Extrusion molding rubber composition and vulcanized rubber

Abstract

To provide a chloroprene rubber composition excellent in scorchability without changing the die swell ratio of an extrusion molding end material and suitable for reuse, and a vulcanized rubber.SOLUTION: An extrusion molding chloroprene rubber composition includes the following (A)-(C) components, the (A) component: mercaptan modified chloroprene rubber, the (B) component: specific cellulose nanofiber and the (C) component: at least one kind selected from a group consisting of a plasticizer, a surfactant and a polyhydric alcohol partial fatty acid ester. A die swell ratio at a shear rate of 100 (1 / sec) between an initial state before performing evaluation molding and a state after performing the evaluation molding has no difference; a melt fracture is not caused in an extrusion molding in die swell ratio measurement; and a Mooney scorch time t5 in the initial state before performing evaluation molding is 8 minutes or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a rubber composition for extrusion molding containing a mercaptan-modified chloroprene rubber and a vulcanized rubber. [Background technology]

[0002] Among various synthetic rubbers, chloroprene rubber has a good balance of physical properties and is therefore used in a wide range of applications, including belts, boots, air springs, pull cloths, vibration-proof rubber, hoses, electric wires, rolls, wipers, gaskets, gloves, and adhesives.

[0003] Many products, including hoses, electrical wires, rolls, wipers, and gaskets, are manufactured using extrusion molding. Due to its inherent nature, extrusion molding generates a large amount of scrap material, making its reuse a challenge. The scrap compound generated during extrusion molding is subject to shear stress, which causes the rubber molecules to become disentangled. Furthermore, the rubber is also affected by heat, resulting in changes in the shrinkage rate of the unvulcanized material (hereafter referred to as the die swell ratio), deterioration in scorch time, and deterioration in physical properties. Because the die swell ratio affects the dimensions and dimensional accuracy of the resulting product, as well as the design of the extrusion die, rubber materials with minimal die swell ratio change during extrusion molding are desired in order to reuse scrap compounds. Furthermore, poor scorch time increases the likelihood of poor appearance, such as discoloration and rough surfaces due to poor plasticization of the rubber. Therefore, rubber materials with as little scorch time as possible during extrusion molding are desired in order to reuse scrap compounds. Furthermore, in terms of physical properties, in order to avoid a decline in the performance of each product, a rubber material with as little change in physical properties as possible is required in order to reuse scrap compounds.

[0004] Chloroprene rubber is available in grades that have a small die swelling ratio for extrusion molding applications, but extrusion-grade chloroprene rubber has a shorter scorch time and tends to have inferior physical properties than mercaptan-modified chloroprene rubber or sulfur-modified chloroprene rubber.

[0005] Additionally, common compounding methods include using low-viscosity polymers or adding softeners or plasticizers to lower the rubber viscosity and thereby improve the die swelling ratio, but this can sometimes cause problems with shape retention after extrusion molding, and physical properties also tend to deteriorate.

[0006] Furthermore, a method has been devised in which cellulose fibers are added as compounding agents to improve the die swell ratio, but this method has many problems, such as poor dispersion of the cellulose fibers, deterioration of the finished product surface, reduction in tensile strength and elongation after vulcanization, deterioration of water resistance, and deterioration of compression set.

[0007] Another method proposed for suppressing the die swell ratio is to mix in an ethylene-vinyl acetate copolymer having a hydroxyl group (see, for example, Patent Document 1). In Patent Document 1, examples and comparative examples are compared in which the hardness after vulcanization differs significantly, but when an ethylene-vinyl acetate copolymer is actually blended and various physical properties are compared by adjusting the type and amount of vulcanization chemicals added to achieve the same hardness after vulcanization, although there is an improvement in the die swell ratio, there is a significant decrease in tensile strength and elongation.

[0008] Next, as another method for suppressing the die swelling ratio, a method of adding a fiber-reinforced thermoplastic composition has also been proposed (see, for example, Patent Document 2). However, although the green modulus is significantly improved, the die swelling ratio is not as significantly improved. In addition, the mixing temperature required to mix the thermoplastic composition with the rubber is high, making this method unsuitable for application to chloroprene rubber.

