JP2022067609A - Rubber composition and vulcanized rubber - Google Patents

Abstract

To provide a chloroprene rubber composition excellent in durability.SOLUTION: A rubber composition comprises 0.01 to 0.40 pts. weight of a cellulose nanofiber relative to 100 pts. weight of the chloroprene rubber. A vulcanized sheet made of the rubber composition vulcanized has a 100% tensile stress (M100) increase rate relative to the amount of the cellulose nanofiber added of 0.9 MPa/pts. weight or more, and exhibits 5 times or more durability in comparison with those without addition of the cellulose nanofiber.SELECTED DRAWING: None

Description

The present invention relates to a rubber composition containing a chloroprene rubber.

Chloroprene rubber is used in a wide range of applications because it has a good balance of physical properties among various synthetic rubbers. For example, it is used for belts, hoses, boots, air springs, wet suits, pulling cloths, adhesives, etc. There is. Chloroprene rubber includes general-purpose mercaptan modification and sulfur-modified chloroprene with excellent dynamic characteristics, and the latter is more durable, but further improvement in durability is required due to the recent demand for higher performance. ..

Normally, durability can be improved by adjusting the blending amount of reinforcing materials such as carbon black and silica and plasticizer, molding temperature and molding method, but these are because the hardness of the target molded product is determined. There is a limit to the prescription of. Further, even if the durability can be improved, there is a problem that the compression set and the wear resistance are deteriorated.

Therefore, a fiber-shaped reinforcing material has been proposed, and a tire or the like containing nano-order cellulose fibers has been proposed. (For example, refer to Patent Document 1.) However, hydrophilic cellulose has a low reinforcing effect because it is inferior in dispersibility with respect to hydrophobic rubber, and further, the hydroxyl groups of the cellulose are aggregated by hydrogen bonds and the durability is impaired. As a countermeasure, a tire in which nano-order cellulose and a dispersant for dispersing the cellulose and a silane coupling agent for fixing the cellulose are blended with natural rubber latex has been proposed. (For example, refer to Patent Documents 2 and 3.) However, these methods require a separate agent for dispersing rubber and cellulose such as a dispersant, which increases the cost. Further, it was obtained by directly kneading and dispersing the mechanically deflated aqueous dispersion of nano-order cellulose in an amount of 1 to 25 parts by weight of the rubber component with respect to 100 parts by weight of the rubber component, together with the polymer and the compounding agent. A conveyor belt having excellent durability, strength, and abrasion resistance by vulcanizing a rubber composition has been proposed (see, for example, Patent Document 4). However, while it is effective in applications such as conveyor belts where the heat generation characteristics of the material are important, it is generally durable and wear resistant when 1 to 25 parts by weight of nano-order cellulose is added. Decreases. Further, in the method of directly kneading the aqueous dispersion of nano-order cellulose, the hydroxyl groups of the cellulose are aggregated by hydrogen bonds, and excellent durability cannot be obtained. Therefore, an aqueous dispersion of nano-order cellulose was mixed with chloroprene latex in an amount of 1 to 7 parts by weight with respect to 100 parts by weight of the rubber component to prepare a cellulose nanofiber-dispersed rubber latex mixed solution to disperse the cellulose nanofibers. By sulfurizing the rubber composition obtained by kneading the polymer obtained by removing water from the rubber latex mixture together with the compounding agent, a chloroprene rubber composition showing excellent tensile stress with low strain can be obtained. Proposed. (For example, refer to Patent Document 5.) However, it is generally known that the durability deteriorates when the tensile stress with low strain increases, and the increase in tensile stress with low strain and the durability have a contradictory relationship. ..

Japanese Unexamined Patent Publication No. 2006-206864 Japanese Unexamined Patent Publication No. 2009-191197 Japanese Unexamined Patent Publication No. 2009-191198 Japanese Unexamined Patent Publication No. 2020-7156 Japanese Unexamined Patent Publication No. 2019-104896

The present invention has been made in view of this problem, and an object thereof is to provide a chloroprene rubber composition having excellent durability.

