Sheet

Abstract

To provide a sheet which includes a fiber layer containing fine fibrous cellulose and an inorganic layer and is capable of exhibiting excellent durability.SOLUTION: The present invention relates to a sheet which has a fiber layer, resin layers respectively disposed on both surfaces of the fiber layer, and an inorganic layer formed on at lease one of the resin layers. The fiber layer contains fibrous cellulose whose fiber width is 1000 nm or less, and hydrophilic macromolecule. The hydrophilic macromolecule has a constitutional unit containing hydroxy group.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sheet, particularly to a sheet comprising fine fibrous cellulose. [Background technology]

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

[0003] As fibrous cellulose, fine fibrous cellulose with a fiber diameter of 1 μm or less is also known. The development of sheets made of such fine fibrous cellulose, composites comprising a fine fibrous cellulose-containing sheet and a resin layer, and composite sheets comprising a fine fibrous cellulose-containing sheet and an inorganic layer is being considered.

[0004] For example, Patent Document 1 discloses a laminate comprising a first layer made of an inorganic compound and a second layer containing cellulose fibers having a fiber width of 380 nm or less in the short direction, on at least one surface of a substrate made of a polymer composition. Patent Document 1 considers that the above configuration can be used to obtain a laminate with barrier properties. Patent Document 2 also discloses a composite sheet including a substrate sheet layer containing fine fibers and an inorganic layer formed on at least one side of the substrate sheet layer. In the examples of Patent Document 2, polyethylene glycol is added to the substrate sheet layer containing fine fibers. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-125814 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-37031 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, composite sheets containing a fine fibrous cellulose-containing sheet and an inorganic layer are known. Composite sheets containing a fine fibrous cellulose-containing sheet and an inorganic layer have a wide range of applications, and depending on the application, high durability may be required for the composite sheet. However, conventional composite sheets sometimes do not achieve sufficient durability, and improvements have been sought.

[0007] Therefore, in order to solve these problems of the conventional technology, the present inventors have conducted research with the aim of providing a sheet having a fiber layer containing fine fibrous cellulose and an inorganic layer, which sheet can exhibit excellent durability. [Means for solving the problem]

[0008] Specifically, the present invention has the following configuration.

[0009] [1] A sheet having a fiber layer, a resin layer on both sides of the fiber layer, and an inorganic layer formed on at least one side of the resin layer, the fiber layer contains fibrous cellulose having a fiber width of 1000 nm or less and a hydrophilic polymer; The hydrophilic polymer has a structural unit containing a hydroxyl group. [2] The sheet according to [1], wherein the hydrophilic polymer is polyvinyl alcohol or a cellulose derivative. [3] The sheet according to [1] or [2], wherein the fibrous cellulose has an ionic substituent. [4] The sheet according to [3], wherein the ionic substituent is a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group. [5] The sheet according to any one of [1] to [4], wherein the inorganic layer contains at least one selected from the group consisting of titanium oxide, aluminum oxide, and silicon dioxide. [6] The sheet according to any one of [1] to [5], wherein the inorganic layer has a thickness of 10 nm or more. [7] The sheet according to any one of [1] to [6], wherein the inorganic layer has a thickness of 500 nm or less. [8] The sheet according to any one of [1] to [7], wherein the thickness of each of the resin layers is 10 μm or less. [9] The sheet according to any one of [1] to [8], wherein the resin layer contains an amorphous resin.

[10] The sheet according to any one of [1] to [9], wherein the resin layer is a solvent-coated layer.

[11] The sheet according to any one of [1] to

[10] , wherein the exposed surface of the inorganic layer has a surface roughness of 10 nm or less.

[12] The sheet according to any one of [1] to

[11] , which has a haze value of 1.0% or less.

[13] The sheet according to any one of [1] to

[12] , which has a haze value of 1.5% or less after being placed in an environment of 85°C and a relative humidity of 85% for 240 hours.

[14] Water vapor transmission rate of 10 g / m 2 The sheet according to any one of [1] to

[13] , wherein the sheet is / day or less.

[15] The sheet according to any one of [1] to

[14] , which is for an optical member. [Effects of the Invention]

[0010] According to the present invention, it is possible to obtain a sheet having a fiber layer containing fine fibrous cellulose and an inorganic layer, which sheet can exhibit excellent durability. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view illustrating the configuration of the sheet of this embodiment. [Figure 2] FIG. 2 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having phosphorus oxo acid groups and pH. [Figure 3] FIG. 3 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a carboxy group and the pH. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below. The following description of the components may be based on representative embodiments and specific examples, but the present invention is not limited to such embodiments.

[0013] (sheet) This embodiment is a sheet having a fiber layer, resin layers on both sides of the fiber layer, and an inorganic layer formed on at least one side of the resin layer. The fiber layer contains fibrous cellulose having a fiber width of 1000 nm or less and a hydrophilic polymer, and the hydrophilic polymer has a structural unit containing a hydroxyl group. In this specification, fibrous cellulose having a fiber width of 1000 nm or less is also referred to as fine fibrous cellulose or CNF.

[0014] The sheet of the present embodiment has the above-described configuration and is therefore excellent in durability. In this specification, the durability of a sheet can be evaluated as being good when the sheet exhibits a small change in haze before and after being placed in a high-temperature, high-humidity environment for a long period of time and a small change in weight before and after being placed in a high-temperature, high-humidity environment for a long period of time.

[0015] Specifically, the durability of a laminate sheet can be evaluated by leaving the laminate sheet at 85°C and 85% relative humidity for 10 days (240 hours) and calculating the change in haze and weight of the laminate sheet before and after the above-mentioned conditions (before and after a durability test). The haze of the laminate sheet before and after the durability test is measured in accordance with JIS K 7136:2000 using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.), and the difference in haze (Δhaze) between the laminate sheet before and after the durability test is preferably less than 1.5%. The weight change of the laminate sheet after the durability test is calculated using the following formula, and the weight change of the laminate sheet is preferably less than 10%. Weight change rate (%) = ((weight of laminate sheet after durability test - weight of laminate sheet before durability test) / weight of laminate sheet before durability test) x 100 Weight of laminate sheet before durability test: Weight of the laminate sheet before the durability test, which is the weight (g) of the laminate sheet after conditioning under conditions of 23°C and 50% relative humidity. Weight of laminate sheet after durability test: Weight of the laminate sheet after the durability test (standing at 85°C and 85% relative humidity for 10 days (240 hours)), measured immediately after the test (g).

[0016] The sheet of this embodiment also has excellent resistance to yellowing. For example, when a laminate sheet is left to stand for 10 days (240 hours) under conditions of 85°C and a relative humidity of 85%, the change in yellowness (ΔYI value) of the laminate sheet before and after the above-mentioned condition treatment (before and after a durability test) is preferably 10 or less, more preferably 5 or less, even more preferably 2.5 or less, and even more preferably 2 or less. The lower limit of the change in yellowness (ΔYI value) of the laminate sheet before and after a durability test is not particularly limited, and may be 0. The change in yellowness (ΔYI value) of the laminate sheet before and after a durability test is calculated using the following formula, and the yellowness (YI) of the laminate sheet is a value measured in accordance with JIS K 7373:2006. ΔYI = (YI of the laminated sheet after the durability test) - (YI of the laminated sheet before the durability test)

[0017] The fiber layer contains a hydrophilic polymer having a structural unit containing a hydroxyl group, which can suppress decomposition (degradation of polymerization degree) of the hydrophilic polymer even under high temperature and high humidity conditions, and is therefore thought to be able to suppress an increase in haze when placed in a high temperature and high humidity environment. Furthermore, when the polymer contained in the fiber layer decomposes (degradation of polymerization degree), components derived from the polymer are precipitated on the surface of the fiber layer, which is thought to cause an increase in haze, etc. Furthermore, by providing resin layers on both sides of the fiber layer and then providing an inorganic layer on top of them, water vapor permeability can be suppressed and moisture absorption can be suppressed, effectively suppressing an increase in haze when placed in a high temperature and high humidity environment, and also suppressing weight change of the entire sheet.

[0018] FIG. 1 is a cross-sectional view illustrating the configuration of a sheet according to this embodiment. As shown in FIG. 1, a sheet 10 according to this embodiment includes a fiber layer 2 containing fine fibrous cellulose, resin layers 6 (first and second resin layers) containing a resin as a main component on both sides of the fiber layer 2, and an inorganic layer 8 (first and second inorganic layer) on the resin layer 6. While FIG. 1 depicts a configuration in which inorganic layers 6 are provided on both sides, in this embodiment, an inorganic layer 6 may be provided on only one side. As shown in FIG. 1, the sheet 10 according to this embodiment has a laminated structure, and is therefore sometimes referred to as a laminated sheet. In the inorganic layer 8 / resin layer 6 / fiber layer 2 / resin layer 6 / inorganic layer 8 configuration of the sheet 10, other layers such as adhesive layers may be provided between the inorganic layer and the resin layer, and between the resin layer and the fiber layer. However, in this embodiment, it is preferable that the layers are directly laminated together in contact with each other.

[0019] In the sheet of this embodiment, the surface roughness (Ra) of the exposed surface of the inorganic layer is preferably 10 nm or less, more preferably 8.5 nm or less, and even more preferably 7 nm or less. The lower limit of the surface roughness (Ra) of the exposed surface of the inorganic layer is not particularly limited, but is preferably 0.5 nm or more, for example. When inorganic layers are provided on both sides of the sheet, it is preferable that the surface roughness (Ra) of both sides of the sheet is within the above range. In this case, the surface roughness (Ra) of the surface on one side facing the inorganic layer (first inorganic layer) and the surface on the other side facing the inorganic layer (second inorganic layer) may be the same value or may be different values ​​within the above range.

[0020] The surface roughness (Ra) of the sheet conforms to JIS B 0601:1994 and is a value measured using an optical interference non-contact surface profiler. An example of an optical interference non-contact surface profiler is the VertScan 2.0 R5500GML non-contact surface / layer cross-sectional profile measuring system manufactured by Ryoka Systems Co., Ltd. Surface roughness is measured using a 10x objective lens over a measurement range of 470 μm x 350 μm, and the arithmetic mean roughness (Ra) is calculated from the average value.

[0021] The haze of the sheet is preferably 1.0% or less, more preferably 0.7% or less, and even more preferably 0.5% or less. The haze of the sheet is a value measured using a haze meter in accordance with JIS K 7136:2000. As the haze meter, for example, HM-150 manufactured by Murakami Color Research Laboratory Co., Ltd. can be used.

[0022] As described above, the sheet of this embodiment can exhibit excellent transparency even when a resin layer and an inorganic layer are laminated. In this embodiment, the transparency of the sheet can be achieved, for example, by reducing the surface roughness of the sheet or by appropriately selecting the fine fibrous cellulose or hydrophilic polymer contained in the fiber layer. Because the sheet of this embodiment is an extremely transparent sheet, it is useful, for example, as a sheet for optical components or for bonding optical components. Furthermore, in addition to applications for optical components, it is also suitable for applications requiring high transparency.

[0023] The total light transmittance of the sheet is preferably 85% or more, and more preferably 90% or more. Here, the total light transmittance of the sheet is a value measured using a haze meter in accordance with JIS K 7361-1:1997. As the haze meter, for example, HM-150 manufactured by Murakami Color Research Laboratory Co., Ltd. can be used.

[0024] The water vapor permeability of the sheet is 100g / m 2 / day or less, and 50 g / m 2 / day or less is more preferable, and 10g / m2 / day or less is more preferable, and 5g / m 2 / day. The lower limit of the water vapor permeability of the sheet is not particularly limited, but is preferably 0 g / m 2 / day or more. The water vapor transmission rate is measured in accordance with JIS K 7129-2:2019 using a moisture permeability measuring device, and is a value measured under conditions of 40°C and a relative humidity of 90%. As the moisture permeability measuring device, for example, a PERMATRAN-W 3 / 33 manufactured by Mocon Co., Ltd. can be used.

[0025] The tensile modulus of the sheet at 23°C and 50% relative humidity is preferably 2.5 GPa or more, more preferably 5 GPa or more, even more preferably 7 GPa or more, even more preferably 9 GPa or more, and particularly preferably 10 GPa or more. The tensile modulus of the sheet at 23°C and 50% relative humidity is preferably 30 GPa or less. The tensile modulus of the sheet is a value measured in accordance with JIS P 8113:2006, and is a value calculated from the maximum positive slope of the SS curve (stress-strain curve).

[0026] The total thickness of the sheet is not particularly limited, but is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more. The total thickness of the sheet is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 600 μm or less. The thickness of the sheet is preferably adjusted appropriately depending on the application. The thickness of the sheet can be measured using a constant pressure thickness gauge (PG-02, manufactured by TECLOCK CORPORATION).

[0027] The overall basis weight of the sheet is 10 g / m 2 It is preferable that the content is 20 g / m or more. 2 More preferably, it is 30 g / m or more. 2The total basis weight of the sheet is not particularly limited, but is preferably 5000 g / m or more. 2 Preferably, it is 2500 g / m or less. 2 More preferably, it is 1000 g / m or less. 2 More preferably, it is 500 g / m or less. 2 The following is particularly preferred: The basis weight of the sheet is measured in accordance with JIS P 8124:2011.

[0028] The overall density of the sheet is 1.0 g / cm 3 It is preferable that the concentration is 1.2 g / cm or more. 3 More preferably, it is 1.3 g / cm or more. 3 More preferably, it is 1.4 g / cm or more. 3 It is particularly preferable that the density of the sheet is calculated by dividing the basis weight of the sheet by the thickness. The thickness of the sheet can be measured using a constant pressure thickness gauge (PG-02, manufactured by TECLOCK CORPORATION).

[0029] The moisture content (moisture content) of the sheet is preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 10% by mass or less, and particularly preferably 5% by mass or less. Here, the moisture content of the sheet can be evaluated as follows. Specifically, the sheet is cut into 5 cm x 5 cm test pieces, and the test pieces are conditioned at 23°C and 50% relative humidity for 24 hours, and then dried in a thermostatic oven at 105°C until completely dry. The weight of the test piece after conditioning is W (g), the weight of the test piece after drying is D, and the value calculated by (WD) / W x 100 is the moisture content (mass%) of the sheet. By keeping the moisture content of the sheet within the above range, tensile properties such as tensile modulus can be improved.

[0030] (Inorganic layer) The material constituting the inorganic layer is not particularly limited, and examples thereof include aluminum, silicon, magnesium, zinc, tin, nickel, and titanium; their oxides, carbides, nitrides, oxidized carbides, oxidized nitrides, and oxidized carbonitrides; and mixtures thereof. Among these, the inorganic layer preferably contains at least one material selected from the group consisting of titanium oxide, aluminum oxide, silicon oxide (silicon dioxide), silicon nitride, aluminum nitride, silicon oxide carbide, silicon oxynitride, silicon oxide carbonitride, aluminum oxide carbide, and aluminum oxynitride, and more preferably contains at least one material selected from the group consisting of titanium oxide, aluminum oxide, and silicon dioxide. The inorganic layer may also contain a mixture of these materials. By using the above materials as the material constituting the inorganic layer, the water vapor permeability can be more effectively increased, and the durability of the entire sheet can also be improved.

[0031] The method for forming the inorganic layer is not particularly limited. Generally, methods for forming thin films are roughly divided into chemical vapor deposition (CVD) and physical vapor deposition (PVD), and either method may be employed. Specific examples of CVD methods include plasma CVD, which uses plasma, and catalytic chemical vapor deposition (Cat-CVD), which uses a heated catalyst to catalytically decompose a material gas. Specific examples of PVD methods include vacuum deposition, ion plating, ion-assisted deposition, molecular beam deposition, and sputtering.

[0032] Atomic layer deposition (ALD) can also be used to form inorganic layers. ALD is a method for forming thin films atomically by alternately supplying the source gases of each element that make up the film to be formed to the surface on which the layer is to be formed. While it has the drawback of a slow film formation speed, it has the advantage of being able to coat even complex surfaces more cleanly than plasma CVD, and to deposit thin films with fewer defects. ALD also has the advantage of being able to control film thickness at the nanometer level, making it relatively easy to cover large surfaces. Furthermore, the use of plasma in ALD is expected to improve reaction speed, enable lower processing temperatures, and reduce unreacted gases.

[0033] The thickness of the inorganic layer is not particularly limited, but is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 15 nm or more. From the viewpoints of transparency and flexibility, the thickness of the inorganic layer is preferably 1000 nm or less, more preferably 800 nm or less, and even more preferably 500 nm or less. When the sheet has two or more inorganic layers, the thickness of the inorganic layer refers to the thickness of each inorganic layer.

[0034] (resin layer) The resin layer is a layer whose main component is a natural resin or a synthetic resin. Here, the main component refers to a component that is contained in an amount of 50% by mass or more relative to the total mass of the resin layer. The resin content is preferably 60% by mass or more relative to the total mass of the resin layer, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. The resin content may be 100% by mass.

[0035] In this embodiment, the thickness of each resin layer is preferably 10 μm or less, more preferably 8 μm or less, even more preferably 6 μm or less, even more preferably 5 μm or less, and particularly preferably 4 μm or less. The thickness of each resin layer is preferably 0.1 μm or more. It is preferable that the thicknesses of both resin layers (first resin layer and second resin layer) provided on each side of the fiber layer are within the above ranges. Here, the thickness of the resin layer constituting the sheet is a value measured by cutting out a cross section of the sheet using an ultramicrotome UC-7 (manufactured by JEOL Ltd.) and observing the cross section with an electron microscope, a magnifying glass, or visually.

