Sheet and manufacturing method thereof

Abstract

To provide a sheet that has high transparency, has fine irregularities on the surface, and exhibits high affinity with a biopolymer, and a method for producing the sheet.SOLUTION: A sheet comprises fine fibrous cellulose having a fiber width of 1,000 nm or less. At least one side of the sheet is provided with irregularities. The haze is 80% or less. The irregularities have an average interval Sm of 60 μm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a sheet and a method for producing the same. [Background technology]

[0002] Conventionally, various types of irregularities have been formed on the surface of a sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less to impart functionality to the sheet. Patent Document 1 describes an optical film that is highly productive and has excellent antiglare properties, and that includes a transparent film and a hard coat layer formed on the transparent film, in which the hard coat layer is formed from a cured product of a curable composition containing a curable resin precursor and nanofibers, and the surface of the hard coat layer has an uneven structure with an average spacing Sm of 5 to 40 μm and a ten-point average roughness Rz of 0.8 to 2.5 μm. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-006448 Summary of the Invention [Problem to be solved by the invention]

[0004] The optical film described in Patent Document 1 involves a curing step, which causes problems in production, and the resulting film is thought to have high hardness and low affinity for biopolymers. An object of the present invention is to provide a sheet that has high transparency, has fine irregularities on the surface, and has excellent affinity for biopolymers, and a method for producing the sheet. [Means for solving the problem]

[0005] The present inventors have found that the above problems can be solved by a sheet that contains fine fibrous cellulose, has a specific uneven shape, and has a haze of a specific value or less. The present invention provides the following <1> ~ <20> Regarding. <1> A sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less, the sheet having an uneven shape on at least one surface, a haze of 80% or less, and an average spacing Sm of the uneven shapes of 60 μm or less. <2> Total light transmittance is 85% or more. <1> The sheet described in <3> Haze is 5% or less, <1> or <2> The sheet described in <4> Total light transmittance is 90% or more. <1> ~ <3> A sheet according to any one of the above. <5> The average spacing Sm of the uneven shape is 10 nm or more and 1 μm or less. <1> ~ <4> A sheet according to any one of the above. <6> The arithmetic mean roughness Ra of the surface having the irregularities is 700 nm or less. <1> ~ <5> A sheet according to any one of the above. <7> The uneven shape is scattered, <1> ~ <6> A sheet according to any one of the above. <8> The uneven shape is formed by transferring an uneven shape of a microstructure having an average spacing Sm of 10 nm or more and 500 nm or less. <1> ~ <7> A sheet according to any one of the above. <9> Further containing a hydrophilic polymer, <1> ~ <8> A sheet according to any one of the above. <10> The hydrophilic polymer is at least one selected from the group consisting of polyvinyl alcohol, modified polyvinyl alcohol, polyalkylene glycol, polyalkylene oxide, and cellulose derivatives. <9> The sheet described in <11> The cellulose derivative is a cellulose ether. <10> The sheet described in <12> The cellulose ether is at least one selected from the group consisting of hydroxypropyl methylcellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxyethyl methylcellulose, methylcellulose, and carboxymethylcellulose. <11> The sheet described in <13> The composition contains 10 parts by mass or more and 400 parts by mass or less of a hydrophilic polymer relative to 100 parts by mass of fine fibrous cellulose, <9> ~ <12> A sheet according to any one of the above. <14> The total content of fine fibrous cellulose and hydrophilic polymer in the solid content of the sheet is 80% by mass or more. <9> ~ <13> A sheet according to any one of the above. <15> The thickness of the sheet is 5 μm or more and 300 μm or less. <1> ~ <14> A sheet according to any one of the above. <16> For biopolymer adsorption, <1> ~ <15> A sheet according to any one of the above. <17> A method for producing a sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less, the sheet having an uneven shape on at least one surface thereof, a haze of 80% or less, and an average spacing Sm of the uneven shapes of 60 μm or less, comprising: A method for producing a sheet, comprising the following steps A1 and A2 in this order: Step A1: A step of spreading a liquid sheet raw material containing fine fibrous cellulose having a fiber width of 1000 nm or less on a substrate having an uneven surface. Step A2: A step of drying the sheet material in this state to obtain a sheet with the concave-convex pattern transferred thereto. <18> A method for producing a sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less, the sheet having an uneven shape on at least one surface thereof, a haze of 80% or less, and an average spacing Sm of the uneven shapes of 60 μm or less, comprising: A method for producing a sheet, comprising the following steps B1 and B2 in this order: Step B1: A step of placing a sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less on a substrate having an uneven surface to obtain a laminate. Step B2: A step of pressing the laminate under heat to transfer the concave-convex pattern <19> A method for producing a sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less, the sheet having an uneven shape on at least one surface thereof, a haze of 80% or less, and an average spacing Sm of the uneven shapes of 60 μm or less, comprising: A method for producing a sheet comprising the following steps C1 to C3 in this order: Step C1: A step of placing a wet sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less on a substrate having an uneven surface to obtain a laminate. Step C2: Pressurizing the laminate to adhere the sheet to the substrate Step C3: A step of drying the sheet while it is in close contact with the substrate to obtain a sheet with the concave-convex pattern transferred thereto. <20> A release layer is provided on the surface of the substrate. <17> ~ <19> 10. A method for producing the sheet according to any one of the above. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a sheet that has high transparency, has fine irregularities on the surface, and has excellent affinity for biopolymers, and a method for producing the sheet. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fine fibrous cellulose having phosphorus oxo acid groups and pH. [Figure 2] FIG. 2 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fine fibrous cellulose having carboxy groups and pH. [Figure 3] FIG. 3 is a cross-sectional perspective view showing an example of a nanobuckling sheet. [Figure 4] FIG. 4 is a cross-sectional perspective view showing an example of a nanodot array. [Figure 5] FIG. 5 is a cross-sectional perspective view showing another example of a nanodot array. DETAILED DESCRIPTION OF THE INVENTION

[0008] Sheet The sheet of the present invention is a sheet containing fine fibrous cellulose (hereinafter simply referred to as "fine fibrous cellulose" or "CNF") having a fiber width of 1000 nm or less, and has an uneven shape on at least one surface of the sheet, a haze of 80% or less, and an average spacing Sm of the uneven shapes of 60 μm or less. According to the present invention, a sheet having high transparency, fine irregularities on the surface, and excellent affinity for biopolymers is provided. Although the detailed mechanism by which the above effects are obtained is unknown, it is thought that part of it is as follows. Unlike synthetic resin materials such as plastics, cellulose has high biocompatibility and low environmental impact, and therefore, studies are being conducted to impart functionality to this material and use it in biochemical and medical applications. Microfibrous cellulose is a fiber obtained by defibrating cellulose to the nano-level, where the fiber width is 1000 nm or less. Sheets made from microfibrous cellulose are highly transparent and are used in a variety of applications that require transparency. However, sheets made from commonly obtained microfibrous cellulose have a smooth surface, which poses the problem of low adsorption efficiency with substances unless chemical modification or the like is performed. In the present invention, it has been discovered that by forming a sheet with a specific uneven shape, the adsorption of substances, particularly biopolymers, can be improved while maintaining low haze. The present invention will be described in further detail below.

[0009] <Fine fibrous cellulose> The sheet of the present invention contains fine fibrous cellulose. Fine fibrous cellulose is fibrous cellulose with a fiber width of 1,000 nm or less. The fiber width of fibrous cellulose can be measured, for example, by observation using an electron microscope. The fiber width of the fine fibrous cellulose is 1,000 nm or less. The fiber width of the 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 particularly preferably 2 nm or more and 10 nm or less. By making the 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 more easily realize the effects of the fine fibrous cellulose, such as improved strength, rigidity, and dimensional stability.

[0010] The average fiber width of the fine fibrous cellulose is, for example, 1,000 nm or less. The average fiber width of the fine fibrous cellulose is preferably 2 nm or more and 1,000 nm or less, more preferably 2 nm or more and 100 nm or less, even more preferably 2 nm or more and 50 nm or less, and particularly preferably 2 nm or more and 10 nm or less. By making the average fiber width of the fine fibrous cellulose 2 nm or more, it is possible to suppress the dissolution of the cellulose molecules in water, and more easily realize the effects of the fine fibrous cellulose, such as improved strength, rigidity, and dimensional stability. The fine fibrous cellulose is, for example, monofilament cellulose.

[0011] The 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 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for TEM observation. When wide fibers are included, SEM images 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 must be adjusted to meet the following conditions. (1) Draw a line X at any point in the observed image, and 20 or more fibers intersect with the line X. (2) Draw a line Y that intersects the line perpendicularly within the same image, and 20 or more fibers intersect the line Y.

[0012] For observation images that satisfy the above conditions, the widths of the fibers intersecting with lines X and Y are visually read. In this way, three or more sets of observation images of at least the surface portions that do not overlap each other are obtained. Next, for each image, the widths of the fibers intersecting with lines X and Y are read. In this way, the widths of at least 20 fibers x 2 x 3 = 120 fibers are read. The average value of the read fiber widths is then taken as the average fiber width of the fibrous cellulose.

[0013] The fiber length of the fine fibrous cellulose is not particularly limited, but is preferably 0.1 μm to 1,000 μm, more preferably 0.1 μm to 800 μm, and even more preferably 0.1 μm to 600 μm. By setting the fiber length within the above range, destruction of the crystalline regions of the fine fibrous cellulose can be suppressed. It also becomes possible to set the slurry viscosity of the fine fibrous cellulose within an appropriate range. The fiber length of the fine fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

[0014] 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 from a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromated with graphite. Specifically, the cellulose can be identified from the presence of typical peaks at two positions, around 2θ=14° to 17° and around 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 allows for even better performance in terms of heat resistance and low linear thermal expansion coefficient. The degree of crystallinity can be determined by measuring an X-ray diffraction profile and using the pattern in a conventional manner (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0015] The axial ratio (fiber length / fiber width) of the fine fibrous cellulose is not particularly limited, but is preferably 20 to 10,000, and more preferably 50 to 1,000. By setting the axial ratio at or above the lower limit, it is easy to form a sheet containing the fine fibrous cellulose. Furthermore, sufficient viscosity is easily obtained when a solvent dispersion is prepared. Setting the axial ratio at or below the upper limit is preferable, for example, because it makes handling, such as dilution, easier when treating the fine fibrous cellulose as an aqueous dispersion.

[0016] The fine fibrous cellulose in this embodiment preferably has at least one of an ionic group and a nonionic group. From the viewpoint of improving the dispersibility of the fibers in the dispersion medium and increasing the defibration efficiency in the defibration treatment, it is more preferable that the fine fibrous cellulose has an ionic group. The ionic group may include, for example, either one or both of an anionic group and a cationic group. Furthermore, the nonionic group may include, for example, an alkyl group and an acyl group. In this embodiment, it is particularly preferable that the ionic group has an anionic group. Note that it is preferable that the cellulose has an ionic group, preferably an anionic group, at least during the defibration treatment, and the ionic group may be removed after the defibration treatment. Furthermore, the fine fibrous cellulose does not need to be subjected to a treatment for introducing ionic groups.

[0017] Examples of anionic groups as ionic groups include phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups (sometimes simply referred to as phosphorus oxoacid groups), carboxy groups or substituents derived from carboxy groups (sometimes simply referred to as carboxy groups), sulfur oxoacid groups or substituents derived from sulfur oxoacid groups (sometimes simply referred to as sulfur oxoacid groups), xanthate groups, phosphonic groups, phosphine groups, 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, sulfur oxoacid groups, substituents derived from sulfur oxoacid groups, carboxymethyl groups, carboxyethyl groups, and sulfonic groups; 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 substituents derived from sulfur oxoacid groups; and 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, for example, even under alkaline or acidic conditions, making it easier to obtain a high-strength, highly transparent sheet. Examples of cationic groups as ionic groups include ammonium groups, phosphonium groups, sulfonium groups, etc. Among these, the cationic group is preferably an ammonium group.

[0018] The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group is, for example, a substituent represented by the following formula (1). A plurality of types of substituents represented by the following formula (1) may be introduced into each fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (1) may be the same or different.

[0019] [ka]

[0020] In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (where a=b×m). At least one of the n α and α' is O. - and the rest are R or OR. Note that all of α and α' are O - The n α's may all be the same or may be different. b+ is a cation of one or more valences consisting of organic or inorganic substances.

[0021] R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived therefrom. In formula (1), n ​​is preferably 1.

[0022] Examples of saturated linear hydrocarbon groups include, but are not limited to, methyl, ethyl, n-propyl, or n-butyl groups. Examples of saturated branched hydrocarbon groups include, but are not limited to, i-propyl or t-butyl groups. Examples of saturated cyclic hydrocarbon groups include, but are not limited to, cyclopentyl or cyclohexyl groups. Examples of unsaturated linear hydrocarbon groups include, but are not limited to, vinyl or allyl groups. Examples of unsaturated branched hydrocarbon groups include, but are not limited to, i-propenyl or 3-butenyl groups. Examples of unsaturated cyclic hydrocarbon groups include, but are not limited to, cyclopentenyl or cyclohexenyl groups. Examples of aromatic groups include, but are not limited to, phenyl or naphthyl groups.

[0023] Furthermore, examples of the derivative group in R include, but are not limited to, functional groups in which at least one functional group selected from the group consisting of a carboxy group, a carboxylate group (—COO—), a hydroxy group, an amino group, and an ammonium group is added to or substituted on the main chain or side chain of the above-mentioned hydrocarbon groups. 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 finely divided cellulose fibers. When multiple Rs are present in formula (1) or when multiple types of substituents represented by formula (1) are introduced into the fibrous cellulose, the multiple Rs may be the same or different.

[0024] β b+ is a monovalent or higher cation made of an organic or inorganic substance. Examples of monovalent or higher cations made of an organic substance include organic onium ions. Examples of organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of monovalent or higher cations made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. It should be noted that in formula (1), β b+ When a plurality of β b+ may be the same or different. The monovalent or higher cations 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 material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0025] More specifically, examples of the phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group include a phosphate group (-POH), a salt of a phosphate group, a phosphorous acid (phosphonic acid) group (-POH), and a salt of a phosphite (phosphonic acid) group. The phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group may also be a group in which a phosphate group is condensed (e.g., a pyrophosphate group), a group in which a phosphonic acid is condensed (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), an alkyl phosphonic acid group (e.g., a methylphosphonic acid group), etc.

[0026] 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 substituents represented by the following formula (2) may be introduced into each fibrous cellulose. In this case, the introduced plurality of substituents represented by the following formula (2) may be the same or different.

[0027] [ka]

[0028] In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (where 1 = b × m). When n is 2 or more, multiple p's may be the same number or different numbers. In the above structural formula, β b+is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. Note that when multiple types of substituents represented by the above formula (2) are introduced into the fibrous cellulose, the multiple β b+ may be the same or different. The monovalent or higher cations 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 material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0029] The amount of ionic groups introduced into the fine fibrous cellulose is, for example, preferably 0.10 mmol / g or more per gram (mass) of fine fibrous cellulose, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and particularly preferably 1.00 mmol / g or more. The amount of ionic groups introduced into the fine fibrous cellulose is, for example, preferably 5.20 mmol / g or less per gram (mass) of fibrous cellulose, more preferably 3.65 mmol / g or less, even more preferably 3.50 mmol / g or less, and even more preferably 3.00 mmol / g or less. By controlling the amount of ionic groups introduced within the above range, it is possible to facilitate the refinement of the fiber raw material and improve the stability of the fine fibrous cellulose. Furthermore, by controlling the amount of ionic groups introduced within the above range, excellent properties can be exhibited in various applications, such as a thickener for fine fibrous cellulose. Here, the denominator in the unit mmol / g is the value of the counter ion of the ionic group being a hydrogen ion (H + ) indicates the mass of the fine fibrous cellulose when

[0030] The amount of ionic groups introduced into the fibrous cellulose can be measured, for example, by neutralization titration, which involves measuring the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to a slurry containing the obtained fibrous cellulose. FIG. 1 is a graph showing the relationship between the amount of NaOH added dropwise to fibrous cellulose having phosphorus oxo acid groups and pH.

[0031] 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 the fibrous cellulose is measured, for example, as follows. First, a slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement object may be subjected to a defibration treatment similar to the defibration treatment step described below before the treatment with the strongly acidic ion exchange resin. Next, the change in pH is observed while adding aqueous sodium hydroxide solution, and a titration curve like the one shown in the upper part of Figure 1 is obtained. The titration curve shown in the upper part of Figure 1 plots the measured pH against the amount of alkali added, while the titration curve shown in the lower part of Figure 1 plots the pH increment (derivative value) (1 / mmol) against the amount of alkali added. In this neutralization titration, two points of maximum increment (derivative value of pH with respect to the amount of alkali added) are confirmed on the curve plotting the measured pH against the amount of alkali added. Of these, the first maximum increment obtained after starting to add alkali is called the first endpoint, and the next maximum increment obtained is called the second endpoint. The amount of alkali required from the start of titration to the first endpoint is equal to the amount of first dissociated acid from the fibrous cellulose contained in the slurry used for titration; the amount of alkali required from the first endpoint to the second endpoint is equal to the amount of second dissociated acid from the fibrous cellulose contained in the slurry used for titration; and the amount of alkali required from the start of titration to the second endpoint is equal to the total amount of dissociated acid from the fibrous cellulose contained in the slurry used for titration. The amount of alkali required from the start of titration to the first endpoint divided by the solids content (g) in the slurry to be titrated is the amount of phosphorus oxo acid groups introduced (mmol / g). Note that the term "amount of phosphorus oxo acid groups introduced" (or "amount of phosphorus oxo acid groups") simply refers to the amount of first dissociated acid. In Figure 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, if the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the apparent amount of weakly acidic groups in the phosphorus oxoacid group (also referred to herein as the second dissociated acid amount) decreases, and the amount of alkali required in Region 2 is less than the amount required in Region 1. On the other hand, the amount of strongly acidic groups in the phosphorus oxoacid group (also referred to herein as the first dissociated acid amount) corresponds to the amount of phosphorus atoms regardless of whether condensation occurs. Furthermore, if the phosphorus oxoacid group is a phosphite group, the phosphorus oxoacid group no longer contains weakly acidic groups, and the amount of alkali required in Region 2 is reduced or may even be zero. In this case, there is only one point on the titration curve where the pH increment is maximized. The above-mentioned amount of introduced phosphorus oxoacid groups (mmol / g) indicates the amount of phosphorus oxoacid groups in the acid-form fibrous cellulose (hereinafter referred to as the amount of phosphorus oxoacid groups (acid form)) because the denominator indicates the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the phosphorus oxoacid groups are substituted with an arbitrary cation C so as to be charge equivalent, the amount of phosphorus oxoacid groups in the fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of phosphorus oxoacid groups (C form)) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula. Amount of phosphorus oxoacid group (C type) = Amount of phosphorus oxoacid group (acid type) / {1 + (W - 1) × A / 1000} A [mmol / g]: total amount of anions derived from phosphorus oxoacid groups in fibrous cellulose (sum of the amount of strong acidic groups and weak acidic groups in phosphorus oxoacid groups) W: Formula weight per valence of cation C (for example, Na is 23, Al is 9)

[0032] FIG. 2 is a graph showing the relationship between the amount of NaOH added dropwise to fibrous cellulose having carboxy groups and pH. The amount of carboxyl groups introduced into the fibrous cellulose can be measured, for example, as follows. First, a slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement object may be subjected to a defibration treatment similar to the defibration treatment step described below before treatment with the strongly acidic ion exchange resin. Next, a sodium hydroxide aqueous solution is added while observing the change in pH, 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 step described below. As shown in Figure 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) reaches a maximum on the curve plotting the measured pH against the amount of alkali added. This maximum increment is called the first endpoint. Here, the region from the start of the titration to the first endpoint in Figure 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the slurry used for titration. The amount of alkali introduced (mmol / g) was calculated by dividing the amount of alkali (mmol) required in the first region of the titration curve by the solids content (g) in the fine fibrous cellulose-containing slurry to be titrated. The amount of carboxyl groups introduced (mmol / g) is calculated based on the amount of carboxyl groups introduced (mmol / g) when the counter ions of the carboxyl groups are hydrogen ions (H + ) (hereinafter referred to as the amount of carboxy groups (acid type)) per 1 g of fibrous cellulose.

