JP6990190B2 - Method for manufacturing rubber composition - Google Patents

Description

The present invention relates to a method for producing a rubber composition containing cellulosic fibers.

Rubber compositions containing rubber and cellulosic fibers are known to have excellent mechanical strength. For example, Patent Document 1 describes a rubber / short fiber master batch obtained by stirring and mixing a water dispersion of short fibers having an average fiber diameter of less than 0.5 μm and a rubber latex and removing water from the mixture. Are listed. The document describes that short fibers having an average fiber diameter of less than 0.5 μm are uniformly dispersed in rubber by mixing and drying a dispersion liquid obtained by fibrilizing short fibers in water and rubber latex. ing. It is also described that a rubber composition having an excellent balance between rubber reinforcing property and fatigue resistance can be produced from this rubber / staple fiber masterbatch. However, since the compatibility between rubber and cellulosic fibers is generally low, the strength of the rubber composition containing rubber and cellulosic fibers is insufficient. Therefore, it has been studied to use a silane coupling agent to improve compatibility and to introduce a long-chain alkyl group into a cellulose fiber (for example, Patent Documents 2 and 3).

Japanese Unexamined Patent Publication No. 2006-206864 Japanese Unexamined Patent Publication No. 2009-191198 Japanese Unexamined Patent Publication No. 2014-125607

However, there is a problem that the reagents used in the methods described in Patent Documents 2 and 3 are expensive. Further, these methods have a problem that the reaction rate is low and a sufficient strength improving effect cannot be obtained.
An object of the present invention is to provide a rubber composition having good compatibility between rubber and a cellulosic fiber and capable of exhibiting sufficient reinforcing properties.

The present invention provides the following [1] to [6].
[1] A step of adding a divalent or trivalent metal salt, or a divalent or trivalent metal salt and an acid to a mixed solution containing chloroprene rubber and a cellulosic fiber to coagulate the rubber component. , A method for producing a rubber composition.
[2] The method for producing a rubber composition according to [1], wherein the metal salt is a calcium salt.
[3] The method for producing a rubber composition according to [1] or [2], wherein the acid is acetic acid or sulfuric acid.
[4] The rubber composition according to any one of [1] to [3], wherein the cellulosic fiber contains at least one selected from the group consisting of oxidized cellulose fiber, carboxymethylated cellulose fiber and cationized cellulose fiber. Manufacturing method.
[5] The method for producing a rubber composition according to any one of [1] to [4], wherein the length-weighted average fiber length of the cellulosic fiber is 50 to 2000 nm.
[6] The method according to any one of [1] to [5], wherein the length-weighted average fiber diameter of the cellulosic fiber is 2 to 500 nm.

According to the present invention, it is possible to provide a rubber composition having good compatibility between rubber and a cellulosic fiber and capable of exhibiting sufficient reinforcing properties.

The present invention relates to a method for producing a rubber composition, which comprises a step (coagulation step) of adding a metal salt or a metal salt and an acid to a mixed solution containing chloroprene rubber and a cellulosic fiber to coagulate the chloroprene rubber. The rubber composition produced by this method has good compatibility between the rubber and the cellulosic fiber, can exhibit sufficient reinforcing properties, and can maintain the reinforcing properties even when a large strain is applied. The effect of the present invention is specifically expressed in a rubber composition containing chloroprene rubber and cellulosic fibers.

<1. Coagulation process>
In the present invention, coagulation (coagulation method) means that the rubber component is aggregated by adding an acid or a metal salt to a liquid such as a suspension (dispersion liquid) containing the rubber component, and as a result, the rubber component is separated (solidified). It is a process (process, method) for liquid separation).

The coagulation step comprises mixing chloroprene rubber and cellulosic fibers to obtain a mixed solution containing them, and adding a metal salt or an acid or a metal salt to the mixed solution.

<1.1. Metal salt ＞
The metal salt used for coagulation is preferably a divalent or trivalent metal salt. It is presumed that divalent or trivalent metal ions contribute to the improvement of the compatibility between the chloroprene rubber and the cellulosic fiber, and the reinforcing property of the rubber composition can be improved. Examples of the divalent or trivalent metal salt include calcium salts such as calcium chloride and calcium nitrate, magnesium salts such as magnesium chloride and magnesium sulfate, and aluminum salts such as aluminum chloride and aluminum sulfate, and calcium salts and magnesium. Salts are preferred, calcium salts are more preferred, and calcium chloride is even more preferred. It is presumed that calcium ions have a high contribution to improving the compatibility between chloroprene rubber and cellulosic fibers and improving the reinforcing property of the rubber composition. The metal salt may be one kind or a combination of two or more kinds.
The amount of the metal salt added to the mixed solution is not particularly limited, but the concentration of the metal salt in the total mixed solution is preferably adjusted to be 0.1% by weight or more, more preferably 0.3% by weight or more. Just do it. The upper limit is not particularly limited, but is preferably 3.0% by weight or less, and more preferably 2.0% by weight or less. Therefore, the concentration of the metal salt in the premix may be adjusted to be preferably 0.1 to 3.0% by weight, more preferably 0.3 to 2.0% by weight.

<1.2. Acid>
As the acid used for coagulation, either an organic acid or an inorganic acid can be used. As the organic acid, formic acid, acetic acid and the like are preferable. As the inorganic acid, sulfuric acid, hydrochloric acid, carbonic acid and the like are preferable. Of these, acetic acid and sulfuric acid are more preferable. The conditions for adding the acid differ depending on the type of metal salt, but in general, the pH in the mixed solution after the addition of the acid is adjusted to be preferably 3.0 or higher, more preferably 3.5 or higher, still more preferably 4.0 or higher. do it. The upper limit is not particularly limited, but is preferably 8.0 or less, more preferably 7.0 or less, still more preferably 6.0 or less, still more preferably 5.0 or less. Therefore, the pH is preferably 3.0 to 8.0, more preferably 3.5 to 7.0, still more preferably 4.0 to 7.0, 4.0 to 6.0, or pH 4.0 to 5. It may be adjusted to be 0.0. The acid may be one kind or a combination of two or more kinds.

In solidification, it is preferable to add a metal salt, or to add both a metal salt and an acid, and to add a divalent or trivalent metal salt, or to perform divalent or 3 valent. It is more preferable to add both the valent metal salt and the acid. When both the addition of the metal salt and the addition of the acid are performed, the timing of the addition of the metal salt and the addition of the acid is not particularly limited, but it is preferable to add the acid after the addition of the metal salt.

<1.3. Cellulose fiber>
In the present invention, the cellulosic fiber may be a cellulosic fiber having a fiber diameter on the order of micron or a cellulose nanofiber having a fiber diameter on the nano order obtained by chemically modifying the cellulosic fiber as necessary and then defibrating the fiber.

The origin of the cellulose fiber is not particularly limited, and examples thereof include plants, animals (for example, ascidians), algae, microorganisms (for example, acetobacter), and microbial products. Examples of plant-derived cellulose fibers include wood, bamboo, hemp, jute, kenaf, farmland waste, cloth, pulp (conifer unbleached kraft pulp (NUKP), conifer bleached kraft pulp (NBKP), and broadleaf unbleached kraft pulp. (LUKP), broad-leaved bleached kraft pulp (LBKP), coniferous unbleached sulphite pulp (NUSP), coniferous bleached sulphite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, used paper, etc.). The raw material of the cellulose fiber used in the present invention may be any one or a combination thereof, but is preferably a cellulose fiber derived from a plant or a microorganism, and more preferably a cellulose fiber derived from a plant.

The average fiber diameter of the cellulose fibers is not particularly limited, but is usually about 30 to 60 μm in the case of softwood kraft pulp, which is a general pulp, and usually about 10 to 30 μm in the case of hardwood kraft pulp. The average fiber diameter of pulps other than softwood kraft pulp and hardwood kraft pulp that have undergone general purification is usually about 50 μm. For example, when a raw material obtained by purifying a material having a size of several cm such as a chip is used, it is preferable to perform mechanical treatment with a dissociator such as a refiner or a beater to adjust the average fiber diameter to about 50 μm to obtain cellulose fibers.

The average fiber diameter of the cellulosic fiber (for example, cellulose nanofiber) is usually about 2 to 500 nm in terms of the length-weighted average fiber diameter, but is preferably 2 to 50 nm. The average fiber length is preferably 50 to 2000 nm in terms of length-weighted average fiber length. Atomic force microscope (AFM) or transmission electron microscope (TEM) is used for the length-weighted average fiber diameter and the length-weighted average fiber length (hereinafter, also simply referred to as "average fiber diameter" and "average fiber length"). It is obtained by observing each fiber. The average aspect ratio of cellulosic fibers (for example, cellulose nanofibers) is usually 10 or more. The upper limit is not particularly limited, but is usually 1000 or less. The average aspect ratio can be calculated by the following formula.

Average aspect ratio = average fiber length / average fiber diameter

Hereinafter, a method for producing cellulose nanofibers will be described. For convenience, the cellulose fiber that is the raw material of the cellulose nanofiber is also referred to as "cellulose raw material".

[Degeneration]
The cellulose raw material has three hydroxyl groups per glucose unit and can be subjected to various chemical denaturations. In the present invention, both the chemically modified cellulosic raw material and the non-chemically modified cellulosic raw material can be used as cellulosic fibers. When the chemically modified cellulose raw material is used, the fineness of the fiber is sufficiently advanced to obtain cellulose nanofibers having a uniform fiber length and fiber diameter, so that a sufficient reinforcing effect can be exhibited when composited with rubber. Therefore, as the cellulosic fiber, a cellulosic fiber obtained through chemical modification is preferable. Examples of the chemical denaturation include oxidation, etherification, phosphorylation, esterification, silane coupling, fluorination, cationization and the like. Of these, oxidation (carboxylation), etherification, cationization, and esterification are preferable. Hereinafter, chemical denaturation will be described.

[Oxidation]
The amount of carboxyl groups in the oxidized cellulose or cellulose nanofibers obtained by this treatment is preferably 0.5 mmol / g or more, more preferably 0.8 mmol / g or more, still more preferably 1. It is 0 mmol / g or more. The upper limit of the amount is preferably 3.0 mmol / g or less, more preferably 2.5 mmol / g or less, and further preferably 2.0 mmol / g or less. Therefore, the amount is preferably 0.5 to 3.0 mmol / g, more preferably 0.8 to 2.5 mmol / g, still more preferably 1.0 to 2.0 mmol / g. The amount of carboxyl groups of cellulose oxide and the amount of carboxyl groups of cellulose oxide nanofibers obtained from the cellulose oxide are usually the same.

