Manufacturing method for composite material

Abstract

To provide a manufacturing method for a composite material containing fibrous cellulose and resin, in which drying can be appropriately controlled in heating and drying using a heated cylindrical dryer, and in which an exfoliation property and strength are excellent and coloration is suppressed.SOLUTION: A manufacturing method for a composite material including fibrous cellulose and a resin, comprises a step of heating and drying a dispersion liquid of a mixture of the fibrous cellulose and the resin in an aqueous medium in a heated cylindrical dryer to obtain the composite material. In the step of obtaining the composite material, A expressed in formula (A) is heated and dried to fall into a range between 0.20 and 9.00, inclusive. A=ρ+Q / {k×w×v×(x / ρ)} (A).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a composite material. [Background technology]

[0002] In recent years, materials made from renewable natural fibers have been attracting attention due to the need to replace petroleum resources and growing environmental awareness. Among natural fibers, fibrous cellulose with a fiber diameter of 10 μm to 50 μm, especially wood-derived fibrous cellulose (pulp), has been widely used mainly in paper products.

[0003] As fibrous cellulose, fine fibrous cellulose with an average fiber width of 1000 nm or less is also known. Fine fibrous cellulose has attracted attention as a new material and has a wide range of applications. For example, the development of sheets, resin composites, and thickeners containing fine fibrous cellulose is underway. Furthermore, composite materials in which fine fibrous cellulose is combined with resin emulsions and / or rubber latex are being considered.

[0004] Cited Document 1 discloses a method for producing a masterbatch, which includes a step of mixing a rubber component and a cellulose-based fiber and heating the mixture at 100 to 300°C for 5 to 600 minutes. Cited Document 2 discloses a method for producing a rubber composition containing cellulose nanofibers having phosphate groups. Cited Document 3 discloses a method for producing a masterbatch, which includes a step of mixing cellulose nanofibers having acid groups with a rubber component and heating the mixture at 100 to 300°C for 5 to 600 minutes. Cited Document 4 discloses a method for producing a composite material, which includes a step of removing water from a mixture containing fine cellulose fiber and a resin emulsion and having a solid content concentration of 1.8 mass% or less. In all of Cited Documents 1 to 4, fibrous cellulose is mixed with a resin emulsion and / or rubber latex, and then the mixture is dried by oven drying or vacuum drying to obtain a composite material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 012507 [Patent Document 2] Japanese Patent Application Publication No. 2018-131574 [Patent Document 3] Japanese Patent Application Publication No. 2018-123238 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-93882 Summary of the Invention [Problem to be solved by the invention]

[0006] When a composite material is obtained by drying a mixture of fibrous cellulose and a resin, the mixture is provided as a dispersion with a low solids concentration, which makes drying time long and reduces productivity. Furthermore, conventional oven drying or vacuum drying is disadvantageous in terms of operation. The inventors have discovered that adopting a heated cylindrical dryer significantly shortens the drying time compared to conventional oven drying or vacuum drying, resulting in superior productivity. Furthermore, they have also discovered that drying using a heated cylindrical dryer is advantageous in terms of operation, assuming continuous production, because the dried product can be obtained continuously.

[0007] On the other hand, the present inventors have found that in the case of drying using a heated cylindrical dryer, it is difficult to control the drying, and insufficient drying can result in a decrease in peelability and strength of the dried product, or conversely, excessive drying can easily result in a decrease in strength and coloration of the dried product. This is a problem specific to heat drying by conventional oven drying or vacuum drying, and does not arise in heat drying of materials other than mixtures of fibrous cellulose and resin.

[0008] The present invention solves the above-mentioned problems, and aims to provide a method for producing a composite material containing fibrous cellulose and a resin, which method allows for appropriate drying control during heating and drying using a heated cylindrical dryer, and produces a composite material that has excellent peelability and strength and suppressed discoloration. [Means for solving the problem]

[0009] As a result of investigations aimed at solving the above-mentioned problems, the inventors discovered that the above-mentioned problems can be solved by controlling the drying conditions in a process in which a dispersion of a mixture of fibrous cellulose and a resin in an aqueous medium is heated and dried in a heated cylindrical dryer to obtain a composite material, so that a value that serves as an indicator of the drying state of the composite material, calculated using a specific formula, falls within a specific numerical range, and thus completed the present invention. That is, the present invention relates to the following [1] to [5]. [1] A method for producing a composite material containing fibrous cellulose and a resin, comprising: a step of heating and drying a dispersion of a mixture of the fibrous cellulose and the resin in an aqueous medium using a heating cylindrical dryer to obtain the composite material, The method for producing a composite material, wherein in the step of obtaining the composite material, the dispersion is heated and dried so that A, represented by the following formula (A), is 0.20 or more and 9.00 or less. A=ρ+Q / {k×w×v×(x / ρ)} (A) (In the above formula (A), ρ represents the solid content concentration (mass basis) of the dispersion [-], Q represents the amount of heat per second [J / sec] given to the dispersion from the heating cylindrical dryer, k is the amount of heat required to evaporate 1g of water at 25℃, 2442 [J / g]. w represents the cylinder width [m] of the heating cylindrical dryer, v represents the cylinder rotation speed [m / sec] of the heating cylindrical dryer, x represents the thickness [μm] of the composite material. [2] The method for producing a composite material according to [1], wherein the surface temperature of the heating cylindrical dryer is 80°C or higher and 250°C or lower. [3] The method for producing a composite material according to [1] or [2], wherein the heating and drying time is from 2 seconds to 1800 seconds. [4] The method for producing a composite material according to any one of [1] to [3], wherein the heating cylindrical dryer is a drum dryer. [5] The method for producing a composite material according to any one of [1] to [4], wherein the ρ is 0.005[-] or more and 0.200[-] or less. [Effects of the Invention]

[0010] According to the present disclosure, there is provided a method for producing a composite material containing fibrous cellulose and a resin, which can appropriately control drying during heating and drying using a heated cylindrical dryer, and can produce a composite material that has excellent peelability and strength and suppressed discoloration. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic side cross-sectional view of a double drum dryer, which is an example of a heating cylindrical dryer. [Figure 2] FIG. 1 is a side view schematic diagram of a double drum dryer, which is an example of a heating cylindrical dryer. [Figure 3] 1A and 1B are a schematic diagram and a cross-sectional diagram of a sheet-like mixture before heat drying and a composite material after heat drying. [Figure 4] 1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fine fibrous cellulose having phosphorus oxo acid groups and pH. [Figure 5] 1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a carboxy group and pH. DETAILED DESCRIPTION OF THE INVENTION

[0012] Unless otherwise specified, the expressions "XX to YY" or "XX to YY" representing a numerical range mean a numerical range including the lower and upper limits, which are the endpoints. When a numerical range is described in stages, the upper and lower limits of each numerical range can be combined in any way.

[0013] [Manufacturing method for composite materials] A method for producing a composite material (hereinafter simply referred to as "composite material production method") that is one embodiment of the present invention is a method for producing a composite material containing fibrous cellulose and a resin, and includes a step of heating and drying a dispersion of a mixture of the fibrous cellulose and the resin in an aqueous medium in a heated cylindrical dryer to obtain a composite material, and in the step of obtaining the composite material, the dispersion is heated and dried so that A, represented by the following formula (A), is 0.20 or more and 9.00 or less. A=ρ+Q / {k×w×v×(x / ρ)} (A) (In the above formula (A), ρ represents the solids concentration (by mass) of the dispersion [-], Q represents the amount of heat per second [J / sec] given to the dispersion from the heated cylindrical dryer, k represents the amount of heat required to evaporate 1 g of water at 25°C (2442 [J / g]), w represents the cylinder width of the heated cylindrical dryer [m], v represents the cylinder rotation speed of the heated cylindrical dryer [m / sec], and x represents the film thickness of the composite material [μm].)

[0014] When a dispersion of a mixture of fibrous cellulose and a resin in an aqueous medium is heated and dried, the drying time is long because the mixture of fibrous cellulose and a resin is provided as a dispersion with a low solids concentration. The inventors have found that, while drying using a heated cylindrical dryer requires a significantly shorter drying time than conventional oven drying or vacuum drying, it is difficult to control the drying process, and that insufficient drying can lead to reduced peelability of the dried product, or excessive drying can lead to reduced strength and discoloration of the composite material. In contrast, the present invention provides a composite material with a good drying state by controlling the drying conditions so that a value that serves as an indicator of the drying state of the composite material, calculated using a specific formula, falls within a specific numerical range.

[0015] [Mixing process] The composite material obtained by the composite material manufacturing method contains fibrous cellulose and a resin, which also contains a rubber component. In the method for producing a composite material, first, fibrous cellulose and a resin are mixed together to prepare a dispersion of the mixture in an aqueous medium (hereinafter, simply referred to as a "dispersion of the mixture").

[0016] For example, fibrous cellulose and a resin can be mixed and dispersed in an aqueous medium to obtain a dispersion of the mixture. Alternatively, an aqueous dispersion of fibrous cellulose and an aqueous dispersion of a resin can be mixed to obtain a dispersion of the mixture. The aqueous dispersion of the resin can be, for example, at least one selected from the group consisting of a resin emulsion and a rubber latex. The mixing can be carried out using a known device such as a homomixer, homogenizer, propeller stirrer, etc. The mixing temperature is not limited, but room temperature (20 to 30° C.) is preferred. The mixing time can also be adjusted appropriately.

[0017] The resin emulsion is preferably a dispersion in which a resin is dispersed in an aqueous medium. The rubber latex is preferably a dispersion in which a rubber component is dispersed in an aqueous medium. The aqueous medium contains water as a main component, and the content of water in the entire aqueous medium is preferably 50 to 100 mass%, more preferably 100 to 200 mass%. The content is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, and even more preferably 95 to 100% by mass. In addition to water, known organic solvents may be contained to the extent that the effects of the present disclosure are not impaired.

[0018] The lower limit of the solids concentration ρ (mass basis) of the mixture dispersion is preferably 0.005 [-] or more, more preferably 0.010 [-] or more, and even more preferably 0.030 [-] or more. The upper limit of the solids concentration of the mixture dispersion is preferably 0.200 [-] or less, more preferably 0.105 [-] or less. By having the solids concentration of the mixture dispersion within the above range, the amount of energy required to remove water can be reduced, and further, aggregation of fibrous cellulose in the resulting composite material is less likely to occur, preventing a decrease in strength.

[0019] The solids concentration of the mixture dispersion can be calculated by the following formula (I) from the mass of the dried product obtained by drying a predetermined amount of the dispersion in a dryer at 105°C until it reaches a constant weight and the mass of the mixture dispersion subjected to drying. Solid concentration of the mixture dispersion [-] = mass of dried material [g] / mass of the mixture dispersion used for drying [g] (I) The solids concentration ρ of the mixture dispersion may be, for example, 0.005 to 0.200 [-], 0.005 to 0.105 [-], 0.005 to 0.080 [-], 0.010 to 0.080, or 0.040 to 0.070 [-].

[0020] In the dispersion of the mixture, the lower limit of the content of fibrous cellulose solids per 100 parts by mass of resin solids is preferably 5 parts by mass or more, more preferably 10 parts by mass or more. The upper limit of the content of fibrous cellulose per 100 parts by mass of resin is preferably 500 parts by mass or less, more preferably 50 parts by mass or less. By ensuring that the content of fibrous cellulose per 100 parts by mass of resin is within the above range, a sufficient resin reinforcing effect can be obtained by the fibrous cellulose, and the processability of the composite material can be improved. The content of the fibrous cellulose relative to 100 parts by mass of the resin may be, for example, 5 to 500 parts by mass, 10 to 50 parts by mass, or 15 to 25 parts by mass.

[0021] [Heat drying process] In the method for producing the composite material, the obtained dispersion of the mixture is heated and dried in a heating cylindrical dryer to obtain a composite material containing fibrous cellulose and a resin (hereinafter also simply referred to as "composite material").

[0022] The heating and drying step using a heating cylindrical dryer in the manufacturing method of a composite material will be described with reference to the drawings. Figure 1 is a schematic side cross-sectional view of a double drum dryer 10, which is an example of a heating cylindrical dryer, and Figure 2 is a schematic side view of the double drum dryer 10. First, a heat transfer medium (generally steam) is introduced into the rotating cylinder (drum) 1, and a mixture dispersion is introduced into the feed section 2. The introduced mixture dispersion adheres to the surface of the heated cylinder 1 as a sheet-like mixture 3, which is then quickly dried by heating. As the cylinder 1 rotates, the sheet-like mixture 3 is scraped off by a fixed scraper 4, and a composite material 5 (heat-dried material) can be obtained.

[0023] If we assume that all of the heat given to the mixture dispersion by the heated cylindrical dryer is used to evaporate the water in the mixture dispersion, the following formula (B) holds true. (r×θ / v)×Q={(x / ρ)×r×θ×w}×(c-ρ)×k (B)

[0024] First, the left side of equation (B) is explained. r is the cylinder radius of the heated cylindrical dryer [m], θ is the angle [rad] of the part where the sheet mixture contacts the surface of the cylinder, and v is is the rotation speed of the cylinder of the heated cylinder dryer [m / sec]. In other words, r × θ / v represents the time [sec] that the sheet mixture is in contact with the surface of the cylinder.

[0025] Additionally, Q is the amount of heat per second [J / sec] given to the mixture dispersion from the heated cylindrical dryer. In other words, (r×θ / v)×Q represents the amount of heat [J] given to the mixture dispersion from the heated cylindrical dryer.

[0026] Next, the right side of equation (B) will be explained. First, let us assume that the sheet-like mixture before heat drying and the composite material after heat drying are both thin rectangular parallelepipeds, and use Figure 3 to explain. x is the film thickness [μm] of the composite material (after heat drying), and ρ is the solids concentration [-] of the sheet-like mixture (before heat drying). Here, assuming that the density of the composite material (after heat drying) is the same as the density of water, and further assuming that the dimensions change only in the thickness direction before and after heat drying, x / ρ represents the film thickness [μm] of the sheet-like mixture (before heat drying).

[0027] w is the cylinder width [m] of the heated cylindrical dryer, and represents the width [m] of the sheet mixture (before heat drying) and the composite material (after heat drying). Also, r × θ represents the length [m] of the sheet mixture (before heat drying) and the composite material (after heat drying). That is, (x / ρ) × r × θ × w × 10 -6 is the volume [m 3 ].

