Rubber composition and tires

Abstract

This disclosure provides a rubber composition that achieves both toughness and processability. [Solution] The rubber composition of this disclosure contains a rubber component and polypropylene, wherein the rubber component contains 30 parts by mass or more of natural rubber per 100 parts by mass of the rubber component, and the polypropylene is characterized in that its melt viscosity measured at 170°C is 50 mPa·s or more and 10,000 mPa·s or less, and its melting point measured by differential scanning calorimeter is 90°C or more and 140°C or less. Preferably, the weight-average molecular weight of the polypropylene is 3,000 or more and less than 30,000.

Description

[Technical Field]

[0001] This disclosure relates to rubber compositions and tires. [Background technology]

[0002] Due to the demand for preventing aging and discoloration of tires, such as pneumatic tires, various improvements have been made to the rubber compositions used as tread materials.

[0003] For example, Patent Document 1 discloses a rubber composition comprising (a) at least one rubber component selected from the group consisting of natural rubber, isoprene rubber, butadiene rubber, and styrene-butadiene rubber, and (b) a polyolefin wax having a melting point measured by differential scanning calorimeter (DSC) in the range of 60 to 100°C and a number-average molecular weight (Mn) measured by gel permeation chromatography (GPC) in the range of 400 to 5,000, characterized in that the polyolefin wax (b) is contained in a ratio of 0.1 to 10 parts by weight per 100 parts by weight of the rubber component.

[0004] Furthermore, Patent Document 2 describes a diene-based rubber containing natural rubber and polybutadiene rubber, in which polybutadiene rubber accounts for 30 parts by mass or more. In this diene-based rubber, 0.5 to 20 parts by mass of thermally expandable microcapsules are added per 100 parts by mass, and the density measured according to JIS K7112 is 0.85 to 0.96 g / cm³. 3 The present invention discloses a rubber composition for tires characterized by containing 0.5 to 10 parts by mass of polyethylene wax having a weight-average molecular weight of 1,000 to 20,000 and a modifying group in its side chain. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2003-292684 [Patent Document 2] Japanese Patent Publication No. 2019-172817 [Overview of the project] [Problems that the invention aims to solve]

[0006] In addition to the above requirements, there is a need to improve the toughness of rubber compositions, such as those that can be used in tires, specifically in the treads of pneumatic tires. However, there is a problem in that improving the toughness of a rubber composition may result in insufficient processability of the rubber composition.

[0007] The purpose of this disclosure is to provide a rubber composition that achieves both toughness and processability. [Means for solving the problem]

[0008] The Disclosing Party has found that the above problem can be achieved by the following means: It contains rubber components and polypropylene. The aforementioned rubber component contains 30 parts by mass or more of natural rubber per 100 parts by mass of the aforementioned rubber component. The polypropylene has a melt viscosity measured at 170°C of 50 mPa·s or more and 10,000 mPa·s or less, and a melting point measured by differential scanning calorimeter of 90°C or more and 140°C or less. A rubber composition characterized by the following features. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide a rubber composition that achieves both toughness and processability. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure will be described in detail below. However, this disclosure is not limited to the embodiments described below, and can be implemented in various modified forms within the scope of the essence of the disclosure.

[0011] 1. Rubber composition The rubber composition of this disclosure contains a rubber component and polypropylene. Here, the rubber component contains 30 parts by mass or more of natural rubber per 100 parts by mass of the rubber component. The polypropylene has a melt viscosity of 50 mPa·s to 10,000 mPa·s measured at 170°C, and a melting point of 90°C to 140°C measured by differential scanning calorimeter.

[0012] While not limited by principle, the principle by which the rubber composition of this disclosure can achieve both toughness and processability is as follows:

[0013] The inventors have found that by using a specific polypropylene as the resin component in a rubber composition containing natural rubber, the toughness of the rubber composition can be improved. However, depending on the type of polypropylene, the Mooney viscosity of the rubber composition may also increase along with the improvement in toughness. An increase in the Mooney viscosity of the rubber composition leads to a decrease in the processability of the rubber composition.

