Layered sheet, laminate, thermally processed article, transparent member, and production methods for layered sheet and thermally processed article

Abstract

The present invention provides a layered sheet that, when combined with a resin film or the like in a laminate, has excellent rigidity and does not readily generate bubbles when thermally processed, a laminate that comprises the layered sheet, a thermally processed article that is obtained by thermally processing the laminate, a transparent member that includes the thermally processed article, and production methods for the layered sheet and the thermally processed article.　This layered sheet (i) includes a fine fibrous cellulose–containing layer that contains fine fibrous cellulose that has a fiber width of no more than 1000 nm, has an adhesive layer 1a on one surface of the fine fibrous cellulose–containing layer, and has an organic solvent content that satisfies a specific condition or (ii) includes a fine fibrous cellulose–containing layer that contains fine fibrous cellulose that has a fiber width of no more than 1000 nm, has an adhesive layer 1a on one surface of the fine fibrous cellulose–containing layer, has an adhesive layer 1b on the other surface, and has an organic solvent content that satisfies a specific condition.

Description

Laminated sheet, laminate, heat-processed product, transparent member, and method for manufacturing laminated sheet and heat-processed product

[0001] The present invention relates to a laminate sheet, a laminate, a thermally processed product, a transparent member, and a method for producing the laminate sheet and the thermally processed product.

[0002] In recent years, materials using renewable natural fibers have been attracting attention due to the need to replace petroleum resources and growing environmental awareness. Among natural fibers, fibrous cellulose with a fiber width of 10 μm to 50 μm, particularly wood-derived fibrous cellulose (pulp), has been widely used, primarily in paper products. As fibrous cellulose, fine fibrous cellulose with a fiber width of 1,000 nm or less is also known. Furthermore, sheets composed of such fine fibrous cellulose, as well as composite sheets and molded articles containing fine fibrous cellulose and resin, have been developed. It is known that sheets and molded articles containing fine fibrous cellulose have significantly increased fiber-to-fiber contact points, resulting in significantly improved tensile strength and other properties. Patent Document 1 discloses a polycarbonate resin / cellulose fiber laminate comprising a polycarbonate resin layer and a cellulose fiber layer, in which the thickness of the polycarbonate resin layer is 1.4 times or more the thickness of the cellulose fiber layer, with the aim of providing a composite that has high transparency, high elasticity, a low linear expansion coefficient, a good balance of properties such as impact resistance, and is also easy to produce by laminating the polycarbonate resin layer and the cellulose fiber layer.

[0003] Patent No. 4985573

[0004] Because fine fibrous cellulose-containing sheets have excellent mechanical strength, such as tensile strength, and excellent transparency, they are expected to be used as laminates combined with adhesive layers, resin films, etc., for various display devices, optical components such as various solar cells, and window materials for various vehicles and buildings. However, the inventors' studies have revealed that when a laminate sheet obtained by forming an adhesive layer on a fine fibrous cellulose-containing sheet is combined with a resin film, etc. to form a laminate, and then heated and processed into a desired shape, bubbles are generated in the resulting processed product, resulting in a problem of reduced appearance and transparency of the thermally processed product. Furthermore, to further improve product quality when used in the above applications, it is desirable to improve the rigidity of the laminate. Therefore, the present invention aims to provide a laminate sheet that, when combined with a resin film, etc., has excellent rigidity and is less likely to generate bubbles even when thermally processed, a laminate including the laminate sheet, a thermally processed product obtained by thermally processing the laminate, and a transparent member including the thermally processed product, as well as a method for producing the laminate sheet and the thermally processed product.

[0005] That is, the present invention relates to the following items <1> to <21>: <1> A laminate sheet, (i) having an adhesive layer 1a on one side of a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1,000 nm or less, and satisfying at least one of the following conditions A and B, or (ii) having an adhesive layer 1a on one side of a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1,000 nm or less, and an adhesive layer 1b on the other side, and satisfying at least one of the following conditions C and D. Condition A: The total content of organic solvents in the fine fibrous cellulose-containing layer and adhesive layer 1a is, by mass, 0.1 ppm or more and 40 ppm or less. Condition B: The content of organic solvents in adhesive layer 1a is, by mass, 0.5 ppm or more and 200 ppm or less. Condition C: The total content of organic solvents in the fine fibrous cellulose-containing layer, adhesive layer 1a and adhesive layer 1b is, by mass, 0.1 ppm or more and 60 ppm or less. Condition D: The total content of organic solvents in adhesive layer 1a and adhesive layer 1b is, by mass, 0.5 ppm or more and 300 ppm or less. <2> The laminate sheet according to <1>, wherein the thicknesses of adhesive layer 1a and adhesive layer 1b are both 1 μm or more and 50 μm or less. <3> The laminate sheet according to <1> or <2>, wherein (i) has an adhesive layer 1a and a resin film or a protective film, in this order, on one side of the fine fibrous cellulose-containing layer, and (ii) has an adhesive layer 1a and a resin film or a protective film, in this order, on one side of the fine fibrous cellulose-containing layer. <4> The laminate sheet according to any one of <1> to <3>, wherein the fine fibrous cellulose-containing layer contains a hydrophilic polymer. <5> The laminate sheet according to <4>, wherein the hydrophilic polymer contains a nonionic water-soluble cellulose ether and / or polyvinyl alcohol. <6> The laminate sheet according to <5>, wherein the fine fibrous cellulose-containing layer is a single layer, the hydrophilic polymer contains a nonionic water-soluble cellulose ether, and the content of the nonionic water-soluble cellulose ether in the hydrophilic polymer is 80 mass% or more.<7> The laminate sheet according to <6>, wherein the mass ratio of nonionic water-soluble cellulose ether to fine fibrous cellulose (nonionic water-soluble cellulose ether / fine fibrous cellulose) in the fine fibrous cellulose-containing layer is 10 / 90 or more and 90 / 10 or less. <8> The laminate sheet according to <5>, wherein the fine fibrous cellulose-containing layer is a multilayer structure including a fine fibrous cellulose-containing layer 1a containing polyvinyl alcohol and a fine fibrous cellulose-containing layer 1b containing nonionic water-soluble cellulose ether. <9> The laminate sheet according to <8>, wherein the mass ratio of polyvinyl alcohol to fine fibrous cellulose (polyvinyl alcohol / fine fibrous cellulose) in the fine fibrous cellulose-containing layer 1a is 25 / 75 or more and 90 / 10 or less. <10> The laminate sheet according to any one of <1> to <9>, wherein the fine fibrous cellulose has an anionic group. <11> The laminate sheet according to <10>, wherein the anionic group includes a phosphorus oxo acid group or a group derived from a phosphorus oxo acid group. <12> A laminate comprising the laminate sheet (ii) according to <3>, the laminate sheet having a resin film, on at least one surface of a core resin plate, wherein the core resin plate contains a polycarbonate resin, and the adhesive layer 1b of the laminate sheet is in contact with the core resin plate. <13> The laminate according to <12>, having a haze of 5.0% or less. <14> The laminate according to <12> or <13>, having a haze difference of 2.0% or less before and after heating at 170°C for 10 minutes. <15> A method for producing a thermally processed product, comprising a step of thermally processing the laminate according to any one of <12> to <14>. <16> A thermally processed product obtained by thermally processing the laminate according to any one of <12> to <14>. <17> A transparent member comprising the thermally processed product according to <16>. <18> A method for producing the laminate sheet according to any one of <1> to <11>, comprising the following steps 1 and 2:Step 1: a step of applying and drying a coating liquid for a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1,000 nm or less to obtain a fine fibrous cellulose-containing layer Step 2: a step of applying and drying a coating liquid for an adhesive layer on one side of the fine fibrous cellulose-containing layer obtained in Step 1 to form adhesive layer 1a or 1b <19> The method for producing a laminate sheet according to <18>, wherein Step 2 is a step of applying a coating liquid for an adhesive layer to one side of the fine fibrous cellulose-containing layer obtained in Step 1, and then drying at 80°C or higher for 5 minutes or more to form adhesive layer 1a or 1b. <20> A method for producing a laminate sheet according to <18> or <19>, further comprising the following Step 3 after Step 2: Step 3: A step of applying a coating liquid for an adhesive layer to a surface of the fine fibrous cellulose-containing layer opposite to the surface on which the adhesive layer 1a or 1b is formed, and drying the applied liquid to form the adhesive layer 1b or 1a. <21> The method for producing a laminate sheet according to any one of <18> to <20>, further comprising the following step 4 after step 2: Step 4: A step of attaching a resin film or a protective film onto the adhesive layer 1a or 1b.

[0006] According to the present invention, there are provided a laminate sheet which is a laminate combined with a resin film or the like and which has excellent rigidity and is less likely to generate bubbles even when thermally processed, a laminate comprising the laminate sheet, a thermally processed product obtained by thermally processing the laminate, and a transparent member including the thermally processed product, as well as methods for manufacturing the laminate sheet and the thermally processed product.

[0007] Fig. 1 is a graph showing the relationship between the amount of NaOH added dropwise to a slurry containing fine fibrous cellulose having phosphorus oxo acid groups and pH. Fig. 2 is a graph showing the relationship between the amount of NaOH added dropwise to a slurry containing fine fibrous cellulose having carboxy groups and pH.

[0008] Hereinafter, embodiments of the present invention will be described. In this specification, the range "X to Y" means "X or more and Y or less." In this specification, the upper and lower limits of the numerical ranges can be combined arbitrarily. In this specification, the components contained or may be contained in each layer constituting the laminate sheet or laminate may be used alone or in combination of two or more.

[0009] [Laminated Sheet] The laminated sheet of the present invention (i) has an adhesive layer 1a on one side of a fine fibrous cellulose-containing layer (single layer or multi-layer) containing fine fibrous cellulose having a fiber width of 1,000 nm or less, and satisfies at least one of the following conditions A and B, or (ii) has an adhesive layer 1a on one side of a fine fibrous cellulose-containing layer (single layer or multi-layer) containing fine fibrous cellulose having a fiber width of 1,000 nm or less, and has an adhesive layer 1b on the other side, and satisfies at least one of the following conditions C and D. Condition A: The total content of organic solvents in the fine fibrous cellulose-containing layer (single layer or multi-layer) and adhesive layer 1a is 0.1 ppm or more and 40 ppm or less by mass. Condition B: The content of organic solvents in adhesive layer 1a is 0.5 ppm or more and 200 ppm or less by mass. Condition C: The total content of organic solvents in the fine fibrous cellulose-containing layer (single layer or multi-layer), adhesive layer 1a and adhesive layer 1b is 0.1 ppm or more and 60 ppm or less by mass. Condition D: The total content of organic solvents in adhesive layer 1a and adhesive layer 1b is 0.5 ppm or more and 300 ppm or less by mass.

[0010] The laminate sheet of the present invention is thought to be less likely to generate bubbles even when thermally processed in the form of (i) having a resin film on the adhesive layer 1a, the form (ii) having a resin film on the adhesive layer 1a, or a laminate having any of these forms, because the content of the organic solvent in the adhesive layers 1a and 1b is controlled within a specific range. As additional effects, the laminate having the laminate sheet of this embodiment is less likely to yellow, has low haze, high total light transmittance, and is excellent in rigidity and visibility.

[0011] Under condition A, the total content of organic solvents in the fine fibrous cellulose-containing layer and the adhesive layer 1a may be 1 ppm or more, 3 ppm or more, or 5 ppm or more, and may be 35 ppm or less, 30 ppm or less, or 20 ppm or less.

[0012] Under condition B, the content of the organic solvent in the adhesive layer 1a may be 10 ppm or more, 30 ppm or more, or 50 ppm or more, and may be 185 ppm or less, 170 ppm or less, or 155 ppm or less.

[0013] Under condition C, the total content of organic solvents in the fine fibrous cellulose-containing layer, adhesive layer 1a, and adhesive layer 1b may be 1 ppm or more, 3 ppm or more, or 5 ppm or more, and may be 50 ppm or less, 40 ppm or less, or 30 ppm or less.

[0014] Under condition D, the total content of organic solvents in adhesive layer 1a and adhesive layer 1b may be 10 ppm or more, 30 ppm or more, or 50 ppm or more, and may be 185 ppm or less, 170 ppm or less, or 155 ppm or less.

[0015] [Fine fibrous cellulose-containing layer] The laminate sheet of this embodiment (i) has an adhesive layer 1a on one side of a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1,000 nm or less, or (ii) has an adhesive layer 1a on one side of a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1,000 nm or less and an adhesive layer 1b on the other side. The fine fibrous cellulose-containing layer may be a single layer or multiple layers. When the fine fibrous cellulose-containing layer is multiple layers, it is preferably two to five layers, more preferably four layers or less, even more preferably three layers or less, and even more preferably two layers.

[0016] <Fine fibrous cellulose> Fine fibrous cellulose is fibrous cellulose having a fiber width of 1,000 nm or less. The fiber width of fibrous cellulose can be measured, for example, by observation using an electron microscope. The fiber width of fine fibrous cellulose is 1,000 nm or less. The fiber width of fine fibrous cellulose is preferably 2 nm or more and 1,000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and even more preferably 2 nm or more and 10 nm or less. By making the fiber width of fine fibrous cellulose 2 nm or more, dissolution of cellulose molecules in water can be suppressed, and the effects of fine fibrous cellulose, such as improved strength and dimensional stability, can be more easily achieved.

[0017] The average fiber width of the fine fibrous cellulose is, for example, 1,000 nm or less. The average fiber width of the fine fibrous cellulose is preferably 2 nm or more and 1,000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and even more preferably 2 nm or more and 10 nm or less. By making the average fiber width of the fine fibrous cellulose 2 nm or more, it is possible to suppress the dissolution of the cellulose molecules in water, and to more easily achieve the effects of the fine fibrous cellulose, such as improving strength and dimensional stability. The fine fibrous cellulose is, for example, monofilament cellulose.

[0018] The number-average fiber width of fine fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fine fibrous cellulose with a concentration of 0.01% by mass to 0.1% by mass is prepared, and this suspension is cast on a hydrophilically treated carbon film-coated grid to prepare a sample for transmission electron microscope (TEM) observation. When wide fibers are included, a scanning electron microscope (SEM) image of the surface cast on glass may be observed. Next, electron microscope images are observed at magnifications of 1,000x, 5,000x, 10,000x, or 50,000x, depending on the width of the fibers to be observed. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions: (1) A line X is drawn at any location within the observed image, and 20 or more fibers intersect with line X. (2) A line Y is drawn within the same image, perpendicular to line X, and 20 or more fibers intersect line Y.

[0019] For observation images that satisfy the above conditions, the widths of fibers intersecting with lines X and Y are visually read. In this way, three or more sets of observation images of at least the surface portions that do not overlap each other are obtained. Next, for each image, the widths of fibers intersecting with lines X and Y are read. In this way, the widths of at least 20 fibers x 2 x 3 = 120 fibers are read. The average of the read fiber widths is then taken as the number-average fiber width of the fibrous cellulose.

[0020] The fiber length of the fine fibrous cellulose is not particularly limited, but is preferably 0.1 μm or more and 1,000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and even more preferably 0.1 μm or more and 600 μm or less. By setting the fiber length within the above range, destruction of the crystalline regions of the fine fibrous cellulose can be suppressed. It also becomes possible to set the slurry viscosity of the fine fibrous cellulose within an appropriate range. The fiber length of the fine fibrous cellulose can be determined by image analysis using, for example, TEM, SEM, or atomic force microscope (AFM).

[0021] The fine fibrous cellulose preferably has a type I crystal structure. The fact that the fine fibrous cellulose has a type I crystal structure can be identified by a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromated with graphite. Specifically, it can be identified by the presence of typical peaks at two positions: near 2θ=14° to 17° and near 2θ=22° to 23°. The proportion of type I crystal structure in the fine fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. This can be expected to provide even better performance in terms of the expression of a low linear thermal expansion coefficient. The degree of crystallinity can be determined by measuring the X-ray diffraction profile and using a conventional method from the pattern (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0022] The axial ratio (fiber length / fiber width) of the fine fibrous cellulose is not particularly limited, but is preferably, for example, 20 to 10,000, and more preferably 50 to 1,000. By setting the axial ratio to the above lower limit or more, a sheet containing the fine fibrous cellulose can be easily formed. By setting the axial ratio to the above upper limit or less, it is preferable in that, for example, when the fine fibrous cellulose is used as an aqueous dispersion, handling such as dilution becomes easier.

[0023] The fine fibrous cellulose in this embodiment preferably has at least one of an ionic substituent and a nonionic substituent. From the viewpoint of improving the dispersibility of fibers in a dispersion medium and increasing the defibration efficiency in the defibration treatment, it is more preferable that the fine fibrous cellulose has an ionic substituent. The ionic substituent may include, for example, either an anionic group or a cationic group, or both. Furthermore, the nonionic substituent may include, for example, an alkyl group and an acyl group. In this embodiment, it is particularly preferable that the ionic substituent has an anionic group. Furthermore, the ionic substituent is preferably a group that is introduced into the fine fibrous cellulose via an ester bond or an ether bond, and more preferably a group that is introduced into the fine fibrous cellulose via an ester bond. In this case, the ester bond is preferably formed by dehydration condensation between the fine fibrous cellulose and a compound that becomes the ionic substituent. Note that the fine fibrous cellulose does not need to be subjected to a treatment to introduce an ionic substituent.