The oxidation method is not particularly limited, but as an example, the cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a substance selected from the group consisting of bromide, iodide and a mixture thereof. There is a way to do it. According to this method, the primary hydroxyl group at the C6 position of the glucopyranose ring on the surface of cellulose is selectively oxidized to generate a group selected from the group consisting of an aldehyde group, a carboxyl group, and a carboxylate group. The concentration of the cellulose raw material at the time of the reaction is not particularly limited, but is preferably 5% by weight or less.

The N-oxyl compound is a compound capable of generating a nitroxy radical. Examples of the nitroxyl radical include 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). The N-oxyl compound may be any compound that promotes the desired oxidation reaction, and is not particularly limited. The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing cellulose as a raw material. For example, 0.01 mmol or more is preferable, and 0.02 mmol or more is more preferable with respect to 1 g of cellulose that is completely dried. The upper limit is preferably 10 mmol or less, more preferably 1 mmol or less, still more preferably 0.5 mmol or less. Therefore, the amount of the N-oxyl compound used is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, still more preferably 0.02 to 0.5 mmol with respect to 1 g of the dry cellulose.

The bromide is a compound containing bromine, and examples thereof include alkali metals bromide that can be dissociated and ionized in water, such as sodium bromide. Further, the iodide is a compound containing iodine, and examples thereof include an alkali metal iodide. The amount of bromide or iodide used can be selected within the range in which the oxidation reaction can be promoted. The total amount of bromide and iodide is preferably 0.1 mmol or more, more preferably 0.5 mmol or more, based on 1 g of dry cellulose. The upper limit of the amount is preferably 100 mmol or less, more preferably 10 mmol or less, still more preferably 5 mmol or less. Therefore, the total amount of bromide and iodide is preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, still more preferably 0.5 to 5 mmol with respect to 1 g of dry cellulose.

The oxidizing agent is not particularly limited, and examples thereof include halogen, hypohalogenic acid, subhalogenic acid, perhalogenic acid, salts thereof, halogen oxides, and peroxides. Among them, hypochlorous acid or a salt thereof is preferable, hypochlorous acid or a salt thereof is more preferable, and sodium hypochlorite is further preferable, because it is inexpensive and has a small environmental load. The amount of the oxidizing agent used is preferably 0.5 mmol or more, more preferably 1 mmol or more, still more preferably 3 mmol or more, based on 1 g of the dry cellulose. The upper limit of the amount is preferably 500 mmol or less, more preferably 50 mmol or less, still more preferably 25 mmol or less. Therefore, the amount of the oxidizing agent used is preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, still more preferably 1 to 25 mmol, and particularly preferably 3 to 10 mmol with respect to 1 g of the dry cellulose. When the N-oxyl compound is used, the amount of the oxidizing agent used is preferably 1 mol or more with respect to 1 mol of the N-oxyl compound, and the upper limit is preferably 40 mol. Therefore, the amount of the oxidizing agent used is preferably 1 to 40 mol with respect to 1 mol of the N-oxyl compound.

Conditions such as pH and temperature during the oxidation reaction are not particularly limited, and in general, the oxidation reaction proceeds efficiently even under relatively mild conditions. The reaction temperature is preferably 4 ° C. or higher, more preferably 15 ° C. or higher. The upper limit of the temperature is preferably 40 ° C. or lower, more preferably 30 ° C. or lower. Therefore, the reaction temperature is preferably 4 to 40 ° C, and may be about 15 to 30 ° C, that is, room temperature. The pH of the reaction solution is preferably 8 or more, more preferably 10 or more. The upper limit of pH is preferably 12 or less, more preferably 11 or less. Therefore, the pH of the reaction solution is preferably about 8 to 12, more preferably about 10 to 11. Usually, as the oxidation reaction progresses, a carboxyl group is generated in the cellulose, so that the pH of the reaction solution tends to decrease. Therefore, in order to efficiently proceed the oxidation reaction, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution in the above range. Water is preferable as the reaction medium for oxidation because it is easy to handle and side reactions are unlikely to occur.

The reaction time in oxidation can be appropriately set according to the degree of progress of oxidation, and is usually 0.5 hours or more, and the upper limit thereof is usually 6 hours or less, preferably 4 hours or less. Therefore, the reaction time in oxidation is usually about 0.5 to 6 hours, for example, about 0.5 to 4 hours. Oxidation may be carried out in two or more steps. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the first-stage reaction again under the same or different reaction conditions, the efficiency is not affected by the reaction inhibition by the salt produced as a by-product in the first-stage reaction. Can be oxidized well.

Another example of the carboxylation (oxidation) method is ozonolysis. By this oxidation reaction, the hydroxyl groups at at least the 2-position and the 6-position of the glucopyranose ring constituting the cellulose are oxidized, and the cellulose chain is decomposed. Ozone treatment is usually carried out by bringing a gas containing ozone into contact with a cellulose raw material. The ozone concentration in the gas is preferably 50 g / m ³ or more. The upper limit is preferably 250 g / m ³ or less, more preferably 220 g / m ³ or less. Therefore, the ozone concentration in the gas is preferably 50 to 250 g / m ³ , more preferably 50 to 220 g / m ³ . The amount of ozone added is preferably 0.1% by weight or more, more preferably 5% by weight or more, based on 100% by weight of the solid content of the cellulose raw material. The upper limit of the amount of ozone added is usually 30% by weight or less. Therefore, the amount of ozone added is preferably 0.1 to 30% by weight, more preferably 5 to 30% by weight, based on 100% by weight of the solid content of the cellulose raw material. The ozone treatment temperature is usually 0 ° C. or higher, preferably 20 ° C. or higher, and the upper limit is usually 50 ° C. or lower. Therefore, the ozone treatment temperature is preferably 0 to 50 ° C, more preferably 20 to 50 ° C. The ozone treatment time is usually 1 minute or more, preferably 30 minutes or more, and the upper limit is usually 360 minutes or less. Therefore, the ozone treatment time is usually about 1 to 360 minutes, preferably about 30 to 360 minutes. When the ozone treatment conditions are within the above range, it is possible to prevent the cellulose from being excessively oxidized and decomposed, and the yield of the oxidized cellulose becomes good.

The ozone-treated cellulose may be further subjected to a post-oxidation treatment using an oxidizing agent. The oxidizing agent used for the additional oxidation treatment is not particularly limited, and examples thereof include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. Examples of the method of the additional oxidation treatment include a method of dissolving these oxidizing agents in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and immersing the cellulose raw material in the oxidizing agent solution. The amount of carboxyl group, carboxylate group, and aldehyde group contained in the oxidized cellulose nanofiber can be adjusted by controlling the oxidation conditions such as the amount of the oxidizing agent added and the reaction time.

An example of a method for measuring the amount of carboxyl groups will be described below. Prepare 60 mL of a 0.5 wt% slurry (aqueous dispersion) of cellulose oxide, add a 0.1 M hydrochloric acid aqueous solution to adjust the pH to 2.5, and then add a 0.05 N sodium hydroxide aqueous solution to bring the pH to 11. Measure the electrical conductivity until it becomes. It can be calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization step of a weak acid in which the change in electrical conductivity is gradual.

Carboxyl group amount [mmol / g cellulose oxide or cellulose nanofiber] = a [mL] x 0.05 / cellulose oxide weight [g]

The product after oxidation may be subjected to desalting treatment. Desalting means that a salt (a countercation of a carboxylate group, for example, a sodium salt) contained in a reaction product (salt type) is replaced with a proton to form an acid type. By desalting treatment, the countercation of the carboxylate group introduced into the reaction product can be proton-substituted to obtain an acid-type carboxyl group-modified cellulose fiber. Desalination can be performed at any time before or after the defibration treatment described below. Examples of the post-oxidation desalting method include a method of adjusting the inside of the system to be acidic and a method of contacting cellulose oxide with a cation exchange resin. When the system is adjusted to be acidic, the pH in the system is preferably adjusted to 2 to 6, more preferably 2 to 5, and even more preferably 2.3 to 5. Acids (eg, inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, nitric acid, nitrite, phosphoric acid; organic acids such as acetic acid, lactic acid, oxalic acid, citric acid, formic acid) are usually used to adjust to acidity. After the addition of the acid, a cleaning treatment may be appropriately performed. As the cation exchange resin, either a strongly acidic ion exchange resin or a weakly acidic ion exchange resin can be used as long as the counterion is H ⁺ . The ratio of the two when the cellulose oxide is brought into contact with the cation exchange resin is not particularly limited, and a person skilled in the art can appropriately set the ratio from the viewpoint of efficiently performing proton substitution. The cation exchange resin after contact may be recovered by a conventional method such as suction filtration.

[Aetherization]
As etherification, carboxymethyl (ether), methyl (ether), ethyl (ether), cyanoethyl (ether), hydroxyethyl (ether), hydroxypropyl (ether), ethyl hydroxyethyl (ether) And hydroxypropylmethyl (ether) conversion. The method of carboxymethylation will be described below as an example.

The degree of carboxymethyl substitution per anhydrous glucose unit in the carboxymethylated cellulose or cellulose nanofiber obtained by carboxymethylation is preferably 0.01 or more, more preferably 0.05 or more, still more preferably 0.10 or more. The upper limit of the degree of substitution is preferably 0.50 or less, more preferably 0.40 or less, still more preferably 0.35 or less or 0.30 or less. Therefore, the degree of carboxymethyl group substitution is preferably 0.01 to 0.50, more preferably 0.05 to 0.40, and even more preferably 0.10 to 0.35 or 0.10 to 0.30. The amount of carboxyl groups of the carboxymethylated cellulose and the amount of the carboxyl groups of the carboxymethylated cellulose nanofibers obtained from the carboxymethylated cellulose are usually the same.

The carboxymethylation method is not particularly limited, and examples thereof include a method in which a cellulose raw material as a bottoming raw material is converted into a marcel and then etherified. A solvent is usually used for the reaction. Examples of the solvent include water, alcohol (for example, lower alcohol) and a mixed solvent thereof. Examples of the lower alcohol include methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butyl alcohol, isobutyl alcohol, and tertiary butyl alcohol. The mixing ratio of the lower alcohol in the mixed solvent is usually 60% by weight or more or 95% by weight or less, preferably 60 to 95% by weight. The amount of the solvent is usually 3 times by weight with respect to the cellulose raw material. The upper limit of the amount is not particularly limited, but is 20 times by weight. Therefore, the amount of the solvent is preferably 3 to 20 times by weight.

