Laminated sheet

Abstract

The present invention addresses the problem of providing a laminated sheet which has a fiber layer containing microfibrous cellulose, and is provided with yellowing resistance and curling resistance. The present invention pertains to a laminated sheet obtained by directly layering at least two fiber layers containing fibrous cellulose, the substituent group introduction amount of which is less than 0.5mmol / g, and the fiber width of which is no greater than 1,000nm, wherein each fiber layer has a different fibrous cellulose content percentage in the thickness direction thereof.

Description

[Technical Field]

[0001] This invention relates to a laminated sheet. [Background technology]

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

[0003] Among fibrous celluloses, fine fibrous cellulose with a fiber diameter of 1 μm or less is also known. Fine fibrous cellulose is attracting attention as a new material, and its applications are diverse. For example, development is underway on sheets, resin composites, and thickeners containing fine fibrous cellulose.

[0004] For example, Patent Document 1 discloses a method for producing microfibers, comprising the steps of (a) introducing substituents having electrostatic and / or steric functionalities into a microfiber raw material to obtain substituent-introduced fibers, (b) mechanically processing the substituent-introduced fibers, and (c) removing some or all of the introduced substituents from the substituent-introduced microfibers obtained in step (b) to obtain substituent-removed microfibers. Patent Document 2 also discloses a method for producing a de-esterified compound, comprising the step of heating a compound having an ester derived from phosphoric acid and / or an ester derived from a carboxylic acid in the presence of a nitrogen-containing compound exhibiting basicity. These documents explore the removal of substituents introduced into microfibers.

[0005] Patent Document 3 discloses a method for manufacturing a microfiber-containing sheet, comprising at least the steps of: (a) introducing substituents having electrostatic and / or steric functionalities into a fiber raw material to obtain substituent-introduced fibers; (b) mechanically processing the substituent-introduced fibers obtained in step (a) to obtain substituent-introduced microfibers; (c) preparing a sheet from the substituent-introduced microfibers obtained in step (b); and (d) removing at least a portion of the introduced substituents from the sheet obtained in step (c). Here, a method for removing substituents after forming a sheet from substituent-containing microfibers is being investigated.

[0006] Furthermore, Patent Documents 4 and 5 disclose a method for producing cellulose xantate nanofibers, which involves defibrating cellulose xantate or a cation-substituted cellulose xantate. Patent Document 4 also investigates a method for returning cellulose xantate nanofibers to unmodified cellulose by regenerating them as needed. In addition, Patent Document 5 discloses a sheet containing derivative functional group-depleted cellulose microfibers, in which functional groups are removed from cellulose derivative microfibers, resulting in an average fiber diameter of 3 nm to 300 nm. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2013 / 176049 [Patent Document 2] Japanese Patent 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 Publication No. 2019-7101 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In the process of advancing research on a sheet containing microfibrillar cellulose, the inventors have found that coloring or curling may occur in the process of manufacturing or storing the sheet containing microfibrillar cellulose.

[0009] Therefore, in order to solve such problems of the prior art, the inventors have proceeded with investigations aiming to provide a sheet containing microfibrillar cellulose that has both yellowing resistance and curl resistance.

Means for Solving the Problems

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

[0011] [1] A laminated sheet formed by directly laminating two or more fiber layers containing fibrillar cellulose with a substituent introduction amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less, wherein each fiber layer has a different content rate of fibrillar cellulose in the thickness direction, the laminated sheet. [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 of the oxygen-containing organic compound is 1.8 or more. [3] The laminated sheet according to [2], wherein the difference in the ratio of atomic% of carbon C to oxygen O between the front and back surfaces of the laminated sheet is 0.2 or less. [4] A laminated sheet formed by directly laminating two fiber layers containing fibrillar cellulose with a substituent introduction amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less, A laminated sheet according to any one of [1] to [3], wherein fibrous cellulose is unevenly distributed on the side where each fiber layer is in contact. [5] A laminated sheet according to any one of [1] to [4], wherein the substituent is an anionic group. [6] The laminated sheet according to [5], wherein the anionic group is a phosphorus oxoacid group or a functional group derived from a phosphorus oxoacid group. [7] A laminated sheet according to any one of [1] to [6], wherein the fibrous cellulose has a carbamide group. [8] A laminated 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 / cm³ 3 The laminated sheet described in any of [1] to [8] above.

[10] A laminated 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] A laminated 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 laminated sheet according to

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

[13] The laminated sheet according to

[11] or

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

[14] The laminated sheet according to any one of

[11] to

[13] , wherein the resin layer further comprises an adhesion promoter.

[15] The laminated sheet according to

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

[16] 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 resin contained in the resin layer, as described in

[14] or

[15] .

[17] A laminated sheet described in any of [1] to

[16] , wherein the YI value is 2.5 or less.

[18] A laminated sheet as described in any of [1] to

[17] , wherein the haze is 80% or less.

[19] A laminated sheet as described in any of [1] to

[18] , for use as an optical component.

[20] A laminate comprising a laminated sheet described in any of [1] to

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

[0012] According to the present invention, a laminated sheet can be obtained that possesses both resistance to yellowing and resistance to curling. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a cross-sectional view illustrating the structure of the laminated sheet of the present invention. [Figure 2] Figure 2 is a graph showing the relationship between the amount of NaOH added to a slurry containing fibrous cellulose with phosphorus oxoacid groups and the pH. [Modes for carrying out the invention]

[0014] The present invention will be described in detail below. The following descriptions of constituent elements may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, numerical ranges represented by "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits.

[0015] (Laminated sheet) The present invention relates to a laminated sheet obtained by directly laminating two or more fiber layers containing fibrous cellulose, the substituent amount being less than 0.5 mmol / g and the fiber width being 1000 nm or less. In this laminated sheet, each fiber layer has a different fibrous cellulose content in the thickness direction of each fiber layer.

[0016] Figure 1 is a cross-sectional view illustrating the structure of the laminated sheet of the present invention. As shown in Figure 1, the laminated sheet of the present invention has two or more fiber layers. In Figure 1, a laminated sheet 100 having two fiber layers is illustrated, in which case the laminated sheet 100 has a fiber layer 10 (first fiber layer) and a fiber layer 20 (second fiber layer). Furthermore, each fiber layer is directly laminated to the others.

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

[0018] The fibrous cellulose content of each fiber layer can be determined, for example, by measuring the fibrous cellulose content on the front and back surfaces of each fiber layer. If the fibrous cellulose content on the front and back surfaces differs, it can be determined that the fibrous cellulose content of each fiber layer fluctuates in the thickness direction. The fibrous cellulose content on the front and back surfaces of each fiber layer can be evaluated, for example, by calculating the atomic percentage ratio of carbon (C) to oxygen (O), as described later.

[0019] Conventionally, to obtain highly transparent sheets, researchers have investigated increasing the amount of substituents introduced into fine fibrous cellulose, thereby obtaining fine fibrous cellulose with a smaller fiber width. However, when fine fibrous cellulose with a high amount of substituents is incorporated into a sheet in this way, the sheet tends to become discolored when heated during the sheet manufacturing process or in the usage environment. To solve this problem, it is conceivable to control the substituent introduction process to keep the amount of substituents introduced into the fine fibrous cellulose low. However, the inventors have discovered 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 extremely during the sheet manufacturing process, and a flat sheet cannot be obtained. Therefore, the inventors have diligently investigated how to manufacture a sheet in which curling is suppressed even when the amount of substituents introduced into the fine fibrous cellulose is low. As a result, the inventors found that by laminating two or more fiber layers containing fibrous cellulose with a substituent amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less, and further varying the fibrous cellulose content of each fiber layer in the thickness direction, it is possible to suppress both discoloration and curling in the sheet. Thus, the present invention has succeeded in suppressing discoloration and curling in a sheet containing fine fibrous cellulose with a low substituent amount.

[0020] In this embodiment, the YI value of the laminated sheet is preferably 2.5 or less, and more preferably 2.0 or less. The lower limit of the YI value of the laminated sheet is not particularly limited, but it is preferably 0.1 or higher. Here, the YI value of the laminated sheet is the YI value measured in accordance with JIS K 7373:2006. For example, a Colour Cute i (manufactured by Suga Test Instruments Co., Ltd.) can be used as the YI value measuring device. The YI value described above is the YI value measured before heating the laminated sheet, as will be described later, and is therefore sometimes referred to as the initial YI value.

[0021] In this embodiment, the YI value after heating the laminated sheet 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 laminated sheet after heating at 160°C for 6 hours is not particularly limited, but it is preferably 0.1 or higher. 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 in the laminated 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 in the laminated sheet is not particularly limited, but it is preferably 0.1% or more. Here, the YI increase rate of the laminated sheet is the increase in the YI value of the laminated sheet before and after heating the laminated sheet at 160°C for 6 hours. Specifically, the YI increase rate is 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 laminated sheet is the YI value measured in accordance with JIS K 7373:2006.

[0023] The curl resistance of the laminated sheet in this embodiment can be evaluated by measuring the height (curl amount) (mm) of the four corners of the sheet after a predetermined period of time. Specifically, the laminated sheet is cut into 100 mm squares and left on a flat surface for 4 hours or more in an environment of 23°C and 50% relative humidity. After leaving it, the height (mm) of the four corners of the sheet is measured, and the average value is taken as the measured curl amount. The measured 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 amount is within the above range, the laminated sheet can be evaluated as having excellent curl resistance.

[0024] The total light transmittance of the laminated sheet is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and particularly preferably 80% or more. Furthermore, if even greater transparency is required for optical components, the total light transmittance of the laminated sheet is preferably 85% or more, and more preferably 90% or more. By setting the total light transmittance of the laminated sheet within the above range, it becomes possible to apply the laminated sheet of the present invention to applications where transparent glass was conventionally used. Here, the total light transmittance is a value measured using a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute Co., Ltd.) in accordance with JIS K 7361-1:1997.

[0025] The haze of the laminated sheet is preferably 80% or less, more preferably 70% or less, and more preferably 60% or less. If further transparency is required for optical components, the haze of the laminated sheet is preferably 10% or less, more preferably 5% or less, and more preferably 2% or less. The lower limit of the haze of the laminated sheet is not particularly limited and may be 0%. Here, the haze is a value measured using a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute Co., Ltd.) in accordance with JIS K 7136:2000.

[0026] The overall thickness of the laminated 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. Furthermore, the overall thickness of the laminated sheet is preferably 1000 μm or less. The thickness of the laminated sheet can be adjusted as appropriate depending on the application.

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

[0028] The overall density of the fiber layer constituting the laminated sheet is preferably 1.0 g / cm 3 or more, more preferably 1.2 g / cm 3 or more, still more preferably 1.4 g / cm 3 or more. Also, the overall density of the fiber layer constituting the laminated sheet is preferably 1.7 g / cm 3 or less, more preferably 1.65 g / cm 3 or less, still more preferably 1.6 g / cm 3 or less.

[0029] The density of the fiber layer is calculated in accordance with JIS P 8118:2014 from the basis weight and thickness of the fiber layer. 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 microfibrillated cellulose, the density of the fiber layer is the density including any component other than microfibrillated cellulose.

[0030] In this embodiment, the fiber layer is preferably a non-porous layer. Here, the fiber layer being non-porous means that the overall density of the fiber layer is 1.0 g / cm 3 or more. If the overall density of the fiber layer is 1.0 g / cm 3 or more, it means that the porosity contained in the fiber layer is suppressed to a predetermined value or less, and it is distinguished from a porous sheet or layer. Also, the fiber layer being non-porous is also characterized by the porosity being 15% by volume or less. The porosity of the fiber layer referred to here is simply determined by the following formula (a). Equation (a): Void ratio (volume %) = {1 - B / (M × A × t)} × 100 Here, A is the area of ​​the fiber layer (cm²). 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 also particularly preferable that the surface roughness of both surfaces of the fiber layer be within the above range. By setting the surface roughness within the above range, the transparency of the laminated sheet can be increased. Specifically, the haze of the laminated sheet can be reduced. Here, the arithmetic mean surface roughness of the fiber layer is the arithmetic mean roughness of at least one surface of the fiber layer. The arithmetic mean surface roughness 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. Furthermore, the surface pH of the fiber layer is preferably 10 or lower, more preferably 9 or lower, and even more preferably 8 or lower. Setting the surface pH of the fiber layer within the above range makes it easier to obtain the effect of suppressing yellowing. In order to set 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 manufacturing process described later. When measuring the surface pH of the fiber layer, 10 μL of deionized water is dropped onto a 1 cm square area on the surface of the fiber layer using a micropipette, and the pH of that area is measured using a flat-type pH composite electrode (6261-10C; manufactured by HORIBA).

[0033] The fiber layers constituting the laminated sheet may be two or more, preferably 10 or fewer, more preferably 8 or fewer, and even more preferably 6 or fewer. In particular, it is especially preferable that the fiber layers constituting the laminated sheet be two. When the fiber layers constituting the laminated sheet are two, it is preferable that the fibrous cellulose is unevenly distributed on the side where each fiber layer is in contact. That is, in a laminated sheet formed by directly laminating two fiber layers containing fibrous cellulose with a composting 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 is present in the region near the interface of each fiber layer.

[0034] Furthermore, when the fiber layers constituting the laminated sheet consist of an even number of layers, it is preferable that the fibrous cellulose is present symmetrically with respect to the central plane of all fiber layers. In other words, it is preferable that the fibrous cellulose content varies symmetrically from the central plane of all fiber layers to each surface.

[0035] In this embodiment, the laminated sheet preferably contains an oxygen-containing organic compound in the fiber layer. 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. Hydrophilic oxygen-containing organic compounds can improve the strength, density, and chemical resistance of the fiber layer. The hydrophilic oxygen-containing organic compound is preferably such that its SP value is 9.0 or higher. Furthermore, the hydrophilic oxygen-containing organic compound is preferably such that 1 g or more of the oxygen-containing organic compound dissolves in 100 ml of deionized 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, alkyl acrylate copolymers, urethane copolymers, and cellulose derivatives (hydroxyethylcellulose, carboxyethylcellulose, carboxymethylcellulose, etc.); and hydrophilic low molecular weight compounds such as glycerin, sorbitol, and ethylene glycol. Among these, oxygen-containing organic compounds with an atomic% ratio of carbon (C) to oxygen (O) of 1.8 or higher are preferably used. Specifically, polyvinyl alcohol, modified polyvinyl alcohol, polyalkylene oxides (polyethylene oxide, polypropylene oxide, etc.), and polyacrylamide are preferably used as oxygen-containing organic compounds. Note that the atomic% ratio of carbon (C) to oxygen (O) of oxygen-containing organic compounds is a theoretical value calculated from the number of carbon and oxygen atoms. Thus, it is preferable that each fiber layer in the laminated sheet of the present invention contains fibrous cellulose having a substituent introduction 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 with a molecular weight of 50,000 to 8,000,000. While the molecular weight of the oxygen-containing organic compound is preferably between 100,000 and 5,000,000, it may also be a low molecular weight, for example, less than 1,000.

