Intermediate and method for producing intermediate

Abstract

An intermediate according to one embodiment of the present invention comprises: a rubber component; a cellulose nanofiber containing a carboxyl group; and a cation having a valence of 3 or more. The cellulose nanofibers include nanofibers derived from oxidized cellulose oxidized using an N-oxy compound. In addition, an intermediate according to one embodiment of the present invention comprises: a rubber component; a cellulose nanofiber containing a carboxyl group; and a polymer having a repeating unit derived from an unsaturated carboxylic acid salt containing a monovalent metal ion and / or an unsaturated carboxylic acid salt containing a monovalent metal ion, the cellulose nanofibers including nanofibers derived from oxidized cellulose oxidized using an N-oxy compound.

Description

Technical Field

[0001] The present invention relates to an intermediate containing cellulose nanofiber (Cellulose Nanofiber; CNF) and a method for producing the intermediate. Background Art

[0002] In recent years, plant-derived cellulose nanofibers with low environmental impact have attracted attention in SDGs (Sustainable Development Goals). Among them, a rubber composite material using cellulose nanofibers as a fiber reinforcement has been proposed (Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2017-95611 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] However, cellulose nanofibers are generally provided to the market as aqueous dispersions, and therefore, must be mixed with a dispersion (latex) of a rubber component and then dried to obtain a solid rubber composite material. Furthermore, during the drying process, the cellulose nanofibers will bind to each other and agglomerate, and therefore, many agglomerates are likely to remain in the rubber composite material. It is known that these agglomerates will affect the basic physical properties of rubber products such as tensile strength and elongation at break.

[0008] Therefore, an object of the present invention is to provide an intermediate containing cellulose nanofibers, which reduces the agglomeration of cellulose nanofibers and is easily applicable to rubber products, and a method for producing the intermediate.

[0009] Solutions for solving problems

[0010] The present invention has been made to solve at least a part of the above-mentioned problems, and can be implemented as the following aspects or application examples.

[0011] [1] One embodiment of the intermediate of the present invention is characterized in that it comprises:

[0012] Rubber ingredients;

[0013] cellulose nanofibers containing carboxyl groups; and

[0014] Cations with a valence of 3 or more,

[0015] The cellulose nanofibers include nanofibers derived from oxidized cellulose oxidized using an N-oxyl compound.

[0016] [2] In one embodiment of the intermediate, it can be,

[0017] The trivalent or higher cations are aluminum ions and / or iron ions.

[0018] [3] One embodiment of the intermediate of the present invention is characterized in that it comprises:

[0019] Rubber ingredients;

[0020] cellulose nanofibers containing carboxyl groups; and

[0021] An unsaturated carboxylate containing a monovalent metal ion and / or a polymer having a repeating unit derived from an unsaturated carboxylate containing a monovalent metal ion,

[0022] The cellulose nanofibers include nanofibers derived from oxidized cellulose oxidized using an N-oxyl compound.

[0023] [4] In one embodiment of the intermediate, it can be,

[0024] The unsaturated carboxylate is sodium acrylate and / or sodium methacrylate.

[0025] [5] In one embodiment of the intermediate, it can be,

[0026] The rubber component is natural rubber, carboxyl-modified nitrile rubber or carboxyl-modified styrene butadiene rubber.

[0027] [6] In one embodiment of the intermediate, it can be,

[0028] The cellulose nanofibers have a structure in which a carboxyl group is introduced by oxidizing the hydroxyl group at the 6th position of the glucopyranose ring constituting cellulose.

[0029] [7] In one embodiment of the intermediate, it can be,

[0030] Include:

[0031] 100 parts by mass of the rubber component;

[0032] The cellulose nanofibers are in an amount of 10 parts by mass or more and less than 100 parts by mass; and

[0033] at least one selected from the trivalent or higher cations, the unsaturated carboxylates containing monovalent metal ions, and the polymer having repeating units derived from the unsaturated carboxylates containing monovalent metal ions in an amount of 0.50 to 6.00 times the equivalent of the carboxyl groups contained in the cellulose nanofibers,

[0034] The average fiber diameter of the cellulose nanofibers is 2 nm to 8 nm, and the average fiber length of the cellulose nanofibers is 200 nm to 800 nm.

[0035] The cellulose nanofibers have a carboxyl group content of 1.2 mmol / g to 1.7 mmol / g.

[0036] [8] One embodiment of the method for producing an intermediate of the present invention is characterized by comprising:

[0037] A step of mixing a rubber latex, a CNF aqueous dispersion, and at least one selected from an inorganic acid polyvalent metal salt containing a trivalent or higher cation, an unsaturated carboxylate containing a monovalent metal ion, and a polymer having a repeating unit derived from the unsaturated carboxylate containing a monovalent metal ion to obtain a mixed solution, wherein the rubber latex contains 100 parts by mass of a rubber component, and the CNF aqueous dispersion is obtained by dispersing 10 parts by mass or more and less than 100 parts by mass of cellulose nanofibers containing a carboxyl group in an aqueous solvent;

[0038] A step of kneading the mixed solution;

[0039] a step of drying the mixed solution after the kneading step to obtain a mixture having a water content of 3% or less; and

[0040] The step of kneading the mixture to obtain an intermediate,

[0041] The cellulose nanofibers include nanofibers derived from oxidized cellulose oxidized using an N-oxyl compound.

[0042] Effects of the Invention

[0043] According to one embodiment of the intermediate of the present invention, the cellulose nanofiber has a small number of aggregates, so the reinforcing property is excellent, and the cellulose nanofiber is easily applied to the rubber product by using it as a masterbatch of the rubber product. In addition, according to one embodiment of the method for producing the intermediate of the present invention, an intermediate with a small number of aggregates of the cellulose nanofiber can be produced, and the cellulose nanofiber is easily applied to the rubber product by using the intermediate as a masterbatch of the rubber product. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The present invention is a flow chart of a method for producing an intermediate according to an embodiment.

[0045] Figure 2 This is a SEM image of the tensile fracture surface of the cross-linked sample of Example 1-1.

[0046] Figure 3It is the SEM image of the tensile fracture surface of the cross-linked sample of Example 1-4.

[0047] Figure 4 This is a SEM image of the tensile fracture surface of the crosslinked sample of Comparative Example 1-3. DETAILED DESCRIPTION

[0048] Hereinafter, preferred embodiments of the present invention will be described in detail using the accompanying drawings. Moreover, the embodiments described below do not unduly limit the contents of the present invention as described in the claims. In addition, all the structures described below are not necessarily essential components of the present invention.

[0049] A. Intermediates

[0050] The intermediate of the first embodiment includes: a rubber component; cellulose nanofibers containing carboxyl groups; and trivalent or higher cations, wherein the cellulose nanofibers include nanofibers derived from oxidized cellulose oxidized using an N-oxyl compound. In addition, unless otherwise specified, "to" means that the upper limit and the lower limit are included.

[0051] The intermediate of the second embodiment comprises: a rubber component; cellulose nanofibers containing carboxyl groups; and an unsaturated carboxylate containing a monovalent metal ion and / or a polymer having repeating units derived from an unsaturated carboxylate containing a monovalent metal ion, wherein the cellulose nanofibers comprise nanofibers derived from oxidized cellulose formed by oxidation using an N-oxyl compound.