Mercerization is usually carried out by mixing a bottoming material and a mercerizing agent. Examples of the mercerizing agent include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of the mercerizing agent used is preferably 0.5 times mol or more, more preferably 1.0 times mol or more, and even more preferably 1.5 times mol or more per anhydrous glucose residue of the bottoming material. The upper limit of the amount is usually 20 times mol or less, preferably 10 times mol or less, and more preferably 5 times mol or less. Therefore, the amount of the mercerizing agent used is preferably 0.5 to 20 times mol, more preferably 1.0 to 10 times mol, and even more preferably 1.5 to 5 times mol.

The reaction temperature for mercerization is usually 0 ° C. or higher, preferably 10 ° C. or higher, and the upper limit is usually 70 ° C. or lower, preferably 60 ° C. or lower. Therefore, the reaction temperature is usually 0 to 70 ° C, preferably 10 to 60 ° C. The reaction time is usually 15 minutes or longer, preferably 30 minutes or longer. The upper limit of the time is usually 8 hours or less, preferably 7 hours or less. Therefore, the reaction time is usually 15 minutes to 8 hours, preferably 30 minutes to 7 hours.

The etherification reaction is usually carried out by adding a carboxymethylating agent to the reaction system after mercerization. Examples of the carboxymethylating agent include sodium monochloroacetate. The amount of the carboxymethylating agent added is usually preferably 0.05 times or more, more preferably 0.5 times or more, still more preferably 0.8 times or more per glucose residue of the cellulose raw material. The upper limit of the amount is usually 10.0 times mol or less, preferably 5 times mol or less, and more preferably 3 times mol or less. Therefore, the amount is preferably 0.05 to 10.0 times mol, more preferably 0.5 to 5 times mol, and even more preferably 0.8 to 3 times mol. The reaction temperature is usually 30 ° C. or higher, preferably 40 ° C. or higher, and the upper limit is usually 90 ° C. or lower, preferably 80 ° C. or lower. Therefore, the reaction temperature is usually 30 to 90 ° C, preferably 40 to 80 ° C. The reaction time is usually 30 minutes or more, preferably 1 hour or more, and the upper limit thereof is usually 10 hours or less, preferably 4 hours or less. Therefore, the reaction time is usually 30 minutes to 10 hours, preferably 1 hour to 4 hours. If necessary, the reaction solution may be stirred during the carboxymethylation reaction.

The degree of carboxymethyl substitution per glucose unit of carboxymethylated cellulose nanofibers is measured, for example, by the following method. That is, 1) Approximately 2.0 g of carboxymethylated cellulose (absolutely dried) is precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 2) Add 100 mL of nitrate methanol solution prepared by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol, and shake for 3 hours to convert the carboxymethyl cellulose salt (carboxymethylated cellulose) into acid-type carboxymethyl cellulose. 3) Weigh 1.5 to 2.0 g of acid-type carboxymethylated cellulose (absolutely dry) and place in a 300 mL Erlenmeyer flask with a stopper. 4) Wet the acid-type carboxymethylated cellulose with 15 mL of 80% methanol, add 100 mL of 0.1 N NaOH, and shake at room temperature for 3 hours. 5) Using phenolphthalein as an indicator, back titrate excess NaOH with 0.1 N H ₂ SO ₄ . 6) Calculate the degree of carboxymethyl substitution (DS) by the following equation:
A = [(100 x F'-(0.1 N H ₂ SO ₄ ) (mL) x F) x 0.1] / (absolute dry mass (g) of acid-type carboxymethylated cellulose)
DS = 0.162 x A / (1-0.058 x A)
A: 1N NaOH amount (mL) required to neutralize 1 g of acid-type carboxymethylated cellulose
F: 0.1N H ₂ SO ₄ factor F': 0.1N NaOH factor

The product after carboxymethylation may be subjected to desalting treatment. Desalting is similar to post-oxidation desalting, in which a salt (a countercation of a carboxylate group, for example, a sodium salt) contained in a reaction product (salt type) is replaced with a proton to form an acid type. means. Desalination can be performed at any time before or after the defibration treatment described below. Examples of the desalting method after carboxymethylation include a method of contacting carboxymethylated cellulose with a cation exchange resin. As the cation exchange resin, either a strongly acidic ion exchange resin or a weakly acidic ion exchange resin can be used as long as the counterion is H ⁺ . The ratio of the two when the carboxymethylated cellulose is brought into contact with the cation exchange resin is not particularly limited, and a person skilled in the art can appropriately set the ratio from the viewpoint of efficiently performing proton substitution. As an example, the ratio can be adjusted so that the pH of the carboxymethylated cellulose aqueous dispersion after the addition of the cation exchange resin is preferably 2 to 6, more preferably 2 to 5. The cation exchange resin after contact may be recovered by a conventional method such as suction filtration.

[Cationation]
The cationized cellulose nanofiber obtained by cationization may contain a cation such as ammonium, phosphonium, sulfonium, or a group having the cation in the molecule. The cationized cellulose nanofibers preferably contain a group having ammonium, more preferably a group having quaternary ammonium.

The cationization method is not particularly limited, and examples thereof include a method of reacting a cellulose raw material with a cationizing agent and a catalyst in the presence of water or alcohol. Examples of the cationizing agent include glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydrite (eg, 3-chloro-2-hydroxypropyltrimethylammonium hydride), and halohydrin types thereof. By using any of these, a cationized cellulose having a group containing a quaternary ammonium can be obtained. Examples of the catalyst include alkali metals hydroxide such as sodium hydroxide and potassium hydroxide. Examples of the alcohol include alcohols having 1 to 4 carbon atoms. The amount of the cationizing agent is preferably 5% by weight or more, more preferably 10% by weight or more, based on 100% by weight of the cellulose raw material. The upper limit of the amount is usually 800% by weight or less, preferably 500% by weight or less. The amount of the catalyst is preferably 0.5% by weight or more, more preferably 1% by weight or more, based on 100% by weight of the cellulose fibers. The upper limit of the amount is usually 70% by weight or less, preferably 30% by weight or less. The amount of alcohol is preferably 50% by weight or more, more preferably 100% by weight or more, based on 100% by weight of the cellulose fiber. The upper limit of the amount is usually 50,000% by weight or less, preferably 500% by weight or less.

The reaction temperature during cationization is usually 10 ° C. or higher, preferably 30 ° C. or higher, and the upper limit is usually 90 ° C. or lower, preferably 80 ° C. or lower. The reaction time is usually 10 minutes or more, preferably 30 minutes or more, and the upper limit is usually 10 hours or less, preferably 5 hours or less. If necessary, the reaction solution may be stirred during the cationization reaction.

The degree of cation substitution per glucose unit of cationized cellulose can be adjusted by the amount of cationizing agent added and the composition ratio of water or alcohol. The degree of cation substitution indicates the number of introduced substituents per unit structure (glucopyranose ring) constituting cellulose. That is, the degree of cation substitution is defined as "the value obtained by dividing the number of moles of the introduced substituent by the total number of moles of the hydroxyl groups of the glucopyranose ring". Since pure cellulose has three substitutable hydroxyl groups per unit structure (glucopyranose ring), the theoretical maximum value of the degree of cation substitution is 3 (minimum value is 0).

The degree of cation substitution per glucose unit of the cationized cellulose nanofiber is preferably 0.01 or more, more preferably 0.02 or more, still more preferably 0.03 or more. The upper limit of the degree of substitution is preferably 0.40 or less, more preferably 0.30 or less, and even more preferably 0.20 or less. Therefore, the degree of cation substitution is preferably 0.01 to 0.40, more preferably 0.02 to 0.30, and even more preferably 0.03 to 0.20. By introducing a cationic substituent into the cellulose, the celluloses electrically repel each other. Therefore, cellulose having a cation substituent introduced can be easily nano-defibrated. When the degree of cation substitution per glucose unit is 0.01 or more, nano-defibration can be sufficiently performed. On the other hand, when the degree of cation substitution per glucose unit is 0.40 or less, swelling or dissolution can be suppressed, whereby the fiber morphology can be maintained and the situation where the nanofiber cannot be obtained can be prevented. The amount of carboxyl groups of the cationized cellulose and the amount of carboxyl groups of the cationized cellulose nanofibers obtained from the cationized cellulose are usually the same.

An example of a method for measuring the degree of cation substitution per glucose unit will be described below. After the sample (cationized cellulose) is dried, the nitrogen content is measured with a total nitrogen analyzer TN-10 (manufactured by Mitsubishi Chemical Corporation). For example, when 3-chloro-2-hydroxypropyltrimethylammonium chloride is used as the cationizing agent, the degree of cation substitution is calculated by the following equation. The degree of cation substitution referred to here is an average value of the number of moles of substituents per mole of anhydrous glucose unit.

Degree of substitution = (162 × N) / (1-116 × N)
N: Nitrogen content per 1 g of cationized cellulose (mol)

[Esterification]
The method of esterification is not particularly limited, and examples thereof include a method of reacting a cellulose raw material with compound A, which will be described later. Examples of the method for reacting the compound A with the cellulose raw material include a method of mixing the powder or the aqueous solution of the compound A with the cellulose raw material, a method of adding the aqueous solution of the compound A to the slurry of the cellulose raw material, and the like. Of these, a method of mixing an aqueous solution of compound A with a cellulose raw material or a slurry thereof is preferable because the uniformity of the reaction can be enhanced and the esterification efficiency can be enhanced.

Examples of the compound A include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. Compound A may be in the form of a salt. Among the above, a phosphoric acid-based compound is preferable because it is low in cost, easy to handle, and the phosphoric acid group can be introduced into the cellulose of the pulp fiber to improve the defibration efficiency. The phosphoric acid-based compound may be a compound having a phosphoric acid group, for example, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, diphosphate. Examples thereof include potassium hydrogen, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate and the like. .. The phosphoric acid-based compound used may be one of these or a combination of two or more thereof. Of these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, and phosphoric acid from the viewpoint of high efficiency of introducing phosphoric acid group, easy to defibrate in the defibration process, and easy to apply industrially. Ammonium salts are preferable, and sodium dihydrogen phosphate and disodium hydrogen phosphate are more preferable. Further, since the uniformity of the reaction is enhanced and the efficiency of introducing a phosphoric acid group is increased, it is preferable to use an aqueous solution of a phosphoric acid-based compound for esterification. The pH of the aqueous solution of the phosphoric acid-based compound is preferably 7 or less from the viewpoint of increasing the efficiency of introducing the phosphoric acid group, and more preferably 3 to 7 from the viewpoint of suppressing the hydrolysis of the pulp fiber.