Against this background, the present inventor diligently studied to solve the above problems, and found that the vulcanized product obtained by vulcanizing and molding a rubber composition containing chloroprene rubber and cellulose nanofibers had excellent durability. Found to show sex. That is, each aspect of the present invention is [1] to [5] shown below.
[1] A rubber composition containing 0.01 to 0.40 parts by weight of cellulose nanofibers with respect to 100 parts by weight of chloroprene rubber, and 100% tensile stress (M100) of a vulcanized sheet obtained by vulcanizing the rubber composition. The rubber is characterized in that the increase width is 0.9 MPa / part by weight or more with respect to the amount of cellulose nanofibers added, and the durability is 5 times or more as compared with the rubber to which the cellulose nanofibers are not added. Composition.

The vulcanization sheet used was prepared by adjusting the amount of carbon black added to the compound in order to unify the hardness (Hs) described in JIS K6253 (2012). Further, the increase width of M100 is obtained by subtracting the value of M100 of the vulcanization sheet not containing cellulose nanofibers from the value of M100 of the vulcanization sheet containing cellulose nanofibers and dividing by the amount of cellulose nanofibers contained. Calculated. Further, the durability was evaluated by the number of times of bending when the crack starting from the cut reached 10 mm by repeatedly bending and deforming the test piece which had been cut in advance according to JIS K6260 (2017).
[2] The average fiber diameter of cellulose nanofibers is 10 to 300 nm, the average fiber length is 0.3 to 200 μm, the lignin content is 20% by weight or less, and the hydroxymethyl group of cellulose is a carboxylic acid or a carboxylic acid. The rubber composition according to [1], which is not modified with a salt.
[3] The chloroprene rubber according to [1] or [2], wherein the chloroprene rubber contains a carboxylic acid or an alkali metal salt of the carboxylic acid in an amount of 3 to 7% by weight and is modified with sulfur. Rubber composition.
[4] The rubber composition according to any one of [1] to [3], wherein the cellulose nanofibers are not denatured and are defibrated only by mechanical treatment.
[5] A vulcanized rubber according to any one of [1] to [4], which is a vulcanized product of the rubber composition.

By using the rubber composition of the present invention, vulcanized rubber having excellent durability can be obtained at low cost.

Hereinafter, the present invention will be described in detail.

The rubber composition according to one aspect of the present invention is a rubber composition containing 0.01 to 0.40 parts by weight of cellulose nanofibers with respect to 100 parts by weight of chloroprene rubber, and is vulcanized by vulcanizing the rubber composition. The increase width of 100% tensile stress (M100) of the sheet is 0.9 MPa / part by weight or more with respect to the amount of cellulose nanofibers added, and the durability is 5 times or more that of the one without cellulose nanofibers added. A rubber composition characterized by exhibiting sex.

The vulcanization sheet used was prepared by adjusting the amount of carbon black added to the compound in order to unify the hardness (Hs) described in JIS K6253 (2012). Further, the increase width of M100 is obtained by subtracting the value of M100 of the vulcanization sheet not containing cellulose nanofibers from the value of M100 of the vulcanization sheet containing cellulose nanofibers and dividing by the amount of cellulose nanofibers contained. Calculated. Further, the durability was evaluated by the number of times of bending when the crack starting from the cut reached 10 mm by repeatedly bending and deforming the test piece which had been cut in advance according to JIS K6260 (2017).

The chloroprene rubber is a rubber obtained by polymerizing chloroprene or chloroprene and a monomer copolymerizable therewith. The chloroprene rubber includes a mercaptan-modified chloroprene rubber and a sulfur-modified chloroprene rubber having excellent dynamic characteristics, and the latter has a feature of being more durable. In the present invention, the durability can be improved by compounding the cellulose nanofibers, but the sulfur-modified chloroprene rubber which can obtain more effect is preferable.

