Sheet and laminate

Abstract

The present application aims to provide a sheet having high transparency, suppression of yellowing caused by heating, and high tensile elastic modulus, and also excellent softness, and a laminate having the sheet. The sheet of the present application contains microfine fibrous cellulose having a fiber width of 10 nm or less, and a cellulose derivative having a weight average molecular weight of 1.0 x 10 4 3.0 x 10 5 the following cellulose derivative.

Description

Technical Field

[0001] The present invention relates to sheets and laminates having the sheets. Background Technology

[0002] In recent years, due to the substitution of petroleum resources and the increasing awareness of environmental protection, materials made from reproducible natural fibers have received much attention. Among natural fibers, fibrous cellulose with a fiber diameter of 10μm or more but less than 50μm, especially fibrous cellulose derived from wood (pulp), has long been widely used in paper products.

[0003] As fibrous cellulose, microfibrillated cellulose with a fiber diameter of less than 1 μm is also known. Furthermore, sheets composed of such microfibrillated cellulose and sheets comprising microfibrillated cellulose and resin have been developed. It is known that with these sheets, tensile strength and other properties are significantly improved due to the substantial increase in the number of contact points between the fibers.

[0004] For example, Patent Documents 1-4 disclose sheets comprising microfibrillated cellulose and resin. Patent Document 1 describes a sheet comprising fibrous cellulose having anionic functional groups and a fiber width of 1000 nm or less, wherein the YI increase rate of the sheet is 1500% or less.

[0005] In addition, Patent Document 2 describes a cellulose fiber composite comprising cellulose fibers with a number-average fiber diameter of 4 to 100 nm and a matrix, wherein the haze of the cellulose fiber composite is 2 or less, and the YI value after repeated heating treatment at 190°C for 4 hours 4 times is 25 or less.

[0006] In addition, Patent Document 3 describes a modified cellulose fiber composite polyvinyl alcohol film, which comprises a polyvinyl alcohol resin and modified cellulose fibers.

[0007] Furthermore, Patent Document 4 discloses a resin composition comprising one or more resins selected from the group consisting of thermoplastic resins and curable resins, and modified cellulose fibers, wherein the curable resin is selected from epoxy resins, (meth)acrylic resins, phenolic resins, unsaturated polyester resins, polyurethane resins, or polyimide resins.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2019-108488

[0011] Patent Document 2: Japanese Patent Application Publication No. 2011-144363

[0012] Patent Document 3: Japanese Patent Application Publication No. 2017-052840

[0013] Patent Document 4: Japanese Patent Application Publication No. 2017-052940 Summary of the Invention

[0014] The problem the invention aims to solve

[0015] If sheets containing fine fibrous cellulose are heated, yellowing may sometimes occur due to the heating, as in Patent Documents 1 and 2. Various attempts have been made to suppress yellowing.

[0016] In addition, the sheets containing microfibrillated cellulose described in Patent Documents 1 to 4 have high rigidity and high tensile modulus, but low softness and poor formability.

[0017] The object of the present invention is to provide a sheet material with high transparency, suppression of yellowing caused by heating, high tensile modulus of elasticity, and excellent flexibility; and a laminate having the sheet material.

[0018] Solution for solving the problem

[0019] The inventors have discovered that the above-mentioned problems can be solved by using sheets containing microfibrillated cellulose and specific cellulose derivatives.

[0020] This invention relates to the following <1> ~ <20> .

[0021] <1> A sheet material comprising:

[0022] Fine fibrous cellulose with a fiber width of less than 10 nm; and

[0023] The weight-average molecular weight is 1.0 × 10⁻⁶. 4 Above and 3.0×10 5 The following are cellulose derivatives.

[0024] <2> according to <1> The sheet material, wherein the aforementioned microfibrillated cellulose has anionic groups.

[0025] <3> according to <1> or <2> The sheet material wherein the aforementioned microfibrillated cellulose has phosphorus oxyacid groups or groups derived from phosphorus oxyacid groups.

[0026] <4> according to <1> ~ <3> The sheet as described in any one of the above, wherein the amount of anionic groups in the aforementioned microfibrillary cellulose is less than 0.50 mmol / g.

[0027] <5> according to <2> or <3> The sheet material wherein the amount of anionic groups in the aforementioned microfibrillary cellulose is 0.80 mmol / g or more.

[0028] <6> according to <1> ~ <5> The sheet in any one of the following methods, wherein the aforementioned microfibrillary cellulose comprises urea groups.

[0029] <7> according to <1> ~ <6> The sheet as described in any one of the above-mentioned cellulose derivatives is a water-soluble cellulose ether.

[0030] <8> according to <7> The sheet material wherein the aforementioned water-soluble cellulose ether is nonionic.

[0031] <9> according to <7> or <8> The sheet material wherein the aforementioned water-soluble cellulose ether has at least one functional group selected from the group consisting of methoxy and hydroxypropoxy groups.

[0032] <10> according to <7> ~ <9> The sheet material described in any one of the above statements, wherein the aforementioned water-soluble cellulose ether is selected from the group consisting of methylcellulose and hydroxypropyl methylcellulose.

[0033] <11> according to <1> ~ <10> The sheet as described in any one of the above, wherein the total content of microfibrillated cellulose and cellulose derivatives in the solid composition of the aforementioned sheet is 90% by mass or more.

[0034] <12> according to <1> ~ <11> The sheet as described in any one of the above statements, wherein the content of microfibrillated cellulose in the solid composition of the aforementioned sheet is 50% by mass or more.

[0035] <13> according to <1> ~ <12> The sheet as described in any one of the above, wherein the change in yellowness index (YI value) of the aforementioned sheet before and after heating at 160°C for 6 hours is less than 1.5.

[0036] <14> according to <1> ~ <13> The sheet as described in any one of the above, wherein the haze of the aforementioned sheet is less than 5%.

[0037] <15> according to <1> ~ <14> The sheet as described in any one of the above, wherein the total light transmittance of the aforementioned sheet is 90% or more.

[0038] <16> according to <1> ~ <15> The sheet as described in any one of the above, wherein the tensile modulus of elasticity of the aforementioned sheet is 6.5 GPa or higher.

[0039] <17> according to <1> ~ <16> The sheet as described in any one of the above, wherein the tensile elongation of the aforementioned sheet is 3% or more.

[0040] <18> A layered body having <1> ~ <17> The sheet as described in any one of the above, wherein at least one side of the sheet has a resin layer.

[0041] <19> according to <1> ~ <17> The sheet described in any one of the above is used for optical components.

[0042] <20> according to <1> ~ <17> The sheet described in any one of the above is used for food containers, tableware or straws.

[0043] The effects of the invention

[0044] According to the present invention, a sheet having high transparency, suppressing yellowing caused by heating, and having high tensile modulus and excellent flexibility can be provided; as well as a laminate having the sheet. Attached Figure Description

[0045] Figure 1 This is a graph showing the relationship between the amount of NaOH added and pH for a slurry containing fine fibrous cellulose with phosphorus-containing oxyacid groups.

[0046] Figure 2 This is a graph showing the relationship between the amount of NaOH added and pH for a slurry containing fine fibrous cellulose with carboxyl groups.

[0047] Figure 3 This is a schematic diagram illustrating a method for evaluating the formability of sheet materials. Detailed Implementation

[0048] [Sheet]

[0049] The sheet material of the present invention comprises microfibrillated cellulose with a fiber width of less than 10 nm (hereinafter also referred to as "microfibrillated cellulose") and a weight-average molecular weight of 1.0 × 10⁻⁶. 4 Above and 3.0×10 5 The following cellulose derivatives. According to the present invention, sheets with high transparency, inhibition of yellowing caused by heating, high tensile modulus of elasticity, and excellent softness can be provided.

[0050] Microfibrillated cellulose is a fiber obtained by breaking down cellulose into nanofibers with a fiber width of less than 10 nm. Sheets containing microfibrillated cellulose have high transparency and are used in various applications requiring transparency. On the other hand, sheets made from conventionally obtained microfibrillated cellulose have the problem of yellowing due to heating. In addition, sheets containing microfibrillated cellulose have excellent stiffness and can achieve a high tensile modulus of elasticity; however, they suffer from low flexibility.

[0051] In the past, attempts have been made to address the above problems by modifying the microfibrillated cellulose and adding other components, but these methods have not been able to solve all of the problems.

[0052] The inventors have determined through in-depth research that by using cellulose containing microfibrillated cellulose and cellulose derivatives with a specific weight-average molecular weight, yellowing during heating can be suppressed compared to previous methods, thereby maintaining both rigidity and excellent softness.

[0053] The reasons for achieving the above effects are not yet clear, but it can be speculated that the high affinity of fine fibrous cellulose to cellulose derivatives and the low amount of yellowing functional groups in cellulose derivatives may contribute to the above effects.

[0054] The present invention will now be described in further detail.

[0055] <Fine fibrous cellulose>

[0056] The sheet material of this invention contains microfibrillated cellulose.

[0057] Microfibrillated cellulose is fibrous cellulose with a fiber width of less than 10 nm. It should be noted that the fiber width of fibrous cellulose can be measured by methods such as electron microscopy.

[0058] The fiber width of the microfibrillated cellulose is 10 nm or less. From the viewpoint that it is easier to exhibit the effect of inhibiting the dissolution of cellulose molecules in water and improving the strength, rigidity and dimensional stability by utilizing microfibrillated cellulose, the fiber width of the microfibrillated cellulose is, for example, 1 nm or more, preferably 2 nm or more, and 10 nm or less, preferably 8 nm or less, more preferably 6 nm or less, and even more preferably 5 nm or less.

[0059] The average fiber width of the microfibrillated cellulose is preferably 2 nm or more and 10 nm or less, more preferably 2 nm or more and 5 nm or less. By making the average fiber width of the microfibrillated cellulose 2 nm or more, it is easier to exhibit the effect of inhibiting the dissolution of cellulose molecules in water and improving strength, rigidity, and dimensional stability using microfibrillated cellulose. It should be noted that the microfibrillated cellulose is, for example, monofibrous cellulose.

[0060] The average fiber width of the fine fibrous cellulose was measured, for example, using an electron microscope as follows: First, an aqueous suspension of fibrous cellulose with a concentration of 0.05% by mass or more and 0.1% by mass or less was prepared. This suspension was then cast onto a hydrophilically treated carbon film covering a grid to create a sample for TEM observation. In the case of fibers with large widths, SEM images of the surface cast on glass could be observed. Next, depending on the width of the fiber being observed, electron microscope images were observed at any magnification of 1,000x, 5,000x, 10,000x, or 50,000x. The sample, observation conditions, and magnification were adjusted in a manner that satisfied the following conditions.

[0061] (1) Draw a straight line X at any point in the observed image, with more than 20 fibers intersecting the straight line X.

[0062] (2) Draw a straight line Y that intersects the line perpendicularly within the same image, with more than 20 fibers intersecting the line Y.

[0063] For the observation images that meet the above conditions, the widths of the fibers intersecting lines X and Y are visually read. This process is repeated to obtain at least three sets of observation images of non-overlapping surface portions. Next, for each image, the widths of the fibers intersecting lines X and Y are read. Thus, the widths of at least 20 × 2 × 3 = 120 fibers are read. The average value of the read fiber widths is taken as the average fiber width of the fibrous cellulose.

[0064] The fiber length of the microfibrillated cellulose is not particularly limited, but is preferably 0.1 μm or more and 1,000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and even more preferably 0.1 μm or more and 600 μm or less. By setting the fiber length within the above range, the destruction of the crystalline regions of the microfibrillated cellulose can be suppressed. Furthermore, the viscosity of the microfibrillated cellulose slurry can also be set within an appropriate range. It should be noted that the fiber length of the microfibrillated cellulose can be determined, for example, based on image analysis using TEM, SEM, or AFM.

[0065] The fine fibrous cellulose preferably has a type I crystal structure. Here, the type I crystal structure of the fine fibrous cellulose can be identified by the diffraction curves obtained from a wide-angle X-ray diffraction pattern using CuKα monochromatized graphite. Specifically, it can be identified by the presence of typical peaks at two locations: above 2θ = 14° and below 17°, and above 2θ = 22° and below 23°.

[0066] The proportion of type I crystal structure in the fine fibrous cellulose is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. This results in superior performance in terms of heat resistance and low linear thermal expansion. Regarding crystallinity, it is determined by measuring the X-ray diffraction pattern and using conventional methods (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0067] The axial ratio (fiber length / fiber width) of the microfiber cellulose is not particularly limited, but is preferably 20 or more and 10,000 or less, more preferably 50 or more and 1,000 or less. By setting the axial ratio to the lower limit or above, it is easy to form sheets containing microfiber cellulose. In addition, sufficient thickening properties are easily obtained when producing solvent dispersions. By setting the axial ratio to the upper limit or below, it is preferable to facilitate operations such as dilution when treating microfiber cellulose, for example, in the form of an aqueous dispersion.

[0068] The microfiber cellulose in this embodiment preferably has at least one of, for example, ionic groups and nonionic groups. From the viewpoint of improving the dispersibility of fibers in the dispersion medium and improving the defiberization efficiency in the defiberization process, the microfiber cellulose is more preferably provided with ionic groups. As ionic groups, they may include, for example, any one or both of anionic and cationic groups. In addition, as nonionic groups, they may include, for example, alkyl and acyl groups. In this embodiment, as ionic groups, anionic groups are particularly preferred. It should be noted that it is preferable that the ionic groups are present at least during the defiberization process, and preferably that the anionic groups are present, although the ionic groups may also be removed after the defiberization process.

[0069] Alternatively, the treatment of introducing ionic groups into the microfibrillated cellulose can be omitted.

