Laminated sheet

Abstract

An object of the present invention is to provide a laminated sheet having a fiber layer comprising ultrafine cellulose fibers, which has both yellowing resistance and curling resistance.SOLUTION: The present invention relates to a laminated sheet obtained by directly laminating two or more fiber layers comprising cellulose fibers having an amount of substituents introduced of less than 0. 5mmol / g and fiber widths of 1000nm or less, wherein the fiber layers have different cellulose fiber contents in the thickness direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminated sheet. [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] Fibrous cellulose, also known as microfibrous cellulose, has a fiber diameter of 1 μm or less. Microfibrous cellulose is attracting attention as a new material with a wide range of applications. For example, development of sheets, resin composites, and thickeners containing microfibrous cellulose is underway.

[0004] For example, Patent Document 1 discloses a method for producing fine fibers, which includes the steps of (a) introducing substituents having electrostatic and / or steric functionality into a fine fiber raw material to obtain substituted fibers, (b) mechanically treating the substituted fibers, and (c) eliminating some or all of the introduced substituents from the substituted fine fibers obtained in step (b) to obtain substituted-free fine fibers. Patent Document 2 also discloses a method for producing a deesterified compound, which includes a step of heating a compound having a phosphoric acid-derived ester and / or a carboxylic acid-derived ester in the presence of a basic nitrogen-containing compound. These documents discuss eliminating the substituents introduced into the fine fibers.

[0005] Patent Document 3 discloses a method for producing a fine fiber-containing sheet, which comprises at least the steps of (a) introducing substituents having electrostatic and / or steric functionality into a fiber raw material to obtain substituted fibers, (b) mechanically treating the substituted fibers obtained in step (a) to obtain substituted fine fibers, (c) preparing a sheet from the substituted fine fibers obtained in step (b), and (d) eliminating at least a portion of the introduced substituents from the sheet obtained in step (c). Here, a method for eliminating the substituents after forming a sheet from substituted fine fibers is investigated.

[0006] Furthermore, Patent Documents 4 and 5 disclose methods for producing cellulose xanthate nanofibers, in which cellulose xanthate or a cation-substituted cellulose xanthate is defibrated. Patent Document 4 also considers a method for returning cellulose xanthate nanofibers to unmodified cellulose by regenerating the nanofibers as needed. Patent Document 5 also discloses a sheet containing cellulose fine fibers from which functional groups have been removed, the average fiber diameter of which is 3 nm or more and 300 nm or less. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2013 / 176049 [Patent Document 2] Japanese Patent Application Publication No. 2015-098526 [Patent Document 3] International Publication No. 2015 / 182438 [Patent Document 4] International Publication No. 2017 / 111103 [Patent Document 5] Japanese Patent Application Publication No. 2019-7101 Summary of the Invention [Problem to be solved by the invention]

[0008] In the course of their research into sheets containing fine fibrous cellulose, the present inventors have discovered that discoloration and curling may occur in some cases during the manufacturing and storage processes of sheets containing fine fibrous cellulose.

[0009] Therefore, in order to solve these problems of the conventional technology, the present inventors have conducted research with the aim of providing a sheet containing fine fibrous cellulose that is both resistant to yellowing and resistant to curling. [Means for solving the problem]

[0010] As a result of intensive research to solve the above problems, the inventors have found that a laminated sheet having both yellowing resistance and curl resistance can be obtained by laminating two or more fiber layers containing fibrous cellulose having an introduced substituent amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less, and varying the content of fibrous cellulose in each fiber layer. Specifically, the present invention has the following configuration.

[0011] [1] A laminated sheet obtained by directly laminating two or more fiber layers containing fibrous cellulose having an introduced amount of substituents of less than 0.5 mmol / g and a fiber width of 1000 nm or less, A laminated sheet in which each fiber layer has a different content of fibrous cellulose in the thickness direction. [2] The laminated sheet according to [1], wherein the fiber layer further contains an oxygen-containing organic compound, and the ratio of atomic % of carbon (C) to oxygen (O) in the oxygen-containing organic compound is 1.8 or more. [3] The laminate sheet according to [2], wherein the difference in atomic percentage ratio of carbon C to oxygen O on the front and back surfaces of the laminate sheet is 0.2 or less. [4] A laminated sheet obtained by directly laminating two fiber layers containing fibrous cellulose having an introduced amount of substituents of less than 0.5 mmol / g and a fiber width of 1000 nm or less, The laminated sheet according to any one of [1] to [3], wherein the fibrous cellulose is unevenly distributed on the side where the respective fiber layers are in contact with each other. [5] The laminate sheet according to any one of [1] to [4], wherein the substituent is an anionic group. [6] The laminate sheet according to [5], wherein the anionic group is a phosphorus oxo acid group or a functional group derived from a phosphorus oxo acid group. [7] The laminate sheet according to any one of [1] to [6], wherein the fibrous cellulose has a carbamide group. [8] The laminate sheet according to any one of [1] to [7], wherein the total thickness of the fiber layer is 20 μm or more. [9] The overall density of the fiber layer is 1.0 g / cm 3 The laminate sheet according to any one of [1] to [8] above.

[10] The laminate sheet according to any one of [1] to [9], wherein the number average fiber width of the fibrous cellulose contained in the fiber layer is 1 to 10 nm.

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

[10] , further comprising a resin layer on at least one side of the fiber layer.

[12] The laminate sheet according to

[11] , wherein the resin layer is directly laminated on the fiber layer.

[13] The laminate sheet according to

[11] or

[12] , wherein the resin layer contains at least one resin selected from polycarbonate resins and acrylic resins.

[14] The laminate sheet according to any one of

[11] to

[13] , wherein the resin layer further contains an adhesion aid.

[15] The laminate sheet according to

[14] , wherein the adhesion aid is at least one selected from an isocyanate compound and an organosilicon compound.

[16] The laminate sheet according to

[14] or

[15] , wherein the adhesion aid is an isocyanate compound, and the content of the isocyanate compound is 10 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the resin contained in the resin layer.

[17] The laminate sheet according to any one of [1] to

[16] , which has a YI value of 2.5 or less.

[18] The laminate sheet according to any one of [1] to

[17] , which has a haze of 80% or less.

[19] The laminate sheet according to any one of [1] to

[18] , which is for use as an optical member.

[20] A laminate comprising the laminate sheet according to any one of [1] to

[19] and an adherend. [Effects of the Invention]

[0012] According to the present invention, a laminate sheet having both yellowing resistance and curl resistance can be obtained. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view illustrating the configuration of the laminate sheet of the present invention. [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. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below. The following description of the constituent elements may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0015] (Laminated sheet) The present invention relates to a laminated sheet formed by directly laminating two or more fiber layers containing fibrous cellulose having an introduced substituent group amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less, wherein the fibrous cellulose content of each fiber layer in the thickness direction of the laminated sheet is different from that of the other fiber layers.

[0016] Fig. 1 is a cross-sectional view illustrating the configuration of a laminate sheet of the present invention. As shown in Fig. 1, the laminate sheet of the present invention has two or more fiber layers. Fig. 1 illustrates a laminate sheet 100 having two fiber layers, in which case the laminate sheet 100 has fiber layer 10 (first fiber layer) and fiber layer 20 (second fiber layer). The fiber layers are directly laminated to each other.

[0017] In the present invention, each fiber layer of the laminated sheet has a different content of fibrous cellulose in the thickness direction. This means that the content of fibrous cellulose in each fiber layer varies in the thickness direction of each fiber layer. Each fiber layer may have a concentration gradient of fibrous cellulose in the thickness direction of each fiber layer. Furthermore, when each fiber layer is divided into three equal parts in the thickness direction, the content of fibrous cellulose contained in each of the three regions may be different.

[0018] The fibrous cellulose content of each fiber layer can be determined by, for example, measuring the fibrous cellulose content on the front and back surfaces of each fiber layer, and if the fibrous cellulose contents on the front and back surfaces are different, it can be determined that the fibrous cellulose content of each fiber layer varies in the thickness direction. The fibrous cellulose content on the front and back surfaces of each fiber layer can be evaluated by, for example, calculating the atomic % ratio of carbon (C) to oxygen (O), as described below.

[0019] In the past, attempts have been made to increase the amount of substituents introduced into fine fibrous cellulose to obtain highly transparent sheets, thereby obtaining fine fibrous cellulose with a narrow fiber width. However, when fine fibrous cellulose with a high amount of substituents is incorporated into a sheet, the sheet tends to discolor when heated during the sheet production process or in the usage environment. To solve this problem, it is conceivable to control the amount of substituents introduced into the fine fibrous cellulose by controlling the substituent introduction process. However, the present inventors have found that when the amount of substituents introduced into the fine fibrous cellulose is low, such as less than 0.5 mmol / g, the sheet curls excessively during the sheet production process, making it impossible to obtain a flat sheet. Therefore, the present inventors have conducted extensive research to produce a sheet with reduced curling, even when the amount of substituents introduced into the fine fibrous cellulose is low. As a result, the present inventors have found that by laminating two or more fiber layers containing fibrous cellulose having an introduced substituent content of less than 0.5 mmol / g and a fiber width of 1000 nm or less, and further varying the content of fibrous cellulose in each fiber layer in the thickness direction, it is possible to suppress the occurrence of curling while suppressing the occurrence of coloring in the sheet. Thus, the present invention has succeeded in suppressing the occurrence of coloring and curling in a sheet containing fine fibrous cellulose with a low substituent content.

[0020] In this embodiment, the YI value of the laminate sheet is preferably 2.5 or less, more preferably 2.0 or less. The lower limit of the YI value of the laminate sheet is not particularly limited, but is preferably 0.1 or more. The YI value of the laminate sheet is measured in accordance with JIS K 7373:2006. An example of a device that can be used to measure the YI value is Colour Cute i (manufactured by Suga Test Instruments Co., Ltd.). The above-mentioned YI value is measured before the laminate sheet is heated, as described below, and is therefore sometimes referred to as the initial YI value.

[0021] In this embodiment, the YI value of the laminate sheet after heating at 160°C for 6 hours is preferably 22 or less, more preferably 20 or less, and even more preferably 16 or less. The lower limit of the YI value of the laminate sheet after heating at 160°C for 6 hours is not particularly limited, but is preferably 0.1 or more. The YI value after heating at 160°C for 6 hours is sometimes referred to as the post-heating YI value.

[0022] The YI increase rate of the laminate sheet of this embodiment is preferably 1400% or less, more preferably 1300% or less, even more preferably 1200% or less, even more preferably 1100% or less, and particularly preferably 1000% or less. The lower limit of the YI increase rate of the laminate sheet is not particularly limited, but is preferably 0.1% or more. Here, the YI increase rate of the laminate sheet refers to the increase rate of the YI value of the laminate sheet before and after heating the laminate sheet at 160°C for 6 hours. Specifically, the YI increase rate is a value calculated using the following formula: YI increase rate (%) = (YI value of laminated sheet after heating - YI value of laminated sheet before heating) / YI value of laminated sheet before heating × 100 In the above formula, the YI value of the laminate sheet is a YI value measured in accordance with JIS K 7373:2006.

[0023] The curl resistance of the laminate sheet of this embodiment can be evaluated by measuring the height (curl amount) (mm) of the four corners of the sheet after a predetermined time has elapsed. Specifically, the laminate sheet is cut into 100 mm squares and left on a flat surface in an environment of 23°C and 50% relative humidity for at least 4 hours. After leaving it, the heights (mm) of the four corners of the sheet are measured, and the average value is taken as the measured curl (curl amount). The measured curl (curl amount) is preferably 30 mm or less, more preferably 20 mm or less, even more preferably 10 mm or less, and particularly preferably 8 mm or less. If the measured curl (curl amount) is within the above range, the laminate sheet can be evaluated as having excellent curl resistance.

[0024] The total light transmittance of the laminate sheet is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and particularly preferably 80% or more. When even greater transparency is required for optical components, the total light transmittance of the laminate sheet is preferably 85% or more, more preferably 90% or more. By setting the total light transmittance of the laminate sheet within the above range, the laminate sheet of the present invention can be applied to applications where transparent glass has traditionally been used. Here, the total light transmittance is a value measured in accordance with JIS K 7361-1:1997 using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.).

[0025] The haze of the laminate sheet is preferably 80% or less, more preferably 70% or less, and even more preferably 60% or less. When higher transparency is required for use as an optical component, the haze of the laminate sheet is preferably 10% or less, more preferably 5% or less, and even more preferably 2% or less. The lower limit of the haze of the laminate sheet is not particularly limited, and may be 0%. The haze here is a value measured in accordance with JIS K 7136:2000 using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.).

[0026] The total thickness of the laminate sheet is not particularly limited, but is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 15 μm or more, and particularly preferably 20 μm or more. The total thickness of the laminate sheet is preferably 1000 μm or less. The thickness of the laminate sheet can be adjusted appropriately depending on the application.

[0027] The thickness of each fiber layer constituting the laminate sheet is preferably 2.5 μm or more, more preferably 5 μm or more, even more preferably 7.5 μm or more, and particularly preferably 10 μm or more. The thickness of each fiber layer is preferably 500 μm or less. Here, the thickness of the fiber layer constituting the laminate sheet is a value measured by cutting out a cross section of the laminate sheet using an ultramicrotome UC-7 (manufactured by JEOL) and observing the cross section with an electron microscope, a magnifying glass, or visually.

[0028] The overall density of the fiber layers that make up the laminated 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 1.4 g / cm or more. 3 It is more preferable that the total density of the fiber layers constituting the laminated sheet is 1.7 g / cm or more. 3 Preferably, it is 1.65 g / cm or less. 3 More preferably, it is 1.6 g / cm or less. 3 It is even more preferable that:

[0029] The density of the fiber layer is calculated from the basis weight and thickness of the fiber layer in accordance with JIS P 8118:2014. The basis weight of the fiber layer can be calculated in accordance with JIS P 8124:2011. When the fiber layer contains any component other than fine fibrous cellulose, the density of the fiber layer is the density including the optional component other than fine fibrous cellulose.

[0030] 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 / cm3 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, it means that the porosity of the fibrous layer is kept below a specified value, and the fibrous layer is distinguished from a porous sheet or layer. A fibrous layer is also characterized as being non-porous by a porosity of 15% by volume or less. The porosity of the fibrous layer referred to here is simply calculated using 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 cellulose.

