JP2023023570A - Rubber composition and vulcanized rubber - Google Patents

Abstract

To provide a chloroprene rubber composition having excellent durability.SOLUTION: Disclosed is a rubber composition in which 0.01 to 0.90 pts.wt. of cellulose nanofiber is included based on 100 pts.wt. of mercaptan-modified chloroprene rubber. The increase width of 100% tensile stress (M100) of a vulcanized sheet of the rubber composition is 0.9 MPa/pts.wt. or more based on the addition amount of cellulose nanofiber, and this composition has durability of double or more compared to that of one to which cellulose nanofiber is not added.SELECTED DRAWING: None

Description

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

Among various synthetic rubbers, chloroprene rubber has well-balanced physical properties, so it is used in a wide range of applications, such as belts, hoses, boots, air springs, wet suits, stretch fabrics, anti-vibration rubber, adhesives, etc. used for Chloroprene rubber is divided into general-purpose mercaptan-modified, sulfur-modified chloroprene with excellent dynamic properties, and xanthogen-modified with excellent mechanical properties.

In recent years, due to the demand for higher performance, improvement in durability is required in various applications. There are evaluation methods such as flex crack test, flexometer test, tensile fatigue test, etc. for the durability of rubber materials. Improvements can be made by adjusting the method, but these formulations are limited by the hardness of the target molding.

Therefore, fiber-shaped reinforcing materials have been proposed, and tires and the like containing nano-order cellulose fibers have been proposed. (See, for example, Patent Document 1.) However, hydrophilic cellulose is inferior in dispersibility to hydrophobic rubber, and therefore has a low reinforcing effect. As a countermeasure, a tire has been proposed in which natural rubber latex is compounded with nano-order cellulose, a dispersant for dispersing it, and a silane coupling agent for fixing it. (See, for example, Patent Documents 2 and 3.) However, these methods require a separate agent such as a dispersant for dispersing the rubber and cellulose, which increases the cost. In addition, an aqueous dispersion of mechanically fibrillated nano-order cellulose was obtained by directly kneading and dispersing the cellulose in an amount of 1 to 25 parts by weight with respect to 100 parts by weight of the rubber component together with the polymer and the compounding agent. Conveyor belts having excellent durability, strength, and abrasion resistance have been proposed by vulcanizing rubber compositions (see, for example, Patent Document 4). However, while it is effective in applications such as conveyor belts where the heat generation properties of the material during use are important, in general, blending 1 to 25 parts by weight of nano-order cellulose improves durability and abrasion resistance. decreases. Moreover, in the method of directly kneading an aqueous dispersion of nano-order cellulose, the hydroxyl groups of cellulose aggregate due to hydrogen bonding, and excellent durability cannot be obtained. Therefore, an aqueous dispersion of nano-order cellulose is mixed with chloroprene latex in an amount of 1 to 7 parts by weight per 100 parts by weight of the rubber component to prepare a cellulose nanofiber-dispersed rubber latex mixed solution, and the cellulose nanofibers are dispersed. By vulcanizing a rubber composition obtained by kneading a polymer obtained by removing water from a rubber latex mixture together with a compounding agent, a chloroprene rubber composition exhibiting low strain and excellent tensile stress is produced. Proposed. (For example, see Patent Document 5.) However, it is generally known that when the low-strain tensile stress increases, the durability deteriorates, and the increase in the low-strain tensile stress and the durability are in a conflicting relationship. .

