Rubber composition for pneumatic tire, vulcanized rubber and pneumatic tire

Abstract

To provide a rubber composition for a pneumatic tire which serves as a raw material for a vulcanized rubber having excellent rubber strength, especially for a vulcanized rubber useful as a rubber part for a pneumatic tire.SOLUTION: There is provided a rubber composition for a pneumatic tire which comprises a rubber component containing a diene-based rubber and a modified diene-based rubber, carbon black and a sulfonic acid-modified cellulose nanofiber. When the total amount of the rubber component is defined as 100 pts.mass, the rubber composition preferably contains 0.1 to 50 pts.mass of the cellulose nanofiber, preferably contains 1 to 80 pts.mass of carbon black and preferably contains 1 to 100 pts.mass of the modified diene-based rubber. In addition, the modified diene-based rubber preferably is a diene-based rubber having a polar group.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a rubber composition for a pneumatic tire, a vulcanized rubber, and a pneumatic tire including the vulcanized rubber as a rubber portion. [Background technology]

[0002] In general, in order to improve the durability of a pneumatic tire, there is a method of increasing the rubber strength of the rubber portion constituting the pneumatic tire. One method of increasing the rubber strength is to increase the amount of filler such as carbon black or silica, but this tends to reduce the elongation of the rubber constituting the pneumatic tire, thereby deteriorating the durability.

[0003] Patent Document 1 listed below describes a rubber composition containing a rubber component and fibrous cellulose, in which the amount of substituents introduced into the fibrous cellulose is less than 0.5 mmol / g, and the number average fiber width of the fibrous cellulose contained in the rubber composition is 1 to 100 nm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-191841 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above Patent Document 1, since the object is to provide a rubber composition that can be used to mold a rubber molded body having excellent design properties and suppressed coloring, carbon black that would turn the rubber molded body into a solid black color is not blended into the rubber composition, and furthermore, no consideration is given to a molded body that exhibits rubber strength suitable for use in pneumatic tires.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a rubber composition for pneumatic tires, which is a raw material for vulcanized rubber having excellent rubber strength, particularly vulcanized rubber useful for the rubber portion of pneumatic tires. [Means for solving the problem]

[0007] The above problems can be solved by the following configuration: That is, the present invention relates to a rubber composition (1) for a pneumatic tire, which comprises a rubber component containing a diene rubber and a modified diene rubber, carbon black, and phosphoric acid-modified cellulose nanofiber.

[0008] In the rubber composition for pneumatic tires (1), the rubber composition for pneumatic tires preferably contains 0.1 to 50 parts by mass of the cellulose nanofibers when the total amount of the rubber components is taken as 100 parts by mass.

[0009] In the rubber composition for pneumatic tires (1) or (2), the rubber composition for pneumatic tires preferably contains 1 to 80 parts by mass of the carbon black when the total amount of the rubber components is taken as 100 parts by mass.

[0010] In any one of the rubber compositions for pneumatic tires (1) to (3), a rubber composition for pneumatic tires (4) is preferred, which contains 1 to 100 parts by mass of the modified diene rubber when the total amount of the rubber components is taken as 100 parts by mass.

[0011] In any one of the rubber compositions for pneumatic tires (1) to (4), the modified diene rubber is preferably a rubber composition for pneumatic tires (5) that is a diene rubber having a polar group.

[0012] In the above-mentioned rubber composition for pneumatic tires (5), the modified diene rubber is preferably a diene rubber modified with an epoxy group, or a diene rubber obtained by graft polymerizing a vinyl compound having a polar group onto a diene rubber, which is a rubber composition for pneumatic tires (6).

[0013] The present invention also relates to a vulcanized rubber (7) obtained by vulcanizing any one of the rubber compositions for pneumatic tires (1) to (6).

[0014] The present invention further relates to a pneumatic tire (8) having a rubber portion made of vulcanized rubber (7). Effect of the Invention

[0015] The rubber composition for pneumatic tires according to the present invention contains carbon black and phosphoric acid-modified cellulose nanofibers in a diene rubber. It is difficult to disperse cellulose nanofibers in a diene rubber due to the strong cohesive force of the cellulose nanofibers, but in the present invention, the dispersibility of the cellulose nanofibers in the diene rubber is improved by using phosphoric acid-modified cellulose nanofibers and blending a modified diene rubber as a dispersion aid. As a result, the vulcanized rubber of the rubber composition for pneumatic tires according to the present invention has excellent rubber strength and is therefore particularly useful as the rubber portion of a pneumatic tire. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The rubber composition for a pneumatic tire according to the present invention contains a rubber component containing a diene rubber and a modified diene rubber, carbon black, and phosphoric acid-modified cellulose nanofibers.

