Laminate

Abstract

The purpose of the present invention is to provide a laminate that is less susceptible to adherence thereto by dirt such as dust and that has excellent laser cutter processability.　This laminate comprises: a microfibrous cellulose-containing layer that contains microfibrous cellulose having a fiber width of 1-1,000 nm; and a cationic layer that is on at least one surface of the microfibrous cellulose-containing layer and that contains a cationic compound.

Description

Laminate

[0001] The present invention relates to a laminate.

[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 made from such fine fibrous cellulose, composite sheets containing fine fibrous cellulose and resins, and molded articles 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 significant improvements in tensile strength and other properties. Patent Document 1 discloses a sheet obtained by ultraviolet curing a sheet composition containing an ultraviolet-polymerizable compound and fine fibrous cellulose having a fiber width of 1,000 nm or less, with the aim of providing a sheet having a low coefficient of linear thermal expansion, high transparency with reduced yellowing, and a high tensile modulus, and the sheet has a coefficient of linear thermal expansion of 30 ppm / K or less at 100°C or higher and 150°C or lower, and a yellow index (YI value) of 5 or less.

[0003] Japanese Patent Application Laid-Open No. 2022-104299

[0004] Because microfibrous cellulose-containing sheets have excellent mechanical strength, such as tensile strength, and also have excellent transparency, they can be combined with resin layers and other layers to form laminates, which can be used as components for various products, including precision instruments such as display devices, electronic devices, and home appliances. To be used as a component for such products, the laminates are required to have properties that make them resistant to the adhesion of dust and other debris. Furthermore, to process the laminates with a laser cutter to obtain components of desired shapes, the laminates are required to have excellent laser cutter processability, i.e., properties that prevent whitening and reduced transparency in the processed areas even when processed with a laser cutter. However, Patent Document 1 does not address these properties. The present invention aims to provide a laminate that is resistant to the adhesion of dust and other debris, and has excellent laser cutter processability.

[0005] The present inventors have found that the above-mentioned problems can be solved by a laminate having a combination of a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1 nm to 1,000 nm and a cationic layer containing a cationic compound on at least one surface of the fine fibrous cellulose-containing layer. Specifically, the present invention relates to the following items <1> to <12>. <1> A laminate having a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1 nm to 1,000 nm and a cationic layer containing a cationic compound on at least one surface of the fine fibrous cellulose-containing layer. <2> The laminate according to <1>, in which the fine fibrous cellulose has an anionic group. <3> The laminate according to <2>, in which the anionic group includes at least one selected from the group consisting of a phosphorus oxoacid group, a sulfur oxoacid group, a carboxy group, and a xanthate group. <4> The laminate according to either <2> or <3>, in which the amount of anionic group introduced into the fine fibrous cellulose is less than 0.5 mmol / g. <5> The laminate according to any one of <1> to <4>, wherein the cationic compound has an amino group. <6> The laminate according to any one of <1> to <5>, wherein the content of fine fibrous cellulose in the fine fibrous cellulose-containing layer is 30% by mass or more. <7> The laminate according to any one of <1> to <6>, wherein the fine fibrous cellulose-containing layer contains a hydrophilic polymer, and the content of the hydrophilic polymer per 100 parts by mass of the fine fibrous cellulose is 5 parts by mass or more and 40 parts by mass or less. <8> The laminate according to any one of <1> to <7>, wherein the total light transmittance is 80% or more. <9> The laminate according to any one of <1> to <8>, wherein the linear thermal expansion coefficient in the measurement range of 100°C to 150°C is 70 ppm / K or less. <10> The laminate according to any one of <1> to <9>, wherein the tensile modulus at 23°C is 5.0 GPa or more. <11> The laminate according to any one of <1> to <10>, which has a cationic layer on one side of the fine fibrous cellulose-containing layer and a base film layer on the side opposite to the side having the cationic layer. <12> The laminate according to any one of <1> to <11>, in which the fine fibrous cellulose-containing layer and the cationic layer are in contact with each other.

[0006] According to the present invention, a laminate is provided which is resistant to adhesion of dirt and other contaminants and has excellent processability with a laser cutter.

[0007] Fig. 1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a phosphorus oxo acid group and pH. Fig. 2 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a carboxy group and pH.

[0008] Hereinafter, embodiments of the present invention will be described. In this specification, "X to Y" indicating a numerical range means "X or more and Y or less." In addition, in this specification, the upper and lower limits of a numerical range can be combined in any combination.

[0009] [Laminate] The laminate of this embodiment has a fine fibrous cellulose-containing layer containing fine fibrous cellulose having a fiber width of 1 nm or more and 1,000 nm or less, and a cationic layer containing a cationic compound on at least one surface of the fine fibrous cellulose-containing layer. The laminate of this embodiment may have a cationic layer on a part of the surface of the fine fibrous cellulose-containing layer, or may have a cationic layer on the entire surface of the fine fibrous cellulose-containing layer. In addition, in the laminate of this embodiment, it is preferable that the fine fibrous cellulose-containing layer and the cationic layer are in contact with each other, that is, there is no other layer between the fine fibrous cellulose-containing layer and the cationic layer. It is preferable that the laminate of this embodiment does not have a layer on the cationic layer.

[0010] The laminate of this embodiment is resistant to adhesion of dust and other debris and has excellent laser cutter processability. The reason why the laminate of this embodiment exhibits the above-mentioned effects is unclear, but is thought to be as follows. The laminate of this embodiment has a cationic layer, which can impart antistatic properties to at least one surface of the fine fibrous cellulose-containing layer. Although the detailed mechanism is unclear, it is believed that the presence of a cationic layer prevents particles generated during laser cutting from adhering to the processed area, thereby resulting in excellent laser cutter processability. Furthermore, it has been found that the sheet of this embodiment also has an additional effect of being excellent in at least one of total light transmittance, haze, tensile strength, tensile modulus, linear thermal expansion coefficient, and water resistance. This embodiment will be described in more detail below. The components contained or potentially contained in each layer of the laminate of the present embodiment may be used alone or in combination of two or more. Each layer of the laminate of this embodiment may be a single layer or a multilayer. In the case of a multi-layer structure, the components contained or the components that can be contained in each of the layers constituting the multi-layer structure may be the same as or different from each other.

[0011] [Fine Fibrous Cellulose-Containing Layer] The fine fibrous cellulose-containing layer of the present embodiment contains fine fibrous cellulose having a fiber width of 1 nm or more and 1,000 nm or less.

[0012] <Fine fibrous cellulose> Fine fibrous cellulose is fibrous cellulose having a fiber width of 1 nm or more and 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 nm or more and 1,000 nm or less. The fiber width of fine fibrous cellulose is, for example, 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 still 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, rigidity, and dimensional stability, can be more easily achieved.

[0013] The number-average fiber width of the fine fibrous cellulose is, for example, 1 nm or more and 1,000 nm or less. The number-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 number-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 improved strength, rigidity, and dimensional stability. The fine fibrous cellulose is, for example, monofilamentous cellulose.

[0014] The number-average fiber width of fine fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fibrous cellulose with a concentration of 0.01% by mass to 0.1% by mass is prepared, and this suspension is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for transmission electron microscope (TEM) observation. When wide fibers are included, an SEM image of the surface cast onto glass may be observed. Next, electron microscope images are observed at magnifications of 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 this line X. (2) A line Y is drawn within the same image, perpendicular to the line X, and 20 or more fibers intersect with this line Y.

[0015] 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.

[0016] 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, a TEM, a scanning electron microscope (SEM), or an atomic force microscope (AFM).

[0017] 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: 2θ=14° to 17° and 2θ=22° to 23°. The proportion of type I crystal structure in the fine fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. This can be expected to provide even better performance in terms of heat resistance and low linear thermal expansion coefficient. The degree of crystallinity can be determined by measuring the X-ray diffraction profile and using the pattern in a conventional manner (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0018] The axial ratio (fiber length / fiber width) of the fine fibrous cellulose is not particularly limited, but is, for example, preferably 20 to 10,000, 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.

[0019] 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, from the viewpoint of total light transmittance and haze, 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 of 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.

[0020] 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 these, 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. It is more preferably 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. It is more preferably 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. It is particularly preferably a phosphorus oxoacid group. By introducing a phosphorus oxoacid group as an anionic group, 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.

[0021] 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.

[0022]

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028]

[0029] 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.

[0030] The amount of ionic substituent introduced into the fine fibrous cellulose is, for example, preferably 0.05 mmol / g or more and 5.20 mmol / g or less, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, still more preferably 0.50 mmol / g or more, even more preferably 1.00 mmol / g or more, and more preferably 3.65 mmol / g or less, even more preferably 3.50 mmol / g or less, still more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, and even more preferably 2.00 mmol / g or less, per 1 g (mass) of fine fibrous cellulose. By keeping 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 the ratio of the counter ion of the ionic substituent to the hydrogen ion (H ＋) indicates the mass of the fine fibrous cellulose when

[0031] The amount of ionic substituents (preferably anionic groups) introduced into the fine fibrous cellulose is preferably 0.01 mmol / g or more but less than 0.50 mmol / g, more preferably 0.40 mmol / g or less, even more preferably 0.30 mmol / g or less, still more preferably 0.25 mmol / g or less, even more preferably 0.15 mmol / g or less, and more preferably 0.02 mmol / g or more, even more preferably 0.03 mmol / g or more, per 1 g (mass) of fine fibrous cellulose. From the viewpoint of the water resistance of the laminate, the amount of ionic substituents (preferably anionic groups) introduced into the fine fibrous cellulose is preferably equal to or greater than the above-mentioned lower limit, and from the viewpoint of the total light transmittance and haze of the laminate, it is preferably equal to or less than the above-mentioned upper limit. Such low-substituent-content fine fibrous cellulose may be obtained, for example, by subjecting the ionic substituent introduction step, followed by a defibration treatment step and a substituent removal treatment step, as described below.

[0032] 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.