JP 2006-206864 A JP 2009-191197 A JP 2009-191198 A JP 2020-7156 A JP 2019-104896 A

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

Under such circumstances, the present inventors conducted intensive studies to solve the above problems, and found that a vulcanizate obtained by vulcanization molding of a rubber composition containing a mercaptan-modified chloroprene rubber and cellulose nanofibers is excellent. It has been found that it exhibits excellent durability. That is, each aspect of the present invention is [1] to [5] shown below.
[1] A rubber composition containing 0.01 to 0.90 parts by weight of cellulose nanofibers with respect to 100 parts by weight of mercaptan-modified chloroprene rubber, wherein the vulcanized sheet obtained by vulcanizing the rubber composition has a 100% tensile stress ( M100) is increased by 0.9 MPa/part by weight or more with respect to the amount of cellulose nanofiber added, and the rubber composition exhibits durability that is at least twice as high as that of a composition to which no cellulose nanofiber is added. .

The vulcanized sheet 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). The range of increase in M100 is obtained by subtracting the M100 value of the vulcanized sheet containing no cellulose nanofibers from the M100 value of the vulcanized sheet containing cellulose nanofibers, and dividing by the amount of cellulose nanofibers contained. Calculated. Further, the durability was evaluated by applying tensile fatigue of a constant amplitude according to JIS K6270 (2018) and counting the number of repetitions required until the test piece fractured.
[2] The cellulose nanofiber has an average fiber diameter of 10 to 300 nm, an average fiber length of 0.3 to 200 μm, a lignin content of 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 salt.
[3] The rubber composition according to [1] or [2], wherein the chloroprene rubber contains 3 to 7% by weight of a carboxylic acid or an alkali metal salt of a carboxylic acid.
[4] The rubber composition according to any one of [1] to [3], wherein the cellulose nanofibers are unmodified and fibrillated only by mechanical treatment.
[5] A vulcanized rubber which is a vulcanizate of the rubber composition according to any one of [1] to [4].

By using the rubber composition of the present invention, a vulcanized rubber having excellent durability as measured by a tensile fatigue test can be obtained at low cost.

The present invention will be described in detail below.

A rubber composition that is one aspect of the present invention is a rubber composition containing 0.01 to 0.90 parts by weight of cellulose nanofibers with respect to 100 parts by weight of mercaptan-modified chloroprene rubber, and the rubber composition is vulcanized. The increase in the 100% tensile stress (M100) of the vulcanized sheet is 0.9 MPa/part by weight or more with respect to the amount of cellulose nanofiber added, and is at least twice that of the sheet without the addition of cellulose nanofiber. It is a rubber composition that exhibits the durability of

The vulcanized sheet 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). The range of increase in M100 is obtained by subtracting the M100 value of the vulcanized sheet containing no cellulose nanofibers from the M100 value of the vulcanized sheet containing cellulose nanofibers, and dividing by the amount of cellulose nanofibers contained. Calculated. Further, the durability was evaluated by applying tensile fatigue of a constant amplitude according to JIS K6270 (2018) and counting the number of repetitions required until the test piece fractured.

Chloroprene rubber is rubber obtained by polymerizing chloroprene or chloroprene and a monomer copolymerizable therewith. Chloroprene rubber includes mercaptan-modified chloroprene rubber, sulfur-modified chloroprene rubber with excellent dynamic properties, and xanthogen-modified chloroprene rubber with excellent mechanical properties. Sulfur-modified chloroprene rubber is characterized by excellent flex crack resistance, but mercaptan-modified rubber is superior in tensile fatigue. In the present invention, mercaptan-modified chloroprene rubber is used because the durability measured by the tensile fatigue test can be improved by compounding cellulose nanofibers, and more effects can be obtained.

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

Examples of monomers copolymerizable with chloroprene include sulfur, 2,3-dichloro-1,3-butadiene, 2-cyano-1,3-butadiene, 1-chloro-1,3-butadiene, , 1,3-butadiene, styrene, acrylonitrile, methyl methacrylate, methacrylic acid, acrylic acid, and the like, and one or more of these may be used in combination, and are appropriately used depending on the required physical properties.

Although the amount of the copolymerizable monomer is not particularly limited, it is generally used in an amount of 30 parts by weight or less per 100 parts by weight of the chloroprene rubber as long as the properties of the chloroprene polymer are not impaired. In particular, sulfur is preferably 3 parts by weight or less, more preferably 1 part by weight or less per 100 parts by weight of the chloroprene monomer, so as to obtain a good balance between heat resistance and physical properties.