[0052] The intermediate of the first embodiment and the second embodiment can also be used as a master batch for compounding cellulose nanofibers into rubber products. The intermediate is in a state of no water or little water through the drying process described later, so, usually, the cellulose nanofibers are easy to agglomerate due to hydrogen bonds, but the rubber component, and trivalent or higher cations and / or unsaturated carboxylates, This aggregation is suppressed. Therefore, at least there are no agglomerates of cellulose that can be confirmed by visual observation (visual observation of an image under a scanning electron microscope) in the intermediate. As an agglomerate of cellulose that can be confirmed by visual observation, if the agglomerate has a maximum width of more than 10μm, it can be distinguished in most cases, and if the agglomerate has a maximum width of more than 50μm, it can be reliably distinguished.

[0053] In addition, when the intermediate is mixed with the matrix material as a masterbatch, the cellulose nanofibers of the intermediate are easily fibrillated and dispersed by the rubber component, and the cations of trivalence or more derived from the inorganic acid polyvalent metal salt and / or the metal ions of monovalence or more derived from the unsaturated carboxylic acid salt. Therefore, based on the intermediate, since the cellulose nanofibers have few agglomerates, the reinforcement of the rubber product is excellent, and the cellulose nanofibers are easily applied to the rubber product only by being used as a masterbatch of the rubber product and diluted with the rubber component. The qualification of the intermediate is judged by at least not confirming the agglomerates in visual observation, but only by visually observing a part of the intermediate to confirm the agglomerates can not judge the overall state, so it cannot be said that this is sufficient. Therefore, it is preferred to judge the fibrillation and dispersion of the cellulose nanofibers by the physical property inspection of the intermediate. As the physical property of the intermediate, the 50% modulus (σ50) in the tensile test can be greatly improved by the compounding of the cellulose nanofibers as a judgment criterion, and the improvement of the tensile strength (TS) can also be used as a judgment criterion for the intermediate. Although the increase in elongation at break (Eb) is also an important factor, the elongation at break (Eb) decreases when the content of cellulose nanofibers increases, so it is preferred to change the judgment standard according to the increase rate of 50% modulus. In addition, the elongation at break (Eb) of the rubber product obtained by using the intermediate as a masterbatch and diluting it is improved compared to the intermediate, so there is no problem when using the rubber product. As a criterion for judging whether the intermediate is qualified or not, the comprehensive judgment criterion of the embodiment described later can be used.

[0054] In order to use the intermediate as a masterbatch, it is desirable that the content of cellulose nanofibers in the intermediate is high in operation, but when the content of cellulose nanofibers increases, the manufacture of the intermediate becomes difficult. Therefore, the content of cellulose nanofibers in the intermediate can be 10 parts by mass or more and less than 100 parts by mass, for example, 20 to 50 parts by mass, relative to 100 parts by mass of the rubber component. In actual rubber products, cellulose nanofibers are expected to be less than 10 parts by mass, so if the content of cellulose nanofibers is more than 10 parts by mass, more preferably more than 20 parts by mass, it is possible to manufacture rubber products with a small amount of intermediates, so it is advantageous. In addition, when the content of cellulose nanofibers is more than 100 parts by mass, processing is almost impossible, if it is less than 100 parts by mass, it can be processed, and if it is less than 50 parts by mass, processing becomes easier.

[0055] The intermediate can contain at least one selected from trivalent or higher cations, unsaturated carboxylates containing monovalent metal ions, and polymers having repeating units derived from unsaturated carboxylates containing monovalent metal ions in an amount of 0.50 to 6.00 times the equivalent of carboxyl groups contained in the cellulose nanofibers.

[0056] B. Raw materials

[0057] Next, each raw material used for producing the intermediate body of the first embodiment and the second embodiment will be described.

[0058] B-1. Cellulose nanofibers

[0059] Cellulose nanofibers contain carboxyl groups. Since cellulose nanofibers have carboxyl groups, they are easily fibrillated in the process of fibrillation from cellulose raw materials by repelling each other of carboxyl groups as anionic groups. The content of carboxyl groups in cellulose nanofibers can be 1.2 mmol / g to 1.7 mmol / g. When the content of carboxyl groups in cellulose nanofibers is 1.2 mmol / g or less, cellulose nanofibers tend to be insufficiently fibrillated. When the content of carboxyl groups in cellulose nanofibers exceeds 1.7 mmol / g, the molecular weight of cellulose nanofibers may decrease due to damage caused by TEMPO oxidation, or a part of the cellulose nanofibers may become a water-soluble polysaccharide component separated from the fiber component and dissolved during washing, resulting in a decrease in yield. The content of carboxyl groups is measured by preparing a slurry of 0.5 to 1% by mass from a sample of cellulose nanofibers whose dry mass is accurately weighed, and after the pH is adjusted to about 2.5 by a 0.1 M hydrochloric acid aqueous solution, a 0.05 M sodium hydroxide aqueous solution is dripped to measure the conductivity. The measurement is continued until the pH becomes about 11. The carboxyl group content was determined using the following formula from the amount of sodium hydroxide (V) consumed in the neutralization step of the weak acid whose conductivity changes slowly.

[0060] Carboxyl content (mmol / g) = V (ml) × 0.05 / dry mass of cellulose sample (g)

[0061] The average fiber diameter of cellulose nanofiber is preferably more than 2nm and less than 8nm, more preferably more than 2nm and less than 6nm. In addition, the average fiber length of cellulose nanofiber is preferably more than 200nm and less than 800nm, more preferably more than 300nm and less than 600nm. When the average fiber diameter and the average fiber length are in the range, as the reinforcing effect of rubber products, such as rigidity, tensile strength, elongation when breaking, etc. can be improved, so it is preferred. The average fiber diameter and the average fiber length are the arithmetic mean of the fiber diameter and the fiber length obtained from the result of observing each fiber using a field emission scanning electron microscope (FE-SEM).

[0062] Cellulose nanofibers can be obtained in the market as an aqueous dispersion. The solid content of the cellulose nanofibers in the cellulose nanofiber aqueous dispersion can be 0.01% to 5% by mass, and can preferably be 0.1% to 2% by mass. When the solid content of the cellulose nanofibers in the aqueous dispersion is less than 0.01% by mass, the drying process described later will take time. If the solid content of the cellulose nanofibers in the aqueous dispersion exceeds 5% by mass, the inorganic acid polyvalent metal salt and the unsaturated carboxylate described later cannot be uniformly treated, and agglomerates of the cellulose nanofibers are easily generated.

[0063] As the raw material of cellulose nanofiber, it can be the raw material derived from plant materials such as wood, or it can be the raw material derived from animal materials such as sea squirts or microorganisms such as bacteria other than plant materials. In addition, as the preparation method of cellulose nanofiber using the raw material of plant materials, for example, it is possible to use a method of physically fibrillating the raw material by applying a physical treatment to the raw material after chemical treatment to make it easy to fibrillate, or a method of physically fibrillating the raw material by a known method of using a high shear force of a machine such as a high pressure homogenizer method, a grinding mill grinding method, a freezing pulverization method, a strong shear force kneading method, a ball mill pulverization method, etc.

