Sheets and laminates

Abstract

The present invention provides a sheet that has high transparency, suppresses yellowing due to heating, has a high tensile modulus, and is also highly flexible, as well as a laminate having the sheet. [Solution] The sheet of the present invention comprises fine fibrous cellulose with a fiber width of 10 nm or less, and a weight-average molecular weight of 1.0 × 10 4 The above 3.0 × 10 5 This includes the following cellulose derivatives.

Description

[Technical Field]

[0001] The present invention relates to a sheet and a laminate having the sheet. [Background technology]

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

[0003] As a type of fibrous cellulose, fine fibrous cellulose with a fiber diameter of 1 μm or less is also known. Furthermore, sheets composed of such fine fibrous cellulose, as well as sheets containing fine fibrous cellulose and resin, have been developed. In these sheets, the number of contact points between fibers is significantly increased, which is known to greatly improve tensile strength and other properties.

[0004] For example, Patent Documents 1 to 4 disclose sheets containing fine fibrous cellulose and resin. Patent Document 1 describes a sheet containing fibrous cellulose having anionic functional groups and a fiber width of 1000 nm or less, wherein the YI increase rate is 1500% or less. Furthermore, Patent Document 2 describes a cellulose fiber composite comprising cellulose fibers and a matrix having a number-average fiber diameter of 4 to 100 nm, having a haze of 2 or less, and a YI value of 25 or less after four repeated heat treatments at 190°C for 4 hours. Furthermore, Patent Document 3 describes a modified cellulose fiber composite polyvinyl alcohol film containing a polyvinyl alcohol-based resin and modified cellulose fibers. Furthermore, Patent Document 4 discloses a resin composition containing a thermoplastic resin and one or more resins selected from the group consisting of a curable resin selected from epoxy resin, (meth)acrylic resin, phenol resin, unsaturated polyester resin, polyurethane resin, or polyimide resin, and modified cellulose fibers.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] When a sheet containing microfibrillar cellulose is heated, yellowing due to heating may occur, and various attempts have been made for the purpose of suppressing yellowing, as in Patent Documents 1 and 2. In addition, the sheets containing microfibrillar cellulose described in Patent Documents 1 to 4 were high in rigidity and tensile modulus, but low in flexibility and poor in formability. An object of the present invention is to provide a sheet having high transparency, suppressed yellowing by heating, high tensile modulus, and excellent flexibility, and a laminate having the sheet.

Means for Solving the Problems

[0007] The present inventors have found that the above problems can be solved by a sheet containing microfibrillar cellulose and a specific cellulose derivative. The present invention relates to the following <1> to <20>. <1> Fine fibrous cellulose with a fiber width of 10 nm or less, and a weight-average molecular weight of 1.0 × 10⁶ 4 The above 3.0 × 10 5 A sheet containing the following cellulose derivatives. <2> The aforementioned fine fibrous cellulose has anionic groups, <1> The sheet described above. <3> The aforementioned fine fibrous cellulose has a phosphorus oxoacid group or a group derived from a phosphorus oxoacid group, <1> or <2> The sheet described above. <4> The amount of anionic groups in the aforementioned fine fibrous cellulose is less than 0.50 mmol / g. <1> ~ <3> The sheet listed in one of the following options. <5> The amount of anionic groups in the aforementioned fine fibrous cellulose is 0.80 mmol / g or more. <2> or <3> The sheet described above. <6> The aforementioned fine fibrous cellulose contains a carbamide group. <1> ~ <5> The sheet listed in one of the following options. <7> The cellulose derivative is a water-soluble cellulose ether. <1> ~ <6> The sheet listed in one of the following options. <8> The aforementioned water-soluble cellulose ether is nonionic. <7> The sheet described above. <9> The water-soluble cellulose ether has at least one functional group selected from the group consisting of a methoxy group and a hydroxypropoxy group. <7> or <8> The sheet described above. <10> The water-soluble cellulose ether is selected from the group consisting of methylcellulose and hydroxypropylmethylcellulose. <7> ~ <9> The sheet listed in one of the following options. <11> The total content of fine fibrous cellulose and cellulose derivatives in the solid content of the sheet is 90% by mass or more. <1> ~ <10> The sheet listed in one of the following options. <12> The sheet contains 50% by mass or more of fine fibrous cellulose in its solid content. <1> ~ <11> The sheet listed in one of the following options. <13> The change in the Yellow Index (YI value) of the aforementioned sheet before and after heating at 160°C for 6 hours is 1.5 or less. <1> ~ <12> The sheet listed in one of the following options. <14> The haze of the aforementioned sheet is 5% or less. <1> ~ <13> The sheet listed in one of the following options. <15> The total light transmittance of the aforementioned sheet is 90% or more. <1> ~ <14> The sheet listed in one of the following options. <16> The tensile modulus of the sheet is 6.5 GPa or higher. <1> ~ <15> The sheet listed in one of the following options. <17> The tensile elongation of the aforementioned sheet is 3% or more. <1> ~ <16> The sheet listed in one of the following options. <18> <1> ~ <17> A laminate comprising a sheet described in any one of the above, and a resin layer on at least one surface of the sheet. <19> For optical components, <1> ~ <17> The sheet listed in one of the following options. <20> For food containers, cutlery, or straws. <1> ~ <17> The sheet listed in one of the following options. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a sheet that has high transparency, suppresses yellowing due to heating, has a high tensile modulus of elasticity, and is also highly flexible, as well as a laminate having the sheet. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a graph showing the relationship between the amount of NaOH added to a slurry containing fine fibrous cellulose with phosphorus oxoacid groups and the pH. [Figure 2] Figure 2 is a graph showing the relationship between the amount of NaOH added to a slurry containing fine fibrous cellulose with carboxyl groups and the pH. [Figure 3] This is a schematic diagram illustrating a method for evaluating the moldability of sheets. [Modes for carrying out the invention]

[0010] [Sheet] The sheet of the present invention comprises fine fibrous cellulose with a fiber width of 10 nm or less (hereinafter also simply referred to as "fine fibrous cellulose") and a weight-average molecular weight of 1.0 × 10⁻⁶ 4 The above 3.0 × 10 5 The present invention provides a sheet that has high transparency, suppresses yellowing due to heating, has a high tensile modulus, and is also highly flexible. Fine fibrous cellulose is a fiber obtained by defibrating cellulose to a nanoscale with a fiber width of 10 nm or less. Sheets containing fine fibrous cellulose have high transparency and are used in a variety of applications where transparency is required. On the other hand, sheets made from generally obtained fine fibrous cellulose have the problem of yellowing when heated. In addition, sheets containing fine fibrous cellulose have the problem of low flexibility, although they have excellent rigidity and can be obtained with high tensile modulus. Conventionally, attempts have been made to solve the above problems by modifying the microfiber cellulose or by incorporating other components, but it has not been possible to solve all of the above problems. As a result of diligent research by the inventors, it has become clear that by including fine fibrous cellulose and a cellulose derivative having a specific weight-average molecular weight, yellowing during heating is suppressed compared to conventional materials, and furthermore, flexibility is excellent while maintaining rigidity. Although the reason for the above effects is unclear, it is presumed that the high affinity between the fine fibrous cellulose and the cellulose derivative, as well as the low amount of functional groups in the cellulose derivative that cause yellowing, contribute to these effects. The present invention will be described in more detail below.

[0011] <Fine fibrous cellulose> The sheet of the present invention contains fine fibrous cellulose. Fine fibrous cellulose is fibrous cellulose with a fiber width of 10 nm or less. The fiber width of fibrous cellulose can be measured, for example, by electron microscopy. The fiber width of the fine fibrous cellulose is 10 nm or less. From the viewpoint of suppressing the dissolution of cellulose molecules in water and making it easier to exhibit the effects of improved strength, rigidity, and dimensional stability provided by the fine fibrous cellulose, the fiber width of the fine fibrous cellulose is, for example, 1 nm or more, preferably 2 nm or more, 10 nm or less, preferably 8 nm or less, more preferably 6 nm or less, and even more preferably 5 nm or less.

[0012] The average fiber width of the fine fibrous cellulose is preferably 2 nm to 10 nm, and more preferably 2 nm to 5 nm. By setting the average fiber width of the fine fibrous cellulose to 2 nm or more, the solubility of the cellulose molecules in water is suppressed, making it easier to exhibit the effects of improved strength, rigidity, and dimensional stability provided by the fine fibrous cellulose. The fine fibrous cellulose is, for example, monofilamentous cellulose.

[0013] 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% to 0.1% by mass is prepared, and this suspension is cast onto a hydrophilic carbon film-coated grid to prepare a sample for TEM observation. If wide fibers are present, an SEM image of the surface cast on glass may be observed. Next, observation is performed using an electron microscope image at a magnification 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 should be adjusted to meet the following conditions. (1) A straight line X is drawn at any point in the observed image, and 20 or more fibers intersect with this straight line X. (2) A line Y is drawn perpendicular to the line in the same image, and 20 or more fibers intersect with line Y.

[0014] For observation images that satisfy the above conditions, the width of the fibers intersecting with lines X and Y is visually read. In this way, at least three sets of observation images of surface areas that do not overlap are obtained. Next, for each image, the width of the fibers intersecting with lines X and Y is read. This allows for the reading of at least 20 × 2 × 3 = 120 fiber widths. The average of the read fiber widths is then taken as the average fiber width of the fibrous cellulose.

[0015] The fiber length of the fine fibrous cellulose is not particularly limited, but is preferably between 0.1 μm and 1,000 μm, more preferably between 0.1 μm and 800 μm, and even more preferably between 0.1 μm and 600 μm. By keeping the fiber length within the above range, the breakdown of the crystalline region of the fine fibrous cellulose can be suppressed. It is also possible to set the slurry viscosity of the fine fibrous cellulose within an appropriate range. The fiber length of the fine fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

[0016] It is preferable that the fine fibrous cellulose has a type I crystalline structure. Here, the presence of a type I crystalline structure in fine fibrous cellulose can be identified in the diffraction profile obtained from wide-angle X-ray diffraction images using graphite-monochromatized CuKα (λ=1.5418Å). Specifically, it can be identified by the presence of typical peaks at two locations: around 2θ=14° to 17° and around 2θ=22° to 23°. The proportion of type I crystalline structures in the fine fibrous cellulose is 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 is determined by measuring the X-ray diffraction profile and analyzing the pattern using a conventional method (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0017] 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. Setting the axial ratio above the lower limit makes it easier to form sheets containing the fine fibrous cellulose. Also, it is easier to obtain sufficient viscosity when preparing a solvent dispersion. Setting the axial ratio below the upper limit is preferable in that it makes handling easier, such as dilution, when handling the fine fibrous cellulose as an aqueous dispersion.

[0018] In this embodiment, the fine fibrous cellulose preferably has at least one of, for example, an ionic group and a nonionic group. From the viewpoint of improving the dispersibility of fibers in the dispersion medium and increasing the defibration efficiency in the defibration process, it is more preferable that the fine fibrous cellulose has an ionic group. The ionic group may include, for example, either an anionic group or a cationic group, or both. 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 is an anionic group. It is preferable that the cellulose has an ionic group, preferably an anionic group, at least during the defibration process, and the ionic group may be removed after the defibration process. Furthermore, the fine fibrous cellulose does not necessarily need to be subjected to a treatment that introduces ionic groups.

[0019] 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), carboxyl groups or substituents derived from carboxyl groups (sometimes simply referred to as carboxyl groups), sulfur oxoacid groups or substituents derived from sulfur oxoacid groups (sometimes simply referred to as sulfur oxoacid groups), xantate groups, phosphone groups, phosphine groups, sulfone groups, carboxyalkyl groups, etc. 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, carboxyl groups, sulfur oxoacid groups, substituents derived from sulfur oxoacid groups, carboxymethyl groups, carboxyethyl groups, and sulfone groups; more preferably at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxyl 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 enhanced, even under alkaline or acidic conditions, resulting in easier acquisition of high-strength and highly transparent sheets. Examples of cationic groups as ionic groups include ammonium groups, phosphonium groups, and sulfonium groups. Among these, ammonium groups are preferred as the cationic group.

[0020] A phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group is, for example, a substituent represented by the following formula (1). Multiple substituents represented by the following formula (1) may be introduced into each fibrous cellulose. In this case, the multiple substituents represented by the following formula (1) may be the same or different.

[0021] [ka]

[0022] In equation (1), a, b, and n are natural numbers, and m is any number (where a = b × m). Of the n α and α', at least one is O - And the rest are R or OR. Note that all of each α and α' are O - It is acceptable for this to be the case. The n αs may all be the same, or they may all be different. β b+ It is a cation with one or more valencies, composed of organic or inorganic substances.

[0023] R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a derivative thereof. In formula (1), n ​​is preferably 1.

[0024] 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.

[0025] In addition, examples of the inductive group in R include functional groups in which at least one type selected from functional groups such as a carboxy group, a carboxylate group (-COO-), a hydroxy group, an amino group, and an ammonium group is added or substituted with respect to the main chain or side chain of the above various hydrocarbon groups, but it is not particularly limited. The number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphonooxy acid group can be set within an appropriate range, penetration into the fiber raw material can be facilitated, and the yield of microcrystalline cellulose fibers can also be increased. When there are a plurality of Rs in formula (1) or when a plurality of types of substituents represented by the above formula (1) are introduced into fibrous cellulose, the plurality of existing Rs may be the same or different from each other.

[0026] β b+ is a cation of one or more valences composed of an organic or inorganic substance. Examples of the cation of one or more valences composed of an organic substance include organic onium ions. Examples of the organic onium ion include, for example, an organic ammonium ion and an organic phosphonium ion. Examples of the organic ammonium ion include, for example, an aliphatic ammonium ion and an aromatic ammonium ion, and examples of the organic phosphonium ion include, for example, an aliphatic phosphonium ion and an aromatic phosphonium ion. Examples of the cation of one or more valences 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, and the like. When there are a plurality of βs in formula (1) or when a plurality of types of substituents represented by the above formula (1) are introduced into fibrous cellulose, the plurality of existing βs may be the same or different from each other. As the cation of one or more valences composed of an organic or inorganic substance, ions of sodium or potassium, which are less likely to cause yellowing when the fiber raw material containing β is heated and are easy to use industrially, are preferable, but it is not particularly limited. b+ When there are a plurality of βs present or when a plurality of types of substituents represented by the above formula (1) are introduced into fibrous cellulose, the plurality of existing βs b+ may be the same or different from each other. As the cation of one or more valences composed of an organic or inorganic substance, β b+ is preferably an ion of sodium or potassium, which is less likely to cause yellowing when the fiber raw material containing it is heated and is easy to use industrially, but it is not particularly limited.

[0027] More specifically, substituents derived from a phosphorus oxoacid group include a phosphate group (-PO3H2), a salt of a phosphate group, a phosphonotic group (phosphonic acid group) (-PO2H2), and a salt of a phosphonotic group (phosphonic acid group). Furthermore, substituents derived from a phosphorus oxoacid group may also be groups formed by condensation of a phosphate group (e.g., a pyrophosphate group), groups formed by condensation of a phosphonic acid (e.g., a polyphosphonic acid group), phosphate ester groups (e.g., monomethyl phosphate group, polyoxyethylene alkyl phosphate group), alkylphosphonic acid groups (e.g., a methylphosphonic acid group), and the like.