The chloroprene rubber preferably contains 3 to 7% by weight of a carboxylic acid or an alkali metal salt of a carboxylic acid. A content of 3% by weight or more provides excellent emulsion stability during chloroprene polymerization, and a content of 7% by weight or less provides excellent processability and a stable quality rubber product.

In the emulsion polymerization of chloroprene rubber, for example, the above monomers are 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. A method of terminating the polymerization by adding a terminator can be used.

Examples of emulsifiers include alkali metal salts of carboxylic acids and alkali metal salts of sulfonic acids. Examples include alkali metal salts, alkali metal salts of polycarboxylic acids, nonionic emulsifiers such as polyoxyethylene alkyl ethers, and water-soluble polymer compounds. Alkali metal salts include, for example, lithium, sodium, potassium, cesium and the like. These may be one type or two or more types, but from the viewpoint of polymerization stability, cohesiveness during drying, and rubber performance, it is preferable to contain an alkali metal salt of a carboxylic acid. It preferably contains an alkali metal salt of rosin acid, more preferably a potassium salt of rosin acid.

The amount of the emulsifier is not particularly limited, but considering the stability of the chloroprene rubber latex obtained after polymerization, it is preferably 3 to 10 parts by weight per 100 parts by weight of the chloroprene rubber. Among them, the alkali metal salt of carboxylic acid is preferably contained in an amount of 3 to 8 parts by weight, more preferably 5 to 7 parts by weight.

In order to maintain the stability of the polymerization liquid, it is preferable to adjust the pH to 11 or higher with a pH adjuster. Below this, the alkali metal salt of the carboxylic acid is acidified and the stability of the latex is lowered. 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, inorganic or organic peroxides such as hydrogen peroxide and tertiary butyl hydroperoxide, etc. are used. be able to. Further, these may be used alone or in combination with reducing substances such as thiosulfate, thiosulfite, hydrosulfite, organic amine, etc., in a redox system.

Examples of chain transfer agents include molecular weight modifiers such as alkylmercaptans, halogenated hydrocarbons, alkylxanthogen disulfides, alkylxanthogen polysulfides, and sulfur. is preferred. The amount of the chain transfer agent is not particularly limited as long as it is an amount used in general radical polymerization for adjusting the molecular weight. For the flexibility and good mechanical properties of the vulcanized rubber obtained by molding, it is preferably 0.01 to 1.0% by weight with respect to 100% by weight of the monomer mixture other than the chain transfer agent.

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

The timing of completion of the polymerization is not particularly limited, but a monomer conversion rate of 60% or more can ensure production volume, and a monomer conversion rate of 95% or less prevents the polymerization time from becoming too long. , 60 to 95% is preferable in terms of productivity.

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

In the rubber composition of the present invention, the content of cellulose nanofibers is 0.01 to 0.90 parts by weight per 100 parts by weight of chloroprene rubber. By setting the amount of cellulose nanofibers to 0.01 parts by weight or more and 0.90 parts by weight or less, an effect of improving durability can be obtained.