[0024] Examples of anionic groups as ionic substituents include phosphorus oxo acid groups or substituents derived from phosphorus oxo acid groups (sometimes simply referred to as phosphorus oxo acid groups), carboxy groups or substituents derived from carboxy groups (sometimes simply referred to as carboxy groups), sulfur oxo acid groups or substituents derived from sulfur oxo acid groups (sometimes simply referred to as sulfur oxo acid groups), xanthate groups or substituents derived from xanthate groups (sometimes simply referred to as xanthate groups), phosphonic groups or substituents derived from phosphonic groups, phosphine groups or substituents derived from phosphine groups, sulfonic groups or substituents derived from sulfonic groups, and carboxyalkyl groups. Among them, the anionic group is preferably at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxy groups, carboxymethyl groups, carboxyethyl groups, sulfur oxoacid groups and sulfur oxoacid groups, xanthate groups, and sulfonic acid groups. More preferably, the anionic group is at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxy groups, sulfur oxoacid groups, and sulfur oxoacid groups. More preferably, the anionic group is at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxy groups, sulfur oxoacid groups, and sulfur oxoacid groups. By introducing a phosphorus oxoacid group as an anionic group, for example, the dispersibility of fibrous cellulose can be further improved even under alkaline or acidic conditions, resulting in a high-strength, highly transparent fine fibrous cellulose-containing layer. Examples of cationic groups as ionic substituents include ammonium groups, phosphonium groups, sulfonium groups, etc. Among these, the cationic group is preferably an ammonium group.

[0025] The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group is, for example, a substituent represented by the following formula (1). A plurality of substituents represented by the following formula (1) may be introduced into each fine fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (1) may be the same or different.

[0026]

[0027] In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (where a=b×m). At least one (preferably a) of n α and α′ is O. － and the rest are R or OR. Note that all of α and α' are O － The n α's may all be the same or may be different. ｂ＋ is a monovalent or higher cation composed of an organic or inorganic substance. R is each a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived from any of these. In addition, α in formula (1) may be a group derived from a cellulose molecular chain. In addition, in formula (1), n ​​is preferably 1.

[0028] Examples of saturated linear hydrocarbon groups include, but are not limited to, a methyl group, an ethyl group, an n-propyl group, an n-butyl group, and the like. Examples of saturated branched hydrocarbon groups include, but are not limited to, an i-propyl group, an t-butyl group, and the like. Examples of saturated cyclic hydrocarbon groups include, but are not limited to, a cyclopentyl group, an cyclohexyl group, and the like. Examples of unsaturated linear hydrocarbon groups include, but are not limited to, a vinyl group, an allyl group, and the like. Examples of unsaturated branched hydrocarbon groups include, but are not limited to, an i-propenyl group, an 3-butenyl group, and the like. Examples of unsaturated cyclic hydrocarbon groups include, but are not limited to, a cyclopentenyl group, an cyclohexenyl group, and the like. Examples of aromatic groups include, but are not limited to, a phenyl group, an naphthyl group, and the like. In addition, the derivative group in R may be a carboxy group, a carboxylate group (-COO), or the like, which is bonded to the main chain or side chain of the above-mentioned various hydrocarbon groups. －), a hydroxy group, an amino group, and the like. Examples of functional groups include, but are not limited to, functional groups to which at least one type of functional group selected from the group consisting of an alkyl group, a hydroxy group, and an amino group 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, facilitating penetration into the fiber raw material and increasing the yield of fine fibrous cellulose. When multiple Rs are present in formula (1) or when multiple types of substituents represented by formula (1) are introduced into the fine fibrous cellulose, the multiple Rs present may be the same or different.

[0029] β ｂ＋ is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include, but are not limited to, ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. These can be used alone or in combination of two or more types. Note that β in formula (1) ｂ＋ When a plurality of β ｂ＋ may be the same or different. The monovalent or higher cations made of organic or inorganic substances include β ｂ＋ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0030] More specifically, the phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group is a phosphate group (-PO ３ H ２ ), salts of phosphate groups, phosphite groups (phosphonic acid groups) (-PO ２ H ２ and salts of phosphorous acid groups (phosphonic acid groups). The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group may be a group in which a phosphoric acid group is condensed (e.g., a pyrophosphate group), a group in which a phosphonic acid is condensed (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), an alkyl phosphonic acid group (e.g., a methyl phosphonic acid group), or the like.

[0031] The sulfur oxoacid group (a sulfur oxoacid group or a substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). A plurality of types of substituents represented by the following formula (2) may be introduced into each fine fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (2) may be the same or different.

[0032]

[0033] In formula (2), b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (where 1 = b × m). When n is 2 or more, multiple p's may be the same number or different numbers. In formula (2), β ｂ＋is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. Note that when multiple types of substituents represented by the above formula (2) are introduced into the fine fibrous cellulose, the multiple β ｂ＋ may be the same or different. The monovalent or higher cations made of organic or inorganic substances include β ｂ＋ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0034] The amount of ionic substituent introduced into the fine fibrous cellulose is, for example, preferably 0.05 mmol / g or more per 1 g (mass) of fine fibrous cellulose, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and even more preferably 1.00 mmol / g or more. Furthermore, the amount of ionic substituent introduced into the fine fibrous cellulose is, for example, preferably 5.20 mmol / g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol / g or less, even more preferably 3.50 mmol / g or less, and even more preferably 3.00 mmol / g or less. By setting the amount of ionic substituent (preferably anionic group) introduced within the above range, it is possible to facilitate the micronization of the fiber raw material and to increase the stability of the fine fibrous cellulose. Here, the denominator in the unit mmol / g is calculated based on the fact that the counter ion of the ionic substituent is a hydrogen ion (H ＋ ) indicates the mass of the fine fibrous cellulose when

[0035] Furthermore, the amount of ionic substituents (preferably anionic groups) introduced into the fine fibrous cellulose is, from the viewpoint of the water absorption of the laminate, preferably less than 0.50 mmol / g per 1 g (mass) of fine fibrous cellulose, more preferably 0.40 mmol / g or less, even more preferably 0.30 mmol / g or less, even more preferably 0.25 mmol / g or less, and even more preferably 0.15 mmol / g or less, and from the viewpoint of the total light transmittance and haze of the laminate, preferably 0.01 mmol / g or more, more preferably 0.02 mmol / g or more, and even more preferably 0.03 mmol / g or more. Such low-substituent amount fine fibrous cellulose may be obtained, for example, by subjecting the fine fibrous cellulose to a treatment to remove substituents, as described below.

[0036] The amount of ionic substituents introduced into the fine fibrous cellulose can be measured, for example, by neutralization titration, in which an alkali such as an aqueous sodium hydroxide solution is added to a slurry containing the obtained fine fibrous cellulose, and the amount introduced is measured by determining the change in pH.

[0037] FIG. 1 is a graph showing the relationship between the amount of NaOH added dropwise to a slurry containing fibrous cellulose having phosphorus oxo acid groups and pH. The amount of phosphorus oxo acid groups introduced into fibrous cellulose is measured, for example, as follows. First, a slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement target may be subjected to a defibration treatment similar to the defibration treatment process described below before treatment with the strongly acidic ion exchange resin. Next, the change in pH is observed while adding aqueous sodium hydroxide solution, and a titration curve such as that shown in the upper part of FIG. 1 is obtained. The titration curve shown in the upper part of FIG. 1 plots the measured pH against the amount of alkali added, while the titration curve shown in the lower part of FIG. 1 plots the pH increment (differential value) (1 / mmol) against the amount of alkali added. In this neutralization titration, two points at which the increment (differential value of pH with respect to the amount of alkali added) is maximized are identified on the curve plotting the measured pH against the amount of alkali added. Of these, the first maximum point of the increment obtained after starting the addition of alkali is called the first endpoint, and the next maximum point of the increment is called the second endpoint. The amount of alkali required from the start of titration to the first endpoint is equal to the amount of first dissociated acid of the fibrous cellulose contained in the slurry used for titration, the amount of alkali required from the first endpoint to the second endpoint is equal to the amount of second dissociated acid of the fibrous cellulose contained in the slurry used for titration, and the amount of alkali required from the start of titration to the second endpoint is equal to the total amount of dissociated acid of the fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali required from the start of titration to the first endpoint by the solids content (g) in the slurry to be titrated is the amount of phosphorus oxo acid group introduced (mmol / g). Note that when simply referring to the amount of phosphorus oxo acid group introduced (or amount of phosphorus oxo acid group), it refers to the amount of first dissociated acid. 1, the region from the start of titration to the first endpoint is referred to as Region 1, and the region from the first endpoint to the second endpoint is referred to as Region 2. For example, when the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the amount of weak acid groups in the phosphorus oxoacid group (also referred to herein as the second dissociated acid amount) appears to decrease, and the amount of alkali required in Region 2 becomes smaller than the amount of alkali required in Region 1.On the other hand, the amount of strong acid groups in the phosphorus oxoacid group (also referred to herein as the amount of first dissociated acid) is equal to the amount of phosphorus atoms, regardless of whether condensation occurs or not. Furthermore, when the phosphorus oxoacid group is a phosphorous acid group, the phosphorus oxoacid group does not contain any weakly acidic groups, so the amount of alkali required for the second region may be reduced or even zero. In this case, the titration curve will have only one point at which the pH increment is maximized. The above-mentioned amount of introduced phosphorus oxoacid groups (mmol / g) indicates the amount of phosphorus oxoacid groups in the acid-form fibrous cellulose (hereinafter referred to as the amount of phosphorus oxoacid groups (acid form)), since the denominator indicates the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the phosphorus oxoacid groups are substituted with any cation C so as to be charge equivalent, the amount of phosphorus oxoacid groups possessed by the fibrous cellulose when the cation C is the counter ion (hereinafter referred to as the amount of phosphorus oxoacid groups (type C)) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Amount of phosphorus oxoacid groups (type C) = Amount of phosphorus oxoacid groups (acid type) / {1 + (W - 1) × A / 1,000}, where A [mmol / g] is the total amount of anions derived from phosphorus oxoacid groups possessed by the fibrous cellulose (the sum of the amount of strongly acidic groups and the amount of weakly acidic groups in the phosphorus oxoacid groups), and W is the formula weight per valence of the cation C (for example, 23 for Na and 9 for Al).

[0038] FIG. 2 is a graph showing the relationship between the amount of NaOH added to carboxyl-containing fine fibrous cellulose and pH. The amount of carboxyl groups introduced into fine fibrous cellulose is measured, for example, as follows. First, a slurry containing fine fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement object may be subjected to a defibration treatment similar to the defibration treatment process described below before treatment with the strongly acidic ion exchange resin. Next, the change in pH is observed while adding aqueous sodium hydroxide, and a titration curve such as that shown in FIG. 2 is obtained. If necessary, the measurement object may be subjected to a defibration treatment similar to the defibration treatment process described below. As shown in FIG. 2, in this neutralization titration, a single point is observed where the increment (the differential value of pH with respect to the amount of alkali added) is maximized on the curve plotting the measured pH against the amount of alkali added. This maximum increment point is called the first endpoint. Here, the region from the start of titration to the first endpoint in FIG. 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the slurry used in the titration. The amount of alkali (mmol) required in the first region of the titration curve was divided by the solid content (g) in the fine fibrous cellulose-containing slurry to be titrated to calculate the amount of carboxyl groups introduced (mmol / g). Note that the amount of carboxyl groups introduced (mmol / g) was calculated based on the case where the counter ions of the carboxyl groups were hydrogen ions (H ＋ ) (hereinafter referred to as the amount of carboxy groups (acid type)) per 1 g of mass of fibrous cellulose.

[0039] The above-mentioned amount of carboxy groups introduced (mmol / g) indicates the amount of carboxy groups possessed by the acid-form fibrous cellulose (hereinafter referred to as the amount of carboxy groups (acid form)), since the denominator is the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the carboxy groups are substituted with any cation C so as to be charge equivalent, the amount of carboxy groups possessed by the fibrous cellulose in which the cation C is the counter ion (hereinafter referred to as the amount of carboxy groups (C form)) (mmol / g) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Amount of carboxy groups (C form) = Amount of carboxy groups (acid form) / {1 + (W - 1) × (Amount of carboxy groups (acid form)) / 1,000} W: Formula weight per valence of cation C (for example, 23 for Na, 9 for Al)

[0040] In measuring the amount of substituents by titration, if too much sodium hydroxide aqueous solution is added or if the titration interval is too short, the amount of substituents may be lower than expected, and an accurate value may not be obtained. An appropriate amount of addition and titration interval, for example, is preferably a 0.1 N sodium hydroxide aqueous solution titrated at 10 to 50 μL intervals over 5 to 30 seconds. Furthermore, to eliminate the influence of carbon dioxide dissolved in the fibrous cellulose-containing slurry, it is preferable to perform measurements while blowing an inert gas such as nitrogen gas into the slurry, for example, from 15 minutes before the start of titration until the end of titration.

[0041] The amount of sulfur oxoacid groups or sulfonic groups introduced into fibrous cellulose can be calculated by freeze-drying a slurry containing fibrous cellulose and then pulverizing the sample to measure the amount of sulfur. Specifically, a slurry containing fibrous cellulose is freeze-dried, and the resulting pulverized sample is subjected to pressure-heat decomposition using nitric acid in a sealed container, after which the sample is appropriately diluted and the amount of sulfur is measured by ICP-OES. The value calculated by dividing the value by the bone dry mass of the fibrous cellulose tested is taken as the amount of sulfur oxoacid groups or sulfonic groups (unit: mmol / g) of the fibrous cellulose.

[0042] <<Method for Producing Fine Fibrous Cellulose>> (Cellulose-Containing Fiber Raw Material) Fine fibrous cellulose is produced from a cellulose-containing fiber raw material. The cellulose-containing fiber raw material is not particularly limited, but pulp is preferably used because it is easily available and inexpensive. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not particularly limited to, chemical pulp such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen-bleached kraft pulp (OKP), semi-chemical pulp such as semi-chemical pulp (SCP) and chemi-groundwood pulp (CGP), and mechanical pulp such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Non-wood pulps include, but are not limited to, cotton-based pulps such as cotton linters and cotton lint, and non-wood pulps such as hemp, straw, and bagasse. Deinked pulps include, but are not limited to, deinked pulp made from recycled paper. The pulps of this embodiment may be used alone or in combination. Among the above pulps, wood pulp and deinked pulp are preferred from the viewpoint of availability. Furthermore, among wood pulps, chemical pulps are more preferred, with kraft pulp and sulfite pulp being even more preferred, because they have a high cellulose content, resulting in a high yield of fine fibrous cellulose during defibration, and because cellulose decomposition in the pulp is minimal, resulting in the production of long-fiber fine fibrous cellulose with a high axial ratio. Using long-fiber fine fibrous cellulose with a high axial ratio tends to increase viscosity. Cellulose-containing fiber raw materials include, for example, cellulose contained in sea squirts and bacterial cellulose produced by acetic acid bacteria. Furthermore, instead of fiber raw materials containing cellulose, fibers formed from linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can also be used.

[0043] In order to obtain the fine fibrous cellulose into which the above-mentioned ionic substituents have been introduced, it is preferable to have an ionic substituent introduction step for introducing an ionic substituent into the above-mentioned cellulose-containing fiber raw material, a washing step, an alkali treatment step (neutralization step), and a defibration treatment step in this order, and instead of or in addition to the washing step, an acid treatment step may be included. Examples of the ionic substituent introduction step include a phosphorus oxo acid group introduction step, a carboxy group introduction step, a sulfur oxo acid group introduction step, a xanthate group introduction step, a phosphonic or phosphine group introduction step, a sulfonic group introduction step, and a cationic group introduction step. Each of these steps will be explained below.

[0044] (Ionic Substituent Introduction Step) - Phosphorus Oxo Acid Group Introduction Step - The phosphorus oxo acid group introduction step is a step of reacting a cellulose-containing fiber raw material with at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing phosphorus oxo acid groups by reacting with hydroxyl groups possessed by the cellulose-containing fiber raw material. This step results in a fiber into which phosphorus oxo acid groups have been introduced. In the phosphorus oxo acid group introduction step according to this embodiment, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). Alternatively, the cellulose-containing fiber raw material may be reacted with compound A in the absence of compound B. One example of a method for reacting compound A with a fiber raw material in the coexistence of compound B is a method in which compound A and compound B are mixed with a dry, wet, or slurried fiber raw material. Of these, using a dry or wet fiber raw material is preferred because it results in high reaction uniformity, and using a dry fiber raw material is particularly preferred. The form of the fiber raw material is not particularly limited, but is preferably, for example, in the form of a cotton or thin sheet. Compound A and compound B can be added to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state heated to or above their melting point. Of these, adding them in the form of a solution dissolved in a solvent, particularly an aqueous solution, is preferred because it results in high reaction uniformity. Compound A and compound B may be added to the fiber raw material simultaneously, separately, or as a mixture. The method of adding compound A and compound B is not particularly limited, but when compound A and compound B are in solution form, the fiber raw material may be immersed in the solution to absorb the liquid and then removed, or the solution may be added dropwise to the fiber raw material. Alternatively, the required amounts of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material, and then the excess compound A and compound B may be removed by squeezing or filtration.

[0045] The compound A used in this embodiment may be any compound that has a phosphorus atom and can form an ester bond with cellulose, including, but not limited to, phosphoric acid or a salt thereof, phosphorous acid or a salt thereof, dehydrated condensed phosphoric acid or a salt thereof, and phosphoric anhydride (diphosphorus pentoxide). Phosphoric acid can be used with various purities, such as 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid. Phosphorous acid can be, for example, 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acid is a compound in which two or more molecules of phosphoric acid are condensed by a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, which can be neutralized to various degrees. Among these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, or ammonium salt of phosphoric acid is preferred from the viewpoints of high efficiency of introduction of phosphorus oxoacid groups, easier improvement of defibration efficiency in the defibration step described below, low cost, and ease of industrial application, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, or ammonium dihydrogen phosphate is more preferred. The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted into the amount of phosphorus atoms, the amount of phosphorus atoms added per 100 parts by mass of fiber raw material (bone dry mass) is preferably 0.5 parts by mass or more and 100 parts by mass or less, more preferably 1 part by mass or more and 50 parts by mass or less, and even more preferably 2 parts by mass or more and 30 parts by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to the above upper limit or less, a balance between the yield improvement effect and cost can be achieved.

[0046] As described above, compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. Furthermore, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved. The amount of compound B added per 100 parts by mass (bone dry mass) of the fiber raw material is not particularly limited, but is, for example, preferably 1 part by mass or more and 500 parts by mass or less, more preferably 10 parts by mass or more and 400 parts by mass or less, and even more preferably 100 parts by mass or more and 350 parts by mass or less.