[0033] The above-mentioned amount of carboxy groups introduced (mmol / g) indicates the amount of carboxy groups in the acid-form fibrous cellulose (hereinafter referred to as the amount of carboxy groups (acid form)) because 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 in the fibrous cellulose with the cation C as 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 carboxyl group (C type) = Amount of carboxyl group (acid type) / {1 + (W - 1) × (Amount of carboxyl group (acid type)) / 1000} W: Formula weight per valence of cation C (for example, Na is 23, Al is 9)

[0034] The amount of sulfur oxoacid and sulfonic acid groups introduced into the fine fibrous cellulose can be determined by wet ashing the resulting fibrous cellulose using perchloric acid and concentrated nitric acid, then diluting it at an appropriate ratio and measuring the amount of sulfur by ICP atomic emission spectrometry. The amount of sulfur divided by the bone-dry mass of the fibrous cellulose used is taken as the amount of sulfur oxoacid groups and sulfonic acid groups (unit: mmol / g).

[0035] When measuring the amount of substituents by titration, adding too much sodium hydroxide solution or titrating too quickly can result in lower than expected amounts of substituents, leading to inaccurate values. For example, an appropriate amount and interval is desirable: titrating 10-50 μL of 0.1 N sodium hydroxide solution over 5-30 seconds. To eliminate the influence of carbon dioxide dissolved in the fibrous cellulose-containing slurry, it is also desirable to measure the amount of substituents while blowing an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration until the end of titration. The measurement of the amount of ionic groups by the above-mentioned method is applied to fine fibrous cellulose with a fiber width of 1,000 nm or less. When measuring the amount of ionic groups in pulp fibers with a fiber width of more than 1,000 nm, the pulp fibers are first refined before measurement.

[0036] In the present invention, as described above, the fine fibrous cellulose may be obtained by removing at least a portion of the ionic groups from the fine fibrous cellulose defibrated by introducing the above-mentioned ionic groups. Note that the ionic groups do not have to be completely removed, and it is preferable to remove the ionic groups so that the amount of ionic groups is less than 0.5 mmol / g, for example. In this case, it is preferable to remove the ionic groups from the defibrated fine fibrous cellulose and then perform a uniform dispersion treatment to obtain a fine fibrous cellulose dispersion. By removing the ionic groups, it is possible to obtain a sheet that has excellent shape retention (water resistance) after immersion in water, which is preferable.

[0037] [Method for producing fine fibrous cellulose] (cellulose-containing fiber materials) Fine fibrous cellulose is produced from a fiber raw material containing cellulose. Although the cellulose-containing fiber raw material is not particularly limited, pulp is preferably used because of its ease of availability and low cost. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not limited to, chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen-bleached kraft pulp (OKP), semi-chemical pulps such as semi-chemical pulp (SCP) and chemi-ground wood pulp (CGP), and mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Examples of non-wood pulp include, but are not limited to, cotton-based pulps such as cotton linters and cotton lint, and non-wood pulps such as hemp, straw, bamboo, and bagasse. The deinked pulp is not particularly limited, but may be, for example, deinked pulp made from recycled paper. The pulp of this embodiment may be one of the above types alone or a mixture of two or more types. Among the above pulps, wood pulp and deinked pulp are preferred from the viewpoint of ease of availability. Furthermore, among wood pulps, chemical pulp is more preferred, and kraft pulp and sulfite pulp are even more preferred, from the viewpoint of a high cellulose content, a high yield of fine fibrous cellulose during defibration treatment, and small decomposition of cellulose in the pulp to obtain long-fiber fine fibrous cellulose with a large axial ratio. Note that the use of long-fiber fine fibrous cellulose with a large axial ratio tends to increase viscosity. As a fiber raw material containing cellulose, for example, cellulose contained in sea squirts and bacterial cellulose produced by acetic acid bacteria can be used. 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.

[0038] To obtain the above-mentioned fine fibrous cellulose having ionic groups introduced therein, it is preferable to have an ionic group introduction step for introducing ionic groups 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 an acid treatment step may be included instead of or in addition to the washing step. Examples of the ionic group introduction step include a phosphorus oxo acid group introduction step, a carboxy group introduction step, and a sulfur oxo acid group introduction step. Each of these steps will be explained below.

[0039] (Ionic group introduction step) -Phosphorus oxoacid group introduction process- The phosphorus oxo acid group introduction step involves 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 in the cellulose-containing fiber raw material, thereby obtaining a phosphorus oxo acid group-introduced fiber. In the phosphate group introduction step according to this embodiment, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). Alternatively, the cellulose-containing fiber raw material with compound A may be reacted in the absence of compound B. One example of a method for reacting compound A with a fiber raw material in the presence of compound B is to mix compound A and compound B with a fiber raw material in a dry, wet, or slurry state. Among these methods, using a dry or wet fiber raw material is preferred because of the high uniformity of the reaction, and using a dry fiber raw material is particularly preferred. The form of the fiber raw material is not particularly limited, but is preferably a cotton-like or thin sheet form. Compound A and compound B can be added to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state heated to or above their melting point. Among these methods, adding compound A and compound B in the form of a solution dissolved in a solvent, especially an aqueous solution, is preferred because of the high uniformity of the reaction. Compound A and compound B may be added to the fiber raw material simultaneously, separately, or as a mixture. The method for adding compound A and compound B is not particularly limited. When compound A and compound B are in solution form, the fiber raw material may be immersed in the solution and allowed to absorb the liquid before being removed, or the solution may be added dropwise to the fiber raw material. Alternatively, the required amounts of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material, and then the excess compound A and compound B may be removed by squeezing or filtration.

[0040] The compound A used in this embodiment may be any compound that has a phosphorus atom and can form an ester bond with cellulose, and examples thereof include, but are not limited to, phosphoric acid or a salt thereof, phosphorous acid or a salt thereof, dehydrated condensed phosphoric acid or a salt thereof, and phosphoric anhydride (diphosphorus pentoxide). Phosphoric acid can be used with various purities, such as 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid. Phosphorous acid can be, for example, 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acid is formed by the condensation of two or more molecules of phosphoric acid through a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, and these can be neutralized to various degrees. Among these, phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts of phosphoric acid are preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, and ammonium dihydrogen phosphate are more preferred, from the viewpoints of high efficiency in introducing phosphate groups, easier improvement of defibration efficiency in the defibration step described below, low cost, and ease of industrial application. The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted into the amount of phosphorus atoms, the amount of phosphorus atoms added to the fiber raw material (bone dry mass) is preferably 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to the above upper limit or less, a balance can be achieved between the effect of improving the yield and costs.

[0041] As described above, the compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of the compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, it is preferable to use an aqueous solution of compound B. 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 relative to the fiber raw material (bone dry mass) is not particularly limited, but is preferably, for example, 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, and even more preferably 100% by mass or more and 350% by mass or less.

[0042] In the reaction of a fiber material containing cellulose with compound A, the reaction system may contain, in addition to compound B, amides or amines, for example. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is known to act as a particularly good reaction catalyst.

[0043] In the phosphorus oxo acid group introduction step, it is preferable to add or mix compound A or the like 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 preferably, for example, from 50°C to 300°C, more preferably from 100°C to 250°C, and even more preferably from 130°C to 200°C. Furthermore, various types of equipment having heat transfer media can be used for the heat treatment, including, for example, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized-bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized-bed dryer, a flash dryer, a reduced-pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, and a high-frequency dryer.

[0044] In the heat treatment according to this embodiment, for example, compound A may be added to a thin sheet-like fiber raw material by impregnation or other methods, followed by heating, or heating while kneading or stirring the fiber raw material and compound A in a kneader or the like. This makes it possible to suppress unevenness in the concentration of compound A in the fiber raw material and more uniformly introduce phosphate groups onto the surface of the cellulose fibers contained in the fiber raw material. This is thought to be because, when water molecules move to the surface of the fiber raw material as it dries, dissolved compound A is attracted to the water molecules by surface tension, preventing it from migrating to the surface of the fiber raw material in the same way (i.e., causing unevenness in the concentration of compound A). Furthermore, the heating device used for the heat treatment is preferably one that can constantly discharge, to the outside of the system, moisture contained in the slurry and moisture generated during the dehydration condensation (phosphorylation) reaction between compound A and hydroxyl groups contained in cellulose or the like in the fiber raw material. Examples of such heating devices include an oven with a blower system. Constantly discharging moisture from the system not only suppresses the hydrolysis of phosphate ester bonds, which is the reverse reaction of phosphate esterification, but also suppresses acid hydrolysis of sugar chains in the fiber. This makes it possible to obtain fine fibrous cellulose with a high axial ratio. The heat treatment time is, for example, preferably from 1 second to 300 minutes after the water content has been substantially removed from the fiber raw material, more preferably from 1 second to 1,000 seconds, and even more preferably from 10 seconds to 800 seconds. In this embodiment, the amount of phosphorus oxo acid groups introduced can be kept within a preferred range by setting the heating temperature and heating time within appropriate ranges.

[0045] The phosphorus oxo acid group introduction step may be carried out at least once, but may also be carried out twice or more. By carrying out the phosphorus oxo acid group introduction step twice or more, a large number of phosphorus oxo acid groups can be introduced into the fiber raw material. In the present embodiment, a preferred example is when the phosphorus oxo acid group introduction step is carried out twice.

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

[0047] -Carboxy group introduction process- The carboxyl group introduction process is carried out by treating a fiber raw material containing cellulose with an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, or TEMPO oxidation treatment, 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 group derived from carboxylic acid 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 group derived from carboxylic acid include, but are not limited to, imidized products of acid anhydrides of compounds having carboxy groups, and derivatives of acid anhydrides of compounds having carboxy groups. Examples of imidized products of acid anhydrides of compounds having carboxy groups include, but are not limited to, imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0048] Acid anhydrides of compounds having a group derived from carboxylic acid include, but are not limited to, acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, etc. Furthermore, derivatives of acid anhydrides of compounds having a group derived from carboxylic acid include, but are not limited to, 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 a substituent such as an alkyl group or a phenyl group.

[0049] 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 called 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 carried out under conditions of a pH of 10 to 11. This type of treatment is also called alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be carried out, 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 a fiber raw material. The amount of carboxyl groups introduced into the fiber raw material varies depending on the type of substituent. For example, when carboxyl groups are introduced by TEMPO oxidation, the amount is preferably 0.10 mmol / g or more per gram (mass) of fibrous cellulose, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and particularly preferably 0.90 mmol / g or more. The amount is preferably 2.5 mmol / g or less, more preferably 2.20 mmol / g or less, and even more preferably 2.00 mmol / g or less. Furthermore, when the substituent is a carboxymethyl group, the amount may be 5.8 mmol / g or less per gram (mass) of fibrous cellulose.

[0050] -Sulfur oxoacid group introduction process- The process for producing fine fibrous cellulose may include, for example, a sulfur oxoacid group introduction step as an ionic substituent introduction step, in which hydroxyl groups in a cellulose-containing fiber raw material react with sulfur oxoacids to obtain cellulose fibers having sulfur oxoacid groups (sulfur oxoacid group-introduced fibers).

[0051] In the sulfur oxo acid group introduction step, instead of compound A in the above-described <Phosphorus oxo acid group introduction step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfur oxo acid groups by reacting with hydroxyl groups in cellulose-containing fiber raw materials is used. Compound C may be any compound containing a sulfur atom and capable of forming an ester bond with cellulose, including, but not limited to, sulfuric acid or its salts, sulfurous acid or its salts, and sulfuric acid amides. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid). Sulfurous acid can be 5% aqueous sulfurous acid. Sulfates or sulfites include lithium, sodium, potassium, and ammonium salts of sulfates or sulfites, which can be neutralized to various degrees. Sulfamic acid or the like can be used as the sulfuric acid amide. In the sulfur oxo acid group introduction step, it is preferable to use compound B in the above-described <Phosphorus oxo acid group introduction step> as well.

[0052] In the sulfur oxoacid group introduction step, the cellulose raw material is preferably mixed with an aqueous solution containing a sulfur oxoacid and urea and / or a urea derivative, and then the cellulose raw material is subjected to a heat treatment. The heat treatment temperature is preferably selected so that the sulfur oxoacid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. The heat treatment temperature is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

[0053] In the heat treatment step, heating is preferably carried out until substantially all moisture is removed. Therefore, the heat treatment time varies depending on the moisture content of the cellulose raw material and the amount of aqueous solution containing sulfur oxoacid and urea and / or a urea derivative added, but is preferably set to, for example, 10 seconds or more and 10,000 seconds or less. 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, or high-frequency dryer.

[0054] The amount of sulfur oxoacid groups introduced into the cellulose raw material is preferably 0.05 mmol / g or more, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, and particularly preferably 0.90 mmol / g or more. Furthermore, the amount of sulfur oxoacid groups introduced into the cellulose raw material is preferably 5.00 mmol / g or less, more preferably 3.00 mmol / g or less. By keeping the amount of sulfur oxoacid groups introduced within the above range, it is possible to easily pulverize the fiber raw material and improve the stability of the fibrous cellulose.

[0055] -Oxidation step using a chlorine-based oxidizing agent (second carboxyl group introduction step)- The process for producing fine fibrous cellulose may include, for example, an oxidation step using a chlorine-based oxidizing agent as a step for introducing an ionic substituent. In the oxidation step using a chlorine-based oxidizing agent, the chlorine-based oxidizing agent is added to a wet or dry fiber raw material having a hydroxyl group to cause a reaction, thereby introducing a carboxyl group into the fiber raw material.

[0056] Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorites, chlorous acid, chlorites, chloric acid, chlorates, perchloric acid, perchlorates, chlorine dioxide, etc. From the viewpoints of efficiency of introducing substituents, and therefore defibration efficiency, cost, and ease of handling, sodium hypochlorite, sodium chlorite, and chlorine dioxide are preferred. The chlorine-based oxidizing agent may be added to the fiber raw material as a reagent as it is, or may be dissolved in an appropriate solvent and then added.

[0057] 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% by mass to 1,000% by mass, more preferably from 5% by mass to 500% by mass, and even more preferably from 10% by mass to 100% by mass. The amount of chlorine-based oxidizing agent added per 100 parts by mass of fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 10 parts by mass or more and 10,000 parts by mass or less, and even more preferably 100 parts by mass or more and 5,000 parts by mass or less.

[0058] The reaction time with the chlorine-based oxidizing agent in the oxidation step using the chlorine-based oxidizing agent may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. The pH during the reaction is preferably 5 or more and 15 or less, more preferably 7 or more and 14 or less, and even more preferably 9 or more and 13 or less. At the start of the reaction and during the reaction, the pH is preferably maintained constant (for example, pH 11) by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0059] -Xanthate group introduction process (xanthogen acid esterification process)- The process for producing fine fibrous cellulose may include, for example, a xanthate group introduction process (hereinafter also referred to as a xanthation process) as an ionic substituent introduction process. In the xanthation process, carbon disulfide and an alkali compound are added to a wet or dry fiber raw material having a hydroxyl group to cause a reaction, thereby introducing a xanthate group into the fiber raw material. Specifically, carbon disulfide is added to a fiber raw material that has been converted into alkali cellulose by the method described below, and the reaction is carried out.

[0060] <Alkali cellulose> When introducing ionic functional groups into a fiber raw material, it is preferable to convert the cellulose contained in the fiber raw material into alkali cellulose by treating the cellulose with an alkaline solution. This treatment causes ionic dissociation of some of the hydroxyl groups in the cellulose, thereby increasing its nucleophilicity (reactivity). The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. Due to their high versatility, it is preferable to use, for example, sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, or tetrabutylammonium hydroxide. The conversion into alkali cellulose may be carried out simultaneously with the introduction of ionic functional groups, before the introduction, or at both stages.

[0061] 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.

[0062] The alkaline solution concentration is preferably 0.01 mol / L to 4 mol / L in molar concentration, more preferably 0.1 mol / L to 3 mol / L in molar concentration, and even more preferably 1 mol / L to 2.5 mol / L in molar concentration. In particular, when the treatment temperature is less than 10° C., the concentration is preferably 1 mol / L to 2 mol / L in molar concentration.

[0063] The treatment time for alkali cellulose formation is preferably 1 minute or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more, and the alkali treatment time is preferably 6 hours or less, more preferably 5 hours or less, and even more preferably 4 hours or less.

[0064] By adjusting the type of alkaline solution, treatment temperature, concentration, and immersion time as described above, it is possible to suppress the penetration of the alkaline solution into the crystalline regions of cellulose, making it easier to maintain the crystalline structure of cellulose type I, and increasing the yield of fine fibrous cellulose.

[0065] When the introduction of ionic functional groups and the conversion to alkali cellulose are not carried out simultaneously, the alkali cellulose obtained by the alkali treatment is preferably subjected to solid-liquid separation and water removal using a common deliquoring method such as centrifugation or filtration. This improves the reaction efficiency in the subsequent ionic functional group introduction step. The cellulose fiber concentration after solid-liquid separation is preferably 5% to 50%, more preferably 10% to 40%, and even more preferably 15% to 35%.

[0066] -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 phosphonic or phosphine group (compound E) is used as an essential component. A ), an optional alkali compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having hydroxyl groups and reacted to introduce phosphonic or phosphine groups into the fiber raw material.

