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 diene-based rubber, carbon black and a sulfonic acid-modified cellulose nanofiber. When the total amount of the diene-based rubber is 100 pts.mass, the rubber composition preferably contains 0.1 to 50 pts.mass of the cellulose nanofiber and preferably contains 1 to 80 pts.mass carbon black. When content of the carbon black is defined as X when the total amount of the diene-based rubber is defined as 100 pts.mass and the content of the cellulose nanofiber is defined as Y, X+Y<80 and 0.05<Y / (X+Y)<0.5 is more preferably satisfied.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 view of the above circumstances, and an object thereof is to provide a vulcanized rubber excellent in rubber strength, particularly a rubber composition for a pneumatic tire that serves as a raw material for a vulcanized rubber useful as a rubber part of a pneumatic tire.

Means for Solving the Problems

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

[0008] In the above rubber composition for a pneumatic tire (1), when the total amount of the diene rubber is 100 parts by mass, a rubber composition for a pneumatic tire (2) containing 0.1 to 50 parts by mass of the cellulose nanofiber is preferable.

[0009] In the above rubber composition for a pneumatic tire (1) or (2), when the total amount of the diene rubber is 100 parts by mass, a rubber composition for a pneumatic tire (3) containing 1 to 80 parts by mass of the carbon black is preferable.

[0010] In any of the above rubber compositions for a pneumatic tire (1) to (3), when the content of the carbon black is X and the content of the cellulose nanofiber is Y when the total amount of the diene rubber is 100 parts by mass, a rubber composition for a pneumatic tire (4) satisfying X + Y < 80 and 0.05 < Y / (X + Y) < 0.5 is preferable.

[0011] The present invention also relates to a vulcanized rubber (5) obtained by vulcanizing and molding any of the rubber compositions for a pneumatic tire (1) to (4).

[0012] Furthermore, the present invention relates to a pneumatic tire (6) including the vulcanized rubber (5) as a rubber part.

Effects of the Invention

[0013] 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 rubber component 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 in combination with carbon black. 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.

[0014] In the rubber composition for pneumatic tires according to the present invention, the use of phosphoric acid-modified cellulose nanofibers provides excellent dispersibility in diene rubber even when used in combination with carbon black, so that even if the total amount of carbon black and cellulose nanofibers is reduced to some extent, the rubber strength of the final vulcanized rubber can be maintained while the rubber elongation can be sufficiently ensured. This makes it possible to improve the tensile product, which is the product of the "tensile strength" and the "elongation rate", of the rubber, which is preferable because it improves durability, particularly when used as the rubber portion of a pneumatic tire. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The rubber composition for a pneumatic tire according to the present invention contains a diene rubber, carbon black, and phosphoric acid-modified cellulose nanofibers.

[0016] 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.

[0017] Carbon black can be used, for example, carbon black used in the normal rubber industry such as SAF, ISAF, HAF, FEF, GPF, etc., and conductive carbon black such as acetylene black and ketjen black. In the rubber composition for pneumatic tires according to the present invention, it is preferable to blend 1 to 80 parts by mass of carbon black, and more preferably 30 to 60 parts by mass, based on 100 parts by mass of the diene rubber.

[0018] The phosphoric acid-modified cellulose nanofibers are those in which a phosphate group is introduced as a substituent into fibrous cellulose, and for example, the phosphoric acid-modified cellulose nanofibers described in JP-A-2021-191841 can be used. From the viewpoint of improving the dispersibility of the phosphoric acid-modified cellulose nanofibers in the diene rubber and finally improving the rubber strength of the vulcanized rubber obtained, the average fiber diameter of the phosphoric acid-modified cellulose nanofibers is preferably 1 to 100 nm, and the average fiber length is preferably 0.1 to 1000 μm. The content of the phosphoric acid-modified cellulose nanofibers 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.