The chloroprene rubber can be obtained by emulsion polymerization of chloroprene, or chloroprene and a monomer copolymerizable therewith.

Examples of the monomer copolymerizable with chloroprene include 2,3-dichloro-1,3-butadiene, 2-cyano-1,3-butadiene, and 1-chloro-1,3-butadiene, in addition to sulfur. , 1,3-butadiene, styrene, acrylonitrile, methyl methacrylate, methacrylic acid, acrylic acid and the like, and one or more of them can be used in combination, and they are used in a timely manner according to the required physical properties.

The amount of the copolymerizable monomer is not particularly limited, but generally 30 parts by weight or less is used with respect to 100 parts by weight of the chloroprene rubber so as not to impair the characteristics of the chloroprene polymer. In particular, sulfur is preferably 3 parts by weight or less, more preferably 1 part by weight or less, based on 100 parts by weight of the chloroprene monomer so that the balance between heat resistance and physical properties is good.

The chloroprene rubber preferably contains a carboxylic acid or an alkali metal salt of the carboxylic acid in an amount of 3 to 7% by weight. When the content is 3% by weight or more, the emulsification stability during chloroprene polymerization is excellent, and when the content is 7% by weight or less, the rubber product is excellent in processability and stable in quality.

In the emulsion polymerization of chloroprene rubber, for example, the above-mentioned monomer is mixed with an emulsifier, water, a polymerization initiator, a chain transfer agent, other stabilizers, etc., polymerized at a predetermined temperature, and polymerized at a predetermined polymerization conversion rate. Examples thereof include a method of adding a terminator to terminate the polymerization.

Examples of the emulsifier include alkali metal salts of carboxylic acids and alkali metal salts of sulfonic acid. For example, alkali metal salts of logoic acid, alkali metal salts of alkylbenzene sulfonic acid, alkali metal salts of fatty acids, and alkenyl succinic acid. Examples thereof include alkali metal salts, alkali metal salts of polycarboxylic acids, nonionic emulsifiers such as polyoxyethylene alkyl ethers, and water-soluble polymer compounds. Examples of the alkali metal salt include lithium, sodium, potassium, cesium and the like. These may be one kind or may contain two or more kinds, but it is preferable to contain an alkali metal salt of a carboxylic acid from the viewpoint of polymerization stability, cohesiveness at the time of drying, and rubber performance. It is preferable to contain an alkali metal salt of loginic acid and further a potassium salt of loginic acid.

The amount of the emulsifier is not particularly limited, but is preferably 3 to 10 parts by weight with respect to 100 parts by weight of the chloroprene rubber in consideration of the stability of the chloroprene rubber latex obtained after the polymerization. The alkali metal salt of the carboxylic acid is preferably 3 to 8 parts by weight, more preferably 5 to 7 parts by weight.
In order to maintain the stability of the polymer solution, it is preferable to set the pH to 11 or more with a pH adjuster. Below this, the alkali metal salt of the carboxylic acid is acidified and the stability of the latex is reduced. Examples of the pH adjuster include basic compounds such as sodium hydroxide, potassium hydroxide, sodium phosphate, potassium phosphate, triethylamine, diethylamine, triethanolamine, diethanolamine, ethanolamine, and ammonia. The above can be used alone or in combination.

As the emulsion polymerization initiator, known free radical substances such as peroxides such as potassium persulfate and ammonium persulfate, and inorganic or organic peroxides such as hydrogen peroxide and tertiary butyl hydroperoxide are used. be able to. In addition, these may be used alone or in a redox system in combination with a reducing substance, for example, thiosulfate, thiosulfite, hydrosulfite, organic amine and the like.

The polymerization temperature is not particularly limited, but is preferably in the range of 10 to 50 ° C.