[0039] The content of oxygen-containing organic compounds 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 fibrous cellulose contained in each fiber layer. Furthermore, the content of oxygen-containing organic compounds 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 fine fibrous cellulose contained in each fiber layer.

[0040] In the laminated sheet of this embodiment, the difference in the ratio of atomic percent of 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, the difference in the ratio of atomic percent of carbon (C) and oxygen (O) on the front and back surfaces is preferably 0. By keeping the difference in the ratio of atomic percent of carbon (C) and oxygen (O) on the front and back surfaces of the laminated sheet within the above range, the curl resistance of the laminated sheet can be more effectively improved.

[0041] Each fiber layer may contain additional optional components in addition to fibrous cellulose and the oxygen-containing organic compounds mentioned above. Examples of optional components include defoamers, lubricants, UV absorbers, dyes, pigments, stabilizers, surfactants, and preservatives (e.g., phenoxyethanol).

[0042] Furthermore, each fiber layer may contain organic ions as optional components. Examples of organic ions include tetraalkylammonium ions and tetraalkylphosphonium ions. Examples of tetraalkylammonium ions include tetramethylammonium ions, tetraethylammonium ions, tetrapropylammonium ions, tetrabutylammonium ions, tetrapentylammonium ions, tetrahexylammonium ions, tetraheptylammonium ions, tributylmethylammonium ions, lauryltrimethylammonium ions, cetyltrimethylammonium ions, stearyltrimethylammonium ions, octyldimethylethylammonium ions, lauryldimethylethylammonium ions, didecyldimethylammonium ions, lauryldimethylbenzylammonium ions, and tributylbenzylammonium ions. Examples of tetraalkylphosphonium ions include tetramethylphosphonium ions, tetraethylphosphonium ions, tetrapropylphosphonium ions, tetrabutylphosphonium ions, and lauryltrimethylphosphonium ions. In addition, examples of 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 laminated sheet contains fibrous cellulose with a substituent amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less. In this specification, fibrous cellulose with 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 microfiber 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 microfiber 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 fine fibrous cellulose with a fiber width of 1000 nm or less. More preferably, the fiber width of the fibrous cellulose is 100 nm or less, and even more preferably 8 nm or less. However, it is preferable that the fiber width of the fibrous cellulose is 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 so that the cellulose concentration is 0.01% by mass or more and 0.1% by mass or less, and cast onto a hydrophilized carbon film coated grid. After drying, it is stained with uranyl acetate and observed using a transmission electron microscope (TEM, JEOL-2000EX, manufactured by JEOL Ltd.). At that time, axes of arbitrary image width are assumed in the obtained image, both vertically and horizontally, and the magnification is adjusted so that 20 or more fibers intersect with these axes. After obtaining an observation image that satisfies this condition, two random axes are drawn vertically and horizontally for each image, and the fiber width of the fibers intersecting the axes is read visually. In this way, three non-overlapping observation images are taken, and the fiber width values ​​of the fibers that intersect the two axes are read (20 or more fibers × 2 × 3 = 120 or more fibers). (1) A straight line X is drawn at any point in the observed image, and 20 or more fibers intersect with this straight line X. (2) A line Y is drawn perpendicular to the line in the same image, and 20 or more fibers intersect with line Y. Furthermore, the number-average fiber width of the fine fibrous cellulose contained in the fiber layer can be calculated from the fiber width obtained by the above method.

[0047] Furthermore, the fact that the number-average fiber width of the fibrous cellulose contained in each fiber layer is 1 to 10 nm means that the fiber layer substantially does not contain coarse cellulose fibers, and moreover, that the fiber width of 70% or more of the fibrous cellulose is 10 nm or less. Of the total fibrous cellulose contained in the fiber layer, the proportion of fine fibrous cellulose with 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 percentage of fine fibrous cellulose with a fiber width of 10 nm or less is the 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 fibers with a fiber width of 10 nm or less / Total number of fibrous cellulose fibers) × 100

[0048] The fiber length of the fine fibrous cellulose is not particularly limited, but is preferably between 0.1 μm and 1000 μm, more preferably between 0.1 μm and 800 μm, and even more preferably between 0.1 μm and 600 μm. By keeping the fiber length within the above range, the breakdown of the crystalline region of the fine fibrous cellulose can be suppressed. It is also 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] It is preferable that the fine fibrous cellulose has a type I crystalline structure. Here, the presence of a type I crystalline structure in fine fibrous cellulose can be identified in the diffraction profile obtained from a wide-angle X-ray diffraction photograph using graphite-monochromatized CuKα (λ=1.5418Å). Specifically, it can be identified by the presence of typical peaks at two locations: around 2θ=14° to 17° and around 2θ=22° to 23°. The proportion of type I crystalline structure in the fine fibrous cellulose is 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 analyzing its pattern using a conventional method (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 50 to 10,000, and more preferably 100 to 1,000. Setting the axial ratio above the lower limit makes it easier to form a sheet containing the fine fibrous cellulose. Setting the axial ratio below the upper limit is preferable in that it makes handling easier, such as dilution, when handling the fibrous cellulose as a dispersion.

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

[0052] The cellulose components in microfibrous cellulose can be classified into α-cellulose components and hemicellulose components. A lower proportion of hemicellulose is preferable because it is easier to suppress yellowing over time and yellowing due to heat. The proportion of hemicellulose in the microfibrous 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 microfiber cellulose and the free nitrogen contained in the microfiber cellulose dispersion (hereinafter sometimes referred to as "nitrogen content," "amount of nitrogen contained in microfiber cellulose," or "amount of nitrogen in microfiber 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. Furthermore, the amount of nitrogen contained in the microfiber cellulose is preferably 0.001 mmol / g or more. The amount of nitrogen in the microfiber cellulose is measured by the following method. First, the dispersion containing microfiber cellulose is adjusted to a solid content 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 the nitrogen content (mmol / g) is calculated by dividing it by the amount of cellulose (g) used for measurement. The above nitrogen amount is the total amount of nitrogen bonded to the microfiber cellulose by ionic and / or covalent bonds, and free nitrogen dissolved in the dispersion that is not bonded to the microfiber cellulose by ionic and / or covalent bonds.

[0054] In this embodiment, the amount of substituent introduced into the microfibrous cellulose is less than 0.5 mmol / g, and the substituent is preferably anionic. That is, the microfibrous cellulose of the present invention is obtained by subjecting microfibrous cellulose having anionic groups to a substituent removal treatment, and the microfibrous cellulose of the present invention is substituent-removed microfibrous 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), carboxyl groups or substituents derived from carboxyl groups (sometimes simply referred to as carboxyl groups), sulfone groups or substituents derived from sulfone groups (sometimes simply referred to as sulfone groups), and xantate groups or substituents derived from xantate groups (sometimes simply referred to as xantate groups). When a sulfone group or 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 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 is more preferably a substituent derived from phosphorus oxoacid groups.

[0056] A phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group is, for example, a substituent represented by the following formula (1). Multiple substituents represented by the following formula (1) may be introduced into each microfiber cellulose. In this case, the multiple substituents represented by the following formula (1) may be the same or different.

[0057] [ka]

[0058] In equation (1), a, b, and n are natural numbers, and m is any number (where a = b × m). Of the n α and α', at least one is O - The rest are R or OR. Note that all of each α and α' are O - It is acceptable for this to be the case. The n αs may all be the same, or they may all be different. β b+ It is a cation with one or more valencies, composed 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 derivative thereof. In formula (1), n ​​is preferably 1.

[0060] Examples of saturated linear hydrocarbon groups include, but are not limited to, methyl, ethyl, n-propyl, or n-butyl groups. Examples of saturated branched hydrocarbon groups include, but are not limited to, i-propyl or t-butyl groups. Examples of saturated cyclic hydrocarbon groups include, but are not limited to, cyclopentyl or cyclohexyl groups. Examples of unsaturated linear hydrocarbon groups include, but are not limited to, vinyl or allyl groups. Examples of unsaturated branched hydrocarbon groups include, but are not limited to, i-propenyl or 3-butenyl groups. Examples of unsaturated cyclic hydrocarbon groups include, but are not limited to, cyclopentenyl or cyclohexenyl groups. Examples of aromatic groups include, but are not limited to, phenyl or naphthyl groups.

[0061] Furthermore, the derivative group in R is a carboxyl group or carboxylate group (-COO) attached to the main chain or side chain of the above-mentioned hydrocarbon groups. - Examples of functional groups include, but are not particularly limited to, a functional group in which at least one selected from functional groups such as hydroxyl groups, amino groups, and ammonium groups is added or substituted. Furthermore, the number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphorus oxoacid group can be set within an appropriate range, which facilitates penetration into the fiber raw material and can also increase the yield of fine cellulose fibers. In addition, when there are multiple Rs in formula (1) or when multiple substituents represented by the above formula (1) are introduced into fine fibrous cellulose, the multiple Rs may be the same or different.

[0062] βb+ β is a cation with one or more valencies composed of organic or inorganic substances. Examples of cations with one or more valencies composed of organic substances include organic onium ions. Examples of organic onium ions include organic ammonium ions and organic onium ions. Examples of organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of cations with one or more valencies composed of inorganic substances include alkali metal ions such as sodium, potassium, or lithium, divalent metal ions such as calcium or magnesium, hydrogen ions, and ammonium ions. Note that β is included in formula (1). b+ If multiple β atoms exist, or if multiple substituents represented by formula (1) above are introduced into the fine fibrous cellulose, then multiple β atoms exist. b+ These may be the same or different. As a monovalent or more cation consisting of organic or inorganic material, β b+ Sodium or potassium ions are preferred because they do not easily yellow when the fiber raw material containing them is heated and are readily available for industrial use, but the material is not particularly limited.

[0063] More specifically, substituents derived from a phosphorus oxoacid group include a phosphate group (-PO3H2), a salt of a phosphate group, a phosphonotic group (phosphonic acid group) (-PO2H2), and a salt of a phosphonotic group (phosphonic acid group). Furthermore, substituents derived from a phosphorus oxoacid group may also be groups formed by condensation of a phosphate group (e.g., a pyrophosphate group), groups formed by condensation of a phosphonic acid (e.g., a polyphosphonic acid group), phosphate ester groups (e.g., monomethyl phosphate group, polyoxyethylene alkyl phosphate group), alkylphosphonic acid groups (e.g., a methylphosphonic acid group), and the like.

[0064] Furthermore, the sulfone group (sulfone group or substituent derived from a sulfone group) is preferably a sulfur oxoacid group (sulfur oxoacid group or substituent derived from a sulfur oxoacid group), and is preferably a substituent represented by the following formula (2). Multiple substituents represented by the following formula (2) may be introduced into each microfiber cellulose. In this case, the multiple 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 any number (where 1 = b × m). Note that if n is 2 or greater, the multiple p values ​​may be the same number or different numbers. In the above structural formula, β b+ β is a cation with one or more valencies composed of organic or inorganic substances. Examples of cations with one or more valencies composed of organic substances include organic onium ions. Examples of organic onium ions include organic ammonium ions and organic onium ions. Examples of organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of cations with one or more valencies composed of inorganic substances include alkali metal ions such as sodium, potassium, or lithium, divalent metal ions such as calcium or magnesium, hydrogen ions, and ammonium ions. When multiple substituents represented by the above formula (2) are introduced into fine fibrous cellulose, multiple β atoms are present. b+ These may be the same or different. As a monovalent or more cation consisting of organic or inorganic material, β b+ Sodium or potassium ions are preferred because they do not easily yellow when the fiber raw material containing them is heated, and they are also readily available for industrial use, but the invention is not particularly limited.

[0067] The amount of anionic groups introduced into fine fibrous cellulose can be measured, for example, by neutralization titration. In neutralization titration, the amount introduced is determined by adding an alkali such as an aqueous sodium hydroxide solution to a slurry containing the obtained fine fibrous cellulose and observing the change in pH.

[0068] Figure 2 is a graph showing the relationship between the amount of NaOH added to a slurry containing fine fibrous cellulose with phosphorus oxoacid groups and the pH. The amount of phosphorus oxoacid groups introduced into the fine fibrous cellulose can be measured, for example, as follows. First, the slurry containing fine fibrous cellulose is treated with a strong acid ion exchange resin. If necessary, a defibration treatment similar to the defibration treatment step described later may be performed on the sample to be measured before treatment with the strong acid ion exchange resin. Next, the pH change is observed while adding sodium hydroxide solution, and a titration curve like the one shown in the upper part of Figure 2 is obtained. In the titration curve shown in the upper part of Figure 2, the measured pH is plotted against the amount of alkali added, and in the titration curve shown in the lower part of Figure 2, the increment (derivative value) (1 / mmol) of pH with respect to the amount of alkali added is plotted. In this neutralization titration, two points are observed in the curve plotting the measured pH against the amount of alkali added where the increment (derivative value of pH with respect to the amount of alkali added) is maximum. 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 the titration to the first endpoint is equal to the amount of the first dissociated acid from the fine fibrous cellulose contained in the slurry used for titration. The amount of alkali required from the first endpoint to the second endpoint is equal to the amount of the second dissociated acid from the fine fibrous cellulose contained 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 from the fine fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali required from the start of the titration to the first endpoint by the solid content (g) of the slurry being titrated is the amount of phosphorus oxoacid groups introduced (mmol / g). Note that when simply referred to as the amount of phosphorus oxoacid groups introduced (or amount of phosphorus oxoacid groups), it refers to the amount of the first dissociated acid. In Figure 2, the region from the start of titration to the first endpoint is called the first region, and the region from the first endpoint to the second endpoint is called the second region. For example, if the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the amount of weakly acidic group in the phosphorus oxoacid group (also referred to as the amount of the second dissociated acid in this specification) appears to decrease, and the amount of alkali required in the second region becomes less than the amount of alkali required in the first region. On the other hand, the amount of strongly acidic group in the phosphorus oxoacid group (also referred to as the amount of the first dissociated acid in this specification) is equal to the amount of phosphorus atoms, regardless of whether condensation occurs or not. Also, if the phosphorus oxoacid group is a phosphorous acid group, there is no weakly acidic group in the phosphorus oxoacid group, so the amount of alkali required in the second region becomes less, or in some cases, the amount of alkali required in the second region becomes zero. In this case, there is only one point on the titration curve where the pH increment is maximum.