[0031] In this embodiment, the surface roughness of at least one surface of the fiber layer is preferably 50 nm or less, more preferably 30 nm or less, and even more preferably 10 nm or less. It is particularly preferable that the surface roughness of both surfaces of the fiber layer is within the above range. By setting the surface roughness within the above range, the transparency of the laminate sheet can be improved. Specifically, the haze of the laminate sheet can be reduced. Here, the surface roughness (arithmetic mean) of the fiber layer is the arithmetic mean roughness of at least one surface of the fiber layer. The surface roughness (arithmetic mean) is a value obtained by measuring the arithmetic mean roughness of a 3 μm square area using an atomic force microscope (NanoScope IIIa, manufactured by Veeco).

[0032] In this embodiment, the surface pH of the fiber layer is preferably 3 or higher, more preferably 4 or higher, and even more preferably 5 or higher. The surface pH of the fiber layer is preferably 10 or lower, more preferably 9 or lower, and even more preferably 8 or lower. By controlling the surface pH of the fiber layer within the above range, the effect of inhibiting yellowing can be more easily achieved. In order to control the surface pH of the fiber layer within the above range, it is preferable to appropriately adjust the pH of the fine fibrous cellulose dispersion obtained in the production process described below. The surface pH of the fiber layer is measured by dropping 10 μL of ion-exchanged water onto a 1 cm square area of ​​the surface of the fiber layer using a micropipette, and measuring the pH of that area using a flat pH composite electrode (6261-10C; manufactured by HORIBA).

[0033] The number of fiber layers constituting the laminate sheet may be two or more, preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. Of these, it is particularly preferable that the number of fiber layers constituting the laminate sheet be two. When the laminate sheet has two fiber layers, it is preferable that the fibrous cellulose be unevenly distributed on the side where the fiber layers contact each other. That is, in a laminate sheet formed by directly laminating two fiber layers containing fibrous cellulose having an introduced group amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less, it is preferable that a large amount of fibrous cellulose be present in the region near the interface between the fiber layers.

[0034] When the laminated sheet is composed of an even number of fiber layers, the fibrous cellulose is preferably present symmetrically with respect to the central plane of all fiber layers, i.e., the content of fibrous cellulose preferably varies symmetrically from the central plane to each surface of all fiber layers.

[0035] In the laminate sheet of the present embodiment, the fiber layer preferably further contains an oxygen-containing organic compound. The oxygen-containing organic compound is preferably non-fibrous, and such non-fibrous oxygen-containing organic compounds do not include fine fibrous cellulose or thermoplastic resin fibers.

[0036] The oxygen-containing organic compound is preferably a hydrophilic organic compound. The hydrophilic oxygen-containing organic compound can improve the strength, density, chemical resistance, etc. of the fiber layer. The hydrophilic oxygen-containing organic compound preferably has an SP value of 9.0 or more. Furthermore, the hydrophilic oxygen-containing organic compound is preferably one in which 1 g or more of the oxygen-containing organic compound dissolves in 100 ml of ion-exchanged water.

[0037] Examples of oxygen-containing organic compounds include hydrophilic polymers such as polyethylene glycol, polyalkylene oxides (polyethylene oxide, polypropylene oxide, etc.), casein, dextrin, starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol (acetoacetylated polyvinyl alcohol, etc.), polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylates, polyacrylamide, acrylic acid alkyl ester copolymers, urethane copolymers, and cellulose derivatives (hydroxyethyl cellulose, carboxyethyl cellulose, carboxymethyl cellulose, etc.); and hydrophilic low-molecular-weight compounds such as glycerin, sorbitol, and ethylene glycol. Among these, oxygen-containing organic compounds having an atomic % ratio of carbon (C) to oxygen (O) of 1.8 or more are preferred. Specifically, oxygen-containing organic compounds such as polyvinyl alcohol, modified polyvinyl alcohol, polyalkylene oxides (polyethylene oxide, polypropylene oxide, etc.), and polyacrylamide are preferred. The atomic % ratio of carbon (C) to oxygen (O) in oxygen-containing organic compounds is a theoretical value calculated from the number of carbon atoms and oxygen atoms. Thus, each fiber layer in the laminated sheet of the present invention preferably contains fibrous cellulose having an introduced substituent amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less, and an oxygen-containing organic compound having an atomic % ratio of carbon (C) to oxygen (O) of 1.8 or more.

[0038] The oxygen-containing organic compound is preferably an organic polymer having a molecular weight of 50,000 to 8,000,000. The molecular weight of the oxygen-containing organic compound is also preferably 100,000 to 5,000,000, but may also be a low molecular weight compound having a molecular weight of less than 1,000, for example.

[0039] The content of the oxygen-containing organic compound in each fiber layer is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the fibrous cellulose in each fiber layer. The content of the oxygen-containing organic compound in each fiber layer is preferably 1,000 parts by mass or less, more preferably 500 parts by mass or less, and even more preferably 200 parts by mass or less, per 100 parts by mass of the fine fibrous cellulose in each fiber layer.

[0040] In the laminate sheet of this embodiment, the difference in atomic % ratio between carbon (C) and oxygen (O) on the front and back surfaces is preferably 0.2 or less, and more preferably 0.1 or less. In particular, it is particularly preferable that the difference in atomic % ratio between carbon (C) and oxygen (O) on the front and back surfaces is 0. By setting the difference in atomic % ratio between carbon (C) and oxygen (O) on the front and back surfaces of the laminate sheet within the above range, the curl resistance of the laminate sheet can be more effectively improved.

[0041] In addition to the fibrous cellulose and the oxygen-containing organic compound, each fiber layer may contain other optional components, such as antifoaming agents, lubricants, UV absorbers, dyes, pigments, stabilizers, surfactants, and preservatives (e.g., phenoxyethanol).

[0042] Each fiber layer may also contain an organic ion as an optional component. Examples of the organic ion include tetraalkylammonium ions and tetraalkylphosphonium ions. Examples of the 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 the tetraalkylphosphonium ions include tetramethylphosphonium ions, tetraethylphosphonium ions, tetrapropylphosphonium ions, tetrabutylphosphonium ions, and lauryltrimethylphosphonium ions. Examples of the tetrapropylonium ions and tetrabutylonium ions include tetra-n-propylonium ions and tetra-n-butylonium ions, respectively.

[0043] <Fine fibrous cellulose> Each fiber layer constituting the laminate sheet contains fibrous cellulose having an introduced substituent content of less than 0.5 mmol / g and a fiber width of 1000 nm or less. In this specification, fibrous cellulose having a fiber width of 1000 nm or less is also referred to as fine fibrous cellulose or CNF.

[0044] The amount of substituent introduced into the fine fibrous cellulose may be less than 0.5 mmol / g, preferably 0.4 mmol / g or less, more preferably 0.3 mmol / g or less, even more preferably 0.25 mmol / g or less, and particularly preferably 0.15 mmol / g or less. The amount of substituent introduced into the fine fibrous cellulose may be 0.0 mmol / g, but is preferably 0.03 mmol / g or more, more preferably 0.04 mmol / g or more, even more preferably 0.05 mmol / g or more, and particularly preferably 0.07 mmol / g or more.

[0045] The fibrous cellulose is a fine fibrous cellulose having a fiber width of 1000 nm or less. The fiber width of the fibrous cellulose is more preferably 100 nm or less, and even more preferably 8 nm or less. The fiber width of the fibrous cellulose is preferably 1 nm or more.

[0046] The number-average fiber width of the fibrous cellulose contained in each fiber layer is preferably 1 to 50 nm, more preferably 1 to 30 nm, even more preferably 1 to 10 nm, even more preferably 1 to 9 nm, even more preferably 1 to 8 nm, and particularly preferably 1 to 7 nm. Here, the fiber width of the fibrous cellulose is measured, for example, using electron microscopy as follows: First, the fibrous cellulose is dispersed in water to a cellulose concentration of 0.01% by mass or more and 0.1% by mass or less, and cast onto a hydrophilically treated carbon film-coated grid. After drying, the grid is stained with uranyl acetate and observed using a transmission electron microscope (TEM, manufactured by JEOL Ltd., JEOL-2000EX). In this case, an arbitrary vertical or horizontal axis of the image width is assumed within the obtained image, and the magnification is adjusted so that 20 or more fibers intersect with the axis. After obtaining an observation image that satisfies these conditions, two random axes are drawn vertically and horizontally per image, and the fiber widths of the fibers intersecting the axes are visually determined. In this way, three non-overlapping observation images are taken, and the fiber width values ​​of the fibers intersecting the two axes are read for each image (20 or more x 2 x 3 = 120 or more). (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 the fine fibrous cellulose contained in the fiber layer, the number average fiber width can be calculated from the fiber width obtained by the above method.

[0047] The number-average fiber width of the fibrous cellulose contained in each fiber layer of 1 to 10 nm means that the fiber layer does not substantially contain coarse cellulose fibers, and that 70% or more of the fibrous cellulose has a fiber width of 10 nm or less. Of the total fibrous cellulose contained in the fiber layer, the proportion of fine fibrous cellulose having a fiber width of 10 nm or less is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. Here, the proportion of fine fibrous cellulose having a fiber width of 10 nm or less is a value expressed by the following formula. Percentage of fine fibrous cellulose with a fiber width of 10 nm or less (%) = (Number of fine fibrous cellulose with a fiber width of 10 nm or less / Total number of fibrous cellulose) × 100

[0048] The fiber length of the fine 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 fine fibrous cellulose can be suppressed. It also becomes possible to set the slurry viscosity of the fine fibrous cellulose within an appropriate range. The fiber length of the fine fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

[0049] The fine fibrous cellulose preferably has a type I crystal structure. The presence of type I crystal structure in fine 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 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. 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).

[0050] The axial ratio (fiber length / fiber width) of the fine fibrous cellulose is not particularly limited, but is preferably, for example, from 50 to 10,000, and more preferably from 100 to 1,000. By setting the axial ratio to the above lower limit or more, a sheet containing the 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 the fibrous cellulose is used as a dispersion, handling such as dilution becomes easier.

[0051] The fine fibrous cellulose in this embodiment has, for example, both crystalline regions and amorphous regions. Fine fibrous cellulose having both crystalline regions and amorphous regions and having an axial ratio within the above range is realized by the method for producing fine fibrous cellulose described below.

[0052] The cellulose components in the fine fibrous cellulose can be classified into α-cellulose components and hemicellulose components. A lower hemicellulose ratio is preferable because it is easier to obtain the effect of inhibiting yellowing over time and yellowing due to heat. The hemicellulose ratio of the fine fibrous cellulose of the present invention is preferably less than 30%, more preferably less than 25%, and even more preferably less than 20%.

[0053] The total amount of nitrogen contained in the fine fibrous cellulose and the free nitrogen contained in the fine fibrous cellulose dispersion (hereinafter sometimes referred to as the "nitrogen amount," "nitrogen amount contained in the fine fibrous cellulose," or "nitrogen amount in the fine fibrous cellulose") is preferably 0.08 mmol / g or less, more preferably 0.04 mmol / g or less, and even more preferably 0.02 mmol / g or less. The amount of nitrogen contained in the fine fibrous cellulose is preferably 0.001 mmol / g or more. The nitrogen amount in the fine fibrous cellulose is a value measured by the following method. First, a dispersion containing fine fibrous cellulose is adjusted to a solids concentration of 1% by mass and decomposed by the Kjeldahl method (JIS K 0102 2016 44.1). After decomposition, the amount of ammonium ions (mmol) is measured by cation chromatography and divided by the amount of cellulose (g) used in the measurement to calculate the nitrogen content (mmol / g). The above-mentioned amount of nitrogen is the total amount of nitrogen bound to the fine fibrous cellulose by ionic and / or covalent bonds and free nitrogen dissolved in the dispersion that is not bound to the fine fibrous cellulose by ionic and / or covalent bonds.

[0054] In this embodiment, the amount of substituents introduced into the fine fibrous cellulose is less than 0.5 mmol / g, and the substituents referred to here are preferably anionic groups. That is, the fine fibrous cellulose of the present invention is obtained by subjecting fine fibrous cellulose having anionic groups to a substituent removal treatment, and the fine fibrous cellulose of the present invention is substituent-removed fine fibrous cellulose.

[0055] Examples of anionic groups include phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups (sometimes simply referred to as phosphorus oxoacid groups), carboxy groups or substituents derived from carboxy groups (sometimes simply referred to as carboxy groups), sulfone groups or substituents derived from sulfone groups (sometimes simply referred to as sulfone groups), and xanthate groups or substituents derived from xanthate groups (sometimes simply referred to as xanthate groups). When a sulfone group or a substituent derived from a sulfone group is introduced via an ester bond, the substituent may also be referred to as a sulfur oxoacid group or a substituent derived from a sulfur oxoacid group (sometimes simply referred to as a sulfur oxoacid group). Among these, the anionic group is preferably at least one selected from phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups and sulfone groups or substituents derived from sulfone groups, and more preferably a phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group.

[0056] The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group is, for example, a substituent represented by the following formula (1). A plurality of substituents represented by the following formula (1) may be introduced into each fine fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (1) may be the same or different.

[0057] [ka]

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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 such functional group, may be 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, facilitating penetration into the fiber raw material and increasing the yield of fine cellulose fibers. When multiple Rs are present in formula (1) or when multiple types of substituents represented by formula (1) are introduced into the fine fibrous cellulose, the multiple Rs may be the same or different.

[0062] βb+ is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic onium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. It should be noted that in formula (1), β b+ When a plurality of β b+ may be the same or different. The monovalent or higher cations consisting of organic or inorganic substances include β b+ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0063] 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).

[0064] Furthermore, the sulfone group (sulfone group or a substituent derived from a sulfone group) is preferably a sulfur oxoacid group (sulfone oxoacid group or a substituent derived from a sulfur oxoacid group), and is preferably, for example, a substituent represented by the following formula (2). A plurality of substituents represented by the following formula (2) may be introduced into each fine fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (2) may be the same or different.

[0065] [ka]

[0066] 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 made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic onium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. Note that when multiple types of substituents represented by the above formula (2) are introduced into the fine fibrous cellulose, the multiple β b+ may be the same or different. The monovalent or higher cations consisting of organic or inorganic substances include β b+ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0067] The amount of anionic groups introduced into the fine 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 fine fibrous cellulose.