[0064] The method for oxidizing the cellulose raw material is not particularly limited, but as one example, there can be mentioned a method of oxidizing the cellulose raw material in water using an oxidant in the presence of an N-oxyl compound, and a substance selected from the group consisting of bromide, iodide, or a mixture thereof. According to this method, the primary hydroxyl group at the C6 position of the pyranose glucopyranose ring on the surface of the 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 mass or less.

[0065] The N-oxyl compound refers to a compound that can generate a nitroxyl radical. Examples of the nitroxyl radical include 2,2,6,6-tetramethylpiperidinyl 1-oxyl (TEMPO). As the N-oxyl compound, any compound can be used as long as it promotes the target oxidation reaction.

[0066] The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount that can oxidize the cellulose that will become the raw material. For example, it is preferably 0.01 mmol or more, and more preferably 0.02 mmol or more, relative to 1 g of absolute dry cellulose. The upper limit is preferably 10 mmol or less, more preferably 1 mmol or less, and even more preferably 0.5 mmol or less. Therefore, the amount of the N-oxyl compound used is preferably 0.01 mmol to 10 mmol, more preferably 0.01 mmol to 1 mmol, and even more preferably 0.02 mmol to 0.5 mmol, relative to 1 g of absolute dry cellulose.

[0067] Bromide refers to a compound containing bromine, for example, alkali metal bromide that can dissociate and ionize in water, such as sodium bromide, etc. In addition, iodide refers to a compound containing iodine, for example, alkali metal iodide can be mentioned. The amount of bromide or iodide used can be selected within the range that can promote the oxidation reaction. The total amount of bromide and iodide is preferably 0.1mmol or more, more preferably 0.5mmol or more relative to 1g of absolute dry cellulose. The upper limit is preferably 100mmol or less, more preferably 10mmol or less, and further preferably 5mmol or less. Therefore, the total amount of bromide and iodide is preferably 0.1-100mmol, more preferably 0.1-10mmol, and further preferably 0.5-5mmol relative to 1g of absolute dry cellulose.

[0068] The oxidant is not particularly limited, and examples thereof include halogen, hypohalous acid, halogenous acid, perhalogen acid, their salts, halogen oxides, peroxides, and the like. Among them, hypohalous acid or its salt can be used, more preferably hypochlorous acid or its salt, and more preferably sodium hypochlorite, from the perspective of being cheap and having little environmental load. The amount of the oxidant used is preferably 0.5 mmol or more, more preferably 1 mmol or more, and more preferably 3 mmol or more relative to 1 g of absolutely dry cellulose. The upper limit is preferably 500 mmol or less, more preferably 50 mmol or less, and more preferably 25 mmol or less. Therefore, the amount of the oxidant used is preferably 0.5 mmol to 500 mmol, more preferably 0.5 mmol to 50 mmol, more preferably 1 mmol to 25 mmol, and most preferably 3 to 10 mmol relative to 1 mol of absolutely dry cellulose. In the case of using an N-oxyl compound, the amount of the oxidant used is preferably 1 mol or more relative to 1 mol of the N-oxyl compound. The upper limit is preferably 40 mol. Therefore, the amount of the oxidant used is preferably 1 mmol to 40 mol relative to 1 mol of the N-oxyl compound.

[0069] The conditions such as pH and temperature during the oxidation reaction are not particularly limited. Generally speaking, the oxidation reaction will proceed efficiently even under relatively mild conditions. The reaction temperature is preferably above 4°C, and more preferably above 15°C. The upper limit is preferably below 40°C, and more preferably below 30°C. Therefore, the temperature is preferably 4°C to 40°C, and can be about 15°C to 30°C, that is, it can be room temperature. The pH of the reaction solution is preferably above 8, and more preferably above 10. The upper limit is preferably below 12, and more preferably below 11. Therefore, the pH of the reaction solution is preferably 8 to 12, and more preferably about 10 to 11. Generally, carboxyl groups are generated in cellulose as the oxidation reaction proceeds, and therefore, the pH of the reaction solution tends to decrease. Therefore, in order to make the oxidation reaction proceed efficiently, it is preferred to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution within the above range. For reasons such as easy operability and less prone to side reactions, the reaction medium during oxidation is preferably water.

[0070] The reaction time of oxidation can be appropriately set according to the degree of oxidation, and is usually more than 0.5 hours. The upper limit is usually less than 6 hours, preferably less than 4 hours. Therefore, the reaction time of oxidation is usually 0.5 hours to 6 hours, for example, 0.5 hours to 4 hours.

[0071] The oxidation may be carried out by dividing the reaction into two or more stages. For example, by filtering out the oxidized cellulose obtained after the first stage reaction and oxidizing it again under the same or different reaction conditions, the oxidation can be efficiently performed without being hindered by the salt generated as a by-product in the first stage reaction.

[0072] As another example of the carboxylation (oxidation) method, there can be cited a method of oxidation by ozone treatment. Through this oxidation reaction, at least the hydroxyl groups at the 2nd and 6th positions of the pyranose ring constituting cellulose are oxidized, and the cellulose chain is decomposed. Ozone treatment is usually carried out by contacting a gas containing ozone with the cellulose raw material. The ozone concentration in the gas is preferably 50 g / m 3 The upper limit is preferably 250 g / m 3 Below, more preferably 220g / m 3 Therefore, the ozone concentration in the gas is preferably 50 g / m 3 ~250g / m 3 , more preferably 50g / m 3 ~220g / m 3. The amount of ozone added is preferably 0.1% by mass or more, and more preferably 5% by mass or more, relative to 100% by mass of the solid content of the cellulose raw material. The upper limit is usually 30% by mass or less. Therefore, the amount of ozone added is preferably 0.1% by mass to 30% by mass, and more preferably 5% by mass to 30% by mass, relative to 100% by mass of the solid content of the cellulose raw material. The ozone treatment temperature is usually above 0°C, and preferably above 20°C. The upper limit is usually below 50°C. Therefore, the ozone treatment temperature is preferably 0°C to 50°C, and more preferably 20°C to 50°C. The ozone treatment time is usually more than 1 minute, and preferably more than 30 minutes. The upper limit is usually 360 minutes or less. Therefore, the ozone treatment time is usually about 1 minute to 360 minutes, and preferably about 30 minutes to 360 minutes. When the conditions for ozone treatment are within the above range, excessive oxidation and decomposition of cellulose can be prevented, and the yield of oxidized cellulose becomes good.

[0073] After the ozone treatment, the resultant product may be subjected to additional oxidation treatment using an oxidant. The oxidant used for the additional oxidation treatment is not particularly limited, and examples thereof include chlorine compounds such as chlorine dioxide and sodium chlorite; oxygen, hydrogen peroxide, persulfate, and peracetic acid. As a method for the additional oxidation treatment, for example, there is a method in which these oxidants are dissolved in a polar organic solvent such as water or alcohol to prepare an oxidant solution, and the cellulose raw material is immersed in the oxidant solution.

[0074] The amount of carboxyl groups, carboxylate groups, and aldehyde groups contained in the cellulose nanofibers can be adjusted by controlling oxidation conditions such as the amount of the oxidant added and the reaction time.