[0070] Regarding anionic groups as ionic groups, examples include, for instance, phosphorus oxyacid groups or substituents derived from phosphorus oxyacid groups (sometimes simply referred to as phosphorus oxyacid groups), carboxyl groups or substituents derived from carboxyl groups (sometimes simply referred to as carboxyl groups), sulfur oxyacid groups or substituents derived from sulfur oxyacid groups (sometimes simply referred to as sulfur oxyacid groups), xanthate groups, phosphonic acid groups, phosphonic groups, sulfonyl groups, carboxylalkyl groups, etc. Preferably, the anionic group is at least one selected from the group consisting of phosphorus oxyacid groups, substituents derived from phosphorus oxyacid groups, carboxyl groups, sulfur oxyacid groups, substituents derived from sulfur oxyacid groups, carboxymethyl groups, carboxyethyl groups, and sulfonyl groups; more preferably, it is at least one selected from the group consisting of phosphorus oxyacid groups, substituents derived from phosphorus oxyacid groups, carboxyl groups, sulfur oxyacid groups, and substituents derived from sulfur oxyacid groups; and particularly preferably, it is a phosphorus oxyacid group. By introducing phosphorus-containing oxyacid groups as anionic groups, the dispersibility of fibrous cellulose can be further improved under conditions such as alkaline and acidic conditions, resulting in the easy acquisition of high-strength and highly transparent sheets.

[0071] Examples of cationic groups that can be considered as ionic groups include ammonium groups, phosphonium groups, and sulfonium groups. Among these, the ammonium group is preferred as the cationic group.

[0072] The oxyacid group of phosphorus or the substituent derived from the oxyacid group of phosphorus is, for example, a substituent shown in formula (1) below. Various substituents shown in formula (1) below can be introduced into each fibrous cellulose. In this case, the various substituents shown in formula (1) below can be the same or different from each other.

[0073]

[0074] In equation (1), a, b, and n are natural numbers, and m is any number (where a = b × m). At least one of the n existing α and α' is 0. - The rest are R or OR. It should be noted that all α and α' are O. - Alternatively, the n α values ​​can be all identical or all distinct. β b+ It is a cation with a valence of 1 or higher formed from organic or inorganic matter.

[0075] R can be 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. Furthermore, in formula (1), n ​​is preferably 1.

[0076] Examples of saturated linear hydrocarbon groups include methyl, ethyl, n-propyl, or n-butyl, without particular limitation. Examples of saturated branched hydrocarbon groups include isopropyl or tert-butyl, without particular limitation. Examples of saturated cyclic hydrocarbon groups include cyclopentyl or cyclohexyl, without particular limitation. Examples of unsaturated linear hydrocarbon groups include vinyl or allyl, without particular limitation. Examples of unsaturated branched hydrocarbon groups include isopropenyl or 3-butenyl, without particular limitation. Examples of unsaturated cyclic hydrocarbon groups include cyclopentenyl, cyclohexenyl, etc., without particular limitation. Examples of aromatic groups include phenyl or naphthyl, without particular limitation.

[0077] Furthermore, as a derived group in R, it can be any functional group that has been added to or substituted into the main chain or side chain of the various hydrocarbon groups mentioned above, and is in a state selected from at least one of the functional groups such as carboxyl, carboxylic acid ester (-COO-), hydroxyl, amino, and ammonium groups, without particular limitation. In addition, the number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R to the above range, the molecular weight of the oxyacid group of phosphorus can be set to an appropriate range, and it can also be easily impregnated into the fiber raw material, thereby improving the yield of microcellulose fibers. It should be noted that when there are multiple Rs in formula (1), and when multiple substituents shown in formula (1) are introduced into fibrous cellulose, the multiple Rs may be the same or different from each other.

[0078] β b+ A cation with a valence of 1 or higher formed from organic or inorganic matter. Examples of cations with a valence of 1 or higher formed from organic matter include organonium ions. Examples of organonium ions include organoammonium ions and organophosphorus ions. Examples of organoammonium ions include aliphatic ammonium ions and aromatic ammonium ions. Examples of organophosphorus ions include aliphatic phosphorus ions and aromatic phosphorus ions. Examples of cations with a valence of 1 or higher formed from inorganic matter include ions of alkali metals such as sodium, potassium, or lithium; ions of divalent metals such as calcium or magnesium; hydrogen ions; and ammonium ions. It should be noted that multiple β-ions exist in formula (1). b+ In the case of introducing multiple substituents as shown in formula (1) into fibrous cellulose, multiple β-substituents exist. b+ They can be the same or different. As a cation with a valence of 1 or higher formed from organic or inorganic matter, it is preferred to include β-cations. b+ The fiber raw materials are not prone to yellowing when heated and contain sodium or potassium ions that are readily available for industrial use; there are no particular restrictions.

[0079] As substituents for phosphorus oxyacid groups or oxyacid groups derived from phosphorus, more specifically, examples include phosphate groups (-PO3H2), salts of phosphate groups, phosphite groups (phosphonic acid groups) (-PO2H2), and salts of phosphite groups (phosphonic acid groups). Furthermore, substituents for phosphorus oxyacid groups or oxyacid groups derived from phosphorus can be groups obtained by condensation of phosphate groups (e.g., pyrophosphate groups), groups obtained by condensation of phosphonic acids (e.g., polyphosphonic acid groups), phosphate ester groups (e.g., monomethyl phosphate groups, polyoxyethylene alkyl phosphate groups), alkyl phosphonic acid groups (e.g., methylphosphonic acid groups), etc.

[0080] Furthermore, the sulfur-containing oxyacid group (or a substituent derived from the sulfur-containing oxyacid group) is, for example, a substituent shown in formula (2) below. Various substituents shown in formula (2) below can be introduced into each fibrous cellulose. In this case, the multiple substituents shown in formula (2) below can be the same or different from each other.

[0081]

[0082] 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). It should be noted that when n is 2 or higher, multiple p values ​​can be the same number or different numbers. In the above structural formula, β... b+ These are cations with a valence of 1 or higher formed from organic or inorganic substances. Examples of cations with a valence of 1 or higher formed from organic substances include organonium ions. Examples of organonium ions include organoammonium ions and organophosphorus ions. Examples of organoammonium ions include aliphatic ammonium ions and aromatic ammonium ions. Examples of organophosphorus ions include aliphatic phosphorus ions and aromatic phosphorus ions. Examples of cations with a valence of 1 or higher formed from inorganic substances include ions of alkali metals such as sodium, potassium, or lithium; ions of divalent metals such as calcium or magnesium; hydrogen ions; and ammonium ions. It should be noted that when multiple substituents shown in formula (2) are introduced into fibrous cellulose, multiple β-substituents exist. b+ They can be the same or different. As a cation with a valence of 1 or higher formed from organic or inorganic matter, it is preferred to include β-cations. b+ The fiber raw materials are not prone to yellowing when heated and contain sodium or potassium ions that are readily available for industrial use; there are no particular restrictions.

[0083] Regarding the amount of ionic groups introduced into fibrous cellulose, for example, relative to 1 g (mass) of fibrous cellulose, it is preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, further 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, regarding the amount of ionic groups introduced into fibrous cellulose, for example, relative to 1 g (mass) of fibrous cellulose, it is preferably 5.20 mmol / g or less, more preferably 3.65 mmol / g or less, further preferably 3.50 mmol / g or less, and even more preferably 3.00 mmol / g or less. By setting the amount of ionic groups introduced within the above range, it is easier to micronize the fiber raw material, and the stability of the microfiber cellulose can be improved. In addition, by setting the amount of ionic groups introduced within the above range, the microfiber cellulose can exhibit excellent properties in various applications such as thickeners.

[0084] Here, the denominator in the unit mmol / g indicates that the counter ion of the ionic group is the hydrogen ion (H+). + The quality of fibrous cellulose at that time.

[0085] It should be noted that the ionic groups introduced into the fibrous cellulose can remain directly on the microfiber cellulose, or they can be removed after the microfiber cellulose has been formed, as described later. From the viewpoint of suppressing yellowing caused by heating the sheet, it is preferable to remove the ionic groups.

[0086] The amount of ionic groups introduced into fibrous cellulose can be determined, for example, by neutralization titration. In a neutralization titration-based determination, the amount introduced is determined by measuring the pH change while adding an alkali such as an aqueous solution of sodium hydroxide to a slurry containing the resulting fibrous cellulose.

[0087] Figure 1 This is a graph showing the relationship between the amount of NaOH added and pH for fibrous cellulose containing phosphorus oxyacid groups.

[0088] Figure 1 This is a graph showing the relationship between the amount of NaOH added and pH for fibrous cellulose slurry containing oxyacid groups with phosphorus. The amount of oxyacid groups with phosphorus introduced into the fibrous cellulose was determined, for example, as follows.

[0089] First, the slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. It should be noted that, if necessary, the sample may undergo the same defiberization treatment as described later before treatment with the strongly acidic ion exchange resin.

[0090] Next, while adding sodium hydroxide solution, the pH change was observed to obtain... Figure 1 The titration curve is shown on the upper side. Figure 1 The titration curve shown on the upper side plots the pH measured relative to the amount of alkali added. Figure 1 The titration curve shown on the lower part plots the pH increment (differential value) (1 / mmol) relative to the amount of alkali added. In this neutralization titration, two points where the pH increment (differential value of pH relative to the amount of alkali added) reaches its maximum are identified in the curve plotting pH relative to the amount of alkali added. The point where the maximum increment is obtained first at the start of alkali addition is called the first endpoint, and the point where the maximum increment is obtained next is called the second endpoint. The amount of alkali required from the start of titration to the first endpoint is equal to the first dissociation acid amount of fibrous cellulose contained in the slurry being titrated; the amount of alkali required from the first endpoint to the second endpoint is equal to the second dissociation acid amount of fibrous cellulose contained in the slurry being titrated; and the amount of alkali required from the start of titration to the second endpoint is equal to the total dissociation acid amount of fibrous cellulose contained in the slurry being titrated. Furthermore, the value obtained by dividing the amount of alkali required from the start of titration to the first endpoint by the solids content (g) in the slurry being titrated is called the amount of phosphorus oxyacid group introduced (mmol / g). It should be noted that, when referred to simply as the amount of oxyacid group introduced by phosphorus (or the amount of oxyacid group of phosphorus), it indicates the amount of the first dissociative acid.

[0091] It should be noted that, in Figure 1 In this titration, the region from the start of the 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, when the oxyacid group of phosphorus is a phosphate group, when this phosphate group undergoes condensation, the apparent amount of weak acidic group in the oxyacid group of phosphorus (also referred to as the second dissociated acid amount in this specification) decreases, and the amount of base required in the second region is less than that required in the first region. On the other hand, the amount of strong acidic group in the oxyacid group of phosphorus (also referred to as the first dissociated acid amount in this specification) remains consistent with the atomic weight of phosphorus regardless of whether condensation occurs. Furthermore, when the oxyacid group of phosphorus is a phosphorous acid group, since there is no weak acidic group in the oxyacid group of phosphorus, sometimes the amount of base required in the second region decreases or even becomes zero. In this case, the point where the pH increment reaches its maximum in the titration curve becomes a single point.

[0092] It should be noted that since the denominator represents the mass of acidic fibrous cellulose, the above-mentioned amount of phosphorus oxyacid group introduction (mmol / g) represents the amount of phosphorus oxyacid group present in acidic fibrous cellulose (hereinafter referred to as the amount of phosphorus oxyacid group (acidic)). On the other hand, when the counter ion of phosphorus oxyacid group is replaced by any cation C in a charge equivalent manner, the amount of phosphorus oxyacid group present in fibrous cellulose with cation C as the counter ion can be determined by converting the denominator to the mass of fibrous cellulose with cation C as the counter ion (hereinafter referred to as the amount of phosphorus oxyacid group (C-type)).

[0093] That is, the calculation is performed using the following formula.

[0094] The amount of oxyacid groups in phosphorus (C-type) = The amount of oxyacid groups in phosphorus (acid-type) / {1 + (W-1) × A / 1000}

[0095] A [mmol / g]: The total anionic content of phosphorus-derived oxyacid groups in fibrous cellulose (the sum of the strong acid group content and the weak acid group content of phosphorus oxyacid groups).

[0096] W: The formula weight of each monovalent cation C (e.g., 23 for Na, 9 for Al).

[0097] Figure 2 This is a graph showing the relationship between the amount of NaOH added and pH for fibrous cellulose with carboxyl groups.

[0098] The amount of carboxyl groups introduced into the cellulose was determined, for example, as follows.

[0099] First, the slurry containing fibrous cellulose was treated with a strongly acidic ion exchange resin. It should be noted that, if necessary, the sample can undergo the same defiberization treatment as described later before treatment with the strongly acidic ion exchange resin. Next, the pH change was observed while adding sodium hydroxide aqueous solution to obtain... Figure 2 The titration curve is shown. It should be noted that, if necessary, the analyte can undergo the same defibering treatment as described later.

[0100] like Figure 2 As shown, in this neutralization titration, a point is identified in the curve plotting pH measured with respect to the amount of alkali added, where the increment (the derivative of pH with respect to the amount of alkali added) reaches its maximum. This maximum point is called the first endpoint. Here, [the text continues with further details about the endpoint]. Figure 2The region from the start of titration to the first endpoint is called the first region. The amount of alkali required for the first region is equal to the amount of carboxyl groups in the slurry used for titration. Furthermore, the amount of carboxyl groups introduced (mmol / g) is calculated by dividing the amount of alkali (mmol) required for the first region of the titration curve by the solid content (g) in the slurry containing fine fibrous cellulose, which is being titrated.

[0101] It should be noted that the above carboxyl group introduction amount (mmol / g) indicates that the counter ion of the carboxyl group is the hydrogen ion (H+). + The amount of substituents in 1g of fibrous cellulose (hereinafter referred to as the amount of carboxyl groups (acid type)).

[0102] It should be noted that since the denominator is the mass of acidic fibrous cellulose, the above-mentioned carboxyl group introduction amount (mmol / g) represents the amount of carboxyl groups possessed by acidic fibrous cellulose (hereinafter referred to as carboxyl group amount (acidic type)). On the other hand, when the counter ion of the carboxyl group is replaced with any cation C in a charge equivalent manner, the amount of carboxyl groups possessed by fibrous cellulose with cation C as the counter ion can be determined by converting the denominator to the mass of fibrous cellulose with cation C as the counter ion (hereinafter referred to as carboxyl group amount (C type)) (mmol / g).

[0103] That is, the calculation is performed using the following formula.