[0028] c is the solid content concentration (mass basis) of the composite material (after heat drying) [-]. In other words, c-ρ represents the difference in solid content concentration before and after heat drying. This is added to the volume [m 3 ] multiplied by {(x / ρ)×r×θ×w×10 -6}×(c-ρ) is the volume of water evaporated from the sheet mixture [m 3 ].

[0029] k is the amount of heat required to evaporate 1 g of water at 25°C, 2442 [J / g]. Add this to the volume of water {(x / ρ)×r×θ×w×10 -6}×(c-ρ)[m 3 ]={(x / ρ)×r×θ×w}×(c-ρ)[cm 3 ] multiplied by {(x / ρ)×r×θ×w}×(c-ρ)×k represents the amount of heat [J] used to evaporate water from the sheet mixture. The value of k was calculated by dividing the heat of vaporization of water at 25°C (43.99 kJ / mol) by the molecular weight of water (18.01528 g / mol), and multiplying by 1,000 for unit conversion. The values ​​were taken from the following literature: "Science Chronology 2009", National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Maruzen Publishing Co., Ltd., November 2008, p. 364 and p. 492

[0030] Assuming that the amount of heat (r×θ / v)×Q[J] given to the mixture dispersion from the heated cylindrical dryer, calculated as above, is equal to the amount of heat used to evaporate water from the sheet-like mixture (mixture dispersion), {(x / ρ)×r×θ×w}×(c-ρ)×k[J], then equation (B) holds. Here, c is the solids concentration [-] of the composite material (after heat drying), a value that serves as an index of the drying state; setting c=A and rearranging the equation with A as the left-hand side gives the following equation (A). A=ρ+Q / {k×w×v×(x / ρ)} (A)

[0031] The present inventors have found that a value that is an index of the drying state of a composite material obtained by heat drying using a heating cylindrical dryer can be derived from formula (A). As a result of further intensive research, they have found that when a dispersion of a mixture is heat dried to obtain a composite material, drying is carried out so that A represented by formula (A) is 0.20 or more and 9.00 or less, thereby making it possible to produce a composite material that has excellent peelability and strength and is suppressed from discoloring.

[0032] If A is less than 0.20, the composite material will be insufficiently dried, resulting in poor peelability from the cylinder of the heated cylinder dryer and a decrease in strength. If A is more than 9.00, the composite material will be overdried. , strength is reduced, and coloration occurs.

[0033] The difficulty in controlling drying, which can easily lead to insufficient or excessive drying, resulting in reduced peelability and strength, and coloration, are problems specific to the present invention, in which a mixture of fibrous cellulose and a resin, which is provided as a dispersion liquid with a low solids concentration, is heated and dried in a heated cylindrical dryer. In other words, the problems of the present invention are problems that do not arise in conventional oven drying or vacuum drying, or in the heat drying of materials other than a mixture of fibrous cellulose and a resin in a heated cylindrical dryer.

[0034] In a method for producing a composite material, a dispersion of a mixture of fibrous cellulose and a resin in an aqueous medium is heated and dried in a heated cylindrical dryer, which produces a composite material with superior strength and reduced coloration compared to conventional oven drying or vacuum drying. This is thought to be because the heated cylindrical dryer can heat-dry the mixture dispersion while forming a thin film, allowing the mixture dispersion to be heated and dried more uniformly than conventional oven drying or vacuum drying.

[0035] The lower limit of the value A, which is an index of the dry state of the composite material, is preferably 0.35 or more, more preferably 0.60 or more, even more preferably 0.80 or more, and even more preferably 0.88 or more. The upper limit of A is preferably 7.50 or less, more preferably 5.00 or less, even more preferably 3.00 or less, even more preferably 2.00 or less, particularly preferably 1.50 or less, and most preferably 1.00 or less. A may be, for example, 0.25 to 7.50, 0.35 to 5.00, 0.60 to 3.00, 0.60 to 2.00, 0.80 to 1.50, 0.80 to 1.00, or 0.88 to 1.00.

[0036] The lower limit of the surface temperature of the heating cylindrical dryer is preferably 80° C. or higher, more preferably 90° C. or higher, and the upper limit of the surface temperature is preferably 250° C. or lower, more preferably 200° C. or lower. The surface temperature of the heated cylindrical dryer refers to the temperature of the cylinder surface that comes into contact with the mixture. The surface temperature of the heated cylindrical dryer may be, for example, 80 to 250°C, 90 to 200°C, or 95 to 180°C. When the surface temperature of the heated cylindrical dryer is within the above range, production efficiency is good and the value A can be easily adjusted, making it possible to obtain a dried product that is excellent in appearance and tensile strength.

[0037] The lower limit of the heat drying time in the heating cylindrical dryer is preferably 2 seconds or more, more preferably 4 seconds or more, and the upper limit of the heat drying time is preferably 1800 seconds or less, more preferably 600 seconds or less. The heat-drying time [sec] in a heating cylinder dryer refers to the time [sec] that the sheet-like mixture is in contact with the surface of the cylinder, and can be calculated by r × θ / v as described above. The heat-drying time may be, for example, 2 to 1800 seconds, 4 to 600 seconds, or 6 to 400 seconds. When the heat-drying time is within the above range, a dried product that is neither underdried nor overdried is obtained, and the product has excellent releasability from the drum.

[0038] The lower limit of the thickness x of the composite material is preferably 2.0 μm or more, more preferably 4.0 μm or more, and the upper limit of the thickness x is preferably 80.0 μm or less, more preferably 65.0 μm or less. The film thickness x of the composite material may be, for example, 2.0 to 80.0 μm, 4.0 to 65.0 μm, or 5.0 to 60.0 μm. When the film thickness x of the composite material is within the above range, the releasability from the drum is excellent. The film thickness x of the composite material varies depending on the rotation speed of the drum, It can be adjusted by the solid content concentration of the raw material. The film thickness x can be measured, for example, using a constant pressure thickness measuring device (PG-02, manufactured by TECLOCK CORPORATION). Specifically, a sheet cut into a size of 50 mm or more square is conditioned at 23°C and a relative humidity of 50% for 24 hours, and then the thickness is measured at four arbitrary points, and the average value is taken as the thickness of the sheet.

[0039] The lower limit of the thickness of the sheet-like mixture (before heat drying) calculated by x / ρ is preferably 50 μm or more, more preferably 80 μm or more, and the upper limit of the thickness of the sheet-like mixture is preferably 800 μm or less, more preferably 700 μm or less. The thickness of the sheet-like mixture may be, for example, 50 to 800 μm, 80 to 700 μm, or 90 to 600 μm. When the thickness of the sheet-like mixture is within the above range, a dried product that is excellent in releasability from the drum can be obtained.

[0040] The lower limit of the amount of heat Q per second imparted to the mixture dispersion from the heating cylindrical dryer is preferably 500 [J / sec] or more, more preferably 800 [J / sec] or more. The upper limit of the amount of heat Q is not particularly limited, but is usually 50,000 [J / sec] or less. The amount of heat Q may be, for example, 500 to 50,000 [J / sec], 800 to 30,000 [J / sec], or 1,000 to 10,000 [J / sec]. When the amount of heat Q is within the above range, it becomes easier to control the degree of drying of the raw material.

[0041] The amount of heat Q [J / sec] given per second to the mixture dispersion from the heated cylindrical dryer is the amount of heat given to the heated cylindrical dryer by its heat source per unit time. Examples of heat sources include, but are not limited to, steam boilers, hot water boilers, and electric heaters. For example, when using a steam boiler as the heat source, the heat can be calculated by multiplying the value of the latent heat of vaporization (h"-h') of steam at a constant pressure listed in the saturated steam table by the steam consumption per unit time, and then multiplying this by the heat transfer efficiency (90%). The saturated steam table can be cited from the following website. "Technical Notebook 7. Saturated Steam Table", [online], Nichias Corporation, Nichias Gasket NAVI, [searched May 26, 2022], Internet<URL:https: / / www.nichias.co.jp / gasketnavi / technology / detail.html?id=323>

[0042] When an electric heater is used as the heat source, the output efficiency is calculated by dividing the measured current value by the rated current value, and then multiplying the rated wattage by the output efficiency and then multiplying that by the heat transfer efficiency (90%).

[0043] The lower limit of the cylinder width w of the heating cylinder dryer is preferably 0.1 m or more, more preferably 0.2 m or more. The upper limit of the cylinder width w is not particularly limited, but is usually 7 m or less. The cylinder width w may be, for example, 0.1 to 7 m, or 0.2 to 5 m. When the cylinder width w is within the above range, a dried product with a uniform thickness can be obtained.

[0044] The lower limit of the cylinder rotation speed v of the heating cylinder dryer is preferably 0.001 m / sec or more, more preferably 0.002 m / sec. The upper limit of the cylinder rotation speed v is not particularly limited, but is usually 35 m / sec or less. The cylinder rotation speed v may be, for example, 0.001 to 3.5 [m / sec], or may be 0.002 to 0.2 [m / sec]. By keeping the cylinder rotation speed v within the above range, the time the mixture is in contact with the heated drum can be kept within an appropriate range, and a dried product with excellent appearance and tensile properties can be obtained.

[0045] The heating cylinder dryer used in the manufacturing process of composite materials is a machine that puts a heat medium inside the cylinder and heats it. Any conductive heating dryer that heats and dries the mixture by bringing it into contact with the surface of a heated cylinder may be used. For example, a drum dryer such as a double drum dryer, single drum dryer, or twin drum dryer may be used, as well as a cylinder dryer or Yankee dryer. Among these, from the viewpoint of heat drying efficiency, the heated cylindrical dryer is preferably a double drum dryer or a cylinder dryer. In the case of a heated cylindrical dryer like the one described above, equation (B), which shows the relationship between the amount of heat given to the mixture and the amount of heat used to evaporate the water, holds, and equation (A) also holds.

[0046] [Other processes] The method for producing a composite material may include other steps in addition to the mixing step and the heat-drying step. For example, when a dispersion containing fibrous cellulose is mixed with a rubber latex in the mixing step, an uncrosslinked rubber composition can be produced by adding a crosslinking agent and kneading the mixture.

[0047] Kneading is a process in which a crosslinking agent and other compounding ingredients are uniformly dispersed in a masterbatch (which, in this invention, refers to a composition containing a rubber component and fibrous cellulose but no crosslinking agent). Kneading can be performed using known methods, such as a Banbury mixer, kneader, or open roll. Examples of crosslinking agents include sulfur and peroxides. Other compounding ingredients include vulcanization accelerators such as sulfenamides (e.g., Nt-butyl-2-benzothiazole sulfenamide), zinc oxide, and stearic acid, vulcanization accelerator assistants, reinforcing agents such as carbon black and silica, silane coupling agents, oils, cured resins, waxes, antioxidants, peptizers, colorants, and pH adjusters, all of which are commonly used in the rubber industry. Alternatively, a rubber component can be added to the masterbatch along with the crosslinking agent and kneaded to produce a rubber composition with a diluted cellulose nanofiber concentration.

[0048] After kneading, molding may be carried out as necessary. Examples of molding equipment include mold molding, injection molding, extrusion molding, blow molding, and foam molding, and may be appropriately selected depending on the shape, application, and molding method of the final product.

[0049] Regarding crosslinking, there are no particular limitations on the temperature as long as the crosslinking reaction proceeds, but generally, a crosslinked rubber composition is obtained by heating an uncrosslinked rubber composition obtained by kneading to crosslink (also called vulcanization when sulfur is contained). The heating temperature is preferably 140°C or higher, and preferably 200°C or lower, and more preferably 180°C or lower. Therefore, the heating temperature is preferably about 140 to 200°C, and more preferably about 140 to 180°C. For crosslinking, for example, a vulcanization device that performs mold vulcanization, can vulcanization, continuous vulcanization, etc. can be used.

[0050] [Fibrous cellulose] The fibrous cellulose is not particularly limited, and any known fibrous cellulose can be used. The upper limit of the fiber width of the fibrous cellulose (hereinafter simply referred to as "fibrous cellulose") used in the manufacturing method of the composite material is preferably 1000 nm or less, more preferably 100 nm or less, even more preferably 50 nm or less, even more preferably 20 nm or less, and particularly preferably 10 nm or less. In this specification, fibrous cellulose having a fiber width of 1000 nm or less is also referred to as fine fibrous cellulose, although coarse fibrous cellulose having a fiber width of more than 1000 nm may also be used.

[0051] The average fiber width of the fibrous cellulose is, for example, 1000 nm or less. The average fiber width of the fibrous cellulose is, for example, preferably 2 nm or more and 1000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and particularly preferably 2 nm or more and 10 nm or less. The fibrous cellulose is, for example, monofilament cellulose.

[0052] The fiber width of fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fibrous cellulose with a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for TEM observation. When wide fibers are included, an SEM image of the surface cast onto glass may be observed. Next, electron microscope images are observed at magnifications of 1000x, 5000x, 10000x, or 50000x, depending on the width of the fibers to be observed. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions.

[0053] (1) Draw a line X at any point in the observed image, and 20 or more fibers intersect with the line X. (2) Draw a line Y that intersects the line perpendicularly within the same image, and 20 or more fibers intersect the line Y.

[0054] For observation images that satisfy the above conditions, the widths of fibers intersecting with lines X and Y are visually read. In this way, three or more sets of observation images of at least the surface portions that do not overlap each other are obtained. Next, for each image, the widths of fibers intersecting with lines X and Y are read. In this way, the widths of at least 20 fibers x 2 x 3 = 120 fibers are read. The average of the read fiber widths is then taken as the number-average fiber width of the fibrous cellulose.

[0055] The fiber length of the fibrous cellulose is not particularly limited, but is preferably, for example, 0.1 μm to 1000 μm, more preferably 0.1 μm to 800 μm, and even more preferably 0.1 μm to 600 μm. By keeping the fiber length within the above range, destruction of the crystalline regions of the fibrous cellulose can be suppressed. The fiber length of the fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

[0056] The fibrous cellulose preferably has a type I crystal structure. The presence of type I crystal structure in fibrous cellulose can be identified by a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromated with graphite. Specifically, it can be identified by the presence of two typical peaks at two positions: 2θ=14° to 17° and 2θ=22° to 23°. The proportion of type I crystal structure in the fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. The degree of crystallinity can be determined by measuring the X-ray diffraction profile and using the pattern in a conventional manner (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0057] The axial ratio (fiber length / fiber width) of the fibrous cellulose is not particularly limited, but is preferably, for example, from 50 to 10,000, and more preferably from 100 to 1,000. By setting the axial ratio to the above lower limit or more, a composite material containing fibrous cellulose can be easily formed. By setting the axial ratio to the above upper limit or less, it is preferable in that, for example, when treating the fibrous cellulose as a dispersion, handling such as dilution becomes easier.