[0028] Furthermore, the sulfur oxoacid group (sulfur oxoacid group or substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). Multiple substituents represented by the following formula (2) may be introduced into each fibrous cellulose. In this case, the substituents represented by the following formula (2) that are introduced may be the same or different.

[0029] [ka]

[0030] In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is any number (where 1 = b × m). Note that if n is 2 or greater, the multiple p values ​​may be the same number or different numbers. In the above structural formula, β b+β is a cation with one or more valencies composed of organic or inorganic substances. Examples of cations with one or more valencies composed of organic substances include organic onium ions. Examples of organic onium ions include organic ammonium ions and organic 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 cations with one or more valencies composed of inorganic substances include alkali metal ions such as sodium, potassium, or lithium, divalent metal ions such as calcium or magnesium, hydrogen ions, and ammonium ions. When multiple substituents represented by the above formula (2) are introduced into fibrous cellulose, multiple β atoms are present. b+ These may be the same or different. As a monovalent or greater cation consisting of organic or inorganic material, β b+ Sodium or potassium ions are preferred because they do not easily yellow when the fiber raw material containing them is heated and are readily available for industrial use, but the material is not particularly limited.

[0031] The amount of ionic groups introduced into fibrous cellulose is preferably 0.10 mmol / g or more per 1 g (mass) of fibrous cellulose, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, even more preferably 0.80 mmol / g or more, and particularly preferably 1.00 mmol / g or more. Furthermore, the amount of ionic groups introduced into fibrous cellulose is preferably 5.20 mmol / g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol / g or less, even more preferably 3.50 mmol / g or less, and even more preferably 3.00 mmol / g or less. By keeping 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. In addition, by keeping the amount of ionic groups introduced within the above range, fine fibrous cellulose can exhibit good properties in various applications such as thickeners. Here, the denominator in mmol / g is the counterion of the ionic group being a hydrogen ion (H + This shows the mass of fibrous cellulose when ). The ionic groups introduced into the fibrous cellulose may remain in the fine fibrous cellulose, or they may be removed after the cellulose has been formed into fine fibrous cellulose, as will be described later. From the viewpoint of suppressing yellowing of the sheet due to heating, it is preferable to remove the ionic groups.

[0032] The amount of ionic groups introduced into fibrous cellulose can be measured, for example, by neutralization titration. In neutralization titration, the amount introduced is determined by adding an alkali such as an aqueous sodium hydroxide solution to the slurry containing the obtained fibrous cellulose and observing the change in pH. Figure 1 is a graph showing the relationship between the amount of NaOH added to fibrous cellulose containing phosphorus oxoacid groups and pH.

[0033] Figure 1 is a graph showing the relationship between the amount of NaOH added to a slurry containing fibrous cellulose with phosphorus oxoacid groups and the pH. The amount of phosphorus oxoacid groups introduced into the fibrous cellulose can be measured, for example, as follows. First, the slurry containing fibrous cellulose is treated with a strong acid ion exchange resin. If necessary, a defibration treatment similar to the defibration treatment process described later may be performed on the sample to be measured before treatment with the strong acid ion exchange resin. Next, the pH change is observed while adding an aqueous sodium hydroxide solution, and a titration curve like the one shown in the upper part of Figure 1 is obtained. In the titration curve shown in the upper part of Figure 1, the measured pH is plotted against the amount of alkali added, and in the titration curve shown in the lower part of Figure 1, the increment (derivative value) (1 / mmol) of pH with respect to the amount of alkali added is plotted. In this neutralization titration, two points are observed in the curve plotting the measured pH against the amount of alkali added where the increment (derivative value of pH with respect to the amount of alkali added) is maximum. Of these, the first maximum increment obtained after starting to add alkali is called the first endpoint, and the next maximum increment obtained is called the second endpoint. The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of the first dissociated acid from the fibrous cellulose contained in the slurry used for titration. The amount of alkali required from the first endpoint to the second endpoint is equal to the amount of the second dissociated acid from the fibrous cellulose contained in the slurry used for titration. The amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid from the fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali required from the start of the titration to the first endpoint by the solid content (g) of the slurry being titrated is the amount of phosphorus oxoacid groups introduced (mmol / g). Note that when simply referred to as the amount of phosphorus oxoacid groups introduced (or amount of phosphorus oxoacid groups), it refers to the amount of the first dissociated acid. In Figure 1, the region from the start of titration to the first endpoint is called the first region, and the region from the first endpoint to the second endpoint is called the second region. For example, if the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the amount of weakly acidic group in the phosphorus oxoacid group (also referred to as the amount of the second dissociated acid in this specification) appears to decrease, and the amount of alkali required in the second region becomes less than the amount of alkali required in the first region. On the other hand, the amount of strongly acidic group in the phosphorus oxoacid group (also referred to as the amount of the first dissociated acid in this specification) is equal to the amount of phosphorus atoms, regardless of whether condensation occurs or not. Also, if the phosphorus oxoacid group is a phosphite group, there is no weakly acidic group in the phosphorus oxoacid group, so the amount of alkali required in the second region becomes less, or in some cases, the amount of alkali required in the second region becomes zero. In this case, there is only one point on the titration curve where the pH increment is maximum. The amount of phosphorus oxoacid groups introduced (mmol / g) mentioned above represents the amount of phosphorus oxoacid groups present in acid-type fibrous cellulose (hereinafter referred to as phosphorus oxoacid group amount (acid type)), since the denominator represents the mass of acid-type fibrous cellulose. On the other hand, if the counterion of the phosphorus oxoacid group is substituted with an arbitrary cation C such that it is equivalent in charge, the amount of phosphorus oxoacid groups present in fibrous cellulose with cation C as the counterion can be determined by converting the denominator to the mass of fibrous cellulose when cation C is the counterion (hereinafter referred to as phosphorus oxoacid group amount (C type)). In other words, it is calculated using the following formula. Phosphorus oxoacid group amount (C type) = Phosphorus oxoacid group amount (acid type) / {1 + (W - 1) × A / 1000} A [mmol / g]: Total amount of anions derived from phosphorus oxoacid groups in fibrous cellulose (the sum of the strongly acidic and weakly acidic groups of the phosphorus oxoacid group). W: Formula weight per unit charge of the cation C (e.g., Na is 23, Al is 9)

[0034] Figure 2 is a graph showing the relationship between the amount of NaOH added to fibrous cellulose containing carboxyl groups and the pH. The amount of carboxyl groups introduced into fibrous cellulose can be measured, for example, as follows: First, the slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, a defibration treatment similar to the defibration treatment described later may be performed on the sample before treatment with the strongly acidic ion exchange resin. Next, the pH change is observed while adding an aqueous sodium hydroxide solution to obtain a titration curve as shown in Figure 2. If necessary, a defibration treatment similar to the defibration treatment described later may be performed on the sample. As shown in Figure 2, in this neutralization titration, a single point is observed in the curve plotting the measured pH against the amount of alkali added, where the increment (the derivative of pH with respect to the amount of alkali added) is maximum. This point of 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 required in the first region of the titration curve (mmol) was then divided by the solid content (g) of the fine fibrous cellulose-containing slurry being titrated to calculate the amount of carboxyl groups introduced (mmol / g). The amount of carboxyl group introduced (mmol / g) mentioned above is calculated based on the fact that the counterion of the carboxyl group is a hydrogen ion (H + This shows the amount of substituents per gram of mass of fibrous cellulose when ) (hereinafter referred to as the amount of carboxyl groups (acid type)).

[0035] The above-mentioned amount of carboxyl groups introduced (mmol / g) represents the amount of carboxyl groups present in acidic fibrous cellulose (hereinafter referred to as carboxyl group amount (acidic type)), since the denominator is the mass of acidic fibrous cellulose. On the other hand, if the counterion of the carboxyl group is substituted with an arbitrary cation C such that it is equivalent in charge, the amount of carboxyl groups present in fibrous cellulose where the cation C is the counterion (hereinafter referred to as carboxyl group amount (C type)) (mmol / g) can be determined by converting the denominator to the mass of fibrous cellulose when the cation C is the counterion. In other words, it is calculated using the following formula. Carboxylate group weight (C type) = Carboxylate group weight (acid type) / {1 + (W - 1) × (Carboxylate group weight (acid type)) / 1000} W: Formula weight per unit charge of the cation C (e.g., Na is 23, Al is 9)

[0036] Furthermore, the amount of sulfur oxoacid groups and sulfone groups introduced into the fine fibrous cellulose is determined by wet ashing the obtained fibrous cellulose with perchloric acid and concentrated nitric acid, then diluting it to an appropriate ratio and measuring the sulfur content by ICP emission spectrometry. The amount of sulfur obtained by dividing this sulfur content by the oven-dry mass of the fibrous cellulose tested is defined as the amount of sulfur oxoacid groups and sulfonic acid groups (unit: mmol / g).

[0037] When measuring substituent amounts by titration, if the amount of sodium hydroxide aqueous solution added is too large or the titration interval is too short, accurate values ​​may not be obtained, resulting in a lower substituent amount than intended. Appropriate titration amounts and intervals include, for example, titrating with 10 to 57 μL of 0.1 N sodium hydroxide aqueous solution over 5 to 30 seconds. Furthermore, to eliminate the influence of carbon dioxide dissolved in the fibrous cellulose-containing slurry, it is desirable to blow an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration until the end of the titration while performing the measurement. The above method for measuring the amount of ionic groups is applicable 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 exceeding 1,000 nm, the pulp fibers should be pulverized before measurement.

[0038] In the present invention, as described above, the fine fibrous cellulose may be obtained by removing at least some of the ionic groups from the fine fibrous cellulose that has been defibrated by introducing the ionic groups described above. From the viewpoint of lowering the YI value before heating and suppressing yellowing due to heating, it is preferable to remove the ionic groups. It should be noted that the removal of ionic groups does not have to be complete; for example, it is preferable to remove the ionic groups so that the amount of ionic groups is less than 0.50 mmol / g. 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. Removing the ionic groups is preferable because it results in a sheet with a low YI value and suppressed yellowing due to heating.

[0039] The microfibrous cellulose may have carbamide groups derived from urea and / or urea derivatives added in the manufacturing process of the microfibrous cellulose described later. In this case, the amount of carbamide groups introduced into the microfibrous cellulose (amount of carbamide groups) is preferably 1.50 mmol / g or less per 1 g (mass) of microfibrous cellulose, more preferably 1.00 mmol / g or less, even more preferably 0.30 mmol / g or less, and particularly preferably 0.20 mmol / g or less. The amount of carbamide groups introduced into the fibrous cellulose (amount of carbamide groups) may be 0.00 mmol / g. Since carbamide groups and phosphorus oxoacid groups are introduced by reaction with the hydroxyl groups of cellulose, the amount of phosphorus oxoacid groups introduced decreases as the amount of carbamide groups introduced increases. Therefore, by keeping the amount of carbamide groups introduced within the above range, the amount of phosphorus oxoacid groups introduced can be increased and set within an appropriate range. Furthermore, since carbamide groups themselves are not electrically conductive, the introduction of carbamide groups does not produce a charge repulsion effect (the fine effect of fibrous cellulose). Therefore, by keeping the amount of carbamide groups introduced within the above range, the amount of phosphorus oxoacid groups introduced can be increased, which more effectively improves the dispersibility of fibrous cellulose in the solvent, making it easier to obtain a highly transparent dispersion containing fine fibrous cellulose.

[0040] The amount of carbamide groups introduced is determined by measuring the amount of nitrogen covalently bonded to the fibrous cellulose. Specifically, ionic nitrogen (ammonium ions) is liberated and removed from the material containing fibrous cellulose, and then the amount of nitrogen is measured by trace nitrogen analysis. The liberation of ionic nitrogen (ammonium ions) is carried out under conditions that substantially do not remove the nitrogen covalently bonded to the cellulose. For example, after the phosphorus oxoacid group introduction step, ammonium ions may be liberated by alkaline treatment, washed and removed, and then defibration treatment may be performed, or ammonium ions may be adsorbed and removed by a strongly acidic ion exchange resin after the defibration treatment step. As a measuring instrument for the amount of nitrogen by trace nitrogen analysis, for example, the TN-110 trace total nitrogen analyzer manufactured by Mitsubishi Chemical Analytec Corporation can be used. Before measurement, the fibrous cellulose is dried at a low temperature (for example, in a vacuum dryer at 40°C for 24 hours) until it is completely dry. The amount of carbamide groups introduced per unit mass of fibrous cellulose (mmol / g) is calculated by dividing the nitrogen content per unit mass of fibrous cellulose (g / g), obtained by trace nitrogen analysis, by the atomic weight of nitrogen.

[0041] [Method for producing fine fibrous cellulose] (Fiber raw materials containing cellulose) Fine fibrous cellulose is produced from cellulose-containing fiber raw materials. While there are no particular limitations on the cellulose-containing fiber raw materials, pulp is preferred due to its availability and low cost. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolved pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen-bleached kraft pulp (OKP), as well as semi-chemical pulp such as semi-chemical pulp (SCP) and chemigroundwood pulp (CGP), and mechanical pulp such as crushed wood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Examples of non-wood pulp include cotton pulp such as cotton linters and cotton lint, and non-wood pulp such as hemp, straw, bamboo, and bagasse. The deinked pulp is not particularly limited, but examples include deinked pulp made from recycled paper. The pulp in this embodiment may be one of the above types used alone, or two or more types may be used in mixture form. Among the pulps mentioned above, wood pulp and deinked pulp are preferred from the standpoint of ease of availability. Among wood pulps, chemical pulp is more preferred from the standpoint of having a high cellulose ratio and a high yield of fine fibrous cellulose during defibration, and from the standpoint of obtaining long-fiber fine fibrous cellulose with a large axial ratio due to minimal cellulose decomposition in the pulp. Kraft pulp and sulfite pulp are even more preferred. It should be noted that using long-fiber fine fibrous cellulose with a large axial ratio tends to result in higher viscosity. As fiber raw materials containing cellulose, for example, cellulose found in sea squirts or bacterial cellulose produced by acetic acid bacteria can be used. Furthermore, instead of using cellulose-containing fiber raw materials, fibers formed from linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can also be used.

[0042] To obtain fine fibrous cellulose into which ionic groups have been introduced as described above, it is preferable to have an ionic group introduction step, 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 the washing step, or in addition to the washing step. Examples of ionic group introduction steps include a phosphorus oxoacid group introduction step, a carboxyl group introduction step, and a sulfur oxoacid group introduction step. Each of these will be described below.

[0043] (Ionic group introduction process) -Phosphorus oxoacid group introduction process- The phosphorus oxoacid 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 oxoacid groups by reacting with the hydroxyl groups present in the cellulose-containing fiber raw material. This step results in the production of phosphorus oxoacid group-introduced fibers. 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 reaction of the cellulose-containing fiber raw material with compound A may be carried out in the absence of compound B. One example of a method for reacting compound A with compound B to a fiber raw material is to mix compound A and compound B with the fiber raw material in a dry, wet, or slurry state. Of these, it is preferable to use a fiber raw material in a dry or wet state, and particularly preferable to use a fiber raw material in a dry state, due to the high uniformity of the reaction. The form of the fiber raw material is not particularly limited, but for example, it is preferably in the form of cotton or a thin sheet. Compounds A and B can be added to the fiber raw material in the form of powder, a solution dissolved in a solvent, or after being heated above the melting point and melted. Of these, it is preferable to add them in the form of a solution dissolved in a solvent, particularly an aqueous solution, due to the high uniformity of the reaction. Compounds A and B may be added to the fiber raw material simultaneously, separately, or as a mixture. The method of adding compounds A and B is not particularly limited, but if compounds A and B are in solution form, the fiber raw material may be immersed in the solution and then removed, or the solution may be added dropwise to the fiber raw material. Alternatively, the required amounts of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material, and then the excess compound A and compound B may be removed by pressing or filtration.