[0104] Carboxyl group amount (C type) = Carboxyl group amount (acid type) / {1 + (W-1) × (Carboxyl group amount (acid type)) / 1000}

[0105] W: The formula weight of each monovalent cation C (e.g., 23 for Na, 9 for Al).

[0106] In addition, regarding the amount of oxyacid groups / sulfonates of sulfur introduced into the microfibrillated cellulose, the sulfur content was determined by wet ashing of the obtained fibrous cellulose with perchloric acid and concentrated nitric acid, followed by dilution at an appropriate ratio, and by ICP emission spectroscopy analysis.

[0107] The value obtained by dividing the sulfur content by the absolute dry mass of the fibrous cellulose used in the test is denoted as the sulfur oxyacid content / sulfonic acid content (unit: mmol / g).

[0108] It should be noted that in the determination of substituent amounts based on titration, if too much sodium hydroxide aqueous solution is added or the titration interval is too short, the amount of substituent may be lower than the original value, sometimes resulting in inaccurate values. Ideally, the amount of sodium hydroxide should be titrated with 10–57 μL of 0.1N sodium hydroxide aqueous solution over 5–30 seconds. Furthermore, to eliminate the influence of carbon dioxide dissolved in cellulose-containing slurries, it is ideal to perform the measurement while blowing an inert gas such as nitrogen into the slurry, for example, from 15 minutes before the start of the titration until the end of the titration.

[0109] The determination of the amount of ionic groups based on the above method was applied to microfibrillated cellulose with a fiber width of less than 1,000 nm. When determining the amount of ionic groups in pulp fibers with a fiber width of more than 1,000 nm, the pulp fibers were micronized before the determination was performed.

[0110] In this invention, as described above, the microfibrillated cellulose can be obtained by removing at least a portion of the ionic groups from the microfibrillated cellulose obtained by introducing the aforementioned ionic groups and then defibrinating it. From the viewpoints of reducing the YI value before heating and suppressing yellowing caused by heating, it is preferable to remove the ionic groups. It should be noted that the removal of ionic groups may not be complete; for example, it is preferable to remove the ionic groups in a manner where the amount of ionic groups is less than 0.50 mmol / g.

[0111] In this case, it is preferable to perform a uniform dispersion treatment after removing ionic groups from the defibrinated microfibrillated cellulose to obtain a microfibrillated cellulose dispersion. By removing ionic groups, a sheet with a low YI value and suppressed yellowing caused by heating is obtained, which is therefore preferred.

[0112] The microfibrillated cellulose may contain urea groups derived from urea and / or urea derivatives added during the manufacturing process of the microfibrillated cellulose (described later). In this case, the amount of urea groups introduced into the microfibrillated cellulose (urea group amount) is preferably 1.50 mmol / g or less, more preferably 1.00 mmol / g or less, further preferably 0.30 mmol / g or less, and particularly preferably 0.20 mmol / g or less, relative to 1 g (mass) of microfibrillated cellulose. It should be noted that the amount of urea groups introduced into the fibrous cellulose (urea group amount) can be 0.00 mmol / g. Urea groups and phosphorus oxyacid groups are introduced by reacting with the hydroxyl groups of cellulose; therefore, the more urea groups are introduced, the less phosphorus oxyacid groups are introduced. Therefore, by setting the amount of urea groups introduced within the above range, the amount of phosphorus oxyacid groups introduced can be increased, and an appropriate range can be set. It should be noted that urea groups themselves are not conductive; therefore, a charge repulsion effect (microfibrillation effect of fibrous cellulose) cannot be obtained by introducing urea groups. Therefore, by setting the amount of urea group introduced within the above range, the amount of phosphorus oxyacid group introduced can be increased, thereby more effectively improving the dispersibility of fibrous cellulose relative to the solvent and easily obtaining a highly transparent dispersion containing fine fibrous cellulose.

[0113] The amount of urea introduced is determined by measuring the amount of nitrogen covalently bonded to fibrous cellulose. Specifically, the nitrogen content is determined using micro-nitrogen analysis after ionizing and removing ionic nitrogen (ammonium ions) from the analyte containing fibrous cellulose. The ionization of ionic nitrogen (ammonium ions) is carried out under conditions where the nitrogen covalently bonded to cellulose is substantially not removed. For example, ammonium ions can be ionized by alkaline treatment after the oxyacid group introduction step of phosphorus, followed by washing and defibrillation, or ammonium ions can be removed by adsorption using a strong acid ion exchange resin after the defibrillation step. As a nitrogen content analyzer based on micro-nitrogen analysis, a micro total nitrogen analyzer such as the TN-110 manufactured by Mitsubishi Chemical Analytech Co., Ltd. can be used. Before measurement, the fibrous cellulose is dried to an absolutely dry state at a low temperature (e.g., in a vacuum desiccator, 40°C for 24 hours). The amount of urea 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.

[0114] [Method for manufacturing microfibrillary cellulose]

[0115] (Fiber raw materials containing cellulose)

[0116] Fine fibrous cellulose is made from cellulose-containing fibrous raw materials.

[0117] As a cellulose-containing fiber raw material, there are no particular limitations, but from the viewpoint of easy availability and low cost, pulp is preferred. Examples of pulp include wood pulp, non-wood pulp, and deinking pulp. As wood pulp, there are no particular limitations, but examples include chemical pulps such as broadleaf kraft pulp (LBKP), softleaf kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), alkaline pulp (AP), unbleached kraft pulp (UKP), and oxygen-bleached kraft pulp (OKP); semi-chemical pulps such as semi-chemical pulp (SCP) and chemical groundwood pulp (CGP); and mechanical pulps such as wood chip pulp (GP) and thermomechanical pulps (TMP, BCTMP). As non-wood pulp, there are no particular limitations, but examples include cotton pulps such as cotton linters and lint; and non-wood pulps such as hemp, wheat straw, bamboo, and bagasse. As deinking pulp, there are no particular limitations, but examples include deinking pulp made from recycled paper. The pulp in this embodiment can be made using one of the above-mentioned types alone, or two or more types can be used in combination.

[0118] Of the aforementioned pulps, from the viewpoint of ease of acquisition, wood pulp and deinking pulp are preferred, for example. Furthermore, among wood pulps, from the viewpoint of a high cellulose ratio and a high yield of fine fibrous cellulose during defibrillation, and from the viewpoint of obtaining fine fibrous cellulose with minimal cellulose breakdown and a high axial ratio in the pulp, chemical pulp is more preferred, and buffalo hide pulp and sulfite pulp are even more preferred. It should be noted that if fine fibrous cellulose with a high axial ratio is used, there is a tendency for the viscosity to increase.

[0119] As a cellulose-containing fiber raw material, for example, cellulose contained in sea tunicates or bacterial cellulose produced by acetic acid bacteria can also be utilized.

[0120] Alternatively, fibers formed from linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can be used instead of cellulose-containing fiber raw materials.

[0121] To obtain the fine fibrous cellulose with ionic groups introduced as described above, it is preferable to sequentially include: an ionic group introduction step for introducing ionic groups into the cellulose-containing fiber raw material, a washing step, an alkali treatment step (neutralization step), and a defiberization step. Alternatively, an acid treatment step may be included in addition to the washing step. Examples of ionic group introduction steps include the introduction of phosphorus oxyacid groups, the introduction of carboxyl groups, and the introduction of sulfur oxyacid groups. These will be described separately below.

[0122] (Ionic group introduction process)

[0123] - Phosphorus oxyacid group introduction process-

[0124] The phosphorus oxyacid group introduction process is as follows: by reacting with the hydroxyl groups present in the cellulose-containing cellulose fiber raw material, at least one compound selected from compounds capable of introducing phosphorus oxyacid groups (hereinafter also referred to as "Compound A") is applied to the cellulose-containing cellulose fiber raw material. Through this process, phosphorus oxyacid group introduced fibers are obtained.

[0125] In the phosphate group introduction process described in this embodiment, the reaction between the cellulose-containing fiber raw material and compound A can be carried out in the presence of at least one of urea and its derivatives (hereinafter also referred to as "compound B"). Alternatively, the reaction between the cellulose-containing fiber raw material and compound A can be carried out in the absence of compound B.

[0126] As an example of a method for applying compound A to a fiber raw material in the presence of compound B, one method is to mix compound A and compound B in a dry, wet, or slurry-like state. Among these, from the perspective of high reaction uniformity, using a dry or wet fiber raw material is preferred, and particularly preferred is using a dry fiber raw material. The form of the fiber raw material is not particularly limited; for example, cotton-like or sheet-like forms are preferred. One method is to add compound A and compound B to the fiber raw material separately in powder form, in a solution dissolved in a solvent, or by heating to above their melting point to melt them. Among these, from the perspective of high reaction uniformity, adding them in a solution dissolved in a solvent, especially in an aqueous solution, is preferred. Furthermore, compound A and compound B can be added to the fiber raw material simultaneously, separately, or in the form of a mixture. As for the method of adding compound A and compound B, there is no particular limitation; when compound A and compound B are in solution form, the fiber raw material can be immersed in the solution to absorb the liquid and then removed, or the solution can be added dropwise to the fiber raw material. Alternatively, the necessary amounts of compound A and compound B can be added to the fiber raw material, or excess amounts of compound A and compound B can be added to the fiber raw material and then removed by pressing and filtering.

[0127] Compound A used in this embodiment can be any compound having a phosphorus atom and capable of forming an ester bond with cellulose. Examples include phosphoric acid or its salts, phosphorous acid or its salts, dehydrated condensed phosphoric acid or its salts, anhydrous phosphoric acid (phosphorus pentoxide), etc., without particular limitation. Phosphoric acid of various purities can be used, for example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid. Phosphorous acid, for example, 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acid is obtained by condensing two or more molecules of phosphoric acid through a dehydration reaction; 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, which can be prepared to various degrees of neutralization.

[0128] Among these, from the viewpoints of high phosphate group introduction efficiency, easy to further improve defiberization efficiency in the subsequent defiberization process, low cost and easy industrial application, phosphoric acid, sodium salt of phosphate, potassium salt of phosphate or ammonium salt of phosphate are preferred, and more preferably phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate or ammonium dihydrogen phosphate.

[0129] The amount of compound A added relative to the fiber raw material is not particularly limited. For example, when converting the amount of compound A added to phosphorus atomic weight, the amount of phosphorus atoms added relative to the fiber raw material (absolute dry weight) is preferably 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added relative to the fiber raw material within the above range, the yield of microfibrillated cellulose can be further improved. On the other hand, by setting the amount of phosphorus atoms added relative to the fiber raw material below the above upper limit, a balance can be achieved between the effect of improving yield and cost.

[0130] The compound B used in this embodiment, as described above, is selected from at least one of urea and its derivatives. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea.

[0131] From the viewpoint of improving reaction uniformity, compound B is preferably used in the form of an aqueous solution. Furthermore, from the viewpoint of further improving reaction uniformity, it is preferable to use an aqueous solution containing both compound A and compound B.

[0132] The amount of compound B added relative to the fiber raw material (absolute dry weight) is not particularly limited. For example, it is preferably 1% or more and 500% or less by mass, more preferably 10% or more and 400% or less by mass, and even more preferably 100% or more and 350% or less by mass.

[0133] In the reaction of cellulose-containing fiber raw materials with compound A, in addition to compound B, amides or amines may also 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.

[0134] In the process of introducing phosphorus oxyacid groups, it is preferable to heat-treat the fiber raw material after adding or mixing compound A, etc. As for the heat treatment temperature, it is preferable to select a temperature that can both suppress the thermal decomposition and hydrolysis reaction of the fiber and effectively introduce the phosphorus oxyacid groups. The heat treatment temperature is preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower. Furthermore, the heat treatment can be performed using machines equipped with various heat media, such as stirring dryers, rotary dryers, disc dryers, roller heating devices, plate heating devices, fluidized bed dryers, belt dryers, filter dryers, vibrating flow dryers, airflow dryers, reduced pressure dryers, infrared heating devices, far-infrared heating devices, microwave heating devices, and high-frequency drying devices.

[0135] In the heat treatment described in this embodiment, methods such as adding compound A to the sheet-like fiber material by impregnation or similar methods, followed by heating, or mixing or stirring the fiber material with compound A using a kneader or similar method while heating, can suppress uneven concentrations of compound A in the fiber material and more uniformly introduce phosphate groups onto the surface of the cellulose fibers contained in the fiber material. This can be attributed to the fact that when water molecules move towards the surface of the fiber material during drying, it can suppress the attraction of dissolved compound A to water molecules due to surface tension, thus preventing it from moving towards the surface of the fiber material (i.e., preventing uneven concentrations of compound A).

[0136] Furthermore, the heating device used in the heat treatment is preferably one that can continuously remove moisture generated during the dehydration condensation (phosphoesterification) reaction of water retained in the slurry and hydroxyl groups contained in cellulose and other fiber raw materials to the outside of the device system. Examples of such heating devices include, for instance, air-blown ovens. By continuously removing moisture from the device system, the hydrolysis of phosphate ester bonds, which is the reverse reaction of phosphoesterification, can be suppressed, and consequently, the acid hydrolysis of sugar chains in the fiber can also be suppressed. Therefore, fine fibrous cellulose with a high axial ratio can be obtained.

[0137] The heat treatment time is preferably, for example, 1 second or more and 300 minutes or less from the point at which moisture is substantially removed from the fiber raw material, more preferably 1 second or more and 1,000 seconds or less, and even more preferably 10 seconds or more and 800 seconds or less. In this embodiment, by setting the heating temperature and heating time to an appropriate range, the amount of phosphorus oxyacid groups introduced can be set to a preferred range.

[0138] The phosphorus oxyacid group introduction process only needs to be performed at least once, and can be repeated more than twice. By performing the phosphorus oxyacid group introduction process more than twice, a large amount of phosphorus oxyacid groups can be introduced into the fiber raw material. In this embodiment, as a preferred example, the case of performing the phosphorus oxyacid group introduction process twice can be listed.