Examples of the esterification method include the following methods. Compound A is added to a suspension of a cellulose raw material (for example, a solid content concentration of 0.1 to 10% by weight) with stirring to introduce a phosphoric acid group into the cellulose. When the compound A is a phosphoric acid-based compound, the amount of the compound A added to 100 parts by weight of the cellulose raw material is preferably 0.2 parts by weight or more and more preferably 1 part by weight or more as the amount of the phosphorus element. Thereby, the yield of the fine fibrous cellulose can be further improved. The upper limit of the amount is preferably 500 parts by weight or less, more preferably 400 parts by weight or less. This makes it possible to efficiently obtain a yield commensurate with the amount of compound A used. Therefore, 0.2 to 500 parts by weight is preferable, and 1 to 400 parts by weight is more preferable.

When the compound A is reacted with the cellulose raw material, the compound B may be further added to the reaction system. Examples of the method of adding the compound B to the reaction system include a method of adding the compound B to the slurry of the cellulose raw material, the aqueous solution of the compound A, or the slurry of the cellulose raw material and the compound A. The compound B is not particularly limited, but a compound exhibiting basicity is preferable, and a nitrogen-containing compound exhibiting basicity is more preferable. "Showing basicity" usually means that the aqueous solution of compound B exhibits a pink to red color in the presence of a phenolphthalein indicator, or that the pH of the aqueous solution of compound B is greater than 7. The nitrogen-containing compound exhibiting basicity is not particularly limited as long as the effect of the present invention is exhibited, but a compound having an amino group is preferable. For example, urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine and the like can be mentioned. Of these, urea is preferable because it is low in cost and easy to handle. The amount of compound B added is preferably 2 to 1000 parts by weight, more preferably 100 to 700 parts by weight. The reaction temperature is preferably 0 to 95 ° C, more preferably 30 to 90 ° C. The reaction time is not particularly limited, but is usually about 1 to 600 minutes, preferably 30 to 480 minutes. When the conditions of the esterification reaction are within any of these ranges, it is possible to prevent the cellulose from being excessively esterified and easily dissolved, and it is possible to improve the yield of the phosphate esterified cellulose. ..

After reacting the cellulose raw material with compound A, an esterified cellulose suspension is usually obtained. The esterified cellulose suspension is dehydrated as needed. It is preferable to perform heat treatment after dehydration. This makes it possible to suppress the hydrolysis of the cellulose raw material. The heating temperature is preferably 100 to 170 ° C., and is heated at 130 ° C. or lower (more preferably 110 ° C. or lower) while water is contained during the heat treatment, and then heated at 100 to 170 ° C. after removing the water. It is more preferable to process.

In phosphoric acid esterified cellulose, a phosphate group substituent is introduced into the cellulose raw material, and the celluloses electrically repel each other. Therefore, the phosphate esterified cellulose can be easily nano-defibrated. The degree of phosphate group substitution per glucose unit of the phosphoric acid esterified cellulose is preferably 0.001 or more. As a result, sufficient defibration (for example, nano-defibration) can be carried out. The upper limit of the degree of substitution is preferably 0.60. This can prevent the swelling or dissolution of the phosphate esterified cellulose and prevent the situation where nanofibers cannot be obtained. Therefore, the degree of substitution is preferably 0.001 to 0.60. The amount of carboxyl groups of the phosphoric acid esterified cellulose and the amount of carboxyl groups of the phosphoric acid esterified cellulose nanofibers obtained from the phosphoric acid esterified cellulose are usually the same value.

The product after phosphoric acid esterification may be subjected to desalting treatment. Desalting means that the salt (for example, sodium salt) contained in the reaction product (salt type) is replaced with a proton to form an acid type, as in the case of desalting after oxidation and desalting after carboxymethylation. do. Desalination can be performed at any time before or after the defibration treatment described below. Examples of the desalting method after phosphorylation include a method of contacting phosphate esterified cellulose with a cation exchange resin.
It is preferable that the phosphoric acid esterified cellulose is subjected to a washing treatment such as washing with cold water after boiling. As a result, defibration can be performed efficiently.

[Defibration]
The defibration of the cellulose raw material may be performed before or after the chemical modification of the cellulose raw material. The defibration treatment may be performed once or a plurality of times. In the case of multiple times, the timing of each defibration may be any time. The defibration treatment is usually physical defibration.

The device used for defibration is not particularly limited, and examples thereof include high-speed rotary type, colloidal mill type, high-pressure type, roll mill type, ultrasonic type, and the like, preferably a high-pressure or ultra-high pressure homogenizer, and a wet high pressure. Alternatively, an ultrahigh pressure homogenizer is more preferable. The apparatus preferably can apply a strong shearing force to the cellulose raw material or modified cellulose (usually a dispersion). The pressure that can be applied by the device is preferably 50 MPa or more, more preferably 100 MPa or more, still more preferably 140 MPa or more. The apparatus is preferably a wet high-pressure or ultra-high pressure homogenizer capable of applying the above pressure to the cellulose raw material or modified cellulose (usually a dispersion) and applying a strong shearing force. As a result, defibration can be performed efficiently.

When defibration is performed on a dispersion of a cellulose raw material, the solid content concentration of the cellulose raw material in the dispersion is usually 0.1% by weight or more, preferably 0.2% by weight or more, more preferably 0.3. It is more than% by weight. As a result, the amount of the liquid becomes appropriate with respect to the amount of the cellulose fiber raw material, which can be efficient. The upper limit of the concentration is usually 10% by weight or less, preferably 6% by weight or less. This allows the liquidity to be maintained.

Prior to defibration (preferably defibration with a high-pressure homogenizer) or, if necessary, a dispersion treatment performed before defibration, pretreatment may be performed as necessary. Pretreatment may be performed using a mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer.

The cellulosic fiber preferably contains at least one type of cellulose nanofiber obtained through the above-mentioned chemical modification, and contains at least one type selected from the group consisting of oxidized cellulose fiber, carboxymethylated cellulose fiber and cationized cellulose fiber. Is more preferable.

Cellulose nanofibers may undergo a treatment other than chemical denaturation and normal defibration treatment in the manufacturing process. Examples of such treatment include filtration treatment, staple treatment, and a combination of two or more of these.

[Filtration process]
The timing of the filtration treatment is not particularly limited, but it is usually after the defibration treatment, and may be performed on a dispersion liquid of modified cellulose after the defibration treatment (eg, an aqueous dispersion liquid such as an aqueous dispersion liquid). This makes it possible to remove foreign substances (eg, undefibrated fibers) remaining due to insufficient defibration treatment. Further, when the modified cellulose fiber is used for producing the rubber composition, it is possible to suppress the breakage of the rubber composition starting from the remaining foreign matter and the problem caused by the breakage (eg, the decrease in the strength of the rubber composition).

Examples of the filtration treatment include a pressure filtration treatment and a pressure reduction filtration treatment. The pressure conditions (differential pressure) in the pressure filtration treatment and the pressure reduction filtration treatment are not particularly limited, but are, for example, 0.01 MPa or more, preferably 0.01 to 10 MPa. When the differential pressure is 0.01 MPa or more, it is possible to omit the dilution of the dispersion liquid to obtain a sufficient filtration treatment amount (preferably, the dilution is not performed in consideration of the subsequent steps). Since the differential pressure is 0.01 to 10 MPa, a sufficient filtration treatment amount can be obtained even when the concentration of the modified cellulose fiber in the dispersion liquid or the viscosity of the dispersion liquid is high. The concentration of the modified cellulose fiber at the time of filtration is usually 0.1 to 5% by mass, preferably 0.2 to 4% by mass, and more preferably 0.5 to 3% by mass.

A filtration device is usually used for the filtration process. The filtration device is not particularly limited, and examples thereof include a nutche type, a candle type, a leaf disk type, a drum type, a filter press type, a belt filter type, and the like. The amount of filtration treatment is not particularly limited, but is preferably 10 L / m ² or more, and more preferably 100 L / m ² or more per hour.

The filter medium used for the filtration treatment includes, for example, a filter made of a material such as metal fiber, cellulose, polypropylene, polyester, nylon, glass, cotton, polytetrafluoroethylene, polyphenylene sulfide, and a combination thereof; membrane filter; filter cloth; metal. A filter made by sintering a material such as powder; or a slit-shaped filter can be mentioned. Among these, a filter made of metal fiber and a membrane filter are preferable.

The average pore size of the filter medium is not particularly limited when the filtration aid is used in combination. On the other hand, when the filter aid is not used in combination, the average pore size of the filter medium is preferably 0.01 to 100 μm, more preferably 0.1 to 50 μm, and even more preferably 1 to 30 μm. When the average pore size is 0.01 μm or more, the filtration rate can be sufficient. On the other hand, when it is 100 μm or less, foreign matter can be sufficiently caught and the filtration effect can be easily obtained.

In the filtration treatment, a filtration aid may be used if necessary. In the filtration process using a filter aid (auxiliary agent filtration process), the filter layer formed on the filter medium can be removed by using the filter aid, so that clogging of the filter medium can be easily cleared and continuous. Filtration processing can be performed. The average particle size of the filtration aid is preferably 150 μm or less, more preferably 1 to 150 μm, still more preferably 10 to 75 μm, still more preferably 15 to 45 μm, and particularly preferably 25 to 45 μm. When the average particle size exceeds 1 μm, the decrease in the filtration rate can be suppressed. When the average particle size is less than 150 μm, foreign matter can be sufficiently caught and the filtration process can be performed efficiently.

The shape of the filtration aid is not particularly limited, and examples thereof include substantially granular shapes such as substantially spherical (eg, diatomaceous earth) and substantially rod-shaped (eg, powdered cellulose). The average particle size of the filtration aid can be measured by a laser diffraction measuring device compliant with JIS Z8825-1 regardless of its shape.