[0036] Examples of natural resins include rosin-based resins such as rosin, rosin ester, and hydrogenated rosin ester.

[0037] Examples of synthetic resins include polycarbonate resin, polyester resin, polyethylene naphthalate resin, polyethylene resin, polypropylene resin, polyimide resin, polystyrene resin, urethane resin, acrylic resin, and fluororesin. Among them, the synthetic resin is preferably an amorphous resin, more preferably at least one selected from the group consisting of polycarbonate resin, urethane resin, acrylic resin, and fluororesin, and even more preferably at least one selected from the group consisting of polycarbonate resin and acrylic resin. Note that acrylic resin also includes urethane acrylic resin.

[0038] Examples of the polycarbonate resin constituting the resin layer include aromatic polycarbonate resins and aliphatic polycarbonate resins. Specific examples of these polycarbonate resins are known, such as the polycarbonate resins described in JP-A-2010-023275.

[0039] The resin layer preferably contains a hydrophobic resin. In this specification, a hydrophobic resin is defined as a resin having a contact angle with water of 60 degrees or more in a dry state. Here, "in a dry state" means that the hydrophobic resin is not in a state in which it has affinity with water, such as when it is in an emulsion state.

[0040] The resin layer may contain an adhesion aid. Examples of the adhesion aid include a compound containing at least one selected from the group consisting of an isocyanate group, a carbodiimide group, an epoxy group, an oxazoline group, an amino group, and a silanol group, and an organosilicon compound. Examples of the organosilicon compound include a silane coupling agent condensate and a silane coupling agent. Among these, the adhesion aid is preferably a compound containing an isocyanate group (isocyanate compound), and the resin layer preferably contains an isocyanate compound.

[0041] The isocyanate compound may be a polyisocyanate compound or a polyfunctional isocyanate. Specific examples of the polyisocyanate compound include aromatic polyisocyanates having 6 to 20 carbon atoms excluding the carbon atoms in the NCO group, aliphatic polyisocyanates having 2 to 18 carbon atoms, alicyclic polyisocyanates having 6 to 15 carbon atoms, aralkyl polyisocyanates having 8 to 15 carbon atoms, modified products of these polyisocyanates, and mixtures of two or more of these. Among these, alicyclic polyisocyanates having 6 to 15 carbon atoms, i.e., isocyanurates, are preferably used.

[0042] Specific examples of alicyclic polyisocyanates include isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI), cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, bis(2-isocyanatoethyl)-4-cyclohexene-1,2-dicarboxylate, 2,5-norbornane diisocyanate, and 2,6-norbornane diisocyanate.

[0043] Examples of the organosilicon compound include compounds having a siloxane structure or compounds that form a siloxane structure by condensation. For example, silane coupling agents or condensates of silane coupling agents can be mentioned. The silane coupling agent may have a functional group other than an alkoxysilyl group, or may not have any other functional group. Examples of functional groups other than an alkoxysilyl group include a vinyl group, an epoxy group, a styryl group, a methacryloxy group, an acryloxy group, an amino group, a ureido group, a mercapto group, a sulfide group, an isocyanate group, etc. The silane coupling agent used in this embodiment is preferably a silane coupling agent containing a methacryloxy group.

[0044] Specific examples of silane coupling agents having methacryloxy groups in the molecule include methacryloxypropylmethyldimethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropylmethyldiethoxysilane, methacryloxypropyltriethoxysilane, 1,3-bis(3-methacryloxypropyl)tetramethyldisiloxane, etc. Among these, at least one selected from methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, and 1,3-bis(3-methacryloxypropyl)tetramethyldisiloxane is preferably used. The silane coupling agent preferably contains three or more alkoxysilyl groups.

[0045] In the silane coupling agent, silanol groups are generated after hydrolysis, and it is preferable that at least some of the silanol groups remain even after the fiber layer is laminated. Because silanol groups are hydrophilic groups, increasing the hydrophilicity of the surface of the resin layer facing the fiber layer can also improve the adhesion between the resin layer and the fiber layer.

[0046] The adhesion aid may be contained in a state of being uniformly dispersed in the resin layer. Here, the state in which the adhesion aid is uniformly dispersed in the resin layer refers to a state in which, when the concentrations of the adhesion aid are measured in the following three regions ((a) to (c)) and the concentrations of any two regions are compared, the difference in concentration is no more than two times. (a) The region from the surface of the resin layer facing the fiber layer to 10% of the total thickness of the resin layer (b) A region extending from the surface of the resin layer opposite the surface of the fiber layer to 10% of the total thickness of the resin layer. (c) The area within ±5% of the total thickness (total 10%) from the center plane of the resin layer in the thickness direction

[0047] The adhesion aid may be unevenly distributed in the region of the resin layer facing the fiber layer. For example, when an organosilicon compound is used as the adhesion aid, the organosilicon compound may be unevenly distributed in the region of the resin layer facing the fiber layer. Here, the state of being unevenly distributed in the region of the resin layer on the fiber layer side means that when the concentrations in the following two regions ((d) and (e)) are measured, there is a difference of two times or more between these concentrations. (d) The region from the fiber layer side of the resin layer to 10% of the total thickness of the resin layer (e) The area within ±5% of the total thickness (total 10%) from the center plane of the resin layer in the thickness direction Here, the concentration of the adhesion aid is a value measured by an X-ray electron spectrometer or an infrared spectrophotometer, and is a value obtained by cutting out a cross section of a predetermined area of ​​the sheet with an ultramicrotome UC-7 (manufactured by JEOL Ltd.) and measuring the cross section with the same device.

[0048] An organosilicon compound-containing layer may be provided on the surface of the resin layer facing the fiber layer, and such a state is also included in the state in which the organosilicon compound is unevenly distributed in the region of the resin layer facing the fiber layer. The organosilicon compound-containing layer may be a coating layer formed by applying an organosilicon compound-containing coating liquid. In addition, when an organosilicon compound-containing layer is provided on the surface of the resin layer facing the fiber layer, in the above region (d), "the surface of the resin layer facing the fiber layer" shall be read as "the exposed surface of the organosilicon compound-containing layer," and "the thickness of the entire resin layer" shall be read as "the total thickness of the resin layer and the organosilicon compound-containing layer."

[0049] The content of the adhesion aid is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the resin contained in the resin layer, and is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, relative to 100 parts by mass of the resin contained in the resin layer. When the adhesion aid is an isocyanate compound, the content of the isocyanate compound is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 18 parts by mass or more, relative to 100 parts by mass of the resin contained in the resin layer, and is preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less, relative to 100 parts by mass of the resin contained in the resin layer. When the adhesion aid is an organosilicon compound, the content of the organosilicon compound is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, per 100 parts by mass of the resin contained in the resin layer. Furthermore, the content of the organosilicon compound is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of the resin contained in the resin layer. By setting the content of the adhesion aid within the above range, the adhesion between the fiber layer and the resin layer can be more effectively improved.

[0050] When the adhesion aid is an isocyanate compound, the content of isocyanate groups in the resin layer is preferably 0.5 mmol / g or more, more preferably 0.6 mmol / g or more, even more preferably 0.8 mmol / g or more, and particularly preferably 0.9 mmol / g or more. The content of isocyanate groups in the resin layer is preferably 3.0 mmol / g or less, more preferably 2.5 mmol / g or less, even more preferably 2.0 mmol / g or less, and particularly preferably 1.5 mmol / g or less.

[0051] The surface of the resin layer facing the fiber layer may be subjected to a surface treatment. Examples of surface treatment methods include corona treatment, plasma discharge treatment, UV irradiation treatment, electron beam irradiation treatment, and flame treatment. Among these, the surface treatment is preferably at least one selected from corona treatment and plasma discharge treatment. The plasma discharge treatment is preferably vacuum plasma discharge treatment.

[0052] The resin layer may contain optional components other than the synthetic resin, as long as the effects of the present embodiment are not impaired. Examples of optional components include known components used in the field of resin films, such as fillers, pigments, dyes, and ultraviolet absorbers.

[0053] In this embodiment, the resin layer may be an ultraviolet-curable resin layer or a solvent-coated layer. Among these, the resin layer is preferably a solvent-coated layer. That is, the resin layer is preferably a layer formed by applying a resin coating liquid containing a solvent onto a fiber layer and curing the applied resin coating liquid. By using a solvent-coated resin layer in this way, the surface roughness of the sheet can be reduced, and a sheet exhibiting higher transparency can be efficiently produced.

[0054] When the resin layer is an ultraviolet-curable resin layer, the resin coating liquid preferably contains a photopolymerization initiator. For example, a resin coating liquid containing a solvent and a photopolymerization initiator is applied to a fiber layer, the solvent is evaporated by heating and drying, and then ultraviolet light is irradiated to form a resin layer. The amount of ultraviolet light irradiation is optional as long as it is within a range in which the photopolymerization initiator generates radicals.

[0055] (fiber layer) The fiber layer contains fibrous cellulose (fine fibrous cellulose) having a fiber width of 1000 nm or less and a hydrophilic polymer having a structural unit containing a hydroxyl group. The content of the fine fibrous cellulose in the fiber layer is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and even more preferably 40% by mass or more, based on the total mass of the fiber layer.

[0056] The thickness of the fiber layer is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more. The thickness of the fiber layer is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 600 μm or less. The thickness of the fiber layer constituting the sheet is measured by cutting out a cross section of the sheet using an ultramicrotome UC-7 (JEOL Ltd.) and observing the cross section with an electron microscope, a magnifying glass, or visually.

[0057] The density of the fiber layer is 1.0 g / cm 3 It is preferable that the concentration is 1.1 g / cm or more. 3 More preferably, it is 1.2 g / cm or more. 3 It is more preferable that the density of the fiber layer is 1.8 g / cm or more. 3 Preferably, it is 1.7 g / cm or less. 3 More preferably, it is 1.6 g / cm or less. 3 It is even more preferable that:

[0058] The density of the fiber layer is calculated from the basis weight and thickness of the fiber layer. The basis weight of the fiber layer is calculated according to the following method after cutting the sheet using an ultramicrotome UC-7 (JEOL Ltd.) so that only the fiber layer remains. Sheets cut into pieces 50 mm square or larger are conditioned at 23°C and a relative humidity of 50% for 24 hours, and then weighed. The basis weight is calculated by dividing the weight by the area of ​​the cut sheet. Note that if the fiber layer contains optional components other than fine fibrous cellulose, the density of the fiber layer is the density including the optional components other than fine fibrous cellulose.

[0059] In this embodiment, the fibrous layer is preferably a non-porous layer. Here, the term "non-porous" means that the density of the entire fibrous layer is 1.0 g / cm or less. 3 This means that the density of the entire fiber layer is 1.0 g / cm or more. 3 If this is the case or higher, it means that the void ratio contained in the fiber layer is kept below a predetermined value, and the fiber layer is distinguished from a porous sheet or layer. The non-porous nature of the fibrous layer is also characterized by a porosity of 15% by volume or less. The porosity of the fibrous layer here can be calculated simply by the following formula (a): Formula (a): Porosity (volume%) = {1-B / (M×A×t)}×100 where A is the area of ​​the fiber layer (cm 2 ), t is the thickness of the fiber layer (cm), B is the mass of the fiber layer (g), and M is the density of the solid content that constitutes the fiber layer.

[0060] <Fine fibrous cellulose> The fiber layer contains fibrous cellulose having a fiber width of 1000 nm or less. The fiber width of the fibrous cellulose is preferably 100 nm or less, more preferably 50 nm or less, even more preferably 20 nm or less, even more preferably 10 nm or less, and particularly preferably 8 nm or less. By setting the fiber width of the fibrous cellulose within the above range, the dispersibility of the fibrous cellulose can be more effectively improved, making it easier to obtain a fiber layer with high strength and high transparency.

[0061] The fiber width of fibrous cellulose can be measured, for example, by observation under an electron microscope. The average fiber width of fibrous cellulose is, for example, 1000 nm or less. The average fiber width of fibrous cellulose is, for example, preferably 2 nm or more and 1000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, even more preferably 2 nm or more and 20 nm or less, and particularly preferably 2 nm or more and 10 nm or less. By making the average fiber width of fibrous cellulose 2 nm or more, it becomes easier to suppress the dissolution of cellulose molecules in water. Note that the fibrous cellulose is, for example, monofilamentous cellulose.

[0062] The average fiber width of fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fibrous cellulose with a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for TEM observation. When wide fibers are included, an SEM image of the surface cast onto glass may be observed. Next, electron microscope images are observed at magnifications of 1000x, 5000x, 10000x, or 50000x, depending on the width of the fibers to be observed. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions. (1) Draw a line X at any point in the observed image, and 20 or more fibers intersect with the line X. (2) Draw a line Y that intersects the line perpendicularly within the same image, and 20 or more fibers intersect the line Y. For observation images that satisfy the above conditions, the widths of the fibers intersecting with lines X and Y are visually read. In this way, three or more sets of observation images of at least the surface portions that do not overlap each other are obtained. Next, for each image, the widths of the fibers intersecting with lines X and Y are read. In this way, the widths of at least 20 fibers x 2 x 3 = 120 fibers are read. The average value of the read fiber widths is then taken as the average fiber width of the fibrous cellulose.

[0063] The fiber length of the fibrous cellulose is not particularly limited, but 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 fibrous cellulose can be suppressed. It also becomes possible to set the slurry viscosity of the fibrous cellulose within an appropriate range. The fiber length of the fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

[0064] The fibrous cellulose preferably has a type I crystal structure. The presence of type I crystal structure in fibrous cellulose can be identified by a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromated with graphite. Specifically, it can be identified by the presence of two typical peaks at two positions: 2θ=14° to 17° and 2θ=22° to 23°. The proportion of type I crystal structure in the fine fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. This can be expected to provide even better performance in terms of heat resistance and low linear thermal expansion coefficient. The degree of crystallinity can be determined by measuring the X-ray diffraction profile and using the pattern in a conventional manner (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0065] The axial ratio (fiber length / fiber width) of the fibrous cellulose is not particularly limited, but is preferably, for example, 20 to 10,000, and more preferably 50 to 1,000. By setting the axial ratio to the above lower limit or more, a sheet containing fine fibrous cellulose can be easily formed. By setting the axial ratio to the above upper limit or less, it is preferable in that, for example, when treating the fibrous cellulose as a dispersion, handling such as dilution becomes easier.

[0066] The fibrous cellulose in this embodiment has, for example, both crystalline regions and amorphous regions. In particular, fine fibrous cellulose having both crystalline regions and amorphous regions and a high axial ratio is realized by the method for producing fine fibrous cellulose described below.

[0067] The fibrous cellulose preferably has an ionic substituent. The fibrous cellulose has an ionic substituent, which improves the dispersibility of the fibrous cellulose in a dispersion medium and increases the defibration efficiency in the defibration treatment. The ionic substituent may include, for example, either an anionic group or a cationic group, or both. In this embodiment, it is particularly preferable that the ionic substituent has an anionic group. Furthermore, the ionic substituent is preferably a group that is introduced into the fibrous cellulose via an ester bond or an ether bond, and more preferably a group that is introduced into the fibrous cellulose via an ester bond. In this case, the ester bond is formed by dehydration condensation of a hydroxyl group of the fibrous cellulose and a compound that becomes the ionic substituent.

[0068] Examples of the anionic group include a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group (sometimes simply referred to as a phosphorus oxo 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 phosphonic group or a substituent derived from a phosphonic group (sometimes simply referred to as a phosphonic group), a phosphine group or a substituent derived from a phosphine group (sometimes simply referred to as a phosphine group), a sulfonic group or a substituent derived from a sulfonic group (sometimes simply referred to as a sulfonic group), and a carboxyalkyl group (including a carboxymethyl group and a carboxyethyl group). Among these, the anionic group is preferably at least one selected from the group consisting of a phosphorus oxo acid group, a substituent derived from a phosphorus oxo acid group, a carboxy group, a substituent derived from a carboxy group, a carboxyalkyl group, a sulfur oxo acid group, and a substituent derived from a sulfur oxo acid group, more preferably at least one selected from the group consisting of a phosphorus oxo acid group, a substituent derived from a phosphorus oxo acid group, a carboxy group, a substituent derived from a carboxy group, a sulfur oxo acid group, and a substituent derived from a sulfur oxo acid group, and particularly preferably a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group. Introducing a phosphorus oxo acid group as the anionic group can further enhance the dispersibility of the fibrous cellulose, for example, even under alkaline or acidic conditions, making it easier to obtain a fiber layer with high strength and transparency.

[0069] Examples of the cationic group include an ammonium group, a phosphonium group, a sulfonium group, etc. Among these, the cationic group is preferably an ammonium group.

[0070] The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group is, for example, a substituent represented by the following formula (1). A plurality of types of substituents represented by the following formula (1) may be introduced into each fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (1) may be the same or different.

[0071] [ka]

[0072] In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (where a=b×m). At least one of the n α and α' is O. - and the rest are R or OR. Note that all of α and α' are O - The n α's may all be the same or may be different. b+ is a cation of one or more valences consisting of organic or inorganic substances.