[0044] Compound A used in this embodiment may be any compound having a phosphorus atom and capable of forming an ester bond with cellulose, such as phosphoric acid or its salts, phosphorous acid or its salts, dehydrated condensed phosphoric acid or its salts, or phosphoric anhydride (phosphorus pentoxide), but is not particularly limited. As phosphoric acid, various purities can be used, for example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid can be used. As phosphorous acid, for example, 99% phosphorous acid (phosphonic acid) can be used. Dehydrated condensed phosphoric acid is obtained by condensing two or more molecules of phosphoric acid through a dehydration reaction, and examples include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, and these can be neutralized to various degrees. Of these, phosphoric acid, sodium phosphoric acid, potassium phosphoric acid, or ammonium phosphoric acid are preferred from the viewpoint of high efficiency in introducing phosphate groups, ease of improving defibration efficiency in the defibration process described later, low cost, and ease of industrial application, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, or ammonium dihydrogen phosphate are more preferred. The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted to the amount of phosphorus atoms, it is preferable that the amount of phosphorus atoms added to the fiber raw material (oven-dry mass) be 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By keeping the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, by keeping the amount of phosphorus atoms added to the fiber raw material below the above upper limit, it is possible to balance the effect of improving yield with cost.

[0045] Compound B used in this embodiment is at least one selected from urea and its derivatives, as described above. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, it is preferable to use compound B as an aqueous solution. Furthermore, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved. The amount of compound B added to the fiber raw material (absolute dry weight) is not particularly limited, but is preferably 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, and even more preferably 100% by mass or more and 350% by mass or less.

[0046] In the reaction of cellulose-containing fiber raw materials with compound A, in addition to compound B, other substances such as amides or amines may be included in the reaction system. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is particularly known to act as a good reaction catalyst.

[0047] In the phosphorus oxoacid group introduction process, it is preferable to add or mix compound A or the like to the fiber raw material and then subject the fiber raw material to heat treatment. The heat treatment temperature is preferably selected to efficiently introduce phosphorus oxoacid groups while suppressing thermal decomposition and hydrolysis reactions of the fibers. The heat treatment temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C. Furthermore, various heat transfer devices can be used for the heat treatment, such as agitation dryers, rotary dryers, disc dryers, roll-type heaters, plate-type heaters, fluidized bed dryers, band-type dryers, filtration dryers, vibrating fluidized bed dryers, airflow dryers, vacuum dryers, infrared heaters, far-infrared heaters, microwave heaters, and high-frequency dryers.

[0048] In the heat treatment according to this embodiment, for example, a method can be employed in which compound A is added to a thin sheet-like fiber raw material by impregnation or other methods, and then heated, or a method can be employed in which the fiber raw material and compound A are kneaded or stirred while heating. This makes it possible to suppress uneven concentration of compound A in the fiber raw material and to introduce phosphate groups more uniformly to the surface of the cellulose fibers contained in the fiber raw material. This is thought to be because, as water molecules move to the surface of the fiber raw material during drying, dissolved compound A is attracted to the water molecules by surface tension and similarly moves to the surface of the fiber raw material (i.e., uneven concentration of compound A is created), and this can be suppressed. Furthermore, the heating device used for the heat treatment is preferably one that can constantly discharge moisture from the device system, such as moisture retained in the slurry and moisture generated by the dehydration condensation (phosphate esterification) reaction between compound A and hydroxyl groups contained in cellulose in the fiber raw material. Examples of such heating devices include ovens with a forced-air system. By constantly discharging moisture from the device system, it is possible to suppress the hydrolysis reaction of phosphate ester bonds, which is the reverse reaction of phosphate esterification, as well as the acid hydrolysis of sugar chains in the fibers. As a result, it becomes possible to obtain fine fibrous cellulose with a high axial ratio. The heating time is preferably, for example, 1 second to 300 minutes after substantially removing moisture from the fiber raw material, more preferably 1 second to 1,000 seconds, and even more preferably 10 seconds to 800 seconds. In this embodiment, by setting the heating temperature and heating time within an appropriate range, the amount of phosphorus oxoacid group introduced can be kept within a preferred range.

[0049] The phosphorus oxoacid group introduction step only needs to be performed at least once, but it can also be repeated two or more times. By performing the phosphorus oxoacid group introduction step two or more times, a large number of phosphorus oxoacid groups can be introduced into the fiber raw material. In this embodiment, one example of a preferred embodiment is the case in which the phosphorus oxoacid group introduction step is performed twice.

[0050] The amount of phosphorus oxoacid groups introduced into the fiber raw material is preferably 0.10 mmol / g or more per 1 g (mass) of fibrous cellulose, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, even more preferably 0.80 mmol / g or more, and particularly preferably 1.00 mmol / g or more. Furthermore, the amount of phosphorus oxoacid groups introduced into the fiber raw material is preferably 5.20 mmol / g or less per 1 g (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, the micronization of the fiber raw material can be facilitated, and the stability of the fine fibrous cellulose can be enhanced.

[0051] -Carboxyle group introduction process- The carboxyl group introduction process is carried out by treating the cellulose-containing fiber raw material with oxidation treatments such as ozono-oxidation, Fenton-type oxidation, or TEMPO oxidation treatment, or with a compound having a carboxylic acid-derived group or its derivative, or with an acid anhydride or its derivative of a compound having a carboxylic acid-derived group. Compounds having a carboxylic acid-derived group are not particularly limited, but examples include 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. Furthermore, derivatives of compounds having a carboxylic acid-derived group are not particularly limited, but examples include imidides of acid anhydrides of compounds having a carboxyl group, and derivatives of acid anhydrides of compounds having a carboxyl group. Imidides of acid anhydrides of compounds having a carboxyl group are not particularly limited, but examples include imidides of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0052] Acid anhydrides of compounds having a carboxylic acid-derived group are not particularly limited, but examples include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Furthermore, derivatives of acid anhydrides of compounds having a carboxylic acid-derived group are not particularly limited, but examples include acid anhydrides of compounds having a carboxyl group, such as dimethyl maleic anhydride, diethyl maleic anhydride, and diphenyl maleic anhydride, in which at least some of the hydrogen atoms are substituted with substituents such as alkyl groups and phenyl groups.

[0053] In the carboxyl group introduction step, when performing TEMPO oxidation treatment, it is preferable to carry out the treatment under conditions where the pH is between 6 and 8. Such treatment is also called neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment can be carried out, 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 (pH=6.8). Furthermore, by including sodium hypochlorite, the aldehyde generated during the oxidation process can be efficiently oxidized to the carboxyl group. Furthermore, the TEMPO oxidation treatment may be carried out under conditions where the pH is between 10 and 11. This type of treatment is also called alkaline TEMPO oxidation treatment. Alkaline TEMPO oxidation treatment can be carried out, for example, by adding nitroxy radicals such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp used 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 introducing carboxyl groups by TEMPO oxidation, it is preferable to have 0.10 mmol / g or more per 1 g (mass) of fibrous cellulose, more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, even more preferably 0.80 mmol / g or more, and particularly preferable to have 0.90 mmol / g or more. It is also preferable to have 2.5 mmol / g or less, more preferably 2.20 mmol / g or less, and even more preferably 2.00 mmol / g or less. In addition, when the substituent is a carboxymethyl group, it may be 5.8 mmol / g or less per 1 g (mass) of fibrous cellulose.

[0054] -Sulfur oxoacid group introduction process- The manufacturing process for fine fibrous cellulose may include, for example, a sulfur oxoacid group introduction step as an ionic substituent introduction step. In the sulfur oxoacid group introduction step, a cellulose fiber having a sulfur oxoacid group can be obtained by the reaction of a sulfur oxoacid with a hydroxyl group present in the cellulose-containing fiber raw material.

[0055] In the sulfur oxoacid group introduction step, instead of compound A in the <phosphorus oxoacid group introduction step> described above, at least one compound (hereinafter also referred to as "compound C") selected from compounds that can introduce sulfur oxoacid groups by reacting with hydroxyl groups present in the cellulose-containing fiber raw material is used. Compound C can be any compound that has a sulfur atom and can form an ester bond with cellulose, and examples include sulfuric acid or its salts, sulfurous acid or its salts, and sulfuric acid amides, but is not particularly limited. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid) can be used. As sulfurous acid, 5% sulfurous acid water can be used. As sulfates or sulfurous acid salts, examples include lithium salts, sodium salts, potassium salts, and ammonium salts of sulfates or sulfurous acid salts, and these can be neutralized to various degrees. As sulfuric acid amides, sulfamic acid can be used. In the sulfur oxoacid group introduction step, it is preferable to use compound B in the <phosphorus oxoacid group introduction step> described above in the same manner.

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

[0057] In the heat treatment process, it is preferable to heat until substantially all moisture is removed. Therefore, the heat treatment time varies depending on the amount of moisture contained in the cellulose raw material, the amount of sulfur oxoacid and aqueous solution containing urea and / or urea derivatives added, but it is preferable to heat for at least 10 seconds and no more than 10,000 seconds. Various heat transfer devices can be used for the heat treatment, such as agitation dryers, rotary dryers, disc dryers, roll-type heaters, plate-type heaters, fluidized bed dryers, band-type dryers, filtration dryers, vibrating fluidized bed dryers, airflow dryers, vacuum dryers, infrared heaters, far-infrared heaters, microwave heaters, and high-frequency dryers.

[0058] The amount of sulfur oxoacid groups introduced into the cellulose raw material is preferably 0.05 mmol / g or more, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, even more preferably 0.80 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, and more preferably 3.00 mmol / g or less. By keeping the amount of sulfur oxoacid groups introduced within the above range, it is possible to facilitate the refinement of the fiber raw material and improve the stability of the fibrous cellulose.

[0059] - Oxidation process using a chlorine-based oxidizing agent (second carboxyl group introduction process) - The manufacturing process for fine fibrous cellulose may include an ionic substituent introduction step, such as an oxidation step using a chlorine-based oxidizing agent. In the oxidation step using a chlorine-based oxidizing agent, a carboxyl group is introduced into the fiber raw material by adding the chlorine-based oxidizing agent to a hydroxyl-containing fiber raw material in a wet or dry state and carrying out the reaction.

[0060] Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorite, chlorous acid, chlorite, chloric acid, chlorate, perchloric acid, perchlorate, and chlorine dioxide. Sodium hypochlorite, sodium chlorite, and chlorine dioxide are preferred in terms of substituent introduction efficiency, consequently defibration efficiency, cost, and ease of handling. The chlorine-based oxidizing agent can be added directly to the fiber raw material, or it can be dissolved in a suitable solvent before being added.

[0061] In the oxidation process using a chlorine-based oxidizing agent, the concentration of the chlorine-based oxidizing agent in the solution is preferably 1% by mass or more and 1,000% by mass or less, more preferably 5% by mass or more and 500% by mass or less, and even more preferably 10% by mass or more and 100% by mass or less, when converted to an effective chlorine concentration. 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.

[0062] The reaction time with the chlorine-based oxidizing agent in the oxidation step may vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and even more preferably 20 minutes or more and 400 minutes or less. The pH during the reaction is preferably between 5 and 15, more preferably between 7 and 14, and even more preferably between 9 and 13. Furthermore, it is preferable to maintain a constant pH (e.g., pH 11) at the start of the reaction and throughout the reaction by adding hydrochloric acid or sodium hydroxide as appropriate. After the reaction, excess reaction reagents and by-products may be washed away with water by filtration or other means.

[0063] - Xantate group introduction process (xanthogenic acid esterification process) - The manufacturing process for fine fibrous cellulose may include an ionic substituent introduction step, such as a xantate group introduction step (hereinafter also referred to as the xantate formation step). In the xantate formation step, xantate groups are introduced into the fiber raw material by adding carbon disulfide and an alkali compound to a hydroxyl-containing fiber raw material in a wet or dry state and carrying out the reaction. Specifically, carbon disulfide is added to a fiber raw material that has been alkali-celluloseized by the method described later, and the reaction is carried out.

[0064] ≪Alkali-cellulose formation≫ When introducing ionic functional groups into fiber raw materials, it is preferable to react the cellulose contained in the fiber raw material with an alkaline solution to alkalize the cellulose. This treatment causes some of the hydroxyl groups of the cellulose to ionically dissociate, 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. For their versatility, it is preferable to use, for example, sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, or tetrabutylammonium hydroxide. Alkalicelluloseization may be performed simultaneously with the introduction of ionic functional groups, as a preliminary step, or at both timings.

[0065] The solution temperature at which alkali cellulose formation is initiated is preferably 0°C to 50°C, more preferably 5°C to 40°C, and even more preferably 10°C to 30°C.

[0066] The concentration of the alkaline solution is preferably 0.01 mol / L or more and 4 mol / L or less as a molar concentration, more preferably 0.1 mol / L or more and 3 mol / L or less, and even more preferably 1 mol / L or more and 2.5 mol / L or less. In particular, when the processing temperature is below 10°C, it is preferable that the concentration is 1 mol / L or more and 2 mol / L or less.

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

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

[0069] If the introduction of ionic functional groups and alkali cellulose formation are not carried out simultaneously, it is preferable to separate the alkali cellulose obtained from the alkali treatment into solid and liquid by general deliquidation methods such as centrifugation or filtration to remove moisture. This improves the reaction efficiency in the subsequent ionic functional group introduction step. The cellulose fiber concentration after solid and liquid separation is preferably 5% to 50%, more preferably 10% to 40%, and even more preferably 15% to 35%.

[0070] -Phosphozonic group or phosphine group introduction step (phosphoalkylation step)- The ionic substituent introduction step may include a phosphone group or phosphine group introduction step (phosphoalkylation step). In the phosphoalkylation step, a compound having a reactive group and a phospho group or phosphine group (compound E) is used as an essential component. A ) , by adding an alkaline compound, compound B selected from the aforementioned urea and its derivatives as an optional component, to a hydroxyl-containing fiber raw material in a wet or dry state and carrying out the reaction, a phosphone group or phosphine group is introduced into the fiber raw material.

[0071] Examples of reactive groups include alkyl halides, vinyl groups, and epoxy groups (glycidyl groups). Compound E AExamples include vinylphosphonic acid, phenylvinylphosphonic acid, and phenylvinylphosphinic acid. Compound E is chosen from the standpoint of substituent introduction efficiency, and consequently defibrillation efficiency, cost, and ease of handling. A It is preferable that it be vinylphosphonic acid. Furthermore, it is also preferable to use compound B from the <phosphorus oxoacid group introduction step> described above as an optional component, and the amount added is also preferably as described above.

