JP2009249449A - Rubber composition and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition that exhibits satisfactory durability and rigidity by enhancing dispersibility and reinforcing properties of a reinforcing filler composed of a cellulosic fiber in a rubber component, and its manufacturing method. <P>SOLUTION: The rubber composition comprises a cellulose nanofiber in the rubber compound, where the cellulose fiber is featured in that a part or the whole of -OH groups thereof are masked with a masking agent in order to inhibit hydrogen bonding of the -OH groups, that the cellulose nanofiber has an average fiber diameter within the range of 1-1,000 nm and an average fiber length within the range of 0.1-100 μm, and the like. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a rubber composition and a method for producing the same, and more specifically, to improve the dispersibility of fibers as a reinforcing filler in a rubber component, and to provide a reinforced rubber excellent in durability and rigidity, and the same. The present invention relates to a rubber composition capable of providing a rubber product such as a used tire and a method for producing the same.

In general, rubber such as tire products is added with a granular inorganic reinforcing material such as carbon black or silica to increase its strength and rigidity. However, such a granular inorganic reinforcing material has a limit in its reinforcing performance because of its shape. Therefore, a technique has been proposed in which short fibers are selected as a rubber reinforcing material to improve hardness, modulus, and the like (see, for example, Patent Document 1). In addition, it has been proposed to use a master batch containing aramid short fibers of 0.5 to 1000 μm for tire rubber (see, for example, Patent Document 2). Furthermore, a rubber composition in which cellulose fibers are combined with rubber has been proposed (see, for example, Patent Document 3).
Japanese Patent Laid-Open No. 10-7811 JP 2001-164052 A JP 2006-206864 A

By the way, when a fiber such as a cellulose-based fiber is used as a rubber reinforcing material, a composite of hydrophilic cellulose and hydrophobic rubber has a poor dispersibility in the rubber of the reinforcing material and has sufficient durability and rigidity. I can't show it. Further, the reinforcing property of the fiber / rubber interface is not sufficient. For this reason, when the rubber is subjected to mechanical stress, separation or peeling of the fiber occurs, and sufficient strength and durability cannot be obtained.
Accordingly, it is an object of the present invention to provide a rubber composition that exhibits sufficient durability and rigidity by enhancing dispersibility and reinforcement of a reinforcing filler made of cellulosic fibers into a rubber component, and a method for producing the same.

  The present inventor has intensively studied to solve the above-mentioned problems. As a cellulose-based fiber, cellulose nanofiber having an average fiber diameter of nano-order is used as a rubber reinforcing material, and in the reinforcing material, the dispersibility is enhanced. By masking -OH groups (free hydroxyl groups) in cellulose nanofibers, which are reinforcing materials, with a masking agent, the dispersibility to rubber components is improved, and in particular, ester bonds such as acetylation are used for masking. By applying it, it was found that the dispersibility at the interface with the rubber component was further improved, and as a result, it was expected to enhance the reinforcing property, and the present invention was completed.

  That is, the rubber composition and the manufacturing method thereof according to the present invention are characterized by the configuration or means described in the following (1) to (8).

  (1). In the rubber composition containing cellulose nanofibers in the rubber component, part or all of the —OH groups are masked with a masking agent in order to inhibit hydrogen bonding of —OH groups of the cellulose fibers. A rubber composition.

(2). The said cellulose nanofiber is a rubber composition of the said (1) description whose average fiber diameter exists in the range of 1-1000 nm, and whose average fiber length exists in the range of 0.1-100 micrometers.
(3). The said cellulose nanofiber is a rubber composition of the said (1) or (2) description contained in the range of 1-50 with respect to 100 mass parts of rubber components.
(4). The rubber composition according to any one of (1) to (3) above, wherein the mask made of the masking agent is a fatty acid ester bond.
(5). The rubber composition according to (4), wherein the fatty acid has 1 to 17 carbon atoms.
(6). The said fiber is a rubber composition as described in said (1)-(5) in which 67% or more of the total -OH group in a fiber is masked with the mask agent.