[0047] In the reaction of a fiber raw material containing cellulose with compound A, the reaction system may contain, in addition to compound B, for example, amides or amines. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is known to function as a particularly good reaction catalyst.

[0048] In the phosphorus oxo acid group introduction step, it is preferable to add or mix compound A or the like to or with the fiber raw material, and then heat-treat the fiber raw material. The heat treatment temperature is preferably selected so that the phosphorus oxo acid group can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower. Various types of equipment having heat transfer media can be used for the heat treatment, including, for example, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized-bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized-bed dryer, a flash dryer, a reduced-pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, and a high-frequency dryer.

[0049] In the heat treatment according to this embodiment, for example, compound A may be added to a thin sheet-like fiber raw material by impregnation or other methods, followed by heating, or heating while kneading or stirring the fiber raw material and compound A in a kneader or the like. This suppresses unevenness in the concentration of compound A in the fiber raw material, enabling phosphorus oxoacid groups to be more uniformly introduced onto the surface of the cellulose fibers contained in the fiber raw material. This is thought to be due to the fact that, when water molecules move to the surface of the fiber raw material as it dries, the dissolved compound A is attracted to the water molecules by surface tension and is prevented from migrating to the surface of the fiber raw material (i.e., causing unevenness in the concentration of compound A). Furthermore, it is preferable that the heating device used in the heat treatment is a device that can constantly discharge, to the outside of the device system, moisture retained in the slurry and moisture generated by the dehydration condensation (phosphate esterification) reaction between compound A and hydroxyl groups contained in cellulose or the like in the fiber raw material. Examples of such heating devices include a blower oven. By constantly draining the water from the apparatus, it is possible to suppress the hydrolysis of phosphate ester bonds, which is the reverse reaction of phosphate esterification, and also to suppress acid hydrolysis of sugar chains in the fibers. This makes it possible to obtain fine fibrous cellulose with a high axial ratio. The heat treatment time is, for example, preferably 1 second to 300 minutes, more preferably 1 second to 1,000 seconds, and even more preferably 10 seconds to 800 seconds, after the water has been substantially removed from the fiber raw material. In this embodiment, the amount of phosphorus oxo acid groups introduced can be kept within a preferred range by setting the heating temperature and heating time within appropriate ranges.

[0050] The amount of phosphorus oxoacid groups introduced into the fiber raw material is, for example, preferably 0.05 mmol / g or more per 1 g (mass) of fine fibrous cellulose, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and even more preferably 1.00 mmol / g or more. The amount of phosphorus oxoacid groups introduced into the fiber raw material is, for example, preferably 5.20 mmol / g or less per 1 g (mass) of fine fibrous cellulose, more preferably 3.65 mmol / g or less, and even more preferably 3.00 mmol / g or less. By keeping the amount of phosphorus oxoacid groups introduced within the above range, it is possible to facilitate the micronization of the fiber raw material and improve the stability of the fine fibrous cellulose.

[0051] -Carboxy Group Introduction Process- The carboxyl group introduction process is carried out by treating a cellulose-containing fiber raw material with an oxidation process such as ozone oxidation, oxidation by the Fenton method, or TEMPO oxidation, or with a compound having a carboxylic acid-derived group or a derivative thereof, or an acid anhydride of a compound having a carboxylic acid-derived group or a derivative thereof. Examples of compounds having a carboxylic acid-derived group include, but are not limited to, dicarboxylic acid compounds such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, and itaconic acid, and tricarboxylic acid compounds such as citric acid and aconitic acid. Examples of derivatives of compounds having a carboxylic acid-derived group include, but are not limited to, imidized products of acid anhydrides of compounds having a carboxyl group, and derivatives of acid anhydrides of compounds having a carboxyl group. Examples of imidized products of acid anhydrides of compounds having a carboxyl group include, but are not limited to, imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0052] The acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, etc. Furthermore, the derivative of an acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include acid anhydrides of compounds having carboxy groups such as dimethylmaleic anhydride, diethylmaleic anhydride, diphenylmaleic anhydride, etc. in which at least some of the hydrogen atoms have been substituted with substituents such as alkyl groups or phenyl groups.

[0053] When TEMPO oxidation treatment is performed in the carboxyl group introduction step, it is preferable to perform the treatment under conditions of pH 6 or higher and 8 or lower. This type of treatment is also referred to as neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment can be performed, for example, by adding pulp as the fiber raw material, a nitroxy radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to a sodium phosphate buffer solution (pH = 6.8). Furthermore, by adding sodium chlorite, aldehydes generated during the oxidation process can be efficiently oxidized to carboxyl groups. The TEMPO oxidation treatment may also be performed under conditions of pH 10 or higher and 11 or lower. This type of treatment is also referred to as alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be performed, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp as the fiber raw material. The amount of carboxy groups introduced into the fiber raw material varies depending on the type of substituent. For example, when carboxy groups are introduced by TEMPO oxidation, the amount is preferably 0.05 mmol / g or more, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and even more preferably 0.90 mmol / g or more per 1 g (mass) of fine fibrous cellulose. Also, the amount is preferably 3.65 mmol / g or less, more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, even more preferably 2.20 mmol / g or less, and even more preferably 2.00 mmol / g or less. Furthermore, when the substituent is a carboxymethyl group, the amount may be 5.8 mmol / g or less per 1 g (mass) of fine fibrous cellulose. By setting the amount of carboxy groups introduced within the above range, it is possible to facilitate the refinement of cellulose fibers in the refinement treatment step and improve the stability of the fine fibrous cellulose.

[0054] -Sulfur oxoacid group introduction step- The process for producing fine fibrous cellulose may include, for example, a sulfur oxoacid group introduction step as an ionic substituent introduction step. In the sulfur oxoacid group introduction step, hydroxyl groups in a fiber raw material containing cellulose are reacted with sulfur oxoacids to obtain cellulose fibers having sulfur oxoacid groups (sulfur oxoacid group-introduced fibers).

[0055] In the sulfur oxo acid group introduction step, instead of compound A in the above-described <Phosphorus oxo acid group introduction step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfur oxo acid groups by reacting with hydroxyl groups in a fiber raw material containing cellulose is used. Compound C may be any compound containing a sulfur atom and capable of forming an ester bond with cellulose, including, but not limited to, sulfuric acid or a salt thereof, sulfurous acid or a salt thereof, and sulfuric acid amide. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid). Examples of sulfurous acid include 5% aqueous sulfurous acid. Examples of sulfates or sulfites include lithium, sodium, potassium, and ammonium salts of sulfates or sulfites, which can be neutralized to various degrees. Examples of sulfuric acid amides include sulfamic acid. In the sulfur oxo acid group introduction step, it is preferable to use compound B in the above-described <Phosphorus oxo acid group introduction step> as well.

[0056] In the sulfur oxoacid group introduction step, it is preferable to mix a cellulose raw material with an aqueous solution containing a sulfur oxoacid and urea and / or a urea derivative, and then heat-treat the cellulose raw material. The heat-treatment temperature is preferably selected so that sulfur oxoacid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat-treatment temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. The heat-treatment temperature is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

[0057] In the heat treatment step, heating is preferably performed until substantially all moisture is removed. Therefore, the heat treatment time varies depending on the amount of moisture contained in the cellulose raw material and the amount of aqueous solution containing sulfur oxoacid and urea and / or a urea derivative added, but is preferably, for example, 10 seconds to 10,000 seconds. For the heat treatment, various devices having a heat medium can be used, such as an agitator dryer, rotary dryer, disk dryer, roll-type heater, plate-type heater, fluidized-bed dryer, band-type dryer, filtration dryer, vibration fluidized dryer, flash dryer, reduced-pressure dryer, infrared heater, far-infrared heater, microwave heater, and high-frequency dryer.

[0058] The amount of sulfur oxoacid groups introduced into the cellulose raw material is preferably 0.05 mmol / g or more, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and even more preferably 0.90 mmol / g or more. The amount of sulfur oxoacid groups introduced into the cellulose raw material is preferably 5.00 mmol / g or less, more preferably 3.00 mmol / g or less. By keeping the amount of sulfur oxoacid groups introduced within the above range, it is possible to easily pulverize the fiber raw material and improve the stability of the fibrous cellulose.

[0059] - Oxidation step using a chlorine-based oxidizing agent (second carboxyl group introduction step) - The ionic substituent introduction step may include an oxidation step using a chlorine-based oxidizing agent. In the oxidation step using a chlorine-based oxidizing agent, a chlorine-based oxidizing agent is added to a wet or dry fiber raw material having a hydroxyl group to cause a reaction, thereby introducing a carboxyl group into the fiber raw material.

[0060] Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorites, chlorous acid, chlorites, chloric acid, chlorates, perchloric acid, perchlorates, and chlorine dioxide. From the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling, the chlorine-based oxidizing agent is preferably sodium hypochlorite, sodium chlorite, or chlorine dioxide. When adding a chlorine-based oxidizing agent, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or may be dissolved in an appropriate solvent and added.

[0061] The concentration of the chlorine-based oxidizing agent in the solution in the oxidation step using the chlorine-based oxidizing agent is, for example, preferably 1 to 1,000 mass %, more preferably 5 to 500 mass %, and even more preferably 10 to 100 mass %, calculated as an effective chlorine concentration. The amount of the chlorine-based oxidizing agent added per 100 parts by mass of the fiber raw material is preferably 1 to 100,000 parts by mass, more preferably 10 to 10,000 parts by mass, and even more preferably 100 to 5,000 parts by mass.

[0062] The reaction time with the chlorine-based oxidizing agent in the oxidation step using the chlorine-based oxidizing agent may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. The pH during the reaction is preferably from 5 to 15, more preferably from 7 to 14, and even more preferably from 9 to 13. At the start of the reaction, the pH during the reaction is preferably maintained constant (for example, pH 11) by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0063] -Xanthate group introduction step (xanthogenic acid esterification step)- The ionic substituent introduction step may include, for example, a xanthate group introduction step (hereinafter also referred to as a xanthation step). In the xanthation step, carbon disulfide and an alkali compound are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a xanthate group into the fiber raw material. Specifically, carbon disulfide is added to a fiber raw material that has been converted into alkali cellulose by the method described below, and the reaction is carried out.

[0064] ((Alkali Cellulose Formation)) When introducing an ionic substituent into a fiber raw material, it is preferable to convert the cellulose contained in the fiber raw material into alkali cellulose by treating the cellulose with an alkaline solution. This treatment causes ionic dissociation of some of the hydroxyl groups of the cellulose, thereby increasing the nucleophilicity (reactivity). The alkaline compound contained in the alkaline solution is not particularly limited, and may be an inorganic alkaline compound or an organic alkaline compound. Due to their high versatility, it is preferable to use, for example, sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, or tetrabutylammonium hydroxide. The conversion into alkali cellulose may be carried out simultaneously with the introduction of the ionic substituent, before the introduction, or at both the same time.

[0065] The solution temperature at the start of alkali cellulose formation is preferably 0°C or higher and 50°C or lower, more preferably 5°C or higher and 40°C or lower, and even more preferably 10°C or higher and 30°C or lower.

[0066] The alkali concentration in the alkaline solution is preferably 0.01 mol / L or more and 4 mol / L or less, more preferably 0.1 mol / L or more and 3 mol / L or less, and even more preferably 1 mol / L or more and 2.5 mol / L or less, in terms of molar concentration. In particular, when the treatment temperature in alkali cellulose formation is less than 10° C., the alkali concentration is preferably 1 mol / L or more and 2 mol / L or less.

[0067] The treatment time for alkali cellulose formation is preferably 1 minute or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more, and the alkali treatment time is preferably 6 hours or less, more preferably 5 hours or less, and even more preferably 4 hours or less.

[0068] By adjusting the type of alkaline solution, treatment temperature, concentration, and immersion time as described above, it is possible to suppress penetration of the alkaline solution into the crystalline regions of cellulose, making it easier to maintain the cellulose type I crystal structure and increasing the yield of fine fibrous cellulose.

[0069] When the introduction of ionic substituents and the conversion to alkali cellulose are not carried out simultaneously, the conversion to alkali cellulose is preferably carried out before the introduction of ionic substituents. In this case, the alkali cellulose obtained by the conversion to alkali cellulose treatment is preferably subjected to solid-liquid separation by a common deliquoring method such as centrifugation or filtration to remove moisture. This improves the reaction efficiency in the subsequent ionic substituent introduction step. The cellulose fiber concentration after solid-liquid separation is preferably 5% to 50%, more preferably 10% to 40%, and even more preferably 15% to 35%.

[0070] - Phosphonic or Phosphine Group Introduction Step (Phosphoalkylation Step) - The ionic substituent introduction step may include a phosphonic or phosphine group introduction step (phosphoalkylation step). In the phosphoalkylation step, a compound having a reactive group and a phospho or phosphine group (compound E) is used as an essential component. Ａ ), and an optional component, an alkali compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group, and the reaction is carried out to introduce a phosphonic group or a phosphine group into the fiber raw material.

[0071] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). ＡExamples of the compound include vinylphosphonic acid, phenylvinylphosphonic acid, and phenylvinylphosphinic acid. In terms of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling, Compound E Ａ is preferably vinylphosphonic acid. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0072] Compound E Ａ When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as it is, or may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0073] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0074] Compound E Ａ The amount of addition per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0075] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0076] - Sulfonic acid group introduction step (sulfoalkylation step) - The ionic substituent introduction step may include a sulfonic acid group introduction step (sulfoalkylation step). In the sulfoalkylation, a compound having a reactive group and a sulfonic acid group (compound E) is used as an essential component. Ｂ) and, as an optional component, an alkali compound and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a sulfonic acid group into the fiber raw material.

[0077] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Ｂ Examples of suitable acrylic acid esters include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, and 2-acrylamido-2-methylpropanesulfonic acid. Among these, compound E is particularly preferred in terms of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. Ｂ is preferably sodium vinyl sulfonate. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0078] Compound E Ｂ When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as it is, or may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0079] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0080] Compound E Ｂ The amount of addition per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0081] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 15 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0082] -Carboxyalkylation Step (Third Carboxy Group Introduction Step)- The ionic substituent introduction step may include a carboxyalkylation step. As an essential component, a compound having a reactive group and a carboxy group (compound E Ｃ ), and an optional component, an alkaline compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a carboxyl group into the fiber raw material.

[0083] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Ｃ As the compound, monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred from the viewpoints of the efficiency of introducing the substituent, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, it is also preferred to use, as an optional component, the compound B in the above-mentioned <Phosphorus oxoacid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0084] Compound E Ｃ When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as it is, or may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0085] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0086] Compound EＣ The amount of addition per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0087] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 3 minutes to 500 minutes, and even more preferably from 5 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0088] -Cationic group introduction step (cationization step)- As an essential component, a compound having a reactive group and a cationic group (compound E Ｄ ), and an optional component, an alkaline compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a cationic group into the fiber raw material.

[0089] Examples of reactive groups include halogenated alkyl groups, vinyl groups, and epoxy groups (glycidyl groups). Examples of cationic groups include ammonium groups, phosphonium groups, and sulfonium groups. Among these, the cationic group is preferably an ammonium group. Compound E Ｄ As the compound, glycidyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, etc. are preferred from the viewpoints of the efficiency of introducing the substituent, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, it is also preferable to use, as an optional component, the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner. The amount added is also preferably as described above.

[0090] Compound E Ｄ When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as it is, or may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0091] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0092] Compound E Ｄ The amount of addition per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0093] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 5 minutes to 500 minutes, and even more preferably from 10 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0094] (Washing step) In the method for producing fine fibrous cellulose in this embodiment, a washing step can be carried out on the ionic substituent-introduced fibers as needed. The washing step is carried out by washing the ionic substituent-introduced fibers with water or an organic solvent, for example. The washing step may be carried out after each step described below, and the number of washings carried out in each washing step is not particularly limited.

[0095] (Alkali Treatment (Neutralization Treatment) Step) When producing fine fibrous cellulose, an alkali treatment (neutralization treatment) may be performed on the fiber raw material between the ionic substituent introduction step and the defibration treatment step described below. The alkali treatment method is not particularly limited, and for example, a method of immersing the ionic substituent-introduced fibers in an alkaline solution is mentioned. 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, for example, sodium hydroxide or potassium hydroxide as the alkali compound because of its high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. Among these, the solvent contained in the alkaline solution is preferably a polar solvent containing water or a polar organic solvent such as an alcohol, and more preferably an aqueous solvent containing at least water. As the alkaline solution, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of its high versatility. The temperature of the alkaline solution in the alkali treatment step is not particularly limited, and is preferably, for example, from 5°C to 80°C, and more preferably from 10°C to 60°C. The immersion time of the ionic substituent-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably, for example, from 5 to 30 minutes, and more preferably from 10 to 20 minutes. The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but is, for example, preferably from 100 to 100,000% by mass, and more preferably from 1,000 to 10,000% by mass, based on the bone dry mass of the ionic substituent-introduced fiber.

[0096] In order to reduce the amount of alkaline solution used in the alkali treatment step, the ionic substituent-introduced fiber may be washed with water or an organic solvent after the ionic substituent-introducing step and before the alkali treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkali-treated ionic substituent-introduced fiber with water or an organic solvent after the alkali treatment step and before the defibrating step.

[0097] (Acid Treatment Step) When producing fine fibrous cellulose, an acid treatment may be performed on the fiber raw material between the step of introducing an ionic substituent and the defibration treatment step described below. For example, the ionic substituent introduction step, acid treatment step, alkali treatment step, and defibration treatment step may be performed in this order. The acid treatment method is not particularly limited, but an example is a method of immersing the fiber raw material in an acid-containing acidic solution. The concentration of the acidic solution used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less. The pH of the acidic solution used is also not particularly limited, but is preferably 0 to 4, and more preferably 1 to 3. Examples of acids that can be used in the acidic solution include inorganic acids, sulfonic acids, and carboxylic acids. Examples of inorganic acids include sulfuric acid, nitric acid, 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, it is particularly preferable to use hydrochloric acid or sulfuric acid. The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably, for example, from 5°C to 100°C, and more preferably from 20°C to 90°C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is, for example, preferably from 5 minutes to 120 minutes, and more preferably from 10 minutes to 60 minutes. The amount of the acid solution used in the acid treatment is not particularly limited, but is, for example, preferably from 100% by mass to 100,000% by mass, and more preferably from 1,000% by mass to 10,000% by mass, based on the bone dry mass of the fiber raw material.