[0072] Compound E A When adding the reagent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or it may be added after being dissolved in a suitable solvent. It is preferable that the fiber raw material be alkali-cellulosed beforehand or simultaneously with the reaction. The method of alkali-cellulosed treatment is as described above.

[0073] The reaction temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C.

[0074] Compound E A The amount 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 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0075] The reaction time may vary depending on the reaction temperature, but is preferably between 1 minute and 1,000 minutes, more preferably between 10 minutes and 500 minutes, and even more preferably between 15 minutes and 400 minutes. After the reaction, excess reaction reagents, by-products, etc., may be washed away with water by filtration or other means.

[0076] -Sulfone group introduction process (sulfoalkylation process)- The manufacturing process for microfibrous cellulose may include, for example, a sulfone group introduction step (sulfoalkylation step) as an ionic substituent introduction step. In sulfoalkylation, a compound having a reactive group and a sulfone group (compound E) is used as an essential component. B ) and, as an optional component, an alkali compound and compound B selected from urea and its derivatives as described above, are added to a hydroxyl-containing fiber raw material in a wet or dry state and the reaction is carried out to introduce sulfone groups into the fiber raw material.

[0077] Examples of reactive groups include alkyl halides, vinyl groups, and epoxy groups (glycidyl groups). Compound E B Examples include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, and 2-acrylamido-2-methylpropanesulfonic acid. Among these, sodium vinylsulfonate is preferred in terms of substituent introduction efficiency, and consequently defibrillation efficiency, cost, and ease of handling. Furthermore, it is also preferable to use compound B from the <phosphorus oxoacid group introduction step> described above as an optional component, and the amount added is also preferably as described above.

[0078] Compound E B The reagent may be added directly to the fiber raw material, or it may be dissolved in a suitable solvent before being added. It is preferable that the fiber raw material be alkali-cellulosed beforehand or alkali-cellulosed simultaneously with the reaction. The method of alkali-cellulosed reaction is as described above.

[0079] The reaction temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C.

[0080] Compound E BThe amount 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 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0081] The reaction time may vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 10 minutes or more and 500 minutes or less, and even more preferably 20 minutes or more and 400 minutes or less. Furthermore, after the reaction, excess reaction reagents, by-products, etc., may be washed away with water by filtration or other means.

[0082] -Carboxyalkylation process (third carboxyl group introduction process)- The manufacturing process for microfibrous cellulose may include, for example, a carboxyalkylation step as an ionic substituent introduction step. An essential component is a compound having a reactive group and a carboxyl group (compound E C ) Adding an alkaline compound and compound B, selected from urea and its derivatives as described above, as optional components to a hydroxyl-containing fiber raw material in a wet or dry state and carrying out a reaction introduces a carboxyl group to the fiber raw material.

[0083] Examples of reactive groups include alkyl halides, vinyl groups, and epoxy groups (glycidyl groups). Compound E C From the viewpoint of substituent introduction efficiency, and consequently defibration efficiency, cost, and ease of handling, monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred. Furthermore, it is also preferable to use compound B from the <phosphorus oxoacid group introduction step> described above as an optional component, and the amount added is also preferably as described above.

[0084] Compound E CThe reagent may be added directly to the fiber raw material, or it may be dissolved in a suitable solvent before being added. It is preferable that the fiber raw material be alkali-cellulosed beforehand or alkali-cellulosed simultaneously with the reaction. The method of alkali-cellulosed reaction is as described above.

[0085] The reaction temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C.

[0086] Compound E C The amount 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 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0087] The reaction time may vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 3 minutes or more and 500 minutes or less, and even more preferably 5 minutes or more and 400 minutes or less. Furthermore, after the reaction, excess reaction reagents, by-products, etc., may be washed away with water by filtration or other means.

[0088] - Cationic group introduction process (cationization process) - As an essential component, a compound having a reactive group and a cationic group (compound E D ) Adding an alkaline compound, compound B selected from urea and its derivatives as an optional component, to a hydroxyl-containing fiber raw material in a wet or dry state and carrying out a reaction introduces a cationic group to the fiber raw material.

[0089] Examples of reactive groups include alkyl halides, vinyl groups, and epoxy groups (glycidyl groups).

[0090] Compound E DAs such, glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride, etc. are preferred in terms of substituent introduction efficiency, and consequently defibration efficiency, cost, and ease of handling.

[0091] Furthermore, it is also preferable to use compound B from the <phosphorus oxoacid group introduction step> described above as an optional component. The amount added is also preferably as described above.

[0092] Compound E D The reagent may be added directly to the fiber raw material, or it may be dissolved in a suitable solvent before being added. It is preferable that the fiber raw material be alkali-cellulosed beforehand or alkali-cellulosed simultaneously with the reaction. The method of alkali-cellulosed reaction is as described above.

[0093] The reaction temperature is preferably, for example, 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C.

[0094] Compound E D The amount 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 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.

[0095] The reaction time may vary depending on the reaction temperature, but is preferably, for example, 1 minute or more and 1,000 minutes or less, more preferably 5 minutes or more and 500 minutes or less, and even more preferably 10 minutes or more and 400 minutes or less. Furthermore, after the reaction, excess reaction reagents, by-products, etc., may be washed away with water by filtration or other means.

[0096] (Washing process) In the method for producing fine fibrous cellulose according to this embodiment, a washing step can be performed on the ionic group-introduced fibers as needed. The washing step is performed, for example, by washing the ionic group-introduced fibers with water or an organic solvent. Furthermore, the washing step may be performed after each of the steps described later, and the number of washing steps performed in each washing step is not particularly limited.

[0097] (Alkali treatment process) When producing fine fibrous cellulose, an alkaline treatment may be performed on the fiber raw material between the ionic group introduction step and the defibration treatment step described later. The method of alkaline treatment is not particularly limited, but one example is immersing the ionic group-introduced fibers in an alkaline solution. The alkali compound contained in the alkaline solution is not particularly limited and may be an inorganic alkali compound or an organic alkali compound. In this embodiment, it is preferable to use sodium hydroxide or potassium hydroxide as the alkali compound due to its high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. In particular, the solvent contained in the alkaline solution is preferably water or a polar solvent including a polar organic solvent such as alcohol, and more preferably an aqueous solvent containing at least water. As the alkaline solution, for example, an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide is preferred due to its high versatility. The temperature of the alkaline solution in the alkaline treatment process is not particularly limited, but is preferably 5°C to 80°C, and more preferably 10°C to 60°C. The immersion time of the ionic group-introduced fiber in the alkaline solution in the alkaline treatment process is not particularly limited, but is preferably 5 minutes to 30 minutes, and more preferably 10 minutes to 20 minutes. The amount of alkaline solution used in the alkaline treatment is not particularly limited, but is preferably 100% to 100,000% by mass, and more preferably 1,000% to 10,000% by mass, relative to the absolute dry mass of the ionic group-introduced fiber. If the fine fibrous cellulose has anionic groups, the alkaline treatment may be a neutralization treatment or ion exchange treatment of those anionic groups. In this case, the temperature of the alkaline solution is preferably room temperature.

[0098] To reduce the amount of alkaline solution used in the alkaline treatment process, the ionic group-introduced fibers may be washed with water or an organic solvent after the ionic group introduction process and before the alkaline treatment process. After the alkaline treatment process and before the defibration process, it is preferable to wash the alkaline-treated ionic group-introduced fibers with water or an organic solvent to improve handling.

[0099] (Acid treatment process) When producing fine fibrous cellulose, an acid treatment may be performed on the fiber raw material between the step of introducing ionic groups and the defibration treatment step described later. For example, the ionic group introduction step, acid treatment step, alkali treatment step, and defibration treatment step may be performed in this order. The method of acid treatment is not particularly limited, but one example is immersing the fiber raw material in an acidic solution containing an acid. The concentration of the acidic solution used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less. The pH of the acidic solution used is not particularly limited, but is preferably 0 to 4, and more preferably 1 to 3. Examples of acids that can be included in the acidic solution include inorganic acids, sulfonic acids, carboxylic acids, etc. Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid. Among these, the use of hydrochloric acid or sulfuric acid is particularly preferred. The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably 5°C to 100°C, and more preferably 20°C to 90°C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is preferably 5 minutes to 120 minutes, and more preferably 10 minutes to 60 minutes. The amount of acid solution used in the acid treatment is not particularly limited, but is preferably 100% to 100,000% by mass, and more preferably 1,000% to 10,000% by mass, relative to the absolute dry mass of the fiber raw material. If the fine fibrous cellulose has cationic groups, the acid treatment may be a neutralization treatment or ion exchange treatment of those cationic groups. In this case, the temperature of the acid solution is preferably room temperature.

[0100] (Fibring process) By performing a defibration treatment on ionic group-introduced fibers, fine fibrous cellulose can be obtained. In the defibration process, for example, a defibration device can be used. The defibration device is not particularly limited, but examples include high-speed defibrators, grinders (stone mill type grinders), high-pressure homogenizers or ultra-high-pressure homogenizers, high-pressure impact grinders, ball mills, bead mills, disc refiners, conical refiners, twin-screw kneaders, vibrating mills, homomixers under high-speed rotation, ultrasonic dispersers, or beaters. Among the above defibration devices, it is more preferable to use high-speed defibrators, high-pressure homogenizers, or ultra-high-pressure homogenizers, which have less influence from the grinding media and less risk of contamination.

[0101] In the defibration process, for example, it is preferable to dilute the ionic group-introduced fibers with a dispersion medium to form a slurry. As the dispersion medium, one or more selected from water and organic solvents such as polar organic solvents can be used. The polar organic solvent is not particularly limited, but for example, alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotonic polar solvents are preferred. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

[0102] The solid content concentration of the fine fibrous cellulose during the defibration process can be set as appropriate. Furthermore, the slurry obtained by dispersing the phosphorus oxoacid group-introduced fibers in a dispersion medium may contain solid components other than the phosphorus oxoacid group-introduced fibers, such as hydrogen-bonding urea.

[0103] (Method for 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, which are substituents, from the fine fibrous cellulose that has been defibrated by introducing the ionic groups described above. From the viewpoint of lowering the YI value of the sheet and suppressing yellowing due to heating, it is preferable to remove the ionic groups. In this case, it is preferable to include a step (Step I) of removing at least a portion of substituents from fine fibrous cellulose having substituents, preferably ionic groups, and having a fiber width of 1000 nm or less, and a step (Step II) of uniform dispersion treatment after Step I. Furthermore, it is preferable that the fine fibrous cellulose subjected to step I has a step to reduce the amount of nitrogen (nitrogen removal step) before the defibration treatment.

[0104] -Nitrogen removal process- The manufacturing process for the fine fibrous cellulose subjected to step I may further include a step to reduce the amount of nitrogen (nitrogen removal treatment step). By reducing the amount of nitrogen, it is possible to obtain fine fibrous cellulose that can further suppress discoloration. The nitrogen removal treatment step may be provided after the uniform dispersion treatment step in step II described later, but it is preferable to provide it before the uniform dispersion treatment step in step II described later. It is also preferable to provide it before the defibration treatment step described above.

[0105] In the nitrogen removal process, it is preferable to adjust the pH of the slurry containing the anionic group-introduced fibers to 10 or higher and then perform a heat treatment. In the heat treatment, it is preferable to set the slurry temperature to 50°C or higher and 100°C or lower, and the heating time to 15 minutes or higher and 180 minutes or lower. When adjusting the pH of the slurry containing the anionic group-introduced fibers, it is preferable to add an alkaline compound that can be used in the alkali treatment process described above to the slurry.

[0106] After the nitrogen removal process, a washing process can be performed on the anionic group-introduced fibers as needed. The washing process is carried out, for example, by washing the anionic group-introduced fibers with water or an organic solvent. Furthermore, there is no particular limit to the number of washing cycles performed in each washing process.

[0107] -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 substituents from fine fibrous cellulose having substituents and a fiber width of 10 nm or less. In this specification, the step (Step I) of removing at least a portion of substituents from fine fibrous cellulose is also referred to as the substituent removal step.

[0108] The substituent removal process includes steps such as heat treatment, enzymatic treatment, acid treatment, and alkali treatment of fine fibrous cellulose having substituents and a fiber width of 10 nm or less. These may be performed individually or in combination. Among these, the substituent removal process is preferably a heat treatment or an enzymatic treatment. By going through the above treatment process, at least a portion of the substituents are removed from the fine fibrous cellulose having substituents and a fiber width of 10 nm or less, and for example, fine fibrous cellulose with a substituent introduction amount of less than 0.5 mmol / g can be obtained. The above-described substituent removal process is particularly suitable when the substituent is a phosphorus oxoacid group or a sulfur oxoacid group. The amount of substituent introduced after the substituent removal process 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.

[0109] The substituent removal process is preferably carried out in slurry form. Specifically, the substituent removal process is preferably a process of heat treatment, enzymatic treatment, acid treatment, alkali treatment, etc., of a slurry containing fine fibrous cellulose having substituents and a fiber width of 10 nm or less. By carrying out the substituent removal process in slurry form, it is possible to prevent the formation of coloring substances caused by heating during the substituent removal process, as well as the residue of added or generated acids, alkalis, salts, etc. This makes it possible to suppress discoloration when the fine fibrous cellulose obtained through step II is made into a slurry or sheet. Furthermore, if a salt removal process is carried out after the substituent removal process to remove salts derived from the substituents, it is also possible to improve the efficiency of salt removal.

[0110] When a substituent removal treatment is performed on a slurry containing fine fibrous cellulose having substituents and a fiber width of 10 nm or less, the concentration of fine fibrous cellulose in the slurry is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. Furthermore, the concentration of fine fibrous cellulose in the slurry is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. By keeping the concentration of fine fibrous cellulose in the slurry within the above range, the substituent removal treatment can be performed more efficiently. In addition, by keeping the concentration of fine fibrous cellulose in the slurry within the above range, it is possible to prevent the residue of coloring substances generated by heating during the substituent removal treatment, as well as added or generated acids, alkalis, salts, etc. This makes it possible to suppress coloring when the fine fibrous cellulose obtained through step II is made into a slurry or sheet. Furthermore, when a salt removal treatment is performed on the salts derived from the substituents removed after the substituent removal treatment, it is also possible to improve the efficiency of salt removal.

[0111] When the substituent removal process involves heat-treating fine fibrous cellulose having substituents and a fiber width of 10 nm or less, the heating temperature in the heat-treating process is preferably 40°C or higher, more preferably 50°C or higher, and even more preferably 60°C or higher. Furthermore, the heating temperature in the heat-treating process is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower. In particular, when the substituents on the fine fibrous cellulose subjected to the substituent removal process are phosphorus oxoacid groups or sulfone groups, the heating temperature in the heat-treating process is preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher.

[0112] If the substituent removal process is a heat treatment process, the heating equipment that can be used in the heat treatment process is not particularly limited, but may include hot air heaters, steam heaters, electric heaters, hydrothermal heaters, thermal heaters, infrared heaters, far-infrared heaters, microwave heaters, high-frequency heaters, stirring dryers, rotary dryers, disc dryers, roll-type heaters, plate-type heaters, fluidized bed dryers, band-type dryers, filtration dryers, vibrating fluidized bed dryers, airflow dryers, and vacuum dryers. From the viewpoint of preventing evaporation, heating is preferably carried out in a closed system, and from the viewpoint of increasing the heating temperature, it is preferable to carry out the heating in a pressure-resistant device or container. The heat treatment may be a batch process, a batch continuous process, or a continuous process.