[0069] The amount of phosphorus oxoacid groups introduced (mmol / g) mentioned above represents the amount of phosphorus oxoacid groups present in the acid-type microfibrous cellulose, since the denominator represents the mass of acid-type microfibrous cellulose (hereinafter referred to as phosphorus oxoacid group amount (acid type)). On the other hand, if the counterion of the phosphorus oxoacid group is substituted with an arbitrary cation C such that it has an equivalent charge, the amount of phosphorus oxoacid groups present in the microfibrous cellulose with cation C as the counterion can be determined by converting the denominator to the mass of microfibrous cellulose with cation C as the counterion (hereinafter referred to as phosphorus oxoacid group amount (C type)). In other words, it is calculated using the following formula. Phosphorus oxoacid group amount (C type) = Phosphorus oxoacid group amount (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 acids from phosphorus oxoacid groups) W: Formula weight per unit charge of the cation C (for example, Na is 23, Al is 9)

[0070] In measuring the amount of anionic groups by titration, if the amount of sodium hydroxide aqueous solution added is too large or the titration interval is too short, accurate values ​​may not be obtained, resulting in a lower-than-true amount of anionic groups. Appropriate titration volumes and intervals include, for example, titrating with 10-50 μL of 0.1N sodium hydroxide aqueous solution every 5-30 seconds. Furthermore, to eliminate the influence of carbon dioxide dissolved in the fine fibrous cellulose-containing slurry, it is desirable to blow an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration until the end of the titration while performing the measurement.

[0071] Furthermore, the amount of sulfone groups introduced into the 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 pressurized thermal decomposition with nitric acid in a sealed container. After appropriate dilution, the sulfur content is measured by ICP-OES. The value obtained by dividing by the oven-dry mass of the fine fibrous cellulose is taken as the amount of sulfone groups in the fine fibrous cellulose (unit: mmol / g).

[0072] The amount of xantate groups introduced into fine fibrous cellulose can be measured by the Bredee method as follows: First, 40 mL of saturated ammonium chloride solution is added to 1.5 parts by mass (dry mass) of fine fibrous cellulose, and the mixture is thoroughly mixed while crushing the sample with a glass rod. After standing for about 15 minutes, the mixture 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, 50 mL of 0.5 M sodium hydroxide solution (5°C) is added and stirred, and the mixture is left to stand for 15 minutes. Phenolphthalein solution is added until the solution turns pink, then 1.5 M acetic acid is added, and 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 well, and 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 a 0.05 mol / L sodium thiosulfate solution, and the amount of xantate groups is calculated from the titration volume of sodium thiosulfate and the oven-dry mass of fine fibrous cellulose using the following formula. Xantate group amount (mmol / g) = (0.05 × 10 × 2 - 0.05 × sodium thiosulfate titration volume (mL)) / 1000 / oven-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 derivative thereof. Among these, R is particularly preferably 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 fine fibrous cellulose, further grinding the sample, and performing trace nitrogen analysis. The amount of carbamide groups introduced per unit mass of fine fibrous cellulose (mmol / g) can be calculated by dividing the nitrogen content per unit mass of fine fibrous cellulose (g / g) obtained by trace nitrogen analysis by the atomic weight of nitrogen.

[0077] In this embodiment, when the fine fibrous cellulose used to form the fiber layer is an aqueous dispersion with 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, and 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 liquid obtained when an aqueous dispersion of fine fibrous cellulose with a concentration of 0.1% by mass is centrifuged at 12000G for 10 minutes.

[0078] In addition, 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 fibrous 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 B-type viscometer (BLOOKFIELD T-LVT analog viscometer). The measurement conditions are 23°C and a rotation speed of 3 rpm, and the viscosity is measured 3 minutes after the start of measurement. In addition, the dispersion to be measured is left to stand for 24 hours in an environment of 23°C and 50% relative humidity before measurement, so that the liquid temperature of the dispersion is 23°C.

[0081] It is preferable that the amount of free nitrogen in the dispersion containing fine fibrous cellulose used to form the fibrous layer be low. The amount of free nitrogen in the dispersion can be measured by measuring the nitrogen concentration in the filtrate when the fine fibrous cellulose dispersion is filtered. For example, the free nitrogen concentration in a dispersion with a fine fibrous cellulose concentration of 0.2% by mass 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. Note that the nitrogen concentration in a dispersion with a fine fibrous cellulose concentration of 0.2% by mass may be 0 ppm. Free nitrogen present in the dispersion can cause discoloration, so by keeping the nitrogen concentration in the filtrate within the above range, yellowing of the dispersion and sheet containing fine fibrous cellulose can be more effectively suppressed. The method for measuring the nitrogen concentration in the filtrate is as follows. First, distilled water is added to achieve a fine fibrous cellulose concentration of 0.2% by mass. After stirring for 24 hours, the mixture is filtered using a filter medium with a pore size of 0.45 μm to obtain the filtrate. Then, the nitrogen concentration (ppm) in the filtrate is measured by trace nitrogen analysis.

[0082] (Method for producing microfiber cellulose) The fine fibrous cellulose described above is preferably obtained by step (A) of removing at least a portion of the substituents from fine fibrous cellulose having substituents and a fiber width of 1000 nm or less. Here, the substituents on the fine fibrous cellulose subjected to step (A) are preferably anionic groups, and more preferably phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups. Furthermore, it is preferable that the fine fibrous cellulose subjected to step (A) has a carbamide group.

[0083] (Process (A)) Step (A) is a step of removing at least some of the substituents from fine fibrous cellulose having substituents and a fiber width of 1000 nm or less. Below, we will first describe a method for producing fine fibrous cellulose having substituents and a fiber width of 1000 nm or less (fine fibrous cellulose used in step (A)).

[0084] <Fiber raw materials> The fine fibrous cellulose used in process (A) is produced from a cellulose-containing fiber raw material. The cellulose-containing fiber raw material is not particularly limited, but pulp is preferred because it is readily available and inexpensive. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp are not particularly limited, but include chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolved 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 chemigroundwood pulp (CGP); and mechanical pulps such as crushed wood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Non-wood pulp is not particularly limited, but examples include cotton pulp such as cotton linters and cotton lint, and non-wood pulp such as hemp, straw, and bagasse. Deinking pulp is not particularly limited, but examples include deinking pulp made from recycled paper. The pulp in this embodiment may be one of the above types used alone, or two or more types may be used in mixture. Among the above pulps, wood pulp and deinking pulp are preferred from the viewpoint of ease of availability. Among wood pulps, chemical pulp is more preferred from the viewpoint of a high cellulose ratio and a high yield of fine fibrous cellulose during defibration treatment, and from the viewpoint of obtaining long-fiber fine fibrous cellulose with a large axial ratio due to minimal cellulose decomposition in the pulp. Kraft pulp and sulfite pulp are even more preferred. It should be noted that using long-fiber fine fibrous cellulose with a large axial ratio tends to increase viscosity.

[0085] As fiber raw materials containing cellulose, for example, cellulose contained in sea squirts or bacterial cellulose produced by acetic acid bacteria can be used. Alternatively, instead of fiber raw materials containing cellulose, fibers formed from linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can be used.

[0086] <Phosphorus oxoacid group introduction process> The fine fibrous cellulose used in step (A) has substituents. For this reason, the manufacturing process for the fine fibrous cellulose used in step (A) preferably includes a substituent introduction step, and more preferably an anionic group introduction step. An anionic group introduction step is, for example, a phosphorus oxoacid group introduction step. The phosphorus oxoacid group introduction step is a step in which at least one compound (hereinafter also referred to as "compound A") selected from compounds that can introduce phosphorus oxoacid groups by reacting with hydroxyl groups present in the cellulose-containing fiber raw material is reacted with the cellulose-containing fiber raw material. This step yields phosphorus oxoacid group-introduced fibers.

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

[0088] One example of a method for reacting compound A with a fiber raw material in the presence of compound B is to mix compound A and compound B with the fiber raw material in a dry, wet, or slurry state. Of these, it is preferable to use a fiber raw material in a dry or wet state, and particularly preferable to use a fiber raw material in a dry state, because of the high uniformity of the reaction. The form of the fiber raw material is not particularly limited, but for example, it is preferably in the form of cotton or a thin sheet. Compounds A and B can be added to the fiber raw material in the form of powder, a solution dissolved in a solvent, or after being heated above the melting point and melted. Of these, it is preferable to add them in the form of a solution dissolved in a solvent, particularly an aqueous solution, because of the high uniformity of the reaction. Compounds A and B may be added to the fiber raw material simultaneously, separately, or as a mixture. There are no particular limitations on the method of adding compounds A and B, but if compounds A and B are in solution form, the fiber raw material may be immersed in the solution 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 pressing or filtration.

[0089] Compound A used in this embodiment may be any compound having a phosphorus atom and capable of forming an ester bond with cellulose, and is not particularly limited to, but includes phosphoric acid or its salts, phosphorous acid or its salts, dehydrated condensed phosphoric acid or its salts, and phosphoric anhydride (phosphorus pentoxide). As phosphoric acid, various purities can be used, for example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid can be used. As phosphorous acid, 99% phosphorous acid (phosphonic acid) can be used. Dehydrated condensed phosphoric acid is obtained by condensing two or more molecules of phosphoric acid through a dehydration reaction, and examples 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, and these can be neutralized to various degrees. Of these, phosphoric acid, sodium phosphoric acid, potassium phosphoric acid, ammonium phosphoric acid, or phosphorous acid, sodium phosphorous acid, potassium phosphorous acid, or ammonium phosphorous acid are preferred from the viewpoint of having high efficiency in introducing phosphate groups, easily improving the defibration efficiency in the defibration process described later, being low cost, and being easily applicable industrially. Phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid or sodium phosphorous acid 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 to the amount of phosphorus atoms, it is preferable that the amount of phosphorus atoms added to the fiber raw material (oven-dry mass) be 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 keeping 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 keeping the amount of phosphorus atoms added to the fiber raw material below the above upper limit, it is possible to balance the effect of improving yield with cost.

[0091] Compound B used in this embodiment is at least one selected from urea and its derivatives, as described above. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, it is preferable to use compound B 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 to the fiber raw material (absolute dry weight) is not particularly limited, but is preferably 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 cellulose-containing fiber raw materials with compound A, in addition to compound B, other substances such as amides or amines may be included in the reaction system. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is known to act as a particularly good reaction catalyst.

[0094] In the phosphorus oxoacid group introduction step, it is preferable to add or mix compounds A and B to the fiber raw material and then subject the fiber raw material to heat treatment. The heat treatment temperature is preferably selected to efficiently introduce phosphorus oxoacid groups while suppressing thermal decomposition and hydrolysis reactions of the fibers. The heat treatment temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C. Furthermore, various heat transfer devices can be used for the heat treatment, such as hot air dryers, agitation dryers, rotary dryers, disc dryers, roll-type heaters, plate-type heaters, fluidized bed dryers, band-type dryers, filtration dryers, vibrating fluidized bed dryers, airflow dryers, vacuum dryers, infrared heaters, far-infrared heaters, microwave heaters, and high-frequency dryers.

[0095] In the heat treatment according to this embodiment, for example, a method can be employed in which compound A is added to a thin sheet-like fiber raw material by impregnation or other methods, and then heated, or a method can be employed in which the fiber raw material and compound A are kneaded or stirred while heating. This makes it possible to suppress uneven concentration of compound A in the fiber raw material and to introduce phosphorus oxoacid groups more uniformly to the surface of the cellulose fibers contained in the fiber raw material. This is thought to be because, as water molecules move to the surface of the fiber raw material during drying, dissolved compound A is attracted to the water molecules by surface tension and similarly moves to the surface of the fiber raw material (i.e., uneven concentration of compound A is produced), and this can be suppressed.

[0096] Furthermore, the heating device used for the heat treatment is preferably one that can constantly discharge, for example, the moisture held in the slurry and the moisture generated by the dehydration condensation (phosphate esterification) reaction between compound A and hydroxyl groups contained in cellulose, etc., in the fiber raw material, to the outside of the device system. Examples of such heating devices include a forced-air oven. By constantly discharging moisture from the device system, it is possible to 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 fibers. As a result, it becomes possible to obtain fine fibrous cellulose with a high axial ratio.

[0097] The heating time is preferably between 1 second and 300 minutes, more preferably between 1 second and 1000 seconds, and even more preferably between 10 seconds and 800 seconds, after substantially all moisture has been removed from the fiber raw material. In this embodiment, the amount of phosphorus oxoacid groups introduced can be kept within a preferred range by setting the heating temperature and heating time within an appropriate range.

[0098] The phosphorus oxoacid group introduction process only needs to be performed at least once, but it can also be repeated two or more times. By performing the phosphorus oxoacid group introduction process two or more times, a large number of phosphorus oxoacid groups can be introduced into the fiber raw material.

[0099] The amount of phosphorus oxoacid groups introduced in the phosphorus oxoacid 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 phosphorus oxoacid groups introduced is preferably 5.20 mmol / g or less per 1 g (mass) of fiber raw material, more preferably 3.65 mmol / g or less, and even more preferably 3.00 mmol / g or less. Note that the amount of phosphorus oxoacid groups introduced in the phosphorus oxoacid group introduction step being within the above range means that the amount of substituents introduced into the fine fibrous cellulose subjected to step (A) is within the above range. By setting the amount of phosphorus oxoacid groups introduced within the above range, the amount of substituents introduced into the fine fibrous cellulose subjected to step (A) can be set within the above range, and as a result, it becomes easier to produce fine fibrous cellulose with a final fiber width of 10 nm or less. Furthermore, the transparency of dispersions and sheets containing the fine fibrous cellulose of the present invention can be more effectively enhanced.

[0100] <Process for introducing sulfone groups (sulfur oxoacid groups)> The manufacturing process for the fine fibrous cellulose used in process (A) may include a sulfone group introduction step as an anionic group introduction step. In the sulfone group introduction step, a cellulose fiber having a sulfone group (sulfone group introduced fiber) can be obtained by reacting a sulfonic acid with a hydroxyl group present in the cellulose-containing fiber raw material.

[0101] In the sulfone group introduction step, instead of compound A in the <phosphorus oxoacid group introduction step> described above, at least one compound (hereinafter also referred to as "compound C") selected from compounds that can introduce sulfone groups by reacting with hydroxyl groups present in the cellulose-containing fiber raw material is used. Compound C can be any compound having a sulfur atom and capable of forming an ester bond with cellulose, and examples include sulfuric acid or its salts, sulfite or its salts, and sulfuric acid amides, but is not particularly limited. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid) can be used. As sulfite, 5% sulfurous acid water can be used. As sulfates or sulfites, lithium salts, sodium salts, potassium salts, and ammonium salts of sulfates or sulfites can be used, and these can be neutralized to various degrees. As sulfuric acid amides, sulfamic acid can be used. In the sulfone group introduction step, it is preferable to use compound B in the same manner as in the <phosphorus oxoacid group introduction step> described above.