[0098] (Defibrillation Treatment Step) Fine fibrous cellulose is obtained by defibrillating the ionic substituent-introduced fibers in the defibrillation treatment step. In the defibrillation treatment step, for example, a defibrillation treatment device can be used. The defibrillation treatment device is not particularly limited, and examples that can be used include a high-speed defibrillator, a grinder (stone mill-type grinder), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision grinder, a ball mill, a bead mill, a disk-type refiner, a conical refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater. Among the above defibrillation treatment devices, it is more preferable to use a high-speed defibrillator, a high-pressure homogenizer, or an ultra-high-pressure homogenizer, which are less affected by the grinding media and have less risk of contamination.

[0099] In the defibration process, it is preferable to dilute the ionic substituent-introduced fibers with a dispersion medium to form a slurry. The dispersion medium can be one or more selected from water and organic solvents such as polar organic solvents. The polar organic solvent is not particularly limited, but examples thereof include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

[0100] The solids concentration of the fine fibrous cellulose during the defibration treatment can be appropriately set. The slurry obtained by dispersing the phosphorus oxo acid group-introduced fibers in a dispersion medium may contain solids other than the phosphorus oxo acid group-introduced fibers, such as urea, which has hydrogen bonding properties.

[0101] (Nitrogen Removal Treatment) The process for producing fine fibrous cellulose may further include a step of reducing the nitrogen content (nitrogen removal treatment step). By reducing the nitrogen content, fine fibrous cellulose that can further suppress discoloration can be obtained. The nitrogen removal treatment step is preferably performed before the defibration treatment step.

[0102] In the nitrogen removal treatment step, it is preferable to adjust the pH of the slurry containing the substituent-introduced fibers to 10 or more and then perform a heat treatment. In the heat treatment, the liquid temperature of the slurry is preferably 50°C or more and 100°C or less, and the heating time is preferably 15 minutes or more and 180 minutes or less. When adjusting the pH of the slurry containing the substituent-introduced fibers, it is preferable to add an alkali compound that can be used in the above-mentioned alkali treatment step to the slurry.

[0103] After the nitrogen removal treatment step, the ionic substituent-introduced fiber may be subjected to a washing step, if necessary. The washing step is carried out by washing the ionic substituent-introduced fiber with, for example, water or an organic solvent. The number of washing steps to be carried out in each washing step is not particularly limited.

[0104] (Substituent Removal Treatment) The method for producing fine fibrous cellulose may include a step of removing at least a portion of the substituents from fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less. By undergoing such a step, it is possible to obtain fine fibrous cellulose having a small fiber width but a low amount of introduced substituents. In this specification, the step of removing at least a portion of the substituents from the fine fibrous cellulose is also referred to as a substituent removal treatment step.

[0105] Examples of the substituent removal treatment step include a step of heat treating a fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, a step of enzyme treatment, a step of acid treatment, a step of alkali treatment, etc. These may be performed alone or in combination. Among these, the substituent removal treatment step is preferably a step of heat treatment or a step of enzyme treatment. By undergoing the above treatment step, at least a portion of the substituents are removed from the fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, and fine fibrous cellulose having an introduced amount of substituents of less than 0.5 mmol / g can be obtained. By forming a fine fibrous cellulose-containing layer using such fine fibrous cellulose, a laminate with better water resistance can be obtained.

[0106] The substituent removal treatment step is preferably carried out in the form of a slurry. That is, the substituent removal treatment step is preferably a step of subjecting a slurry containing a substituent-containing fine fibrous cellulose having a fiber width of 1,000 nm or less to a heat treatment, an enzyme treatment, an acid treatment, an alkali treatment, or the like. By carrying out the substituent removal treatment step in the form of a slurry, it is possible to prevent the residue of colored substances generated by heating or the like during the substituent removal treatment, as well as added or generated acids, alkalis, salts, etc. This makes it possible to suppress coloration of the fine fibrous cellulose-containing layer. Furthermore, when a treatment is carried out to remove salts derived from the substituents removed after the substituent removal treatment, it is also possible to increase the salt removal efficiency.

[0107] When a substituent removal treatment is performed on a slurry containing fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, the concentration of the fine fibrous cellulose in the slurry is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. Furthermore, the concentration of the fine fibrous cellulose in the slurry is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. By controlling the concentration of the fine fibrous cellulose in the slurry within the above range, the substituent removal treatment can be performed more efficiently. Furthermore, by controlling the concentration of the fine fibrous cellulose in the slurry within the above range, it is possible to prevent the residue of colored substances caused by heating during the substituent removal treatment, as well as added or generated acids, alkalis, salts, etc. This can suppress coloration of the fine fibrous cellulose-containing layer. Furthermore, when a treatment is performed to remove salts derived from the substituents removed after the substituent removal treatment, it is also possible to improve the salt removal efficiency.

[0108] When the substituent removal treatment step is a step of heat-treating fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, the heating temperature in the heat treatment step is preferably 40° C. or higher, more preferably 50° C. or higher, and even more preferably 60° C. or higher. The heating temperature in the heat treatment step is preferably 250° C. or lower, more preferably 230° C. or lower, and even more preferably 200° C. or lower. In particular, when the substituent in the fine fibrous cellulose subjected to the substituent removal treatment step is a phosphorus oxo acid group, the heating temperature in the heat treatment step is preferably 80° C. or higher, more preferably 100° C. or higher, and even more preferably 120° C. or higher.

[0109] When the substituent removal treatment step is a heat treatment step, the heating device that can be used in the heat treatment step is not particularly limited, and examples that can be used include a hot air heater, a steam heater, an electric heater, a hydrothermal heater, a thermal heater, an infrared heater, a far-infrared heater, a microwave heater, a high-frequency heater, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, a flash dryer, and a reduced-pressure dryer. From the viewpoint of preventing evaporation, the heating is preferably carried out in a closed system, and from the viewpoint of further increasing the heating temperature, it is preferably carried out in a pressure-resistant device or container. The heat treatment may be a batch process, a batch continuous process, or a continuous process.

[0110] When the substituent removal treatment step is a step of enzymatically treating fine fibrous cellulose having substituents and a fiber width of 1,000 nm or less, it is preferable to use a phosphate ester hydrolase, a sulfate ester hydrolase, or the like in the enzymatic treatment step depending on the type of substituent.

[0111] In the enzyme treatment step, the enzyme is preferably added so that the enzymatic activity per 1 g of fine fibrous cellulose is 0.1 nkat or more, more preferably 1.0 nkat or more, and even more preferably 10 nkat or more. Furthermore, the enzyme is preferably added so that the enzymatic activity per 1 g of fine fibrous cellulose is 100,000 nkat or less, more preferably 50,000 nkat or less, and even more preferably 10,000 nkat or less. After adding the enzyme to the fine fibrous cellulose dispersion (slurry), it is preferable to treat it at a temperature of 0°C or higher but lower than 50°C for 1 minute or longer but 100 hours or shorter.

[0112] After the enzymatic reaction, a step of deactivating the enzyme may be performed. Examples of the method for deactivating the enzyme include a method of adding an acid component or an alkali component to the enzymatically treated slurry to deactivate the enzyme, and a method of increasing the temperature of the enzymatically treated slurry to 90°C or higher to deactivate the enzyme.

[0113] When the substituent removal treatment step is a step of acid-treating fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, it is preferable to add an acid compound that can be used in the acid treatment step described above to the slurry in the acid treatment step.

[0114] When the substituent removal treatment step is a step of alkali treating fine fibrous cellulose having a substituent and a fiber width of 1,000 nm or less, it is preferable to add an alkali compound that can be used in the alkali treatment step described above to the slurry in the alkali treatment step.

[0115] In the substituent removal treatment step, it is preferable that the substituent removal reaction proceeds uniformly. To proceed with the reaction uniformly, for example, the slurry containing the fine fibrous cellulose may be stirred, or the specific surface area of ​​the slurry may be increased. As a method for stirring the slurry, external mechanical shear may be applied, or self-stirring may be promoted by increasing the liquid feed rate of the slurry during the reaction.

[0116] In the substituent removal treatment step, spacer molecules may be added. The spacer molecules penetrate between adjacent fine fibrous cellulose particles, thereby acting as spacers to create fine spaces between the fine fibrous cellulose particles. Adding such spacer molecules in the substituent removal treatment step can suppress aggregation of the fine fibrous cellulose particles after the substituent removal treatment. This can more effectively increase the transparency of the fine fibrous cellulose-containing layer.

[0117] The spacer molecule is preferably a water-soluble organic compound. Examples of water-soluble organic compounds include sugars, water-soluble polymers, and urea. Specific examples include trehalose, urea, polyethylene glycol (PEG), polyethylene oxide (PEO), carboxymethyl cellulose, and polyvinyl alcohol (PVA). Furthermore, examples of water-soluble organic compounds that can be used include alkyl methacrylate-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, and starches such as amylose; glycerin, diglycerin, polyglycerin, hyaluronic acid, and metal salts of hyaluronic acid.

[0118] Also, known pigments can be used as spacer molecules, such as kaolin (containing clay), calcium carbonate, titanium oxide, zinc oxide, amorphous silica (containing colloidal silica), aluminum oxide, zeolite, sepiolite, smectite, synthetic smectite, magnesium silicate, magnesium carbonate, magnesium oxide, diatomaceous earth, styrene-based plastic pigments, hydrotalcite, urea resin-based plastic pigments, and benzoguanamine-based plastic pigments.

[0119] (pH Adjustment Step) When the above-mentioned substituent removal treatment step is carried out in the form of a slurry, a step of adjusting the pH of the slurry containing the fine fibrous cellulose may be carried out before the substituent removal treatment step. For example, an ionic substituent is introduced into the cellulose fiber, and the counter ion of this ionic substituent is Na. ＋In this case, the slurry containing the defibrated fine fibrous cellulose exhibits a weak alkaline pH. If the slurry is heated in this state, monosaccharides, which are one of the causes of 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. Similarly, monosaccharides may be generated under acidic conditions, so it is preferable to adjust the pH of the slurry to 3 or more.

[0120] Furthermore, when the substituted fine fibrous cellulose is a phosphate-containing fine fibrous cellulose, from the viewpoint of improving the efficiency of removing the substituents, it is preferable that the phosphorus of the phosphate group is in a state susceptible to nucleophilic attack. The phosphorus susceptible to nucleophilic attack is cellulose -O-P(=O)(-O-H ＋ ) (-O-Na ＋ To achieve this state, the pH of the slurry is preferably adjusted to 3 or more and 8 or less, and more preferably adjusted to 4 or more and 6 or less.

[0121] The means for adjusting the pH is not particularly limited, and for example, an acid component or an alkali component may be added to a slurry containing fine fibrous cellulose. The acid component may be either an inorganic acid or an organic acid. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Examples of organic acids include formic acid, acetic acid, citric acid, malic acid, lactic acid, adipic acid, sebacic acid, stearic acid, maleic acid, succinic acid, tartaric acid, fumaric acid, and gluconic acid. The alkali component may be an inorganic alkali compound or an organic alkali compound. Examples of inorganic alkali compounds include lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium bicarbonate, potassium carbonate, potassium bicarbonate, sodium carbonate, and sodium bicarbonate. Examples of the organic alkali compound include ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, butylamine, diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, cyclohexylamine, aniline, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, pyridine, and N,N-dimethyl-4-aminopyridine.

[0122] In addition, in the pH adjustment step, ion exchange treatment may be performed to adjust the pH. In the ion exchange treatment, a strongly acidic cation exchange resin or a weakly acidic ion exchange resin can be used. By treating with an appropriate amount of cation exchange resin for a sufficient time, a slurry containing fine fibrous cellulose having the desired pH can be obtained. Furthermore, in the pH adjustment step, the addition of an acid component or an alkali component may be combined with the ion exchange treatment.

[0123] (Salt Removal Treatment) After the substituent removal treatment step, it is preferable to perform a treatment to remove salts derived from the removed substituents. Removing the salts derived from the substituents makes it easier to obtain fine fibrous cellulose that can suppress coloration. The means for removing the salts derived from the substituents is not particularly limited, and examples thereof include a washing treatment and an ion exchange treatment. The washing treatment is performed by washing the fine fibrous cellulose that has aggregated in the substituent removal treatment with, for example, water or an organic solvent. In the ion exchange treatment, an ion exchange resin can be used.

[0124] (Uniform Dispersion Treatment) After the substituent removal treatment step, a step of uniformly dispersing the fine fibrous cellulose obtained through the substituent removal treatment may be provided. By subjecting the fine fibrous cellulose to the substituent removal treatment, at least a portion of the fine fibrous cellulose is aggregated. The uniform dispersion treatment step is a step of uniformly dispersing the aggregated fine fibrous cellulose.

[0125] In the uniform dispersion treatment step, for example, a high-speed defibrator, grinder (stone mill type grinder), high-pressure homogenizer, high-pressure collision type grinder, ball mill, bead mill, disk type refiner, conical refiner, twin-screw kneader, vibration mill, homomixer under high-speed rotation, ultrasonic disperser or beater can be used. Among the above-mentioned uniform dispersion treatment devices, it is more preferable to use a high-speed defibrator or high-pressure homogenizer.

[0126] The treatment conditions in the uniform dispersion treatment step are not particularly limited, but it is preferable to increase the maximum movement speed of the fine fibrous cellulose during treatment and the pressure during treatment. In a high-speed defibrator, the peripheral speed is preferably 20 m / sec or more, more preferably 25 m / sec or more, and even more preferably 30 m / sec or more. A high-pressure homogenizer is more preferably used because it has a higher maximum movement speed of the fine fibrous cellulose during treatment and a higher pressure during treatment than a high-speed defibrator. In high-pressure homogenizer treatment, the pressure during treatment is preferably 1 MPa or more and 350 MPa or less, more preferably 10 MPa or more and 300 MPa or less, and even more preferably 50 MPa or more and 250 MPa or less.

[0127] In the uniform dispersion treatment step, the above-mentioned spacer molecules may be newly added. By adding such spacer molecules in the uniform dispersion treatment step, the fine fibrous cellulose can be dispersed more uniformly and smoothly. This makes it possible to more effectively improve the transparency of the fine fibrous cellulose-containing layer.

[0128] In the fine fibrous cellulose-containing layer of this embodiment, the content of fine fibrous cellulose in the solid content of the fine fibrous cellulose-containing layer is, from the viewpoint of improving the rigidity of the laminate, preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, still more preferably 25% by mass or more, and preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less, and still more preferably 75% by mass or less. When the fine fibrous cellulose-containing layer of this embodiment is a multilayered layer, it is preferable that the content of fine fibrous cellulose in the solid content of each layer is within the above range. As the fine fibrous cellulose, fine fibrous cellulose containing an ionic group and unmodified fine fibrous cellulose may be used in combination.

[0129] In this embodiment, the fine fibrous cellulose may be a combination of fine fibrous cellulose containing ionic groups and unmodified fine fibrous cellulose. Furthermore, in addition to the fine fibrous cellulose, coarse cellulose fibers having a fiber width exceeding 1 μm may also be contained. In the following description, fine fibrous cellulose and coarse cellulose fibers are collectively referred to as "cellulose fibers." The fiber width of the coarse cellulose fibers is not particularly limited as long as it is 1 μm or more, but is preferably 1 μm or more and 100 μm or less, more preferably 5 μm or more, even more preferably 10 μm or more, and more preferably 50 μm or less, and even more preferably 40 μm or less. The fiber width of the coarse cellulose fibers can be determined using a fiber length distribution measuring device (for example, an FS5 manufactured by Valmet or an L&W Fiber Tester Plus manufactured by ABB).

[0130] The coarse cellulose fibers may have ionic substituents to improve dispersibility in the fine fibrous cellulose-containing layer. Preferred embodiments of the ionic substituents are the same as those for the fine fibrous cellulose, and the preferred ranges of the type and amount of the substituents are also the same. The coarse cellulose fibers are preferably obtained by introducing ionic groups into the fiber raw material and then gently defibrating the raw material. Examples of defibrators used for the gentle defibration process include refiners such as disk refiners and conical refiners.

[0131] When coarse cellulose fibers are contained, the preferred content of fine fibrous cellulose in the above-mentioned fine fibrous cellulose-containing layer is the preferred range of the total content of fibrous cellulose, i.e., fine fibrous cellulose and coarse cellulose fibers. When coarse cellulose fibers are contained, the content of coarse cellulose fibers per 100 parts by mass of fibrous cellulose (total of fine fibrous cellulose and coarse cellulose fibers) is preferably 1 part by mass or more and 80 parts by mass or less, more preferably 3 parts by mass or more, even more preferably 5 parts by mass or more, and preferably 60 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 20 parts by mass or less. When the content of coarse cellulose fibers is within the above range, coarse cellulose fibers can be produced more cheaply than fine fibrous cellulose, so the laminate can be produced more cheaply.