[0075] B-2. Rubber component

[0076] The rubber component of the intermediate is provided by using a rubber latex containing a rubber component as a raw material. The rubber component is natural rubber (NR), carboxyl-modified nitrile rubber (X-NBR) or carboxyl-modified styrene butadiene rubber (X-SBR). The weight average molecular weight of the rubber component is preferably 50,000 to 3,000,000, and more preferably 100,000 to 2,000,000. In addition, in the present invention, the so-called "weight average molecular weight" refers to a value measured by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent and converted to standard polystyrene.

[0077] Carboxyl modified acrylonitrile butadiene rubber (carboxyl modified acrylonitrile butadiene rubber) or carboxyl modified styrene butadiene rubber are carboxyl functionalized modified diene rubbers with carboxyl.Carboxyl modified acrylonitrile butadiene rubber or carboxyl modified styrene butadiene rubber can improve the affinity with the cellulose nanofiber with carboxyl by having carboxyl, and therefore, when mixing, carboxyl is combined with cellulose nanofiber to bring into play the function of improving fibrillation ability. It can be considered in addition that natural rubber improves fibrillation ability by the interaction of the free radical generated by plastication and cellulose nanofiber.

[0078] In addition, the intermediate may also be compounded with a known filler compounded in the rubber composition. Examples of fillers include carbon black, silica, clay, aluminum hydroxide, calcium carbonate, mica, talc, aluminum hydroxide, aluminum oxide, titanium oxide, barium sulfate, lecithin, etc. These fillers may be compounded alone or in combination, but since the intermediate is used as a masterbatch for compounding into a matrix material, the filler may also be compounded when the matrix material and the intermediate are mixed.

[0079] B-3. ​​Inorganic acid polyvalent metal salt

[0080] An inorganic acid polyvalent metal salt containing a cation having a valence of 3 or more is used for the manufacture of an intermediate. Therefore, the inorganic acid polyvalent metal salt is water-soluble. The solubility of the inorganic acid polyvalent metal salt relative to 100 ml of water at 20°C can be 10 g / 100 ml or more. By mixing a water-soluble inorganic acid polyvalent metal salt with a CNF aqueous dispersion and latex, the cation having a valence of 3 or more reacts with the carboxyl group of the cellulose nanofiber, whereby the inorganic acid polyvalent metal salt acts as a pseudo-crosslink between the cellulose nanofibers. As a polyvalent metal, one or more selected from metals having a valence of 3 or more, such as iron and aluminum, which are cations having a valence of 3 or more, can be cited. By including such a polyvalent metal, the cellulose nanofibers have the function of pseudo-crosslinking each other. As an inorganic acid, for example, one or more selected from nitric acid, sulfuric acid, and hydrogen chloride (hydrochloric acid) can be cited.

[0081] Examples of the inorganic acid polyvalent metal salt include one or more selected from aluminum chloride, iron chloride, aluminum nitrate, iron (III) nitrate, aluminum sulfate, iron (III) sulfate, potassium aluminum sulfate, and hydrates thereof.

[0082] The amount of the water-soluble inorganic acid polyvalent metal salt can be appropriately adjusted according to the salt type and the purpose of the blending, and can be blended in such a manner that the trivalent or higher cations in the intermediate are 0.50 to 6.00 times the equivalent relative to the carboxyl groups of the cellulose nanofibers. The amount of the inorganic acid polyvalent metal salt is described in "C. Method for producing the intermediate".

[0083] The intermediate of the first embodiment contains trivalent or higher cations. The trivalent or higher cations can be derived from inorganic acid polyvalent metal salts. The trivalent or higher cations can be aluminum ions and / or iron ions. The inorganic acid in the intermediate can also be removed by washing.

[0084] B-4. Unsaturated carboxylate

[0085] Unsaturated carboxylates containing univalent metal ions are used for the manufacture of intermediates. Therefore, unsaturated carboxylates are water-soluble. As unsaturated carboxylates, (meth) acrylic acid, maleic acid (anhydride), fumaric acid, itaconic acid (anhydride), crotonic acid and their salts can be shown. By mixing water-soluble unsaturated carboxylates containing univalent metal ions with CNF aqueous dispersion and latex, carboxyl and carbonyl groups form hydrogen bonds with carbonyl or hydroxyl groups of cellulose nanofibers, thereby playing a role of pseudo cross-linking between cellulose nanofibers. As metals forming their salts, for example, univalent metals such as sodium, potassium, and lithium can be shown. It can be considered that this is because, unlike inorganic acid polyvalent metal salts, carboxyl and carbonyl groups can form hydrogen bonds even if they are univalent metals. Here, "(meth) acrylic acid" is a general term for methacrylic acid and acrylic acid. Unsaturated carboxylates can be sodium acrylate and / or sodium methacrylate. In addition, when forming a compound of an unsaturated carboxylate, one of the above-mentioned metals can be used to form a metal salt compound, or two or more can be used. The content of the unsaturated carboxylate is described in "C. Method for producing intermediate".

[0086] B-5. Polymer having repeating units derived from unsaturated carboxylate

[0087] Polymers with repeating units derived from unsaturated carboxylates containing univalent metal ions are used for the manufacture of intermediates. Therefore, polymers with repeating units derived from unsaturated carboxylates are water-soluble. As unsaturated carboxylates, (meth) acrylic acid, maleic acid (anhydride), fumaric acid, itaconic acid (anhydride), crotonic acid and their salts can be shown. By mixing a water-soluble polymer with repeating units derived from unsaturated carboxylates containing univalent metal ions with a cellulose nanofiber aqueous dispersion and latex, carboxyl and carbonyl groups form hydrogen bonds with carbonyl or hydroxyl groups of cellulose nanofibers, thereby playing a role in pseudo-crosslinking of cellulose nanofibers. As metals forming their salts, for example, univalent metals such as sodium, potassium, and lithium can be shown. The unsaturated carboxylates as repeating units of the polymer can be sodium acrylate and / or sodium methacrylate. The polymer can also contain repeating units derived from monomers other than unsaturated carboxylates. In addition, when forming the polymer, one metal among the above-mentioned metals can be used to form a metal salt compound, or more than two metals can be used. The content of the polymer is described in "C. Method for producing intermediate".

[0088] The intermediate of the second embodiment includes an unsaturated carboxylate containing a monovalent metal ion and / or a polymer having a repeating unit derived from an unsaturated carboxylate containing a monovalent metal ion. Examples of the metal ion include monovalent metal ions such as sodium, potassium, and lithium.

[0089] C. Method for producing intermediates

[0090] Next, the method for producing the intermediate is described. Figure 1 The flowchart of the method for producing an intermediate of one embodiment. The method for producing an intermediate can use the raw material of B described above. The method for producing an intermediate can obtain the intermediate of the first embodiment or the second embodiment described in A described above.

[0091] like Figure 1 As shown, the method for producing an intermediate includes: a step of obtaining a mixed solution (S10); a step of kneading (S20); a step of obtaining a mixture (S30); and a step of obtaining an intermediate (S40).

