiment may contain various additives that are generally used in rubber compositions, such as zinc oxide, stearic acid, antioxidants, oils, waxes, vulcanizing agents, and vulcanization accelerators. When silica is used in combination with carbon black as a filler, a silane coupling agent may be added. The amount of the silane coupling agent added is preferably 2 to 20 mass % relative to the amount of silica added.

[0034] As the vulcanizing agent, sulfur is preferably used. The amount of the vulcanizing agent is not particularly limited, but is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, relative to 100 parts by mass of the diene rubber. In addition, as the vulcanization accelerator, for example, various vulcanization accelerators such as sulfenamide-based, thiuram-based, thiazole-based, and guanidine-based vulcanization accelerators can be mentioned, and any one of them can be used alone or in combination of two or more. The amount of the vulcanization accelerator is not particularly limited, but is preferably 0.1 to 7 parts by mass, more preferably 0.5 to 5 parts by mass, relative to 100 parts by mass of the diene rubber.

[0035] The rubber composition according to the present embodiment can be prepared by kneading in a conventional manner using a commonly used mixer such as a Banbury mixer, a kneader, a roll, etc. That is, for example, in the first mixing stage (non-pro kneading step), additives other than the vulcanizing agent and the vulcanization accelerator are added and mixed with the diene rubber together with the filler and the ether ester, and then, in the final mixing stage (pro kneading step), the vulcanizing agent and the vulcanization accelerator are added and mixed to the obtained mixture to prepare an unvulcanized rubber composition.

[0036] The rubber composition according to the present embodiment can be used as a rubber composition for tires. Examples of tires include pneumatic tires for various applications and sizes, such as tires for passenger cars and heavy-duty tires for trucks and buses. A tire according to one embodiment has a rubber portion made of the rubber composition. Examples of application sites of tires include tread rubber and sidewall rubber, and the rubber composition is preferably used as tread rubber.

[0037] The tread rubber of a pneumatic tire may be of a two-layer structure consisting of a cap rubber and a base rubber, or of a single-layer structure in which the two are integrated. In the case of the single-layer structure, the tread rubber may be formed from the above-mentioned rubber composition. In the case of the two-layer structure, the cap rubber may be formed from the above-mentioned rubber composition, and the base rubber may be formed from the above-mentioned rubber composition.

[0038] The method for producing a pneumatic tire is not particularly limited. For example, the rubber composition is extruded into a predetermined shape according to a conventional method, and is combined with other parts to produce an unvulcanized tire (green tire). For example, the rubber composition is used to produce a tread rubber, which is combined with other tire components to produce an unvulcanized tire. Thereafter, a pneumatic tire can be produced by vulcanizing and molding at, for example, 140 to 180°C.

[0039] In addition, the various numerical ranges including the above-mentioned blending amount, carbon number, average degree of esterification, average number of moles added, and HLB can each be arbitrarily combined with their upper and lower limit values, and all such combinations are considered to be preferred numerical ranges and are described in this specification. EXAMPLES

[0040] Examples will be shown below, but the present invention is not limited to these examples.

[0041] [Method for measuring average degree of esterification] The average degree of esterification is 13 The measurements were performed using C-NMR. The measurement conditions were: 13 C, observation frequency: 100.648 MHz, pulse width: 90°C, solvent: CDCl3, concentration: 5 mass%. The following calculation formula was used for the calculation method. Degree of esterification = (peak area of ​​ester carbon appearing at about 173.8 ppm) / (peak area of ​​carbon (I) below appearing at about 78.3 ppm) [ka]

[0042] [Examples 1 to 6, Comparative Example 1] Using a Banbury mixer, according to the formulation (parts by mass) shown in Table 1 below, first, in the first mixing stage, compounding ingredients other than sulfur and vulcanization accelerator were added to the rubber component and kneaded (discharge temperature = 160°C), and then, in the final mixing stage, sulfur and vulcanization accelerator were added to the obtained kneaded product and kneaded (discharge temperature = 90°C) to prepare a rubber composition. The "CB ratio" in Table 1 is the ratio (mass%) of carbon black in the filler. Details of each component in Table 1 are as follows.

[0043] Natural rubber: RSS#3 Carbon black: "Seast 6" (N2SA=119m) manufactured by Tokai Carbon Co., Ltd. 2 / g) Silica: EVONIK Ultrasil VN3 Silane coupling agent: EVONIK "Si69" Zinc oxide: "Zinc oxide type 2" manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: NOF Corp. "Beads stearic acid" Anti-aging agent: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator: Sansera NS-G manufactured by Sanshin Chemical Industry Co., Ltd. Sulfur: Tsurumi Chemical Industry Co., Ltd. "Powdered sulfur"

[0044] Ether ester A: fatty acid ester (monoester) of polyoxyethylene glyceryl ether represented by formula (2). Synthesized in accordance with the method described in

[0040] of JP2019-131696A. a+b+c=5, fatty acyl group: -COC 17 H 33 , average degree of esterification = 1.1, HLB = 8