[0073] R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived therefrom. In formula (1), n ​​is preferably 1.

[0074] Examples of saturated linear hydrocarbon groups include, but are not limited to, methyl, ethyl, n-propyl, and n-butyl groups. Examples of saturated branched hydrocarbon groups include, but are not limited to, i-propyl and t-butyl groups. Examples of saturated cyclic hydrocarbon groups include, but are not limited to, cyclopentyl and cyclohexyl groups. Examples of unsaturated linear hydrocarbon groups include, but are not limited to, vinyl and allyl groups. Examples of unsaturated branched hydrocarbon groups include, but are not limited to, i-propenyl and 3-butenyl groups. Examples of unsaturated cyclic hydrocarbon groups include, but are not limited to, cyclopentenyl and cyclohexenyl groups. Examples of aromatic groups include, but are not limited to, phenyl and naphthyl groups.

[0075] In addition, the derivative group in R is a carboxy group, a carboxylate group (-COO - ), a hydroxy group, an amino group, an ammonium group, or another functional group to which at least one functional group selected from the group consisting of hydroxy, amino, and ammonium groups is added or substituted, but is not particularly limited. The number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphorus oxoacid group can be set within an appropriate range, which facilitates penetration into the fiber raw material and increases the yield of fibrous cellulose. Note that when there are multiple Rs in formula (1) or when multiple types of substituents represented by the above formula (1) are introduced into the fibrous cellulose, the multiple Rs may be the same or different.

[0076] β b+is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. It should be noted that in formula (1), β b+ When a plurality of β b+ may be the same or different. The monovalent or higher cations consisting of organic or inorganic substances include β b+ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0077] More specifically, examples of the phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group include a phosphate group (-POH), a salt of a phosphate group, a phosphorous acid (phosphonic acid) group (-POH), and a salt of a phosphite (phosphonic acid) group. The phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group may also be a group in which a phosphate group is condensed (e.g., a pyrophosphate group), a group in which a phosphonic acid is condensed (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), or an alkyl phosphonic acid group (e.g., a methylphosphonic acid group).

[0078] The sulfur oxoacid group (a sulfur oxoacid group or a substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). A plurality of types of substituents represented by the following formula (2) may be introduced into each fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (2) may be the same or different.

[0079] [ka]

[0080] In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (where 1 = b × m). When n is 2 or more, multiple p's may be the same number or different numbers. In the above structural formula, 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 phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium 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, etc. Note that when multiple types of substituents represented by the above formula (2) are introduced into the fibrous cellulose, the multiple β b+ may be the same or different. The monovalent or higher cations consisting of organic or inorganic substances include β b+ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0081] The amount of ionic substituent introduced into fibrous cellulose is, for example, preferably 0.05 mmol / g or more per 1 g (mass) of fibrous cellulose, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.40 mmol / g or more, and particularly preferably 0.60 mmol / g or more. The amount of ionic substituent introduced into fibrous cellulose is, for example, preferably 5.20 mmol / g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol / g or less, even more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, and particularly preferably 2.00 mmol / g or less. Here, the denominator in the unit mmol / g is calculated based on the fact that the counter ion of the ionic substituent is a hydrogen ion (H + ) indicates the mass of the fibrous cellulose when the amount of ionic substituent introduced is within the above range. By setting the amount of ionic substituent introduced within the above range, it is possible to easily refine the fiber raw material and improve the stability of the fibrous cellulose. Furthermore, by setting the amount of ionic substituent introduced within the above range, it is easier to obtain a highly transparent sheet.

[0082] The amount of ionic substituent introduced into the fibrous cellulose may be, for example, less than 0.50 mmol / g per 1 g (mass) of fibrous cellulose, 0.40 mmol / g or less, 0.30 mmol / g or less, 0.25 mmol / g or less, or 0.15 mmol / g or less. Fibrous cellulose having an ionic substituent content (introduction amount) within the above range is obtained, for example, through a substituent removal treatment step as described below. That is, the fibrous cellulose contained in the fibrous layer may be fibrous cellulose after the substituent removal treatment. By using fibrous cellulose after the substituent removal treatment as the fibrous cellulose, yellowing of the fibrous layer and the laminate sheet can be more effectively suppressed, particularly yellowing under high-temperature and high-humidity environments.

[0083] The amount of ionic substituents introduced into the fibrous cellulose can be measured, for example, by neutralization titration, which involves measuring the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to a slurry containing the obtained fibrous cellulose.

[0084] 2 is a graph showing the relationship between the amount of NaOH added dropwise to a slurry containing fibrous cellulose having phosphorus oxo acid groups as ionic substituents and pH. The amount of phosphorus oxo acid groups introduced into the fibrous cellulose is measured, for example, as follows. First, a slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement object may be subjected to a defibration treatment similar to the defibration treatment step described below before the treatment with the strongly acidic ion exchange resin. Next, the change in pH is observed while adding aqueous sodium hydroxide solution, and a titration curve like the one shown in the upper part of Figure 2 is obtained. The titration curve shown in the upper part of Figure 2 plots the measured pH against the amount of alkali added, while the titration curve shown in the lower part of Figure 2 plots the pH increment (derivative value) (1 / mmol) against the amount of alkali added. In this neutralization titration, two points of maximum increment (derivative value of pH with respect to the amount of alkali added) are confirmed on the curve plotting the measured pH against the amount of alkali added. Of these, the first maximum increment obtained after starting to add alkali is called the first endpoint, and the next maximum increment obtained is called the second endpoint. The amount of alkali required from the start of titration to the first endpoint is equal to the amount of first dissociated acid from the fibrous cellulose contained in the slurry used for titration; the amount of alkali required from the first endpoint to the second endpoint is equal to the amount of second dissociated acid from the fibrous cellulose contained in the slurry used for titration; and the amount of alkali required from the start of titration to the second endpoint is equal to the total amount of dissociated acid from the fibrous cellulose contained in the slurry used for titration. The amount of alkali required from the start of titration to the first endpoint divided by the solids content (g) in the slurry to be titrated is the amount of phosphorus oxo acid groups introduced (mmol / g). Note that the term "amount of phosphorus oxo acid groups introduced" (or "amount of phosphorus oxo acid groups") simply refers to the amount of first dissociated acid. In Figure 2, the region from the start of titration to the first endpoint is referred to as Region 1, and the region from the first endpoint to the second endpoint is referred to as Region 2. For example, if the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the apparent amount of weak acid groups in the phosphorus oxoacid group (amount of second dissociated acid) decreases, and the amount of alkali required in Region 2 is less than the amount required in Region 1. On the other hand, the amount of strong acid groups in the phosphorus oxoacid group (amount of first dissociated acid) is equal to the amount of phosphorus atoms, regardless of whether condensation occurs. Furthermore, if the phosphorus oxoacid group is a phosphite group, the phosphorus oxoacid group no longer contains weak acid groups, and the amount of alkali required in Region 2 is reduced or may even be zero. In this case, there is only one point on the titration curve where the pH increment is maximized.

[0085] The above-mentioned amount of introduced phosphorus oxoacid groups (mmol / g) indicates the amount of phosphorus oxoacid groups in the acid-form fibrous cellulose (hereinafter referred to as the amount of phosphorus oxoacid groups (acid form)) because the denominator indicates the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the phosphorus oxoacid groups are substituted with an arbitrary cation C so as to be charge equivalent, the amount of phosphorus oxoacid groups in the fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of phosphorus oxoacid groups (C form)) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula. Amount of phosphorus oxoacid group (C type) = Amount of phosphorus oxoacid group (acid type) / {1 + (W - 1) × A / 1000} A [mmol / g]: total amount of anions derived from phosphorus oxoacid groups in fibrous cellulose (total amount of dissociated acid from phosphorus oxoacid groups) W: Formula weight per valence of cation C (for example, Na is 23, Al is 9)

[0086] 3 is a graph showing the relationship between the amount of NaOH added dropwise to a dispersion containing fibrous cellulose having carboxy groups as ionic substituents and pH. The amount of carboxy groups introduced into the fibrous cellulose is measured, for example, as follows. First, a dispersion containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement object may be subjected to a defibration treatment similar to the defibration treatment step described below before the treatment with the strongly acidic ion exchange resin. Next, the change in pH was observed while adding aqueous sodium hydroxide solution, and a titration curve like that shown in the upper part of Figure 3 was obtained. The titration curve shown in the upper part of Figure 3 plots the measured pH against the amount of added alkali, while the titration curve shown in the lower part of Figure 3 plots the pH increment (derivative value) (1 / mmol) against the amount of added alkali. In this neutralization titration, a single point was identified in the curve plotting the measured pH against the amount of added alkali, where the increment (derivative value of pH with respect to the amount of added alkali) reached a maximum. This maximum point is called the first endpoint. Here, the region from the start of the titration to the first endpoint in Figure 3 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the dispersion used for titration. The amount of alkali required in the first region of the titration curve (mmol) is then divided by the solids content (g) in the dispersion containing the fibrous cellulose to be titrated to calculate the amount of carboxyl groups introduced (mmol / g).

[0087] The above-mentioned amount of carboxy groups introduced (mmol / g) indicates the amount of carboxy groups in the acid-form fibrous cellulose (hereinafter referred to as the amount of carboxy groups (acid form)), since the denominator is the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the carboxy groups are substituted with an arbitrary cation C so as to be charge equivalent, the amount of carboxy groups in the fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of carboxy groups (C form)) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Amount of carboxyl group (C type) = Amount of carboxyl group (acid type) / {1 + (W - 1) × (Amount of carboxyl group (acid type)) / 1000} W: Formula weight per valence of cation C (for example, Na is 23, Al is 9)

[0088] When measuring the amount of ionic substituents by titration, adding too many drops of sodium hydroxide or titrating too quickly can result in lower ionic substituents than expected, leading to inaccurate values. An appropriate amount and interval is, for example, titrating 10–50 μL of 0.1 N sodium hydroxide every 5–30 seconds. To eliminate the influence of carbon dioxide dissolved in the fibrous cellulose-containing slurry, it is also recommended to measure the amount of ionic substituents while blowing an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration until the end of titration.

[0089] The amount of sulfur oxoacid or sulfonic acid groups introduced into fibrous cellulose can be calculated by wet ashing the fibrous cellulose using perchloric acid and concentrated nitric acid, diluting it at an appropriate ratio, and measuring the amount of sulfur by ICP atomic emission spectrometry. The amount of sulfur oxoacid or sulfonic acid groups (unit: mmol / g) is calculated by dividing the amount of sulfur by the bone dry mass of the fibrous cellulose tested.

[0090] The amount of xanthate groups introduced into fibrous cellulose can be measured using the Bredee method as follows. First, 40 mL of saturated ammonium chloride solution is added to 1.5 parts by mass (bone dry mass) of fibrous cellulose. The sample is crushed with a glass rod and mixed thoroughly. After leaving for approximately 15 minutes, the sample is filtered through GFP filter paper (GS-25, manufactured by Advantec) and thoroughly washed with saturated ammonium chloride solution. Next, the sample, including the GFP filter paper, is placed in a 500 mL tall beaker, and 50 mL of 0.5 M sodium hydroxide solution (5 °C) is added, stirred, and left for 15 minutes. Phenolphthalein solution is added until the solution turns pink, and then 1.5 M acetic acid is added. The point at which the solution changes from pink to colorless is considered the neutralization point. After neutralization, 250 mL of distilled water is added and stirred thoroughly. 10 mL of 1.5 M acetic acid and 10 mL of 0.05 mol / L iodine solution are added using a volumetric pipette. Then, this solution is titrated with 0.05 mol / L sodium thiosulfate solution, and the amount of xanthate groups is calculated using the following formula from the titration amount of sodium thiosulfate and the bone dry mass of the fibrous cellulose. Amount of xanthate group (mmol / g) = (0.05 × 10 × 2 - 0.05 × sodium thiosulfate titration (mL)) / 1000 / bone-dry mass of fibrous cellulose (g)

[0091] <Manufacturing process for fine fibrous cellulose> <Fiber raw materials> Fine fibrous cellulose is produced from a cellulose-containing fiber raw material. While the cellulose-containing fiber raw material is not particularly limited, pulp is preferably used due to its availability and low cost. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not limited to, chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen-bleached kraft pulp (OKP); semi-chemical pulps such as semi-chemical pulp (SCP) and chemi-ground wood pulp (CGP); and mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Examples of non-wood pulp include, but are not limited to, cotton-based pulps such as cotton linters and cotton lint, and non-wood pulps such as hemp, wheat straw, and bagasse. The deinked pulp is not particularly limited, but examples thereof include deinked pulp made from waste paper. The pulp of this embodiment may be one of the above types used alone, or a mixture of two or more types. Among the above pulps, wood pulp and deinked pulp are preferred from the viewpoint of ease of availability. Furthermore, among wood pulps, chemical pulp is more preferred, and kraft pulp and sulfite pulp are even more preferred, from the viewpoints of a high cellulose ratio, a high yield of fine fibrous cellulose during defibration treatment, and the fact that decomposition of cellulose in the pulp is small and long-fiber fine fibrous cellulose with a large axial ratio can be obtained. Note that the viscosity tends to increase when long-fiber fine fibrous cellulose with a large axial ratio is used.

[0092] Examples of cellulose-containing fiber raw materials include cellulose contained in sea squirts and bacterial cellulose produced by acetic acid bacteria.Furthermore, instead of cellulose-containing fiber raw materials, fibers formed from linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can also be used.

[0093] <Phosphorus oxoacid group introduction step> The process for producing fine fibrous cellulose preferably includes a step of introducing an ionic substituent, and an example of the step of introducing an ionic substituent is a step of introducing a phosphorus oxo acid group. The step of introducing a phosphorus oxo acid group is a step of reacting a cellulose-containing fiber raw material with at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing a phosphorus oxo acid group by reacting with a hydroxyl group possessed by the cellulose-containing fiber raw material. This step results in the production of a fiber into which a phosphorus oxo acid group has been introduced.

[0094] In the phosphorus oxoacid group introduction step according to this embodiment, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). Alternatively, the cellulose-containing fiber raw material with compound A may be reacted in the absence of compound B.

[0095] One example of a method for reacting compound A with a fiber raw material in the presence of compound B is to mix compound A and compound B with a fiber raw material in a dry, wet, or slurry state. Among these methods, using a dry or wet fiber raw material is preferred because of the high uniformity of the reaction, and using a dry fiber raw material is particularly preferred. The form of the fiber raw material is not particularly limited, but is preferably a cotton-like or thin sheet form. Compound A and compound B may be added to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state heated to or above their melting point. Among these methods, adding compound A and compound B in the form of a solution dissolved in a solvent, particularly an aqueous solution, is preferred because of the high uniformity of the reaction. Compound A and compound B may be added to the fiber raw material simultaneously, separately, or as a mixture. The method for adding compound A and compound B is not particularly limited. When compound A and compound B are in solution form, the fiber raw material may be immersed in the solution and allowed to absorb the liquid before being removed, or the solution may be added dropwise to the fiber raw material. Alternatively, the required amounts of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material, and then the excess compound A and compound B may be removed by squeezing or filtration.

[0096] The compound A used in this embodiment may be any compound that has a phosphorus atom and can form an ester bond with cellulose, including, but not limited to, phosphoric acid or a salt thereof, phosphorous acid or a salt thereof, dehydrated condensed phosphoric acid or a salt thereof, and phosphoric anhydride (diphosphorus pentoxide). Phosphoric acids of various purities can be used, such as 100% phosphoric acid (orthophosphoric acid) and 85% phosphoric acid. Phosphorous acids include 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acids are formed by the condensation of two or more molecules of phosphoric acid through a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, which can be neutralized to various degrees. Among these, from the viewpoints of high efficiency of introduction of phosphate groups, ease of further improving defibration efficiency in the defibration step described below, low cost, and ease of industrial application, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid, or phosphorous acid, sodium salt of phosphorous acid, potassium salt of phosphorous acid, ammonium salt of phosphorous acid are preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid, sodium phosphite, sodium hydrogen phosphite are more preferred.

[0097] The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted into the amount of phosphorus atoms, the amount of phosphorus atoms added to the fiber raw material (bone dry mass) is preferably 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to the above upper limit or less, a balance can be achieved between the yield improvement effect and costs.

[0098] As described above, compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. Furthermore, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved.

[0099] The amount of compound B added relative to the fiber raw material (bone dry mass) is not particularly limited, but is preferably, for example, 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, and even more preferably 100% by mass or more and 350% by mass or less.

[0100] In the reaction of a fiber material containing cellulose with compound A, the reaction system may contain, in addition to compound B, amides or amines, for example. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is known to function as a particularly good reaction catalyst.

[0101] In the phosphorus oxo acid group introduction step, it is preferable to add or mix compound A or the like to the fiber raw material and then heat-treat the fiber raw material. The heat treatment temperature is preferably selected so that the phosphorus oxo acid group can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably, for example, from 50°C to 300°C, more preferably from 100°C to 250°C, and even more preferably from 130°C to 200°C. Furthermore, various types of equipment having heat transfer media can be used for the heat treatment, including, for example, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized-bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized-bed dryer, a flash dryer, a reduced-pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, and a high-frequency dryer.