[0017] Examples of diene rubbers include natural rubber (NR), polyisoprene rubber (IR), polybutadiene (BR), polystyrene butadiene rubber (SBR), chloroprene rubber (CR), and nitrile rubber (NBR). Modified diene rubbers may also be used. Examples of modified diene rubbers include diene rubbers having polar groups, and examples of polar groups include (meth)acrylic groups and epoxy groups.

[0018] The modified diene rubber may be a diene rubber having a polar group, specifically a diene rubber modified with an epoxy group, or a diene rubber in which a vinyl compound having a polar group is graft-polymerized onto the diene rubber. Examples of the vinyl compound having a polar group include methyl acrylate and methyl methacrylate. The rubber composition for pneumatic tires according to the present invention preferably contains 1 to 100 parts by mass, and more preferably 1 to 20 parts by mass of the modified diene rubber when the total amount of the rubber component is taken as 100 parts by mass.

[0019] The carbon black may be, for example, SAF, ISAF, HAF, FEF, GPF, or other carbon black generally used in the rubber industry, or conductive carbon black such as acetylene black or ketjen black. The rubber composition for pneumatic tires according to the present invention preferably contains 1 to 80 parts by mass, and more preferably 30 to 60 parts by mass, of carbon black per 100 parts by mass of diene rubber.

[0020] The phosphoric acid-modified cellulose nanofiber is a fibrous cellulose in which a phosphoric acid group is introduced as a substituent, and for example, the phosphoric acid-modified cellulose nanofiber described in JP 2021-191841 A can be used. From the viewpoint of improving the dispersibility of the phosphoric acid-modified cellulose nanofiber in the diene rubber and improving the rubber strength of the finally obtained vulcanized rubber, the average fiber diameter of the phosphoric acid-modified cellulose nanofiber is preferably 0.1 to 100 nm, and the average fiber length is preferably 0.1 to 1000 μm. The content of the phosphoric acid-modified cellulose nanofiber in the rubber composition for pneumatic tires is preferably 0.1 to 50 parts by mass, and more preferably 0.5 to 10 parts by mass, when the total amount of the diene rubber is 100 parts by mass.

[0021] The rubber composition for a pneumatic tire according to the present invention can contain, in addition to a rubber component containing a diene rubber and a modified diene rubber, carbon black, and phosphoric acid-modified cellulose nanofiber, a filler such as silica can be blended therein.

[0022] As the silica, wet silica, dry silica, sol-gel silica, surface-treated silica, etc., which are generally used for rubber reinforcement, are used. Among them, wet silica is preferred. The amount of silica blended in the rubber composition for tire tread according to the present invention is preferably about the same as that of the carbon black.

[0023] When silica is blended, it is preferable to use a silane coupling agent in combination. The silane coupling agent is not particularly limited as long as it contains sulfur in the molecule, and various silane coupling agents that are blended together with silica in rubber compositions can be used. Examples of the silanes include sulfide silanes such as bis(3-triethoxysilylpropyl)tetrasulfide (e.g., "Si69" manufactured by Degussa), bis(3-triethoxysilylpropyl)disulfide (e.g., "Si75" manufactured by Degussa), bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, and bis(2-trimethoxysilylethyl)disulfide; mercaptosilanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, mercaptopropylmethyldimethoxysilane, mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane; and protected mercaptosilanes such as 3-octanoylthio-1-propyltriethoxysilane and 3-propionylthiopropyltrimethoxysilane.

[0024] The rubber composition for pneumatic tires according to the present invention can contain, in addition to a rubber component containing a diene rubber and a modified diene rubber, carbon black, and phosphoric acid-modified cellulose nanofiber, vulcanization compounding agents, antioxidants, zinc oxide, stearic acid, softeners such as wax and oil, processing aids, and the like.

[0025] Examples of vulcanization compounding agents include vulcanizing agents such as sulfur and organic peroxides, vulcanization accelerators, vulcanization acceleration assistants, and vulcanization retarders.

