JP6700741B2 - Rubber composition - Google Patents

Description

  The present invention relates to a rubber composition. Specifically, it relates to a rubber composition containing cellulose nanofibers.

  In recent years, a technique of improving various strengths in a rubber composition such as tensile strength by including a material called cellulose nanofiber, which is produced by finely loosening plant fibers to a nano level, in a rubber composition is known. ..

  For example, Patent Document 1 describes a masterbatch of rubber/short fibers obtained by stirring and mixing short fibers having an average diameter of less than 0.5 μm and rubber latex, and examples of the short fibers include cellulose. ing. According to this document, short fibers having an average fiber diameter of less than 0.5 μm are previously fibrillated in water to obtain a dispersion, which is mixed with rubber latex and dried to uniformly disperse the short fibers in the rubber. It is said that the rubber composition can be dispersed, and by using this rubber/short fiber masterbatch, it is possible to obtain a rubber composition having a good balance between rubber reinforcement and fatigue resistance.

  Patent Document 2 discloses a method for producing a rubber composition for a tire, which contains a rubber component, microfibrillated plant fibers such as cellulose microfibrils, a phenol resin, and a curing agent. According to this document, by using a microfibrillated plant fiber and a phenol resin in combination, the reinforcing effect of the phenol resin and the reinforcing effect of the microfibrillated plant fiber act synergistically to ensure sufficient reinforcing properties. It is said to be possible.

JP, 2006-206864, A Japanese Patent No. 5616369

  In the rubber composition of Patent Document 1, it is considered that the short fibers and the rubber component are bonded by an intermolecular force, but the intermolecular force is a relatively weak bond as compared with other bonds. Therefore, when a large strain is applied to the rubber composition of Patent Document 1, the bond may be broken, that is, a void may occur between the short fiber and the rubber component, and as a result, sufficient reinforcement cannot be obtained. There were cases.

  In the rubber composition of Patent Document 2, although a certain effect can be expected, the adhesion between the microfibrillated plant fiber and the rubber component cannot be said to be sufficient, and further improvement has been demanded.

  Therefore, an object of the present invention is to provide a rubber composition having a sufficient reinforcing property even when a large strain is applied.

  In order to solve the above problems, the present inventors have conducted extensive studies, and as a result, heat-treating a material containing a chemically modified cellulose nanofiber, a methylene acceptor compound, a methylene donor compound, and a rubber component, it is sufficient. It was found that a rubber composition having various reinforcing properties can be obtained.

That is, the present invention provides the following.
[1] A rubber composition containing a modified cellulose nanofiber and a rubber component.
[2] The rubber composition according to [1], wherein the modified cellulose nanofibers include at least one selected from the group consisting of oxidized cellulose nanofibers, carboxymethylated cellulose nanofibers and cationized cellulose nanofibers.
[3] The rubber composition according to [2], wherein the amount of carboxyl groups based on the absolute dry weight of the oxidized cellulose nanofibers is 0.5 mmol/g to 3.0 mmol/g.
[4] The rubber composition according to [2], wherein the carboxylated cellulose nanofibers have a degree of carboxymethyl substitution per anhydroglucose unit of 0.01 to 0.50.
[5] The rubber composition according to [2], wherein the cation substitution degree per glucose unit of the cationized cellulose nanofiber is 0.01 to 0.40.
[6] The rubber composition according to any one of [1] to [5], further including a methylene acceptor compound and a methylene donor compound.
[7] The rubber composition according to [6], wherein the methylene acceptor compound is at least one selected from the group consisting of resorcin, resorcin derivative and resorcin resin.
[8] The rubber composition as described in [5] or [6], wherein the methylene donor compound is hexamethylenetetramine.
[9] The method for producing a rubber composition according to [1] to [8], which comprises mixing a material containing a modified cellulose nanofiber and a rubber component.
[10] The production method according to [9], in which materials other than sulfur and a vulcanization accelerator are first mixed and heated, and then sulfur and a vulcanization accelerator are mixed and heated again.

  According to the present invention, it is possible to provide a rubber composition having sufficient reinforcing properties even when a large strain is applied.

  The reason why such effects are obtained in the rubber composition of the present invention is not clear, but it is presumed as follows. A three-dimensional structure is formed between the rubber component and the modified cellulose nanofiber, and the hydroxyl group in the structure forms a chemical bond (eg, covalent bond, hydrogen bond) with the functional group in the modified cellulose nanofiber, Is believed to have contributed to the improvement of adhesiveness.

  The rubber composition of the present invention contains at least a modified cellulose nanofiber and a rubber component.

<Modified cellulose nanofibers>
The modified cellulose nanofiber is a fine fiber obtained by modifying and defibrating a cellulose raw material. The average fiber diameter of the cellulose nanofibers is usually about 3 to 500 nm. The average fiber diameter and the average fiber length can be obtained by averaging the fiber diameters and fiber lengths obtained from the results of observing each fiber using a field emission scanning electron microscope (FE-SEM).