[0009] Furthermore, although the above-mentioned methods have various problems, they are all methods for improving the die swell ratio, but they do not address the die swell ratio, scorch, or physical properties when recycling scrap materials. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 50-159536 [Patent Document 2] Japanese Patent Application Publication No. 7-330961 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in consideration of this problem, and its object is to provide a chloroprene rubber composition and vulcanized rubber that do not change the die swelling ratio of extrusion molding waste materials, have excellent scorch resistance, and are suitable for reuse. [Means for solving the problem]

[0012] The present inventors have conducted extensive research to solve the above problems and have found that a rubber composition containing chloroprene rubber and cellulose nanofibers does not experience a decrease in die swelling ratio even after shear stress and heat are applied during extrusion molding, and has excellent scorch resistance. That is, the present invention provides the following aspects [1] to [4]. [1] Contains the following components (A) to (C): Component (A): mercaptan-modified chloroprene rubber Component (B): 1.0 to 3.0 parts by weight of cellulose nanofibers with 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 hydroxymethyl groups not modified with carboxylic acid or carboxylate salt, per 100 parts by weight of component (A). Component (C): 1 to 20 parts by weight of at least one selected from the group consisting of plasticizers, surfactants, and partial fatty acid esters of polyhydric alcohols, based on 100 parts by weight of the total of components (A) and (B). A chloroprene rubber composition for extrusion molding in which there is no difference in the die swell ratio at a shear rate of 100 (1 / sec) between the initial state before molding for evaluation and the state after molding for evaluation, no melt fracture occurs in the extrusion molded product in die swell ratio measurement, and the Mooney scorch time t5 in the initial state before molding for evaluation is 8 minutes or more. <Evaluation molding> The CR rubber composition for evaluation was placed in an oven heated to 70°C for 20 minutes, and then mixed with an 8-inch roll at a gap of 1.4 mm for 10 minutes. [2] The chloroprene rubber composition for extrusion molding according to [1], wherein the cellulose nanofibers are unmodified and defibrated only by mechanical treatment. [3] The chloroprene rubber composition for extrusion molding according to [1] or [2], wherein the mercaptan-modified chloroprene rubber contains 3 to 7% by weight of a carboxylic acid or an alkali metal salt of a carboxylic acid. [4] A vulcanized rubber which is a vulcanizate of the chloroprene rubber composition for extrusion molding according to any one of [1] to [3]. [Effects of the Invention]

[0013] According to the present invention, there are provided a chloroprene rubber composition for extrusion molding and a vulcanized rubber which do not suffer a decrease in die swelling ratio when extrusion molding waste material compounds are reused and which have excellent scorch resistance. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below.

[0015] The chloroprene rubber composition for extrusion molding according to one embodiment of the present invention comprises: Contains the following components (A) to (C): Component (A): mercaptan-modified chloroprene rubber Component (B): 1.0 to 3.0 parts by weight of cellulose nanofibers with 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 hydroxymethyl groups not modified with carboxylic acid or carboxylate salt, per 100 parts by weight of component (A). Component (C): 1 to 20 parts by weight of at least one selected from the group consisting of plasticizers, surfactants, and partial fatty acid esters of polyhydric alcohols, based on 100 parts by weight of the total of components (A) and (B). The chloroprene rubber composition for extrusion molding has no difference in die swell ratio at a shear rate of 100 (1 / sec) between the initial state before molding for evaluation and the state after molding for evaluation, does not cause melt fracture in the extrusion molded product in die swell ratio measurement, and has a Mooney scorch time t5 of 8 minutes or more in the initial state before molding for evaluation. <Evaluation molding> The CR rubber composition for evaluation was placed in an oven heated to 70°C for 20 minutes, and then mixed with an 8-inch roll at a gap of 1.4 mm for 10 minutes.

[0016] Chloroprene rubber can be obtained by emulsion polymerization of chloroprene or chloroprene and a monomer copolymerizable therewith.

[0017] Examples of monomers copolymerizable with chloroprene include, in addition to 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, and acrylic acid. One or more of these can be used in combination, and are used appropriately depending on the required physical properties.

[0018] Although the amount of copolymerizable monomer is not particularly limited, it is generally 30 parts by weight or less per 100 parts by weight of chloroprene rubber so as not to impair the properties of the chloroprene polymer. In particular, for sulfur, the amount is preferably 3 parts by weight or less, more preferably 1 part by weight or less, per 100 parts by weight of chloroprene monomer to achieve a good balance between heat resistance and physical properties.

[0019] The chloroprene rubber preferably contains 3 to 7% by weight of carboxylic acid or alkali metal salt of carboxylic acid. When the content is 3% by weight or more, excellent emulsion stability is achieved during chloroprene polymerization, and when the content is 7% by weight or less, excellent processability and stable quality of the resulting rubber product can be obtained.

[0020] In emulsion polymerization of chloroprene rubber, for example, the above-mentioned monomers are mixed with an emulsifier, water, a polymerization initiator, a chain transfer agent, other stabilizers, etc., and polymerization is carried out at a predetermined temperature, and a polymerization terminator is added to terminate the polymerization at a predetermined polymerization conversion rate.

