JP6994345B2 - Rubber composition and molded products - Google Patents

Description

The present invention relates to a rubber composition containing a cellulosic fiber, a molded product, and a method for producing the same.

Rubber compositions containing rubber and cellulosic fibers are known to have excellent mechanical strength. For example, Patent Document 1 describes a master batch of rubber / cellulosic fibers obtained by stirring and mixing a cellulosic fiber having an average fiber diameter of less than 0.5 μm and a rubber latex. According to the document, a dispersion liquid obtained by fibrillating cellulosic fibers having an average fiber diameter of less than 0.5 μm in water and a rubber latex are mixed and dried to make the cellulosic fibers uniform in the rubber. It is said that a master batch of rubber / cellulosic fibers dispersed in a rubber / cellulose fiber can be obtained, and a rubber composition having an excellent balance between rubber reinforcing property and fatigue resistance can be produced from the master batch.

However, since the compatibility between rubber and cellulosic fibers is generally low, sufficient strength has not been obtained for the rubber composition. Therefore, in order to improve the compatibility between rubber and the cellulosic fiber, the use of a coupling agent, the introduction of a long-chain alkyl group into the cellulosic fiber, and the like have been studied (for example, Patent Document 2, Patent Document 2, etc.). 3).

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

However, the above method has a problem that the reagent used is expensive. Further, the above method has 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 capable of producing a molded product having improved compatibility between a rubber component and a cellulosic fiber and having sufficient reinforcing properties.

As a result of diligent studies on the above problems, the present inventors have found that the above problems can be solved by including a methylene acceptor compound and a methylene donor compound in the rubber component and the cellulosic fiber, and complete the present invention. It came to.
The present invention provides the following [1] to [9].
[1] A rubber composition containing a rubber component, a cellulosic fiber, a methylene acceptor compound and a methylene donor compound.
[2] The rubber composition according to the above [1], wherein the rubber component is chloroprene rubber.
[3] The rubber composition according to the above [1] or [2], wherein the cellulosic fiber contains at least one selected from the group consisting of oxidized cellulose fiber, carboxymethylated cellulose fiber and cationized cellulose fiber.
[4] The rubber composition according to any one of the above [1] to [3], wherein the methylene acceptor compound is at least one selected from the group consisting of resorcin, a resorcin derivative and a resorcin-based resin.
[5] The rubber composition according to any one of the above [1] to [4], wherein the methylene donor compound is hexamethylenetetramine.
[6] The rubber composition according to any one of the above [1] to [5], wherein the length-weighted average fiber length of the cellulosic fiber is 50 to 2000 nm, and the length-weighted average fiber diameter is 2 to 500 nm.
[7] A molded product using the rubber composition according to any one of the above [1] to [6].
[8] The method for producing a molded product according to the above [7], which comprises the following steps (a1) and (a2).
(A1) A step of mixing a rubber component with a cellulosic fiber, a methylene acceptor compound and a methylene donor compound to obtain a mixture (1).
(A2) A step of heating the mixture (1) obtained in the above step (a1) at 40 ° C. or higher and lower than 100 ° C. for 1 to 24 hours and molding to obtain a molded product.
[9] The method for producing a molded product according to the above [7], which comprises the following steps (b1) to (b3).
(B1) A step of mixing a rubber component and a cellulosic fiber to obtain a mixture (2).
(B2) A step of obtaining a heat-treated product obtained by heating the mixture (2) obtained in the above step (b1) at 40 ° C. or higher and lower than 100 ° C. for 1 to 24 hours.
(B3) A step of mixing a methylene acceptor compound and a methylene donor compound with the heat-treated product obtained in the step (b2) and molding to obtain a molded product.

According to the present invention, it is possible to provide a rubber composition capable of producing a molded product having improved compatibility between a rubber component and a cellulosic fiber and having sufficient reinforcing properties.

3 is a chart showing strain-stress curves of Examples 1 to 3 and Comparative Examples 1 and 2.

[1. Rubber composition]
The rubber composition of the present invention contains at least a cellulosic fiber, a rubber component, a methylene acceptor compound, and a methylene donor compound.

[1-1. Cellulose fiber]
In the present invention, as the cellulosic fiber, 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 it can be used. ..

Cellulose fibers are not particularly limited, and examples thereof include those derived from plants, animals (for example, ascidians), algae, microorganisms (for example, acetobacter), and microorganism 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 cellulose fiber may be any one or a combination thereof, but is preferably a cellulosic 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 fiber is not particularly limited. In the case of softwood kraft pulp, which is a general pulp, it is about 30 to 60 μm, and in the case of hardwood kraft pulp, it is about 10 to 30 μm. In the case of other pulps, the average fiber diameter of the cellulose fibers that have undergone general purification is about 50 μm. For example, when using purified cellulose fibers such as chips having a size of several cm, it is preferable to perform mechanical treatment with a breaker such as a refiner or a beater to adjust the average fiber diameter to about 50 μm.