[0058] The fibrous cellulose in this embodiment has, for example, both crystalline regions and amorphous regions. Fibrous cellulose having both crystalline regions and amorphous regions and having an axial ratio within the above range is realized by the method for producing fibrous cellulose described below.

[0059] The fine fibrous cellulose in this embodiment preferably has an ionic substituent. The ionic substituent may include, for example, either or both of an anionic group and a cationic group. In this embodiment, the ionic substituent is preferably an anionic group. It is particularly preferred that the ionic substituent has an ionic group. The ionic substituent is preferably a group that is introduced into the fine fibrous cellulose via an ester bond or an ether bond, and more preferably a group that is introduced into the fine fibrous cellulose via an ester bond. In this case, the ester bond is preferably formed by dehydration condensation of the fine fibrous cellulose and a compound that serves as the ionic substituent.

[0060] Examples of anionic groups as ionic groups include phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups (sometimes simply referred to as phosphorus oxoacid groups), carboxy groups or substituents derived from carboxy groups (sometimes simply referred to as carboxy groups), sulfur oxoacid groups or substituents derived from sulfur oxoacid groups (sometimes simply referred to as sulfur oxoacid groups), xanthate groups or substituents derived from xanthate groups (sometimes simply referred to as xanthate groups), phosphonic groups or substituents derived from phosphonic groups, phosphine groups or substituents derived from phosphine groups, sulfonic groups or substituents derived from sulfonic groups, and carboxyalkyl groups. Among these, the anionic group is preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxy group, a sulfur oxoacid group, a substituent derived from a sulfur oxoacid group, a carboxymethyl group, a carboxyethyl group, and a sulfone group, more preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxy group, a sulfur oxoacid group, and a substituent derived from a sulfur oxoacid group, and particularly preferably a phosphorus oxoacid group. By introducing a phosphorus oxoacid group as the anionic group, the dispersibility of the fine fibrous cellulose can be further improved, for example, even under alkaline or acidic conditions, making it easier to obtain a high-strength, highly transparent sheet. Examples of cationic groups as ionic groups include ammonium groups, phosphonium groups, sulfonium groups, etc. Among these, the cationic group is preferably an ammonium group.

[0061] The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group is, for example, a substituent represented by the following formula (1). A plurality of substituents represented by the following formula (1) may be introduced into each fine fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (1) may be the same or different.

[0062] [ka]

[0063] In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (where a=b×m). At least one of the n α and α' is O. - and the rest are R or OR. Note that all of α and α' are O - The n α's may all be the same or may be different. b+ is a cation of one or more valences consisting of organic or inorganic substances.

[0064] R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated It is a cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived from any of these. In formula (1), n ​​is preferably 1.

[0065] Examples of saturated linear hydrocarbon groups include, but are not limited to, methyl, ethyl, n-propyl, and n-butyl groups. Examples of saturated branched hydrocarbon groups include, but are not limited to, i-propyl and t-butyl groups. Examples of saturated cyclic hydrocarbon groups include, but are not limited to, cyclopentyl and cyclohexyl groups. Examples of unsaturated linear hydrocarbon groups include, but are not limited to, vinyl and allyl groups. Examples of unsaturated branched hydrocarbon groups include, but are not limited to, i-propenyl and 3-butenyl groups. Examples of unsaturated cyclic hydrocarbon groups include, but are not limited to, cyclopentenyl and cyclohexenyl groups. Examples of aromatic groups include, but are not limited to, phenyl and naphthyl groups.

[0066] In addition, the derivative group in R is a carboxy group, a carboxylate group (-COO -), a hydroxy group, an amino group, an ammonium group, or another functional group to which at least one functional group selected from the group consisting of hydroxy, amino, and ammonium groups is added or substituted, but is not particularly limited. The number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphorus oxoacid group can be set within an appropriate range, which facilitates penetration into the fiber raw material and increases the yield of fine fibrous cellulose. When multiple Rs are present in formula (1) or when multiple types of substituents represented by formula (1) are introduced into the fine fibrous cellulose, the multiple Rs may be the same or different.

[0067] β b+ is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic onium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. It should be noted that in formula (1), β b+ When a plurality of β b+ may be the same or different. The monovalent or higher cations consisting of organic or inorganic substances include β b+ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0068] More specifically, examples of the phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group include a phosphate group (-POH), a salt of a phosphate group, a phosphorous acid (phosphonic acid) group (-POH), and a salt of a phosphite (phosphonic acid) group. The phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group may also be a group in which a phosphate group is condensed (e.g., a pyrophosphate group), a group in which a phosphonic acid is condensed (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), or an alkyl phosphonic acid group (e.g., a methylphosphonic acid group).

[0069] The sulfur oxoacid group (a sulfur oxoacid group or a substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). A plurality of types of substituents represented by the following formula (2) may be introduced into each fine fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (2) The substituents represented by the formula (I) may be the same or different.

[0070] [ka]

[0071] In formula (2), b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (where 1 = b × m). When n is 2 or more, multiple p's may be the same number or different numbers. In formula (2), β b+is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic onium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. Note that when multiple types of substituents represented by formula (2) are introduced into the fine fibrous cellulose, the multiple β b+ may be the same or different. The monovalent or higher cations consisting of organic or inorganic substances include β b+ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0072] The amount of ionic substituent introduced into the fine fibrous cellulose is, for example, preferably 0.10 mmol / g or more per 1 g (mass) of fine fibrous cellulose, more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, and particularly preferably 0.60 mmol / g or more. The amount of ionic substituent introduced into the fine fibrous cellulose is, for example, preferably 5.20 mmol / g or less per 1 g (mass) of fine fibrous cellulose, more preferably 3.65 mmol / g or less, even more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, even more preferably 2.00 mmol / g or less, even more preferably 1.50 mmol / g or less, and particularly preferably 1.00 mmol / g or less. Here, the denominator in the unit mmol / g is calculated based on the fact that the counter ion of the ionic substituent is a hydrogen ion (H +By setting the amount of ionic substituent introduced within the above range, it is possible to easily refine the fiber raw material and improve the stability of the fine fibrous cellulose.

[0073] The amount of ionic substituents introduced into the fine fibrous cellulose can be measured, for example, by neutralization titration after the cellulose fibers have been subjected to a micronization treatment. In the measurement by neutralization titration, the amount introduced is measured by determining the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to a slurry containing the obtained fine fibrous cellulose.

[0074] 4 is a graph showing the relationship between the amount of NaOH added dropwise to a slurry containing fine fibrous cellulose having phosphorus oxo acid groups and pH. The amount of phosphorus oxo acid groups introduced into the fine fibrous cellulose is measured, for example, as follows. First, ion-exchanged water was added to the target cellulose fiber, and the solid content was adjusted to 0.2% by mass. This slurry is treated four times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (slurry) containing fine fibrous cellulose. The fine fibrous cellulose dispersion is then treated with a strongly acidic ion exchange resin. Next, the change in pH is observed while adding aqueous sodium hydroxide solution, and a titration curve like the one shown in the upper part of Figure 4 is obtained. The titration curve shown in the upper part of Figure 4 plots the measured pH against the amount of alkali added, while the titration curve shown in the lower part of Figure 4 plots the pH increment (derivative value) (1 / mmol) against the amount of alkali added. In this neutralization titration, two points of maximum increment (derivative value of pH with respect to the amount of alkali added) are confirmed on the curve plotting the measured pH against the amount of alkali added. Of these, the first maximum increment obtained after starting to add alkali is called the first endpoint, and the next maximum increment obtained is called the second endpoint. The amount of alkali required from the start of titration to the first endpoint is equal to the amount of first dissociated acid from the fine fibrous cellulose contained in the slurry used for titration; the amount of alkali required from the first endpoint to the second endpoint is equal to the amount of second dissociated acid from the fine fibrous cellulose contained in the slurry used for titration; and the amount of alkali required from the start of titration to the second endpoint is equal to the total amount of dissociated acid from the fine fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali required from the start of titration to the first endpoint by the solids content (g) in the slurry to be titrated is the amount of phosphorus oxo acid groups introduced (mmol / g). Note that the term "amount of phosphorus oxo acid groups introduced" (or "amount of phosphorus oxo acid groups") simply refers to the amount of first dissociated acid. In Figure 4, the region from the start of titration to the first endpoint is referred to as Region 1, and the region from the first endpoint to the second endpoint is referred to as Region 2. For example, if the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the apparent amount of weakly acidic groups in the phosphorus oxoacid group (also referred to herein as the second dissociated acid amount) decreases, and the amount of alkali required in Region 2 is less than the amount required in Region 1. On the other hand, the amount of strongly acidic groups in the phosphorus oxoacid group (also referred to herein as the first dissociated acid amount) corresponds to the amount of phosphorus atoms regardless of whether condensation occurs. Furthermore, if the phosphorus oxoacid group is a phosphite group, the phosphorus oxoacid group no longer contains weakly acidic groups, and the amount of alkali required in Region 2 is reduced or may even be zero. In this case, there is only one point on the titration curve where the pH increment is maximized.

[0075] The above-mentioned amount of introduced phosphorus oxoacid groups (mmol / g) indicates the amount of phosphorus oxoacid groups in the acid-form fine fibrous cellulose (hereinafter referred to as the amount of phosphorus oxoacid groups (acid form)), since the denominator indicates the mass of the acid-form fine fibrous cellulose. On the other hand, when the counter ions of the phosphorus oxoacid groups are substituted with an arbitrary cation C so as to be charge equivalent, the amount of phosphorus oxoacid groups in the fine fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of phosphorus oxoacid groups (C form)) can be determined by converting the denominator to the mass of the fine fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Amount of phosphorus oxoacid groups (C type) = Amount of phosphorus oxoacid groups (acid type) / {1 + (W - 1) × P / 1000} P [mmol / g]: total amount of anions derived from phosphorus oxoacid groups in fibrous cellulose (total amount of dissociated acid from phosphorus oxoacid groups) W: Formula weight per valence of cation C (e.g., Na is 23, Al is 9)

[0076] 5 is a graph showing the relationship between the amount of NaOH added dropwise to a dispersion of fine fibrous cellulose having carboxy groups as ionic substituents and pH. The amount of carboxy groups introduced into the fine fibrous cellulose is measured, for example, as follows. First, ion-exchanged water is added to the cellulose fiber to be treated to prepare a slurry with a solid content of 0.2% by mass. This slurry is treated four times at a pressure of 200 MPa in a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine cellulose-containing fine fibrous cellulose. A fibrous cellulose dispersion (slurry) is obtained, and the fine fibrous cellulose dispersion is then treated with a strongly acidic ion exchange resin. Next, the change in pH was observed while adding aqueous sodium hydroxide solution, and a titration curve like that shown in the upper part of Figure 5 was obtained. The titration curve shown in the upper part of Figure 5 plots the measured pH against the amount of added alkali, while the titration curve shown in the lower part of Figure 5 plots the pH increment (derivative value) (1 / mmol) against the amount of added alkali. In this neutralization titration, a single point was identified in the curve plotting the measured pH against the amount of added alkali, where the increment (derivative value of pH with respect to the amount of added alkali) reached a maximum. This maximum point is called the first endpoint. Here, the region from the start of the titration to the first endpoint in Figure 5 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the dispersion used for titration. The amount of alkali required in the first region of the titration curve (mmol) is then divided by the solids content (g) in the dispersion containing the fine fibrous cellulose to be titrated to calculate the amount of carboxyl groups introduced (mmol / g).

[0077] The above-mentioned amount of carboxy groups introduced (mmol / g) indicates the amount of carboxy groups in the acid-form fine fibrous cellulose (hereinafter referred to as the amount of carboxy groups (acid form)), since the denominator is the mass of the acid-form fine fibrous cellulose. On the other hand, when the counter ions of the carboxy groups are substituted with any cation C so as to be charge equivalent, the amount of carboxy groups in the fine fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of carboxy groups (C form)) can be determined by converting the denominator to the mass of the fine fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Amount of carboxyl group (C type) = Amount of carboxyl group (acid type) / {1 + (W - 1) × (Amount of carboxyl group (acid type)) / 1000} W: Formula weight per valence of cation C (for example, Na is 23, Al is 9)

[0078] When measuring the amount of ionic substituents by titration, adding too much sodium hydroxide solution or titrating too quickly can result in lower ionic substituent levels than expected, leading to inaccurate results. For example, a suitable amount and interval is to titrate 10–50 μL of 0.1 N sodium hydroxide solution every 5–30 seconds. To eliminate the influence of carbon dioxide dissolved in the fine fibrous cellulose dispersion, it is also recommended to measure the amount of ionic substituents while blowing an inert gas such as nitrogen into the slurry from 15 minutes before the start of titration until the end of titration.

[0079] The amount of sulfate ester groups and sulfone groups introduced into the fine fibrous cellulose can be determined by wet ashing the obtained fine fibrous cellulose using perchloric acid and concentrated nitric acid, diluting it at an appropriate ratio, and measuring the amount of sulfur by ICP atomic emission spectrometry. The amount of sulfur divided by the bone-dry mass of the fine fibrous cellulose used is taken as the amount of sulfur oxoacid groups and sulfonic acid groups (unit: mmol / g).

[0080] To obtain fine fibrous cellulose having an ionic substituent introduced therein, it is preferable to have an ionic substituent introduction step for introducing an ionic substituent into the above-mentioned cellulose-containing fiber raw material, a washing step, an alkali treatment step (neutralization step), and a defibration treatment step in this order, and an acid treatment step may be included instead of or in addition to the washing step. Examples of the ionic substituent introduction step include a phosphorus oxo acid group introduction step, a carboxy group introduction step, a sulfur oxo acid group introduction step, a xanthate group introduction step, a phosphonic or phosphine group introduction step, a sulfonic group introduction step, and a cationic group introduction step. Each of these steps will be explained below.

[0081] <Phosphorus oxoacid group introduction step> When obtaining cellulose fibers having ionic substituents, the ionic substituents are preferably added to the cellulose fibers before the pulverization treatment step. It is preferable to provide a substituent introduction step. An example of the ionic substituent introduction step is a phosphorus oxo acid group introduction step. The phosphorus oxo acid group introduction step is a step of reacting at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing phosphorus oxo acid groups by reacting with hydroxyl groups possessed by a cellulose-containing fiber raw material with the cellulose-containing fiber raw material. This step results in the production of cellulose fibers having phosphorus oxo acid groups.