Further, the rubber composition which is one embodiment of the present invention is prepared by mixing an aqueous dispersion of cellulose nanofibers with chloroprene latex to prepare a cellulose nanofiber-dispersed rubber latex mixture, and adding water to 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 with an emulsifier, and may be an emulsion obtained by emulsion polymerization of a chloroprene monomer and an unsaturated monomer copolymerizable, or a chloroprene rubber. is dissolved in an organic solvent such as toluene and then emulsified by mixing 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. Although lignin is contained in wood or the like, which is the raw material of cellulose nanofibers, cellulose nanofibers containing a large amount of lignin impair the stability of chloroprene latex, so the amount of lignin contained is preferably 20% by weight or less. It is preferably 10% by weight or less, more preferably 5% by weight or less. The fibrillation treatment of cellulose is mainly performed by mechanical treatment, and by adding various functional groups by chemical treatment and using mechanical treatment together, it is performed to a finer single nano level. In the present invention, in order to improve the dispersion state of cellulose nanofibers in rubber and obtain excellent durability, cellulose nanofibers having a surface tension of 60 mN/m or less in a 1% by weight aqueous dispersion of cellulose nanofibers are used. It is preferable to use Examples of such cellulose nanofibers include cellulose nanofibers that are fibrillated only by mechanical treatment without chemical treatment and have amphipathic properties. Since the cellulose nanofibers are not chemically treated and do not contain carboxylates and carboxylic acids, the cellulose nanofibers are well dispersed in the rubber, and the durability of the vulcanized rubber obtained is improved. Therefore, it is preferable to use cellulose that does not contain carboxylates and carboxylic acids. Amphiphilicity means that cellulose nanofibers have both a hydrophilic portion that has a high affinity for water and a hydrophobic portion that has a small affinity for water. It can be obtained by causing the samples to face and collide at high speed. Having amphiphilicity increases the affinity between hydrophobic rubber and cellulose, and a smaller mixing amount can significantly improve durability. Pure water generally has a surface tension of about 72 mN/m, but the surface tension decreases as the hydrophobicity increases. If 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 high affinity with rubber.

In the rubber composition which is 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 carboxylic acid or 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. Moreover, by setting the average fiber diameter to 300 nm or less, the increase in viscosity of the cellulose nanofiber-containing chloroprene rubber composition is suppressed, and moldability is improved. More preferably, the average fiber diameter is 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 rubber vulcanizates containing cellulose nanofibers. It is possible to suppress the viscosity increase of , and it is excellent in moldability. More preferably, the average fiber length is 0.5 to 100 μm. In addition, unmodified cellulose nanofibers are preferred because chemically modified cellulose nanofibers are much more expensive than unmodified ones.

The method of mixing the chloroprene rubber latex and the aqueous dispersion of cellulose nanofibers is not particularly limited, and a propeller-type stirring device, a homomixer, a high-pressure homogenizer, or the like is used to mix the aqueous dispersion of chloroprene latex and cellulose nanofibers. It can be obtained by mixing until it becomes uniform in appearance (no lumps, etc.).

Methods for removing water (drying method) from the cellulose nanofiber-dispersed rubber latex mixture include drying by heating, coagulation with acid or salt, and freeze-drying. Therefore, the method of precipitating (freezing and solidifying) the rubber by freezing, washing away the excess emulsifier and the like with water, and then drying with hot air is the most efficient and easy drying method, and is therefore preferable.

In the method of freeze-coagulating and drying the cellulose nanofiber-dispersed rubber latex mixture, the viscosity of the cellulose nanofiber-dispersed rubber latex mixture is preferably 1500 mPa·s or less. A viscosity of 1,500 mPa·s or less is preferable because handling is good, and a viscosity of 1,000 mPa·s or less and 30 mPa·s or more is preferable.

In addition, by setting the solid content of the cellulose nanofiber dispersed rubber latex mixture to 20% by weight or more, the strength of the rubber increases and the handling in continuous production improves, and from the balance with the viscosity, 20% to 40% by weight 25% by weight or more and 35% by weight or less is preferable.

In the rubber composition of one aspect of the present invention, the vulcanized sheet has a 100% tensile stress (M100) increase of 0.9 MPa/part by weight or more with respect to the amount of cellulose nanofiber added, Moreover, the durability is more than twice as high as that of the product without the addition of cellulose nanofibers.