[0033] 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).

[0034] 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.

[0035] 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)

[0036] 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.

[0037] 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.

[0038] <<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.

[0039] 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.

[0040] (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 obtained by heating 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 for 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.

[0041] 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.

[0042] 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 of the fiber raw material (bone dry mass) 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] The amount of phosphorus oxoacid groups introduced into the fiber raw material is, for example, preferably 0.05 mmol / g or more and 5.20 mmol / g or less, more preferably 0.10 mmol / g or more, 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, still more preferably 1.00 mmol / g or more, and more preferably 3.65 mmol / g or less, even more preferably 3.00 mmol / g or less, per 1 g (mass) of fine fibrous cellulose. By keeping the amount of phosphorus oxoacid groups introduced within the above ranges, it is possible to facilitate the micronization of the fiber raw material and increase the stability of the fine fibrous cellulose.

[0047] The amount of phosphorus oxoacid groups introduced into the fine fibrous cellulose is preferably 0.01 mmol / g or more but less than 0.50 mmol / g, more preferably 0.40 mmol / g or less, even more preferably 0.30 mmol / g or less, still more preferably 0.25 mmol / g or less, even more preferably 0.15 mmol / g or less, and more preferably 0.02 mmol / g or more, even more preferably 0.03 mmol / g or more, per 1 g (mass) of fine fibrous cellulose. From the viewpoint of the water resistance of the laminate, the amount of phosphorus oxoacid groups introduced into the fine fibrous cellulose is preferably equal to or greater than the above-mentioned lower limit, and from the viewpoint of the total light transmittance and haze of the laminate, it is preferably equal to or less than the above-mentioned upper limit. Such low-substituent-content fine fibrous cellulose may be obtained, for example, by subjecting the ionic substituent introduction step, followed by a defibration treatment step and a substituent removal treatment step, as described below.

[0048] -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.

[0049] 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.

[0050] 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 per 1 g (mass) of fine fibrous cellulose is preferably 0.05 mmol / g or more and 3.65 mmol / g or less, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, still more preferably 0.50 mmol / g or more, even more preferably 0.90 mmol / g or more, and more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, still more preferably 2.20 mmol / g or less, and even more preferably 2.00 mmol / g or less. Alternatively, 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 micronization of cellulose fibers in the micronization treatment step and improve the stability of the fine fibrous cellulose.

[0051] -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).

[0052] 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.

[0053] In the sulfur oxoacid group introduction step, a cellulose raw material is preferably mixed with an aqueous solution containing a sulfur oxoacid and urea and / or a urea derivative, and then the cellulose raw material is subjected to a heat treatment. The heat treatment temperature is preferably selected so that the sulfur oxoacid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably 100°C or higher and 300°C or lower, more preferably 120°C or higher, even more preferably 150°C or higher, and more preferably 250°C or lower, even more preferably 200°C or lower.

[0054] In the heat treatment step, heating is preferably performed until substantially no moisture is present. 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.

[0055] The amount of sulfur oxoacid groups introduced into the fiber raw material is preferably 0.05 mmol / g or more and 5.00 mmol / g or less, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, still more preferably 0.50 mmol / g or more, even more preferably 0.90 mmol / g or more, and 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 to improve the stability of fibrous cellulose.

[0056] The amount of sulfur oxoacid groups introduced into the fine fibrous cellulose is preferably 0.01 mmol / g or more but less than 0.50 mmol / g, more preferably 0.40 mmol / g or less, even more preferably 0.30 mmol / g or less, still more preferably 0.25 mmol / g or less, even more preferably 0.15 mmol / g or less, and more preferably 0.02 mmol / g or more, even more preferably 0.03 mmol / g or more, per 1 g (mass) of fine fibrous cellulose. From the viewpoint of the water resistance of the laminate, the amount of sulfur oxoacid groups introduced into the fine fibrous cellulose is preferably equal to or greater than the lower limit mentioned above, and from the viewpoint of the total light transmittance and haze of the laminate, it is preferably equal to or less than the upper limit mentioned above. Such low-substituent amount fine fibrous cellulose may be obtained, for example, by subjecting the fine fibrous cellulose to a treatment for removing substituents, as described below.

[0057] - 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.

[0058] 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.

[0059] The concentration of the chlorine-based oxidizing agent in the solution in the oxidation step using the chlorine-based oxidizing agent is, for example, converted into an effective chlorine concentration, preferably from 1 to 1,000% by mass, more preferably from 5 to 500% by mass, and even more preferably from 10 to 100% by mass. The amount of the chlorine-based oxidizing agent added per 100 parts by mass of the fiber raw material is preferably from 1 to 100,000 parts by mass, more preferably from 10 to 10,000 parts by mass, and even more preferably from 100 to 5,000 parts by mass.

[0060] 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, for example, preferably 1 minute to 1,000 minutes, more preferably 10 minutes to 500 minutes, and even more preferably 20 minutes to 400 minutes. The pH during the reaction is preferably 5 to 15, more preferably 7 to 14, and even more preferably 9 to 13. At the start of the reaction, the pH is preferably maintained constant (for example, pH 11) during the reaction by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0061] -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.

[0062] ((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.

[0063] 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.

[0064] 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.

[0065] The treatment time for alkali cellulose formation is preferably 1 minute or more and 6 hours or less, more preferably 10 minutes or more, even more preferably 30 minutes or more, and more preferably 5 hours or less, even more preferably 4 hours or less.

[0066] 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.

[0067] When the introduction of ionic substituents and the conversion to alkali cellulose are not carried out simultaneously, the conversion to alkali cellulose is preferably carried out before the introduction of ionic substituents. In this case, the alkali cellulose obtained by the conversion to alkali cellulose treatment is preferably subjected to solid-liquid separation by a common deliquoring method such as centrifugation or filtration to remove water. This improves the reaction efficiency in the subsequent ionic substituent introduction step. The cellulose fiber concentration after solid-liquid separation is preferably 5% or more and 50% or less, more preferably 10% or more and 40% or less, and even more preferably 15% or more and 35% or less.

[0068] - 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.

[0069] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Ａ Examples 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 EＡ 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.

[0070] Compound E Ａ When adding, the reagent (solid or liquid) may be added directly to the fiber raw material, 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.

[0071] The reaction 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.

[0072] Compound E Ａ The amount of the additive 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.

[0073] The reaction time may vary depending on the reaction temperature, but is, for example, 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.

[0074] - 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.

[0075] 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.

[0076] Compound E Ｂ When adding, the reagent (solid or liquid) may be added directly to the fiber raw material, 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.

[0077] The reaction 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.

[0078] Compound E Ｂ The amount of the additive 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.

[0079] The reaction time may vary depending on the reaction temperature, but is, for example, preferably 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.

[0080] -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.

[0081] 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.

[0082] Compound E Ｃ When adding, the reagent (solid or liquid) may be added directly to the fiber raw material, 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.

[0083] The reaction 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.

[0084] Compound E Ｃ The amount of the additive 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.

[0085] The reaction time may vary depending on the reaction temperature, but is, for example, preferably from 1 minute to 1,000 minutes, more preferably from 3 minutes to 500 minutes, and even more preferably from 5 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0086] -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.

[0087] 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.

[0088] Compound E Ｄ When adding, the reagent (solid or liquid) may be added directly to the fiber raw material, 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.

[0089] The reaction 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.

[0090] Compound E ＤThe amount of the additive 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.

[0091] The reaction time may vary depending on the reaction temperature, but is, for example, 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.

[0092] (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.

[0093] (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 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 may be used. The alkaline compound contained in the alkaline solution is not particularly limited, and may be an inorganic alkaline compound or an organic alkaline compound. In this embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of 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 water or a polar solvent including 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, for example, preferably 5°C or higher and 80°C or lower, more preferably 10°C or higher and 60°C or lower. The immersion time of the ionic substituent-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is, for example, preferably 5 to 30 minutes, more preferably 10 to 20 minutes. The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but is, for example, preferably 100 to 100,000 parts by mass, more preferably 1,000 to 10,000 parts by mass, per 100 parts by mass of the bone dry mass of the ionic substituent-introduced fiber.

[0094] 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.

[0095] (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 thereof 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, more preferably 5% by mass or less. The pH of the acidic solution used is not particularly limited, but is preferably 0 to 4, 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 parts by mass to 100,000 parts by mass, and more preferably from 1,000 parts by mass to 10,000 parts by mass, per 100 parts by mass of the bone dry mass of the fiber raw material.

[0096] (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.

[0097] 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).

[0098] 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.

[0099] (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.

[0100] In the nitrogen removal treatment step, it is preferable to adjust the pH of the slurry containing the substituted fiber to 10 or more and then perform a heat treatment. In the heat treatment, the liquid temperature of the slurry is preferably 50°C or more and 100°C or less, and the heating time is preferably 15 minutes or more and 180 minutes or less. When adjusting the pH of the slurry containing the substituted fiber, it is preferable to add an alkali compound that can be used in the above-mentioned alkali treatment step to the slurry.

[0101] After the nitrogen removal treatment step, the substituted fiber may be subjected to a washing step as needed. 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.

[0102] (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 nm to 1,000 nm. 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.

[0103] 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 nm to 1,000 nm, a step of enzymatic treatment, an acid treatment, an alkali treatment, etc. These may be performed alone or in combination. Among these, the substituent removal treatment step is preferably a step of heat treating or an 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 nm to 1,000 nm, and fine fibrous cellulose having an introduction amount 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.

[0104] 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 nm to 1,000 nm 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, and 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.

[0105] When a substituent removal treatment is performed on a slurry containing fine fibrous cellulose having a substituent and a fiber width of 1 nm to 1,000 nm, the concentration of the fine fibrous cellulose in the slurry is preferably 0.05% by mass to 20% by mass, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and 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, and 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.