[0102] In the heat treatment according to this embodiment, for example, compound A may be added to a thin sheet-like fiber raw material by impregnation or other methods, followed by heating, or heating while kneading or stirring the fiber raw material and compound A in a kneader or the like. This makes it possible to suppress unevenness in the concentration of compound A in the fiber raw material and more uniformly introduce phosphorus oxoacid groups onto the surface of the cellulose fibers contained in the fiber raw material. This is thought to be because, when water molecules move to the surface of the fiber raw material as it dries, dissolved compound A is attracted to the water molecules by surface tension, preventing it from migrating to the surface of the fiber raw material (i.e., causing unevenness in the concentration of compound A).

[0103] Furthermore, the heating device used for the heat treatment is preferably one that can constantly discharge, to the outside of the device system, for example, the water retained in the slurry and the water generated in the dehydration condensation (phosphorylation) reaction between compound A and hydroxyl groups contained in cellulose or the like in the fiber raw material. Examples of such heating devices include an oven with a blower system. Constantly discharging the water from the device system can suppress the hydrolysis reaction of phosphate ester bonds, which is the reverse reaction of phosphate esterification, as well as the acid hydrolysis of sugar chains in the fiber. This makes it possible to obtain fine fibrous cellulose with a high axial ratio.

[0104] The heat treatment time is preferably from 1 second to 300 minutes after the water content has been substantially removed from the fiber raw material, more preferably from 1 second to 1,000 seconds, and even more preferably from 10 seconds to 800 seconds. In this embodiment, the amount of phosphorus oxo acid groups introduced can be kept within a preferred range by setting the heating temperature and heating time within appropriate ranges.

[0105] The phosphorus oxo acid group introduction step may be carried out at least once, but may also be carried out twice or more. By carrying out the phosphorus oxo acid group introduction step twice or more, a large number of phosphorus oxo acid groups can be introduced into the fiber raw material.

[0106] The amount of phosphorus oxoacid groups introduced in the phosphorus oxoacid group introduction step is, for example, preferably 0.10 mmol / g or more per gram (mass) of fine fibrous cellulose, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and particularly preferably 1.00 mmol / g or more. The amount of phosphorus oxoacid groups introduced in the phosphorus oxoacid group introduction step is, for example, preferably 5.20 mmol / g or less per gram (mass) of fine fibrous cellulose, more preferably 3.65 mmol / g or less, and even more preferably 3.00 mmol / g or less. By keeping the amount of phosphorus oxoacid groups introduced within the above range, it is possible to facilitate the micronization of the fiber raw material and improve the stability of the fine fibrous cellulose.

[0107] In addition, when a substituent removal treatment step as described below is included in the production process of fine fibrous cellulose, the amount of phosphorus oxoacid groups in the final fine fibrous cellulose may be, for example, less than 0.50 mmol / g per gram (mass) of fine fibrous cellulose, 0.40 mmol / g or less, 0.30 mmol / g or less, 0.25 mmol / g or less, or 0.15 mmol / g or less.

[0108] <Carboxy group introduction step> The process for producing fine fibrous cellulose may include, for example, a carboxyl group introduction step as an ionic substituent introduction step. The carboxyl group introduction step is carried out by subjecting a cellulose-containing fiber raw material to an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, or TEMPO oxidation treatment, or by treating the cellulose-containing fiber raw material with a compound having a carboxylic acid-derived group or a derivative thereof, or an acid anhydride of a compound having a carboxylic acid-derived group or a derivative thereof.

[0109] The compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. Furthermore, the derivative of the compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include imidized products of acid anhydrides of compounds having carboxy groups, and derivatives of acid anhydrides of compounds having carboxy groups. The imidized products of acid anhydrides of compounds having carboxy groups are not particularly limited, but examples thereof include imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0110] The acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, etc. Furthermore, the derivative of an acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include acid anhydrides of compounds having carboxy groups such as dimethylmaleic anhydride, diethylmaleic anhydride, diphenylmaleic anhydride, etc. in which at least some of the hydrogen atoms have been substituted with substituents such as alkyl groups or phenyl groups.

[0111] When TEMPO oxidation is performed in the carboxyl group introduction step, it is preferable to perform the treatment under conditions of pH 6 or higher and pH 8 or lower. This type of treatment is also called neutral TEMPO oxidation. Neutral TEMPO oxidation can be performed, for example, by adding pulp as the fiber raw material, a nitroxy 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). The presence of sodium chlorite further allows aldehydes generated during the oxidation process to be efficiently oxidized to carboxyl groups. The TEMPO oxidation may also be performed under conditions of pH 10 or higher and pH 11 or lower. This type of treatment is also called alkaline TEMPO oxidation. The alkaline TEMPO oxidation can be performed, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp as the fiber raw material.

[0112] The amount of carboxy groups introduced in the carboxy group introduction step varies depending on the type of substituent, but for example, when carboxy groups are introduced by TEMPO oxidation, it is preferably 0.10 mmol / g or more per 1 g (mass) of fine fibrous cellulose, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and particularly preferably 0.90 mmol / g or more. Furthermore, the amount of carboxy groups introduced in the carboxy group introduction step is preferably 2.5 mmol / g or less, more preferably 2.20 mmol / g or less, and even more preferably 2.00 mmol / g or less. Additionally, when the substituent is a carboxymethyl group, it may be 5.8 mmol / g or less per 1 g (mass) of fine fibrous cellulose.

[0113] In addition, when a substituent removal treatment step as described below is included in the production process of fine fibrous cellulose, the amount of carboxy groups in the finally obtained fine fibrous cellulose may be, for example, less than 0.50 mmol / g per 1 g (mass) of fine fibrous cellulose, 0.40 mmol / g or less, 0.30 mmol / g or less, 0.25 mmol / g or less, or 0.15 mmol / g or less.

[0114] <Sulfur oxoacid group introduction step> The process for producing fine fibrous cellulose may include, for example, a sulfur oxoacid group introduction step as an ionic substituent introduction step, in which hydroxyl groups in a cellulose-containing fiber raw material react with sulfur oxoacid to obtain cellulose fibers having sulfur oxoacid groups (sulfur oxoacid group-introduced fibers).

[0115] In the sulfur oxo acid group introduction step, instead of compound A in the above-described <Phosphorus oxo acid group introduction step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfur oxo acid groups by reacting with hydroxyl groups in cellulose-containing fiber raw materials is used. Compound C may be any compound containing a sulfur atom and capable of forming an ester bond with cellulose, including, but not limited to, sulfuric acid or its salts, sulfurous acid or its salts, and sulfuric acid amides. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid). Sulfurous acid can be 5% aqueous sulfurous acid. Sulfates or sulfites can be lithium, sodium, potassium, or ammonium salts of sulfates or sulfites, which can be neutralized to various degrees. Sulfamic acid or the like can be used as the sulfuric acid amide. In the sulfur oxo acid group introduction step, it is preferable to use compound B in the above-described <Phosphorus oxo acid group introduction step> as well.

[0116] In the sulfur oxoacid group introduction step, the cellulose raw material is preferably mixed with an aqueous solution containing a sulfur oxoacid and urea and / or a urea derivative, and then the cellulose raw material is subjected to a heat treatment. The heat treatment temperature is preferably selected so that the sulfur oxoacid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. The heat treatment temperature is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

[0117] In the heat treatment step, heating is preferably performed until substantially all moisture is removed. Therefore, the heat treatment time varies depending on the amount of moisture contained in the cellulose raw material and the amount of aqueous solution containing sulfur oxoacid and urea and / or a urea derivative added, but is preferably, for example, 10 to 10,000 seconds. For the heat treatment, various devices having a heat medium can be used, such as a hot air dryer, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, an airflow dryer, a reduced-pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, or a high-frequency dryer.

[0118] The amount of sulfur oxoacid groups introduced in the sulfur oxoacid group introduction step 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 0.50 mmol / g or more. The amount of sulfur oxoacid groups introduced in the sulfur oxoacid group introduction step is preferably 5.00 mmol / g or less, more preferably 3.00 mmol / g or less. By ensuring that the amount of sulfur oxoacid groups introduced falls within the above range, it is possible to facilitate the pulverization of the fiber raw material and improve the stability of the fibrous cellulose. Furthermore, by ensuring that the amount of sulfur oxoacid groups introduced falls within the above range, it is possible to easily obtain a sheet that is inhibited from yellowing when heated.

[0119] In addition, when a substituent removal treatment step as described below is included in the production process of fine fibrous cellulose, the amount of sulfur oxoacid groups in the finally obtained fine fibrous cellulose may be, for example, less than 0.50 mmol / g per 1 g (mass) of fine fibrous cellulose, 0.40 mmol / g or less, 0.30 mmol / g or less, 0.25 mmol / g or less, or 0.15 mmol / g or less.

[0120] <Oxidation step using a chlorine-based oxidizing agent (second carboxyl group introduction step)> The process for producing fine fibrous cellulose may include an oxidation step using a chlorine-based oxidizing agent as an ionic substituent introduction step. In the oxidation step using a chlorine-based oxidizing agent, the chlorine-based oxidizing agent is added to a wet or dry fiber raw material having a hydroxyl group to cause a reaction, thereby introducing a carboxyl group into the fiber raw material.

[0121] Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorites, chlorous acid, chlorites, chloric acid, chlorates, perchloric acid, perchlorates, and chlorine dioxide. From the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling, the chlorine-based oxidizing agent is preferably sodium hypochlorite, sodium chlorite, or chlorine dioxide. When adding a chlorine-based oxidizing agent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or may be dissolved in an appropriate solvent and then added.

[0122] The concentration of the chlorine-based oxidizing agent in the solution in the oxidation step using the chlorine-based oxidizing agent, converted into an effective chlorine concentration, is preferably 1 to 1,000% by mass, more preferably 5 to 500% by mass, and even more preferably 10 to 100% by mass. The amount of the chlorine-based oxidizing agent added per 100 parts by mass of the fiber raw material is preferably 1 to 100,000 parts by mass, more preferably 10 to 10,000 parts by mass, and even more preferably 100 to 5,000 parts by mass.

[0123] The reaction time with the chlorine-based oxidizing agent in the oxidation step using the chlorine-based oxidizing agent varies depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. The pH during the reaction is preferably from 5 to 15, more preferably from 7 to 14, and even more preferably from 9 to 13. At the start of the reaction, the pH is preferably maintained constant (for example, pH 11) during the reaction by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0124] <Xanthate group introduction step (xanthogen acid esterification step)> The process for producing fine fibrous cellulose may include, for example, a xanthate group introduction process (hereinafter also referred to as a xanthation process) as an ionic substituent introduction process. In the xanthation process, carbon disulfide and an alkali compound are added to a wet or dry fiber raw material having a hydroxyl group to cause a reaction, thereby introducing a xanthate group into the fiber raw material. Specifically, carbon disulfide is added to a fiber raw material that has been converted into alkali cellulose by the method described below, and the reaction is carried out.

[0125] <<Alkali cellulose>> When introducing ionic substituents into a fiber raw material, it is preferable to convert the cellulose contained in the fiber raw material into alkali cellulose by treating the cellulose with an alkaline solution. This treatment causes ionic dissociation of some of the hydroxyl groups in the cellulose, thereby increasing the nucleophilicity (reactivity). The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. Due to their high versatility, it is preferable to use, for example, sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, or tetrabutylammonium hydroxide. The conversion into alkali cellulose may be carried out simultaneously with the introduction of ionic substituents, before the introduction, or at both the same time.

[0126] The solution temperature at the start of alkali cellulose formation is preferably 0°C or higher and 50°C or lower, more preferably 5°C or higher and 40°C or lower, and even more preferably 10°C or higher and 30°C or lower.

[0127] The alkali concentration in the alkaline solution is preferably 0.01 mol / L to 4 mol / L in molar concentration, more preferably 0.1 mol / L to 3 mol / L in molar concentration, and even more preferably 1 mol / L to 2.5 mol / L in molar concentration. In particular, when the treatment temperature for alkali cellulose formation is less than 10° C., the alkali concentration is preferably 1 mol / L to 2 mol / L in molar concentration.

[0128] The treatment time for alkali cellulose formation is preferably 1 minute or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more, and the alkali treatment time is preferably 6 hours or less, more preferably 5 hours or less, and even more preferably 4 hours or less.

[0129] By adjusting the type of alkaline solution, treatment temperature, concentration, and immersion time as described above, it is possible to suppress the penetration of the alkaline solution into the crystalline regions of cellulose, making it easier to maintain the crystalline structure of cellulose type I, and increasing the yield of fine fibrous cellulose.

[0130] When the introduction of ionic substituents and the conversion to alkali cellulose are not carried out simultaneously, the conversion to alkali cellulose is preferably carried out before the introduction of ionic substituents. In this case, the alkali cellulose obtained by the conversion to alkali cellulose treatment is preferably subjected to solid-liquid separation by a common deliquoring method such as centrifugation or filtration to remove water. This improves the reaction efficiency in the subsequent ionic substituent introduction step. The cellulose fiber concentration after solid-liquid separation is preferably 5% to 50%, more preferably 10% to 40%, and even more preferably 15% to 35%.

[0131] <Phosphonic or Phosphine Group Introduction Step (Phosphoalkylation Step)> The process for producing fine fibrous cellulose may include a step of introducing a phosphonic or phosphine group (phosphoalkylation step) as an ionic substituent introduction step. In the phosphoalkylation step, a compound having a reactive group and a phosphonic or phosphine group (compound E) is used as an essential component. A ), an optional alkali compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having hydroxyl groups and reacted to introduce phosphonic or phosphine groups into the fiber raw material.

[0132] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E A Examples of suitable compounds include vinyl phosphonic acid, phenyl vinyl phosphonic acid, and phenyl vinyl phosphinic acid. From the viewpoints of the efficiency of introducing substituents, the defibration efficiency, cost, and ease of handling, Compound E A is preferably vinylphosphonic acid. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0133] Compound E A When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0134] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0135] Compound E AThe amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0136] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0137] <Sulfonic Group Introduction Step (Sulfoalkylation Step) (Second Sulfonic Group Introduction Step)> The ionic substituent introduction step may include a sulfone group introduction step (sulfoalkylation step). In the sulfoalkylation, a compound having a reactive group and a sulfone group (compound E) is used as an essential component. B ) and, as an optional component, an alkali compound and a compound B selected from the aforementioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a sulfonic acid group into the fiber raw material.

[0138] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E B Examples of suitable olefin sulfonates include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, and 2-acrylamido-2-methylpropanesulfonic acid. Among these, compound E is particularly preferred in terms of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. B is preferably sodium vinyl sulfonate. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0139] Compound E BWhen adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0140] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0141] Compound E B The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0142] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 15 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0143] <Carboxyalkylation step (third carboxy group introduction step)> The process for producing fine fibrous cellulose may include a carboxyalkylation step as an ionic substituent introduction step. As an essential component, a compound having a reactive group and a carboxy group (compound E C ), an optional alkaline compound, and compound B selected from the aforementioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a carboxyl group into the fiber raw material.

[0144] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E CAs the chloroisothiazolinone, monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred from the standpoints of efficiency in introducing substituents, and therefore defibration efficiency, cost, and ease of handling. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0145] Compound E C When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0146] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0147] Compound E C The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0148] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 3 minutes to 500 minutes, and even more preferably from 5 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0149] <Cationic group introduction step (cationization step)> As an essential component, a compound having a reactive group and a cationic group (compound E D), an optional alkaline compound, and a compound B selected from the aforementioned urea and its derivatives are added to a wet or dry fiber raw material having hydroxyl groups and reacted to introduce cationic groups into the fiber raw material.

[0150] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Examples of the cationic group include an ammonium group, a phosphonium group, a sulfonium group, etc. Among these, the cationic group is preferably an ammonium group. Compound E D As the alkyl group, glycidyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, etc. are preferred from the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> as an optional component in the same manner. The amount added is also preferably as described above.

[0151] Compound E D When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0152] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0153] Compound E D The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0154] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0155] <Cleaning process> In the method for producing fine fibrous cellulose according to the present embodiment, a washing step can be carried out on the ionic substituent-introduced fibers as needed. The washing step is carried out by washing the ionic substituent-introduced fibers with water or an organic solvent, for example. The washing step may be carried out after each step described below, and the number of washing steps carried out in each washing step is not particularly limited.

[0156] <Alkali treatment process> When producing fine fibrous cellulose, the fiber raw material may be subjected to an alkali treatment between the step of introducing an ionic substituent and the defibration treatment step described below. The alkali treatment method is not particularly limited, but examples thereof include a method of immersing the ionic substituent-introduced fiber in an alkali solution.

[0157] The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. In this embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of their high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. Among these, the solvent contained in the alkaline solution is preferably water or a polar solvent including a polar organic solvent such as an alcohol, and more preferably an aqueous solvent including at least water. As the alkaline solution, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of their high versatility.

[0158] The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably, for example, 5°C to 80°C, and more preferably 10°C to 60°C. The immersion time of the ionic substituent-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is, for example, preferably 5 minutes to 30 minutes, and more preferably 10 minutes to 20 minutes. The amount of alkaline solution used in the alkaline treatment is not particularly limited, but is, for example, preferably 100% by mass to 100,000% by mass, and more preferably 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the ionic substituent-introduced fiber. When the fibrous cellulose has anionic groups, the alkaline treatment may involve neutralization and / or ion exchange of the anionic groups. In this case, the temperature of the alkaline solution is preferably room temperature.