The average aspect ratio of the modified cellulose nanofibers is usually 50 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:
Aspect ratio = average fiber length / average fiber diameter

  The origin of the cellulose raw material, which is the raw material of the modified cellulose nanofibers, is not particularly limited, and examples thereof include plants (for example, wood, bamboo, hemp, jute, kenaf, agricultural land waste, cloth, pulp (softwood unbleached kraft pulp (NUKP ), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP) thermomechanical pulp (TMP) ), recycled pulp, waste paper, etc.), animals (for example, ascidians), algae, microorganisms (for example, acetic acid bacteria (acetobacter)), microbial products, etc. The cellulose raw material used in the present invention is any of these. It may be present or a combination of two or more kinds, but it is preferably a plant- or microorganism-derived cellulose raw material (for example, cellulose fiber), and more preferably a plant-derived cellulose raw material (for example, cellulose fiber). is there.

  The number average fiber diameter of the cellulose raw material is not particularly limited, but it is about 30 to 60 μm in the case of a general softwood kraft pulp, and about 10 to 30 μm in the case of a hardwood kraft pulp. In the case of other pulps, those having undergone general refining have a size of about 50 μm. For example, when a chip or the like having a size of several cm is purified, it is preferable to perform mechanical treatment with a disintegrator such as a refiner or beater to adjust the size to about 50 μm.

<Degeneration>
The modified cellulose nanofiber can exhibit sufficient reinforcement. The reason is that the modification of the cellulose raw material sufficiently promotes the miniaturization of the fibers, and a uniform fiber length and fiber diameter can be obtained. In addition, it is possible to secure a sufficient number of fibers having a fiber length and a fiber diameter effective for exerting the reinforcing property.

  The modification method for modifying the cellulose raw material is not particularly limited, and examples thereof include chemical modifications such as oxidation, etherification, phosphorylation, esterification, silane coupling, fluorination, and cationization. Of these, oxidation using an N-oxyl compound, carboxymethylation, and cationization are preferable.

<Oxidation>
When the cellulose raw material is modified by oxidation, the amount of carboxyl groups based on the absolute dry weight of the obtained oxidized cellulose or cellulose nanofibers is preferably 0.5 mmol/g or more, more preferably 0.8 mmol/g or more, and further preferably It is 1.0 mmol/g or more. The upper limit 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, 0.5 mmol/g to 3.0 mmol/g is preferable, 0.8 mmol/g to 2.5 mmol/g is more preferable, and 1.0 mmol/g to 2.0 mmol/g is further preferable.

  The method of oxidation is not particularly limited, but as one example, cellulose 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 or a mixture thereof. Examples include a method of oxidizing the raw material. 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 during the reaction is not particularly limited, but is preferably 5% by weight or less.

  The N-oxyl compound means 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 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 absolutely dried cellulose. 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, per 1 g of absolutely dry cellulose.

  The bromide is a compound containing bromine, and examples thereof include alkali metal bromide capable of dissociating and ionizing in water, such as sodium bromide. Further, iodide is a compound containing iodine, and examples thereof include alkali metal iodide. The amount of bromide or iodide used may be selected within a range that can accelerate the oxidation reaction. 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 absolutely dried cellulose. The upper limit 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, per 1 g of absolutely dried cellulose.

  The oxidizing agent is not particularly limited, but examples thereof include halogen, hypohalous acid, halogenous acid, perhalogenic acid, salts thereof, halogen oxides, and peroxides. Among them, hypohalous 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 low environmental load. The amount of the oxidizing agent used is preferably 0.5 mmol or more, more preferably 1 mmol or more, and further preferably 3 mmol or more, with respect to 1 g of absolutely dried cellulose. The upper limit is preferably 500 mmol or less, more preferably 50 mmol or less, and further 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 most preferably 3 to 10 mmol per 1 g of absolutely dry cellulose. When using the N-oxyl compound, the amount of the oxidizing agent used is preferably 1 mol or more per 1 mol of the N-oxyl compound. The upper limit is preferably 40 mol. Therefore, the amount of the oxidizing agent used is preferably 1 to 40 mol per 1 mol of the N-oxyl compound.

  Conditions such as pH and temperature during the oxidation reaction are not particularly limited, and generally, 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 is preferably 40°C or lower, more preferably 30°C or lower. Therefore, the 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 higher, more preferably 10 or higher. The upper limit is preferably 12 or less, more preferably 11 or less. Therefore, the pH of the reaction solution is preferably 8 to 12, more preferably 10 to 11. Usually, a carboxyl group is generated in cellulose as the oxidation reaction progresses, so that the pH of the reaction solution tends to decrease. Therefore, in order to allow the oxidation reaction to proceed efficiently, it is preferable to maintain the pH of the reaction solution within the above range by adding an alkaline solution such as an aqueous solution of sodium hydroxide. Water is preferable as the reaction medium during the 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. The upper limit is usually 6 hours or less, preferably 4 hours or less. Therefore, the reaction time in oxidation is usually 0.5 to 6 hours, for example, 0.5 to 4 hours.

  The 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-step reaction again under the same or different reaction conditions, the reaction efficiency of the first-step reaction is not affected by the salt produced as a by-product. Can be well oxidized.