[0106] When the substituent removal treatment step is a step of heat-treating fine fibrous cellulose having a substituent and a fiber width of 1 nm to 1,000 nm, the heating temperature in the heat treatment step is preferably 40° C. or higher and 250° C. or lower, more preferably 50° C. or higher, even more preferably 60° C. or higher, more preferably 230° C. or lower, and even more preferably 200° C. or lower. In particular, when the substituent on the fine fibrous cellulose to be 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.

[0107] 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.

[0108] When the substituent removal treatment step is a step of enzymatically treating fine fibrous cellulose having substituents and having a fiber width of 1 nm or more and 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.

[0109] In the enzyme treatment step, the enzyme is added so that the enzyme activity per 1 g of fine fibrous cellulose is preferably 0.1 nkat or more and 100,000 nkat or less, more preferably 1.0 nkat or more, even more preferably 10 nkat or more, 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 under conditions of 0°C or more and less than 50°C for 1 minute to 100 hours.

[0110] 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.

[0111] When the substituent removal treatment step is a step of acid-treating fine fibrous cellulose having a substituent and having a fiber width of 1 nm or more and 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.

[0112] When the substituent removal treatment step is a step of alkali treating fine fibrous cellulose having a substituent and having a fiber width of 1 nm or more and 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] (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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] (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.

[0122] (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.

[0123] 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.

[0124] 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 the case of a high-speed defibrator, the peripheral speed is preferably 20 m / sec or more, more preferably 25 m / sec or more, and even more preferably 30 m / sec or more. A high-pressure homogenizer is more preferably used because it has a higher maximum movement speed of the fine fibrous cellulose during treatment and a higher pressure during treatment than a high-speed defibrator. In high-pressure homogenizer treatment, the pressure during treatment is preferably 1 MPa or more 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.

[0125] 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.

[0126] 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 preferably 30% by mass or more and 99% by mass or less, more preferably 45% by mass or more, even more preferably 60% by mass or more, even more preferably 75% by mass or more, and more preferably 96% by mass or less, even more preferably 93% by mass or less, and even more preferably 90% by mass or less, from the viewpoint of increasing the tensile modulus of elasticity, reducing the linear thermal expansion coefficient, and obtaining a laminate that is resistant to dust adhesion and has excellent laser cutter processability. As the fine fibrous cellulose, fine fibrous cellulose containing ionic groups and unmodified fine fibrous cellulose may be used in combination. When used in combination, the content of the fine fibrous cellulose containing ionic groups in the fine fibrous cellulose is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, and 99% by mass or less.

[0127] <Hydrophilic Polymer> In view of ease of production of the fine fibrous cellulose-containing layer in the present embodiment, the fine fibrous cellulose-containing layer preferably contains a hydrophilic polymer. Examples of the hydrophilic polymer include polyethylene glycol, polyethylene oxide, casein, dextrin, starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol (e.g., acetoacetylated polyvinyl alcohol), polyvinyl butyral, polyvinyl pyrrolidone, polyvinyl methyl ether, polyacrylates, polyacrylamide, acrylic acid alkyl ester copolymers, urethane copolymers, and cellulose derivatives (e.g., hydroxyethyl cellulose, carboxyethyl cellulose, carboxymethyl cellulose), etc., among which polyethylene oxide, polyvinyl alcohol, modified polyvinyl alcohol, and cellulose derivatives are preferred, and polyethylene oxide is more preferred.

[0128] The viscosity average molecular weight of the polyethylene oxide is, for example, 2,000,000 or more and 7,500,000 or less, preferably 3,000,000 or more, more preferably 4,000,000 or more, and preferably 6,500,000 or less, more preferably 5,500,000 or less. When a commercially available product is used as the hydrophilic compound, the viscosity average molecular weight can be the value published by the manufacturer.

[0129] In the fine fibrous cellulose-containing layer in this embodiment, the content of the hydrophilic polymer is, from the viewpoint of resistance to adhesion of dust and other debris and laser cutter processability, preferably 5 parts by mass or more and 40 parts by mass or less, more preferably 35 parts by mass or less, even more preferably 30 parts by mass or less, still more preferably 25 parts by mass or less, and more preferably 8 parts by mass or more, even more preferably 12 parts by mass or more, and still more preferably 15 parts by mass or more, relative to 100 parts by mass of the fine fibrous cellulose.

[0130] In the fine fibrous cellulose-containing layer of this embodiment, the sum of the content of fine fibrous cellulose and the content of hydrophilic polymer in the solid content of the fine fibrous cellulose-containing layer 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 more, and 100% by mass or less, from the viewpoint of obtaining a laminate that is resistant to dust adhesion and has excellent laser cutter processability.

[0131] <Other Components> The fine fibrous cellulose-containing layer of this embodiment may contain components (other components) other than fine fibrous cellulose and hydrophilic polymers. Examples of other components include 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, stabilizers, magnetic powders, alignment promoters, plasticizers, dispersants, color inhibitors, polymerization inhibitors, pH adjusters, and crosslinking agents. In the fine fibrous cellulose-containing layer of this embodiment, the 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.

[0132] <Thickness> The thickness of the fine fibrous cellulose-containing layer in this embodiment is preferably 5 μm or more and 1,000 μm or less, more preferably 10 μm or more, even more preferably 15 μm or more, and even more preferably 20 μm or more, and more preferably 800 μm or less, even more preferably 600 μm or less, even more preferably 400 μm or less, even more preferably 200 μm or less, even more preferably 100 μm or less, and even more preferably 50 μm or less. The thickness of the fine fibrous cellulose-containing layer is preferably adjusted appropriately depending on the application of the laminate. When the fine fibrous cellulose-containing layer is a multilayer structure, it is preferable that the total thickness of each layer be within the above range.

[0133] <Basis Weight> The basis weight of the fine fibrous cellulose-containing layer in this embodiment is preferably 5 g / m ２1,000g / m or more ２ More preferably, it is 10 g / m or less. ２ More preferably, 15 g / m ２ More preferably, 20 g / m ２ More preferably, it is 500 g / m or more. ２ More preferably, 100 g / m or less ２ More preferably, 50 g / m or less ２ When the fine fibrous cellulose-containing layer is a multi-layered structure, it is preferable that the total basis weight of the layers is within the above range.

[0134] <Density> The density of the fine fibrous cellulose-containing layer in this embodiment is preferably 1.00 g / cm ３ 3.00g / cm or more ３ or less, more preferably 1.10 g / cm ３ More preferably, 1.20 g / cm ３ More preferably, it is 1.70 g / cm or more. ３ More preferably, 1.60 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 the thickness.

[0135] [Cationic Layer] The cationic layer in this embodiment contains a cationic compound.

[0136] <Cationic Compound> The "cationic compound" contained in the cationic layer in this embodiment is a compound that has a cationic group and exhibits cationic properties as a whole. The "cationic compound" does not include the above-mentioned fine fibrous cellulose (having a cationic group). The "cationic group" contained in the cationic compound refers to a cationic group or a group that can be ionized to become a cationic group. Examples of the cationic group include an amino group and a phosphonium group, with an amino group being preferred. Examples of the amino group include a primary amino group, a secondary amino group, a tertiary amino group, and a quaternary ammonium group. The cationic compound may be a low molecular weight compound (cationic low molecular weight compound) or a polymer (cationic polymer), with a cationic polymer being preferred. The cationic polymer may be a chain polymerization polymer or a step-growth polymerization polymer. The chain polymerization polymer may be a homopolymer or a copolymer. The copolymer may be polymerized in a random, block, or graft configuration.

[0137] Specific examples of cationic low molecular weight compounds include amine compounds and cationic surfactants, such as those described in JP-A-2023-87001, JP-A-2023-64090, and JP-A-2023-84122. Specific examples of amine compounds include bis-hydroxyethyl laurylamine, dimethylethanolamine, diethylethanolamine, diethanolamine, methyldiethanolamine, N,N-dimethylaminohexanol, N,N-dimethylaminoethoxyethanol, N,N-dimethylaminoethoxyethoxyethanol, N,N,N'-trimethylaminoethylethanolamine, N-methyl-N-(dimethylaminopropyl)aminoethanol, and other hydroxyl group-containing amine compounds, lauryldimethylamine, lauryldimethylamine, lauryldimethylamidopropylamine, cocoylamidopropylamine, alkyldimethylamine, alkoxyalkyldimethylamine, and alkylamidoalkyldimethylamine. Specific examples of cationic surfactants include quaternary ammonium salts having an aliphatic chain, such as lauryltrimethylammonium chloride and laurylamidopropyltrimethylammonium chloride, and cationic surfactants obtained by ionizing the above-mentioned amine compounds. The molecular weight of the cationic low-molecular-weight compound is, for example, 30 to 1,000, preferably 50 or more, more preferably 100 or more, and preferably 800 or less, more preferably 600 or less.

[0138] Specific examples of cationic polymers include the following polymers, including the cationic resins described in JP-A-2010-253824: polyethyleneimine polyallylamine α-polylysine, ε-polylysine dimethyldiallylammonium chloride-acrylamide copolymer cationic cellulose derivatives (such as a salt of hydroxyethyl cellulose that reacts with trimethylammonium-substituted epoxide) polysaccharide polymers (such as cationic starch derivatives) polyalkylene polyamines such as polyethylene polyamine and polypropylene polyamine, or derivatives thereof acrylic polymers having secondary or tertiary amino groups or quaternary ammonium groups, or copolymers of acrylamide having secondary or tertiary amino groups or quaternary ammonium groups polyvinylamine and polyvinylamidines dicyandiamide-based cationic compounds typified by dicyandiamide-formalin copolymer polyamine-based cationic compounds typified by dicyandiamide-polyethyleneamine copolymer epichlorohydrin-dimethylamine copolymer diallyldimethylammonium-SO ２ Polycondensation product - Diallylamine salt -SO ２ Polycondensation polymers, diallyldimethylammonium chloride polymers, allylamine salt copolymers, dialkylaminoethyl (meth)acrylate quaternary salt copolymers, acrylamide-diallylamine copolymers, cationic resins having a five-membered ring amidine structure, etc. Note that cationic cellulose derivatives are not included in the polysaccharide polymers.

