Method for producing composite material

Abstract

To provide a method for producing a composite material including fine fibrous cellulose and a rubber component, which prevents formation of rubber component agglomerates and achieves superior strength.SOLUTION: A method for producing a composite material including fibrous cellulose and a rubber component comprises an introduction step in which a latex of the rubber component is introduced to a dispersion of the fibrous cellulose. Introduction means in the introduction step utilizes potential energy as a power source.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In recent years, due to the replacement of petroleum resources and the increasing environmental awareness, materials using renewable natural fibers have attracted attention. Among natural fibers, fibrous cellulose having a fiber diameter of 10 μm or more and 50 μm or less, particularly fibrous cellulose (pulp) derived from wood, has been widely used mainly as paper products.

[0003] As fibrous cellulose, microfibrillar cellulose having an average fiber width of 1000 nm or less is also known. Microfibrillar cellulose has attracted attention as a new material, and its applications are diverse. For example, the development of sheets, resin composites, and thickeners containing microfibrillar cellulose has been promoted. In addition, the use of microfibrillar cellulose as a composite material in which it is combined with a rubber component such as rubber latex has also been studied.

[0004] Patent Document 1 discloses a method for manufacturing a masterbatch including: (A) a step of treating a cellulose-based raw material with a phosphoric acid-based compound to obtain a modified cellulose; (B) a step of defibrating and dispersing the modified cellulose to obtain cellulose nanofibers; (C) a step of acidifying the cellulose nanofibers to obtain acid-type cellulose nanofibers; and (D) a step of mixing the acid-type cellulose nanofibers and a rubber component.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the production of a composite material containing fibrous cellulose such as microfibrillar cellulose and a rubber component, when a latex of the rubber component is introduced into a dispersion of the fibrous cellulose and mixed, it is usually introduced using an introducing device such as a pump. However, in the introducing method using an introducing device such as a pump, agglomerates of the rubber component are generated, and regular cleaning (maintenance) of the introducing device and the mixing device is required. Therefore, the inventors have recognized that this is disadvantageous in operation. Furthermore, it has also been found that when a composite material with fibrous cellulose is produced in a state where agglomerates of the rubber component are generated, the strength of the composite material decreases.

[0007] The present disclosure solves the above problems and provides a method for producing a composite material containing fibrous cellulose and a rubber component that prevents the generation of agglomerates of the rubber component and has excellent strength.

Means for Solving the Problems

[0008] As a result of investigations to solve the above problems, the inventors have found that the above problems can be solved by introducing the latex of the rubber component into the dispersion of the fibrous cellulose using potential energy as a power source, and have completed the present invention.

[0009] That is, the present invention relates to the following [1] to [9]. [1] A method for producing a composite material containing fibrous cellulose and a rubber component, including an introducing step of introducing the latex of the rubber component into the dispersion of the fibrous cellulose and, a method for producing a composite material, wherein the introducing means in the introducing step uses potential energy as a power source. [2] The method for producing a composite material according to [1], wherein the fibrous cellulose is microfibrillar cellulose having an average fiber width of 1 nm or more and 1000 nm or less, or high-refined pulp having a freeness of 130 mL or more and 350 mL or less. [3] In the input step, the latex of the rubber component is dropped and introduced from above into the dispersion of the fibrous cellulose, the method for producing a composite material according to [1] or [2]. [4] The input means uses only the potential energy as the power source, the method for producing a composite material according to any one of [1] to [3]. [5] In the input step, the input rate of the latex of the rubber component with respect to 1 L of the dispersion of the fibrous cellulose is 0.01 L / min to 1.00 L / min, the method for producing a composite material according to any one of [1] to [4]. [6] In the input step, the viscosity of the dispersion of the fibrous cellulose is 1 mPa·s to 20000 mPa·s, the method for producing a composite material according to any one of [1] to [5]. [7] In the input step, the solid content concentration of the dispersion of the fibrous cellulose is 0.1 mass% to 10.0 mass%, the method for producing a composite material according to any one of [1] to [6]. [8] In the input step, the latex of the rubber component is introduced during the stirring of the dispersion of the fibrous cellulose, the method for producing a composite material according to any one of [1] to [7]. [9] In the input step, the stirring speed (peripheral speed) of the dispersion of the fibrous cellulose calculated by the following formula (I) is 1 m / min to 50 m / min, the method for producing a composite material according to [8]. Stirring speed (peripheral speed) [m / min] = Diameter of the stirring blade [m] × π × Rotation speed of the stirring blade [rpm] ··· (I)

Advantages of the Invention

[0010] According to the present disclosure, it is possible to provide a method for producing a composite material including fibrous cellulose and a rubber component that prevents the generation of agglomerates of the rubber component and is excellent in strength.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

[0012] The description of "XX or more and YY or less" or "XX to YY" representing a numerical range means a numerical range including the lower limit and the upper limit which are the endpoints, unless otherwise specified. When the numerical ranges are described stepwise the upper limit and the lower limit of each numerical range can be arbitrarily combined.

[0013] [Method for Producing Composite Material] A method for producing a composite material according to an embodiment of the present disclosure (hereinafter, also simply referred to as "method for producing a composite material") is a method for producing a composite material including fibrous cellulose and a rubber component, including an introducing step of introducing latex of the rubber component into a dispersion of the fibrous cellulose, and the introducing means in the introducing step uses potential energy as a power source.

[0014] [Introducing Step] The method for producing a composite material includes an introducing step (hereinafter, also simply referred to as "introducing step") of introducing latex of a rubber component into a dispersion of fibrous cellulose. The power source of the introducing means in the introducing step is potential energy.

[0015] The charging means using potential energy as the power source is not particularly limited. For example, there is a method of dropping the latex of the rubber component from above and charging it into the dispersion of fibrous cellulose. The dropping may be through a pipe or without passing through a pipe. The charging process will be described by taking FIGS. 1 and 2 as examples.

[0016] The device used in the charging process is provided with a can container B (reference numeral 11) filled with the latex of the rubber component above a can container A (reference numeral 14) filled with the dispersion of fibrous cellulose. The can container B is provided with a pipe 12 capable of dropping the latex from the can container B and a valve 13 capable of controlling the dropping of the latex. The can container A is provided with a stirring device 15. When dropping the latex of the rubber component from above, the valve 13 can be opened and the latex can be charged into the can container A via the pipe 12. Also, as shown in FIG. 2, instead of the can container B, a hopper 21 filled with the latex of the rubber component may be used (FIG. 2).

[0017] At the time of charging, it is not limited to pipes or hoppers, and the principle of a siphon may be used. In FIGS. 1 and 2, the pipe is linear, but the shape of the pipe is not particularly limited and may have a curve, for example, it may be spiral. When charging the entire amount of the prepared latex of the rubber component into the dispersion of fibrous cellulose, the latex of the rubber component may be installed above the liquid level of the dispersion of fibrous cellulose. It is more preferable that the bottom of the inner surface of the container filled with the latex of the rubber component exists above the liquid level of the dispersion of fibrous cellulose. In the charging process, it is preferable to charge the latex using potential energy as the power source, for example, by these means so as not to generate agglomerates of the rubber component.

[0018] The rubber component has a property of being likely to coagulate when exposed to air. When introducing the latex of the rubber component, it is usually introduced using an introducing device such as a pump. However, in such an introducing device, a shearing force is applied to the rubber component, so it is considered that the contact frequency between the air and the rubber component increases and the rubber component coagulates to generate agglomerates. On the other hand, when the power source of the introducing means is potential energy, the inventors consider that the shearing force applied to the rubber component can be reduced, so the generation of agglomerates of the rubber component can be suppressed.

[0019] Therefore, at the time of introduction, as long as the shearing force is such that the rubber component is not aggregated, in addition to potential energy, other energies such as electrical energy may be used in combination as the power source. For example, a pump may be used in combination with a slight power that does not aggregate the rubber component. When using a siphon-type device, etc., a pump or the like may be used until the siphon starts. The power source is preferably only potential energy, and more preferably does not use other energies such as electrical energy as the power source.

[0020] Furthermore, when producing a composite material with fibrous cellulose in a state where agglomerates of the rubber component have occurred cracks are likely to occur in the composite material due to the agglomerates, and the mechanical properties of the composite material are lowered. Therefore, the inventors consider that by suppressing the generation of agglomerates of the rubber component, a composite material excellent in strength can be obtained. The latex of the rubber component may be stirred with a shearing force such that agglomerates of the rubber component do not occur.

[0021] In the introducing step, the latex of the rubber component may be introduced into the dispersion of fibrous cellulose in a stationary state, but it is preferable that the latex of the rubber component is introduced during the stirring of the dispersion of fibrous cellulose. As the stirring device, for example, known stirring devices such as a disperser, a homomixer, and a clar mixer can be used.

[0022] During the stirring of the fibrous cellulose dispersion, the latex of the rubber component is introduced, which makes it easier to suppress the generation of agglomerates of the rubber component, and further makes it easier to suppress the contamination due to the adhesion of the latex to the stirring device by the stirring.

[0023] The lower limit value of the stirring speed (peripheral speed) of the fibrous cellulose dispersion in the charging step is preferably 1 m / min or more, more preferably 2 m / min or more, and still more preferably 3 m / min or more. Also, the upper limit value of the stirring speed (peripheral speed) is preferably 50 m / min or less, more preferably 40 m / min or less, still more preferably 30 m / min or less, and even more preferably 15 m / min or less. The stirring speed (peripheral speed) of the dispersion may be, for example, 1 m / min to 50 m / min, 2 m / min to 40 m / min, 3 m / min to 30 m / min, or 3 m / min to 15 m / min. When the stirring speed (peripheral speed) of the dispersion is within the above range, it becomes easier to suppress the contamination due to the adhesion of the latex to the mixing device.

[0024] The stirring speed (peripheral speed) of the fibrous cellulose dispersion can be calculated by the following formula (I). Stirring speed (peripheral speed) [m / min] = Diameter of the stirring blade [m] × π × Rotation speed of the stirring blade [rpm] ···(I)

[0025] The lower limit value of the charging speed of the latex of the rubber component with respect to 1 L of the fibrous cellulose dispersion in the charging step is preferably 0.01 L / min or more, more preferably 0.03 L / min or more, and still more preferably 0.05 L / min or more. Also, the upper limit value of the charging speed is preferably 1.00 L / min or less, more preferably 0.75 L / min or less, and still more preferably 0.50 L / min or less. The charging rate of the latex with respect to 1 L of the fibrous cellulose dispersion may be, for example, 0.01 L / min to 1.00 L / min, may be 0.03 L / min to 0.75 L / min, or may be 0.05 L / min to 0.50 L / min. By the charging rate of the latex being within the above range, the occurrence of aggregation can be further suppressed while maintaining the operability.

[0026] The lower limit value of the viscosity of the fibrous cellulose dispersion in the charging step is preferably 1 mPa·s or more, more preferably 10 mPa·s or more, and still more preferably 100 mPa·s or more. The upper limit value of the viscosity is preferably 20000 mPa·s or less, more preferably 19000 mPa·s or less, and still more preferably 18500 mPa·s or less. The viscosity of the dispersion in the charging step may be, for example, 1 mPa·s to 20000 mPa·s, may be 10 mPa·s to 19000 mPa·s, or may be 100 mPa·s to 18500 mPa·s. By the viscosity of the dispersion in the charging step being within the above range, the generation of agglomerates of the rubber component is more easily suppressed, and furthermore, a composite material with better strength is more easily obtained.

[0027] Here, the "viscosity of the fibrous cellulose dispersion in the charging step" refers to the viscosity of the fibrous cellulose dispersion immediately before charging the latex of the rubber component, and is a value measured by rotating for 3 minutes under the condition of 30 rpm using a B-type viscometer. When charging the latex of the rubber component during the stirring of the fibrous cellulose dispersion, the viscosity measurement is started within 30 seconds after collecting the dispersion during stirring. As the B-type viscometer, for example, the analog viscometer T-LVT manufactured by BLOOKFIELD can be used.

[0028] ​In the feeding step, the lower limit of the solid content concentration of the fibrous cellulose dispersion is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and still more preferably 0.5% by mass or more. Also, the upper limit of the solid content concentration of the fibrous cellulose dispersion is preferably 10.0% by mass or less, more preferably 5.0% by mass or less, still more preferably 3.0% by mass or less, and even more preferably 2.0% by mass or less. When the solid content concentration of the fibrous cellulose dispersion in the feeding step is within the above range, it becomes easier to further suppress the generation of agglomerates of the rubber component, and furthermore, it becomes easier to obtain a composite material having better strength. The solid content concentration of the fibrous cellulose dispersion in the feeding step may be, for example, 0.1% to 10.0% by mass, 0.3% to 5.0% by mass, 0.5% to 3.0% by mass, or 0.5% to 2.0% by mass.

[0029] In the feeding step, the lower limit of the solid content concentration of the latex of the rubber component is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 20% by mass or more, and even more preferably 40% by mass or more. Also, the upper limit of the solid content concentration of the latex of the rubber component is preferably 80% by mass or less, more preferably 75% by mass or less, still more preferably 70% by mass or less. When the solid content concentration of the latex of the rubber component in the feeding step is within the above range, it is possible to suppress the aggregation of the latex while maintaining the efficiency in the subsequent drying step. The solid content concentration of the latex of the rubber component in the feeding step may be, for example, 10 to 80% by mass, 15 to 75% by mass, 20 to 70% by mass, or 40 to 70% by mass.