[0132] <Hydrophilic Polymer> In the present embodiment, the fine fibrous cellulose-containing layer preferably contains a hydrophilic polymer from the viewpoint of ease of production of the fine fibrous cellulose-containing layer. A hydrophilic polymer generally refers to a polymer compound that is easily dissolved, swelled, or wetted in water. Examples of hydrophilic polymers include polymer compounds having ionic groups such as carboxyl groups, sulfone groups, or amino groups in the molecular structure, and polymer compounds having nonionic hydrophilic groups such as hydroxyl groups, amide groups, ether groups, or polyoxyethylene groups or polyoxypropylene groups. Examples of hydrophilic polymers include carboxyvinyl polymers; polyvinyl alcohol; alkyl methacrylate-acrylic acid copolymers; polyvinylpyrrolidone; polyvinyl methyl ether; polyacrylates such as sodium polyacrylate; alkyl acrylate copolymers; urethane copolymers; modified polyesters; modified polyimides; polyalkylene glycols such as polyethylene glycol, polyethylene oxide, and polypropylene glycol; polycations such as polyacrylamide and polyethyleneimine; polyanions; amphoteric polymers; xanthan gum, guar gum, tamarind gum, carrageenan, locust bean gum, and crumbly gum. Examples of thickening polysaccharides include inseed, alginic acid, metal salts of alginic acid, pullulan, sakuran, and pectin; cellulose derivatives include carboxymethylcellulose, carboxyethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, and hydroxyethylcellulose; starches include cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, dextrin, and amylose; glycerins such as polyglycerin; hyaluronic acid, metal salts of hyaluronic acid; proteins such as casein.In addition, these hydrophilic polymers may be copolymers.In addition, "polyvinyl alcohol" includes modified polyvinyl alcohol.

[0133] The hydrophilic polymer preferably contains polyvinyl alcohol, polyalkylene glycol, or a cellulose derivative, more preferably polyvinyl alcohol or a cellulose derivative. The cellulose derivative is preferably a nonionic water-soluble cellulose ether such as methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, or hydroxyethyl cellulose, more preferably hydroxypropyl methyl cellulose.

[0134] When the fine fibrous cellulose-containing layer is a single layer, the hydrophilic polymer preferably contains a nonionic water-soluble cellulose ether and / or polyvinyl alcohol, more preferably a nonionic water-soluble cellulose ether. The term "water-soluble" means that 1 g or more dissolves in 100 g of water at any temperature between 0 ° C. and 100 ° C. The term "polymer" means that the average molecular weight (weight average molecular weight when having a molecular weight distribution) is 1,000 or more, preferably 1,500 or more, more preferably 2,000 or more. When a nonionic water-soluble cellulose ether is contained, the content of the nonionic water-soluble cellulose ether in the hydrophilic polymer is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or less, and 100% by mass or less.

[0135] When the fine fibrous cellulose-containing layer in this embodiment is a single layer, from the viewpoint of improving the rigidity of the laminated sheet, the mass ratio of hydrophilic polymer to fine fibrous cellulose (hydrophilic polymer / fine fibrous cellulose) in the fine fibrous cellulose-containing layer is preferably 5 / 95 or more and 90 / 10 or less, more preferably 10 / 90 or more, even more preferably 20 / 80 or more, still more preferably 25 / 75 or more, and more preferably 85 / 15 or less, even more preferably 80 / 20 or less, and still more preferably 75 / 25 or less.

[0136] When the fine fibrous cellulose-containing layer in this embodiment is a single layer, from the viewpoint of improving the rigidity of the laminated sheet, the mass ratio of nonionic water-soluble cellulose ether to fine fibrous cellulose in the fine fibrous cellulose-containing layer (nonionic water-soluble cellulose ether / fine fibrous cellulose) is preferably 10 / 90 or more and 90 / 10 or less, more preferably 15 / 85 or more, even more preferably 20 / 80 or more, still more preferably 25 / 75 or more, and more preferably 85 / 15 or less, even more preferably 80 / 20 or less, and still more preferably 75 / 25 or less.

[0137] When the fine fibrous cellulose-containing layer in this embodiment is a single layer, the total content of the fine fibrous cellulose and the hydrophilic polymer in the solid content of the fine fibrous cellulose-containing layer is, from the viewpoint of improving the rigidity of the laminate, preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, and is 100% by mass or less.

[0138] When the fine fibrous cellulose-containing layer is a multi-layer structure, it preferably includes a fine fibrous cellulose-containing layer 1a containing polyvinyl alcohol and a fine fibrous cellulose-containing layer 1b containing a nonionic water-soluble cellulose ether. In the laminate described below, it is preferred that the fine fibrous cellulose-containing layer 1b containing the nonionic water-soluble cellulose ether be in contact with the core resin plate.

[0139] In the present embodiment, when the fine fibrous cellulose-containing layer is a multilayer structure, the mass ratio of hydrophilic polymer to fine fibrous cellulose (hydrophilic polymer / fine fibrous cellulose) in each layer constituting the fine fibrous cellulose-containing layer is preferably 5 / 95 or more and 90 / 10 or less, more preferably 10 / 90 or more, even more preferably 20 / 80 or more, and more preferably 80 / 20 or less, even more preferably 70 / 30 or less, and even more preferably 60 / 40 or less.

[0140] In the fine fibrous cellulose-containing layer 1a of this embodiment, the mass ratio of polyvinyl alcohol to fine fibrous cellulose (polyvinyl alcohol / fine fibrous cellulose) is, from the viewpoint of interlayer adhesion, preferably 25 / 75 or more and 90 / 10 or less, more preferably 75 / 25 or less, even more preferably 60 / 40 or less, still more preferably 45 / 55 or less, and even more preferably 40 / 60 or less.

[0141] In the fine fibrous cellulose-containing layer 1b in this embodiment, the mass ratio of nonionic water-soluble cellulose ether to fine fibrous cellulose (nonionic water-soluble cellulose ether / fine fibrous cellulose) is, from the viewpoint of interlayer adhesion, preferably 5 / 95 or more and 90 / 10 or less, more preferably 10 / 90 or more, even more preferably 20 / 80 or more, and more preferably 70 / 30 or less, even more preferably 60 / 40 or less, still more preferably 50 / 50 or less, and even more preferably 40 / 60 or less.

[0142] When the fine fibrous cellulose-containing layer in this embodiment is a multilayered layer, the total content of fine fibrous cellulose and hydrophilic polymer in the solid content of each layer constituting the fine fibrous cellulose-containing layer is, from the viewpoint of improving the rigidity of the laminate, preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, and is 100% by mass or less.

[0143] <Other Components> The fine fibrous cellulose-containing layer of this embodiment may contain components (other components) other than the fine fibrous cellulose having a fiber width of 1,000 nm or less and the hydrophilic polymer. Examples of other components include fibrous cellulose having a fiber width of more than 1,000 nm, hydrophilic low-molecular-weight compounds, paper strength agents, thermoplastic resins, surfactants, organic ions, coupling agents, inorganic layered compounds, inorganic compounds, leveling agents, preservatives, antifoaming agents, organic particles, lubricants, antistatic agents, UV protection agents, dyes, pigments, stabilizers, magnetic powders, orientation promoters, plasticizers, dispersants, color inhibitors, polymerization inhibitors, pH adjusters, and crosslinking agents. In the fine fibrous cellulose-containing layer of this embodiment, the total content of "other components" in the solid content of the fine fibrous cellulose-containing layer can be, for example, 5% by mass or less, 3% by mass or less, 1% by mass or less, or even 0% by mass.

[0144] <Thickness> The thickness of the fine fibrous cellulose-containing layer in this embodiment is preferably 10 μm or more and 100 μm or less, more preferably 15 μm or more, even more preferably 20 μm or more, and more preferably 80 μm or less, even more preferably 60 μm or less. When the fine fibrous cellulose-containing layer is a multi-layered layer, it is preferable that the total thickness is within the above range. It is preferable that the thickness of the fine fibrous cellulose-containing layer is appropriately adjusted depending on the application of the laminate sheet or laminate.

[0145] <Basis Weight> The basis weight of the fine fibrous cellulose-containing layer in this embodiment is preferably 20 g / m ２ 110g / m or more ２ More preferably, it is 30 g / m or less. ２ More preferably, 40 g / m ２ More preferably, it is 90 g / m or more. ２ More preferably 70 g / m or less ２ The basis weight of the fine fibrous cellulose-containing layer is preferably within the above range. When the fine fibrous cellulose-containing layer is a multi-layered layer, the total basis weight is preferably within the above range. The basis weight of the fine fibrous cellulose-containing layer is preferably adjusted appropriately depending on the application of the laminate sheet or laminate.

[0146] <Density> The density of the fine fibrous cellulose-containing layer in this embodiment is preferably 0.6 g / cm ３ 2.5g / cm or more ３ or less, more preferably 0.8 g / cm ３ More preferably, it is 1.0 g / cm ３ More preferably, it is 2.2 g / cm or more. ３ More preferably, 1.9 g / cm or less ３ The density of the fine fibrous cellulose-containing layer is calculated by dividing the basis weight of the fine fibrous cellulose-containing layer by its thickness. When the fine fibrous cellulose-containing layer is a multi-layered layer, the density is calculated by dividing the total basis weight by the total thickness.

[0147] [Adhesive Layers 1a, 1b] The laminate sheet of this embodiment has either (i) an adhesive layer 1a on one side of a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1,000 nm or less, or (ii) an adhesive layer 1a on one side of a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1,000 nm or less, and an adhesive layer 1b on the other side. The components contained and the components that can be contained in each of the adhesive layers 1a and 1b may be the same or different, but are preferably the same. Note that the components contained and the components that can be contained in each of the adhesive layers 1a and 1b are preferably the same. Hereinafter, adhesive layers 1a and 1b will be collectively referred to simply as "adhesive layers."

[0148] Examples of adhesives constituting the adhesive layer include polycarbonate resins, acrylic resins, polyester resins, vinyl chloride resins, vinyl acetate resins, urethane resins, silicone resins, epoxy resins, ethylene / vinyl acetate copolymer resins, polyvinyl alcohol resins, ethylene-vinyl alcohol copolymer resins, and rubber emulsions such as styrene-butadiene rubber (SBR) and nitrile rubber (NBR). Of these, one or more selected from the group consisting of polycarbonate resins, acrylic resins, and polyester resins are preferred, with polycarbonate resins being more preferred. Examples of polycarbonate resins that can be used include the polycarbonate copolymers described in JP 2008-24919 A.

[0149] The adhesive layer is preferably formed from an adhesive composition containing an adhesive aid (formed using an adhesive composition containing an adhesive aid). Examples of the adhesive aid include compounds containing at least one selected from an isocyanate group, a carbodiimide group, an epoxy group, an oxazoline group, an amino group, and a silanol group. Among these, compounds containing an isocyanate group (isocyanate compounds) are preferred as the adhesive aid from the viewpoint of excellent adhesion to the fine fibrous cellulose-containing layer.

[0150] The adhesive composition preferably contains an adhesive and an adhesive aid, more preferably contains one or more resins selected from the group consisting of polycarbonate-based resins, acrylic-based resins, and polyester-based resins, and an isocyanate compound, and even more preferably contains a polycarbonate-based resin and an isocyanate compound.

[0151] In the adhesive composition, the content of the adhesive aid relative to 100 parts by mass of the adhesive is preferably 5 parts by mass or more and 30 parts by mass or less, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and more preferably 25 parts by mass or less, even more preferably 20 parts by mass or less, from the viewpoint of improving adhesiveness.

[0152] The adhesive composition preferably contains an organic solvent, and examples of the organic solvent include toluene, methylene chloride, tetrahydrofuran, tetraglyme, dimethyl carbonate, methyl ethyl ketone, ethyl acetate, dimethylacetamide, and styrene.

[0153] From the viewpoints of coatability and solvent removal, the solids concentration of the adhesive composition is preferably 1% by mass or more and 25% by mass or less, more preferably 4% by mass or more, even more preferably 7% by mass or more, and more preferably 20% by mass or less, even more preferably 15% by mass or less.

[0154] <Thickness> In this embodiment, the thickness of each adhesive layer is preferably 1 μm or more and 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, still more preferably 20 μm or less, and even more preferably 10 μm or less. The thicknesses of the adhesive layers 1 a and 1 b may be the same or different. It is preferable to adjust the thickness of the adhesive layer appropriately depending on the application of the laminate sheet or laminate.

[0155] <Resin film, protective film> In the laminate sheet of the present embodiment, (i) preferably has an adhesive layer 1a and a resin film or a protective film in this order on one side of the fine fibrous cellulose-containing layer, and (ii) preferably has an adhesive layer 1a and a resin film or a protective film in this order on one side of the fine fibrous cellulose-containing layer, and an adhesive layer 1b on the other side.

[0156] The resin constituting the resin film can be selected depending on the application of the laminate sheet or laminate, and is preferably at least one selected from the group consisting of polyolefin resin, cyclic olefin resin, polycarbonate resin, polyethylene terephthalate resin, polyethylene naphthalate resin, polyimide resin, polystyrene resin and acrylic resin, and more preferably polycarbonate.

[0157] The protective film is preferably a polyethylene film, a polyethylene terephthalate film, a polyethylene naphthalate film, a polyimide film, or a fluororesin film. In the laminate sheet of this embodiment, for example, during the production stage of the laminate, the protective film can be peeled off and a resin film can be laminated on the adhesive layer 1 a.

[0158] <Thickness> The thickness of each resin film layer in this embodiment is preferably 30 μm or more and 500 μm or less, more preferably 50 μm or more, even more preferably 70 μm or more, and more preferably 400 μm or less, even more preferably 350 μm or less, still more preferably 300 μm or less, and even more preferably 250 μm or less. The thickness of the resin film is preferably adjusted appropriately depending on the application of the laminate sheet or laminate. The thickness of each protective film layer in this embodiment is preferably 20 μm or more and 300 μm or less, more preferably 30 μm or more, even more preferably 40 μm or more, and more preferably 250 μm or less, and even more preferably 200 μm or less.

[0159] [Laminate] The laminate of this embodiment has a laminate sheet (ii) having a resin film on at least one side of a core resin plate, the core resin plate containing a polycarbonate resin, and the adhesive layer 1b of the laminate sheet contacts the core resin plate. When the laminate of this embodiment has laminate sheets on both sides of the core resin plate, the components contained in the layer or film constituting the laminate sheet on one side, the components that may be contained, the thickness, density, and basis weight of the layer or film, and the components contained in the layer or film constituting the laminate sheet on the other side, the components that may be contained, the thickness, density, and basis weight of the layer or film may be the same or different.

[0160] [Core Resin Plate] The laminate of this embodiment has a core resin plate. The core resin plate contains a polycarbonate-based resin. "Polycarbonate-based resin" refers to a resin containing a moiety in which structural units are repeatedly bonded via carbonate groups (-O-(C=O)-O-). From the viewpoint of improving the rigidity of the laminate, the content of the polycarbonate-based resin in the core resin plate is preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, still more preferably 85% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, and 100% by mass or less. In addition to the polycarbonate-based resin, the core resin plate may also contain, for example, an acrylonitrile butadiene styrene copolymer or a polymethyl methacrylate resin.

[0161] <Thickness> In this embodiment, the thickness of each core resin plate is preferably 200 μm or more and 4,500 μm or less, more preferably 400 μm or more, even more preferably 800 μm or more, and more preferably 4,000 μm or less, even more preferably 3,500 μm or less. The thickness of the core resin plate is preferably adjusted appropriately depending on the application of the laminate.

[0162] [Laminate Properties] [Haze] The haze of the laminate of this embodiment (the laminate before heating, described below) is preferably 5.0% or less, more preferably 4.0% or less, even more preferably 3.0% or less, and even more preferably 1.5% or less. Meanwhile, the lower limit of the haze of the laminate may be, for example, 0%. The laminate of this embodiment has a haze difference before and after heating at 170°C for 10 minutes (haze after heating - haze before heating) of preferably 2.0% or less, more preferably 1.6% or less, even more preferably 1.2% or less, even more preferably 0.8% or less, even more preferably 0.4% or less, and even more preferably 0.3% or less, and may even be 0%. The haze of the laminate can be controlled by the fiber width of the fine fibrous cellulose, the type of ionic group, the amount of ionic group introduced, the type of hydrophilic polymer, the type of resin constituting the resin film, the content of fine fibrous cellulose and hydrophilic polymer in the fine fibrous cellulose-containing layer, the thickness of each layer constituting the laminate, and the like. The haze of the laminate is a value measured in accordance with JIS K 7136:2000.

[0163] [Yellow Index] The yellow index (YI value) of the laminate of this embodiment is preferably 4.50 or less, more preferably 3.00 or less, and even more preferably 2.50 or less, from the viewpoint of application to various applications, with no particular lower limit. A YI value within the above range is preferable because it allows for the production of thermally processed products with reduced yellowing. The YI value of the laminate can be controlled by the fiber width of the fine fibrous cellulose, the type of ionic group, the amount of ionic group introduced, the type of hydrophilic polymer, the type of resin constituting the resin film, the content of fine fibrous cellulose and hydrophilic polymer in the fine fibrous cellulose-containing layer, the thickness of each layer constituting the laminate, and the like. The YI value of the laminate is a value measured in accordance with JIS K 7373:2006.

[0164] [Total Light Transmittance] The total light transmittance of the laminate of this embodiment is preferably 80% or more, more preferably 83% or more, and even more preferably 85% or more. Meanwhile, the upper limit of the total light transmittance of the laminate may be, for example, 100%. The total light transmittance of the laminate can be controlled by the fiber width of the fine fibrous cellulose, the type of ionic group, the amount of ionic group introduced, the type of hydrophilic polymer, the type of resin constituting the resin film, the content of the fine fibrous cellulose and hydrophilic polymer in the fine fibrous cellulose-containing layer, the thickness of each layer constituting the laminate, and the like. The total light transmittance of the laminate is a value measured in accordance with JIS K 7361-1:1997.

[0165] [Thickness] The thickness of the laminate of this embodiment is preferably 500 μm or more and 5,000 μm or less, more preferably 700 μm or more, even more preferably 900 μm or more, and more preferably 4,500 μm or less, even more preferably 4,000 μm or less, and still more preferably 3,500 μm or less. It is preferable to adjust the thickness of the laminate appropriately depending on the application.