The average fiber diameter of the cellulose nanofibers is usually about 2 to 500 nm, preferably 2 to 50 nm in terms of the length-weighted average fiber diameter. The average fiber length of the cellulose nanofibers is preferably 50 to 2000 nm in terms of the 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 lower limit of the average aspect ratio of 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 (1).

Equation (1): Average aspect ratio = average fiber length / average fiber diameter The following describes a method for producing cellulose nanofibers. For convenience, the cellulose fiber that is the raw material of the cellulose nanofiber is also referred to as "cellulose raw material".

[1-1-1. Degeneration]
The cellulose raw material has three hydroxyl groups per glucose unit and can be subjected to various chemical denaturations. As the cellulose raw material, either a chemically modified cellulose raw material or a non-chemically modified cellulose raw material can be used. However, when the chemically modified cellulose raw material is used, the fineness of the fibers is sufficiently advanced to obtain cellulose nanofibers having a uniform average fiber length and average fiber diameter. Therefore, it is possible to manufacture a molded product that exhibits a sufficient reinforcing effect when compounded with a rubber component. Therefore, chemically modified cellulose raw materials are preferred. Examples of chemical denaturation include oxidation, etherification, phosphorylation, esterification, silane coupling, fluorination, and cationization. Of these, oxidation (carboxylation), etherification, cationization, and esterification are preferable. Hereinafter, these chemical denaturations will be described.

[Oxidation]
The lower limit of the amount of carboxyl groups in cellulose oxide or cellulose oxide nanofibers (collectively referred to as "cellulose oxide fibers") obtained by the oxidation treatment is preferably 0.5 mmol / g or more with respect to the absolute dry weight. It is more preferably 0.8 mmol / g or more, still more preferably 1.0 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 oxidation method is not particularly limited. As an example of the oxidation method, there is a method of oxidizing a cellulose raw material in water using an oxidizing agent in the presence of an N-oxyl compound and a chemical substance selected from the group consisting of bromide, iodide and a mixture thereof. Can be mentioned. According to this method, a carbon atom having a primary hydroxyl group at the C6 position of the glucopyranose ring on the surface of cellulose is selectively oxidized, and at least one functional group selected from the group consisting of an aldehyde group, a carboxyl group, and a carboxylate group is functionalized. A group is born. The concentration of the cellulose raw material at the time of the reaction is not particularly limited, but is preferably 5% by mass 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). As the N-oxyl compound, any compound can be used as long as it is a compound that promotes the desired oxidation reaction.

The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing the cellulose 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 an absolute dry cellulose raw material. 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 cellulose raw material to be completely dried.

Bromide is a compound containing bromine. Examples of the bromide include alkali metal bromides that can be dissociated and ionized in water, for example, sodium bromide. The iodide is a compound containing iodine, and examples thereof include 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 lower limit of the total amount of bromide and iodide is preferably 0.1 mmol or more, more preferably 0.5 mmol or more, with respect to 1 g of the dry dry cellulose raw material. 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 the dry cellulose raw material.

The oxidizing agent is not particularly limited. Examples thereof include halogens, hypohalogenic acids, subhalogenic acids, perhalogenic acids, 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 lower limit of 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, with respect to 1 g of the dry cellulose raw material. The upper limit of the amount is preferably 500 mmol or less, more preferably 50 mmol or less, further preferably 25 mmol or less, still more preferably 10 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, still more preferably 3 to 10 mmol with respect to 1 g of the dry dry cellulose raw material. ..
When an N-oxyl compound is used, the lower limit of the amount of the oxidizing agent used is preferably 1 mol or more with respect to 1 mol of the N-oxyl compound. The upper limit thereof is preferably 40 mol or less. 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 the oxidation reaction usually proceeds efficiently even under relatively mild conditions.
The lower limit of 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 lower limit of 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.
Normally, the pH of the reaction solution tends to decrease because a carboxyl group is generated in the cellulose as the oxidation reaction progresses. 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. The lower limit of the reaction time is usually 0.5 hours or more. The upper limit thereof is usually 6 hours or less, preferably 4 hours or less. Therefore, the reaction time in oxidation is usually 0.5 to 6 hours, preferably 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. In 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 lower limit of 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, and 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 lower limit of the amount of ozone added is preferably 0.1% by mass or more, more preferably 5% by mass or more, based on 100% by mass of the solid content of the cellulose raw material. The upper limit of the amount of ozone added is usually 30% by mass or less. Therefore, the amount of ozone added is preferably 0.1 to 30% by mass, more preferably 5 to 30% by mass, based on 100% by mass of the solid content of the cellulose raw material.