[0092] S10: The process of obtaining a mixed solution is to mix rubber latex, CNF aqueous dispersion, and at least one selected from an inorganic acid polyvalent metal salt containing trivalent or higher cations, an unsaturated carboxylate containing a monovalent metal ion, and a polymer having a repeating unit derived from the unsaturated carboxylate containing a monovalent metal ion to obtain a mixed solution, wherein the rubber latex contains 100 parts by mass of a rubber component, and the CNF aqueous dispersion is formed by dispersing 10 parts by mass or more and less than 100 parts by mass of cellulose nanofibers containing a carboxyl group in an aqueous solvent. The rubber latex, CNF aqueous dispersion, inorganic acid polyvalent metal salt, and unsaturated carboxylate are all provided in an aqueous solvent and can be mixed using a known stirrer. As a stirrer, for example, a magnetic stirrer, a propeller stirrer, etc. can be used.

[0093] The amount of cellulose nanofibers in the process of obtaining the mixed solution is more than 10 parts by mass relative to 100 parts by mass of the rubber component, thereby, the intermediate can be provided to the market as a masterbatch containing a high concentration of cellulose nanofibers, and the amount is preferably more than 20 parts by mass. In addition, if the amount is less than 100 parts by mass, although it takes time to work, it can be stirred or kneaded, and in order to improve workability, the amount is preferably less than 50 parts by mass. The rubber component is not limited as long as it can be used as rubber latex, but is preferably natural rubber, carboxyl-modified nitrile rubber, and carboxyl-modified styrene butadiene rubber.

[0094] Although inorganic acid polyvalent metal salt, unsaturated carboxylate and polymer having repeating units derived from unsaturated carboxylate can be combined for compounding, it is preferred to compound them separately. The compounding amount of inorganic acid polyvalent metal salt, unsaturated carboxylate and polymer having repeating units derived from unsaturated carboxylate can be appropriately adjusted according to the salt type and compounding purpose. The mixed solution is compounded to contain 0.50 times equivalent to 6.00 times equivalent of cations of trivalence or more, unsaturated carboxylates containing univalent metal ions, and polymer having repeating units derived from unsaturated carboxylates containing univalent metal ions, at least one selected from. In theory, 1 times equivalent is appropriate, but according to the type of latex and the required characteristics of rubber products, less than 1 times equivalent can be compounded, and more than 1 times equivalent can be compounded for reasons such as uneven distribution of additives and incompatibility of local structures. As described above, if it is 0.50 times equivalent or more, the aggregation of cellulose nanofibers can be suppressed due to the development of pseudo cross-linking structure, so it is preferred. If it is 6.00 times equivalent or less, the aggregation of the remaining inorganic acid polyvalent metal salt, unsaturated carboxylate, and polymer having repeating units derived from unsaturated carboxylate has a relatively small effect on the rubber product, so it is preferred. In addition, from the viewpoint of suppressing the aggregation of cellulose nanofibers and the aggregation of the remaining materials, the amount of metal ions is preferably 2.00 times equivalent to 3.50 times equivalent relative to the carboxyl group of the cellulose nanofiber.

[0095] Here, the amount of metal ions can be calculated based on the molar amount of carboxyl groups contained in the cellulose nanofibers. For example, if the carboxyl groups of the cellulose nanofibers used in S10 are 1.5 mmol / g, the amount of inorganic acid polyvalent metal salts, unsaturated carboxylates, and polymers having repeating units derived from unsaturated carboxylates can be calculated in a manner that is 0.50 to 6.00 times the molar amount.

[0096] For example, if the carboxyl group of cellulose nanofiber is 1.5 mmol / g, then 20 g (20 parts by mass) of cellulose nanofiber is 30 mmol / g, and if it is iron (III) sulfate as a hydrate with a purity of 70%, it contains 10.5 mmol / g of charge derived from trivalent iron ions, so 8.6 g of iron sulfate hydrate is added at 3 times the equivalent (30×3 / 10.5), and the concentration of iron sulfate in the pretreatment liquid becomes 4.7% by mass. In addition, the content of the inorganic acid polyvalent metal salt is, for example, 0.50 times the equivalent to 6.00 times the equivalent of iron ions relative to the carboxyl group of cellulose nanofiber in the case of iron sulfate hydrate with a purity of 70%, and therefore, it is 1.15% by mass to 12.4% by mass in the pretreatment liquid in terms of solid content, preferably 4.5% by mass to 7.7% by mass (2.00 times the equivalent to 3.50 times the equivalent).

[0097] S20: The kneading process is a process of kneading the mixed solution obtained by S10. In the process of kneading the mixed solution, it is preferred that the viscosity of the mixed solution at 25°C measured by a vibration viscometer in accordance with JIS Z8803 (2011) is 200mPa·s to 500mPa·s. As a vibration viscometer, for example, a tuning fork vibration rheometer can be used. If the viscosity of the mixed solution is within the above range, the restoring force brought by the elasticity of the mixed solution can be used for kneading. The region in which the mixed solution exhibits elasticity is a range in which the elastic modulus is constant regardless of stress by obtaining a stress-strain curve through a dynamic viscoelasticity test, and is a range in which stress is proportional to strain. Such an elastic region can also be inferred from the viscosity of the mixed solution. Kneading can be performed by a device that can give a certain degree of shear force to the mixed solution, such as a self-rotating revolution mixer, a three-roller, a double-roller, etc. S10 can be performed until the viscosity of the mixed solution becomes nonlinear (becomes a state like a non-Newtonian fluid).

[0098] S30: The process of obtaining a mixture is a process of drying the mixed liquid after the kneading process of S20 to obtain a mixture with a moisture content of less than 3%. If the moisture content of the dried mixture is less than 3%, the kneading process of S40 can be performed. In addition, the moisture content of the dried mixture is preferably less than 2%. The moisture content can be measured using a heating and drying moisture meter. In addition, the moisture content can also be calculated from the blending amount by measuring the mass before and after drying. The drying of S30 can be any method that can efficiently remove the aqueous solvent in the mixed liquid, and a known method can be used, such as degassing while heating.

[0099] S40: The process of obtaining an intermediate is a process of kneading the mixture obtained in S30 to obtain an intermediate. The mixture has many agglomerates formed by the aggregation of cellulose nanofibers due to the drying in S30. It is speculated that the presence of the rubber component and metal ions, unsaturated carboxylates, etc. in the mixture inhibits the bonding of cellulose nanofibers to each other. By kneading the mixture with high shear force in this state, the cellulose nanofibers are fibrillated and dispersed in the rubber component. The kneading in S40 can be performed by largely moving the cellulose nanofibers by utilizing the recovery brought about by the elasticity of the rubber component after compressing the mixture.

[0100] The kneading in S40 can be performed by thin-passing using, for example, open rolls with a roll interval set to more than 0 mm and 0.5 mm or less and a roll temperature set to 0° C. to 50° C.

[0101] First, before the thin-pass process, the mixture is wound around one of the rollers for kneading, and the molecular chains of the rubber component are appropriately cut to generate free radicals. Since the free radicals of the rubber component, especially natural rubber, are easily linked to the cellulose nanofibers, it is preferred to include this process in the production method of the intermediate using natural rubber.