[0102] In the sulfone group introduction step, it is preferable to mix the cellulose raw material with an aqueous solution containing sulfonic acid and urea and / or a urea derivative, and then heat-treat the cellulose raw material. The heat treatment temperature is preferably selected to efficiently introduce sulfone groups while suppressing thermal decomposition and hydrolysis reactions of the fibers. The heat treatment temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. Furthermore, 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 process, it is preferable to heat until substantially all moisture is removed. Therefore, the heat treatment time varies depending on the amount of moisture contained in the cellulose raw material, the amount of sulfonic acid, and the amount of aqueous solution containing urea and / or urea derivatives added, but it is preferable to heat for 10 seconds or more and 10,000 seconds or less. Various heat transfer devices can be used for the heat treatment, such as hot air dryers, agitation dryers, rotary dryers, disc dryers, roll-type heaters, plate-type heaters, fluidized bed dryers, band-type dryers, filtration dryers, vibrating fluidized bed dryers, airflow dryers, vacuum dryers, infrared heaters, far-infrared heaters, microwave heaters, and high-frequency dryers.

[0104] The amount of sulfone groups introduced in the sulfone 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 sulfone groups introduced is preferably 5.00 mmol / g or less per 1 g (mass) of fiber raw material, and more preferably 3.00 mmol / g or less. Note that the amount of sulfone groups introduced in the sulfone group introduction step being within the above range means that the amount of substituents introduced into the fine fibrous cellulose subjected to step (A) is within the above range. By setting the amount of sulfone groups introduced within the above range, the amount of substituents introduced into the fine fibrous cellulose subjected to step (A) can be set within the above range, and as a result, it becomes easier to produce fine fibrous cellulose with a fiber width of 10 nm or less. In addition, the transparency of the dispersion or sheet containing the fine fibrous cellulose of the present invention can be more effectively enhanced.

[0105] <Xantate group introduction process> The manufacturing process for the fine fibrous cellulose used in process (A) may include a xantate group introduction process as an anionic group introduction process. The xantate group introduction process involves substituting the hydroxyl groups in the cellulose-containing fiber raw material with xantate groups represented by the following formula (2) to obtain cellulose fibers having xantate groups (xantate group introduced fibers). ―OCSS - M + ...(2) Here, M + is at least one selected from hydrogen ions, monovalent metal ions, ammonium ions, aliphatic or aromatic ammonium ions.

[0106] In the xantate group introduction process, first, the fiber raw material containing the cellulose is treated with an alkaline solution to obtain alkaline cellulose. Examples of alkaline solutions include aqueous alkali metal hydroxide solutions and alkaline earth metal hydroxide solutions. Among these, the alkaline solution is preferably an aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide, and is 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, and 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 to above the above lower limit, the mercellation of cellulose can be sufficiently advanced, the amount of by-products generated during the subsequent xantate formation can be reduced, and as a result, the yield of xantate group-introduced fibers can be increased. This allows the defibration treatment described later to be carried out more effectively. Furthermore, by keeping the alkali metal hydroxide concentration below the above upper limit, it is possible to suppress the penetration of the alkali metal hydroxide aqueous solution into the crystalline region of cellulose while still promoting mercerization. This makes it easier to maintain the type I cellulose crystalline structure and further increase the yield of fine fibrous cellulose.

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

[0108] It is preferable to remove as much of the aqueous solution as possible from the alkali cellulose obtained by the above alkali treatment by solid-liquid separation. This reduces the water content during the subsequent xantate treatment and promotes the reaction. As for the solid-liquid separation method, general dehydration methods such as centrifugation or filtration can be used. It is preferable that the concentration of alkali metal hydroxide in the alkali cellulose after solid-liquid separation is 3% by mass or more and 8% by mass or less of the total mass of the alkali cellulose after solid-liquid separation.

[0109] In the xantate group introduction process, an alkali treatment is followed by a xantate treatment process. In the xantate treatment process, alkali cellulose is reacted with carbon disulfide (CS2) to form (-O - Na + )Based on (-OCSS - Na + ) A xantate group-introduced fiber is obtained using this group. In the above, the metal ions introduced into alkali cellulose are, representatively, Na + As described above, similar reactions proceed with other alkali metal ions.

[0110] In the xantate treatment, it is preferable to supply 10% by mass or more of carbon disulfide relative to the oven-dry mass of cellulose in the alkali cellulose. Furthermore, in the xantate treatment, the contact time between carbon disulfide and alkali cellulose is preferably 30 minutes or more, and more preferably 1 hour or more. Although xantate treatment proceeds rapidly upon contact of carbon disulfide with alkali cellulose, it takes time for the 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 even into the dehydrated alkali cellulose mass, and almost complete the reactive xantate treatment.

[0111] The reaction temperature in the xantate treatment is preferably 46°C or lower. Keeping the reaction temperature within this range makes it easier to suppress the decomposition of alkali cellulose. Furthermore, keeping the reaction temperature within this range makes it easier to react uniformly, which suppresses the formation of by-products and also helps to suppress the removal of the generated xantate groups.

[0112] The amount of xantate groups introduced in the xantate 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 xantate groups introduced is preferably 5.00 mmol / g or less per 1 g (mass) of fiber raw material, and more preferably 3.00 mmol / g or less. Note that the amount of xantate groups introduced in the xantate group introduction step being 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 xantate 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, and as a result, it becomes easier to produce fine fibrous cellulose with a fiber width of 10 nm or less. In addition, the transparency of dispersions and sheets containing the fine fibrous cellulose of the present invention can be more effectively enhanced.

[0113] <Washing process> In the manufacturing process of the fine fibrous cellulose used in process (A), a washing process may be performed on the anionic group-introduced fibers as needed. The washing process is carried out, for example, by washing the anionic group-introduced fibers with water or an organic solvent. Furthermore, the washing process may be performed after each of the processes described later, and the number of washing cycles performed in each washing process is not particularly limited.

[0114] <Alkali treatment process> In the manufacturing process of the fine fibrous cellulose used in process (A), an alkaline treatment may be performed on the fiber raw material between the anionic group introduction process and the defibration treatment process described later. The method of alkaline treatment is not particularly limited, but one example is immersing the anionic group-introduced fibers in an alkaline solution.

[0115] The alkali compound contained in the alkaline solution is not particularly limited and may be an inorganic alkali compound or an organic alkali compound. In this embodiment, it is preferable to use sodium hydroxide or potassium hydroxide as the alkali compound due to its high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. In particular, the solvent contained in the alkaline solution is preferably water or a polar solvent including a polar organic solvent such as alcohol, and more preferably an aqueous solvent containing at least water. As the alkaline solution, for example, an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide is preferred due to its high versatility.

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

[0117] To reduce the amount of alkaline solution used in the alkaline treatment process, the anionic group-introduced fibers may be washed with water or an organic solvent after the anionic group introduction process and before the alkaline treatment process. After the alkaline treatment process and before the defibration process, it is preferable to wash the alkaline-treated anionic group-introduced fibers with water or an organic solvent to improve handling.

[0118] <Acid treatment process> In the manufacturing process for the fine fibrous cellulose used in process (A), an acid treatment may be performed on the fiber raw material between the anionic group introduction step and the defibration treatment step described later. For example, the anionic group introduction step, acid treatment, alkali treatment, and defibration treatment may be performed in this order.

[0119] The method of acid treatment is not particularly limited, but one example is immersing the fiber raw material in an acidic solution containing an acid. The concentration of the acidic solution used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less. The pH of the acidic solution used is not particularly limited, but is preferably 0 to 4, and more preferably 1 to 3. Examples of acids that can be included in the acidic solution include inorganic acids, sulfonic acids, carboxylic acids, etc. Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, 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, the use of 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 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 preferably 5 minutes to 120 minutes, and more preferably 10 minutes to 60 minutes. The amount of acid solution used in the acid treatment is not particularly limited, but is preferably 100% to 100,000% by mass, and more preferably 1,000% to 10,000% by mass, relative to the absolute dry mass of the fiber raw material.

[0121] <Nitrogen removal treatment> The manufacturing process for the fine fibrous cellulose used in process (A) may further include a process to reduce the amount of nitrogen introduced into the fibrous cellulose and the amount of nitrogen present in the system (nitrogen removal process). By reducing the amount of nitrogen, it is possible to obtain fine fibrous cellulose that can further suppress discoloration. The nitrogen removal process may be provided after the uniform dispersion process in process (B) described later, but it is preferable to provide it before the uniform dispersion process in process (B) described later. It is also preferable to provide it before the defibration process in process (A) described later.

[0122] In the nitrogen removal process, it is preferable to adjust the pH of the slurry containing the anionic group-introduced fibers to 10 or higher and then perform a heat treatment. In the heat treatment, it is preferable to set the slurry temperature to 50°C or higher and 100°C or lower, and the heating time to 15 minutes or higher and 180 minutes or lower. When adjusting the pH of the slurry containing the anionic group-introduced fibers, it is preferable to add an alkaline compound that can be used in the alkali treatment process described above to the slurry.

[0123] After the nitrogen removal treatment process, a washing process can be performed on the anionic group-introduced fibers as needed. The washing process is carried out, for example, by washing the anionic group-introduced fibers with water or an organic solvent. Furthermore, there is no particular limit to the number of washing cycles performed in each washing process.

[0124] <Fibrillation treatment> The manufacturing process for the fine fibrous cellulose used in process (A) includes a defibration process. This yields fine fibrous cellulose having substituents and a fiber width of 1000 nm or less. In the defibration process, for example, a defibration apparatus can be used. The defibration apparatus is not particularly limited, but for example, a high-speed defibrator, grinder (stone mill type grinder), high-pressure homogenizer or ultra-high-pressure homogenizer, high-pressure impact grinder, ball mill, bead mill, disc type refiner, conical refiner, twin-screw kneader, vibrating mill, homomixer under high-speed rotation, ultrasonic disperser, or beater can be used. Among the above defibration apparatuses, it is more preferable to use a high-speed defibrator, high-pressure homogenizer, or ultra-high-pressure homogenizer, which have less influence from the grinding media and less risk of contamination.

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

[0126] In the defibration process, for example, it is preferable to dilute the anionic group-introduced fibers with a dispersion medium to form a slurry. As the dispersion medium, one or more selected from water and organic solvents such as polar organic solvents can be used. The polar organic solvent is not particularly limited, but for example, alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents are preferred. 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 process can be set as appropriate. Furthermore, the slurry obtained by dispersing the anionic group-introduced fibers in a dispersion medium may contain solid components other than the anionic group-introduced fibers, such as hydrogen-bonding urea.

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

[0129] The substituent removal process includes steps such as heat treatment, enzymatic treatment, acid treatment, and alkali treatment of fine fibrous cellulose having substituents and a fiber width of 1000 nm or less. These may be performed individually or in combination. Among these, the substituent removal process is preferably a heat treatment or an enzymatic treatment. By going through the above treatment process, 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 a substituent introduction amount of less than 0.5 mmol / g can be obtained.

[0130] The substituent removal process is preferably carried out in slurry form. Specifically, the substituent removal process is preferably a process of heat treatment, enzymatic treatment, acid treatment, alkali treatment, etc., of a slurry containing fine fibrous cellulose having substituents and a fiber width of 1000 nm or less. By carrying out the substituent removal process in slurry form, it is possible to prevent the formation of coloring substances caused by heating during substituent removal, as well as the residue of added or generated acids, alkalis, salts, etc. This makes it possible to suppress coloring when the fine fibrous cellulose obtained through process (B) is made into a slurry or sheet. Furthermore, if a salt removal process is carried out after substituent removal, it is possible to improve the efficiency of salt removal.

[0131] When performing substituent removal treatment on a slurry containing fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, the concentration of 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. Furthermore, the concentration of 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 setting the concentration of fine fibrous cellulose in the slurry within the above range, substituent removal treatment can be performed more efficiently. In addition, by setting the concentration of fine fibrous cellulose in the slurry within the above range, it is possible to prevent the residue of coloring substances generated by heating during substituent removal treatment, as well as added or generated acids, alkalis, salts, etc. This makes it possible to suppress coloring when the fine fibrous cellulose obtained through step (B) is made into a slurry or sheet. Furthermore, when performing a salt removal treatment for substituent-derived salts after substituent removal treatment, it is also possible to improve the efficiency of salt removal.

[0132] When the substituent removal process involves heat-treating fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, the heating temperature in the heat treatment process 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 process is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower. In particular, when the substituents on the fine fibrous cellulose subjected to the substituent removal process are phosphorus oxoacid groups or sulfone groups, the heating temperature in the heat treatment process is preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher.

[0133] If the substituent removal process is a heat treatment process, the heating equipment that can be used in the heat treatment process is not particularly limited, but may include hot air heaters, steam heaters, electric heaters, hydrothermal heaters, thermal heaters, infrared heaters, far-infrared heaters, microwave heaters, high-frequency heaters, stirring dryers, rotary dryers, disc dryers, roll-type heaters, plate-type heaters, fluidized bed dryers, band-type dryers, filtration dryers, vibrating fluidized bed dryers, airflow dryers, and vacuum dryers. From the viewpoint of preventing evaporation, heating is preferably carried out in a closed system, and from the viewpoint of increasing the heating temperature, it is preferable to carry out the heating in a pressure-resistant device or container. The heat treatment may be a batch process, a batch continuous process, or a continuous process.

[0134] If the substituent removal process involves enzymatically treating fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, it is preferable to use phosphate hydrolase, sulfate hydrolase, etc., in the enzymatic treatment process.

[0135] In the enzyme treatment step, it is preferable to add enzymes so that the enzyme activity is 0.1 nkat or more per 1 g of fine fibrous cellulose, more preferably 1.0 nkat or more, and even more preferably 10 nkat or more. Furthermore, it is preferable to add enzymes so that the enzyme activity is 100,000 nkat or less per 1 g of fine fibrous cellulose, more preferably 50,000 nkat or less, and even more preferably 10,000 nkat or less. After adding enzymes to the fine fibrous cellulose dispersion (slurry), it is preferable to treat the material for 1 minute to 100 hours under conditions of 0°C to less than 50°C.

[0136] A step to deactivate the enzyme after the enzymatic reaction may be included. Methods for deactivating the enzyme include adding an acidic or alkaline component to the enzyme-treated slurry to deactivate the enzyme, or raising the temperature of the enzyme-treated slurry to 90°C or higher to deactivate the enzyme.

[0137] If the substituent removal process is a process of acid-treating fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, it is preferable to add an acid compound that can be used in the above-described acid treatment process to the slurry during the acid treatment process.

[0138] If the substituent removal step is a step of alkali treatment of fine fibrous cellulose having substituents 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 during the alkali treatment step.