The lower limit of the ozone treatment temperature is usually 0 ° C. or higher, preferably 20 ° C. or higher. The upper limit thereof is usually 50 ° C. or lower. Therefore, the ozone treatment temperature is preferably 0 to 50 ° C, more preferably 20 to 50 ° C.
The lower limit of the ozone treatment time is usually 1 minute or more, preferably 30 minutes or more. 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. Examples thereof include chlorine dioxide, chlorine compounds such as sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. As a method of the additional oxidation treatment, for example, 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 ozone-treated cellulose in the oxidizing agent solution is used. Can be mentioned. The amount of the carboxyl group, the carboxylate group, and the aldehyde group contained in the cellulose oxide or the cellulose oxide nanofiber can be adjusted by controlling the oxidation conditions such as the addition amount of the oxidizing agent 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% by mass slurry (aqueous dispersion) of cellulose oxide, and add a 0.1 M hydrochloric acid aqueous solution to adjust the pH to 2.5. A 0.05 N sodium hydroxide aqueous solution is added dropwise to the acidified aqueous dispersion, and the electric conductivity is measured until the pH reaches 11. From the amount of sodium hydroxide (a) consumed in the neutralization step of a weak acid whose electrical conductivity changes slowly, the amount of carboxyl group can be calculated using the following formula (2).
The amount of carboxyl groups of cellulose oxide and cellulose oxide nanofibers are usually the same.

Formula (2): Amount of carboxyl group [mmol / g cellulose oxide or cellulose oxide nanofiber] = a [mL] × 0.05 / mass of cellulose oxide [g]

[Aetherization]
As etherification, carboxymethyl (ether), methyl (ether), ethyl (ether), cyanoethyl (ether), hydroxyethyl (ether), hydroxypropyl (ether), ethyl hydroxyethyl (ether) Examples include conversion to hydroxypropylmethyl (ether). From this, the method of carboxymethylation will be described below as an example.

The lower limit of the degree of carboxymethyl substitution per anhydrous glucose unit in carboxymethylated cellulose or carboxymethylated cellulose nanofibers (collectively referred to as "carboxymethylated cellulose fibers") obtained by carboxymethylation is 0.01. The above is preferable, 0.05 or more is more preferable, and 0.10 or more is further preferable. The upper limit of the degree of substitution is preferably 0.50 or less, more preferably 0.40 or less, and even more preferably 0.35 or less. Therefore, the degree of carboxymethyl substitution is preferably 0.01 to 0.50, more preferably 0.05 to 0.40, and even more preferably 0.10 to 0.35.

The carboxymethylation method is not particularly limited. For example, there is a method of converting a cellulose raw material as a starting material into a marcel and then etherifying it. 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 t-butyl alcohol. The mixing ratio of the lower alcohol in the mixed solvent is usually 60% by mass or more or 95% by mass or less, preferably 60 to 95% by mass. The lower limit of the amount of the solvent is usually three times or more in terms of mass with respect to the cellulose raw material. The upper limit of the amount is not particularly limited, but is 20 times or less. Therefore, the amount of the solvent is preferably 3 to 20 times the mass of the cellulose raw material.

Mercerization is usually carried out by mixing a starting material and a mercerizing agent. Examples of the mercerizing agent include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide. The lower limit of the amount of the mercerizing agent used is preferably 0.5 times or more, more preferably 1.0 times or more, still more preferably 1.5 times or more, in terms of molars, per anhydrous glucose residue as a starting material. The upper limit of the amount is usually 20 times or less, preferably 10 times or less, and more preferably 5 times or less. Therefore, the amount of the mercerizing agent used is preferably 0.5 to 20 times, more preferably 1.0 to 10 times, and further 1.5 to 5 times, in terms of molar amount, per anhydrous glucose residue of the starting material. preferable.

The lower limit of the reaction temperature for mercerization is usually 0 ° C. or higher, preferably 10 ° C. or higher. The upper limit thereof 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 lower limit of the reaction time is usually 15 minutes or more, preferably 30 minutes or more. 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 lower limit of 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 in terms of molar amount per glucose residue of the cellulose raw material. .. The upper limit of the amount is usually 10.0 times or less, preferably 5 times or less, and more preferably 3 times or less. Therefore, the amount thereof is preferably 0.05 to 10.0 times, more preferably 0.5 to 5 times, still more preferably 0.8 to 0.8 times, in terms of molar amount, per glucose residue of the cellulose raw material. It is three times.

The lower limit of the reaction temperature is usually 30 ° C. or higher, preferably 40 ° C. or higher. The upper limit thereof 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 lower limit of the reaction time is usually 30 minutes or more, preferably 1 hour or more. 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 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 can be 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 containing 100 mL of special grade concentrated nitric acid to 1000 mL of methanol, and shake for 3 hours to convert the carboxymethyl cellulose salt (carboxymethyl 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) The degree of carboxymethyl substitution (DS) is calculated by the following equation (3).
The degree of carboxymethyl substitution between the carboxymethylated cellulose and the carboxymethylated cellulose nanofibers is usually the same.

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)
Equation (3): DS = 0.162 × A / (1-0.058 × A)
A: 1N NaOH amount (mL) required for neutralization of 1 g of acid-type carboxymethylated cellulose
F: 0.1N H ₂ SO ₄ factor F': 0.1N NaOH factor

[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 method of cationization is not particularly limited. For example, a method of reacting a cellulose raw material with a cationizing agent and a catalyst in the presence of water or alcohol can be mentioned.
Examples of the cationizing agent include glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydrite (eg, 3-chloro-2-hydroxypropyltrimethylammonium hydrite), and halohydrin types thereof. .. By using any of these, cationized cellulose having a group containing a quaternary ammonium can be obtained.
Examples of the catalyst include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide.
Examples of the alcohol include alcohols having 1 to 4 carbon atoms.