[0102] Next, a thin pass process can be performed. The thin pass process is to use a double roller with a roller interval set to be greater than 0 mm and less than 0.5 mm, and to perform thin passing at 0°C to 50°C. The roller interval is a set value, and if the mixture can enter the small gap between the rollers, the mixture can be squeezed out from the small gap. In this process, for example, the roller interval can be set to, for example, 0.1 mm to 0.5 mm, and the mixture is put into an open roller for 1 to 10 times of thin passing. The surface speed ratio of the two rollers can be 1.05 to 3.00, and can be further 1.05 to 1.2. By using such a surface speed ratio, the desired high shear force can be obtained.

[0103] The mixture extruded from the narrow gap between the rollers is greatly deformed by the restoring force of the elasticity of the rubber component, and the cellulose nanofibers move greatly together with the rubber component. The intermediate obtained by thin-passing is rolled and pressed into a sheet of a predetermined thickness, for example, 100 μm to 500 μm.

[0104] In the thin-pass process, in order to obtain the highest possible shear force, the roller temperature can be set to, for example, 0°C to 50°C, and can be further set to a relatively low temperature of 5°C to 30°C. The measured temperature of the intermediate (mixture) can also be adjusted to 0°C to 50°C, and can be further adjusted to 5°C to 30°C. By adjusting to such a temperature range, the elasticity of the rubber component can be used to fibrillate the cellulose nanofibers, and the fibrillated cellulose nanofibers can be dispersed in the intermediate.

[0105] By this thin-pass process, the intermediate does not have agglomerates of cellulose nanofibers that can be confirmed by visual observation. The maximum width of such agglomerates is 10 μm or more. Since there are no agglomerates in the intermediate, there are no agglomerates that are easy to become the starting point of fracture in the rubber product using the intermediate as a masterbatch, so it is possible to manufacture a rubber product with excellent mechanical properties.

[0106] The step of obtaining the intermediate in S40 is not limited to the open roll method described above, and may also use, for example, a closed kneading method or a multi-screw extrusion kneading method. Furthermore, the intermediate obtained by the production method can be mixed as a masterbatch with a polymer substance serving as a matrix.

[0107] As used in this specification and claims, “at least one of A, B, and C” or “one or more of A, B, and C” in connection with the enumeration of one or more elements is intended to include only A, only B, only C, the group of A and B, the group of A and C, the group of B and C, the group of A, B, and C, etc.

[0108] The present invention may omit part of the configuration or combine the various embodiments and modifications within the scope of the features and effects described in the present application.

[0109] The present invention includes a configuration substantially the same as the configuration described in the embodiment (a configuration having the same performance, method and result, or a configuration having the same purpose and effect). In addition, the present invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration having the same effect as the configuration described in the embodiment or a configuration capable of achieving the same purpose. In addition, the present invention includes a configuration in which a known technology is added to the configuration described in the embodiment.

[0110] Example

[0111] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0112] (Production of cellulose nanofibers)

[0113] 5.00 g (absolute dry) of bleached unbeaten kraft pulp (whiteness 85%) from coniferous trees was added to 500 ml of an aqueous solution in which 39 mg (0.05 mmol relative to 1 g of cellulose) of TEMPO (Sigma Aldrich) and 514 mg (1.0 mmol relative to 1 g of cellulose) of sodium bromide were dissolved, and stirred until the pulp was evenly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that the sodium hypochlorite became 6.0 mmol / g, and the oxidation reaction was started. During the reaction, the pH in the system decreased, but 3M sodium hydroxide aqueous solution was added successively to adjust the pH to 10. The reaction was terminated at the point where the sodium hypochlorite was consumed and the pH in the system no longer changed. After the mixture after the reaction was acidified with hydrochloric acid, it was filtered with 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 carboxyl content was 1.6 mmol / g. It 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 a dispersion of TEMPO oxidized cellulose nanofibers (TOCN). The average fiber diameter of TOCN was 3 nm and the average fiber length was 550 nm.

[0114] (1) Sample preparation

[0115] (1-1) Example 1-1 to Example 1-4

[0116] The rubber latex shown in Table 1, a cellulose nanofiber aqueous dispersion (solvent is water) with a TOCN concentration of 1% (can also be diluted to 0.4% to 0.7%), and an aqueous solution of iron (III) sulfate or aluminum sulfate dissolved to about 30% were kneaded in an autogenous-revolution mixer (manufactured by THINKY, autogenous-revolution mixer) to obtain a mixed solution.

[0117] Next, the mixed liquid was poured into a barrel and dried in an oven at 40 to 50° C. for about 24 hours to remove the aqueous solvent to obtain a mixture. The water content of the obtained mixture was 5% or less in the entire mixture.

[0118] Next, after the mixture was wound onto an open roll (double roll, manufactured by Yasuda Seiki Co., Ltd., 191-TH test mixing roll) for kneading, the mixture was thin-passed (roll temperature 10°C to 30°C, roll interval 0.3 mm or less, roll speed ratio 1.1) to obtain an intermediate.

[0119] Furthermore, in order to evaluate the mechanical properties of the intermediate, the mixture was again wound on an open roll, a crosslinking agent was added and mixed, and the extruded sheet was press-formed at 165° C. for 30 minutes to obtain a crosslinked sample of each example in a sheet form with a thickness of 1 mm.

[0120] Here,

[0121] "XNBR": carboxyl-modified NBR latex, manufactured by Zeon Co., Ltd., Japan, Nipol 1571C2, solid content 45% by mass

[0122] "TOCN": TEMPO oxidized cellulose nanofibers, manufactured by Nippon Paper Industries, Ltd., TOCN Cellenpia, carboxyl content 1.6 mmol / g, average fiber diameter 3 nm, average fiber length 550 nm,

[0123] “Fe 2 (SO 4 ) 3 ”: Manufactured by Kanto Chemical Co., Ltd., iron (III) sulfate n-hydrate, 3.03 times the equivalent in Example 1-1, 3.01 times the equivalent in Example 1-2, and 1.51 times the equivalent in Example 1-3,

[0124] “Al 2 (SO 4 ) 3 ”: Aluminum sulfate (anhydrous), manufactured by Fujifilm Wako Co., Ltd., 5.87 times the equivalent weight was blended in Example 1-4,

[0125] Although not described in the tables, in each Example, PERCUMYL D manufactured by NOF Corporation was blended in an amount of 3.2 phr as a crosslinking agent.

[0126] (1-2) Comparative Examples 1-1 to 1-5

[0127] Using the rubber latex shown in Table 2, an aqueous dispersion (solvent: water) of cellulose nanofibers having a concentration of 1% of TEMPO oxidized cellulose nanofibers (which can also be diluted to 0.4% to 0.7%), and an aqueous solution of iron (III) sulfate, aluminum sulfate, or zinc sulfate, intermediates and sheet-like samples of each comparative example were obtained in the same manner as in Examples 1-1 to 1-4. Comparative Example 1-1 was a pure rubber compound without cellulose nanofibers, and Comparative Example 1-3 was a compound without cellulose nanofibers but with the same amount of iron sulfate as in Example 1-2.

[0128] Here,

[0129] “ZnSO 4”: Manufactured by Wako Pure Chemical Industries, Ltd., zinc sulfate, blended in 2.31 times the equivalent in Comparative Example 1-4.