[0113] When the substituent removal process involves enzymatically treating fine fibrous cellulose having substituents and a fiber width of 10 nm or less, it is preferable to use phosphate hydrolase, sulfate hydrolase, or the like in the enzymatic treatment process, depending on the type of substituent. In the enzyme treatment step, enzyme is added to 1 g of fine fibrous cellulose such that the enzyme activity is preferably 0.1 nkat or higher, more preferably 1.0 nkat or higher, and even more preferably 10 nkat or higher. Alternatively, enzyme may be added to 1 g of fine fibrous cellulose such that the enzyme activity 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 the mixture for 1 minute to 100 hours under conditions of 0°C to less than 50°C. A step to deactivate the enzyme after the enzymatic reaction may be included. Methods for deactivating the enzyme include adding an acidic or alkaline component to the enzyme-treated slurry to deactivate the enzyme, or raising the temperature of the enzyme-treated slurry to 90°C or higher to deactivate the enzyme.

[0114] If the substituent removal step is a step of acid-treating fine fibrous cellulose having substituents and a fiber width of 10 nm or less, it is preferable to add an acid compound that can be used in the above-described acid treatment step to the slurry during the acid treatment step.

[0115] If the substituent removal step is a step of alkali treatment of fine fibrous cellulose having substituents and a fiber width of 10 nm or less, it is preferable to add an alkali compound that can be used in the alkali treatment step described above to the slurry during the alkali treatment step.

[0116] In the substituent removal process, it is preferable that the substituent removal reaction proceeds uniformly. To ensure uniform reaction, for example, the slurry containing fine fibrous cellulose may be stirred, or the specific surface area of ​​the slurry may be increased. Methods of stirring the slurry include applying external mechanical shear, or promoting self-stirring by increasing the slurry delivery rate during the reaction.

[0117] In the substituent removal process, spacer molecules may be added. These spacer molecules penetrate between adjacent microfibrous cellulose molecules, thereby acting as spacers to create fine spaces between them. Adding such spacer molecules during the substituent removal process can suppress the aggregation of microfibrous cellulose after the treatment. This allows for a more effective improvement in the transparency of dispersions and sheets containing microfibrous cellulose. The spacer molecule is preferably a water-soluble organic compound. Examples of water-soluble organic compounds include sugars, water-soluble polymers, and urea. Specifically, examples include trehalose, urea, polyethylene glycol (PEG), polyethylene oxide (PEO), carboxymethylcellulose, and polyvinyl alcohol (PVA). Furthermore, water-soluble organic compounds such as 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, pectin, cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, amylose, and other starches, as well as glycerin, diglycerin, polyglycerin, hyaluronic acid, and metal salts of hyaluronic acid can also be used.

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

[0119] -pH adjustment process- If the substituent removal process is carried out in slurry form, a step to adjust the pH of the slurry containing fine fibrous cellulose may be provided before the substituent removal process. For example, anionic groups may be introduced into cellulose fibers, and the counterions of these anionic groups may be Na +In this case, the slurry containing the fine fibrous cellulose after defibration will be weakly alkaline. If heated in this state, monosaccharides, which are one of the causes of discoloration, may be generated due to the decomposition of cellulose, so it is preferable to adjust the pH of the slurry to 8 or below. Similarly, monosaccharides may also be generated under acidic conditions, so it is preferable to adjust the pH of the slurry to 3 or above.

[0120] Furthermore, if the substituted microfiber cellulose is a microfiber cellulose having a phosphate group, it is preferable that the phosphorus of the phosphate group is in a state that is easily susceptible to nucleophilic attack, from the viewpoint of improving the efficiency of substituent removal. Cellulose-OP(=O)(-O-H+)(-O-Na) is susceptible to nucleophilic attack. + This represents a neutralization degree of 1, and to achieve this state, it is preferable to adjust the pH of the slurry to 3 or more and 8 or less, and more preferably to adjust the pH to 4 or more and 6 or less.

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

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

[0123] <Salt removal process> It is preferable to remove salts derived from the removed substituents after the substituent removal process. Removing the substituent-derived salts makes it easier to obtain fine fibrous cellulose that can suppress discoloration. The means for removing substituent-derived salts are not particularly limited, but examples include washing and ion exchange. Washing is performed by washing the fine fibrous cellulose aggregated in the substituent removal process with, for example, water or an organic solvent. In the ion exchange process, an ion exchange resin can be used.

[0124] -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 substituents from fine fibrous cellulose having substituents and a fiber width of 1000 nm or less, and a step (Step II) of uniform dispersion treatment after Step I. The uniform dispersion treatment step (Step II) is a step of uniformly dispersing the fine fibrous cellulose obtained after the substituent removal treatment in Step I. In Step I, by subjecting the fine fibrous cellulose to the substituent removal treatment, at least a portion of the fine fibrous cellulose aggregates. Step II is a step of uniformly dispersing the fine fibrous cellulose that has been aggregated in this way. The state in which the fine fibrous cellulose is uniformly dispersed in Step II refers to a state in which the fiber width of the fine fibrous cellulose is 10 nm or less. Thus, even with a low substituent introduction amount of less than 0.50 mmol / g, the fine fibrous cellulose obtained by the production method of this embodiment has a fiber width of 10 nm or less.

[0125] In the process of uniform dispersion (process II), for example, a high-speed defibrator, grinder (stone mill type grinder), high-pressure homogenizer, high-pressure impact grinder, ball mill, bead mill, disc refiner, conical refiner, twin-screw kneader, vibrating mill, homomixer under high-speed rotation, ultrasonic disperser, or beater can be used. Among the above uniform dispersion processing devices, the use of a high-speed defibrator and a high-pressure homogenizer is more preferable. The processing conditions in the uniform dispersion process (Step II) are not particularly limited, but it is preferable to increase the maximum movement speed of the fine fibrous cellulose during processing and the processing pressure. In a high-speed defibrator, the peripheral speed is preferably 20 m / sec or more, more preferably 25 m / sec or more, and even more preferably 30 m / sec or more. A high-pressure homogenizer can be used more preferably than a high-speed defibrator because it allows for a higher maximum movement speed of the fine fibrous cellulose during processing and a higher processing pressure. In high-pressure homogenizer processing, the processing pressure is preferably 1 MPa to 350 MPa, more preferably 10 MPa to 300 MPa, and even more preferably 50 MPa to 250 MPa.

[0126] Furthermore, in step II, the aforementioned spacer molecules may be added. By adding such spacer molecules in the uniform dispersion process of step II, the uniform dispersion of the fine fibrous cellulose can be performed more smoothly. This makes it possible to more effectively improve the transparency of the dispersion liquid or sheet containing the fine fibrous cellulose.

[0127] The content of fine fibrous cellulose in the solid content of the sheet is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 25% by mass or more, even more preferably 50% by mass or more, particularly preferably 65% ​​by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, even more preferably 80% by mass or less, particularly preferably 75% by mass or less, from the viewpoint of obtaining transparency of the sheet, suppression of yellowing due to heating, high tensile modulus, and high flexibility. As the fine fibrous cellulose, a combination of fine fibrous cellulose containing ionic groups and unmodified fine fibrous cellulose may be used.

[0128] <Cellulose derivatives> In the present invention, the sheet contains, in addition to the above-mentioned fine fibrous cellulose, a weight-average molecular weight of 1.0 × 10 4 The above 3.0 × 10 5The following cellulose derivatives are included. By using a sheet containing fine fibrous cellulose and a cellulose derivative having a specific weight-average molecular weight, a sheet can be obtained that has high transparency, suppresses yellowing due to heating, has a high tensile modulus, and is also highly flexible. The weight-average molecular weight of the cellulose derivative is preferably 2.5 × 10⁶, from the viewpoint of achieving both high tensile modulus and high tensile elongation, and suppressing yellowing before and after heating, while also considering shape stability as a sheet and suppressing gelation. 4 The above is more comfortable 5.0 × 10 4 More preferably 1.0 × 10 5 The above, and preferably 2.8 × 10 5 Below, 5 The following applies: The weight-average molecular weight of cellulose derivatives is measured by gel permeation chromatography (GPC-MALLS) using light scattering.

[0129] As a cellulose derivative, a water-soluble cellulose ether is preferred from the viewpoint of increasing affinity with fine fibrous cellulose and from the viewpoint of easy addition to a slurry of fine fibrous cellulose (dispersion of fine fibrous cellulose). Here, water soluble means that 1 g or more dissolves in 100 g of water at 20°C. Furthermore, cellulose ethers are a general term for cellulose derivatives in which the hydroxyl groups of cellulose have been etherified. Examples of water-soluble cellulose ethers include methylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylcellulose, and carboxyethylcellulose. Furthermore, the water-soluble cellulose is preferably a nonionic water-soluble cellulose ether from the viewpoint of suppressing yellowing of the sheet due to heating. Examples of nonionic water-soluble cellulose ethers include methylcellulose, hydroxyethyl methylcellulose, hydroxypropyl methylcellulose, ethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose. The nonionic water-soluble cellulose ether preferably has at least one functional group selected from the group consisting of methoxy groups and hydroxypropoxy groups, more preferably selected from the group consisting of methylcellulose and hydroxypropylmethylcellulose, and even more preferably hydroxypropylmethylcellulose.

[0130] When the cellulose derivative is methylcellulose, the degree of substitution of the methoxy group is preferably 0.5 or more, more preferably 0.8 or more, even more preferably 1.0 or more, even more preferably 1.2 or more, particularly preferably 1.5 or more, and preferably 3.0 or less, more preferably 2.6 or less, even more preferably 2.2 or less, and even more preferably 2.0 or less. When the cellulose derivative is hydroxypropyl methylcellulose, the preferred range for the degree of substitution of the methoxy group is the same as the degree of substitution of the methoxy group in methylcellulose described above. Furthermore, the degree of substitution of the hydroxypropoxy group is preferably 0.08 or higher, more preferably 0.10 or higher, even more preferably 0.12 or higher, even more preferably 0.15 or higher, particularly preferably 0.18 or higher, and preferably 0.50 or lower, more preferably 0.40 or lower, even more preferably 0.35 or lower, and even more preferably 0.30 or lower.

[0131] The content of cellulose derivatives in the solid content of the sheet is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 75% by mass or less, even more preferably 50% by mass or less, particularly preferably 35% by mass or less, and preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, even more preferably 20% by mass or more, particularly preferably 25% by mass or more, from the viewpoint of obtaining transparency of the sheet, suppression of yellowing due to heating, high tensile modulus, and high flexibility.

[0132] In this embodiment, the total content of fine fibrous cellulose and cellulose derivatives in the solid content of the sheet is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more, and 100% by mass or less, and particularly preferably 100% by mass, from the viewpoint of obtaining transparency of the sheet, suppression of yellowing due to heating, high tensile modulus, and high flexibility.

[0133] <Optional ingredients> The sheet may contain optional components in addition to fine fibrous cellulose and cellulose derivatives. Examples of optional components include hydrophilic polymers (excluding cellulose derivatives), hydrophilic low molecular weights, paper strength enhancers, thermoplastic resins, surfactants, organic ions, coupling agents, inorganic layered compounds, inorganic compounds, leveling agents, preservatives, defoamers, organic particles, lubricants, antistatic agents, UV protection agents, dyes, pigments, stabilizers, magnetic powders, orientation enhancers, plasticizers, dispersants, color inhibitors, polymerization inhibitors, pH adjusters, and crosslinking agents.

[0134] Examples of hydrophilic polymers include polyethylene glycol, polyethylene oxide, polyvinyl alcohol, modified polyvinyl alcohol (acetoacetylated polyvinyl alcohol, etc.), polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylates, polyacrylamide, alkyl acrylate copolymers, and urethane copolymers. Examples of hydrophilic low molecular weight molecules include glycerin, sorbitol, and ethylene glycol. Examples of organic ions include tetraalkylammonium ions and tetraalkylphosphonium ions. Examples of tetraalkylammonium ions include tetramethylammonium ions, tetraethylammonium ions, tetrapropylammonium ions, tetrabutylammonium ions, tetrapentylammonium ions, tetrahexylammonium ions, tetraheptylammonium ions, tributylmethylammonium ions, lauryltrimethylammonium ions, cetyltrimethylammonium ions, stearyltrimethylammonium ions, octyldimethylethylammonium ions, lauryldimethylethylammonium ions, didecyldimethylammonium ions, lauryldimethylbenzylammonium ions, and tributylbenzylammonium ions. Examples of tetraalkylphosphonium ions include tetramethylphosphonium ions, tetraethylphosphonium ions, tetrapropylphosphonium ions, tetrabutylphosphonium ions, and lauryltrimethylphosphonium ions. Additionally, examples of tetrapropylonium ions and tetrabutylonium ions include tetra-n-propylonium ions and tetra-n-butylonium ions, respectively.

[0135] <Sheet Characteristics> [Yellow Index] When the sheet of this embodiment is heated at 160°C for 6 hours, the change in the yellow index (YI value) before and after heating is preferably 5.0 or less, more preferably 4.5 or less, even more preferably 3.5 or less, even more preferably 2.5 or less, even more preferably 1.5 or less, even more preferably 1.2 or less, and even more preferably 1.0, with no particular lower limit. It is preferable that the change in the YI value before and after heating is within the above range because yellowing due to heating is suppressed. The YI value before heating is preferably 1.2 or less, more preferably 1.0 or less, even more preferably 0.8 or less, and still more preferably 0.5 or less. The lower limit is not particularly limited. Furthermore, the YI value after heating is preferably 5.0 or less, more preferably 4.0 or less, even more preferably 3.0 or less, even more preferably 2.5 or less, even more preferably 2.0 or less, and even more preferably 1.5 or less. The YI value is measured in accordance with JIS K 7373:2006.

[0136] [Hayes] The sheet of this embodiment preferably has a haze content of 5% or less. A haze content of 5% or less is preferable because it provides excellent transparency. The sheet haze is preferably 5% or less, more preferably 4% or less, even more preferably 3% or less, and still more preferably 2% or less. The haze of the sheet is measured using a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute Co., Ltd.) in accordance with JIS K 7136:2000.

[0137] [Total light transmittance] The total light transmittance of the sheet in this embodiment 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%. It is preferable that the total light transmittance of the sheet is within the above range because it exhibits excellent transparency. Here, the total light transmittance of the sheet is a value measured using a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute Co., Ltd.) in accordance with, for example, JIS K 7361-1:1997.

[0138] The tensile modulus of the sheet in this embodiment is preferably 4.0 GPa or higher, more preferably 5.5 GPa or higher, even more preferably 6.5 GPa or higher, even more preferably 7.5 GPa or higher, and particularly preferably 8.0 GPa or higher. There is no upper limit, but from the viewpoint of balancing flexibility, it is preferably 15 GPa or lower, more preferably 12 GPa or lower, and even more preferably 10 GPa or lower. A tensile modulus of the sheet within the above range is preferable because it exhibits excellent rigidity. Here, the tensile modulus of the sheet is a value measured using a Tensilon tensile testing machine (manufactured by A&D Company, Limited) in accordance with JIS P 8113:2006, for example. When measuring the tensile modulus, the test specimen is prepared by conditioned it at 23°C and 50% relative humidity for 24 hours, and the measurement is performed under the conditions of 23°C and 50% relative humidity.