The lower limit of the amount of the cationizing agent is preferably 5% by mass or more, more preferably 10% by mass or more, based on 100% by mass of the cellulose raw material. The upper limit of the amount is usually 800% by mass or less, preferably 500% by mass or less.
The lower limit of the amount of the catalyst is preferably 0.5% by mass or more, and more preferably 1% by mass or more with respect to 100% by mass of the cellulose raw material. The upper limit of the amount is usually 70% by mass or less, preferably 30% by mass or less, more preferably 7% by mass or less, and further preferably 3% by mass or less.
The lower limit of the amount of alcohol is preferably 50% by mass or more, and more preferably 100% by mass or more with respect to 100% by mass of the cellulose raw material. The upper limit of the amount is usually 50,000% by mass or less, preferably 500% by mass or less.

The lower limit of the reaction temperature at the time of cationization is usually 10 ° C. or higher, preferably 30 ° C. or higher. The upper limit thereof is usually 90 ° C. or lower, preferably 80 ° C. or lower. The lower limit of the reaction time is usually 10 minutes or more, preferably 30 minutes or more. The upper limit thereof 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 or cationized cellulose nanofiber (collectively referred to as "cationized cellulose fiber") can be adjusted by the amount of cationizing agent added and the composition ratio of water or alcohol. can. The degree of cation substitution indicates the number of moles of substituents introduced 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 maximum value of the degree of cation substitution is theoretically 3 (minimum value is 0).

The lower limit of 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, the cellulose into which a cation substituent is 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. Therefore, the fiber morphology can be maintained, and a situation that cannot be obtained as nanofibers can be prevented.

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 formula (4). 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.
The degree of cation substitution between the cationized cellulose and the cationized cellulose nanofibers is usually the same.
Equation (4): 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. For example, a method of reacting the cellulose raw material with the compound A described later can be mentioned. 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, and a method of adding the aqueous solution of the compound A to the slurry of the cellulose raw material. 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 is increased and the esterification efficiency is increased.

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, and ammonium metaphosphate. 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 introduction of phosphoric acid group, easy defibration in the defibration process, and easy industrial application. 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 introduction efficiency of the 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 mass) with stirring to introduce a phosphate group into the cellulose. When the compound A is a phosphoric acid-based compound, the lower limit of the addition amount (as the amount of phosphorus element) of the compound A is preferably 0.2 parts by mass or more, more preferably 1 part by mass or more with respect to 100 parts by mass of the cellulose raw material. preferable. Thereby, the yield of the fine fibrous cellulose can be further improved. The upper limit of the amount is preferably 500 parts by mass or less, more preferably 400 parts by mass or less. This makes it possible to efficiently obtain a yield commensurate with the amount of compound A used. Therefore, the amount of compound A added is preferably 0.2 to 500 parts by mass, more preferably 1 to 400 parts by mass.

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 basic compound 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. Examples thereof include urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine and hexamethylenediamine. 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 mass, more preferably 100 to 700 parts by mass. 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 after removing the water, the temperature is 100 to 170 ° C. Heat treatment is more preferable.

In phosphoric acid esterified cellulose, a phosphoric acid group is introduced as a substituent into the cellulose raw material, and the celluloses electrically repel each other. Therefore, the phosphate esterified cellulose can be easily nano-defibrated. The lower limit of the degree of phosphoric acid 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 or less. As a result, it is possible to prevent the swelling or dissolution of the phosphoric acid esterified cellulose and prevent the situation where nanofibers cannot be obtained. Therefore, the degree of substitution is preferably 0.001 to 0.60. 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.

[1-1-2. Defibering]
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 usually means 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, and ultrasonic type devices. Among them, a high-pressure or ultra-high pressure homogenizer is preferable, and a wet high-pressure or ultra-high 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, and further 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 a 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 lower limit of the solid content concentration of the cellulose raw material in the dispersion is usually 0.1% by mass or more, preferably 0.2% by mass or more. , More preferably 0.3% by mass or more. As a result, the amount of the liquid becomes appropriate with respect to the amount of the cellulose raw material, and the efficiency becomes high. The upper limit of the concentration is usually 10% by mass or less, preferably 6% by mass or less. This makes it possible to maintain liquidity.

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. The pretreatment may be performed using a mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer.

[Form of cellulosic fibers to be mixed]
The form of the cellulosic fiber mixed with the rubber component is not particularly limited. For example, 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 may be used for mixing. The concentration of the cellulosic fiber in the dispersion liquid can be 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 can be 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 mass with respect to the cellulosic fibers. However, the amount of the dispersion medium can be appropriately adjusted by adding a liquid medium or further drying.