[0014] The inventors have found that by using polypropylene having a melt viscosity of 50 mPa·s to 10,000 mPa·s measured at 170°C and a melting point of 90°C to 140°C measured by a differential scanning calorimeter, it is possible to improve the toughness of a rubber composition while suppressing the increase in Mooney viscosity.

[0015] The rubber composition disclosed herein is suitable for use as a tire component due to its excellent toughness. In particular, it is suitable for heavy-duty tires (truck and bus tires) that are subject to high loads and severe conditions, and is especially suitable for use as a tread, which is a component that comes into contact with the ground and is subject to wear and chipping.

[0016] 1-1. Rubber components The rubber component used in the rubber composition of the present invention contains 30 parts by mass or more of natural rubber (NR) when the total amount is 100 parts by mass.

[0017] When the total amount of the rubber component is 100 parts by mass, it contains 30 parts by mass or more of natural rubber, more preferably 40 parts by mass or more, and even more preferably 50 parts by mass or more. The rubber component may consist only of natural rubber. When the proportion of natural rubber in the rubber component is high, the dispersion state of polypropylene is made uniform, and it becomes easier to exhibit strength.

[0018] As the natural rubber, natural rubber standardized by the Green Book (International Quality Packaging Standard for Various Grades of Natural Rubber) can be used.

[0019] The rubber component can contain rubbers other than natural rubber. Such rubbers are preferably, for example, synthetic isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), or acrylonitrile-butadiene copolymer rubber (NBR). Among them, from the viewpoint of improving the effects of the present invention, a combined system of NR and BR is preferable.

[0020] 1-2. Polypropylene In the present disclosure, polypropylene means a polymer in which the proportion of propylene monomer in the whole polymer is 90 mol% or more.

[0021] Polypropylene can contain at least one of a homopolymer of propylene monomer, a copolymer composed of propylene monomer, ethylene monomer, and 1-butene monomer, or a copolymer composed of propylene monomer and ethylene monomer. Polypropylene may be a random copolymer. Examples of the copolymer of polypropylene include a propylene-ethylene-1-butene random copolymer, a propylene-ethylene random copolymer, and a propylene-ethylene block copolymer. Polypropylene may consist only of a homopolymer of propylene monomer.

[0022] When polypropylene is a copolymer, the proportion of monomers other than propylene monomer to the total polymer may be greater than 0 mol% of 10 mol% or less, greater than 0 mol% of 8 mol% or less, greater than 0 mol% of 6 mol% or less, greater than 0 mol% of 4 mol% or less, or greater than 0 mol% of 2 mol% or less.

[0023] Polypropylene has a melt viscosity of 50 mPa·s to 10,000 mPa·s, measured at 170°C. Melt viscosity can be measured in accordance with JIS K 6862:1984.

[0024] If the melt viscosity measured at 170°C is greater than 10,000 mPa·s, the Mooney viscosity will be high. High Mooney viscosity reduces the processability of the rubber composition. The melt viscosity is between 50 mPa·s and 10,000 mPa·s, more preferably between 1,000 mPa·s and 10,000 mPa·s, and even more preferably between 3,000 mPa·s and 10,000 mPa·s. If the melt viscosity is too low, when mixing with the rubber component, the viscosity difference between the rubber and polypropylene will be large, making it difficult for the rubber to incorporate the polypropylene.

[0025] Polypropylene has a melting point of 90°C to 140°C as measured by differential scanning calorimeter. The melting point can be measured using differential scanning calorimeter in accordance with JIS K 7121:1987.

[0026] If the melting point of polypropylene is higher than 140°C, it becomes necessary to operate manufacturing equipment at high temperatures in industrial production, increasing the difficulty of manufacturing. On the other hand, if the melting point of polypropylene is lower than 90°C, the rubber composition will lack heat resistance as a product.

[0027] The melting point of polypropylene is preferably 90°C or higher and less than 140°C. More preferably 90°C or higher and 130°C or lower, and even more preferably 95°C or higher and 125°C or lower. If the melting point is too high, it is likely to remain undissolved during mixing, resulting in insufficient dispersion of polypropylene, poor elongation at break, and restrictions on mixing conditions such as having to set a high mixing temperature, which is undesirable.