[0045] Ether ester B: fatty acid ester (monoester) of polyoxyethylene glyceryl ether represented by formula (2). Synthesized in accordance with the method described in

[0041] of JP 2019-131696 A. a+b+c=11.8, fatty acyl group: -COC 17 H 33 , average degree of esterification = 1.2, HLB = 13

[0046] Ether ester C: fatty acid ester (diester) of polyoxyethylene glyceryl ether represented by formula (2). Synthesized in accordance with the method described in

[0043] of JP 2019-131696 A. a+b+c=6, fatty acyl group: -COC 17 H 33 , average degree of esterification = 2.1, HLB = 6

[0047] For each of the rubber compositions obtained, tear resistance, abrasion resistance, and flex fatigue resistance were evaluated using test pieces of a predetermined shape that had been vulcanized at 160° C. for 30 minutes. The evaluation methods were as follows.

[0048] Tear resistance: Tear strength (crescent-shaped test piece) was measured in accordance with JIS K6252, and expressed as an index with the value of Comparative Example 1 taken as 100. A higher value indicates a higher tear strength.

[0049] Abrasion resistance: In accordance with JIS K6264, a Lambourn abrasion tester manufactured by Iwamoto Seisakusho Co., Ltd. was used to measure the abrasion loss under conditions of a slip ratio of 30%, a load of 40N, and a sand drop rate of 20g / min. The reciprocal of the measured value was expressed as an index, with the value of Comparative Example 1 set at 100. A larger value indicates better abrasion resistance.

[0050] Flex fatigue resistance: According to JIS K6260, the time until a 10 mm crack occurs in the test piece is measured, and the time is expressed as an index with the value of Comparative Example 1 being 100. A larger value indicates better flex fatigue resistance.

[0051] [Table 1]

[0052] The results are shown in Table 1. In the formulation in which carbon black was the main filler, Examples 1 to 6 in which ether esters A to C were blended showed improved tear resistance, abrasion resistance, and flex fatigue resistance compared to Comparative Example 1 in which no ether ester was blended.

[0053] [Example 11 and Comparative Example 11] Rubber compositions were prepared in the same manner as in Example 1, according to the formulation (parts by mass) shown in Table 2 below, and the tear resistance, abrasion resistance, and flex fatigue resistance were evaluated. In Table 2, BR is polybutadiene rubber ("BR150L" manufactured by Ube Industries, Ltd.), and the other components are the same as in Table 1. In the evaluation of each of the tear resistance, abrasion resistance, and flex fatigue resistance, the values ​​of Comparative Example 11 were set to 100 instead of Comparative Example 1, and indexes were calculated.

[0054] [Table 2]

[0055] The results are shown in Table 2. Even when the filler was carbon black alone (CB ratio = 100 mass%), Example 11, which contained ether ester, had improved tear resistance, abrasion resistance, and flex fatigue resistance compared to Comparative Example 11, which did not contain any ether ester.

[0056] [Example 21 and Comparative Example 21] Rubber compositions were prepared in the same manner as in Example 1, according to the formulation (parts by mass) shown in Table 3 below, and the tear resistance, abrasion resistance, and flex fatigue resistance were evaluated. The components in Table 3 are the same as those in Tables 1 and 2. In the evaluation of each of the tear resistance, abrasion resistance, and flex fatigue resistance, the values ​​of Comparative Example 21 were set to 100 instead of Comparative Example 1, and indexed.

[0057] [Table 3]

[0058] The results are shown in Table 3. Even when the filler was mainly composed of carbon black and the amount of silica was increased (CB ratio = 52.4 mass%), Example 21, which contained ether ester, had improved tear resistance, abrasion resistance, and flexural fatigue resistance compared to Comparative Example 21, which did not contain the ether ester.

[0059] As described above, by using a fatty acid ester of polyoxyalkylene glyceryl ether in a formulation in which carbon black is the main filler, rather than in a formulation in which silica is the main filler, the unexpected effect of excellent tear resistance, abrasion resistance, and flexural fatigue resistance was obtained.

[0060] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included in the scope and gist of the invention as well as the invention and its equivalents described in the claims.

Claims

1. A rubber composition for tires comprising a diene rubber, a filler, and a fatty acid ester of a polyoxyalkylene glyceryl ether represented by the following general formula (1), wherein 100 mass % of the filler is carbon black: 【Chemistry 1】 In formula (1), R １ , R ２ and R ３ each independently represents a hydrogen atom or an aliphatic acyl group having 6 to 30 carbon atoms; R ４ , R ５ and R ６ each independently represents an alkylene group having 2 to 4 carbon atoms, and a, b, and c represent the average number of moles of alkylene oxide added.

2. 2. The rubber composition for tires according to claim 1, comprising 0.5 to 10 parts by mass of the fatty acid ester of the polyoxyalkylene glyceryl ether per 100 parts by mass of the diene rubber.

3. 3. The rubber composition for tires according to claim 1, wherein the fatty acid ester of the polyoxyalkylene glyceryl ether has an HLB of 3 to 13.

4. A tire comprising the rubber composition for tires according to any one of claims 1 to 3.

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