[0030] [Mixing step] The manufacturing method of the composite material preferably further includes a mixing step of mixing a dispersion of fibrous cellulose and a dispersion of a rubber component after the charging step. When the fibrous cellulose and the rubber component are uniformly mixed by the mixing step, it becomes easier to suppress the generation of agglomerates of the rubber component, and furthermore, it becomes easier to obtain a composite material with better strength.

[0031] As the mixing device used in the mixing step, the above-mentioned stirring device may be used, or known fluid mixing devices such as an in-line mixer, a static mixer, and an OHR mixer may be used. Further, the mixing device is not particularly limited as long as it can mix fluids. For example, a liquid feeding device such as a screw pump (monopump, twin-screw pump) or a dispersing device such as a wet atomizing device can be used as the mixing device in the mixing step because fluid mixing occurs during liquid feeding or dispersion.

[0032] In the mixing step, the lower limit value of the solid content concentration of the mixed liquid of the dispersion of fibrous cellulose and the latex of the rubber component (hereinafter also simply referred to as "mixed liquid") is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and still more preferably 3.0% by mass or more. The upper limit value of the solid content concentration of the mixed liquid is preferably 20.0% by mass or less, more preferably 15.0% by mass or less, and still more preferably 10.0% by mass or less. The solid content concentration of the mixed liquid may be, for example, 0.5 to 20.0% by mass, 1.0 to 15.0% by mass, or 3.0 to 10.0% by mass.

[0033] When the solid content concentration of the mixed liquid is within the above range, the fibrous cellulose and the rubber component can be uniformly mixed, and it becomes easier to manufacture a composite material with excellent strength. Furthermore, in the drying step after the mixing step, the amount of energy for removing the solvent can be reduced, and furthermore, it becomes difficult for aggregation to occur between the fine fibrous celluloses in the obtained composite material.

[0034] The solid content concentration can be calculated by the following formula (II) from the mass of the obtained dried product after drying a predetermined amount of the dispersion, latex, or mixed solution in a dryer at 105 °C until a constant weight is achieved and the mass of the liquid subjected to drying. Solid content concentration of the liquid subjected to drying [%] = mass of the dried product [g] / mass of the liquid subjected to drying [g] × 100 (II)

[0035] In the mixed solution, the lower limit of the amount of fibrous cellulose solid content with respect to 100 parts by mass of the rubber component solid content is preferably 5 parts by mass or more, more preferably 10 parts by mass or more. Also, the upper limit of the amount of fibrous cellulose solid content with respect to 100 parts by mass of the rubber component is preferably 500 parts by mass or less, more preferably 50 parts by mass or less. When the amount of fibrous cellulose solid content with respect to 100 parts by mass of the rubber component is within the above range, it becomes easier to obtain a sufficient reinforcing effect by the fibrous cellulose, and it also becomes easier to improve the processability of the composite material. The amount of fibrous cellulose solid content with respect to 100 parts by mass of the rubber component may be, for example, 5 to 500 parts by mass, 10 to 50 parts by mass, or 15 to 25 parts by mass.

[0036] [Heating and Drying Step] The method for producing the composite material may further include a step of heating and drying the mixed solution containing the fibrous cellulose and the rubber component obtained in the charging step or the mixing step. For the heating and drying step of the mixed solution, known heating and drying devices can be used, such as hot air drying devices, stirring drying devices, rotary drying devices, disk drying devices, roll-type heating devices, plate-type heating devices, fluidized bed drying devices, band-type drying devices, filtration drying devices, vibrating fluidized bed drying devices, pneumatic drying devices, vacuum drying devices, infrared heating devices, far-infrared heating devices, microwave heating devices, high-frequency drying devices, etc.

[0037] [Other Steps] The method for producing the composite material may include other steps in addition to the aforementioned charging step, mixing step, and heating and drying step. For example, an uncrosslinked rubber composition can be produced by adding a crosslinking agent to the dried product obtained in the heating and drying step and kneading.

[0038] Mixing refers to the process of uniformly dispersing a crosslinking agent and other compounding agents in a masterbatch (in the present invention, it refers to a composition containing a rubber component and fibrous cellulose but not containing a crosslinking agent). Mixing can be carried out as is known in the art. For example, it can be carried out using a Banbury mixer, kneader, open roll, etc. Examples of the crosslinking agent include sulfur and peroxide. Examples of other compounding agents include vulcanization accelerators such as sulfenamide (N-t-butyl-2-benzothiazole sulfenamide, etc.), zinc oxide, stearic acid, vulcanization accelerator aids, reinforcing agents such as carbon black and silica, silane coupling agents, oils, curing resins, waxes, anti-aging agents, peptizing agents, colorants, pH adjusters, and the like that can be used in the field of rubber. Further, a rubber component can be added to the masterbatch together with the crosslinking agent and kneaded to obtain a rubber composition with a diluted fibrous cellulose concentration.

[0039] After the mixing is completed, molding may be carried out as necessary. Examples of the molding apparatus include die molding, injection molding, extrusion molding, blow molding, foam molding, etc., and it may be appropriately selected according to the shape, use, and molding method of the final product. For crosslinking, as long as the conditions for the crosslinking reaction proceed, there is no particular limitation on the temperature. Generally, when the uncrosslinked rubber composition obtained by kneading is heated for crosslinking (also referred to as vulcanization when sulfur is included), a crosslinked rubber composition can be obtained. The heating temperature is preferably 140°C or higher, 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 apparatus for performing mold vulcanization, can vulcanization, continuous vulcanization, etc. can be used.

[0040] Regarding crosslinking, as long as the conditions for the crosslinking reaction proceed, there is no particular limitation on the temperature. Generally, when the uncrosslinked rubber composition obtained by kneading is heated for crosslinking (also referred to as vulcanization when sulfur is included), a crosslinked rubber composition can be obtained. The heating temperature is preferably 140°C or higher, 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 apparatus for performing mold vulcanization, can vulcanization, continuous vulcanization, etc. can be used.

[0041] [Fibrous Cellulose] The fibrous cellulose is not particularly limited, and known ones can be used. The fibrous cellulose is preferably microfibrillar cellulose with an average fiber width of 1 nm or more and 1000 nm or less, or high-refined pulp with a freeness of 130 mL or more and 350 mL or less. Pulp with a freeness greater than 350 mL may also be used.

[0042] Pulp can be used as the raw material of the fibrous cellulose. The main component of the pulp is cellulose fiber. Examples of the pulp include chemical pulp, mechanical pulp, wastepaper pulp, non-wood pulp, and the like.

[0043] Examples of the chemical pulp include pulp derived from softwood (NKP), pulp derived from hardwood (LKP), and the like. Examples of the pulp derived from softwood include unbleached kraft pulp from softwood (NUKP), bleached kraft pulp from softwood (NBKP), semi-bleached kraft pulp from softwood (NSBKP), sulfite pulp from softwood (NSP), and the like. Examples of the pulp derived from hardwood include unbleached kraft pulp from hardwood (LUKP), bleached kraft pulp from hardwood (LBKP), semi-bleached kraft pulp from hardwood (LSBKP), sulfite pulp from hardwood (LSP), and the like.

[0044] Examples of the mechanical pulp include stone groundwood pulp (SGP), pressure groundwood pulp (PGW), refiner groundwood pulp (RGP), thermomechanical pulp (TGP), chemigroundwood pulp (CGP), groundwood pulp (GP), thermomechanical pulp (TMP), and the like.

[0045] Examples of the wastepaper pulp include disintegrated wastepaper pulp, disintegrated and deinked wastepaper pulp, disintegrated, deinked, and bleached wastepaper pulp. Examples of the wastepaper used as the raw material of the wastepaper pulp include tea wastepaper, kraft envelope wastepaper, magazine wastepaper, newspaper wastepaper, flyer wastepaper, office wastepaper, corrugated cardboard wastepaper, high-quality wastepaper, Kent wastepaper, imitation wastepaper, deed wastepaper, and the like. Examples of non-wood pulp include various pulps such as pulp chemically or mechanically produced from non-wood fibers such as kenaf, cotton, hemp, and reed. These pulps may be used individually or in combination of two or more. Among them, chemical pulp is preferred.

[0046] When using high-refined pulp for fibrous cellulose, the freeness (Canadian Standard Freeness (CSF)) of the high-refined pulp is preferably 130 mL or more and 350 mL or less, more preferably 150 mL or more and 300 mL or less, and even more preferably 180 mL or more and 250 mL or less. The freeness of the pulp (unit: mL CSF) is measured according to JIS P8121-2.

[0047] The fibrous cellulose is more preferably microfibrillated cellulose. Being microfibrillated cellulose is preferable in that the strength of the rubber composite can be further improved. The upper limit value of the fiber width of the microfibrillated cellulose (hereinafter also simply referred to as "microfibrillated cellulose") is preferably 1000 nm or less, more preferably 100 nm or less, even more preferably 50 nm or less, still more preferably 20 nm or less, and particularly preferably 10 nm or less.

[0048] The average fiber width of the microfibrillated cellulose is, for example, 1000 nm or less. The average fiber width of the microfibrillated cellulose is preferably, for example, 1 nm or more and 1000 nm or less, more preferably 2 nm or more and 1000 nm or less, even more preferably 2 nm or more and 100 nm or less, still more preferably 2 nm or more and 50 nm or less, and particularly preferably 2 nm or more and 10 nm or less. Note that the microfibrillated cellulose is, for example, single-fiber cellulose.

[0049] The fiber width of microfibrillar cellulose is measured as follows using, for example, an electron microscope. First, an aqueous suspension of microfibrillar 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 carbon film-coated grid that has been hydrophilized to obtain a sample for TEM observation. When fibers with a wide width are included, the SEM image of the surface cast on glass may be observed. Next, observation is performed on an electron microscope image at any one of magnifications of 1000 times, 5000 times, 10000 times, or 50000 times according to the width of the fiber to be observed. However, the sample, observation conditions, and magnification are adjusted so as to satisfy the following conditions.

[0050] (1) Draw a straight line X at an arbitrary position within the observation image, and 20 or more fibers intersect the straight line X. (2) Draw a straight line Y that intersects perpendicularly to the straight line within the same image, and 20 or more fibers intersect the straight line Y.

[0051] For an observation image that satisfies the above conditions, visually read the widths of the fibers that intersect the straight line X and the straight line Y. In this way, obtain three or more observation images of surface portions that do not overlap with each other at least. Next, for each image, read the widths of the fibers that intersect the straight line X and the straight line Y. As a result, at least 20 × 2 × 3 = 120 fiber widths are read. Then, the average value of the read fiber widths is defined as the number average fiber width of the microfibrillar cellulose.

[0052] The fiber length of microfibrillar cellulose is not particularly limited, but for example, it is preferably 0.1 μm or more and 1000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and even more preferably 0.1 μm or more and 600 μm or less. By setting the fiber length within the above range, destruction of the crystalline regions of the microfibrillar cellulose can be suppressed. The fiber length of the microfibrillar cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

[0053] The microfibrillar cellulose preferably has a type I crystal structure. Here, the fact that the microfibrillar cellulose has a type I crystal structure can be identified from the diffraction profile obtained from a wide-angle X-ray diffraction photograph using graphite-monochromated CuKα (λ = 1.5418 Å). Specifically, it can be identified because it has typical peaks at two positions around 2θ = 14° or more and 17° or less and around 2θ = 22° or more and 23° or less. The proportion of the type I crystal structure in the microfibrillar cellulose is preferably, for example, 30% or more, more preferably 40% or more, and even more preferably 50% or more. Regarding the crystallinity, an X-ray diffraction profile is measured, and it is determined by a conventional method from the pattern (Seagal et al., Textile Research Journal, Vol. 29, page 786, 1959).

[0054] The axial ratio (fiber length / fiber width) of the microfibrillar cellulose is not particularly limited, but is preferably, for example, 50 or more and 10,000 or less, and more preferably 100 or more and 1,000 or less. By setting the axial ratio to the above lower limit or more, it becomes easier to form a composite material containing the microfibrillar cellulose. By setting the axial ratio to the above upper limit or less, it is preferable in terms of facilitating handling such as dilution when, for example, the microfibrillar cellulose is treated as a dispersion liquid.

[0055] The microfibrillar cellulose in the present embodiment has, for example, both a crystalline region and an amorphous region. The microfibrillar cellulose having both a crystalline region and an amorphous region and having an axial ratio within the above range is realized by the method for producing microfibrillar cellulose described later.

[0056] The microfibrillar cellulose in this embodiment preferably has an ionic substituent. The ionic substituent can include, for example, either or both of an anionic group and a cationic group. In this embodiment, it is particularly preferable to have an anionic group as the ionic substituent. Further, the ionic substituent is preferably a group introduced into the microfibrillar cellulose via an ester bond or an ether bond, and more preferably a group introduced into the microfibrillar cellulose via an ester bond. In this case, the ester bond is preferably formed by dehydration condensation of the microfibrillar cellulose and a compound that becomes the ionic substituent.