(7). In the method for producing a rubber composition according to the above (1) to (6), a rubber latex and a slurry of the fiber dispersed in water are mixed, and then the mixed solution is dried to remove water. A process for producing a rubber composition, characterized in that
(8). The cellulose nanofiber in the slurry is characterized in that part or all of the —OH group is masked with a masking agent in advance in order to inhibit hydrogen bonding of the —OH group of the fiber. Of producing a rubber composition.

  The rubber composition of the present invention can improve the dispersibility between the hydrophilic cellulose nanofibers and the hydrophobic rubber component. That is, by masking the —OH group portion of cellulose nanofibers with an acetylated product or an alkylated product, that is, inhibiting the hydrogen bonding ability of —OH groups, preventing aggregation of fibers and improving compatibility with rubber components, The reinforcing property of fiber and rubber can be improved and the strength can be increased.

Hereinafter, the best mode for carrying out a preferred embodiment of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments and examples.
The rubber composition according to the present invention contains cellulose nanofibers having an average fiber diameter of nano-order and a dispersant in the rubber component.

The rubber component of the rubber composition according to the present invention is not particularly limited, but examples of those that can be used for tire products include the following rubber components.
The rubber component is roughly classified and selected from natural rubber and synthetic rubber, and a mixture of both may be used. The synthetic rubber is not particularly limited and can be appropriately selected from known ones according to the purpose. A diene rubber is preferable, and a styrene-butadiene copolymer (SBR), polyisoprene (IR), polybutadiene (BR) is used. ), Acrylonitrile-butadiene rubber, chloroprene rubber, and butyl rubber.

The cellulose nanofibers blended in the rubber composition according to the present invention preferably have an average fiber diameter in the range of 1 to 1000 nm and an average fiber length in the range of 0.1 to 100 μm. In particular, the average fiber diameter of cellulose nanofibers is more preferably in the range of 1 to 500 nm, and the average fiber length is more preferably in the range of 5 to 50 μm. When the average fiber particle size and the average fiber length are less than the above ranges, the dispersibility decreases, and when the average fiber particle sizes and average fiber lengths exceed the above ranges, the reinforcing performance decreases.
Here, the average fiber diameter and the average fiber length are measured by a pore electrical resistance method (Coulter principle method) by dispersing fibers in an ethylene glycol solution.
Moreover, it is preferable that the said cellulose nanofiber is contained in the range of 1-50 mass parts with respect to 100 mass parts of rubber components, especially the range of 3-20 mass parts. If the amount of fiber is small, the reinforcing effect is not sufficient, and if the amount is large, the processability of rubber becomes worse.

  Cellulose nanofibers blended in the rubber composition of the present invention have a masked -OH group portion. Examples of the masking agent include fatty acid compounds such as a reaction of substituting the hydrogen atom of the OH group with acetic anhydride for an acetyl group, and acetylating agents such as acetyl chloride. As the reaction solvent, solvents such as water, alcohol, acetonitrile, DMF, THF, ether and the like are used. In particular, in the mask method using a fatty acid compound, an acidic catalyst such as sulfuric acid can be used.

The number of carbon atoms of the fatty acid compound is preferably in the range of 1 to 17, particularly 1 to 6. When the number of carbons exceeds the above range, the reaction rate with the —OH group becomes worse.
Moreover, as long as the hydrogen bonding ability of the —OH group is hindered, the carbon chain may contain atoms such as oxygen, nitrogen and sulfur, and other halogen atoms. However, it is preferable that these do not contain an atom having hydrogen bonding ability such as oxygen because of compatibility with the rubber component.