[0068] 2 is a graph showing the relationship between the amount of NaOH added dropwise to a slurry containing fine fibrous cellulose having phosphorus oxo acid groups and pH. The amount of phosphorus oxo acid groups introduced into the fine fibrous cellulose is measured, for example, as follows. First, a slurry containing fine 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 of the fine fibrous cellulose contained in the slurry used for titration; the amount of alkali required from the first endpoint to the second endpoint is equal to the amount of second dissociated acid of the fine fibrous cellulose contained in the slurry used for titration; and the amount of alkali required from the start of titration to the second endpoint is equal to the total amount of dissociated acid of the fine fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali required from the start of titration to the first endpoint by the solids content (g) in the slurry to be titrated is the amount of phosphorus oxo acid group introduced (mmol / g). Note that the term "amount of phosphorus oxo acid group introduced" (or "amount of phosphorus oxo acid group") 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 weakly acidic groups in the phosphorus oxoacid group (also referred to herein as the second dissociated acid amount) decreases, and the amount of alkali required in Region 2 becomes smaller than the amount required in Region 1. On the other hand, the amount of strongly acidic groups in the phosphorus oxoacid group (also referred to herein as the first dissociated acid amount) corresponds to the amount of phosphorus atoms regardless of whether condensation occurs. Furthermore, if the phosphorus oxoacid group is a phosphite group, the phosphorus oxoacid group no longer contains weakly acidic groups, and the amount of alkali required in Region 2 becomes smaller or may even become zero. In this case, there is only one point on the titration curve where the pH increment becomes maximum.

[0069] The above-mentioned amount of introduced phosphorus oxoacid groups (mmol / g) indicates the amount of phosphorus oxoacid groups in the acid-form fine fibrous cellulose (hereinafter referred to as the amount of phosphorus oxoacid groups (acid form)), since the denominator indicates the mass of the acid-form fine fibrous cellulose. On the other hand, when the counter ions of the phosphorus oxoacid groups are substituted with any cation C so as to be charge equivalent, the amount of phosphorus oxoacid groups in the fine fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of phosphorus oxoacid groups (C form)) can be determined by converting the denominator to the mass of the fine fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula. Amount of phosphorus oxoacid 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 fine 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)

[0070] When measuring the amount of anionic groups by titration, adding too much sodium hydroxide solution or titrating too quickly can result in a lower anionic group content than expected, making it difficult to obtain accurate values. For example, an appropriate amount and titration interval is desirable, such as titrating 10 to 50 μL of 0.1 N sodium hydroxide solution every 5 to 30 seconds. To eliminate the influence of carbon dioxide dissolved in the fine fibrous cellulose-containing slurry, it is also desirable to measure the amount of anionic groups by blowing an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration until the end of titration.

[0071] The amount of sulfonic groups introduced into fine fibrous cellulose can be calculated by freeze-drying a slurry containing fine fibrous cellulose and then measuring the sulfur content of the pulverized sample. Specifically, the slurry containing fine fibrous cellulose is freeze-dried and the pulverized sample is subjected to pressure-heat decomposition using nitric acid in a sealed container, then appropriately diluted and the sulfur content is measured by ICP-OES. The value calculated by dividing by the bone dry mass of the fine fibrous cellulose tested is taken as the amount of sulfonic groups (unit: mmol / g) of the fine fibrous cellulose.

[0072] The amount of xanthate groups introduced into microfibrous 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 microfibrous 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, along with 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 fine fibrous cellulose. 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)

[0073] In this embodiment, the fine fibrous cellulose preferably has a carbamide group. In this specification, the carbamide group is preferably a group represented by the following structural formula:

[0074] [ka]

[0075] In the above structural formula, 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 aromatic group, or a group derived from any of these. Among these, it is particularly preferable that R is a hydrogen atom.

[0076] The amount of carbamide groups introduced into the fine fibrous cellulose is preferably 0.001 mmol / g or more. Furthermore, the amount of carbamide groups introduced into the fine fibrous cellulose is preferably 0.08 mmol / g or less, more preferably 0.04 mmol / g or less, and even more preferably 0.02 mmol / g or less. Here, the amount of carbamide groups introduced into the fine fibrous cellulose can be calculated by freeze-drying a slurry containing the fine fibrous cellulose and then pulverizing the resulting sample, and then subjecting the resulting sample to trace nitrogen analysis. The amount of carbamide groups introduced per unit mass of the fine fibrous cellulose (mmol / g) can be calculated by dividing the nitrogen content (g / g) per unit mass of the fine fibrous cellulose obtained by trace nitrogen analysis by the atomic weight of nitrogen.

[0077] In this embodiment, when the fine fibrous cellulose used to form the fibrous layer is dispersed in water at a concentration of 0.1% by mass and the nanofiber yield is calculated using the following formula, the nanofiber yield is preferably 95% by mass or more, more preferably 96% by mass or more. The nanofiber yield may also be 100% by mass. Nanofiber yield [mass%] = C / 0.1 × 100 Here, C is the concentration of fine fibrous cellulose contained in the supernatant obtained when an aqueous dispersion containing 0.1% by mass of fine fibrous cellulose is centrifuged at 12,000 G for 10 minutes.

[0078] Also, in the present embodiment, when the microfibrillar cellulose used for forming the fiber layer is a water dispersion with a concentration of 0.2% by mass, the haze of the water dispersion is preferably 5.0% or less, more preferably 4.0% or less, and even more preferably 3.0% or less. Note that the haze of the water dispersion may be 0%. If the haze of the water dispersion with a concentration of 0.2% by mass is within the above range, it can be determined that the dispersion is transparent. Here, the haze of the water dispersion is a value measured in accordance with JIS K 7136:2000 using a haze meter and a glass cell for liquids with an optical path length of 1 cm. The zero-point measurement is performed using ion-exchanged water placed in the same glass cell. Further, the dispersion to be measured is allowed to stand for 24 hours in an environment of 23°C and a relative humidity of 50% before measurement, and the liquid temperature of the dispersion is set to 23°C.

[0079] In the present embodiment, when the microfibrillar cellulose used for forming the fiber layer is a dispersion (water dispersion) with a concentration of 1% by mass, the pH of the dispersion is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more. Also, the pH of the dispersion is preferably 10 or less, more preferably 9 or less, and even more preferably 8 or less. By setting the pH of the dispersion within the above range, yellowing of the dispersion and the sheet can be more effectively suppressed. Note that, in order to set the pH of the dispersion within the above range, the same method as the <pH adjustment step> described later can also be employed.

[0080] In this embodiment, when the fine fibrous cellulose used to form the fiber layer is a dispersion (aqueous dispersion) with a concentration of 0.4% by mass, the viscosity of the dispersion at 23°C is preferably 100 mPa·s or more, more preferably 1000 mPa·s or more, and even more preferably 2000 mPa·s or more. Furthermore, the viscosity of the dispersion at 23°C is preferably 200,000 mPa·s or less, and more preferably 100,000 mPa·s or less. The viscosity of a dispersion with a fine fibrous cellulose concentration of 0.4% by mass can be measured using a Brookfield T-LVT type viscometer. The measurement conditions are 23°C, a rotation speed of 3 rpm, and the viscosity is measured 3 minutes after the start of measurement. Furthermore, the dispersion to be measured is allowed to stand for 24 hours in an environment of 23°C and 50% relative humidity, and the liquid temperature of the dispersion is brought to 23°C.

[0081] The amount of free nitrogen in the dispersion containing fine fibrous cellulose used to form the fibrous layer is preferably small. The amount of free nitrogen in the dispersion can be measured by measuring the nitrogen concentration in the filtrate obtained by filtering the fine fibrous cellulose dispersion. For example, the free nitrogen concentration in a dispersion containing 0.2% by mass of fine fibrous cellulose is preferably 100 ppm or less, more preferably 80 ppm or less, even more preferably 70 ppm or less, even more preferably 60 ppm or less, even more preferably 50 ppm or less, even more preferably 40 ppm or less, and particularly preferably 30 ppm or less. The nitrogen concentration in a dispersion containing 0.2% by mass of fine fibrous cellulose may be 0 ppm. Since free nitrogen present in the dispersion can cause coloration, yellowing of the dispersion and sheet containing fine fibrous cellulose can be more effectively suppressed by keeping the nitrogen concentration in the filtrate within the above range. The nitrogen concentration in the filtrate is measured as follows. First, distilled water is added so that the concentration of fine fibrous cellulose becomes 0.2% by mass, and after stirring for 24 hours, the mixture is filtered using a filter medium with a pore size of 0.45 μm to obtain a filtrate. The nitrogen concentration (ppm) in the filtrate is then measured by trace nitrogen analysis.

[0082] (Method of producing fine fibrous cellulose) The above-mentioned fine fibrous cellulose is preferably obtained by subjecting fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less to step (A) of removing at least a portion of the substituent. Here, the substituent possessed by the fine fibrous cellulose subjected to step (A) is preferably an anionic group, more preferably a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group. Furthermore, the fine fibrous cellulose subjected to step (A) preferably has a carbamide group.

[0083] (Process (A)) Step (A) is 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. First, a method for producing fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less (fine fibrous cellulose subjected to step (A)) will be described below.

[0084] <Fiber raw materials> The fine fibrous cellulose used in step (A) is produced from a cellulose-containing fiber raw material. The cellulose-containing fiber raw material is not particularly limited, but pulp is preferably used because of 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-groundwood pulp (CGP); and mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Non-wood pulps include, but are not limited to, cotton-based pulps such as cotton linters and cotton lint, and non-wood pulps such as hemp, straw, and bagasse. Deinked pulps include, but are not limited to, deinked pulp made from recycled paper. The pulp of this embodiment may be used alone or in combination with two or more of the above. Among the above pulps, wood pulp and deinked pulp are preferred from the viewpoint of ease of availability. Furthermore, among wood pulps, chemical pulps are more preferred, and kraft pulp and sulfite pulp are even more preferred, from the viewpoints of a high cellulose content, a high yield of fine fibrous cellulose during defibration treatment, and the fact that cellulose in the pulp is less decomposed and long-fiber fine fibrous cellulose with a large axial ratio can be obtained. Note that the use of long-fiber fine fibrous cellulose with a large axial ratio tends to increase viscosity.

[0085] 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.

[0086] <Phosphorus oxoacid group introduction step> The fine fibrous cellulose subjected to step (A) has a substituent. Therefore, the process for producing the fine fibrous cellulose subjected to step (A) preferably includes a substituent introduction step, and more preferably an anionic group introduction step. An example of the anionic group introduction step is a phosphorus oxo acid group introduction step. The phosphorus oxo acid group introduction step is a step in which at least one compound selected from compounds capable of introducing a phosphorus oxo acid group by reacting with a hydroxyl group possessed by a cellulose-containing fiber raw material (hereinafter also referred to as "compound A") is allowed to act on 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.

[0087] In the phosphorus oxoacid group introduction step according to this embodiment, the reaction of the cellulose-containing fiber raw material with compound A is preferably carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B").

[0088] An example of a method for reacting compound A with a fiber raw material in the presence of compound B is a method in which compound A and compound B are mixed with a fiber raw material in a dry, wet, or slurry state. Among these, using a fiber raw material in a dry or wet state is preferred because of the high uniformity of the reaction, and using a fiber raw material in a dry state is particularly preferred. The form of the fiber raw material is not particularly limited, but is preferably in the form of a cotton or thin sheet. 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 obtained by heating to or above their melting point. Among these, 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 the form of a solution, the fiber raw material may be immersed in the solution to absorb the liquid and then 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.

[0089] The compound A used in this embodiment may be any compound that has a phosphorus atom and is capable of forming an ester bond with cellulose, and examples thereof include, but are 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 acid can be used with various purities, such as 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid. Phosphorous acid can be 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acid is formed by condensing two or more molecules of phosphoric acid through a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, which can be neutralized to various degrees. Among these, from the viewpoints of high efficiency of introduction of phosphate groups, ease of further improving defibration efficiency in the defibration step described below, low cost, and ease of industrial application, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid, or phosphorous acid, sodium salt of phosphorous acid, potassium salt of phosphorous acid, ammonium salt of phosphorous acid are preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid, sodium phosphite are more preferred.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] In the reaction of a fiber raw 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 in particular is known to act as a good reaction catalyst.

[0094] In the phosphorus oxo acid group introduction step, it is preferable to add or mix compound A and compound B 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 hot air dryer, agitator dryer, rotary dryer, disk dryer, roll-type heater, plate-type heater, fluidized-bed dryer, band-type dryer, filtration dryer, vibration fluidized dryer, flash dryer, reduced-pressure dryer, infrared heater, far-infrared heater, microwave heater, and high-frequency dryer.

[0095] 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).

[0096] 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.

[0097] 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.

[0098] 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.

[0099] The amount of phosphorus oxo acid groups introduced in the phosphorus oxo acid group introduction step is preferably 0.60 mmol / g or more, more preferably 0.70 mmol / g or more, even more preferably 0.80 mmol / g or more, even more preferably 1.00 mmol / g or more, and particularly preferably 1.20 mmol / g or more per gram (mass) of fiber raw material. The amount of phosphorus oxo acid groups introduced is, for example, preferably 5.20 mmol / g or less, more preferably 3.65 mmol / g or less, and even more preferably 3.00 mmol / g or less per gram (mass) of fiber raw material. The fact that the amount of phosphorus oxo acid groups introduced in the phosphorus oxo acid group introduction step is within the above range means that the amount of substituents introduced into the fine fibrous cellulose used in step (A) is within the above range. By ensuring that the amount of phosphorus oxo acid groups introduced is within the above range, the amount of substituents introduced into the fine fibrous cellulose used in step (A) can be kept within the above range, which makes it easier to produce fine fibrous cellulose with a final fiber width of 10 nm or less. Furthermore, the transparency of the dispersion and sheet containing the fine fibrous cellulose of the present invention can be more effectively improved.

[0100] <Sulfonic acid group (sulfur oxoacid group) introduction step> The process for producing fine fibrous cellulose subjected to step (A) may include a sulfonic acid group introduction step as an anionic group introduction step, in which hydroxyl groups in a cellulose-containing fiber raw material react with sulfonic acid to obtain cellulose fibers having sulfonic acid groups (sulfonic acid-introduced fibers).

[0101] In the sulfonic acid group introduction step, instead of compound A in the above-described <Phosphorus Oxo Acid Group Introduction Step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfonic acid groups by reacting with hydroxyl groups in a cellulose-containing fiber raw material is used. Compound C may be any compound 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 sulfonic acid group introduction step, it is preferable to use compound B in the above-described <Phosphorus Oxo Acid Group Introduction Step> in the same manner.

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

[0103] In the heat treatment step, 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 sulfonic acid 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.