[0021] Examples of emulsifiers include alkali metal salts of carboxylic acids and alkali metal salts of sulfonic acids, such as alkali metal salts of rosin acid, alkali metal salts of alkylbenzenesulfonic acids, alkali metal salts of fatty acids, alkali metal salts of alkenylsuccinic acids, alkali metal salts of polycarboxylic acids, and nonionic emulsifiers such as polyoxyethylene alkyl ethers, as well as water-soluble polymer compounds. Examples of alkali metal salts include lithium, sodium, potassium, and cesium. These may be used alone or in combination with two or more other types. However, from the viewpoints of polymerization stability, cohesion during drying, and rubber performance, it is preferable to use an alkali metal salt of carboxylic acid, and in particular, it is preferable to use an alkali metal salt of rosin acid, and more preferably, it is preferable to use a potassium salt of rosin acid.

[0022] The amount of 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 chloroprene rubber, and the amount of alkali metal salt of carboxylic acid is preferably 3 to 8 parts by weight, more preferably 5 to 7 parts by weight.

[0023] In order to maintain the stability of the polymerization solution, it is preferable to adjust the pH to 11 or higher using a pH adjuster. At a pH of 11 or higher, the alkali metal salt of carboxylic acid is not acidified, and the stability of the latex is not 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, and any of these can be used alone or in combination.

[0024] As the emulsion polymerization initiator, known free radical substances can be used, for example, peroxides such as potassium persulfate and ammonium persulfate, hydrogen peroxide, inorganic or organic peroxides such as tertiary butyl hydroperoxide, etc. These may be used alone or in combination with reducing substances such as thiosulfates, thiosulfites, hydrosulfites, organic amines, etc. in a redox system.

[0025] Examples of chain transfer agents include molecular weight regulators such as alkyl mercaptans, halogenated hydrocarbons, alkyl xanthogen disulfides, alkyl xanthogen polysulfides, and sulfur, and n-dodecyl mercaptan is preferred for mercaptan modification from the viewpoint of workability. The amount of chain transfer agent is not particularly limited as long as it is an amount used in general radical polymerization for molecular weight adjustment, but it is preferably 0.01 to 1.0 wt% relative to 100 wt% of the monomer mixture other than the chain transfer agent in order to achieve the desired molecular weight and toluene-insoluble content of the resulting polymer and to achieve the desired flexibility and good mechanical properties of the vulcanized rubber obtained by dip molding.

[0026] The polymerization temperature is not particularly limited, but is preferably in the range of 10 to 50°C.

[0027] The time when the polymerization is to be completed is not particularly limited, but a monomer conversion rate of 60% or more can ensure the production amount, and a monomer conversion rate of 95% or less prevents the polymerization time from becoming too long, so a range of 60 to 95% is preferred in terms of productivity.

[0028] The polymerization terminator is not particularly limited as long as it is a commonly used terminator, and examples thereof include phenothiazine, 2,6-t-butyl-4-methylphenol, and hydroxylamine.

[0029] In the case of sulfur-modified chloroprene copolymerized with sulfur, it is possible to add a deflocculating agent and a deflocculating aid to the polymerization-stopped latex and continue peptization until a suitable Mooney viscosity is obtained. The deflocculating agent includes thiuram compounds such as tetraethylthiuram disulfide, tetrabutylthiuram disulfide, and tetraoctylthiuram disulfide, which can be added in an emulsified state using the above-mentioned emulsifiers, etc. The peptizing reaction initiator includes thiocarbamic acid compounds such as sodium dibutyldithiocarbamate and ammonium dimethyldithiocarbamate, etc.

[0030] As the chloroprene rubber, mercaptan-modified chloroprene rubber is used.

[0031] Cellulose nanofibers are cellulose fibers contained in wood that have been defibrated to an average fiber diameter of several nanometers to several tens of nanometers.

[0032] Cellulose defibration processes can be carried out primarily by mechanical processing alone, or by chemical processing to impart various functional groups and then mechanical processing to achieve even finer single-nano levels.

[0033] Cellulose nanofibers modified by chemical treatment are much more expensive than unmodified ones, so unmodified ones are preferred. Furthermore, when the hydroxymethyl groups of cellulose are modified with carboxylic acids and carboxylates by chemical treatment, the dispersion state of the cellulose nanofibers in the rubber deteriorates, so cellulose nanofibers that do not contain carboxylic acids or carboxylates are preferred.

[0034] Furthermore, it is preferable to use cellulose nanofibers whose surface tension in a 1% by weight aqueous dispersion is 60 mN / m or less. Examples of such cellulose nanofibers include amphiphilic cellulose nanofibers. Amphiphilicity refers to the cellulose nanofibers possessing both hydrophilic and hydrophobic portions with high and low water affinity, respectively. This can be achieved by high-speed head-on collision of aqueous suspension samples, as described in Japanese Patent Publication No. 5419120. Amphiphilicity enhances the affinity between cellulose and hydrophobic rubber, resulting in significant improvements in mechanical properties with a smaller mixing volume. Generally, the surface tension of pure water is approximately 72 mN / m, but the greater the hydrophobicity, the lower the surface tension. A cellulose nanofiber aqueous dispersion with a surface tension of 60 mN / m or less at a 1% by weight concentration is considered to be amphiphilic and have high affinity with rubber.