[0026] The sulfur used as the vulcanization compounding agent may be any ordinary rubber sulfur, such as powdered sulfur, precipitated sulfur, insoluble sulfur, highly dispersible sulfur, etc.

[0027] As the vulcanization accelerator, those vulcanization accelerators usually used for rubber vulcanization, such as 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 alone or in appropriate mixtures.

[0028] As the age resistor, age resistors generally used for rubber, such as aromatic amine-based age resistors, amine-ketone-based age resistors, monophenol-based age resistors, bisphenol-based age resistors, polyphenol-based age resistors, dithiocarbamate-based age resistors, and thiourea-based age resistors, may be used alone or in appropriate mixtures.

[0029] The rubber composition for pneumatic tires according to the present invention is obtained by kneading a rubber component containing a diene rubber and a modified diene rubber, carbon black, and phosphoric acid-modified cellulose nanofiber, vulcanization compounding agents, antioxidants, zinc oxide, stearic acid, softeners such as wax and oil, processing aids, and the like, using a kneading machine typically used in the rubber industry, such as a Banbury mixer, a kneader, or a roll.

[0030] The method for compounding each of the above components is not particularly limited, and may be any of a method in which the compounding components other than the vulcanization compounding agents such as the sulfur-based vulcanizing agent and the vulcanization accelerator are previously mixed to prepare a master batch, and the remaining components are added and further kneaded, a method in which the components are added in any order and kneaded, and a method in which all the components are added simultaneously and kneaded.

[0031] The vulcanized rubber of the rubber composition for a pneumatic tire according to the present invention has particularly excellent rubber strength, and therefore a pneumatic tire having a tread or sidewall constituted by a rubber portion formed by vulcanizing the rubber composition for a pneumatic tire according to the present invention has particularly excellent durability. EXAMPLES

[0032] Examples specifically illustrating the configuration and effects of the present invention will be described below. The evaluation items in the examples were evaluated according to the following evaluation conditions for the rubber samples obtained by heating and vulcanizing each rubber composition at 150°C for 25 minutes.

[0033] (1) Stress at 100% elongation Samples were prepared using JIS No. 3 dumbbells, and the stress (modulus M100 (MPa)) of the obtained vulcanized rubber at 100% elongation was measured in accordance with JIS K6251. The evaluation was expressed as an index evaluation with the measured value of Comparative Example 1 set to 100 for Examples 1 to 4, and the measured value of Comparative Example 3 set to 100 for Examples 5 to 8. A larger value means a larger stress at 100% elongation, which means better performance.

[0034] (2) Breaking strength The breaking strength was measured by a tensile test (dumbbell-shaped No. 3) in accordance with JIS K6251. The evaluation was expressed as an index evaluation for Examples 1 to 4, with the measured value for Comparative Example 1 being set at 100, and for Examples 5 to 8, with the measured value for Comparative Example 3 being set at 100. A larger value means a higher and more favorable breaking strength.

[0035] (Preparation of Rubber Composition) According to the compounding recipes in Tables 1 and 2, the rubber compositions of Examples 1 to 8 and Comparative Examples 1 to 4 were compounded and kneaded using a normal Banbury mixer to prepare rubber compositions. Each compounding ingredient listed in Tables 1 and 2 is shown below (in Tables 1 and 2, the compounding amount of each compounding ingredient is shown in parts by mass relative to 100 parts by mass of the rubber component). a) Natural rubber (NR): Product name "RSS#3" b) Modified diene rubber Modified natural rubber in which acrylic resin (PMMA) is graft-polymerized onto natural rubber: Product name "MGNR", manufactured by Muang Mai Guthrie Public Company Limited Natural rubber with an epoxidation rate of 25 mol% (modified natural rubber): Product name "ENR25", manufactured by Muang Mai Guthrie Public Company Limited Natural rubber with an epoxidation rate of 50 mol% (modified natural rubber): Product name "ENR50", manufactured by Muang Mai Guthrie Public Company Limited c) Carbon black: Product name "N339 Seast KH", manufactured by Tokai Carbon Co., Ltd. d) Phosphoric acid-modified cellulose nanofiber: Product name "Cellulose nanofiber, natural rubber mixture", manufactured by Oji Holdings Co., Ltd. d) Zinc oxide: Product name "Zinc oxide type 1", manufactured by Mitsui Mining & Smelting Co., Ltd. e) Stearic acid: Trade name "Lunac S-20", manufactured by Kao Corporation f) Sulfur: Product name "Powdered sulfur for rubber 150 mesh", manufactured by Hosoi Chemical Industry Co., Ltd. g) Vulcanization accelerator: Trade name "Noccela CZ", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0036] [Table 1]

[0037] From the results in Table 1, it can be seen that the rubber compositions of Examples 1 to 4 have excellent dispersibility of cellulose nanofibers due to the dispersing effect of MGNR, which is a modified diene rubber, and fully exert the reinforcing effect, resulting in an improved modulus of the vulcanized rubber.