Further, a mixed solution of a cellulosic fiber and a water-soluble polymer solution, a dry solid of the mixed solution, a wet solid of the mixed solution, and the like can also be used. The amount of the liquid medium in the mixture and the dry solid may be in the above range. 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, and starch. Waste powder, positive starch, phosphorylated starch, corn starch, Arabic gum, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, chitosan, casein, albumin, soybean protein solution, peptone, polyvinyl alcohol, polyacrylamide, polyvinylpyrrolidone, Polyvinyl acetate, polyamino acid, polylactic acid, polyaronic acid, polyglycerin, latex, rosin-based sizing agent, petroleum resin-based sizing agent, urea resin, melamine resin, epoxy resin, polyamide resin, polyamide / polyamine resin, polyethyleneimine, polyamine , Vegetable gums, polyethylene oxides, hydrophilic crosslinked polymers, polyacrylic acid salts such as sodium polyacrylic acid, starch polyacrylic acid copolymers, tamarind gums, guar gums, and colloidal silicas, and mixtures thereof. Among these, it is preferable to use carboxymethyl cellulose and a salt thereof 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. For example, spray drying, squeezing, air drying, hot air drying, or vacuum drying can be mentioned. Examples of the drying device include a continuous drying device (for example, a 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, and an air flow drying device. Equipment, spray dryer drying device, spray drying device, cylindrical drying device, drum drying device, screw conveyor drying device, rotary 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 drying device, stirring drying device). 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.

[1-2. Rubber component]
The rubber component is usually a component containing an organic polymer as a main component, having a high elastic limit and a low elastic modulus. The rubber component is roughly classified into natural rubber and synthetic rubber, and in the present invention, any of them may be used, or a combination of both may be used.
The natural rubber may be natural rubber in a narrow sense without chemical modification, or chemically modified natural rubber such as hydride natural rubber, chlorinated natural rubber, chlorosulfonated natural rubber, and epoxidized natural rubber. , Deproteinized natural rubber may be used.
Examples of synthetic rubber include butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), isoprene rubber (IR), butyl rubber (IIR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), and styrene. -Diene rubber such as isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, isoprene-butadiene copolymer rubber, ethylene-propylene rubber (EPM, EPDM), acrylic rubber (ACM), epichlorohydrin rubber (CO, ECO), fluororubber (FKM), silicone rubber (Q), urethane rubber (U), chlorosulfonated polyethylene (CSM) can be mentioned.
The rubber component may be one kind alone or a combination of two or more kinds.

The rubber component may be either solid or liquid. Examples of the liquid rubber component include a dispersion liquid of the rubber component and a solution of the rubber component. Examples of the solvent include water and organic solvents. In the present invention, an excellent effect is exhibited by containing chloroprene rubber (CR) as a rubber component.

[1-3. Methylene acceptor compound and methylene donor compound]
The rubber composition of the present invention contains a methylene acceptor compound and 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 compounds having a phenolic hydroxyl group 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, and linoleic acid.

The methylene donor compound is a compound that can usually 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 cashew modification. Examples thereof include a combination of a phenol resin and hexamethylenetetramine, and a combination of a phenol resin and hexamethylenetetramine. Of these, a combination of cresol, cresol derivative or cresol-based resin and pentamethoxymethylmelamine, and a combination of resorcin, resorcin derivative or resorcin-based resin and hexamethylenetetramine are preferable.

[1-4. Content]
The lower limit of the content of the cellulosic fiber in the rubber composition is preferably 1% by mass or more, more preferably 2% by mass or more, still more preferably 3% by mass or more, based on 100% by mass of the rubber component. Thereby, the effect of improving the tensile strength can be sufficiently exhibited. The upper limit value is preferably 50% by mass or less, preferably 40% by mass or less, and further preferably 30% by mass or less. This makes it possible to maintain processability in the manufacturing process. Therefore, the content of the cellulosic fiber is preferably 1 to 50% by mass, more preferably 2 to 40% by mass, still more preferably 3 to 30% by mass.

The lower limit of the content of the methylene acceptor compound is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, still more preferably 1.3% by mass or more with respect to 100% by mass of the rubber component. Even more preferably, it is 5.5% by mass or more. Thereby, the effect of improving the tensile strength can be sufficiently exhibited. The upper limit value is preferably 50% by mass or less, more preferably 20% by mass or less, still more preferably 10% by mass or less. This makes it possible to maintain processability in the manufacturing process. Therefore, the content of the methylene acceptor compound is preferably 0.5 to 50% by mass, more preferably 1.0 to 20% by mass, further preferably 1.3 to 20% by mass, and 1.5 to 10% by mass. Is even more preferable.

The lower limit of the content of the methylene donor compound is preferably 10% by mass or more, more preferably 20% by mass or more, still more preferably 25% by mass or more, based on 100% by mass of the methylene acceptor compound. Thereby, the effect of improving the tensile strength can be sufficiently exhibited. The upper limit value is preferably 100% by mass or less, more preferably 90% by mass or less, still more preferably 85% by mass or less. This makes it possible to maintain processability in the manufacturing process. Therefore, the content of the methylene donor compound is preferably 10 to 100% by mass, more preferably 20 to 90% by mass, still more preferably 25 to 85% by mass, based on 100% by mass of the methylene acceptor compound.