[0082] In the phosphorus oxoacid group introduction step according to this embodiment, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). Alternatively, the cellulose-containing fiber raw material with compound A may be reacted in the absence of compound B.

[0083] One example of a method for reacting compound A with a fiber raw material in the presence of compound B is to mix compound A and compound B with a fiber raw material in a dry, wet, or slurry state. Among these methods, using a dry or wet fiber raw material is preferred because of the high uniformity of the reaction, and using a dry fiber raw material is particularly preferred. The form of the fiber raw material is not particularly limited, but is preferably a cotton-like or thin sheet form. Compound A and compound B may be added to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state heated to or above their melting point. Among these methods, adding compound A and compound B in the form of a solution dissolved in a solvent, particularly an aqueous solution, is preferred because of the high uniformity of the reaction. Compound A and compound B may be added to the fiber raw material simultaneously, separately, or as a mixture. The method for adding compound A and compound B is not particularly limited. When compound A and compound B are in solution form, the fiber raw material may be immersed in the solution and allowed to absorb the liquid before being removed, or the solution may be added dropwise to the fiber raw material. Alternatively, the required amounts of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material, and then the excess compound A and compound B may be removed by squeezing or filtration.

[0084] The compound A used in this embodiment may be any compound that has a phosphorus atom and can form an ester bond with cellulose, including, but not limited to, phosphoric acid or a salt thereof, phosphorous acid or a salt thereof, dehydrated condensed phosphoric acid or a salt thereof, and phosphoric anhydride (diphosphorus pentoxide). Phosphoric acids of various purities can be used, such as 100% phosphoric acid (orthophosphoric acid) and 85% phosphoric acid. Phosphorous acids include 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acids are formed by the condensation of two or more molecules of phosphoric acid through a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, which can be neutralized to various degrees. Among these, from the viewpoints of high efficiency of introduction of phosphate groups, ease of further improving defibration efficiency in the defibration step described below, low cost, and ease of industrial application, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid, or phosphorous acid, sodium salt of phosphorous acid, potassium salt of phosphorous acid, ammonium salt of phosphorous acid are preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid, sodium phosphite are more preferred.

[0085] The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted into the amount of phosphorus atoms, the amount of phosphorus atoms added to the fiber raw material (bone dry mass) is preferably 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, the amount of phosphorus atoms added to the fiber raw material By setting the amount to the above upper limit or less, it is possible to achieve a balance between the effect of improving the yield and the cost.

[0086] As described above, compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. Furthermore, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved.

[0087] The amount of compound B added relative to the fiber raw material (bone dry mass) is not particularly limited, but is preferably, for example, 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, and even more preferably 100% by mass or more and 350% by mass or less.

[0088] In the reaction of a fiber material containing cellulose with compound A, the reaction system may contain, in addition to compound B, amides or amines, for example. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is known to function as a particularly good reaction catalyst.

[0089] In the phosphorus oxo acid group introduction step, it is preferable to add or mix compound A or the like to the fiber raw material and then heat-treat the fiber raw material. The heat treatment temperature is preferably selected so that the phosphorus oxo acid group can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably, for example, from 50°C to 300°C, more preferably from 100°C to 250°C, and even more preferably from 130°C to 200°C. Furthermore, various types of equipment having heat transfer media can be used for the heat treatment, including, for example, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized-bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized-bed dryer, a flash dryer, a reduced-pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, and a high-frequency dryer.

[0090] In the heat treatment according to this embodiment, for example, compound A may be added to a thin sheet-like fiber raw material by impregnation or other methods, followed by heating, or heating while kneading or stirring the fiber raw material and compound A in a kneader or the like. This makes it possible to suppress unevenness in the concentration of compound A in the fiber raw material and more uniformly introduce phosphorus oxoacid groups onto the surface of the cellulose fibers contained in the fiber raw material. This is thought to be because, when water molecules move to the surface of the fiber raw material as it dries, dissolved compound A is attracted to the water molecules by surface tension, preventing it from migrating to the surface of the fiber raw material (i.e., causing unevenness in the concentration of compound A).

[0091] Furthermore, the heating device used for the heat treatment is preferably one that can constantly discharge, to the outside of the device system, for example, the water retained in the slurry and the water generated in the dehydration condensation (phosphorylation) reaction between compound A and hydroxyl groups contained in cellulose or the like in the fiber raw material. Examples of such heating devices include an oven with a blower system. Constantly discharging the water from the device system can suppress the hydrolysis reaction of phosphate ester bonds, which is the reverse reaction of phosphate esterification, as well as the acid hydrolysis of sugar chains in the fiber. This makes it possible to obtain fine fibrous cellulose with a high axial ratio.

[0092] The heat treatment time is preferably from 1 second to 300 minutes after the water content has been substantially removed from the fiber raw material, more preferably from 1 second to 1,000 seconds, and even more preferably from 10 seconds to 800 seconds. In this embodiment, the amount of phosphorus oxo acid groups introduced can be kept within a preferred range by setting the heating temperature and heating time within appropriate ranges.

[0093] The phosphorus oxo acid group introduction step may be carried out at least once, but may also be carried out twice or more. By carrying out the phosphorus oxo acid group introduction step twice or more, a large number of phosphorus oxo acid groups can be introduced into the fiber raw material.

[0094] The amount of phosphorus oxoacid groups introduced into the fiber raw material is, for example, preferably 0.10 mmol / g or more per gram (mass) of cellulose fiber, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and particularly preferably 1.00 mmol / g or more. The amount of phosphorus oxoacid groups introduced into the fiber raw material is, for example, preferably 5.20 mmol / g or less per gram (mass) of cellulose fiber, more preferably 3.65 mmol / g or less, and even more preferably 3.00 mmol / g or less. By keeping the amount of phosphorus oxoacid groups introduced within the above range, it is possible to facilitate the finening of cellulose fibers in the fine-finishing treatment step and improve the stability of the fine fibrous cellulose.

[0095] <Carboxy group introduction step> The ionic substituent introduction step may include a carboxyl group introduction step, which is carried out by subjecting a cellulose-containing fiber raw material to an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, or TEMPO oxidation treatment, or by treating the cellulose-containing fiber raw material with a compound having a carboxylic acid-derived group or a derivative thereof, or an acid anhydride of a compound having a carboxylic acid-derived group or a derivative thereof.

[0096] The compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. Furthermore, the derivative of the compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include imidized products of acid anhydrides of compounds having carboxy groups, and derivatives of acid anhydrides of compounds having carboxy groups. The imidized products of acid anhydrides of compounds having carboxy groups are not particularly limited, but examples thereof include imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0097] The acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, etc. Furthermore, the derivative of an acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include acid anhydrides of compounds having carboxy groups such as dimethylmaleic anhydride, diethylmaleic anhydride, diphenylmaleic anhydride, etc. in which at least some of the hydrogen atoms have been substituted with substituents such as alkyl groups or phenyl groups.

[0098] When TEMPO oxidation treatment is performed in the carboxyl group introduction step, it is preferable to perform the treatment under conditions of pH 6 or higher and 8 or lower. Such treatment is also called neutral TEMPO oxidation treatment. The neutral TEMPO oxidation treatment is carried out by, for example, adding pulp as a fiber raw material, a nitroxy radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and hypochlorite as a sacrificial reagent to a sodium phosphate buffer solution (pH = 6.8). This can be achieved by adding sodium hypochlorite. Furthermore, by adding sodium chlorite, the aldehydes generated during the oxidation process can be efficiently oxidized to carboxyl groups. TEMPO oxidation treatment may also be carried out under conditions of a pH of 10 to 11. This type of treatment is also called alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be carried out, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp as a fiber raw material.

[0099] The amount of carboxyl groups introduced into cellulose fibers varies depending on the type of substituent. For example, when carboxyl groups are introduced by TEMPO oxidation, the amount is preferably 0.10 mmol / g or more per gram (mass) of cellulose fibers, more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, and particularly preferably 0.60 mmol / g or more. Furthermore, the amount of carboxyl groups introduced into cellulose fibers is preferably 3.65 mmol / g or less, more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, even more preferably 2.00 mmol / g or less, even more preferably 1.50 mmol / g or less, and particularly preferably 1.00 mmol / g or less. Furthermore, when the substituent is a carboxymethyl group, the amount of carboxyl groups introduced may be 5.8 mmol / g or less per gram (mass) of cellulose fibers. By keeping the amount of carboxyl groups introduced within the above range, cellulose fibers can be easily refined in the refinement process and the stability of the fine fibrous cellulose can be improved.

[0100] <Sulfonic group introduction step> The ionic substituent introduction step may include a sulfonic group introduction step, in which hydroxyl groups in a fiber raw material containing cellulose react with sulfur oxoacid to obtain cellulose fibers having sulfonic groups (sulfonic group-introduced fibers).

[0101] In the sulfonic acid group introduction step, instead of compound A in the above-described <Phosphorus Oxo Acid Group Introduction Step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfonic acid groups by reacting with hydroxyl groups in a cellulose-containing fiber raw material is used. Compound C may be any compound having a sulfur atom and capable of forming an ester bond with cellulose, including, but not limited to, sulfuric acid or its salts, sulfurous acid or its salts, and sulfuric acid amides. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid). Sulfurous acid can be 5% aqueous sulfurous acid. Sulfates or sulfites can be lithium, sodium, potassium, or ammonium salts of sulfates or sulfites, which can be neutralized to various degrees. Sulfamic acid or the like can be used as the sulfuric acid amide. In the sulfonic acid group introduction step, it is preferable to use compound B in the above-described <Phosphorus Oxo Acid Group Introduction Step> in the same manner.

[0102] In the sulfonic acid introduction step, the cellulose raw material is preferably mixed with an aqueous solution containing sulfur oxoacid and urea and / or a urea derivative, and then the cellulose raw material is subjected to a heat treatment. The heat treatment temperature is preferably selected so that sulfonic acid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. The heat treatment temperature is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

[0103] In the heat treatment step, it is preferable to heat until the moisture is substantially eliminated. Therefore, the heat treatment time is determined depending on the moisture content, sulfur oxoacid, urea and the like contained in the cellulose raw material. The heating time varies depending on the amount of the aqueous solution containing the urea derivative and / or the urea derivative added, but is preferably 10 seconds or more and 10,000 seconds or less. For example, a device having a variety of heat media can be used for the heat treatment, such as a hot air dryer, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, an airflow dryer, a reduced-pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, or a high-frequency dryer.

[0104] The amount of sulfonic groups introduced into the cellulose raw material is preferably 0.05 mmol / g or more, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, and particularly preferably 0.50 mmol / g or more. Furthermore, the amount of sulfonic groups introduced into the cellulose raw material is preferably 5.00 mmol / g or less, more preferably 3.00 mmol / g or less. By keeping the amount of sulfonic groups introduced within the above range, it is possible to facilitate the fine pulverization of cellulose fibers in the fine pulverization treatment step and to increase the stability of the fine fibrous cellulose.

[0105] <Oxidation step using a chlorine-based oxidizing agent (second carboxyl group introduction step)> The ionic substituent introduction step may include an oxidation step using a chlorine-based oxidizing agent, in which a chlorine-based oxidizing agent is added to a wet or dry fiber raw material having a hydroxyl group to cause a reaction, thereby introducing a carboxyl group into the fiber raw material.

[0106] Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorites, chlorous acid, chlorites, chloric acid, chlorates, perchloric acid, perchlorates, and chlorine dioxide. From the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling, the chlorine-based oxidizing agent is preferably sodium hypochlorite, sodium chlorite, or chlorine dioxide. When adding a chlorine-based oxidizing agent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or may be dissolved in an appropriate solvent and then added.

[0107] The concentration of the chlorine-based oxidizing agent in the solution in the oxidation step using the chlorine-based oxidizing agent, converted into an effective chlorine concentration, is preferably 1 to 1,000% by mass, more preferably 5 to 500% by mass, and even more preferably 10 to 100% by mass. The amount of the chlorine-based oxidizing agent added per 100 parts by mass of the fiber raw material is preferably 1 to 100,000 parts by mass, more preferably 10 to 10,000 parts by mass, and even more preferably 100 to 5,000 parts by mass.

[0108] The reaction time with the chlorine-based oxidizing agent in the oxidation step using the chlorine-based oxidizing agent varies depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. The pH during the reaction is preferably from 5 to 15, more preferably from 7 to 14, and even more preferably from 9 to 13. At the start of the reaction, the pH is preferably maintained constant (for example, pH 11) during the reaction by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0109] <Xanthate group introduction step> The process for producing fine fibrous cellulose may include a xanthate group introduction step as an ionic substituent introduction step. In the xanthate group introduction step, hydroxyl groups in a fiber raw material containing cellulose are substituted with xanthate groups represented by the following formula (3), thereby obtaining cellulose fibers having xanthate groups (xanthate group-introduced fibers). -OCSS - M + ...(3) where M + is at least one selected from the group consisting of hydrogen ions, monovalent metal ions, ammonium ions, and aliphatic or aromatic ammonium ions.

[0110] In the xanthate group introduction process, the cellulose-containing fiber raw material is first treated with an alkaline solution to obtain alkali cellulose. Examples of alkaline solutions include an aqueous alkali metal hydroxide solution and an aqueous alkaline earth metal hydroxide solution. Among these, the alkaline solution is preferably an aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide, and particularly preferably an aqueous sodium hydroxide solution. When the alkaline solution is an aqueous alkali metal hydroxide solution, the alkali metal hydroxide concentration in the aqueous alkali metal hydroxide solution is preferably 4% by mass or more, more preferably 5% by mass or more. Furthermore, the alkali metal hydroxide concentration in the aqueous alkali metal hydroxide solution is preferably 9% by mass or less. By setting the alkali metal hydroxide concentration at or above the lower limit, the mercerization of cellulose can be sufficiently promoted, the amount of by-products generated during the subsequent xanthation can be reduced, and as a result, the yield of xanthate group-introduced fiber can be increased. This allows the defibration process described below to be performed more effectively. Furthermore, by setting the alkali metal hydroxide concentration to the above upper limit or less, it is possible to prevent the aqueous alkali metal hydroxide solution from penetrating into the crystalline regions of cellulose while allowing mercerization to proceed, which makes it easier to maintain the cellulose type I crystal structure and further increases the yield of fine fibrous cellulose.