[0104] The amount of sulfonic groups introduced in the sulfonic group introduction step is preferably 0.60 mmol / g or more, more preferably 0.70 mmol / g or more, even more preferably 0.80 mmol / g or more, even more preferably 1.00 mmol / g or more, and particularly preferably 1.20 mmol / g or more per gram (mass) of fiber raw material. The amount of sulfonic groups introduced is preferably 5.00 mmol / g or less, more preferably 3.00 mmol / g or less, per gram (mass) of fiber raw material. The fact that the amount of sulfonic groups introduced in the sulfonic group introduction step is within the above range means that the amount of substituents introduced into the fine fibrous cellulose used in step (A) is within the above range. By setting the amount of sulfonic groups introduced within the above range, the amount of substituents introduced into the fine fibrous cellulose used in step (A) can be set within the above range, which makes it easier to produce fine fibrous cellulose having a fiber width of 10 nm or less. Furthermore, the transparency of the dispersion or sheet containing the fine fibrous cellulose of the present invention can be more effectively improved.

[0105] <Xanthate group introduction step> The process for producing fine fibrous cellulose subjected to step (A) may include a xanthate group introduction step as an anionic group introduction step. The xanthate group introduction step substitutes hydroxyl groups in a fiber raw material containing cellulose with xanthate groups represented by the following formula (2), thereby obtaining cellulose fibers having xanthate groups (xanthate group-introduced fibers). -OCSS - M + ……(2) where M + is at least one selected from the group consisting of hydrogen ions, monovalent metal ions, ammonium ions, and aliphatic or aromatic ammonium ions.

[0106] In the xanthate group introduction process, the cellulose-containing fiber raw material is first treated with an alkaline solution to obtain alkali cellulose. Examples of alkaline solutions include an aqueous alkali metal hydroxide solution and an aqueous alkaline earth metal hydroxide solution. Among these, the alkaline solution is preferably an aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide, and particularly preferably an aqueous sodium hydroxide solution. When the alkaline solution is an aqueous alkali metal hydroxide solution, the alkali metal hydroxide concentration in the aqueous alkali metal hydroxide solution is preferably 4% by mass or more, more preferably 5% by mass or more. Furthermore, the alkali metal hydroxide concentration in the aqueous alkali metal hydroxide solution is preferably 9% by mass or less. By setting the alkali metal hydroxide concentration at or above the lower limit, the mercerization of cellulose can be sufficiently promoted, the amount of by-products generated during the subsequent xanthation can be reduced, and as a result, the yield of xanthate group-introduced fiber can be increased. This allows the defibration process described below to be performed more effectively. Furthermore, by setting the alkali metal hydroxide concentration to the above upper limit or less, it is possible to prevent the aqueous alkali metal hydroxide solution from penetrating into the crystalline regions of cellulose while allowing mercerization to proceed, which makes it easier to maintain the cellulose type I crystal structure and further increases the yield of fine fibrous cellulose.

[0107] The alkali treatment time is preferably 30 minutes or more, more preferably 1 hour or more. The alkali treatment time is preferably 6 hours or less, more preferably 5 hours or less. By setting the alkali treatment time within the above range, the final yield can be increased, and productivity can be improved.

[0108] The alkali cellulose obtained by the alkali treatment is preferably subjected to solid-liquid separation to remove as much aqueous solution as possible. This reduces the water content during the subsequent xanthate treatment, thereby accelerating the reaction. As a method for solid-liquid separation, a general dehydration method such as centrifugation or filtration can be used. The concentration of alkali metal hydroxide contained in the alkali cellulose after solid-liquid separation is preferably 3% by mass or more and 8% by mass or less based on the total mass of the alkali cellulose after solid-liquid separation.

[0109] In the xanthate group introduction step, a xanthate treatment step is carried out after alkali treatment. In the xanthate treatment step, alkali cellulose is reacted with carbon disulfide (CS2) to form (-O - Na + ) group (-OCSS - Na + ) group to obtain xanthate group-introduced fibers. In the above, the metal ions introduced into the alkali cellulose are typically Na + However, similar reactions occur with other alkali metal ions.

[0110] In the xanthation treatment, it is preferable to supply 10% by mass or more of carbon disulfide relative to the bone dry mass of cellulose in the alkali cellulose. Furthermore, in the xanthation treatment, the contact time between carbon disulfide and alkali cellulose is preferably 30 minutes or more, more preferably 1 hour or more. Although the contact of carbon disulfide with alkali cellulose allows xanthation to proceed quickly, it takes time for carbon disulfide to penetrate into the interior of the alkali cellulose, so it is preferable to set the reaction time within the above range. On the other hand, the contact time between carbon disulfide and alkali cellulose can be 6 hours or less, which allows sufficient penetration into the alkali cellulose mass after dehydration, allowing reactive xanthation to be almost completed.

[0111] The reaction temperature in the xanthate treatment is preferably 46 ° C or less. By setting the reaction temperature within the above range, it is easy to suppress the decomposition of alkali cellulose. In addition, by setting the reaction temperature within the above range, it is easy to react uniformly, so it is possible to suppress the generation of by-products, and further, it is also possible to suppress the removal of the generated xanthate group.

[0112] The amount of xanthate groups introduced in the xanthate group introduction step is preferably 0.60 mmol / g or more per 1 g (mass) of fiber raw material, more preferably 0.70 mmol / g or more, even more preferably 0.80 mmol / g or more, even more preferably 1.00 mmol / g or more, and particularly preferably 1.20 mmol / g or more. Furthermore, the amount of xanthate groups introduced is, for example, preferably 5.00 mmol / g or less per 1 g (mass) of fiber raw material, more preferably 3.00 mmol / g or less. The fact that the amount of xanthate groups introduced in the xanthate group introduction step is within the above range means that the amount of substituents introduced into the fine fibrous cellulose used in step (A) is within the above range. By setting the amount of xanthate groups introduced within the above range, the amount of substituents introduced into the fine fibrous cellulose used in step (A) can be set within the above range, making it easier to produce fine fibrous cellulose with a fiber width of 10 nm or less. Furthermore, the transparency of the dispersion or sheet containing the fine fibrous cellulose of the present invention can be more effectively improved.

[0113] <Cleaning process> In the production process of fine fibrous cellulose to be subjected to step (A), a washing step can be carried out on the anionic group-introduced fibers, if necessary. The washing step is carried out by washing the anionic group-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 washings carried out in each washing step is not particularly limited.

[0114] <Alkali treatment process> In the process for producing fine fibrous cellulose subjected to step (A), the fiber raw material may be subjected to an alkali treatment between the anionic group introduction step and the defibration treatment step described below. The alkali treatment method is not particularly limited, but an example thereof is a method in which the anionic group-introduced fiber is immersed in an alkali solution.

[0115] 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 a polar solvent including water or 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.

[0116] The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably, for example, from 5°C to 80°C, and more preferably from 10°C to 60°C. The immersion time of the anionic group-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is, for example, preferably from 5 minutes to 30 minutes, and more preferably from 10 minutes to 20 minutes. The amount of alkaline solution used in the alkaline treatment is not particularly limited, but is, for example, preferably from 100% by mass to 100,000% by mass, and more preferably from 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the anionic group-introduced fiber.

[0117] In order to reduce the amount of alkaline solution used in the alkaline treatment step, the anionic group-introduced fiber may be washed with water or an organic solvent after the anionic group-introducing step and before the alkaline treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkaline-treated anionic group-introduced fiber with water or an organic solvent after the alkaline treatment step and before the defibrating treatment step.

[0118] <Acid treatment process> In the production process of the fine fibrous cellulose subjected to step (A), the fibrous raw material may be subjected to an acid treatment between the step of introducing anionic groups and the defibration treatment step described below. For example, the anionic group introduction step, acid treatment, alkali treatment, and defibration treatment may be performed in this order.

[0119] 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.

[0120] The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably, for example, 5°C to 100°C, and more preferably, 20°C to 90°C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is, for example, preferably, 5 minutes to 120 minutes, and more preferably, 10 minutes to 60 minutes. The amount of the acid solution used in the acid treatment is not particularly limited, but is, for example, preferably, 100 mass% to 100,000 mass%, and more preferably, 1,000 mass% to 10,000 mass%, based on the absolute dry mass of the fiber raw material.

[0121] <Nitrogen removal treatment> The process for producing fine fibrous cellulose subjected to step (A) 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 that can further suppress discoloration can be obtained. The nitrogen removal treatment step may be performed after the uniform dispersion treatment step in step (B) described below, but is preferably performed before the uniform dispersion treatment step in step (B) described below. It is also preferably performed before the defibration treatment step in step (A) described below.

[0122] In the nitrogen removal treatment step, it is preferable to adjust the pH of the slurry containing the anionic group-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 anionic group-introduced fiber, it is preferable to add an alkali compound that can be used in the above-mentioned alkali treatment step to the slurry.

[0123] After the nitrogen removal treatment step, the anionic group-introduced fiber may be subjected to a washing step, if necessary. The washing step is carried out by washing the anionic group-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.

[0124] <Defibrillation processing> The production process for fine fibrous cellulose subjected to step (A) includes a defibration treatment step. This produces fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less. 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), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision grinder, a ball mill, a bead mill, a disk 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.

[0125] The processing conditions in the defibration processing step are not particularly limited, but for example, when a high-pressure homogenizer is used, the pressure during processing is preferably 1 MPa or more and 350 MPa or less, more preferably 10 MPa or more and 300 MPa or less, and even more preferably 50 MPa or more and 250 MPa or less.

[0126] In the defibration process, for example, the anionic group-introduced fibers are preferably diluted with a dispersion medium to form a slurry. The dispersion medium can be one or more selected from water and organic solvents such as polar organic solvents. The polar organic solvent is not particularly limited, but examples thereof include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

[0127] 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 anionic group-introduced fibers in a dispersion medium may contain solids other than the anionic group-introduced fibers, such as urea having hydrogen bonding properties.

[0128] <Substituent removal treatment> The method for producing fine fibrous cellulose of the present invention includes a step (A) of removing at least a portion of the substituents from fine fibrous cellulose having substituents and having a fiber width of 1000 nm or less. In this specification, the step of removing at least a portion of the substituents from the fine fibrous cellulose is also referred to as a substituent removal treatment step.

[0129] 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 can be removed from fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, and fine fibrous cellulose with an introduced substituent amount of less than 0.5 mmol / g can be obtained.

[0130] The substituent removal treatment step is preferably carried out in the form of a slurry. That is, the substituent removal treatment step is preferably a step of subjecting a slurry containing a substituent-containing fine fibrous cellulose having a fiber width of 1000 nm or less to a heat treatment, an enzyme treatment, an acid treatment, an alkali treatment, or the like. By carrying out the substituent removal treatment step in the form of a slurry, it is possible to prevent the residue of colored substances generated by heating or the like during the substituent removal treatment, as well as acids, alkalis, salts, and the like that are added or generated. This makes it possible to suppress coloration when the fine fibrous cellulose obtained through step (B) is made into a slurry or 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.

[0131] When a substituent removal treatment is performed on a slurry containing fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, the concentration of the fine fibrous cellulose in the slurry is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. The concentration of the fine fibrous cellulose in the slurry is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. By controlling the concentration of the fine fibrous cellulose in the slurry within the above range, the substituent removal treatment can be performed more efficiently. Furthermore, by controlling the concentration of the fine fibrous cellulose in the slurry within the above range, it is possible to prevent the residue of colored substances resulting from heating or the like during the substituent removal treatment, as well as added or generated acids, alkalis, salts, etc. This can suppress coloration when the fine fibrous cellulose obtained through step (B) is made into a slurry or 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 increase the efficiency of salt removal.

[0132] When the substituent removal treatment step is a step of heat-treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, the heating temperature in the heat treatment step is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher. Furthermore, the heating temperature in the heat treatment step is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower. In particular, when the substituent on the fine fibrous cellulose subjected to the substituent removal treatment step is a phosphorus oxo acid group or a sulfone group, the heating temperature in the heat treatment step is preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] In the substituent removal treatment step, it is preferable that the substituent removal reaction proceeds uniformly. To proceed with the reaction uniformly, for example, the slurry containing the fine fibrous cellulose may be stirred, or the specific surface area of ​​the slurry may be increased. As a method for stirring the slurry, external mechanical shear may be applied, or self-stirring may be promoted by increasing the liquid feed rate of the slurry during the reaction.

[0140] 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 after the substituent removal treatment. This can more effectively improve the transparency of dispersions and sheets containing fine fibrous cellulose.

[0141] 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.

[0142] 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.

[0143] <pH adjustment step> When the substituent removal treatment step is performed in a slurry state, a step of adjusting the pH of the slurry containing microfibrillar cellulose may be provided before the substituent removal treatment step. For example, an anionic group is introduced into the cellulose fiber, and the counter ion of this anionic group is Na +In this case, the slurry containing the defibrated fine fibrous cellulose exhibits a weak alkaline pH. If the slurry is heated in this state, monosaccharides, which are one of the causes of coloration, may be generated due to the decomposition of the 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] <Salt removal treatment> After the substituent removal treatment step, it is preferable to carry out a treatment to remove salts derived from the removed substituents. Removing the salts derived from the substituents makes it easier to obtain fine fibrous cellulose that can suppress coloration. The means for removing the salts derived from the substituents is not particularly limited, and examples thereof include a washing treatment. The washing treatment is carried out by washing the fine fibrous cellulose that has aggregated in the substituent removal treatment with, for example, water or an organic solvent. From the viewpoint of more effectively suppressing yellowing, it is preferable to carry out the washing treatment by filtration dehydration, centrifugal dehydration, or centrifugation.

[0148] (Process (B)) The method for producing fine fibrous cellulose may include step (A) 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, and step (B) of uniformly dispersing the cellulose after step (A). Step (B) of uniformly dispersing the cellulose obtained after the substituent removal treatment in step (A) is uniformly dispersed. By undergoing step (B), the fiber width of the fine fibrous cellulose can be easily reduced, even though the amount of introduced substituents is as low as less than 0.5 mmol / g.

[0149] In the uniform dispersion treatment step (B), 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.

[0150] The treatment conditions in step (B) of uniform dispersion treatment are not particularly limited, but it is preferable to increase the maximum movement speed of the fine fibrous cellulose during treatment and the pressure during treatment. In the case of a high-speed defibrator, the peripheral speed is preferably 20 m / sec or more, more preferably 25 m / sec or more, and even more preferably 30 m / sec or more. A high-pressure homogenizer is more preferably used because it has a higher maximum movement speed of the fine fibrous cellulose during treatment and a higher pressure during treatment than a high-speed defibrator. In high-pressure homogenizer treatment, the pressure during treatment is preferably 1 MPa or more, more preferably 10 MPa or more, even more preferably 50 MPa or more, and particularly preferably 100 MPa or more. In addition, in high-pressure homogenizer treatment, the pressure during treatment is preferably 350 MPa or less, more preferably 300 MPa or less, and even more preferably 250 MPa or less.