[1-5. Optional ingredient]
The rubber composition of the present invention may contain one or more optional components, if necessary. Optional components include, for example, reinforcing agents (carbon black, silica, etc.), silane coupling agents, sulfur, vulcanization accelerators, vulcanization accelerator aids (zinc oxide, stearic acid), oils, cured resins, waxes, and aging. Examples thereof include compounding agents that can be used in the rubber industry, such as inhibitors and colorants. Among these, sulfur, a vulcanization accelerator, and a vulcanization accelerator aid are preferable. Examples of the vulcanization accelerator include Nt-butyl-2-benzothiazolesulfenamide.

When the rubber composition contains sulfur, the lower limit of the content thereof is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and further preferably 1.7% by mass or more with respect to the rubber component. preferable. The upper limit is preferably 10% by mass or less, more preferably 7% by mass or less, still more preferably 5% by mass or less.

When the rubber composition contains a vulcanization accelerator, the lower limit of the content thereof is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and 0.4% by mass with respect to the rubber component. The above is more preferable. The upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less.

[2. Molding]
The molded product of the present invention is made by using the above-mentioned rubber composition. Since the compatibility between the rubber component in the rubber composition and the cellulosic fiber is improved, it has sufficient reinforcing properties.

The use of the molded product of the present invention is not particularly limited, and for example, transportation equipment such as automobiles, trains, ships, flights, and belt conveyors; electrical appliances such as personal computers, televisions, telephones, and watches; mobile communication equipment such as mobile phones. ; Portable music playback equipment, video playback equipment, printing equipment, copying equipment, sporting goods; building materials; office equipment such as stationery, containers, containers. Other than these, it can be applied to members using rubber or flexible plastic, and is preferably applied to industrial belts. Examples thereof include flat belts, conveyor belts, cogged belts, V-belts, rib belts and round belts.

[3. Production method]
The method for producing the molded product of the present invention is not particularly limited. For example, the following manufacturing method can be mentioned.

[3-1. Manufacturing method a]
As an example of the method for producing a molded product of the present invention, (a1) a step of mixing a rubber component with a cellulosic fiber, a methylene acceptor compound and a methylene donor compound to obtain a mixture (1) (rubber composition), (a2). Examples of the production method a include a step of heating the mixture (1) obtained in the step (a1) at 40 ° C. or higher and lower than 100 ° C. for 1 to 24 hours and molding the mixture to obtain a molded product.
The order of addition of each component in (a1) of the production method a is not particularly limited, and each component may be mixed at once, or one of the components may be mixed first and then the remaining components may be mixed. You may. Further, it is preferable that the heat treatment temperature of (a2) of the production method a is 40 ° C. or higher and lower than 100 ° C., and the treatment time is 1 to 24 hours. Within this range, damage to the rubber component can be suppressed.
As the production method a, more specifically, a mixture obtained by mixing a dispersion liquid of a cellulosic fiber and a dispersion liquid (latex) of a rubber component (eg, stirring with a mixer or the like) and removing water to obtain a mixture (usually a solid substance). ), Add a component containing a methylene acceptor compound and a methylene donor compound, and knead and knead (eg, an apparatus such as an open roll). According to this method, chemically modified cellulose nanofibers can be uniformly dispersed in the rubber component.

[3-2. Manufacturing method b]
As another example of the method for producing a molded product of the present invention, (b1) a step of mixing a rubber component and a cellulose-based fiber to obtain a mixture (2), and (b2) a step of mixing the mixture (2) obtained in the step (b1). A step of obtaining a heat-treated product (master batch) heated at 40 ° C. or higher and lower than 100 ° C. for 1 to 24 hours, a methylene acceptor compound and a methylene donor compound are mixed with the heat-treated product obtained in the step (b3) step (b2). Examples thereof include a manufacturing method b having a step of molding to obtain a molded product. Thereby, any component can be uniformly dispersed.
Further, it is preferable that the heat treatment temperature of (b2) is 40 ° C. or higher and lower than 100 ° C., and the treatment time is 1 to 24 hours. Within this range, damage to the rubber component can be suppressed. In the order of addition of the methylene acceptor compound and the methylene donor compound in (b3), each component may be mixed at once, or any component may be mixed first and then the remaining components may be mixed. ..

Examples of the kneading and kneading device include a Banbury mixer, a kneader, and an open roll.

[3-3. Other manufacturing methods]
As another production method, a method of adding other components to the rubber component in an arbitrary order and mixing them can be mentioned. More specifically, the solid substance of the rubber component is mixed with the solid substance of the cellulosic fiber, the methylene acceptor compound, and the methylene donor compound in an arbitrary order, and similarly kneaded and kneaded with an apparatus such as an open roll. .. This makes it possible to omit the step of removing water.

[mixture]
The temperature at the time of mixing (for example, at the time of kneading and kneading) may be about room temperature (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 for heating 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. It is preferable that the sulfur and the vulcanization accelerator are added later than the methylene acceptor compound and the methylene donor compound. That is, a rubber composition containing a methylene acceptor compound and a methylene donor compound is mixed without adding sulfur and a vulcanization accelerator, and after starting kneading, sulfur and a vulcanization accelerator are added to further knead and mix. It is preferable to 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.