[0166] [Method for manufacturing laminate sheet] The method for manufacturing a laminate sheet of this embodiment can provide the following laminate sheet: (i) a laminate sheet having an adhesive layer 1a on one side of a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1,000 nm or less, and satisfying at least one of the following conditions A and B, or (ii) a laminate sheet having an adhesive layer 1a on one side of a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1,000 nm or less, and an adhesive layer 1b on the other side, and satisfying at least one of the following conditions C and D. Condition A: The total content of organic solvents in the fine fibrous cellulose-containing layer and adhesive layer 1a is 0.1 ppm or more and 40 ppm or less by mass. Condition B: The content of organic solvents in adhesive layer 1a is 0.5 ppm or more and 200 ppm or less by mass. Condition C: The total content of organic solvents in the fine fibrous cellulose-containing layer, adhesive layer 1a and adhesive layer 1b is 0.1 ppm or more and 60 ppm or less by mass. Condition D: The total content of organic solvents in adhesive layer 1a and adhesive layer 1b is 0.5 ppm or more and 300 ppm or less by mass.

[0167] Hereinafter, laminate sheet manufacturing methods 1 and 2 will be described as methods for manufacturing a laminate sheet according to this embodiment. As a method for manufacturing a laminate sheet according to this embodiment, laminate sheet manufacturing method 1 is preferred. Laminate sheet manufacturing method 1 includes the following steps 1 and 2. Step 1: A step of applying and drying a coating liquid for a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1,000 nm or less to obtain a fine fibrous cellulose-containing layer. Step 2: A step of applying and drying a coating liquid for an adhesive layer on one side of the fine fibrous cellulose-containing layer obtained in step 1 to form adhesive layer 1a or 1b.

[0168] The coating liquid for the fine fibrous cellulose-containing layer used in the method for producing a laminate sheet of this embodiment can be obtained by mixing fine fibrous cellulose, water, and, if necessary, a hydrophilic polymer. The coating liquid for the fine fibrous cellulose-containing layer can be obtained, for example, by preparing a water dispersion of fine fibrous cellulose in the production of fine fibrous cellulose and mixing this water dispersion with an aqueous solution of a hydrophilic polymer. The coating liquid for the adhesive layer used in the method for producing a laminate sheet of this embodiment can be obtained by dissolving or dispersing the components contained in the resulting adhesive layer in an organic solvent, and for example, the above-mentioned adhesive composition can be used.

[0169] [Step 1] In step 1, a coating liquid for a fine fibrous cellulose-containing layer is coated on a substrate and dried. The drying temperature is preferably 50°C or higher and 130°C or lower, more preferably 65°C or higher, even more preferably 80°C or higher, and more preferably 120°C or lower, and even more preferably 110°C or lower. The drying time is preferably 5 minutes or higher and 120 minutes or lower, more preferably 15 minutes or higher, even more preferably 30 minutes or higher, and more preferably 105 minutes or lower, and even more preferably 90 minutes or lower. Drying may be carried out under atmospheric pressure or under reduced pressure. Furthermore, when drying is carried out multiple times, it is preferable that the total drying time is within the above range at the above drying temperature. It is also preferable that each drying time is within the above range. The same applies to the drying described below. As the substrate, a polyethylene terephthalate substrate, an acrylic resin substrate, a polycarbonate substrate, a polyethylene substrate, a polyethylene substrate, and a polyimide substrate can be used.

[0170] [Step 2] In step 2, an adhesive layer coating liquid is applied to one side of the fine fibrous cellulose-containing layer obtained in step 1 and dried to form adhesive layer 1a or 1b. The drying temperature is preferably 50°C or higher and 130°C or lower, more preferably 60°C or higher, even more preferably 70°C or higher, still more preferably 80°C or higher, even more preferably 90°C or higher, and more preferably 120°C or lower, even more preferably 110°C or lower. The drying time is preferably 1 minute or higher and 120 minutes or lower, more preferably 3 minutes or higher, even more preferably 5 minutes or higher, even more preferably 7 minutes or higher, even more preferably 10 minutes or higher, and more preferably 90 minutes or lower, even more preferably 60 minutes or lower.

[0171] The laminate sheet manufacturing method 1 preferably further includes the following step 3 after step 2. In step 3, an adhesive layer coating liquid is applied to the other surface of the fine fibrous cellulose-containing layer (the surface opposite to the surface on which the adhesive layer 1a or 1b is formed) and dried to form the adhesive layer 1b or 1a. The drying temperature is preferably 40°C or higher and 100°C or lower, more preferably 50°C or higher, even more preferably 60°C or higher, more preferably 90°C or lower, and even more preferably 80°C or lower. The drying time is preferably 1 minute or higher and 120 minutes or lower, more preferably 2 minutes or higher, even more preferably 3 minutes or higher, more preferably 90 minutes or lower, and even more preferably 60 minutes or lower. The laminate sheet manufacturing method 1 may further include an additional heat treatment after step 2 or 3 to further strengthen the adhesion between the adhesive layer and the fine fibrous cellulose-containing layer. The heating temperature is preferably 50°C or higher and 120°C or lower, more preferably 70°C or higher and 100°C or lower. The heating time is preferably from 5 hours to 150 hours, more preferably from 15 hours to 100 hours.

[0172] The manufacturing method 1 of the laminated sheet may further include the following step 4 after step 2. Step 4: A step of attaching a resin film or a protective film onto the adhesive layer 1a or 1b. Step 4 may be performed before step 3 or after step 3, as long as it is performed after step 2.

[0173] The method for producing a laminate sheet 2 includes the following steps I and II in this order: Step I: A step of applying a coating liquid for an adhesive layer onto a resin film and drying the coating liquid to form an adhesive layer 1a; Step II: A step of applying a coating liquid for a fine fibrous cellulose-containing layer onto the adhesive layer 1a obtained in step 1 and drying the coating liquid to form a fine fibrous cellulose-containing layer.

[0174] [Step I] In step I, an adhesive layer coating liquid is applied to a resin film and dried to form an adhesive layer 1a. The drying temperature is preferably 50°C or higher and 130°C or lower, more preferably 60°C or higher, even more preferably 70°C or higher, and more preferably 115°C or lower, and even more preferably 100°C or lower. The drying time is preferably 1 minute or higher and 30 minutes or lower, more preferably 3 minutes or higher, even more preferably 5 minutes or higher, and more preferably 25 minutes or lower, and even more preferably 20 minutes or lower.

[0175] [Step II] In step II, a fine fibrous cellulose-containing layer is formed by coating and drying a coating liquid for the fine fibrous cellulose-containing layer on the adhesive layer 1a obtained in step I. The drying temperature is preferably 50°C or higher and 130°C or lower, more preferably 65°C or higher, even more preferably 80°C or higher, and more preferably 120°C or lower, and even more preferably 110°C or lower. The drying time is preferably 5 minutes or higher and 120 minutes or lower, more preferably 15 minutes or higher, even more preferably 30 minutes or higher, and more preferably 105 minutes or lower, and even more preferably 90 minutes or lower.

[0176] [Step III] The laminate sheet manufacturing method 2 may include Step III after Step II. Step III: A step of applying an adhesive layer coating liquid to the fine fibrous cellulose-containing layer obtained in Step 2 and drying the coating liquid to form an adhesive layer 1b. The drying temperature in Step III is preferably 50°C or higher and 130°C or lower, more preferably 55°C or higher, even more preferably 60°C or higher, and more preferably 115°C or lower, and even more preferably 100°C or lower. The drying time is preferably 1 minute or higher and 30 minutes or lower, more preferably 3 minutes or higher, even more preferably 5 minutes or higher, more preferably 20 minutes or lower, and even more preferably 10 minutes or lower. Furthermore, after Step III, an additional heat treatment may be performed to further strengthen the adhesion between the adhesive layer and the fine fibrous cellulose-containing layer. The heating temperature is preferably 50°C or higher and 120°C or lower, more preferably 70°C or higher and 100°C or lower. The heating time is preferably 5 hours or higher and 150 hours or lower, more preferably 15 hours or higher and 100 hours or lower.

[0177] [Laminate Manufacturing Method] The laminate manufacturing method of this embodiment (Laminate Manufacturing Method 1) includes any one of the following steps P to S. Step P: A step of placing a resin film on one surface of adhesive layer 1a or adhesive layer 1b of the laminate sheet (adhesive layer 1a-fine fibrous cellulose-containing layer-adhesive layer 1b) obtained in laminate sheet manufacturing method 1, placing a core resin plate on the other surface, and applying pressure. The pressure is preferably 0.1 MPa or more and 10 MPa or less, more preferably 0.3 MPa or more, even more preferably 0.5 MPa or more, more preferably 7.5 MPa or less, and even more preferably 5.0 MPa or less. The temperature during pressing is preferably 130°C or more and 190°C or less, more preferably 135°C or more, even more preferably 140°C or more, more preferably 185°C or less, and even more preferably 180°C or less. The pressing time is preferably 15 seconds or more and 30 minutes or less, more preferably 30 seconds or more, even more preferably 1 minute or more, more preferably 20 minutes or less, and even more preferably 10 minutes or less. Step Q: A step of placing a core resin plate on the adhesive layer 1b of the laminate sheet (resin film-adhesive layer 1a-fine fibrous cellulose-containing layer-adhesive layer 1b) obtained in the laminate sheet manufacturing method 1 and applying pressure. The pressure is preferably 0.1 MPa or more and 10 MPa or less, more preferably 0.3 MPa or more, even more preferably 0.5 MPa or more, and more preferably 7.5 MPa or less, and even more preferably 5.0 MPa or less. The temperature during pressing is preferably 130°C or more and 190°C or less, more preferably 135°C or more, even more preferably 140°C or more, and more preferably 185°C or less, and even more preferably 180°C or less. The pressing time is preferably 15 seconds or more and 60 minutes or less, more preferably 30 seconds or more, even more preferably 1 minute or more, and more preferably 40 minutes or less, and even more preferably 20 minutes or less.Step R: A step of preparing two laminate sheets (adhesive layer 1a-fine fibrous cellulose-containing layer-adhesive layer 1b) obtained in laminate sheet manufacturing method 1, two resin films, and one core resin plate, arranging these in the order of "resin film-adhesive layer 1a-fine fibrous cellulose-containing layer-adhesive layer 1b-core resin plate-adhesive layer 1b-fine fibrous cellulose-containing layer-adhesive layer 1a-resin film" or "resin film-adhesive layer 1b-fine fibrous cellulose-containing layer-adhesive layer 1a-core resin plate-adhesive layer 1a-fine fibrous cellulose-containing layer-adhesive layer 1b-resin film", and applying pressure. The pressure is preferably 0.1 MPa or more and 10 MPa or less, more preferably 0.3 MPa or more, even more preferably 0.5 MPa or more, and more preferably 7.5 MPa or less, even more preferably 5.0 MPa or less. The temperature during pressing is preferably 130° C. or higher and 190° C. or lower, more preferably 135° C. or higher, even more preferably 140° C. or higher, and more preferably 185° C. or lower, and even more preferably 180° C. or lower. The pressing time is preferably 15 seconds or higher and 60 minutes or lower, more preferably 30 seconds or higher, even more preferably 1 minute or higher, and more preferably 40 minutes or lower, and even more preferably 20 minutes or lower. Step S: Two laminate sheets (resin film - adhesive layer 1a - fine fibrous cellulose-containing layer - adhesive layer 1b) obtained in the laminate sheet manufacturing method 1 and one core resin plate are prepared, and these are arranged in the order of "resin film - adhesive layer 1a - fine fibrous cellulose-containing layer - adhesive layer 1b - core resin plate - adhesive layer 1b - fine fibrous cellulose-containing layer - adhesive layer 1a - resin film", and pressurized. The pressure is preferably 0.1 MPa or more and 10 MPa or less, more preferably 0.3 MPa or more, even more preferably 0.5 MPa or more, and more preferably 7.5 MPa or less, even more preferably 5.0 MPa or less. The temperature during pressurization is preferably 130°C or more and 190°C or less, more preferably 135°C or more, even more preferably 140°C or more, and more preferably 185°C or less, even more preferably 180°C or less.The pressurization time is preferably 15 seconds or more and 60 minutes or less, more preferably 30 seconds or more, even more preferably 1 minute or more, and more preferably 40 minutes or less, even more preferably 20 minutes or less.

[0178] Another laminate manufacturing method (laminate manufacturing method 2) of this embodiment has the following step T and the following step U or V. Step T: A step of applying an adhesive layer coating liquid onto a resin film and drying to form an adhesive layer 1a. The drying temperature is preferably 50°C or higher and 130°C or lower, more preferably 60°C or higher, even more preferably 70°C or higher, and more preferably 115°C or lower, and even more preferably 100°C or lower. The drying time is preferably 1 minute or higher and 30 minutes or lower, more preferably 3 minutes or higher, even more preferably 5 minutes or higher, and more preferably 25 minutes or lower, and even more preferably 20 minutes or lower. Step U: A step of arranging the laminate sheet (fine fibrous cellulose-containing layer-adhesive layer 1b) obtained in the laminate sheet manufacturing method 1, the laminate sheet (resin film-adhesive layer 1a) obtained in step T, and the core resin plate in the order of "resin film-adhesive layer 1a-fine fibrous cellulose-containing layer-adhesive layer 1b-core resin plate" and applying pressure. The pressure is preferably 0.1 MPa or more and 10 MPa or less, more preferably 0.3 MPa or more, even more preferably 0.5 MPa or more, and more preferably 7.5 MPa or less, and even more preferably 5.0 MPa or less. The temperature during pressing is preferably 130°C or more and 190°C or less, more preferably 135°C or more, even more preferably 140°C or more, and more preferably 185°C or less, and even more preferably 180°C or less. The pressing time is preferably 15 seconds or more and 60 minutes or less, more preferably 30 seconds or more, even more preferably 1 minute or more, and more preferably 40 minutes or less, and even more preferably 20 minutes or less.Step V: Two laminate sheets (fine fibrous cellulose-containing layer-adhesive layer 1b) obtained in the laminate sheet manufacturing method 1, two laminate sheets (resin film-adhesive layer 1a) obtained in step T, and one core resin plate are arranged in the following order: "resin film-adhesive layer 1a-fine fibrous cellulose-containing layer-adhesive layer 1b-core resin plate-adhesive layer 1b-fine fibrous cellulose-containing layer-adhesive layer 1a-resin film" and pressurized. The pressure is preferably 0.1 MPa or more and 10 MPa or less, more preferably 0.3 MPa or more, even more preferably 0.5 MPa or more, and more preferably 7.5 MPa or less, even more preferably 5.0 MPa or less. The temperature during pressing is preferably 130°C or more and 190°C or less, more preferably 135°C or more, even more preferably 140°C or more, and more preferably 185°C or less, even more preferably 180°C or less. The pressurization time is preferably 15 seconds or more and 60 minutes or less, more preferably 30 seconds or more, even more preferably 1 minute or more, and more preferably 40 minutes or less, even more preferably 20 minutes or less.

[0179] Yet another method for producing a laminate according to this embodiment (Laminate Production Method 3) includes the following Step W or X. Step W: A step of placing a core resin plate on adhesive layer 1b of the laminate sheet (resin film-adhesive layer 1a-fine fibrous cellulose-containing layer-adhesive layer 1b) obtained in Laminate Sheet Production Method 2, and applying pressure. The pressure is preferably 0.1 MPa or more and 10 MPa or less, more preferably 0.3 MPa or more, even more preferably 0.5 MPa or more, and more preferably 7.5 MPa or less, and even more preferably 5.0 MPa or less. The temperature during pressing is preferably 130°C or more and 190°C or less, more preferably 135°C or more, even more preferably 140°C or more, and more preferably 185°C or less, and even more preferably 180°C or less. The pressing time is preferably 15 seconds or more and 60 minutes or less, more preferably 30 seconds or more, even more preferably 1 minute or more, and more preferably 40 minutes or less, and even more preferably 20 minutes or less. Step X: Two laminate sheets (resin film-adhesive layer 1a-fine fibrous cellulose-containing layer-adhesive layer 1b) obtained in method 2 for producing a laminate sheet and one core resin plate are arranged in the following order: "resin film-adhesive layer 1a-fine fibrous cellulose-containing layer-adhesive layer 1b-core resin plate-adhesive layer 1b-fine fibrous cellulose-containing layer-adhesive layer 1a-resin film," and pressurized. The pressure is preferably 0.1 MPa or more and 10 MPa or less, more preferably 0.3 MPa or more, even more preferably 0.5 MPa or more, and more preferably 7.5 MPa or less, even more preferably 5.0 MPa or less. The temperature during pressurization is preferably 130°C or more and 190°C or less, more preferably 135°C or more, even more preferably 140°C or more, and more preferably 185°C or less, even more preferably 180°C or less. The pressurization time is preferably 15 seconds or more and 60 minutes or less, more preferably 30 seconds or more, even more preferably 1 minute or more, and more preferably 40 minutes or less, even more preferably 20 minutes or less.

[0180] The laminate including the laminate sheet of the present embodiment is suitable for optical components such as various display devices and various solar cells, etc. It is also suitable for applications such as substrates for electronic devices, separators for electrochemical devices, components for home appliances, window materials for various vehicles and buildings, interior materials, exterior materials, and packaging materials.

[0181] [Method for manufacturing a thermally processed product] A laminate having the laminate sheet of this embodiment can be thermally processed to form a thermally processed product of a desired shape. The method for manufacturing a thermally processed product of this embodiment includes a step of thermally processing the laminate. In the thermal processing step, for example, the laminate can be heated and pressed against a mold to form a thermally processed product (thermal press molding), or can be bent (thermal bending) to obtain a thermally processed product of a desired shape. The heating temperature for the thermal processing is preferably 140°C or higher and 200°C or lower, more preferably 150°C or higher, even more preferably 160°C or higher, and more preferably 190°C or lower, and even more preferably 180°C or lower. The heating time is, for example, 1 minute or higher and 30 minutes or lower, and may be 2 minutes or higher, 3 minutes or higher, 20 minutes or lower, or 10 minutes or lower. The bending radius in the thermal processing is, for example, 10 mm or more and 4,000 mm or less, and may be 30 mm or more, 50 mm or more, and may be 3,000 mm or less, or 2,000 mm or less.

[0182] Examples of the heat-processed products include transparent members or components of transparent members such as windows of various transport vehicles, display devices, lenses, transparent containers and light-transmitting substrates, windows of buildings, interior materials and exterior materials.