[0035] Furthermore, wood and other raw materials for cellulose nanofibers contain lignin, and since cellulose nanofibers containing a large amount of lignin may impair the stability of chloroprene latex, the amount of lignin contained is preferably 20% by weight or less, more preferably 10% by weight or less, and even more preferably 5% by weight or less.

[0036] In the present invention, it is preferable to use cellulose nanofibers that have been defibrated only by mechanical treatment without chemical treatment, in order to avoid the cellulose nanofibers becoming expensive and to avoid worsening the dispersion state of the cellulose nanofibers in the rubber. Furthermore, it is preferable that the cellulose nanofibers have amphiphilic properties in order to increase their affinity with the rubber.

[0037] It is desirable to use cellulose nanofibers having an average fiber diameter of 10 to 300 nm, preferably 10 to 100 nm, and an average fiber length of 0.3 to 200 μm, preferably 0.3 to 100 μm.

[0038] In the rubber composition of the present invention, the content of cellulose nanofibers is 1.0 to 3.0 parts by weight per 100 parts by weight of chloroprene rubber. If the content is less than 1.0 part by weight, the effect of improving the rate of change in die swelling ratio cannot be obtained, and if the content exceeds 3.0 parts by weight, handling properties when mixing the cellulose nanofibers deteriorate.

[0039] The rubber composition can be obtained by mixing an aqueous dispersion of cellulose nanofibers with chloroprene latex to prepare a cellulose nanofiber-dispersed rubber latex mixture, removing water from the cellulose nanofiber-dispersed rubber latex mixture, and then mixing the mixture with a reinforcing agent, filler, acid acceptor, vulcanizing agent, and other chemicals such as plasticizers, processing aids, and antioxidants as needed.

[0040] The chloroprene latex is not particularly limited as long as it is chloroprene rubber emulsified and dispersed in water with an emulsifier, and examples thereof include an emulsion obtained by emulsion polymerization of an unsaturated monomer copolymerizable with a chloroprene monomer, and an emulsion obtained by dissolving chloroprene rubber in an organic solvent such as toluene and then mixing it with water and an emulsifier.

[0041] There are no particular limitations on the method for mixing the chloroprene rubber latex and the aqueous dispersion of cellulose nanofibers, and the mixture can be obtained by using a propeller-type stirring device, a homomixer, a high-pressure homogenizer, or the like, and mixing the chloroprene latex and the aqueous dispersion of cellulose nanofibers until they appear uniform (no lumps, etc.).

[0042] Methods for removing water (drying methods) from the cellulose nanofiber-dispersed rubber latex mixture include heat drying, coagulation with acid or salt, and freeze drying. However, coagulation leaves emulsifier, coagulation liquid, and water inside the rubber, so the most efficient and easiest method for drying is to precipitate the rubber by freezing (freeze coagulation), wash off the excess emulsifier, etc., and then dry with hot air. Furthermore, freeze drying after adjusting the pH of the cellulose nanofiber-dispersed rubber latex mixture to 10 or less is even more preferable, so that the rubber can be more easily precipitated.

[0043] In the method of freezing and coagulating the cellulose nanofiber-dispersed rubber latex mixture and then drying it, the viscosity of the cellulose nanofiber-dispersed rubber latex mixture is preferably 1000 mPa·s or less, and more preferably 600 mPa or less.

[0044] The solid content of the cellulose nanofiber-dispersed rubber latex mixture liquid is preferably 20% by weight or more, and more preferably 25% by weight or more and 35% by weight or less.

[0045] The resulting cellulose nanofiber-containing rubber composition can be mixed with at least one selected from the group consisting of plasticizers, surfactants, and partial fatty acid esters of polyhydric alcohols (1 to 20 parts by weight total per 100 parts by weight of the cellulose nanofiber-containing chloroprene rubber composition), as well as reinforcing agents, fillers, acid acceptors, vulcanizing agents, and other chemicals such as processing aids and antioxidants, as needed. Examples of plasticizers include phthalates, adipates, sebacates, azelates, dodecanoates, trimellitates, polyetheresters, thioethers, glycerins, phosphite esters, oleic acids, vegetable oils, aroma oils, naphthenic oils, paraffin oils, chlorinated paraffins, and diethylene glycols. Examples of surfactants include metal soaps, fatty acid esters, fatty acid amides, and fatty acids. Examples of partial fatty acid esters of polyhydric alcohols include glycerin monostearate, sorbitan monooleate, and polyglycerin fatty acid esters. Examples of reinforcing agents include carbon black and silica. Examples of fillers include clay, calcium carbonate, talc, titanium oxide, barium sulfate, aluminum hydroxide, wollastonite, and diatomaceous earth. Examples of acid acceptors include magnesium oxide, hydrotalcites, hydroxides, and epoxy compounds. Examples of vulcanizing agents include sulfur, thioureas, peroxides, and diamines. Examples of processing aids include stearic acid, stearates, paraffin waxes, microcrystalline waxes, polyethylene waxes, carnauba wax, beeswax, and ozone wax. Examples of antioxidants include aromatic secondary amines, amine ketones, monophenols, bisphenols, polyphenols, benzimidazoles, dithiocarbamates, phosphorous acids, and organic thioacids.