[0139] The weight-average molecular weight of the cationic polymer is, for example, more than 1,000 and not more than 2,000,000, preferably not less than 1,500, more preferably not less than 2,000, and is preferably not more than 1,000,000, more preferably not more than 500,000. The weight-average molecular weight can be measured by gel permeation chromatography (GPC). When a commercially available product is used as the cationic compound, the weight-average molecular weight can be determined by the published value of the manufacturer.

[0140] When a cationic low-molecular-weight compound is used in the cationic layer of the present embodiment, the content of the cationic low-molecular-weight compound in the solid content of the cationic layer is preferably 30% by mass or more and 100% by mass or less, more preferably 40% by mass or more, even more preferably 50% by mass or more, still more preferably 60% by mass or more, and more preferably 95% by mass or less, even more preferably 90% by mass or less, and still more preferably 85% by mass or less, from the viewpoint of obtaining a laminate that is resistant to dust adhesion and has excellent laser cutter processability.

[0141] In the cationic layer of this embodiment, when a cationic polymer is used, the content of the cationic polymer in the solid content of the cationic layer is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and still more preferably 95% by mass or more, and 100% by mass or less, from the viewpoint of obtaining a laminate that is resistant to dust adhesion and has excellent laser cutter processability. In addition, in the cationic layer of this embodiment, when a cationic low molecular weight compound and a cationic polymer are used in combination, the preferred range of the total content of the cationic low molecular weight compound and the cationic polymer in the solid content of the cationic layer is the same as the preferred range of the content of the cationic polymer.

[0142] In the cationic layer of this embodiment, when a cationic low molecular weight compound is used, it is preferable to use it in combination with a resin component such as polyethylene glycol, polyethylene oxide, casein, dextrin, starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol (such as acetoacetylated polyvinyl alcohol), polyvinyl butyral, polyvinyl pyrrolidone, polyvinyl methyl ether, polyacrylates, polyacrylamide, acrylic acid alkyl ester copolymers, urethane copolymers, cellulose derivatives (such as hydroxyethyl cellulose, carboxyethyl cellulose, carboxymethyl cellulose), etc. In the cationic layer of this embodiment, when a cationic low molecular weight compound is used as the cationic compound, the content of the resin component in the solid content of the cationic layer is preferably 0% by mass or more and 70% by mass or less, more preferably 5% by mass or more, even more preferably 10% by mass or more, still more preferably 15% by mass or more, and more preferably 60% by mass or less, even more preferably 50% by mass or less, and still more preferably 40% by mass or less.

[0143] <Other Components> The cationic layer of this embodiment may contain components (other components) other than the cationic compound and the resin component. Examples of other components include rheology modifiers, fillers, UV absorbers, light stabilizers, heat stabilizers, antioxidants, antistatic agents, lubricants, flame retardants, antibacterial agents, antifungal agents, antifriction agents, light scattering agents, and gloss adjusters. In the cationic layer of this embodiment, the content of the "other components" in the solid content of the cationic layer may 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> From the viewpoint of obtaining a laminate that is resistant to dust adhesion and has excellent laser cutter processability, the thickness of the cationic layer in this embodiment is preferably 0.1 nm or more and 5 μm or less, more preferably 5 nm or more, even more preferably 10 nm or more, still more preferably 30 nm or more, even more preferably 50 nm or more, and more preferably 2.5 μm or less, even more preferably 1 μm or less, still more preferably 500 nm or less, even more preferably 100 nm or less. The thickness of the cationic layer is preferably adjusted appropriately depending on the application of the laminate. When the cationic layer is a multilayered layer, it is preferable that the total thickness of each layer be within the above range.

[0145] <Basis Weight> The basis weight of the cationic layer in this embodiment is preferably 0.1 mg / m from the viewpoint of obtaining a laminate that is resistant to dust adhesion and has excellent laser cutter processability. ２ 200mg / m or more ２ or less, more preferably 0.5 mg / m ２ or more, more preferably 3.0 mg / m ２ More preferably, 5.0 mg / m ２ or more, and more preferably 150 mg / m ２ More preferably, 100 mg / m ２ More preferably, 80 mg / m ２ When the cationic layer is a multi-layered layer, it is preferable that the total basis weight of the layers is within the above range.

[0146] <Density> The density of the cationic layer in this embodiment is preferably 0.1 g / cm ３ 3.0g / cm or more ３ More preferably, it is 0.3 g / cm or less. ３ More preferably, 0.5 g / cm ３ More preferably, it is 2.5 g / cm or more. ３ More preferably 2.0 g / cm or less ３ The density of the cationic layer is calculated by dividing the basis weight of the cationic layer by the thickness.

[0147] [Base Film Layer] When the laminate of this embodiment has a cationic layer on one side of the fine fibrous cellulose-containing layer, the side opposite the side having the cationic layer of the fine fibrous cellulose-containing layer may have no layer, or may have a base film layer. Examples of polymers constituting the base film layer include synthetic resins such as polyethylene terephthalate, polycarbonate, polyethylene naphthalate, polyethylene, polypropylene, polyimide, polystyrene, and acrylic, as well as natural resins such as rosin, rosin ester, and hydrogenated rosin ester. The thickness of the base film layer in this embodiment is preferably 50 μm or more and 500 μm or less, more preferably 100 μm or more, even more preferably 150 μm or more, and more preferably 400 μm or less, and even more preferably 300 μm or less. It is preferable to adjust the thickness of the base film layer appropriately depending on the application of the laminate.

[0148] [Other Layers] When the laminate of this embodiment has the above-mentioned base film layer, it may have, for example, an adhesive layer and / or a primer layer between the base film layer and the fine fibrous cellulose-containing layer. Furthermore, it may have an adhesive layer and / or a primer layer on the side of the base film layer opposite to the side having the fine fibrous cellulose-containing layer. Furthermore, the base film layer may be subjected to a surface treatment such as a corona treatment or a plasma treatment.

[0149] [Laminate Properties] [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 is 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 cationic compound, the presence or absence of a base film layer, the type of base film layer, and the content of the fine fibrous cellulose and hydrophilic polymer in the fine fibrous cellulose-containing layer. The total light transmittance of the laminate is a value measured by the method described in the examples.

[0150] [Haze] The haze of the laminate of this embodiment is preferably 4.5% or less, more preferably 3.5% or less, even more preferably 3.0% or less, and even more preferably 2.5% or less. On the other hand, the lower limit of the haze of the laminate may be, for example, 0%. The haze of the laminate is 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 cationic compound, the presence or absence of a base film layer, the type of base film layer, the content of the fine fibrous cellulose and hydrophilic polymer in the fine fibrous cellulose-containing layer, the unevenness of the surface of the fine fibrous cellulose-containing layer, etc. The haze of the laminate is a value measured by the method described in the examples.

[0151] [Tensile Strength] The tensile strength of the laminate of this embodiment at 23°C and 50% relative humidity is preferably 105 MPa or more and 185 MPa or less, more preferably 110 MPa or more, even more preferably 115 MPa or more, and more preferably 180 MPa or less, even more preferably 175 MPa or less. The tensile strength of the laminate is controlled by the fiber width of the fine fibrous cellulose, the type of hydrophilic polymer, the type of cationic compound, the presence or absence of a base film layer, the type of base film layer, the content of the fine fibrous cellulose and hydrophilic polymer in the fine fibrous cellulose-containing layer, etc. The tensile strength of the laminate is a value measured by the method described in the examples.

[0152] [Tensile Modulus] The tensile modulus of the laminate of this embodiment at 23°C is preferably 4.0 GPa or more and 16.0 GPa or less, more preferably 4.5 GPa or more, even more preferably 5.0 GPa or more, and more preferably 15.5 GPa or less, even more preferably 15.0 GPa or less. The tensile modulus of the laminate is controlled by the fiber width of the fine fibrous cellulose, the type of hydrophilic polymer, the type of cationic compound, the presence or absence of a base film layer, the type of base film layer, the contents of the fine fibrous cellulose and hydrophilic polymer in the fine fibrous cellulose-containing layer, etc. The tensile modulus of the laminate is a value measured at a relative humidity of 50%, and specifically, is measured by the method described in the examples.

[0153] [Linear Thermal Expansion Coefficient] The laminate of this embodiment preferably has a linear thermal expansion coefficient of 70 ppm / K or less in the measurement range of 100°C or more and 150°C or less. While a low linear thermal expansion coefficient is preferable, from the viewpoint of manufacturing, it is more preferably 55 ppm / K or less, even more preferably 45 ppm / K or less, even more preferably 35 ppm / K or less, even more preferably 25 ppm / K or less, and even more preferably 15 ppm / K or less. The lower limit of the linear thermal expansion coefficient is not particularly limited, and may be, for example, 0 ppm / K or less. The linear thermal expansion coefficient of the laminate at 100 to 150°C is 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 cationic compound, the presence or absence of a base film layer, the type of base film layer, the contents of the fine fibrous cellulose and the hydrophilic polymer in the fine fibrous cellulose-containing layer, and the like. The linear thermal expansion coefficient of the laminate in the measurement range of 100° C. or more and 150° C. or less is measured by the method described in the examples.

[0154] [Water Absorption] From the viewpoint of maintaining the shape, the laminate of this embodiment has a water absorption represented by the following formula (1), which is, for example, less than 2,000%, preferably 1,500% or less, more preferably 1,000% or less, and for example, 100% or more: Water Absorption=(W−Wd) / Wd×100 (1) (W is the mass of the laminate after immersion in ion-exchanged water for 24 hours, and Wd is the mass of the laminate after conditioning at 23° C. and a relative humidity of 50% for 24 hours.)