[0057] Examples of the anionic group as the ionic group include, for example, a phosphooxo acid group or a substituent derived from a phosphooxo acid group (sometimes simply referred to as a phosphooxo acid group), a carboxy group or a substituent derived from a carboxy group (sometimes simply referred to as a carboxy group), a sulfur oxo acid group or a substituent derived from a sulfur oxo acid group (sometimes simply referred to as a sulfur oxo acid group), a xanthate group or a substituent derived from a xanthate group (sometimes simply referred to as a xanthate group), a phosphon group or a substituent derived from a phosphon group, a phosphine group or a substituent derived from a phosphine group, a sulfone group or a substituent derived from a sulfone group, a carboxyalkyl group, and the like. Among them, the anionic group is preferably at least one selected from the group consisting of a phosphooxo acid group, a substituent derived from a phosphooxo acid group, a carboxy group, a sulfur oxo acid group, a substituent derived from a sulfur oxo acid group, a carboxymethyl group, a carboxyethyl group, and a sulfone group, more preferably at least one selected from the group consisting of a phosphooxo acid group, a substituent derived from a phosphooxo acid group, a carboxy group, a sulfur oxo acid group, and a substituent derived from a sulfur oxo acid group, and particularly preferably a phosphooxo acid group. By introducing a phosphooxo acid group as the anionic group, for example, even under alkaline conditions or acidic conditions, the dispersibility of the microfibrillar cellulose can be further enhanced, and as a result, a high-strength and highly transparent sheet can be easily obtained. Examples of the cationic group as the ionic group include an ammonium group, a phosphonium group, a sulfonium group, and the like. Among them, the cationic group is preferably an ammonium group.

[0058] The phosphooxo acid group or the substituent derived from the phosphooxo 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 fibrillar cellulose. In this case, the plurality of substituents represented by the following formula (1) introduced may be the same or different from each other.

[0059]

Chemical formula

[0060] In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (provided that 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 each α and α' may be O - . The n α may all be the same or different from each other. β b+ is a monovalent or higher cation composed of an organic or inorganic substance.

[0061] Each R is a hydrogen atom, a saturated - straight - chain hydrocarbon group, a saturated - branched - chain hydrocarbon group, a saturated - cyclic hydrocarbon group, an unsaturated - straight - chain hydrocarbon group, an unsaturated - branched - chain hydrocarbon group, an unsaturated - cyclic hydrocarbon group, an aromatic group, or a derivative group thereof. Also, in formula (1), n is preferably 1.

[0062] Examples of the saturated straight-chain hydrocarbon group include, but are not particularly limited to, a methyl group, an ethyl group, an n-propyl group, or an n-butyl group. Examples of the saturated branched-chain hydrocarbon group include, but are not particularly limited to, an i-propyl group, or a t-butyl group. Examples of the saturated cyclic hydrocarbon group include, but are not particularly limited to, a cyclopentyl group, or a cyclohexyl group. Examples of the unsaturated straight-chain hydrocarbon group include, but are not particularly limited to, a vinyl group, or an allyl group. Examples of the unsaturated branched-chain hydrocarbon group include, but are not particularly limited to, an i-propenyl group, or a 3-butenyl group. Examples of the unsaturated cyclic hydrocarbon group include, but are not particularly limited to, a cyclopentenyl group, a cyclohexenyl group. Examples of the aromatic group include, but are not particularly limited to, a phenyl group, or a naphthyl group.

[0063] In addition, examples of the derivative group in R include a functional group in which at least one type selected from functional groups such as a carboxy group, a carboxylate group (-COO - )), a hydroxy group, an amino group, and an ammonium group is added or substituted with respect to the main chain or side chain of the above various hydrocarbon groups, but are 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 phosphonooxy acid group can be set within an appropriate range, penetration into the fiber raw material can be facilitated, and the yield of microfibrillar cellulose can also be increased. When there are a plurality of Rs in formula (1) or when a plurality of types of substituents represented by formula (1) are introduced into the microfibrillar cellulose, the plurality of existing Rs may be the same or different from each other.

[0064] β b+is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of the organic onium ions include, for example, organic ammonium ions and organic onium ions. Examples of the organic ammonium ions include, for example, aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic onium ions include, for example, aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed 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. When there are a plurality of β in formula (1) or when a plurality of substituents represented by formula (1) are introduced into the microfibrillar cellulose, the plurality of β b+ may be the same or different from each other. As the monovalent or higher cation composed of an organic or inorganic substance, sodium or potassium ions, which are less likely to turn yellow when the fiber raw material containing β b+ is heated and are easy to use industrially, are preferred, but are not particularly limited. b+ More specifically, examples of the phosphonooxy acid group or the substituent derived from the phosphonooxy acid group include a phosphoric acid group (-PO3H2), a salt of the phosphoric acid group, a phosphorous acid group (phosphonic acid group) (-PO2H2), and a salt of the phosphorous acid group (phosphonic acid group). Further, the phosphonooxy acid group or the substituent derived from the phosphonooxy acid group may be a group in which phosphoric acid groups are condensed (for example, a pyrophosphoric acid group), a group in which phosphonic acids are condensed (for example, a polyphosphonic acid group), a phosphoric acid ester group (for example, a monomethyl phosphoric acid group, a polyoxyethylene alkyl phosphoric acid group), an alkyl phosphonic acid group (for example, a methyl phosphonic acid group), etc.

[0065]

[0066] ​Further, the sulfur oxo acid group (sulfur oxo acid group or a substituent derived from a sulfur oxo acid 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 microfibrillar cellulose. In this case, the plurality of substituents represented by the following formula (2) introduced may be the same or different from each other.

[0067]

Chemical formula

[0068] In formula (2), b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (provided that 1 = b × m). When n is 2 or more, the plurality of p's may be the same number or different numbers. In formula (2), β b+ is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed 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 composed 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, and the like. When a plurality of types of substituents represented by formula (2) are introduced into the microfibrillar cellulose, the plurality of βs b+ may be the same or different from each other. As the monovalent or higher cation composed of an organic or inorganic substance, sodium or potassium ions, which are less likely to turn yellow when the fiber raw material containing β b+ is heated and are easy to use industrially, are preferable, but are not particularly limited.

[0069] The amount of ionic substituents introduced into microfibrillar cellulose is preferably, for example, 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, still more preferably 0.40 mmol / g or more, and particularly preferably 0.60 mmol / g or more per 1 g (mass) of microfibrillar cellulose. Also, the amount of ionic substituents introduced into microfibrillar cellulose is preferably, for example, 5.20 mmol / g or less, more preferably 3.65 mmol / g or less, still more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, still even more preferably 2.00 mmol / g or less, yet still even more preferably 1.50 mmol / g or less, and particularly preferably 1.00 mmol / g or less per 1 g (mass) of microfibrillar cellulose. Here, the denominator in mmol / g indicates the mass of microfibrillar cellulose when the counter ion of the ionic substituent is a hydrogen ion (H + ). By setting the amount of ionic substituents introduced within the above range, the fibrillation of the fiber raw material can be facilitated, and the stability of microfibrillar cellulose can be enhanced.

[0070] The amount of ionic substituents introduced into microfibrillar cellulose can be measured, for example, by a neutralization titration method after subjecting the cellulose fiber to a fibrillation treatment. In the measurement by the neutralization titration method, the amount introduced is measured by determining the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to the obtained slurry containing microfibrillar cellulose.

[0071] Figure 3 is a graph showing the relationship between the amount of NaOH dropped and the pH for a slurry containing microfibrillar cellulose having phosphono-oxy acid groups. The amount of phosphono-oxy acid groups introduced into microfibrillar cellulose is measured, for example, as follows. First, ion-exchanged water is added to the target cellulose fiber to prepare a slurry with a solid content concentration of 0.2% by mass. This slurry is treated 4 times at a pressure of 200 MPa using a wet atomization device (manufactured by Sugino Machine Limited, Starburst) to obtain a microfibrillated cellulose dispersion (slurry) containing microfibrillated cellulose. Then, the microfibrillated cellulose dispersion is treated with a strongly acidic ion-exchange resin. Next, while adding an aqueous sodium hydroxide solution, the change in pH is observed to obtain a titration curve as shown in the upper part of FIG. 3. In the titration curve shown in the upper part of FIG. 3, the pH measured with respect to the amount of alkali added is plotted, and in the titration curve shown in the lower part of FIG. 3, the increment (differential value) (1 / mmol) of pH with respect to the amount of alkali added is plotted. In this neutralization titration, in the curve where the pH measured with respect to the amount of alkali added is plotted, two points where the increment (differential value of pH with respect to the amount of alkali dropped) becomes maximum are confirmed. Among these, the first maximum point of the increment obtained first after starting to add the alkali is called the first end point, and the next maximum point of the increment is called the second end point. The amount of alkali required from the start of titration to the first end point is equal to the first dissociation acid amount of the microfibrillated cellulose contained in the slurry used for titration, and the amount of alkali required from the first end point to the second end point is equal to the second dissociation acid amount of the microfibrillated cellulose contained in the slurry used for titration, and the amount of alkali required from the start of titration to the second end point is equal to the total dissociation acid amount of the microfibrillated cellulose contained in the slurry used for titration. And the value obtained by dividing the amount of alkali required from the start of titration to the first end point by the solid content (g) in the titration target slurry becomes the amount of phosphonooxy group introduced (mmol / g). Note that when simply referring to the amount of phosphonooxy group introduced (or the amount of phosphonooxy group), it represents the first dissociation acid amount. In FIG. 3, the region from the start of titration to the first end point is referred to as the first region, and the region from the first end point to the second end point is referred to as the second region. For example, when the phosphooxo acid group is a phosphate group and this phosphate group undergoes condensation, apparently, the amount of weak acidic groups in the phosphooxo acid group (also referred to as the second dissociation acid amount in this specification) decreases, and the amount of alkali required in the second region becomes less than the amount of alkali required in the first region. On the other hand, the amount of strong acidic groups in the phosphooxo acid group (also referred to as the first dissociation acid amount in this specification) coincides with the amount of phosphorus atoms regardless of the presence or absence of condensation. Further, when the phosphooxo acid group is a phosphorous acid group, since there are no weak acidic groups in the phosphooxo acid group, the amount of alkali required in the second region may decrease or the amount of alkali required in the second region may be zero. In this case, in the titration curve, there is only one point where the increment of pH becomes maximum.

[0072] Note that since the denominator in the above-mentioned introduction amount of phosphooxo acid groups (mmol / g) indicates the mass of the acid-form microfibrillar cellulose, it represents the amount of phosphooxo acid groups possessed by the acid-form microfibrillar cellulose (hereinafter referred to as the amount of phosphooxo acid groups (acid form)). On the other hand, when the counter ion of the phosphooxo acid group is replaced with an arbitrary cation C so as to be charge equivalent, by converting the denominator to the mass of the microfibrillar cellulose when the cation C is the counter ion, the amount of phosphooxo acid groups possessed by the microfibrillar cellulose having the cation C as the counter ion (hereinafter referred to as the amount of phosphooxo acid groups (C form)) can be obtained. That is, it is calculated by the following calculation formula. Amount of phosphooxo acid groups (C form) = Amount of phosphooxo acid groups (acid form) / {1 + (W - 1) × P / 1000} P [mmol / g]: Total amount of anions derived from phosphooxo acid groups possessed by microfibrillar cellulose (total dissociation acid amount of phosphooxo acid groups) W: Formula weight per monovalent of cation C (for example, Na is 23, Al is 9)

[0073] FIG. 4 is a graph showing the relationship between the amount of NaOH dropped and pH for a dispersion of microfibrillar cellulose having a carboxy group as an ionic substituent. The introduction amount of carboxy groups into the microfibrillar cellulose is measured, for example, as follows. First, ion-exchanged water is added to the target cellulose fiber to prepare a slurry with a solid content concentration of 0.2% by mass. This slurry is treated 4 times at a pressure of 200 MPa using a wet atomization device (manufactured by Sugino Machine Limited, Starburst) to obtain a microfibrillated cellulose dispersion (slurry) containing microfibrillated cellulose. Then, the microfibrillated cellulose dispersion is treated with a strongly acidic ion exchange resin. Next, while adding an aqueous sodium hydroxide solution, the change in pH is observed to obtain a titration curve as shown in the upper part of FIG. 4. In the titration curve shown in the upper part of FIG. 4, the pH measured with respect to the amount of alkali added is plotted, and in the titration curve shown in the lower part of FIG. 4, the increment (differential value) (1 / mmol) of pH with respect to the amount of alkali added is plotted. In this neutralization titration, in the curve where the pH measured with respect to the amount of alkali added is plotted, one point where the increment (differential value of pH with respect to the amount of alkali dropped) is maximized is confirmed, and this maximum point is called the first end point. Here, the region from the start of titration to the first end point in FIG. 4 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. Then, the amount of carboxyl group introduction (mmol / g) is calculated by dividing the amount of alkali (mmol) required in the first region of the titration curve by the solid content (g) in the dispersion containing the microfibrillated cellulose to be titrated.