[0038] The dispersibility and aggregate size of the cellulose nanofibers of the rubber compositions according to Examples 1 to 4 and the rubber composition according to Comparative Example 2 were measured by a scanning electron microscope ("SU3500" manufactured by Hitachi High-Technologies Corporation). In the vulcanized rubber of the rubber composition according to Examples 1 to 3, the aggregate size of the cellulose nanofibers was 110 μm or less, and in the vulcanized rubber of the rubber composition according to Example 4, the aggregate size of the cellulose nanofibers was 80 μm or less. On the other hand, in the vulcanized rubber of the rubber composition according to Comparative Example 2, the aggregate size of the cellulose nanofibers was 300 to 400 μm. From these results, it can be understood that the rubber compositions according to Examples 1 to 4 have excellent dispersibility of the cellulose nanofibers due to the dispersing effect of the modified diene rubber MGNR, and as a result, have excellent reinforcing effect of the cellulose nanofibers.

[0039] [Table 2]

[0040] The results in Table 2 show that the rubber compositions of Examples 5 to 8 have excellent dispersibility of cellulose nanofibers due to the dispersing effect of the modified natural rubbers ENR25 and ENR50, and fully exert their reinforcing effect, resulting in improved modulus of the vulcanized rubber.

[0041] The dispersibility and aggregate size of the cellulose nanofibers of the rubber compositions according to Examples 5 to 8 and the rubber composition according to Comparative Example 2 were measured by a scanning electron microscope ("SU3500" manufactured by Hitachi High-Technologies Corporation). In the vulcanized rubber of the rubber composition according to Example 5, the aggregate size of the cellulose nanofibers was 100 μm or less, in the vulcanized rubber of the rubber composition according to Examples 6 to 7, the aggregate size of the cellulose nanofibers was 90 μm or less, and in the vulcanized rubber of the rubber composition according to Example 8, the aggregate size of the cellulose nanofibers was 50 μm or less. On the other hand, in the vulcanized rubber of the rubber composition according to Comparative Example 2, the aggregate size of the cellulose nanofibers was 300 to 400 μm. From these results, it can be understood that the rubber compositions according to Examples 5 to 8 have excellent dispersibility of the cellulose nanofibers due to the dispersing effect of the modified diene rubber MGNR, and as a result, have excellent reinforcing effect of the cellulose nanofibers.

Claims

1. A rubber composition for pneumatic tires, comprising a rubber component containing a diene rubber and a modified diene rubber, carbon black, and phosphoric acid-modified cellulose nanofiber.

2. The rubber composition for pneumatic tires according to claim 1, wherein the cellulose nanofiber is contained in an amount of 0.1 to 50 parts by mass when the total amount of the rubber component is 100 parts by mass.

3. 2. The rubber composition for pneumatic tires according to claim 1, wherein the carbon black is contained in an amount of 1 to 80 parts by mass when the total amount of the rubber components is taken as 100 parts by mass.

4. 2. The rubber composition for pneumatic tires according to claim 1, wherein the modified diene rubber is contained in an amount of 1 to 100 parts by mass when the total amount of the rubber components is taken as 100 parts by mass.

5. The rubber composition for a pneumatic tire according to claim 1 , wherein the modified diene rubber is a diene rubber having a polar group.

6. 6. The rubber composition for pneumatic tires according to claim 5, wherein the modified diene rubber is a diene rubber modified with an epoxy group, or a diene rubber in which a vinyl compound having a polar group is graft polymerized onto the diene rubber.

7. A vulcanized rubber obtained by vulcanizing the rubber composition for a pneumatic tire according to claim 1 .

8. A pneumatic tire comprising the vulcanized rubber according to claim 7 as a rubber portion.

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