Another example of the carboxylation (oxidation) method is a method of oxidizing by ozone treatment. This oxidation reaction oxidizes at least the 2-position and 6-position hydroxyl groups of the glucopyranose ring constituting the cellulose and causes the decomposition of the cellulose chain. Ozone treatment is usually performed 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 50~220g / m ^3. The amount of ozone added is preferably 0.1 part by weight or more, and more preferably 5% by weight or more, based on 100% by weight of the solid content of the cellulose raw material. The upper limit is usually 30% by weight or less. Therefore, the amount of ozone added is preferably 0.1 to 30% by weight, and 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. 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 longer, preferably 30 minutes or longer. 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 conditions of the ozone treatment 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 resulting product obtained after the ozone treatment may be subjected to an additional oxidization treatment using an oxidant. The oxidizing agent used in the additional oxidation treatment is not particularly limited, but examples thereof include chlorine-based compounds such as chlorine dioxide and sodium chlorite; oxygen, hydrogen peroxide, persulfuric acid, peracetic acid and the like. Examples of the method of additional oxidation treatment include a method in which these oxidizing agents are dissolved in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and the cellulose raw material is dipped in the oxidizing agent solution.

  The amounts of the carboxyl group, carboxylate group and aldehyde group contained in the oxidized cellulose nanofibers can be adjusted by controlling the oxidizing conditions such as the addition amount of the oxidizing agent and the reaction time.

An example of the method for measuring the amount of carboxyl groups will be described below. After preparing 60 ml of 0.5 wt% slurry (aqueous dispersion) of oxidized cellulose and adding 0.1 M hydrochloric acid aqueous solution to pH 2.5, 0.05 N sodium hydroxide aqueous solution was added dropwise to adjust the pH to 11. Measure electrical conductivity until It can be calculated from the amount of sodium hydroxide (a) consumed in the neutralization step of a weak acid with a gradual change in electrical conductivity using the following formula:
Amount of carboxyl group [mmol/g oxidized cellulose or cellulose nanofiber]=a [ml]×0.05/weight of oxidized cellulose [g]

<Carboxymethylation>
When the cellulose raw material is modified by carboxylation, the degree of carboxymethyl substitution per anhydroglucose unit in the obtained carboxylated cellulose or cellulose nanofibers is preferably 0.01 or more, more preferably 0.05 or more, and 0.10 or more. It is more preferable that the above is satisfied. The upper limit is preferably 0.50 or less, more preferably 0.40 or less, still more preferably 0.35 or less. Therefore, the carboxymethyl group substitution degree is preferably 0.01 to 0.50, more preferably 0.05 to 0.40, and further preferably 0.10 to 0.30.

  The method of carboxylation is not particularly limited, and examples thereof include a method of mercerizing a cellulose raw material as a bottoming raw material and then etherifying it. A common solvent is used in the carboxylation 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-butanol, isobutanol, and tertiary butanol. The mixing ratio of the lower alcohol in the mixed solvent is usually 60% by weight or more or 95% by weight or less, and preferably 60 to 95% by weight. The amount of the solvent is usually 3 times the weight of the cellulose raw material. The upper limit is not particularly limited, but is 20 times by weight. Therefore, the amount of the solvent is preferably 3 to 20 times by weight.

  The mercerization is usually carried out by mixing the bottoming raw material and the mercerizing agent. Examples of the mercerizing agent include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. The amount of the mercerization agent used is preferably 0.5 times or more, more preferably 1.0 times or more, and even more preferably 1.5 times or more, per anhydroglucose residue of the bottoming raw material. The upper limit is usually 20 times mol or less, preferably 10 times mol or less, more preferably 5 times mol or less, therefore, 0.5 to 20 times mol is preferable, 1.0 to 10 times mol is more preferable, and 1 It is more preferably 0.5 to 5 times mol.

  The reaction temperature for mercerization is usually 0° C. or higher, preferably 10° C. or higher. 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 is usually 8 hours or less, preferably 7 hours or less. Therefore, it is usually 15 minutes to 8 hours, preferably 30 minutes to 7 hours.

  The etherification reaction is usually performed 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, and even more preferably 0.8 times or more, per glucose residue of the cellulose raw material. The upper limit is usually 10.0 times or less, preferably 5 times or less, more preferably 3 times or less, and therefore preferably 0.05 to 10.0 times, more preferably 0.5 to 10. 5 and 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 longer, preferably 1 hour or longer. The upper limit 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. The reaction solution may be stirred during the carboxylation reaction, if desired.