[0139] Regarding the amount of phosphorus oxyacid groups introduced into the fibrous raw material, for example, relative to 1 g (mass) of fibrous cellulose, it is preferably 0.10 mmol / g or more, 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, regarding the amount of phosphorus oxyacid groups introduced into the fibrous raw material, for example, relative to 1 g (mass) of fibrous cellulose, it is preferably 5.20 mmol / g or less, more preferably 3.65 mmol / g or less, and even more preferably 3.00 mmol / g or less. By setting the amount of phosphorus oxyacid groups introduced within the above range, it is easier to micronize the fibrous raw material, and the stability of the microfiber cellulose can be improved.

[0140] -Carboxyl group introduction process-

[0141] The carboxyl introduction process is carried out by treating cellulose-containing fibrous raw materials with oxidation treatments such as ozone oxidation, Fenton-based oxidation, and TEMPO oxidation, or with compounds having groups derived from carboxylic acids or their derivatives, or with anhydrides of compounds having groups derived from carboxylic acids or their derivatives.

[0142] Compounds having a group derived from a carboxylic acid are not particularly limited, and 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 group derived from a carboxylic acid are not particularly limited, and examples include imides of anhydrides of compounds having a carboxyl group, and derivatives of anhydrides of compounds having a carboxyl group. Imides of anhydrides of compounds having a carboxyl group are not particularly limited, and examples include imides of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0143] Anhydrides, which are compounds having groups derived from carboxylic acids, are not particularly limited, and examples include anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, and itaconic anhydride. Furthermore, derivatives of anhydrides of compounds having groups derived from carboxylic acids are not particularly limited, and examples include substances where at least some hydrogen atoms in the anhydrides of carboxyl compounds such as dimethylmaleic anhydride, diethylmaleic anhydride, and diphenylmaleic anhydride are substituted with substituents such as alkyl or phenyl groups.

[0144] In the carboxyl group introduction process, when performing TEMPO oxidation treatment, it is preferable to carry out the treatment under conditions, for example, a pH of 6 or higher and 8 or lower. This treatment is also called neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment can be carried out, for example, by adding pulp as a cellulose raw material, TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy radical) or other nitroso radicals as a catalyst, and sodium hypochlorite as a sacrificial agent to a sodium phosphate buffer (pH = 6.8). Furthermore, by coexisting with sodium chlorite, the aldehydes generated during the oxidation process can be effectively oxidized to carboxyl groups.

[0145] Furthermore, TEMPO oxidation treatment can be carried out under conditions where the pH is above 10 and below 11. This treatment is also known as alkaline TEMPO oxidation treatment. Alkaline TEMPO oxidation treatment can be carried out, for example, by adding nitrogen radicals such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidant to pulp as a cellulose raw material.

[0146] The amount of carboxyl groups introduced into the fibrous raw material varies depending on the type of substituent. For example, when introducing carboxyl groups using TEMPO oxidation, the amount is preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, further 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, relative to 1 g (mass) of fibrous cellulose. It is also preferably 2.5 mmol / g or less, more preferably 2.20 mmol / g or less, and even more preferably 2.00 mmol / g or less. Furthermore, when the substituent is a carboxymethyl group, the amount can be 5.8 mmol / g or less, relative to 1 g (mass) of fibrous cellulose.

[0147] -Sulfur-containing oxyacid group introduction process-

[0148] In the manufacturing process of microfibrillated cellulose, an ionic substituent introduction process may include, for example, a sulfur-containing oxyacid group introduction process. In the sulfur-containing oxyacid group introduction process, by reacting the hydroxyl groups of the cellulose-containing fiber raw material with sulfur-containing oxyacids, cellulose fibers having sulfur-containing oxyacid groups can be obtained (sulfur-containing oxyacid group introduced fibers).

[0149] In the sulfur oxyacid group introduction step, instead of compound A in the above-described <phosphorus oxyacid group introduction step>, at least one compound selected from compounds capable of introducing sulfur oxyacid groups by reacting with hydroxyl groups present in cellulose-containing fiber raw materials (hereinafter also referred to as "compound C") is used. As compound C, any compound having a sulfur atom and capable of forming an ester bond with cellulose is acceptable; examples include sulfuric acid or its salts, sulfurous acid or its salts, and sulfate amides, etc., without particular limitation. As sulfuric acid, sulfuric acid of various purities can be used, such as 96% sulfuric acid (concentrated sulfuric acid). As sulfurous acid, a 5% aqueous solution of sulfurous acid can be used. As sulfates or sulfites, examples include lithium salts, sodium salts, potassium salts, ammonium salts, etc., of sulfates or sulfites, which can be prepared to various degrees of neutralization. As sulfate amides, aminosulfonic acid, etc., can be used. In the sulfur oxyacid group introduction step, compound B from the above-described <phosphorus oxyacid group introduction step> is preferably used in the same manner.

[0150] In the process of introducing sulfur-containing oxyacid groups, it is preferable to heat-treat the cellulose raw material after mixing an aqueous solution containing a sulfur-containing oxyacid and urea and / or urea derivatives into the cellulose raw material. As the heat treatment temperature, it is preferable to select a temperature that can both inhibit the thermal decomposition and hydrolysis of the fiber and effectively introduce the sulfur-containing oxyacid groups. 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.

[0151] In the heat treatment process, it is preferable to heat until there is substantially no moisture left. Therefore, the heat treatment time varies depending on the moisture content of the cellulose raw material, the amount of sulfur-containing oxyacids, and the amount of aqueous solution of urea and / or urea derivatives added; for example, it is preferably set to 10 seconds or more and 10,000 seconds or less. The heat treatment can be performed using machines equipped with various heat media, such as stirred drying devices, rotary drying devices, disc drying devices, roller heating devices, plate heating devices, fluidized bed drying devices, belt drying devices, filter drying devices, vibrating flow drying devices, airflow drying devices, reduced pressure drying devices, infrared heating devices, far-infrared heating devices, microwave heating devices, and high-frequency drying devices.

[0152] The amount of sulfur-containing oxyacid groups introduced into the cellulose raw material is preferably 0.05 mmol / g or more, more preferably 0.10 mmol / g or more, further 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-containing oxyacid groups introduced into the cellulose raw material is preferably 5.00 mmol / g or less, more preferably 3.00 mmol / g or less. By setting the amount of sulfur-containing oxyacid groups introduced within the above range, the cellulose raw material can be easily micronized, and the stability of fibrous cellulose can be improved.

[0153] -Oxidation process based on chlorine-based oxidants (second carboxyl group introduction process)-

[0154] In the manufacturing process of microfibrillated cellulose, the process of introducing ionic substituents may include, for example, an oxidation process based on chlorine-based oxidants. In the oxidation process based on chlorine-based oxidants, carboxyl groups are introduced into the cellulose raw material by adding the chlorine-based oxidant to a hydroxyl-containing cellulose raw material in a wet or dry state and reacting it.

[0155] Examples of chlorine-based oxidants include hypochlorous acid, hypochlorite, chlorite, chloric acid, chlorate, perchloric acid, perchlorate, and chlorine dioxide. From the perspectives of substituent introduction efficiency, resulting in fiber debonding efficiency, cost, and ease of processing, sodium hypochlorite, sodium chlorite, and chlorine dioxide are preferred.

[0156] Regarding chlorine-based oxidants, the reagents can be added directly to the fiber raw materials, or they can be dissolved in a suitable solvent for addition.

[0157] In the oxidation process based on chlorine-based oxidants, the concentration of the chlorine-based oxidant in the solution, for example converted to an effective chlorine concentration, 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.

[0158] The amount of chlorine-based oxidant added relative to 100 parts by weight of the fiber raw material is preferably 1 part by weight or more and 100,000 parts by weight or less, more preferably 10 parts by weight or more and 10,000 parts by weight or less, and even more preferably 100 parts by weight or more and 5,000 parts by weight or less.

[0159] The reaction time with the chlorine-based oxidant in the oxidation process may vary depending on the reaction temperature. For example, it is preferably 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.

[0160] The pH during the reaction is preferably 5 or higher and 15 or lower, more preferably 7 or higher and 14 or lower, and even more preferably 9 or higher and 13 or lower. Furthermore, the pH is preferably kept constant (e.g., pH 11) at the start of the reaction and during the reaction, while appropriately adding hydrochloric acid and sodium hydroxide. After the reaction, any remaining reaction reagents and byproducts can be washed / removed with water by filtration or the like.

[0161] -Xanthate group introduction process (xanthate esterification process)-

[0162] In the manufacturing process of microfibrillated cellulose, an ionic substituent introduction process may include, for example, a xanthate group introduction process (hereinafter also referred to as a xanthate esterification process). In the xanthate esterification process, xanthate groups are introduced into the cellulose raw material by adding carbon disulfide and an alkali compound to a moist or dry cellulose raw material and reacting the mixture. Specifically, carbon disulfide is added to the cellulose raw material that has undergone alkali celluloseification using the method described later, and a reaction is carried out.

[0163] Alkali cellulose

[0164] When introducing ionic functional groups into fiber raw materials, it is preferable to act an alkaline solution on the cellulose contained in the fiber raw material to perform alkali celluloseization. This treatment causes some of the hydroxyl groups in the cellulose to dissociate, thereby increasing nucleophilicity (reactivity). The alkaline compound contained in the alkaline solution is not particularly limited and can be either inorganic or organic. For versatility, compounds such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide are preferred. Alkali celluloseization can be carried out simultaneously with the introduction of ionic functional groups, as a preceding stage, or at both points in time.

[0165] The solution temperature at the start of alkali cellulose formation is preferably 0°C or higher and 50°C or lower, more preferably 5°C or higher and 40°C or lower, and even more preferably 10°C or higher and 30°C or lower.

[0166] As for the concentration of the alkaline solution, in terms of molar concentration, it is preferably 0.01 mol / L or more and 4 mol / L or less, more preferably 0.1 mol / L or more and 3 mol / L or less, and even more preferably 1 mol / L or more and 2.5 mol / L or less. Especially when the processing temperature is below 10°C, it is preferably 1 mol / L or more and 2 mol / L or less.

[0167] 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. Furthermore, the alkali treatment time is preferably 6 hours or less, more preferably 5 hours or less, and even more preferably 4 hours or less.

[0168] By adjusting the type of alkaline solution, treatment temperature, concentration, and soaking time as described above, it is possible to inhibit the penetration of the alkaline solution into the crystalline regions of cellulose, easily maintain the type I crystal structure of cellulose, and improve the yield of fine fibrous cellulose.

[0169] When ionic functional groups are introduced and alkali cellulose is not performed simultaneously, the alkali cellulose obtained by alkali treatment is preferably subjected to solid-liquid separation and moisture removal beforehand using conventional dehydration methods such as centrifugation and filtration. This improves the reaction efficiency in the subsequent ionic functional group introduction process. The concentration of cellulose fibers after solid-liquid separation is preferably 5% or more and 50% or less, more preferably 10% or more and 40% or less, and even more preferably 15% or more and 35% or less.

[0170] - Phosphonic acid or phosphonic group introduction process (phosphoalkylation process)-

[0171] As an ionic substituent introduction process, it may include a phosphonate group or phosphine group introduction process (phosphoalkylation process). In the phosphoalkylation process, a compound (compound E) having a reactive group and having a phosphorus group or a phosphine group, which is an essential component, is introduced. A The alkali compound, selected as an optional component, and compound B, selected from urea and its derivatives, are added to a hydroxyl-containing fiber material in a wet or dry state and reacted to introduce phosphonic acid groups or phosphonic groups into the fiber material.

[0172] Examples of reactive groups include haloalkyl groups, vinyl groups, and epoxy groups (glycidyl groups).

[0173] As compound E A Examples include vinylphosphonic acid, phenylvinylphosphonic acid, and phenylvinylphosphonic acid. From the perspective of substituent introduction efficiency, and consequently defibrillation efficiency, cost, and ease of processing, compound E... A Vinylphosphonic acid is preferred.

[0174] Furthermore, as an optional component, it is also preferable to use compound B, which is also used in the above-described <phosphorus oxyacid group introduction process>, and preferably in the same amount as described above.

[0175] Adding compound E A It can be added directly to the fiber raw material in the form of a reagent (solid or liquid), or it can be added by dissolving it in a suitable solvent. Preferably, the fiber raw material is pre-treated with alkali cellulose or alkali cellulose during the reaction. The method of alkali cellulose treatment is as described above.

[0176] The reaction temperature is preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0177] Compound E A The amount added relative to 100 parts by weight of fiber raw material is preferably 1 part by weight or more and 100,000 parts by weight or less, more preferably 2 parts by weight or more and 10,000 parts by weight or less, and even more preferably 5 parts by weight or more and 1,000 parts by weight or less.

[0178] The reaction time may vary depending on the reaction temperature, and is preferably 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 15 minutes or more and 400 minutes or less. Furthermore, after the reaction, any remaining reaction reagents, byproducts, etc., can be washed / removed with water by filtration or the like.

[0179] -Sulfonation introduction process (sulfonylation process)-

[0180] In the manufacturing process of microfibrillated cellulose, the introduction of ionic substituents may include, for example, a sulfonation introduction process (sulfonylation). In sulfonylation, a compound (compound E) having reactive groups and a sulfonyl group, which is an essential component, is introduced. B The alkali compound, selected from urea and its derivatives, and the aforementioned compound B are added to a hydroxyl-containing fiber material in a wet or dry state and reacted to introduce sulfonyl groups into the fiber material.

[0181] Examples of reactive groups include haloalkyl groups, vinyl groups, and epoxy groups (glycidyl groups).

[0182] As compound E B Examples include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, and 2-acrylamide-2-methylpropanesulfonic acid. Among these, sodium vinylsulfonate is preferred from the perspectives of substituent introduction efficiency, resulting in fiber debonding efficiency, cost, and ease of processing.

[0183] Furthermore, as an optional component, compound B from the above-described <phosphorus oxyacid group introduction process> is preferably used, and the amount added is preferably as described above.

[0184] Regarding compound E B The reagent can be added directly to the fiber raw material, or it can be dissolved in a suitable solvent before addition. Preferably, the fiber raw material is pre-treated with alkali cellulose or alkali cellulose during the reaction. The method of alkali cellulose treatment is as described above.