[0111] The alkali treatment time is preferably 30 minutes or more, more preferably 1 hour or more. The alkali treatment time is preferably 6 hours or less, more preferably 5 hours or less. By setting the alkali treatment time within the above range, the final yield can be increased, and productivity can be improved.

[0112] The alkali cellulose obtained by the alkali treatment is preferably subjected to solid-liquid separation to remove as much aqueous solution as possible. This reduces the water content during the subsequent xanthate treatment, thereby accelerating the reaction. As a method for solid-liquid separation, a general dehydration method such as centrifugation or filtration can be used. The concentration of alkali metal hydroxide contained in the alkali cellulose after solid-liquid separation is preferably 3% by mass or more and 8% by mass or less based on the total mass of the alkali cellulose after solid-liquid separation.

[0113] In the xanthate group introduction step, a xanthate treatment step is carried out after alkali treatment. In the xanthate treatment step, alkali cellulose is reacted with carbon disulfide (CS2) to form (-O - Na + ) group (-OCSS - Na + ) group to obtain xanthate group-introduced fibers. In the above, the metal ions introduced into the alkali cellulose are typically Na + However, similar reactions occur with other alkali metal ions.

[0114] In the xanthation treatment, it is preferable to supply 10% by mass or more of carbon disulfide relative to the bone dry mass of cellulose in the alkali cellulose. Furthermore, in the xanthation treatment, the contact time between carbon disulfide and alkali cellulose is preferably 30 minutes or more, more preferably 1 hour or more. Although the contact of carbon disulfide with alkali cellulose allows xanthation to proceed quickly, it takes time for carbon disulfide to penetrate into the interior of the alkali cellulose, so it is preferable to set the reaction time within the above range. On the other hand, the contact time between carbon disulfide and alkali cellulose can be 6 hours or less, which allows sufficient penetration into the alkali cellulose mass after dehydration, allowing reactive xanthation to be almost completed.

[0115] The reaction temperature in the xanthate treatment is preferably 46°C or less. By setting the reaction temperature within the above range, it is easy to suppress the decomposition of alkali cellulose. In addition, by setting the reaction temperature within the above range, it is easy to react uniformly, so that the generation of by-products can be suppressed, and further, the removal of the generated xanthate group can be suppressed.

[0116] The amount of xanthate group introduced in the xanthate group introduction step is preferably 0.60 mmol / g or more per 1 g (mass) of fiber raw material, more preferably 0.70 mmol / g or more, even more preferably 0.80 mmol / g or more, even more preferably 1.00 mmol / g or more, and particularly preferably 1.20 mmol / g or more. In addition, the amount of xanthate group introduced is, for example, preferably 5.00 mmol / g or less per 1 g (mass) of fiber raw material, more preferably 3.00 mmol / g or less. By setting the amount of xanthate group introduced within the above range, it becomes easier to obtain a sheet with excellent transparency and excellent yellowing resistance.

[0117] <Phosphonic or Phosphine Group Introduction Step (Phosphoalkylation Step)> The ionic substituent introduction step may include a phosphonic or phosphine group introduction step (phosphoalkylation step). In the phosphoalkylation step, a compound having a reactive group and a phosphonic or phosphine group (compound E) is used as an essential component. A ), an optional alkali compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having hydroxyl groups and reacted to introduce phosphonic or phosphine groups into the fiber raw material.

[0118] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E A Examples of suitable compounds include vinyl phosphonic acid, phenyl vinyl phosphonic acid, and phenyl vinyl phosphinic acid. From the viewpoints of the efficiency of introducing substituents, the defibration efficiency, cost, and ease of handling, Compound E A is preferably vinylphosphonic acid. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0119] Compound E A When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0120] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0121] Compound E AThe amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0122] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0123] <Sulfonic Group Introduction Step (Sulfoalkylation Step) (Second Sulfonic Group Introduction Step)> The ionic substituent introduction step may include a sulfone group introduction step (sulfoalkylation step). In the sulfoalkylation, a compound having a reactive group and a sulfone group as essential components is introduced. Compound (Compound E B ) and, as an optional component, an alkali compound and a compound B selected from the aforementioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a sulfonic acid group into the fiber raw material.

[0124] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E B Examples of suitable olefin sulfonates include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, and 2-acrylamido-2-methylpropanesulfonic acid. Among these, compound E is particularly preferred in terms of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. B is preferably sodium vinyl sulfonate. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0125] Compound EB When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0126] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0127] Compound E B The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0128] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 15 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0129] <Carboxyalkylation step (third carboxy group introduction step)> The ionic substituent introduction step may include a carboxyalkylation step. As an essential component, a compound having a reactive group and a carboxy group (compound E C ), an optional alkaline compound, and compound B selected from the aforementioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a carboxyl group into the fiber raw material.

[0130] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E CAs the chloroisothiazolinone, monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred from the standpoints of efficiency in introducing substituents, and therefore defibration efficiency, cost, and ease of handling. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0131] Compound E C When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as it is, or it may be dissolved in an appropriate solvent and added. It is preferable that the fiber raw material is converted into alkali cellulose in advance or simultaneously with the reaction. The method for lysing is as described above.

[0132] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0133] Compound E C The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0134] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 3 minutes to 500 minutes, and even more preferably from 5 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0135] <Cationic group introduction step (cationization step)> As an essential component, a compound having a reactive group and a cationic group (compound E D), an optional alkaline compound, and a compound B selected from the aforementioned urea and its derivatives are added to a wet or dry fiber raw material having hydroxyl groups and reacted to introduce cationic groups into the fiber raw material.

[0136] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Examples of the cationic group include an ammonium group, a phosphonium group, a sulfonium group, etc. Among these, the cationic group is preferably an ammonium group. Compound E D As the alkyl group, glycidyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, etc. are preferred from the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> as an optional component in the same manner. The amount added is also preferably as described above.

[0137] Compound E D When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0138] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0139] Compound E D The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0140] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 5 minutes to 500 minutes, and even more preferably from 10 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0141] <Cleaning process> In the process of obtaining cellulose fibers having ionic substituents, a washing step can be carried out on the fibers having ionic substituents introduced therein, if necessary. The washing step is carried out by washing the fibers having ionic substituents introduced therein with, for example, water or an organic solvent. The washing step may be carried out after each of the steps described below, and the number of washing steps carried out in each washing step is not particularly limited.

[0142] <Alkali treatment process> In the process for obtaining cellulose fibers having ionic substituents, an alkali treatment step may be performed between the ionic substituent introduction step and the micronization step. The alkali treatment method is not particularly limited, but examples thereof include a method of immersing the ionic substituent-introduced fibers in an alkali solution.

[0143] The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. In this embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of their high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. Among these, the solvent contained in the alkaline solution is preferably water or a polar solvent including a polar organic solvent such as an alcohol, and more preferably an aqueous solvent including at least water. As the alkaline solution, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of their high versatility.

[0144] The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably, for example, from 5°C to 80°C, and more preferably from 10°C to 60°C. The immersion time of the ionic substituent-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is, for example, preferably from 5 minutes to 30 minutes, and more preferably from 10 minutes to 20 minutes. The amount of alkaline solution used in the alkaline treatment is not particularly limited, but is, for example, preferably from 100% by mass to 100,000% by mass, and more preferably from 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the ionic substituent-introduced fiber.

[0145] In order to reduce the amount of alkaline solution used in the alkaline treatment step, the ionic substituent-introduced fiber may be washed with water or an organic solvent after the ionic substituent-introducing step and before the alkaline treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkaline-treated ionic substituent-introduced fiber with water or an organic solvent after the alkaline treatment step and before the micronization treatment step.

[0146] <Acid treatment process> In the process for obtaining cellulose fibers having an ionic substituent, an acid treatment step may be provided between the ionic substituent introduction step and the micronization treatment step. For example, the ionic substituent introduction step, acid treatment, alkali treatment, and micronization treatment may be performed in this order.

[0147] The acid treatment method is not particularly limited, but examples thereof include a method of immersing the fiber raw material in an acidic solution containing an acid. The concentration of the acidic solution used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less. The pH of the acidic solution used is also not particularly limited, but is preferably 0 to 4, and more preferably 1 to 3. Examples of acids that can be used in the acidic solution include inorganic acids, sulfonic acids, and carboxylic acids. Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, and the like. Examples of the carboxylic acid include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, tartaric acid, etc. Among these, it is particularly preferable to use hydrochloric acid or sulfuric acid.

[0148] The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably, for example, 5°C to 100°C, and more preferably, 20°C to 90°C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is, for example, preferably, 5 minutes to 120 minutes, and more preferably, 10 minutes to 60 minutes. The amount of the acid solution used in the acid treatment is not particularly limited, but is, for example, preferably, 100 mass% to 100,000 mass%, and more preferably, 1,000 mass% to 10,000 mass%, based on the absolute dry mass of the fiber raw material.

[0149] <Defibrillation process> Fine fibrous cellulose can be obtained by defibrating raw fiber material or ionic group-introduced fiber in a defibration treatment step. Defibration treatment is also called micronization treatment. In the defibration treatment step, for example, a defibration treatment device can be used. The defibration treatment device is not particularly limited, but examples that can be used include high-speed defibrators, grinders (stone mill-type grinders), high-pressure homogenizers, ultra-high-pressure homogenizers, high-pressure collision grinders, ball mills, bead mills, disk-type refiners, conical refiners, twin-screw kneaders, vibration mills, homomixers under high-speed rotation, ultrasonic dispersers, and beaters. Among the above defibration treatment devices, it is more preferable to use high-speed defibrators, high-pressure homogenizers, and ultra-high-pressure homogenizers, which are less affected by the grinding media and have less risk of contamination.

[0150] In the defibration process, for example, the fiber raw material or the ionic group-introduced fiber is preferably diluted with a dispersion medium to form a slurry. The dispersion medium can be one or more selected from water and organic solvents such as polar organic solvents. The polar organic solvent is not particularly limited, but examples thereof include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

[0151] The solid content concentration of the fine fibrous cellulose during the defibration treatment can be appropriately set. In addition, the slurry obtained by dispersing the ionic group-introduced fibers in a dispersion medium may contain solids other than the ionic group-introduced fibers, such as urea having hydrogen bonding properties.

[0152] <Substituent removal treatment> The method for producing fine fibrous cellulose may include a substituent removal treatment step of removing at least a portion of the substituents from fine fibrous cellulose having substituents and having a fiber width of 1000 nm or less. In this specification, the step of removing at least a portion of the substituents from the fine fibrous cellulose obtained by the above-mentioned step is also referred to as the substituent removal treatment step.

[0153] The substituent removal treatment step includes a step of heat treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, a step of enzymatically treating the cellulose, a step of acid treating the cellulose, and a step of alkali treating the cellulose. These may be carried out alone or in combination. Among these, the substituent removal treatment step is preferably a heat treatment step or an enzyme treatment step. By undergoing the above treatment steps, at least a portion of the substituents can be removed from fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, thereby obtaining fine fibrous cellulose having an introduced substituent amount of less than 0.5 mmol / g.

[0154] The substituent removal treatment step is preferably carried out in the form of a slurry. That is, the substituent removal treatment step is preferably a step of subjecting a slurry containing a substituent-containing fine fibrous cellulose having a fiber width of 1000 nm or less to a heat treatment, an enzyme treatment, an acid treatment, an alkali treatment, or the like. By carrying out the substituent removal treatment step in the form of a slurry, it is possible to prevent the residue of colored substances generated by heating or the like during the substituent removal treatment, as well as acids, alkalis, salts, and the like that are added or generated. This makes it possible to suppress the coloration of the fine fibrous cellulose obtained through step (B). Furthermore, when a treatment is carried out to remove salts derived from the substituents removed after the substituent removal treatment, it is also possible to increase the efficiency of salt removal.

[0155] When a substituent removal treatment is performed on a slurry containing fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, the concentration of the fine fibrous cellulose in the slurry is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. The concentration of the fine fibrous cellulose in the slurry is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. By controlling the concentration of the fine fibrous cellulose in the slurry within the above range, the substituent removal treatment can be performed more efficiently. Furthermore, by controlling the concentration of the fine fibrous cellulose in the slurry within the above range, it is possible to prevent the residue of colored substances caused by heating during the substituent removal treatment, as well as added or generated acids, alkalis, salts, etc. This can suppress the coloration of the fine fibrous cellulose obtained through step (B). Furthermore, when a treatment is performed to remove salts derived from the substituents removed after the substituent removal treatment, it is also possible to increase the efficiency of salt removal.

[0156] When the substituent removal treatment step is a step of heat-treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, the heating temperature in the heat treatment step is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher. Furthermore, the heating temperature in the heat treatment step is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower. In particular, when the substituent on the fine fibrous cellulose subjected to the substituent removal treatment step is a phosphorus oxo acid group or a sulfone group, the heating temperature in the heat treatment step is preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher.

[0157] When the substituent removal treatment step is a heat treatment step, the heating device that can be used in the heat treatment step is not particularly limited, and examples that can be used include a hot air heater, a steam heater, an electric heater, a hydrothermal heater, a thermal heater, an infrared heater, a far-infrared heater, a microwave heater, a high-frequency heater, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, a flash dryer, and a reduced-pressure dryer. From the viewpoint of preventing evaporation, the heating is preferably carried out in a closed system, and from the viewpoint of further increasing the heating temperature, it is preferably carried out in a pressure-resistant device or container. The heat treatment may be a batch process, a batch continuous process, or a continuous process.

[0158] When the substituent removal treatment step is a step of enzymatically treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, the enzymatic treatment step includes the step of hydrolyzing a phosphate ester. It is preferable to use a hydrolase, a sulfate ester hydrolase, or the like.

[0159] In the enzyme treatment step, the enzyme is preferably added so that the enzymatic activity per 1 g of fine fibrous cellulose is 0.1 nkat or more, more preferably 1.0 nkat or more, and even more preferably 10 nkat or more. The enzyme is preferably added so that the enzymatic activity per 1 g of fine fibrous cellulose is 100,000 nkat or less, more preferably 50,000 nkat or less, and even more preferably 10,000 nkat or less. After adding the enzyme to the fine fibrous cellulose dispersion (slurry), it is preferable to treat the dispersion (slurry) at a temperature of 0°C or higher but lower than 50°C for 1 minute to 100 hours.

[0160] After the enzymatic reaction, a step of deactivating the enzyme may be carried out. Examples of methods for deactivating the enzyme include adding an acid or alkali component to the enzymatically treated slurry to deactivate the enzyme, and raising the temperature of the enzymatically treated slurry to 90°C or higher to deactivate the enzyme.