[0159] In order to reduce the amount of alkaline solution used in the alkali treatment step, the ionic substituent-introduced fiber may be washed with water or an organic solvent after the ionic substituent-introducing step and before the alkali treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkali-treated ionic substituent-introduced fiber with water or an organic solvent after the alkali treatment step and before the defibrating step.

[0160] <Acid treatment process> When producing fine fibrous cellulose, the fiber raw material may be subjected to an acid treatment between the step of introducing an ionic substituent and the defibration treatment step described below. For example, the step of introducing an ionic substituent, the acid treatment, the alkali treatment, and the defibration treatment may be performed in this order.

[0161] The acid treatment method is not particularly limited, but examples include a method of immersing the fiber raw material in an acid-containing acid solution. The concentration of the acid solution used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less. The pH of the acid solution used is also not particularly limited, but is preferably 0 to 4, and more preferably 1 to 3. Examples of the acid contained in the acid solution include inorganic acids, sulfonic acids, and carboxylic acids. Examples of inorganic acids include sulfuric acid, nitric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid. Among these, hydrochloric acid or sulfuric acid is particularly preferred.

[0162] The temperature of the acid solution used in the acid treatment is not particularly limited, but is preferably from 5°C to 100°C, and more preferably from 20°C to 90°C. The immersion time in the acid solution used in the acid treatment is not particularly limited, but is preferably from 5 to 120 minutes, and more preferably from 10 to 60 minutes. The amount of the acid solution used in the acid treatment is not particularly limited, but is preferably from 100% to 100,000% by mass, and more preferably from 1,000% to 10,000% by mass, based on the absolute dry mass of the fiber raw material. When the fine fibrous cellulose has cationic groups, the acid treatment may involve neutralization and / or ion exchange of the cationic groups. In this case, the temperature of the acid solution is preferably room temperature.

[0163] <Defibrillation processing> Fine fibrous cellulose is obtained by defibrating the ionic substituent-introduced fibers in a defibration treatment step. In the defibration treatment step, for example, a defibration treatment device can be used. The defibration treatment device is not particularly limited, but examples that can be used include a high-speed defibrator, a grinder (stone mill-type grinder), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision grinder, 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. Among the above defibration treatment devices, it is more preferable to use a high-speed defibrator, a high-pressure homogenizer, or an ultra-high-pressure homogenizer, which are less affected by the grinding media and have less risk of contamination.

[0164] In the defibration process, it is preferable to dilute the ionic substituent-introduced fibers with a dispersion medium to form a slurry. The dispersion medium can be one or more selected from water and organic solvents such as polar organic solvents. The polar organic solvent is not particularly limited, but examples thereof include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

[0165] The solid content concentration of the fine fibrous cellulose during the defibration treatment can be appropriately set. In addition, the slurry obtained by dispersing the ionic substituent-introduced fibers in a dispersion medium may contain solids other than the ionic substituent-introduced fibers, such as urea having hydrogen bonding properties.

[0166] <Nitrogen removal treatment process> The process for producing fine fibrous cellulose may further include a step of reducing the amount of nitrogen introduced into the fibrous cellulose or the amount of nitrogen present in the system (nitrogen removal treatment step). By reducing the amount of nitrogen, fine fibrous cellulose can be obtained that can further suppress discoloration. The nitrogen removal treatment step may be carried out after the defibration treatment step, but is preferably carried out before the defibration treatment step.

[0167] In the nitrogen removal treatment step, it is preferable to adjust the pH of the slurry containing the ionic substituent-introduced fiber to 10 or more and then perform a heat treatment. In the heat treatment, the liquid temperature of the slurry is preferably 50°C or more and 100°C or less, and the heating time is preferably 15 minutes or more and 180 minutes or less. When adjusting the pH of the slurry containing the ionic substituent-introduced fiber, it is preferable to add an alkali compound that can be used in the above-mentioned alkali treatment step to the slurry.

[0168] After the nitrogen removal treatment step, the ionic substituent-introduced fiber may be subjected to a washing step, if necessary. The washing step is carried out by washing the ionic substituent-introduced fiber with, for example, water or an organic solvent. The number of washing steps to be carried out in each washing step is not particularly limited.

[0169] <Substituent Removal Treatment Step> The method for producing fine fibrous cellulose may include a step of removing at least a portion of the substituents from fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less. By undergoing such a step, it is possible to obtain fine fibrous cellulose having a small amount of introduced substituents but a small fiber width. In this specification, the step of removing at least a portion of the substituents from the fine fibrous cellulose is also referred to as a substituent removal treatment step.

[0170] Examples of the substituent removal treatment step include a step of heat treating, enzyme treating, acid treating, alkali treating, etc., fine fibrous cellulose having substituents and a fiber width of 1000 nm or less. These may be performed alone or in combination. Among these, the substituent removal treatment step is preferably a heat treating step or an enzyme treating step. By undergoing the above treatment steps, at least a portion of the substituents is removed from the fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, and, for example, fine fibrous cellulose having an introduced amount of substituents of less than 0.5 mmol / g can be obtained.

[0171] The substituent removal treatment step is preferably carried out in the form of a slurry. That is, the substituent removal treatment step is preferably a step of subjecting a slurry containing a fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less to a heat treatment, an enzyme treatment, an acid treatment, an alkali treatment, or the like. By carrying out the substituent removal treatment step in the form of a slurry, it is possible to prevent the residue of colored substances generated by heating or the like during the substituent removal treatment, as well as added or generated acids, alkalis, salts, and the like. This makes it possible to suppress coloration of the fiber layer or laminate sheet. Furthermore, when a treatment is carried out to remove salts derived from the substituents removed after the substituent removal treatment, it is also possible to increase the efficiency of salt removal.

[0172] When a substituent removal treatment is performed on a slurry containing fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, the concentration of the fine fibrous cellulose in the slurry is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. The concentration of the fine fibrous cellulose in the slurry is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. By maintaining 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 maintaining the concentration of the fine fibrous cellulose in the slurry within the above range, it is possible to prevent the residue of colored substances caused by heating during the substituent removal treatment, as well as added or generated acids, alkalis, salts, etc. This can suppress the coloration of the fiber layer and laminate sheet. Furthermore, when a treatment is performed to remove salts derived from the substituents removed after the substituent removal treatment, it is also possible to improve the salt removal efficiency.

[0173] When the substituent removal treatment step is a step of heat-treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, the heating temperature in the heat treatment step is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher. Furthermore, the heating temperature in the heat treatment step is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower. In particular, when the substituent in the fine fibrous cellulose subjected to the substituent removal treatment step is a phosphorus oxo acid group, the heating temperature in the heat treatment step is preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher.

[0174] When the substituent removal treatment step is a heat treatment step, the heating device that can be used in the heat treatment step is not particularly limited, and examples that can be used include a hot air heater, a steam heater, an electric heater, a hydrothermal heater, a thermal heater, an infrared heater, a far-infrared heater, a microwave heater, a high-frequency heater, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, a flash dryer, and a reduced-pressure dryer. From the viewpoint of preventing evaporation, the heating is preferably carried out in a closed system, and from the viewpoint of further increasing the heating temperature, it is preferably carried out in a pressure-resistant device or container. The heat treatment may be a batch process, a batch continuous process, or a continuous process.

[0175] When the substituent removal treatment step is a step of enzymatically treating fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, it is preferable to use a phosphate ester hydrolase, a sulfate ester hydrolase, or the like in the enzymatic treatment step depending on the type of substituent.

[0176] In the enzyme treatment step, the enzyme is preferably added so that the enzymatic activity per 1 g of fine fibrous cellulose is 0.1 nkat or more, more preferably 1.0 nkat or more, and even more preferably 10 nkat or more. The enzyme is preferably added so that the enzymatic activity per 1 g of fine fibrous cellulose is 100,000 nkat or less, more preferably 50,000 nkat or less, and even more preferably 10,000 nkat or less. After adding the enzyme to the fine fibrous cellulose dispersion (slurry), it is preferable to treat the dispersion (slurry) at a temperature of 0°C or higher but lower than 50°C for 1 minute to 100 hours.

[0177] After the enzymatic reaction, a step of deactivating the enzyme may be carried out. Examples of methods for deactivating the enzyme include adding an acid or alkali component to the enzymatically treated slurry to deactivate the enzyme, and raising the temperature of the enzymatically treated slurry to 90°C or higher to deactivate the enzyme.

[0178] When the substituent removal treatment step is a step of acid treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, it is preferable to add an acid compound that can be used in the acid treatment step described above to the slurry in the acid treatment step.

[0179] When the substituent removal treatment step is a step of alkali treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, it is preferable to add an alkali compound that can be used in the alkali treatment step described above to the slurry in the alkali treatment step.

[0180] In the substituent removal treatment step, it is preferable that the substituent removal reaction proceeds uniformly. To proceed with the reaction uniformly, for example, the slurry containing the fine fibrous cellulose may be stirred, or the specific surface area of ​​the slurry in contact with the heating medium may be increased. As a method for stirring the slurry, external mechanical shear may be applied, or self-stirring may be promoted by increasing the liquid feed rate of the slurry during the reaction.

[0181] In the substituent removal treatment step, spacer molecules may be added. The spacer molecules penetrate between adjacent fine fibrous cellulose particles, thereby acting as spacers to create fine spaces between the fine fibrous cellulose particles. Adding such spacer molecules in the substituent removal treatment step can suppress aggregation of the fine fibrous cellulose particles after the substituent removal treatment. This can more effectively improve the transparency of the fiber layer or laminate sheet.

[0182] The spacer molecule is preferably a water-soluble organic compound. Examples of the water-soluble organic compound include sugars, water-soluble polymers, urea, and the like. Specifically, trehalose, urea, polyethylene glycol (PEG), polyethylene oxide (PEO), carboxymethyl cellulose, polyvinyl alcohol (PVA), and the like can be mentioned. Further, as the water-soluble organic compound, alkyl methacrylate-acrylic acid copolymer, polyvinyl pyrrolidone, sodium polyacrylate, propylene glycol, dipropylene glycol, polypropylene glycol, isoprene glycol, hexylene glycol, 1,3-butylene glycol, polyacrylamide, xanthan gum, guar gum, tamarind gum, carrageenan, locust bean gum, quince seed, alginic acid, pullulan, carrageenan, pectin, cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, amylose and other starches, glycerin, diglycerin, polyglycerin, hyaluronic acid, metal salts of hyaluronic acid can also be used.

[0183] 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.

[0184] <pH adjustment step> When the above-described 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 ionic substituent is introduced into the cellulose fiber, and the counter ion of this ionic substituent is Na +In this case, the slurry containing the defibrated fine fibrous cellulose exhibits a weak alkaline pH. If the slurry is heated in this state, monosaccharides, which are one of the causes of coloration, may be generated due to the decomposition of cellulose, so the pH of the slurry is preferably adjusted to 8 or less, more preferably to 6 or less. Similarly, monosaccharides may be generated under acidic conditions, so the pH of the slurry is preferably adjusted to 3 or more, more preferably to 4 or more.

[0185] Furthermore, when the substituted fine fibrous cellulose is a phosphate-containing fine fibrous cellulose, it is preferable that the phosphorus of the phosphate group is susceptible to nucleophilic attack, from the viewpoint of improving the efficiency of removing the substituent. The phosphorus susceptible to nucleophilic attack is cellulose-OP(=O)(-OH + )(-O-Na + To achieve this state, the pH of the slurry is preferably adjusted to 3 or more and 8 or less, and more preferably adjusted to 4 or more and 6 or less.

[0186] The means for adjusting the pH is not particularly limited, and for example, an acid component or an alkali component may be added to a slurry containing fine fibrous cellulose. The acid component may be either an inorganic acid or an organic acid. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Examples of organic acids include formic acid, acetic acid, citric acid, malic acid, lactic acid, adipic acid, sebacic acid, stearic acid, maleic acid, succinic acid, tartaric acid, fumaric acid, and gluconic acid. The alkali component may be an inorganic alkali compound or an organic alkali compound. Examples of inorganic alkali compounds include lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium bicarbonate, potassium carbonate, potassium bicarbonate, sodium carbonate, and sodium bicarbonate. Examples of organic alkali compounds include ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, butylamine, diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, cyclohexylamine, aniline, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, pyridine, and N,N-dimethyl-4-aminopyridine.

[0187] In addition, in the pH adjustment step, an ion exchange treatment may be performed to adjust the pH. A strong acid cation exchange resin or a weak acid ion exchange resin can be used in the ion exchange treatment. By treating with an appropriate amount of cation exchange resin for a sufficient time, a slurry containing fine fibrous cellulose with the desired pH can be obtained. Furthermore, in the pH adjustment step, the addition of an acid component or an alkali component may be combined with the ion exchange treatment.

[0188] <Salt removal process> After the substituent removal treatment step, it is preferable to carry out a treatment to remove salts derived from the removed substituents. Removing the salts derived from the substituents makes it easier to obtain fine fibrous cellulose that can suppress coloration. The means for removing the salts derived from the substituents is not particularly limited, and examples thereof include a washing treatment. The washing treatment is carried out by washing the fine fibrous cellulose that has aggregated in the substituent removal treatment with, for example, water or an organic solvent. From the viewpoint of more effectively suppressing yellowing, it is preferable to carry out the washing treatment by filtration dehydration, centrifugal dehydration, or centrifugation.

[0189] <Uniform dispersion treatment process> The substituent removal treatment step may be followed by a step of uniformly dispersing the fine fibrous cellulose obtained through the substituent removal treatment. By subjecting the fine fibrous cellulose to the substituent removal treatment, at least a portion of the fine fibrous cellulose is aggregated. The uniform dispersion treatment step is a step of uniformly dispersing the aggregated fine fibrous cellulose.

[0190] In the uniform dispersion treatment step, for example, a high-speed defibrator, grinder (stone mill type grinder), high-pressure homogenizer, high-pressure collision type grinder, ball mill, bead mill, disk type refiner, conical refiner, twin-screw kneader, vibration mill, homomixer under high-speed rotation, ultrasonic disperser or beater can be used. Among the above-mentioned uniform dispersion treatment devices, it is more preferable to use a high-speed defibrator or high-pressure homogenizer.

[0191] The treatment conditions for the uniform dispersion treatment step are not particularly limited, but it is preferable to increase the maximum movement speed of the fine fibrous cellulose during treatment and the pressure during treatment. In the case of a high-speed defibrator, the peripheral speed is preferably 20 m / sec or more, more preferably 25 m / sec or more, and even more preferably 30 m / sec or more. A high-pressure homogenizer is more preferably used because it has a higher maximum movement speed of the fine fibrous cellulose during treatment and a higher pressure during treatment than a high-speed defibrator. In high-pressure homogenizer treatment, the pressure during treatment is preferably 1 MPa or more, more preferably 10 MPa or more, even more preferably 50 MPa or more, and particularly preferably 100 MPa or more. Furthermore, in high-pressure homogenizer treatment, the pressure during treatment is preferably 350 MPa or less, more preferably 300 MPa or less, and even more preferably 250 MPa or less.

[0192] In the uniform dispersion treatment step, the above-mentioned spacer molecules may be added. By adding such spacer molecules in the uniform dispersion treatment step, the fine fibrous cellulose can be dispersed more uniformly and smoothly. This can more effectively improve the transparency of the fiber layer and the laminate sheet.

[0193] <Hydrophilic polymer> The fiber layer contains a hydrophilic polymer having a structural unit containing a hydroxyl group. The hydrophilic polymer preferably has an SP value of 9.0 or more. The hydrophilic polymer preferably dissolves 1 g or more of an oxygen-containing organic compound in 100 ml of ion-exchanged water.

[0194] Examples of hydrophilic polymers having a structural unit containing a hydroxyl group include dextrin, starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol (e.g., acetoacetylated polyvinyl alcohol), polyvinyl butyral, cellulose derivatives (e.g., hydroxyethyl cellulose, carboxyethyl cellulose, carboxymethyl cellulose), etc. Among these, from the viewpoint of improving the durability of the laminate sheet, the hydrophilic polymer is preferably polyvinyl alcohol or a cellulose derivative.

[0195] When polyvinyl alcohol is blended in the fiber layer, the saponification degree of the polyvinyl alcohol is preferably 99.9% or less, more preferably 99% or less, and even more preferably 95% or less. Furthermore, the saponification degree of the polyvinyl alcohol is preferably 85% or more. By incorporating polyvinyl alcohol having a saponification degree within the above range into the fiber layer, the transparency of the fiber layer can be more effectively increased, resulting in a sheet with higher transparency.

[0196] When a cellulose derivative is blended in the fiber layer, the weight average molecular weight of the cellulose derivative is preferably 2.5 × 10 from the viewpoints of achieving shape stability as a fiber layer, suppressing gelation while forming a fiber layer, achieving both a high tensile modulus and a high tensile elongation, and suppressing yellowing before and after heating. 4 More preferably, 5.0 × 10 4 More preferably, 1.0 × 10 5 and preferably 2.8 x 10 5 Less than or equal to 2.6 × 10 5 The weight-average molecular weight of the cellulose derivative is measured by gel permeation chromatography using light scattering (GPC-MALLS method).