[0185] The reaction temperature is preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0186] Compound E B The amount added relative to 100 parts by weight of fiber raw material is preferably 1 part by weight or more and 100,000 parts by weight or less, more preferably 2 parts by weight or more and 10,000 parts by weight or less, and even more preferably 5 parts by weight or more and 1,000 parts by weight or less.

[0187] The reaction time may vary depending on the reaction temperature, for example, preferably more than 1 minute and less than 1,000 minutes, more preferably more than 10 minutes and less than 500 minutes, and even more preferably more than 20 minutes and less than 400 minutes.

[0188] In addition, after the reaction, the remaining reaction reagents, byproducts, etc. can be washed / removed by filtration or other means.

[0189] -Carboxyl alkylation process (third carboxyl introduction process)-

[0190] In the manufacturing process of microfibrillated cellulose, the process of introducing ionic substituents may include, for example, a carboxyl alkylation process. This is achieved by introducing a compound (compound E) with reactive groups and a carboxyl group, which is an essential component. C The alkali compound, selected as an optional component, and compound B, selected from urea and its derivatives, are added to a hydroxyl-containing fiber material in a moist or dry state and reacted to introduce carboxyl groups into the fiber material.

[0191] Examples of reactive groups include haloalkyl groups, vinyl groups, and epoxy groups (glycidyl groups).

[0192] As compound E C From the perspective of the efficiency of substituent introduction, and consequently the efficiency of defibrillation, cost, and ease of processing, monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred.

[0193] Furthermore, as an optional component, compound B from the above-described <phosphorus oxyacid group introduction process> is also preferred, and the amount added is preferably as described above.

[0194] Regarding compound E C The reagent can be added directly to the fiber raw material, or it can be dissolved in a suitable solvent for addition. Preferably, the fiber raw material is pre-alkali-cellulosed or alkali-cellulosed simultaneously with the reaction. The method of alkali-cellulosed is as described above.

[0195] The reaction temperature is preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0196] Compound E C The amount added relative to 100 parts by weight of fiber raw material is preferably 1 part by weight or more and 100,000 parts by weight or less, more preferably 2 parts by weight or more and 10,000 parts by weight or less, and even more preferably 5 parts by weight or more and 1,000 parts by weight or less.

[0197] The reaction time may vary depending on the reaction temperature, for example, preferably 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.

[0198] In addition, after the reaction, the remaining reaction reagents, byproducts, etc. can be washed / removed by filtration or other means.

[0199] -Catonic group introduction process (cationization process)-

[0200] By using compounds (compound E) that have reactive and cationic groups as essential components D The alkali compound, selected as an optional component, and compound B, selected from urea and its derivatives, are added to a hydroxyl-containing fiber material in a wet or dry state and reacted to introduce cationic groups into the fiber material.

[0201] Examples of reactive groups include haloalkyl groups, vinyl groups, and epoxy groups (glycidyl groups).

[0202] As compound E D From the perspective of the efficiency of substituent introduction, and consequently the efficiency of defibrillation, cost, and ease of processing, glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride, etc. are preferred.

[0203] Furthermore, as an optional component, compound B from the aforementioned <phosphorus oxyacid group introduction process> is also preferably used. The preferred amount added is also as described above.

[0204] Regarding compound E D The reagent can be added directly to the fiber raw material, or it can be dissolved in a suitable solvent for addition. Preferably, the fiber raw material is pre-alkali-cellulosed or alkali-cellulosed simultaneously with the reaction. The method of alkali-cellulosed is as described above.

[0205] The reaction temperature is preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0206] Compound E D The amount added relative to 100 parts by weight of fiber raw material is preferably 1 part by weight or more and 100,000 parts by weight or less, more preferably 2 parts by weight or more and 10,000 parts by weight or less, and even more preferably 5 parts by weight or more and 1,000 parts by weight or less.

[0207] The reaction time may vary depending on the reaction temperature, for example, preferably 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.

[0208] In addition, after the reaction, the remaining reaction reagents, byproducts, etc. can be washed / removed by filtration or other means.

[0209] (Cleaning process)

[0210] In the method for manufacturing microfibrillated cellulose according to this embodiment, a cleaning step can be performed on the fibers to which ionic groups have been introduced, as needed. The cleaning step is performed by, for example, using water or an organic solvent to clean the fibers to which ionic groups have been introduced. Furthermore, the cleaning step can be performed after the steps described later, and the number of cleaning cycles performed in each cleaning step is not particularly limited.

[0211] (Alkali treatment process)

[0212] In the manufacture of microfibrillated cellulose, the fiber raw material can be alkali-treated between the ionic group introduction step and the defiberization process described later. There are no particular limitations on the alkali treatment method; for example, immersing the fiber in an alkaline solution to introduce ionic groups can be cited.

[0213] The alkaline compound contained in the alkaline solution is not particularly limited and can be either an inorganic or organic alkaline compound. In this embodiment, for the sake of versatility, sodium hydroxide or potassium hydroxide is preferred as the alkaline compound. Furthermore, the solvent contained in the alkaline solution can be either water or an organic solvent. Preferably, the solvent contained in the alkaline solution is a polar solvent containing water or a polar organic solvent such as an alcohol, and more preferably an aqueous solvent containing at least water. For the sake of versatility, an aqueous solution of sodium hydroxide or potassium hydroxide is preferred, for example.

[0214] The temperature of the alkaline solution in the alkali treatment process is not particularly limited, but is preferably 5°C or higher and 80°C or lower, more preferably 10°C or higher and 60°C or lower. The immersion time of the ionic group-introduced fibers in the alkaline solution in the alkali treatment process is not particularly limited, but is preferably 5 minutes or higher and 30 minutes or lower, more preferably 10 minutes or higher and 20 minutes or lower. The amount of alkaline solution used in the alkali treatment is not particularly limited, but is preferably 100% by mass or higher and 100,000% by mass or lower, more preferably 1,000% by mass or higher and 10,000% by mass or lower, relative to the absolute dry mass of the ionic group-introduced fibers.

[0215] When the fine fibrous cellulose has anionic groups, alkaline treatment can be used to neutralize or exchange these anionic groups. In this case, the temperature of the alkaline solution is preferably room temperature.

[0216] To reduce the amount of alkaline solution used in the alkali treatment process, the fibers with introduced ionic groups can be cleaned with water or organic solvents after the ionic group introduction process and before the alkali treatment process. From the viewpoint of improving processability, it is preferable to clean the alkali-treated fibers with introduced ionic groups using water or organic solvents after the alkali treatment process and before the debonding process.

[0217] (Acid treatment process)

[0218] In the manufacture of microfibrillated cellulose, the cellulose raw material can be acid-treated between the step of introducing ionic groups and the subsequent defiberization process. For example, the steps of introducing ionic groups, acid treatment, alkali treatment, and defiberization can be performed sequentially.

[0219] The method of acid treatment is not particularly limited, and examples include immersing the fiber raw material in an acidic solution containing acid. The concentration of the acidic solution used is not particularly limited; for example, it is preferably 10% by mass or less, more preferably 5% by mass or less. Furthermore, the pH of the acidic solution used is not particularly limited; for example, it is preferably 0 or higher and 4 or lower, more preferably 1 or higher and 3 or lower. The acid contained in the acidic solution can be, for example, inorganic acids, sulfonic acids, carboxylic acids, etc. Examples of inorganic acids include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorite, chloric acid, perchloric acid, phosphoric acid, boric acid, etc. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid, etc. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, tartaric acid, etc. Among these, hydrochloric acid or sulfuric acid is particularly preferred.

[0220] The temperature of the acid solution used in the acid treatment is not particularly limited, but is preferably 5°C or higher and 100°C or lower, more preferably 20°C or higher and 90°C or lower. The immersion time in the acid solution during acid treatment is not particularly limited, but is preferably 5 minutes or higher and 120 minutes or lower, more preferably 10 minutes or higher and 60 minutes or lower. The amount of acid solution used in the acid treatment is not particularly limited, but is preferably 100% by mass or higher and 100,000% by mass or lower, more preferably 1,000% by mass or higher and 10,000% by mass or lower, relative to the absolute dry weight of the fiber raw material.

[0221] When the fine fibrous cellulose has cationic groups, acid treatment can be used to neutralize or exchange these cationic groups. In this case, the temperature of the acid solution is preferably room temperature.

[0222] (Fiber debonding process)

[0223] By using a defiberization process to introduce ionic groups into the fiber, microfiber-like cellulose is obtained.

[0224] In the fiber debonding process, a fiber debonding device can be used. There are no particular limitations on the fiber debonding device; for example, a high-speed fiber debonder, a pulverizer (stone mill type pulverizer), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure impact pulverizer, a ball mill, a bead mill, a disc homogenizer, a conical homogenizer, a twin-screw mixer, a vibratory mill, a high-speed rotating homogenizing agitator, an ultrasonic disperser, or a pulping machine can be used. Among the above-mentioned fiber debonding devices, a high-speed fiber debonder, a high-pressure homogenizer, or an ultra-high-pressure homogenizer are more preferred as they have less influence from the pulverizing media and a lower risk of contamination.

[0225] In the fiber debonding process, for example, it is preferable to introduce ionic groups into the fiber and dilute it with a dispersion medium to form a slurry. As the dispersion medium, one or more organic solvents selected from water and polar organic solvents can be used. There are no particular limitations on the polar organic solvent, but alcohols, polyols, ketones, ethers, esters, and aprotic polar solvents are preferred. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutanol. Examples of polyols include ethylene glycol, propylene glycol, and glycerol. 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-pyrrolidone (NMP).

[0226] The concentration of solid components in the fine fibrous cellulose during defibrillation can be set appropriately.

[0227] In addition, the slurry obtained by dispersing phosphorus-containing oxyacid group-introducing fibers into a dispersion medium may contain solid components other than phosphorus-containing oxyacid group-introducing fibers, such as urea with hydrogen bonding.

[0228] (Method for manufacturing fine fibrous cellulose with substituents removed)

[0229] In this invention, the microfibrillated cellulose can be a substance obtained by removing the ionic groups that are substituents from microfibrillated cellulose that has been incorporated with the aforementioned ionic groups and then defibrinated. From the viewpoints of reducing the YI value of the sheet and suppressing yellowing caused by heating, it is preferable to remove the ionic groups.

[0230] In this case, the preferred steps include: a step (step I) of removing at least a portion of the substituents from microfibrillated cellulose having substituents, preferably having ionic groups and having a fiber width of less than 1000 nm; and a step II of performing a uniform dispersion treatment after the aforementioned step I.

[0231] In addition, the fine fibrous cellulose supplied to step I preferably has a step (denitrification treatment step) that reduces the nitrogen content before the defibrillation treatment.

[0232] -Denitrification process-

[0233] The manufacturing process of the fine fibrous cellulose supplied in step I may further include a process for reducing the nitrogen content (a denitrification process). By reducing the nitrogen content, fine fibrous cellulose with further suppressed coloration can be obtained. The denitrification process may be arranged after the uniform dispersion process in step II described later, and preferably before the uniform dispersion process in step II described later. In addition, it is preferable to arrange it before the aforementioned defibrillation process.

[0234] In the denitrification process, it is preferable to adjust the pH of the slurry containing anionic groups introduced into the fibers to 10 or higher, and then subject it to heat treatment. During heat treatment, the liquid temperature of the slurry is preferably set to 50°C or higher and 100°C or lower, and the heating time is preferably set to 15 minutes or higher and 180 minutes or lower. When adjusting the pH of the slurry containing anionic groups introduced into the fibers, it is preferable to add an alkaline compound that can be used in the aforementioned alkaline treatment process.

[0235] Following the denitrification process, a cleaning process can be performed on the fibers to which the anionic groups have been introduced, as needed. The cleaning process is carried out by, for example, using water or an organic solvent to clean the fibers. Furthermore, there is no particular limitation on the number of cleaning cycles performed in each cleaning process.

[0236] -Process I-

[0237] In this invention, the method for manufacturing microfibrillary cellulose may include a step (step I) of removing at least a portion of the substituents from microfibrillary cellulose having substituents and a fiber width of less than 10 nm. In this specification, the step (step I) of removing at least a portion of the substituents from microfibrillary cellulose is also referred to as the substituent removal treatment step.

[0238] Examples of substituent removal treatment steps include: heat treatment of microfibrillated cellulose with substituents and a fiber width of 10 nm or less; enzyme treatment; acid treatment; and alkali treatment. These steps can be performed individually or in combination. Preferably, the substituent removal treatment step involves either heat treatment or enzyme treatment. By undergoing these treatment steps, at least a portion of the substituents are removed from the microfibrillated cellulose with substituents and a fiber width of 10 nm or less, resulting in microfibrillated cellulose with, for example, a substituent introduction amount of less than 0.5 mmol / g.

[0239] It should be noted that the above-mentioned substituent removal process is suitable when the substituent is a phosphorus-containing oxyacid group or a sulfur-containing oxyacid group.

[0240] The amount of substituent introduced after the substituent removal treatment step is preferably 0.3 mmol / g or less, more preferably 0.2 mmol / g or less, and even more preferably 0.1 mmol / g or less.

[0241] The substituent removal process is preferably performed in a slurry form. Specifically, the substituent removal process is preferably a process involving heat treatment, enzyme treatment, acid treatment, or alkali treatment of a slurry containing microfibrillated cellulose fibers with substituents and a fiber width of 10 nm or less. By performing the substituent removal process in a slurry form, it is possible to prevent the accumulation of coloring substances, added or generated acids, alkalis, salts, etc., caused by heating during the substituent removal process. This suppresses coloring when the microfibrillated cellulose obtained in step II is produced into slurries or sheets. Furthermore, when salt removal treatment derived from the removed substituents is performed after the substituent removal process, the salt removal efficiency can be improved.

[0242] When performing a substituent removal treatment on a slurry containing fine fibrous cellulose with substituents and a fiber width of 10 nm or less, the concentration of the fine fibrous cellulose in the slurry is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more. Furthermore, the concentration of the fine fibrous cellulose in the slurry is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. By setting the concentration of the fine fibrous cellulose in the slurry within the above range, the substituent removal treatment can be performed more efficiently. Furthermore, by setting the concentration of the fine fibrous cellulose in the slurry within the above range, the residues of coloring substances, added or generated acids, alkalis, salts, etc., caused by heating during the substituent removal treatment can be prevented. Therefore, coloring when the fine fibrous cellulose obtained through step II is made into slurry or sheets can be suppressed. In addition, when performing a salt removal treatment derived from the removed substituents after the substituent removal treatment, the salt removal efficiency can also be improved.