[0151] In step (B), the above-mentioned spacer molecules may be added. By adding such spacer molecules in the uniform dispersion treatment step (B), the uniform dispersion treatment of the fine fibrous cellulose can be carried out more smoothly. This makes it possible to more effectively improve the transparency of the dispersion liquid and sheet containing the fine fibrous cellulose.

[0152] (resin layer) The laminate sheet of the present invention may further include a resin layer on at least one side of the fiber layer. When the laminate sheet further includes a resin layer, the resin layer is preferably a layer that is directly laminated on the fiber layer, and the resin layer and the fiber layer are preferably in contact with each other on one side. In addition, the resin layer is preferably a resin layer formed by coating (coated resin layer).

[0153] In the laminate sheet of the present invention, the resin layer may be provided on both sides of the fiber layer. That is, the laminate sheet of the present invention may have a configuration of resin layer / first fiber layer / second fiber layer / ... / Xth fiber layer / resin layer, and preferably has a configuration of resin layer / first fiber layer / second fiber layer / resin layer.

[0154] 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, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more relative to the total mass of the resin layer. The resin content may be 100% by mass or may be 95% by mass or less.

[0155] Examples of natural resins include rosin-based resins such as rosin, rosin ester, and hydrogenated rosin ester.

[0156] The synthetic resin is preferably at least one selected from, for example, polycarbonate resin, polyethylene terephthalate resin, polyethylene naphthalate resin, polyethylene resin, polypropylene resin, cyclic olefin resin, polyimide resin, polystyrene resin, and acrylic resin. Among them, the synthetic resin is preferably at least one selected from polycarbonate resin and acrylic resin, and more preferably polycarbonate resin. The acrylic resin is preferably at least one selected from polyacrylonitrile and poly(meth)acrylate.

[0157] 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.

[0158] In the laminate sheet, the resin layer preferably contains an adhesion aid. Examples of the adhesion aid include a compound containing at least one selected from an isocyanate group, a carbodiimide group, an epoxy group, an oxazoline group, an amino group, a silanol group, and an alkoxysilyl group, and an organosilicon compound. Among these, the adhesion aid is preferably at least one selected from a compound containing an isocyanate group (isocyanate compound) and an organosilicon compound. Examples of the organosilicon compound include a silane coupling agent condensate and a silane coupling agent.

[0159] 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.

[0160] 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.

[0161] Examples of the organosilicon compound include a compound having a siloxane structure or a compound that forms a siloxane structure by condensation. For example, examples of the organosilicon compound include a silane coupling agent or a condensate of a silane coupling agent. 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.

[0162] 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.

[0163] The silane coupling agent may be one having an alkoxysilyl group, or one that generates a silanol group after hydrolysis. In this case, it is preferable that at least a portion of the alkoxysilyl group and the silanol group remain even after the fiber layer is laminated. Since the silanol group is a hydrophilic group, increasing the hydrophilicity of the surface of the resin layer facing the fiber layer can more effectively improve the adhesion between the resin layer and the fiber layer.

[0164] 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

[0165] 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 laminated sheet with an ultramicrotome UC-7 (manufactured by JEOL) and measuring the cross section with the same device.

[0166] 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."

[0167] 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, and 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.

[0168] 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.

[0169] 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.

[0170] The surface of the resin layer facing the fiber layer may have a micro-relief structure. Having a micro-relief structure on the surface of the resin layer facing the fiber layer can more effectively improve the adhesion between the fiber layer and the resin layer. When the surface of the resin layer facing the fiber layer has a micro-relief structure, it is preferable that such a structure be formed by a treatment process such as blasting, embossing, etching, corona treatment, or plasma discharge treatment. In this specification, a micro-relief structure refers to a structure in which 10 or more recesses exist on a single line of 1 mm length drawn at any location. To measure the number of recesses, the laminated sheet is immersed in ion-exchange water for 24 hours, and then the fiber layer is peeled from the resin layer. The surface of the resin layer facing the fiber layer can then be scanned with a stylus surface roughness meter (Surfcorder series, manufactured by Kosaka Laboratory Co., Ltd.). When the pitch of the irregularities is extremely small, on the order of submicrons or nanometers, the number of irregularities can be measured from images observed with a scanning probe microscope (AFM5000II and AFM5100N, manufactured by Hitachi High-Tech Science Corporation).

[0171] The resin layer may contain optional components other than the synthetic resin, such as fillers, pigments, dyes, and ultraviolet absorbers, which are known components used in the field of resin films.

[0172] When the laminate sheet of the present invention has a resin layer, it is preferable that the interlayer adhesion between the fiber layer and the resin layer is high. Specifically, in accordance with JIS K 5400, 2 When 100 cross-cuts of this type are inserted, cellophane tape (manufactured by Nichiban Co., Ltd.) is applied and pressed onto them, and then peeled in a 90° direction, it is preferable that the number of squares where the fiber layer has peeled from the resin layer is less than 5 points. In such cases, it can be determined that the interlayer adhesion between the fiber layer and the resin layer is good. The number of peeled squares is more preferably 3 points or less, even more preferably 1 point or less, and particularly preferably 0 points.

[0173] When the laminate sheet of the present invention has a resin layer, the fiber layer can also function as a layer for reinforcing the resin layer. This increases the strength of the laminate sheet itself. Furthermore, when the laminate sheet is attached to an adherend such as another resin film or resin plate, the fiber layer also functions as a layer for reinforcing the adherend. For example, by using a resin plate such as a polycarbonate plate as the adherend and attaching the laminate sheet to this resin plate, the mechanical strength of the resin plate can be reinforced. Thus, a laminate sheet having a fiber layer also has the effect of reinforcing the adherend.

[0174] When the laminate sheet of the present invention has a resin layer, the thickness of the resin layer is preferably 0.5 μm or more, more preferably 1 μm or more, even more preferably 2 μm or more, and particularly preferably 3 μm or more. The thickness of the resin layer is preferably 15,000 μm or less, more preferably 5,000 μm or less, and even more preferably 500 μm or less. Here, the thickness of the resin layer constituting the laminate sheet is a value measured by cutting out a cross section of the laminate sheet using an ultramicrotome UC-7 (manufactured by JEOL) and observing the cross section with an electron microscope, a magnifying glass, or visually.

[0175] The ratio of the total thickness of the resin layers to the total thickness of the fiber layers (thickness of resin layer / thickness of fiber layer) is preferably 10 or less, more preferably 5 or less, and even more preferably 1 or less. Furthermore, for example, when the resin layer is a coated layer formed by coating, the ratio of the total thickness of the resin layers to the total thickness of the fiber layers (thickness of resin layer / thickness of fiber layer) may be 0.5 or less, 0.2 or less, 0.15 or less, or 0.1 or less.

[0176] (Method of manufacturing laminated sheet) The method for producing a laminate sheet of the present invention includes the steps of forming a first fiber layer containing fibrous cellulose having an introduced substituent group amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less, and forming a second fiber layer on the first fiber layer, the second fiber layer containing fibrous cellulose having an introduced substituent group amount of less than 0.5 mmol / g in the pressure-sensitive adhesive layer and a fiber width of 1000 nm or less. The method for producing a laminate sheet of the present invention may further include the steps of forming a third fiber layer, a fourth fiber layer, and so on, an Xth fiber layer.

[0177] The step of forming a first fiber layer containing fibrous cellulose having an introduced substituent amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less preferably includes a step of coating a fine fibrous cellulose dispersion (slurry containing fine fibrous cellulose) on a substrate or a step of making a paper from the fine fibrous cellulose dispersion. The step of forming a second fiber layer containing fibrous cellulose having an introduced substituent amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less preferably includes a step of coating a fine fibrous cellulose dispersion (slurry containing fine fibrous cellulose) on the first fiber layer or a step of laminating a second fiber layer formed by making a paper from the fine fibrous cellulose dispersion on the first fiber layer.

[0178] The fine fibrous cellulose dispersion (slurry containing fine fibrous cellulose) may contain oxygen-containing organic compounds and optional components contained in the fiber layer, and it is preferable that the nanofiber yield, haze, pH, viscosity, free nitrogen content, etc. of the fine fibrous cellulose dispersion are within the numerical ranges described in the above section <Fine fibrous cellulose>.

[0179] <Coating process> The process of coating a substrate with a fine fibrous cellulose dispersion (slurry containing fine fibrous cellulose) (hereinafter also referred to as the coating process) involves coating a substrate with the fine fibrous cellulose dispersion, drying the coating, and peeling off the resulting fine fibrous cellulose-containing sheet from the substrate to obtain a sheet. Sheets can be produced continuously by using a coating device and a long substrate. The concentration of the fine fibrous cellulose dispersion to be coated is not particularly limited, but is preferably 0.05% by mass or more and 10% by mass or less.

[0180] The quality of the substrate used in the coating process is not particularly limited, but a substrate with high wettability with the fine fibrous cellulose dispersion can suppress shrinkage of the sheet during drying, but it is preferable to select a substrate that allows the sheet formed after drying to be easily peeled off. Among these, a resin plate or a metal plate is preferred, but is not particularly limited. For example, resin plates such as acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, and polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates, and iron plates, and those with oxidation-treated surfaces, stainless steel plates, brass plates, etc. can be used.

[0181] In the coating process, if the viscosity of the fine fibrous cellulose dispersion is low and it spreads on the substrate, a blocking frame may be fixed to the substrate to obtain a fine fibrous cellulose-containing sheet of a predetermined thickness and basis weight. The quality of the blocking frame is not particularly limited, but it is preferable to select one that allows the edge of the sheet to be easily peeled off after drying. Among these, molded resin plates or metal plates are preferred, but are not particularly limited. For example, resin plates such as acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, and polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates, and iron plates, and those with their surfaces oxidized, as well as molded stainless steel plates and brass plates, can be used.

[0182] Examples of a coater that can be used to coat the fine fibrous cellulose dispersion include a bar coater, a roll coater, a gravure coater, a die coater, a curtain coater, and an air doctor coater. Bar coaters, die coaters, curtain coaters, and spray coaters are preferred because they can achieve a more uniform thickness.

[0183] The coating temperature is not particularly limited, but is preferably from 20° C. to 45° C. If the coating temperature is equal to or higher than the lower limit, the fine fibrous cellulose dispersion can be easily coated, and if the coating temperature is equal to or lower than the upper limit, evaporation of the dispersion medium during coating can be suppressed.

[0184] In the coating process, the finished sheet weight is 10 g / m 2 More than 100g / m 2 It is preferable to coat the fine fibrous cellulose dispersion so that the basis weight falls within the above range. By coating the dispersion so that the basis weight falls within the above range, a fiber layer with excellent strength can be obtained.

[0185] The process for producing a fine fibrous cellulose-containing sheet preferably includes a step of drying the fine fibrous cellulose dispersion coated on the substrate. The drying method is not particularly limited, and may be either a non-contact drying method or a method in which the sheet is dried while being restrained, or a combination of these methods.

[0186] Non-contact drying methods are not particularly limited, but include a method of drying by heating with hot air, infrared rays, far-infrared rays, or near-infrared rays (heat drying method), and a method of drying by vacuum drying (vacuum drying method). Heat drying and vacuum drying may be combined, but heat drying is usually used. Drying with infrared rays, far-infrared rays, or near-infrared rays can be performed using an infrared device, a far-infrared device, or a near-infrared device, but is not particularly limited. 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. Setting the heating temperature at or above the lower limit allows the dispersion medium to volatilize quickly, while setting the heating temperature at or below the upper limit reduces the cost required for heating and prevents the fine fibrous cellulose from discoloring due to heat.

[0187] After drying, the obtained fine fibrous cellulose-containing sheet is peeled off from the substrate, but when the substrate is a sheet, the fine fibrous cellulose-containing sheet and the substrate may be rolled up while still stacked, and the fine fibrous cellulose-containing sheet may be peeled off from the processing substrate just before use. In this way, a fine fibrous cellulose-containing sheet that will become a fiber layer is obtained.

[0188] <Paper making process> The manufacturing process of the fine fibrous cellulose-containing sheet that becomes the fiber layer may include a process of making paper from a fine fibrous cellulose dispersion. Examples of papermaking machines used in the papermaking process include continuous papermaking machines such as Fourdrinier, cylinder, and tilting machines, and multi-layer papermaking machines that combine these. In the papermaking process, known papermaking methods such as handmaking may be used.

[0189] In the papermaking process, a fine fibrous cellulose dispersion is filtered and dehydrated on a wire to obtain a wet sheet, which is then pressed and dried to obtain a sheet. The concentration of the fine fibrous cellulose dispersion is not particularly limited, but is preferably 0.05% by mass or more and 5% by mass or less. When filtering and dehydrating the fine fibrous cellulose dispersion, the filter cloth used during filtration is not particularly limited, but it is important that the fine fibrous cellulose does not pass through and that the filtration rate is not too slow. Such filter cloths are not particularly limited, but 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. Specific examples include, but are not limited to, porous membranes of polytetrafluoroethylene with pore sizes of 0.1 μm to 20 μm, e.g., 1 μm, and woven polyethylene terephthalate or polyethylene with pore sizes of 0.1 μm to 20 μm, e.g., 1 μm.

[0190] The method for producing a sheet from a fine fibrous cellulose dispersion is not particularly limited, and examples include a method using the production apparatus described in WO2011 / 013567. This production apparatus includes a water squeezing section in which the fine fibrous cellulose dispersion is discharged onto the upper surface of an endless belt and the dispersion medium is squeezed out of the discharged fine fibrous cellulose dispersion to produce a web, and a drying section in which the web is dried to produce a fibrous 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.

[0191] The dehydration method that can be used in the present invention is not particularly limited, but includes dehydration methods commonly used in paper production, such as a method of dehydrating using a Fourdrinier, cylinder, or inclined wire, followed by dehydration using a roll press. The drying method is also not particularly limited, but includes methods commonly used in paper production, such as a cylinder dryer, Yankee dryer, hot air dryer, near-infrared heater, or infrared heater.

[0192] <Inversion process> The method for producing a laminated sheet of the present invention preferably includes a step of inverting the formed fiber layer between steps of forming each fiber layer. In the inverting step, the formed fiber layer or layers are inverted so that the front surface (top surface) of the formed fiber layer or layers becomes the back surface (bottom surface). By providing such a step, the curl resistance of the sheet can be more effectively improved.