After the mixing is completed, molding is performed as necessary. Examples of the molding apparatus include mold molding, injection molding, extrusion molding, hollow molding, and foam molding. It may be appropriately selected according to the shape, application and molding method of the final product.

It is preferable to heat (vulcanization, crosslinking) after the mixing is completed, preferably after molding. As a result, the methylene acceptor compound and the methylene donor compound 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, thereby effectively producing the molded product. Can be reinforced. The heating temperature is preferably 150 ° C. or higher. The upper limit is preferably 200 ° C. or lower, more preferably 180 ° C. or lower. Therefore, the heating temperature is preferably about 150 to 200 ° C, more preferably about 150 to 180 ° C. Examples of the heating device include vulcanization devices such as mold vulcanization, can vulcanization, and continuous vulcanization.

If necessary, a finishing process may be performed before making the final product. Examples of the finishing treatment include polishing, surface treatment, lip finishing, lip cutting, and chlorine treatment. Of these processes, only one may be performed, or two or more may be performed in combination.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.
Unless otherwise specified, the method for measuring the physical property value shall be the measurement method described above. Further, "part" means a mass part.

<Manufacturing example 1. Manufacture of Oxidized Cellulose Nanofibers>
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. Since the pH in the system decreased during the reaction, a 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 (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.

<Manufacturing example 2. Manufacture 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) in dry mass and 111 g of sodium hydroxide in dry mass (molar equivalent per anhydrous glucose residue of starting material). 2.25 times) was added, and water was added so that the pulp solid content became 20% (w / v). After stirring at 30 ° C. for 30 minutes, 216 g (active ingredient equivalent, 1.5 times per glucose residue of pulp in terms of molars) was added, and the mixture was stirred for 30 minutes. After raising the temperature to 70 ° C. and stirring for 1 hour, 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 adjusted to a solid content of 1% (w / v) with water and treated with a high-pressure homogenizer (20 ° C., 150 MPa) 5 times to obtain carboxymethylated cellulose nanofibers. The average fiber diameter was 15 nm and the aspect ratio was 50.

<Manufacturing example 3. Manufacture of cationized cellulose nanofibers>
To the pulp that can stir the pulp, 200 g of pulp (NBKP, manufactured by Nippon Paper Industries, Ltd.) by dry weight and 24 g of sodium hydroxide by dry weight are added, and the pulp solid concentration becomes 15% (w / v). So water was added. 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 concentration of 1% (w / v) and treated twice with a high-pressure homogenizer (20 ° C., 154 MPa) to obtain cationized cellulose nanofibers. 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>
500 g of water dispersion having a solid content of 1% of the solid content concentration of the cellulose oxide nanofibers obtained in Production Example 1, 200 g of chloroprene rubber latex (trade name: Shouplen, manufactured by Showa Denko Co., Ltd., solid content concentration of 50%), 25 g of a 10% aqueous solution of resorcin, 16 g of a 10% aqueous solution of hexamethylenetetramine was mixed so that the mass ratio of rubber component: modified cellulose nanofiber: methylene acceptor compound: methylene donor compound was 100: 5: 2.5: 1.6, and TK homo. The mixture was stirred with a mixer (6000 rpm) for 30 minutes. The aqueous suspension was dried in a heating oven at 70 ° C. for 10 hours to obtain a masterbatch.

152.7 g of this masterbatch was kneaded in an open roll (manufactured by Kansai Roll Co., Ltd.) at 60 ° C. for 5 minutes. Next, 0.7 g of stearic acid (0.5% by mass with respect to the rubber component), 8.4 g of zinc oxide (6% by mass with respect to the rubber component), and 4.9 g of sulfur (3.5% by mass with respect to the rubber component). , 1 g (0.7% by mass with respect to the rubber component) of a vulcanization accelerator (BBS, Nt-butyl-2-benzothiazolesulfenamide) was added, and an open roll (manufactured by Kansai Roll Co., Ltd.) was used at 60 ° C. Was kneaded for 10 minutes to obtain a sheet of unvulcanized rubber composition.

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 was cut into test pieces having a predetermined shape, and the tensile strength, which is one of the reinforcing properties, was measured according to JIS K6251 "Vulcanized rubber and thermoplastic rubber-How to determine tensile properties". The results are shown in FIG. 1 and Table 1. It should be noted that 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 procedure as in Example 1 was carried out except that the mass ratio of the methylene acceptor compound was 1.25 and the mass ratio of the methylene donor compound was 0.8 with respect to 100 parts of the rubber component. The results are shown in FIG. 1 and Table 1.

<Example 3>
500 g of an aqueous dispersion having a solid content of 1% of the cellulose oxide nanofibers obtained in Production Example 1 and 200 g of a chloroprene rubber latex (trade name: Shoprene, Showa Denko, Inc., solid content concentration of 50%) are mixed and modified with a rubber component. The mass ratio with the cellulose nanofibers was 100: 5, and the mixture was stirred with a TK homomixer (6000 rpm) for 30 minutes. The aqueous suspension was dried in a heating oven at 70 ° C. for 10 hours to obtain a masterbatch.