The carboxymethyl substitution degree per glucose unit of the carboxylated cellulose nanofiber may be measured, for example, by the following method. That is, 1) About 2.0 g of carboxymethylated cellulose (absolutely dry) is precisely weighed and placed in a 300 mL Erlenmeyer flask with a stopper. 2) Add 1000 mL of methanol to 100 mL of special-grade concentrated nitric acid and shake for 3 hours to convert carboxymethyl cellulose salt (CM cellulose) into hydrogen CM cellulose. 3) 1.5 to 2.0 g of hydrogenated CM cellulose (absolutely dried) is precisely weighed and placed in a 300 mL Erlenmeyer flask with a ground stopper. 4) Wet hydrogenated CM cellulose with 15% of 80% methanol, add 100 mL of 0.1N NaOH, and shake at room temperature for 3 hours. 5) Back titration of excess NaOH with 0.1 N H ₂ SO ₄ using phenolphthalein as an indicator. 6) Calculate the degree of carboxymethyl substitution (DS) by the following formula:

A=[(100×F′−(0.1N H ₂ SO ₄ )(mL)×F)×0.1]/(absolute dry mass (g) of hydrogenated CM cellulose)
DS=0.162×A/(1-0.058×A)
A: 1N NaOH amount (mL) required to neutralize 1 g of hydrogenated CM-modified cellulose
F : 0.1 N H ₂ SO ₄ factor
F' : Factor of 0.1N NaOH

<Cationization>
When the cellulose raw material is modified by cationization, the cationized cellulose nanofibers obtained may contain a cation such as ammonium, phosphonium, or sulfonium, or a group having the cation in the molecule. The cationized cellulose nanofiber preferably contains a group having ammonium, and 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 and/or alcohol. Examples of the cationizing agent include glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium hydride (eg, 3-chloro-2-hydroxypropyltrimethylammonium hydride), and halohydrin-type compounds thereof. By using any of these, cationized cellulose having a group containing a quaternary ammonium can be obtained. Examples of the catalyst include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. Examples of alcohols include alcohols having 1 to 4 carbon atoms. The amount of the cationizing agent is preferably 5% by weight or more, and more preferably 10% by weight or more based on 100% by weight of the cellulose raw material. The upper limit 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, and more preferably 1% by weight or more based on 100% by weight of the cellulose fiber. The upper limit is usually 7% by weight or less, preferably 3% by weight or less. The amount of alcohol is preferably 50% by weight or more, and more preferably 100% by weight or more, based on 100% by weight of the cellulose fiber. The upper limit is usually 50,000% by weight or less, preferably 500% by weight or less.

  The reaction temperature at the time of 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 longer, preferably 30 minutes or longer. The upper limit is usually 10 hours or less, preferably 5 hours or less. The reaction solution may be stirred during the cationization reaction, if necessary.

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

  The cation substitution degree per glucose unit of the cationized cellulose nanofibers is preferably 0.01 or more, more preferably 0.02 or more, still more preferably 0.03 or more. The upper limit is preferably 0.40 or less, more preferably 0.30 or less, and further preferably 0.20 or less. Therefore, it is preferably 0.01 to 0.40, more preferably 0.02 to 0.30, and further preferably 0.03 to 0.20. By introducing a cationic substituent into cellulose, the cellulose electrically repels each other. Therefore, the cellulose having the cation substituent introduced therein can be easily nano-disentangled. When the degree of cation substitution per glucose unit is 0.01 or more, sufficient nano-defibration can be 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 a situation where nanofibers cannot be obtained is prevented. be able to.

An example of a method for measuring the degree of cation substitution per glucose unit will be described below. After drying the sample (cationized cellulose), the nitrogen content is measured with a total nitrogen analyzer TN-10 (Mitsubishi Chemical), and the degree of cationization is calculated by the following formula. The cation substitution degree here is an average value of the number of moles of the substituent per mole of anhydrous glucose unit.
Degree of cation substitution=(162×N)/(1-151.6×N)
N: Nitrogen content

<Dispersion>
When the cellulose raw material is subjected to the modification treatment or the defibration treatment, the cellulose raw material may be dispersed to prepare a dispersion of the cellulose raw material. The solvent for dispersing the cellulose raw material is preferably water because the cellulose raw material is hydrophilic.

<defibration>
The defibration may be performed before or after the modification treatment of the cellulose raw material. Moreover, the defibration may be performed once or a plurality of times. In the case of multiple times, each defibration time may be any time.

  The apparatus used for defibration is not particularly limited, but examples thereof include high-speed rotation type, colloid mill type, high pressure type, roll mill type, ultrasonic type, and other types of devices, and high pressure or ultra high pressure homogenizers are preferable, and wet high pressure is used. Alternatively, an ultrahigh pressure homogenizer is more preferable. The device is preferably capable of applying 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 ultrahigh-pressure homogenizer capable of applying the above-mentioned pressure to the cellulose raw material or modified cellulose (usually a dispersion) and applying a strong shearing force. Thereby, defibration can be efficiently performed.

  When defibrating the dispersion of the 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% by weight or more. It is more than weight %. As a result, the liquid amount relative to the amount of the cellulose fiber raw material becomes appropriate and efficient. The upper limit is usually 10% by weight or less, preferably 6% by weight or less. This makes it possible to maintain fluidity.