The time to finish the polymerization is not particularly limited, but the production amount can be secured by setting the conversion rate of the monomer to 60% or more, and the polymerization time does not become too long by setting it to 95% or less. , 60-95% is preferable in terms of productivity.

The polymerization terminator is not particularly limited as long as it is a commonly used terminator, and for example, phenothiazine, 2,6-t-butyl-4-methylphenol, hydroxylamine and the like can be used.

In the case of sulfur-modified chloroprene copolymerized with sulfur, it is possible to subsequently add a defibrating agent and a defibrating aid to the postpolymerized latex and deflocculate until an appropriate Mooney viscosity is obtained. Examples of the thawing agent include thiuram compounds such as tetraethyl thiuram disulfide, tetrabutyl thiuram disulfide, and tetraoctyl thiuram disulfide, which can be added in an emulsified state using the above emulsifier or the like. Examples of the defoliction reaction initiator include thiocarbamic acid compounds such as sodium dibutyldithiocarbamate and ammonium dimethyldithiocarbamate.

The gluing temperature can be in the range of 5 to 60 ° C, preferably in the range of 20 to 50 ° C. Generally, the higher the deflocculation temperature, the faster the deflocculation reaction.

The Mooney viscosity for terminating the glutinating reaction is not particularly limited as long as it satisfies the high elastic stress of the present invention, but is preferably 20 to 80 in consideration of kneading workability.

In the rubber composition of the present invention, the content of cellulose nanofibers is 0.01 to 0.40 parts by weight with respect to 100 parts by weight of chloroprene rubber. By setting the amount of cellulose nanofibers to 0.01 parts by weight or more and 0.40 parts by weight or less, the effect of improving durability can be obtained.

Further, in the rubber composition according to one aspect of the present invention, an aqueous dispersion of cellulose nanofibers is mixed with chloroprene latex to prepare a cellulose nanofiber-dispersed rubber latex mixture, and water is prepared from the cellulose nanofiber-dispersed rubber latex mixture. Can be obtained by removing.

The chloroprene latex is not particularly limited as long as the chloroprene rubber is emulsified and dispersed in water by an emulsifier, and is an emulsion obtained by emulsion-polymerizing an unsaturated monomer copolymerizable with the chloroprene monomer or a chloroprene rubber. Is emulsified by dissolving it in an organic solvent such as toluene and then mixing it with water and an emulsifier.

Cellulose nanofibers are obtained by defibrating cellulose fibers contained in wood to an average fiber diameter of several nanometers to several tens of nanometers. Wood and the like, which are raw materials for cellulose nanofibers, contain lignin, but since cellulose nanofibers containing a large amount of lignin impair the stability of chloroprene latex, the amount of lignin contained is preferably 20% by weight or less. It is preferably 10% by weight or less, and more preferably 5% by weight or less. Cellulose defibration treatment is mainly carried out by mechanical treatment, or by adding various functional groups by chemical treatment and using mechanical treatment in combination, it is carried out to a finer single nano level. In the present invention, in order to improve the dispersed state of cellulose nanofibers in rubber and obtain excellent durability, cellulose nanofibers having a surface tension of 1% by weight of an aqueous dispersion of cellulose nanofibers of 60 mN / m or less are used. It is preferable to use it. Examples of such cellulose nanofibers include cellulose nanofibers which are deflated only by mechanical treatment without performing chemical treatment and have amphipathic properties. By not chemically treating the cellulose nanofibers and having no carboxylic acid salt and carboxylic acid, the dispersed state of the cellulose nanofibers in the rubber is improved, and the durability of the obtained vulture rubber is improved. Therefore, it is preferable to use cellulose that does not contain a carboxylate and a carboxylic acid. Amphiphile means that cellulose nanofibers have both a hydrophilic part having a large affinity for water and a hydrophobic part having a small affinity with water, and as described in Japanese Patent No. 5419120, water suspension. It can be obtained by colliding samples at high speed. By having amphipathic properties, the affinity between the hydrophobic rubber and cellulose becomes high, and a large improvement effect in durability can be obtained with a smaller mixing amount. Generally, the surface tension of pure water is about 72 mN / m, but the larger the hydrophobicity, the smaller the surface tension. When the aqueous dispersion of cellulose nanofibers has a concentration of 1% by weight and a surface tension of 60 mN / m or less, it has amphipathic properties and has a high affinity with rubber.