[0028] The weight-average molecular weight of polypropylene is preferably 3,000 or more and less than 30,000, more preferably 10,000 or more and less than 30,000, and even more preferably 20,000 or more and less than 30,000.

[0029] The rubber composition preferably contains 1 to 60 parts by mass of polypropylene per 100 parts by mass of rubber component, more preferably 3 to 50 parts by mass, and even more preferably 5 to 40 parts by mass.

[0030] When the polypropylene content is within this range, the toughness of the rubber composition is particularly high, and the increase in Mooney viscosity can be particularly suppressed.

[0031] 1-3. Other ingredients The rubber composition of this disclosure may optionally contain other components, such as vulcanizing or crosslinking agents; vulcanizing or crosslinking accelerators; various fillers such as carbon black, silica, clay, talc, calcium carbonate, and aluminum hydroxide; antioxidants; plasticizers; resins; curing agents; silane coupling agents; and processing aids, which are commonly used in rubber compositions.

[0032] These additives can be mixed in a conventional manner to form a composition which can then be used for vulcanization or crosslinking. The amounts of these additives used can also be conventional amounts, as long as they do not contradict the purpose of the present invention.

[0033] From the viewpoint of improving the effects of the present invention, the rubber composition of this disclosure preferably contains carbon black and / or silica as a filler.

[0034] When using carbon black, from the viewpoint of improving the effect of the present invention, the nitrogen adsorption specific surface area (N2SA) should be 20-300 m². 2 It is preferable that the value be / g, and 40-150m 2 It is even more preferable that the nitrogen adsorption specific surface area (N2SA) of carbon black is 60-120 m².2 The value may be expressed as / g. Note that the nitrogen adsorption specific surface area (N2SA) is the value obtained in accordance with JIS K6217-2.

[0035] When using silica, from the viewpoint of improving the effect of the present invention, a nitrogen adsorption specific surface area (N2SA) of 20 to 300 m² is desirable. 2 It is preferable that the value be / g, and 80-250m 2 It is even more preferable that the nitrogen adsorption specific surface area (N2SA) of silica is 60-120 m². 2 / g is acceptable.

[0036] The rubber composition of this disclosure preferably contains 5 to 150 parts by mass of filler per 100 parts by mass of rubber component. The filler content is more preferably 5 to 150 parts by mass, even more preferably 10 to 110 parts by mass, and even more preferably 30 to 100 parts by mass per 100 parts by mass of rubber component.

[0037] 1-4. Manufacturing method The rubber composition of this disclosure can be produced by kneading a rubber component with polypropylene, and optionally mixing sulfur and a vulcanization accelerator into the kneaded mixture. The kneading of the rubber component with polypropylene can be carried out using a mixer, such as a Banbury mixer. The kneading temperature may be, for example, 60°C to 180°C. The kneading time may be 1 minute to 5 hours. The crosslinking agent and vulcanization accelerator can be mixed into the kneaded mixture, for example, by rolling.

[0038] 2. Tires The tire of this disclosure is a tire in which at least a portion of its constituent members is the rubber composition of this disclosure. The tire of this disclosure may be a pneumatic tire.

[0039] The tire of the present disclosure preferably has all or at least a part of the tread constituted by the rubber composition of the present disclosure. Generally, since the tread is a member that comes into contact with the ground and involves wear and chipping among the constituent members of the tire, the rubber composition of the present disclosure has high toughness, and thus the durability of the tire can be improved by using it for the tread. On the other hand, since the rubber composition of the present disclosure also has excellent processability, the production efficiency of the tire is good.

[0040] The tire of the present disclosure has high benefits of its effects when it is a heavy-duty tire (truck and bus tire) with high load and high severity.