A chloroprene rubber vulcanizate having amphiphilic cellulose nanofibers has a high affinity between hydrophobic rubber and cellulose, so that a vulcanized sheet obtained by vulcanizing a rubber composition has a 100% tensile strength (M100). The range of increase is increased, and a large improvement in durability can be obtained with a smaller mixing amount. If the increase in 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 affinity with A vulcanized sheet obtained by vulcanizing a rubber composition in which rubber and cellulose nanofibers are sufficiently compatible exhibits durability that is at least twice that of a sheet without the addition of cellulose nanofibers, demonstrating excellent durability. .

The vulcanized rubber, which is one aspect of the present invention, is made by compounding and kneading various compounding agents in the same manner as ordinary chloroprene rubber, and curing the above rubber composition at an appropriate vulcanization temperature by about 90% with respect to the maximum torque of the test material. obtained by vulcanizing up to The resulting vulcanized rubber has excellent durability compared to a chloroprene rubber vulcanizate that does not contain cellulose nanofibers and a chloroprene rubber vulcanizate that contains cellulose nanofibers that do not have amphipathic properties, which have the same hardness. It can be used for various purposes due to its excellent properties. In particular, a chloroprene rubber vulcanizate having amphipathic cellulose nanofibers exhibits excellent durability, exhibits excellent tensile stress at low strain, and has the characteristic of greatly improving 100% tensile stress. It is particularly suitable for anti-vibration rubber, wipers, CVJ boots, ball joint boots, foams, etc., which require high durability.

EXAMPLES The present invention will be specifically described below by way of examples, but the present invention is not limited only to these examples.

<Creation of chloroprene latex>
As a monomer mixture, 0.2 parts by weight of mercaptan is added to 100 parts by weight of chloroprene, 4.0 parts by weight of potassium salt of rosin acid, 0.3 parts by weight of sodium salt of condensate of naphthalenesulfonic acid and formaldehyde, Mix and stir with an emulsified aqueous solution containing 0.3 parts of oleic sulfate, 0.2 parts by weight of sodium hydroxide, and 100 parts by weight of water to emulsify. A polymerization catalyst consisting of 0.01 parts by weight of sodium sulfate and 20 parts by weight of water was added at a constant rate by a pump to carry out polymerization. Polymerization was carried out by adding a polymerization catalyst until the polymerization conversion reached 70%, and a polymerization terminator consisting of 0.01 parts by weight of phenothiazine, 5.0 parts by weight of chloroprene and 0.5 parts by weight of water was added to polymerize. stopped. Subsequently, unreacted chloroprene was removed and recovered by steam stripping under reduced pressure to obtain a mercaptan-modified chloroprene rubber latex.

<Creation of chloroprene (rubber composition) containing cellulose nanofibers>
A predetermined amount of an aqueous dispersion of cellulose nanofibers is added to a mercaptan-modified chloroprene rubber latex, mixed for 10 minutes at 2,000 rpm in an auto homomixer (PRIMIX: PRIMIX), and then freeze-coagulated to precipitate the polymer. , dried.

<Creating a compound>
For 100 parts by weight of mercaptan-modified chloroprene rubber containing cellulose nanofibers, the parts by weight shown in Table 1 of carbon black (Seist SO manufactured by Tokai Carbon Co., Ltd.), 4 parts by weight of magnesium oxide (manufactured by Kyowa Chemical Industry Co., Ltd.), stearin Acid (manufactured by Shin Nippon Rika Co., Ltd.) 1.5 parts by weight, zinc oxide (manufactured by Sakai Chemical Co., Ltd.) 5 parts by weight, Nonflex OD-3 (manufactured by Seiko Chemical Co., Ltd.) 2 parts by weight, Nocrac DP ( 0.35 parts by weight of Ouchi Shinko Kagaku Co., Ltd.) and 5 parts by weight of DOA (manufactured by Daihachi Kagaku Kogyo Co., Ltd.) are mixed in a kneader kneader, and after cooling, Suncellar #22C (Sanshin Chemical ( Co., Ltd.) and 0.5 parts by weight of Noccellar TT-P (manufactured by Ouchi Shinko Kagaku Co., Ltd.) were mixed in an open-roll kneader to obtain a cellulose nanofiber-containing chloroprene rubber compound.