In the rubber composition according to one aspect of the present invention, the average fiber diameter obtained by mechanical treatment is 10 to 300 nm, the average fiber length is 0.3 to 200 μm, and the hydroxymethyl group of cellulose is a carboxylic acid or a carboxylic acid salt. It is preferable to use cellulose nanofibers that have not been modified with. By setting the average fiber diameter to 10 nm or more, the viscosity of the cellulose nanofiber-dispersed rubber latex can be suppressed, and workability in the rubber manufacturing process can be maintained. Further, when the average fiber diameter is 300 nm or less, the increase in viscosity of the cellulose nanofiber-containing chloroprene rubber composition is suppressed, and the molding processability is improved. The average fiber diameter is more preferably 10 to 100 nm. On the other hand, cellulose nanofibers having an average fiber length of 0.3 μm or more are excellent in the effect of improving the tensile stress of the cellulose nanofiber-containing rubber sulfide, and by setting the average fiber length to 200 μm or less, the cellulose nanofiber-containing rubber composition It is possible to suppress the increase in viscosity of cellulose and it is excellent in molding processability. The average fiber length is more preferably 0.5 to 100 μm. Further, since the cellulose nanofibers hydrophobized by chemical modification are very expensive compared to the unmodified one, the unmodified one is preferable.

The method of mixing the aqueous dispersion of chloroprene rubber latex and cellulose nanofibers is not particularly limited, and an aqueous dispersion of chloroprene latex and cellulose nanofibers can be obtained by using a propeller-type agitator, a homomixer, a high-pressure homogenizer, or the like. It can be obtained by mixing until the appearance is uniform (no lumps or the like).

Methods for removing water from the cellulose nanofiber-dispersed rubber latex mixture (drying method) include heat drying, agglomeration with acid or salt, and freeze-drying. The method of precipitating (freezing and coagulating) rubber by freezing, removing excess emulsifier and the like by washing with water, and then drying with hot air is the most efficient and easy to dry, and is preferable.

In the method of freezing and coagulating from the cellulose nanofiber-dispersed rubber latex mixture and drying, the viscosity of the cellulose nanofiber-dispersed rubber latex mixture is preferably 1500 mPa · s or less. When the viscosity is 1500 mPa · s or less, handling is good and preferable, and further preferably 1000 mPa · s or less and 30 mPa · s or more.

Further, by setting the solid content of the cellulose nanofiber-dispersed rubber latex mixture to 20% by weight or more, the strength of the rubber is increased, the handling in continuous production is improved, and the balance with the viscosity is 20% by weight or more and 40% by weight. Hereinafter, more preferably 25% by weight or more and 35% by weight or less.

In the rubber composition according to one aspect of the present invention, the increase width of 100% tensile stress (M100) of the vulcanized vulcanized sheet is 0.9 MPa / part by weight or more with respect to the amount of cellulose nanofibers added. Moreover, it is characterized in that it exhibits a durability of 5 times or more as compared with that without addition of cellulose nanofibers.