[0130] (1-3) Agglutination evaluation

[0131] The presence or absence of agglomerates was confirmed by visually observing the fracture surface of each sample of the cross-linked product formed by cross-linking each intermediate under a scanning electron microscope after the tensile test. Agglomerates are parts of the cellulose nanofibers where fibrillation is insufficient, and the agglomerates that can be visually observed have a maximum width of more than 10 μm. The evaluation criteria are to visually observe the tensile fracture surface of the sample, and if there are no agglomerates, it is recorded as "0". Otherwise, based on the size of the visually observed agglomerates, if the maximum width is more than 50 μm, it is recorded as "×", and if the maximum width is more than 10 μm and less than 50 μm, it is recorded as "△" and recorded in Tables 1 and 2. In addition, Figure 2 to Figure 4 The SEM images of the tensile fracture surfaces of the crosslinked samples of Example 1-1, Example 1-4 and Comparative Example 1-3 were taken. Figure 2 and Figure 3 In the SEM images of Examples 1-2 and 1-4, no aggregates could be confirmed. Figure 4 In the SEM image of Comparative Example 1-3, aggregates having a maximum width of 50 μm or more were confirmed.

[0132] (1-4) Tensile test

[0133] For each sheet-like crosslinked product sample, a test piece punched into a dumbbell shape of JIS No. 6 was subjected to a tensile test using a tensile testing machine Autograph AG-X manufactured by Shimadzu Corporation at 23±2°C, a distance between markings of 20 mm, and a tensile speed of 500 mm / min in accordance with JIS K6251, and the 50% modulus (σ50 (MPa)), tensile strength (TS (MPa)), and elongation at break (Eb (%)) were measured. In addition, for each of the 50% modulus (σ50 (MPa)), tensile strength (TS (MPa)), and elongation at break (Eb (%)), the increase rate ((AB)×100 / B (%), where A is the measured value of the example and B is the measured value of the comparative example 1-1) was calculated by comparison with the measured results of the comparative example 1-1 compounded as pure rubber. The measured results and the calculated results are shown in Tables 1 and 2.

[0134] (1-5) Comprehensive judgment

[0135] The above-mentioned aggregation evaluation and the above-mentioned tensile test results were combined to perform a comprehensive judgment. In the comprehensive judgment, "0" means a qualified product that satisfies any one of the following conditions (a) to (c), and "×" means a defective product otherwise.

[0136] (a) The aggregation evaluation of the cross-linked sample is "0", the σ50 increase rate is 50% or more and less than 300%, and the TS increase rate does not decrease (does not become negative);

[0137] (b) The aggregation evaluation of the cross-linked sample is "0", the σ50 increase rate is 300% or more and less than 900%, and the Eb increase rate is -50% or more;

[0138] (c) The aggregation evaluation of the cross-linked sample was "0", the σ50 increase rate was 900% or more, and the Eb increase rate was -70% or more.

[0139]

Table 1

[0140]

[0141]

Table 2

[0142]

[0143] In the cross-linked samples of Examples 1-1 to 1-4, no aggregates larger than 10 μm were visually confirmed. In addition, the increase rate of 50% modulus (σ50) of the cross-linked samples of Examples 1-1 to 1-4 was 80% or more compared with the cross-linked sample of Comparative Example 1-1. In particular, in Examples 1-1, 2, and 4 in which 3 times the equivalent of inorganic acid polyvalent metal salt was added, the increase rate of 50% modulus (σ50) was 170% or more. In addition, the tensile strength (TS) and elongation at break (Eb) of the cross-linked samples of Examples 1-1 to 1-4 increased compared with the cross-linked sample of Comparative Example 1-1.

[0144] In the crosslinked samples of Examples 1-1 to 1-4, the elongation at break (Eb) did not decrease as much as in the crosslinked samples of Comparative Examples 1-2 and 1-4 containing cellulose nanofibers.

[0145] The crosslinked samples of Comparative Examples 1-3 contained iron sulfate but did not contain cellulose nanofibers, so the 50% modulus (σ50) and tensile strength (TS) decreased. In addition, the crosslinked samples of Comparative Examples 1-5 were not only difficult to process but also had significant agglomerates, so no crosslinked samples were produced.

[0146] (2-1) Example 2-1 to Example 2-5

[0147] Using the rubber latex shown in Table 3, an aqueous dispersion (solvent is water) of cellulose nanofibers having a concentration of 1% of TEMPO oxidized cellulose nanofibers (can also be diluted to 0.4% to 0.7%), and an aqueous solution of sodium acrylate (AANa) or a mixture of sodium acrylate (AANa) and iron (III) sulfate, samples of crosslinked bodies and sheet-like crosslinked bodies were obtained in the same manner as in Examples 1-1 to 1-4. Here, the "AANa" of Example 2-1 was blended in 3.47 times the equivalent, the "AANa" of Example 2-2 was blended in 1.74 times the equivalent, the "AANa" of Example 2-3 was blended in 0.85 times the equivalent, and the "AANa" of Example 2-4 was blended in 3.44 times the equivalent. In addition, in Example 2-5, "Fe 2 (SO 4 ) 3 ” is mixed with 0.91 times the equivalent, and “AANa” is mixed with 1.72 times the equivalent. In addition, “XNBR”, “TOCN”, “Fe 2 (SO 4 ) 3 The same materials as in Example 1-1 etc. were used.

[0148] Here,

[0149] "AANa": manufactured by Asada Chemical Industries, Ltd., sodium acrylate.

[0150] (2-2) Comparative Example 2-1

[0151] Using the rubber latex shown in Table 4, an aqueous dispersion (solvent: water) of TEMPO oxidized cellulose nanofibers at a concentration of 1% (can also be diluted to 0.4% to 0.7%), and an aqueous solution of calcium acrylate (AACa), samples of each comparative example in the form of a cross-linked body and a sheet were obtained in the same manner as in Examples 2-1 to 2-5.

[0152] Here,

[0153] "AACa": manufactured by Asada Chemical Industry Co., Ltd., calcium acrylate, blended in an amount of 4.03 times the equivalent in Comparative Example 2-1.

[0154] (2-3) Agglutination evaluation and tensile test

[0155] The presence or absence of agglomerates was visually confirmed for each cross-linked sample, and the evaluation was performed in the same manner as in Example 1-1. In addition, for each sheet-like cross-linked sample, a tensile test was performed in the same manner as in Example 1-1, and the 50% modulus (σ50 (MPa)), tensile strength (TS (MPa)), and elongation at break (Eb (%)) were measured. In addition, each increase rate was calculated by taking each measured value of Examples 2-1 to 2-5 and Comparative Example 2-1 as A and the measured value of Comparative Example 1-1 as B. The measurement results and calculation results are shown in Tables 3 and 4.

[0156] (2-4) Comprehensive judgment

[0157] The criterion for comprehensive determination is the same as that of (1-5) above.