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

<morphology of modified cellulose nanofibers>
The form of the modified cellulose nanofibers combined with the rubber component is not particularly limited, and examples thereof include a modified cellulose nanofiber dispersion, a dry solid of the dispersion, a wet solid of the dispersion, a cellulose nanofiber and an aqueous solution. Examples of the mixture include a liquid mixture with a water-soluble polymer, a dry solid product of the liquid mixture, and a wet solid product of the liquid mixture. Wet solids are solids that are intermediate between the dispersion and the dry solids. Examples of the water-soluble polymer include cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, ethyl cellulose), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginate, pullulan, starch, starch starch, and kudzu. Powder, positive starch, phosphorylated starch, corn starch, gum arabic, locust bean gum, gellan gum, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, chitosan, casein, albumin, soy protein melt, peptone, polyvinyl alcohol, poly Acrylamide, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyamino acid, polylactic acid, polymalic 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 gum, polyethylene oxide, hydrophilic cross-linked polymer, polyacrylate, starch polyacrylic acid copolymer, tamarind gum, gellan gum, pectin, guar gum and colloidal silica and one of them The above mixture may be mentioned. Among these, it is preferable to use carboxymethyl cellulose and salts thereof from the viewpoint of compatibility.

<Dry>
The dry solid matter and the wet solid matter of the modified cellulose nanofibers may be prepared by drying the dispersion liquid of the modified cellulose nanofibers or the mixed solution of the modified cellulose nanofibers and the water-soluble polymer. The drying method is not particularly limited, and examples thereof include spray drying, pressing, air drying, hot air drying, and vacuum drying. As the drying device, for example, a continuous tunnel drying device, a band drying device, a vertical drying device, a vertical turbo drying device, a multi-stage disc drying device, an aeration drying device, a rotary drying device, an air flow drying device, a spray dryer drying device. , Spray dryers, cylinder dryers, drum dryers, screw conveyor dryers, rotary dryers with heating tubes, vibration transport dryers, batch-type box dryers, aeration dryers, vacuum box dryers, and A stirring and drying device and the like can be mentioned. These drying devices may be used alone or in combination of two or more. The dryer is preferably a drum dryer. As a result, heat energy can be directly directly supplied to the material to be dried, so that energy efficiency can be improved. Further, the dried product can be immediately recovered without applying more heat than necessary.

<Rubber component>
The rubber component is usually a component having an organic polymer as a main component and having a high elastic limit and a low elastic modulus. The rubber component is roughly classified into natural rubber and synthetic rubber, and any of them may be used in the present invention, or a combination of both may be used. The natural rubber may be a natural rubber in a narrow sense that is not chemically modified, or may be a chemically modified natural rubber such as chlorinated natural rubber, chlorosulfonated natural rubber, or epoxidized natural rubber. Examples of the synthetic rubber include butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), isoprene rubber (IR), butyl rubber (IIR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber, styrene-isoprene copolymer Diene rubbers such as polymer 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), and chlorosulfonated polyethylene (CSM). Examples of the natural rubber include hydrogenated natural rubber and deproteinized natural rubber. The rubber component may be a single type or a combination of two or more types. The rubber component may be solid or liquid. Examples of the liquid rubber component include a rubber component dispersion liquid and a rubber component solution. Examples of the solvent include water and organic solvents.

<Methylene acceptor compound and methylene donor compound>
The rubber composition of the present invention may contain 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 being mixed with a methylene donor compound and heated. Examples of the methylene acceptor compound include phenol compounds such as phenol, resorcinol, resorcin, and cresol and derivatives thereof, resorcin-based resins, cresol-based resins, and phenol resins. Examples of the phenol resin include condensates of the above phenol compounds and their derivatives with aldehyde compounds such as formaldehyde and acetaldehyde. Phenolic resins can be classified into novolac resins (acidic catalysts) and resole resins (alkaline catalysts) depending on the catalyst used for condensation, but either 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 usually a compound capable of donating a methylene group and capable of undergoing a curing reaction when mixed with a methylene acceptor compound and heated. Examples of the methylene acceptor compound include hexamethylenetetramine and melamine derivatives. Examples of the melamine derivative include hexamethylolmelamine, hexamethoxymethylmelamine, pentamethoxymethylmelamine, pentamethoxymethylolmelamine, hexaethoxymethylmelamine, and hexakis-(methoxymethyl)melamine.

  Examples of the combination of the methylene acceptor compound and the methylene donor compound include cresol, a cresol derivative or a cresol resin and pentamethoxymethylmelamine, resorcin, a resorcin derivative or a resorcin resin and hexamethylenetetramine, and cashew-modified phenol. Examples include a combination of a resin and hexamethylenetetramine, and a combination of a phenol resin and hexamethylenetetramine. Among them, a combination of cresol, a cresol derivative or a cresol resin and pentamethoxymethylmelamine, and a combination of resorcin, a resorcin derivative or resorcin resin and hexamethylenetetramine are preferable.

<Content>
The content of the modified cellulose nanofibers in the rubber composition is preferably 1% by weight or more, more preferably 2% by weight or more, still more preferably 3% by weight or more, based on 100% by weight of the rubber component. Thereby, the effect of improving the tensile strength can be sufficiently exhibited. The upper limit is preferably 50% by weight or less, preferably 40% by weight or less, and further preferably 30% by weight or less. Thereby, the workability in the manufacturing process can be maintained. Therefore, it is preferably 1 to 50% by weight.