[0067] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E AExamples of suitable vinyl phosphonic acids include vinyl phosphonic acid, phenyl vinyl phosphonic acid, phenyl vinyl phosphinic acid, etc. Vinyl phosphonic acid is preferred from the viewpoints of the efficiency of introducing a substituent, and hence the defibration efficiency, cost, and ease of handling. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0068] Compound E A When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0069] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0070] Compound E A The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0071] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 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.

[0072] -Sulfonic acid group introduction step (sulfoalkylation step)- The process for producing fine fibrous cellulose may include, for example, a sulfonic acid group introduction step (sulfoalkylation step) as an ionic substituent introduction 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 alkaline compound, and the aforementioned compound B selected from 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.

[0073] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E B Examples of suitable sulfonates include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, 2-acrylamido-2-methylpropanesulfonic acid, etc. Among these, sodium vinylsulfonate is preferred from the standpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0074] Compound E B The reagent may be added to the fiber raw material as is, or may be dissolved in an appropriate solvent and then 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.

[0075] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0076] Compound E BThe amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0077] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 15 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0078] -Carboxyalkylation step (third carboxy group introduction step)- The process for producing fine fibrous cellulose may include, for example, a carboxyalkylation step as an ionic substituent introduction step. C ), an optional alkaline compound, and the aforementioned compound B selected from 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.

[0079] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E C As the chloroisothiazolinone, monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred from the standpoints of efficiency in introducing substituents, and therefore defibration efficiency, cost, and ease of handling. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0080] Compound E CThe reagent may be added to the fiber raw material as is, or may be dissolved in an appropriate solvent and then 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.

[0081] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0082] Compound E C The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0083] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 3 minutes to 500 minutes, and even more preferably from 5 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0084] -Cationic group introduction step (cationization step)- As an essential component, a compound having a reactive group and a cationic group (compound E D ), an optional alkaline compound, and the aforementioned compound B selected from urea and its derivatives are added to a wet or dry fiber raw material having hydroxyl groups and reacted to introduce cationic groups into the fiber raw material.

[0085] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group).

[0086] Compound E DAs the alkyl group, glycidyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, etc. are preferred from the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling.

[0087] Furthermore, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> as an optional component in the same manner. The amount added is also preferably as described above.

[0088] Compound E D The reagent may be added to the fiber raw material as is, or may be dissolved in an appropriate solvent and then 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 temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0090] Compound E D The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0091] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 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] (Cleaning process) In the method for producing fine fibrous cellulose according to the present embodiment, the ionic group-introduced fibers may be subjected to a washing step as needed. The washing step is carried out by washing the ionic group-introduced fibers with water or an organic solvent, for example. The washing step may be carried out after each step described below, and the number of washing steps carried out in each washing step is not particularly limited.

[0093] (Alkali treatment process) When producing fine fibrous cellulose, the fiber raw material may be subjected to an alkali treatment between the ionic group introduction step and the defibration step described below. The alkali treatment method is not particularly limited, but an example thereof is a method of immersing the ionic group-introduced fiber in an alkali solution. The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. In this embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of their high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. Among these, the solvent contained in the alkaline solution is preferably water or a polar solvent including a polar organic solvent such as an alcohol, and more preferably an aqueous solvent including at least water. As the alkaline solution, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of their high versatility. The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably from 5°C to 80°C, and more preferably from 10°C to 60°C. The immersion time of the ionic group-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably from 5 minutes to 30 minutes, and more preferably from 10 minutes to 20 minutes. The amount of alkaline solution used in the alkaline treatment is not particularly limited, but is preferably from 100% by mass to 100,000% by mass, and more preferably from 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the ionic group-introduced fiber. When the fine fibrous cellulose has anionic groups, the alkali treatment may be a neutralization treatment or ion exchange treatment of the anionic groups. In this case, the temperature of the alkali solution is preferably room temperature.

[0094] In order to reduce the amount of alkaline solution used in the alkaline treatment step, the ionic group-introduced fiber may be washed with water or an organic solvent after the ionic group-introducing step and before the alkaline treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkaline-treated ionic group-introduced fiber with water or an organic solvent after the alkaline treatment step and before the defibrating treatment step.

[0095] (Acid treatment process) When producing fine fibrous cellulose, the fiber raw material may be subjected to an acid treatment between the step of introducing ionic groups and the defibration treatment step described below. For example, the ionic group 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 examples include a method of immersing the fiber raw material in an acid-containing acid solution. The concentration of the acid solution used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less. The pH of the acid solution used is also not particularly limited, but is preferably 0 to 4, and more preferably 1 to 3. Examples of the acid contained in the acid solution include inorganic acids, sulfonic acids, and carboxylic acids. Examples of inorganic acids include sulfuric acid, nitric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid. Among these, hydrochloric acid or sulfuric acid is particularly preferred. The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably from 5°C to 100°C, and more preferably from 20°C to 90°C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is 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 preferably from 100% to 100,000% by mass, and more preferably from 1,000% to 10,000% by mass, based on the absolute dry mass of the fiber raw material.

[0096] (Defibrillation process) By subjecting the ionic group-introduced fibers to defibration treatment in a defibration treatment step, fine fibrous cellulose can be obtained. In the defibration treatment step, for example, a defibration treatment device can be used. The defibration treatment device is not particularly limited, but examples that can be used include a high-speed defibrator, grinder (stone mill-type grinder), high-pressure homogenizer, ultra-high-pressure homogenizer, high-pressure collision grinder, ball mill, bead mill, disk-type refiner, conical refiner, twin-screw kneader, vibration mill, homomixer under high-speed rotation, ultrasonic disperser, or beater. Among the above defibration treatment devices, it is more preferable to use a high-speed defibrator, high-pressure homogenizer, or 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 group-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 solid content 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 solid components other than the phosphorus oxo acid group-introduced fibers, such as urea having hydrogen bonding properties.

[0099] (Method of producing fine fibrous cellulose from which substituents have been removed) In the present invention, the fine fibrous cellulose may be obtained by removing the ionic groups as substituents from the fine fibrous cellulose which has been defibrated by introducing the above-mentioned ionic groups. In this case, it is preferable to include a step (Step I) of removing at least a portion of the substituents from fine fibrous cellulose having a substituent, preferably an ionic group, and a fiber width of 1000 nm or less, and a step II of uniformly dispersing the cellulose after Step I. Furthermore, the fine fibrous cellulose to be subjected to step I preferably undergoes a step of reducing the nitrogen content (nitrogen removal treatment step) before the defibration treatment.

[0100] -Nitrogen removal treatment process- The process for producing the fine fibrous cellulose subjected to Step I may further include a step of reducing the nitrogen content (nitrogen removal treatment step). By reducing the nitrogen content, it is possible to obtain fine fibrous cellulose that can further suppress discoloration. The nitrogen removal treatment step may be carried out after the uniform dispersion treatment step in Step II described below, but is preferably carried out before the uniform dispersion treatment step in Step II described below. It is also preferably carried out before the above-mentioned defibration treatment step.

[0101] In the nitrogen removal treatment step, it is preferable to adjust the pH of the slurry containing the anionic group-introduced fiber to 10 or more and then perform a heat treatment. In the heat treatment, the liquid temperature of the slurry is preferably 50°C or more and 100°C or less, and the heating time is preferably 15 minutes or more and 180 minutes or less. When adjusting the pH of the slurry containing the anionic group-introduced fiber, it is preferable to add an alkali compound that can be used in the above-mentioned alkali treatment step to the slurry.

[0102] After the nitrogen removal treatment step, the anionic group-introduced fiber may be subjected to a washing step, if necessary. The washing step is carried out by washing the anionic group-introduced fiber with, for example, water or an organic solvent. The number of washings carried out in each washing step is not particularly limited.

[0103] -Process I- In the present invention, the method for producing fine fibrous cellulose may include a step (Step I) of removing at least a portion of the substituents from fine fibrous cellulose having substituents and having a fiber width of 1000 nm or less. In this specification, the step (Step I) of removing at least a portion of the substituents from the fine fibrous cellulose is also referred to as a substituent removal treatment step.

[0104] Examples of the substituent removal treatment step include a step of heat treating, enzyme treating, acid treating, alkali treating, etc., fine fibrous cellulose having substituents and a fiber width of 1000 nm or less. These may be performed alone or in combination. Among these, the substituent removal treatment step is preferably a heat treating step or an enzyme treating step. By undergoing the above treatment steps, at least a portion of the substituents is removed from the fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, and for example, fine fibrous cellulose having an introduced amount of substituents of less than 0.5 mmol / g can be obtained. The amount of introduced substituents after the substituent removal treatment step is preferably 0.3 mmol / g or less, more preferably 0.2 mmol / g or less, and even more preferably 0.1 mmol / g or less.

[0105] The substituent removal treatment step is preferably carried out in the form of a slurry. That is, the substituent removal treatment step is preferably a step of subjecting a slurry containing a substituent-containing fine fibrous cellulose having a fiber width of 1000 nm or less to a heat treatment, an enzyme treatment, an acid treatment, an alkali treatment, or the like. By carrying out the substituent removal treatment step in the form of a slurry, it is possible to prevent the residue of colored substances generated by heating or the like during the substituent removal treatment, as well as acids, alkalis, salts, and the like that are added or generated. This makes it possible to suppress coloration when the fine fibrous cellulose obtained through step II is made into a slurry or sheet. Furthermore, when a treatment is carried out to remove salts derived from the substituents removed after the substituent removal treatment, it is also possible to increase the efficiency of salt removal.

[0106] When a substituent removal treatment is performed on a slurry containing fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, the concentration of the fine fibrous cellulose in the slurry is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. The concentration of the fine fibrous cellulose in the slurry is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. By controlling the concentration of the fine fibrous cellulose in the slurry within the above range, the substituent removal treatment can be performed more efficiently. Furthermore, by controlling the concentration of the fine fibrous cellulose in the slurry within the above range, it is possible to prevent the residue of colored substances caused by heating or the like during the substituent removal treatment, as well as added or generated acids, alkalis, salts, etc. This can suppress coloration when the fine fibrous cellulose obtained through Step II is made into a slurry or sheet. Furthermore, when a treatment is performed to remove salts derived from the removed substituents after the substituent removal treatment, it is also possible to increase the efficiency of salt removal.

[0107] When the substituent removal treatment step is a step of heat-treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, the heating temperature in the heat treatment step is preferably 40° C. or higher, more preferably 50° C. or higher, and even more preferably 60° C. or higher. The heating temperature in the heat treatment step is preferably 250° C. or lower, more preferably 230° C. or lower, and even more preferably 200° C. or lower. In particular, when the substituent on the fine fibrous cellulose subjected to the substituent removal treatment step is a phosphorus oxo acid group or a sulfone group, the heating temperature in the heat treatment step is preferably 80° C. or higher, more preferably 100° C. or higher, and even more preferably 120° C. or higher.

[0108] 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 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.

[0109] When the substituent removal treatment step is a step of enzymatically treating fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, it is preferable to use a phosphate ester hydrolase, a sulfate ester hydrolase, or the like in the enzymatic treatment step depending on the type of substituent. In the enzyme treatment step, the enzyme is added so that the enzymatic activity per 1 g of fine fibrous cellulose is preferably 0.1 nkat or more, more preferably 1.0 nkat or more, and even more preferably 10 nkat or more. Furthermore, the enzyme is added so that the enzymatic activity per 1 g of fine fibrous cellulose is preferably 100,000 nkat or less, more preferably 50,000 nkat or less, and even more preferably 10,000 nkat or less. After adding the enzyme to the fine fibrous cellulose dispersion (slurry), it is preferable to treat it at a temperature of 0°C or higher and lower than 50°C for 1 minute to 100 hours. After the enzymatic reaction, a step of deactivating the enzyme may be carried out. Examples of methods for deactivating the enzyme include adding an acid or alkali component to the enzymatically treated slurry to deactivate the enzyme, and raising the temperature of the enzymatically treated slurry to 90°C or higher to deactivate the enzyme.

[0110] When the substituent removal treatment step is a step of acid treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, it is preferable to add an acid compound that can be used in the acid treatment step described above to the slurry in the acid treatment step.

[0111] When the substituent removal treatment step is a step of alkali treating fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, it is preferable to add an alkali compound that can be used in the alkali treatment step described above to the slurry in the alkali treatment step.

[0112] 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.

[0113] In the substituent removal treatment step, spacer molecules may be added. The spacer molecules penetrate between adjacent fine fibrous cellulose particles, thereby acting as spacers to create fine spaces between the fine fibrous cellulose particles. Adding such spacer molecules in the substituent removal treatment step can suppress aggregation of the fine fibrous cellulose after the substituent removal treatment. This can more effectively improve the transparency of dispersions and sheets containing fine fibrous cellulose. 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). Additionally, 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, cationic starch, raw starch, oxidized starch, etherified starch, esterified starch, starches such as amylose, glycerin, diglycerin, polyglycerin, hyaluronic acid, and metal salts of hyaluronic acid.

[0114] 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.

[0115] -pH adjustment process- When the 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, anionic groups are introduced into the cellulose fibers, and the counter ions of the anionic groups are 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, the decomposition of cellulose may produce monosaccharides, which are one of the causes of discoloration, so it is preferable to adjust the pH of the slurry to 8 or less. Similarly, monosaccharides may be produced under acidic conditions, so it is preferable to adjust the pH of the slurry to 3 or more.

[0116] Furthermore, when the substituted fine fibrous cellulose is a phosphate-containing fine fibrous cellulose, it is preferable that the phosphorus of the phosphate group is susceptible to nucleophilic attack in order to improve the efficiency of removing the substituent. The phosphorus susceptible to nucleophilic attack is cellulose-OP(=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.

[0117] 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 either an inorganic alkali compound or an organic alkali compound. Examples of inorganic alkali compounds include lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium bicarbonate, potassium carbonate, potassium bicarbonate, sodium carbonate, and sodium bicarbonate. Examples of organic alkali compounds include ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, butylamine, diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, cyclohexylamine, aniline, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, pyridine, and N,N-dimethyl-4-aminopyridine.

[0118] In addition, in the pH adjustment step, an ion exchange treatment may be performed to adjust the pH. A strong acid cation exchange resin or a weak acid ion exchange resin can be used in the ion exchange treatment. By treating with an appropriate amount of cation exchange resin for a sufficient time, a slurry containing fine fibrous cellulose with the desired pH can be obtained. Furthermore, in the pH adjustment step, the addition of an acid component or an alkali component may be combined with the ion exchange treatment.

[0119] <Salt removal treatment> After the substituent removal treatment step, it is preferable to carry out a treatment to remove salts derived from the removed substituents. Removing the salts derived from the substituents makes it easier to obtain fine fibrous cellulose that can suppress coloration. The means for removing the salts derived from the substituents is not particularly limited, but examples include washing treatment and ion exchange treatment. The washing treatment is carried out by washing the fine fibrous cellulose that has aggregated in the substituent removal treatment with water or an organic solvent. In the ion exchange treatment, an ion exchange resin can be used.

[0120] -Process II- In this embodiment, the method for producing fine fibrous cellulose may include a step (Step I) of removing at least a portion of the substituents from fine fibrous cellulose having a substituent and a fiber width of 1000 nm or less, and a step (Step II) of performing a uniform dispersion treatment after Step I. The uniform dispersion treatment step (Step II) is a step of uniformly dispersing the fine fibrous cellulose obtained through the substituent removal treatment in Step I. In Step I, the fine fibrous cellulose is subjected to the substituent removal treatment, thereby causing at least a portion of the fine fibrous cellulose to aggregate. Step II is a step of uniformly dispersing the aggregated fine fibrous cellulose. In Step II, the state in which the fine fibrous cellulose is uniformly dispersed refers to a state in which the fiber width of the fine fibrous cellulose is 10 nm or less. Thus, the fine fibrous cellulose obtained in this embodiment has a fiber width of 10 nm or less, even though the amount of introduced substituents is low, for example, less than 0.5 mmol / g.

[0121] In the uniform dispersion treatment step (step II), 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. The treatment conditions for the uniform dispersion treatment step (Step II) are not particularly limited, but it is preferable to increase the maximum movement speed of the fine fibrous cellulose during treatment and the pressure during treatment. In a high-speed defibrator, the peripheral speed is preferably 20 m / sec or more, more preferably 25 m / sec or more, and even more preferably 30 m / sec or more. A high-pressure homogenizer is more preferably used because it has a higher maximum movement speed of the fine fibrous cellulose during treatment and a higher pressure during treatment than a high-speed defibrator. In high-pressure homogenizer treatment, the pressure during treatment is preferably 1 MPa or more and 350 MPa or less, more preferably 10 MPa or more and 300 MPa or less, and even more preferably 50 MPa or more and 250 MPa or less.

[0122] In Step II, the above-mentioned spacer molecules may be added. By adding such spacer molecules in the uniform dispersion treatment step of Step II, the fine fibrous cellulose can be dispersed more smoothly and uniformly. This makes it possible to more effectively improve the transparency of the dispersion or sheet containing the fine fibrous cellulose.

[0123] From the viewpoint of sheet transparency and enabling the formation of fine patterns, the content of fine fibrous cellulose in the solid content of the sheet is preferably 10% by mass or more, more preferably 50% by mass or more, even more preferably 65% ​​by mass or more, and preferably 100% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less. As the fine fibrous cellulose, a fine fibrous cellulose containing an ionic group and an unmodified fine fibrous cellulose may be used in combination.

[0124] <Hydrophilic polymer> In the present invention, the sheet preferably contains a hydrophilic polymer. Examples of hydrophilic polymers include carboxyvinyl polymers, polyvinyl alcohol, alkyl methacrylate-acrylic acid copolymers, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylates such as sodium polyacrylate, alkyl acrylate copolymers, urethane copolymers, modified polyesters, modified polyimides, polyalkylene glycols such as polyethylene glycol and polypropylene glycol, polycations such as polyacrylamide and polyethyleneimine, polyanions, amphoteric polymers, xanthan gum, guar gum, tamarind gum, carrageenan, locust bean gum, and quince seeds. Examples of the hydrophilic polymer include thickening polysaccharides such as alginic acid, metal salts of alginic acid, pullulan, sacran, and pectin; cellulose derivatives such as carboxymethylcellulose, carboxyethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, and hydroxyethylcellulose; starches such as cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, dextrin, and amylose; glycerins such as polyglycerin; hyaluronic acid, metal salts of hyaluronic acid; and proteins such as casein. Also, copolymers of these hydrophilic polymers may be used. The cellulose derivative is preferably a cellulose ether.