[0139] In the substituent removal process, it is preferable that the substituent removal reaction proceeds uniformly. To ensure uniform reaction, for example, the slurry containing fine fibrous cellulose may be stirred, or the specific surface area of ​​the slurry may be increased. Methods of stirring the slurry include applying external mechanical shear, or promoting self-stirring by increasing the slurry delivery rate during the reaction.

[0140] In the substituent removal process, spacer molecules may be added. These spacer molecules penetrate between adjacent microfibrous cellulose molecules, thereby acting as spacers to create fine spaces between them. Adding such spacer molecules during the substituent removal process can suppress the aggregation of microfibrous cellulose after the treatment. This allows for a more effective improvement in the transparency of dispersions and sheets containing microfibrous 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), etc. can be mentioned. Further, as the water-soluble organic compound, methacrylic acid alkyl·acrylic acid copolymer, polyvinylpyrrolidone, 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, etc. 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 fine fibrous cellulose after defibration will be weakly alkaline. If heated in this state, monosaccharides, which are one of the causes of discoloration, may be generated due to the decomposition of cellulose, so it is preferable to adjust the pH of the slurry to 8 or less, and more preferably to 6 or less. Similarly, monosaccharides may also be generated under acidic conditions, so it is preferable to adjust the pH of the slurry to 3 or more, and more preferably to 4 or more.

[0144] Furthermore, if the substituted microfiber cellulose is a microfiber cellulose having a phosphate group, it is preferable that the phosphorus of the phosphate group is in a state that is easily susceptible to nucleophilic attack, from the viewpoint of improving the efficiency of substituent removal. Cellulose-OP(=O)(-OH) is susceptible to nucleophilic attack. + )(-O-Na + This represents a neutralization degree of 1, and to achieve this state, it is preferable to adjust the pH of the slurry to 3 or more and 8 or less, and more preferably to adjust the pH to 4 or more and 6 or less.

[0145] The means of adjusting the pH are not particularly limited, but for example, an acidic or alkaline component may be added to a slurry containing fine fibrous cellulose. The acidic 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 alkaline 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] Furthermore, in the pH adjustment process, ion exchange treatment may be performed to adjust the pH. For ion exchange treatment, a strongly acidic cation exchange resin or a weakly acidic ion exchange resin can be used. By treating with an appropriate amount of cation exchange resin for a sufficient amount of time, a slurry containing fine fibrous cellulose at the desired pH can be obtained. In addition, the pH adjustment process may be combined with the addition of acidic or alkaline components and ion exchange treatment.

[0147] <Salt removal process> After the substituent removal process, it is preferable to remove salts derived from the removed substituents. Removing the substituent-derived salts makes it easier to obtain fine fibrous cellulose that can suppress discoloration. The means for removing substituent-derived salts are not particularly limited, but washing is one example. The washing is carried out by washing the fine fibrous cellulose aggregated in the substituent removal process with water or an organic solvent, for example. From the viewpoint of more effectively suppressing yellowing, the washing is preferably carried out by filtration dehydration, centrifugal dehydration, or centrifugation.

[0148] (Process (B)) A method for producing fine fibrous cellulose may include a step (A) of removing at least some of the substituents from fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, and a step (B) of uniform dispersion treatment after step (A). The uniform dispersion treatment step (B) is a step of uniformly dispersing the fine fibrous cellulose obtained after the substituent removal treatment in step (A). By going through step (B), it becomes easy to reduce the fiber width of the fine fibrous cellulose even with a low substituent introduction amount of less than 0.5 mmol / g.

[0149] In the uniform dispersion process (B), for example, a high-speed defibrator, grinder (stone mill type grinder), high-pressure homogenizer, high-pressure impact grinder, ball mill, bead mill, disc refiner, conical refiner, twin-screw kneader, vibrating mill, homomixer under high-speed rotation, ultrasonic disperser, or beater can be used. Among the above uniform dispersion processing devices, the use of a high-speed defibrator and a high-pressure homogenizer is more preferable.

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

[0151] Furthermore, in step (B), the aforementioned spacer molecules may be added. By adding such spacer molecules in the uniform dispersion process of step (B), the uniform dispersion 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 or sheet containing the fine fibrous cellulose.

[0152] (Resin layer) The laminated sheet of the present invention may further have a resin layer on at least one side of the fiber layer. When the laminated sheet further has a resin layer, the resin layer is a layer directly laminated to the fiber layer, and it is preferable that the resin layer and the fiber layer are in contact on either side. Furthermore, it is preferable that the resin layer is a resin layer formed by coating (coated resin layer).

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

[0154] The resin layer is a layer mainly composed of natural resin or synthetic resin. Here, the main component refers to a component that is present in 50% or more of the total mass of the resin layer. The resin content is preferably 60% or more of the total mass of the resin layer, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more. The resin content may be 100% or 95% or less of the total mass of the resin layer.

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

[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 these, 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 polycarbonate resins that constitute the resin layer include aromatic polycarbonate resins and aliphatic polycarbonate resins. Specific examples of these polycarbonate resins are publicly known, such as the polycarbonate resin described in Japanese Patent Publication No. 2010-023275.

[0158] In laminated sheets, the resin layer preferably contains an adhesion promoter. Examples of adhesion promoters include compounds containing at least one selected from isocyanate groups, carbodiimide groups, epoxy groups, oxazoline groups, amino groups, silanol groups, and alkoxysilyl groups, and organosilicon compounds. Among these, it is preferable that the adhesion promoter is at least one selected from compounds containing isocyanate groups (isocyanate compounds) and organosilicon compounds. Examples of organosilicon compounds include silane coupling agent condensates and silane coupling agents.

[0159] Examples of isocyanate compounds include polyisocyanate compounds or polyfunctional isocyanates. Specifically, examples of polyisocyanate compounds include aromatic polyisocyanates with 6 to 20 carbon atoms excluding the carbon in the NCO group, aliphatic polyisocyanates with 2 to 18 carbon atoms, alicyclic polyisocyanates with 6 to 15 carbon atoms, aralkyl polyisocyanates with 8 to 15 carbon atoms, modified products of these polyisocyanates, and mixtures of two or more of these. Among these, alicyclic polyisocyanates with 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 organosilicon compounds include compounds having a siloxane structure or compounds that form a siloxane structure by condensation. For example, examples of organosilicon compounds include silane coupling agents or condensates of silane coupling agents. Silane coupling agents may have functional groups other than alkoxysilyl groups, or they may not have functional groups other than alkoxysilyl groups. Examples of functional groups other than alkoxysilyl groups include vinyl groups, epoxy groups, styryl groups, methacryloxy groups, acryloxy groups, amino groups, ureido groups, mercapto groups, sulfide groups, and isocyanate groups. 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 a methacryloxy group in the molecule include, for example, methacryloxypropylmethyldimethoxysilane, methacryloxypropyltrimethoxysilane, methacryloxypropylmethyldiethoxysilane, methacryloxypropyltriethoxysilane, and 1,3-bis(3-methacryloxypropyl)tetramethyldisiloxane. Among these, at least one selected from methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, and 1,3-bis(3-methacryloxypropyl)tetramethyldisiloxane is preferably used. It is preferable that the silane coupling agent contains three or more alkoxysilyl groups.

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

[0164] The adhesion aid may be included in the resin layer in a uniformly dispersed state. Here, a state in which the adhesion aid is uniformly dispersed in the resin layer means that when the concentrations in the following three regions ((a) to (c)) are measured and any two of the concentrations in any two regions do not differ by more than two times. (a) The area from the fiber layer side of the resin layer up to 10% of the total thickness of the resin layer (b) The area from the side of the resin layer opposite to the fiber layer side up to 10% of the total thickness of the resin layer (c) A region within ±5% of the total thickness (10% in total) from the center plane in the thickness direction of the resin layer.

[0165] Furthermore, the adhesion aid may be unevenly distributed in the region of the resin layer that is on the fiber layer side. 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 that is on the fiber layer side. Here, the state of uneven distribution in the fiber layer region of the resin layer refers to a state in which, when measuring the concentrations in the following two regions ((d) and (e)), there is a difference of more than twofold between these concentrations. (d) The area from the fiber layer side of the resin layer up to 10% of the total thickness of the resin layer (e) A region within ±5% of the total thickness (10% in total) from the center plane in the thickness direction of the resin layer. Here, the concentration of the adhesion promoter is a value measured by an X-ray electron spectrometer or an infrared spectrophotometer, obtained by cutting a cross-section of a predetermined area of ​​the laminated sheet using an ultramicrotome UC-7 (manufactured by JEOL Corporation) and measuring the said cross-section with the said device.

[0166] An organosilicon compound-containing layer may be provided on the surface of the resin layer facing the fiber layer, and this 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 solution. Furthermore, if an organosilicon compound-containing layer is provided on the fiber-layer-side surface of the resin layer, in the above region (d), "fiber-layer-side surface of the resin layer" shall be read as "exposed surface of the organosilicon compound-containing layer," and "total thickness of the resin layer" shall be read as "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, and more preferably 0.5 parts by mass or more, per 100 parts by mass of resin contained in the resin layer. Furthermore, the content of the adhesion aid is preferably 40 parts by mass or less, and more preferably 35 parts by mass or less, per 100 parts by mass of 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, based on 100 parts by mass of resin contained in the resin layer. Furthermore, the content of the isocyanate compound 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, based on 100 parts by mass of 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, and more preferably 0.5 parts by mass or more, per 100 parts by mass of resin contained in the resin layer. Furthermore, the content of the organosilicon compound is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of resin contained in the resin layer. By keeping 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 isocyanate group content 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. Furthermore, the isocyanate group content 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, it is preferable that the surface treatment be at least one selected from corona treatment and plasma discharge treatment. In addition, it is preferable that the plasma discharge treatment be vacuum plasma discharge treatment.

[0170] The surface of the resin layer facing the fiber layer may have a fine uneven structure. Having a fine uneven 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 fine uneven structure, it is preferable that such a structure is formed by a processing step such as blasting, embossing, etching, corona treatment, or plasma discharge treatment. In this specification, a fine uneven structure refers to a structure in which there are 10 or more recesses on a straight line of 1 mm in length drawn at an arbitrary location. To measure the number of recesses, the laminated sheet is immersed in ion-exchanged water for 24 hours, and then the fiber layer is peeled off from the resin layer. After that, the surface of the resin layer facing the fiber layer can be scanned with a stylus-type surface roughness meter (Kosaka Laboratory Co., Ltd., SurfCorder series) to measure the number of recesses. When the pitch of surface irregularities is extremely small, on the submicron or nanoscale, the number of irregularities can be measured from the observation image using a scanning probe microscope (Hitachi High-Tech Science Corporation, AFM5000II and AFM5100N).

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

[0172] When the laminated 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, a 1 mm layer is applied to the surface of the fiber layer side of the laminated sheet. 2 When 100 cross-cuts are placed, cellophane tape (manufactured by Nichiban Co., Ltd.) is applied on top, pressed down, and then peeled off in a 90° direction, it is preferable that the number of squares in which the fiber layer is peeled from the resin layer is less than 5. In such cases, it can be determined that the interlayer adhesion between the fiber layer and the resin layer is good. It is more preferable that the number of peeled squares be 3 or less, even more preferable that be 1 or less, and particularly preferable that be 0.

[0173] When the laminated sheet of the present invention has a resin layer, the fiber layer can also function as a layer to reinforce the resin layer. Therefore, the strength of the laminated sheet itself is increased. Furthermore, when the laminated sheet is bonded to other substrates such as resin films or resin plates, the fiber layer also functions as a layer to reinforce the substrate. For example, by using a resin plate such as a polycarbonate plate as the substrate and bonding the laminated sheet to this resin plate, the mechanical strength of the resin plate can be reinforced. Thus, a laminated sheet having a fiber layer also possesses the effect of reinforcing the substrate.

[0174] When the laminated 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. Furthermore, 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 laminated sheet is a value measured by cutting a cross-section of the laminated sheet with an ultramicrotome UC-7 (manufactured by JEOL Corporation) and observing the cross-section with an electron microscope, magnifying glass, or visual inspection.

[0175] The ratio of the total thickness of the resin layer to the total thickness of the fiber layer (thickness of the resin layer / thickness of the fiber layer) is preferably 10 or less, more preferably 5 or less, and even more preferably 1 or less. Furthermore, for example, if the resin layer is a coated layer formed by coating, the ratio of the total thickness of the resin layer to the total thickness of the fiber layer (thickness of the resin layer / thickness of the 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 sheets) The present invention provides a method for producing a laminated sheet, comprising the steps of: forming a first fiber layer containing fibrous cellulose having a substituent 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 containing fibrous cellulose having an adhesive substituent amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less. The present invention also provides a method for producing a laminated sheet, which may further include the steps of forming a third fiber layer, a fourth fiber layer, ... a Xth fiber layer.

[0177] The step of forming a first fiber layer containing fibrous cellulose having a 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 (fine fibrous cellulose-containing slurry) onto a substrate or a step of papermaking using a fine fibrous cellulose dispersion. Furthermore, the step of forming a second fiber layer containing fibrous cellulose having a 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 (fine fibrous cellulose-containing slurry) onto the first fiber layer or a step of laminating the second fiber layer formed by papermaking using a fine fibrous cellulose dispersion onto the first fiber layer.

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

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

[0180] The quality of the substrate used in the coating process is not particularly limited, but a substrate with high wettability to a fine fibrous cellulose dispersion is preferable as it can suppress shrinkage of the sheet during drying. However, it is preferable to select a substrate that allows the sheet formed after drying to be easily peeled off. Among these, 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, as well as metal plates such as aluminum plates, zinc plates, copper plates, and iron plates, and those whose surfaces have been oxidized, 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 damming 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 damming frame is not particularly limited, but it is preferable to select one that allows the edges of the sheet that adhere after drying to be easily peeled off. 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 whose surfaces have been oxidized, as well as molded stainless steel plates, brass plates, etc., can be used.

[0182] For coating a fine fibrous cellulose dispersion, a bar coater, roll coater, gravure coater, die coater, curtain coater, air doctor coater, etc., can be used. 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 it is preferably between 20°C and 45°C. If the coating temperature is above the lower limit, the fine fibrous cellulose dispersion can be easily coated, and if it is below the upper limit, the volatilization of the dispersion medium during coating can be suppressed.

[0184] In the coating process, the finished basis weight of the sheet is 10 g / m². 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 fibrous layer with excellent strength can be obtained.

[0185] The manufacturing process for a sheet containing fine fibrous cellulose preferably includes a step of drying a dispersion of fine fibrous cellulose coated onto a substrate. The drying method is not particularly limited, but may be a non-contact drying method, a method of drying while restraining the sheet, or a combination of these.