[0046] Furthermore, the vulcanized rubber, which is one embodiment of the present invention, can be obtained by vulcanizing the above rubber composition at an appropriate vulcanization temperature until the test material is cured by about 90% based on the maximum torque.

[0047] The obtained rubber composition does not have a decrease in die swelling ratio when recycling extrusion molding waste material compounds, and has excellent scorch resistance, compared to rubber compositions that do not contain cellulose nanofibers. Therefore, it is suitable for reuse. [Example]

[0048] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0049] <Preparation of chloroprene latex> A monomer mixture of 100 parts by weight of chloroprene and 0.2 parts by weight of mercaptan was mixed with an aqueous emulsion containing 4.0 parts by weight of potassium salt of rosin acid, 0.3 parts by weight of the sodium salt of a condensate of naphthalenesulfonic acid and formaldehyde, 0.3 parts by weight of sulfate of oleic acid, 0.2 parts by weight of sodium hydroxide, and 100 parts by weight of water. The mixture was emulsified by stirring, and a polymerization catalyst consisting of 0.1 parts by weight of potassium persulfate, 0.01 parts by weight of sodium anthraquinone-β-sulfonate, and 20 parts by weight of water was added at a constant rate via a pump to carry out polymerization. The polymerization was continued with the addition of the polymerization catalyst until a polymerization conversion rate of 70% was reached, at which point the polymerization was terminated by the addition of 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. Subsequently, unreacted chloroprene was removed and recovered by steam stripping under reduced pressure, yielding a mercaptan-modified chloroprene rubber latex.

[0050] To 100 parts by weight of chloroprene, 0.5 parts by weight of xanthogen was added, and the mixture was mixed with an emulsifying aqueous solution containing 4.0 parts by weight of potassium salt of rosin acid, 0.3 parts by weight of the sodium salt of a condensate of naphthalenesulfonic acid and formaldehyde, 0.3 parts by weight of the sodium salt of a condensate of naphthalenesulfonic acid and formaldehyde, 0.2 parts by weight of sodium hydroxide, and 100 parts by weight of water. A polymerization catalyst consisting of 0.1 parts by weight of potassium persulfate, 0.01 parts by weight of sodium anthraquinone-β-sulfonate, and 20 parts by weight of water was added at a constant rate using a pump to carry out polymerization. The polymerization was continued by adding the polymerization catalyst until a polymerization conversion of 70% was reached, and then the polymerization was terminated by adding 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. Subsequently, unreacted chloroprene was removed and recovered by steam stripping under reduced pressure to obtain a latex of xanthogen-modified chloroprene polymer A. Next, a latex of mercaptan-modified chloroprene polymer B was obtained in the same manner as for chloroprene polymer A, except that the polymerization recipe was changed to 0.2 parts by weight of mercaptan per 100 parts by weight of chloroprene, and the polymerization addition rate was set to 90%. The latexes of chloroprene polymers A and B were mixed in a ratio of 4:1 to obtain an extrusion-grade chloroprene latex.

[0051] Furthermore, 0.3 parts by weight of sulfur was added to 100 parts by weight of chloroprene as a monomer mixture, and the mixture was mixed with an emulsifying aqueous solution containing 4.0 parts by weight of potassium salt of rosin acid, 0.5 parts by weight of sodium salt of a condensate of naphthalenesulfonic acid and formaldehyde, 0.05 parts by weight of sodium hydroxide, 1.0 part by weight of sodium orthophosphate, and 100 parts by weight of water, and emulsified by stirring. To this was added a polymerization catalyst consisting of 1.0 part by weight of potassium persulfate, 0.01 part by weight of sodium anthraquinone-β-sulfonate, and 30 parts by weight of water at a constant rate using a pump to carry out polymerization. The polymerization was carried out by adding a polymerization catalyst until a polymerization conversion rate of 70% was reached, and then a polymerization terminator consisting of 0.01 part by weight of thiodiphenylamine, 0.05 part by weight of 4-t-butylcatechol, 2,2'-methylenebis-4-methyl-6-t-butylphenol, 0.1 part by weight of diethylhydroxylamine, 0.05 part by weight of sodium lauryl sulfate, 5.0 parts by weight of chloroprene, and 1.0 part by weight of water was added to terminate the polymerization. Subsequently, a toluene solution of 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 peptized 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 a sulfur-modified chloroprene rubber latex.