[0125] As the hydrophilic polymer, from the viewpoint of obtaining a sheet having excellent transparency and flexibility and a finely textured shape, and from the viewpoint of affinity for biopolymers, it is preferable to use at least one selected from the group consisting of polyvinyl alcohol, modified polyvinyl alcohol, polyalkylene glycol, polyalkylene oxide, and cellulose ether, and it is more preferable to use at least one selected from the group consisting of polyethylene oxide, polyvinyl alcohol, and cellulose ether. The polyvinyl alcohol is a partially saponified or completely saponified polyvinyl alcohol. Examples of modified polyvinyl alcohol include ethylene-modified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, silicon-modified polyvinyl alcohol, acetoacetyl-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, etc. Among these, acetoacetyl-modified polyvinyl alcohol is preferred. The polyalkylene glycol has an average molecular weight of 20,000 or less, and examples thereof include polyethylene glycol, polypropylene glycol, and polybutylene glycol, with polyethylene glycol and polypropylene glycol being preferred, and polyethylene glycol being more preferred. The polyalkylene oxide has a viscosity-average molecular weight of more than 20,000, and examples thereof include polyethylene oxide, polypropylene oxide, and polybutylene oxide, preferably polyethylene oxide and polypropylene oxide, and more preferably polyethylene oxide. From the viewpoint of obtaining a sheet excellent in strength and biopolymer adsorption, the viscosity-average molecular weight of the polyalkylene oxide is preferably 200,000 or more, more preferably more than 500,000, even more preferably 1,000,000 or more, still more preferably 2,000,000 or more, particularly preferably 3,000,000 or more, and preferably 10,000,000 or less, more preferably 8,000,000 or less, and even more preferably 6,000,000 or less.

[0126] Cellulose ether is a compound in which the hydroxyl groups of cellulose are converted into ethers. Preferred examples of cellulose ethers include hydroxypropyl methylcellulose, hydroxyethyl cellulose, hydroxyethyl methylcellulose, methylcellulose, carboxyethyl cellulose, and carboxymethyl cellulose. Among these, hydroxypropyl methylcellulose, hydroxyethyl cellulose, hydroxyethyl methylcellulose, methylcellulose, and carboxymethyl cellulose are more preferred, and hydroxypropyl methylcellulose is even more preferred. The weight average molecular weight of the cellulose ether is preferably 1.0×10 to obtain a sheet excellent in strength and biopolymer adsorption. 4 More preferably, 3.0 × 104 More preferably, 5.0 × 10 4 and preferably 1.0×10 6 Less than or equal to 5.0 × 10 5 or less, more preferably 3.0 × 10 5 The weight average molecular weight of the cellulose ether is measured by gel permeation chromatography (GPC). Furthermore, from the viewpoint of obtaining a sheet having excellent strength and biopolymer adsorption properties, the degree of substitution of the cellulose ether is, overall, preferably 0.4 or more, more preferably 0.6 or more, even more preferably 0.8 or more, and even more preferably 1.0 or more, and is preferably 2.8 or less, more preferably 2.5 or less, and even more preferably 2.3 or less. Furthermore, when the cellulose ether is hydroxypropyl methylcellulose or hydroxyethyl methylcellulose, the molar substitution of hydroxypropoxy groups or hydroxyethoxy groups is preferably 0.01 or more, more preferably 0.05 or more, even more preferably 0.10 or more, and preferably 0.50 or less, more preferably 0.40 or less, even more preferably 0.30 or less. Here, the degree of substitution means the average number of hydroxyl groups substituted with a substituent per glucose ring unit of cellulose, and the number of moles of substitution means the average number of moles of substituents added per glucose ring unit.

[0127] When the sheet contains a hydrophilic polymer, the content of the hydrophilic polymer per 100 parts by mass of fine fibrous cellulose is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, from the viewpoints of excellent strength and transparency, forming a fine uneven shape, and improving affinity for biopolymers, and is preferably 400 parts by mass or less, more preferably 100 parts by mass or less, even more preferably 50 parts by mass or less. When the sheet contains a cellulose ether as a hydrophilic polymer, the content of cellulose ether per 100 parts by mass of fine fibrous cellulose is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, from the viewpoints of excellent strength and transparency, having a fine uneven shape, and improving affinity for biopolymers, and is preferably 400 parts by mass or less, more preferably 300 parts by mass or less, even more preferably 200 parts by mass or less.

[0128] In this embodiment, the total content of fine fibrous cellulose and hydrophilic polymer in the solid content of the sheet is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, from the viewpoints of obtaining high transparency, forming a fine uneven shape, and affinity with biopolymers, and is 100% by mass or less, with 100% by mass being particularly preferred.

[0129] <Other ingredients> In addition to the fine fibrous cellulose and hydrophilic polymer, the sheet may contain, for example, one or more selected from paper strength agents, thermoplastic resins (excluding hydrophilic polymers), surfactants, organic ions, coupling agents, inorganic layered compounds, inorganic compounds, leveling agents, preservatives, antifoaming agents, organic particles, lubricants, antistatic agents, UV protection agents, dyes, pigments, stabilizers, magnetic powders, alignment promoters, plasticizers, dispersants, and crosslinking agents. Among these, wet strength agents are preferred, such as polyamine polyamide epichlorohydrin (PAE), urea formaldehyde resin, and melamine formaldehyde resin. The content of the wet strength agent is not particularly limited, but when added, it is preferably 0.05 parts by mass or more, more preferably 0.07 parts by mass or more, and preferably 1.0 part by mass or less, more preferably 0.7 part by mass or less, per 100 parts by mass of fine fibrous cellulose (bone dry mass). The addition of a paper strength agent, preferably a wet strength agent, is preferred because it allows for a sheet to be obtained that has excellent shape retention (water resistance) after immersion in water. Furthermore, from the viewpoint of imparting water resistance, the sheet may contain a thermoplastic resin (excluding hydrophilic polymers), and examples of the thermoplastic resin include polyolefin resins such as polyethylene resin and polypropylene resin. The thermoplastic resin is preferably added to the sheet raw material in the form of an emulsion. The content of the thermoplastic resin is not particularly limited, but when a thermoplastic resin is added, it is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and preferably 50 parts by mass or less, more preferably 30 parts by mass or less, per 100 parts by mass of the fine fibrous cellulose (bone dry mass). The sheet may contain a solvent, such as water or an organic solvent, such as a polar organic solvent, which are exemplified as the dispersion medium in the defibration treatment step.

[0130] The content of the solvent including water in the sheet is, for example, preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 5% by mass or more, based on the total mass of the sheet. This allows the sheet to be flexible. On the other hand, the content of the solvent in the sheet is, for example, more preferably 15% by mass or less, based on the total mass of the sheet. This allows a sheet that is excellent in transferability of the surface shape of the substrate to be obtained only when it is in a wet state.

[0131] The solvent contained in the sheet is preferably water. The water content (mass%) in the sheet can be calculated, for example, by the following procedure. First, a 100 mm square sheet is conditioned for 24 hours under conditions of a temperature of 23°C and a relative humidity of 50%, and then the mass of the sheet, W0, is measured. Next, this sheet is dried in a constant temperature dryer at 105°C for 16 hours, and then the mass of the sheet, W1, is measured. From the measured mass, the solvent content in the sheet is calculated according to the following formula 2. (Equation 2) Water content in sheet = (1 - W1 / W0) x 100

[0132] <Sheet characteristics> [Haze] The sheet of this embodiment has a haze of 80% or less. When the haze is 80% or less, the sheet has excellent transparency, and the adsorption of biopolymers to the sheet can be easily analyzed and observed, for example, using an optical microscope or image analysis. The haze of the sheet is preferably 60% or less, more preferably 50% or less, even more preferably 30% or less, still more preferably 10% or less, particularly preferably 5% or less, and most preferably 3% or less. Forming a textured surface tends to increase haze, but as will be described later, forming the textured surface using a fine structure (for example, nanodot array (Japan registered trademark)) in which the average spacing Sm of the textured surface is 10 nm or more and 500 nm or less is preferable because it results in a sheet with low haze. The haze of the sheet is measured in accordance with JIS K 7136:2000 using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.).

[0133] [Total light transmittance] The sheet of this embodiment preferably has excellent transparency, and the total light transmittance of the sheet is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The upper limit of the total light transmittance of the sheet is not particularly limited, and may be, for example, 100%. Here, the total light transmittance of the sheet is a value measured, for example, in accordance with JIS K 7361-1:1997 using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.).

[0134] [Uneven shape] The sheet of this embodiment has an uneven shape on at least one surface. Note that the sheet of this embodiment may have an uneven shape on at least one surface, and may also have an uneven shape on the other surface, which may be selected appropriately depending on the application. (Average spacing of uneven shapes Sm) The average spacing Sm of the uneven shape is 60 μm or less from the viewpoint of significantly increasing the surface area, and is preferably 45 μm or less, more preferably 10 μm or less, even more preferably 1 μm or less, still more preferably 500 nm or less, and particularly preferably 200 nm or less. The lower limit of the average spacing Sm of the uneven shape is not particularly limited, but from the viewpoint of ease of production, it is preferably 10 nm or more, more preferably 30 nm or more, and even more preferably 50 nm or more. In the present invention, the uneven shape is preferably formed by transferring a fine structure having an average spacing Sm of 10 nm to 500 nm. The fine structure is preferably a scattered fine structure. The fine structure and the transfer of the fine structure will be described later. The mean spacing Sm of unevenness is measured in accordance with JIS B 0601:1994 and refers to the average length of the roughness curve elements. A reference length L is extracted from the roughness curve in the direction of the mean line, and the sum of the lengths of the mean lines corresponding to one peak and one adjacent valley is calculated, and the average value is expressed. In the case of finer irregularities, it is difficult to measure in accordance with JIS B 0601: 1994. In such cases, the irregular surface is used as the observation surface, and the length of the interval between the bases of the irregularities is measured at 10 points, and the average value is taken as Sm. Specifically, it is measured by the method described in the Examples. When the unevenness is a fine uneven shape with an average spacing Sm of 1 μm or less, a sheet with particularly small haze and excellent transparency can be obtained, which is preferable.

[0135] (arithmetic mean roughness Ra) In the sheet of this embodiment, the arithmetic mean height of the surface having the uneven shape is preferably 700 nm or less, more preferably 600 nm or less, even more preferably 300 nm or less, and even more preferably 150 nm or less, from the viewpoint of obtaining a sheet with low haze and excellent transparency, and the lower limit is not particularly limited, but from the viewpoint of ease of production, it is preferably 10 nm or more, more preferably 30 nm or more, and even more preferably 50 nm or more. The arithmetic mean roughness Ra is measured in accordance with JIS B 0601:1994, and is calculated by extracting a reference length L from the roughness curve in the direction of the mean line, and then averaging the absolute values ​​of the deviations from the mean line of this extracted section to the measurement curve. Specifically, it is measured by the method described in the Examples.

[0136] (Type of uneven shape) In this embodiment, the uneven shape on the sheet surface is not particularly limited, and may be either a periodic uneven shape or a non-periodic uneven shape, but a periodic uneven shape is preferable from the viewpoint of being able to form a finer uneven shape. The periodic uneven shape may be a recess (groove) extending in one direction on the surface, or may be a shape having scattered recesses or protrusions, but from the viewpoint of more effectively increasing the surface area, scattered uneven shapes are preferable, and from the viewpoint of ease of manufacturing, an uneven shape with scattered recesses is preferable. As will be described later, the above-mentioned uneven shape is preferably formed by transferring the surface shape of a transfer substrate having unevenness (hereinafter also referred to as "uneven transfer substrate").

[0137] [Thickness] In this embodiment, from the viewpoints of strength, transparency, and economy, the thickness of the sheet is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, and preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less. The thickness of the sheet can be measured using a constant pressure thickness gauge (PG-02, manufactured by TECLOCK CORPORATION). Specifically, a sheet cut into a size of 50 mm square or larger is conditioned at 23°C and a relative humidity of 50% for 24 hours, and then the thickness is measured at four arbitrary points, and the average value is taken as the thickness of the sheet.

[0138] [Basis weight and density] The basis weight of the sheet is not particularly limited, but is preferably 5 g / m 2 More preferably, 10 g / m 2 More preferably, 20 g / m 2 and preferably 300 g / m 2 or less, more preferably 200 g / m 2 More preferably, 100 g / m or less 2 Here, the basis weight of the sheet is a value calculated according to the following method. Specifically, a sheet cut into a size of 50 mm square or larger is conditioned at 23°C and a relative humidity of 50% for 24 hours, and then the mass is measured and divided by the area of ​​the cut sheet to calculate the basis weight of the sheet. The density of the sheet is not particularly limited, but is preferably 0.1 g / cm 3 More preferably, 0.5 g / cm 3 More preferably, 0.8 g / cm 3 and preferably 5.0 g / cm 3 or less, more preferably 3.0 g / cm 3 or less, more preferably 1.7 g / cm 3 Here, the density of the sheet can be calculated by measuring the thickness and mass of a 50 mm square sheet after humidifying it under conditions of 23° C. and 50% RH for 24 hours.

[0139] <Use of the sheet> The use of the sheet of this embodiment is not particularly limited, but it is preferably a sheet for adsorbing biopolymers. Biopolymers refer to high molecular weight organic compounds present in living organisms, and examples include carbohydrates, proteins (enzymes, peptides), nucleic acids, and glycoproteins. In addition, in the present invention, biopolymers include biological tissues and cells. Among these, the sheet of the present embodiment preferably has at least the function of adsorbing proteins, and more preferably also has the ability to adsorb biological tissues and cells. It is expected that the sheet can be used to quantify the amount of a specific protein in a sample by reacting an antibody against the protein adsorbed onto the sheet, or to quantify the amount of a specific protein expressed in cells by adsorbing cells onto the sheet. The sheet of this embodiment is not limited to the uses described above, and may be used, for example, as an anti-glare film, an anti-reflection film, a soundproofing film, or an adsorption film for dust and dirt, and is not particularly limited thereto.

[0140] [Sheet manufacturing method] The method for producing the sheet of the present embodiment is preferably selected from the group consisting of the following methods A, B, and C. The sheet of the present embodiment described above is preferably produced by any one of the following methods A to C. Method A: A method for producing a sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less, the sheet having an uneven shape on at least one surface, a haze of 80% or less, and an average spacing Sm of the uneven shapes of 60 μm or less, the method comprising the following steps A1 and A2 in this order: Step A1: A step of spreading a liquid sheet raw material containing fine fibrous cellulose having a fiber width of 1000 nm or less on a substrate having an uneven surface. Step A2: A step of drying the sheet material in this state to obtain a sheet with the concave-convex pattern transferred thereto. Method B: A method for producing a sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less, the sheet having an uneven shape on at least one surface, a haze of 80% or less, and an average spacing Sm of the uneven shapes of 60 μm or less, the method comprising the following steps B1 and B2 in this order: Step B1: A step of placing a sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less on a substrate having an uneven surface to obtain a laminate. Step B2: A step of pressing the laminate under heat to transfer the concave-convex pattern Method C: A method for producing a sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less, the sheet having an uneven shape on at least one surface, a haze of 80% or less, and an average spacing Sm of the uneven shapes of 60 μm or less, the method comprising the following steps C1 to C3 in this order: Step C1: A step of placing a wet sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less on a substrate having an uneven surface to obtain a laminate. Step C2: Pressurizing the laminate to adhere the sheet to the substrate Step C3: A step of drying the sheet while it is in close contact with the substrate to obtain a sheet with the concave-convex pattern transferred thereto.

[0141] Below, we will explain Method A, and then Methods B and C. <Method A> Method A includes the following steps A1 and A2 in this order. Step A1: A step of spreading a liquid sheet raw material containing fine fibrous cellulose having a fiber width of 1000 nm or less on a substrate having an uneven surface. Step A2: A step of drying the sheet material in this state to obtain a sheet with the concave-convex pattern transferred thereto.

[0142] [Process A1] The liquid sheet raw material used in step A1, which contains a substrate having irregularities and fine fibrous cellulose with a fiber width of 1000 nm or less, will be described. (Uneven substrate) The substrate having the irregularities is not particularly limited as long as the average spacing Sm of the irregularities in the resulting sheet is 60 μm or less. The material of the substrate having the irregularities is not particularly limited, but from the viewpoint of unfolding the sheet material, it is preferable that the surface shape does not change when the sheet material is unfolded. Specifically, the surface of the substrate is preferably formed of a material selected from metal, silicon, ceramics, plastic, glass, and rubber.

[0143] Examples of the substrate having a porous irregular shape include a membrane filter, a glass filter, a release paper, a metal mesh, and the like. Membrane filters are commercially available from ADVANTEC, GVS, and the like, and can be appropriately selected depending on the desired average spacing Sm of the concave-convex shape. That is, a membrane filter can be appropriately selected so as to obtain the desired average spacing Sm of the concave-convex shape. When a membrane filter is used as a substrate having concave-convex shapes, the concave-convex shape formed is not one that corresponds to the filter pore size, but generally, a concave-convex shape with Sm of, for example, about 10 μm or more and 60 μm or less is formed. Furthermore, the concave-convex shape does not have a clear periodicity.

[0144] Examples of substrates having a structure (convex or concave shape) extending in one direction on the order of micrometers to nanometers as the uneven shape include lenticular lenses and Nanobuckling (registered trademark of Japan). Nanobuckling is a sheet having a nanobuckling shape, which is obtained by compressing a hard layer provided on one side of a film substrate in approximately one direction, resulting in a meandering deformation. Nanobuckling can be obtained, for example, by methods described in JP 2011-224916 A and JP 2008-302591 A. For example, when a nanobuckling shape is produced by heat shrinkage, the heat-shrunk sheet itself can be used as the nanobuckling, or the shape of the heat-shrunk sheet can be transferred to form a substrate with irregularities; there are no particular limitations. Nanobuckling sheets, such as those commercially available from Oji F-Tex Co., Ltd., can also be used. The nanobuckling sheet is, for example, a laminate of a PET film and an acrylic resin layer, with a nanobuckling structure having multiple meandering, wavy ridges formed in the acrylic resin layer. Fig. 3 is a cross-sectional perspective view showing an example of a nanobuckling sheet. In Fig. 3, nanobuckling sheet 10 includes substrate 11 and hard layer 12 provided on one side of substrate 11, and hard layer 12 has an uneven shape 12a. Uneven shape 12a has wavy unevenness that runs along approximately one direction, and the wavy unevenness meanders, with recessed bottoms 12b.