[0161] When the substituent removal treatment step is a step of acid treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, it is preferable to add an acid compound that can be used in the acid treatment step described above to the slurry in the acid treatment step.

[0162] When the substituent removal treatment step is a step of alkali treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, it is preferable to add an alkali compound that can be used in the alkali treatment step described above to the slurry in the alkali treatment step.

[0163] In the substituent removal treatment step, it is preferable that the substituent removal reaction proceeds uniformly. To proceed with the reaction uniformly, for example, the slurry containing the fine fibrous cellulose may be stirred, or the specific surface area of ​​the slurry may be increased. As a method for stirring the slurry, external mechanical shear may be applied, or self-stirring may be promoted by increasing the liquid feed rate of the slurry during the reaction.

[0164] In the substituent removal treatment step, spacer molecules may be added. The spacer molecules penetrate between adjacent fine fibrous cellulose particles, thereby acting as spacers to create fine spaces between the fine fibrous cellulose particles. Adding such spacer molecules in the substituent removal treatment step can suppress aggregation of the fine fibrous cellulose particles after the substituent removal treatment. This can more effectively improve the design and tensile properties of molded articles containing fine fibrous cellulose.

[0165] The spacer molecule is preferably a water-soluble organic compound. Examples of the water-soluble organic compound include sugars, water-soluble polymers, urea, and the like. Specifically, trehalose, urea, polyethylene glycol (PEG), polyethylene oxide (PEO), carboxymethyl cellulose, polyvinyl alcohol (PVA), and the like can be mentioned. Further, as the water-soluble organic compound, alkyl methacrylate-acrylic acid copolymer, polyvinyl pyrrolidone, sodium polyacrylate, propylene glycol, dipropylene glycol, polypropylene glycol, isoprene glycol, hexylene glycol, 1,3-butylene glycol, polyacrylamide, xanthan gum, guar gum, tamarind gum, carrageenan, locust bean gum, quince seed, alginic acid, pullulan, carrageenan, pectin, cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, amylose and other starches, glycerin, diglycerin, polyglycerin, hyaluronic acid, metal salts of hyaluronic acid can also be used.

[0166] Also, known pigments can be used as the spacer molecule. For example, kaolin (including clay), calcium carbonate, titanium oxide, zinc oxide, amorphous silica (including colloidal silica), aluminum oxide, zeolite, sepiolite, smectite, synthetic smectite, magnesium silicate, magnesium carbonate, magnesium oxide, diatomaceous earth, styrene-based plastic pigment, hydrotalcite, urea resin-based plastic pigment, benzoguanamine-based plastic pigment, and the like can be mentioned.

[0167] <pH adjustment step>

[0168] When the substituent removal treatment step is performed in a slurry state, a step of adjusting the pH of the slurry containing microfibrillar cellulose may be provided before the substituent removal treatment step. For example, an anionic group is introduced into the cellulose fiber, and the counter ion of this anionic group is Na +In this case, the slurry containing the defibrated fine fibrous cellulose exhibits a weak alkaline pH. If the slurry is heated in this state, monosaccharides, which are one of the causes of coloration, may be generated due to the decomposition of cellulose, so the pH of the slurry is preferably adjusted to 8 or less, more preferably to 6 or less. Similarly, monosaccharides may be generated under acidic conditions, so the pH of the slurry is preferably adjusted to 3 or more, more preferably to 4 or more.

[0169] Furthermore, when the substituted fine fibrous cellulose is a phosphate-containing fine fibrous cellulose, it is preferable that the phosphorus of the phosphate group is susceptible to nucleophilic attack, from the viewpoint of improving the efficiency of removing the substituent. The phosphorus susceptible to nucleophilic attack is cellulose-OP(=O)(-OH + )(-O-Na + To achieve this state, the pH of the slurry is preferably adjusted to 3 or more and 8 or less, and more preferably adjusted to 4 or more and 6 or less.

[0170] The means for adjusting the pH is not particularly limited, and for example, an acid component or an alkali component may be added to a slurry containing fine fibrous cellulose. The acid component may be either an inorganic acid or an organic acid. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Examples of organic acids include formic acid, acetic acid, citric acid, malic acid, lactic acid, adipic acid, sebacic acid, stearic acid, maleic acid, succinic acid, tartaric acid, fumaric acid, and gluconic acid. The alkali component may be an inorganic alkali compound or an organic alkali compound. Examples of inorganic alkali compounds include lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium bicarbonate, potassium carbonate, potassium bicarbonate, sodium carbonate, and sodium bicarbonate. Examples of organic alkali compounds include ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, butylamine, diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, cyclohexylamine, aniline, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, pyridine, and N,N-dimethyl-4-aminopyridine.

[0171] In addition, in the pH adjustment step, an ion exchange treatment may be performed to adjust the pH. A strong acid cation exchange resin or a weak acid ion exchange resin can be used in the ion exchange treatment. By treating with an appropriate amount of cation exchange resin for a sufficient time, a slurry containing fine fibrous cellulose with the desired pH can be obtained. Furthermore, in the pH adjustment step, the addition of an acid component or an alkali component may be combined with the ion exchange treatment.

[0172] <Salt removal treatment> After the substituent removal treatment step, it is preferable to carry out a treatment to remove salts derived from the removed substituents. Removing the salts derived from the substituents makes it easier to obtain fine fibrous cellulose that can suppress coloration. The means for removing the salts derived from the substituents is not particularly limited, and examples thereof include a washing treatment. The washing treatment is carried out by washing the fine fibrous cellulose that has aggregated in the substituent removal treatment with, for example, water or an organic solvent. From the viewpoint of more effectively suppressing yellowing, it is preferable to carry out the washing treatment by filtration dehydration, centrifugal dehydration, or centrifugation.

[0173] <Uniform dispersion processing> The method for producing fine fibrous cellulose may include a substituent removal treatment step of removing at least a portion of the substituents from fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, and a uniform dispersion treatment step after the substituent removal treatment. The uniform dispersion treatment step is a step of uniformly dispersing the fine fibrous cellulose obtained through the substituent removal treatment in the substituent removal treatment step. The state in which the fine fibrous cellulose is uniformly dispersed in the uniform dispersion treatment step refers to a state in which the fiber width of the fine fibrous cellulose is 100 nm or less. By undergoing the uniform dispersion treatment step, the number average fiber width of the fine fibrous cellulose can be easily adjusted to 100 nm or less, preferably 50 nm or less, even if the amount of introduced substituents is as low as less than 0.5 mmol / g.

[0174] In the uniform dispersion treatment step, for example, a high-speed defibrator, grinder (stone mill type grinder), high-pressure homogenizer, high-pressure collision type grinder, ball mill, bead mill, disk type refiner, conical refiner, twin-screw kneader, vibration mill, homomixer under high-speed rotation, ultrasonic disperser or beater can be used. Among the above-mentioned uniform dispersion treatment devices, it is more preferable to use a high-speed defibrator or high-pressure homogenizer.

[0175] The treatment conditions for the uniform dispersion treatment step are not particularly limited, but it is preferable to increase the maximum movement speed of the fine fibrous cellulose during treatment and the pressure during treatment. In the case of a high-speed defibrator, the peripheral speed is preferably 20 m / sec or more, more preferably 25 m / sec or more, and even more preferably 30 m / sec or more. A high-pressure homogenizer is more preferably used because it has a higher maximum movement speed of the fine fibrous cellulose during treatment and a higher pressure during treatment than a high-speed defibrator. In high-pressure homogenizer treatment, the pressure during treatment is preferably 1 MPa or more, more preferably 10 MPa or more, even more preferably 50 MPa or more, and particularly preferably 100 MPa or more. In addition, in high-pressure homogenizer treatment, the pressure during treatment is preferably 350 MPa or less, more preferably 300 MPa or less, and even more preferably 250 MPa or less.

[0176] In the uniform dispersion treatment step, the above-mentioned spacer molecules may be newly added. By adding such spacer molecules in the uniform dispersion treatment step (B), the fine fibrous cellulose can be more smoothly dispersed uniformly.

[0177] [resin] The resin used in the manufacturing method of the composite material (hereinafter simply referred to as "resin") may be a natural resin or a synthetic resin. The resin may be a rubber component or a plastic. The resin is preferably in a colloidal state.

[0178] The rubber component used in the method for producing a composite material may be, for example, natural rubber (NR) or synthetic rubber. Examples of synthetic rubber include styrene-butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), ethylene propylene rubber (EPDM), butyl rubber (IIR), chlorobutyl rubber (CIIR), acrylic rubber (ACM), and silicone rubber ( Examples of nitrile rubber include hydrogenated nitrile rubber; modified nitrile rubbers such as carboxyl-modified nitrile rubber, silicone-modified nitrile rubber, maleic acid-modified nitrile rubber, and hydroxyl-modified nitrile rubber, as well as hydrogenated versions of these; and acrylonitrile-butadiene-isoprene copolymers in which part of the butadiene has been replaced with isoprene. Hydrogenated nitrile rubber (H-NBR) is sometimes called hydrogenated nitrile rubber or hydrogenated acrylonitrile-butadiene rubber. Hydrogenated nitrile rubber can be obtained by hydrogenating the double bonds contained in nitrile rubber. Examples of natural rubber include natural rubber (NR), modified natural rubber such as epoxidized natural rubber (ENR), hydrogenated natural rubber, and deproteinized natural rubber. These rubber components may be used alone or in combination of two or more. These rubber components may be pre-crosslinked raw materials that do not have a crosslinked structure, or may have a crosslinked structure.

[0179] Among these, the rubber component is preferably at least one selected from natural rubber, nitrile rubber, butadiene rubber, and styrene-butadiene rubber, more preferably at least one selected from natural rubber and nitrile rubber, and even more preferably at least one selected from natural rubber and hydrogenated nitrile rubber. The rubber component may be a pre-crosslinked raw material, and for example, the rubber component is preferably at least one pre-crosslinked raw material selected from natural rubber and nitrile rubber, and more preferably at least one pre-crosslinked raw material selected from natural rubber and hydrogenated nitrile rubber. When the rubber component is a pre-crosslinked raw material, the rubber component is preferably a latex of these rubber components. By using the above rubber component as the rubber component, coloration is suppressed and a composite material with excellent tensile properties is more easily obtained.

[0180] The plastic used in the composite manufacturing method may be either a thermoplastic or a thermosetting plastic. Furthermore, the plastic is preferably a plastic emulsion. Examples of thermoplastic plastics include polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, ethylene-vinyl acetate copolymer, poly(meth)acrylic acid alkyl ester polymer, (meth)acrylic acid alkyl ester copolymer, polyester, polycarbonate, polyamide, polyacetal, and polyphenylene oxide. Examples of thermosetting plastics include polyurethane, epoxy resin, oxetane resin, phenolic resin, urea resin, melamine resin, unsaturated polyester resin, silicone resin, and diallyl phthalate resin. Among these, the plastic is preferably at least one selected from polypropylene, polyethylene, polystyrene, and polyvinyl chloride, with polypropylene being more preferred. [Example]

[0181] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0182] <Production Example A1> [Phosphorylation] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 A sheet-like product with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012 was used.

[0183] This raw pulp was subjected to phosphorus oxo-oxidation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (bone dry mass) of the raw pulp to adjust the total weight to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, to obtain a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 250 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining a phosphorylated pulp.

[0184] The resulting phosphorylated pulp was then washed. 100 g (bone dry mass) of phosphorylated pulp was mixed with 10 L of ion-exchanged water to obtain a pulp dispersion. The pulp was stirred to uniformly disperse the pulp, and then repeatedly filtered and dehydrated. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0185] Next, the washed phosphorylated pulp was neutralized as follows: First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous solution of sodium hydroxide was added little by little while stirring to obtain a phosphorylated pulp slurry with a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated and washed to obtain a neutralized phosphorylated pulp.

[0186] The infrared absorption spectrum of the obtained phosphorylated pulp was measured using FT-IR. -1 Absorption due to the P=O of phosphate groups was observed around 2θ = 14° to 17° and 2θ = 22° to 23°, confirming the addition of phosphate groups to the pulp. Furthermore, when the obtained phosphorylated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals. The amount of phosphate groups (amount of first dissociated acid) measured by the method described below in [Measurement of phosphorus oxo acid group amount] was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0187] Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2.2% by mass. This slurry was treated twice at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0188] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of phosphate groups (amount of first dissociated acid) measured by the method described below in [Measurement of amount of phosphorus oxo acid group] was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0189] <Manufacturing example B1> [Phosphorous] The same procedure as in Production Example A1 was carried out except that 33 parts by mass of phosphorous acid (phosphonic acid) was used instead of ammonium dihydrogen phosphate, to obtain a fine fibrous cellulose dispersion containing phosphited pulp and fine fibrous cellulose.

[0190] The infrared absorption spectrum of the obtained phosphorous-oxidized pulp was measured using FT-IR. -1 The absorption due to P=O of the phosphonic acid group, which is a tautomer of the phosphorous acid group, was observed around the 2θ=14° to 17° and the 2θ=22° to 23°. This confirmed that the phosphorous acid group (phosphonic acid group) had been added to the pulp. Furthermore, when the obtained phosphorous-oxidized pulp was analyzed using an X-ray diffractometer, the absorption was found to be around the 2θ=14° to 17° and the 2θ=22° to 23°. Typical peaks were observed at two positions, confirming the presence of cellulose type I crystals. The amount of phosphorous acid groups (amount of first dissociated acid) measured by the measurement method described below in [Measurement of amount of phosphorus oxo acid group] was 1.51 mmol / g. The total amount of dissociated acid was 1.54 mmol / g.

[0191] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of phosphorous groups (amount of first dissociated acid) of the obtained fine fibrous cellulose, measured by the method described below in [Measurement of amount of phosphorus oxo acid group], was 1.51 mmol / g. The total amount of dissociated acid was 1.54 mmol / g.

[0192] <Manufacturing example C1> [Sulfation] The same procedure as in Production Example A1 was carried out, except that 38 parts by mass of amidosulfonic acid (sulfamic acid) was used instead of ammonium dihydrogen phosphate and the heating time was extended to 20 minutes, to obtain a fine fibrous cellulose dispersion containing sulfated pulp and fine cellulose.