[0074] Note that since the denominator of the above-introduced carboxyl group amount (mmol / g) is the mass of the acid-type microfibrillated cellulose, it indicates the amount of carboxyl groups (hereinafter referred to as the carboxyl group amount (acid type)) possessed by the acid-type microfibrillated cellulose. On the other hand, when the counter ion of the carboxyl group is replaced with an arbitrary cation C so that the charge equivalent is achieved, by converting the denominator to the mass of the microfibrillated cellulose when the cation C is the counter ion, the amount of carboxyl groups (hereinafter referred to as the carboxyl group amount (C type)) possessed by the microfibrillated cellulose with the cation C as the counter ion can be obtained. That is, it is calculated by the following calculation formula. Carboxyl group amount (C type) = Carboxyl group amount (acid type) / {1 + (W - 1) × (Carboxyl group amount (acid type)) / 1000} W: Formula weight per monovalent cation C (e.g., 23 for Na, 9 for Al)

[0075] In the measurement of the amount of ionic substituents by titration, accurate values may not be obtained, such as when the dropping amount of one drop of aqueous sodium hydroxide solution is too large or the titration interval is too short, resulting in a lower amount of ionic substituents than the actual value. Appropriate dropping amounts and titration intervals are, for example, preferably titrating 10 - 50 μL of 0.1 N aqueous sodium hydroxide solution every 5 - 30 seconds. Also, in order to eliminate the influence of carbon dioxide dissolved in the microfibrillar cellulose dispersion, for example, from 15 minutes before the start of titration to the end of titration, it is desirable to measure while blowing an inert gas such as nitrogen gas into the slurry and so on.

[0076] Also, the amount of sulfate ester groups and sulfone groups introduced into the microfibrillar cellulose is measured by ICP emission spectrometry after wet ashing the obtained microfibrillar cellulose using perchloric acid and concentrated nitric acid and then diluting it at an appropriate magnification to measure the sulfur content. The value obtained by dividing this sulfur content by the absolute dry mass of the tested microfibrillar cellulose is defined as the amount of sulfur oxoacid groups and sulfone groups (unit: mmol / g).

[0077] In order to obtain microfibrillar cellulose with ionic substituents introduced as described above, it is preferable to have an ionic substituent introduction step, a washing step, an alkali treatment step (neutralization step), and a fibrillation treatment step in this order for the fiber raw material containing cellulose described above. Instead of the washing step, or in addition to the washing step, an acid treatment step may be included. Also, an enzyme treatment step may be included after the fibrillation treatment step. Examples of the ionic substituent introduction step include a phosphorous oxoacid group introduction step, a carboxy group introduction step, a sulfur oxoacid group introduction step, a xanthate group introduction step, a phosphonate or phosphine group introduction step, a sulfone group introduction step, and a cation group introduction step. Each will be described below.

[0078] <Phosphorous Oxoacid Group Introduction Step> When obtaining cellulose fibers having an ionic substituent, it is preferable to provide an ionic substituent introduction step before the fibrillation treatment step. Examples of the ionic substituent introduction step include a phosphonooxy group introduction step. The phosphonooxy group introduction step is a step of allowing at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing a phosphonooxy group to act on a fiber raw material containing cellulose by reacting with a hydroxyl group of the fiber raw material containing cellulose. By this step, cellulose fibers having a phosphonooxy group can be obtained.

[0079] In the phosphonooxy group introduction step according to this embodiment, the reaction between the fiber raw material containing cellulose and 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"). On the other hand, the reaction between the fiber raw material containing cellulose and compound A may be carried out in the absence of compound B.

[0080] As an example of a method for allowing Compound A to act on a fiber raw material in the co - presence of Compound B, a method of mixing Compound A and Compound B with the fiber raw material in a dry state, a wet state, or a slurry state can be mentioned. Among these, it is preferable to use the fiber raw material in a dry state or a wet state because of the high uniformity of the reaction, and it is particularly preferable to use the fiber raw material in a dry state. The form of the fiber raw material is not particularly limited, but for example, it is preferably in a cotton - like or thin - sheet - like form. For Compound A and Compound B, methods of adding them to the fiber raw material in a powdery form, in a solution form dissolved in a solvent, or in a molten state heated above the melting point can be mentioned. Among these, because of the high uniformity of the reaction, it is preferable to add them in a solution form dissolved in a solvent, particularly in an aqueous solution state. Also, Compound A and Compound B may be added to the fiber raw material simultaneously, separately, or as a mixture. The method of adding Compound A and Compound B is not particularly limited, but when Compound A and Compound B are in a solution state, the fiber raw material may be immersed in the solution to absorb the liquid and then taken out, or the solution may be dropped onto the fiber raw material. Also, the required amounts of Compound A and Compound B may be added to the fiber raw material, or after adding excessive amounts of Compound A and Compound B to the fiber raw material respectively, the excess Compound A and Compound B may be removed by pressing or filtration.

[0081] The Compound A used in this embodiment may be any compound having a phosphorus atom and capable of forming an ester bond with cellulose, such as phosphoric acid or its salt, phosphorous acid or its salt, dehydrated condensed phosphoric acid or its salt, phosphoric anhydride (phosphorus pentoxide), etc., but is not particularly limited. It is not used. As the phosphoric acid, those with various purities can be used. For example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid can be used. As the phosphorous acid, 99% phosphorous acid (phosphonic acid) can be mentioned. The dehydrated condensed phosphoric acid is a substance in which two or more molecules of phosphoric acid are condensed by a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. As the phosphate, phosphite, and dehydrated condensed phosphate, lithium salts, sodium salts, potassium salts, ammonium salts, etc. of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid can be mentioned, and these can have various degrees of neutralization. Among these, from the viewpoints of high introduction efficiency of the phosphate group, easier improvement of the fibrillation efficiency in the fibrillation step described later, low cost, and easy 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 preferable, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid, sodium phosphite are more preferable.

[0082] The addition amount of Compound A to the fiber raw material is not particularly limited. For example, when the addition amount of Compound A is converted to the phosphorus atomic weight, the addition amount of phosphorus atoms to the fiber raw material (dry mass) is preferably 0.5 mass% or more and 100 mass% or less, more preferably 1 mass% or more and 50 mass% or less, and even more preferably 2 mass% or more and 30 mass% or less. By setting the addition amount of phosphorus atoms to the fiber raw material within the above range, the yield of the microfibrillar cellulose can be further improved. On the other hand, by setting the addition amount of phosphorus atoms to the fiber raw material below the above upper limit value, the balance between the effect of improving the yield and the cost can be achieved.

[0083] Compound B used in this embodiment is at least one selected from urea and its derivatives as described above. 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. Further, 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.

[0084] The addition amount of compound B relative to the fiber raw material (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.

[0085] In the reaction of the fiber raw material containing cellulose and compound A, in addition to compound B, for example, amides or amines may be contained in the reaction system. Examples of amides include formamide, dimethylformamide, acetamide, dimethylacetamide, and the like. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine, and the like. Among these, triethylamine is particularly known to act as a good reaction catalyst.

[0086] In the step of introducing the phosphooxo acid group, after adding or mixing Compound A or the like to the fiber raw material, it is preferable to subject the fiber raw material to heat treatment. As the heat treatment temperature, it is preferable to select a temperature at which the phosphooxo acid group can be efficiently introduced while suppressing thermal decomposition and hydrolysis reactions of the fiber. The heat treatment temperature is preferably, for example, 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. Also, for the heat treatment, equipment having various heat media can be used. For example, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heating device, a plate-type heating device, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer device, a pneumatic dryer, a vacuum dryer, an infrared heating device, a far-infrared heating device, a microwave heating device, and a high-frequency dryer can be used.

[0087] In the heat treatment according to this embodiment, for example, after adding Compound A to a thin sheet-like fiber raw material by a method such as impregnation, a method of heating or a method of heating while kneading or stirring the fiber raw material and Compound A with a kneader or the like can be adopted. Thereby, it becomes possible to suppress the concentration unevenness of Compound A in the fiber raw material and to introduce the phosphooxo acid group more uniformly onto the surface of the cellulose fiber contained in the fiber raw material. This is presumably because when water molecules move to the surface of the fiber raw material during drying, the dissolved Compound A is attracted to the water molecules by surface tension and also moves to the surface of the fiber raw material (that is, concentration unevenness of Compound A occurs), which can be suppressed.

[0088] In addition, the heating device used for the heat treatment is preferably a device that can always discharge moisture held by the slurry and moisture generated by the dehydration condensation (phosphoric acid esterification) reaction between the hydroxyl groups contained in the compound A and cellulose in the fiber raw material, etc., to the outside of the device system. Examples of such a heating device include a blower-type oven. By always discharging the moisture in the device system, in addition to suppressing the hydrolysis reaction of the phosphoric acid ester bond, which is the reverse reaction of phosphoric acid esterification, it is also possible to suppress the acid hydrolysis of the sugar chain in the fiber. Therefore, it becomes possible to obtain microfibrillar cellulose with a high aspect ratio.

[0089] The heat treatment time is preferably, for example, 1 second or more and 300 minutes or less, more preferably 1 second or more and 1000 seconds or less, and even more preferably 10 seconds or more and 800 seconds or less, after substantially removing moisture from the fiber raw material. In this embodiment, by setting the heating temperature and heating time within an appropriate range, the introduction amount of the phosphonooxy group can be made within a preferable range.

[0090] The phosphonooxy group introduction step may be performed at least once, but can also be repeated two or more times. By performing the phosphonooxy group introduction step two or more times, a large amount of phosphonooxy groups can be introduced into the fiber raw material.

[0091] The introduction amount of the phosphonooxy group with respect to the fiber raw material is preferably, for example, 0.10 mmol / g or more, 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 per 1 g (mass) of cellulose fiber. Also, the introduction amount of the phosphonooxy group with respect to the fiber raw material is preferably, for example, 5.20 mmol / g or less, more preferably 3.65 mmol / g or less, and even more preferably 3.00 mmol / g or less per 1 g (mass) of cellulose fiber. By setting the introduction amount of the phosphonooxy group within the above range, the fibrillation of cellulose fiber in the fibrillation treatment step can be facilitated, and the stability of microfibrillar cellulose can be enhanced.

[0092] <Carboxy group introduction step> As the ionic substituent introduction step, a carboxy group introduction step may be included. The carboxy group introduction step is performed by subjecting a fiber raw material containing cellulose to an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, TEMPO oxidation treatment, or treatment with a compound having a group derived from a carboxylic acid or a derivative thereof, or an acid anhydride of a compound having a group derived from a carboxylic acid or a derivative thereof.

[0093] The compound having a group derived from a carboxylic acid is not particularly limited, and 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. Also, ca The derivative of the compound having a group derived from a carboxylic acid is not particularly limited, and examples thereof include imidized products of acid anhydrides of compounds having a carboxy group and derivatives of acid anhydrides of compounds having a carboxy group. The imidized product of the acid anhydride of the compound having a carboxy group is not particularly limited, and examples thereof include imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0094] The acid anhydride of the compound having a group derived from a carboxylic acid is not particularly limited, and examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Also, the derivative of the acid anhydride of the compound having a group derived from a carboxylic acid is not particularly limited, and examples thereof include those in which at least a part of the hydrogen atoms of the acid anhydride of the compound having a carboxy group, such as dimethyl maleic anhydride, diethyl maleic anhydride, and diphenyl maleic anhydride, are substituted with substituents such as an alkyl group and a phenyl group.

[0095] In the carboxy group introduction step, when performing TEMPO oxidation treatment, for example, it is preferable to carry out the treatment under the conditions where the pH is 6 or more and 8 or less. Such treatment is also referred to as neutral TEMPO oxidation treatment. The neutral TEMPO oxidation treatment can be carried out, for example, by adding pulp as a fiber raw material, a nitroxyl radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to a sodium phosphate buffer solution (pH = 6.8). Furthermore, by co-existing sodium chlorite, the aldehyde generated in the oxidation process can be efficiently oxidized to a carboxy group. Also, the TEMPO oxidation treatment may be carried out under the conditions where the pH is 10 or more and 11 or less. Such treatment is also referred to as alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be carried out, for example, by adding a nitroxyl 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.

[0096] The amount of carboxyl groups introduced into the cellulose fibers varies depending on the type of substituent. For example, when introducing carboxyl groups by TEMPO oxidation, it is preferably 0.10 mmol / g or more, 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 per 1 g (mass) of the cellulose fibers. Also, the amount of carboxyl groups introduced into the 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, still more preferably 2.00 mmol / g or less, yet even more preferably 1.50 mmol / g or less, and particularly preferably 1.00 mmol / g or less. In addition, when the substituent is a carboxymethyl group, the amount of carboxyl groups introduced may be 5.8 mmol / g or less per 1 g (mass) of the cellulose fibers. By setting the amount of carboxyl groups introduced within the above range, the fibrillation of cellulose fibers in the fibrillation treatment step can be facilitated, and the stability of microfibrillated cellulose can be enhanced.

[0097] <Sulfonic Acid Group Introduction Step> As the ionic substituent introduction step, a sulfonic acid group introduction step may be included. In the sulfonic acid group introduction step, a cellulose fiber having a sulfonic acid group (sulfonic acid group-introduced fiber) can be obtained by reacting a hydroxyl group of a fiber raw material containing cellulose with a sulfur oxoacid.