[0145] Examples of substrates having a textured shape with scattered fine structures (convex or concave shapes) on the order of micrometers to nanometers include nanodot arrays (registered Japanese trademarks) and moth-eye structures, as well as fine structures produced by electron beam lithography, interference exposure, anodic oxidation, etc. A nanodot array is a substrate on which nano-sized protrusions are formed in the form of dots, and can be obtained by molding various resin substrates such as acrylic resin, polystyrene resin, polycarbonate resin, and cycloolefin resin, or by directly processing silicon, quartz glass, etc. Nanodot arrays can be designed with a variety of dot shapes, average spacing between dots, dot height, etc. Fig. 4 is a cross-sectional perspective view showing an example of a nanodot array. In Fig. 4, the nanodot array includes a substrate 14 and conical protrusions 116c formed periodically on one side of the substrate 14, spaced apart like dots. Fig. 5 is a cross-sectional perspective view showing another example of a nanodot array. In Fig. 5, the nanodot array includes a substrate 14 and sinusoidal protrusions 116a formed periodically on one side of the substrate 14, spaced apart like dots. The shape of the convex portion is not limited to a conical or sinusoidal shape, but may be a truncated conical shape, a cylindrical shape, or the like. Examples of substrates having a moth-eye structure include moth-eye structure films (e.g., moth-eye anti-reflection films) manufactured by Geomatec Co., Ltd. and Mitsubishi Chemical Corporation. For a method for producing a film having a moth-eye structure, see, for example, JP 2020-076996 A. The method for manufacturing the above-described microstructure is not particularly limited, and examples thereof include colloidal lithography, as described in JP-A-2009-034630, electron beam lithography, interference exposure, and anodic oxidation. Furthermore, the fine structure is not limited to a convex shape, and for example, when concaves and convexes are transferred using the nanoimprint mold described in JP 2009-034630 A, the convex shape will be transferred to the sheet of the present invention. Thus, when transferring a convex shape, among Methods A to C, Method A is particularly suitable. When a substrate having a microstructure is used as the substrate, the sheet of the present invention to which the uneven shape is transferred has an uneven structure in the three-dimensional direction, and in the two-dimensional direction, for example, has a triangular lattice arrangement, a square lattice arrangement, a random arrangement, etc.

[0146] The substrate having the irregularities may have a release layer on its surface. By having a release layer, the sheet obtained through step 2A can be easily peeled off from the substrate having the irregularities, and damage to the irregularities during peeling is suppressed, which is preferable. The release layer may be a layer to which a release agent is applied, or may be a layer containing a binder resin and a release agent. Examples of the release agent include silicone-based compounds and fluorine-based compounds, and when the release layer is formed together with a binder, wax, metal soap, etc. are also usable. Among these, fluorine-based compounds are preferred. Examples of the binder resin include urethane resins, acetal resins, polyamide resins, melamine resins, polyol resins, and polyvinyl alcohol. The thickness of the release layer is not particularly limited, but from the viewpoint of being firmly bonded to the substrate, it is preferably 20 nm or less, more preferably 10 nm or less, and even more preferably 5 nm or less, and is preferably 1 nm or more.

[0147] (Sheet raw material containing fine fibrous cellulose) The liquid sheet raw material containing fine fibrous cellulose (hereinafter also simply referred to as "sheet raw material") that is spread on the substrate having the above-mentioned unevenness is a liquid composition containing the above-mentioned fine fibrous cellulose and, if necessary, a hydrophilic polymer. That is, the sheet raw material is a slurry (dispersion liquid) containing at least fine fibrous cellulose, and may further contain a hydrophilic polymer. The concentration of fine fibrous cellulose in the sheet raw material is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, from the viewpoints of obtaining a uniform sheet with appropriate viscosity when spread and of facilitating drying in step A2, and is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less.

[0148] In step A1, the amount of the sheet material spread on the substrate having the irregularities is not particularly limited, and may be appropriately set so as to obtain the above-mentioned preferable sheet thickness. The method for spreading the sheet material on the substrate having the irregularities is not particularly limited, and may be appropriately selected from known methods. The temperature of the sheet material and the ambient temperature when spreading the sheet material on the substrate having irregularities (hereinafter, the sheet material temperature and the ambient temperature are collectively referred to as the "spreading temperature") are not particularly limited, but are preferably, for example, from 5°C to 80°C, more preferably from 10°C to 60°C, even more preferably from 15°C to 50°C, and particularly preferably from 20°C to 40°C. If the spreading temperature is above the lower limit, the slurry can be spread more easily. If the spreading temperature is below the upper limit, evaporation of the dispersion medium during spreading can be suppressed.

[0149] When the sheet material is spread on a substrate having a textured surface, a frame for blocking may be fixed to the substrate having a textured surface. The frame for blocking 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, a molded resin plate or metal plate is 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 plates with their surfaces oxidized, stainless steel plates, brass plates, etc., can be used. Furthermore, a substrate may be placed below the substrate having the irregularities, and an example of such a substrate is the substrate used in the production of the fine fibrous cellulose-containing sheet used in step B1 described below.

[0150] [Process A2] In step A2, the sheet material spread on the substrate having the irregularities in step A1 is dried in this state to obtain a sheet onto which the irregularities have been transferred. The step of drying the sheet material spread on the substrate having the irregularities is not particularly limited, but may be carried out by, for example, a non-contact drying method, a method of drying while fixing the sheet, or a combination of these. The non-contact drying method is not particularly limited, but for example, a method of drying by heating with hot air, infrared rays, far infrared rays, or near infrared rays (heat drying method), or a method of drying by vacuum (vacuum drying method) can be applied. Although the heat drying method and the vacuum drying method can be combined, the heat drying method is usually applied. Drying by infrared rays, far infrared rays, or near infrared rays can be carried out using, for example, an infrared device, a far infrared device, or a near infrared device, but is not particularly limited. The heating temperature in the heat drying method is not particularly limited, but is preferably 20°C or higher and 150°C or lower, and more preferably 25°C or higher and 105°C or lower. If the heating temperature is higher than the lower limit, the dispersion medium can be quickly volatilized. Furthermore, if the heating temperature is lower than the upper limit, it is possible to reduce the cost required for heating and to prevent discoloration of the fine fibrous cellulose due to heat. The dried sheet is peeled off from the substrate having the irregularities to obtain the sheet of this embodiment.

[0151] <Method B> Method B includes the following steps B1 and B2 in this order. Step B1: A step of placing a sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less on a substrate having an uneven surface to obtain a laminate. Step B2: A step of pressing the laminate under heat to transfer the concave-convex pattern [Process B1] The substrate having irregularities and the sheet containing fine fibrous cellulose with a fiber width of 1000 nm or less used in step B1 will be described below. In the following description, the sheet containing fine fibrous cellulose with a fiber width of 1000 nm or less, which is used in step B1 or step C1 described later, before the formation of the irregular shape, is also referred to as a fine fibrous cellulose-containing sheet.

[0152] (Uneven substrate) Examples of the substrate having projections and recesses used in step B1 include the same substrate as the substrate having projections and recesses used in step A1 described above. The material of the substrate having the irregularities used in the substrate B1 may be appropriately selected from heat-resistant materials, taking into consideration the hot pressing in step B2.

[0153] (sheet containing fine fibrous cellulose) In this embodiment, the fine fibrous cellulose-containing sheet can be obtained, for example, by carrying out the sheet-forming process described below using a liquid composition containing the above-mentioned fine fibrous cellulose and, if necessary, a hydrophilic polymer and other components. The manufacturing process of the fine fibrous cellulose-containing sheet preferably includes at least a coating step of coating a substrate with a slurry containing fine fibrous cellulose, or a papermaking step of making paper from the slurry. This results in a fine fibrous cellulose-containing sheet containing fine fibrous cellulose. As mentioned above, the fine fibrous cellulose-containing sheet preferably contains a hydrophilic polymer in addition to the fine fibrous cellulose.

[0154] - Coating process - In the coating process, for example, a slurry containing fine fibrous cellulose is coated onto a substrate, dried, and the resulting sheet is peeled off from the substrate to obtain a sheet. Furthermore, by using a coating device and a long substrate, sheets can be produced continuously. The material of the substrate used in the coating process is not particularly limited, but a substrate with high wettability with the composition (slurry) is preferable because it can suppress shrinkage of the sheet during drying, but it is preferable to select a substrate that allows the sheet formed after drying to be easily peeled off. Among these, resin films or plates or metal films or plates are preferred, but there are no particular limitations. For example, resin films or plates such as acrylic, polyethylene terephthalate, vinyl chloride, polystyrene, polypropylene, polycarbonate, and polyvinylidene chloride, metal films or plates such as aluminum, zinc, copper, and iron plates, and those with oxidized surfaces, stainless steel films or plates, brass films or plates, etc. can be used. If the viscosity of the slurry is low and it spreads on the substrate during the coating process, a blocking frame may be fixed to the substrate to obtain a sheet of the desired 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, 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 plates with their surfaces oxidized, as well as molded stainless steel plates, brass plates, etc., can be used. The coating machine for coating the substrate with the slurry is not particularly limited, and examples thereof include a roll coater, gravure coater, die coater, curtain coater, air doctor coater, etc. Die coaters, curtain coaters, and spray coaters are particularly preferred because they can make the thickness of the sheet more uniform.

[0155] The slurry temperature and ambient temperature (hereinafter, the slurry temperature and ambient temperature are collectively referred to as "coating temperature") when the slurry is applied to the substrate are not particularly limited, but are preferably, for example, from 5°C to 80°C, more preferably from 10°C to 60°C, even more preferably from 15°C to 50°C, and particularly preferably from 20°C to 40°C. If the coating temperature is above the lower limit, the slurry can be applied more easily. If the coating temperature is below the upper limit, evaporation of the dispersion medium during coating can be suppressed. In the coating step, it is preferable to coat the substrate with the slurry so that the finished sheet has a basis weight and a thickness within the above-mentioned preferred ranges. By coating so that the basis weight and the thickness are within the above-mentioned ranges, a sheet with better transparency, strength, and flexibility can be obtained.

[0156] As described above, the coating step includes a step of drying the slurry coated on the substrate. The step of drying the slurry is not particularly limited, but may be performed by, for example, a non-contact drying method, a method of drying while fixing the sheet, or a combination of these. The non-contact drying method is not particularly limited, but for example, a method of drying by heating with hot air, infrared rays, far infrared rays, or near infrared rays (heat drying method), or a method of drying by vacuum (vacuum drying method) can be applied. Although the heat drying method and the vacuum drying method can be combined, the heat drying method is usually applied. Drying by infrared rays, far infrared rays, or near infrared rays can be carried out using, for example, an infrared device, a far infrared device, or a near infrared device, but is not particularly limited. The heating temperature in the heat drying method is not particularly limited, but is preferably 20°C or higher and 150°C or lower, and more preferably 25°C or higher and 105°C or lower. If the heating temperature is equal to or higher than the lower limit, the dispersion medium can be quickly volatilized. Furthermore, if the heating temperature is equal to or lower than the upper limit, the cost required for heating can be reduced and discoloration of the fibrous cellulose due to heat can be suppressed.

[0157] -Paper making process- The papermaking process is carried out by making paper from the slurry using a papermaking machine. The papermaking machine used in the papermaking process is not particularly limited, but examples include continuous papermaking machines such as Fourdrinier, cylinder, and tilting types, and multi-layer papermaking machines that combine these. In the papermaking process, known papermaking methods such as handmaking may also be used. The papermaking process involves filtering and dewatering the slurry with a wire to obtain a wet sheet, which is then pressed and dried. The filter cloth used to filter and dewater the slurry is not particularly limited, but it is preferable that it does not allow fibrous cellulose to pass through and does not slow the filtration rate too much. Such filter cloths are not particularly limited, but are preferably sheets, woven fabrics, or porous membranes made of organic polymers. The organic polymer is not particularly limited, but is preferably a non-cellulose organic polymer such as polyethylene terephthalate, polyethylene, polypropylene, or polytetrafluoroethylene (PTFE). In this embodiment, examples include porous membranes made of polytetrafluoroethylene with a pore size of 0.1 μm to 20 μm, and woven fabrics made of polyethylene terephthalate or polyethylene with a pore size of 0.1 μm to 20 μm.

[0158] In the papermaking process, a method for producing a sheet from a slurry can be carried out using a production apparatus that includes a water squeezing section in which a slurry containing fine fibrous cellulose is discharged onto the upper surface of an endless belt and the dispersion medium is squeezed out of the discharged slurry to produce a web, and a drying section in which the web is dried to produce a sheet. An endless belt is disposed between the water squeezing section and the drying section, and the web produced in the water squeezing section is transported to the drying section while still on the endless belt.

[0159] The dehydration method used in the papermaking process is not particularly limited, but examples thereof include dehydration methods commonly used in paper manufacturing. Among these, methods in which dehydration is performed using a Fourdrinier, cylinder, or inclined wire, followed by further dehydration using a roll press, are preferred. Furthermore, the drying method used in the papermaking process is not particularly limited, but examples thereof include methods used in paper manufacturing. Among these, drying methods using a cylinder dryer, Yankee dryer, hot air dryer, near-infrared heater, infrared heater, etc. are more preferred.

[0160] The thickness, basis weight, and density of the fine fibrous cellulose-containing sheet may be appropriately set depending on the desired thickness, basis weight, and density of the sheet.

[0161] In step B1, a laminate is obtained by placing a sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less on a substrate having an uneven surface. It is preferable that the substrate having an uneven surface and the sheet containing fine fibrous cellulose are placed so that their centers coincide with each other.

[0162] [Process B2] In step B2, the laminate is pressed under heat to transfer the concaves and convexes. When pressing the laminate obtained in step B1 under heat, it is preferable to sandwich the top and bottom of the laminate between, for example, two stainless steel plates, and then press under heat, from the viewpoint of uniform pressing. The plates used for sandwiching are not particularly limited, and any heat-resistant, flat plate-like plate may be used. The heating temperature is preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher, from the viewpoint of transferring the uneven shape to the fine fibrous cellulose-containing sheet, and is preferably 300°C or lower, more preferably 200°C or lower, and even more preferably 180°C or lower, from the viewpoint of suppressing discoloration of the fine fibrous cellulose-containing sheet. The pressure during pressing is preferably 0.1 MPa or more, more preferably 0.3 MPa or more, even more preferably 0.5 MPa or more, from the viewpoint of transferring the uneven shape to the sheet containing the fine fibrous cellulose and preventing the uneven shape from being crushed, and is preferably 10 MPa or less, more preferably 5 MPa or less, even more preferably 3 MPa or less. The pressing time is preferably 0.05 minutes or more, more preferably 0.1 minutes or more, and even more preferably 0.3 minutes or more, and is preferably 10 minutes or less, more preferably 5 minutes or less, and even more preferably 3 minutes or less. In step B2, the laminate may be heated and then pressed, or may be heated and pressed at the same time. The press used in step B2 is not particularly limited, and may be appropriately selected from known presses. After pressing under heat, the sheet is cooled to room temperature and the fine fibrous cellulose-containing sheet is peeled off from the substrate having the irregularities, thereby obtaining a sheet of the present embodiment having the irregularities transferred thereto.

[0163] <Method C> Method C includes the following steps C1 to C3 in this order. Step C1: A step of placing a wet sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less on a substrate having an uneven surface to obtain a laminate. Step C2: Pressurizing the laminate to adhere the sheet to the substrate Step C3: A step of drying the sheet while it is in close contact with the substrate to obtain a sheet with the concave-convex pattern transferred thereto. [Process C1] Examples of the substrate having projections and recesses used in step C1 include the same substrates having projections and recesses used in steps A1 and B1. Examples of the sheet containing fine fibrous cellulose include the same sheet containing fine fibrous cellulose as that used in step B1. In step C1, the dry fine fibrous cellulose-containing sheet may be placed on the surface of a substrate having an uneven surface and then moistened, but it is preferable to moisten the fine fibrous cellulose-containing sheet in advance and then place it on the surface of a substrate having an uneven surface to obtain a laminate.

[0164] The method for wetting the fine fibrous cellulose-containing sheet is not particularly limited, and may be any method such as spraying water, immersing in a water bath, etc. Among these, immersion in a water bath is preferred from the viewpoint of achieving a sufficiently uniformly wet state. The water used is not particularly limited and may be tap water, ion-exchanged water, distilled water, or the like, but from the viewpoint of obtaining a structure with superior transparency, ion-exchanged water or distilled water is preferred. From the viewpoint of transferring the unevenness of a substrate having an uneven shape, the wet fine fibrous cellulose-containing sheet contains an aqueous medium in an amount of preferably 15 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 150 parts by mass or more, and even more preferably 500 parts by mass or more per 100 parts by mass of the dry mass of the fine fibrous cellulose-containing sheet. Also, from the viewpoint of shortening the drying step and from the viewpoint of the shape stability of the wet fine fibrous cellulose-containing sheet, the wet fine fibrous cellulose-containing sheet contains an aqueous medium in an amount of preferably 10,000 parts by mass or less, more preferably 5,000 parts by mass or less, and even more preferably 3,000 parts by mass or less per 100 parts by mass of the dry mass of the fine fibrous cellulose-containing sheet.

[0165] In step C1, it is preferable to place the fine fibrous cellulose-containing sheet so that no gaps such as air gaps are generated between the substrate having projections and recesses and the fine fibrous cellulose-containing sheet.

[0166] [Process C2] In step C2, the laminate is pressed to adhere the sheet to the substrate. By including step C2, bubbles are removed between the substrate having the irregularities and the fine fibrous cellulose-containing sheet, and adhesion is further improved, so that the fine irregularities are transferred to the fine fibrous cellulose-containing sheet. The pressure application in step C2 is preferably carried out using a roller, for example, a rubber roller.

[0167] [Process C3] In step C3, the fine fibrous cellulose is dried in a state of being in close contact with the substrate having projections and recesses. The drying temperature in step C3 is preferably 10° C. or higher, more preferably 20° C. or higher, even more preferably 25° C. or higher, from the viewpoint of suppressing shrinkage and cracking of the sheet, obtaining a sheet to which the concave-convex shape of the substrate having concave-convex shapes is precisely transferred, and from the viewpoint of productivity, and is preferably 200° C. or lower, more preferably 150° C. or lower, even more preferably 125° C. or lower, still more preferably 100° C. or lower, and even more preferably 80° C. or lower. Drying may be performed at room temperature. Furthermore, the drying time in step C3 is preferably 1 minute or more, more preferably 10 minutes or more, even more preferably 100 minutes or more, from the viewpoint of suppressing shrinkage and cracking of the laminate and obtaining a laminate with excellent flexibility, and from the viewpoint of productivity, and is preferably 48 hours or less, more preferably 24 hours or less, even more preferably 16 hours or less. The drying method is not particularly limited, and may be left to dry or may be a method used in paper manufacturing, such as a cylinder dryer, Yankee dryer, hot air drying, or infrared heater.

[0168] Following step C3, the dried fine fibrous cellulose-containing sheet is peeled off from the laminate to obtain the sheet of this embodiment to which the concave and convex shape of the substrate has been transferred. The method for peeling the sheet from the laminate is not particularly limited, but it is preferable to peel it so that the uneven shape is maintained. The moisture content of the sheet at the time of peeling is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less, from the viewpoint of maintaining the transferred uneven shape, and is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of suppressing cracking of the sheet at the time of peeling. [Example]

[0169] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0170] <Production Example 1> [Phosphorylation] Hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd. was used as the raw material pulp. This raw material pulp was subjected to a phosphating treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (bone dry mass) of the raw material pulp to adjust the composition to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, thereby obtaining a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 250 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining a phosphorylated pulp.