[0183] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. Unless otherwise specified, the following operations were carried out at room temperature (23°C) and a relative humidity of 50%.

[0184] Preparation Example 1 (Preparation of Fine Fibrous Cellulose Dispersion) (Phosphorylation Treatment) A hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd. was used as the raw material pulp. This raw material pulp was subjected to a phosphorylation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (bone dry mass) of the raw material pulp to adjust the composition to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, thereby obtaining a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 250 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining a phosphorylated pulp.

[0185] (Washing Treatment) The resulting phosphorylated pulp was then washed. The washing treatment was carried out by repeatedly adding 10 L of ion-exchanged water to 100 g (bone dry mass) of phosphorylated pulp to obtain a pulp dispersion, stirring the resulting pulp to uniformly disperse the pulp, and then filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0186] (Neutralization Treatment) Next, the washed phosphorylated pulp was neutralized as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous sodium hydroxide solution was added little by little while stirring to obtain a phosphorylated pulp slurry having a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated to obtain a neutralized phosphorylated pulp. Next, the neutralized phosphorylated pulp was subjected to the above-mentioned washing treatment.

[0187] (Nitrogen Removal Treatment) Phosphorylated pulp was added with ion-exchanged water to prepare a slurry with a solids concentration of 4% by mass. A 48% by mass aqueous solution of sodium hydroxide was added to the slurry to adjust the pH to 13.4, and the slurry was heated at a liquid temperature of 85°C for 1 hour. The pulp slurry was then dehydrated, and 10 L of ion-exchanged water was added per 100 g (bone dry mass) of phosphorylated pulp to obtain a pulp dispersion. The pulp was stirred to uniformly disperse, and the filtration and dehydration were repeated to remove excess sodium hydroxide. The removal was terminated when the electrical conductivity of the filtrate reached 100 μS / cm or less. The amount of carbamide groups introduced, determined from the nitrogen content measured by the measurement method described below, was 0.01 mmol / g.

[0188] The infrared absorption spectrum of the phosphorus oxy-oxidized pulp thus obtained was measured using FT-IR. －１ Absorption due to the P=O of the phosphate group was observed near the peak, confirming that the phosphate group had been added to the pulp. Furthermore, when the obtained phosphorylated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming that cellulose type I crystals were maintained. The amount of phosphate groups (amount of first dissociated acid) measured by the measurement method described below was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0189] (Defibrillation Treatment) Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2% by mass. This slurry was treated six times in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0190] (Substituent Removal Treatment (High-Temperature Heat Treatment)) A 20% by mass aqueous citric acid solution was added to the obtained fine fibrous cellulose dispersion, and the pH of the dispersion was adjusted to 5.5. Thereafter, the fine fibrous cellulose dispersion was placed in a pressure-resistant container and heated at a liquid temperature of 160°C for 15 minutes until the amount of phosphate groups reached 0.08 mmol / g. This operation confirmed the formation of fine fibrous cellulose aggregates.

[0191] (Washing treatment of slurry after removal of substituents) The same amount of ion-exchanged water as the slurry was added to the heated slurry to obtain a slurry with a solids concentration of approximately 1% by mass. The slurry was stirred and then filtered and dehydrated. This procedure was repeated to wash the slurry. When the electrical conductivity of the filtrate reached 10 μS / cm or less, ion-exchanged water was added again to obtain a slurry with a solids concentration of approximately 1% by mass, and the mixture was allowed to stand for 24 hours. The filtration and dehydration procedure was then repeated, and the end point of the washing was determined when the electrical conductivity of the filtrate again reached 10 μS / cm or less. Ion-exchanged water was added to the obtained fine fibrous cellulose aggregates to obtain a slurry after removal of substituents. The solids concentration of this slurry was 1.7% by mass.

[0192] (Uniform Dispersion of Slurry After Substituent Removal) Ion-exchanged water was added to the obtained slurry after substituent removal to obtain a slurry with a solids concentration of 1.0% by mass, which was then treated three times at a pressure of 200 MPa using a wet atomization apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a dispersion of substituent-removed fine fibrous cellulose containing substituent-removed fine fibrous cellulose. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. Furthermore, ion-exchanged water was added to the dispersion of substituent-removed fine fibrous cellulose to obtain a dispersion of fine fibrous cellulose with a solids concentration of 0.5% by mass.

[0193] (Measurement of phosphorus oxo acid group content) The phosphorus oxo acid group content (equal to the phosphorus oxo acid group content of phosphorus oxo-oxidized (phosphorylated or phosphorous) pulp) was measured by adding ion-exchanged water to a fine fibrous cellulose dispersion containing the target fine fibrous cellulose to prepare a slurry with a fine fibrous cellulose content of 0.2% by mass. The resulting slurry was treated with an ion-exchange resin and then titrated with an alkali. The ion-exchange resin treatment was performed by adding 1 / 10 by volume of a strongly acidic ion-exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) to the fine fibrous cellulose-containing slurry, shaking for 1 hour, and then pouring the mixture onto a mesh with 90 μm openings to separate the ion-exchange resin from the slurry. In addition, the alkali titration was performed by adding 10 μL of 0.1 N sodium hydroxide aqueous solution to the fine fibrous cellulose-containing slurry after treatment with an ion exchange resin every 5 seconds, while measuring the change in the pH value of the slurry. Nitrogen gas was blown into the slurry 15 minutes before the start of the titration. In this neutralization titration, two maximum points of increment (differential value of pH with respect to the amount of alkali added) were observed on the curve plotting the measured pH against the amount of alkali added. Of these, the maximum point of increment obtained first after starting the addition of alkali is called the first endpoint, and the maximum point of increment obtained next is called the second endpoint (Figure 1). The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of first dissociated acid in the slurry used in the titration. Furthermore, 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 in the titration. The amount of alkali (mmol) required from the start of titration to the first endpoint divided by the solid content (g) in the slurry to be titrated was taken as the amount of phosphorus oxo acid groups (mmol / g). The amount of alkali (mmol) required from the start of titration to the second endpoint divided by the solid content (g) in the slurry to be titrated was taken as the total amount of dissociated acid (mmol / g). The amount of phosphorus oxo acid groups (amount of phosphorus oxo acid groups introduced) (mmol / g) is calculated by dividing the amount of alkali (mmol) required from the start of titration to the second endpoint by the solid content (g) in the slurry to be titrated. ＋ ) and the amount of substituents per 1 g of the fine fibrous cellulose.

[0194] (Measurement of carbamide group amount) The amount of carbamide groups in the fine fibrous cellulose was measured by subjecting the freeze-dried and pulverized sample to a trace total nitrogen analyzer TN-110 manufactured by Mitsubishi Chemical Analytech Co., Ltd. Note that ionic nitrogen was removed during the neutralization and washing processes. The amount of carbamide groups introduced per unit mass of the fine fibrous cellulose (mmol / g) was calculated by dividing the nitrogen content (g / g) per unit mass of the fine fibrous cellulose obtained by trace nitrogen analysis by the atomic weight of nitrogen.

[0195] Preparation Example 2 (Preparation of Hydroxypropyl Methylcellulose Aqueous Solution) Hydroxypropyl methylcellulose (Metolose 65SH-1500, manufactured by Shin-Etsu Chemical Co., Ltd., weight average molecular weight: 2.2 × 10) was added to ion-exchanged water. ５ A hydroxypropylmethylcellulose aqueous solution (solid concentration: 0.5% by mass) containing hydroxypropylmethylcellulose (a hydroxypropylmethylcellulose copolymer having a degree of substitution (methoxy group): 1.8 and a molar substitution number (hydroxypropoxy group): 0.15) was dissolved therein.

[0196] Preparation Example 3 (Preparation of Aqueous Polyvinyl Alcohol Solution) Acetoacetyl group-modified polyvinyl alcohol (GOSENEX (registered trademark) Z-300, manufactured by Mitsubishi Chemical Corporation) was added to ion-exchanged water so as to give a concentration of 12% by mass, and the mixture was stirred at 95° C. for 1 hour to obtain an aqueous polyvinyl alcohol solution. The aqueous polyvinyl alcohol solution was diluted with ion-exchanged water to a solids concentration of 0.5% by mass.

[0197] Preparation Example 4 (Preparation of Mixed Solution 1) 70 parts by mass of a fine fibrous cellulose dispersion (solid content concentration 0.5% by mass) was mixed with 30 parts by mass of an aqueous hydroxypropyl methylcellulose solution (solid content concentration 0.5% by mass) to obtain mixed solution 1.

[0198] Preparation Example 5 (Preparation of Mixed Liquid 2) 70 parts by mass of a fine fibrous cellulose dispersion (solid content concentration 0.5% by mass) was mixed with 15 parts by mass of a hydroxypropyl methylcellulose aqueous solution (solid content concentration 0.5% by mass) and 15 parts by mass of a polyvinyl alcohol aqueous solution (solid content concentration 0.5% by mass), to obtain mixed liquid 2.

[0199] Preparation Example 6 (Preparation of Mixed Liquid 3) 70 parts by mass of a fine fibrous cellulose dispersion (solid content concentration 0.5% by mass) was mixed with 21 parts by mass of an aqueous hydroxypropyl methylcellulose solution (solid content concentration 0.5% by mass) and 9 parts by mass of an aqueous polyvinyl alcohol solution (solid content concentration 0.5% by mass), to obtain mixed liquid 3.

[0200] Preparation Example 7 (Preparation of Mixed Solution 4) Mixed solution 4 was prepared by mixing 70 parts by mass of a fine fibrous cellulose dispersion (solid content concentration: 0.5% by mass) with 30 parts by mass of an aqueous polyvinyl alcohol solution (solid content concentration: 0.5% by mass).

[0201] Preparation Example 8 (Preparation of Mixed Liquid 5) Mixed liquid 5 was obtained by mixing 50 parts by mass of a fine fibrous cellulose dispersion (solid content concentration: 0.5% by mass) with 50 parts by mass of an aqueous polyvinyl alcohol solution (solid content concentration: 0.5% by mass).

[0202] Preparation Example 9 (Preparation of Mixed Solution 6) 30 parts by mass of a fine fibrous cellulose dispersion (solid content concentration 0.5% by mass) was mixed with 70 parts by mass of an aqueous hydroxypropyl methylcellulose solution (solid content concentration 0.5% by mass), to obtain mixed solution 6.

[0203] Preparation Example 10 (Preparation of Coating Liquid for Adhesive Layer) 8.5 parts by mass of a modified polycarbonate resin (Iupizeta FPC-2136, manufactured by Mitsubishi Gas Chemical Company, Inc.), 60 parts by mass of toluene, and 30 parts by mass of methyl ethyl ketone were mixed. 1.5 parts by mass of an isocyanate compound (Duranate TPA-100, manufactured by Asahi Kasei Chemicals Corporation) as an adhesion aid was added to the resulting mixture and mixed, thereby obtaining a coating liquid for adhesive layer.

[0204] Example 1 [Production of Laminated Sheet] (Production of Fine Fibrous Cellulose-Containing Sheet) Finished basis weight: 50 g / m ２ A damming frame (inner dimensions: 250 mm × 250 mm; a single-layer fine fibrous cellulose-containing sheet was obtained by peeling it from the acrylic plate; fine fiber height: 5 cm) was placed on a commercially available acrylic plate, and mixed solution 1 was spread on the frame. After spreading, the sheet was dried in a dryer at 100°C for 1 hour, and the thickness of the fibrous cellulose-containing sheet was 34 μm.

[0205] (Formation of adhesive layer) The adhesive layer coating liquid was applied to one side of the fine fibrous cellulose-containing sheet (the side that was in contact with the acrylic plate) using a bar coater. The adhesive layer coating liquid was then cured by heating at 100°C for 30 minutes, forming an adhesive layer 1b. The adhesive layer coating liquid was then applied to the other side of the fine fibrous cellulose-containing sheet using a bar coater, and the adhesive layer coating liquid was then cured by heating at 70°C for 30 minutes, forming an adhesive layer 1a, and a laminate sheet was obtained. The thickness of each of the adhesive layers 1a and 1b was 3 μm.

[0206] [Laminate Production] The laminate sheet provided with adhesive layers 1a and 1b was cut with a cutter to produce a laminate sheet measuring 50 mm x 50 mm. Next, one core resin plate cut to dimensions of 100 mm x 100 mm from a commercially available polycarbonate plate with a thickness of 1 mm, and two resin films cut to dimensions of 50 mm x 50 mm from a commercially available polycarbonate film with a thickness of 0.2 mm were prepared and stacked to form a resin film / adhesive layer 1a / fine fibrous cellulose-containing layer / adhesive layer 1b / core resin plate / adhesive layer 1b / fine fibrous cellulose-containing layer / adhesive layer 1a / resin film. At this time, the centers of the resin film and laminate sheet were aligned with the center of the core resin plate. This was sandwiched between 1 mm thick, 200 mm x 200 mm stainless steel plates and inserted into a mini test press (manufactured by Toyo Seiki Seisakusho, Ltd., MP-WCH) set at room temperature. The temperature of the mini test press was raised to 150°C over 3 minutes under a pressure of 1 MPa, and after maintaining this state for 5 minutes, it was cooled to 30°C over 5 minutes. The stainless steel plates used had a release agent (Teflerise, manufactured by Odec Co., Ltd.) applied to the clamping surfaces. A laminate was obtained by the above procedure.

[0207] [Production of hot-bent product] The laminate was placed in a dryer set at 170° C. and left to stand for 5 minutes, and then pressed and fixed against a frame having a predetermined radius of curvature (R=120 mm) at 170° C. The laminate was cooled while still pressed against the frame, and then removed from the frame to obtain a hot-bent product having a curvature.

[0208] <Example 2> In the [Adhesive Layer Formation] of Example 1, a laminate sheet having a fine fibrous cellulose layer provided with adhesive layers 1a and 1b was formed, and then the laminate sheet was placed in a dryer set at 80 ° C. and left to stand for 40 hours, followed by additional heat treatment. Furthermore, in the [Laminate Production] of Example 1, instead of the core resin plate (100 mm × 100 mm × 1 mm), a core resin plate cut to dimensions of 100 mm × 100 mm from a commercially available polycarbonate plate having a thickness of 3 mm was used, and instead of the resin film (50 mm × 50 mm × 0.2 mm), two resin films cut to dimensions of 50 mm × 50 mm from a commercially available polycarbonate film having a thickness of 0.1 mm were used. Except for these, a laminate sheet, a laminate, and a heat-bent product having a curvature were obtained in the same manner as in Example 1.

[0209] <Example 3> A laminated sheet, a laminate, and a heat-bent product having a curvature were obtained in the same manner as in Example 1 (preparation of a fine fibrous cellulose-containing sheet), except that mixed liquid 2 was used instead of mixed liquid 1.

[0210] <Example 4> A laminated sheet, a laminate, and a heat-bent product having a curvature were obtained in the same manner as in Example 1 (preparation of a fine fibrous cellulose-containing sheet), except that mixed liquid 3 was used instead of mixed liquid 1.

[0211] Example 5: Finished basis weight: 35 g / m ２ A damming frame (inner dimensions: 250 mm x 250 mm, height: 5 cm) was placed on a commercially available acrylic plate, and the mixed solution 1 was spread thereon. After spreading, the mixed solution was dried in a dryer at 100°C for 1 hour to form a fine fibrous cellulose-containing layer 1b. The basis weight was 15 g / m ２A damming frame (inner dimensions 250 mm x 250 mm, height 5 cm) was placed on the fine fibrous cellulose-containing layer 1b so that the mixed solution 4 was spread. After spreading, the mixture was dried in a dryer at 100 ° C for 1 hour to form a fine fibrous cellulose-containing layer 1a. The laminated fine fibrous cellulose-containing layers 1a and 1b were peeled from the acrylic plate to obtain a two-layer fine fibrous cellulose-containing sheet. In the [Formation of Adhesive Layer] of Example 1, a two-layer fine fibrous cellulose-containing sheet provided with adhesive layers 1a and 1b was formed, and then this laminated sheet was placed in a dryer set at 80 ° C and left to stand for 40 hours, whereupon additional heat treatment was performed. A laminated sheet, a laminate, and a heat-bent product having a curvature were obtained in the same manner as in Example 1, except that in the [Production of Laminate] of Example 1, a two-layer fine fibrous cellulose-containing sheet that had been additionally heat-treated was used instead of the single-layer fine fibrous cellulose-containing sheet.

[0212] <Example 6> A laminated sheet, a laminate, and a hot-bent product having a curvature were obtained in the same manner as in Example 5, except that the drying conditions for the adhesive layer 1a were changed from "70°C for 30 minutes" to "60°C for 5 minutes."

[0213] <Example 7> A laminated sheet, a laminate, and a hot-bent product having a curvature were obtained in the same manner as in Example 5, except that mixed liquid 5 was used instead of mixed liquid 4 in Example 5 and the laminated sheet was not subjected to additional heat treatment.

[0214] <Example 8> In Example 1 (production of a fine fibrous cellulose-containing sheet), a sheet having a finished basis weight of 50 g / m ２ A laminate sheet, a laminate, and a hot-bent product having a curvature were obtained in the same manner as in Example 1, except that Mixture 6 was used instead of Mixture 1.

[0215] Comparative Example 1 In Example 1 (Formation of Adhesive Layer), the adhesive layer coating liquid was applied only to one side (the side not in contact with the acrylic plate) of the single-layer fine fibrous cellulose-containing sheet, and heated at 90 ° C. for 3.3 minutes and 80 ° C. for 6.6 minutes to harden the adhesive layer coating liquid to form adhesive layer 1b, and adhesive layer 1a was not formed. A laminate sheet was obtained in the same manner as in Example 1. The adhesive layer coating liquid was applied to a resin film, and heated at 70 ° C. for 7.5 minutes to harden the adhesive layer coating liquid to form adhesive layer 1a. A laminate having a layer structure of resin film / adhesive layer 1a / fine fibrous cellulose-containing layer / adhesive layer 1b / core resin plate / adhesive layer 1b / fine fibrous cellulose-containing layer / adhesive layer 1a / resin film was obtained in the same manner as in Example 1 (Production of Laminate). A laminate having a curvature was also obtained in the same manner as in Example 1 (Production of Heat-Bent Products).