[0243] When the substituent removal treatment step involves heating microfibrillated cellulose having substituents and a fiber width of 10 nm or less, the heating temperature in the heating treatment step 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 heating treatment step is preferably 250°C or lower, more preferably 230°C or lower, and even more preferably 200°C or lower. Wherein, when the substituents in the microfibrillated cellulose supplied for the substituent removal treatment step are phosphorus-containing oxyacid groups or sulfonates, the heating temperature in the heating treatment step is preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher.

[0244] When the substituent removal process is a heat treatment process, there are no particular limitations on the heating device that can be used in the heat treatment process. Hot air heating devices, steam heating devices, electric heating devices, hydrothermal heating devices, fire-powered heating devices, infrared heating devices, far-infrared heating devices, microwave heating devices, high-frequency heating devices, stirring drying devices, rotary drying devices, disc drying devices, roller heating devices, plate heating devices, fluidized bed drying devices, belt drying devices, filter drying devices, vibrating flow drying devices, airflow drying devices, and reduced pressure drying devices are all acceptable. From the viewpoint of preventing evaporation, heating is preferably carried out in a closed system; furthermore, from the viewpoint of increasing the heating temperature, it is preferably carried out in a pressure-resistant device or container. The heat treatment can be batch processing, batch-continuous processing, or continuous processing.

[0245] When the substituent removal process is an enzymatic treatment of microfibrillated cellulose with substituents and a fiber width of less than 10 nm, the enzyme treatment process preferably uses phosphate ester hydrolase, sulfate ester hydrolase, etc., depending on the type of substituent.

[0246] In the enzyme treatment process, the enzyme is added such that its enzyme activity relative to 1g of microfibrillated cellulose is preferably 0.1 kPa or more, more preferably 1.0 kPa or more, and even more preferably 10 kPa or more. Furthermore, the enzyme is added such that its enzyme activity relative to 1g of microfibrillated cellulose is preferably 100,000 kPa or less, more preferably 50,000 kPa or less, and even more preferably 10,000 kPa or less. After adding the enzyme to the microfibrillated cellulose dispersion (slurry), the treatment is preferably carried out at a temperature of 0°C or higher and less than 50°C for at least 1 minute and at least 100 hours.

[0247] A step can be set up to deactivate the enzyme after the enzyme reaction. Examples of methods for deactivating the enzyme include: adding acidic or alkaline components to the enzyme-treated slurry to deactivate the enzyme, and raising the temperature of the enzyme-treated slurry to above 90°C to deactivate the enzyme.

[0248] When the substituent removal process is an acid treatment process for microfibrillated cellulose with substituents and a fiber width of less than 10 nm, it is preferable to add an oxygen compound that can be used in the above-mentioned acid treatment process to the slurry during the acid treatment process.

[0249] When the substituent removal treatment step is an alkali treatment step of microfibrillated cellulose having substituents and a fiber width of less than 10 nm, it is preferable to add an alkali compound that can be used in the above-mentioned alkali treatment step to the slurry during the alkali treatment step.

[0250] In the substituent removal process, it is preferable to carry out the substituent removal reaction uniformly. To achieve uniform reaction, for example, the slurry containing fine fibrous cellulose can be stirred, or the specific surface area of ​​the slurry can be increased. As a method of stirring the slurry, mechanical shearing can be applied externally, or self-stirring can be promoted by increasing the feed rate of the slurry in the reaction.

[0251] In the substituent removal process, spacer molecules can be added. These spacer molecules enter between adjacent microfibrillary cellulose fibers, thereby functioning as spacers to create microspaces between the microfibrillary cellulose fibers. By adding these spacer molecules in the substituent removal process, the aggregation of the microfibrillary cellulose fibers after the substituent removal process can be suppressed. This, in turn, can more effectively improve the transparency of dispersions and sheets containing microfibrillary cellulose fibers.

[0252] 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), carboxymethyl cellulose, and polyvinyl alcohol (PVA). Other water-soluble organic compounds that can be used include alkyl methacrylate-acrylic acid copolymers, polyvinylpyrrolidone, sodium polyacrylate, propylene glycol, dipropylene glycol, polypropylene glycol, isoprene glycol, hexanediol, 1,3-butanediol, polyacrylamide, xanthan gum, guar gum, tamarind gum, carrageenan, locust bean gum, quince seed, alginic acid, pullulan, carrageenan, pectin, cationic starch, raw starch, oxidized starch, etherified starch, esterified starch, amylose, and other starches, as well as glycerol, diglycerol, polyglycerol, hyaluronic acid, and metal salts of hyaluronic acid.

[0253] In addition, known pigments can be used as spacer molecules. Examples include kaolin (including clay), calcium carbonate, titanium dioxide, zinc oxide, amorphous silica (including colloidal silica), alumina, zeolite, sepiolite, montmorillonite, synthetic montmorillonite, magnesium silicate, magnesium carbonate, magnesium oxide, diatomaceous earth, styrene-based plastic pigments, hydrotalcite, urea resin-based plastic pigments, and benzoguanamine-based plastic pigments.

[0254] -pH Adjustment Procedure-

[0255] When performing the substituent removal process in a slurry form, a step of adjusting the pH of the slurry containing fine fibrous cellulose can be included prior to the substituent removal process. For example, an anionic group can be introduced into the cellulose fibers, and the counterion of this anionic group is Na+. + In this condition, the pulp containing decellulose-decomposed fine fibrous cellulose exhibits a weakly alkaline pH. If heating is performed under these conditions, monosaccharides, which contribute to coloring, may sometimes be produced due to the decomposition of cellulose; therefore, it is preferable to adjust the pH of the pulp to below 8. Furthermore, monosaccharides may also be produced under acidic conditions; therefore, it is preferable to adjust the pH of the pulp to above 3.

[0256] Furthermore, when the substituent-containing microfibrillary cellulose is a phosphate-containing microfibrillary cellulose, from the viewpoint of improving the removal efficiency of the substituent, it is preferable that the phosphorus in the phosphate group is susceptible to nucleophilic attack. Cellulose-OP(=O)(-O-H+)(-O-Na) is susceptible to nucleophilic attack. + To achieve a state where the degree of neutralization is 1, it is preferable to adjust the pH of the slurry to 3 or higher and 8 or lower, and more preferably to adjust the pH to 4 or higher and 6 or lower.

[0257] There are no particular limitations on the methods used to adjust pH. For example, acidic or alkaline components can be added to a slurry containing fine fibrous cellulose. Acidic components can be either inorganic or organic acids. 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. Alkaline components can be either inorganic or organic alkali compounds. 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 base 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.

[0258] In addition, ion exchange treatment can be performed in the pH adjustment process to adjust the pH. During ion exchange treatment, either a strong acid cation exchange resin or a weak acid ion exchange resin can be used. By treating with an appropriate amount of cation exchange resin for a sufficient time, a slurry containing fine fibrous cellulose at the target pH can be obtained. Furthermore, the addition of acidic and alkaline components can be combined with ion exchange treatment in the pH adjustment process.

[0259] <Salt Removal Treatment>

[0260] Following the substituent removal process, it is preferable to perform a salt removal process from the removed substituents. By removing salts from the substituents, fine fibrous cellulose capable of suppressing coloration can be easily obtained. The means of removing salts from the substituents are not particularly limited, and examples include washing and ion exchange treatments. Washing is performed by, for example, washing with water or an organic solvent to remove the fine fibrous cellulose aggregated during the substituent removal process. In ion exchange treatment, an ion exchange resin can be used.

[0261] -Process II-

[0262] In this embodiment, the method for manufacturing microfibrillary cellulose may include: a step (step I) of removing at least a portion of the substituents from microfibrillary cellulose having substituents and a fiber width of 1000 nm or less; and a step (step II) of performing a uniform dispersion treatment after step I. The uniform dispersion treatment step (step II) is a step of uniformly dispersing the microfibrillary cellulose obtained by the substituent removal treatment in step I. In step I, by performing the substituent removal treatment on the microfibrillary cellulose, at least a portion of the microfibrillary cellulose aggregates. Step II is a step of uniformly dispersing the aggregated microfibrillary cellulose. The state of uniformly dispersed microfibrillary cellulose in step II refers to a state where the fiber width of the microfibrillary cellulose is 10 nm or less. Thus, even with a low substituent introduction amount of less than 0.50 mmol / g, the microfibrillary cellulose obtained by the manufacturing method of this embodiment has a fiber width of 10 nm or less.

[0263] In the uniform dispersion process (Process II), equipment such as high-speed defibers, pulverizers (stone mill type pulverizers), high-pressure homogenizers, high-pressure impact pulverizers, ball mills, bead mills, disc homogenizers, conical homogenizers, twin-screw mixers, vibratory mills, high-speed rotating homogenizers, ultrasonic dispersers, or pulpers can be used. Among the above-mentioned uniform dispersion processing equipment, high-speed defibers and high-pressure homogenizers are more preferred.

[0264] The processing conditions in the uniform dispersion treatment step (step II) are not particularly limited, but it is preferable to increase the maximum moving speed of the fine fibrous cellulose during processing and the pressure during processing. In a high-speed defibrillator, the circumferential 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 defibrillator because it allows for greater maximum moving speed of the fine fibrous cellulose during processing and higher pressure during processing. In high-pressure homogenizer processing, the processing pressure is preferably 1 MPa or more and 350 MPa or less, more preferably 10 MPa or more and 300 MPa or less, and even more preferably 50 MPa or more and 250 MPa or less.

[0265] It should be noted that the aforementioned spacer molecules can be added again in step II. By adding these spacer molecules during the uniform dispersion treatment step of step II, the uniform dispersion of the fine fibrous cellulose can be achieved more smoothly. This, in turn, can more effectively improve the transparency of the dispersion and sheet containing the fine fibrous cellulose.

[0266] From the viewpoint of obtaining transparency of the sheet, suppressing yellowing caused by heating, high tensile modulus of elasticity and high softness, the content of fine fibrous cellulose in the solid component of the sheet is preferably 5% by mass or more, more preferably 10% by mass or more, further 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, further preferably 85% by mass or less, even more preferably 80% by mass or less, particularly preferably 75% by mass or less.

[0267] As a type of microfibrillary cellulose, microfibrillary cellulose containing ionic groups and unmodified microfibrillary cellulose can be used in combination.

[0268] <Cellulose derivatives>

[0269] In this invention, the sheet material, in addition to containing the aforementioned fine fibrous cellulose, also contains a weight-average molecular weight of 1.0 × 10⁻⁶. 4 Above and 3.0×10 5 The following cellulose derivatives. By producing sheets containing microfibrillated cellulose and cellulose derivatives with specific weight-average molecular weights, sheets with high transparency, inhibition of heat-induced yellowing, high tensile modulus, and excellent softness are obtained.

[0270] From the perspectives of suppressing the shape stability and gelation of the sheet material, as well as considering both high tensile modulus of elasticity and high tensile elongation, and suppressing yellowing before and after heating, the weight-average molecular weight of the aforementioned cellulose derivative is preferably 2.5 × 10⁻⁶. 4 The above, and more preferably 5.0×10 4 The above, and more preferably 1.0×10 5 The above, and preferably 2.8 × 10 5 The following, and more preferably, is 2.6 × 10 5 the following.

[0271] The weight-average molecular weight of the cellulose derivatives was determined by gel permeation chromatography (GPC-MALLS method) based on light scattering.

[0272] As a cellulose derivative, water-soluble cellulose ethers are preferred from the viewpoints of improving affinity with fine fibrous cellulose and facilitating addition to slurries (fine fibrous cellulose dispersions) of fine fibrous cellulose. Here, water solubility means dissolving 1 g or more relative to 100 g of water at 20°C.

[0273] In addition, cellulose ethers refer to the general term for cellulose derivatives obtained by etherifying the hydroxyl groups of cellulose.

[0274] Examples of water-soluble cellulose ethers include methylcellulose, hydroxyethyl methylcellulose, hydroxypropyl methylcellulose, ethylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and carboxyethyl cellulose.

[0275] Furthermore, from the viewpoint of suppressing yellowing of sheets caused by heating, water-soluble cellulose is preferably a non-ionic water-soluble cellulose ether. Examples of non-ionic water-soluble cellulose ethers include methylcellulose, hydroxyethyl methylcellulose, hydroxypropyl methylcellulose, ethylcellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.

[0276] The nonionic water-soluble cellulose ether preferably has at least one functional group selected from the group consisting of methoxy and hydroxypropoxy, more preferably selected from the group consisting of methylcellulose and hydroxypropylmethylcellulose, and even more preferably hydroxypropylmethylcellulose.

[0277] 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, further 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.

[0278] When the cellulose derivative is hydroxypropyl methylcellulose, the preferred range of methoxy substitution degree is the same as that in the aforementioned methylcellulose. Furthermore, the hydroxypropoxy substitution degree is preferably 0.08 or more, more preferably 0.10 or more, further preferably 0.12 or more, even more preferably 0.15 or more, particularly preferably 0.18 or more, and preferably 0.50 or less, more preferably 0.40 or less, even more preferably 0.35 or less, and even more preferably 0.30 or less.

[0279] From the viewpoint of obtaining transparency of the sheet, suppressing yellowing caused by heating, high tensile modulus of elasticity and high softness, the content of cellulose derivative in the solid component of the sheet is preferably 95% by mass or less, more preferably 90% by mass or less, further 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, further preferably 15% by mass or more, even more preferably 20% by mass or more, particularly preferably 25% by mass or more.

[0280] In this embodiment, from the viewpoint of obtaining transparency of the sheet, suppressing yellowing caused by heating, high tensile modulus of elasticity and high softness, the total content of microfibrillary cellulose and cellulose derivatives in the solid component of the sheet is preferably 60% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, even more preferably 95% by mass or more, and preferably 100% by mass or less, particularly preferably 100% by mass.