The form of the auxiliary agent filtration treatment is not particularly limited, and for example, precoat filtration for forming a layer of the filtering auxiliary agent on the filter medium, and body feed for filtering the mixture obtained by adding the filtering auxiliary agent to the dispersion liquid of the modified cellulose fiber. Filtration, a combination of both can be mentioned. Of these, a combination of both is preferable. As a result, the amount of filtration treatment is improved, and a filtrate of good quality can be obtained. The auxiliary agent filtration treatment may be a multi-stage treatment consisting of two or more filtration steps using different filtration aids. In the case of multi-stage treatment, at least one of the filtration steps is preferably pressure filtration treatment or vacuum filtration treatment.

The filtration aid is not particularly limited, and for example, an inorganic compound and an organic compound are preferable. Preferred examples of the filtration aid include diatomaceous earth, powdered cellulose, pearlite and activated carbon.

Diatomaceous earth refers to soft rock or soil mainly composed of diatom shells, and mainly contains silica. It may contain components other than silica, such as alumina, iron oxide, and alkali metal oxides. Diatomaceous earth is usually porous and has a high porosity. The cake bulk density of diatomaceous earth is preferably about 0.2 to 0.45 g / cm ³ . The diatomaceous earth is preferably a fired product or a flux-fired product. The origin of diatomaceous earth is not particularly limited, but freshwater diatomaceous earth is preferable. Examples of the diatomaceous earth include Celite (registered trademark) manufactured by Celite and Ceratom (registered trademark) manufactured by Eagle Pitcher Minerals.

Powdered cellulose is powdered cellulose, the shape of which is usually rod-axis particles. The method for producing powdered cellulose is not particularly limited, and for example, a method of acid-hydrolyzing wood pulp to remove non-crystalline parts, crushing and sieving, and acid-hydrolyzing selected pulp to purify and purify undecomposed residue. Examples include methods of drying, grinding and sieving. The powdered cellulose can be crystalline or microcrystalline cellulose and preferably has a constant particle size distribution. The degree of cellulose polymerization of powdered cellulose is preferably about 100 to 500. The crystallinity of the powdered cellulose by the X-ray diffraction method is preferably 70 to 90%. The volume average particle size of the powdered cellulose obtained by the laser diffraction type particle size distribution measuring device is preferably 100 μm or less, more preferably 50 μm or less. This makes it possible to obtain a modified cellulose fiber having excellent fluidity after filtration. Examples of the powdered cellulose include KC Flock (registered trademark) manufactured by Nippon Paper Industries, Inc., Theoras (registered trademark) manufactured by Asahi Kasei Chemicals, and Abyssel (registered trademark) manufactured by FMC.

The foreign matter area ratio of the dispersion liquid of the modified cellulose fiber after filtration is preferably 25% or less. The foreign matter area ratio is calculated by the following method. First, a surface tension adjusting agent is added to the dispersion of the modified cellulose fiber, and then the film is thinned. A pair of polarizing plates are arranged on both sides of the thin film so that their polarization axes are orthogonal to each other. Light is irradiated from one polarizing plate side, and a transmitted image is acquired from the other polarizing plate side. The foreign matter area is specified by image analysis of the image, and the foreign matter area ratio per 1 g of the modified cellulose fiber absolute dry mass is calculated. The modified cellulose fiber dispersion after filtration preferably has a foreign matter area ratio of 25% or less in the evaluation method. The foreign matter area ratio is an index of dispersibility, and when the ratio is 25% or less, it has good dispersibility.

[Staple treatment]
The staple treatment is a treatment for appropriately cutting (shortening) the cellulose chain before the treatment, and examples thereof include an ultraviolet irradiation treatment, an oxidative decomposition treatment, a hydrolysis treatment, and a combination of two or more of these. Be done. The staple treatment is preferably a hydrolysis treatment or a combination of the hydrolysis treatment and other treatments.

Prior to the staple treatment, it is preferable to perform a cleaning treatment for cleaning the cellulose fibers. This can suppress side reactions. The conditions of the cleaning treatment are not particularly limited, and the cleaning treatment can be performed by a known method.

Examples of the hydrolysis treatment include an acid hydrolysis treatment in which an acid is added to a cellulose fiber to hydrolyze the cellulose chain, and an alkali hydrolysis treatment in which an alkali is added to the cellulose fiber to hydrolyze the cellulose chain. The reaction medium for the hydrolysis treatment is usually water. This can suppress side reactions.

Examples of the acid include mineral acids such as sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. The hydrolysis treatment is preferably performed on a dispersion liquid of cellulose fibers (eg, a dispersion liquid in an aqueous dispersion medium such as water). This makes it possible to efficiently carry out the hydrolysis reaction. The concentration of cellulose fibers in the dispersion is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, still more preferably 1 to 5% by mass.

The conditions for the acid hydrolysis treatment may be any conditions as long as the acid can act on the amorphous portion of the cellulose molecule, and examples are as follows. The amount of the acid added is preferably 0.01 to 0.5% by mass, more preferably 0.1 to 0.5% by mass, based on the absolute dry mass of the cellulose fibers. When the amount of the acid added is 0.01% by mass or more, the hydrolysis of the cellulose fibers can proceed and the efficiency of nanofiber formation can be improved. When the addition amount is 0.5% by mass or less, excessive hydrolysis of the cellulose fibers can be prevented, and a decrease in the yield of the cellulose fibers can be suppressed.

The pH value of the dispersion medium during the acid hydrolysis treatment is preferably 2.0 to 4.0, more preferably 2.0 or more and less than 3.0. The pH value can be adjusted, for example, by adjusting the amount of acid added. For example, if alkali remains in the dispersion medium, the amount of acid added may be increased. The reaction temperature is, for example, 70 to 120 ° C., and the reaction time is, for example, 1 to 10 hours. After the acid hydrolysis treatment, it is preferable to add an alkali such as sodium hydroxide to neutralize the acid. As a result, nanofiber formation can be efficiently performed.

The conditions for the alkaline hydrolysis treatment are not particularly limited, but examples are as follows. The pH value of the reaction solution is preferably 8 to 14, more preferably 9 to 13, and even more preferably 10 to 12. When the pH value is 8 or more, hydrolysis can proceed and the cellulose fibers can be sufficiently shortened. On the other hand, when the pH value is 14 or less, it is possible to suppress coloring and deterioration of transparency of the cellulose fibers after hydrolysis. The pH value may be adjusted by adding an alkali, and the alkali used is usually water-soluble, and is preferably sodium hydroxide from the viewpoint of production cost.

It is preferable to use an auxiliary agent (eg, oxidizing agent, reducing agent) in the alkaline hydrolysis treatment. When cellulose fibers having a carboxy group are hydrolyzed in an alkaline solution, the cellulose fibers may be colored yellow and their transparency may be reduced due to the formation of double bonds during β elimination. As a result, applicable technology may be limited. However, by using an auxiliary agent, the double bond can be oxidized or reduced, and the coloration and the decrease in transparency can be suppressed. The auxiliary agent may be any as long as it has activity in the alkaline region. From the viewpoint of reaction efficiency, the amount of the auxiliary agent added is preferably 0.1 to 10% by mass, more preferably 0.3 to 5% by mass, and further preferably 0.5 to 2% by mass with respect to the dry cellulose fibers. preferable.

Examples of the oxidizing agent include oxygen, ozone, hydrogen peroxide, and hypochlorite. Among them, as the oxidizing agent, oxygen, hydrogen peroxide and hypochlorite, which are less likely to generate radicals, are preferable, and hydrogen peroxide is more preferable. The oxidizing agent may be used alone or in combination of two or more.

Examples of the reducing agent include sodium borohydride, hydrosulfite, and sulfites. The reducing agent may be used alone or in combination of two or more.

The reaction temperature of the hydrolysis treatment is not particularly limited, but at low temperatures, hydrolysis may be insufficient, resulting in insufficient shorting of fibers, and at high temperatures, the cellulose fibers after hydrolysis may be colored. 40 to 120 ° C. is preferable, 50 to 100 ° C. is more preferable, and 60 to 90 ° C. is further preferable, because such problems can be suppressed and the reaction efficiency can be improved. The reaction time of the hydrolysis treatment is preferably 0.5 to 24 hours, more preferably 1 to 10 hours, still more preferably 2 to 6 hours.

From the viewpoint of reaction efficiency, the concentration of the cellulose fiber in the alkaline solution is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, still more preferably 5 to 10% by mass.

The ultraviolet irradiation treatment is a process of irradiating cellulose fibers with ultraviolet rays. The reason why the cellulose fibers are shortened by ultraviolet irradiation is presumed as follows. Ultraviolet rays act directly on cellulose and hemicellulose to cause low molecular weight and shorten cellulose chains.

The wavelength of ultraviolet rays is preferably 100 to 400 nm, more preferably 100 to 300 nm, and even more preferably 135 to 260 nm. By using ultraviolet rays having a wavelength of 135 to 260 nm, it can act directly on cellulose or hemicellulose to easily cause low molecular weight.

The light source for irradiating ultraviolet rays may irradiate light in the wavelength range of 100 to 400 nm, and examples thereof include xenon short arc lamps, ultra-high pressure mercury lamps, high pressure mercury lamps, low pressure mercury lamps, deuterium lamps, and metal halide lamps. .. These light sources may be used alone or in any combination of two or more. The combination of two or more types of light sources is preferably a combination of a plurality of light sources having different wavelength characteristics. As a result, the number of cut points in the cellulose chain or hemicellulose chain can be increased by simultaneously irradiating ultraviolet rays having different wavelengths.

When irradiating with ultraviolet rays, a container containing a cellulose fiber dispersion is usually used. For example, when using ultraviolet rays of 300 to 400 nm, a container made of hard glass may be used. When ultraviolet rays having a wavelength shorter than 300 nm are used, a quartz glass container that allows the ultraviolet rays to be transmitted more may be used. The material of the part that does not participate in the light transmission reaction of the container may be appropriately selected from the materials that are less deteriorated with respect to the wavelength of the ultraviolet rays used.

The concentration of the cellulose fibers in the dispersion liquid when irradiated with ultraviolet rays is preferably 0.1 to 12% by mass, more preferably 0.5 to 5% by mass, and further preferably 1 to 3% by mass. When the concentration of carboxymethylated cellulose is 0.1% by mass or more, energy efficiency can be improved. When the concentration of the cellulose fibers is 12% by mass or less, the fluidity of the cellulose fibers in the ultraviolet irradiation device becomes good, and the reaction efficiency can be improved.