[0158]

Table 3

[0159]

[0160]

Table 4

[0161]

[0162] In the cross-linked samples of Examples 2-1 to 2-5, no aggregates larger than 10 μm were visually confirmed. In addition, the increase rate of 50% modulus (σ50) of the cross-linked samples of Examples 2-1 to 2-5 was 300% or more compared with the cross-linked sample of Comparative Example 1-1. In particular, as shown in Example 2-3, even if the unsaturated carboxylate is a small amount compared with the inorganic acid polyvalent metal salt, it greatly affects the increase of 50% modulus (σ50). In addition, the increase rate of tensile strength (TS) of the cross-linked samples of Examples 2-1 to 2-5 was 14% or more, and the increase rate of elongation at break (Eb) was -50% or more compared with the cross-linked sample of Comparative Example 1-1.

[0163] Although the cross-linked sample of Comparative Example 2-1 contained calcium acrylate, the presence of aggregates was obvious when visually observed, and the elongation at break (Eb) was less than -50%.

[0164] (3-1) Example 3-1 to Example 3-4

[0165] Using the rubber latex shown in Table 5, an aqueous dispersion (solvent: water) of cellulose nanofibers having a concentration of 1% (or diluted to 0.4% to 0.7%) of TEMPO oxidized cellulose nanofibers, and an aqueous solution of iron (III) sulfate, sodium acrylate (AANa), sodium methacrylate (MANa), or sodium polyacrylate (PAANa), samples of crosslinked products and sheet-like crosslinked products were obtained in the same manner as in Examples 1-1 to 1-4. Here, the "Fe 2 O 2 O 3 N 2 O 4 ...2 (SO 4 ) 3 " was blended with 3.01 times the equivalent, "AANa" of Example 3-2 was blended with 3.47 times the equivalent, "MANa" of Example 3-3 was blended with 3.45 times the equivalent, and "PAANa" of Example 3-4 was blended with 3.47 times the equivalent. In addition, "TOCN", "Fe 2 (SO 4 ) 3 " used the same materials as in Example 1-1, etc., and "AANa" used the same materials as in Example 2-1, etc.

[0166] Here,

[0167] "NR": manufactured by Regitex, natural rubber latex, ULACOL, solid content 61% by mass

[0168] "MANa": manufactured by Asada Chemical Industries, Ltd., sodium methacrylate, CAS No. 5536-61-8,

[0169] "PAANa": manufactured by Toa Gosei Co., Ltd., sodium polyacrylate, Aron T50.

[0170] (3-2) Comparative Examples 3-1 to 3-4

[0171] Crosslinked products and sheet-like samples of each comparative example were obtained in the same manner as in Examples 3-1 to 3-4 using the rubber latex shown in Tables 6 and 7, an aqueous dispersion (solvent: water) of cellulose nanofibers having a concentration of 1% of TEMPO oxidized cellulose nanofibers (which can also be diluted to 0.4% to 0.7%), and an aqueous solution of iron (III) sulfate or calcium acrylate (AACa). Comparative Example 3-1 is a pure rubber compound containing no cellulose nanofibers.

[0172] (3-3) Agglutination evaluation and tensile test

[0173] The presence or absence of agglomerates was visually confirmed for each cross-linked sample, and the evaluation was performed in the same manner as in Example 1-1. In addition, for each sheet-like cross-linked sample, a tensile test was performed in the same manner as in Example 1-1, and the 50% modulus (σ50 (MPa)), tensile strength (TS (MPa)), and elongation at break (Eb (%)) were measured. In addition, each increase rate was calculated by taking the measured values ​​of Examples 3-1 to 3-4 and Comparative Examples 3-2 to 3-4 as A and the measured value of Comparative Example 3-1 as B. The measurement results and calculation results are shown in Tables 5 and 6.

[0174] (3-4) Comprehensive judgment

[0175] The criterion for comprehensive determination is the same as that of (1-5) above.

[0176]

Table 5

[0177]

[0178]

Table 6

[0179]

[0180] In the cross-linked samples of Examples 3-1 to 3-4, no aggregates larger than 10 μm were visually confirmed. In addition, the cross-linked samples of Examples 3-1 to 3-4 had an increase rate of 400% or more in 50% modulus (σ50) compared to the cross-linked sample of Comparative Example 3-1. The cross-linked samples of Examples 3-1 to 3-4 had an increase rate of 350% or more in tensile strength (TS) and an increase rate of -39% or more in elongation at break (Eb) compared to the cross-linked sample of Comparative Example 3-1.

[0181] In the cross-linked sample of Comparative Example 3-2, many aggregates of 10 μm or more and less than 50 μm were visually confirmed.

Claims

1. An intermediate, characterized in that: Include: Rubber composition; cellulose nanofibers containing carboxyl groups; and Cations with a valence of 3 or more, The cellulose nanofibers include nanofibers derived from oxidized cellulose oxidized using an N-oxyl compound.

2. The intermediate according to claim 1, wherein The trivalent or higher cations are aluminum ions and / or iron ions.

3. An intermediate, characterized in that: Include: Rubber composition; cellulose nanofibers containing carboxyl groups; and An unsaturated carboxylate containing a monovalent metal ion and / or a polymer having a repeating unit derived from an unsaturated carboxylate containing a monovalent metal ion, The cellulose nanofibers include nanofibers derived from oxidized cellulose oxidized using an N-oxyl compound.

4. The intermediate according to claim 3, wherein The unsaturated carboxylate is sodium acrylate and / or sodium methacrylate.

5. The intermediate according to any one of claims 1 to 4, wherein The rubber component is natural rubber, carboxyl-modified nitrile rubber or carboxyl-modified styrene butadiene rubber.

6. The intermediate according to any one of claims 1 to 4, wherein The cellulose nanofibers have a structure in which a carboxyl group is introduced by oxidizing the hydroxyl group at the 6th position of the glucopyranose ring constituting cellulose.

7. The intermediate according to any one of claims 1 to 4, wherein Include: 100 parts by mass of the rubber component; The cellulose nanofibers are in an amount of 10 parts by mass or more and less than 100 parts by mass; and at least one selected from the trivalent or higher cations, the unsaturated carboxylates containing monovalent metal ions, and the polymer having repeating units derived from the unsaturated carboxylates containing monovalent metal ions in an amount of 0.50 to 6.00 times the equivalent of the carboxyl groups contained in the cellulose nanofibers, The average fiber diameter of the cellulose nanofibers is 2 nm to 8 nm, and the average fiber length of the cellulose nanofibers is 200 nm to 800 nm. The cellulose nanofibers have a carboxyl group content of 1.2 mmol / g to 1.7 mmol / g.

8. A method for producing an intermediate, characterized in that: Include: A step of mixing a rubber latex, a CNF aqueous dispersion, and at least one selected from an inorganic acid polyvalent metal salt containing a trivalent or higher cation, an unsaturated carboxylate containing a monovalent metal ion, and a polymer having a repeating unit derived from the unsaturated carboxylate containing a monovalent metal ion to obtain a mixed solution, wherein the rubber latex contains 100 parts by mass of a rubber component, and the CNF aqueous dispersion is obtained by dispersing 10 parts by mass or more and less than 100 parts by mass of cellulose nanofibers containing a carboxyl group in an aqueous solvent; A step of kneading the mixed solution; a step of drying the mixed solution after the kneading step to obtain a mixture having a water content of 3% or less; and The step of kneading the mixture to obtain an intermediate, The cellulose nanofibers include nanofibers derived from oxidized cellulose oxidized using an N-oxyl compound.

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