In the present invention, in the cellulose nanofiber, 67% or more of the total —OH groups in the fiber is preferably masked with a masking agent. It is preferable that 2 to 3 terms are masked with a mask agent among the three —OH groups of the glucose unit constituting the cellulose nanofiber. That is, the masking degree (acetylation degree in acetylation) is preferably 2.0 or more. If it is less than the said range, since a cellulose nanofiber is solubilized, the form of a nanofiber cannot be hold | maintained.
Here, regarding the evaluation of the degree of masking, particularly the degree of acetylation, a signal in which the δ value in the 'H-NMR spectrum can be assigned to hydrogen of the methyl group of the acetyl group is around 2 ppm, and the structure of cellulose is around 3 to 5 ppm. It can be identified by calculating from the signals that can be assigned to the carbohydrate (pyranose skeleton) that constitutes the 6-membered ring consisting of 5 carbons and 1 carbon of the unit glucose.

  By such treatment, the —OH of the cellulose structure molecule shown in FIG. 1 prevents aggregation of hydrogen bonds between cellulose nanofibers as shown in FIG. 2, so that the masking agent prevents the reinforcing property and adhesion between the fiber and the rubber. Can be improved and the strength can be increased.

  Next, in order to produce a rubber composition in the present invention, first, nanocellulose fibers are acetylated according to the above-described method to mask —OH groups in the fibers. Next, after the fibers are dispersed in water, they are beaten, passed through an orifice, mechanically sheared as appropriate, and dispersed by a high-pressure homogenizer or the like to form a slurry. Actually, fibers having various fiber diameters are commercially available, and in the present invention, these are used after being slurried in water. In this case, the concentration of the fiber in the slurry is preferably in the range of 0.1 to 3 parts by mass with respect to 100 parts by mass of water in terms of manufacturing operation.

The method of mixing the rubber latex and the fiber slurry according to the present invention is not particularly limited, and may be a general method such as a homogenizer, a rotary stirrer, an electromagnetic stirrer, or a propeller stirrer.
In the present invention, water can be removed from the mixed solution by a general method such as oven drying, freeze drying, or spray drying.
Although there is no limitation in particular in solid content concentration of the said liquid mixture in this invention, it is preferable that it is 40 mass% or less, and it is preferable that it exists in the range of 5-15 mass parts. When this solid content concentration exceeds 40 mass%, the viscosity of a liquid mixture will become high too much and the dispersibility of a fiber will fall.

  The rubber composition of the present invention can contain various components usually used in the rubber industry in addition to the above-described compounding components. For example, as various components, fillers (for example, reinforcing fillers such as silica; and inorganic fillers such as calcium carbonate and calcium carbonate); vulcanization accelerators; anti-aging agents; zinc oxide; stearic acid; And additives such as an ozone degradation inhibitor. As vulcanization accelerators, thiazole vulcanization accelerators such as M (2-mercaptobenzothiazole), DM (dibenzothiazyl disulfide) and CZ (N-cyclohexyl-2-benzothiazylsulfenamide); TT And thiuram vulcanization accelerators such as (tetramethylthiuram sulfide); and guanidine vulcanization accelerators such as DPG (diphenylguanidine).

Specifically, the rubber composition can contain 7.0 parts by mass or less of sulfur with respect to 100 parts by mass of the rubber component. In particular, it is the range of 3.0-7.0 mass parts, More preferably, it is the range of 4.0-6.0 mass parts. In the rubber composition, the organic acid cobalt salt can be blended in an amount of 1.0 part by mass or less based on 100 parts by mass of the rubber component. In particular, it is the range of 0.05-1.0 mass part, More preferably, it is the range of 0.3-0.8 mass part. Examples of the cobalt organic acid salt include cobalt naphthenate, cobalt rosinate, or a linear or branched monocarboxylic acid cobalt salt having about 5 to 20 carbon atoms.
Further, it is preferable to add 40 parts by mass or more, more preferably 40 to 100 parts by mass, particularly 50 to 100 parts by mass of carbon black to 100 parts by mass of the rubber component in the rubber composition. Carbon black can be appropriately selected from those usually used in the rubber industry, and examples thereof include SRF, GPF, FER, HAF, ISAF, etc. Among them, GPF and HAF are in terms of balance between physical properties and cost. To preferred.