The temperature at the time of irradiating with ultraviolet rays is preferably 20 to 95 ° C, more preferably 20 to 80 ° C, and even more preferably 20 to 50 ° C. When the temperature is 20 ° C. or higher, the efficiency of the photooxidation reaction is increased, which is preferable. When the temperature is 95 ° C. or lower, there is no risk of adverse effects such as deterioration of the quality of carboxymethylated cellulose, and there is no risk of the pressure inside the reaction device exceeding atmospheric pressure, so it is necessary to design the device in consideration of pressure resistance. It is preferable because it loses its sex.

The pH value when irradiating with ultraviolet rays is not particularly limited, but a neutral region, for example, a pH value of about 6.0 to 8.0 is preferable in consideration of process simplification.

The amount of ultraviolet rays received by the cellulose fibers can be controlled as needed. As the control method, for example, the residence time of the cellulose fiber in the irradiation reaction device is adjusted, the energy amount of the irradiation light source is adjusted, and the concentration of the cellulose fiber in the irradiation device is adjusted (eg, adjustment by water dilution, air or nitrogen, etc.). Adjustment by blowing the inert gas into the cellulose fiber). The degree of control of the residence time and the concentration can be appropriately set according to the target quality of the cellulose fiber after irradiation with ultraviolet rays (fiber length, degree of polymerization of cellulose, etc.).

When the ultraviolet irradiation treatment is performed in the presence of auxiliary agents such as oxygen, ozone, and peroxides (hydrogen peroxide, peracetic acid, sodium percarbonate, sodium perborate, etc.), the efficiency of the photooxidation reaction increases. preferable.

When irradiating ultraviolet rays in the wavelength range of 135 to 242 nm, ozone is generated from the air existing in the gas phase portion (peripheral portion of the light source) around the light source. Ozone thus generated secondarily can be used as an auxiliary agent for ultraviolet irradiation treatment. As a result, the amount of ozone supplied from outside the system can be reduced or the supply can be omitted. The method of using ozone purified from the air existing in the periphery of the light source as an auxiliary agent for the ultraviolet irradiation treatment is not particularly limited. For example, while continuously supplying air to the periphery of the light source, the generated ozone is continuously produced. There is a method of extracting the extracted ozone and injecting the extracted ozone into the cellulose fiber. By supplying oxygen to the periphery of the light source, a larger amount of ozone can be generated in the system, and the generated ozone can be used as an auxiliary agent for the photooxidation reaction.

The ultraviolet irradiation treatment may be repeated a plurality of times. The number of repetitions can be appropriately set according to conditions such as the quality of the target cellulose fiber. For example, when the wavelength of ultraviolet rays is 100 to 400 nm, preferably 135 to 260 nm, it is preferably 1 to 10 times, more preferably 2 to 5 times. The irradiation time per irradiation is preferably 0.5 to 10 hours, more preferably 0.5 to 3 hours.

The oxidative decomposition treatment is usually performed by using hydrogen peroxide and ozone in combination. Ozone can be generated by a known method using an ozone generator using air or oxygen as a raw material. The amount of ozone added (mass equivalent) is preferably 0.1 to 3 times, more preferably 0.3 to 2.5 times, and 0.5 to 1.5 times the absolute dry mass of the cellulose fiber. More preferred. When it is 0.1 times or more, the amorphous part of cellulose can be sufficiently decomposed. When it is 3 times or less, excessive decomposition of cellulose can be suppressed, and a decrease in the yield of cellulose fibers can be prevented. The amount of hydrogen peroxide added (in terms of mass) is preferably 0.001 to 1.5 times, more preferably 0.1 to 1.0 times the absolute dry mass of the cellulose fiber. When it is 0.001 times or more, the synergistic action of ozone and hydrogen peroxide can be exhibited. If it is 1.5 times or less, oxidative decomposition can proceed sufficiently and the cost can be suppressed.

The conditions of the oxidative decomposition treatment (for example, pH and temperature) are not particularly limited, but when ozone and hydrogen peroxide are used, they are as follows. The pH value is preferably 2 to 12, more preferably 4 to 10, still more preferably 6 to 8, and the temperature is preferably 10 to 90 ° C, more preferably 20 to 70 ° C, still more preferably 30 to 50. The temperature is ° C., and the reaction time is preferably 1 to 20 hours, more preferably 2 to 10 hours, still more preferably 3 to 6 hours. As a result, the treatment can be carried out with good reaction efficiency.

The apparatus used for the oxidative decomposition treatment may be any known apparatus. Devices include, for example, a reaction chamber, a stirrer, a chemical injection device, a heater, and a conventional reactor equipped with a pH electrode.

When the defibration treatment is performed after the oxidative decomposition treatment using ozone and hydrogen peroxide, the ozone and hydrogen peroxide remaining in the aqueous solution can effectively act in the defibration step, so that the cellulose fibers can be further shortened. Can be promoted.

<1.4. Morphology of cellulosic fibers to be mixed>
When preparing the mixed solution in the coagulation step, the form of the cellulosic fiber mixed with the rubber component is not particularly limited. Examples of the form include a dispersion in which cellulosic fibers are dispersed in a dispersion medium, a dry solid of the dispersion, and a wet solid of the dispersion. The concentration of the cellulosic fiber in the dispersion is usually 0.1 to 5% (w / v) when the dispersion medium is water. When the dispersion medium contains an organic solvent such as alcohol in addition to water, the concentration is usually 0.1 to 20% (w / v). The wet solid is a solid in an intermediate aspect between the dispersion and the dry solid. The amount of the dispersion medium in the wet solid obtained by dehydrating the dispersion liquid by a usual method is preferably 5 to 15% by weight based on the cellulosic fibers, but the amount of the dispersion medium is preferably added by adding a liquid medium or further drying. Can be adjusted as appropriate.

In addition, examples of the above-mentioned form include a mixed solution of a cellulosic fiber and a water-soluble polymer solution, a dry solid of the mixed solution, and a wet solid of the mixed solution. The amount of the liquid medium in the mixture and the dry solid may be in the range of the amount of the dispersion medium of the wet solid as described above. Examples of the water-soluble polymer include cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, ethyl cellulose), xanthan gum, xyloglucane, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginate, purulan, starch, shavings, and waste. Powder, Positive Starch, Phosphorescent Starch, Corn Starch, Arabian Gum, Locust Bean Gum, Gellan Gum, Polydexstrose, Pectin, Chitin, Water Soluble Chitin, Chitosan, Casein, Albumin, Soy Protein Dissolved, Peptone, Polyvinyl Alcohol, Polyacrylamide, Polyvinylpyrrolidone, polyvinylacetate, polyamino acid, polylactic acid, polyapple acid, polyglycerin, latex, rosin-based sizing agent, petroleum resin-based sizing agent, urea resin, melamine resin, epoxy resin, polyamide resin, polyamide / polyamine resin, polyethylene Immin, polyamine, vegetable gum, polyethylene oxide, hydrophilic cross-linked polymers, polyacrylic acid salts (eg, sodium polyacrylic acid), starch polyacrylic acid copolymers, tamarind gum, guar gum, and colloidal silica, and mixtures thereof. Can be mentioned. Of these, carboxymethyl cellulose and salts thereof are preferable from the viewpoint of solubility.

The dry solid and the wet solid can be prepared by drying a dispersion of cellulosic fibers or a mixed solution of cellulosic fibers and a water-soluble polymer. The drying method is not particularly limited, and examples thereof include spray drying, squeezing, air drying, hot air drying, and vacuum drying. Examples of the drying device include a continuous tunnel drying device, a band drying device, a vertical drying device, a vertical turbo drying device, a multi-stage disk drying device, an aeration drying device, a rotary drying device, an air flow drying device, and a spray dryer drying device. , Spray drying device, Cylindrical drying device, Drum drying device, Screw conveyor drying device, Rotating drying device with heating tube, Vibration transport drying device, Batch type drying device (for example, box type drying device, aeration drying device, vacuum box type) A drying device or a stirring and drying device) can be mentioned. These drying devices may be used alone or in combination of two or more. The drum drying device is preferable because it can uniformly supply heat energy directly to the object to be dried, so that it has high energy efficiency and can immediately recover the dried product without applying heat more than necessary.

<1.5. Rubber component>
In the present invention, chloroprene rubber is used as the rubber component. Chloroprene rubber (CR) exhibits crystallinity similar to that of natural rubber (NR). Chloroprene rubber is characterized by satisfying various properties such as heat resistance, oil resistance, ozone resistance, chemical resistance, fatigue resistance, flame retardancy, weather resistance, and adhesiveness in a well-balanced manner.

In the present invention, chloroprene rubber and other rubber components can be used in combination as long as the desired effect is not impaired. Other rubber components include, for example, natural rubber, chlorinated natural rubber, hydrided natural rubber, chlorosulfonated natural rubber, epoxidized natural rubber, deproteinized natural rubber, butadiene rubber (BR), styrene-butadiene copolymer. Rubber (SBR), isoprene rubber (IR), butyl rubber (IIR), acrylonitrile-butadiene rubber (NBR), styrene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, isoprene-butadiene copolymer rubber, etc. Diene rubber, ethylene-propylene rubber (EPM, EPDM), acrylic rubber (ACM), epichlorohydrin rubber (CO, ECO), fluororubber (FKM), silicone rubber (Q), urethane rubber (U), chloro Styrene sulfonate (CSM) can be mentioned.

The form of mixing the chloroprene rubber and the rubber component used as necessary with the cellulosic fiber is not particularly limited. For example, a dispersion of cellulosic fibers, a dry solid of the dispersion, or a wet solid of the dispersion is mixed with chloroprene rubber and, if necessary, a rubber component (solid) or a dispersion thereof. The form is mentioned. Of these, a form in which a dispersion liquid of cellulosic fibers and a dispersion liquid of chloroprene rubber and a rubber component used as needed are mixed is preferable.

<1.6. Addition amount>
The amount of the cellulosic fiber added at the time of preparing the mixed solution is preferably 1% by weight or more with respect to 100% by weight of the rubber component (when other rubber components are contained, the total of chloroprene rubber and other rubber components), 2 weight by weight. % Or more is more preferable, and 3% by weight or more is further preferable. The effect of improving the tensile strength of the rubber composition thus obtained can be sufficiently exhibited. The upper limit is preferably 50% by weight or less, more preferably 40% by weight or less, still more preferably 30% by weight or less. This makes it possible to maintain processability in the manufacturing process. Therefore, 1 to 50% by weight is preferable.