[0155] [Thickness] The thickness of the laminate of this embodiment is preferably 10 μm or more and 1,500 μm or less, more preferably 15 μm or more, even more preferably 20 μm or more, and more preferably 1,200 μm or less, even more preferably 900 μm or less, still more preferably 600 μm or less, even more preferably 300 μm or less, even more preferably 100 μm or less, and even more preferably 50 μm or less. When the laminate of this embodiment does not have a base film layer, the thickness of the laminate (cationic layer-fine fibrous cellulose-containing layer) is preferably 10 μm or more and 250 μm or less, more preferably 15 μm or more, even more preferably 20 μm or more, and more preferably 200 μm or less, even more preferably 150 μm or less, still more preferably 100 μm or less, even more preferably 50 μm or less, and even more preferably 35 μm or less. When the laminate of this embodiment has a base film layer, the thickness of the laminate (cationic layer-fine fibrous cellulose-containing layer-base film layer) is preferably 100 μm or more and 1,500 μm or less, more preferably 150 μm or more, even more preferably 200 μm or more, still more preferably 250 μm or more, and more preferably 1,200 μm or less, even more preferably 900 μm or less, still more preferably 600 μm or less, and even more preferably 300 μm or less. It is preferable to adjust the thickness of the laminate appropriately depending on the application.

[0156] [Basis Weight] The basis weight of the laminate of this embodiment is preferably 10 g / m ２ 2,500g / m or more ２ More preferably, it is 20 g / m or less. ２ More preferably, 30 g / m ２ More preferably, it is 2,000 g / m or more. ２ More preferably, 1,500 g / m or less ２ More preferably, 1,000 g / m or less ２ More preferably, 500 g / m or less ２ More preferably, 100 g / m or less ２ More preferably, 50 g / m or less ２When the laminate of the present embodiment does not have a base film layer, the basis weight of the laminate (cationic layer-fine fibrous cellulose-containing layer) is preferably 10 g / m ２ More than 250g / m ２ More preferably, it is 20 g / m or less. ２ More preferably, 30 g / m ２ More preferably, it is 200 g / m or more. ２ More preferably 150 g / m or less ２ More preferably, 100 g / m or less ２ More preferably, 50 g / m or less ２ When the laminate of the present embodiment has a base film layer, the basis weight of the laminate (cationic layer - fine fibrous cellulose-containing layer - base film layer) is preferably 100 g / m ２ 2,500g / m or more ２ More preferably, it is 200 g / m or less. ２ More preferably, 300 g / m ２ More preferably, 350 g / m ２ More preferably, it is 2,000 g / m or more. ２ More preferably, 1,500 g / m or less ２ More preferably, 1,000 g / m or less ２ More preferably 450 g / m or less ２ The following is the result.

[0157] [Density] The density of the laminate of this embodiment is preferably 1.0 g / cm ３ 3.0g / cm or more ３ More preferably, it is 1.1 g / cm or less. ３ More preferably, 1.2 g / cm ３ More preferably, it is 1.7 g / cm or more. ３ More preferably, 1.5 g / cm or less ３ The density of the laminate is calculated by dividing the basis weight of the laminate by its thickness.

[0158] [Method for Producing Laminate] The laminate of this embodiment can be produced, for example, by carrying out a step of producing a fine fibrous cellulose-containing sheet and a step of forming a cationic layer in this order.

[0159] [Process for Producing a Fine Fibrous Cellulose-Containing Sheet] The process for producing a fine fibrous cellulose-containing sheet is carried out using a liquid composition (slurry (dispersion medium is, for example, water)) containing the above-mentioned fine fibrous cellulose, and, if necessary, a hydrophilic polymer, and other components. For example, a fine fibrous cellulose-containing sheet can be obtained by coating a slurry containing fine fibrous cellulose and a hydrophilic compound on the above-mentioned base film layer, drying the layer, and peeling the resulting fine fibrous cellulose-containing sheet from the base. Furthermore, by using a coating device and a long or continuous base material, sheets can be produced continuously. When obtaining a laminate having a base film layer on the side of the fine fibrous cellulose-containing layer opposite to the side having the cationic layer, the above-mentioned base film layer is used as the base material, and the cationic layer-forming process described below is carried out without peeling the fine fibrous cellulose-containing sheet from the base material. In addition to the above-mentioned base film layer, examples of substrates that can be used in the process for producing a fine fibrous cellulose-containing sheet include metal films and plates such as aluminum, zinc, copper, and iron plates, and their surfaces subjected to oxidation treatment, stainless steel films and plates, and brass films and plates. In the production process of a fine fibrous cellulose-containing sheet, if the viscosity of the slurry is low and it spreads on the substrate, a blocking frame may be fixed to the substrate to obtain a sheet of a predetermined thickness and basis weight. The blocking frame is not particularly limited, but it is preferable to select one that allows the edge of the sheet to be easily peeled off after drying. From this perspective, molded resin or metal plates are more preferable. In this embodiment, for example, resin plates such as acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, polypropylene plates, polycarbonate plates, and polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates, and iron plates, and metal plates with their surfaces oxidized, stainless steel plates, brass plates, etc. can be used. The coating machine used to apply the slurry to the substrate is not particularly limited, but for example, a roll coater, gravure coater, die coater, curtain coater, air doctor coater, etc. can be used.A die coater, curtain coater, or spray coater is particularly preferred since it can make the thickness of the sheet more uniform.

[0160] After the slurry is applied to the substrate, the slurry is dried in a dryer. The drying temperature can be, for example, 30° C. or higher and 150° C. or lower, and can be 40° C. or higher and 120° C. or lower.

[0161] [Cationic layer forming process] The cationic layer forming process is carried out using a solution containing the above-mentioned cationic compound and other components.The solvent for the above solution can be, for example, methanol, ethanol, isopropyl alcohol, ethylene glycol, dimethyl sulfoxide (DMSO), acetonitrile, acetic acid, water, etc.The above solution is applied to the fine fibrous cellulose-containing sheet in the same manner as in the preparation process of the fine fibrous cellulose-containing sheet, and dried to form a cationic layer, so that the fine fibrous cellulose-containing sheet becomes the fine fibrous cellulose-containing layer, and the laminate of this embodiment can be obtained, which has a cationic layer on the fine fibrous cellulose-containing layer.

[0162] The laminate of this embodiment is resistant to adhesion of dust and other debris and has excellent laser cutter processability, making it applicable to a variety of uses. Specifically, it is suitable for use as a light-transmitting substrate for various display devices, solar cells, and the like. It is also applicable to uses such as substrates for electronic devices, components for home appliances, window materials for various vehicles and buildings, interior materials, exterior materials, packaging materials, and components for medical devices.

[0163] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0164] <Production Example A> [Phosphorylation Treatment] Softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. was used as the raw material pulp. This raw material pulp was subjected to a phosphating treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (bone dry mass) of the raw material pulp to adjust the composition to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, thereby obtaining a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated for 250 seconds in a hot air dryer at 165°C to introduce phosphate groups into the cellulose in the pulp, thereby obtaining a phosphorylated pulp.

[0165] [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 solution 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.

[0166] [Neutralization Treatment] Next, the washed phosphorylated pulp was neutralized as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous solution of sodium hydroxide was added little by little while stirring to obtain a phosphorylated pulp slurry 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.

[0167] The infrared absorption spectrum of the phosphorus oxy-oxidized pulp thus obtained was measured using FT-IR. －１ The absorption due to P=O of the phosphate group was observed around the 2θ=14° to 17° angle and the 2θ=22° to 23° angle.

[0168] [Defibrillation Treatment] Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated six times at a pressure of 200 MPa using a wet pulverization apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion A containing fine fibrous cellulose. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2 to 5 nm. The number-average fiber width of the fine fibrous cellulose measured in the [Number Average Fiber Width Measurement] section described below was 3 nm. X-ray diffraction confirmed that the fine fibrous cellulose maintained cellulose type I crystallinity. The amount of phosphate groups (amount of first dissociated acid (amount of strong acid groups)) measured by the measurement method described in the [Phosphorus Oxo Acid Group Amount] section described below was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0169] <Production Example B> After the neutralization treatment of the phosphorylated pulp of Production Example A, the following treatment was carried out to obtain a substituent-removed fine fibrous cellulose dispersion containing substituent-removed fine fibrous cellulose.

[0170] [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 for 1 hour at a temperature of 85°C. 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 pulp was repeatedly filtered and dehydrated to remove excess sodium hydroxide. The removal was terminated when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0171] The infrared absorption spectrum of the phosphorus oxy-oxidized pulp thus obtained was measured using FT-IR. －１ Absorption due to P=O of phosphate groups was observed near the pulp, confirming that phosphate groups had been added to the pulp.

[0172] [Defibrillation Treatment] Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated six times at a pressure of 200 MPa using a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2 to 5 nm. X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystal structure. The amount of phosphate groups (first dissociated acid amount, strong acid group amount) measured by the measurement method described below in [Measurement of phosphorus oxo acid group amount] was 1.35 mmol / g. The total dissociated acid amount was 2.30 mmol / g.

[0173] [Substituent Removal Treatment (High-Temperature Heat Treatment)] A 1.0% by mass aqueous citric acid solution was added to the fine fibrous cellulose dispersion, and the pH of the dispersion was adjusted to 5.5. The resulting slurry was placed in a pressure-resistant container and heated at a liquid temperature of 160°C for 15 minutes. Heating was continued until the amount of phosphate groups reached 0.08 mmol / g. The formation of fine fibrous cellulose aggregates was confirmed by this operation.

[0174] [Washing Treatment of Slurry After Substituent Removal] The heated slurry was added with the same amount of ion-exchanged water as the slurry to obtain a slurry with a solids concentration of approximately 1% by mass. This slurry was stirred and then repeatedly filtered and dehydrated 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, which was then allowed to stand for 24 hours. The filtration and dehydration 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 substituent removal. The solids concentration of this slurry was 1.7% by mass.