[0139] The tensile elongation of the sheet in this embodiment is preferably 3% or more, more preferably 4% or more, even more preferably 5% or more, and even more preferably 7% or more. There is no upper limit, but from the viewpoint of balancing rigidity and flexibility, it is preferably 50% or less, more preferably 40% or less, even more preferably 30% or less, and even more preferably 20% or less. A tensile elongation within the above range is preferable because it provides excellent flexibility. The tensile elongation of the sheet was measured using a Tensilon tensile testing machine (manufactured by A&D Company, Limited) in accordance with JIS K 7127:1999. When measuring the tensile modulus of elasticity, the test specimen was conditioned for 24 hours at 23°C and 50% relative humidity, and the measurement was performed under the conditions of 23°C and 50% relative humidity.

[0140] The tensile strength of the sheet in this embodiment is preferably 60 MPa or more, more preferably 70 MPa or more, even more preferably 80 MPa or more, and even more preferably 85 MPa or more. There is no upper limit, but from the viewpoint of balancing rigidity and flexibility, it is preferably 200 MPa or less, more preferably 180 MPa or less, even more preferably 160 MPa or less, and even more preferably 150 MPa or less. The tensile strength of the sheet was measured using a Tensilon tensile testing machine (manufactured by A&D Company, Limited) in accordance with JIS K 7127:1999. When measuring tensile strength, the test specimen was conditioned for 24 hours at 23°C and 50% relative humidity, and the measurement was performed under the conditions of 23°C and 50% relative humidity.

[0141] The surface pH of the sheet of the present invention is preferably 5.00 or higher, more preferably 5.20 or higher, and even more preferably 5.40 or higher. Furthermore, the surface pH of the sheet is preferably 7.0 or lower. The surface pH of the sheet is a value measured, for example, with a calibrated pH meter (Horiba, Ltd., F-53). The surface pH of the sheet is measured by moistening a small amount of water on the sheet and then contacting that area with a flat-type pH composite electrode (Horiba, Ltd., 6261-10C).

[0142] [Thickness] The thickness of the sheet in this embodiment is not particularly limited, but is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. Furthermore, the sheet thickness is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. The sheet thickness is preferably adjusted as appropriate depending on the application. The sheet thickness can be measured using a constant-pressure thickness gauge (TECLOCK CORPORATION, PG-02). The sheet thickness is measured according to the following method: A sheet cut to a size of 50 mm square or larger is conditioned at 23°C and 50% relative humidity for 24 hours, and then the thickness of four arbitrary points is measured, and the average value is taken as the sheet thickness.

[0143] [Basic weight] The basis weight of the sheet is 10 g / m². 2 Preferably, it is 20 g / m 2 It is more preferable that the amount be greater than or equal to 30 g / m 2 It is even more preferable that the above conditions are met. Furthermore, while there are no particular restrictions on the basis weight of the sheet, 1000 g / m² is preferred. 2 Preferably, it is 500g / m 2 It is more preferable that the following conditions apply: 200 g / m² 2 It is even more preferable that the following conditions apply: 100 g / m² 2 The following is particularly preferable: The basis weight of the sheet is calculated according to the following method: A sheet cut to a size of 50 mm square or larger is conditioned at 23°C and 50% relative humidity for 24 hours, its mass is measured, and this mass is divided by the area of ​​the cut sheet to calculate the basis weight of the sheet.

[0144] (density) The density of the sheet is 1.00 g / cm³. 3 Preferably, it is 1.10 g / cm³ or more. 3 It is more preferable that the amount be greater than or equal to 1.20 g / cm³. 3 It is even more preferable that the above conditions are met. Furthermore, the density of the sheet is not particularly limited, but 3.00 g / cm³ is preferable. 3 Preferably, it is 1.70 g / cm³. 3 It is more preferable that the following is the case: 1.50 g / cm³ 3 The following is even more preferable: The density of the sheet is calculated by dividing the basis weight of the sheet by its thickness.

[0145] The sheet of this embodiment is preferably not a porous sheet. That is, the void ratio and porosity are preferably 10% or less, more preferably 3% or less, even more preferably 1% or less, and even more preferably 0.1% or less.

[0146] [Method of manufacturing the sheet] This paper describes a sheet containing fine fibrous cellulose and cellulose derivatives with a fiber width of 10 nm or less. In this embodiment, the sheet can be obtained by performing a sheet formation process described later using a liquid composition containing, for example, the fine fibrous cellulose and cellulose derivatives described above, as well as other components. The sheet manufacturing process preferably includes at least a coating step of coating the composition onto a substrate, or a papermaking step of forming the slurry into paper. This yields a sheet containing fine fibrous cellulose and cellulose derivatives.

[0147] -Coating Process- In the coating process, for example, a slurry containing fine fibrous cellulose and cellulose derivatives is coated onto a substrate, and the resulting sheet is dried and then peeled off the substrate to obtain a sheet. Furthermore, by using a coating apparatus and a long or continuous substrate, sheets can be produced continuously. The material of the substrate used in the coating process is not particularly limited, but a material with high wettability to the composition (slurry) is preferable as it can suppress shrinkage of the sheet during drying. However, it is preferable to select a material 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 are not particularly limited. For example, resin films or plates such as acrylic, polyethylene terephthalate, vinyl chloride, polystyrene, polypropylene, polycarbonate, and polyvinylidene chloride, metal films or plates of aluminum, zinc, copper, and iron, and those with oxidized surfaces, stainless steel films or plates, brass films or plates, etc. can be used. In the coating process, if the viscosity of the slurry is low and it spreads on the substrate, a damming frame may be fixed to the substrate to obtain a sheet of a predetermined thickness and basis weight. The damming frame is not particularly limited, but it is preferable to select one that allows the edges of the sheet that adhere after drying to be easily peeled off. From this viewpoint, 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, as well as metal plates such as aluminum plates, zinc plates, copper plates, and iron plates, and those whose surfaces have been oxidized, stainless steel plates, brass plates, etc., can be used. The coating machine used to apply the slurry to the substrate is not particularly limited, but for example, a roll coater, gravure coater, die coater, curtain coater, air doctor coater, etc. can be used. Die coaters, curtain coaters, and spray coaters are particularly preferred because they can make the sheet thickness more uniform.

[0148] The slurry temperature and ambient temperature (hereinafter, the slurry temperature and ambient temperature are collectively referred to as the "coating temperature") when coating the slurry onto the substrate are not particularly limited, but are preferably 5°C to 80°C, more preferably 10°C to 60°C, even more preferably 15°C to 50°C, and particularly preferably 20°C to 40°C. If the coating temperature is above the lower limit, the slurry can be coated more easily. If the coating temperature is below the upper limit, the volatilization of the dispersion medium during coating can be suppressed. In the coating process, it is preferable to coat the substrate with the slurry so that the finished basis weight and thickness of the sheet fall within the preferred range described above. By coating the substrate with the basis weight and thickness within the above range, a sheet with superior transparency, rigidity, and flexibility can be obtained.

[0149] As described above, the coating process includes a step of drying the slurry coated onto the substrate. The step of drying the slurry 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. Non-contact drying methods are not particularly limited, but can include methods of drying by heating with hot air, infrared rays, far-infrared rays, or near-infrared rays (heat drying method), or methods of drying in a vacuum (vacuum drying method). Heat drying and vacuum drying methods can be combined, but heat drying is usually used. Drying with infrared rays, far-infrared rays, or near-infrared rays is not particularly limited, but can be carried out using, for example, an infrared device, a far-infrared device, or a near-infrared device. The heating temperature in the heat drying method is not particularly limited, but is preferably between 20°C and 150°C, and more preferably between 25°C and 105°C. If the heating temperature is above the lower limit, the dispersion medium can be rapidly volatilized. If the heating temperature is below the upper limit, the cost required for heating and the discoloration of fibrous cellulose due to heat can be suppressed.

[0150] -Paper making process- The papermaking process is carried out by forming a slurry into paper using a papermaking machine. The papermaking machine used in the papermaking process is not particularly limited, but examples include continuous papermaking machines such as screenmills, cylinder screens, and inclined papermaking machines, or multi-layer papermaking machines that combine these types of machines. Known papermaking methods, such as manual papermaking, may also be employed in the papermaking process. The papermaking process involves filtering and dewatering the slurry using a wire to obtain a wet paper sheet, and then pressing and drying this sheet. The filter cloth used for filtering and dewatering the slurry is not particularly limited, but it is more preferable that it does not allow fibrous cellulose to pass through and does not slow down the filtration rate too much. Such a filter cloth is not particularly limited, but sheets, fabrics, or porous membranes made of organic polymers are preferred. The organic polymer is not particularly limited, but non-cellulose organic polymers such as polyethylene terephthalate, polyethylene, polypropylene, and polytetrafluoroethylene (PTFE) are preferred. In this embodiment, examples include a porous membrane of polytetrafluoroethylene with a pore size of 0.1 μm to 20 μm, and fabrics of polyethylene terephthalate or polyethylene with a pore size of 0.1 μm to 20 μm.

[0151] In the papermaking process, a method for producing a sheet from a slurry can be carried out using a manufacturing apparatus that includes, for example, a watering section which discharges a slurry containing fine fibrous cellulose onto the upper surface of an endless belt, and a drying section which drains the dispersion medium from the discharged slurry to produce a web, and a drying section which dries the web to produce a sheet. An endless belt is arranged from the watering section to the drying section, and the web produced in the watering section is transported to the drying section while remaining on the endless belt.

[0152] The dewatering methods used in the papermaking process are not limited, but include methods commonly used in paper manufacturing. Among these, a method of dewatering with a long screen, circular screen, or inclined wire, followed by further dewatering with a roll press, is preferred. The drying methods used in the papermaking process are not limited, but include methods commonly used in paper manufacturing. Among these, drying methods using a cylinder dryer, Yankee dryer, hot air drying, near-infrared heater, or infrared heater are more preferred.

[0153] The sheet thickness, basis weight, and density can be set appropriately according to the desired thickness, basis weight, and density of the sheet.

[0154] [Laminated structure] The present invention may also relate to a laminate having a structure in which other layers are further laminated on the sheet described above. Such other layers may be provided on both surfaces of the sheet, or on only one surface of the sheet. Examples of other layers laminated on at least one surface of the sheet include a resin layer and an inorganic layer, with a resin layer being preferred. Furthermore, the laminate may be constructed by further laminating another layer on the side of the resin layer that is not in contact with the sheet. Examples of other layers in this case include polyethylene film, polypropylene film, cycloolefin polymer film, polyimide film, and the like.

[0155] The thickness of the other layers in the laminate is not particularly limited, but is preferably 20 μm or more, more preferably 50 μm or more, and even more preferably 100 μm or more. It is also preferably 5000 μm or less, more preferably 1000 μm or less, and even more preferably 500 μm or less. However, for example, if the resin layer is a coated layer formed by coating, the thickness of the resin layer may be 1 μm or more, 2 μm or more, or 3 μm or more. Furthermore, the thickness of the resin layer is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less.

[0156] <Resin layer> The resin layer is a layer mainly composed of natural resin or synthetic resin. Here, the main component refers to a component that is present in 50% or more of the total mass of the resin layer. The resin content is preferably 60% or more of the total mass of the resin layer, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more. The resin content may be 100% or 95% or less of the total mass of the resin layer.

[0157] Examples of natural resins include rosin-based resins such as rosin, rosin esters, and hydrogenated rosin esters. The synthetic resin is preferably at least one selected from, for example, polycarbonate resin, polyethylene terephthalate resin, polyethylene naphthalate resin, polyethylene resin, polypropylene resin, polyimide resin, polystyrene resin, and acrylic resin. Among these, the synthetic resin is preferably at least one selected from polycarbonate resin, acrylic resin, and polypropylene resin, and more preferably polycarbonate resin.

[0158] Examples of polycarbonate resins that constitute the resin layer include aromatic polycarbonate resins and aliphatic polycarbonate resins. Specific examples of these polycarbonate resins are publicly known, such as the polycarbonate resin described in Japanese Patent Publication No. 2010-023275.

[0159] Examples of polypropylene resins that constitute the resin layer include acid-modified polypropylene resins and chlorinated polypropylene resins. Among these, acid-modified polypropylene resins are preferred, and maleic acid-modified polypropylene resins or maleic anhydride-modified polypropylene resins are even more preferred.

[0160] The resin layer may consist of a single resin, or it may be a copolymer formed by copolymerization or graft polymerization of multiple resin components. Alternatively, it may be used as a blended material obtained by mixing multiple resin components through a physical process.

[0161] An adhesive layer may be provided between the sheet and the resin layer, or there may be no adhesive layer, and the sheet and the resin layer may be in direct contact. If an adhesive layer is provided between the sheet and the resin layer, an acrylic resin can be used as the adhesive constituting the adhesive layer. Other adhesives besides acrylic resins include, for example, polyvinyl chloride resin, (meth)acrylic acid ester resin, styrene / acrylic acid ester copolymer resin, vinyl acetate resin, vinyl acetate / (meth)acrylic acid ester copolymer resin, urethane resin, silicone resin, epoxy resin, ethylene / vinyl acetate copolymer resin, polyester resin, polyvinyl alcohol resin, ethylene vinyl alcohol copolymer resin, and rubber emulsions such as SBR and NBR.

[0162] If no adhesive layer is provided between the sheet and the resin layer, the resin layer may contain an adhesion aid, and the surface of the resin layer may be subjected to surface treatment such as hydrophilization. Examples of adhesion aids include compounds containing at least one selected from isocyanate groups, carbodiimide groups, epoxy groups, oxazoline groups, amino groups, and silanol groups, as well as organosilicon compounds. Among these, it is preferable that the adhesion aid be at least one selected from compounds containing isocyanate groups (isocyanate compounds) and organosilicon compounds. Examples of organosilicon compounds include silane coupling agent condensates and silane coupling agents. Surface treatment methods include corona treatment, plasma discharge treatment, UV irradiation treatment, electron beam irradiation treatment, and flame treatment.

[0163] <Inorganic layer> The materials constituting the inorganic layer are not particularly limited, but examples include aluminum, silicon, magnesium, zinc, tin, nickel, titanium; oxides, carbides, nitrides, oxide carbides, oxide nitrides, or oxide carbnitrides thereof; or mixtures thereof. From the viewpoint of being able to stably maintain high moisture resistance, silicon oxide, silicon nitride, silicon oxide carbide, silicon oxide nitride, silicon oxide carbnitride, aluminum oxide, aluminum nitride, aluminum oxide carbide, oxide aluminum nitride, or mixtures thereof are preferred.

[0164] The method for forming the inorganic layer is not particularly limited. Generally, methods for forming thin films can be broadly classified into chemical vapor deposition (CVD) and physical vapor deposition (PVD), and either method may be used. Specific examples of CVD methods include plasma CVD, which utilizes plasma, and catalytic chemical vapor deposition (Cat-CVD), which uses a heated catalyst to catalytically decompose the material gas. Specific examples of PVD methods include vacuum deposition, ion plating, and sputtering.