Examples

[0041] 3. Examples 1 to 12 and Comparative Examples 1 to 3 3-1. Raw materials 3-1-1. Enumeration of raw materials The following raw materials were used in the amounts described in Tables 1 and 2 shown in "2-5. Results" below to prepare samples of Examples 1 to 12 and Comparative Examples 1 to 3: Natural rubber (NR): SIR20 Butadiene rubber (BR): Nipol BR1220 manufactured by Zeon Corporation, number average molecular weight = 1.8×10 5 Silica: ULTRASIL VN3GR manufactured by Evonik, nitrogen adsorption specific surface area (N2SA) = 177m 2 / g, CTAB specific surface area = 166m 2 / g) Carbon black (CB): Showblack N234, trade name, manufactured by Cabot Japan, nitrogen adsorption specific surface area (N2SA) = 114m 2 / g) Silane coupling agent: Si69, bis(3-triethoxysilylpropyl)tetrasulfide) manufactured by Evonik Degussa Zinc oxide: Three types of zinc oxide manufactured by Shoei Chemical Industry Co., Ltd. Stearic acid: YR Stearic acid manufactured by NOF Corporation Antioxidant: SANTOFLEX 6PPD manufactured by Flexsys Wax: OZOACE-0015A manufactured by Nippon Seiro Co., Ltd. Oil: Showa Shell Sekiyu Co., Ltd. Extract No. 4S Sulfur: Oil-treated sulfur manufactured by Karuizawa Smelting Co., Ltd. Vulcanization accelerator 1NS: Sanshin Chemical Industry Co., Ltd., Sunceller NS-G Vulcanization accelerator 2D: Noxellar D, manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Polyethylene wax (PE wax): Manufactured by Clariant Chemicals Co., Ltd. LICOWAX PE 190 Polypropylene for molding (PP for molding): Prime Polypropylene J106G Polypropylene Wax 1 (PP Wax 1): Manufactured by Clariant Chemicals Co., Ltd. LICOCENE PP 6502 Polypropylene Wax 2 (PP Wax 2): Manufactured by Clariant Chemicals Co., Ltd. LICOCENE PP 6102 Polypropylene Wax 3 (PP Wax 3): Manufactured by Clariant Chemicals Co., Ltd. LICOCENE PP 3602

[0042] 3-1-2. Measurement of physical properties of PP wax and PE wax, etc. (1) Melt viscosity In accordance with JIS K 6862:1984, the melt viscosity of polypropylene wax (PP wax) and polyethylene wax (PE wax) was measured at a test temperature of 170°C (140°C for polyethylene wax). The measurement results are shown in Tables 1 and 2 below in "2-5. Results".

[0043] (2) Melting point measured by differential scanning calorimeter In accordance with JIS K 7121:1987, the melting points (Tm) of PP wax and PE wax were measured using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min. The melting point was defined as the temperature at the peak of the melting. The measurement results are shown in Tables 1 and 2 in "2-5. Results" below.

[0044] 3-2. Sample preparation (1) Mixing of rubber composition The components of the materials listed in Tables 1 and 2, shown in "2-5. Results" below, excluding sulfur and the vulcanization accelerator, were mixed in a Banbury mixer at 80°C for 5 minutes. The temperature reached during mixing was 150°C. Next, the sulfur and vulcanization accelerator were mixed using a roll to obtain the rubber compositions for each example. For Comparative Example 3, the mixing conditions were adjusted so that the temperature reached exceeded the melting point of the resin.

[0045] (2) Preparation of vulcanized rubber sheets for evaluation Each of the obtained rubber compositions (unvulcanized) was press-vulcanized using a mold (15 cm × 15 cm × 2 mm) at 148°C for 30 minutes to obtain the vulcanized rubber sheets for each example.

[0046] 3-3. Measurement of Mooney viscosity For each example of rubber composition, i.e., the unvulcanized rubber for each example, the viscosity was measured using a Mooney viscometer with an L-type rotor (38.1 mm diameter, 5.5 mm thickness) in accordance with JIS K 6300-1:2013, under the conditions of a preheating time of 1 minute, rotor rotation time of 4 minutes, 100°C, and 2 rpm.

[0047] The results obtained are expressed as relative values ​​with the Mooney viscosity of Comparative Example 1 set to 100, and are shown in Tables 1 and 2 below in "2-5. Results". A smaller relative value indicates lower viscosity and superior moldability.