Since the chloroprene rubber vulcanized product having cellulose nanofibers having amphipathic properties has a high affinity between the hydrophobic rubber and cellulose, the 100% tension (M100) of the vulcanized sheet obtained by vulcanizing the rubber composition The amount of increase is increased, and a large improvement effect in durability can be obtained with a smaller mixing amount. When the increase width of 100% tensile stress (M100) of the vulcanized sheet obtained by vulcanizing the rubber composition is 0.9 MPa / part by weight or more with respect to the amount of cellulose nanofibers added, the cellulose nanofibers are sufficiently rubber. Shows that it is compatible with. A vulcanized sheet obtained by vulcanizing a rubber composition in which rubber and cellulose nanofibers have a sufficient affinity has a durability of 5 times or more as compared with that without the addition of cellulose nanofibers, and exhibits excellent durability. ..

The vulcanized rubber, which is one aspect of the present invention, is kneaded with various compounding agents in the same manner as ordinary chloroprene rubber, and the above rubber composition is cured by about 90% with respect to the maximum torque of the test material at an appropriate vulcanization temperature. Obtained by vulcanization up to. The obtained vulcanized rubber has excellent durability as compared with a chloroprene rubber vulcanized product containing cellulose nanofibers having the same hardness and a chloroprene rubber vulcanized product containing cellulose nanofibers having no amphipathicity. It can be used for various purposes to show its properties. In particular, the chloroprene rubber vulcanized product having cellulose nanofibers having amphipathic properties shows excellent durability, low strain and excellent tensile stress, and has a feature that 100% tensile stress is greatly improved. It is particularly suitable for anti-vibration rubber, wipers, CVJ boots, ball joint boots, foams and the like, which require high durability.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

<Creation of chloroprene latex>
As a monomer mixture, 0.3 parts by weight of sulfur was added to 100 parts by weight of chloroprene, 4.0 parts by weight of potassium salt of logonic acid, 0.5 parts by weight of sodium salt of condensate of naphthalene sulfonic acid and formaldehyde, Mix and stir with an emulsified aqueous solution containing 0.05 parts by weight of sodium hydroxide, 1.0 part by weight of orthophosphate, and 100 parts by weight of water, and emulsify the mixture, which contains 1.0 part by weight of potassium persulfate and anthraquinone-β-sulfonic acid. Polymerization was carried out by adding a polymerization catalyst consisting of 0.01 part by weight of sodium and 30 parts by weight of water at a constant rate by a pump. Polymerization is carried out by adding a polymerization catalyst until the polymerization conversion rate reaches 70%, to which 0.01 part by weight of thiodiphenylamine, 4-t-butylcatechol, 2,2'-methylenebis-4-methyl-6-t- Polymerization was stopped by adding a polymerization inhibitor consisting of 0.05 parts by weight of butylphenol, 0.1 part by weight of diethylhydroxylamine, 0.05 parts by weight of sodium lauryl sulfate, 5.0 parts by weight of chloroprene, and 1.0 part by weight of water. I let you. Subsequently, 2 parts by weight of tetraethylthiuram disulfide emulsified with potassium rosinate and 0.3 part by weight of sodium dibutyldithiocarbamate were added to the mixture, and the mixture was deflocculated at 40 ° C. until the Mooney viscosity reached 60. After that, unreacted chloroprene was removed and recovered by steam stripping under reduced pressure to obtain chloroprene rubber latex.

<Preparation of chloroprene (rubber composition) containing cellulose nanofibers>
A predetermined amount of an aqueous dispersion of cellulose nanofibers is added to the chloroprene rubber latex, mixed with an autohomo mixer (PRIMIX manufactured by PRIMIX) at 2,000 rpm for 10 minutes, and then the polymer is precipitated by freeze-coagulation and dried. I let you.

<Creating a compound>
For 100 parts by weight of chloroprene rubber containing cellulose nanofibers, 4 parts by weight of carbon black (Seast SO manufactured by Tokai Carbon Co., Ltd.), magnesium oxide (manufactured by Kyowa Chemical Industry Co., Ltd.), and stearic acid (manufactured by Kyowa Chemical Industry Co., Ltd.) are shown in Table 1. 1.5 parts by weight of Shin Nihon Rika Co., Ltd., 5 parts by weight of zinc oxide (manufactured by Sakai Chemical Co., Ltd.), 2 parts by weight of non-flex OD-3 (manufactured by Seiko Chemical Co., Ltd.), Nocrack DP (Ouchi) 0.35 parts by weight of (manufactured by Shinko Kagaku Co., Ltd.) and 5 parts by weight of DOA (manufactured by Daihachi Chemical Industry Co., Ltd.) were mixed by a kneader kneader to obtain a chloroprene rubber compound containing cellulose nanofibers.