<2. Solid-liquid separation process (dehydration process), washing process>
The production method of the present invention preferably further includes at least one step selected from the group consisting of a solid-liquid separation step and a water washing step, and more preferably further includes both steps. Thereby, the content of impurities in the rubber composition can be reduced, and the strength of the rubber composition can be improved. As for the mode of the solid-liquid separation step and the water washing step, it is preferable that the set of the solid-liquid separation and the water washing is repeated twice or more.

The solid-liquid separation step (dehydration step) is a step of solid-liquid separation of the mixed liquid containing the solidified rubber component obtained in the solidification step. Therefore, the time for performing the solid-liquid separation step is usually after the solidification step. The solid-liquid separation is preferably performed using a filter medium. Examples of the filter medium include a filter made of a material such as metal fiber, cellulose, polypropylene, polyester, nylon, glass, cotton, polytetrafluoroethylene, and polyphenylene sulfide, a membrane, a filter cloth, and a filter made by sintering metal powder. Alternatively, a slit-shaped filter may be mentioned. Among these, a nylon filter is preferable. The average pore size of the filter medium is preferably 0.01 to 100 μm, more preferably 0.1 to 50 μm, and even more preferably 1 to 30 μm.

The water washing step is a step of washing the solid phase obtained in the solid-liquid separation step.

<3. Drying process>
The production method of the present invention may further include a drying step. This makes it possible to obtain a masterbatch with a small amount of water. The drying step is a step of subjecting the treatment liquid obtained by the coagulation step or the treatment liquid obtained by the solid-liquid separation step and the washing step, which are subsequently performed as necessary, to drying by heating. Conditions such as heating temperature and heating time are not particularly limited. The heating temperature is preferably 40 ° C. or higher. The upper limit is preferably less than 100 ° C. The heating time is preferably 1 hour or more. The upper limit is preferably 24 hours or less. By setting the heating conditions within the above range, damage to the rubber component can be suppressed. Heating may be performed using a dryer such as an oven.

<4. Methylene acceptor compound and / or methylene donor compound addition step>
The production method of the present invention may further include a step of adding a methylene acceptor compound and / or a methylene donor compound.
The methylene acceptor compound is usually a compound that can accept a methylene group and can undergo a curing reaction by mixing with a methylene donor compound and heating. Examples of the methylene acceptor compound include phenol compounds such as phenol, resorcinol, resorcin, and cresol and their derivatives, resorcin-based resin, cresol-based resin, and phenol resin. Examples of the phenol resin include a condensate of the above-mentioned phenol compound and its derivative and an aldehyde compound such as formaldehyde and acetaldehyde. The phenolic resin can be classified into a novolak resin (acidic catalyst) and a resol resin (alkaline catalyst) depending on the catalyst at the time of condensation, and any of them may be used in the present invention. The phenolic resin may be modified with oil or fatty acid. Examples of oils and fatty acids include rosin oil, tall oil, cashew oil, linoleic acid, oleic acid, linoleic acid and the like.

The methylene donor compound is usually a compound that can donate a methylene group and can undergo a curing reaction by being mixed with a methylene acceptor compound and heated. Examples of the methylene donor compound include hexamethylenetetramine and melamine derivatives. Examples of the melamine derivative include hexamethylol melamine, hexamethoxymethyl melamine, pentamethoxymethyl melamine, pentamethoxymethylol melamine, hexaethoxymethyl melamine, and hexaxyl- (methoxymethyl) melamine.

Examples of the combination of the methylene acceptor compound and the methylene donor compound include a combination of cresol, a cresol derivative or a cresol-based resin and pentamethoxymethylmelamine, a combination of resorcin, a resorcin derivative or a resorcin-based resin and hexamethylenetetramine, and a cashew-modified phenol. Examples thereof include a combination of a resin and hexamethylenetetramine, and a combination of a phenol resin and hexamethylenetetramine. Of these, a combination of cresol, cresol derivative or cresol resin and pentamethoxymethylmelamine, or a combination of resorcin, resorcin derivative or resorcin resin and hexamethylenetetramine is preferable.

The amount of the methylene acceptor compound added is preferably 0.5% by weight or more, more preferably 1.0% by weight or more, still more preferably 1.3% by weight or more, and 1.5% by weight with respect to 100% by weight of the rubber component. % Or more is even more preferable. Thereby, the effect of improving the tensile strength can be sufficiently exhibited. The upper limit is preferably 50% by weight or less, preferably 20% by weight or less, and even more preferably 10% by weight or less. This makes it possible to maintain processability in the manufacturing process. Therefore, 0.5 to 50% by weight is preferable, 1.0 to 50% by weight or 1.0 to 20% by weight is more preferable, 1.3 to 20% by weight is further preferable, and 1.5 to 10% by weight is more preferable. Even more preferable.

The amount of the methylene donor compound added is preferably 10% by weight or more, more preferably 20% by weight or more, still more preferably 25% by weight or more with respect to 100% by weight of the methylene acceptor compound. Thereby, the effect of improving the tensile strength can be sufficiently exhibited. The upper limit is preferably 100% by weight or less, preferably 90% by weight or less, and even more preferably 85% by weight or less. This makes it possible to maintain processability in the manufacturing process. Therefore, 10 to 100% by weight is preferable, 20 to 90% by weight is more preferable, and 25 to 85% by weight is further preferable.

The time for performing this step may be either during or after the solidification step. For example, an embodiment in which a methylene acceptor compound / methylene donor compound is mixed with them when preparing a mixed solution of chloroprene and a cellulosic fiber; the methylene acceptor compound / methylene donor compound is added to the master batch obtained after the drying step. Aspects are mentioned.

<5. Mixing process>
The mixing step is a step of mixing the processed product (master batch) after the solidification step (obtained through other steps if necessary) as it is or by adding an arbitrary component as necessary. The temperature at the time of mixing (for example, at the time of kneading and kneading) may be about room temperature (for example, about 15 to 30 ° C.), but may be heated to a high temperature so that the rubber component does not undergo a crosslinking reaction. .. For example, it is 140 ° C. or lower, more preferably 120 ° C. or lower. The lower limit is 40 ° C. or higher, preferably 60 ° C. or higher. Therefore, the heating temperature is preferably about 40 to 140 ° C, more preferably about 60 to 120 ° C.

Optional components include, for example, reinforcing agents (eg, carbon black, silica, etc.), silane coupling agents, sulfur, zinc oxide, stearic acid, vulcanization accelerators, vulcanization accelerator aids, oils, cured resins, waxes, aging. Inhibitors, colorants, vulcanization accelerators, softeners, plasticizers, curing agents (eg phenolic resins, high styrene resins, etc.), foaming agents, fillers (carbon black, silica, etc.), coupling agents, adhesives (For example, macrone resin, phenol, terpene resin, petroleum hydrocarbon resin, rosin derivative, etc.), dispersant (eg, fatty acid, etc.), adhesion enhancer (eg, organic cobalt salt, etc.), lubricant (eg, paraffin, etc.) Examples thereof include compounding agents that can be used in the rubber industry such as hydrocarbon resins, fatty acids, fatty acid derivatives, etc.). Of these, sulfur and vulcanization accelerators are preferable. Examples of the vulcanization accelerator include Nt-butyl-2-benzothiazolesulfenamide (BBS). The optional component may be one kind or two or more kinds.

The timing of addition of the optional component is not particularly limited. The time for adding sulfur and the vulcanization accelerator is preferably later than the time for adding the methylene acceptor compound and / or the methylene donor compound. When the step of adding the methylene acceptor compound and / or the methylene donor compound is performed in the middle of the mixing step, the methylene acceptor compound and the material containing the methylene donor compound are mixed and kneaded without adding sulfur and a vulcanization accelerator. It is preferable to start and then add sulfur and a vulcanization accelerator to further knead and knead. As a result, the methylene acceptor compound and the methylene donor compound are pre-condensed by heating, and the interaction between the condensate and the rubber component and the cellulosic fiber can be effectively exhibited.

The amount of sulfur added is preferably 1.0% by weight or more, more preferably 1.5% by weight or more, still more preferably 1.7% by weight or more with respect to the rubber component. The upper limit is preferably 10% by weight or less, preferably 7% by weight or less, and even more preferably 5% by weight or less.

The amount of the vulcanization accelerator added is preferably 0.1% by weight or more, more preferably 0.3% by weight or more, still more preferably 0.4% by weight or more with respect to the rubber component. The upper limit is preferably 5% by weight or less, preferably 3% by weight or less, and even more preferably 2% by weight or less.

In the mixing step, molding may be performed as needed after the mixing is completed. Examples of the molding apparatus include mold molding, injection molding, extrusion molding, hollow molding, foam molding and the like, which may be appropriately selected according to the shape, application and molding method of the final product.

In the mixing step, it is preferable to heat (vulcanization, crosslinking) after the mixing is completed, preferably after molding. This can effectively reinforce the rubber composition. When a methylene acceptor compound and / or a methylene donor compound is added, these compounds undergo a condensation reaction by heating to form a three-dimensional network structure, and this structure interacts with the rubber component and the cellulosic fiber, respectively. , The rubber composition can be reinforced more effectively. The heating temperature is preferably 150 ° C. or higher, the upper limit is preferably 200 ° C. or lower, and more preferably 180 ° C. or lower. Therefore, about 150 to 200 ° C. is preferable, and about 150 to 180 ° C. is more preferable. Examples of the heating device include vulcanization devices such as mold vulcanization, can vulcanization, and continuous vulcanization.

In the mixing step, a finishing process may be performed at the end (before the final product), if necessary. Examples of the finishing treatment include polishing, surface treatment, lip finishing, lip cutting, chlorine treatment and the like, and only one of these treatments may be performed or a combination of two or more thereof may be performed.