[0098] In the sulfonic acid group introduction step, instead of Compound A in the above-described <Phosphorus Oxoacid Group Introduction Step>, at least one compound selected from compounds capable of introducing a sulfonic acid group by reacting with a hydroxyl group of a fiber raw material containing cellulose (hereinafter also referred to as "Compound C") is used. As Compound C, a compound having a sulfur atom and capable of forming an ester bond with cellulose Any substance may be used, and examples include sulfuric acid or its salts, sulfurous acid or its salts, sulfamic acid, etc., but it is not particularly limited. As sulfuric acid, those with various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid) can be used. As sulfurous acid, 5% sulfurous acid water can be mentioned. As the sulfate or sulfite, lithium salts, sodium salts, potassium salts, ammonium salts, etc. of sulfate or sulfite can be mentioned, and these can have various degrees of neutralization. As sulfamic acid, sulfamic acid, etc. can be used. In the sulfone group introduction step, it is preferable to use the compound B in the <phosphorus oxo acid group introduction step> described above in the same manner.

[0099] In the sulfone group introduction step, it is preferable to mix an aqueous solution containing a sulfur oxo acid, and urea and / or a urea derivative with the cellulose raw material, and then perform a heat treatment on the cellulose raw material. As the heat treatment temperature, it is preferable to select a temperature at which the sulfone group can be efficiently introduced while suppressing the thermal decomposition and hydrolysis reaction 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. Also, the heat treatment temperature is preferably 300 °C or lower, more preferably 250 °C or lower, and even more preferably 200 °C or lower.

[0100] In the heat treatment step, it is preferable to heat until substantially no moisture remains. For this reason, the heat treatment time varies depending on the amount of moisture contained in the cellulose raw material, the sulfur oxo acid, and the addition amount of the aqueous solution containing urea and / or a urea derivative, but for example, it is preferably 10 seconds or more and 10000 seconds or less. For the heat treatment, various devices having a heat medium can be used, for example, a hot air dryer, a stirring dryer, a rotary dryer, a disk dryer, a roll type heating device, a plate type heating device, a fluidized bed dryer, a band type dryer, a filtration dryer, a vibration fluidized dryer, a pneumatic dryer, a vacuum dryer, an infrared heating device, a far infrared heating device, a microwave heating device, a high frequency dryer can be used.

[0101] The introduction amount of sulfonic groups to the cellulose raw material is preferably 0.05 mmol / g or more, more preferably 0.10 mmol / g or more, still 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. Also, the introduction amount of sulfonic groups to the cellulose raw material is preferably 5.00 mmol / g or less, and more preferably 3.00 mmol / g or less. By setting the introduction amount of sulfonic groups within the above range, the fibrillation of cellulose fibers in the fibrillation treatment step can be facilitated, and the stability of microfibrillar cellulose can be enhanced.

[0102] <Oxidation step with a chlorine-based oxidizing agent (second carboxy group introduction step)> As the ionic substituent introduction step, an oxidation step with a chlorine-based oxidizing agent may be included. In the oxidation step with a chlorine-based oxidizing agent, a carboxy group is introduced into the fiber raw material by adding a chlorine-based oxidizing agent to the fiber raw material having a hydroxyl group in a wet or dry state and carrying out a reaction.

[0103] Examples of the chlorine-based oxidizing agent include hypochlorous acid, hypochlorite, chlorous acid, chlorite, chloric acid, chlorate, perchloric acid, perchlorate, chlorine dioxide, etc. From the viewpoints of the introduction efficiency of substituents, and thus the fibrillation efficiency, cost, and ease of handling, the chlorine-based oxidizing agent is preferably sodium hypochlorite, sodium chlorite, or chlorine dioxide. When adding the chlorine-based oxidizing agent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or it may be dissolved in an appropriate solvent and then added.

[0104] The concentration of the chlorine-based oxidizing agent in the solution in the oxidation step with a chlorine-based oxidizing agent is preferably 1 mass% or more and 1,000 mass% or less, more preferably 5 mass% or more and 500 mass% or less, and still more preferably 10 mass% or more and 100 mass% or less, when converted to the available chlorine concentration, for example. It is more preferable. The addition amount of the chlorine-based oxidizing agent with respect to 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 10 parts by mass or more and 10,000 parts by mass or less, and even more preferably 100 parts by mass or more and 5,000 parts by mass or less.

[0105] The reaction time with the chlorine-based oxidizing agent in the oxidation step using the chlorine-based oxidizing agent can vary depending on the reaction temperature. For example, it is preferably 1 minute or more and 1,000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and even more preferably 20 minutes or more and 400 minutes or less. The pH during the reaction is preferably 5 or more and 15 or less, more preferably 7 or more and 14 or less, and even more preferably 9 or more and 13 or less. Also, at the start of the reaction and during the reaction, it is preferable to maintain a constant pH (for example, pH 11) while appropriately adding hydrochloric acid or sodium hydroxide. Further, after the reaction, excess reaction reagents, by-products, etc. may be washed and removed by filtration or the like.

[0106] <Zanthate group introduction step> The production process of the microfibrous cellulose may include a zanthate group introduction step as an ionic substituent introduction step. In the zanthate group introduction step, a cellulose fiber having a zanthate group (zanthate group-introduced fiber) can be obtained by substituting the hydroxyl group of the fiber raw material containing cellulose with a zanthate group represented by the following formula (3). ―OCSS - M + ……(3) Here, M + is at least one selected from a hydrogen ion, a monovalent metal ion, an ammonium ion, an aliphatic or aromatic ammonium ion.

[0107] In the step of introducing a xanthate group, first, an alkali treatment is performed by treating a fiber raw material containing the above cellulose with an alkali solution to obtain alkali cellulose. Examples of the alkali solution include an aqueous solution of an alkali metal hydroxide and an aqueous solution of an alkaline earth metal hydroxide. Among them, the alkali solution is preferably an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, and particularly preferably an aqueous solution of sodium hydroxide. When the alkali solution is an aqueous solution of an alkali metal hydroxide, the concentration of the alkali metal hydroxide in the aqueous solution of the alkali metal hydroxide is preferably 4% by mass or more, and more preferably 5% by mass or more. Further, the concentration of the alkali metal hydroxide in the aqueous solution of the alkali metal hydroxide is preferably 9% by mass or less. By setting the concentration of the alkali metal hydroxide to the above lower limit value or more, the mercerization of cellulose can proceed sufficiently, the amount of by-products generated during subsequent xanthation can be reduced, and as a result, the yield of the fiber with a xanthate group introduced can be increased. Thereby, the defibrillation treatment described later can be performed more effectively. Further, by setting the concentration of the alkali metal hydroxide to the above upper limit value or less, it is possible to suppress the penetration of the aqueous solution of the alkali metal hydroxide into the crystal region of cellulose while allowing mercerization to proceed, so that the crystal structure of cellulose I is easily maintained, and the yield of microfibrillar cellulose can be further increased.

[0108] The time of the above alkali treatment is preferably 30 minutes or more, and more preferably 1 hour or more. Further, the time of the alkali treatment is preferably 6 hours or less, and more preferably 5 hours or less. By setting the time of the alkali treatment within the above range, the final yield can be increased and the productivity can be increased.

[0109] The alkali cellulose obtained by the above alkali treatment is preferably subjected to solid-liquid separation thereafter to remove the aqueous solution component as much as possible. This can reduce the water content during the subsequent xanthation treatment and promote the reaction. As the method of solid-liquid separation, for example, general dehydration methods such as centrifugation and 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.

[0110] In the xanthate group introduction step, a xanthation treatment step is performed after the alkali treatment. In the xanthation treatment step, carbon disulfide (CS2) is reacted with alkali cellulose to convert the (-O - Na + ) group into a (-OCSS - Na + ) group to obtain xanthate group-introduced fibers. In the above, although the metal ions introduced into the alkali cellulose are typically described as Na + , the same reaction proceeds with other alkali metal ions.

[0111] In the xanthation treatment, it is preferable to supply 10% by mass or more of carbon disulfide based on the absolute dry mass of cellulose in the alkali cellulose. Also, in the xanthation treatment, the contact time between carbon disulfide and alkali cellulose is preferably 30 minutes or more, and more preferably 1 hour or more. Xanthation proceeds rapidly when carbon disulfide contacts the alkali cellulose, but it takes time for carbon disulfide to penetrate into the interior of the alkali cellulose. Therefore, 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 may be 6 hours or less, whereby sufficient penetration can proceed even with respect to the mass of the alkali cellulose after dehydration, and xanthation that enables reaction can be almost completed.

[0112] ​The reaction temperature in the zanthate treatment is preferably 46°C or lower. By setting the reaction temperature within the above range, it becomes easier to suppress the decomposition of alkali cellulose. Also, by setting the reaction temperature within the above range, the reaction tends to occur uniformly, so the generation of by-products can be suppressed, and furthermore, the removal of the generated zanthate groups can also be suppressed.

[0113] The amount of zanthate groups introduced in the zanthate group introduction step is preferably 0.60 mmol / g or more, more preferably 0.70 mmol / g or more, further preferably 0.80 mmol / g or more, still more preferably 1.00 mmol / g or more, and particularly preferably 1.20 mmol / g or more per 1 g (mass) of the fiber raw material. Also, the amount of zanthate groups introduced is preferably 5.00 mmol / g or less, more preferably 3.00 mmol / g or less per 1 g (mass) of the fiber raw material, for example. By setting the amount of zanthate groups introduced within the above range, it becomes easier to obtain a sheet excellent in transparency and excellent in yellowing resistance.

[0114] <Phosphonate group or phosphine group introduction step (phosphoalkylation step)> As the ionic substituent introduction step, a phosphonate group or phosphine group introduction step (phosphoalkylation step) may be included. In the phosphoalkylation step, as essential components, a compound having a reactive group and a phosphonate group or phosphine group (compound E A ), and as optional components, an alkali compound, and a compound B selected from the aforementioned urea and its derivatives are added to a fiber raw material having a hydroxyl group in a wet or dry state and reacted, whereby a phosphonate group or phosphine group is introduced into the fiber raw material.

[0115] Examples of the reactive group include an alkyl halide group, a vinyl group, an epoxy group (glycidyl group), and the like. Compound E A include, for example, vinylphosphonic acid, phenylvinylphosphonic acid, phenylvinylphosphinic acid, and the like. From the viewpoints of the introduction efficiency of substituents, and thus the defibrillation efficiency, cost, and ease of handling, compound EA is preferably vinylphosphonic acid. Furthermore, as an optional component, it is also preferable to similarly use compound B in the above-described <phosphooxo acid group introduction step>, and the addition amount is also preferably as described above.

[0116] Compound E A When adding, it may be added directly to the fiber raw material as a reagent (solid or liquid), or it may be dissolved in a suitable solvent and added. The fiber raw material is preferably alkali cellulose-ized in advance or alkali cellulose-ized simultaneously with the reaction. The method of alkali cellulose-ization is as described above. -ized, or preferably alkali cellulose-ized simultaneously with the reaction. The method of alkali cellulose-ization is as described above.

[0117] The temperature during the reaction is preferably, for example, 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.

[0118] Compound E A The addition amount of Compound E relative to 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.

[0119] The reaction time can vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and even more preferably 20 minutes or more and 400 minutes or less. Also, after the reaction, excess reaction reagents, by-products, etc. may be washed and removed by filtration or the like.

[0120] <Sulfone group introduction step (sulfonalkylation step) (second sulfone group introduction step)> As the ionic substituent introduction step, a sulfone group introduction step (sulfonalkylation step) may be included. In sulfonalkylation, as an essential component, a compound having a reactive group and a sulfone group (Compound E BAnd, by adding, as an optional component, an alkali compound and Compound B selected from the above-described urea and its derivatives to a fiber raw material having a hydroxyl group in a wet or dry state and carrying out a reaction, a sulfone group is introduced into the fiber raw material.

[0121] Examples of the reactive group include an alkyl halide group, a vinyl group, an epoxy group (glycidyl group), and the like. Compound E B Examples of Compound E include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and the like. Among them, from the viewpoints of the introduction efficiency of the substituent, and thus the defibrillation efficiency, cost, and ease of handling, Compound E B is preferably sodium vinylsulfonate. Furthermore, as an optional component, it is also preferable to similarly use Compound B in the above-described <phosphooxo acid group introduction step>, and the addition amount is also preferably as described above.

[0122] Compound E B When adding Compound E, it may be added directly to the fiber raw material as a reagent (solid or liquid), or it may be dissolved in a suitable solvent and then added. The fiber raw material is preferably alkali cellulose-ized in advance or alkali cellulose-ized simultaneously with the reaction. The method of alkali cellulose-ization is as described above.

[0123] The temperature during the reaction is preferably, for example, 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.

[0124] Compound E B The addition amount of Compound E with respect to 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.

[0125] The reaction time can vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and even more preferably 15 minutes or more and 400 minutes or less. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0126] <Carboxyalkylation step (third carboxy group introduction step)> As the ionic substituent introduction step, a carboxyalkylation step may be included. As an essential component, a compound having a reactive group and a carboxy group (Compound E C ), as an optional component, an alkali compound, and Compound B selected from the above-mentioned urea and its derivatives are added to a fibrous raw material having a hydroxyl group in a wet or dry state to carry out a reaction, whereby a carboxy group is introduced into the fibrous raw material.

[0127] Examples of the reactive group include an alkyl halide group, a vinyl group, an epoxy group (glycidyl group), and the like. Compound E C is preferably monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, or sodium 3-chloropropionate from the viewpoints of the introduction efficiency of the substituent, and thus the defibrillation efficiency, cost, and ease of handling. Furthermore, as an optional component, it is also preferable to use Compound B in the above-mentioned <phosphooxo acid group introduction step> in the same manner, and the addition amount is preferably the same as described above.