[0193] More specifically, the method for producing a laminate sheet of the present invention preferably includes the steps of forming a first fiber layer containing fibrous cellulose having an introduced substituent group amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less, in this order, inverting the first fiber layer, and forming a second fiber layer on the first fiber layer containing fibrous cellulose having an introduced substituent group amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less. In a laminate sheet formed through such steps, curling is further suppressed.

[0194] <Lamination of resin layers> When the laminate sheet of the present invention has a resin layer, it preferably includes a step of forming a resin layer on at least one side of the fiber layer. In this case, the step of forming the resin layer is preferably a step of coating a resin composition on the fiber layer. Furthermore, the method for producing a laminate sheet of the present invention may include a step of forming, on a pre-formed resin layer, a first fiber layer containing fibrous cellulose having an introduced substituent group amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less, and a step of forming, on the first fiber layer, a second fiber layer containing fibrous cellulose having an introduced substituent group amount of less than 0.5 mmol / g in the pressure-sensitive adhesive layer and a fiber width of 1000 nm or less.

[0195] When applying a resin composition to a fiber layer or forming a resin layer, it is preferable to apply a resin composition containing a resin, form a coating film, and then provide a drying step.

[0196] In addition to the above-mentioned methods, the laminate sheet can also be produced by placing a resin layer on a fiber layer and hot pressing it, or by placing the fiber layer in an injection molding die and injecting heated, molten resin into the die to bond the resin layer to the fiber layer.

[0197] (Laminate) The present invention may also relate to a laminate obtained by laminating the above-mentioned laminate sheet and an adherend. Examples of the adherend include an organic film (hereinafter also referred to as an organic layer) and an inorganic film (hereinafter also referred to as an inorganic layer). Among these, the laminate of the present invention is preferably a laminate obtained by laminating the above-mentioned laminate sheet and an organic film. Examples of the organic film include a resin film, a resin plate, and a resin molded product.

[0198] Resin films, resin plates, and resin molded articles (hereinafter simply referred to as resin films) are layers 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 film. The content of the resin component is preferably 60% by mass or more relative to the total mass of the resin film, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. The content of the resin component may be 100% by mass relative to the total mass of the resin film.

[0199] Examples of natural resins include rosin-based resins such as rosin, rosin ester, and hydrogenated rosin ester.

[0200] Examples of synthetic resins include polyolefin resins, cyclic olefin resins, polycarbonate resins, polyethylene terephthalate resins, polyethylene naphthalate resins, polyimide resins, polystyrene resins, acrylic resins, etc. Among these, the synthetic resin is preferably a polyolefin resin, and preferably contains at least one selected from polyethylene resins and polypropylene resins.

[0201] The method for forming the organic layer is not particularly limited, but examples thereof include a coating method, an injection molding method, and a heat-and-press method. In the coating method, it is preferable to coat the resin composition forming the organic layer on the resin layer of the laminate sheet and then heat-cure or photo-cure it. In the heat-and-press method, it is preferable to heat-press a resin film superimposed on the resin layer of the laminate sheet. The heat-press conditions can be appropriately selected with reference to the glass transition temperature of the resin film, etc.

[0202] The material constituting the inorganic layer is not particularly limited, but examples thereof include aluminum, silicon, magnesium, zinc, tin, nickel, and titanium; their oxides, carbides, nitrides, oxycarbides, oxynitrides, and oxycarbonitrides; and mixtures thereof. From the viewpoint of stably maintaining high moisture resistance, silicon oxide, silicon nitride, silicon oxide carbide, silicon oxynitride, silicon oxycarbonitride, aluminum oxide, aluminum nitride, aluminum oxide carbide, aluminum oxynitride, and mixtures thereof are preferred.

[0203] The method for forming the inorganic layer is not particularly limited, and examples thereof include chemical vapor deposition (CVD) and physical vapor deposition (PVD). 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, and sputtering. Atomic layer deposition (ALD) can also be used to form the inorganic layer. ALD is a method for forming a thin film atomically by alternately supplying source gases of each element constituting the film to be formed to the surface on which the layer is to be formed.

[0204] (Application) The laminate sheet of the present invention is a laminate sheet that is transparent, has high mechanical strength, and exhibits reduced coloration. Taking advantage of these excellent optical properties, the laminate sheet is suitable for optical components. For example, it can be used as a light-transmitting substrate for various display devices, various solar cells, and the like. The laminate sheet of the present invention is also suitable for applications such as substrates for electronic devices, components for home appliances, window materials for various vehicles and buildings, interior materials, exterior materials, and packaging materials. [Example]

[0205] 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.

[0206] <Production Example 1> [Phosphorylation] Hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd. was used as the raw material pulp. This raw material pulp was subjected to a phosphating 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 material pulp to adjust the composition to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, thereby obtaining 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.

[0207] [Cleaning process] 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.

[0208] [Neutralization treatment] 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 to obtain a neutralized phosphorylated pulp. Next, the neutralized phosphorylated pulp was subjected to the above-mentioned washing treatment.

[0209] The infrared absorption spectrum of the obtained phosphorus oxyoxidized pulp was measured using FT-IR. -1 The absorption due to the P=O of the phosphate group was observed around the 2θ=14° to 17° and the 2θ=22° to 23° angle, confirming that the pulp had phosphate groups. The phosphorylated pulp was analyzed using an X-ray diffractometer, and 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.

[0210] [Fiber defibration processing] Ion-exchanged water was added to the resulting phosphorylated pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was processed six times at a pressure of 200 MPa using a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that the fine fibrous cellulose maintained cellulose type I crystallinity. The amount of phosphate groups (amount of first dissociated acid groups, strong acid groups) measured by the method described below for measuring the amount of phosphorus oxo acid groups was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0211] <Production Example 2> A fine fibrous cellulose dispersion containing phosphorylated pulp and fine fibrous cellulose was obtained in the same manner as in Production Example 1, except that the following nitrogen removal treatment was carried out after the phosphorylated pulp was washed and neutralized.

[0212] [Nitrogen removal treatment] Deionized water was added to phosphorylated pulp 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 of phosphorylated pulp (bone dry mass) 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 completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0213] The infrared absorption spectrum of the obtained phosphorus oxyoxidized pulp was measured using FT-IR. -1 Absorption 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 (first dissociated acid amount, strong acid group amount) measured by the method described below in [Measurement of phosphorus oxoacid group amount] was 1.35 mmol / g. The total amount of dissociated acid was 2.30 mmol / g.

[0214] <Production Example 3> [Phosphorous Treatment] The same procedure as in Production Example 1 was carried out, except that 33 parts by mass of phosphorous acid (phosphonic acid) was used instead of ammonium dihydrogen phosphate in the phosphating treatment, to obtain a fine fibrous cellulose dispersion containing phosphorylated pulp and fine fibrous cellulose.

[0215] The infrared absorption spectrum of the phosphorylated pulp obtained was measured using FT-IR. -1Absorption due to P=O of the phosphonic acid group, which is a tautomer of the phosphorous acid group, was observed near the peak, confirming that phosphorous acid groups (phosphonic acid 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 phosphorous acid groups (amount of first dissociated acid), measured by the method described below in [Measurement of phosphorus oxoacid group amount], was 1.51 mmol / g, and the total amount of dissociated acid was 1.54 mmol / g.

[0216] <Production Example 4> [Sulfation treatment] The same procedure as in Production Example 1 was carried out, except that 38 parts by mass of amidosulfonic acid (sulfamic acid) was used instead of ammonium dihydrogen phosphate in the phosphorylation treatment and the heating time was extended to 19 minutes, to obtain a fine fibrous cellulose dispersion containing sulfated pulp and fine fibrous cellulose.

[0217] The infrared absorption spectrum of the sulfated pulp obtained was measured using FT-IR. -1 Absorption due to sulfate groups (sulfonic groups) was observed around 1000 kJ / g, confirming that sulfate groups (sulfonic groups) had been added to the pulp. X-ray diffraction also confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystal structure. The amount of sulfonic groups measured by the method described in [Measurement of sulfonic group amount] below was 1.12 mmol / g.

[0218] <Production Example 5> The same operation as in Production Example 1 was performed except that the following xanthation treatment was performed instead of the phosphate treatment, to obtain a fine fibrous cellulose dispersion containing xanthated pulp and fine fibrous cellulose.

[0219] [Xanthate treatment] To 100 parts by mass (bone dry mass) of raw pulp (hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd.), 2500 parts by mass of an 8.5% by mass aqueous solution of sodium hydroxide was added, and the mixture was stirred at room temperature for 3 hours to perform an alkali treatment. The pulp after this alkali treatment was subjected to solid-liquid separation by centrifugation (filter cloth 400 mesh, 3000 rpm for 5 minutes) to obtain a dehydrated alkali cellulose. To 10 parts by mass (bone dry mass) of the obtained alkali cellulose, 3.5 parts by mass of carbon disulfide was added, and the sulfurization reaction was carried out at room temperature for 4.5 hours to perform a xanthate formation treatment.

[0220] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. The amount of xanthate groups measured by the measurement method described below in [Measurement of xanthate group amount] was 1.73 mmol / g.

[0221] [measurement] [Measurement of Haze of Dispersion] The haze of the dispersion was measured by diluting the fibrous cellulose dispersion with ion-exchanged water to 0.2% by mass, and then measuring the haze using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory) and a glass cell for liquids with a 1 cm optical path length (MG-40, manufactured by Fujiwara Seisakusho, reverse optical path) in accordance with JIS K 7136:2000. Zero-point measurement was performed using ion-exchanged water placed in the same glass cell. The dispersion to be measured was allowed to stand for 24 hours in an environment of 23°C and 50% relative humidity before measurement. The liquid temperature of the dispersion during measurement was 23°C.

[0222] [Nanofiber yield measurement] The nanofiber yield after centrifuging the fibrous cellulose dispersion was measured using the method described below. The nanofiber yield is an indicator of the yield of fine fibrous cellulose; the higher the nanofiber yield, the higher the yield of fine fibrous cellulose. Each dispersion was adjusted to a cellulose concentration of 0.1% by mass and centrifuged at 12,000 G for 10 minutes using a refrigerated high-speed centrifuge (Kokusan Co., Ltd., H-2000B). The resulting supernatant was recovered and its cellulose concentration was measured. The yield of fine fibrous cellulose was calculated based on the following formula: Nanofiber yield (mass%) = cellulose concentration in supernatant (mass%) / 0.1 × 100

[0223] [Measuring the amount of nitrogen] The total amount of nitrogen contained in the fibrous cellulose and the free nitrogen contained in the fibrous cellulose dispersion was measured using the following method. Each dispersion was adjusted to a solids concentration of 1% by mass and decomposed using the Kjeldahl method (JIS K 0102 44.1). After decomposition, the amount of ammonium ions (mmol) was measured using cation chromatography and divided by the amount of cellulose (g) used in the measurement to calculate the nitrogen content (mmol / g).

[0224] [Table 1]

[0225] Example 1 [Substituent removal treatment (high temperature heat treatment)] A 20% by mass aqueous citric acid solution was added to the fine fibrous cellulose dispersion containing the fine fibrous cellulose obtained in Production Example 1, and the pH of the dispersion was adjusted to 5.5. The resulting slurry was placed in a pressure-resistant container and heated at a liquid temperature of 160°C for 15 minutes until the amount of phosphate groups became less than 0.08 mmol / g. The formation of fine fibrous cellulose aggregates was confirmed by this operation.

[0226] [Cleaning of slurry 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.

[0227] [Uniform dispersion of slurry after removing substituents] Ion-exchanged water was added to the resulting slurry after the removal of substituents to give a slurry with a solids concentration of 1.0% by mass. This slurry had a pH of 5.5. Treatment was carried out three times at a pressure of 200 MPa using a wet atomization apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a dispersion of substituent-removed fine fibrous cellulose containing the substituent-removed fine fibrous cellulose. The number-average fiber width of the substituent-removed fine fibrous cellulose measured in the "Fiber Width Measurement" section described below was 4 nm, and the proportion of fine fibrous cellulose with a fiber width of 10 nm or less out of all the fibrous cellulose contained in the dispersion was 98%.

[0228] [Sheet production 1] Acetoacetyl group-modified polyvinyl alcohol (Gohsenex Z-200, manufactured by Mitsubishi Chemical Corporation) was added to ion-exchanged water to a concentration of 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.

[0229] The substituent-removed microfibrous cellulose dispersion and the polyvinyl alcohol aqueous solution were each diluted with ion-exchanged water to a solids concentration of 0.6% by mass. Next, 50 parts by mass of the diluted substituent-removed microfibrous cellulose dispersion and 50 parts by mass of the diluted polyvinyl alcohol aqueous solution were mixed to obtain a mixed solution. The mixed solution was then weighed out so that the finished sheet thickness would be 12.5 μm and spread on a commercially available glass plate. A damming frame (inner dimensions 250 mm × 250 mm, height 5 cm) was placed on the glass plate to achieve the desired thickness. The mixture was then dried in a dryer at 140 ° C for 1 hour. The same mixed solution was then weighed out and spread on top of the diluted solution to a finished thickness of 12.5 μm, and dried in a dryer at 140 ° C for 1 hour. The sheet was peeled off from the glass plate to obtain a laminated sheet with a total thickness of 25 μm.

[0230] <Example 2> The mixed solution obtained in [Sheet Preparation 1] of Example 1 was weighed out so that the finished thickness of the sheet would be 25 μm, and spread on a commercially available glass plate. A damming frame (inner dimensions 250 mm × 250 mm, height 5 cm) was placed on the glass plate to achieve the desired thickness. The sheet was then dried in a dryer at 140°C for 1 hour. The same mixed solution was then weighed out and spread on top of the sheet so that the finished thickness would be 25 μm, and dried in a dryer at 140°C for 1 hour. The sheet was peeled off from the glass plate to obtain a laminated sheet with a total thickness of 50 μm.