<6. Uses of rubber composition>
The use of the rubber composition obtained by the production method of the present invention is not particularly limited, and for example, transportation equipment such as automobiles, trains, ships, airplanes, and belt conveyors; electrical appliances such as personal computers, televisions, telephones, and watches; mobile phones. Mobile communication equipment such as telephones; portable music playback equipment, video playback equipment, printing equipment, copying equipment, sporting goods; building materials; office equipment such as stationery, containers, containers. In addition to these, it can be applied to members using rubber or flexible plastic, and is preferably applied to industrial belts. Examples of industrial belts include flat belts, conveyor belts, cogged belts, V-belts, rib belts, and round belts.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

<Production Example 1> Production of Oxidized Cellulose Nanofiber (1)
5.00 g (absolutely dry) of bleached unbeaten kraft pulp (whiteness 85%) derived from coniferous trees, 39 mg (0.05 mmol per 1 g of absolute dry cellulose) and 514 mg (absolutely dry) of TEMPO (Sigma Aldrich). It was added to 500 ml of an aqueous solution in which 1.0 mmol) was dissolved in 1 g of cellulose, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that the sodium hypochlorite content was 5.5 mmol / g, and the oxidation reaction was started at room temperature. Although the pH in the system decreased during the reaction, 3M aqueous sodium hydroxide solution was sequentially added to adjust the pH to 10. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system did not change. The mixture after the reaction was filtered through a glass filter to separate the pulp, and the pulp was thoroughly washed with water to obtain oxidized pulp (oxidized (carboxylated) cellulose). The pulp yield at this time was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.6 mmol / g. This was adjusted to 1.0% (w / v) with water and treated three times with an ultra-high pressure homogenizer (20 ° C., 150 MPa) to obtain an oxidized cellulose nanofiber dispersion. The average fiber diameter was 3 nm and the aspect ratio was 250.

<Production Example 2> Production of Oxidized Cellulose Nanofiber (2)
A 5% (w / v) slurry of cellulose oxide of Production Example 1 was prepared, and 2% (active ingredient equivalent) of 30% (w / v) hydrogen peroxide solution was added to the solid content of cellulose oxide to add 1 M. The pH was adjusted to 12 with sodium hydroxide. This slurry was hydrolyzed at 80 ° C. for 2 hours. Then, it was filtered with a glass filter and washed thoroughly with water. The hydrolyzed 5% (w / v) oxidized cellulose slurry was treated three times with an ultra-high pressure homogenizer (20 ° C., 150 MPa) to obtain an oxidized cellulose nanofiber dispersion. The average fiber diameter was 5 nm and the aspect ratio was 60.

<Production Example 3> Production of carboxymethylated cellulose nanofibers In a stirrer capable of mixing pulp, 200 g of pulp (NBKP (coniferous bleached kraft pulp), manufactured by Nippon Paper Industries) by dry mass and sodium hydroxide by dry mass 111 g (2.25 times mol per anhydrous glucose residue of the bottoming material) was added, and water was added so that the pulp solid content became 20% (w / v). Then, after stirring at 30 ° C. for 30 minutes, 216 g of sodium monochloroacetate (active ingredient equivalent, 1.5 times mol per glucose residue of pulp) was added. After stirring for 30 minutes, the temperature was raised to 70 ° C. and the mixture was stirred for 1 hour. Then, the reaction product was taken out, neutralized and washed to obtain a carboxylmethylated pulp having a carboxymethyl substitution degree of 0.25 per glucose unit. This was treated with water to a solid content concentration of 1% and treated with a high-pressure homogenizer at a pressure of 20 ° C. and 150 MPa five times to obtain carboxymethylated cellulose nanofibers. The average fiber diameter was 15 nm and the aspect ratio was 50.

<Production Example 4> Production of cationized cellulose nanofibers To a pulper capable of stirring pulp, 200 g of pulp (NBKP, manufactured by Nippon Paper Industries) by dry weight and 24 g of sodium hydroxide by dry weight are added to bring the pulp solid concentration to 15%. Water was added so that it would be. Then, after stirring at 30 ° C. for 30 minutes, the temperature was raised to 70 ° C., and 200 g (active ingredient equivalent) of 3-chloro-2-hydroxypropyltrimethylammonium chloride was added as a cationizing agent. After reacting for 1 hour, the reactants were taken out, neutralized and washed to give a cation-modified pulp with a degree of cation substitution of 0.05 per glucose unit. This was adjusted to a solid content concentration of 1%, and treated twice with a high-pressure homogenizer at a pressure of 20 ° C. and 140 MPa. The average fiber diameter was 25 nm and the aspect ratio was 50.

The amount of carboxyl group, degree of carboxymethyl substitution, and degree of cation substitution in the above production example were measured by the method described in the upper section.

<Example 1>
A mixture of 1000 g of an aqueous dispersion having a solid content of 0.5% of the cellulose oxide nanofibers obtained in Production Example 1 and 1000 g of a suspension having a solid content of 10% of chloroprene rubber latex was mixed to obtain a rubber component: weight of modified cellulose nanofibers. The ratio was 100: 5, and the mixture was stirred with a TK homomixer (6000 rpm) for 30 minutes. While stirring this mixture with a three-one motor (150 to 300 rpm), add 10% calcium chloride so that the concentration in the total mixture becomes 0.5%, and separate the solid and liquid with a nylon mesh with an opening of 5 μm. Then, it was dried in a heating oven at 70 ° C. for 10 hours to obtain a masterbatch. 168 g of this masterbatch was kneaded in an open roll (manufactured by Kansai Roll Co., Ltd.) at 60 ° C. for 5 minutes. Next, stearic acid is 0.5% by weight with respect to the rubber component, zinc oxide is 6% by weight with respect to the rubber component), sulfur is 3.5% by weight with respect to the rubber component, and a vulcanization accelerator (BBS, Nt). -Butyl-2-benzothiazolesulfur amide) was added in an amount of 0.7% by weight based on the rubber component, and kneaded at 60 ° C. for 10 minutes using an open roll (manufactured by Kansai Roll Co., Ltd.) to form an unvulcanized rubber composition. I got a sheet of things. This sheet was sandwiched between dies and press-vulcanized at 160 ° C. for 15 minutes to obtain a sheet of a vulcanized rubber composition having a thickness of 2 mm. This is cut into test pieces having a predetermined shape, and according to JIS K6251 "Sulfurized rubber and thermoplastic rubber-How to determine tensile properties", tensile strength (50% tensile stress (M50), 100), which is one of the reinforcing properties. % Tensile stress (M100), 300% tensile stress (M300), and breaking strength) were measured. The results are shown in Table 1. The larger each value is, the better the vulcanized rubber composition is reinforced, indicating that the mechanical strength of the rubber is excellent.

<Example 2>
The same as in Example 1 except that after solidification, solid-liquid separation was performed with a nylon mesh having an opening of 5 μm, the obtained solid material was washed with water, and solid-liquid separation was performed again with a nylon mesh having an opening of 5 μm to recover the solid material. Got the way. The results are shown in Table 1.

<Example 3>
The procedure was the same as in Example 2 except that the cellulose oxide nanofibers obtained in Production Example 2 were used. The results are shown in Table 1.

<Example 4>
The procedure was the same as in Example 2 except that the coagulant was magnesium chloride. The results are shown in Table 1.

<Example 5>
The procedure was the same as in Example 2 except that the coagulant was aluminum sulfate. The results are shown in Table 1.

<Example 6>
Calcium chloride was added so that the concentration in the total mixture was 0.3%, and then 5% by weight acetic acid was added until the pH in the mixture became 5, in the same manner as in Example 2. went. The results are shown in Table 1.

<Example 7>
Calcium chloride was added so that the concentration in the total mixture was 0.3%, and then 5% by weight sulfuric acid was added until the pH in the mixture became 5, in the same manner as in Example 2. went. The results are shown in Table 1.

<Example 8>
The same method as in Example 1 was carried out except that 20 parts by weight of the cellulose oxide nanofibers obtained in Production Example 1 was blended with respect to 100 parts of the rubber component. The results are shown in Table 1.

<Example 9>
The same as in Example 8 except that after solidification, solid-liquid separation was performed with a nylon mesh having an opening of 5 μm, the obtained solid material was washed with water, and solid-liquid separation was performed again with a nylon mesh having an opening of 5 μm to recover the solid material. Got the way. The results are shown in Table 1.

<Example 10>
The procedure was the same as in Example 2 except that the carboxymethylated cellulose nanofibers obtained in Production Example 3 were used. The results are shown in Table 1.

<Example 11>
The procedure was the same as in Example 2 except that the cationized cellulose nanofibers obtained in Production Example 4 were used. The results are shown in Table 1.

<Example 12>
Instead of kneading 168 g of the masterbatch at 60 ° C. for 10 minutes using an open roll, 1.3% by weight of resorcin with respect to the rubber component and 0.8% by weight of hexamethylenetetramine with respect to the rubber component with respect to 168 g of the masterbatch. It was added and kneaded with an open roll (manufactured by Kansai Roll Co., Ltd.) at 60 ° C. for 10 minutes in the same manner as in Example 2. The results are shown in Table 1.

<Comparative Example 1>
The same method as in Example 1 was carried out except that the coagulation treatment was not carried out. The results are shown in Table 1.

<Comparative Example 2>
The same method as in Example 3 was carried out except that the coagulation treatment was not carried out. The results are shown in Table 1.

<Comparative Example 3>
The procedure was the same as in Example 1 except that the coagulant was sodium chloride. Since coagulation did not proceed well with this coagulant and it was difficult to prepare an evaluation sample, measurement results of tensile strength could not be obtained. The results are shown in Table 1.

<Comparative Example 4>
The same method as in Example 10 was carried out except that the coagulation treatment was not carried out. The results are shown in Table 1.

<Comparative Example 5>
The same method as in Example 11 was carried out except that the coagulation treatment was not carried out. The results are shown in Table 1.

<Comparative Example 6>
The procedure was the same as in Example 2 except that the cellulose nanofibers were not blended. The results are shown in Table 1.

<Comparative Example 7>
It was carried out in the same manner as in Comparative Example 6 except that the coagulation treatment was not carried out. The results are shown in Table 1.

Claims (6)

A rubber composition comprising a step of adding a divalent or trivalent metal salt, or a divalent or trivalent metal salt and an acid to a mixed solution containing chloroprene rubber and a cellulosic fiber to coagulate the rubber component. How to make things. The method according to claim 1, wherein the metal salt is a calcium salt. The method according to claim 1 or 2, wherein the acid is acetic acid or sulfuric acid. The method according to any one of claims 1 to 3, wherein the cellulosic fiber comprises at least one selected from the group consisting of oxidized cellulose fiber, carboxymethylated cellulose fiber and cationized cellulose fiber. The method according to any one of claims 1 to 4, wherein the length-weighted average fiber length of the cellulosic fiber is 50 to 2000 nm. The method according to any one of claims 1 to 5, wherein the length-weighted average fiber diameter of the cellulosic fiber is 2 to 500 nm.