[0165] Another method for forming inorganic layers is atomic layer deposition (ALD). ALD is a method for forming thin films at the atomic layer level by alternately supplying the raw material gases of each element that constitute the film to be formed to the surface on which the layer is to be formed. Although it has the disadvantage of a slow film deposition rate, it has the advantage of being able to neatly cover even complex shapes and deposit thin films with fewer defects, more so than plasma CVD. In addition, ALD has advantages such as being able to control the film thickness on the nano-order and being relatively easy to cover large surfaces. Furthermore, by using plasma, ALD can be expected to improve reaction rates, enable low-temperature processing, and reduce unreacted gases.

[0166] <Uses of the sheet> The sheet of this embodiment is suitable for optical components such as various display devices and various solar cells. It is also suitable for applications such as substrates for electronic equipment, separators for electrochemical elements, components for home appliances, window materials for various vehicles and buildings, interior materials, exterior materials, and packaging materials. Furthermore, it is suitable for applications such as yarn, filters, textiles, cushioning materials, sponges, and abrasives, as well as for using the sheet itself as a reinforcing material. Furthermore, the sheet of the present invention is also suitable for use in food containers such as plates, cups, and trays, cutlery such as knives, spoons, and forks, and straws. The sheet of this embodiment exhibits transparency and suppressed yellowing due to heating, making it suitable for optical components where transparency and yellowing are problematic. Furthermore, due to its excellent tensile modulus and tensile elongation, it is also suitable for various molded products such as food containers, cutlery, and straws, which were previously difficult to apply due to cracking during processing. Furthermore, in the above-mentioned applications, the sheet itself may be used, or a laminate in which a resin layer or inorganic layer is laminated onto the sheet may be used. [Examples]

[0167] The features of the present invention will be further described below with reference to examples and comparative examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following specific examples.

[0168] <Manufacturing Example 1> [Phosphorication treatment] As the raw material pulp, hardwood pulp (dry sheet) manufactured by Oji Paper Co., Ltd. was used. This raw material pulp was subjected to phosphorylation treatment as follows: First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (oven-dry mass) of the raw material pulp to adjust the mixture to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water to obtain chemically impregnated pulp. Next, the obtained chemically impregnated pulp was heated in a hot air dryer at 165°C for 250 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining phosphorylated pulp.

[0169] [Cleaning process] Next, the obtained phosphorylated pulp was subjected to a washing treatment. The washing treatment was carried out by repeatedly adding 10 L of deionized water to 100 g (oven-dry mass) of phosphorylated pulp to obtain a pulp dispersion, stirring the mixture to ensure uniform dispersion of the pulp, and then filtering and dewatering it. The washing was terminated when the electrical conductivity of the filtrate fell to 100 μS / cm or less.

[0170] [Neutralization treatment] Next, the washed phosphorylated pulp was subjected to a neutralization treatment as follows. First, the washed phosphorylated pulp was diluted with 10 L of deionized water, and then a 1N sodium hydroxide aqueous solution was gradually added while stirring to obtain a phosphorylated pulp slurry with a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated to obtain phosphorylated pulp that had undergone neutralization treatment. Then, the phosphorylated pulp that had undergone neutralization treatment was subjected to the washing treatment described above.

[0171] [Nitrogen removal treatment] A slurry with a solid content of 4% by mass was prepared by adding deionized water to phosphorylated pulp. A 48% by mass aqueous sodium hydroxide solution was added to the slurry to adjust the pH to 13.4, and the slurry was heated at a temperature of 85°C for 1 hour. Subsequently, this pulp slurry was dehydrated, and the pulp dispersion obtained by pouring 10 L of deionized water over 100 g (dry mass) of phosphorylated pulp was stirred to ensure uniform dispersion of the pulp, and the process of filtration and dewatering was repeated to remove excess sodium hydroxide. The removal process was terminated when the electrical conductivity of the filtrate was 100 μS / cm or less. The amount of carbamide groups introduced, as determined by the nitrogen content measured by the measurement method described later, was 0.01 mmol / g.

[0172] The resulting phosphorus oxoxide pulp was subjected to infrared absorption spectroscopy using FT-IR. The result showed that at 1230 cm⁻¹... -1 Absorption based on the P=O of phosphate groups was observed in the vicinity, confirming that phosphate groups were added to the pulp. Furthermore, when the obtained phosphorylated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming that the cellulose type I crystal structure was maintained. The amount of phosphate groups (amount of first dissociated acid) measured by the measurement method described later was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0173] [Fibrillation treatment] Deionized water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2% by mass. This slurry was processed six times at a pressure of 200 MPa using a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose.

[0174] [Substituent removal treatment (high-temperature heat treatment)] A dispersion of fine fibrous cellulose was placed in a pressure-resistant container and heated at 160°C for 15 minutes until the phosphate group content reached 0.08 mmol / g. This procedure confirmed the formation of fine fibrous cellulose aggregates.

[0175] [Washing treatment of slurry after substituent removal] After heating, an equal amount of deionized water was added to the slurry to obtain a slurry with a solid content of approximately 1% by mass. The slurry was then stirred, and the filtration and dewatering process was repeated to wash the slurry. When the electrical conductivity of the filtrate fell below 10 μS / cm, deionized water was added again to obtain a slurry with a solid content of approximately 1% by mass, and the slurry was allowed to stand for 24 hours. The filtration and dewatering process was repeated again, and the washing was terminated when the electrical conductivity of the filtrate fell below 10 μS / cm once more. Deionized water was added to the obtained fine fibrous cellulose aggregates, and after substituent removal, a slurry was obtained. The solid content of this slurry was 1.7% by mass.

[0176] [Uniform dispersion of slurry after substituent removal] Deionized water was added to the obtained substituent-removed slurry to obtain a slurry with a solid content concentration of 1.0% by mass. This slurry was then processed three times at a pressure of 200 MPa using a wet atomizing apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain substituent-removed fine fibrous cellulose dispersion (A) containing substituent-removed fine fibrous cellulose. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 4 nm.

[0177] <Manufacturing Example 2> The phosphorylated pulp obtained in Production Example 1 after washing and neutralization was subjected to the following treatment to obtain a fine fibrous cellulose dispersion (B) containing fine fibrous cellulose.

[0178] [Fibrillation treatment] Deionized water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2% by mass. This slurry was processed six times at a pressure of 200 MPa using a wet atomizing device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that this fine fibrous cellulose maintained type I cellulose crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured to be 3-5 nm using a transmission electron microscope. The amount of phosphate groups (first dissociation amount) measured by the measurement method described later in the section on the measurement of phosphorus oxoacid groups was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0179] <Manufacturing Example 3> [Phosphorus oxidation treatment] The procedure was carried out in the same manner as in Production Example 2, except that 33 parts by mass of phosphorous acid (phosphonic acid) were used instead of ammonium dihydrogen phosphate in the phosphorylation treatment, to obtain phosphorous pulp.

[0180] The resulting phosphorylated pulp was subjected to infrared absorption spectroscopy using FT-IR. The result showed that at 1210 cm⁻¹, the absorption spectrum was measured. -1 Absorption based on P=O of the phosphonic acid group, a tautomer of the phosphite group, was observed in the vicinity, confirming that phosphite groups (phosphonic acid groups) were attached to the pulp. Furthermore, when the obtained phosphite-oxidized pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of type I cellulose crystals.

[0181] [Fibrillation treatment] Deionized water was added to the obtained phosphite pulp to prepare a slurry with a solid content of 2% by mass. This slurry was processed six times at a pressure of 200 MPa using a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (C) containing fine fibrous cellulose. X-ray diffraction confirmed that this fine fibrous cellulose maintained type I cellulose crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured to be 3-5 nm using a transmission electron microscope. The amount of phosphite groups (amount of first dissociated acid), as measured by the phosphorus oxoacid group measurement method described later, was 1.51 mmol / g. The total amount of dissociated acid was 1.54 mmol / g.

[0182] <Manufacturing Example 4> [TEMPO oxidation treatment] Hardwood pulp (dry sheet) manufactured by Oji Paper Co., Ltd. was used as the raw material pulp. This raw material pulp was subjected to alkaline TEMPO oxidation treatment as follows. First, the above raw material pulp, equivalent to 100 parts by mass (dry weight), 1.6 parts by mass of TEMPO(2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by mass of sodium bromide were dispersed in 10,000 parts by mass of water. Next, a 13% by mass sodium hypochlorite aqueous solution was added to a concentration of 3.8 mmol per 1.0 g of pulp to initiate the reaction. During the reaction, a 0.5 M sodium hydroxide aqueous solution was added dropwise to maintain the pH between 10 and 10.5, and the reaction was considered complete when no further change in pH was observed.

[0183] [Cleaning process] Next, the obtained TEMPO-oxidized pulp was subjected to a washing treatment. The washing treatment was carried out by dewatering the pulp slurry after TEMPO oxidation to obtain a dewatered sheet, adding 5000 parts by mass of deionized water, stirring to uniformly disperse the sheet, and then repeating the filtration and dewatering process. The washing was terminated when the electrical conductivity of the filtrate became 100 μS / cm or less.

[0184] [Oxidation treatment] The remaining aldehyde groups in this dehydrated sheet were subjected to further oxidation treatment as follows: 100 parts by mass of the dehydrated sheet (equivalent to 100 parts by mass) was dispersed in 10,000 parts by mass of 0.1 mol / L acetate buffer (pH 4.8). Then, 113 parts by mass of 80% sodium chlorite was added, and the mixture was immediately sealed. The mixture was then stirred at 500 rpm using a magnetic stirrer at room temperature for 48 hours to obtain a pulp slurry.

[0185] [Cleaning process] Next, the obtained oxidized TEMPO oxidized pulp was subjected to a washing treatment. The washing treatment was carried out by dewatering the pulp slurry after oxidization to obtain a dewatered sheet, adding 5000 parts by mass of deionized water, stirring to uniformly disperse the sheet, and then repeating the filtration and dewatering process. The washing was terminated when the electrical conductivity of the filtrate became 100 μS / cm or less.

[0186] The amount of carboxyl groups in the resulting TEMPO-oxidized pulp, as measured by the method described later, was 1.30 mmol / g. Furthermore, when the obtained TEMPO-oxidized pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two locations: around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of type I cellulose crystals.

[0187] [Fibrillation treatment] Deionized water was added to the obtained TEMPO-oxidized pulp to prepare a slurry with a solid content of 2% by mass. This slurry was processed six times at a pressure of 200 MPa using a wet atomizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (D) containing fine fibrous cellulose. X-ray diffraction confirmed that this fine fibrous cellulose maintained type I cellulose crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured to be 3-5 nm using a transmission electron microscope. The amount of carboxyl groups measured by the measurement method described later was 1.30 mmol / g.

[0188] <Manufacturing Example 5> [Sulfur oxo-oxidation treatment] Sulfated pulp was obtained by the same procedure as in Production Example 1, except that 38 parts by mass of sulfuric acid amidosulfate were used instead of ammonium dihydrogen phosphate. However, the heating time in the hot air dryer was 20 minutes.

[0189] The obtained sulfated pulp was subjected to infrared absorption spectroscopy using FT-IR. The results showed that 1220–1260 cm⁻¹ -1 Absorption based on sulfate groups was observed in the vicinity, confirming that sulfate groups were attached to the pulp.

[0190] [Fibrillation treatment] After adding deionized water to the obtained sulfated pulp, the mixture was stirred to obtain a 2% by mass slurry. This slurry was processed six times at a pressure of 200 MPa using a wet atomizing apparatus (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (E) containing fine fibrous cellulose. X-ray diffraction confirmed that this fine fibrous cellulose maintained type I cellulose crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 2-5 nm. The amount of sulfate groups, as measured by the sulfur oxoacid group measurement method described later, was 1.47 mmol / g.

[0191] <Measurement> [Measurement of phosphorus oxoacid group content] The amount of phosphorus oxoacid groups in microfibrous cellulose (equal to the amount of phosphorus oxoacid groups in phosphorus oxoxide pulp) was measured by adding ion-exchanged water to a microfibrous cellulose dispersion containing the target microfibrous cellulose to a content of 0.2% by mass, treating it with an ion-exchange resin, and then performing titration with an alkali. The ion exchange resin treatment was performed by adding 1 / 10 the volume of 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 a mesh size of 90 μm to separate the resin from the slurry. Furthermore, the alkali titration was performed by adding 10 μL of 0.1 N sodium hydroxide aqueous solution to a fine fibrous cellulose-containing slurry after treatment with ion exchange resin, while measuring the change in the slurry's pH value. Nitrogen gas was blown into the slurry starting 15 minutes before the titration began. In this neutralization titration, two points were observed where the increment (the derivative of pH with respect to the amount of alkali added) was maximum on the curve plotting the measured pH against the amount of alkali added. Of these, the first maximum increment obtained after starting alkali addition is called the first endpoint, and the next maximum increment obtained 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 the first dissociated acid in the slurry used for titration. Also, the amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid in the slurry used for titration. The amount of alkali (mmol) required from the start of the titration to the first endpoint was divided by the solid content (g) in the slurry being titrated to determine the amount of phosphorus oxoacid groups (amount of first dissociated acid) (mmol / g). Furthermore, the amount of alkali (mmol) required from the start of the titration to the second endpoint was divided by the solid content (g) in the slurry being titrated to determine the total amount of dissociated acid (mmol / g).

[0192] [Measurement of carboxyl group content] The amount of carboxyl groups in microfibrous cellulose (equal to the amount of carboxyl groups in TEMPO-oxidized pulp) was measured by adding ion-exchanged water to a microfibrous cellulose dispersion containing the target microfibrous cellulose to a content of 0.2% by mass, treating it with an ion-exchange resin, and then performing titration with an alkali. The ion exchange resin treatment was performed by adding 1 / 10 the volume of strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) to a slurry containing 0.2% by mass of fine fibrous cellulose, shaking for 1 hour, and then pouring the mixture onto a mesh with a mesh size of 90 μm to separate the resin from the slurry. In addition, the titration using an alkali was carried out by measuring the change in the pH value shown by the fibrous cellulose-containing slurry after treatment with an ion-exchange resin while adding a 0.1 N aqueous sodium hydroxide solution thereto. When observing the change in pH while adding the aqueous sodium hydroxide solution, a titration curve as shown in Fig. 2 is obtained. As shown in Fig. 2, in this neutral titration, in the curve plotting the measured pH against the added amount of alkali, one point where the increment (the differential value with respect to the amount of alkali dropped for pH) becomes maximum is observed. This maximum point of the increment is called the first end point. Here, the region from the start of titration to the first end point in Fig. 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxy groups in the slurry used for the titration. Then, the amount of introduced carboxy groups (mmol / g) was calculated by dividing the amount of alkali (mmol) required in the first region of the titration curve by the solid content (g) in the microfibrillated cellulose-containing slurry to be titrated. Note that the above-mentioned amount of introduced carboxy groups (mmol / g) indicates the amount of substituents per 1 g of the mass of fibrous cellulose when the counter ion of the carboxy group is a hydrogen ion (H + ), and hereinafter is referred to as the amount of carboxy groups (acid form).