When the rubber composition contains a methylene acceptor compound, its content is preferably 1% by weight or more, more preferably 1.3% by weight or more, still more preferably 1.5% by weight or more, based on 100% by weight of the rubber component. .. Thereby, the effect of improving the tensile strength can be sufficiently exhibited. The upper limit is preferably 50% by weight or less , more preferably 20% by weight or less, still more preferably 10% by weight or less . Thereby, the workability in the manufacturing process can be maintained. Therefore, 1 to 50% by weight is preferable, 1.3 to 20 % by weight is more preferable, and 1.5 to 10 % by weight is further preferable.

  When the rubber composition contains a methylene donor compound, its content is preferably 10% by weight, more preferably 20% by weight or more, still more preferably 25% by weight or more, based on 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 more preferably 85% by weight or less. Thereby, the workability in the manufacturing process can be maintained. 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 rubber composition of the present invention may contain one or more optional components as required. Examples of optional components include reinforcing agents (carbon black, silica, etc.), silane coupling agents, sulfur, zinc oxide, stearic acid, vulcanization accelerators, vulcanization accelerator aids, oils, cured resins, waxes, antioxidants. Compounding agents that can be used in the rubber industry, such as colorants. Of these, sulfur and vulcanization accelerators are preferable. Examples of the vulcanization accelerator include Nt-butyl-2-benzothiazole sulfenamide.

  When the rubber composition contains sulfur, the content thereof 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, based on the rubber component. The upper limit is preferably 10% by weight or less, more preferably 7% by weight or less, and further preferably 5% by weight or less.

  When the rubber composition contains a vulcanization accelerator, its content is preferably 0.1% by weight, more preferably 0.3% by weight or more, still more preferably 0.4% by weight or more, based on the rubber component. The upper limit is preferably 5% by weight or less, more preferably 3% by weight or less, and further preferably 2% by weight or less.

<Manufacturing method>
The rubber composition can be produced by mixing the modified cellulose nanofiber, the rubber component, and each component contained as necessary.

  The order of adding the materials in the mixing is not particularly limited, and the respective components may be mixed at once, or any of the materials may be mixed first and then the remaining materials may be mixed. As a first example, there is a method in which the modified cellulose nanofibers and the rubber component are first mixed, and then the other material (for example, a methylene acceptor compound and a methylene donor compound) is mixed in the obtained masterbatch. Specifically, for example, a modified cellulose nanofiber dispersion and a rubber component dispersion (latex) are mixed (eg, stirring with a mixer), water is removed, and the resulting masterbatch (usually a solid) is added. On the other hand, a component containing a methylene acceptor compound and a methylene donor compound is added and the mixture is kneaded and kneaded (eg, an apparatus such as an open roll). Thereby, the chemically modified cellulose nanofibers can be uniformly dispersed in the rubber component.

  A second example is a method of mixing modified cellulose nanofibers, a rubber component, a methylene acceptor compound, and a methylene donor compound at once to remove water. Specifically, for example, a modified cellulose nanofiber dispersion, a rubber component dispersion (latex), a methylene acceptor compound, and a methylene donor compound are mixed (eg, stirring with a mixer or the like), and water is obtained from the resulting mixture. Remove. This makes it possible to uniformly disperse any component.

  The method for removing water from the masterbatch or the mixture is not particularly limited, and examples thereof include a method of drying with a dryer such as an oven and a method of adjusting pH to 2 to 6 to solidify and dehydrating and drying.

  A third example is a method in which other components are added to the rubber component in an arbitrary order and mixed. Specifically, for example, a modified cellulose nanofiber rubber component solid matter, a modified cellulose nanofiber solid matter, a methylene acceptor compound, a methylene donor compound are mixed in any order, and similarly in an apparatus such as an open roll. Masticate and knead. Thereby, the step of removing water can be omitted.

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

  The temperature at the time of mixing (for example, at the time of mastication and kneading) may be about room temperature (about 15 to 30° C.), or 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, and more preferably 120° C. or lower. The lower limit is 70°C or higher, preferably 80°C or higher. Therefore, the heating temperature is preferably about 80 to 140°C, more preferably about 80 to 120°C. The sulfur and the vulcanization accelerator are preferably added after the methylene acceptor compound and the methylene donor compound. That is, after mixing a material containing a methylene acceptor compound and a methylene donor compound without adding sulfur and a vulcanization accelerator and starting mastication, sulfur and a vulcanization accelerator are added to further masticate and knead the mixture. It is preferable to carry out. Thereby, the methylene acceptor compound and the methylene donor compound are preliminarily condensed by heating, and the interaction between the condensate and the rubber component and the chemically modified cellulose nanofibers can be effectively exhibited.

  After completion of the mixing, molding may be performed if necessary. Examples of the molding apparatus include mold molding, injection molding, extrusion molding, blow molding, foam molding, and the like, and may be appropriately selected depending on the shape, application, and molding method of the final product.