[0171] [Cleaning process] The resulting phosphorylated pulp was then washed. 100 g (bone dry mass) of phosphorylated pulp was mixed with 10 L of ion-exchanged water to obtain a pulp dispersion. The pulp was stirred to uniformly disperse the pulp, and then repeatedly filtered and dehydrated. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0172] [Neutralization treatment] Next, the washed phosphorylated pulp was neutralized as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous solution of sodium hydroxide was added little by little while stirring to obtain a phosphorylated pulp slurry with a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated to obtain a neutralized phosphorylated pulp. Next, the neutralized phosphorylated pulp was subjected to the above-mentioned washing treatment.

[0173] The infrared absorption spectrum of the obtained phosphorus oxyoxidized pulp was measured using FT-IR. -1 The absorption due to the P=O of the phosphate group was observed around the 2θ=14° to 17° and the 2θ=22° to 23° angle, confirming that the pulp had phosphate groups. The phosphorylated pulp was analyzed using an X-ray diffractometer, and typical peaks were observed at two positions, around 2θ=14° to 17° and 2θ=22° to 23°, confirming the presence of cellulose type I crystals.

[0174] [Fiber defibration processing] 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 pulverizer (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. The number-average fiber width of the fine fibrous cellulose measured in the "Fiber Width Measurement" section described below was 3 nm. X-ray diffraction confirmed that the fine fibrous cellulose maintained cellulose type I crystal structure. The amount of phosphate groups (amount of first dissociated acid groups, strong acid groups) measured by the method described in the "Amount of Phosphorus Oxo Acid Groups" section described below was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0175] <Production Example 2> [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 weight of the raw material pulp (dry mass equivalent), 1.6 parts by weight of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by weight of sodium bromide were dispersed in 10,000 parts by weight of water. Next, a 13% by weight aqueous solution of sodium hypochlorite was added to 1.0 g of pulp to achieve a concentration of 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.

[0176] The resulting TEMPO-oxidized pulp was then washed. The pulp slurry after TEMPO oxidation was dehydrated to obtain a dehydrated sheet, to which 5,000 parts by mass of ion-exchanged water was added, and the sheet was stirred to uniformly disperse the pulp. This process was repeated until the electrical conductivity of the filtrate reached 100 μS / cm or less, marking the end of the washing process.

[0177] The obtained TEMPO-oxidized pulp was analyzed using an X-ray diffractometer. Typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals. X-ray diffraction also confirmed that the obtained fibrous cellulose maintained cellulose type I crystals.

[0178] A fine fibrous cellulose dispersion containing fine fibrous cellulose was obtained in the same manner as in Production Example 1, except that the above-mentioned TEMPO-oxidized pulp was used in the [defibration treatment] of Production Example 1. The fiber width of the fine fibrous cellulose in the fine fibrous cellulose dispersion 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 "Fiber Width Measurement" section described below was 3 nm. X-ray diffraction confirmed that the fine fibrous cellulose maintained cellulose type I crystals. The amount of carboxy groups measured by the method described below in [Measurement of amount of carboxy groups] was 1.30 mmol / g.

[0179] <Production Example 3> [Phosphorous Treatment] The same procedure as in Production Example 1 was carried out, except that 33 parts by mass of phosphorous acid (phosphonic acid) was used instead of ammonium dihydrogen phosphate in the [Phosphorylation Treatment] of Production Example 1, to obtain a fine fibrous cellulose dispersion containing phosphorous-containing pulp and fine fibrous cellulose.

[0180] The infrared absorption spectrum of the obtained phosphorous-oxidized pulp was measured using FT-IR. -1 Absorption due to P=O of the phosphonic acid group, which is a tautomer of the phosphorous acid group, was observed near the center, confirming that phosphorous acid groups (phosphonic acid groups) 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 "Fiber Width Measurement" 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 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 4> [Sulfation treatment] The same procedure as in Production Example 1 was carried out, except that 38 parts by mass of amidosulfonic acid (sulfamic acid) was used instead of ammonium dihydrogen phosphate in the phosphorylation treatment and the heating time was extended to 20 minutes, to obtain a fine fibrous cellulose dispersion containing sulfated pulp and fine fibrous cellulose.

[0182] The infrared absorption spectrum of the sulfated pulp obtained was measured using FT-IR. -1Absorption due to sulfur oxoacid groups (sulfate groups) was observed near the nucleus, confirming that sulfur oxoacid groups (sulfate 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 "Fiber Width Measurement" 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 sulfur oxoacid groups measured in the "Measurement of Sulfur Oxoacid Group Amount" section described below was 1.47 mmol / g.

[0183] <Production Example 5> After washing and neutralization of the phosphorylated pulp of Production Example 1, the following treatments were carried out to obtain a dispersion of substituent-removed fine fibrous cellulose containing substituent-removed fine fibrous cellulose. [Nitrogen removal treatment] Deionized water was added to phosphorylated pulp to prepare a slurry with a solids concentration of 4% by mass. A 48% by mass aqueous solution of sodium hydroxide was added to the slurry to adjust the pH to 13.4, and the slurry was heated for 1 hour at a temperature of 85°C. The pulp slurry was then dehydrated, and 10 L of deionized water was added to 100 g of phosphorylated pulp (bone dry mass) to obtain a pulp dispersion. The pulp was stirred to uniformly disperse, and the filtration and dehydration process was repeated to remove excess sodium hydroxide. The removal was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less. The infrared absorption spectrum of the obtained phosphorus oxyoxidized pulp was measured using FT-IR. -1 Absorption due to P=O of phosphate groups was observed near the pulp, confirming that phosphate groups had been added to the pulp.

[0184] [Fiber defibration processing] 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 pulverizer (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. The number-average fiber width of the fine fibrous cellulose measured in the "Fiber Width Measurement" 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 phosphate groups (amount of first dissociated acid group, amount of strong acid group) measured by the measurement method described in the "Measurement of Amount of Phosphorus Oxo Acid Group" section described below was 1.35 mmol / g. The total amount of dissociated acid was 2.30 mmol / g.

[0185] [Substituent removal treatment (high temperature heat treatment)] A 1.0% by mass aqueous citric acid solution was added to the fine fibrous cellulose dispersion to adjust the pH of the dispersion to 5.5. The resulting slurry was placed in a pressure vessel 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. This operation confirmed the formation of fine fibrous cellulose aggregates.

[0186] [Cleaning of slurry after removing substituents] After heating, an equal amount of ion-exchanged water was added to the slurry to obtain a slurry with a solids concentration of approximately 1% by mass. This slurry was then stirred and 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 process was then repeated, and the washing endpoint was reached when the electrical conductivity of the filtrate again reached 10 μS / cm or less. Ion-exchanged water was added to the resulting fine fibrous cellulose aggregates to remove the substituents and obtain a slurry. The solids concentration of this slurry was 1.7% by mass.

[0187] [Uniform dispersion of slurry after removing substituents] Ion-exchanged water was added to the resulting slurry after the removal of substituents to give a slurry with a solids concentration of 1.0% by mass, which was then treated three times at a pressure of 200 MPa in a wet atomization apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a dispersion of the removed-substituent fine fibrous cellulose containing the removed-substituent fine fibrous cellulose. The number-average fiber width of the removed-substituent fine fibrous cellulose, as measured in the "Measurement of fiber width" section described below, was 4 nm.

[0188] <Production Example 6> [Hypochlorous acid oxidation treatment] A sheet (solids concentration 90% by mass) made from softwood bleached kraft pulp (NBKP) was mixed in a hand mixer (Lab Millser PLUS, manufactured by Osaka Chemical Co., Ltd.) at 20,000 rpm for 15 seconds to produce a fluffy fluffed pulp (solids concentration 90% by mass). Sodium hypochlorite pentahydrate was then added to ion-exchanged water to prepare an aqueous solution with a sodium hypochlorite solids concentration of 22% by mass. 9,000 parts by mass of a 22% sodium hypochlorite aqueous solution was added to 100 parts by mass of the fluffy fluffed pulp, and the mixture was reacted for 2 hours in a warm bath at 30°C to obtain carboxylated pulp. During the reaction, the pH was maintained at 11 by adding 1N aqueous sodium hydroxide solution as needed.

[0189] [Cleaning process] The resulting carboxylated pulp was then washed. The washing process consisted of pouring ion-exchanged water over the resulting carboxylated pulp to obtain a pulp dispersion, stirring the resulting dispersion to uniformly disperse the pulp, and then repeatedly filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0190] In addition, the obtained carboxyl-introduced pulp was analyzed using an X-ray diffraction device, and typical peaks were confirmed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0191] [Fiber defibration processing] Ion-exchanged water was added to the obtained carboxyl-introduced pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0192] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2 to 5 nm. The number-average fiber width of the fine fibrous cellulose measured in the "Fiber Width Measurement" section described below was 3 nm. The amount of carboxy groups in the obtained fine fibrous cellulose measured by the measurement method described below was 0.70 mmol / g.

[0193] <Production Example 7> [Maleic acid esterification treatment] A sheet (solids concentration 90% by mass) made from bleached softwood kraft pulp (NBKP) was mixed for 15 seconds at 20,000 rpm using a hand mixer (Lab Millser PLUS, manufactured by Osaka Chemical Co., Ltd.) to produce a fluffy fluffing pulp (solids concentration 90% by mass). 100 parts by mass of the fluffy fluffing pulp and 50 parts by mass of maleic anhydride were placed in an autoclave and mixed at 150°C for 2 hours to obtain a carboxyl-introduced pulp.

[0194] [Cleaning process] The resulting carboxylated pulp was then washed. The washing process consisted of pouring ion-exchanged water over the resulting carboxylated pulp to obtain a pulp dispersion, stirring the resulting dispersion to uniformly disperse the pulp, and then repeatedly filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0195] The infrared absorption spectrum of the obtained carboxyl-introduced pulp was measured using FT-IR. -1The absorption due to carboxyl groups was observed around 2θ = 14° to 17° and 2θ = 22° to 23°, confirming that the pulp had been maleated. Furthermore, when the carboxyl-group-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0196] [Fiber defibration processing] Ion-exchanged water was added to the obtained carboxyl-introduced pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0197] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2 to 5 nm. The number-average fiber width of the fine fibrous cellulose measured in the "Fiber Width Measurement" section described below was 3 nm. The amount of carboxy groups in the obtained fine fibrous cellulose measured by the measurement method described below was 1.22 mmol / g.

[0198] <Production Example 8> [Carboxymethylation treatment] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 A sheet-like product with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012 was used. To 100 parts by mass (bone dry mass) of this raw pulp, a chemical solution consisting of 83 parts by mass of 12N NaOH aqueous solution, 175 parts by mass of sodium monochloroacetate, and 313 parts by mass of ion-exchanged water (total 571 parts by mass) was added to obtain a chemical-impregnated pulp. The obtained chemical-impregnated pulp was then heated in a water bath at 95°C for 60 minutes to introduce carboxymethyl groups (carboxy groups) into the cellulose in the pulp, thereby obtaining a carboxy-introduced pulp.

[0199] [Cleaning process] The resulting carboxylated pulp was then washed. The washing process consisted of pouring ion-exchanged water over the resulting carboxylated pulp to obtain a pulp dispersion, stirring the resulting dispersion to uniformly disperse the pulp, and then repeatedly filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0200] In addition, when the carboxyl-group-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were confirmed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0201] [Fiber defibration processing] Ion-exchanged water was added to the obtained carboxyl-introduced pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0202] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2 to 5 nm. The number-average fiber width of the fine fibrous cellulose measured in the "Fiber Width Measurement" section described below was 3 nm. The amount of carboxy groups in the obtained fine fibrous cellulose measured by the measurement method described below was 1.21 mmol / g.

[0203] <Production Example 9> [Carboxyethylation treatment] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 A sheet-like product with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012 was used. To 100 parts by mass (bone dry mass) of this raw pulp, a chemical solution consisting of 250 parts by mass of 12N NaOH aqueous solution, 163 parts by mass of 2-chloropropionic acid, and 140 parts by mass of ion-exchanged water (total 553 parts by mass) was added to obtain a chemical-impregnated pulp. The obtained chemical-impregnated pulp was then heated in a hot air dryer at 165°C for 10 minutes to introduce carboxyethyl groups (carboxy groups) into the cellulose in the pulp, thereby obtaining a carboxy-introduced pulp.

[0204] [Cleaning process] The resulting carboxylated pulp was then washed. The washing process consisted of pouring ion-exchanged water over the resulting carboxylated pulp to obtain a pulp dispersion, stirring the resulting dispersion to uniformly disperse the pulp, and then repeatedly filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0205] [Neutralization treatment] Next, the washed carboxylated pulp was neutralized as follows: First, the washed carboxylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous sodium hydroxide solution was added little by little while stirring to obtain a carboxylated pulp slurry with a pH of 12 to 13. Next, the carboxylated pulp slurry was dehydrated and washed to obtain a neutralized carboxylated pulp.

[0206] In addition, when the carboxyl-group-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were confirmed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0207] [Fiber defibration processing] Ion-exchanged water was added to the obtained carboxyl-introduced pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0208] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2 to 5 nm. The number-average fiber width of the fine fibrous cellulose measured in the "Fiber Width Measurement" section described below was 3 nm. The amount of carboxy groups in the obtained fine fibrous cellulose measured by the measurement method described below was 1.41 mmol / g.

[0209] <Production Example 10> [Sulfoethylation treatment] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 A sheet-like product with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012 was used. To 100 parts by mass (bone dry mass) of this raw pulp, a chemical solution consisting of 180 parts by mass of a 2N NaOH aqueous solution and 780 parts by mass of a 25% by mass sodium vinyl sulfonate aqueous solution (total 960 parts by mass) was added to obtain a chemical solution-impregnated pulp. The obtained chemical solution-impregnated pulp was then heated in a hot air dryer at 165°C for 16 minutes to introduce sulfoethyl groups (sulfonic groups) into the cellulose in the pulp, yielding a sulfoethyl group-introduced pulp (sulfonic group-introduced pulp).

[0210] [Cleaning process] The resulting sulfoethylated pulp was then washed. The washing process consisted of pouring ion-exchanged water over the resulting sulfoethylated pulp to obtain a pulp dispersion, stirring the resulting dispersion to uniformly disperse the pulp, and then repeatedly filtering and dehydrating the pulp. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0211] In addition, when sulfoethyl group-introduced pulp was tested and analyzed using an X-ray diffractometer, typical peaks were confirmed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0212] [Fiber defibration processing] Ion-exchanged water was added to the obtained sulfoethyl group-introduced pulp to prepare a slurry with a solid content of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0213] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2 to 5 nm. The number-average fiber width of the fine fibrous cellulose measured in the "Fiber Width Measurement" section described below was 3 nm. The amount of sulfoethyl groups (amount of sulfonic groups) of the obtained fine fibrous cellulose measured by the measurement method described below was 1.48 mmol / g.

[0214] <Production Example 11> [Cationization treatment] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 A sheet-like product with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012 was used. To 100 parts by mass (bone dry mass) of this raw pulp, a chemical solution consisting of 180 parts by mass of a 1N NaOH aqueous solution and 325 parts by mass of a cationizing agent (Catiomaster G, manufactured by Yokkaichi Synthetic Co., Ltd., glycidyl trimethylammonium chloride, purity 73.1% by mass, moisture content 20.2% by mass) (total 505 parts by mass) was added to obtain a chemical solution-impregnated pulp. The obtained chemical solution-impregnated pulp was then heated in a hot air dryer at 165°C for 12 minutes to introduce cationic groups into the cellulose in the pulp, yielding a cationic group-introduced pulp.

[0215] [Cleaning process] The resulting cationic group-introduced pulp was then washed. The washing was performed by pouring ion-exchanged water over the resulting cationic group-introduced pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0216] [Neutralization treatment] Next, the washed cationic group-introduced pulp was neutralized as follows: First, the washed cationic group-introduced pulp was diluted with 10 L of ion-exchanged water, and then 1 N hydrochloric acid was added little by little while stirring to obtain a cationic group-introduced pulp slurry with a pH of 1 to 2. Next, the cationic group-introduced pulp slurry was dehydrated and washed to obtain a neutralized cationic group-introduced pulp.

[0217] Analysis using an X-ray diffractometer confirmed typical peaks at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0218] [Fiber defibration processing] Ion-exchanged water was added to the obtained cationic group-introduced pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0219] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2 to 5 nm. The number-average fiber width of the fine fibrous cellulose measured in the "Fiber Width Measurement" section described below was 3 nm. The amount of cationic groups measured in the cationic group measurement method described below was 1.45 mmol / g.

[0220] Example 1 [Sheet production] Polyethylene oxide (PEO-18P, manufactured by Sumitomo Seika Chemicals Co., Ltd.) 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 dissolve. By the above procedure, an aqueous polyethylene oxide solution was obtained.

[0221] The fine fibrous cellulose dispersion obtained in Production Example 1 and the polyethylene oxide aqueous solution were each diluted with ion-exchanged water to a solid content concentration of 1.0% by mass. Next, 20 parts by mass of polyethylene oxide were added to 100 parts by mass of the fine fibrous cellulose to obtain a mixed solution. Furthermore, the finished basis weight of the sheet was 35 g / m. 2 The mixture was measured so that the thickness of the mixture was 180 mm × 180 mm and spread on a commercially available acrylic plate. A damming frame (inner dimensions: 180 mm × 180 mm, height: 50 mm) was placed on the acrylic plate to achieve the desired thickness. The mixture 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.

[0222] [Formation of unevenness] The fine fibrous cellulose-containing sheet was cut into 150 mm square pieces and placed on a cellulose acetate membrane filter (manufactured by ADVANTEC, C045A142C) with a diameter of 142 mm and a pore size of 0.45 μm, with the centers aligned. These were then sandwiched between two 200 mm square stainless steel plates. The sheet was then inserted into a mini test press (manufactured by Toyo Seiki Kogyo Co., Ltd., MP-WCH) with the upper and lower stainless steel plates in close contact with the iron plate, and heated to 150 °C over 2 minutes. After heating, the pressure was increased to 1 MPa and maintained at this state for 0.5 minutes. The pressure was then removed, the upper and lower stainless steel plates were returned to their close contact with the iron plate, and the sheet was cooled to 30 °C over 1.5 minutes. The sheet was then peeled off from the membrane filter. Using the above procedure, a fine fibrous cellulose-containing sheet with a textured surface was obtained.

[0223] <Example 2> In the [Formation of irregularities] of Example 1, a nanobuckling sheet (manufactured by Oji F-Tex Co., Ltd., a registered Japanese trademark) was used as the transfer substrate instead of the cellulose acetate membrane filter. The nanobuckling sheet was a laminate of a PET film and an acrylic resin layer, and a nanobuckling structure having a plurality of meandering, wavy ridges was formed on the acrylic resin layer. The average spacing between these ridges was approximately 15 μm. A fine fibrous cellulose-containing sheet with a ridge-transferred irregularity was obtained in the same manner as in Example 1 except for this.