[0128] Compound E C When adding, it may be added to the fibrous raw material as a reagent (solid or liquid) as it is, or it may be dissolved in an appropriate solvent and added. The fibrous raw material is preferably alkali-celluloseized in advance or alkali-celluloseized simultaneously with the reaction. The method of alkali-celluloseization is as described above.

[0129] The temperature during the reaction is preferably, for example, 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.

[0130] Compound E C The addition amount relative to 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.

[0131] The reaction time can vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 3 minutes or more and 500 minutes or less, and even more preferably 5 minutes or more and 400 minutes or less. Further, after the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0132] <Cationic group introduction step (cationization step)> As an essential component, a compound having a reactive group and a cationic group (Compound E D ), and as an optional component, an alkali compound and Compound B selected from the aforementioned urea and its derivatives are added to a fiber raw material having a hydroxyl group in a wet or dry state and reacted to introduce a cation group into the fiber raw material.

[0133] Examples of the reactive group include an alkyl halide group, a vinyl group, an epoxy group (glycidyl group), etc. Examples of the cationic group include an ammonium group, a phosphonium group, a sulfonium group, etc. Among them, the cationic group is preferably an ammonium group. Compound E D As Compound E , glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride, etc. are preferable from the viewpoints of the introduction efficiency of the substituent, and thus the defibrillation efficiency, cost, and ease of handling. Furthermore, as an optional component, it is also preferable to similarly use Compound B in the <phosphooxo acid group introduction step> described above. The addition amount is also preferably the same as described above.

[0134] Compound E D When adding, it may be added directly to the fiber raw material as a reagent (solid or liquid), or it may be dissolved in an appropriate solvent and then added. It is preferable that the fiber raw material is pre-alkali celluloseized or alkali celluloseized simultaneously with the reaction. The method of alkali celluloseization is as described above.

[0135] The temperature during the reaction is preferably, for example, 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.

[0136] Compound E D The addition amount of Compound E with respect to 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.

[0137] The reaction time can vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 5 minutes or more and 500 minutes or less, and even more preferably 10 minutes or more and 400 minutes or less. Also, after the reaction, excess reaction reagents, by-products, etc. may be washed and removed by filtration or the like with water.

[0138] <Washing step> In the step of obtaining cellulose fibers having ionic substituents, a washing step can be performed on the ionic substituent-introduced fibers as necessary. The washing step is performed, for example, by washing the ionic substituent-introduced fibers with water or an organic solvent. Also, the washing step may be performed after each of the steps described below, and the number of washing times performed in each washing step is not particularly limited.

[0139] <Alkali treatment step> In the step of obtaining the cellulose fiber having an ionic substituent, an alkali treatment step may be provided between the ionic substituent introduction step and the fibrillation treatment step. The method of alkali treatment is not particularly limited, and examples thereof include a method of immersing the ionic substituent-introduced fiber in an alkali solution.

[0140] The alkali compound contained in the alkali solution is not particularly limited, and may be an inorganic alkali compound or an organic alkali compound. In the present embodiment, since the versatility is high, for example, it is preferable to use sodium hydroxide or potassium hydroxide as the alkali compound. Further, the solvent contained in the alkali solution may be either water or an organic solvent. Among them, the solvent contained in the alkali solution is preferably a polar solvent containing water or a polar organic solvent exemplified by alcohol, and more preferably an aqueous solvent containing at least water. As the alkali solution, since the versatility is high, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable.

[0141] The temperature of the alkali solution in the alkali treatment step is not particularly limited, but for example, it is preferably 5°C or higher and 80°C or lower, and more preferably 10°C or higher and 60°C or lower. The immersion time of the ionic substituent-introduced fiber in the alkali solution in the alkali treatment step is not particularly limited, but for example, it is preferably 5 minutes or longer and 30 minutes or shorter, and more preferably 10 minutes or longer and 20 minutes or shorter. The amount of the alkali solution used in the alkali treatment is not particularly limited, but for example, it is preferably 100% by mass or more and 100,000% by mass or less, and more preferably 1000% by mass or more and 10,000% by mass or less with respect to the absolute dry mass of the ionic substituent-introduced fiber.

[0142] In order to reduce the amount of the alkali solution used in the alkali treatment step, the introduction of the ionic substituent After the engineering process and before the alkali treatment process, the ionically substituted group-introduced fiber may be washed with water or an organic solvent. After the alkali treatment process and before the fibrillation treatment process, from the viewpoint of improving handleability, it is preferable to wash the ionically substituted group-introduced fiber that has undergone alkali treatment with water or an organic solvent.

[0143] <Acid treatment process> In the process of obtaining cellulose fibers having an ionic substituent, an acid treatment process may be provided between the ionic substituent introduction process and the fibrillation treatment process. For example, the ionic substituent introduction process, acid treatment, alkali treatment, and fibrillation treatment may be performed in this order.

[0144] The method of acid treatment is not particularly limited. For example, a method of immersing the fiber raw material in an acidic liquid containing an acid can be mentioned. The concentration of the acidic liquid to be used is not particularly limited, but for example, it is preferably 10% by mass or less, and more preferably 5% by mass or less. Also, the pH of the acidic liquid to be used is not particularly limited, but for example, it is preferably 0 or more and 4 or less, and more preferably 1 or more and 3 or less. As the acid contained in the acidic liquid, for example, an inorganic acid, sulfonic acid, carboxylic acid, etc. can be used. Examples of the inorganic acid include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, boric acid, etc. Examples of the sulfonic acid include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, etc. 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.

[0145] The temperature of the acid solution in the acid treatment is not particularly limited, but for example, it is preferably 5°C or higher and 100°C or lower, and more preferably 20°C or higher and 90°C or lower. The immersion time in the acid solution in the acid treatment is not particularly limited, but for example, it is preferably 5 minutes or longer and 120 minutes or shorter, and more preferably 10 minutes or longer and 60 minutes or shorter. The amount of the acid solution used in the acid treatment is not particularly limited, but for example, it is preferably 100% by mass or more and 100,000% by mass or less based on the absolute dry mass of the fiber raw material, and more preferably 1,000% by mass or more and 10,000% by mass or less.

[0146] <Fibrillation treatment step> By subjecting the fiber raw material or the ion group-introduced fiber to fibrillation treatment in the fibrillation treatment step, microfibrillar cellulose can be obtained. The fibrillation treatment is also referred to as a refinement treatment. In the fibrillation treatment step, for example, a fibrillation treatment apparatus can be used. The fibrillation treatment apparatus is not particularly limited, but for example, a high-speed fibrillator, a grinder (stone mill type crusher), a high-pressure homogenizer, an ultra-high pressure homogenizer, a high-pressure impact type crusher, a ball mill, a bead mill, a disk type refiner, a conical refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater can be used. Among the above-mentioned fibrillation treatment apparatuses, it is more preferable to use a high-speed fibrillator, a high-pressure homogenizer, or an ultra-high pressure homogenizer, which are less affected by the grinding media and have less risk of contamination.

[0147] In the fibrillation treatment step, for example, it is preferable to dilute the fiber raw material or the ion group-introduced fiber with a dispersion medium to form a slurry. As the dispersion medium, one or more selected from water and organic solvents such as polar organic solvents can be used. The polar organic solvent is not particularly limited, but for example, alcohols, polyhydric alcohols, ketones, ethers, esters, aprotic polar solvents, etc. are preferable. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, isobutyl alcohol, etc. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, glycerin, etc. Examples of ketones include acetone, methyl ethyl ketone (MEK), etc. Examples of ethers include diethyl ether, tetra hydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono n-butyl ether, propylene glycol monomethyl ether, etc. Examples of esters include ethyl acetate, butyl acetate, etc. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), etc.

[0148] The solid content concentration of the microfibrillar cellulose during the fibrillation treatment can be set as appropriate. Further, the slurry obtained by dispersing the ion group-introduced fiber in the dispersion medium may contain solids other than the ion group-introduced fiber, such as hydrogen-bonding urea.

[0149] <Enzyme treatment step> In the enzyme treatment step, an enzyme is added to the microfibrillar cellulose dispersion (slurry). The enzyme used at this time is preferably a cellulase-based enzyme. Cellulase-based enzymes are classified into the carbohydrate hydrolase family based on the higher-order structure of the catalytic domain having the cellulose hydrolysis reaction function. Cellulase-based enzymes are roughly classified into endo-glucanase and cellobiohydrolase according to their cellulose-degrading characteristics. Endo-glucanase has high hydrolyzability for the amorphous part of cellulose, soluble cellooligosaccharides, or cellulose derivatives such as carboxymethyl cellulose, randomly cuts their molecular chains from the inside, and reduces the degree of polymerization. In contrast, cellobiohydrolase decomposes the crystalline part of cellulose to give cellobiose. Also, cellobiohydrolase hydrolyzes from the end of the cellulose molecule and is also called an exo-type or processive enzyme. The enzyme used in the enzyme treatment step is not particularly limited, but it is preferable to use endo-glucanase.

[0150] In the enzyme treatment step, it is preferable to add an enzyme so that the enzyme activity is 0.1 nkat or more per 1 g of microfibrillar cellulose, more preferably add an enzyme so that the enzyme activity is 1.0 nkat or more, and even more preferably add an enzyme so that the enzyme activity is 10 nkat or more. Also, it is preferable to add an enzyme so that the enzyme activity is 100000 nkat or less per 1 g of microfibrillar cellulose, more preferably add an enzyme so that the enzyme activity is 50000 nkat or less, and even more preferably add an enzyme so that the enzyme activity is 10000 nkat or less. After adding the enzyme to the microfibrillar cellulose dispersion (slurry), it is preferably treated under the conditions of 0 °C or more and less than 80 °C for 1 minute or more and 100 hours or less, and then the enzyme is inactivated by placing it under the conditions of 80 °C or more.

[0151] <Substituent removal treatment> The method for producing microfibrillar cellulose may include a substituent removal treatment step of removing at least a part of the substituents from the microfibrillar cellulose having substituents and a fiber width of 1000 nm or less. In this specification, the step of removing at least a part of the substituents from the microfibrillar cellulose obtained in the above-described step is also referred to as the substituent removal treatment step.

[0152] Examples of the substituent removal treatment step include a step of heat-treating microfibrillar cellulose having substituents and a fiber width of 1000 nm or less, a step of enzyme-treating, a step of acid-treating, a step of alkali-treating, and the like. These may be carried out alone or in combination. Among them, the substituent removal treatment step is preferably a step of heat-treating or a step of enzyme-treating. By passing through the above treatment steps, at least a part of the substituents can be removed from the microfibrillar cellulose having substituents and a fiber width of 1000 nm or less, and microfibrillar cellulose having a substituent introduction amount of less than 0.5 mmol / g can be obtained.

[0153] The substituent removal treatment step is preferably carried out in a slurry state. That is, the substituent removal treatment step is preferably a step of heat-treating, a step of enzyme-treating, a step of acid-treating, a step of alkali-treating, etc. on a slurry containing microfibrillar cellulose having substituents and a fiber width of 1000 nm or less. By carrying out the substituent removal treatment step in a slurry state, it is possible to prevent the remaining of coloring substances generated by heating or the like during the substituent removal treatment, and acids, alkalis, salts, etc. added or generated. Thereby, the coloring of the microfibrillar cellulose obtained through step (B) can be suppressed. Further, when performing a removal treatment of salts derived from the substituents removed after the substituent removal treatment, it is also possible to enhance the removal efficiency of the salts.

[0154] When performing a substituent removal treatment 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 still more preferably 0.2% by mass or more. Further, 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 still more preferably 10% by mass or less. By setting 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 setting the concentration of the fine fibrous cellulose in the slurry within the above range, it is possible to prevent the remaining of coloring substances generated by heating or the like during the substituent removal treatment, as well as acids, alkalis, salts, etc. added or generated. Thereby, the coloring of the fine fibrous cellulose obtained through step (B) can be suppressed. Also, when performing a removal treatment of salts derived from the substituents removed after the substituent removal treatment, it is also possible to enhance the salt removal efficiency.

[0155] 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-treating step is preferably 40°C or higher, more preferably 50°C or higher, and still more preferably 60°C or higher. Further, the heating temperature in the heat-treating step is preferably 250°C or lower, more preferably 230°C or lower, and still more preferably 200°C or lower. Among them, when the substituent possessed by the fine fibrous cellulose to be subjected to the substituent removal treatment step is a phosphooxo acid group or a sulfone group, the heating temperature in the heat-treating step is preferably 80°C or higher, more preferably 100°C or higher, and still more preferably 120°C or higher.

[0156] 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, but a hot air heating device, a steam heating device, an electric heating device, a hydrothermal heating device, a fire heating device, an infrared heating device, a far-infrared heating device, a microwave heating device, a high-frequency heating device, a stirring drying device, a rotary drying device, a disk drying device, a roll-type heating device, a plate-type heating device, a fluidized bed drying device, a band-type drying device, a filtration drying device, a vibration fluidized drying device, a pneumatic drying device, or a vacuum drying device can be used. From the viewpoint of preventing evaporation, heating is preferably performed in a closed system, and from the viewpoint of further increasing the heating temperature, it is preferably performed in a pressure-resistant device or container. The heat treatment may be a batch treatment, a batch continuous treatment, or a continuous treatment.