[0197] The cellulose derivative is preferably a water-soluble cellulose ether from the viewpoint of increasing affinity with the fine fibrous cellulose and facilitating addition to a slurry (fine fibrous cellulose dispersion) of the fine fibrous cellulose. Here, "water-soluble" means that 1 g or more dissolves in 100 g of water at 20°C. Furthermore, "cellulose ether" is a general term for cellulose derivatives in which the hydroxy groups of cellulose have been etherified. Preferred examples of water-soluble cellulose ethers include methyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and carboxyethyl cellulose. Furthermore, from the viewpoint of suppressing yellowing of the sheet due to heating, the water-soluble cellulose ether is preferably a nonionic water-soluble cellulose ether. Examples of nonionic water-soluble cellulose ethers include methyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose. The nonionic water-soluble cellulose ether preferably has at least one functional group selected from the group consisting of a methoxy group and a hydroxypropoxy group, more preferably selected from the group consisting of methylcellulose and hydroxypropylmethylcellulose, and even more preferably hydroxypropylmethylcellulose.

[0198] When the cellulose derivative is methylcellulose, the degree of substitution of the methoxy group is preferably 0.5 or more, more preferably 0.8 or more, even more preferably 1.0 or more, still more preferably 1.2 or more, particularly preferably 1.5 or more, and preferably 3.0 or less, more preferably 2.6 or less, even more preferably 2.2 or less, and still more preferably 2.0 or less.

[0199] When the cellulose derivative is hydroxypropylmethylcellulose, the preferred range of the degree of substitution of the methoxy group is the same as that of the methoxy group in the above-mentioned methylcellulose. The degree of substitution of the hydroxypropoxy group is preferably 0.08 or more, more preferably 0.10 or more, even more preferably 0.12 or more, even more preferably 0.15 or more, particularly preferably 0.18 or more, and is preferably 0.50 or less, more preferably 0.40 or less, even more preferably 0.35 or less, and even more preferably 0.30 or less.

[0200] The weight-average molecular weight of the hydrophilic polymer is preferably 10,000 or more, more preferably 50,000 or more, and even more preferably 100,000 or more, and is preferably 8,000,000 or less, and even more preferably 5,000,000 or less.

[0201] The content of the hydrophilic polymer having a hydroxyl group-containing structural unit is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more, based on the total mass of the fiber layer. Furthermore, the content of the hydrophilic polymer having a hydroxyl group-containing structural unit is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less, based on the total mass of the fiber layer. By keeping the content of the hydrophilic polymer having a hydroxyl group-containing structural unit within the above range, it becomes easier to form a fiber layer and a laminate sheet that are excellent in durability and transparency.

[0202] The fiber layer may contain a hydrophilic polymer having a structural unit that does not contain a hydroxyl group, but the content thereof is preferably 1% by mass or less. The fiber layer may also contain spacer molecules used in the above-mentioned substituent removal treatment step, etc., and such spacer molecules include hydrophilic polymers having a structural unit that does not contain a hydroxyl group. When the spacer molecules are hydrophilic polymers having a structural unit that does not contain a hydroxyl group, the content of the spacer molecules is preferably 1% by mass or less relative to the total mass of the fiber layer.

[0203] (optional ingredient) The sheet may contain optional components, such as hydrophilic low-molecular-weight compounds, paper strength agents, thermoplastic resins, surfactants, organic ions, coupling agents, inorganic layered compounds, inorganic compounds, leveling agents, preservatives, antifoaming agents, organic particles, lubricants, antistatic agents, UV protection agents, dyes, pigments, stabilizers, magnetic powders, alignment promoters, plasticizers, dispersants, color inhibitors, polymerization inhibitors, pH adjusters, and crosslinking agents. These optional components may be contained in any of the fiber layer, resin layer, and inorganic layer.

[0204] Examples of hydrophilic low molecules include glycerin, sorbitol, ethylene glycol, etc. In this specification, a hydrophilic low molecule has a weight-average molecular weight of less than 10,000.

[0205] Examples of organic ions include tetraalkylammonium ions and tetraalkylphosphonium ions. Examples of tetraalkylammonium ions include tetramethylammonium ions, tetraethylammonium ions, tetrapropylammonium ions, tetrabutylammonium ions, tetrapentylammonium ions, tetrahexylammonium ions, tetraheptylammonium ions, tributylmethylammonium ions, lauryltrimethylammonium ions, cetyltrimethylammonium ions, stearyltrimethylammonium ions, octyldimethylethylammonium ions, lauryldimethylethylammonium ions, didecyldimethylammonium ions, lauryldimethylbenzylammonium ions, and tributylbenzylammonium ions. Examples of tetraalkylphosphonium ions include tetramethylphosphonium ions, tetraethylphosphonium ions, tetrapropylphosphonium ions, tetrabutylphosphonium ions, and lauryltrimethylphosphonium ions. Examples of tetrapropylonium ions and tetrabutylonium ions include tetra-n-propylonium ions and tetra-n-butylonium ions, respectively.

[0206] (Sheet manufacturing method) The method for manufacturing the sheet includes the steps of forming resin layers on both sides of a fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less and a hydrophilic polymer having a structural unit containing a hydroxyl group, and forming an inorganic layer on at least one side of the resin layer.

[0207] <Resin layer formation process> The step of forming resin layers on both sides of the fiber layer may be a step of laminating a resin film or a resin sheet on both sides of the fiber layer, but is preferably a step of forming resin layers by applying a resin coating liquid to both sides of the fiber layer. Here, the resin coating liquid preferably contains a solvent, and the resin layers formed on both sides of the fiber layer are preferably solvent-coated layers.

[0208] The viscosity of the solvent-containing resin coating liquid is preferably 100 cps or less, more preferably 80 cps or less, and even more preferably 60 cps or less. Here, the viscosity of the resin coating liquid is a value measured using a Brookfield viscometer. The measurement conditions are a rotation speed of 60 rpm, and the viscosity value measured one minute after the start of measurement is taken as the viscosity of the resin coating liquid. As the Brookfield viscometer, for example, an analog viscometer T-LVT manufactured by Brookfield Corporation can be used. By keeping the viscosity of the resin coating liquid within the above range, it becomes easier to control the surface roughness of the sheet within a predetermined range, and as a result, the transparency of the sheet can be more effectively improved.

[0209] The solid content in the resin coating liquid is preferably 12% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less. Here, the solid content in the resin coating liquid refers mainly to the content of the resin component contained in the resin coating liquid, but if the resin coating liquid contains optional components such as an adhesion aid as described below, the content of the optional components is also included.

[0210] The resin coating liquid may contain optional components such as an adhesion aid, if necessary. Preferred examples of the adhesion aid include the adhesion aids described above.

[0211] The step of forming a resin layer by applying a resin coating liquid to both surfaces of a fiber layer can be carried out using a known coating device, such as a blade coater, air knife coater, roll coater, bar coater, gravure coater, microgravure coater, rod blade coater, lip coater, die coater, or curtain coater.

[0212] <Inorganic layer formation process> In the step of forming an inorganic layer on a resin layer, sputtering, CVD, ion-assisted deposition, or ALD is preferably used. For example, an ion beam sputtering device (manufactured by Hakuto Co., Ltd.), a sputtering device (manufactured by Anelva Corporation), an ion-assisted deposition device, or an ALD device can be used to form the inorganic layer.

[0213] <Fiber layer forming process> The sheet manufacturing method includes, as a pre-process prior to the process of forming resin layers on both sides of a fiber layer, a process of forming a fiber layer containing fibrous cellulose having a fiber width of 1000 nm or less and a hydrophilic polymer having structural units containing hydroxyl groups. Here, the process of forming the fiber layer includes a process of obtaining a fibrous cellulose dispersion (hereinafter also referred to as a slurry), and a coating process of applying the fibrous cellulose dispersion to a substrate, or a papermaking process of applying the fibrous cellulose dispersion to a papermaking substrate. This process results in the above-mentioned fiber layer. The fibrous cellulose dispersion is a dispersion containing the above-mentioned fine fibrous cellulose and a hydrophilic polymer having structural units containing hydroxyl groups.

[0214] The surface of the fiber layer obtained through the fiber layer forming step facing the resin layer may be subjected to a surface treatment. Examples of surface treatment methods include corona treatment, plasma discharge treatment, UV irradiation treatment, electron beam irradiation treatment, and flame treatment. Among these, the surface treatment is preferably at least one selected from corona treatment and plasma discharge treatment. The plasma discharge treatment is preferably vacuum plasma discharge treatment.

[0215] <<Coating process>> In the coating process, for example, a fibrous cellulose dispersion (slurry) is coated onto a substrate, dried, and the resulting fiber sheet is peeled off from the substrate to obtain a fiber layer. Furthermore, by using a coating device and a long substrate, the fiber sheet that will become the fiber layer can be produced continuously.

[0216] The material of the substrate used in the coating process is not particularly limited, but a substrate with high wettability with the fibrous cellulose dispersion (slurry) is preferable because it can suppress shrinkage of the fiber sheet during drying. However, it is preferable to select a substrate that allows the formed fiber sheet to be easily peeled off after drying. Among these, resin films or plates or metal films or plates are preferred, but there are no particular limitations. For example, resin films or plates such as polypropylene, acrylic, polyethylene terephthalate, vinyl chloride, polystyrene, polycarbonate, and polyvinylidene chloride; metal films or plates such as aluminum, zinc, copper, and iron plates; and those with oxidized surfaces; stainless steel films or plates; and brass films or plates.

[0217] If the viscosity of the slurry is low and the slurry spreads on the substrate during the coating process, a frame for blocking the substrate may be fixed to obtain a fiber sheet of the desired thickness and basis weight. The type of frame for blocking the substrate is not particularly limited, but it is preferable to select one that allows the edges of the attached fiber sheet to be easily peeled off after drying. From this perspective, molded resin or metal plates are more preferable. In this embodiment, resin plates such as polypropylene plates, acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, polycarbonate plates, and polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates, and iron plates, and plates with their surfaces oxidized, as well as molded stainless steel plates and brass plates, can be used. The coating machine for coating the substrate with the slurry is not particularly limited, and examples thereof include a roll coater, gravure coater, die coater, curtain coater, air doctor coater, etc. Die coaters, curtain coaters, and spray coaters are particularly preferred because they can make the thickness of the fiber sheet more uniform.

[0218] The slurry temperature and ambient temperature when applying the slurry to the substrate are not particularly limited, but are preferably, for example, from 5°C to 80°C, more preferably from 10°C to 60°C, even more preferably from 15°C to 50°C, and particularly preferably from 20°C to 40°C. If the application temperature is above the lower limit, the slurry can be applied more easily. If the application temperature is below the upper limit, evaporation of the dispersion medium during application can be suppressed.

[0219] In the coating process, the finished basis weight of the fiber sheet is preferably 10 g / m 2 More than 100g / m 2 More preferably, 20 g / m 2 More than 60g / m 2 It is preferable to coat the slurry on the substrate so that the basis weight falls within the above range. By coating the slurry so that the basis weight falls within the above range, a fiber sheet with even greater strength can be obtained.

[0220] As described above, the coating step includes a step of drying the slurry coated on the substrate. The step of drying the slurry is not particularly limited, but may be performed by, for example, a non-contact drying method, a method of drying while restraining the fiber sheet, or a combination of these.

[0221] The non-contact drying method is not particularly limited, but for example, a method of drying by heating with hot air, infrared rays, far infrared rays, or near infrared rays (heat drying method), or a method of drying by vacuum (vacuum drying method) can be applied. Although the heat drying method and the vacuum drying method can be combined, the heat drying method is usually applied. Drying by infrared rays, far infrared rays, or near infrared rays can be carried out using, for example, an infrared device, a far infrared device, or a near infrared device, but is not particularly limited.

[0222] The heating temperature in the heat drying method is not particularly limited, but is preferably 20°C or higher and 150°C or lower, and more preferably 25°C or higher and 105°C or lower. If the heating temperature is equal to or higher than the lower limit, the dispersion medium can be quickly volatilized. Furthermore, if the heating temperature is equal to or lower than the upper limit, the cost required for heating can be reduced and discoloration of the fibrous cellulose due to heat can be suppressed.

[0223] <<Paper making process>> The papermaking process is carried out by making paper from the slurry using a papermaking machine. The papermaking machine used in the papermaking process is not particularly limited, but examples include continuous papermaking machines such as Fourdrinier, cylinder, and tilting types, and multi-layer papermaking machines that combine these. In the papermaking process, known papermaking methods such as handmaking may also be used.

[0224] The papermaking process involves filtering and dewatering the slurry with a wire to obtain a wet fiber sheet, which is then pressed and dried. The filter cloth used to filter and dewater the slurry is not particularly limited, but it is preferable that it does not allow fibrous cellulose to pass through and does not slow the filtration rate too much. Such filter cloths are not particularly limited, but fiber sheets, woven fabrics, and porous membranes made of organic polymers are preferred. The organic polymer is not particularly limited, but non-cellulose organic polymers such as polyethylene terephthalate, polyethylene, polypropylene, and polytetrafluoroethylene (PTFE) are preferred. In this embodiment, examples include porous membranes made of polytetrafluoroethylene with a pore size of 0.1 μm to 20 μm, and woven fabrics made of polyethylene terephthalate or polyethylene with a pore size of 0.1 μm to 20 μm.

[0225] A method for producing a fiber sheet from a slurry can be carried out, for example, using a production apparatus including a water squeezing section in which a slurry containing fibrous cellulose is discharged onto the upper surface of an endless belt and the dispersion medium is squeezed out of the discharged slurry to produce a web, and a drying section in which the web is dried to produce a fiber sheet. An endless belt is disposed between the water squeezing section and the drying section, and the web produced in the water squeezing section is transported to the drying section while still on the endless belt.

[0226] The dehydration method used in the papermaking process is not particularly limited, but examples thereof include dehydration methods commonly used in paper manufacturing. Among these, methods in which dehydration is performed using a Fourdrinier, cylinder, or inclined wire, followed by further dehydration using a roll press, are preferred. Furthermore, the drying method used in the papermaking process is not particularly limited, but examples thereof include methods used in paper manufacturing. Among these, drying methods using a cylinder dryer, Yankee dryer, hot air dryer, near-infrared heater, infrared heater, etc. are more preferred.

[0227] (Application) The sheet of this embodiment has high transparency and exhibits excellent durability. Therefore, the sheet of this embodiment is preferably used for optical components. More specifically, the sheet of this embodiment is suitable for use as a light-transmitting substrate such as various display devices and various solar cells. The sheet of this embodiment is also suitable for use as a substrate for electronic devices, a component for home appliances, a window material for various vehicles and buildings, an interior material, an exterior material, a packaging material, a gas barrier material, and the like. [Example]

[0228] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0229] <Production Example A1> The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 A sheet-like product with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012 was used.

[0230] This raw pulp was subjected to phosphorus oxo-oxidation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (bone dry mass) of the raw pulp to adjust the total weight to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, to obtain a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 250 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining a phosphorylated pulp.

[0231] The resulting phosphorylated pulp was then washed. 100 g (bone dry mass) of phosphorylated pulp was mixed with 10 L of ion-exchanged water to obtain a pulp dispersion. The pulp was stirred to uniformly disperse the pulp, and then repeatedly filtered and dehydrated. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0232] Next, the washed phosphorylated pulp was neutralized as follows: First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous solution of sodium hydroxide was added little by little while stirring to obtain a phosphorylated pulp slurry with a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated and washed to obtain a neutralized phosphorylated pulp.

[0233] The infrared absorption spectrum of the obtained phosphorylated pulp was measured using FT-IR. -1Absorption due to the P=O of phosphate groups was observed around 2θ = 14° to 17° and 2θ = 22° to 23°, confirming the addition of phosphate groups to the pulp. Furthermore, when the obtained phosphorylated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals. The amount of phosphate groups (amount of first dissociated acid) measured by the method described below in [Measurement of phosphorus oxo acid group amount] was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0234] Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (A) containing fine fibrous cellulose.

[0235] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of phosphate groups (amount of first dissociated acid) measured by the method described below in [Measurement of amount of phosphorus oxo acid group] was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0236] <Manufacturing example B1> The same procedure as in Production Example A1 was carried out except that 33 parts by mass of phosphorous acid (phosphonic acid) was used instead of ammonium dihydrogen phosphate, to obtain a fine fibrous cellulose dispersion (B) containing phosphite pulp and fine fibrous cellulose.

[0237] The infrared absorption spectrum of the obtained phosphorous-oxidized pulp was measured using FT-IR. -1The absorption due to P=O of the phosphonic acid group, which is a tautomer of the phosphorous acid group, was observed near the α-axis, confirming that the phosphorous acid group (phosphonic acid group) had been added to the pulp. Furthermore, when the obtained phosphorous-oxidized pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ=14° to 17° and around 2θ=22° to 23°, confirming the presence of cellulose type I crystals.

[0238] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of phosphorous groups (amount of first dissociated acid) of the obtained fine fibrous cellulose, measured by the method described below in [Measurement of amount of phosphorus oxo acid group], was 1.51 mmol / g. The total amount of dissociated acid was 1.54 mmol / g.