[0224] Example 3 In the [Formation of irregularities] of Example 1, a sheet containing fine fibrous cellulose with a transferred irregularity was obtained in the same manner as in Example 1, except that a nanodot array (registered Japanese trademark), a silicon wafer with a microstructure having conical protrusions with an average spacing of 100 nm between the protrusions, was used as the transfer substrate instead of the cellulose acetate membrane filter. In this example, a substrate (microstructure) with nano-sized protrusions was obtained with reference to the method described in JP 2009-034630 A. Specifically, the sheet was produced as follows. Colloidal silica particles with an average particle size of 100 nm were coated onto a silicon wafer using the Langmuir-Blodgett technique. The resulting silicon wafer was then subjected to vapor-phase etching using a gas mixture of SF6:CH2F2 = 25:75 to 75:25. The etching conditions were an antenna power of 1500 W, a bias power of 50 to 300 W, and a gas flow rate of 30 to 50 sccm. Scanning electron microscopy of the silicon wafer surface after vapor-phase etching revealed the formation of conical structures with heights of 300 to 400 nm arranged in a triangular lattice pattern with a pitch of approximately 100 nm.

[0225] Example 4 In the [formation of irregularities] of Example 1, a microstructure was used as the transfer substrate in place of the cellulose acetate membrane filter. The microstructure was a silicon wafer imparted with a nanodot array, having conical protrusions with an average spacing of 400 nm between the protrusions and recesses. A microfibrous cellulose-containing sheet with a transferred irregularity was obtained in the same manner as in Example 1. In this example, a substrate (microstructure) with nano-sized protrusions was obtained with reference to the method described in JP 2009-034630 A. Specifically, the fabrication was carried out as follows. Colloidal silica particles with an average particle size of 400 nm were coated onto a silicon wafer using the Langmuir-Blodgett technique. The resulting silicon wafer was then subjected to vapor-phase etching using a gas mixture of SF6:CH2F2 = 25:75 to 75:25. The etching conditions were an antenna power of 1500 W, bias power of 50 to 300 W, and a gas flow rate of 30 to 50 sccm. Scanning electron microscopy of the silicon wafer surface after vapor-phase etching revealed the formation of conical structures with heights of 800 to 1200 nm arranged in a triangular lattice pattern with a pitch of approximately 400 nm.

[0226] <Example 5> [Sheet production] Acetoacetyl group-modified polyvinyl alcohol (Gohsenex Z-200, manufactured by Mitsubishi Chemical Corporation) was added to ion-exchanged water to a concentration of 12% by mass, and the mixture was stirred at 95° C. for 1 hour to dissolve. By the above procedure, an aqueous polyvinyl alcohol solution was obtained. The fine fibrous cellulose dispersion obtained in Production Example 1 and the above aqueous polyvinyl alcohol solution were each diluted with ion-exchanged water to a solid content of 1.0% by mass. Next, 40 parts by mass of polyvinyl alcohol was added to 100 parts by mass of the fine fibrous cellulose to obtain a mixed solution. Furthermore, the finished basis weight of the sheet was 80 g / m. 2The mixture was weighed out so that the thickness was 180 mm × 180 mm, and spread on a commercially available acrylic plate. A damming frame (inner dimensions 180 mm × 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. Thereafter, a fine fibrous cellulose-containing sheet with a transferred unevenness was obtained by the same method as in [Formation of unevenness] in Example 1.

[0227] Example 6 A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 5, except that the transfer substrate used in Example 2 was used instead of the cellulose acetate membrane filter.

[0228] Example 7 A fine fibrous cellulose-containing sheet with a transferred irregularity pattern was obtained in the same manner as in Example 5, except that the transfer substrate used in Example 3 was used instead of the cellulose acetate membrane filter.

[0229] Example 8 A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 5, except that the transfer substrate used in Example 4 was used instead of the cellulose acetate membrane filter.

[0230] Example 9 The fine fibrous cellulose dispersion obtained in Production Example 1 was diluted with ion-exchanged water so that the solid content concentration was 1.0% by mass. The finished basis weight of the sheet was 35 g / m 2 The liquid was measured so that the thickness was 180 mm × 180 mm, and the liquid was spread on a commercially available acrylic plate. A damming frame (inner dimensions 180 mm × 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. Thereafter, a fine fibrous cellulose-containing sheet with a transferred unevenness was obtained by the same method as in [Formation of unevenness] in Example 1.

[0231] Example 10 A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 9, except that the transfer substrate used in Example 2 was used instead of the cellulose acetate membrane filter.

[0232] Example 11 A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 9, except that the transfer substrate used in Example 3 was used instead of the cellulose acetate membrane filter.

[0233] Example 12 A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 9, except that the transfer substrate used in Example 4 was used instead of the cellulose acetate membrane filter.

[0234] Example 13 In Example 1 [Sheet Preparation], a cellulose acetate membrane filter (manufactured by ADVANTEC, C045A142C) was placed on an acrylic plate as a transfer substrate, and the mixed solution was spread on top of it. It was then dried in a dryer set at 70°C and peeled off from the cellulose acetate membrane filter. By the above procedure, a fine fibrous cellulose-containing sheet with a transferred unevenness pattern was obtained.

[0235] Example 14 In Example 13, a fine fibrous cellulose-containing sheet with a transferred unevenness was obtained in the same manner as in Example 13, except that the transfer substrate used in Example 2 was used instead of the cellulose acetate membrane filter as the transfer substrate.

[0236] Example 15 In Example 13, a fine fibrous cellulose-containing sheet with a transferred unevenness was obtained in the same manner as in Example 13, except that the transfer substrate used in Example 3 was used instead of the cellulose acetate membrane filter as the transfer substrate.

[0237] Example 16 In Example 13, a fine fibrous cellulose-containing sheet with a transferred unevenness was obtained in the same manner as in Example 13, except that the transfer substrate used in Example 4 was used instead of the cellulose acetate membrane filter as the transfer substrate.

[0238] Example 17 The fine fibrous cellulose-containing sheet obtained in Example 1 (before the formation of irregularities) was given irregularities by the following procedure. [Formation of unevenness] A 142 mm diameter, 0.45 μm pore size cellulose acetate membrane filter (Advantec, C045A142C) was placed on a commercially available polycarbonate plate. A 150 mm square microfibrous cellulose-containing sheet was immersed in a tray containing distilled water for 10 seconds to moisten it. This sheet was placed on the cellulose membrane filter and covered with a PET film (Toray Industries, Inc., Lumirror S10). Pressure was applied from above the PET film with a rubber roller to remove air bubbles and firmly attach the sheet to the cellulose acetate membrane filter. The PET film was then peeled off, and the periphery of the sheet and the polycarbonate plate were secured with tape. After drying in a 40°C dryer for at least 12 hours, the tape was removed, and the sheet was peeled off from the cellulose acetate membrane filter. Using the above procedure, a microfibrous cellulose-containing sheet with a textured surface was obtained.

[0239] Example 18 A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 17, except that the transfer substrate used in Example 2 was used instead of the cellulose acetate membrane filter.

[0240] Example 19 A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 17, except that the transfer substrate used in Example 3 was used instead of the cellulose acetate membrane filter.

[0241] Example 20 A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 17, except that the transfer substrate used in Example 4 was used instead of the cellulose acetate membrane filter.

[0242] Example 21 A fine fibrous cellulose-containing sheet with a transferred texture was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion obtained in Production Example 2 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 1.

[0243] Example 22 In Example 21, a fine fibrous cellulose-containing sheet with transferred irregularities was obtained in the same manner as in Example 21, except that the transfer substrate used in Example 3 was used instead of the cellulose acetate membrane filter as the transfer substrate.

[0244] Example 23 A fine fibrous cellulose-containing sheet with a transferred texture was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion obtained in Production Example 3 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 1.

[0245] Example 24 In Example 23, a fine fibrous cellulose-containing sheet with transferred irregularities was obtained in the same manner as in Example 23, except that the transfer substrate used in Example 3 was used instead of the cellulose acetate membrane filter as the transfer substrate.

[0246] Example 25 A fine fibrous cellulose-containing sheet with a transferred texture was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion obtained in Production Example 4 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 1.

[0247] Example 26 In Example 25, a fine fibrous cellulose-containing sheet with transferred irregularities was obtained in the same manner as in Example 25, except that the transfer substrate used in Example 3 was used instead of the cellulose acetate membrane filter as the transfer substrate.

[0248] Example 27 A fine fibrous cellulose-containing sheet with a transferred texture was obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion obtained in Production Example 5 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 1.

[0249] Example 28 In Example 27, a fine fibrous cellulose-containing sheet with transferred irregularities was obtained in the same manner as in Example 27, except that the transfer substrate used in Example 3 was used instead of the cellulose acetate membrane filter as the transfer substrate.

[0250] Example 29 The fine fibrous cellulose dispersion obtained in Production Example 1 and the polyethylene oxide aqueous solution obtained in Example 1 were each diluted with ion-exchanged water to a solids concentration of 1.0% by mass. Next, 0.5 parts by mass of polyamine polyamide epichlorohydrin (Seiko PMC Corporation, wet strength agent WS4030) was added to 100 parts by mass of the fine fibrous cellulose and mixed. Then, 20 parts by mass of polyethylene oxide was added to 100 parts by mass of the fine fibrous cellulose and mixed. Furthermore, a polypropylene resin emulsion (Toho Chemical Industry Co., Ltd., HYTEC P-5060P, particle size 30 nm) was added so that the polypropylene resin was 10 parts by mass per 100 parts by mass of the fine fibrous cellulose. Thereafter, a fine fibrous cellulose-containing sheet with a transferred unevenness was obtained in the same manner as in Example 1.

[0251] Example 30 In Example 29, a fine fibrous cellulose-containing sheet with a transferred unevenness was obtained in the same manner as in Example 29, except that the transfer substrate used in Example 3 was used instead of the cellulose acetate membrane filter as the transfer substrate.

[0252] Example 31 In the [Formation of irregularities] of Example 1, a fine fibrous cellulose-containing sheet with transferred irregularities was obtained in the same manner as in Example 1, except that a release paper (manufactured by Oji F-Tex Co., Ltd.) prepared by coating high-quality paper with a silicone-based release agent was used as the transfer substrate instead of the cellulose acetate membrane filter.

[0253] Example 32 [Sheet production] Hydroxypropyl methylcellulose (Metolose 65SH-1500, manufactured by Shin-Etsu Chemical Co., Ltd., degree of methoxy group substitution = 1.8, molar substitution of hydroxypropoxy groups = 0.15, viscosity of 2% aqueous solution at 20°C = 1500 mPa s) was added to ion-exchanged water to a concentration of 2.0 mass%, and the mixture was stirred at room temperature for 1 hour to dissolve. This procedure yielded an aqueous solution of hydroxypropyl methylcellulose. The fine fibrous cellulose dispersion obtained in Production Example 1 and the above hydroxypropyl methylcellulose aqueous solution were each diluted with ion-exchanged water to a solid content of 1.0% by mass. Next, 40 parts by mass of hydroxypropyl methylcellulose was added to 100 parts by mass of the fine fibrous cellulose to obtain a mixed solution. Furthermore, the finished basis weight of the sheet was 95 g / m. 2 The mixed solution was measured so that the thickness of the mixed solution was 180 mm × 180 mm, and the mixed solution was applied to a commercially available acrylic plate. A blocking frame (inner dimensions: 180 mm × 180 mm, height: 50 mm) was placed on the acrylic plate to achieve the specified thickness. The mixed solution 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.

[0254] [Formation of unevenness] The fine fibrous cellulose-containing sheet was cut into 150 mm square pieces and placed on a cellulose acetate membrane filter (manufactured by ADVANTEC, C045A142C) with a diameter of 142 mm and a pore size of 0.45 μm, with the centers aligned. These were then sandwiched between two 200 mm square stainless steel plates. The sheet was then inserted into a mini test press (manufactured by Toyo Seiki Kogyo Co., Ltd., MP-WCH) with the upper and lower stainless steel plates in close contact with the iron plate, and heated to 150 °C over 2 minutes. After heating, the pressure was increased to 1 MPa and maintained at this state for 0.5 minutes. The pressure was then removed, the upper and lower stainless steel plates were returned to their close contact with the iron plate, and the sheet was cooled to 30 °C over 1.5 minutes. The sheet was then peeled off from the membrane filter. Using the above procedure, a fine fibrous cellulose-containing sheet with a textured surface was obtained.

[0255] Example 33 In the [Formation of irregularities] of Example 32, a fine fibrous cellulose-containing sheet with transferred irregularities was obtained in the same manner as in Example 32, except that the transfer substrate used in Example 2 was used instead of the cellulose acetate membrane filter.

[0256] Example 34 In the [Formation of irregularities] of Example 32, a fine fibrous cellulose-containing sheet with transferred irregularities was obtained in the same manner as in Example 32, except that the transfer substrate used in Example 3 was used instead of the cellulose acetate membrane filter.

[0257] Example 35 In the [Formation of irregularities] of Example 32, the irregularities were transferred in the same manner as in Example 32, except that the transfer substrate used in Example 4 was used instead of the cellulose acetate membrane filter, to obtain a sheet containing fine fibrous cellulose.

[0258] Example 36 In the [Sheet Production] of Example 32, a fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 32, except that the amount of hydroxypropyl methylcellulose was 100 parts by mass per 100 parts by mass of fine fibrous cellulose.

[0259] Example 37 A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 36, except that the transfer substrate used in Example 2 was used instead of the cellulose acetate membrane filter.

[0260] Example 38 In Example 36, a sheet containing fine fibrous cellulose with a transferred pattern was obtained in the same manner as in Example 36, except that the transfer substrate used in Example 3 was used instead of the cellulose acetate membrane filter.

[0261] Example 39 A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 36, except that the transfer substrate used in Example 4 was used instead of the cellulose acetate membrane filter.

[0262] <Example 40> A fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 32, except that the fine fibrous cellulose dispersion obtained in Production Example 5 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 1.

[0263] <Example 41> A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 40, except that the transfer substrate used in Example 2 was used instead of the cellulose acetate membrane filter.

[0264] <Example 42> A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 40, except that the transfer substrate used in Example 3 was used instead of the cellulose acetate membrane filter.

[0265] <Example 43> A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 40, except that the transfer substrate used in Example 4 was used instead of the cellulose acetate membrane filter.

[0266] <Example 44> A fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 36, except that the fine fibrous cellulose dispersion obtained in Production Example 5 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 1.

[0267] Example 45 A fine fibrous cellulose-containing sheet with a transferred pattern was obtained in the same manner as in Example 44, except that the transfer substrate used in Example 2 was used instead of the cellulose acetate membrane filter.

[0268] <Example 46> In Example 44, a sheet containing fine fibrous cellulose with a transferred pattern was obtained in the same manner as in Example 44, except that the transfer substrate used in Example 3 was used instead of the cellulose acetate membrane filter.

[0269] Example 47 In Example 44, a sheet containing fine fibrous cellulose with a transferred pattern was obtained in the same manner as in Example 44, except that the transfer substrate used in Example 4 was used instead of the cellulose acetate membrane filter.

[0270] Example 48 [Sheet production] Hydroxyethyl methylcellulose (Metolose SEB-04T, manufactured by Shin-Etsu Chemical Co., Ltd., degree of substitution of methoxy groups = 1.5, molar substitution of hydroxyethoxy groups = 0.20, viscosity of 2% aqueous solution at 20°C = 4000 mPa s) was added to ion-exchanged water to a concentration of 2.0 mass%, and the mixture was stirred at room temperature for 1 hour to dissolve. Using the above procedure, an aqueous solution of hydroxyethyl methylcellulose was obtained. The fine fibrous cellulose dispersion obtained in Production Example 1 and the above hydroxyethyl methyl cellulose aqueous solution were each diluted with ion-exchanged water to a solid content concentration of 1.0% by mass. Next, 40 parts by mass of hydroxyethyl methyl cellulose was added to 100 parts by mass of the fine fibrous cellulose to obtain a mixed solution. Furthermore, the finished basis weight of the sheet was 95 g / m 2 The mixed solution was measured so that the thickness of the mixed solution was 180 mm × 180 mm, and the mixed solution was applied to a commercially available acrylic plate. A blocking frame (inner dimensions: 180 mm × 180 mm, height: 50 mm) was placed on the acrylic plate to achieve the specified thickness. The mixed solution 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.

[0271] [Formation of unevenness] The fine fibrous cellulose-containing sheet was cut into 150 mm square pieces and placed on the nanodot array used in Example 3 so that the centers were aligned. These were then sandwiched between two 200 mm square stainless steel plates. The sheet was then inserted into a mini test press (MP-WCH, manufactured by Toyo Seiki Kogyo Co., Ltd.) with the upper and lower stainless steel plates in close contact with the iron plate, and heated to 150°C over 2 minutes. After heating, the pressure was increased to 1 MPa and maintained at this state for 0.5 minutes. The pressure was then removed, the upper and lower stainless steel plates were returned to their close contact with the iron plate, and the sheet was cooled to 30°C over 1.5 minutes. The sheet was then peeled off from the membrane filter. Using the above procedure, a fine fibrous cellulose-containing sheet with a textured surface was obtained.

[0272] <Example 49> [Sheet production] Methylcellulose (Metolose SM100, manufactured by Shin-Etsu Chemical Co., Ltd., degree of methoxy group substitution = 1.8, viscosity of 2% aqueous solution at 20°C = 100 mPa s) was added to ion-exchanged water to a concentration of 2.0 mass%, and the mixture was stirred at room temperature for 1 hour to dissolve. This procedure yielded an aqueous methylcellulose solution. The fine fibrous cellulose dispersion obtained in Production Example 1 and the above methyl cellulose aqueous solution were each diluted with ion-exchanged water to a solid content concentration of 1.0% by mass. Next, 40 parts by mass of methyl cellulose was added to 100 parts by mass of the fine fibrous cellulose to obtain a mixed solution. Furthermore, the finished basis weight of the sheet was 95 g / m. 2 The mixed solution was measured so that the thickness of the mixed solution was 180 mm × 180 mm, and the mixed solution was applied to a commercially available acrylic plate. A blocking frame (inner dimensions: 180 mm × 180 mm, height: 50 mm) was placed on the acrylic plate to achieve the specified thickness. The mixed solution 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.

[0273] [Formation of unevenness] The fine fibrous cellulose-containing sheet was cut into 150 mm square pieces and placed on the nanodot array used in Example 3 so that the centers were aligned. These were then sandwiched between two 200 mm square stainless steel plates. The sheet was then inserted into a mini test press (MP-WCH, manufactured by Toyo Seiki Kogyo Co., Ltd.) with the upper and lower stainless steel plates in close contact with the iron plate, and heated to 150°C over 2 minutes. After heating, the pressure was increased to 1 MPa and maintained at this state for 0.5 minutes. The pressure was then removed, the upper and lower stainless steel plates were returned to their close contact with the iron plate, and the sheet was cooled to 30°C over 1.5 minutes. The sheet was then peeled off from the membrane filter. Using the above procedure, a fine fibrous cellulose-containing sheet with a textured surface was obtained.