<Creation of vulcanized product>
The obtained cellulose nanofiber-containing chloroprene rubber compound was press-vulcanized at 150 ° C. for 30 minutes to prepare a vulcanized sheet and a test piece for durability test.
<Measurement of hardness of vulcanized product>
The hardness of the obtained vulcanized sheet was evaluated according to JIS K6253 (2012). Type A was selected for the durometer.

<Measurement of 100% tensile stress increase in vulcanized material>
The 100% tensile stress (M100) of the obtained vulcanized sheet was evaluated according to JIS-K-6251 (2012 version) under the conditions of a tensile speed of 500 mm / min and 23 ° C. It was calculated by subtracting the value of M100 of the vulcanization sheet containing no cellulose nanofibers from the value of M100 of the obtained vulcanization sheet containing cellulose nanofibers and dividing by the amount of the cellulose nanofibers contained.

<Measurement of durability of vulcanized products>
The obtained durability test piece was repeatedly bent and deformed according to JIS K6260 (2017), and the rate at which cracks grew from the cut was evaluated. The values in the table represent the number of bends when the crack reaches 10 mm as a ratio with the value of Comparative Example 1 as 100, and the larger the value, the better the durability.

Example 1
Aqueous dispersion of cellulose nanofibers (manufactured by Chuetsu Pulp Co., Ltd., grade: S-1, solid content concentration: 3% by weight, average fiber diameter: about 50 nm, average fiber length: about) with respect to 100 parts by weight of chloroprene rubber. 100 μm, lignin content 1% or less, unmodified, amphoteric) were mixed and stirred by the above method for 10 minutes to obtain a cellulose nanofiber-dispersed rubber latex mixed solution. The mixing amount of the cellulose nanofibers was such that the content of cellulose was 0.05 parts by weight with respect to 100 parts by weight of the rubber component of the solid content. S-1 was an amphipathic cellulose nanofiber produced by mechanical defibration means, and the surface tension at 1 wt% of the aqueous dispersion of the cellulose nanofiber was 55 mN / m.

The cellulose nanoprene rubber composition containing cellulose nanofibers was obtained with a cellulose nanofiber-containing chloroprene rubber compound and a vulcanized sheet according to the above method, and a 100% tensile stress increase width measurement test and durability test of hardness and vulcanized material were carried out. bottom. The results are shown in Table 1. From Table 1, the hardness was 69, the M100 increase width per 1 part by weight of the cellulose nanofiber was 2.0 MPa / part by weight, and the durability was 3467, which were good results.

Example 2
The mixing amount of the cellulose nanofibers is such that the content of the cellulose nanofibers is 0.2 parts by weight with respect to 100 parts by weight of the rubber component of the solid part, and the hardness of the carbon black is the same as that of Example 1. The hardness and hardness of the cellulose nanofiber-containing chloroprene rubber compound and vulture sheet, durability test test piece, wear test test piece, and compression set test piece were obtained in the same manner as in Example 1 except that the amount was adjusted. A durability test was conducted. The results are shown in Table 1. The hardness was 69, the increase width of M100 per 1 part by weight of cellulose nanofiber was 1.0 MPa / part by weight, and the durability was 639, which were good results.