<Creation of vulcanizate>
The resulting cellulose nanofiber-containing mercaptan-modified chloroprene rubber compound was press-vulcanized at 160° C. for 15 minutes to prepare a vulcanized sheet and a durability test specimen.
<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 width of vulcanizate>
The 100% tensile stress (M100) of the obtained vulcanized sheet was evaluated according to JIS-K-6251 (2012 edition) under conditions of a tensile speed of 500 mm/min and 23°C. It was calculated by subtracting the M100 value of the vulcanized sheet containing no cellulose nanofibers from the obtained M100 value of the vulcanized sheet containing cellulose nanofibers and dividing by the amount of cellulose nanofibers contained.

<Measurement of durability of vulcanizates>
According to JIS K6270 (2018), the obtained test piece for durability test was subjected to repeated tensile deformation with a constant amplitude, and the number of repetitions required until the test piece broke was evaluated. The durability values in Table 1 are expressed as a ratio with the value of Comparative Example 1 being 100, and the larger the value, the better the durability.

Example 1
An aqueous dispersion of cellulose nanofibers produced by mechanical fibrillation means (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 100 μm, lignin content of 1% or less, unmodified, amphipathic) are mixed and stirred for 10 minutes by the above method to obtain a cellulose nanofiber-dispersed rubber latex mixture. rice field. The cellulose nanofiber was mixed in an amount such that the cellulose content was 0.2 parts by weight with respect to 100 parts by weight of the solid rubber component.

A cellulose nanofiber-containing mercaptan-modified chloroprene rubber compound, a vulcanized sheet, and a test piece for durability test were obtained from the cellulose nanofiber-containing chloroprene rubber composition according to the above method, and the hardness and tensile stress of the vulcanizate were increased by 100%. A width measurement test and a durability test were carried out. Table 1 shows the results. From Table 1, the hardness was 70, the increase in M100 per 1 part by weight of cellulose nanofiber was 1.0 MPa/part by weight, and the durability was 248, which were good results.

Example 2
The amount of cellulose nanofibers mixed was adjusted so that the content of cellulose nanofibers was 0.4 parts by weight with respect to 100 parts by weight of the rubber component in the solid portion. A cellulose nanofiber-containing mercaptan-modified chloroprene rubber compound, a vulcanized sheet, and a test piece for a durability test were obtained in the same manner as in Example 1 except that the amount was adjusted, and the hardness and the 100% tensile stress increase width of the vulcanizate were measured. A test and a durability test were carried out. Table 1 shows the results. The hardness was 70, the increase in M100 per 1 part by weight of cellulose nanofiber was 1.8 MPa/part by weight, and the durability was 218, which were good results.

Example 3
The amount of cellulose nanofibers mixed was adjusted so that the content of cellulose nanofibers was 0.8 parts by weight with respect to 100 parts by weight of the rubber component in the solid portion. A cellulose nanofiber-containing mercaptan-modified chloroprene rubber compound, a vulcanized sheet, and a test piece for a durability test were obtained in the same manner as in Example 1 except that the amount was adjusted, and the hardness and the 100% tensile stress increase width measurement test of the vulcanizate. , a durability test was performed. Table 1 shows the results. The hardness was 71, the increase in M100 per 1 part by weight of cellulose nanofiber was 1.1 MPa/part by weight, and the durability was 275, which were good results.

Comparative example 1
A mercaptan-modified chloroprene rubber compound, a vulcanized sheet, and a durability test specimen in the same manner as in Example 1 except that the amount of carbon black was adjusted so that the hardness was the same as in Example 1 without mixing cellulose nanofibers. was obtained and hardness and durability tests were carried out. Table 1 shows the results. The hardness was 70 and the durability was 100, indicating insufficient durability.