[0186] Non-contact drying methods are not particularly limited, but can include methods of drying by heating with hot air, infrared rays, far-infrared rays, or near-infrared rays (heat drying method), or methods of drying in a vacuum (vacuum drying method). Heat drying and vacuum drying methods can be combined, but heat drying is usually applied. Drying with infrared rays, far-infrared rays, or near-infrared rays can be performed using infrared devices, far-infrared devices, or near-infrared devices, but are not particularly limited. The heating temperature in the heat drying method is not particularly limited, but is preferably 20°C to 150°C, and more preferably 25°C to 105°C. If the heating temperature is above the lower limit, the dispersion medium can be rapidly volatilized, and if it is below the upper limit, the cost required for heating can be suppressed and discoloration of the fine fibrous cellulose due to heat can be suppressed.

[0187] After drying, the obtained fine fibrous cellulose-containing sheet is peeled off the substrate. However, if the substrate is a sheet, the fine fibrous cellulose-containing sheet and the substrate may be wound together as a laminate, and the fine fibrous cellulose-containing sheet may be peeled off the substrate immediately before use. In this way, a fine fibrous cellulose-containing sheet that forms a fibrous layer is obtained.

[0188] <Paper making process> The manufacturing process for a sheet containing fine fibrous cellulose that forms a fibrous layer may include a step of papermaking a dispersion of fine fibrous cellulose. Examples of papermaking machines used in the papermaking process include continuous papermaking machines such as long-screen type, cylinder type, and inclined type, as well as multi-layer papermaking machines that combine these. Known papermaking methods such as manual papermaking may also be used in the papermaking process.

[0189] In the papermaking process, a fine fibrous cellulose dispersion is filtered and dewatered on a wire to obtain a wet paper sheet, which is then pressed and dried to obtain the sheet. The concentration of the fine fibrous cellulose dispersion is not particularly limited, but 0.05% by mass or more and 5% by mass or less is preferred. When filtering and dewatering the fine fibrous cellulose dispersion, the filter cloth used for filtration is not particularly limited, but it is important that the fine fibrous cellulose does not pass through and the filtration rate does not become too slow. Such a filter cloth is not particularly limited, but sheets, fabrics, or 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. Specifically, examples include porous membranes of polytetrafluoroethylene with a pore size of 0.1 μm to 20 μm, for example, 1 μm, and fabrics of polyethylene terephthalate or polyethylene with a pore size of 0.1 μm to 20 μm, for example, 1 μm, but are not particularly limited.

[0190] The method for producing a sheet from a fine fibrous cellulose dispersion is not particularly limited, but examples include a method using the manufacturing apparatus described in WO2011 / 013567. This manufacturing apparatus includes a watering section that discharges a fine fibrous cellulose dispersion onto the upper surface of an endless belt and generates a web by squeezing out the dispersion medium from the discharged fine fibrous cellulose dispersion, and a drying section that dries the web to generate a fibrous sheet. An endless belt is arranged from the watering section to the drying section, and the web generated in the watering section is transported to the drying section while remaining on the endless belt.

[0191] The dewatering method that can be used in the present invention is not particularly limited, but examples include dewatering methods that are normally used in paper manufacturing, and a method in which dewatering is performed using a long screen, a circular screen, or an inclined wire, followed by dewatering with a roll press is preferred. The drying method is not particularly limited, but examples include methods used in paper manufacturing, such as cylinder dryers, Yankee dryers, hot air drying, near-infrared heaters, and infrared heaters are preferred.

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

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

[0194] <Lamination of resin layers> If the laminated sheet of the present invention has a resin layer, it is preferable to include a step of forming the 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 the fiber layer with a resin composition. Furthermore, the method for manufacturing the laminated sheet of the present invention may include a step of forming a first fiber layer on a pre-formed resin layer, which contains fibrous cellulose having a substituent introduction amount of less than 0.5 mmol / g and a fiber width of 1000 nm or less, and a step of forming a second fiber layer on the first fiber layer, which contains fibrous cellulose having an adhesive layer substituent introduction amount of less than 0.5 mmol / g 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 resin, form a coating film, and then provide a drying step.

[0196] In addition to the methods described above, a method for manufacturing laminated sheets can also be used in which a resin layer is placed on a fiber layer and then heat-pressed. Another method involves placing a fiber layer inside an injection molding die and injecting heated and molten resin into the die to bond the resin layer to the fiber layer.

[0197] (Laminated structure) The present invention may also relate to a laminate formed by laminating the above-described laminated sheet with an adherend. Examples of adherends include organic films (hereinafter also referred to as organic layers) and inorganic films (hereinafter also referred to as inorganic layers). In particular, the laminate of the present invention is preferably a laminate formed by laminating the above-described laminated sheet with an organic film. Examples of organic films include resin films, resin plates, and resin molded articles.

[0198] Resin films, resin plates, and resin molded articles (hereinafter also simply referred to as resin films) are layers mainly composed of natural resins or synthetic resins. Here, the main component refers to a component that is present in an amount of 50% by mass or more of the total mass of the resin film. The resin component 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, based on the total mass of the resin film. The resin component content may also be 100% by mass of the total mass of the resin film.

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

[0200] Examples of synthetic resins include polyolefin resins, cyclic olefin resins, polycarbonate resins, polyethylene terephthalate resins, polyethylene naphthalate resins, polyimide resins, polystyrene resins, and acrylic resins. 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 include coating, injection molding, and heat-pressure methods. In the coating method, it is preferable to coat the resin composition that forms the organic layer onto the resin layer of the laminated sheet and then heat-cur or photo-cur it. In the heat-pressure method, it is preferable to heat-press the resin film while it is stacked on top of the resin layer of the laminated sheet. The heat-pressing conditions in this case can be appropriately selected with reference to the glass transition temperature of the resin film, etc.

[0202] The materials constituting the inorganic layer are not particularly limited, but examples include aluminum, silicon, magnesium, zinc, tin, nickel, titanium; oxides, carbides, nitrides, oxide carbides, oxide nitrides, or oxide carbnitrides thereof; or mixtures thereof. From the viewpoint of being able to stably maintain high moisture resistance, silicon oxide, silicon nitride, silicon oxide carbide, silicon oxide nitride, silicon oxide carbnitride, aluminum oxide, aluminum nitride, aluminum oxide carbide, oxide aluminum nitride, or mixtures thereof are preferred.

[0203] The method for forming the inorganic layer is not particularly limited, but examples include chemical vapor deposition (CVD) and physical vapor deposition (PVD). Specific CVD methods include plasma CVD, which utilizes plasma, and catalytic chemical vapor deposition (Cat-CVD), which uses a heated catalyst to catalytically decompose the material gas. Specific PVD methods include vacuum deposition, ion plating, and sputtering. Atomic layer deposition (ALD) can also be used as a method for forming the inorganic layer. The ALD method forms a thin film at the atomic layer level by alternately supplying the raw material gases of each element constituting the film to be formed to the surface forming the layer.

[0204] (Application) The laminated sheet of the present invention is transparent, has high mechanical strength, and exhibits suppressed discoloration. From the standpoint of utilizing these excellent optical properties, it is suitable for optical components. For example, it can be used as a light-transmitting substrate for various display devices and various solar cells. Furthermore, the laminated 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. [Examples]

[0205] The features of the present invention will be further described below with reference to examples and comparative examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following specific examples.

[0206] <Manufacturing Example 1> [Phosphorication treatment] As the raw material pulp, hardwood pulp (dry sheet) manufactured by Oji Paper Co., Ltd. was used. This raw material pulp was subjected to phosphorylation treatment as follows: First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (oven-dry mass) of the raw material pulp to adjust the mixture to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water to obtain chemically impregnated pulp. Next, the obtained chemically 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 phosphorylated pulp.

[0207] [Cleaning process] Next, the obtained phosphorylated pulp was subjected to a washing treatment. The washing treatment was carried out by repeatedly adding 10 L of deionized water to 100 g (oven-dry mass) of phosphorylated pulp to obtain a pulp dispersion, stirring the mixture to ensure uniform dispersion of the pulp, and then filtering and dewatering it. The washing was terminated when the electrical conductivity of the filtrate fell to 100 μS / cm or less.

[0208] [Neutralization treatment] Next, the washed phosphorylated pulp was subjected to a neutralization treatment as follows. First, the washed phosphorylated pulp was diluted with 10 L of deionized water, and then a 1N sodium hydroxide aqueous solution was gradually added while stirring to obtain a phosphorylated pulp slurry with a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated to obtain phosphorylated pulp that had undergone neutralization treatment. Then, the phosphorylated pulp that had undergone neutralization treatment was subjected to the washing treatment described above.

[0209] The resulting phosphorus oxoxide pulp was subjected to infrared absorption spectroscopy using FT-IR. The result showed that at 1230 cm⁻¹... -1 Absorption based on the P=O of phosphate groups was observed in the vicinity, confirming that phosphate groups were added to the pulp. Furthermore, when the obtained phosphorylated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of type I cellulose crystals.

[0210] [Fibrillation treatment] Deionized water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2% by mass. This slurry was processed six times at a pressure of 200 MPa using a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that this fine fibrous cellulose maintained type I cellulose crystals. The amount of phosphate groups (first dissociated acid amount, strongly acidic group amount) measured by the measurement method described in the section on [Phosphorus Oxoacid Group Amount] below was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0211] <Manufacturing Example 2> A dispersion of fine fibrous cellulose 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 performed after the washing and neutralization treatment of the phosphorylated pulp.

[0212] [Nitrogen removal treatment] A slurry with a solid content of 4% by mass was prepared by adding deionized water to phosphorylated pulp. A 48% by mass aqueous sodium hydroxide solution was added to the slurry to adjust the pH to 13.4, and the slurry was heated at a temperature of 85°C for 1 hour. Subsequently, this pulp slurry was dehydrated, and the pulp dispersion obtained by adding 10 L of deionized water to 100 g (oven-dry mass) of phosphorylated pulp was stirred to ensure uniform dispersion of the pulp, and the process of filtration and dewatering was repeated to remove excess sodium hydroxide. The removal process was terminated when the electrical conductivity of the filtrate was 100 μS / cm or less.

[0213] The resulting phosphorus oxoxide pulp was subjected to infrared absorption spectroscopy using FT-IR. The result showed that at 1230 cm⁻¹... -1 Absorption based on the P=O of phosphate groups was observed in the vicinity, confirming that phosphate groups were added to the pulp. Furthermore, X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained a type I cellulose crystal structure. The amount of phosphate groups (first dissociated acid amount, strongly acidic group amount) measured by the method described in [Measurement of Phosphorus Oxoacid Group Amount] below was 1.35 mmol / g. The total amount of dissociated acid was 2.30 mmol / g.

[0214] <Manufacturing Example 3> [Phosphorus oxidation treatment] Except for using 33 parts by mass of phosphorous acid (phosphonic acid) instead of ammonium dihydrogen phosphate in the phosphorylation treatment, the procedure was carried out in the same manner as in Production Example 1 to obtain a dispersion of fine fibrous cellulose containing phosphorylated pulp and fine fibrous cellulose.

[0215] The resulting phosphorylated pulp was subjected to infrared absorption spectroscopy using FT-IR. The result showed that at 1210 cm⁻¹, the absorption spectrum was measured. -1Absorption based on P=O of the phosphonic acid group, a tautomer of the phosphite group, was observed in the vicinity, confirming that ()phosphite groups (phosphonic acid groups) were added to the pulp. Furthermore, X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained a type I cellulose crystal structure. The amount of ()phosphite groups (amount of first dissociated acid) measured by the measurement method described in [Measurement of Phosphorus Oxoacid Group Amount] below was 1.51 mmol / g, and the total amount of dissociated acid was 1.54 mmol / g.

[0216] <Manufacturing Example 4> [Sulfation treatment] Except for using 38 parts by mass of sulfamic acid (amidosulfate) instead of ammonium dihydrogen phosphate in the phosphorylation treatment and extending the heating time to 19 minutes, the procedure was carried out in the same manner as in Production Example 1 to obtain a dispersion of fine fibrous cellulose containing sulfated pulp and fine fibrous cellulose.

[0217] The obtained sulfated pulp was subjected to infrared absorption spectroscopy using FT-IR. The results showed that 1220-1260 cm⁻¹ -1 Absorption based on sulfate groups (sulfone groups) was observed in the vicinity, confirming that sulfate groups (sulfone groups) were attached to the pulp. Furthermore, X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained a type I cellulose crystal structure. The amount of sulfone groups measured by the method described in [Measurement of Sulfone Group Amount] below was 1.12 mmol / g.

[0218] <Manufacturing Example 5> Except for performing the xantate treatment described below instead of the phosphorylation treatment, the procedure was carried out in the same manner as in Production Example 1 to obtain a dispersion of fine fibrous cellulose containing xantate pulp and fine fibrous cellulose.

[0219] [Xantate treatment] 100 parts by mass (oven-dry mass) of raw material pulp (hardwood pulp (dry sheet) manufactured by Oji Paper Co., Ltd.) were mixed with 2500 parts by mass of an 8.5% by mass sodium hydroxide aqueous solution and stirred at room temperature for 3 hours to perform alkaline treatment. The pulp after alkaline treatment was separated into solid and liquid by centrifugation (400 mesh filter cloth, 3000 rpm for 5 minutes) to obtain dehydrated alkali cellulose. 3.5 parts by mass of carbon disulfide were added to 10 parts by mass (oven-dry mass) of the obtained alkali cellulose and the sulfidation reaction was carried out at room temperature for 4.5 hours to perform xantate treatment.

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

[0221] [measurement] [Measurement of haze in dispersion] The haze of the dispersion was measured by diluting the fibrous cellulose dispersion with deionized water to 0.2% by mass, and then measuring it using a haze meter (HM-150, Murakami Color Technology Research Institute) with a liquid glass cell (MG-40, Fujiwara Seisakusho, reverse path) with a path length of 1 cm, in accordance with JIS K 7136:2000. Zero point measurement was performed using deionized water in the same glass cell. The dispersion to be measured was left to stand for 24 hours at 23°C and 50% relative humidity before measurement. The temperature of the dispersion at the time of measurement was 23°C.

[0222] [Measurement of nanofiber yield] The nanofiber yield after centrifugation of fibrous cellulose dispersions was measured by the method described below. The nanofiber yield is an indicator of the yield of fine fibrous cellulose; a higher nanofiber yield indicates a higher yield of fine fibrous cellulose. Each dispersion was adjusted to a cellulose concentration of 0.1% by mass and centrifuged using a cooled high-speed centrifuge (Kokusan Co., Ltd., H-2000B) at 12000G for 10 minutes. The obtained supernatant was collected, and the cellulose concentration of the supernatant was measured. The yield of fine fibrous cellulose was determined based on the following formula. Nanofiber yield (mass%) = Cellulose concentration in supernatant (mass%) / 0.1 × 100

[0223] [Measuring nitrogen content] The total amount of nitrogen contained in fibrous cellulose and free nitrogen contained in the fibrous cellulose dispersion was measured by the following method. Each dispersion was adjusted to a solid content 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 by cation chromatography and the nitrogen content (mmol / g) was calculated by dividing it by the amount of cellulose used for the measurement (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 a 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 vessel and heated at a liquid temperature of 160°C for 15 minutes until the amount of phosphate groups was less than 0.08 mmol / g. This operation confirmed the formation of fine fibrous cellulose aggregates.