[0157] When the substituent removal treatment step is a step of subjecting fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less to an enzymatic treatment, in the enzymatic treatment step, it is preferable to use a phosphoric acid ester hydrolase, a sulfuric acid ester hydrolase, or the like.

[0158] In the enzymatic treatment step, it is preferable to add an enzyme so that the enzyme activity is 0.1 nkat or more per 1 g of fine fibrous cellulose, more preferably 1.0 nkat or more, and even more preferably 10 nkat or more. Also, it is preferable to add an enzyme so that the enzyme activity is 100000 nkat or less per 1 g of fine fibrous cellulose, more preferably 50000 nkat or less, and even more preferably 10000 nkat or less. After adding the enzyme to the fine fibrous cellulose dispersion (slurry), it is preferable to perform the treatment for 1 minute or more and 100 hours or less under the conditions of 0 °C or more and less than 50 °C. It is more preferable to add the enzyme, and it is even more preferable to add the enzyme so that it is 10000 nkat or less. After adding the enzyme to the fine fibrous cellulose dispersion (slurry), it is preferable to perform the treatment for 1 minute or more and 100 hours or less under the conditions of 0 °C or more and less than 50 °C.

[0159] After the enzymatic reaction, a step of inactivating the enzyme may be provided. Examples of methods for inactivating the enzyme include a method of adding an acid component or an alkali component to the slurry that has undergone the enzyme treatment to inactivate the enzyme, and a method of raising the temperature of the slurry that has undergone the enzyme treatment to 90 °C or higher to inactivate the enzyme.

[0160] When the substituent removal treatment step is a step of subjecting fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less to an acid treatment, in the acid treatment step, it is preferable to add an acid compound that can be used in the above-described acid treatment step to the slurry.

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

[0162] In the substituent removal treatment step, it is preferable that the substituent removal reaction proceeds uniformly. In order to make the reaction proceed uniformly, for example, the slurry containing fine fibrous cellulose may be stirred, or the specific surface area of the slurry may be increased. As a method of stirring the slurry, an external mechanical shear may be applied, or self-stirring may be promoted by increasing the liquid feeding rate of the slurry during the reaction.

[0163] In the substituent removal treatment step, a spacer molecule may be added. The spacer molecule enters between adjacent fine fibrous celluloses and serves as a spacer for providing a fine space between the fine fibrous celluloses. By adding such a spacer molecule in the substituent removal treatment step, aggregation of the fine fibrous cellulose after the substituent removal treatment can be suppressed. Thereby, the designability and tensile properties of the molded body containing the fine fibrous cellulose can be more effectively enhanced.

[0164] 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, starches such as amylose, glycerin, diglycerin, polyglycerin, hyaluronic acid, and metal salts of hyaluronic acid can also be used.

[0165] 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.

[0166] <pH Adjustment Step>

[0167] 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 +When it is in such a case, the slurry containing microfibrillar cellulose after fibrillation shows weak alkalinity. When heating is performed in this state, since monosaccharides, which are one of the coloring factors, may be generated due to the decomposition of cellulose, it is preferable to adjust the pH of the slurry to 8 or less, and more preferably to 6 or less. Also, since monosaccharides may similarly be generated under acidic conditions, it is preferable to adjust the pH of the slurry to 3 or more, and more preferably to 4 or more.

[0168] Further, when the microfibrillar cellulose having a substituent is microfibrillar cellulose having a phosphate group, from the viewpoint of improving the removal efficiency of the substituent, it is preferable that the phosphorus of the phosphate group is in a state where it is easily subjected to nucleophilic attack. What is easily subjected to nucleophilic attack is the state of degree of neutralization 1 represented by cellulose-O-P(=O)(-O-H + )(-O-Na + ). To achieve this state, it is preferable to adjust the pH of the slurry to 3 or more and 8 or less, and more preferably to adjust the pH to 4 or more and 6 or less.

[0169] The means for adjusting the pH is not particularly limited. For example, an acid component or an alkali component may be added to the slurry containing microfibrillar cellulose. The acid component may be either an inorganic acid or an organic acid. Examples of the inorganic acid include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, etc. Examples of the organic acid 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, gluconic acid, etc. The alkali component may be an inorganic alkali compound or an organic alkali compound. Examples of the inorganic alkali compound include lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, etc. Examples of the organic alkali compound 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, N,N-dimethyl-4-aminopyridine, etc.

[0170] Also, in the pH adjustment step, an ion exchange treatment may be performed to adjust the pH. When performing the ion exchange treatment, a strongly acidic cation exchange resin or a weakly acidic ion exchange resin can be used. By treating with an appropriate amount of the cation exchange resin for a sufficient time, a slurry containing microfibrillar cellulose with the desired pH can be obtained. Further, in the pH adjustment step, a combination of adding an acid component or an alkali component and the ion exchange treatment may be employed.

[0171] <Salt removal treatment> After the substituent removal treatment step, it is preferable to perform a treatment for removing salts derived from the removed substituents. By removing salts derived from substituents, it becomes easier to obtain microfibrillar cellulose capable of suppressing coloring. The means for removing salts derived from substituents is not particularly limited, and examples include a washing treatment. The washing treatment is performed, for example, by washing the microfibrillar cellulose aggregated by the substituent removal treatment with water or an organic solvent. From the viewpoint of more effectively suppressing yellowing, the washing treatment is preferably performed by filtration dehydration, centrifugal dehydration, or centrifugal separation.

[0172] <Uniform dispersion treatment> The method for producing microfibrillar cellulose may include a substituent removal treatment step of removing at least a part of substituents from microfibrillar cellulose having substituents and a fiber width of 1000 nm or less, and a step of performing a uniform dispersion treatment after the substituent removal treatment. The step of performing a uniform dispersion treatment is a step of uniformly dispersing the microfibrillar cellulose obtained through the substituent removal treatment in the substituent removal treatment step. The state in which the microfibrillar cellulose in the step of performing a uniform dispersion treatment is uniformly dispersed means a state in which the fiber width of the microfibrillar cellulose is 100 nm or less. By passing through the step of performing a uniform dispersion treatment, the microfibrillar cellulose can easily have a number average fiber width of 100 nm or less, preferably 50 nm or less, although the amount of substituent introduced is a low substituent introduction amount of less than 0.5 mmol / g.

[0173] In the step of performing a uniform dispersion treatment, for example, a high-speed defibrator, a grinder (mortar type crusher), a high-pressure homogenizer, a high-pressure impact type crusher, a ball mill, a bead mill, a disk type refiner, a conical refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater can be used. Among the above-mentioned uniform dispersion treatment apparatuses, it is more preferable to use a high-speed defibrator or a high-pressure homogenizer.

[0174] The processing conditions in the uniform dispersion treatment step are not particularly limited, but it is preferable to increase the maximum moving speed of the fine fibrous cellulose during the treatment and the pressure during the treatment. In 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 can be more preferably used because the maximum moving speed of the fine fibrous cellulose during the treatment and the pressure during the treatment are higher than those of a high-speed defibrator. In the high-pressure homogenizer treatment, the pressure during the 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. Also, in the high-pressure homogenizer treatment, the pressure during the treatment is preferably 350 MPa or less, more preferably 300 MPa or less, and even more preferably 250 MPa or less.

[0175] In addition, in the step of performing the uniform dispersion treatment, the above-described spacer molecules may be newly added. By adding such spacer molecules in the uniform dispersion treatment step of step (B), the uniform dispersion of the fine fibrous cellulose can be performed more smoothly.

[0176] [Rubber component] As the rubber component used in the method for producing the composite material, for example, natural rubber (NR) or synthetic rubber can be used.

[0177] Examples of synthetic rubbers include styrene-butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), ethylene-propylene rubber (EPDM), butyl rubber (IIR), chlorobutyl rubber (CIIR), acrylic rubber (ACM), silicone rubber (Q), fluororubber (FKM), butadiene rubber (BR), epoxidized butadiene rubber (EBR), epichlorohydrin rubber (CO, CEO), urethane rubber (U), polysulfide rubber (T), etc. Examples of nitrile rubbers include hydrogenated nitrile rubber; modified nitrile rubbers such as carboxyl group-modified nitrile rubber (XNBR), silicone-modified nitrile rubber, maleic acid-modified nitrile rubber, hydroxyl group-modified nitrile rubber, or hydrogenated products thereof; acrylonitrile-butadiene-isoprene copolymers in which part of the butadiene is replaced by isoprene, etc. Hydrogenated nitrile rubber (H-NBR) is sometimes referred to as hydrogenated nitrile rubber or hydrogenated acrylonitrile-butadiene rubber. Hydrogenated nitrile rubber can be obtained by hydrogenating the double bonds contained in nitrile rubber.

[0178] Examples of natural rubbers include, in addition to natural rubber (NR), modified natural rubbers such as epoxidized natural rubber (ENR), hydrogenated natural rubber, protein-free natural rubber, etc. These rubber components may be used alone or in combination of two or more. Also, these rubber components may be raw materials before crosslinking having no crosslinked structure or those having a crosslinked structure.

[0179] Among them, 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 carboxyl group-modified nitrile rubber.

[0180] Also, the rubber component may be a raw material before crosslinking. For example, the rubber component is preferably at least one raw material before crosslinking selected from natural rubber and nitrile rubber, and more preferably at least one raw material before crosslinking selected from natural rubber and hydrogenated nitrile rubber. By using the above rubber component as the rubber component, coloring is suppressed, and a composite material excellent in tensile properties can be easily obtained.

Examples

[0181] The features of the present invention will be described more specifically below with reference to Examples and Comparative Examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be appropriately changed 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] As the raw material pulp, softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solid content 93% by mass, basis weight 245 g / m 2 in sheet form, disintegrated, and having a Canadian Standard Freeness (CSF) measured in accordance with JIS P 8121-2:2012 of 700 ml) was used.

[0183] The raw material pulp was subjected to a phosphorus oxooxidation treatment as follows. First, an aqueous mixed solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (dry mass) of the above raw material pulp, and adjusted 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, and a phosphorylated pulp was obtained.

[0184] Next, the obtained phosphorylated pulp was subjected to a washing treatment. The washing treatment was performed by repeating an operation of pouring 10 L of ion-exchanged water into 100 g (dry mass) of the phosphorylated pulp to obtain a pulp dispersion, stirring the pulp dispersion so that the pulp was uniformly dispersed, and then performing filtration and dehydration. The washing end point was determined when the electrical conductivity of the filtrate became 100 μS / cm or less.

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

[0186] The infrared absorption spectrum of the obtained phosphorylated pulp was measured using FT-IR. As a result, an absorption based on P=O of the phosphate group was observed near 1230 cm -1 -1, and it was confirmed that a phosphate group was added to the pulp. Further, when the obtained phosphorylated pulp was tested and analyzed with an X-ray diffractometer, typical peaks were confirmed at two positions near 2θ = 14° or more and 17° or less and near 2θ = 22° or more and 23° or less, and it was confirmed that it had cellulose I-type crystals. The amount of phosphate group (first dissociation acid amount) measured by the measurement method described in [Measurement of amount of phosphooxo acid group] described later was 1.45 mmol / g. The total dissociation acid amount was 2.45 mmol / g. Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry having a solid content concentration of 2.2% by mass. This slurry was treated twice at a pressure of 200 MPa with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) (hereinafter sometimes referred to as "H2 pass") to obtain a microfibrillated cellulose dispersion containing microfibrillated cellulose A1.

[0187]

[0188] ​It was confirmed by X-ray diffraction that the obtained microfibrillar cellulose maintained the cellulose I crystal form. Further, when the average fiber width of the microfibrillar cellulose was measured using a transmission electron microscope, it was 2 nm. The amount of phosphate groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphoxo acid groups] to be described later was 1.45 mmol / g. The total dissociation acid amount was 2.45 mmol / g.

[0189] <Production Example A2> [Enzyme treatment] Ion-exchanged water was added to the phosphorylated pulp obtained in Production Example A1 to prepare a slurry having a solid content concentration of 6.0% by mass. This slurry was treated twice with a wet atomization device (manufactured by Sugino Machine Limited, Starburst) at a pressure of 200 MPa to obtain a microfibrillar cellulose dispersion containing microfibrillar cellulose. To 1000 g of this dispersion (solid content concentration 6.0% by mass, solid content 60 g), an enzyme-containing solution (manufactured by AB Enzymes, ECOPULP R) having an activity of 33000 nkat was added and enzyme treatment was carried out at a temperature of 50°C. The enzyme addition amount at this time was adjusted to 9300 nkat per 1 g of microfibrillar cellulose. The temperature of the obtained dispersion was set to 100°C to inactivate the enzyme. The microfibrillar cellulose obtained by the enzyme treatment is designated as microfibrillar cellulose A2.

[0190] It was confirmed by X-ray diffraction that the obtained microfibrillar cellulose maintained the cellulose I crystal form. Further, when the fiber width of the microfibrillar cellulose was measured using a transmission electron microscope, it was 2 to 5 nm. The average fiber width was 3 nm. Furthermore, in the observation by an optical microscope, it contained fibrous cellulose having a fiber width of 1000 nm or more. The amount of phosphate groups (first dissociation acid amount) measured by the measurement method described in [Measurement of the amount of phosphoxo acid groups] to be described later was 1.45 mmol / g. The total dissociation acid amount was 2.45 mmol / g. Also, the viscosity of a 1% by mass slurry of fibrous cellulose was 4,000 cP.