Comparative example 2
The amount of cellulose nanofibers mixed was adjusted so that the content of cellulose nanofibers was 2.0 parts by weight with respect to 100 parts by weight of the rubber component in the solid portion. A cellulose nanofiber-containing mercaptan-modified chloroprene rubber compound, a vulcanized sheet, and a test piece for a durability test were obtained in the same manner as in Example 1 except that the amount was adjusted, and the hardness and the 100% tensile stress increase width measurement test of the vulcanizate. , a durability test was performed. Table 1 shows the results. The hardness was 71, the increase in M100 per 1 part by weight of cellulose nanofiber was 1.0 MPa/part by weight, and the durability was 112. Although the durability was slightly improved, the improvement effect was insufficient.

Comparative example 3
Sulfur-modified chloroprene rubber was used instead of mercaptan-modified chloroprene rubber, and after mixing the masterbatch, 1.0 parts by weight of Suncellar #22C (manufactured by Sanshin Chemical Co., Ltd.) and Noxcellar TT-P (Ouchi Shinko Kagaku ( A sulfur-modified chloroprene rubber compound was prepared in the same manner as in Comparative Example 1, except that 0.5 parts by weight of the product manufactured by Co., Ltd. was not mixed. The obtained sulfur-modified chloroprene rubber compound was press vulcanized at 150° C. for 30 minutes to prepare a vulcanized sheet and a test piece for durability test. . Table 1 shows the results. The hardness was 71 and the durability was 42, resulting in inferior durability to mercaptan-modified chloroprene rubber.

Comparative example 4
The amount of cellulose nanofibers mixed was adjusted so that the content of cellulose nanofibers was 0.2 parts by weight with respect to 100 parts by weight of the rubber component in the solid portion, and carbon black was added so as to obtain the same hardness as in Comparative Example 3. A cellulose nanofiber-containing sulfur-modified chloroprene rubber compound, a vulcanized sheet, and a test piece for durability test were obtained in the same manner as in Comparative Example 3 except that the amount was adjusted, and the hardness and the 100% tensile stress increase width measurement test of the vulcanizate. , a durability test was performed. Table 1 shows the results. The hardness was 70, the increase in M100 per 1 part by weight of cellulose nanofiber was 0.5 MPa/part by weight, and the durability was 46. Although the durability was slightly improved from Comparative Example 3, the improvement effect was inadequate. was enough.

Claims (5)

A rubber composition containing 0.01 to 0.90 parts by weight of cellulose nanofibers with respect to 100 parts by weight of mercaptan-modified chloroprene rubber, and the 100% tensile stress (M100) of the vulcanized sheet obtained by vulcanizing the rubber composition. A rubber composition having a width of increase of 0.9 MPa/part by weight or more with respect to the amount of cellulose nanofiber added, and exhibiting durability twice or more as high as that of a composition to which no cellulose nanofiber is added.
The vulcanized sheet 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). The range of increase in M100 is obtained by subtracting the M100 value of the vulcanized sheet containing no cellulose nanofibers from the M100 value of the vulcanized sheet containing cellulose nanofibers, and dividing by the amount of cellulose nanofibers contained. Calculated. In addition, durability was evaluated according to JIS K6270 (2018) by applying tensile fatigue with a constant amplitude and repeating the number of times required until the test piece fractured. The cellulose nanofiber has an average fiber diameter of 10 to 300 nm, an average fiber length of 0.3 to 200 μm, a lignin content of 20% by weight or less, and a cellulose hydroxymethyl group modified with a carboxylic acid or a carboxylate. 2. The rubber composition of claim 1, wherein the rubber composition is not 3. The rubber composition according to claim 1, wherein the chloroprene rubber contains 3 to 7% by weight of a carboxylic acid or an alkali metal salt of a carboxylic acid. The rubber composition according to any one of claims 1 to 3, wherein the cellulose nanofibers are unmodified and fibrillated 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.