[0175] [Uniform Dispersion of Substituent-Removed Slurry] Ion-exchanged water was added to the resulting substituent-removed slurry to give a slurry with a solids concentration of 1.0% by mass, which was then treated three times at a pressure of 200 MPa in a wet atomization apparatus (Starburst, manufactured by Sugino Machine Corporation) to obtain a substituent-removed fine fibrous cellulose dispersion B containing substituent-removed fine fibrous cellulose. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and was found to be 2 to 5 nm. The number average fiber width of the substituent-removed fine fibrous cellulose, as measured in the "Measurement of Number Average Fiber Width" section described below, was 4 nm.

[0176] <Production Example C> [TEMPO Oxidation Treatment] Softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. was used as the raw material pulp. This raw material pulp was subjected to an alkaline TEMPO oxidation treatment as follows. First, 100 parts by mass of the raw material pulp (dry mass equivalent), 1.6 parts by mass of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by mass of sodium bromide were dispersed in 10,000 parts by mass of water. Next, a 13% by mass aqueous solution of sodium hypochlorite was added to 1.0 g of pulp so that the concentration was 3.8 mmol, to initiate the reaction. During the reaction, a 0.5 M aqueous solution of sodium hydroxide was added dropwise to maintain the pH at 10 to 10.5. The reaction was considered complete when no further change in pH was observed.

[0177] [Washing Treatment] The resulting TEMPO-oxidized pulp was then subjected to a washing treatment. The washing treatment involved dehydrating the pulp slurry after TEMPO oxidation to obtain a dehydrated sheet, pouring 5,000 parts by mass of ion-exchanged water into the sheet, stirring to uniformly disperse the pulp, and then repeatedly filtering and dehydrating the sheet. The washing endpoint was reached when the electrical conductivity of the filtrate reached 100 μS / cm or less. The resulting TEMPO-oxidized pulp was analyzed using an X-ray diffractometer. Typical peaks were observed at two positions, near 2θ = 14° to 17° and near 2θ = 22° to 23°, confirming the presence of cellulose type I crystals. Furthermore, X-ray diffraction confirmed that the resulting fibrous cellulose maintained cellulose type I crystals.

[0178] [Defibrillation Treatment] A fine fibrous cellulose dispersion C containing fine fibrous cellulose was obtained in the same manner as in Production Example A, except that the above-mentioned TEMPO-oxidized pulp was used in the [Defibrillation Treatment] of Production Example A. The fiber width of the fine fibrous cellulose in the fine fibrous cellulose dispersion C was measured using a transmission electron microscope and found to be 2 to 5 nm. The number-average fiber width of the fine fibrous cellulose measured in the [Number-average fiber width measurement] described below was 3 nm. X-ray diffraction confirmed that this fine fibrous cellulose maintained cellulose type I crystals. The carboxyl group amount measured by the method described in the [Carboxy group amount measurement] described below was 1.80 mmol / g.

[0179] <Production Example D> [Phosphorylation Treatment] The same procedure as in Production Example A was carried out, except that 33 parts by mass of phosphorous acid (phosphonic acid) was used instead of ammonium dihydrogen phosphate in the [Phosphorylation Treatment] of Production Example A, to obtain a fine fibrous cellulose dispersion D containing phosphite pulp and fine fibrous cellulose.

[0180] The infrared absorption spectrum of the obtained phosphorous-containing pulp was measured using FT-IR. －１ Absorption due to P=O of a phosphonic acid group, which is a tautomer of a phosphorous acid group, was observed near the nucleus, confirming that a phosphorous acid group (phosphonic acid group) had been added to the pulp. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and was found to be 2 to 5 nm. The number-average fiber width of the fine fibrous cellulose measured in the "Measurement of Number Average Fiber Width" section described below was 3 nm. X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystal structure. The amount of phosphorous acid groups (amount of first dissociated acid) measured by the measurement method described in the "Measurement of Amount of Phosphorous Oxo Acid Groups" section described below was 1.51 mmol / g, and the total amount of dissociated acid was 1.54 mmol / g.

[0181] Production Example E Substituent removal treatment was carried out in the same manner as in Production Example B, except that the phosphited fine fibrous cellulose of Production Example D was used, to obtain a substituent-removed fine fibrous cellulose dispersion E containing substituent-removed fine fibrous cellulose. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and was found to be 2 to 5 nm. The number average fiber width of the substituent-removed fine fibrous cellulose, measured in the "Measurement of number average fiber width" section described below, was 4 nm.

[0182] <Production Example F> [Sulfur oxo-oxidation treatment] The same operations as in Production Example A were carried out, except that in the [Phosphorylation treatment] of Production Example A, 38 parts by mass of sulfuric acid amide (sulfamic acid) was used instead of ammonium dihydrogen phosphate and the heating time was extended to 20 minutes, to obtain a fine fibrous cellulose dispersion F containing sulfated pulp and fine fibrous cellulose.

[0183] The obtained sulfated pulp was subjected to infrared absorption spectroscopy using FT-IR. －１ Absorption due to sulfate groups (sulfur oxoacid groups) was observed near the peak, confirming that sulfate groups (sulfur oxoacid groups) had been added to the pulp. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2 to 5 nm. The number-average fiber width of the fine fibrous cellulose measured in the "Measurement of Number-Average Fiber Width" section described below was 3 nm. Furthermore, X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystal structure. The amount of sulfur oxoacid groups measured in the "Measurement of Sulfur Oxoacid Group Amount" section described below was 1.47 mmol / g.

[0184] Production Example G Substituent removal treatment was carried out in the same manner as in Production Example B, except that the sulfur oxo-oxidized fine fibrous cellulose of Production Example F was used, to obtain a substituent-removed fine fibrous cellulose dispersion G containing substituent-removed fine fibrous cellulose. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and was found to be 2 to 5 nm. The number average fiber width of the substituent-removed fine fibrous cellulose, as measured in the "Measurement of number average fiber width" section described below, was 4 nm.

[0185] <Production Example H> [No Modification] Softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. was used as the raw material pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was subjected to a refiner treatment and beaten (pre-defibrated) until the CSF was 50 mL or less. The pre-beaten unmodified pulp fibers were treated six times at a pressure of 200 MPa using a wet pulverizer (Starburst manufactured by Sugino Machine Co., Ltd.) to obtain unmodified fine fibrous cellulose (unmodified CNF) dispersion H. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 10 to 50 nm. The fiber width of the fine fibrous cellulose measured by the "Number Average Fiber Width Measurement" described below was 30 nm.

[0186] <Measurement> [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.

[0187] [Measurement of Carboxy Group Amount] The carboxyl group amount of the fine fibrous cellulose (equivalent to the carboxyl group amount of the TEMPO-oxidized pulp) was measured by adding ion-exchange water to a fine fibrous cellulose dispersion containing the target fine fibrous cellulose to adjust the content to 0.2% by mass, treating with an ion exchange resin, and then titrating 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 a 0.2% by mass fine fibrous cellulose-containing slurry, shaking for 1 hour, and then pouring the mixture onto a 90 μm mesh to separate the ion exchange resin and the slurry. The alkali titration was performed by adding 0.1 N aqueous sodium hydroxide to the fine fibrous cellulose-containing slurry after the ion exchange resin treatment and measuring the change in pH of the slurry. Observing the change in pH while adding aqueous sodium hydroxide resulted in a titration curve as shown in FIG. 2. As shown in Figure 2, in this neutralization titration, a point is observed where the increment (differential value of pH with respect to the amount of alkali added) is maximum on the curve plotting the measured pH against the amount of alkali added. This maximum point of the increment is called the first end point. Here, the region from the start of titration to the first end point in Figure 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxy groups in the slurry used for titration. Then, the amount of alkali required in the first region of the titration curve (mmol) was divided by the solid content (g) in the fine fibrous cellulose-containing slurry to be titrated to calculate the amount of carboxy groups introduced (mmol / g). The amount of carboxy groups introduced (mmol / g) is calculated when the counter ions of the carboxy groups are hydrogen ions (H + ) and the amount of substituents per 1 g of the fine fibrous cellulose.

[0188] [Measurement of sulfur oxoacid group content] The sulfur oxoacid group content of the fine fibrous cellulose was measured by subjecting a freeze-dried and pulverized sample to pressurized heating decomposition with sulfuric acid in a sealed container, appropriately diluting the sample, and measuring the sulfur content by inductively coupled plasma optical emission spectroscopy (ICP-OES). The value calculated by dividing the result by the bone dry mass of the fine fibrous cellulose used was taken as the sulfur oxoacid group content (mmol / g) of the fine fibrous cellulose.

[0189] [Measurement of Number-Average Fiber Width] The fiber width of the fine fibrous cellulose was measured using the following method. Each fine fibrous cellulose dispersion was diluted with water to a cellulose concentration of 0.01% by mass or more and 0.1% by mass or less, and cast onto a hydrophilically treated carbon film-coated grid. After drying, the grid was stained with uranyl acetate and observed under a transmission electron microscope (TEM, manufactured by JEOL Ltd., JEOL-2000EX). An arbitrary vertical or horizontal axis representing the image width was assumed within the obtained image, and the magnification was adjusted so that six or more fibers intersected the axis. After obtaining observation images satisfying these conditions, two random axes were drawn vertically and horizontally within each image, and the fiber widths of the fibers intersecting the axes were visually read. Six unique observation images were taken for each dispersion, and the fiber widths of the fibers intersecting each of the two axes were read (6 or more × 2 × 6 = 72 or more). The number-average fiber width was calculated from the fiber widths obtained in this manner.