[0274] Example 50 [Sheet production] Carboxymethyl cellulose (Cellogen F-6HS9, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., degree of etherification = 0.80 to 0.90, viscosity of 1% aqueous solution at 25°C = 3000 to 4000 mPa s) was added to ion-exchanged water to a concentration of 2.0 mass%, and the mixture was stirred at room temperature for 1 hour to dissolve. By the above procedure, an aqueous carboxymethyl cellulose solution was obtained. The fine fibrous cellulose dispersion obtained in Production Example 1 and the above carboxymethyl cellulose aqueous solution were each diluted with ion-exchanged water to a solid content concentration of 1.0% by mass. Next, 40 parts by mass of carboxymethyl cellulose was added to 100 parts by mass of the fine fibrous cellulose to obtain a mixed solution. Furthermore, the finished basis weight of the sheet was 95 g / m 2 The mixed solution was measured so that the thickness of the mixed solution was 180 mm × 180 mm, and the mixed solution was applied to a commercially available acrylic plate. A blocking frame (inner dimensions: 180 mm × 180 mm, height: 50 mm) was placed on the acrylic plate to achieve the specified thickness. The mixed solution 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.

[0275] [Formation of unevenness] The fine fibrous cellulose-containing sheet was cut into 150 mm square pieces and placed on the nanodot array used in Example 3 so that the centers were aligned. These were then sandwiched between two 200 mm square stainless steel plates. The sheet was then inserted into a mini test press (MP-WCH, manufactured by Toyo Seiki Kogyo Co., Ltd.) with the upper and lower stainless steel plates in close contact with the iron plate, and heated to 150°C over 2 minutes. After heating, the pressure was increased to 1 MPa and maintained at this state for 0.5 minutes. The pressure was then removed, the upper and lower stainless steel plates were returned to their close contact with the iron plate, and the sheet was cooled to 30°C over 1.5 minutes. The sheet was then peeled off from the membrane filter. Using the above procedure, a fine fibrous cellulose-containing sheet with a textured surface was obtained.

[0276] <Example 51> The fine fibrous cellulose dispersion and the polyethylene oxide aqueous solution obtained in Production Example 6 were each diluted with ion-exchanged water to a solid content concentration of 1.0% by mass. Next, 20 parts by mass of polyethylene oxide were added to 100 parts by mass of the fine fibrous cellulose to obtain a mixed solution. Furthermore, the finished basis weight of the sheet was 60 g / m. 2The mixed solution was measured so that the thickness was 180 mm × 180 mm, and the mixed solution was applied to a commercially available acrylic plate. A damming frame (inner dimensions 180 mm × 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. This sheet was subjected to the same procedure as in [Formation of irregularities] in Example 1 to obtain a fine fibrous cellulose-containing sheet with irregularities transferred thereto.

[0277] <Example 52> A fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 51, except that the fine fibrous cellulose dispersion obtained in Production Example 7 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 6.

[0278] <Example 53> A fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 51, except that the fine fibrous cellulose dispersion obtained in Production Example 8 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 6.

[0279] <Example 54> A fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 51, except that the fine fibrous cellulose dispersion obtained in Production Example 9 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 6.

[0280] Example 55 A fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 51, except that the fine fibrous cellulose dispersion obtained in Production Example 10 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 6.

[0281] Example 56 A fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 51, except that the fine fibrous cellulose dispersion obtained in Production Example 11 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 6.

[0282] Example 57 [Sheet production] Polyethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., average molecular weight 20,000) 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 dissolve. By the above procedure, an aqueous polyethylene glycol solution was obtained.

[0283] The fine fibrous cellulose dispersion obtained in Production Example 3 and the polyethylene glycol aqueous solution were each diluted with ion-exchanged water to a solid content concentration of 1.0% by mass. Next, 20 parts by mass of polyethylene glycol was added to 100 parts by mass of the fine fibrous cellulose to obtain a mixed solution. Furthermore, the finished basis weight of the sheet was 60 g / m. 2 The mixed solution was measured so that the thickness was 180 mm × 180 mm, and the mixed solution was applied to a commercially available acrylic plate. A damming frame (inner dimensions 180 mm × 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. This sheet was subjected to the same procedure as in [Formation of irregularities] in Example 1 to obtain a fine fibrous cellulose-containing sheet with irregularities transferred thereto.

[0284] <Comparative Example 1> In Example 5, a fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 1, except that the operation of [forming unevenness] was not carried out and the unevenness was not transferred.

[0285] <Comparative Example 2> In Example 9, a fine fibrous cellulose-containing sheet was obtained in the same manner as in Example 1, except that the operation of [forming unevenness] was not carried out and the unevenness was not transferred.

[0286] <Measurement> The fine fibrous cellulose-containing sheets obtained in Examples 1 to 57 and Comparative Examples 1 and 2 were measured according to the following methods.

[0287] (Measurement of phosphorus oxoacid group content) The amount of phosphorus oxo acid groups in the fine fibrous cellulose (equivalent to the amount of phosphorus oxo acid groups in the phosphorus oxo-oxidized pulp) was measured by adding ion-exchanged water to a fine fibrous cellulose dispersion containing the target fine fibrous cellulose to adjust the content to 0.2 mass%, treating the dispersion with ion-exchange resin, and then titrating it with alkali. Treatment with ion exchange resin was carried out by adding 1 / 10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) to the above-mentioned fine fibrous cellulose-containing slurry, shaking for 1 hour, and then pouring it onto a mesh with 90 μm openings to separate the resin from the slurry. In addition, alkali titration was performed by measuring the change in the pH of a slurry containing fine fibrous cellulose after ion exchange resin treatment while adding 10 μL of 0.1 N sodium hydroxide solution every 5 seconds. Nitrogen gas was bubbled through the slurry for 15 minutes before the start of the titration. In this neutralization titration, two maximum points of increment (the derivative of pH with respect to the amount of alkali added) were observed on the plot of pH versus the amount of alkali added. The first maximum point of increment after starting the alkali addition is called the first endpoint, and the second maximum point is called the second endpoint (Figure 1). The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of first dissociated acid in the slurry used for titration. The amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid in the slurry used for titration. The amount of alkali (mmol) required from the start of titration to the first endpoint divided by the solid content (g) in the titrated slurry was defined as the amount of phosphorus oxo acid group (first dissociated acid amount) (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 titrated slurry was defined as the total dissociated acid amount (mmol / g).

[0288] (Measurement of Carboxy Group Amount) The amount of carboxyl groups in the fine fibrous cellulose (equivalent to the amount of carboxyl groups in carboxylated pulp such as TEMPO-oxidized pulp) was measured by adding ion-exchanged water to a fine fibrous cellulose dispersion containing the target fine fibrous cellulose to make the content 0.2 mass%, treating the dispersion with ion-exchange resin, and then titrating it with alkali. Treatment with ion exchange resin was carried out by adding 1 / 10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) to a 0.2% by mass slurry containing fine fibrous cellulose, shaking for 1 hour, and then pouring the mixture onto a mesh with 90 μm openings to separate the resin from the slurry. In addition, alkali titration was performed by measuring the change in pH of the fibrous cellulose-containing slurry after treatment with an ion exchange resin while adding 0.1 N aqueous sodium hydroxide. Observing the change in pH while adding aqueous sodium hydroxide yielded a titration curve like the one shown in Figure 2. As shown in Figure 2, in this neutralization titration, a single point was observed where the increment (the differential value of pH with respect to the amount of alkali added) reached a maximum on the curve plotting the measured pH against the amount of alkali added. This maximum increment was called the first endpoint. The region from the start of the titration to the first endpoint in Figure 2 is called the first region. The amount of alkali required in the first region was equal to the amount of carboxyl groups in the slurry used for titration. The amount of alkali (mmol) required in the first region of the titration curve was divided by the solids content (g) of the fine fibrous cellulose-containing slurry to be titrated to calculate the amount of carboxyl groups introduced (mmol / g). The amount of carboxyl groups introduced (mmol / g) is calculated based on the amount of carboxyl groups introduced (mmol / g) when the counter ions of the carboxyl groups are hydrogen ions (H + ) (hereinafter referred to as the amount of carboxy groups (acid type)) per 1 g of fibrous cellulose.

[0289] (Measurement of sulfur oxoacid and sulfonic acid groups) The amount of sulfur oxoacid or sulfonic acid groups in the fine fibrous cellulose was measured by wet ashing the obtained fibrous cellulose with perchloric acid and concentrated nitric acid, diluting it appropriately, and measuring the amount of sulfur by ICP-OES. The amount of sulfur was divided by the bone-dry mass of the fibrous cellulose used, and the amount of sulfur oxoacid or sulfonic acid groups (mmol / g) was calculated.

[0290] (Measurement of the amount of cationic groups) The amount of cationic groups in the fine fibrous cellulose was determined by carrying out a trace nitrogen analysis and calculating the value using the following formula, which was taken as the amount of cationic groups in the fine fibrous cellulose (mmol / g). (Amount of cationic groups) [mmol / g] = (amount of nitrogen) [g] / 14 × 1000 / (amount of cationic group-introduced fine fibrous cellulose tested) [g]

[0291] [Fiber width measurement] 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 to 0.1% by mass 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, JEOL-2000EX, manufactured by JEOL Ltd.). An arbitrary vertical or horizontal axis representing the image width was assumed within the obtained image, and the magnification was adjusted so that 20 or more fibers intersected the axis. After obtaining an observation image satisfying these conditions, two random axes were drawn vertically and horizontally per image, and the fiber widths of the fibers intersecting the axes were visually determined. Three unique observation images were taken for each dispersion, and the fiber widths of the fibers intersecting the two axes were determined (20 or more × 2 × 3 = 120 or more). The number-average fiber width was calculated from the fiber widths obtained in this manner.

[0292] [Thickness measurement] The thickness of the fine fibrous cellulose-containing sheet was measured using a constant pressure thickness measuring device (PG-02, manufactured by TECLOCK CORPORATION). Specifically, a sheet cut into a size of 50 mm or more was conditioned at 23°C and a relative humidity of 50% for 24 hours, and the thickness was measured at four arbitrary points, and the average value was used as the sheet thickness.

[0293] [Surface roughness measurement] The average spacing Sm of irregularities of the fine fibrous cellulose-containing sheet was first measured by the following method 1. When measurement was not possible using method 1 or when Sm measured by method 1 exceeded 60 μm, it was measured by method 2. Note that if Sm measured by either method was 10 nm or more and 60 μm or less, it was deemed to fall within the scope of the present invention. In addition, the arithmetic mean roughness Ra was measured by method 1. Method 1: The average spacing Sm of irregularities and the arithmetic mean roughness Ra of a sheet containing fine fibrous cellulose were measured using a surface roughness meter (SE-3C, manufactured by Kosaka Laboratory Co., Ltd.). For sheets with transferred irregularities, the transferred surface was used as the measurement surface. In Method 1, the Sm and Ra values ​​were obtained using a method conforming to JIS B 0601:1994. The measurement conditions for the surface roughness meter were a cutoff value of 0.8 mm and an evaluation length of 25 mm. Method 2: The transferred surface of the fine fibrous cellulose-containing sheet was used as the observation surface and observed with a scanning electron microscope. The distance between the bases of adjacent irregularities was measured at 10 points, avoiding overlapping, and the average value was taken as the average distance Sm. The fine fibrous cellulose-containing sheets obtained in Examples 3, 4, 7, 8, 11, 12, 15, 16, 19, 20, 22, 24, 26, 28, 30, 34, 35, 38, 39, 42, 43, and 46 to 50 had fine irregularities that could not be detected by Method 1, so the average spacing Sm was measured by Method 2.

[0294] <Rating 1> The fine fibrous cellulose-containing sheets obtained in Examples 1 to 57 and Comparative Examples 1 and 2 were evaluated according to the following methods.

[0295] [Protein (albumin) adsorption capacity] Test pieces measuring 30 mm square were cut from the sheets. Egg white albumin (Kanto Chemical Co., Inc.) was diluted 100-fold with phosphate buffer (EzPBS(-) manufactured by ATTO Corporation), and 20 μL of the diluted solution was dropped onto the sheets. After air-drying for 30 minutes at 23°C and 50% RH, 0.2% Coomassie Brilliant Blue staining solution (EzStainAqua manufactured by ATTO Corporation) was poured into a petri dish, and the sheets were immersed and held for 5 minutes. During this time, a cleaning solution was prepared by mixing ion-exchange water and methanol in a 60:40 ratio and poured into another petri dish. After 5 minutes, the sheets were removed from the staining solution, immersed in the cleaning solution, and washed for 10 minutes with appropriate shaking. The washed sheets were placed on a polycarbonate plate and dried in a draft until the methanol evaporated. The sheets were then air-dried at 23°C and 50% RH until the water evaporated, and the staining state was observed. The protein (albumin) adsorption capacity was evaluated according to the following criteria. A: After washing, the dye was evenly distributed and sufficiently deep. B: After washing, some unevenness is observed, but the dyeing is still there. C: Slightly stained after washing D: No staining after washing

[0296] The infrared spectra of the albumin-instilled areas of each sheet were measured using a Fourier transform infrared spectrophotometer (FT-IR; ThermoFischer, NicoletNEXUS670) by the ATR method. The infrared spectra were measured under the following conditions: (Infrared Spectroscopic Measurement Conditions) Accumulation count: 64 times, Wavenumber resolution: 4cm -1 , Measurement wavenumber range: 4000 to 650 cm -1 , ATR crystal: diamond, Incident angle: 45° 1540cm originating from the amide group of albumin -1 (C=O bond), and 1650 cm -1It was confirmed whether absorption was observed near the (NH bond), and the evaluation was performed by assigning an A rating to cases where both were observed, and a B rating to cases where neither was observed.

[0297] [Total light transmittance] A test piece measuring 50 mm square was cut out from the sheet. Using this test piece, the total light transmittance was measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K 7361-1:1997.

[0298] [Haze] A test piece measuring 50 mm square was cut out from the sheet, and 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 K 7136:2000.

[0299] [Water resistance (water absorption rate)] A 50 mm square sheet was cut out and conditioned at 23°C and 50% relative humidity for 24 hours. The mass of the sheet was defined as Wd (g), and the mass of the sheet after immersion in ion-exchanged water for 24 hours was defined as W (g). The water absorption rate was calculated using the formula below, and the water resistance was evaluated according to the following criteria (A, B, C). Water absorption rate (%)=(W-Wd) / Wd×100 A: Water absorption rate is less than 1000%, and the shape is maintained extremely well. B: Water absorption rate is over 1000% but less than 2000%, and the shape is maintained. C: Water absorption rate is over 2000% and the shape is barely maintained.

[0300] [Table 1-1]

[0301] [Table 1-2]

[0302] [Table 1-3]

[0303] [Table 1-4]

[0304] [Table 1-5]

[0305] [Table 1-6]

[0306] [Table 1-7]

[0307] [Table 1-8]

[0308] According to Examples 1 to 57, the present invention was able to provide a sheet having high transparency, fine irregularities on the surface, and excellent affinity for biopolymers, and a method for producing the same. On the other hand, the sheets of Comparative Examples 1 and 2, which did not have an uneven surface, did not exhibit any ability to adsorb albumin.

Claims

1. A sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less and a hydrophilic polymer, the total content of fine fibrous cellulose having a fiber width of 1000 nm or less and hydrophilic polymer in the solid content of the sheet is more than 95% by mass; At least one surface of the sheet has an uneven shape, The haze is 80% or less, The average spacing Sm of the uneven shape is 60 μm or less, The arithmetic mean roughness Ra of the surface on which the uneven shape is provided is 700 nm or less. Sheet.

2. The sheet according to claim 1, having a total light transmittance of 85% or more.

3. 3. The sheet according to claim 1, wherein the uneven shape is scattered.

4. The sheet according to any one of claims 1 to 3, wherein the hydrophilic polymer is at least one selected from the group consisting of polyvinyl alcohol, modified polyvinyl alcohol, polyalkylene glycol, polyalkylene oxide, and cellulose derivatives.

5. The sheet according to any one of claims 1 to 4, comprising 10 parts by mass or more and 400 parts by mass or less of a hydrophilic polymer relative to 100 parts by mass of fine fibrous cellulose.

6. The sheet according to any one of claims 1 to 5, wherein the thickness of the sheet is 5 µm or more and 300 µm or less.

7. The sheet according to any one of claims 1 to 6, which is for adsorbing biopolymers.

8. A sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less and a hydrophilic polymer, the total content of fine fibrous cellulose having a fiber width of 1000 nm or less and hydrophilic polymer in the solid content of the sheet is more than 95% by mass; At least one surface of the sheet has an uneven shape, The haze is 80% or less, A method for producing a sheet in which the average spacing Sm of the unevenness is 60 μm or less and the arithmetic mean roughness Ra of the surface on which the unevenness is provided is 700 nm or less, A method for producing a sheet, comprising the following steps A1 and A2 in this order: Step A1: A step of spreading a liquid sheet raw material containing fine fibrous cellulose having a fiber width of 1000 nm or less and a hydrophilic polymer on a substrate having an uneven surface. Step A2: A step of drying the sheet material in this state to obtain a sheet with the concave-convex pattern transferred thereto.

9. A sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less and a hydrophilic polymer, the total content of fine fibrous cellulose having a fiber width of 1000 nm or less and hydrophilic polymer in the solid content of the sheet is more than 95% by mass; At least one surface of the sheet has an uneven shape, The haze is 80% or less, A method for producing a sheet in which the average spacing Sm of the unevenness is 60 μm or less and the arithmetic mean roughness Ra of the surface on which the unevenness is provided is 700 nm or less, A method for producing a sheet, comprising the following steps B1 and B2 in this order: Step B1: A step of placing a sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less and a hydrophilic polymer on a substrate having an uneven surface to obtain a laminate. Step B2: A step of pressing the laminate under heat to transfer the concaves and convexes

10. A sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less, At least one surface of the sheet has an uneven shape, The haze is 80% or less, A method for producing a sheet in which the average spacing Sm of the uneven shapes is 60 μm or less, A method for producing a sheet, comprising the following steps C1 to C3 in this order: Step C1: A step of placing a wet sheet containing fine fibrous cellulose having a fiber width of 1000 nm or less on a substrate having an uneven surface to obtain a laminate. Step C2: Pressurizing the laminate to adhere the sheet to the substrate Step C3: A step of drying the sheet in a state of being in close contact with the substrate to obtain a sheet onto which the concave-convex pattern has been transferred.

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