[0052] <Measurement of the average fiber diameter of cellulose nanofibers> The cellulose nanofibers were diluted with pure water to a concentration of 0.1 wt%, filtered, and dried. After this, they were coated with osmium and observed at 20,000x magnification using a JEOL Ltd. FE-SEM JSM-7100F. One hundred fibers were randomly selected from the obtained observation image, and their fiber diameters were measured. The average value was used as the average fiber diameter.

[0053] <Preparation of Rubber Composition> A predetermined amount of an aqueous dispersion of cellulose nanofiber (Nanoforest, manufactured by Chuetsu Pulp Industries Co., Ltd.) was added to the chloroprene rubber latex, and the mixture was mixed at 2,000 rpm for 10 minutes using an auto homomixer (PRIMIX, manufactured by Primix Corporation). The polymer was then precipitated by freeze coagulation and dried. <Evaluation molding method> The CR rubber composition for evaluation was placed in an oven heated to 70°C for 20 minutes, and then mixed with an 8-inch roll at a gap of 1.4 mm for 10 minutes.

[0054] <Mooney Scorch Measurement> Using a Mooney Viscometer (Shimadzu Corporation: Automatic Mooney Viscometer SMV-301), test pieces were collected and measured in accordance with JIS K 6300-1:2013 to obtain the minimum Mooney viscosity value Vm, the time it takes for the viscosity to rise by 5M from Vm, t5, and the time it takes for the viscosity to rise by 35M, t35.

[0055] <Die swell ratio measurement> The temperature inside the cylinder of a capillary rheometer (ARC2020 manufactured by Alpha Technologies) was set to 70°C, and an orifice length of 1.524 mm, φ1.524 mm, and L / D = 1 were used. After the rubber composition was charged and the temperature was adjusted for 2 minutes, the die swell ratio was calculated by dividing the diameter of the extrudate obtained by extruding at a specified shear rate by the diameter of the orifice. Regarding extrudability, if melt fracture, such as irregularities or spiral streaks, occurred on the surface of the extrudate, it was rated as "poor appearance" (×), and if no irregularities or spiral streaks occurred, it was rated as "good appearance." The melt fracture criterion was determined by measuring approximately 10 mm of the extrudate with a microscope (n = 3) and finding one or more irregularities or streaks of 100 μm or greater. Note that irregularities due to air entrapment were excluded from the evaluation.

[0056] Example 1 An aqueous dispersion of cellulose nanofibers produced by mechanical defibration (Nanoforest S, manufactured by Chuetsu Pulp Co., Ltd., solids concentration: 3 wt%, average fiber diameter: approximately 50 nm, average fiber length: approximately 100 μm, lignin content: 1 wt% or less, unmodified, amphiphilic) was mixed with 100 parts by weight of mercaptan-modified chloroprene rubber and stirred for 10 minutes using the method described above to obtain a cellulose nanofiber-dispersed rubber latex mixture. The amount of cellulose nanofiber mixed was such that the cellulose content was 1.2 wt% per 100 parts by weight of the solid rubber component. The viscosity of the dispersion was 125 mPa·s, which made it easy to handle, and freeze-drying yielded a cellulose nanofiber-containing chloroprene rubber composition.

[0057] This cellulose nanofiber-containing chloroprene rubber composition was mixed with 4 parts by weight of magnesium oxide (Kyowamag (registered trademark) #150, manufactured by Kyowa Chemical Industry Co., Ltd.), 0.5 parts by weight of stearic acid (Stearic Acid 300, manufactured by Shin-Nihon Rika Co., Ltd.), 61 parts by weight of SRF carbon black (Seast (registered trademark) S, manufactured by Tokai Carbon Co., Ltd.), and 20 parts by weight of plasticizer DOS (Daihachi Chemical Industry Co., Ltd.: DOS) in an open roll mixer under conditions of a roll gap of 1.5 mm, a roll surface temperature of approximately 50°C, and a mixing time of approximately 20 minutes. After cooling, the mixture was mixed with 5 parts by weight of zinc oxide (Zinc Oxide Type 2, manufactured by Sakai Chemical Industry Co., Ltd.), 1.0 part by weight of accelerator 2-imidazoline-2-thiol (ETU) (Suncerer® #22-C, manufactured by Sanshin Chemical Industry Co., Ltd.), and 0.5 part by weight of accelerator dibenzothiazole disulfide (MBTS) (Noccela DM, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) in an open roll mixer under conditions of a roll gap of 1.5 mm, a roll surface temperature of approximately 50°C, and a mixing time of approximately 10 minutes to obtain a rubber composition, and Mooney scorch and die swell ratio were measured. Further, evaluation molding was performed using the method described above, and Mooney scorch and die swell ratio were measured. The results are shown in Table 1. As can be seen from Table 1, there was no difference in the die swell ratio at a shear rate of 100 (1 / sec) between the initial state before evaluation molding and after evaluation molding, and the t5 of the Mooney scorch test was 11.5 minutes, both of which were good results.