[0048] 3-4. Measurement of fracture strength For each example of vulcanized rubber sheet, a JIS No. 3 dumbbell test specimen (2 mm thick) was punched out in accordance with JIS K 6251:2023, and the breaking strength [MPa] was measured at room temperature at a tensile speed of 500 mm / min. The obtained results are shown in the breaking strength column as relative values, with the breaking strength of Comparative Example 1 set to 100. A larger relative value indicates higher breaking strength and superior toughening effect.

[0049] 3-5.Results The materials and results for Examples 1-5 and Comparative Examples 1-3 are shown in Table 1. The materials and results for Examples 6-12 are shown in Table 2.

[0050] In Tables 1 and 2, under "Materials," "NR" stands for "Natural Rubber," "BR" for "Butadiene Rubber," "CB" for "Carbon Black," "PE Wax" for "Polyethylene Wax," "PP for Molding" for "Polypropylene for Molding," and "PP Wax" for "Polypropylene Wax."

[0051] Furthermore, in the "Results" section of Tables 1 and 2, both "Strength" and "Processability" are listed as relative values ​​with the measured value in Comparative Example 1 set to 100.

[0052] [Table 1]

[0053] [Table 2]

[0054] This disclosure includes the following aspects: 《Aspect 1》 It contains rubber components and polypropylene. The aforementioned rubber component contains 30 parts by mass or more of natural rubber per 100 parts by mass of the aforementioned rubber component. The polypropylene has a melt viscosity measured at 170°C of 50 mPa·s or more and 10,000 mPa·s or less, and a melting point measured by differential scanning calorimeter of 90°C or more and 140°C or less. A rubber composition characterized by the following features. 《Aspect 2》 The rubber composition according to embodiment 1, characterized in that the weight-average molecular weight of the polypropylene is 3,000 or more and less than 30,000. 《Aspect 3》 The rubber composition according to embodiment 1 or 2, characterized in that the polypropylene contains at least one of a homopolymer of propylene monomer, a copolymer composed of propylene monomer, ethylene monomer, and 1-butene monomer, or a copolymer composed of propylene monomer and ethylene monomer. Appearance 4 The rubber composition according to any one of embodiments 1 to 3, characterized in that it contains 1 to 60 parts by mass of the polypropylene per 100 parts by mass of the rubber component. Appearance 5 The rubber composition according to any one of embodiments 1 to 4, characterized in that it contains 10 to 60 parts by mass of the polypropylene per 100 parts by mass of the rubber component. 《Aspect 6》 The rubber composition according to any one of embodiments 1 to 5, characterized in that it contains 5 parts by mass or more and 150 parts by mass of a filler per 100 parts by mass of the rubber component. Appearance 7 A tire using the rubber composition described in any one of embodiments 1 to 6 for the tread.

Claims

1. It contains rubber components and polypropylene. The aforementioned rubber component contains 30 parts by mass or more of natural rubber per 100 parts by mass of the aforementioned rubber component. The aforementioned polypropylene has a melt viscosity of 50 mPa·s or more and 10,000 mPa·s or less, measured at 170°C, and a melting point of 90°C or more and 140°C or less, measured by a differential scanning calorimeter. A rubber composition characterized by the following features.

2. The rubber composition according to claim 1, characterized in that the weight-average molecular weight of the polypropylene is 3,000 or more and less than 30,000.

3. The rubber composition according to claim 1, characterized in that the polypropylene comprises at least one of a homopolymer of propylene monomer, a copolymer composed of propylene monomer, ethylene monomer, and 1-butene monomer, or a copolymer composed of propylene monomer and ethylene monomer.

4. The rubber composition according to claim 1, characterized in that it contains 1 to 60 parts by mass of the polypropylene per 100 parts by mass of the rubber component.

5. The rubber composition according to claim 1, characterized in that it contains 10 to 60 parts by mass of the polypropylene per 100 parts by mass of the rubber component.

6. The rubber composition according to claim 1, characterized in that it contains 5 to 150 parts by mass of a filler per 100 parts by mass of the rubber component.

7. A tire using the rubber composition described in any one of claims 1 to 6 for the tread.

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