[0190] Example 1 Preparation of a fine fibrous cellulose-containing sheet Polyethylene oxide (PEO-18P, manufactured by Sumitomo Seika Chemicals Co., Ltd., viscosity average molecular weight 4,300,000 to 4,800,000) was added to ion-exchanged water to a concentration of 2.0% by mass, and the mixture was stirred at 25°C for 30 minutes to obtain an aqueous polyethylene oxide solution. Fine fibrous cellulose dispersion B and the above aqueous polyethylene oxide solution were each diluted with ion-exchanged water to a solids concentration of 1.0% by mass. Next, an aqueous polyethylene oxide solution was added in an amount such that 20 parts by mass of polyethylene oxide was added to 100 parts by mass of fine fibrous cellulose in fine fibrous cellulose dispersion B to obtain a mixed solution. Furthermore, the finished basis weight of the fine fibrous cellulose-containing sheet was 35 g / m ２The mixed solution was measured so that the thickness was 180 mm x 180 mm and the mixture was spread on a commercially available acrylic plate. A damming frame (inner dimensions 180 mm x 180 mm, height 50 mm) was placed on the acrylic plate to achieve a predetermined thickness. The sheet was then dried in a dryer set at 70 ° C and peeled off from the acrylic plate to obtain a fine fibrous cellulose-containing sheet. [Formation of cationic layer] Polyethyleneimine (Nacalai Tesque Inc.) was diluted with water to obtain a polyethyleneimine solution (solid content concentration 0.25 mass%). A cationic layer having a finished basis weight of 62.5 mg / m was formed on one side of the fine fibrous cellulose-containing sheet prepared in [Preparation of fine fibrous cellulose-containing sheet]. ２ The polyethyleneimine solution was applied using a bar coater so that the thickness of the coated layer was 100 μm, and then the coated layer was dried in a dryer set at 70° C. to obtain a laminate (layer structure: cationic layer (thickness: approximately 60 nm) - fine fibrous cellulose-containing layer (thickness: 23 μm)).

[0191] Example 2 In the [Formation of Cationic Layer] of Example 1, the finished basis weight of the cationic layer was 6.25 mg / m ２ A laminate (layer structure: cationic layer (thickness: about 6 nm)-fine fibrous cellulose-containing layer (thickness: 23 μm)) was obtained in the same manner as in Example 1, except that:

[0192] Example 3 In the [Formation of Cationic Layer] of Example 1, the finished basis weight of the cationic layer was 0.625 mg / m ２ A laminate (layer structure: cationic layer (thickness: about 0.6 nm)-fine fibrous cellulose-containing layer (thickness: 23 μm)) was obtained in the same manner as in Example 1, except that:

[0193] Example 4 A laminate (layer structure: cationic layer (thickness: approximately 60 nm)-fine fibrous cellulose-containing layer (thickness: 23 μm)) was obtained in the same manner as in Example 1, except that in [Formation of cationic layer] of Example 1, polyethyleneimine (Nacalai Tesque, Inc.) was changed to polyethyleneimine (Nippon Shokubai Co., Ltd., SP-200).

[0194] Example 5 A laminate (layer structure: cationic layer (thickness 60 nm)-fine fibrous cellulose-containing layer (thickness 23 μm)) was obtained in the same manner as in Example 1, except that in [Formation of cationic layer] of Example 1, polyethyleneimine (Nacalai Tesque, Inc.) was changed to polyallylamine (Nittobo Medical Co., Ltd., PAA-03).

[0195] Example 6 A laminate (layer structure: cationic layer (thickness 60 nm)-fine fibrous cellulose-containing layer (thickness 23 μm)) was obtained in the same manner as in Example 1, except that in [Formation of cationic layer] of Example 1, polyethyleneimine (Nacalai Tesque, Inc.) was changed to polyallylamine (Nittobo Medical Co., Ltd., PAA-15C).

[0196] Example 7 A laminate (layer structure: cationic layer (thickness 60 nm)-fine fibrous cellulose-containing layer (thickness 23 μm)) was obtained in the same manner as in Example 1, except that in [Formation of cationic layer] of Example 1, polyethyleneimine (Nacalai Tesque, Inc.) was changed to polyallylamine (Nittobo Medical Co., Ltd., PAA-10L-10C).

[0197] Example 8 A laminate (layer structure: cationic layer (thickness 60 nm)-fine fibrous cellulose-containing layer (thickness 23 μm)) was obtained in the same manner as in Example 1, except that in [Formation of cationic layer] of Example 1, polyethyleneimine (Nacalai Tesque, Inc.) was changed to α-polylysine (Nacalai Tesque, Inc.).

[0198] Example 9 A laminate (layer structure: cationic layer (thickness 60 nm)-fine fibrous cellulose-containing layer (thickness 23 μm)) was obtained in the same manner as in Example 1, except that in [Formation of cationic layer] of Example 1, polyethyleneimine (Nacalai Tesque, Inc.) was changed to ε-polylysine (Nacalai Tesque, Inc.).

[0199] Example 10 A laminate (layer structure: cationic layer (thickness 60 nm)-fine fibrous cellulose-containing layer (thickness 23 μm)) was obtained in the same manner as in Example 1, except that in [Formation of cationic layer] of Example 1, polyethyleneimine (Nacalai Tesque, Inc.) was changed to cationized starch (Nippon Starch Chemical Co., Ltd.).

[0200] Example 11 [Formation of a cationic layer] Dodecyltrimethylammonium chloride (DTMAC, Fujifilm Wako Pure Chemical Industries, Ltd.) was dissolved in water to a solids concentration of 1%. Next, the polyethylene oxide aqueous solution prepared in Example 1 was added in an amount such that 30 parts by mass of polyethylene oxide was added to 70 parts by mass of DTMAC in the DTMAC solution, to obtain a mixed solution. Further, the mixed solution was diluted with water to obtain a DTMAC solution (DTMAC solids concentration 0.25% by mass). A cationic layer having a finished basis weight of 89.3 mg / m was formed on one side of a fine fibrous cellulose-containing sheet prepared in the same manner as in Example 1 [Preparation of a fine fibrous cellulose-containing sheet]. ２ and (DTMAC basis weight is 62.5 mg / m ２ The DTMAC solution was applied using a bar coater so that the thickness of the coated layer was 100 μm. The coated layer was then dried in a dryer set at 70° C. to obtain a laminate (layer structure: cationic layer (thickness: approximately 90 nm) - fine fibrous cellulose-containing layer (thickness: 23 μm)).

[0201] <Example 12> In the [Preparation of a fine fibrous cellulose-containing sheet] of Example 1, a PET film (Cosmoshine, A4360, manufactured by Toyobo Co., Ltd., thickness 250 μm, basis weight 350 g / m) was used instead of the acrylic plate. ２ A laminate (layer structure: cationic layer (thickness 60 nm)--fine fibrous cellulose-containing layer (thickness 23 μm)--PET film layer (thickness 250 μm)) was obtained in the same manner as in Example 1, except that a 60-μm thick cationic layer containing cellulose (thickness 60 nm)--fine fibrous cellulose-containing layer (thickness 23 μm)--PET film layer (thickness 250 μm) was used, and the sheet was not peeled off after drying.

[0202] Example 13 A laminate (layer structure: cationic layer (thickness 60 nm)-fine fibrous cellulose-containing layer (thickness 23 μm)) was obtained in the same manner as in Example 1, except that fine fibrous cellulose dispersion A was used instead of fine fibrous cellulose dispersion B in [Preparation of a fine fibrous cellulose-containing sheet] of Example 1.

[0203] Example 14 A laminate (layer structure: cationic layer (thickness 60 nm)--fine fibrous cellulose-containing layer (thickness 23 μm)--PET film layer (thickness 250 μm)) was obtained in the same manner as in Example 12, except that fine fibrous cellulose dispersion A was used instead of fine fibrous cellulose dispersion B.

[0204] Example 15 A laminate (layer structure: cationic layer (thickness 60 nm)-fine fibrous cellulose-containing layer (thickness 23 μm)) was obtained in the same manner as in Example 1, except that fine fibrous cellulose dispersion C was used instead of fine fibrous cellulose dispersion B in [Preparation of a fine fibrous cellulose-containing sheet] of Example 1.

[0205] Example 16 A laminate (layer structure: cationic layer (thickness 60 nm)-fine fibrous cellulose-containing layer (thickness 23 μm)) was obtained in the same manner as in Example 1, except that fine fibrous cellulose dispersion D was used instead of fine fibrous cellulose dispersion B in [Preparation of a fine fibrous cellulose-containing sheet] of Example 1.

[0206] Example 17 A laminate (layer structure: cationic layer (thickness 60 nm)-fine fibrous cellulose-containing layer (thickness 23 μm)) was obtained in the same manner as in Example 1, except that fine fibrous cellulose dispersion F was used instead of fine fibrous cellulose dispersion B in [Preparation of a fine fibrous cellulose-containing sheet] of Example 1.

[0207] Example 18 A laminate (layer structure: cationic layer (thickness 60 nm)-fine fibrous cellulose-containing layer (thickness 23 μm)) was obtained in the same manner as in Example 1, except that the obtained fine fibrous cellulose dispersion E was used instead of the fine fibrous cellulose dispersion B in [Preparation of a fine fibrous cellulose-containing sheet] of Example 1.

[0208] Example 19 A laminate (layer structure: cationic layer (thickness 60 nm)-fine fibrous cellulose-containing layer (thickness 23 μm)) was obtained in the same manner as in Example 1, except that the obtained fine fibrous cellulose dispersion G was used instead of the fine fibrous cellulose dispersion B in [Preparation of a fine fibrous cellulose-containing sheet] of Example 1.

[0209] Example 20 A laminate (layer structure: cationic layer (thickness 60 nm)-fine fibrous cellulose-containing layer (thickness 23 μm)) was obtained in the same manner as in Example 1, except that the obtained fine fibrous cellulose dispersion H was used instead of the fine fibrous cellulose dispersion B in [Preparation of a fine fibrous cellulose-containing sheet] of Example 1.

[0210] Comparative Example 1 A fine fibrous cellulose-containing sheet (thickness: 23 μm) was obtained in the same manner as in Example 1, except that the step of forming a cationic layer was not carried out.

[0211] Comparative Example 2 A fine fibrous cellulose-containing sheet (thickness: 23 μm) was obtained in the same manner as in Example 13, except that the step of [forming a cationic layer] was not carried out.