[0281] <Optional Ingredients>

[0282] In addition to containing microfibrillated cellulose and cellulose derivatives, sheet materials may also contain optional components. Optional components include, for example, hydrophilic polymers (excluding cellulose derivatives), hydrophilic low molecular weight polymers, 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 protectants, dyes, pigments, stabilizers, magnetic powders, orientation accelerators, plasticizers, dispersants, anti-coloring agents, polymerization inhibitors, pH adjusters, and crosslinking agents.

[0283] It should be noted that examples of hydrophilic polymers include polyethylene glycol, polyethylene oxide, polyvinyl alcohol, modified polyvinyl alcohol (such as acetylated polyvinyl alcohol), polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylates, polyacrylamide, alkyl acrylate copolymers, and urethane copolymers. Examples of hydrophilic low-molecular-weight polymers include glycerol, 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 ion, tetraethylphosphonium ion, tetrapropylphosphonium ion, tetrabutylphosphonium ion, and lauryltrimethylphosphonium ion. Similarly, examples of tetrapropylonium ions and tetrabutylonium ions include tetra-n-propylonium ion and tetra-n-butylonium ion, respectively.

[0284] <Characteristics of Sheets>

[0285] [Yellow Index]

[0286] When the sheet of this embodiment is heated at 160°C for 6 hours, the change in the yellowness 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 limitation on the lower limit. If the change in the YI value before and after heating is within the above range, yellowing caused by heating can be suppressed, and therefore is preferred.

[0287] 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 even more preferably 0.5 or less. There is no particular limitation on the lower limit.

[0288] 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.

[0289] The YI value was determined according to JIS K 7373:2006.

[0290] [Haze]

[0291] The haze of the sheet material in this embodiment is preferably 5% or less. If the haze is 5% or less, the transparency is excellent, and therefore this is preferred.

[0292] The haze of the sheet is preferably 5% or less, more preferably 4% or less, even more preferably 3% or less, and even more preferably 2% or less.

[0293] The haze of the sheet was measured according to JIS K 7136:2000 using a haze meter (Murakami Color Technology Research Institute Co., Ltd., HM-150).

[0294] Total transmittance

[0295] In this embodiment, the total light transmittance of the sheet is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. There is no particular upper limit to the total light transmittance of the sheet; for example, it can be 100%. If the total light transmittance of the sheet is within the above range, the transparency is excellent, and therefore it is preferred.

[0296] Here, the total light transmittance of the sheet is, for example, a value measured according to JIS K 7361-1:1997 using a haze meter (Murakami Color Technology Research Institute Co., Ltd., HM-150).

[0297] The tensile modulus of elasticity of the sheet material 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. Furthermore, there is no particular 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. If the tensile modulus of elasticity of the sheet material is within the above range, its rigidity is excellent, and therefore it is preferred.

[0298] Here, the tensile modulus of elasticity of the sheet is, for example, a value measured according to JIS P 8113:2006 using a TENSILON tensile testing machine (manufactured by A&D). When determining the tensile modulus of elasticity, a sample conditioned for 24 hours at 23°C and 50% relative humidity is used as the test piece, and the measurement is performed at 23°C and 50% relative humidity.

[0299] The tensile elongation of the sheet material in this embodiment is preferably 3% or more, more preferably 4% or more, further preferably 5% or more, and even more preferably 7% or more. There is no particular upper limit, but from the viewpoint of balancing rigidity and flexibility, it is preferably 50% or less, more preferably 40% or less, further preferably 30% or less, and even more preferably 20% or less. If the tensile elongation is within the above range, the flexibility is excellent, and therefore it is preferred.

[0300] The tensile elongation of the sheet was measured according to JIS K 7127:1999 using a TENSILON tensile testing machine (manufactured by A&D). When determining the tensile modulus of elasticity, samples conditioned for 24 hours at 23°C and 50% relative humidity were used as test pieces, and measurements were taken at 23°C and 50% relative humidity.

[0301] The tensile strength of the sheet material in this embodiment is preferably 60 MPa or more, more preferably 70 MPa or more, further preferably 80 MPa or more, and even more preferably 85 MPa or more. There is no particular upper limit, but from the viewpoint of balancing rigidity and flexibility, it is preferably 200 MPa or less, more preferably 180 MPa or less, further preferably 160 MPa or less, and even more preferably 150 MPa or less.

[0302] The tensile strength of the sheet was measured according to JIS K 7127:1999 using a TENSILON tensile testing machine (manufactured by A&D). When determining the tensile strength, samples conditioned for 24 hours at 23°C and 50% relative humidity were used as test pieces, and the test was conducted at 23°C and 50% relative humidity.

[0303] The surface pH of the sheet material 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 material is preferably 7.0 or lower. It should be noted that the surface pH of the sheet material is measured using, for example, a calibrated pH meter (manufactured by Horiba Corporation, F-53). The surface pH of the sheet material is measured by contacting a flat pH composite electrode (manufactured by Horiba Corporation, 6261-10C) with the sheet material after it has been coated with a small amount of water.

[0304] 〔thickness〕

[0305] The thickness of the sheet material 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 material thickness is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less. The sheet material thickness is preferably adjusted appropriately according to its intended use. It should be noted that the sheet material thickness can be measured using a constant pressure thickness gauge (TECLOCK CORPORATION, PG-02). The sheet material thickness is measured according to the following method: After conditioned at 23°C and 50% relative humidity for 24 hours, a sheet material cut into squares of 50 mm or more is measured at any four points, and the average value is taken as the sheet material thickness.

[0306] [Base weight]

[0307] The preferred basis weight of the sheet is 10 g / m². 2 The above, and more preferably 20g / m 2 The above, and more preferably 30g / m 2 That's all. Additionally, the basis weight of the sheet is not particularly limited, but is preferably 1000 g / m². 2 The following, or more preferably, is 500g / m 2 The following, and more preferably 200g / m 2 The following, especially preferred, is 100g / m 2 the following.

[0308] The basis weight of the sheet is calculated as follows: After conditioned at 23°C and 50% relative humidity for 24 hours, the sheet is cut into pieces of at least 50mm square. The mass is then measured, and the basis weight is calculated by dividing the mass by the area of ​​the cut sheet.

[0309] (density)

[0310] The preferred density of the sheet is 1.00 g / cm³. 3 The above, and more preferably 1.10 g / cm 3The above, and more preferably, is 1.20 g / cm³. 3 That's all. Additionally, the density of the sheet is not particularly limited, but is preferably 3.00 g / cm³. 3 The following, or more preferably, is 1.70 g / cm³ 3 The following, and more preferably, is 1.50 g / cm³. 3 The density of the sheet is calculated by dividing the sheet's basis weight by its thickness.

[0311] The sheet material in this embodiment is preferably not a porous sheet material. That is, the porosity and void ratio are preferably 10% or less, more preferably 3% or less, further preferably 1% or less, and even more preferably 0.1% or less.

[0312] [Sheet manufacturing method]

[0313] This document describes sheets containing microfibrillated cellulose and cellulose derivatives with a fiber width of less than 10 nm.

[0314] In this embodiment, the sheet can be obtained, for example, by using a liquid composition containing the above-mentioned microfibrillated cellulose and cellulose derivatives, as well as other components, and performing the sheeting process described later.

[0315] The sheet manufacturing process preferably includes at least a coating process of applying the aforementioned composition to a substrate, or a papermaking process of forming the pulp. This yields a sheet containing fine fibrous cellulose and cellulose derivatives.

[0316] -Coating process-

[0317] In the coating process, a sheet can be obtained by coating a slurry containing microfibrillated cellulose and cellulose derivatives onto a substrate and drying it, thereby peeling the resulting sheet off the substrate. Furthermore, by using a coating apparatus and a strip or continuous substrate, sheet production can be continuous.

[0318] The material of the substrate used in the coating process is not particularly limited. However, a material that can be easily peeled off from the sheet formed after drying is preferred, as it provides high wettability to the composition (slurry) and can suppress sheet shrinkage during drying. Among these, resin films or sheets, or metal films or sheets, are preferred, without particular limitation. Films or sheets made of resins such as acrylics, polyethylene terephthalate, vinyl chloride, polystyrene, polypropylene, polycarbonate, and polyvinylidene chloride can be used; films or sheets made of metals such as aluminum, zinc, copper, and iron plates; and substances obtained by oxidizing their surfaces; stainless steel films or sheets; brass films or sheets, etc.

[0319] In the coating process, when the slurry viscosity is low and spreads on the substrate, a blocking frame can be fixed to the substrate to obtain a sheet of a specified thickness and weight. There are no particular limitations on the blocking frame, but a frame that can be easily peeled off from the ends of the sheet after drying is preferred. From this viewpoint, a frame formed from a resin sheet or a metal sheet is more preferred. In this embodiment, frames formed from resin sheets such as acrylic sheets, polyethylene terephthalate sheets, vinyl chloride sheets, polystyrene sheets, polypropylene sheets, polycarbonate sheets, and polyvinylidene chloride sheets, as well as metal sheets such as aluminum sheets, zinc sheets, copper sheets, and iron sheets, and their surface-oxidized sheets, stainless steel sheets, and brass sheets can be used.

[0320] There are no particular limitations on the coating machine used to apply the slurry to the substrate; for example, a roller coater, gravure coater, die coater, curtain coater, air knife coater, etc., can be used. From the perspective of making the sheet thickness more uniform, die coaters, curtain coaters, and spray coaters are particularly preferred.

[0321] The slurry temperature and ambient temperature (hereinafter, slurry temperature and ambient temperature are collectively referred to as "coating temperature") when applying the slurry to the substrate are not particularly limited. For example, it is preferably 5°C or higher and 80°C or lower, more preferably 10°C or higher and 60°C or lower, even more preferably 15°C or higher and 50°C or lower, and particularly preferably 20°C or higher and 40°C or lower. If the coating temperature is above the lower limit mentioned above, the slurry can be coated more easily. If the coating temperature is below the upper limit mentioned above, the volatilization of the dispersion medium in the coating can be suppressed.

[0322] In the coating process, it is preferable to coat the slurry onto the substrate with the final basis weight and thickness of the sheet falling within the aforementioned preferred range. By coating with the basis weight and thickness falling within the aforementioned range, a sheet with superior transparency, rigidity, and flexibility is obtained.

[0323] The coating process, as described above, includes a process of drying the slurry applied to the substrate. The process of drying the slurry is not particularly limited and can be performed, for example, by a non-contact drying method, or by drying while the sheet is fixed in place, or a combination thereof.

[0324] As a non-contact drying method, there are no particular limitations. Methods such as heating and drying using hot air, infrared radiation, far-infrared radiation, or near-infrared radiation (heat drying method) can be applied; or methods involving vacuum drying can be used (vacuum drying method). Heating and vacuum drying methods can be combined, but heating drying is generally preferred. Drying based on infrared, far-infrared, or near-infrared radiation is not particularly limited and can be performed using, for example, infrared devices, far-infrared devices, or near-infrared devices.

[0325] The heating temperature in the heat drying method is not particularly limited; for example, it is preferably set to 20°C or higher and 150°C or lower, more preferably 25°C or higher and 105°C or lower. Setting the heating temperature above the lower limit allows for rapid evaporation of the dispersion medium. Furthermore, setting the heating temperature below the upper limit allows for the suppression of heating costs and the suppression of heat-induced discoloration of the fibrous cellulose.

[0326] -Papermaking process-

[0327] The papermaking process involves forming paper from pulp using a papermaking machine. There are no particular limitations on the papermaking machine used in this process; examples include continuous papermaking machines such as wire mesh, cylinder mesh, and inclined wire mesh machines, as well as multi-layer papermaking machines combining these types. Known papermaking methods such as hand-making can be employed in the papermaking process.

[0328] The papermaking process involves filtering and dewatering the pulp using a screen to obtain a wet paper sheet, which is then pressurized and dried. The filter cloth used for filtering and dewatering the pulp is not particularly limited, but a filter cloth that prevents fibrous cellulose from passing through and whose filtration speed is not too slow is more preferred. Such a filter cloth is not particularly limited, but sheets, fabrics, or porous membranes formed from organic polymers are preferred. The organic polymer is not particularly limited, but non-cellulose-based organic polymers such as polyethylene terephthalate, polyethylene, polypropylene, and polytetrafluoroethylene (PTFE) are preferred. Examples of suitable materials in this embodiment include porous membranes made of polytetrafluoroethylene with a pore size of 0.1 μm or more and 20 μm or less, and fabrics made of polyethylene terephthalate or polyethylene with a pore size of 0.1 μm or more and 20 μm or less.

[0329] In the papermaking process, the method of manufacturing sheets from pulp can be carried out using a manufacturing apparatus, for example, comprising: a water-pressing section that discharges pulp containing fine fibrous cellulose onto the upper surface of an annular belt and extrudes a dispersion medium from the discharged pulp to generate a fiber web; and a drying section that dries the fiber web to generate a sheet. An annular belt is arranged from the water-pressing section to the drying section, and the fiber web generated in the water-pressing section is conveyed to the drying section in a state of being mounted on the annular belt.

[0330] The dewatering method used in the papermaking process is not particularly limited, and examples of dewatering methods commonly used in paper manufacturing can be listed. Among these, a method that uses a wire mesh, cylinder wire, or inclined wire mesh for dewatering, followed by further dewatering by roller pressure, is preferred. Similarly, the drying method used in the papermaking process is not particularly limited, and examples of methods used in paper manufacturing can be listed. Among these, drying methods using a drum dryer, Yankee dryer, hot air dryer, near-infrared heater, or infrared heater are more preferred.

[0331] The thickness, basis weight, and density of the sheet can be appropriately set according to the desired thickness, basis weight, and density of the sheet.

[0332] [Layered Body]

[0333] The present invention can be a laminate having a structure in which other layers are further laminated on the aforementioned sheet. These other layers may be disposed on both surfaces of the sheet or only on one surface. Examples of other layers laminated on at least one surface of the sheet include, for example, resin layers and inorganic layers, with resin layers being preferred. Alternatively, other layers may be further laminated on the side of the resin layer that is not in contact with the sheet to form the laminate. Examples of such other layers include, for example, polyethylene film, polypropylene film, cyclic olefin polymer film, and polyimide film.