[0231] Example 3 The mixed solution obtained in [Sheet Preparation 1] of Example 1 was measured so that the finished thickness of the sheet would be 12.5 μm and spread on a commercially available glass plate. A damming frame (inner dimensions 250 mm × 250 mm, height 5 cm) was placed on the glass plate to achieve the desired thickness. The sheet was then dried in a dryer at 140 ° C for 1 hour. The sheet was peeled off from the glass plate to obtain Sheet A with a thickness of 12.5 μm. Sheet A was then inverted, and the surface opposite the peeled surface of the glass plate was attached to the glass plate. A damming frame (inner dimensions 200 mm × 200 mm, height 5 cm) was placed on top of the sheet. The same mixed solution was measured and spread on top of the sheet so that the finished thickness would be 12.5 μm, and then dried in a dryer at 140 ° C for 1 hour. The sheet was peeled off from the glass plate to obtain a laminated sheet with a total thickness of 25 μm.

[0232] Example 4 The mixed solution obtained in [Sheet Preparation 1] of Example 1 was measured so that the finished thickness of the sheet would be 25 μm and spread on a commercially available glass plate. A damming frame (inner dimensions 250 mm × 250 mm, height 5 cm) was placed on the glass plate to achieve the desired thickness. The sheet was then dried in a dryer at 140 ° C for 1 hour. The sheet was peeled off from the glass plate to obtain Sheet B with a thickness of 25 μm. Sheet B was then inverted, and the surface opposite the peeled surface of the glass plate was attached to the glass plate. A damming frame (inner dimensions 200 mm × 200 mm, height 5 cm) was placed on top of the sheet. The same mixed solution was measured and spread on top of the sheet so that the finished thickness would be 25 μm, and then dried in a dryer at 140 ° C for 1 hour. The sheet was peeled off from the glass plate to obtain a laminated sheet with a total thickness of 50 μm.

[0233] <Example 5> In [Sheet Preparation 1] of Example 1, 40 parts by mass of the substituent-removed fine fibrous cellulose dispersion was mixed with 60 parts by mass of the diluted polyvinyl alcohol aqueous solution to obtain a mixed solution. Except for using this mixed solution, the same operation as in Example 4 was carried out to obtain a laminated sheet with a total thickness of 50 μm.

[0234] Example 6 In [Sheet Preparation 1] of Example 1, 30 parts by mass of the substituent-removed fine fibrous cellulose dispersion was mixed with 70 parts by mass of the diluted polyvinyl alcohol aqueous solution to obtain a mixed solution. Except for using this mixed solution, the same operation as in Example 4 was carried out to obtain a laminated sheet with a total thickness of 50 μm.

[0235] Example 7 In [Sheet Preparation 1] of Example 1, 10 parts by mass of the substituent-removed fine fibrous cellulose dispersion was mixed with 90 parts by mass of the diluted polyvinyl alcohol aqueous solution to obtain a mixed solution. Except for using this mixed solution, the same operation as in Example 4 was carried out to obtain a laminated sheet with a total thickness of 50 μm.

[0236] Example 8 In [Sheet Preparation 1] of Example 1, 70 parts by mass of the substituent-removed fine fibrous cellulose dispersion was mixed with 30 parts by mass of the diluted polyvinyl alcohol aqueous solution to obtain a mixed solution. Except for using this mixed solution, the same operation as in Example 4 was carried out to obtain a laminated sheet with a total thickness of 50 μm.

[0237] Example 9 In [Sheet Preparation 1] of Example 1, 90 parts by mass of the substituent-removed fine fibrous cellulose dispersion was mixed with 10 parts by mass of the diluted polyvinyl alcohol aqueous solution to obtain a mixed solution. Except for using this mixed solution, the same operation as in Example 4 was carried out to obtain a laminated sheet with a total thickness of 50 μm.

[0238] Example 10 The mixed solution obtained in Example 1 [Sheet Preparation 1] was measured so that the finished thickness of the sheet would be 50 μm and spread on a commercially available glass plate. A damming frame (internal dimensions 250 mm × 250 mm, height 5 cm) was placed on the glass plate to achieve the desired thickness. It was then dried in a 140 ° C. dryer for 1 hour and peeled off from the glass plate to obtain a sheet C with a thickness of 50 μm. Next, sheet C was inverted, and the surface opposite the glass plate peeled surface was attached to the glass plate. A damming frame (internal dimensions 200 mm × 200 mm, height 5 cm) was placed on top of it, and the same mixed solution was measured so that the finished thickness would be 50 μm, spread, and dried in a 140 ° C. dryer for 1 hour. The sheet was peeled off from the glass plate to obtain a laminated sheet with a total thickness of 100 μm.

[0239] Example 11 The mixed solution obtained in [Sheet Preparation 1] of Example 1 was weighed so that the finished thickness of the sheet would be 50 μm, and spread on a commercially available glass plate. A damming frame (inner dimensions 250 mm × 250 mm, height 5 cm) was placed on the glass plate to achieve the desired thickness. The sheet was then dried in a dryer at 140 ° C. for 1 hour and peeled off from the glass plate to obtain a 50 μm-thick sheet C (first layer). Next, Sheet C was inverted, and the surface opposite the peeled surface of the glass plate was attached to the glass plate. A blocking frame (inner dimensions 200 mm x 200 mm, height 5 cm) was placed on top of this, and the same mixed liquid was weighed and spread on top of this to a finished thickness of 50 μm, and dried in a dryer at 140°C for 1 hour (second layer).The same mixed liquid was then weighed and spread on top of this to a finished thickness of 50 μm, and dried in a dryer at 140°C for 1 hour (third layer).Then, it was peeled off from the glass plate to obtain Sheet D with a total thickness of 150 μm. Next, Sheet D was inverted, and the surface opposite to the glass plate peeled surface was attached to a glass plate. A frame for blocking (inner dimensions 150 mm x 150 mm, height 5 cm) was placed, and the same mixed solution was lightly weighed and spread on the first layer described above so that the finished thickness would be 50 μm, and dried in a dryer at 140 ° C for 1 hour (fourth layer), and peeled from the glass plate to obtain a laminated sheet with a total thickness of 200 μm. Note that the laminated sheet obtained in Example 11 was laminated in the order of fourth layer / first layer / second layer / third layer.

[0240] Example 12 A resin composition was obtained by mixing 100 parts by mass of an acrylic resin (manufactured by Taisei Fine Chemical Co., Ltd., ACRYT 8KX-012C, solid content concentration 39% by mass) in which acryloyl groups having hydroxyl groups were graft-polymerized, 38 parts by mass of a polyisocyanate compound (manufactured by Asahi Kasei Chemicals Corporation, TPA-100), and 100 parts by mass of methyl ethyl ketone. Next, one side of the 50 μm-thick laminate sheet obtained in Example 4 was coated with 3 g / m 2 of acrylic acid with a bar coater after drying. 2 After applying the resin layer on one side, the mixture was heated at 100° C. for 1 hour to obtain a laminated sheet having a resin layer on one side.

[0241] Example 13 A resin coating liquid was obtained by mixing 15 parts by mass of a modified polycarbonate resin (Iupizeta FPC-2136, manufactured by Mitsubishi Gas Chemical Company, Inc.), 57 parts by mass of toluene, and 28 parts by mass of methyl ethyl ketone. Next, 2.25 parts by mass of an isocyanate compound (Duranate TPA-100, manufactured by Asahi Kasei Chemicals Corporation) was added as an adhesion aid to the resin coating liquid and mixed to obtain a resin composition. Next, the resin composition was applied to one side of the 50 μm-thick laminate sheet obtained in Example 4 using a bar coater, and after drying, the coating amount on each side was 3 g / m. 2 After that, the resin composition was applied to the opposite surface using a bar coater and dried, and the applied amount after drying on each surface was 3 g / m. 2 After coating so that the resin layer was formed, the resin layer was cured by heating at 100° C. for 1 hour. In this way, a laminated sheet having a resin layer on both sides was obtained.

[0242] Example 14 The substituent removal treatment in Example 1 was carried out at a liquid temperature of 140° C. for 20 minutes to adjust the amount of phosphate groups to 0.40 mmol / g. Except for this, the same operation as in Example 4 was carried out to obtain a laminated sheet.

[0243] Example 15 In the substituent removal treatment in Example 1, heat treatment was carried out without pH adjustment, and the amount of phosphate groups was set to 0.29 mmol / g. Except for this, the same operation as in Example 4 was carried out to obtain a laminated sheet.

[0244] Example 16 The substituent removal treatment in Example 1 was carried out by the following enzyme treatment instead of heat treatment, and further, the slurry after the substituent removal was washed by the following method. Except for this, the same operations as in Example 4 were carried out to obtain a laminated sheet.

[0245] [Substituent removal treatment (enzyme treatment)] A 20% by mass aqueous solution of citric acid was added to the obtained fine fibrous cellulose dispersion, and the slurry was adjusted to pH 5.5. Acid phosphatase (Sumiteam PM, manufactured by Shin-Nippon Chemical Industry Co., Ltd.) was added to the obtained slurry in an amount of 3 parts by mass per 100 parts by mass of fine fibrous cellulose, and the mixture was subjected to enzyme treatment in a water bath at 37°C for 2.5 hours. The formation of fine fibrous cellulose aggregates was confirmed by this procedure.

[0246] [Washing treatment of slurry after removal of substituents by enzyme treatment] To the resulting slurry after the removal of the substituents, one-fifth by volume of a strongly basic ion exchange resin (Amberjet 4400; Organo Corporation, conditioned) and a weakly acidic ion exchange resin (Amberlite IRC76; Organo Corporation, conditioned) were added, and the mixture was shaken for 1 hour. After that, the slurry was washed by pouring it onto a mesh with 90 μm openings to separate the resin from the slurry.

[0247] Example 17 A laminated sheet was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example 2 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 1.

[0248] Example 18 A laminated sheet was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example 3 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 1.

[0249] Example 19 A laminated sheet was obtained in the same manner as in Example 4, except that the fine fibrous cellulose dispersion obtained in Production Example 4 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 1.

[0250] Example 20 The fine fibrous cellulose dispersion obtained in Production Example 5 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 1. Further, the same operation as in Example 4 was carried out, except that the substituent removal treatment (low-temperature heat treatment) described below was carried out instead of the substituent removal treatment (high-temperature heat treatment), to obtain a laminated sheet.

[0251] [Removal of substituents (low-temperature heat treatment)] The obtained fine fibrous cellulose dispersion was heated at a liquid temperature of 40°C for 45 minutes until the amount of xanthate groups became less than 0.08 mmol / g.

[0252] <Example 21> A fine fibrous cellulose-containing laminated sheet was obtained in the same manner as in Example 4, except that the treatment for uniformly dispersing the slurry after removing the substituents was not carried out.

[0253] <Example 22> A laminated sheet containing fine fibrous cellulose was obtained in the same manner as in Example 18, except that the treatment for uniformly dispersing the slurry after removing the substituents was not carried out.

[0254] Example 23 A laminated sheet containing fine fibrous cellulose was obtained in the same manner as in Example 19, except that the treatment for uniformly dispersing the slurry after removing the substituents was not carried out.

[0255] Example 24 A laminated sheet containing fine fibrous cellulose was obtained in the same manner as in Example 20, except that the treatment for uniformly dispersing the slurry after removing the substituents was not carried out.

[0256] Example 25 PEO-15 (manufactured by Sumitomo Seika Chemicals Co., Ltd.) was added to ion-exchanged water to a concentration of 6% by mass, and the mixture was stirred at room temperature for 30 minutes to dissolve. An aqueous polyethylene oxide solution was obtained by the above procedure. Next, the substituent-removed microfibrous cellulose dispersion and the above polyethylene oxide aqueous solution were each diluted with ion-exchanged water to a solids concentration of 0.6% by mass. 50 parts by mass of the diluted substituent-removed microfibrous cellulose dispersion were mixed with 50 parts by mass of the diluted polyethylene oxide aqueous solution to obtain a mixed solution. A laminated sheet with a total thickness of 50 μm was obtained by the same procedure as in Example 4, except that the mixed solution was used instead of the polyvinyl alcohol aqueous solution.

[0257] <Comparative Example 1> Instead of the substituent-removed fine fibrous cellulose dispersion, the fine fibrous cellulose dispersion obtained in Production Example 1 was used, and 50 parts by mass of the fine fibrous cellulose dispersion was mixed with 50 parts by mass of the diluted aqueous polyvinyl alcohol solution to obtain a mixed solution. The mixed solution was then weighed so that the finished thickness of the sheet would be 25 μm, and spread on a commercially available glass plate. A damming frame (inner dimensions 250 mm × 250 mm, height 5 cm) was placed on the glass plate to achieve the desired thickness. The sheet was then dried in a dryer at 140 ° C. for 1 hour and peeled off from the glass plate to obtain a sheet with a thickness of 25 μm.

[0258] <Comparative Example 2> Instead of the substituent-removed fine fibrous cellulose dispersion, the fine fibrous cellulose dispersion obtained in Production Example 3 was used, and 50 parts by mass of the fine fibrous cellulose dispersion were mixed with 50 parts by mass of diluted aqueous polyvinyl alcohol to obtain a mixed solution. The mixed solution was then weighed out so that the finished thickness of the sheet would be 50 μm, and spread on a commercially available glass plate. A damming frame (inner dimensions 250 mm × 250 mm, height 5 cm) was placed on the glass plate to achieve the desired thickness. The sheet was then dried in a dryer at 140 ° C. for 1 hour and peeled off from the glass plate to obtain a sheet with a thickness of 50 μm.

[0259] <Comparative Example 3> Instead of the substituent-removed fine fibrous cellulose dispersion, the fine fibrous cellulose dispersion obtained in Production Example 4 was used, and 50 parts by mass of the fine fibrous cellulose dispersion was mixed with 50 parts by mass of the diluted aqueous polyvinyl alcohol solution to obtain a mixed solution. The mixed solution was then weighed out so that the finished thickness of the sheet would be 50 μm, and spread on a commercially available glass plate. A damming frame (inner dimensions 250 mm × 250 mm, height 5 cm) was placed on the glass plate to achieve the desired thickness. The sheet was then dried in a dryer at 140 ° C. for 1 hour and peeled off from the glass plate to obtain a sheet with a thickness of 50 μm.

[0260] <Comparative Example 4> Instead of the substituent-removed fine fibrous cellulose dispersion, the fine fibrous cellulose dispersion obtained in Production Example 5 was used, and 50 parts by mass of the fine fibrous cellulose dispersion was mixed with 50 parts by mass of the diluted aqueous polyvinyl alcohol solution to obtain a mixed solution. The mixed solution was then weighed out so that the finished thickness of the sheet would be 200 μm, and spread on a commercially available glass plate. A damming frame (inner dimensions 250 mm × 250 mm, height 5 cm) was placed on the glass plate to achieve the desired thickness. The sheet was then dried in a dryer at 140 ° C. for 1 hour and peeled off from the glass plate to obtain a sheet with a thickness of 200 μm.