[0193] The infrared absorption spectrum of the obtained sulfated pulp was measured using FT-IR. -1 Absorption due to the S=O of sulfate ester groups was observed around 2θ = 14° to 17° and 2θ = 22° to 23°, confirming the addition of sulfate ester groups to the pulp. Furthermore, when the obtained sulfated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, near 2θ = 14° to 17° and near 2θ = 22° to 23°, confirming the presence of cellulose type I crystals. The amount of sulfate ester groups measured using the method described below in [Measurement of sulfate ester group amount] was 1.47 mmol / g.

[0194] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of sulfate ester groups in the obtained fine fibrous cellulose, as measured by the method described below in "Measurement of sulfate ester group amount," was 1.47 mmol / g.

[0195] <Production Example D1> [TEMPO oxidation] The raw material pulp used was softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. This raw material pulp was subjected to an alkaline TEMPO oxidation treatment as follows.

[0196] First, 100 parts by weight of the raw pulp (dry mass equivalent), 1.6 parts by weight of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by weight of sodium bromide were dispersed in 10,000 parts by weight of water. Next, a 13% by weight aqueous solution of sodium hypochlorite was added to 1.0 g of pulp to give a concentration of 10 mmol to initiate the reaction. During the reaction, a 0.5 M aqueous solution of sodium hydroxide was added dropwise to maintain the pH at 10 to 10.5. The reaction was considered complete when no further change in pH was observed.

[0197] The resulting TEMPO-oxidized pulp was then washed. The pulp slurry after TEMPO oxidation was dehydrated to obtain a dehydrated sheet, to which 5,000 parts by mass of ion-exchanged water was added, and the sheet was stirred to uniformly disperse the pulp. This process was repeated until the electrical conductivity of the filtrate reached 100 μS / cm or less, marking the end of the washing process.

[0198] The remaining aldehyde groups in this dehydrated sheet were further oxidized as follows: 100 parts by weight of the dehydrated sheet (dry mass equivalent) was dispersed in 10,000 parts by weight of 0.1 mol / L acetate buffer (pH 4.8). 113 parts by weight of 80% by weight sodium chlorite was then added, the container was immediately sealed, and the mixture was stirred at 500 rpm using a magnetic stirrer while reacting at room temperature for 48 hours to obtain a pulp slurry.

[0199] The resulting TEMPO-oxidized pulp was then washed. The pulp slurry after the additional oxidation was dehydrated to obtain a dehydrated sheet, to which 5,000 parts by mass of ion-exchanged water was added, and the sheet was stirred to uniformly disperse the pulp. This process was repeated until the electrical conductivity of the filtrate reached 100 μS / cm or less, marking the end of the washing process.

[0200] The carboxyl group content of the resulting TEMPO-oxidized pulp, as measured by the method described below, was 1.80 mmol / g. Furthermore, when the resulting TEMPO-oxidized pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0201] Ion-exchanged water was added to the obtained TEMPO-oxidized pulp to prepare a slurry with a solids concentration of 2.2% by mass. This slurry was treated twice at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0202] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxyl groups in the obtained fine fibrous cellulose, as measured by the method described below, was 1.80 mmol / g.

[0203] <Manufacturing example E1> [Hypochlorous acid oxidation] A sheet (solids concentration 90% by mass) made from softwood bleached kraft pulp (NBKP) was mixed in a hand mixer (Lab Millser PLUS, manufactured by Osaka Chemical Co., Ltd.) at 20,000 rpm for 15 seconds to produce a fluffy fluffed pulp (solids concentration 90% by mass). Sodium hypochlorite pentahydrate was then added to ion-exchanged water to prepare an aqueous solution with a sodium hypochlorite solids concentration of 22% by mass. 9,000 parts by mass of a 22% sodium hypochlorite aqueous solution was added to 100 parts by mass of the fluffy fluffed pulp, and the mixture was reacted for 2 hours in a warm bath at 30°C to obtain carboxylated pulp. During the reaction, the pH was maintained at 11 by adding 1N aqueous sodium hydroxide solution as needed.

[0204] The resulting carboxylated pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting carboxylated pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0205] The amount of carboxyl groups in the resulting carboxylated pulp was 0.70 mmol / g, as measured by the method described below. Furthermore, when the resulting carboxylated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0206] Ion-exchanged water was added to the obtained carboxyl group-introduced pulp, and the solid content was adjusted to 2.2% by mass. This slurry was treated twice at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Corporation) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0207] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxyl groups in the obtained fine fibrous cellulose, as measured by the method described below, was 0.70 mmol / g.

[0208] <Production Example F1> [Maleic acid esterification] A sheet (solids concentration 90% by mass) made from bleached softwood kraft pulp (NBKP) was mixed for 15 seconds at 20,000 rpm using a hand mixer (Osaka Chemical, Labo Millser PLUS) to produce a fluffy fluffing pulp (solids concentration 90% by mass). 100 parts by mass of the fluffy fluffing pulp and 50 parts by mass of maleic anhydride were placed in an autoclave and mixed at 150°C for 2 hours to obtain a carboxyl-introduced pulp.

[0209] The resulting carboxylated pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting carboxylated pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0210] The infrared absorption spectrum of the obtained carboxyl-introduced pulp was measured using FT-IR. -1 Absorption due to carboxyl groups was observed around 2θ = 14° to 17°, and maleic acid esterification was confirmed. The amount of carboxyl groups in the resulting carboxyl-introduced pulp, as measured by the method described below, was 1.22 mmol / g. Furthermore, when the carboxyl-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0211] Ion-exchanged water was added to the obtained carboxyl-introduced pulp to prepare a slurry with a solids concentration of 2.2% by mass. This slurry was treated twice at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0212] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxyl groups in the obtained fine fibrous cellulose, as measured by the method described below, was 1.22 mmol / g.

[0213] <Manufacturing example G1> [Carboxyethylated] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 A sheet-like product with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012 was used.

[0214] To 100 parts by mass (bone dry mass) of this raw pulp, a chemical solution (553 parts by mass in total) consisting of 250 parts by mass of a 12N NaOH aqueous solution, 163 parts by mass of 2-chloropropionic acid, and 140 parts by mass of ion-exchanged water was added to obtain a chemical-impregnated pulp. The pulp was heated in a hot air dryer at 65°C for 10 minutes to introduce carboxyethyl groups (carboxy groups) into the cellulose in the pulp, yielding carboxy group-introduced pulp.

[0215] The resulting carboxylated pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting carboxylated pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0216] Next, the washed carboxylated pulp was neutralized as follows: First, the washed carboxylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous sodium hydroxide solution was added little by little while stirring to obtain a carboxylated pulp slurry with a pH of 12 to 13. Next, the carboxylated pulp slurry was dehydrated and washed to obtain a neutralized carboxylated pulp.

[0217] The amount of carboxyl groups in the resulting carboxylated pulp was 1.41 mmol / g, as measured by the method described below. Furthermore, when the carboxylated pulp was analyzed using an X-ray diffractometer, typical peaks were confirmed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0218] Ion-exchanged water was added to the obtained carboxyl-introduced pulp to prepare a slurry with a solids concentration of 2.2% by mass. This slurry was treated twice at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0219] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxyl groups in the obtained fine fibrous cellulose, as measured by the method described below, was 1.41 mmol / g.

[0220] <Manufacturing example H1> [Carboxymethylation] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 A sheet-like product with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012 was used.

[0221] To 100 parts by mass (bone dry mass) of this raw pulp, a chemical solution consisting of 83 parts by mass of 12N NaOH aqueous solution, 175 parts by mass of sodium monochloroacetate, and 313 parts by mass of ion-exchanged water (total 571 parts by mass) was added to obtain a chemical-impregnated pulp. The obtained chemical-impregnated pulp was then heated in a water bath at 95°C for 60 minutes to introduce carboxymethyl groups (carboxy groups) into the cellulose in the pulp, thereby obtaining a carboxy-introduced pulp.

[0222] The resulting carboxylated pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting carboxylated pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0223] The amount of carboxyl groups in the obtained carboxyl-introduced pulp was measured by the measurement method described below and was found to be 1.21 mmol / g. Analysis using a ray diffraction device revealed that the 2θ values ​​were in the range of 14° to 17° and 2θ values ​​of 22° or less. Typical peaks were observed at two positions around 23° or less above, confirming the presence of cellulose type I crystals.

[0224] Ion-exchanged water was added to the obtained carboxyl-introduced pulp to prepare a slurry with a solids concentration of 2.2% by mass. This slurry was treated twice at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0225] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxyl groups in the obtained fine fibrous cellulose, as measured by the method described below, was 1.21 mmol / g.

[0226] <Manufacturing Example I1> [Sulfoethylation] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 A sheet-like product with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012 was used.

[0227] To 100 parts by mass (bone dry mass) of this raw pulp, a chemical solution consisting of 180 parts by mass of a 2N NaOH aqueous solution and 780 parts by mass of a 25% by mass sodium vinyl sulfonate aqueous solution (total 960 parts by mass) was added to obtain a chemical solution-impregnated pulp. The obtained chemical solution-impregnated pulp was then heated in a hot air dryer at 165°C for 16 minutes to introduce sulfoethyl groups (sulfonic groups) into the cellulose in the pulp, yielding a sulfoethyl group-introduced pulp (sulfonic group-introduced pulp).

[0228] The resulting sulfoethyl group-introduced pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting sulfoethyl group-introduced pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0229] The sulfoethyl group content (sulfonic acid content) of the resulting sulfoethyl group-introduced pulp was 1.48 mmol / g, as measured by the method described below. Furthermore, when the sulfoethyl group-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0230] Ion-exchanged water was added to the obtained sulfoethyl group-introduced pulp to prepare a slurry with a solid content of 2.2% by mass. This slurry was treated twice at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0231] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of sulfoethyl groups (sulfonic acid groups) of the obtained fine fibrous cellulose, as measured by the method described below, was 1.48 mmol / g.

[0232] <Production Example J1> [Cationization] The raw pulp used was softwood kraft pulp (solid content 93% by mass, Basis weight 245g / m 2 A sheet-like product with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012 was used.

[0233] To 100 parts by mass (bone dry mass) of this raw pulp, a chemical solution consisting of 180 parts by mass of a 1N NaOH aqueous solution and 325 parts by mass of a cationizing agent (Catiomaster G, manufactured by Yokkaichi Synthetic Co., Ltd., glycidyl trimethylammonium chloride, purity 73.1% by mass, moisture content 20.2% by mass) (total 505 parts by mass) was added to obtain a chemical solution-impregnated pulp. The obtained chemical solution-impregnated pulp was then heated in a hot air dryer at 165°C for 12 minutes to introduce cationic groups into the cellulose in the pulp, yielding a cationic group-introduced pulp.

[0234] The resulting cation-group-introduced pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting cation-group-introduced pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0235] Next, the washed cationic group-introduced pulp was neutralized as follows: First, the washed cationic group-introduced pulp was diluted with 10 L of ion-exchanged water, and then 1 N hydrochloric acid was added little by little while stirring to obtain a cationic group-introduced pulp slurry with a pH of 1 to 2. Next, the cationic group-introduced pulp slurry was dehydrated and washed to obtain a cationic group-introduced pulp that had been subjected to a neutralization treatment.

[0236] The resulting cationic group-introduced pulp was subjected to trace nitrogen analysis, and the amount of cationic groups was calculated using the following formula, which was 1.45 mmol / g. Furthermore, when the cationic group-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were confirmed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals. (Amount of cationic groups) [mmol / g] = (amount of nitrogen) / 14 × 1000 / (amount of cationic group-introduced pulp tested)

[0237] Ion-exchanged water was added to the obtained cationic group-introduced pulp to prepare a slurry with a solid content of 2.2% by mass. This slurry was treated twice at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0238] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. Furthermore, trace nitrogen analysis was performed on the obtained fine fibrous cellulose, and the amount of cationic groups calculated using the following formula was found to be 1.45 mmol / g. (Amount of cationic groups) [mmol / g] = (amount of nitrogen) / 14 × 1000 / (amount of fine fibrous cellulose tested)

[0239] <Production Example K1> [Substituent removal treatment] A 20% by mass aqueous citric acid solution was added to the fine fibrous cellulose dispersion obtained in Production Example A1 to adjust the pH of the dispersion to 5.5. The resulting slurry was placed in a pressure-resistant container and heated at a liquid temperature of 160°C for 15 minutes until the amount of phosphate groups reached 0.08 mmol / g. This operation confirmed the formation of fine fibrous cellulose aggregates.

[0240] After heating, add the same amount of ion-exchanged water as the slurry to make the solids concentration approximately 1% by mass. The slurry was washed by repeatedly stirring the slurry and then filtering and dehydrating it. When the electrical conductivity of the filtrate reached 10 μS / cm or less, ion-exchanged water was added again to make a slurry of about 1 mass % and allowed to stand for 24 hours. From there, the filtration and dehydration process was repeated, and the washing endpoint was reached when the electrical conductivity of the filtrate again reached 10 μS / cm or less. Ion-exchanged water was added to the obtained fine fibrous cellulose aggregates, and a slurry was obtained after removing the substituents. The solids concentration of this slurry was 1.7 mass %.

[0241] Ion-exchanged water was added to the resulting slurry after the removal of substituents to make it a slurry with a solids concentration of 1.0% by mass, which was then treated three times at a pressure of 200 MPa in a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing the fine fibrous cellulose after the removal of substituents. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and was found to be 3 to 5 nm.

[0242] <Manufacturing example L1> [No degeneration] A slurry with a solids concentration of 2.2% by mass was prepared using softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. The raw material pulp was treated 30 times in a wet pulverizer (Starburst manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a coarse fibrous cellulose dispersion containing coarse fibrous cellulose with a fiber width of more than 1000 nm.