[0226] [Washing treatment of slurry after substituent removal] After heating, an equal amount of deionized water was added to the slurry to obtain a slurry with a solid content of approximately 1% by mass. The slurry was then stirred, and the filtration and dewatering process was repeated to wash the slurry. When the electrical conductivity of the filtrate fell below 10 μS / cm, deionized water was added again to obtain a slurry with a solid content of approximately 1% by mass, and the slurry was allowed to stand for 24 hours. The filtration and dewatering process was repeated again, and the washing was terminated when the electrical conductivity of the filtrate fell below 10 μS / cm once more. Deionized water was added to the obtained fine fibrous cellulose aggregates, and after substituent removal, a slurry was obtained. The solid content of this slurry was 1.7% by mass.

[0227] [Uniform dispersion treatment of slurry after substituent removal] Deionized water was added to the obtained substituent-removed slurry to obtain a slurry with a solid content of 1.0% by mass. This slurry had a pH of 5.5. It was processed three times at a pressure of 200 MPa using a wet atomizer (Sugino Machine Co., Ltd., Starburst) to obtain a substituent-removed fine fibrous cellulose dispersion containing substituent-removed fine fibrous cellulose. The number-average fiber width of the substituent-removed fine fibrous cellulose, as measured in the [Fiber Width Measurement] section described later, was 4 nm, and the proportion of fine fibrous cellulose with a fiber width of 10 nm or less among the total fibrous cellulose contained in the dispersion was 98%.

[0228] [Creating the sheet 1] A polyvinyl alcohol aqueous solution was obtained by adding acetoacetyl-modified polyvinyl alcohol (Gosenex Z-200, manufactured by Mitsubishi Chemical Corporation) to deionized water to a concentration of 12% by mass, and stirring at 95°C for 1 hour.

[0229] The substituent-removed fine fibrous cellulose dispersion and the above polyvinyl alcohol aqueous solution were each diluted with deionized water to a solid content concentration of 0.6% by mass. Next, 50 parts by mass of the diluted substituent-removed fine fibrous cellulose dispersion were mixed with 50 parts by mass of the diluted polyvinyl alcohol aqueous solution to obtain a mixture. Furthermore, the mixture was measured to obtain a finished sheet thickness of 12.5 μm and spread onto a commercially available glass plate. A damming frame (internal dimensions 250 mm x 250 mm, height 5 cm) was placed on the glass plate to ensure the desired thickness. The mixture was then dried in a 140°C oven for 1 hour. The same mixture was then measured again to obtain a finished thickness of 12.5 μm, spread on top of the glass plate, and dried in a 140°C oven for 1 hour. By peeling the sheet from the glass plate, a laminated sheet with a total thickness of 25 μm was obtained.

[0230] <Example 2> The mixture obtained in [Sheet Preparation 1] of Example 1 was measured out so that the finished sheet thickness would be 25 μm, and spread onto a commercially available glass plate. A damming frame (internal dimensions 250 mm x 250 mm, height 5 cm) was placed on the glass plate to ensure the desired thickness. The sheet was then dried in a 140°C dryer for 1 hour. The same mixture was then measured out again so that the finished thickness would be 25 μm, spread on top, and dried in a 140°C dryer for 1 hour. By peeling the sheet from the glass plate, a laminated sheet with a total thickness of 50 μm was obtained.

[0231] <Example 3> The mixture obtained in [Sheet Preparation 1] of Example 1 was measured to a finished sheet thickness of 12.5 μm and spread onto a commercially available glass plate. A retaining frame (internal dimensions 250 mm x 250 mm, height 5 cm) was placed on the glass plate to ensure the desired thickness. The sheet was then dried in a 140°C dryer for 1 hour. By peeling the sheet from the glass plate, a sheet A with a thickness of 12.5 μm was obtained. Next, sheet A was inverted, and the side opposite the peeled-off side of the glass plate was attached to the glass plate. A retaining frame (internal dimensions 200 mm x 200 mm, height 5 cm) was placed, and the same mixture was measured to a finished thickness of 12.5 μm and spread on top of it. The sheet was then dried in a 140°C dryer for 1 hour. By peeling the sheet from the glass plate, a laminated sheet with a total thickness of 25 μm was obtained.

[0232] <Example 4> The mixed solution obtained in [Sheet Preparation 1] of Example 1 was weighed so that the finished thickness of the sheet would be 25 μm, and then spread on a commercially available glass plate. A frame for damming (inner dimension: 250 mm × 250 mm, height: 5 cm) was placed on the glass plate so as to achieve a predetermined thickness. Then, it was dried in a dryer at 140 °C for 1 hour. By peeling the sheet from the glass plate, a sheet B with a thickness of 25 μm was obtained. Next, the sheet B was inverted, the surface on the opposite side of the glass plate peeling surface was attached to the glass plate, a frame for damming (inner dimension: 200 mm × 200 mm, height: 5 cm) was placed, and the same mixed solution was weighed and spread thereon so that the finished thickness would be 25 μm, and then dried in a dryer at 140 °C for 1 hour. By peeling the sheet from the glass plate, a laminated sheet with a total thickness of 50 μm was obtained.

[0233] <Example 5> In [Sheet Preparation 1] of Example 1, 40 parts by mass of the de-substituted micro-fibrillar 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 operations as in Example 4 were performed 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 de-substituted micro-fibrillar 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 operations as in Example 4 were performed 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 de-substituted micro-fibrillar 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 operations as in Example 4 were performed to obtain a laminated sheet with a total thickness of 50 μm.

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

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

[0238] <Example 10> The mixture obtained in [Sheet Preparation 1] of Example 1 was measured to a size that would result in a finished sheet thickness of 50 μm and spread onto a commercially available glass plate. A retaining frame (internal dimensions 250 mm x 250 mm, height 5 cm) was placed on the glass plate to ensure the desired thickness. After drying in a 140°C dryer for 1 hour, the sheet was peeled off the glass plate to obtain a sheet C with a thickness of 50 μm. Next, sheet C was inverted, and the side opposite the peeled-off surface was attached to the glass plate. A retaining frame (internal dimensions 200 mm x 200 mm, height 5 cm) was placed on top of it, and the same mixture was measured to a size that would result in a finished thickness of 50 μm and spread over it. It was then dried in a 140°C dryer for 1 hour. By peeling the sheet off the glass plate, a laminated sheet with a total thickness of 100 μm was obtained.

[0239] <Example 11> The mixture obtained in [Sheet Preparation 1] of Example 1 was measured out so that the finished sheet thickness would be 50 μm, and spread onto a commercially available glass plate. A damming frame (internal dimensions 250 mm x 250 mm, height 5 cm) was placed on the glass plate to ensure the desired thickness. After drying in a 140°C dryer for 1 hour, the sheet was peeled off the glass plate to obtain sheet C (first layer) with a thickness of 50 μm. Next, sheet C was flipped over, and the side opposite the peel-off surface of the glass plate was attached to the glass plate. A damming frame (internal dimensions 200mm x 200mm, height 5cm) was placed on top of it. The same mixture was weighed and spread over the frame so that the finished thickness would be 50μm, and dried in a 140°C dryer for 1 hour (second layer). Then, the same mixture was weighed and spread over the second layer so that the finished thickness would be 50μm, and dried in a 140°C dryer for 1 hour (third layer). By peeling it off from the glass plate, a sheet D with a total thickness of 150μm was obtained. Next, sheet D was flipped over, and the side opposite the peeling surface of the glass plate was attached to the glass plate. A damming frame (internal dimensions 150 mm x 150 mm, height 5 cm) was placed, and the same mixture was lightly weighed and spread onto the first layer described above so that the finished thickness would be 50 μm. It was then dried in a 140°C dryer for 1 hour (fourth layer), and peeled off from the glass plate to obtain a laminated sheet with a total thickness of 200 μm. In Example 11, the laminated sheets were stacked 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 acrylic resin (Acrit 8KX-012C, manufactured by Taisei Fine Chemicals Co., Ltd., with a solid content of 39% by mass) in which hydroxyl-containing acryloyl groups are graft-polymerized, 38 parts by mass of a polyisocyanate compound (TPA-100, manufactured by Asahi Kasei Chemicals Corporation), and 100 parts by mass of methyl ethyl ketone. Then, one side of the 50 μm thick laminated sheet obtained in Example 4 was coated with 3 g / m² after drying with a bar coater. 2 After applying the material in this manner, the sheet was heated at 100°C for 1 hour to obtain a laminated sheet containing a resin layer on one side.

[0241] <Example 13> 15 parts by mass of modified polycarbonate resin (Yupizeta FPC-2136, manufactured by Mitsubishi Gas Chemical Company, Inc.), 57 parts by mass of toluene, and 28 parts by mass of methyl ethyl ketone were mixed to obtain a resin coating solution. Next, 2.25 parts by mass of an isocyanate compound (Duranate TPA-100, manufactured by Asahi Kasei Chemicals Corporation) was added to the resin coating solution as an adhesion promoter and mixed to obtain a resin composition. Then, the above resin composition was applied to one side of a 50 μm thick laminated sheet obtained in Example 4 using a bar coater, and the coating amount after drying of each side was 3 g / m². 2 After applying the mixture, it was heated at 100°C for 1 hour to cure. Furthermore, the same resin composition was applied to the opposite side and dried using a bar coater. The amount of coating on each side after drying was 3g / m². 2 After applying the material in this manner, it was heated at 100°C for 1 hour to cure. In this way, a laminated sheet containing resin layers 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 obtain a phosphate group content of 0.40 mmol / g. Otherwise, the same procedure as in Example 4 was performed to obtain a laminated sheet.

[0243] <Example 15> In the substituent removal treatment in Example 1, heat treatment was performed without pH adjustment, resulting in a phosphate group content of 0.29 mmol / g. Otherwise, the same procedure as in Example 4 was followed to obtain a laminated sheet.

[0244] <Example 16> In Example 1, the substituent removal treatment was carried out by the enzymatic treatment described below instead of heat treatment, and the slurry after substituent removal was washed using the method described below. Otherwise, the same procedure as in Example 4 was followed to obtain a laminated sheet.

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

[0246] [Washing treatment of the slurry after substituent removal by enzymatic treatment] To the obtained slurry after substituent removal, a strongly basic ion exchange resin (Amberjet 4400; Organo Corporation, conditioned) and a weakly acidic ion exchange resin (Amberlite IRC76; Organo Corporation, conditioned) in a volume of 1 / 5 were added, and after shaking treatment for 1 hour, the slurry was poured onto a mesh with a 90-μm opening to separate the resin and the slurry, thereby washing the slurry.

[0247] <Example 17> A laminated sheet was obtained by performing the same operations as in Example 4, except that the microfibrillar cellulose dispersion obtained in Production Example 2 was used instead of the microfibrillar cellulose dispersion obtained in Production Example 1.

[0248] <Example 18> A laminated sheet was obtained by performing the same operations as in Example 4, except that the microfibrillar cellulose dispersion obtained in Production Example 3 was used instead of the microfibrillar cellulose dispersion obtained in Production Example 1.

[0249] <Example 19> A laminated sheet was obtained by performing the same operations as in Example 4, except that the microfibrillar cellulose dispersion obtained in Production Example 4 was used instead of the microfibrillar cellulose dispersion obtained in Production Example 1.

[0250] <Example 20> Instead of the fine fibrous cellulose dispersion obtained in Production Example 1, the fine fibrous cellulose dispersion obtained in Production Example 5 was used. Furthermore, the same procedure as in Example 4 was performed to obtain a laminated sheet, except that the substituent removal treatment (low temperature heat treatment) described later was performed instead of the substituent removal treatment (high temperature heat treatment).

[0251] [Substituent removal (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 xantate groups was less than 0.08 mmol / g.

[0252] <Example 21> A laminated sheet containing fine fibrous cellulose was obtained in the same manner as in Example 4, except that the slurry was not subjected to uniform dispersion treatment after substituent removal.

[0253] <Example 22> A laminated sheet containing fine fibrous cellulose was obtained in the same manner as in Example 18, except that the slurry was not subjected to uniform dispersion treatment after substituent removal.

[0254] <Example 23> A laminated sheet containing fine fibrous cellulose was obtained in the same manner as in Example 19, except that the slurry was not subjected to uniform dispersion treatment after substituent removal.

[0255] <Example 24> A laminated sheet containing fine fibrous cellulose was obtained in the same manner as in Example 20, except that the slurry was not subjected to uniform dispersion treatment after substituent removal.

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

[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. 50 parts by mass of the fine fibrous cellulose dispersion were mixed with 50 parts by mass of diluted polyvinyl alcohol aqueous solution to obtain a mixture. The mixture was then weighed to a finished sheet thickness of 25 μm and spread onto a commercially available glass plate. A damming frame (internal dimensions 250 mm x 250 mm, height 5 cm) was placed on the glass plate to ensure the desired thickness. The mixture was then dried in a 140°C oven for 1 hour and peeled off 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. 50 parts by mass of the fine fibrous cellulose dispersion were mixed with 50 parts by mass of diluted polyvinyl alcohol aqueous solution to obtain a mixture. The mixture was then weighed to obtain a sheet with a finished thickness of 50 μm and spread onto a commercially available glass plate. A damming frame (internal dimensions 250 mm x 250 mm, height 5 cm) was placed on the glass plate to ensure the desired thickness. The mixture was then dried in a 140°C oven for 1 hour and peeled off 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. 50 parts by mass of the fine fibrous cellulose dispersion were mixed with 50 parts by mass of diluted polyvinyl alcohol aqueous solution to obtain a mixture. The mixture was then weighed to obtain a sheet with a finished thickness of 50 μm and spread onto a commercially available glass plate. A damming frame (internal dimensions 250 mm x 250 mm, height 5 cm) was placed on the glass plate to ensure the desired thickness. The sheet was then dried in a 140°C oven for 1 hour and peeled off 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. 50 parts by mass of the fine fibrous cellulose dispersion were mixed with 50 parts by mass of diluted polyvinyl alcohol aqueous solution to obtain a mixture. The mixture was then weighed to a finished sheet thickness of 200 μm and spread onto a commercially available glass plate. A damming frame (internal dimensions 250 mm x 250 mm, height 5 cm) was placed on the glass plate to ensure the desired thickness. The mixture was then dried in a 140°C oven for 1 hour and peeled off the glass plate to obtain a sheet with a thickness of 200 μm.