[0058] Example 2 A cellulose nanofiber-containing chloroprene rubber composition was obtained using the same chloroprene rubber, cellulose content, and method as in Example 1. The viscosity of the dispersion was 125 mPa·s, and there were no problems with handling. This cellulose nanofiber-containing chloroprene rubber composition was mixed with 4 parts by weight of magnesium oxide (Kyowamag (registered trademark) #150, manufactured by Kyowa Chemical Industry Co., Ltd.), 0.5 parts by weight of stearic acid (Stearic Acid 300, manufactured by Shin-Nihon Rika Co., Ltd.), 18 parts by weight of SRF carbon black (Seast (registered trademark) S, manufactured by Tokai Carbon Co., Ltd.), 93 parts by weight of calcium carbonate (Shiraishi Kogyo Co., Ltd.: Hakuenka (registered trademark) CC), and 16 parts by weight of plasticizer DOS (Daihachi Chemical Industry Co., Ltd.: DOS) in an open roll mixer under conditions of a roll gap of 1.5 mm, a roll surface temperature of approximately 50°C, and a mixing time of approximately 20 minutes. After cooling, the mixture was mixed with 5 parts by weight of zinc oxide (Zinc Oxide Type 2, manufactured by Sakai Chemical Industry Co., Ltd.), 1.0 part by weight of accelerator 2-imidazoline-2-thiol (ETU) (Suncerer® #22-C, manufactured by Sanshin Chemical Industry Co., Ltd.), and 0.5 parts by weight of accelerator dibenzothiazole disulfide (MBTS) (Noccela® DM, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) in an open roll mixer under conditions of a roll gap of 1.5 mm, a roll surface temperature of approximately 50°C, and a mixing time of approximately 10 minutes to obtain a rubber composition, which was then subjected to measurements similar to those in Example 1. The results are shown in Table 1. Table 1 indicates that there was no difference in the die swell ratio at a shear rate of 100 (1 / sec) between the initial state before and after evaluation molding, and the t5 value in the Mooney scorch test was 9.6 minutes, both of which were good results.

[0059] Comparative Example 1 A rubber composition was obtained in the same manner as in Example 1, except that cellulose nanofibers were not mixed in and the amount of SRF carbon black was adjusted so that the hardness was similar to that of Example 1, and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1. As can be seen from Table 1, although the t5 value in the Mooney scorch test was good, the die swell ratio at a shear rate of 100 (1 / sec) after evaluation molding was worse than the initial state before evaluation molding.

[0060] Comparative Example 2 A cellulose nanofiber-containing chloroprene rubber composition was obtained in the same manner as in Example 1, except that the chloroprene rubber and cellulose content were changed to 0.4 parts by weight. The viscosity of the dispersion was 25 mPa·s, and handling was not a problem. A rubber composition was obtained in the same manner as in Example 1, except that the amount of SRF carbon black was adjusted to obtain a hardness similar to that of Example 1, and measurements similar to those in Example 1 were carried out. The results are shown in Table 1. As can be seen from Table 1, although the t5 value in the Mooney scorch test was good, the die swell ratio at a shear rate of 100 (1 / sec) after evaluation molding was worse than the initial state before evaluation molding.

[0061] Comparative Example 3 A rubber composition was obtained in the same manner as in Example 2, except that cellulose nanofibers were not mixed in and the amount of SRF carbon black was adjusted so that the hardness was similar to that of Example 2, and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1. As can be seen from Table 1, the t5 in the Mooney scorch test was 8 minutes or less, and the die swell ratio at a shear rate of 100 (1 / sec) after evaluation molding was also worse than the initial state before evaluation molding.

[0062] Comparative Example 4 Without mixing cellulose nanofibers, chloroprene rubber was mixed with 4 parts by weight of magnesium oxide (Kyowamag (registered trademark) #150, manufactured by Kyowa Chemical Industry Co., Ltd.), 0.5 parts by weight of stearic acid (Stearic Acid 300, manufactured by Shin-Nihon Rika Co., Ltd.), and 30 parts by weight of SRF carbon black (Seast (registered trademark) S, manufactured by Tokai Carbon Co., Ltd.) in an open roll mixer under conditions of a roll gap of 1.5 mm, a roll surface temperature of approximately 50°C, and a mixing time of approximately 20 minutes. After cooling, the mixture was mixed with 5 parts by weight of zinc oxide (Zinc Oxide Type 2, manufactured by Sakai Chemical Industry Co., Ltd.), 1.0 part by weight of accelerator 2-imidazoline-2-thiol (ETU) (Suncerer® #22-C, manufactured by Sanshin Chemical Industry Co., Ltd.), and 0.5 parts by weight of accelerator dibenzothiazole disulfide (MBTS) (Noccela® DM, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) in an open roll mixer under conditions of a roll gap of 1.5 mm, a roll surface temperature of approximately 50°C, and a mixing time of approximately 10 minutes to obtain a rubber composition, which was then subjected to measurements similar to those in Example 1. The results are shown in Table 1. Table 1 indicates that although the t5 value in the Mooney scorch test was good, melt fracture occurred in the die swell ratio evaluation.