To 147 g of this masterbatch, 3.5 g of resorcin (2.5% by mass with respect to the rubber component) and 2.24 g of hexamethylenetetramine (64% by mass with respect to resorcin) were added to an open roll (manufactured by Kansai Roll Co., Ltd.). Then, the mixture was kneaded at 60 ° C. for 10 minutes. Next, 0.7 g of stearic acid (0.5% by mass with respect to the rubber component), 8.4 g of zinc oxide (6% by mass with respect to the rubber component), 4.9 g of sulfur (3.5% by mass with respect to the rubber component), Add 1 g (0.7% by mass with respect to the rubber component) of a vulcanization accelerator (BBS, Nt-butyl-2-benzothiazolesulfenamide) and use an open roll (manufactured by Kansai Roll Co., Ltd.) at 60 ° C. Kneading for 10 minutes gave a sheet of unvulcanized rubber composition.

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. The results are shown in FIG. 1 and Table 1.

<Comparative Example 1>
The procedure was the same as in Example 1 except that the cellulose oxide nanofibers, the methylene acceptor compound, and the methylene donor compound were not added. The results are shown in FIG. 1 and Table 1.

<Comparative Example 2>
The procedure was the same as in Example 1 except that the methylene acceptor compound and the methylene donor compound were not added. The results are shown in FIG. 1 and Table 1.

As can be seen from FIGS. 1 and 1, the rubber composition of the present invention was able to produce a molded product having a high modulus value when strained. In particular, when the rubber component, the cellulosic fiber, the methylene acceptor compound and the methylene donor compound were simultaneously heat-treated, the elongation at break was slightly reduced, but the balance between the modulus value and the breaking strength was excellent (Example 1 and). 2). Further, when the methylene acceptor compound and the methylene donor compound were mixed after the rubber component and the cellulosic fiber were heat-treated, the modulus value was high although the breaking strength was slightly lowered in addition to the breaking elongation (implementation). See Example 3). On the other hand, when the methylene acceptor compound and the methylene donor compound were not mixed, the elongation at break was slightly reduced, but the balance between the modulus value and the breaking strength was improved, but the effect could be improved (Comparative Example 2). reference).

Claims (9)

A rubber composition containing a rubber component, a cellulosic fiber, a methylene acceptor compound and a methylene donor compound .
The rubber component is chloroprene rubber,
The cellulosic fiber contains at least one selected from the group consisting of oxidized cellulose fiber, carboxymethylated cellulose fiber and cationized cellulose fiber.
The methylene acceptor compound is at least one selected from the group consisting of resorcin, resorcin derivatives and resorcin-based resins.
The methylene donor compound is hexamethylenetetramine.
Rubber composition. The rubber composition according to claim 1 , wherein the length-weighted average fiber length of the cellulosic fiber is 50 to 2000 nm, and the length-weighted average fiber diameter is 2 to 500 nm. A molded product using the rubber composition according to claim 1 or 2 . A method for producing a molded product of a rubber composition containing a rubber component, a cellulosic fiber, a methylene acceptor compound, and a methylene donor compound, which comprises the following steps (a1) and (a2).
(A1) A step of mixing a rubber component with a cellulosic fiber, a methylene acceptor compound and a methylene donor compound to obtain a mixture (1).
(A2) A step of heating the mixture (1) obtained in the step (a1) at 40 ° C. or higher and lower than 100 ° C. for 1 to 24 hours, and molding after the heating to obtain a molded product. The production method according to claim 4, wherein the rubber component is chloroprene rubber. The production method according to claim 4 or 5, 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 production method according to any one of claims 4 to 6, wherein the methylene acceptor compound is at least one selected from the group consisting of resorcin, a resorcin derivative, and a resorcin-based resin. The production method according to any one of claims 4 to 7, wherein the methylene donor compound is hexamethylenetetramine. A rubber composition containing a rubber component, a cellulosic fiber, a methylene acceptor compound and a methylene donor compound, wherein the cellulosic fiber is selected from the group consisting of an oxidized cellulose fiber, a carboxymethylated cellulose fiber and a cationized cellulose fiber. The methylene acceptor compound is at least one selected from the group consisting of resorcin, resorcin derivatives and resorcin-based resins, including at least one.
A method for producing a molded product of a rubber composition in which the methylene donor compound is hexamethylenetetramine, which comprises the following steps (b1) to (b3).
(B1) A step of mixing a rubber component and a cellulosic fiber to obtain a mixture (2).
(B2) A step of obtaining a heat-treated product obtained by heating the mixture (2) obtained in the above step (b1) at 70 ° C. or higher and lower than 100 ° C. for 1 to 24 hours.
(B3) A step of mixing a methylene acceptor compound and a methylene donor compound with the heat-treated product obtained in the step (b2) and molding to obtain a molded product.

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