[0239] <Manufacturing example C1> The same procedure as in Production Example A1 was carried out, except that 38 parts by mass of amidosulfonic acid (sulfamic acid) was used instead of ammonium dihydrogen phosphate and the heating time was extended to 20 minutes, to obtain a fine fibrous cellulose dispersion (C) containing sulfated pulp and fine cellulose.

[0240] The infrared absorption spectrum of the obtained sulfated pulp was measured using FT-IR. -1 The absorption due to the S=O of the sulfate ester group was observed around the α-axis, confirming that sulfate ester groups had been added to the pulp. Furthermore, when the obtained sulfated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ=14° to 17° and around 2θ=22° to 23°, confirming the presence of cellulose type I crystals.

[0241] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3-5 nm. The amount of sulfur oxoacid groups in the obtained fine fibrous cellulose, as measured by the method described below in [Measurement of sulfur oxoacid group amount and sulfonic group amount], was 1.47 mmol / g.

[0242] <Production Example D1> The raw material pulp used was softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. This raw material pulp was subjected to alkaline TEMPO oxidation treatment as follows.

[0243] First, 100 parts by weight of the raw pulp (dry mass equivalent), 1.6 parts by weight of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by weight of sodium bromide were dispersed in 10,000 parts by weight of water. Next, a 13% by weight aqueous solution of sodium hypochlorite was added to 1.0 g of pulp to give a concentration of 10 mmol to initiate the reaction. During the reaction, a 0.5 M aqueous solution of sodium hydroxide was added dropwise to maintain the pH at 10 to 10.5. The reaction was considered complete when no further change in pH was observed.

[0244] The resulting TEMPO-oxidized pulp was then washed. The pulp slurry after TEMPO oxidation was dehydrated to obtain a dehydrated sheet, to which 5,000 parts by mass of ion-exchanged water was added, and the sheet was stirred to uniformly disperse the pulp. This process was repeated until the electrical conductivity of the filtrate reached 100 μS / cm or less, marking the end of the washing process.

[0245] The remaining aldehyde groups in this dehydrated sheet were further oxidized as follows: 100 parts by weight of the dehydrated sheet (dry mass equivalent) was dispersed in 10,000 parts by weight of 0.1 mol / L acetate buffer (pH 4.8). 113 parts by weight of 80% by weight sodium chlorite was then added, the container was immediately sealed, and the mixture was stirred at 500 rpm using a magnetic stirrer while reacting at room temperature for 48 hours to obtain a pulp slurry.

[0246] The resulting TEMPO-oxidized pulp was then washed. The pulp slurry after the additional oxidation was dehydrated to obtain a dehydrated sheet, to which 5,000 parts by mass of ion-exchanged water was added, and the sheet was stirred to uniformly disperse the pulp. This process was repeated until the electrical conductivity of the filtrate reached 100 μS / cm or less, marking the end of the washing process.

[0247] The obtained TEMPO-oxidized pulp was analyzed using an X-ray diffractometer. Typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0248] Ion-exchanged water was added to the obtained TEMPO-oxidized pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (D) containing fine fibrous cellulose.

[0249] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxy groups in the obtained fine fibrous cellulose, as measured by the method described below in "Measurement of Carboxy Group Amount," was 1.80 mmol / g.

[0250] <Manufacturing example E1> [Hypochlorous acid oxidation] A sheet (solids concentration 90% by mass) made from softwood bleached kraft pulp (NBKP) was mixed in a hand mixer (Lab Millser PLUS, manufactured by Osaka Chemical Co., Ltd.) at 20,000 rpm for 15 seconds to produce a fluffy fluffed pulp (solids concentration 90% by mass). Sodium hypochlorite pentahydrate was then added to ion-exchanged water to prepare an aqueous solution with a sodium hypochlorite solids concentration of 22% by mass. 9,000 parts by mass of a 22% sodium hypochlorite aqueous solution was added to 100 parts by mass of the fluffy fluffed pulp, and the mixture was reacted for 2 hours in a warm bath at 30°C to obtain carboxylated pulp. During the reaction, the pH was maintained at 11 by adding 1N aqueous sodium hydroxide solution as needed.

[0251] The resulting carboxylated pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting carboxylated pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0252] The obtained carboxyl-introduced pulp was analyzed using an X-ray diffractometer. Typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0253] Ion-exchanged water was added to the obtained carboxyl-introduced pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (E) containing fine fibrous cellulose.

[0254] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxy groups in the obtained fine fibrous cellulose, as measured by the method described in "Measurement of Carboxy Group Amount" below, was 0.70 mmol / g.

[0255] <Production Example F1> [Maleic acid esterification] A sheet (solids concentration 90% by mass) made from bleached softwood kraft pulp (NBKP) was mixed for 15 seconds at 20,000 rpm using a hand mixer (Lab Millser PLUS, manufactured by Osaka Chemical Co., Ltd.) to produce a fluffy fluffing pulp (solids concentration 90% by mass). 100 parts by mass of the fluffy fluffing pulp and 50 parts by mass of maleic anhydride were placed in an autoclave and mixed at 150°C for 2 hours to obtain a carboxyl-introduced pulp.

[0256] The resulting carboxylated pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting carboxylated pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0257] The infrared absorption spectrum of the obtained carboxyl-introduced pulp was measured using FT-IR. -1 The absorption due to carboxyl groups was observed around 2θ = 14° to 17° and 2θ = 22° to 23°, confirming that the pulp had been maleated. Furthermore, when the carboxyl-group-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0258] Ion-exchanged water was added to the obtained carboxyl-introduced pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (F) containing fine fibrous cellulose.

[0259] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxy groups in the obtained fine fibrous cellulose, as measured by the method described below in "Measurement of Carboxy Group Amount," was 1.22 mmol / g.

[0260] <Manufacturing example G1> [Carboxyethylated] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 A sheet-like product with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012 was used.

[0261] To 100 parts by mass (bone dry mass) of this raw pulp, a chemical solution consisting of 250 parts by mass of 12N NaOH aqueous solution, 163 parts by mass of 2-chloropropionic acid, and 140 parts by mass of ion-exchanged water (total 553 parts by mass) was added to obtain a chemical-impregnated pulp. The obtained chemical-impregnated pulp was then heated in a hot air dryer at 165°C for 10 minutes to introduce carboxyethyl groups (carboxy groups) into the cellulose in the pulp, thereby obtaining a carboxy-introduced pulp.

[0262] The resulting carboxylated pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting carboxylated pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0263] Next, the washed carboxylated pulp was neutralized as follows: First, the washed carboxylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous sodium hydroxide solution was added little by little while stirring to obtain a carboxylated pulp slurry with a pH of 12 to 13. Next, the carboxylated pulp slurry was dehydrated and washed to obtain a neutralized carboxylated pulp.

[0264] When the carboxyl-group-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming that it contained cellulose type I crystals.

[0265] Ion-exchanged water was added to the obtained carboxyl-introduced pulp to prepare a slurry with a solid content of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (G) containing fine fibrous cellulose.

[0266] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxy groups in the obtained fine fibrous cellulose, as measured by the method described below in "Measurement of Carboxy Group Amount," was 1.41 mmol / g.

[0267] <Manufacturing example H1> [Sulfoethylation] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 A sheet-like product with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012 was used.

[0268] To 100 parts by mass (bone dry mass) of this raw pulp, a chemical solution consisting of 180 parts by mass of a 2N NaOH aqueous solution and 780 parts by mass of a 25% by mass sodium vinyl sulfonate aqueous solution (total 960 parts by mass) was added to obtain a chemical solution-impregnated pulp. The obtained chemical solution-impregnated pulp was then heated in a hot air dryer at 165°C for 16 minutes to introduce sulfoethyl groups (sulfonic groups) into the cellulose in the pulp, yielding a sulfoethyl group-introduced pulp (sulfonic group-introduced pulp).

[0269] The resulting sulfoethyl group-introduced pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting sulfoethyl group-introduced pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0270] When the sulfoethyl group-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0271] Ion-exchanged water was added to the obtained sulfoethyl group-introduced pulp to prepare a slurry with a solid content of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (H) containing fine fibrous cellulose.

[0272] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3-5 nm. The sulfoethyl group content (sulfonic group content) of the obtained fine fibrous cellulose, as measured by the method described below in [Measurement of sulfur oxoacid group content and sulfonic group content], was 1.48 mmol / g.

[0273] <Production Example J1> [Cationization treatment] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 A sheet-like product with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012 was used.

[0274] To 100 parts by mass (bone dry mass) of this raw pulp, a chemical solution consisting of 180 parts by mass of a 1N NaOH aqueous solution and 325 parts by mass of a cationizing agent (Catiomaster G, manufactured by Yokkaichi Synthetic Co., Ltd., glycidyl trimethylammonium chloride, purity 73.1% by mass, moisture content 20.2% by mass) (total 505 parts by mass) was added to obtain a chemical solution-impregnated pulp. The obtained chemical solution-impregnated pulp was then heated in a hot air dryer at 165°C for 12 minutes to introduce cationic groups into the cellulose in the pulp, yielding a cationic group-introduced pulp.

[0275] The resulting cation-group-introduced pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting cation-group-introduced pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0276] Next, the washed cationic group-introduced pulp was neutralized as follows: First, the washed cationic group-introduced pulp was diluted with 10 L of ion-exchanged water, and then 1 N hydrochloric acid was added little by little while stirring to obtain a cationic group-introduced pulp slurry with a pH of 1 to 2. Next, the cationic group-introduced pulp slurry was dehydrated and washed to obtain a cationic group-introduced pulp that had been subjected to a neutralization treatment.

[0277] The cationic group-introduced pulp was analyzed using an X-ray diffractometer. Typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0278] Ion-exchanged water was added to the obtained cationic group-introduced pulp to prepare a slurry with a solid content of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (J) containing fine fibrous cellulose.

[0279] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. Furthermore, trace nitrogen analysis was performed on the obtained fine fibrous cellulose, and the amount of cationic groups calculated using the following formula was found to be 1.45 mmol / g. (Amount of cationic groups) [mmol / g] = (amount of nitrogen) / 14 × 1000 / (amount of fine fibrous cellulose tested)

[0280] <Production Example K1> [Preparation of cellulose treated with substituent removal] <Nitrogen removal treatment> Deionized water was added to the phosphorylated pulp prepared in Production Example A1 to prepare a slurry with a solids concentration of 4% by mass. A 48% by mass aqueous solution of sodium hydroxide was added to the slurry to adjust the pH to 13.4 and heated at 85°C for 1 hour. The pulp slurry was then dehydrated, and 10 L of deionized water was added to 100 g (bone dry mass) of phosphorylated pulp to obtain a pulp dispersion. The pulp was stirred to uniformly disperse, and the filtration and dehydration process was repeated to remove excess sodium hydroxide. The removal was terminated when the electrical conductivity of the filtrate reached 100 μS / cm or less. The amount of carbamide groups introduced, as measured by the measurement method described below, was 0.01 mmol / g.

[0281] The infrared absorption spectrum of the obtained phosphorus oxyoxidized pulp was measured using FT-IR. -1Absorption due to P=O of phosphate groups was observed near the nucleus, confirming that phosphate groups had been added to the pulp. Furthermore, X-ray diffraction confirmed that the resulting fine fibrous cellulose maintained cellulose type I crystallinity. The amount of phosphate groups (amount of first dissociated acid) measured by the method described below in [Measurement of amount of phosphorus oxoacid groups] was 1.35 mmol / g. The total amount of dissociated acid was 2.30 mmol / g.

[0282] <Defibrillation processing> Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0283] <Substituent removal treatment (high temperature heat treatment)> The fine fibrous cellulose dispersion was placed in a pressure vessel and heated at 160°C for 15 minutes until the amount of phosphate groups reached 0.08 mmol / g. This confirmed the formation of fine fibrous cellulose aggregates.

[0284] <Slurry washing process after removing substituents> After heating, the slurry was washed by adding an equal amount of ion-exchanged water to the slurry to obtain a slurry with a solids concentration of approximately 1% by mass. The slurry was then stirred and then filtered and dehydrated. When the electrical conductivity of the filtrate reached 10 μS / cm or less, ion-exchanged water was added again to obtain a slurry with a solids concentration of approximately 1% by mass, which was then allowed to stand for 24 hours. The filtration and dehydration process was then repeated, and the washing endpoint was reached when the electrical conductivity of the filtrate again reached 10 μS / cm or less. Ion-exchanged water was added to the resulting fine fibrous cellulose aggregates, and a slurry was obtained after removing the substituents. The solids concentration of this slurry was 1.7% by mass.

[0285] <Uniform dispersion of slurry after removing substituents> Ion-exchanged water was added to the resulting slurry after removal of the substituents to give a slurry with a solids concentration of 1.0% by mass, which was then treated three times at a pressure of 200 MPa in a wet atomization apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a dispersion of the substituent-removed fine fibrous cellulose (K). The number-average fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 4 nm.

[0286] <Example 1-1> (Dissolution of polyvinyl alcohol) Ion-exchanged water was mixed with acetoacetyl-modified polyvinyl alcohol (Gohsenex, manufactured by Mitsubishi Chemical Corporation). TM Z-200) was added to make the amount 12% by mass, and the mixture was stirred at 95°C for 1 hour to dissolve. By the above procedure, an aqueous polyvinyl alcohol solution was obtained.

[0287] (Formation of fiber layer) The fine fibrous cellulose dispersion (A) and the above polyvinyl alcohol aqueous solution were each diluted with ion-exchanged water to a solid content of 0.6% by mass. Then, 70 parts by mass of the diluted fine fibrous cellulose dispersion were mixed with 30 parts by mass of the diluted polyvinyl alcohol aqueous solution to obtain a mixed solution. Furthermore, the finished basis weight of the sheet was 70 g / m. 2 The mixture was measured so that the weight of the mixture was 100g and spread on a commercially available acrylic plate. A damming frame (inner dimensions 250mm x 250mm, height 5cm) was placed on the acrylic plate to achieve the specified basis weight. The mixture was then dried in a dryer at 70°C for 24 hours and peeled off from the acrylic plate to form a fiber layer (a layer containing fine fibrous cellulose). The thickness of the fiber layer was 50µm.

[0288] (Formation of resin layer) An acrylic polymer resin coating solution was prepared using an acrylic polymer resin (AICA ITRON Z-815-4L, manufactured by AICA Kogyo Co., Ltd.) as a base, by incorporating a low refractive index monomer into the polymerization to adjust the refractive index to 1.52. The viscosity of the resin coating solution, measured using the measurement method described below, was 38 cps. This resin coating solution was applied to one side of the fiber layer (the side in contact with the acrylic plate) using a bar coater. The resulting layer was then heated at 100°C for 1 hour to form a resin layer. A resin layer was then formed on the opposite side of the fiber layer using the same procedure. The resin layer was 3 μm thick per side. This procedure resulted in a laminate sheet in which resin layers were laminated on both sides of the fiber layer.

[0289] (Formation of inorganic layer) The laminated sheet with the resin layer was placed in an ion beam sputtering device (manufactured by Hakuto Co., Ltd.). The device was evacuated and heated at 100°C for 1 hour, then allowed to cool and film deposition was carried out at the lowest possible temperature. Based on the SiO2 film deposition rate of 9.65 nm / min on the silicon substrate by ion beam sputtering, the film deposition time was set to achieve the desired film thickness, and a 20 nm inorganic SiO2 layer was deposited on the resin layer. This resulted in a laminated sheet with a configuration of inorganic layer / resin layer / fiber layer / resin layer.

[0290] <Example 1-2> In Example 1-1, a laminated sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 1-1, except that inorganic layers were formed on both sides to form a structure of inorganic layer / resin layer / fiber layer / resin layer / inorganic layer.

[0291] <Examples 1-3> A laminated sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 1-1, except that the thickness of the inorganic layer was changed to 200 nm.

[0292] <Examples 1-4> A laminated sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 1-2, except that the thickness of the inorganic layer was set to 200 nm.

[0293] <Examples 1-5> A laminated sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 1-2, except that the material of the inorganic layer was changed to TiO2.

[0294] <Examples 1-6> A laminated sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 1-2, except that the material of the inorganic layer was changed to Al2O3.

[0295] <Examples 2-1 to 2-6> In the formation of the fiber layer in Examples 1-1 to 1-6, the amount of diluted fine fibrous cellulose dispersion (A) mixed was changed to 40 parts by mass, and the amount of diluted aqueous polyvinyl alcohol mixed was changed to 60 parts by mass, and laminated sheets were obtained in the same manner as in Examples 1-1 to 1-6, respectively.

[0296] <Example 3-1> In Example 1-2 (formation of resin layer), a resin coating solution was used that was a mixture of 10 parts by mass of modified polycarbonate resin (Mitsubishi Gas Chemical Company, Inc., Iupizeta FPC-2136), 60 parts by mass of toluene, 30 parts by mass of methyl ethyl ketone, and 1.5 parts by mass of an isocyanate compound (Asahi Kasei Chemicals Corporation, Duranate TPA-100) as an adhesion aid. A laminate sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 1-2. The viscosity of the resin coating solution, measured by the measurement method described below, was 30 cps.

[0297] <Example 3-2> A laminated sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 3-1, except that the material of the inorganic layer was changed to TiO2.

[0298] <Example 3-3> A laminated sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 3-1, except that the material of the inorganic layer was changed to Al2O3.