[0063] Comparative Example 5 A cellulose nanofiber-containing chloroprene rubber composition was obtained in the same manner as in Example 1, except that the chloroprene rubber and cellulose content were changed to 1.2 parts by weight. The viscosity of the dispersion was 125 mPa·s, and handling was not a problem. A rubber composition was obtained in the same manner as in Comparative Example 4, except that the amount of SRF carbon black was adjusted to obtain a hardness similar to that of Comparative Examples 4 and 6, and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1. As can be seen from Table 1, although the t5 value in the Mooney scorch test was good, melt fracture occurred in the die swell ratio evaluation.

[0064] Comparative Example 6 A cellulose nanofiber-containing chloroprene rubber composition was obtained in the same manner as in Example 1, except that the chloroprene rubber and cellulose content were changed to 2.0 parts by weight. The viscosity of the dispersion was 300 mPa·s, and handling was not a problem. A rubber composition was obtained in the same manner as in Comparative Example 4, except that the amount of SRF carbon black was adjusted to obtain a hardness similar to that of Comparative Examples 4 and 5, and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1. As can be seen from Table 1, although the t5 value in the Mooney scorch test was good, melt fracture occurred in the die swell ratio evaluation.

[0065] Comparative Example 7 A cellulose nanofiber-containing chloroprene rubber composition was obtained in the same manner as in Example 1, except that the chloroprene rubber and cellulose content were changed to 3.5 parts by weight. The viscosity of the dispersion was 1050 mPa·s, which caused problems with handling.

[0066] Comparative Example 8 A rubber composition was obtained in the same manner as in Comparative Example 4, except that the chloroprene rubber used was changed to extrusion-grade chloroprene rubber, and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1. As can be seen from Table 1, the t5 in the Mooney scorch test was 8 minutes or less, and the die swell ratio at a shear rate of 100 (1 / sec) after evaluation molding was also worse than the initial state before evaluation molding.

[0067] Comparative Examples 9 and 10 The chloroprene rubber used was changed to a sulfur-modified chloroprene rubber, and a rubber composition was obtained in the same manner as in Comparative Example 1 and Example 1, and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1. As shown in Table 1, the t5 value in the Mooney scorch test was good, and the die swelling ratio at a shear rate of 100 (1 / sec) after the evaluation molding was also improved compared to before the evaluation molding. However, this improvement in the die swelling ratio was due to the mastication effect of the sulfur-modified polymer, and both Comparative Examples 11 and 12 showed similar improvement effects, and no improvement in the die swelling ratio due to the addition of cellulose nanofibers was found.

[0068]

Table 1

Claims

1. Contains the following components (A) to (C): Component (A): mercaptan-modified chloroprene rubber Component (B): 1.0 to 3.0 parts by weight of cellulose nanofibers having 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 hydroxymethyl groups not modified with carboxylic acid or carboxylate salt, per 100 parts by weight of component (A). Component (C): 1 to 20 parts by weight of at least one selected from the group consisting of plasticizers, surfactants, and partial fatty acid esters of polyhydric alcohols, based on 100 parts by weight of the total of components (A) and (B). A chloroprene rubber composition for extrusion molding in which there is no difference in the die swell ratio at a shear rate of 100 (1 / sec) between the initial state before molding for evaluation and the state after molding for evaluation, no melt fracture occurs in the extrusion molded product in die swell ratio measurement, and the Mooney scorch time t5 in the initial state before molding for evaluation is 8 minutes or more. <Evaluation molding> The CR rubber composition for evaluation was placed in an oven heated to 70° C. for 20 minutes, and then mixed with an 8-inch roll at a gap of 1.4 mm for 10 minutes.

2. 2. The chloroprene rubber composition for extrusion molding according to claim 1, wherein the cellulose nanofibers are unmodified and defibrated only by mechanical treatment.

3. 2. The chloroprene rubber composition for extrusion molding according to claim 1, wherein the mercaptan-modified chloroprene rubber contains 3 to 7% by weight of a carboxylic acid or an alkali metal salt of a carboxylic acid.

4. A vulcanized rubber which is a vulcanizate of the chloroprene rubber composition for extrusion molding according to any one of claims 1 to 3.

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