Comparative Example 1
A chloroprene rubber compound, a vulcanization sheet, and a test piece for durability test were obtained in the same manner as in Example 1 except that the amount of carbon black was adjusted so as to have the same hardness as in Example 1 without mixing cellulose nanofibers. The hardness and 100% tensile stress increase width measurement test and durability test of the vulcanized material were carried out. The results are shown in Table 1. The hardness was 69 and the durability was 100, and the durability was insufficient.

Comparative Example 2
The mixing amount of the cellulose nanofibers is such that the content of the cellulose nanofibers is 2.0 parts by weight with respect to 100 parts by weight of the rubber component of the solid part, and the hardness of the carbon black is the same as that of Example 1. The hardness and hardness of the cellulose nanofiber-containing chloroprene rubber compound and vulture sheet, durability test test piece, wear test test piece, and compression set test piece were obtained in the same manner as in Example 1 except that the amount was adjusted. A durability test was conducted. The results are shown in Table 1. The hardness was 69, the increase width of M100 per 1 part by weight of cellulose nanofiber was 1.0 MPa / part by weight, and the durability was 37, and the durability was insufficient.

Comparative Example 3
Cellulose nanofibers to be used are made into cellulose nanofibers manufactured by Daicel FineChem Co., Ltd .: KY-100G (solid content concentration: 10% by weight, average fiber diameter: about 0.01 nm to 1 μm, lignin content 20% or less, unmodified). The mixing amount of the nanofibers is such that the content of the cellulose nanofibers is 2.5 parts by weight with respect to 100 parts by weight of the rubber component of the solid part, and the carbon black is made to have the same hardness as in Example 1. Cellulose nanofiber-containing chloroprene rubber compound and vulture sheet, durability test test piece, wear test test piece, compression set test piece were obtained in the same manner as in Example 1 except that the amount was adjusted. A durability test was conducted. KY-100G is a hydrophilic cellulose nanofiber produced by mechanical defibration means, and the surface tension of 1 wt% of the aqueous dispersion of the cellulose nanofiber was 70 mN / m. The results are shown in Table 1. The hardness was 0.7 MPa / part by weight per part by weight of 68 cellulose nanofibers, and the durability was 100, and the durability was insufficient.

Claims (5)

A rubber composition containing 0.01 to 0.40 parts by weight of cellulose nanofibers with respect to 100 parts by weight of chloroprene rubber, and the increase in 100% tensile stress (M100) of the vulcanized sheet obtained by vulcanizing the rubber composition. Is a rubber composition having a durability of 0.9 MPa / part by weight or more with respect to the amount of cellulose nanofibers added, and 5 times or more durability as compared with a rubber composition to which no cellulose nanofibers are added.
The vulcanization sheet used was prepared by adjusting the amount of carbon black added to the compound in order to unify the hardness (Hs) described in JIS K6253 (2012). Further, the increase width of M100 is obtained by subtracting the value of M100 of the vulcanization sheet not containing cellulose nanofibers from the value of M100 of the vulcanization sheet containing cellulose nanofibers and dividing by the amount of cellulose nanofibers contained. Calculated. Further, the durability was evaluated by the number of times of bending when the crack starting from the cut reached 10 mm by repeatedly bending and deforming the test piece which had been cut in advance according to JIS K6260 (2017). The average fiber diameter of cellulose nanofibers is 10 to 300 nm, the average fiber length is 0.3 to 200 μm, the lignin content is 20% by weight or less, and the hydroxymethyl group of cellulose is modified with a carboxylic acid or carboxylic acid salt. The rubber composition according to claim 1, wherein the rubber composition is not made. The rubber composition according to claim 1 or 2, wherein the chloroprene rubber is a chloroprene rubber containing a carboxylic acid or an alkali metal salt of a carboxylic acid in an amount of 3 to 7% by weight and modified with sulfur. The rubber composition according to any one of claims 1 to 3, wherein the cellulose nanofibers are not denatured and are defibrated only by mechanical treatment. A vulcanized rubber, which is a vulcanized product of the rubber composition according to any one of claims 1 to 4.