[0216] <Comparative Example 2> Finished basis weight 15 g / m ２ A damming frame (inner dimensions: 250 mm x 250 mm, height: 5 cm) was placed on a commercially available acrylic plate, and the mixed solution 4 was spread thereon. After spreading, the mixed solution 4 was dried in a dryer at 100°C for 1 hour to form a fine fibrous cellulose-containing layer 1a. The basis weight was 35 g / m ２ A damming frame (inner dimensions 250 mm × 250 mm, height 5 cm) was placed on the fine fibrous cellulose-containing layer 1a so that the mixed solution 1 was spread. After spreading, the mixture was dried in a dryer at 100 ° C. for 1 hour to form a fine fibrous cellulose-containing layer 1b. A laminate having a layer structure of resin film / adhesive layer 1a / fine fibrous cellulose-containing layer 1a / fine fibrous cellulose-containing layer 1b / adhesive layer 1b / core resin plate / adhesive layer 1b / fine fibrous cellulose-containing layer 1b / fine fibrous cellulose-containing layer 1a / adhesive layer 1a / resin film and a laminate having a curvature were obtained in the same manner as in Comparative Example 1, except that the two-layer fine fibrous cellulose-containing sheet obtained by this procedure was used.

[0217] <Comparative Example 3> In the steps of (preparation of a fine fibrous cellulose-containing sheet) and (formation of an adhesive layer) of Example 1, first, a coating liquid for an adhesive layer was applied to a resin film having a thickness of 0.2 mm using a bar coater. The coating liquid for an adhesive layer was cured by heating at 90°C for 3.3 minutes and at 80°C for 6.6 minutes to form an adhesive layer 1a. A sheet having a finished basis weight of 50 g / m2 was applied to the adhesive layer 1a. ２ The mixed solution 1 was developed so that the resultant mixture was as follows: After development, the mixture was dried in a dryer at 100 ° C for 1 hour to form a single-layer fine fibrous cellulose-containing layer. The adhesive layer coating liquid was applied to the single-layer fine fibrous cellulose-containing layer using a bar coater. This was heated at 70 ° C for 7.5 minutes to harden the adhesive layer coating liquid and form an adhesive layer 1b. Using a core resin plate (100 mm × 100 mm × 1 mm) cut from a commercially available polycarbonate plate, a laminate having a layer structure of resin film / adhesive layer 1a / fine fibrous cellulose-containing sheet / adhesive layer 1b / core resin plate / adhesive layer 1b / fine fibrous cellulose-containing sheet / adhesive layer 1a / resin film was obtained in the same manner as in Example 1 [Production of laminate]. Furthermore, a laminate having a curvature was obtained in the same manner as in Example 1 [Production of heat-bent processed product].

[0218] Comparative Example 4 In Comparative Example 3, "a finished basis weight of 50 g / m ２ The mixed solution 1 was spread on the adhesive layer 1a so that the finished basis weight was 15 g / m. ２ After spreading, the mixture 5 was dried in a dryer at 100°C for 1 hour to form a fine fibrous cellulose-containing layer 1a. ２The mixed solution 1 was developed so that the resultant mixture was 100°C. After development, the mixture was dried in a dryer at 100°C for 1 hour to form a fine fibrous cellulose-containing layer 1b, thereby obtaining a two-layer fine fibrous cellulose-containing layer. The adhesive layer coating liquid was applied onto the two-layer fine fibrous cellulose-containing layer using a bar coater. This was heated at 70°C for 7.5 minutes to harden the adhesive layer coating liquid, thereby forming the adhesive layer 1b. Except for this, in the same manner as in Comparative Example 3, a laminate having a layer structure of resin film / adhesive layer 1a / fine fibrous cellulose-containing layer 1a / fine fibrous cellulose-containing layer 1b / adhesive layer 1b / core resin plate / adhesive layer 1b / fine fibrous cellulose-containing layer 1b / fine fibrous cellulose-containing layer 1a / adhesive layer 1a / resin film and a laminate having a curvature were obtained.

[0219] Comparative Example 5 A laminate and a hot-bent product having a curvature were obtained in the same manner as in Comparative Example 4, except that a resin film having a thickness of 0.3 mm was used instead of the resin film having a thickness of 0.2 mm in Comparative Example 4.

[0220] Comparative Example 6 A polycarbonate plate having a thickness of 1.5 mm alone was subjected to bending under the same conditions as in Example 1 (Production of a hot-bent product) to obtain a polycarbonate plate having a curvature.

[0221] <Comparative Example 7> In the [Production of a laminate sheet] of Example 1, the step of (forming an adhesive layer) was omitted. In the [Production of a laminate], after hot pressing, the resin film, the core resin plate, and the fine fibrous cellulose-containing layer were not bonded, and a laminate could not be obtained. Therefore, the [Production of a hot-bent product] could not be carried out.

[0222] <Measurement and Evaluation> (Thickness of Fine Fibrous Cellulose-Containing Layer) In Examples 1 to 4, 8, and Comparative Example 1, the thickness of the fine fibrous cellulose-containing sheet before the adhesive layer was provided was measured using a stylus thickness gauge (Millitron 1202D, manufactured by Mahl). In Comparative Example 7, the thickness of the fine fibrous cellulose-containing sheet obtained in (Preparation of Fine Fibrous Cellulose-Containing Sheet) was measured. In Examples 5 to 7 and Comparative Example 2, the thickness was measured after forming a two-layer fine fibrous cellulose-containing sheet before providing the adhesive layer. Furthermore, the thickness of each layer was calculated taking into account the ratio of the assumed finished basis weight. In Comparative Example 3, the thickness was measured at the stage when the resin film-adhesive layer 1a-fine fibrous cellulose-containing layer was formed, and the thickness of the fine fibrous cellulose-containing layer was calculated by subtracting the thickness of the resin film and the thickness of the adhesive layer 1a from the measured thickness. In Comparative Examples 4 and 5, thicknesses (1), (2), and (3) were measured at the stage of forming the resin film-adhesive layer 1a, the stage of forming the resin film-adhesive layer 1a-fine fibrous cellulose-containing layer 1a, and the stage of forming the resin film-adhesive layer 1a-fine fibrous cellulose-containing layer 1a-fine fibrous cellulose-containing layer 1b. The thickness of the fine fibrous cellulose-containing layer 1a was calculated by subtracting the thickness of (1) from that of (2). The thickness of the fine fibrous cellulose-containing layer 1b was calculated by subtracting the thickness of (2) from that of (3).

[0223] (Thickness of adhesive layer) In all Examples 1 to 8, the thickness of the adhesive layer 1b was calculated by first subtracting the thickness of the fine fibrous cellulose-containing layer measured by the method described above from the thickness of the laminate sheet provided with the adhesive layer 1b. The thickness of the adhesive layer 1a was calculated by subtracting the sum of the thicknesses of the adhesive layer 1b and the fine fibrous cellulose-containing layer from the thickness of the laminate sheet provided with the adhesive layers 1a and 1b. In Comparative Examples 1 and 2, the thickness of the adhesive layer 1a was calculated by subtracting the thickness of the resin film provided with the adhesive layer 1a. The thickness of the adhesive layer 1b was calculated by subtracting the thickness of the fine fibrous cellulose-containing layer measured by the method described above from the thickness of the laminate sheet. In Comparative Examples 3 to 5, the thicknesses (1), (2), and (3) were measured using a stylus thickness gauge (Millitron 1 202D, manufactured by Mahl) at the stage of forming the resin film-adhesive layer 1a, the stage of forming the resin film-adhesive layer 1a-fine fibrous cellulose-containing layer, and the stage of forming the resin film-adhesive layer 1a-fine fibrous cellulose-containing layer-adhesive layer 1b. The thickness of adhesive layer 1a was calculated by subtracting the thickness of the resin film from (1). The thickness of adhesive layer 1b was calculated by subtracting (2) from (3).

[0224] (Amount of Organic Solvent) In Examples 1 to 8, each test piece was cut to 40 mm x 50 mm from a microfibrous cellulose-containing sheet (laminated sheet) on which adhesive layer 1a and adhesive layer 1b were formed, and then shredded to 10 mm x 50 mm. Each shredded material in Examples 1 to 8 was placed in a 20 mL headspace vial, sealed, and measured by headspace-gas chromatography. The sample was heated at 80°C for 20 minutes using a headspace sampler (Agilent Technologies, Inc., 7697A), and the generated gas was measured using a gas chromatograph (with a flame ionization detector) (Agilent Technologies, Inc., 7890A). The organic solvent detected by this method was quantified, and the amount of organic solvent (actual test value) was calculated. The "amount of organic solvent (converted to per adhesive layer)" in Table 1 was calculated by "[amount of organic solvent (actual test value) x thickness of laminate sheet] / [total thickness of adhesive layers 1a and 1b]". In Comparative Examples 1 and 2, test pieces of 40 mm x 50 mm were cut out from a resin film having an adhesive layer 1a and a fine fibrous cellulose-containing sheet having an adhesive layer 1b, and the test pieces were then shredded to 10 mm x 50 mm. Each of the shredded pieces from Comparative Examples 1 and 2 was placed in a 20 mL headspace vial, and the organic solvent was detected and quantified in the same manner as in Examples 1 to 8, resulting in a value of A. Similarly, a resin film having no adhesive layer was also detected and quantified in the same manner, resulting in a value of A'. The "amount of organic solvent (actual test value)" in Table 1 was calculated by "A - A'". The "amount of organic solvent (converted to per adhesive layer)" in Table 1 was calculated by the formula: "[amount of organic solvent (actual test value) x (total thickness of the fine fibrous cellulose-containing sheet, adhesive layers 1a and 1b)] / [total thickness of the adhesive layers 1a and 1b]". In Comparative Examples 3 to 5, test pieces each measuring 40 mm x 50 mm were cut from a laminate sheet having a structure of resin film - adhesive layer 1a - fine fibrous cellulose-containing layer - adhesive layer 1b, and each test piece was shredded to 10 mm x 50 mm. Each of the shredded pieces in Comparative Examples 3 to 5 was placed in a 20 mL headspace vial, and the organic solvent was detected and quantified in the same manner as in Examples 1 to 8, and the value obtained was designated B. Furthermore, for a resin film not provided with an adhesive layer, the value obtained by detection and quantification in the same manner was designated B'.The "amount of organic solvent (actual test value)" in Table 1 is the value obtained by calculation according to "B - B'". Furthermore, the "amount of organic solvent (converted into per adhesive layer)" in Table 1 was calculated according to "[amount of organic solvent (actual test value) x (total thickness of fine fibrous cellulose-containing sheet and adhesive layers 1a and 1b)] / [total thickness of adhesive layers 1a and 1b]".

[0225] (Transparency of Laminate) The total light transmittance of the laminate was measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K 7361-1:1997. The haze (%) of the laminate before and after heating was evaluated in accordance with JIS K 7136:2000. The haze after heating was the haze of the laminate heated at 170°C for 10 minutes. The difference in haze of the laminate before and after heating was calculated using the following method. Difference in haze (%) of laminate before and after heating = haze (%) of laminate after heating - haze (%) of laminate before heating

[0226] (Yellow Index (YI Value) of Laminate) The yellowness of the laminate was measured in accordance with JIS K 7373:2006 using Colour Cute i (manufactured by Suga Test Instruments Co., Ltd.).

[0227] (Presence or absence of bubbles in hot bent products) The number of bubbles generated in the hot bent products was evaluated according to the following criteria. A is pass. A: The number of bubbles generated in the hot bent product is 0. B: The number of bubbles generated in the hot bent product is 1 or more and 10 or less. C: The number of bubbles generated in the hot bent product is more than 10.

[0228] (Visibility of hot-bent products) The visibility of hot-bent products was evaluated according to the following criteria. A: There is absolutely no distortion in the image seen through the hot-bent product. B: There is almost no distortion in the image seen through the hot-bent product. C: The image seen through the hot-bent product is slightly distorted. D: The image seen through the hot-bent product is distorted. E: The image seen through the hot-bent product is significantly distorted.

[0229] (Rigidity of Hot-Bent Products) The rigidity of the hot-bent products was evaluated according to the following criteria: A: A very large force is required to deform the hot-bent product. B: A large force is required to deform the hot-bent product. C: A small force is required to deform the hot-bent product. D: The hot-bent product is easily deformed.

[0230]

[0231]

[0232] (Table notes) PC: Polycarbonate CNF layer: Layer containing fine fibrous cellulose HPMC: Hydroxypropylmethylcellulose PVA: Polyvinyl alcohol Thickness of adhesive layer 1a: 3 μm Thickness of adhesive layer 1b: 3 μm

[0233] Table 1 shows that the hot-bent laminates containing the laminate sheet of the present invention are less likely to develop bubbles (Examples 1 to 8). In contrast, Table 2 shows that Comparative Examples 1 to 5, which do not satisfy either Condition C or Condition D specified in the present invention, developed bubbles, which resulted in increased haze. Furthermore, the polycarbonate plate had poor rigidity (Comparative Example 6).

Claims

1. A laminated sheet, (i) having an adhesive layer 1a on one side of a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1,000 nm or less, and satisfying at least one of the following conditions A and B; or (ii) having an adhesive layer 1a on one side of a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1,000 nm or less, and an adhesive layer 1b on the other side, and satisfying at least one of the following conditions C and D. Condition A: The total content of organic solvents in the fine fibrous cellulose-containing layer and adhesive layer 1a is 0.1 ppm or more and 40 ppm or less by mass. Condition B: The content of organic solvents in adhesive layer 1a is 0.5 ppm or more and 200 ppm or less by mass. Condition C: The total content of organic solvents in the fine fibrous cellulose-containing layer, adhesive layer 1a and adhesive layer 1b is 0.1 ppm or more and 60 ppm or less by mass. Condition D: The total content of organic solvents in adhesive layer 1a and adhesive layer 1b is 0.5 ppm or more and 300 ppm or less by mass.

2. The laminate sheet according to claim 1, wherein the thickness of each of the adhesive layers 1a and 1b is 1 μm or more and 50 μm or less.

3. A laminated sheet according to claim 1 or 2, wherein (i) has an adhesive layer 1a and a resin film or a protective film in this order on one side of the fine fibrous cellulose-containing layer, and (ii) has an adhesive layer 1a and a resin film or a protective film in this order on one side of the fine fibrous cellulose-containing layer.

4. The laminate sheet according to claim 1 or 2, wherein the fine fibrous cellulose-containing layer contains a hydrophilic polymer.

5. The laminate sheet according to claim 4, wherein the hydrophilic polymer contains a nonionic water-soluble cellulose ether and / or polyvinyl alcohol.

6. A laminate sheet according to claim 5, wherein the fine fibrous cellulose-containing layer is a single layer, the hydrophilic polymer contains a nonionic water-soluble cellulose ether, and the content of the nonionic water-soluble cellulose ether in the hydrophilic polymer is 80% by mass or more.

7. A laminate sheet according to claim 6, wherein the mass ratio of nonionic water-soluble cellulose ether to fine fibrous cellulose (nonionic water-soluble cellulose ether / fine fibrous cellulose) in the fine fibrous cellulose-containing layer is 10 / 90 or more and 90 / 10 or less.

8. The laminate sheet according to claim 5, wherein the fine fibrous cellulose-containing layer is a multi-layered structure including a fine fibrous cellulose-containing layer 1a containing polyvinyl alcohol and a fine fibrous cellulose-containing layer 1b containing a nonionic water-soluble cellulose ether.

9. A laminate sheet as described in claim 8, wherein the mass ratio of polyvinyl alcohol to fine fibrous cellulose (polyvinyl alcohol / fine fibrous cellulose) in the fine fibrous cellulose-containing layer 1a is 25 / 75 or more and 90 / 10 or less.

10. The laminated sheet according to claim 1 or 2, wherein the fine fibrous cellulose has anionic groups.

11. The laminate sheet according to claim 10, wherein the anionic group comprises a phosphorus oxoacid group or a group derived from a phosphorus oxoacid group.

12. A laminate having a laminate sheet (ii) according to claim 1 or 2, which has a resin film, on at least one side of a core resin plate, the core resin plate containing a polycarbonate resin, and the adhesive layer 1b of the laminate sheet in contact with the core resin plate.

13. The laminate of claim 12, having a haze of 5.0% or less.

14. The laminate according to claim 12, wherein the difference in haze before and after heating at 170°C for 10 minutes is 2.0% or less.

15. A method for producing a thermally processed product, comprising the step of thermally processing the laminate according to claim 12.

16. A thermally processed product obtained by thermally processing the laminate according to claim 12.

17. A transparent member comprising the thermally processed product according to claim 16.

18. A method for producing the laminated sheet according to claim 1, comprising the following steps 1 and 2: Step 1: A step of applying and drying a coating liquid for a fine fibrous cellulose-containing layer containing fine fibrous cellulose with a fiber width of 1,000 nm or less to obtain a fine fibrous cellulose-containing layer. Step 2: A step of applying and drying a coating liquid for an adhesive layer on one side of the fine fibrous cellulose-containing layer obtained in Step 1 to form adhesive layer 1a or 1b.

19. A method for producing a laminated sheet as described in claim 18, wherein step 2 is a step of applying a coating liquid for the adhesive layer to one side of the fine fibrous cellulose-containing layer obtained in step 1, and then drying the coating liquid at 80°C or higher for 5 minutes or more to form adhesive layer 1a or 1b.

20. A method for producing a laminated sheet according to claim 18 or 19, further comprising the following step 3 after step 2: Step 3: A step of applying a coating liquid for an adhesive layer to the surface of the fine fibrous cellulose-containing layer opposite to the surface on which the adhesive layer 1a or 1b is formed, and drying the coating liquid to form the adhesive layer 1b or 1a.

21. A method for producing a laminated sheet according to claim 18 or 19, further comprising the following step 4 after step 2: Step 4: A step of attaching a resin film or a protective film onto the adhesive layer 1a or 1b

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