[0193] [Measurement of amount of sulfur oxoacid groups] After wet-ashing the obtained fibrous cellulose using perchloric acid and concentrated nitric acid, it was diluted at an appropriate magnification and the amount of sulfur was measured by ICP emission analysis. The value obtained by dividing this amount of sulfur by the absolute dry mass of the tested fibrous cellulose was defined as the amount of sulfur oxoacid groups (unit: mmol / g).

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

[0195] <Example 1> [Dissolution of cellulose ether] Methyl cellulose (manufactured by Shin-Etsu Chemical Co., Ltd., Methocel SM-25, weight average molecular weight: 6.0×10 4 , degree of substitution (methoxy group): 1.8) was added to ion-exchanged water to a concentration of 2% by mass, and stirred at room temperature for 1 hour to dissolve. By the above procedure, an aqueous cellulose ether solution (A) was obtained.

[0196] [Production of sheet] The microfibrillated cellulose dispersion (A) and the above aqueous cellulose ether solution (A) were each diluted with ion-exchanged water so that the solid content concentration became 0.5% by mass. Then, 70 parts by mass of the diluted microfibrillated cellulose dispersion was mixed with 30 parts by mass of the diluted aqueous cellulose ether solution to obtain a mixed solution. Furthermore, the mixed solution was weighed so that the basis weight of the finished sheet became 32 g / m 2 , and spread on a commercially available acrylic plate. Note that a dam frame (inner dimensions 250 mm × 250 mm, height 5 cm) was placed on the acrylic plate so as to obtain a predetermined basis weight. Then, it was dried in a dryer at 100°C for 1 hour and peeled off from the acrylic plate to obtain a microfibrillated cellulose-containing sheet. The thickness of the sheet was 25 μm.

[0197] <Example 2> In [Dissolution of cellulose ether] of Example 1, an aqueous cellulose ether solution (B) in which methyl cellulose (manufactured by Shin-Etsu Chemical Co., Ltd., Methocel SM-400, weight average molecular weight: 1.4×10 5 , degree of substitution (methoxy group): 1.8) was dissolved was obtained. Otherwise, in the same manner as in Example 1, a microfibrillated cellulose-containing sheet was obtained.

[0198] <Example 3> In [Dissolution of cellulose ether] of Example 1, hydroxypropyl methyl cellulose (manufactured by Shin-Etsu Chemical Co., Ltd., Methocel 65SH-50, weight average molecular weight: 7.5×10 4An aqueous cellulose ether solution (D) was obtained by dissolving a compound with a degree of substitution (methoxy group): 1.8 and a number of substituted moles (hydroxypropoxy group): 0.15. Otherwise, a sheet containing fine fibrous cellulose was obtained in the same manner as in Example 1.

[0199] <Example 4> In Example 1, [Dissolution of Cellulose Ether], hydroxypropyl methylcellulose (Shin-Etsu Chemical Co., Ltd., Metroze 65SH-400, weight-average molecular weight: 1.4 × 10) was used. 5 An aqueous cellulose ether solution (E) was obtained by dissolving a compound with a degree of substitution (methoxy group): 1.8 and a number of substituted moles (hydroxypropoxy group): 0.15. Otherwise, a sheet containing fine fibrous cellulose was obtained in the same manner as in Example 1.

[0200] <Example 5> In Example 1, [Dissolution of Cellulose Ether], hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., Metroze 65SH-1500, weight-average molecular weight: 2.2 × 10) was used. 5 An aqueous cellulose ether solution (F) was obtained by dissolving a compound with a degree of substitution (methoxy group): 1.8 and a number of substituted moles (hydroxypropoxy group): 0.15. Otherwise, a sheet containing fine fibrous cellulose was obtained in the same manner as in Example 1.

[0201] <Example 6> In Example 5, the procedure was the same as in Example 5, except that the amount of diluted fine fibrous cellulose dispersion (A) mixed was changed to 50 parts by mass, and the amount of diluted cellulose ether aqueous solution (F) mixed was changed to 50 parts by mass, to obtain a fine fibrous cellulose-containing sheet.

[0202] <Example 7> In Example 5, the mixture was prepared in the same manner as in Example 5, except that the amount of diluted fine fibrous cellulose dispersion (A) was changed to 30 parts by mass and the amount of diluted cellulose ether aqueous solution (F) was changed to 70 parts by mass. A sheet containing fine fibrous cellulose was obtained.

[0203] <Example 8> In Example 5, the amount of the diluted microfibrillated cellulose dispersion (A) was changed to 10 parts by mass, and the amount of the diluted aqueous cellulose ether solution (F) was changed to 90 parts by mass, and a microfibrillated cellulose-containing sheet was obtained in the same manner as in Example 5.

[0204] <Example 9> In Example 5, except that the finished basis weight was changed to 180 g / m 2 a microfibrillated cellulose-containing sheet having a thickness of 150 μm was obtained in the same manner as in Example 5.

[0205] <Example 10> In Example 6, except that the finished basis weight was changed to 180 g / m 2 a microfibrillated cellulose-containing sheet having a thickness of 150 μm was obtained in the same manner as in Example 5.

[0206] <Example 11> A microfibrillated cellulose-containing sheet was obtained in the same manner as in Example 5, except that the microfibrillated cellulose dispersion (B) was used.

[0207] <Example 12> A microfibrillated cellulose-containing sheet was obtained in the same manner as in Example 6, except that the microfibrillated cellulose dispersion (B) was used.

[0208] <Example 13> A microfibrillated cellulose-containing sheet was obtained in the same manner as in Example 5, except that the microfibrillated cellulose dispersion (C) was used.

[0209] <Example 14> A microfibrillated cellulose-containing sheet was obtained in the same manner as in Example 5, except that the microfibrillated cellulose dispersion (D) was used.

[0210] <Example 15> A microfibrillated cellulose-containing sheet was obtained in the same manner as in Example 5, except that the microfibrillated cellulose dispersion (E) was used.

[0211] <Example 16> A laminate was obtained in the same manner as in Example 9, except that the fine fibrous cellulose-containing sheet obtained in Example 9 was subjected to the following treatment, and resin layers were laminated on both sides of the fine fibrous cellulose-containing sheet.

[0212] [Formation of resin layer] A resin coating solution was obtained by mixing 8.5 parts by mass of modified polycarbonate resin (Yupizeta FPC-2136, manufactured by Mitsubishi Gas Chemical Company, Inc.), 60 parts by mass of toluene, and 30 parts by mass of methyl ethyl ketone. Next, 1.5 parts by mass of an isocyanate compound (Duranate TPA-100, manufactured by Asahi Kasei Chemicals Corporation) was added to the resin coating solution as an adhesion promoter and mixed. This resin coating solution was applied to one side of a sheet containing fine fibrous cellulose (the side that was in contact with the acrylic plate) using a bar coater. Then, the resin coating solution was cured by heating at 100°C for 1 hour to form a resin layer. Next, a resin layer was formed on the opposite side of the fine fibrous cellulose using the same procedure to obtain a laminate. The thickness of the resin layer was 3 μm per side.

[0213] <Comparative Example 1> In Example 1, [Dissolution of Cellulose Ether], methylcellulose (Shin-Etsu Chemical Co., Ltd., Metroze SM-8000, weight-average molecular weight: 3.6 × 10⁶) was used. 5 An aqueous cellulose ether solution (C) was obtained by dissolving a compound with a substitution degree (methoxy group): 1.8. Otherwise, a sheet containing fine fibrous cellulose was obtained in the same manner as in Example 1.

[0214] <Comparative Example 2> In Example 1, [Dissolution of Cellulose Ether], hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., Metroze 65SH-15000, weight-average molecular weight: 4.3 × 10) was used. 5 An aqueous cellulose ether solution (G) was obtained by dissolving a compound with a degree of substitution (methoxy group): 1.8 and a number of substituted moles (hydroxypropoxy group): 0.15. Otherwise, a sheet containing fine fibrous cellulose was obtained in the same manner as in Example 1.

[0215] <Comparative Example 3> A sheet containing fine fibrous cellulose was obtained by following the same procedure as in Example 1, except that the [dissolution of cellulose ether] was changed as follows.

[0216] [Dissolution of polyvinyl alcohol] Polyvinyl alcohol (Kuraray Co., Ltd., POVAL 5-74LLA, degree of polymerization: 500, degree of saponification: 74 mol%) was added to deionized water to a concentration of 12% by mass, and the mixture was stirred at 95°C for 1 hour to dissolve it. By following the above procedure, an aqueous solution of polyvinyl alcohol (A) was obtained.

[0217] <Comparative Example 4> A sheet containing fine fibrous cellulose was obtained by following the same procedure as in Example 1, except that the [dissolution of cellulose ether] was changed as follows.

[0218] [Dissolution of polyvinyl alcohol] Polyvinyl alcohol (manufactured by Kuraray Co., Ltd., POVAL 5-98, degree of polymerization: 500, degree of saponification: 99 mol%) was added to deionized water to a concentration of 12% by mass, and the mixture was stirred at 95°C for 1 hour to dissolve it. By following the above procedure, an aqueous solution of polyvinyl alcohol (B) was obtained.

[0219] <Comparative Example 5> A sheet containing fine fibrous cellulose was obtained by following the same procedure as in Example 1, except that the [dissolution of cellulose ether] was changed as follows.

[0220] [Dissolution of polyethylene oxide] Deionized water contains polyethylene oxide (Sumitomo Seika Co., Ltd., PEO-18, viscosity-average molecular weight 4.3 × 10⁻⁶). 6 The solution was then added to a total concentration of 2% by mass and stirred at room temperature for 1 hour to dissolve. By following these steps, an aqueous polyethylene oxide solution was obtained.

[0221] <Comparative Example 6> A sheet containing fine fibrous cellulose was obtained in the same manner as in Example 11, except that the [dissolution of cellulose ether] was changed as follows.

[0222] [Dissolution of polyvinyl alcohol] Polyvinyl alcohol (manufactured by Kuraray Co., Ltd., POVAL 5-98, degree of polymerization: 500, degree of saponification: 99 mol%) was added to deionized water to a concentration of 12% by mass, and the mixture was stirred at 95°C for 1 hour to dissolve it. By following the above procedure, an aqueous solution of polyvinyl alcohol (B) was obtained.

[0223] <Rating> [Measurement of total light transmittance of the sheet] In accordance with JIS K 7361-1:1997, the total light transmittance of the sheet was measured using a haze meter (HM-150, manufactured by Murakami Color Technology Laboratory Co., Ltd.).

[0224] [Haze measurement of the sheet] In accordance with JIS K 7136:2000, the haze of the sheet was measured using a haze meter (HM-150, manufactured by Murakami Color Technology Laboratory Co., Ltd.).

[0225] [Tensile properties of the sheet] In accordance with JIS P 8113:2006, tensile modulus, tensile strength, and tensile elongation were measured using a Tensilon tensile testing machine (manufactured by A&D Co., Ltd.). For the measurements, test specimens were conditioned at 23°C and 50% relative humidity for 24 hours. The tensile modulus was calculated from the maximum positive slope value on the SS curve.

[0226] [Measurement of yellowness of the sheet before and after heating] In accordance with JIS K 7373:2006, the yellowness (YI) of the sheets before and after heating was measured using Colour Cute i (manufactured by Suga Test Instruments Co., Ltd.). The YI after heating was defined as the YI of a sheet heated at 160°C for 6 hours. The change in YI (ΔYI) before and after heating was calculated using the method described below. Change in YI before and after heating (ΔYI) = (Yellowness of the sheet after heating) - (Yellowness of the sheet before heating)

[0227] [Seat appearance] Furthermore, the sheet appearance was evaluated from the YI before and after heating according to the following criteria. A: The change in YI (ΔYI) before and after heating is less than 1.5. B: Change in YI (ΔYI) before and after heating is 1.5 or greater and less than 5.0 C: YI change (ΔYI) before and after heating is 5.0 or higher.

[0228] [Sheet moldability] The sheet was cut into 5cm x 5cm test specimens, and these specimens were conditioned at 23°C and 50% relative humidity for 24 hours. As shown in Figure 3, the test specimens were bent until θ was 0°, and evaluated according to the following criteria. A: The sheet does not crack when bent. B: The sheet cracks when bent.

[0229] [Table 1-1]

[0230] [Table 1-2]

[0231] The sheets obtained in Examples 1-16 exhibited low haze, high total light transmittance, and excellent transparency. Furthermore, they had low YI values ​​before heating, and the increase in YI due to heating was suppressed. In addition, they had high tensile modulus and tensile strength, exhibiting excellent rigidity, as well as high tensile elongation and excellent flexibility. On the other hand, the weight-average molecular weight of the cellulose derivative is 3.0 × 10⁻⁶. 5In Comparative Examples 1 and 2, where the YI (Yield Intensity) exceeded a certain threshold, gelation occurred, making it impossible to form a sheet of uniform thickness. Furthermore, in Comparative Examples 3-6, where polyvinyl alcohol or polyethylene oxide was used instead of cellulose derivatives, the increase in YI due to heating was greater compared to when cellulose derivatives were used. In addition, the tensile elongation was low, cracks occurred in the sheet when bent, and the moldability was poor.

Claims

1. Fine fibrous cellulose with a fiber width of 10 nm or less, Weight-average molecular weight is 1.0 × 10⁻⁶ ４ The above 3.0 x 10 ５ The following cellulose derivatives are included: Seat.

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

3. The sheet according to claim 1 or 2, wherein the fine fibrous cellulose has a phosphorus oxoacid group or a group derived from a phosphorus oxoacid group.

4. The sheet according to any one of claims 1 to 3, wherein the amount of anionic groups in the fine fibrous cellulose is less than 0.50 mmol / g.

5. The sheet according to claim 2 or 3, wherein the amount of anionic groups in the fine fibrous cellulose is 0.80 mmol / g or more.

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

7. The sheet according to any one of claims 1 to 6, wherein the cellulose derivative is a water-soluble cellulose ether.

8. The sheet according to claim 7, wherein the water-soluble cellulose ether is nonionic.

9. The sheet according to claim 7 or 8, wherein the water-soluble cellulose ether has at least one functional group selected from the group consisting of methoxy groups and hydroxypropoxy groups.

10. The sheet according to any one of claims 7 to 9, wherein the water-soluble cellulose ether is selected from the group consisting of methylcellulose and hydroxypropylmethylcellulose.

11. The sheet according to any one of claims 1 to 10, wherein the total content of fine fibrous cellulose and cellulose derivatives in the solid content of the sheet is 90% by mass or more.

12. The sheet according to any one of claims 1 to 11, wherein the content of fine fibrous cellulose in the solid content of the sheet is 50% by mass or more.

13. The sheet according to any one of claims 1 to 12, wherein the change in the yellow index (YI value) before and after heating the sheet at 160°C for 6 hours is 1.5 or less.

14. The sheet according to any one of claims 1 to 13, wherein the haze of the sheet is 5% or less.

15. The sheet according to any one of claims 1 to 14, wherein the total light transmittance of the sheet is 90% or more.

16. The sheet according to any one of claims 1 to 15, wherein the tensile modulus of the sheet is 6.5 GPa or more.

17. The sheet according to any one of claims 1 to 16, wherein the tensile elongation of the sheet is 3% or more.

18. A laminate comprising a sheet according to any one of claims 1 to 17 and a resin layer on at least one surface of the sheet.

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

20. A sheet according to any one of claims 1 to 17, which is for use as a food container, cutlery, or straw.

Images