  In the rubber composition configured as described above, the dispersibility in the slurry becomes uniform and the dispersibility in the rubber is increased by blending the cellulose nanofibers. In particular, when the hydrogen bonding ability structure is sufficiently blocked, and the mask agent itself is hydrophobic, the dispersibility, the affinity to rubber, and the reinforcing property are enhanced, and the reinforcing property can be further improved.

  Next, although an Example and a comparative example demonstrate this invention further in detail, this invention is not restrict | limited to these.

200 g of natural rubber latex (solid content concentration: 60% by mass), cellulose fiber slurry (“Serish” manufactured by Daicel Chemical Industries, Ltd .: average fiber diameter: 100 nm, average fiber length: 45 μm, solid content concentration: 5% by mass) with the following masking agent Then, 300 g of the fibers and 1000 g of water were mixed in a high-speed mixing homogenizer at 3000 rpm for 5 minutes to obtain a cellulose / natural rubber mixed solution.
This was developed on a vat and dried and solidified in an oven at a temperature of 100 ° C. to obtain a cellulose fiber composite natural rubber (fiber composite rubber).
With respect to 100 parts by mass of the rubber component of the fiber composite rubber, a normal kneading is performed by a laboratory kneader according to the configuration shown in Table 1 below, the resulting mixture is pressure-press vulcanized, and a rubber sheet having a thickness of 2 mm Got.
<Evaluation test>
A rubber sheet was punched out with a predetermined dumbbell to prepare a sample piece. The sample piece was subjected to a vulcanized rubber tensile test according to ASTM D412 to measure the breaking stress and breaking strain. The measured values are values in Comparative Example 1 set to 100, and the values in each Example are displayed as indexes.
<Mask method with masking agent>
It is obtained by adding 300 g of the above cellulose fiber slurry, 150 g of acetic anhydride, 150 g of acetic acid and 1 g of sulfuric acid, and stirring and mixing the mixture with warm water at 70 ° C. for 15 minutes and then neutralizing.

  Note 1 in the table: Furnace Black HAF manufactured by Asahi Carbon Co., Ltd. 2; Noxeller DM manufactured by Ouchi Shinsei Chemical Co., Ltd., Note 3: Noxeller NS manufactured by Ouchi Shinsei Chemical Co., Ltd.

  The rubber composition of the present invention has high industrial applicability, which can enhance the dispersibility and reinforcement of the reinforcing material composed of cellulosic fibers in the rubber component and exhibit sufficient durability and rigidity.

FIG. 1 is a diagram showing a general cellulose molecular structure. FIG. 2 is a diagram showing the bonding relationship between cellulose nanofibers and their masking agents.

Claims (8)

In the rubber composition containing cellulose nanofibers in the rubber component,
A rubber composition, wherein a part or all of the —OH groups are masked with a masking agent in order to inhibit hydrogen bonding of —OH groups of the cellulose fibers.   The rubber composition according to claim 1, wherein the cellulose nanofiber has an average fiber diameter in the range of 1 to 1000 nm and an average fiber length in the range of 0.1 to 100 µm.   The said cellulose nanofiber is a rubber composition of Claim 1 or 2 contained in the range of 1-50 with respect to 100 mass parts of rubber components.   The rubber composition according to any one of claims 1 to 3, wherein the mask made of the masking agent is a fatty acid ester bond.   The rubber composition according to claim 4, wherein the fatty acid has 1 to 17 carbon atoms.   The rubber composition according to any one of claims 1 to 5, wherein 67% or more of the total -OH groups in the fiber are masked with a mask agent.   The method for producing a rubber composition according to any one of claims 1 to 6, wherein after mixing the rubber latex and the slurry of the fiber dispersed in water, the mixed solution is dried to remove water. A method for producing a rubber composition, characterized by being obtained as described above.   The cellulose nanofibers in the slurry are masked in part or in whole with a mask agent in order to inhibit hydrogen bonding of -OH groups of the fibers in advance. A method for producing a rubber composition.

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