[0212] Comparative Example 3 A fine fibrous cellulose-containing sheet (thickness: 23 μm) was obtained in the same manner as in Example 15, except that the step of [forming a cationic layer] was not carried out.

[0213] Comparative Example 4 A fine fibrous cellulose-containing sheet (thickness: 23 μm) was obtained in the same manner as in Example 16, except that the step of [forming a cationic layer] was not carried out.

[0214] Comparative Example 5 A fine fibrous cellulose-containing sheet (thickness: 23 μm) was obtained in the same manner as in Example 17, except that the step of [forming a cationic layer] was not carried out.

[0215] Comparative Example 6 A fine fibrous cellulose-containing sheet (thickness: 23 μm) was obtained in the same manner as in Example 18, except that the step of [forming a cationic layer] was not carried out.

[0216] Comparative Example 7 A fine fibrous cellulose-containing sheet (thickness: 23 μm) was obtained in the same manner as in Example 19, except that the step of [forming a cationic layer] was not carried out.

[0217] Comparative Example 8 A fine fibrous cellulose-containing sheet (thickness: 23 μm) was obtained in the same manner as in Example 20, except that the step of [forming a cationic layer] was not carried out.

[0218] Comparative Example 9 A PET film (Cosmoshine A4360, manufactured by Toyobo Co., Ltd., thickness 250 μm) was used.

[0219] Comparative Example 10 A laminate (layer structure: fine fibrous cellulose-containing layer (thickness 23 μm)-PET film layer (thickness 250 μm)) was obtained in the same manner as in Example 12, except that the [formation of a cationic layer] in Example 12 was not performed.

[0220] Comparative Example 11 A laminate (layer structure: fine fibrous cellulose-containing layer (thickness 23 μm)-PET film layer (thickness 250 μm)) was obtained in the same manner as in Example 14, except that the [formation of a cationic layer] in Example 14 was not performed.

[0221] <Measurement and Evaluation of Characteristic Values> [Total Light Transmittance] Test pieces measuring 50 mm square were cut from the laminate, the fine fibrous cellulose-containing sheet, or the PET film. Using these test pieces, the total light transmittance was measured in accordance with JIS K7361-1:1997 using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.). The results are shown in Table 1.

[0222] [Haze] A 50 mm square test piece was cut from the laminate, the fine fibrous cellulose-containing sheet, or the PET film. The haze of this test piece was measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K7136:2000. The results are shown in Table 1.

[0223] [Tensile Strength] Test pieces measuring 80 mm in length and 10 mm in width were cut out from the laminate, the fine fibrous cellulose-containing sheet, or the PET film. The tensile strength (unit: N / m) was measured using a tensile tester Tensilon (manufactured by A&D Co., Ltd.) in accordance with JIS P 8113:2006, except that the test pieces were used and the chuck distance was set to 50 mm. The tensile strength (unit: MPa) was calculated by dividing the tensile strength by the thickness of the test piece. When measuring the tensile strength, the test pieces were conditioned at 23°C and 50% relative humidity for 24 hours. The results are shown in Table 1.

[0224] [Tensile modulus] Test pieces measuring 80 mm in length and 15 mm in width were cut out from the laminate, the fine fibrous cellulose-containing sheet, or the PET film. The tensile modulus was measured using a Tensilon tensile tester (manufactured by A&D Co., Ltd.) in accordance with JIS P 8113:2006, except that the test pieces were used and the chuck distance was set to 50 mm. The tensile modulus was calculated from the maximum positive slope value in the SS curve. When measuring the tensile modulus, the test pieces were conditioned at 23°C and 50% relative humidity for 24 hours. The results are shown in Table 1.

[0225] [Linear thermal expansion coefficient] A test piece 3 mm wide x 30 mm long was cut from the laminate, the fine fibrous cellulose-containing sheet, or the PET film using a laser cutter. The test piece was set in a thermomechanical analyzer (Hitachi High-Tech Science Corporation, TMA7100) in a tensile mode with a chuck distance of 20 mm, a load of 10 g, and a nitrogen atmosphere. The temperature was increased from room temperature to 180 ° C. at a rate of 5 ° C. / min, decreased from 180 ° C. to 25 ° C. at a rate of 5 ° C. / min, and then increased from 25 ° C. to 180 ° C. at a rate of 5 ° C. / min. The linear thermal expansion coefficient was determined from the measured value from 100 ° C. to 150 ° C. during the second temperature increase. The results are shown in Table 1.

[0226] [Water Resistance (Water Absorption)] Two 50 mm square test pieces were cut from the laminate, the fine fibrous cellulose-containing sheet, or the PET film. One test piece was conditioned for 24 hours at 23°C and a relative humidity of 50%. The mass of the conditioned test piece was designated Wd (g), and the mass of the other test piece after immersion in ion-exchanged water for 24 hours was designated W (g). The water absorption was calculated using the following formula, and the water resistance was evaluated according to the following criteria (A, B, C): Water absorption (%) = (W - Wd) / Wd × 100 A: Water absorption of 1,000% or less B: Water absorption of more than 1,000% but less than 2,000% C: Water absorption of 2,000% or more

[0227] [Dust Adhesion] A 50 mm square test piece was cut from the laminate, the fine fibrous cellulose-containing sheet, or the PET film, and one entire side of the test piece was rubbed with a tissue (Hana Celeb Tissue, manufactured by Oji Nepia Co., Ltd.) 10 times to allow dust to adhere. Note that the entire cationic layer side was rubbed with the tissue for Examples 1 to 20, the entire side of one randomly selected test piece was rubbed with the tissue for Comparative Examples 1 to 9, and the entire fine fibrous cellulose-containing layer side was rubbed with the tissue for Comparative Examples 10 and 11. The dust was removed by spraying with a duster for 10 seconds, and the degree of dust adhesion was visually evaluated. A: No dust (fiber) adhesion; B: A small amount of dust (fiber) remains; C: Most of the dust (fiber) cannot be removed after adhesion. The "B" rating of "a small amount of dust (fiber) remains" means that the number of dust particles remaining on the surface of the test piece was 40% or less of the number of dust particles on the surface of the test piece of Comparative Example 9.

[0228] [Laser cutter processability] Test pieces measuring 3 mm wide x 30 mm long were cut out from the laminate, the fine fibrous cellulose-containing sheet, or the PET film using a laser cutter, and the changes in the processed area of ​​the laminate, the fine fibrous cellulose-containing sheet, or the PET film (the area where the laser cutter was applied and the vicinity of that area) were visually evaluated. For the test pieces cut out from the laminate, the laser cutter was applied from the side having the cationic layer. For Comparative Examples 1 to 8, 10, and 11, the laser cutter was applied from the side of the fine fibrous cellulose-containing layer. A: No change in the processed area B: Whitening around the processed area

[0229]

[0230] (Explanation of terms in the table) Actual: Example Ratio: Comparative example Transmittance: Total light transmittance Elastic modulus: Tensile modulus Expansion coefficient: Linear thermal expansion coefficient Processability: Laser cutter processability DTMAC: Dodecyltrimethylammonium chloride (For DTMAC, the molecular weight is listed in the weight average molecular weight column.) CNF: Fine fibrous cellulose PEI: Polyethyleneimine PAA: Polyallylamine PET: Polyethylene terephthalate ND: No data available -: This means that the corresponding component is not contained, etc.

[0231] Table 1 shows that the laminate of this embodiment (layer structure: cationic layer-fine fibrous cellulose-containing layer, or cationic layer-fine fibrous cellulose-containing layer-PET film layer) is resistant to dust adhesion and has excellent laser cutter processability (Examples 1 to 20). In contrast, the fine fibrous cellulose-containing sheet without a cationic layer and the laminate (fine fibrous cellulose-containing layer-PET film layer) without a cationic layer are inferior in laser cutter processability (Comparative Examples 1 to 8, 10, and 11). Furthermore, it is clear that the PET film is prone to dust adhesion and has poor laser cutter processability (Comparative Example 9).

Claims

1. A laminate comprising a fine fibrous cellulose-containing layer containing fine fibrous cellulose with a fiber width of 1 nm to 1,000 nm, and a cationic layer containing a cationic compound on at least one surface of the fine fibrous cellulose-containing layer.

2. The laminate according to claim 1, wherein the fine fibrous cellulose has anionic groups.

3. The laminate according to claim 2, wherein the anionic group comprises at least one selected from the group consisting of a phosphorus oxoacid group, a carboxyl group, a sulfur oxoacid group, and a xantate group.

4. The laminate according to claim 2 or 3, wherein the amount of anionic groups introduced into the fine fibrous cellulose is less than 0.5 mmol / g.

5. The laminate according to claim 1 or 2, wherein the cationic compound has an amino group.

6. The laminate according to claim 1 or 2, wherein the content of fine fibrous cellulose in the fine fibrous cellulose-containing layer is 30% by mass or more.

7. The laminate according to claim 1 or 2, wherein the fine fibrous cellulose-containing layer contains a hydrophilic polymer, and the content of the hydrophilic polymer per 100 parts by mass of fine fibrous cellulose is 5 parts by mass or more and 40 parts by mass or less.

8. The laminate according to claim 1 or 2, wherein the total light transmittance is 80% or more.

9. The laminate according to claim 1 or 2, wherein the coefficient of linear thermal expansion in the measurement range of 100°C to 150°C is 70 ppm / K or less.

10. The laminate according to claim 1 or 2, wherein the tensile modulus of elasticity at 23°C is 5.0 GPa or more.

11. The laminate according to claim 1 or 2, wherein one side of the fine fibrous cellulose-containing layer has a cationic layer, and the side of the fine fibrous cellulose-containing layer opposite to the side having the cationic layer has a base film layer.

12. The laminate according to claim 1 or 2, wherein a fine fibrous cellulose-containing layer and a cationic layer are in contact.