[0191] [Measurement of the amount of phosphoxo acid groups] In the measurement of the amount of phosphoric acid groups (phosphoric acid groups or phosphorous acid groups) in microfibrillar cellulose, first, ion-exchanged water was added to the target microfibrillar cellulose to prepare a slurry with a solid content concentration of 0.2% by mass. The obtained microfibrillar cellulose dispersion was treated with an ion-exchange resin and then measured by titration using an alkali. The treatment with the ion-exchange resin was carried out by adding a strongly acidic ion-exchange resin (Amberjet 1024; Organo Corporation, conditioned) with a volume of 1 / 10 to the above microfibrillar cellulose dispersion, performing a shaking treatment for 1 hour, and then pouring it onto a mesh with an opening of 90 μm to separate the resin and the slurry. Also, the titration using an alkali was performed by measuring the change in the pH value shown by the slurry while adding a 0.1 N aqueous sodium hydroxide solution to the microfibrillar cellulose containing slurry in increments of 10 μL every 5 seconds. Nitrogen gas was blown into the slurry from 15 minutes before the start of the titration until the titration was completed. In this neutralization titration, in the curve obtained by plotting the measured pH against the amount of alkali added, two points where the increment (differential value of pH with respect to the amount of alkali dropped) is maximized are observed. Among these, the first maximum point of the increment obtained first after starting to add the alkali is called the first end point, and the next maximum point of the increment is called the second end point (Figure 3). The amount of alkali required from the start of the titration to the first end point is equal to the amount of the first dissociable acid in the slurry used for the titration. Also, the amount of alkali required from the start of the titration to the second end point is equal to the total amount of dissociable acids in the slurry used for the titration. The value obtained by dividing the amount of alkali required from the start of the titration to the first end point (mmol) by the solid content (g) in the titration target slurry was defined as the amount of phosphoric acid groups (first dissociable acid amount) (mmol / g). Also, the value obtained by dividing the amount of alkali required from the start of the titration to the second end point (mmol) by the solid content (g) in the titration target slurry was defined as the total amount of dissociable acids (mmol / g).

[0192] <Example 1> Into the can container A, the fine fibrous cellulose dispersion obtained in Production Example A1 was charged so that the solid content was 100 parts by mass. Next, ion-exchanged water was charged into the can container so that the solid content concentration of the fine fibrous cellulose was diluted to 1.0% by mass. A Turbine stirrer (general-purpose high-speed stirrer, manufactured by AS ONE Corporation, PM-202) was used as the stirrer, a 6-inch diameter stirring blade was attached, and the fine fibrous cellulose dispersion in the can container was stirred by the stirrer at 1000 rpm for 5 minutes.

[0193] A can container B was installed above the can container A containing the fine fibrous cellulose dispersion. A pipe and a valve were installed at the lower part of the can container B. Into the can container B, an aqueous dispersion of natural rubber latex (Hyper HA, manufactured by Nomura Trading Co., Ltd.) with a solid content concentration of 61% by mass was charged so that the solid content of the rubber component was 500 parts by mass.

[0194] [Charging step] The fine fibrous cellulose dispersion was stirred at a stirring speed (peripheral speed) of 5 m / min with the above-mentioned Turbine stirrer. The valve of the can container B was opened, and the aqueous dispersion of natural rubber latex was dropped from above and charged into the fine fibrous cellulose dispersion. The opening degree of the valve was adjusted so that the charging rate of the natural rubber latex with respect to 1 L of the fine fibrous cellulose dispersion was 0.01 L / min. Immediately before the charging of the natural rubber latex, the fine fibrous cellulose dispersion during stirring was sampled, and the viscosity was measured by rotating it for 3 minutes at 30 rpm using a B-type viscometer (analog viscometer T-LVT, manufactured by BLOOKFIELD). The viscosity measurement was started within 30 seconds after sampling. The cross-sectional schematic diagram of each device used in the charging step in Example 1 is as described in FIG. 1.

[0195] [Mixing step] After pouring the aqueous dispersion of natural rubber latex into the aqueous dispersion of microfibrillar cellulose, while keeping the stirring conditions of the aforementioned Tornade stirrer unchanged, the mixture was stirred for 60 minutes to obtain a mixed solution of the aqueous dispersion of microfibrillar cellulose and the latex of the rubber component. The obtained mixed solution was heated and dried in an oven set at 40 °C for 18 hours to obtain a composite material of microfibrillar cellulose and the rubber component.

[0196] <Examples 2 to 4> A composite material of microfibrillar cellulose and the rubber component was obtained in the same manner as in Example 1, except that the solid content concentration of the aqueous dispersion of microfibrillar cellulose, the stirring speed (peripheral speed) of the aqueous dispersion of microfibrillar cellulose, and the charging rate of the latex were as described in Table 1, respectively.

[0197] <Example 5> Ion-exchanged water was added to the phosphorylated pulp obtained in Production Example A1 to prepare a slurry having a solid content concentration of 2.2% by mass. This slurry was beaten using a single disk refiner (SDR-14 type laboratory refiner manufactured by Aikawa Iron Works Co., Ltd.). The beating was continuously performed for 20 passes to obtain a pulp slurry having a solid content concentration of 2.2% by mass. The obtained pulp slurry was treated once at a pressure of 200 MPa using a wet atomization device (Starburst manufactured by Sugino Machine Limited) to obtain an aqueous dispersion of microfibrillar cellulose containing microfibrillar cellulose A3. (Hereinafter, the production method of the microfibrillar cellulose may be described as "SDR 20 passes + H1 pass"). A composite material of microfibrillar cellulose and the rubber component was obtained in the same manner as in Example 1, except that the conditions described in Table 1 were used with the aqueous dispersion of microfibrillar cellulose thus obtained.

[0198] <Example 6> Ion-exchanged water was added to the phosphorylated pulp obtained in Production Example A1 to prepare a slurry having a solid content concentration of 2.2% by mass. This slurry was beaten using a single disk refiner (SDR-14 type laboratory refiner manufactured by Aikawa Iron Works Co., Ltd.). The beating was continuously performed for 20 passes to obtain an aqueous dispersion of microfibrillar cellulose containing microfibrillar cellulose A4. (Hereinafter, the method for producing the microfibrillar cellulose may be referred to as "SDR20 process") A composite material of the microfibrillar cellulose and the rubber component was obtained in the same manner as in Example 1, except that the microfibrillar cellulose dispersion obtained in this way was used and the conditions described in Table 1 were adopted.

[0199] <Example 7> Fibrous cellulose, which is a highly beaten pulp, was obtained by the following procedure. As the raw material pulp, softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solid content: 93% by mass, basis weight: 245 g / m 2 sheet form, disintegrated, and having a Canadian Standard Freeness (CSF) of 700 ml measured in accordance with JIS P 8121-2:2012) was used. Ion-exchanged water was added to prepare a slurry with a solid content concentration of 4.0% by mass. This slurry was subjected to continuous circulation beating for 2 hours using a double disk refiner (manufactured by Aikawa Iron Works, AW20-250). The freeness of the obtained fibrous cellulose was 225 mL. A composite material of the fibrous cellulose and the rubber component was obtained in the same manner as in Example 1, except that the fibrous cellulose dispersion obtained in this way was used and the conditions described in Table 1 were adopted.

[0200] <Examples 8 - 9> A composite material of the microfibrillar cellulose and the rubber component was obtained in the same manner as in Example 1, except that the microfibrillar cellulose dispersion was not stirred during the addition of natural rubber latex and the addition rate of the latex was as described in Table 1.

[0201] <Examples 10 - 11> A composite material of the microfibrillar cellulose and the rubber component was obtained in the same manner as in Example 1, except that the microfibrillar cellulose dispersion obtained in Production Example A2 was used instead of Production Example A1 and the solid content concentration of the microfibrillar cellulose dispersion was as described in Table 1.

[0202] <Comparative Example 1> In the adding step, the aqueous dispersion of natural rubber latex was added to the fine fibrous cellulose dispersion using a roller pump (RP-1000, Tokyo Rikakikai Co., Ltd.), and a composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Example 1, except that the stirring speed of the fine fibrous cellulose and the adding speed of the latex were set as shown in Table 1. After mixing, agglomerates of the rubber component were observed, and further, dirt due to adhesion of the agglomerates was observed on the stirring device.

[0203] <Comparative Example 2> The fine fibrous cellulose dispersion was not stirred during the addition of the natural rubber latex. A composite material of fine fibrous cellulose and a rubber component was obtained in the same manner as in Comparative Example 1. After mixing, agglomerates of the rubber component were observed, and further, the stirring device was stained with the agglomerates and latex.

[0204] [Tensile strength] The obtained composite material of fine fibrous cellulose and rubber component was used as a test piece to measure the tensile strength. The maximum tensile load was measured using a tensile tester Tensilon (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. The maximum tensile load was divided by the cross-sectional area of ​​the test piece (thickness x width of the test piece [15±0.1 mm]) to calculate the tensile strength (unit: MPa). When measuring the maximum tensile load, 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 with a constant pressure thickness gauge (PG-02, manufactured by TECLOCK CORPORATION). Specifically, a test piece cut into a size of 50 mm square or more was conditioned at 23°C and a relative humidity of 50% for 24 hours, and the thickness was measured at four arbitrary points, and the average value was taken as the thickness of the test piece.

[0205] [comprehensive evaluation] The results of each of the Examples and Comparative Examples were evaluated according to the following evaluation criteria. <Rubber component agglomerates> In each of the examples and comparative examples, after obtaining a mixed solution with the latex of the rubber component, the presence or absence of agglomerates of the rubber component was visually confirmed. When there were no agglomerates, it was marked as "none", and when agglomerates were confirmed, it was described as "present".

[0206] <Stirring device fouling> In each of the examples and comparative examples, after obtaining a mixed solution with the latex of the rubber component, the presence or absence of adhesion of latex agglomerates to the stirring device obtained by stirring the mixed solution was confirmed. The adhesion of agglomerates was evaluated according to the following criteria. <Evaluation criteria> 3: No adhesion of agglomerates was observed. 2: Adhesion of agglomerates was partially observed. 1: Adhesion of agglomerates was sporadically observed.

[0207] A comprehensive evaluation was performed according to the following criteria. <Evaluation criteria> 3: No agglomerates of the rubber component or fouling of the stirring device were observed, and the tensile strength of the composite material was also good. 2: No agglomerates of the rubber component were observed, but the tensile strength of the composite material was slightly low, or fouling of the stirring device was partially observed. 1: Agglomerates of the rubber component or fouling of the stirring device were observed, and the tensile strength of the composite material was not good.

[0208]

Table 1

[0209] As shown in Table 1, in Examples 1 to 11 in which the latex of the rubber component was introduced using the potential energy of dropping from above into the dispersion of fibrous cellulose, agglomerates of the rubber component and fouling of the device could be suppressed, and a composite material with excellent strength was obtained. In Examples 1 to 11 in which the latex of the rubber component was introduced using the potential energy of dropping from above into the dispersion of fibrous cellulose, agglomerates of the rubber component and fouling of the device could be suppressed, and a composite material with excellent strength was obtained.

Explanation of symbols

[0210] 11... Can container B filled with latex of the rubber component, 12... Pipe, 13... Valve, 14... Can container A filled with dispersion of fibrous cellulose, 15... Stirring device, 21... Hopper filled with latex of the rubber component

Claims

1. A method for manufacturing a composite material containing fibrous cellulose and a rubber component, including an input step of introducing a latex of the rubber component into a dispersion of the fibrous cellulose, wherein an input means in the input step uses potential energy as a power source, the method for manufacturing a composite material.

2. The method for manufacturing a composite material according to claim 1, wherein the fibrous cellulose is microfibrillar cellulose having an average fiber width of 1 nm or more and 1000 nm or less, or high-refined pulp having a freeness of 130 mL or more and 350 mL or less.

3. The method for manufacturing a composite material according to claim 1 or 2, wherein in the input step, the latex of the rubber component is dropped and introduced into the dispersion of the fibrous cellulose from above.

4. The method for manufacturing a composite material according to claim 1 or 2, wherein the input means uses only the potential energy as the power source.

5. The method for manufacturing a composite material according to claim 1 or 2, wherein an input rate of the latex of the rubber component with respect to 1 L of the dispersion of the fibrous cellulose in the input step is 0.01 L / min to 1.00 L / min.

6. The method for manufacturing a composite material according to claim 1 or 2, wherein a viscosity of the dispersion of the fibrous cellulose in the input step is 1 mPa·s to 20000 mPa·s.

7. The method for manufacturing a composite material according to claim 1 or 2, wherein a solid content concentration of the dispersion of the fibrous cellulose in the input step is 0.1 mass% to 10.0 mass%.

8. The method for manufacturing a composite material according to claim 1 or 2, wherein in the input step, the latex of the rubber component is introduced during stirring of the dispersion of the fibrous cellulose.

9. The method for manufacturing a composite material according to claim 8, wherein in the input step, the stirring speed (peripheral speed) of the dispersion of the fibrous cellulose calculated by the following formula (I) is 1 m / min to 50 m / min. Stirring speed (peripheral speed) [m / min] = Diameter of the stirring blade [m] × π × Rotational speed of the stirring blade [rpm]... (I)

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