  It is preferable to heat (vulcanize, crosslink) after completion of mixing, 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 cellulose nanofibers, respectively, to effectively improve the rubber composition. Can be reinforced. The heating temperature is preferably 150° C. or higher, and the upper limit is preferably 200° C. or lower, 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.

  If necessary, finishing treatment may be performed before the final product. Examples of the finishing treatment include polishing, surface treatment, lip finishing, lip cutting, chlorine treatment, and the like. Only one of these treatments may be performed, or a combination of two or more may be performed.

  The use of the rubber composition of the present invention is not particularly limited, and examples thereof include transportation equipment such as automobiles, trains, ships, and planes; electric appliances such as personal computers, televisions, telephones, and watches; mobile communication equipment such as mobile phones. Etc.; portable music reproduction equipment, video reproduction equipment, printing equipment, copying equipment, sports equipment, etc.; building materials; office equipment such as stationery, containers, containers, etc. Other than these, it can be applied to a member using rubber or flexible plastic, and is preferably applied to a tire. Examples of tires include pneumatic tires for passenger cars, trucks, buses, heavy vehicles, and the like.

  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 Nanofibers 5.00 g of bleached unbeaten kraft pulp (whiteness 85%) derived from coniferous trees (exterior dryness) was added to 39 mg of TEMPO (Sigma Aldrich) 0 .05 mmol) and sodium bromide 514 mg (1.0 mmol for 1 g of absolutely dried cellulose) were added to 500 ml of an aqueous solution, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that sodium hypochlorite was 5.5 mmol/g, and the oxidation reaction was started at room temperature. Although the pH in the system was lowered during the reaction, 3M sodium hydroxide aqueous 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 stopped changing. The mixture after the reaction was filtered with a glass filter to separate the pulp, and the pulp was sufficiently 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 with an ultrahigh pressure homogenizer (20° C., 150 Mpa) three times 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 carboxymethyl cellulose nanofibers A pulp (NBKP (softwood bleached kraft pulp), manufactured by Nippon Paper Industries, Ltd.) having a dry mass of 200 g and sodium hydroxide having a dry mass in a stirrer with which pulp can be mixed. 111 g (2.25 moles per anhydrous glucose residue of the bottoming raw material) was added, and water was added so that the pulp solid content was 20% (w/v). Then, after stirring for 30 minutes at 30° C., 216 g of sodium monochloroacetate (in terms of active ingredient, 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 carboxymethylated pulp having a carboxymethyl substitution degree of 0.25 per glucose unit. This was made to have a solid content of 1% with water, and fibrillated by treatment with a high-pressure homogenizer at 20° C. and a pressure of 150 MPa five times to obtain carboxymethyl cellulose nanofibers. The average fiber diameter was 15 nm and the aspect ratio was 50.

<Production Example 3> Production of cationized cellulose nanofibers To a pulper capable of stirring pulp, 200 g of pulp (NBKP, manufactured by Nippon Paper Industries Co., Ltd.) in dry weight and 24 g of sodium hydroxide in dry weight were added to produce pulp. Water was added so that the solid concentration was 15%. Then, the mixture was stirred at 30° C. for 30 minutes and then heated to 70° C., and 200 g of 3-chloro-2-hydroxypropyltrimethylammonium chloride (as an active ingredient) was added as a cationizing agent. After reacting for 1 hour, the reaction product was taken out, neutralized and washed to obtain a cation-modified pulp having a cation substitution degree of 0.05 per glucose unit. This was made to have a solid concentration of 1% and was treated twice with a high pressure homogenizer at 20° C. and a pressure of 140 MPa. The average fiber diameter was 25 nm and the aspect ratio was 50.

  The amount of carboxyl groups, the degree of carboxymethyl substitution, and the degree of cation substitution in the above Production Examples were measured by the methods described above.

<Example 1>
325 g of a 1% solid concentration aqueous dispersion of the oxidized cellulose nanofibers obtained in Production Example 1 and 100 g of natural rubber latex (trade name: HA latex, Redex Co., solid content concentration 65%) are mixed to form a rubber component. The weight ratio to the modified cellulose nanofiber was 100:5, and the mixture was stirred for 60 minutes with a TK homomixer (8000 rpm). This aqueous suspension was dried in a heating oven at 70° C. for 10 hours to obtain a masterbatch.

  To this master batch, 1.63 g of resorcinol (2.5% by weight with respect to the rubber component) and 1.04 g of hexamethylenetetramine (63.8% by weight with respect to resorcinol) were added, and an open roll (manufactured by Kansai Roll Co., Ltd.) was added. ) Was kneaded at 30° C. for 10 minutes. Next, 2.3 g of sulfur (3.5% by weight based on the rubber component), 0.5 g of vulcanization accelerator (BBS, Nt-butyl-2-benzothiazole sulfenamide) (0.1% based on the rubber component). 5% by weight) and 3.9 g of zinc oxide (6% by weight with respect to the rubber component), and kneaded at 30° C. for 10 minutes using an open roll (manufactured by Kansai Roll Co., Ltd.) to obtain an unvulcanized rubber composition. Got a sheet of.