[0019] In the rubber composition for pneumatic tires according to the present invention, by using the phosphoric acid-modified cellulose nanofibers, the dispersibility in the diene rubber is excellent and the reinforcing effect is excellent. Therefore, when used in combination with carbon black, the total blending amount of the fillers (the total blending amount of carbon black and cellulose nanofibers) can be reduced compared to the case of blending carbon black alone, so that the rubber elongation can be sufficiently ensured while maintaining the rubber strength of the final vulcanized rubber. In order to improve the tensile product, which is the product of the "tensile strength" and the "elongation rate" of the rubber, when the content of carbon black is X and the content of cellulose nanofibers is Y based on 100 parts by mass of the total amount of the diene rubber, it is preferable that X + Y < 80 and 0.05 < Y / (X + Y) < 0.5. Regarding X + Y, it is more preferable that X + Y < 40.

[0020] The rubber composition for a pneumatic tire according to the present invention may contain, in addition to the diene rubber, carbon black, and phosphoric acid-modified cellulose nanofibers, a filler such as silica.

[0021] 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.

[0022] 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.

[0023] The rubber composition for pneumatic tires according to the present invention can contain, in addition to diene rubber, carbon black, and phosphoric acid-modified cellulose nanofibers, vulcanization compounding agents, antioxidants, zinc oxide, stearic acid, softeners such as wax and oil, processing aids, and the like.

[0024] Examples of vulcanization compounding agents include vulcanizing agents such as sulfur and organic peroxides, vulcanization accelerators, vulcanization acceleration assistants, and vulcanization retarders.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] The rubber composition for pneumatic tires according to the present invention is obtained by kneading diene rubber, carbon black, 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, kneader, or roll.

[0029] 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.

[0030] 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

[0031] 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.

[0032] (1) Rubber hardness The rubber hardness was evaluated by measuring the rubber hardness of the obtained vulcanized rubber test piece at a temperature of 23° C. using a type A durometer in accordance with JIS K6253. The evaluation was expressed as an index evaluation for Examples 1 to 4 with the measured value of Comparative Example 1 being 100, and for Examples 5 to 7 with the measured value of Comparative Example 2 being 100. A larger value means a higher and better rubber hardness.

[0033] (2) 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 2 set to 100 for Examples 5 to 7. A larger value means a larger stress at 100% elongation, which means better performance.

[0034] (3) Tensile product Tensile strength and elongation at break were measured by a tensile test (dumbbell No. 3) in accordance with JIS K6251, and the product was taken as the tensile product. For the evaluation, Examples 1 to 4 were expressed as an index evaluation with the measured value of Comparative Example 1 set to 100, and for Examples 5 to 7, the measured value of Comparative Example 2 set to 100. A larger value means a larger tensile product and better performance.

[0035] (Preparation of Rubber Composition) According to the compounding recipes in Tables 1 and 2, the rubber compositions of Examples 1 to 7 and Comparative Examples 1 and 2 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) Carbon black: Product name "N339 Seast KH", manufactured by Tokai Carbon Co., Ltd. c) Phosphoric acid-modified cellulose nanofiber: Product name "Cellulose nanofiber, natural rubber mixture", manufactured by Oji Holdings Co., Ltd. d) Zinc oxide: Trade 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] The results in Table 1 show that the rubber compositions of Examples 1 to 4, even though they are made by dry mixing cellulose nanofibers with rubber components and other compounding ingredients, have excellent dispersibility of the cellulose nanofibers and fully exert their reinforcing effect, resulting in an improved modulus of the vulcanized rubber.

[0038] [Table 2]

[0039] From the results in Table 2, it can be seen that the rubber compositions of Examples 5 to 7, which are made by dry mixing cellulose nanofibers with a rubber component and other compounding ingredients, have excellent dispersibility of the cellulose nanofibers and fully exert their reinforcing effect, resulting in an improved modulus of the vulcanized rubber. In addition, it can be seen that the rubber compositions of Examples 5 to 7 have a reduced total amount of filler (total amount of carbon black and cellulose nanofiber), and therefore the tensile product of the vulcanized rubber is also improved.

Claims

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

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 diene rubber 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 diene rubber is taken as 100 parts by mass.

4. 2. The rubber composition for a pneumatic tire according to claim 1, wherein, when the total amount of the diene rubber is taken as 100 parts by mass, a content of the carbon black is X and a content of the cellulose nanofiber is Y, X+Y<80 and 0.05<Y / (X+Y)<0.5 are satisfied.

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

6. A pneumatic tire comprising the vulcanized rubber according to claim 5 as a rubber portion.

Images