[0261] <Comparative Example 5> A sheet was obtained in the same manner as in Comparative Example 1, except that the mixed solution of Example 1 was used instead of the mixed solution of Comparative Example 1.

[0262] <Comparative Example 6> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 1 was used instead of the mixed solution of Comparative Example 2.

[0263] <Comparative Example 7> A sheet was obtained in the same manner as in Comparative Example 4, except that the mixed solution of Example 1 was used instead of the mixed solution of Comparative Example 4.

[0264] <Comparative Example 8> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 14 was used instead of the mixed solution of Comparative Example 2.

[0265] <Comparative Example 9> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 15 was used instead of the mixed solution of Comparative Example 2.

[0266] <Comparative Example 10> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 16 was used instead of the mixed solution of Comparative Example 2.

[0267] <Comparative Example 11> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 17 was used instead of the mixed solution of Comparative Example 2.

[0268] <Comparative Example 12> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 18 was used instead of the mixed solution of Comparative Example 2.

[0269] <Comparative Example 13> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 19 was used instead of the mixed solution of Comparative Example 2.

[0270] <Comparative Example 14> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 20 was used instead of the mixed solution of Comparative Example 2.

[0271] <Comparative Example 15> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 21 was used instead of the mixed solution of Comparative Example 2.

[0272] <Comparative Example 16> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 22 was used instead of the mixed solution of Comparative Example 2.

[0273] <Comparative Example 17> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 23 was used instead of the mixed solution of Comparative Example 2.

[0274] <Comparative Example 18> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 24 was used instead of the mixed solution of Comparative Example 2.

[0275] <Comparative Example 19> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 7 was used instead of the mixed solution of Comparative Example 2.

[0276] <Comparative Example 20> A sheet was obtained in the same manner as in Comparative Example 2, except that the mixed solution of Example 8 was used instead of the mixed solution of Comparative Example 2.

[0277] <Comparative Example 21> A sheet was obtained in the same manner as in Example 12, except that the 50 μm thick sheet obtained in Comparative Example 6 was used instead of the laminated sheet of Example 12.

[0278] <Comparative Example 22> A sheet was obtained in the same manner as in Example 13, except that the laminated sheet of Example 13 was replaced with the 50 μm thick sheet obtained in Comparative Example 6.

[0279] [evaluation] The laminated sheets or sheets obtained in the examples and comparative examples were evaluated by the following methods.

[0280] [Fiber width measurement] The fiber width of fibrous cellulose was measured using the following method. Each fibrous cellulose dispersion was diluted with water to a cellulose concentration of 0.01% by mass or more and 0.1% by mass or less and cast onto a hydrophilized carbon film-coated grid. After drying, the grid was stained with uranyl acetate and observed under a transmission electron microscope (TEM, JEOL-2000EX, manufactured by JEOL Ltd.). The obtained image was visualized by imagining arbitrary vertical and horizontal axes of the image width, and the magnification was adjusted so that 20 or more fibers intersected these axes. After obtaining observation images satisfying these conditions, two random axes were drawn vertically and horizontally per image, and the fiber widths of the fibers intersecting the axes were visually determined. Three unique observation images were taken for each dispersion, and the fiber widths of the fibers intersecting each of the two axes were read (20 or more × 2 × 3 = 120 or more). The number-average fiber width was calculated from the fiber widths obtained in this manner. However, for Examples 1 to 25 and Comparative Examples 5 to 22, the measurement was carried out using a dispersion of fine fibrous cellulose from which substituents had been removed, and for Comparative Examples 1 to 4, the measurement was carried out using a dispersion of fine fibrous cellulose.

[0281] [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 the slurry while adding 10 μL of 0.1 N sodium hydroxide solution every 5 seconds to a slurry containing fine fibrous cellulose after ion exchange resin treatment. Nitrogen gas was bubbled through the slurry 15 minutes before the start of the titration. In this neutralization titration, two maximum points of increment (the derivative of pH with respect to the amount of alkali added) were observed on the curve plotting the measured pH against the amount of alkali added. Of these, the first maximum point of increment after starting the alkali addition is called the first endpoint, and the second maximum point of increment is called the second endpoint (Figure 2). 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).

[0282] [Measurement of sulfonic acid group content] The amount of sulfonic acid groups was measured as follows. The fine fibrous cellulose was frozen in a freezer and then dried for three days in a freeze dryer (FreeZone, manufactured by Labconco). The freeze-dried material was then pulverized into powder using a hand mixer (Lab Millser PLUS, manufactured by Osaka Chemical) at 20,000 rpm for 60 seconds. The freeze-dried and pulverized sample was subjected to pressure-thermal decomposition using nitric acid in a sealed container. The sample was then appropriately diluted and the amount of sulfur was measured using ICP-OES. The value calculated by dividing by the bone-dry mass of the fine fibrous cellulose used was taken as the amount of sulfate ester groups (unit: mmol / g).

[0283] [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 fibrous cellulose. 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 using the following formula from the titration amount of sodium thiosulfate and the bone dry mass of 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)

[0284] [Measurement of total light transmittance of laminated sheets] The total light transmittance of the laminated sheet was measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K 7361-1:1997.

[0285] [Haze measurement of laminated sheets] The haze of the laminated sheet was measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K 7136:2000.

[0286] [Yellowness measurement of laminated sheet before and after heating] The yellowness index (YI value) of the laminated sheet was measured before and after heating using Colour Cute i (manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K 7373:2006. The YI value after heating was the YI value of the laminated sheet heated at 160°C for 6 hours. The YI increase rate was measured using the following method. YI increase rate (%) = (YI value of sheet after heating - YI value of sheet before heating) / YI value of sheet before heating × 100

[0287] [Curl measurement] The resulting laminated sheet was cut into 100 mm squares and left on a flat surface at 23°C and 50% relative humidity for at least 4 hours. After leaving the sheet, the heights (mm) of the four corners were measured, and the average value was used as the curl measurement. If the sheet curled excessively, it was marked as ∞.

[0288] [Calculation of C / O ratio (evaluation of uneven distribution of fine fiber cellulose in the fiber layer)] The distribution of fine fibrous cellulose in the fiber layer was determined by calculating the atomic percentage ratio of carbon (C) to oxygen (O) (C / O ratio) using XPS (X-ray photoelectron spectroscopy). When analyzing a laminate sheet, the atomic percentage ratio of carbon (C) to oxygen (O) was calculated for the front and back surfaces of the laminate sheet and the interface between each layer. For example, if each fiber layer is 25 μm thick and two such fiber layers are laminated together to form a 50 μm-thick laminate sheet, XPS analysis was performed on the front surface of the laminate sheet, followed by carefully scraping the laminate sheet with a commercially available razor and XPS analysis of the area scraped 25 μm from the surface. Similarly, XPS analysis was performed on the back surface of the laminate sheet, followed by carefully scraping the laminate sheet with a commercially available razor and XPS analysis of the area scraped 25 μm from the surface. XPS analysis was performed at a measurement depth of 5 nm. While a 1 mm square area is sufficient, scraping a larger area is acceptable for ease of operation. When the laminate sheet had a resin layer, the resin layer was wiped off with a solvent such as MEK to expose the fiber layer, and then the above measurements were carried out.

[0289] [Measurement of pH on the surface of laminated sheets] 10 μL of ion-exchanged water was dropped onto a 1 cm square area on the surface of the laminated sheet using a micropipette, and the pH of that area was measured using a flat pH composite electrode (6261-10C; manufactured by HORIBA). Measurements were taken on both the front and back sides of the sheet, and the average value was taken as the surface pH of the sheet.

[0290] [Table 2]

[0291] [Table 3]

[0292] [Table 4]

[0293] [Table 5]

[0294] AC: Acrylic PIC: Polyisocyanate PC: Polycarbonate OSi: organosilane

[0295] The laminated sheets obtained in the examples had both yellowing resistance and curl resistance.

[0296] <Example 101> (Lamination with resin film) A resin coating liquid was obtained by mixing 15 parts by mass of a modified polycarbonate resin (Iupizeta FPC-2136, manufactured by Mitsubishi Gas Chemical Company, Inc.), 57 parts by mass of toluene, and 28 parts by mass of methyl ethyl ketone. Next, 2.25 parts by mass of an isocyanate compound (Duranate TPA-100, manufactured by Asahi Kasei Chemicals Corporation) as an adhesion aid was added to the resin coating liquid and mixed to obtain a resin composition. Next, the resin composition was applied as a resin film to one side of a 0.3 mm thick polycarbonate sheet (Panlite PC-2151, manufactured by Teijin Limited) using a bar coater in a coating amount of 3 g / m after drying. 2After coating so that the resin film was coated, the mixture was heated at 100°C for 1 hour to cure. Thereafter, the same operation as in Sheet Preparation 1 in Example 1 was carried out, except that the commercially available glass plate used in Sheet Preparation 1 in Example 1 was replaced with a laminate of the resin film and the resin composition, to obtain a 25µm laminate sheet and a laminate of the resin film.

[0297] <Example 102> A resin composition was obtained by mixing 76 parts by mass of a specially modified polyester resin (Arakawa Chemical Industries, Ltd., Aracoat AP2510), 10 parts by mass of a curing agent (Arakawa Chemical Industries, Ltd., CL2502), and 14 parts by mass of methyl ethyl ketone. Next, the resin composition was applied as a resin film to one side of a 0.35 mm thick polyester sheet (Toray Industries, Inc., Lumirror S10) using a bar coater in an amount of 3 g / m after drying. 2 After coating so that the thickness was such that the resin film was thicker than the glass plate, the resin film was heated at 100° C. for 1 hour to cure the resin film. Then, the same operation as in Sheet Preparation 1 in Example 1 was carried out using a laminate of the resin film and the resin composition instead of the commercially available glass plate, to obtain a laminate of a laminate sheet and a resin film having a fiber layer thickness of 25 μm.

[0298] <Example 103> Two 100 mm square pieces of the laminate sheet obtained in Example 13 were prepared by trimming. A 100 mm square, 0.5 mm thick polycarbonate plate was sandwiched between two of these laminate sheets, and these were then sandwiched between two 200 mm square stainless steel plates. The sheet was then inserted into a mini test press (MP-WCH, manufactured by Toyo Seiki Kogyo Co., Ltd.) set at room temperature and heated to 160°C over 3 minutes under a pressure of 0.2 MPa. This state was maintained for 30 seconds, and then cooled to 30°C over 3 minutes. This procedure yielded a laminate with a polycarbonate plate.

[0299] <Example 104> A resin composition was obtained by mixing 76 parts by mass of a special modified polyester resin (Arakawa Chemical Industries, Ltd., Aracoat AP2510), 10 parts by mass of a curing agent (Arakawa Chemical Industries, Ltd., CL2502), and 14 parts by mass of methyl ethyl ketone. Next, the resin composition was applied to one side of the 50 μm-thick laminate sheet obtained in Example 4 using a bar coater in a coating amount of 3 g / m after drying. 2 After that, the resin composition was applied to the opposite surface using a bar coater so that the coating amount after drying was 3 g / m. 2 After applying the resin so that the thickness of the laminate was 100°C, the resin was cured by heating for 1 hour. In this way, a laminate sheet having a resin layer on both sides was obtained. A laminate with a polyethylene terephthalate plate was obtained in the same manner as in Example 103, except that the laminate sheet of Example 13 was replaced with the above laminate sheet and a polyethylene terephthalate plate was used instead of the polycarbonate plate. [Explanation of symbols]

[0300] 10 Fiber layer (first fiber layer) 20 Fiber layer (second fiber layer) 100 laminated sheets

Claims

1. A laminated sheet obtained by directly laminating two or more fiber layers containing fibrous cellulose having an introduced amount of substituents of less than 0.5 mmol / g and a fiber width of 1000 nm or less, A laminated sheet, wherein each fiber layer has a different content of the fibrous cellulose in the thickness direction.

2. The laminate sheet according to claim 1 , wherein the fiber layer further comprises an oxygen-containing organic compound, and the ratio of atomic % of carbon C to oxygen O in the oxygen-containing organic compound is 1.8 or more.

3. 3. The laminate sheet according to claim 2, wherein the difference in atomic % ratio between carbon C and oxygen O on the front and back surfaces of the laminate sheet is 0.2 or less.

4. A laminated sheet obtained by directly laminating two fiber layers containing fibrous cellulose having an introduced amount of substituents of less than 0.5 mmol / g and a fiber width of 1000 nm or less, 4. The laminated sheet according to claim 1, wherein the fibrous cellulose is unevenly distributed on the side where the fiber layers contact each other.

5. The laminate sheet according to any one of claims 1 to 4, wherein the substituent is an anionic group.

6. The laminate sheet according to claim 5 , wherein the anionic group is a phosphorus oxo acid group or a functional group derived from a phosphorus oxo acid group.

7. The laminated sheet according to any one of claims 1 to 6, wherein the fibrous cellulose has a carbamide group.

8. The laminate sheet according to any one of claims 1 to 7, wherein the total thickness of the fiber layer is 20 µm or more.

9. The overall density of the fiber layer is 1.0 g / cm ３ The laminate sheet according to any one of claims 1 to 8.

10. The laminate sheet according to any one of claims 1 to 9, wherein the number average fiber width of the fibrous cellulose contained in the fiber layer is 1 to 10 nm.

11. The laminate sheet according to any one of claims 1 to 10, further comprising a resin layer on at least one surface side of the fiber layer.

12. The laminate sheet according to claim 11 , wherein the resin layer is directly laminated on the fiber layer.

13. The laminate sheet according to claim 11 or 12, wherein the resin layer contains at least one resin selected from a polycarbonate resin and an acrylic resin.

14. The laminate sheet according to any one of claims 11 to 13, wherein the resin layer further contains an adhesion aid.

15. The laminate sheet according to claim 14, wherein the adhesion aid is at least one selected from an isocyanate compound and an organosilicon compound.

16. The laminate sheet according to claim 14 or 15, wherein the adhesion aid is an isocyanate compound, and the content of the isocyanate compound is 10 parts by mass or more and 40 parts by mass or less relative to 100 parts by mass of the resin contained in the resin layer.

17. The laminate sheet according to any one of claims 1 to 16, having a YI value of 2.5 or less.

18. The laminate sheet according to any one of claims 1 to 17, having a haze of 80% or less.

19. The laminate sheet according to any one of claims 1 to 18, which is for use as an optical member.

20. A laminate comprising the laminate sheet according to any one of claims 1 to 19 and an adherend.

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