[0299] <Example 4-1> (Dissolution of cellulose ether) Methylcellulose (Metolose 65SH-1500, manufactured by Shin-Etsu Chemical Co., Ltd., weight-average molecular weight: 2.2 × 10) was added to ion-exchanged water. 5 The resulting mixture was stirred at room temperature for 1 hour to dissolve the cellulose ether in an aqueous solution. Next, the cellulose ether aqueous solution was diluted with ion-exchanged water so that the solid content concentration was 0.6% by mass.

[0300] A laminated sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 1-1 (formation of a fiber layer), except that a diluted cellulose ether aqueous solution was used instead of a diluted polyvinyl alcohol aqueous solution.

[0301] <Examples 4-2 to 4-6> In Examples 1-2 to 1-6 (formation of fiber layer), laminated sheets with an inorganic layer were obtained in the same manner as in Examples 1-2 to 1-6, except that a diluted cellulose ether aqueous solution was used instead of the diluted polyvinyl alcohol aqueous solution.

[0302] <Examples 5-1 to 5-6> In Examples 2-1 to 2-6 (formation of fiber layer), laminated sheets with an inorganic layer were obtained in the same manner as in Examples 2-1 to 2-6, except that a diluted cellulose ether aqueous solution was used instead of a diluted polyvinyl alcohol aqueous solution.

[0303] <Examples 6 to 13> In Example 2-2 (Formation of fibrous layer), a laminated sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 2-2, except that the fine fibrous cellulose dispersion (fine fibrous cellulose dispersion (B to J)) shown in the table below was used instead of the fine fibrous cellulose dispersion (A).

[0304] <Examples 14-1 to 14-6> In Examples 2-1 to 2-6 (formation of fiber layer), laminated sheets with an inorganic layer were obtained in the same manner as in Examples 2-1 to 2-6, except that fine fibrous cellulose dispersion (K) was used instead of fine fibrous cellulose dispersion (A).

[0305] <Examples 15-1 to 15-6> In Examples 5-1 to 5-6 (formation of fiber layer), laminated sheets with an inorganic layer were obtained in the same manner as in Examples 5-1 to 5-6, except that fine fibrous cellulose dispersion (K) was used instead of fine fibrous cellulose dispersion (A).

[0306] Example 16 A laminated sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 3-1 (formation of resin layer), except that a urethane acrylic resin (Acrit 8UA-347A, manufactured by Taisei Fine Chemical Co., Ltd.) having a urethane unit / acrylic unit mass ratio of 2 / 8 was used instead of the polycarbonate resin. The viscosity of the resin coating liquid measured by the measurement method described below was 36 cps.

[0307] Example 17 A laminated sheet having an inorganic layer laminated thereon was obtained in the same procedure as in Example 3-1 (formation of resin layer), except that a polyester resin coating liquid (Elitel UE-3320, manufactured by Unitika Ltd.) was used instead of the polycarbonate resin. The viscosity of the resin coating liquid, measured by the measurement method described below, was 40 cps.

[0308] Example 18 A laminated sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 3-1 (formation of resin layer), except that a fluororesin coating liquid (manufactured by Asahi Glass Co., Ltd., Cytop) was used instead of the polycarbonate resin. The viscosity of the resin coating liquid measured by the measurement method described below was 43 cps.

[0309] <Comparative Example 1> A sheet was obtained in the same manner as in Example 1-1, except that (the formation of the inorganic layer) was not carried out.

[0310] <Comparative Example 2> A sheet was obtained in the same manner as in Example 2-1, except that (the formation of the inorganic layer) was not carried out.

[0311] <Comparative Example 3> (Dissolution of polyethylene oxide) Polyethylene oxide (Sumitomo Seika Chemicals Co., Ltd., PEO-18, viscosity average molecular weight 4.3 × 10 6 ) was added so that the concentration was 2% by mass, and the mixture was stirred at room temperature for 1 hour to dissolve. By the above procedure, an aqueous polyethylene oxide solution was obtained. Next, the aqueous polyethylene oxide solution was diluted with ion-exchanged water to a solids concentration of 0.6% by mass.

[0312] A laminated sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 1-2 (formation of the fiber layer), except that a diluted aqueous polyethylene oxide solution was used instead of the diluted aqueous polyvinyl alcohol solution.

[0313] <Comparative Example 4> Ion-exchanged water was added to a polyurethane resin (Superflex 420, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) to obtain a polyurethane resin solution diluted to 0.6% by mass. A laminated sheet having an inorganic layer laminated thereon was obtained in the same manner as in Example 1-2 (formation of a fiber layer), except that the polyurethane resin solution diluted to 0.6% by mass was used instead of the diluted aqueous polyvinyl alcohol solution.

[0314] <Measurement> [Measurement of phosphorus oxoacid group content] In measuring the amount of phosphorus oxoacid groups (amount of phosphate groups or phosphite groups), ion-exchanged water was first added to the target fine fibrous cellulose to prepare a slurry with a solids concentration of 0.2% by mass. The resulting slurry was treated with an ion-exchange resin and then titrated with an alkali to measure the amount of phosphorus oxoacid groups. Treatment with ion exchange resin was carried out by adding 1 / 10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the above-mentioned fine fibrous cellulose-containing slurry, shaking for 1 hour, and then pouring it onto a mesh with 90 μm openings to separate the resin from the slurry. In addition, alkali titration was performed by measuring the change in the pH of a slurry containing fine fibrous cellulose after ion exchange resin treatment while adding 10 μL of 0.1 N sodium hydroxide solution every 5 seconds. Nitrogen gas was bubbled through the slurry 15 minutes before the start of the titration. In this neutralization titration, two maximum points of increment (the derivative of pH with respect to the amount of alkali added) were observed on the plot of pH versus the amount of alkali added. The first maximum point of increment after starting the addition of alkali is called the first endpoint, and the second maximum point is called the second endpoint (Figure 1). The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of first dissociated acid in the slurry used for titration. The amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid in the slurry used for titration. The amount of alkali (mmol) required from the start of titration to the first endpoint was divided by the solid content (g) in the slurry to be titrated, and the value was taken as the amount of phosphorus oxo acid groups (mmol / g). When measuring the amount of phosphorus oxoacid groups in the pulp, ion-exchanged water was added to the phosphorus oxo-oxidized pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was then treated six times in a wet pulverization apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa, and the resulting dispersion was titrated with alkali in the same manner as described above.

[0315] [Measurement of sulfur oxoacid and sulfonic acid groups] The amount of sulfur oxoacid groups or sulfonic groups was measured as follows. The obtained fine fibrous cellulose (solid content obtained by heating and drying the dispersion) was wet ashed using perchloric acid and concentrated nitric acid, then diluted at an appropriate ratio and the amount of sulfur was measured by ICP atomic emission spectrometry. The amount of sulfur was divided by the bone dry mass of the fine fibrous cellulose tested, and the value was taken as the amount of sulfur oxoacid groups or sulfonic groups (unit: mmol / g).

[0316] [Measurement of xanthate group content] The xanthate group content was measured using the Bredee method. Specifically, 40 mL of saturated ammonium chloride solution was added to 1.5 parts by mass (bone-dry mass) of fine fibrous cellulose (solid content obtained by heating and drying the dispersion). The sample was crushed with a glass rod and mixed thoroughly. After leaving the mixture for approximately 15 minutes, it was filtered through GFP filter paper (GS-25, manufactured by Advantec) and thoroughly washed with saturated ammonium chloride solution. The sample, along with the GFP filter paper, was placed in a 500 mL tall beaker, and 50 mL of 0.5 M sodium hydroxide solution (5 °C) was added and stirred. After leaving the mixture for 15 minutes, phenolphthalein solution was added until the solution turned pink, followed by 1.5 M acetic acid. The point at which the solution changed from pink to colorless was designated as the neutralization point. After neutralization, 250 mL of distilled water was added and stirred thoroughly. 10 mL of 1.5 M acetic acid and 10 mL of 0.05 mol / L iodine solution were added using a volumetric pipette. This solution was then titrated with 0.05 mol / L sodium thiosulfate solution. The amount of xanthate groups was calculated from the titration amount of sodium thiosulfate and the bone dry mass of the fine fibrous cellulose using the following formula. Amount of xanthate group (mmol / g) = (0.05 × 10 × 2 - 0.05 × sodium thiosulfate titration (mL)) / 1000 / bone-dry mass of fine fibrous cellulose (g)

[0317] [Measurement of carboxyl group amount] The amount of carboxy groups in the fine fibrous cellulose was measured by adding ion-exchanged water to a fine fibrous cellulose dispersion containing the target (maleic oxidized, TEMPO oxidized, hypochlorite oxidized, or carboxyethylated) fine fibrous cellulose to make the content 0.2 mass%, treating the dispersion with an ion-exchange resin, and then titrating the dispersion with an alkali. Treatment with ion exchange resin was carried out by adding 1 / 10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) to a 0.2% by mass slurry containing fine fibrous cellulose, shaking for 1 hour, and then pouring the mixture onto a mesh with 90 μm openings to separate the resin from the slurry. In addition, alkali titration was performed by measuring the change in pH of the fibrous cellulose-containing slurry after treatment with an ion exchange resin while adding 0.1 N aqueous sodium hydroxide. Observing the change in pH while adding aqueous sodium hydroxide yielded a titration curve like the one shown in Figure 2. As shown in Figure 2, in this neutralization titration, a single point was observed where the increment (the differential value of pH with respect to the amount of alkali added) reached a maximum on the curve plotting the measured pH against the amount of alkali added. This maximum increment was called the first endpoint. The region from the start of the titration to the first endpoint in Figure 2 is called the first region. The amount of alkali required in the first region was equal to the amount of carboxyl groups in the slurry used for titration. The amount of alkali (mmol) required in the first region of the titration curve was divided by the solids content (g) of the fine fibrous cellulose-containing slurry to be titrated to calculate the amount of carboxyl groups introduced (mmol / g). The amount of carboxyl groups introduced (mmol / g) is calculated based on the amount of carboxyl groups introduced (mmol / g) when the counter ions of the carboxyl groups are hydrogen ions (H + ) (hereinafter referred to as the amount of carboxy groups (acid type)) per 1 g of fibrous cellulose.

[0318] [Measurement of carbamide group content] The amount of carbamide groups introduced into fibrous cellulose (pulp) can be calculated by freeze-drying a slurry containing fibrous cellulose, then pulverizing the sample and performing trace nitrogen analysis. The amount of carbamide groups introduced per unit mass of fibrous cellulose (mmol / g) can be calculated by dividing the nitrogen content (g / g) per unit mass of fibrous cellulose obtained by trace nitrogen analysis by the atomic weight of nitrogen.

[0319] (resin layer thickness) A cross section of the sheet was cut out using an ultramicrotome UC-7 (manufactured by JEOL Ltd., UC-7), and the cross section was observed with an electron microscope, a magnifying glass or visually, and the measured value was taken as the thickness of the resin layer.

[0320] (thickness of inorganic layer) The thickness of the inorganic layer was determined by measuring the difference in film thickness between the inorganic layer-deposited surface and the untreated surface using a stylus-type step thickness gauge (P-6, manufactured by KLA Tencor Corporation), and the difference was taken as the thickness of the inorganic layer.

[0321] (Viscosity of resin coating liquid) The viscosity of the prepared resin coating liquid was measured using a Brookfield viscometer (analog viscometer T-LVT, manufactured by BLOOKFIELD Corporation). The measurement conditions were a rotation speed of 60 rpm, and the viscosity value 1 minute after the start of measurement was taken as the viscosity of the resin coating liquid.

[0322] (Surface roughness (Ra)) The surface roughness of both sides of the laminate sheet was measured in accordance with JIS B 0601:1994 using an optical interference non-contact surface profiler (Ryoka Systems Co., Ltd., non-contact surface / layer cross-sectional profile measurement system VertScan2.0, R5500GML). The surface roughness was calculated using a 10x objective lens over a measurement range of 470 μm x 350 μm. When an inorganic layer was provided on only one side of the laminate sheet, the side on which the inorganic layer was provided was designated as the first side.

[0323] (Transparency (initial haze)) The haze of the laminated sheet was measured in accordance with JIS K 7136:2000 using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.).

[0324] (Durability evaluation) The laminated sheet was cut into 5 cm squares and left to stand for 10 days (240 hours) under conditions of 85°C and 85% relative humidity. The haze of the laminated sheet after the above-mentioned condition treatment (after durability test) (durability evaluation 1) and the weight change rate of the laminated sheet before and after treatment (durability evaluation 2) were evaluated according to the following criteria.

[0325] <Durability rating 1> The difference in haze (Δhaze) of the laminate sheet before and after the durability test was calculated, and the durability of the laminate sheet was evaluated according to the following criteria: The haze of the laminate sheet was measured in accordance with JIS K 7136:2000 using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.). ΔHaze = (Haze of laminate sheet after durability test) - (Haze of laminate sheet before durability test) A: The Δ haze of the laminated sheet before and after the durability test is less than 1.5%. B: The Δ haze of the laminated sheet before and after the durability test is 1.5% or more.

[0326] <Durability rating 2> The weight change rate of the laminate sheet before and after the durability test was calculated using the following formula, and the durability of the laminate sheet was evaluated according to the following criteria. Weight change rate (%) = ((weight of laminate sheet after durability test - weight of laminate sheet before durability test) / weight of laminate sheet before durability test) x 100 Weight of laminate sheet before durability test: Weight of the laminate sheet before the durability test, which is the weight (g) of the laminate sheet after conditioning under conditions of 23°C and 50% relative humidity. Weight of laminate sheet after durability test: Weight of the laminate sheet after the durability test (standing at 85°C and 85% relative humidity for 10 days (240 hours)), measured immediately after the test (g). Evaluation criteria: A: The weight change rate of the laminated sheet is less than 10%. B: The weight change rate of the laminated sheet is 10% or more.

[0327] (Yellowness index change (ΔYI)) The yellowness index (YI) of the laminated sheet before and after the durability test was measured in accordance with JIS K 7373:2006 using Colour Cute i (manufactured by Suga Test Instruments Co., Ltd.), and the change in yellowness index (ΔYI value) was calculated using the following formula. ΔYI = (YI of the laminated sheet after the durability test) - (YI of the laminated sheet before the durability test)

[0328] (Water vapor permeability) The water vapor transmission rate of the laminated sheet was measured in accordance with JIS K JIS K 7129-2:2019 using a moisture permeability measuring device (PERMATRAN-W 3 / 33, manufactured by Mocon) under an atmosphere of 40°C and 90% relative humidity. However, the thickness of the laminated sheet was measured using a constant pressure thickness measuring device (PG-02, manufactured by TECLOCK CORPORATION).

[0329] [Table 1]

[0330] [Table 2]

[0331] [Table 3]

[0332] [Table 4]

[0333] [Table 5]

[0334] [Table 6]

[0335] [Table 7]

[0336] [Table 8]

[0337] [Table 9]

[0338] [Table 10]

[0339] [Table 11]

[0340] In the Examples, the haze and weight change rate of the laminated sheets after the durability test were both low, and the durability was excellent. On the other hand, in the Comparative Examples, the haze or weight change rate of the laminated sheets after the durability test was high, and the durability tended to be insufficient. [Explanation of symbols]

[0341] 2 fiber layers 6 Resin layer 8 Inorganic layer 10 sheets

Claims

1. A sheet having a fiber layer, resin layers on both sides of the fiber layer, and an inorganic layer formed on at least one side of the resin layer, the fiber layer contains fibrous cellulose having a fiber width of 1000 nm or less and a hydrophilic polymer, the hydrophilic polymer has a structural unit containing a hydroxyl group, the resin layer contains at least one selected from the group consisting of polycarbonate resin, urethane resin, acrylic resin, and fluororesin, The sheet for optical members, wherein the inorganic layer contains at least one selected from the group consisting of titanium oxide, aluminum oxide, and silicon dioxide.

2. The sheet for optical members according to claim 1 , wherein the hydrophilic polymer is polyvinyl alcohol or a cellulose derivative.

3. The sheet for optical members according to claim 1 or 2, wherein the fibrous cellulose has an ionic substituent.

4. The sheet for optical members according to claim 3 , wherein the ionic substituent is a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group.

5. The sheet for optical members according to any one of claims 1 to 4, wherein the inorganic layer has a thickness of 10 nm or more.

6. The sheet for optical members according to any one of claims 1 to 5, wherein the inorganic layer has a thickness of 500 nm or less.

7. The sheet for optical members according to any one of claims 1 to 6, wherein the resin layers each have a thickness of 10 µm or less.

8. The sheet for optical members according to any one of claims 1 to 7, wherein the resin layer is a solvent-coated layer.

9. The sheet for optical members according to any one of claims 1 to 8, wherein the exposed surface of the inorganic layer has a surface roughness of 10 nm or less.

10. The sheet for optical members according to any one of claims 1 to 9, which has a haze value of 1.0% or less.

11. The sheet for optical members according to any one of claims 1 to 10, wherein the difference in haze (Δ haze) after being placed in an environment of 85°C and a relative humidity of 85% for 240 hours is less than 1.5%.

12. Water vapor permeability of 10 g / m ２ The sheet for optical members according to any one of claims 1 to 11, wherein the optical member thickness is 1 / day or less.

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