[0261] <Comparative Example 5> A sheet was obtained by performing the same procedure as in Comparative Example 1, except that the mixture of Example 1 was used instead of the mixture of Comparative Example 1.

[0262] <Comparative Example 6> A sheet was obtained by performing the same procedure as in Comparative Example 2, except that the mixture of Example 1 was used instead of the mixture of Comparative Example 2.

[0263] <Comparative Example 7> A sheet was obtained by performing the same procedure as in Comparative Example 4, except that the mixture from Example 1 was used instead of the mixture from Comparative Example 4.

[0264] <Comparative Example 8> The same procedure as in Comparative Example 2 was followed to obtain a sheet, except that the mixture of Example 14 was used instead of the mixture of Comparative Example 2.

[0265] <Comparative Example 9> The same procedure as in Comparative Example 2 was followed to obtain a sheet, except that the mixture of Example 15 was used instead of the mixture of Comparative Example 2.

[0266] <Comparative Example 10> The same procedure as in Comparative Example 2 was followed to obtain a sheet, except that the mixture of Example 16 was used instead of the mixture of Comparative Example 2.

[0267] <Comparative Example 11> The same procedure as in Comparative Example 2 was followed to obtain a sheet, except that the mixture of Example 17 was used instead of the mixture of Comparative Example 2.

[0268] <Comparative Example 12> The same procedure as in Comparative Example 2 was followed to obtain a sheet, except that the mixture of Example 18 was used instead of the mixture of Comparative Example 2.

[0269] <Comparative Example 13> The same procedure as in Comparative Example 2 was followed to obtain a sheet, except that the mixture of Example 19 was used instead of the mixture of Comparative Example 2.

[0270] <Comparative Example 14> The same procedure as in Comparative Example 2 was followed to obtain a sheet, except that the mixture of Example 20 was used instead of the mixture of Comparative Example 2.

[0271] <Comparative Example 15> The same procedure as in Comparative Example 2 was followed to obtain a sheet, except that the mixture of Example 21 was used instead of the mixture of Comparative Example 2.

[0272] <Comparative Example 16> The same procedure as in Comparative Example 2 was followed to obtain a sheet, except that the mixture of Example 22 was used instead of the mixture of Comparative Example 2.

[0273] <Comparative Example 17> The same procedure as in Comparative Example 2 was followed to obtain a sheet, except that the mixture of Example 23 was used instead of the mixture of Comparative Example 2.

[0274] <Comparative Example 18> The same procedure as in Comparative Example 2 was followed to obtain a sheet, except that the mixture of Example 24 was used instead of the mixture of Comparative Example 2.

[0275] <Comparative Example 19> The same procedure as in Comparative Example 2 was followed to obtain a sheet, except that the mixture of Example 7 was used instead of the mixture of Comparative Example 2.

[0276] <Comparative Example 20> The same procedure as in Comparative Example 2 was followed to obtain a sheet, except that the mixture of Example 8 was used instead of the mixture of Comparative Example 2.

[0277] <Comparative Example 21> A sheet was obtained by performing the same procedure as in Example 12, except that a 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 by performing the same procedure as in Example 13, except that a 50 μm thick sheet obtained in Comparative Example 6 was used instead of the laminated sheet of Example 13.

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

[0280] [Measuring fiber width] 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% to 0.1% by mass and cast onto a hydrophilic carbon film coated grid. After drying, it was stained with uranyl acetate and observed using a transmission electron microscope (TEM, JEOL-2000EX, JEOL Ltd.). At that time, axes of arbitrary image width were assumed in the obtained image, and the magnification was adjusted so that 20 or more fibers intersected each axis. After obtaining observation images that met this condition, two random axes were drawn vertically and horizontally for each image, and the fiber width of the fibers intersecting the axes was visually read. Three non-overlapping observation images were taken for each dispersion, and the fiber width values ​​of the fibers intersecting 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 way. However, for Examples 1-25 and Comparative Examples 5-22, the measurements were performed using a substituent-removed fine fibrous cellulose dispersion, while for Comparative Examples 1-4, the measurements were performed using a fine fibrous cellulose dispersion.

[0281] [Measurement of phosphorus oxoacid group content] In measuring the amount of phosphorus oxoacid groups (phosphate groups or phosphite groups), first, ion-exchanged water was added to the target fine fibrous cellulose to prepare a slurry with a solid content of 0.2% by mass. After treating the obtained slurry with an ion-exchange resin, the amount was measured by titration using an alkali. The ion exchange resin treatment was performed by adding 1 / 10 the volume of 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 a mesh size of 90 μm to separate the resin from the slurry. Furthermore, the alkali titration was performed by adding 10 μL of 0.1 N sodium hydroxide aqueous solution to a fine fibrous cellulose-containing slurry after treatment with ion exchange resin, while measuring the change in the pH value of the slurry. Nitrogen gas was blown into the slurry starting 15 minutes before the start of the titration. In this neutralization titration, two points were observed where the increment (the derivative of pH with respect to the amount of alkali added) was maximum on the curve plotting the measured pH against the amount of alkali added. Of these, the first increment maximum obtained after starting to add alkali is called the first endpoint, and the next increment maximum obtained 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 the first dissociated acid in the slurry used for titration. Also, 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. Furthermore, the amount of alkali (mmol) required from the start of the titration to the first endpoint was divided by the solid content (g) in the slurry being titrated to obtain the amount of phosphorus oxoacid groups (mmol / g).

[0282] [Measurement of sulfone group content] The amount of sulfone groups was measured as follows: Fine fibrous cellulose was frozen in a freezer and then dried for 3 days in a freeze-dryer (FreeZone, manufactured by Labconco). The resulting freeze-dried material was pulverized into a powder using a hand mixer (LaboMillser PLUS, manufactured by Osaka Chemical) at a rotation speed of 20,000 rpm for 60 seconds. The freeze-dried and pulverized samples were subjected to pressurized thermal decomposition with nitric acid in a sealed container. After that, the sulfur content was measured by ICP-OES after appropriate dilution. The value calculated by dividing by the oven-dry mass of the fine fibrous cellulose used was defined as the amount of sulfate ester groups (unit: mmol / g).

[0283] [Measurement of xantate base amount] The amount of xantate groups was measured by the Bredee method. Specifically, 1.5 parts by mass (dry weight) of fibrous cellulose was mixed with 40 mL of saturated ammonium chloride solution, and the sample was thoroughly mixed while crushing it with a glass rod. After standing for about 15 minutes, the mixture was filtered through GFP filter paper (GS-25, 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 standing for 15 minutes, phenolphthalein solution was added until the solution turned pink, and then 1.5 M acetic acid was added until the solution changed from pink to colorless, which was considered the neutralization point. After neutralization, 250 mL of distilled water was added and stirred well, and 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 titrated with 0.05 mol / L sodium thiosulfate solution. The amount of xantate group was calculated from the titration volume of sodium thiosulfate and the oven-dry mass of fibrous cellulose using the following formula. Xantate group amount (mmol / g) = (0.05 × 10 × 2 - 0.05 × sodium thiosulfate titration volume (mL)) / 1000 / oven-dry mass of fibrous cellulose (g)

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

[0285] [Haze measurement of laminated sheets] In accordance with JIS K 7136:2000, the haze of the laminated sheets was measured using a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute).

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

[0287] [Curl measurement] The resulting laminated sheet was cut into 100mm squares and left on a flat surface for at least 4 hours in an environment of 23°C and 50% relative humidity. The height (mm) of the four corners after leaving the sheet was measured, and the average value was used as the curl measurement. In cases where the sheet curled and became extremely rounded, it was recorded as infinity.

[0288] [Calculation of C / O ratio (evaluation of the uneven distribution of fine cellulose fibers in the fiber layer)] The distribution of fine cellulose fibers in the fiber layer was determined by calculating the ratio of atomic percent of carbon (C) to atomic percent of oxygen (O) (C / O ratio) using XPS (X-ray photoelectron spectroscopy). When the analysis target was a laminated sheet, the ratio of atomic percent of carbon (C) to atomic percent of oxygen (O) by XPS was calculated for the front and back surfaces of the laminated sheet and the interface of each layer. For example, when performing XPS analysis on a laminated sheet with a thickness of 50 μm, obtained by laminating two fiber layers with a thickness of 25 μm each, the XPS analysis was performed on the surface of the laminated sheet, then the laminated sheet was carefully scraped with a commercially available razor, and XPS analysis was performed on the area scraped 25 μm from the surface. Similarly, the XPS analysis was performed on the back surface of the laminated sheet, then the laminated sheet was carefully scraped with a commercially available razor, and XPS analysis was performed on the area scraped 25 μm from the surface. XPS analysis was performed at a measurement depth of 5 nm. A scraping area of ​​1 mm square is sufficient, but for operational convenience, scraping a larger area is not a problem. If the laminated sheet had a resin layer, the resin layer was wiped off with a solvent such as MEK to expose the fiber layer before performing the above measurements.

[0289] [Measurement of pH on the surface of laminated sheets] 10 μL of deionized water was dropped onto a 1 cm square area of ​​the surface of the obtained laminated sheet using a micropipette, and the pH of that area was measured using a flat-type pH combination electrode (6261-10C; HORIBA). Measurements were performed 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: Organophyllum

[0295] The laminated sheets obtained in the examples demonstrated both resistance to yellowing and resistance to curling.

[0296] <Example 101> (Lamination with resin film) A resin coating solution was obtained by mixing 15 parts by mass of modified polycarbonate resin (Yupizeta 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 to the resin coating solution as an adhesion promoter and mixed to obtain a resin composition. Then, the resin composition was applied to one side of a 0.3 mm thick polycarbonate sheet (Panlite PC-2151, manufactured by Teijin Limited) as a resin film using a bar coater, with a coating amount of 3 g / m² after drying. 2After applying the material in this manner, it was heated at 100°C for 1 hour to cure. Subsequently, the same procedure as in Sheet Preparation 1 in Example 1 was performed using the laminate of the resin film and resin composition instead of the commercially available glass plate, to obtain a 25 μm laminated sheet and a laminate of resin film.

[0297] <Example 102> A resin composition was obtained by mixing 76 parts by mass of special modified polyester resin (Arakawa Chemical Industries, Ltd., Aracoat AP2510), 10 parts by mass of curing agent (Arakawa Chemical Industries, Ltd., CL2502), and 14 parts by mass of methyl ethyl ketone. Next, the above resin composition was applied to one side of a 0.35 mm thick polyester sheet (Toray Industries, Inc., Lumirror S10) as a resin film using a bar coater, with a coating amount of 3 g / m² after drying. 2 After applying the material in this manner, it was heated at 100°C for 1 hour to cure. Subsequently, instead of a commercially available glass plate, the laminate of the above resin film and resin composition was used, and the same procedure as in Sheet Preparation 1 in Example 1 was performed to obtain a laminate of a laminated sheet and resin film with a fiber layer of 25 μm.

[0298] <Example 103> Two 100mm square laminated sheets were prepared, each trimmed from the laminated sheet obtained in Example 13. A 100mm square, 0.5mm thick polycarbonate sheet was sandwiched between these two laminated sheets, and then sandwiched between two 200mm square stainless steel sheets. The resulting structure was then inserted into a mini test press (Toyo Seiki Kogyo Co., Ltd., MP-WCH) set to room temperature and heated to 160°C over 3 minutes under a press pressure of 0.2 MPa. After holding it in this state for 30 seconds, it was cooled to 30°C over 3 minutes. A laminate with a polycarbonate sheet was obtained using the above procedure.

[0299] <Example 104> A resin composition was obtained by mixing 76 parts by mass of special modified polyester resin (Arakawa Chemical Industries, Ltd., Aracoat AP2510), 10 parts by mass of curing agent (Arakawa Chemical Industries, Ltd., CL2502), and 14 parts by mass of methyl ethyl ketone. Next, the above resin composition was applied to one side of the 50 μm thick laminated sheet obtained in Example 4 using a bar coater, with a coating amount of 3 g / m² after drying. 2 After applying the mixture, it was heated at 100°C for 1 hour to cure. Furthermore, the same resin composition was applied to the opposite side using a bar coater, and the coating amount after drying was 3 g / m². 2 After applying the material in this manner, it was heated at 100°C for 1 hour to cure. In this way, a laminated sheet containing resin layers on both sides was obtained. A laminate with a polyethylene terephthalate sheet was obtained in the same manner as in Example 103, except that the above laminated sheet was used instead of the laminated sheet of Example 13, and a polyethylene terephthalate sheet was used instead of a polycarbonate sheet. [Explanation of Symbols]

[0300] 10. Fiber layer (first fiber layer) 20. Fiber layer (second fiber layer) 100 Laminated Sheets

Claims

1. A laminated sheet comprising two layers of fiber containing fibrous cellulose having a substituent introduction amount of 0.03 mmol / g or more and less than 0.5 mmol / g, and a fiber width of 1000 nm or less, Each fiber layer has a different fibrous cellulose content in the thickness direction. A laminated sheet in which the fibrous cellulose is unevenly distributed on the side where each fiber layer is in contact.

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

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

4. The laminated sheet according to any one of claims 1 to 3, wherein the substituent is an anionic group.

5. The laminated sheet according to claim 4, wherein the anionic group is a phosphorus oxoacid group or a functional group derived from a phosphorus oxoacid group.

6. The laminated sheet according to any one of claims 1 to 5, wherein the fibrous cellulose has a carbamide group.

7. The laminated sheet according to any one of claims 1 to 6, wherein the overall thickness of the fiber layer is 20 μm or more.

8. The overall density of the fiber layer is 1.0 g / cm³. ３ The laminated sheet according to any one of claims 1 to 7.

9. The laminated sheet according to any one of claims 1 to 8, wherein the number-average fiber width of the fibrous cellulose contained in the fiber layer is 1 to 10 nm.

10. The laminated sheet according to any one of claims 1 to 9, further comprising a resin layer on at least one side of the fiber layer.

11. The laminated sheet according to claim 10, wherein the resin layer is directly laminated to the fiber layer.

12. The laminated sheet according to claim 10 or 11, wherein the resin layer comprises at least one selected from polycarbonate resin and acrylic resin.

13. The laminated sheet according to any one of claims 10 to 12, wherein the resin layer further comprises an adhesion promoter.

14. The laminated sheet according to claim 13, wherein the adhesion aid is at least one selected from isocyanate compounds and organosilicon compounds.

15. The laminated sheet according to claim 13 or 14, 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 resin contained in the resin layer.

16. A laminated sheet according to any one of claims 1 to 15, wherein the YI value is 2.5 or less.

17. A laminated sheet according to any one of claims 1 to 16, wherein the haze is 80% or less.

18. A laminated sheet according to any one of claims 1 to 17, for use as an optical component.

19. A laminate comprising a laminated sheet according to any one of claims 1 to 18 and an adherend.

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