  The sheet was sandwiched between molds and press-vulcanized at 150° C. for 10 minutes to obtain a vulcanized rubber composition sheet having a thickness of 2 mm. This was cut into a test piece of a predetermined shape, and in accordance with JIS K6251 "vulcanized rubber and thermoplastic rubber-Determination of tensile properties", showing tensile strength which is one of the reinforcing properties, at 100% strain, And the stress at 300% strain was measured. The larger each value is, the better the vulcanized rubber composition is reinforced, and the more excellent the mechanical strength of the rubber is.

  In addition, a test piece different from the above is prepared, and in order to evaluate the wear resistance which is another index of the reinforcing property, in accordance with JIS K6264 "Vulcanized rubber and thermoplastic rubber-Determination of wear resistance-". The abrasion volume was measured using a Taber abrasion tester. The smaller the abrasion volume, the better the vulcanized rubber composition is reinforced.

<Example 2>
The procedure of Example 1 was repeated, except that the oxidized cellulose nanofibers in Example 1 were changed to the carboxymethylated cellulose nanofibers obtained in Production Example 2.

<Example 3>
Example 1 was carried out in the same manner as in Example 1, except that the cationized cellulose nanofiber obtained in Production Example 3 was used instead of the oxidized cellulose nanofiber.

<Comparative Example 1>
Example 1 was repeated except that cellulose fiber was not used and resorcin and hexamethylenetetramine were not added.

<Comparative example 2>
In Example 1, it carried out like Example 1 except not using the cellulose nanofiber.

<Comparative example 3>
Unmodified cellulose nanofibers (average fiber diameter: 30 nm, aspect ratio: 50) obtained by grinding the oxidized cellulose nanofibers in Example 1 with a powder mill (KC Rock W-400, manufactured by Nippon Paper Industries) that is not chemically modified by a disk mill. Except that resorcin and hexamethylenetetramine were not added, the same procedure as in Example 1 was carried out.

<Comparative example 4>
Unmodified cellulose nanofibers (average fiber diameter: 30 nm, aspect ratio: 50) obtained by pulverizing the oxidized cellulose nanofibers in Example 1 into powder cellulose (KC Flock W-400, manufactured by Nippon Paper Industries) that is not chemically modified by a disk mill. The same procedure as in Example 1 was performed, except that

<Comparative Example 5>
The same procedure as in Example 1 was performed except that resorcin and hexamethylenetetramine were not added.

<Comparative example 6>
Example 1 was repeated, except that the oxidized cellulose nanofibers were changed to the carboxymethylated cellulose nanofibers obtained in Production Example 2 and that resorcin and hexamethylenetetramine were not added. .

<Comparative Example 7>
Example 1 was repeated except that the oxidized cellulose nanofibers were changed to the cationized cellulose nanofibers obtained in Production Example 3 and that resorcin and hexamethylenetetramine were not added.

  As is clear from Table 1, in the rubber compositions of Examples 1 to 3 obtained by heat-treating a material containing a modified cellulose nanofiber, a methylene acceptor compound, a methylene donor compound, and a rubber component, the modified cellulose nanofiber is used. For any of Comparative Examples 1 and 2 containing no fibers, Comparative Examples 3 and 4 containing unmodified cellulose nanofibers, and Comparative Examples 5 to 7 containing modified cellulose nanofibers but no methylene acceptor compound and methylene donor compound. However, the stresses at 100% and 300% strains are both high, the wear volume is small, and both are compatible at these high levels, so the rubber composition is well reinforced, and the mechanical strength of the rubber is high. It turns out to be excellent.

Claims (7)

Modified cellulose nanofibers containing at least one member selected from the group consisting of oxidized cellulose nanofibers, carboxymethylated cellulose nanofibers and cationized cellulose nanofibers , rubber component , resorcin or resorcin derivative, methylene acceptor compound, and methylene donor the compound only contains,
A rubber composition, wherein the content of the methylene donor compound is 10 to 90% by weight based on the content of the methylene acceptor compound of 100% by weight . The rubber composition according to claim 1 , wherein the amount of carboxyl groups based on the absolute dry weight of the oxidized cellulose nanofibers is 0.5 mmol/g to 3.0 mmol/g. Carboxymethyl degree of substitution per glucose unit of carboxy methylation cellulose nanofibers is 0.01 to 0.50, the rubber composition according to claim 1 or 2. The rubber composition according to claim 1, wherein the cationized cellulose nanofibers have a degree of cation substitution per glucose unit of 0.01 to 0.40. Methylene donor compound is hexamethylene tetramine, rubber composition according to any one of claims 1 to 4. Modified cellulose nanofibers, a rubber component, a methylene acceptor compound is a resorcinol or resorcinol derivatives, and saw including mixing a material containing a methylene donor compound,
The amount of the methylene donor compound used is 10 to 90% by weight based on 100% by weight of the methylene acceptor compound.
The method for producing a rubber composition according to any one of claims 1-5. The manufacturing method according to claim 6 , wherein the materials other than sulfur and the vulcanization accelerator are first mixed and heated, and then the sulfur and the vulcanization accelerator are mixed and heated again.