[0243] [Measurement of phosphorus oxoacid group content] In measuring the amount of phosphorus oxo acid groups (amount of phosphate groups or amount of phosphite groups) in fine fibrous cellulose, ion-exchanged water was first added to the target fine fibrous cellulose to prepare a slurry with a solids concentration of 0.2% by mass. The resulting fine fibrous cellulose dispersion was treated with an ion-exchange resin and then titrated with an alkali to measure the amount of phosphorus oxo acid groups. Treatment with ion exchange resin was carried out by adding 1 / 10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the above-mentioned fine fibrous cellulose dispersion, shaking for 1 hour, and then pouring it onto a mesh with 90 μm openings to separate the resin from the slurry. In addition, alkali titration was performed by measuring the change in the pH of a slurry containing fine fibrous cellulose after ion exchange resin treatment while adding 10 μL of 0.1 N sodium hydroxide solution every 5 seconds. Nitrogen gas was bubbled through the slurry 15 minutes before the start of the titration. In this neutralization titration, two maximum points of increment (the derivative of pH with respect to the amount of alkali added) were observed on the curve plotting the measured pH against the amount of alkali added. The first maximum point of increment after starting the alkali addition is called the first endpoint, and the second maximum point is called the second endpoint (Figure 4). The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of first dissociated acid in the slurry used for titration. The amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid in the slurry used for titration. The amount of alkali (mmol) required from the start of titration to the first endpoint divided by the solid content (g) in the titrated slurry was defined as the amount of phosphorus oxo acid group (first dissociated acid amount) (mmol / g). The amount of alkali (mmol) required from the start of titration to the second endpoint divided by the solid content (g) in the titrated slurry was defined as the total dissociated acid amount (mmol / g).

[0244] [Measurement of Carboxy Group Amount] The amount of carboxyl groups in the fine fibrous cellulose was measured by adding ion-exchanged water to a fine fibrous cellulose dispersion containing the target fine fibrous cellulose to adjust the content to 0.2 mass%, treating the dispersion with an ion-exchange resin, and then titrating the dispersion with an alkali. Treatment with ion exchange resin was carried out by adding 1 / 10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) to a 0.2% by mass slurry containing fine fibrous cellulose, shaking for 1 hour, and then pouring the mixture onto a mesh with 90 μm openings to separate the resin from the slurry. In addition, alkali titration was performed by measuring the change in the pH of the fibrous cellulose-containing slurry after treatment with an ion exchange resin while adding 0.1 N aqueous sodium hydroxide. Observing the change in pH while adding aqueous sodium hydroxide yielded a titration curve like the one shown in Figure 5. As shown in Figure 5, in this neutralization titration, a single point was observed where the increment (the differential value of pH with respect to the amount of alkali added) reached a maximum on the curve plotting the measured pH against the amount of alkali added. This maximum increment was called the first endpoint. The region from the start of the titration to the first endpoint in Figure 5 is called the first region. The amount of alkali required in the first region was equal to the amount of carboxyl groups in the slurry used for titration. The amount of alkali required in the first region of the titration curve (mmol) was then divided by the solids content (g) of the fine fibrous cellulose-containing slurry to be titrated to calculate the amount of carboxyl groups introduced (mmol / g).

[0245] [Measurement of sulfur oxoacid and sulfonic acid groups] The amount of sulfur oxoacid or sulfonic acid groups in the fine fibrous cellulose was measured by subjecting freeze-dried and pulverized samples to pressure-heat decomposition with sulfuric acid in a sealed container, diluting appropriately, and measuring the amount of sulfur by ICP-OES. The value calculated by dividing by the bone-dry mass of the fine fibrous cellulose used was taken as the amount of sulfur oxoacid or sulfonic acid groups (mmol / g) in the fine fibrous cellulose.

[0246] Example 1 The fine fibrous cellulose dispersion obtained in Production Example A1 was placed in a can container so that the solid content of the fine fibrous cellulose was 100 parts by mass, and then ion-exchanged water was placed in the can container so that the solid content concentration of the fine fibrous cellulose was diluted to 1.0% by mass. A tornado agitator (general-purpose high-speed agitator, PM-202, manufactured by AS ONE Corporation) was used as the agitator, and a stirring blade with a diameter of 6 inches was attached, and the fine fibrous cellulose dispersion in the can container was stirred with the agitator at 1000 rpm for 5 minutes.

[0247] To the obtained 1.0% by mass fine fibrous cellulose dispersion, an aqueous dispersion of natural rubber latex (Hyper HA, manufactured by Nomura Trading Co., Ltd.) with a solid content of 61% by mass was added so that the solid content of the resin (rubber component) was 500 parts by mass, and the mixture was stirred at 1000 rpm for 60 minutes. The amount of natural rubber latex added was adjusted so that the solid content mass of the rubber component in the dispersion was 5 times the solid content mass of the fine fibrous cellulose.

[0248] The resulting dispersion of the mixture of fine fibrous cellulose dispersion and rubber latex was fed to the feed section of a double drum dryer (JM-D02, Johnson Boiler). Heat drying was carried out using the drum dryer under the following conditions: inter-drum clearance 0.25 mm, steam pressure 0.4 MPa, drum surface temperature 150°C, and drum rotation speed 2.0 rpm, yielding a sheet-like composite material of fine fibrous cellulose and rubber components. The heat drying time was 18 seconds.

[0249] In Example 1, the content [mass parts] of fibrous cellulose solids per 100 mass parts of resin solids in the mixture dispersion, the solids concentration ρ [-] of the mixture dispersion, the amount of heat Q [J / sec] given per second from the heated cylindrical dryer to the mixture dispersion, the cylindrical width w [m] of the heated cylindrical dryer, the rotation speed [m / sec] of the heated cylindrical dryer, the film thickness x [μm] of the composite, and the index A of the drying state of the composite were as shown in Table 1.

[0250] <Example 2> The same procedure as in Example 1 was carried out except that the drum rotation speed was set to 2.7 rpm. A composite material of the cellulose and rubber component was obtained. The heating and drying time was 13 seconds. The various manufacturing conditions and the index A of the drying state of the composite material are shown in Table 1.

[0251] Example 3 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the drum rotation speed was set to 5.0 rpm. The heat drying time was 7 seconds. The various production conditions and the index A of the drying state of the composite material are as shown in Table 1.

[0252] Example 4 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the drum rotation speed was set to 10.0 rpm. The heat drying time was 4 seconds. The various production conditions and the index A of the drying state of the composite material are as shown in Table 1.

[0253] <Example 5> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the drum rotation speed was set to 1.0 rpm. The heat drying time was 35 seconds. The various production conditions and the index A of the drying state of the composite material are as shown in Table 1.

[0254] Example 6 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the drum rotation speed was set to 0.25 rpm. The heat drying time was 140 seconds. The various production conditions and the index A of the drying state of the composite material are as shown in Table 1.

[0255] Example 7 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the drum rotation speed was set to 0.1 rpm. The heat drying time was 350 seconds. The various production conditions and the index A of the drying state of the composite material are as shown in Table 1.

[0256] Example 8 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the drum rotation speed was set to 0.025 rpm. The heat drying time was 1,400 seconds. The various production conditions and the index A of the drying state of the composite material are as shown in Table 1.

[0257] Example 9 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that natural rubber latex with a solid content concentration of 61% by mass was added so that the solid content of the resin (rubber component) was 1,000 parts by mass. The solid mass of the rubber component in the dispersion was 10 times the solid mass of the fine fibrous cellulose. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0258] Example 10 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 9, except that after the fine fibrous cellulose dispersion obtained in Production Example A1 was added, ion-exchanged water was added to the can container so that the solid content concentration of the fine fibrous cellulose was diluted to 2.0 mass %. The solid content mass of the rubber component in the dispersion was 10 times the solid content mass of the fine fibrous cellulose. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0259] Example 11 Instead of natural rubber latex, a polypropylene emulsion with a solid content of 39% by mass (Hitec P-5060P, manufactured by Toho Chemical Industry Co., Ltd.) was used as a resin (plastic). A composite material of fine fibrous cellulose and polypropylene was obtained in the same manner as in Example 1, except that the solid content was 25 parts by mass. The solid mass of polypropylene in the dispersion was 0.25 times the solid mass of the fine fibrous cellulose. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0260] Example 12 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that instead of natural rubber latex, hydrogenated nitrile rubber latex (Zetpol 2230LX, manufactured by Zeon Corporation) with a solid content of 40.5% by mass was added so that the solid content of the resin (rubber component) was 500 parts by mass. The solid content mass of the rubber component in the dispersion was five times the solid content mass of the fine fibrous cellulose. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0261] Example 13 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion obtained in Production Example B1 was used instead of Production Example A1. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0262] Example 14 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion obtained in Production Example C1 was used instead of Production Example A1. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0263] Example 15 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion obtained in Production Example D1 was used instead of Production Example A1. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0264] Example 16 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion obtained in Production Example E1 was used instead of Production Example A1. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0265] Example 17 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion obtained in Production Example F1 was used instead of Production Example A1. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0266] Example 18 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion obtained in Production Example G1 was used instead of Production Example A1. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0267] Example 19 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion obtained in Production Example H1 was used instead of Production Example A1. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0268] Example 20 The following was carried out using the fine fibrous cellulose dispersion obtained in Production Example I1 instead of Production Example A1. Other than that, a composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1. Various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0269] <Example 21> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion obtained in Production Example J1 was used instead of Production Example A1. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0270] <Example 22> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion obtained in Production Example K1 was used instead of Production Example A1. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0271] Example 23 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the coarse fibrous cellulose dispersion obtained in Production Example L1 was used instead of Production Example A1. The various production conditions and the index A of the dry state of the composite material are as shown in Table 1.

[0272] Example 24 The dispersion of the mixture of the fine fibrous cellulose dispersion and rubber latex obtained in Example 1 was sandwiched between two sheets of release paper so that the release surface was in contact with the mixture, and the laminate of release paper / mixture / release paper was passed between double rubber rolls with a clearance of 5.8 mm.

[0273] Filter paper was placed on one side of the release paper, and aluminum foil was placed on the other side of the release paper. The aluminum foil / release paper / mixture / release paper / filter paper laminate was then placed in an electrically heated cylinder dryer (DR-200, Kumagai Riki Kogyo Co., Ltd.) with a drum surface temperature of 105°C and a drum rotation speed of 0.5 rpm to heat-dry the mixture, yielding a sheet-like composite of fine fibrous cellulose and a rubber component. The heat-drying time was 70 seconds. The various manufacturing conditions and the index A of the composite's drying state are shown in Table 1.

[0274] Example 25 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 24, except that a cylinder dryer with a steam pressure of 0.4 MPa, a drum surface temperature of 150°C, and a drum rotation speed of 0.5 rpm was used instead of an electrically heated cylinder dryer. The heat drying time was 70 seconds. The various production conditions and the index A of the drying state of the composite material are as shown in Table 1.

[0275] <Example 26> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 25, except that the drum rotation speed was set to 5.0 rpm. The heat drying time was 7 seconds. The various production conditions and the index A of the drying state of the composite material are as shown in Table 1.

[0276] Example 27 A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 25, except that the drum rotation speed was set to 8.0 rpm. The heat drying time was 4 seconds. The various production conditions and the index A of the drying state of the composite material are as shown in Table 1.

[0277] <Comparative Example 1> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the drum rotation speed was set to 20.0 rpm. The heat drying time was 2 seconds. The index A of the wood drying condition was as shown in Table 1.

[0278] <Comparative Example 2> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the drum rotation speed was set to 0.2 rpm. The heat drying time was 175 seconds. The various production conditions and the index A of the drying state of the composite material are as shown in Table 1.

[0279] <Comparative Example 3> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 25, except that the drum rotation speed was set to 20.0 rpm. The heat drying time was 3 seconds. The various production conditions and the index A of the drying state of the composite material are as shown in Table 1.

[0280] <Comparative Example 4> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 25, except that the drum rotation speed was set to 0.1 rpm. The heat drying time was 3,500 seconds. The various production conditions and the index A of the drying state of the composite material are as shown in Table 1.

[0281] <Comparative Example 5> A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the dispersion of the mixture of fine fibrous cellulose dispersion and rubber latex obtained in Example 1 was heated and dried using an incubator with a safety door SPHH-201 (manufactured by Espec Corporation) at a set temperature of 80°C for a heating time of 18 hours. The various production conditions and the index A of the drying state of the composite material were as shown in Table 1.

[0282] [exterior] The resulting composite material of fine fibrous cellulose and rubber component was evaluated according to the following evaluation criteria. (Appearance evaluation criteria) A: No dryness problems or discoloration due to excessive drying B: Slightly poor drying B´: Slight discoloration due to slight over-drying C: Poor drying C´: Coloring due to excessive drying D: Drying is uneven, and some parts are not dry enough due to skinning.

[0283] [Tensile strength] The maximum tensile load was measured using a Tensilon tensile testing machine (manufactured by A&D Co., Ltd.) in accordance with JIS P 8113:2006, except that the length of the test piece was 80 mm and the distance between the chucks was 50 mm. This maximum tensile load was calculated by multiplying the cross-sectional area of ​​the test piece (thickness × width [1 The tensile strength (unit: MPa) was calculated by dividing the maximum tensile load by 5±0.1 mm. When measuring x, the test piece was conditioned at 23°C and a relative humidity of 50% for 24 hours. The thickness of the test piece was measured in the same manner as in the measurement of the composite film thickness x described above.

[0284] [Table 1]

[0285] As shown in Table 1, the index A of the dry state of the composite material is 0.20 or more and 9.00 or less. Compared with the composite materials of Comparative Examples 1 to 5, the composite materials of Examples 1 to 27 were dried in an appropriate manner, had excellent peelability and strength, and were suppressed in coloration. [Explanation of symbols]

[0286] 10...double drum dryer, 1...cylinder, 2...feed section, 3...sheet mixture, 4...scraper, 5...composite material

Claims

1. A method for producing a composite material containing fibrous cellulose and a resin, comprising: a step of heating and drying a dispersion of a mixture of the fibrous cellulose and the resin in an aqueous medium using a heating cylindrical dryer to obtain the composite material, the heated cylindrical dryer is a double drum dryer equipped with a feed section into which the dispersion is introduced, In the step of obtaining the composite material, the dispersion is heated and dried so that A, represented by the following formula (A), is 0.20 or more and 9.00 or less. A=ρ+Q / {k×w×v×(x / ρ)} (A) (In the above formula (A), ρ represents the solid content concentration (by mass) of the dispersion [−], Q represents the amount of heat per second [J / sec] given to the dispersion from the heating cylindrical dryer, k represents the amount of heat required to evaporate 1 g of water at 25 °C, 2442 [J / g], w represents the cylinder width [m] of the heating cylindrical dryer, v represents the cylinder rotation speed [m / sec] of the heating cylindrical dryer, x represents the film thickness of the composite material [μm].

2. The method for producing a composite material according to claim 1, wherein the surface temperature of the heating cylindrical dryer is 80°C or higher and 250°C or lower.

3. The method for producing a composite material according to claim 1 or 2, wherein the heat drying time is from 2 seconds to 1800 seconds.

4. The method for producing a composite material according to claim 1 or 2, wherein the ρ is 0.005 [-] or more and 0.200 [-] or less.

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