[0334] The thickness of 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. Furthermore, it is preferably 5000 μm or less, more preferably 1000 μm or less, and even more preferably 500 μm or less. For example, when the resin layer is a coating layer formed by coating, the thickness of the resin layer can 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.

[0335] <Resin Layer>

[0336] The resin layer is a layer whose main component is natural resin or synthetic resin. Here, the main component refers to a component that contains 50% or more by mass relative to the total mass of the resin layer. The resin content relative to the total mass of the resin layer is preferably 60% or more by mass, more preferably 70% or more by mass, further preferably 80% or more by mass, and particularly preferably 90% or more by mass. It should be noted that the resin content can be set to 100% by mass or 95% or less by mass.

[0337] As natural resins, examples include rosin, rosin esters, hydrogenated rosin esters, and other rosin-based resins.

[0338] The synthetic resin is preferably selected from at least one of polycarbonate resin, polyethylene terephthalate resin, polyethylene naphthalate resin, polyethylene resin, polypropylene resin, polyimide resin, polystyrene resin, and acrylic resin. The synthetic resin is preferably selected from at least one of polycarbonate resin, acrylic resin, and polypropylene resin, and more preferably polycarbonate resin.

[0339] Examples of polycarbonate resins constituting the resin layer include aromatic polycarbonate resins and aliphatic polycarbonate resins. These specific polycarbonate resins are known, and examples include the polycarbonate resin described in Japanese Patent Application Publication No. 2010-023275.

[0340] Examples of polypropylene resins constituting 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 more preferred.

[0341] The resin constituting the resin layer can be a single resin or a copolymer formed by copolymerization or graft polymerization of multiple resin components. Alternatively, it can be used as a blend material formed by mixing multiple resin components through a physical process.

[0342] An adhesive layer can be provided between the sheet and the resin layer; alternatively, the sheet and resin layer can be directly bonded together without an adhesive layer. When an adhesive layer is provided between the sheet and the resin layer, examples of adhesives constituting the adhesive layer include acrylic resins. Other examples of adhesives besides acrylic resins include vinyl chloride resins, (meth)acrylate resins, styrene / acrylate copolymer resins, vinyl acetate resins, vinyl acetate / (meth)acrylate copolymer resins, urethane resins, silicone resins, epoxy resins, ethylene / vinyl acetate copolymer resins, polyester resins, polyvinyl alcohol resins, ethylene-vinyl alcohol copolymer resins, SBR, NBR, and other rubber-based emulsions.

[0343] In the absence of an adhesive layer between the sheet and the resin layer, the resin layer may contain an adhesive agent. In addition, the surface of the resin layer may be treated with a hydrophilic treatment or other surface treatments.

[0344] Examples of sealing aids include compounds containing at least one group selected from isocyanate groups, carbodiimide groups, epoxy groups, oxazoline groups, amino groups, and silanol groups; and organosilicon compounds. Preferably, the sealing aid is selected from at least one group selected from compounds containing isocyanate groups (isocyanate compounds) and organosilicon compounds. Examples of organosilicon compounds include silane coupling agent condensates and silane coupling agents.

[0345] Surface treatment methods include corona treatment, plasma discharge treatment, UV irradiation treatment, electron beam irradiation treatment, and flame treatment.

[0346] <Inorganic layer>

[0347] The materials constituting the inorganic layer are not particularly limited, and examples include aluminum, silicon, magnesium, zinc, tin, nickel, and titanium; their oxides, carbides, nitrides, carbon oxides, nitrogen oxides, or carbonitrides; or mixtures thereof. From the viewpoint of being able to stably maintain high moisture resistance, silicon oxide, silicon nitride, silicon carbide, silicon oxynitride, silicon carbonitride, aluminum oxide, aluminum nitride, aluminum carbide, aluminum oxynitride, or mixtures thereof are preferred.

[0348] There are no particular limitations on the method for forming inorganic layers. Generally speaking, the methods for forming thin films are roughly divided into chemical vapor deposition (CVD) and physical vapor deposition (PVD), and any method can be used. Specifically, examples of CVD methods include plasma CVD using plasma and catalytic chemical vapor deposition (Cat-CVD) which uses a heated catalyst to perform contact thermal decomposition of the material gas. Specific examples of PVD methods include vacuum evaporation, ion plating, and sputtering.

[0349] Alternatively, atomic layer deposition (ALD) can be used to form inorganic layers. ALD involves alternately supplying feed gases of the elements constituting the desired film to the surface of the forming layer, thereby forming a thin film in the form of a single atomic layer. While it suffers from a slow deposition rate, it offers advantages such as superiority over plasma CVD, the ability to perfectly cover even complex shapes, and the production of films with fewer defects. Furthermore, ALD allows for nanometer-level control of film thickness and facilitates the covering of wide areas. Moreover, by using plasma, ALD can be expected to improve reaction rates, enable low-temperature processing, and reduce unreacted gases.

[0350] <Uses of Sheets>

[0351] The sheet material of this embodiment is suitable for use in various display devices, various solar cells, and other optical components. It is also suitable for use as substrates for electronic devices, separators for electrochemical components, components for home appliances, various vehicles, window materials for buildings, interior materials, outer packaging materials, and packaging materials. Furthermore, in addition to applications such as yarns, filters, fabrics, cushioning materials, sponges, and abrasive materials, it is also suitable for use as a reinforcing material.

[0352] In addition, the sheet material of the present invention is also suitable for use as food containers such as dishes, cups, and trays; tableware such as knives, spoons, and forks; and straws.

[0353] The sheet material of this embodiment exhibits reduced transparency and suppressed yellowing caused by heating, making it suitable for applications involving optical components where transparency and yellowing are issues. Furthermore, due to its excellent tensile modulus of elasticity and tensile elongation, it is also suitable for various molded products such as food containers, tableware, and straws, which were previously difficult to apply due to breakage during processing.

[0354] In addition, for the above-mentioned applications, sheets can be used directly, or laminates with resin layers or inorganic layers stacked on the sheets can be used.

[0355] Example

[0356] The following examples and comparative examples illustrate the features of the present invention in more detail. The materials, amounts, proportions, processing contents, processing steps, etc., shown in the following examples may be appropriately modified without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be limited by the specific examples shown below.

[0357] <Manufacturing Example 1>

[0358] [Phosphorylation treatment]

[0359] As raw material pulp, hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd. was used. The raw material pulp was phosphorylated as follows: First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by weight (absolute dry weight) of the above raw material pulp, adjusting the solution to 45 parts by weight of ammonium dihydrogen phosphate, 120 parts by weight of urea, and 150 parts by weight of water, to obtain a solution-impregnated pulp. Next, the solution-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, resulting in phosphoric acid pulp.

[0360] [Cleaning process]

[0361] Next, the obtained phosphorylated pulp was washed. The washing process was carried out by repeatedly performing the following operation: the pulp dispersion obtained by injecting 100g (absolute dry weight) of phosphorylated pulp into 10L of ion-exchanged water was stirred in a way that the pulp was evenly dispersed, and then filtered and dehydrated. The washing endpoint was defined as the point at which the conductivity of the filtrate fell below 100μS / cm.

[0362] [Neutralization treatment]

[0363] Next, the cleaned phosphoric acid pulp was neutralized as follows: First, the cleaned phosphoric acid pulp was diluted with 10L of deionized water, and then 1N sodium hydroxide aqueous solution was added little by little while stirring, thereby obtaining a phosphoric acid pulp with a pH of 12 or higher and 13 or lower. Next, the phosphoric acid pulp was dehydrated and neutralized to obtain phosphoric acid pulp. Then, the neutralized phosphoric acid pulp was subjected to the cleaning process described above.

[0364] [Nitrogen removal treatment]

[0365] Ion-exchanged water was added to phosphorylated pulp to prepare a pulp with a solids content of 4% by mass. A 48% by mass sodium hydroxide aqueous solution was added to the pulp to adjust the pH to 13.4, and the mixture was heated at 85°C for 1 hour. Subsequently, the pulp was dehydrated, and 10 L of ion-exchanged water was added relative to 100 g (absolute dry weight) of the phosphorylated pulp. The resulting pulp dispersion was stirred to ensure uniform pulp dispersion and then filtered for dehydration. This process was repeated to remove residual sodium hydroxide. The removal endpoint was defined as the point at which the conductivity of the filtrate fell below 100 μS / cm. It should be noted that the amount of urea introduced, determined based on the nitrogen content as described later, was 0.01 mmol / g.

[0366] The resulting phosphorus-containing oxygen-acidified pulp was subjected to infrared absorption spectroscopy using FT-IR. The results showed that the absorption spectrum was within 1230 cm⁻¹. -1 The observation of P=O absorption based on phosphate groups nearby confirms the addition of phosphate groups to the pulp. Furthermore, analysis of the resulting phosphorylated pulp using X-ray diffraction revealed typical peaks at two positions: approximately 2θ = 14° to 17° and 2θ = 22° to 23°, confirming the maintenance of cellulose type I crystals. It should be noted that the amount of phosphate groups (first dissociated acid content) measured using the method described later was 1.45 mmol / g. It should also be noted that the total dissociated acid content was 2.45 mmol / g.

[0367] [Fiber Debonding Process]

[0368] Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a pulp with a solids content of 2% by mass. The pulp was then treated six times using a wet micronization apparatus (SUGINO MACHINE, STAR BURST) at a pressure of 200 MPa to obtain a microfibrillated cellulose dispersion containing microfibrillated cellulose.

[0369] [Substituent Removal Treatment (High-Temperature Heat Treatment)]

[0370] The fine fibrous cellulose dispersion was added to a pressure-resistant container and heated at a liquid temperature of 160°C for 15 minutes until the phosphate content reached 0.08 mmol / g. This process confirmed the formation of fine fibrous cellulose aggregates.

[0371] [Cleaning treatment of the slurry after removing substituents]

[0372] Add an equal volume of ion-exchanged water to the heated slurry to prepare a slurry with a solids concentration of approximately 1% by mass. Stir the slurry, then filter and dehydrate it. Repeat this process to wash the slurry. When the conductivity of the filtrate falls below 10 μS / cm, add ion-exchanged water again to prepare a slurry with approximately 1% by mass, and let it stand for 24 hours. Then, repeat the filtration and dehydration process again, using the point where the conductivity of the filtrate falls below 10 μS / cm again as the washing endpoint. Add ion-exchanged water to the resulting fine fibrous cellulose aggregates to obtain a slurry with desubstituents. The solids concentration of this slurry is 1.7% by mass.

[0373] Uniform dispersion of the slurry after removing substituents

[0374] Ion-exchanged water was added to the obtained desubstituented slurry to prepare a slurry with a solid content concentration of 1.0% by mass. This slurry was then treated three times using a wet micronization apparatus (SUGINO MACHINE, STAR BURST) at a pressure of 200 MPa to obtain a substituent-removed microfibrillary cellulose dispersion (A). Furthermore, the fiber width of the microfibrillary cellulose was measured using a transmission electron microscope and found to be 4 nm.

[0375] <Manufacturing Example 2>

[0376] The phosphorylated pulp obtained after cleaning and neutralization treatment in Manufacturing Example 1 was subjected to the following treatment to obtain a microfibrillated cellulose dispersion (B) containing microfibrillated cellulose.

[0377] [Fiber Debonding Process]

[0378] Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a pulp with a solids content of 2% by mass. The pulp was treated six times at a pressure of 200 MPa using a wet micronization apparatus (SUGINO MACHINE, STAR BURST) to obtain a microfibrillated cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that the microfibrillated cellulose maintained type I cellulose crystals. Furthermore, the fiber width of the microfibrillated cellulose was measured using a transmission electron microscope and found to be 3–5 nm. It should be noted that the phosphate content (first dissociation amount) measured using the method described later in the determination of the oxyacid content of phosphorus was 1.45 mmol / g. It should also be noted that the total dissociated acid content was 2.45 mmol / g.

[0379] <Manufacturing Example 3>

[0380] [Phosphorousization treatment]

[0381] In the phosphorylation process, 33 parts by mass of phosphorous acid (phosphonic acid) were used instead of ammonium dihydrogen phosphate. Otherwise, the process was carried out in the same manner as in Manufacturing Example 2 to obtain phosphorylated pulp.

[0382] The resulting phosphorylated pulp was subjected to infrared absorption spectroscopy using FT-IR. The results showed that the absorption spectrum was within 1210 cm⁻¹. -1 The absorption of the P=O group of the phosphonate group, which is a tautomer of the phosphorous group, was observed nearby, confirming that the phosphorous group (phosphonate group) was added to the pulp. Furthermore, the resulting phosphorylated pulp was tested, and analysis using an X-ray diffraction apparatus revealed typical peaks at two positions: near 2θ = 14° to 17° and near 2θ = 22° to 23°, confirming that it possesses cellulose type I crystals.

[0383] [Fiber Debonding Process]

[0384] Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a pulp with a solids content of 2% by mass. The pulp was treated six times at a pressure of 200 MPa using a wet micronization apparatus (SUGINO MACHINE, STAR BURST) to obtain a microfibrillated cellulose dispersion (C) containing fine fibrous cellulose. X-ray diffraction confirmed that the microfibrillated cellulose maintained type I cellulose crystals. Furthermore, the fiber width of the microfibrillated cellulose was measured using transmission electron microscopy and found to be 3–5 nm. It should be noted that the amount of phosphorous acid (first dissociated acid content), measured using the method for determining the oxyacid content of phosphorus described later, was 1.51 mmol / g. It should also be noted that the total dissociated acid content was 1.54 mmol / g.

[0385] <Manufacturing Example 4>

[0386] [TEMPO oxidation treatment]

[0387] As raw material pulp, hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd. was used. The raw material pulp was subjected to alkali TEMPO oxidation treatment as follows.

[0388] First, 100 parts by weight of the above-mentioned raw material pulp, 1.6 parts by weight of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy radical), and 10 parts by weight of sodium bromide were dispersed in 10,000 parts by weight of water. Next, a 13% by weight aqueous solution of sodium hypochlorite was added at a concentration of 3.8 mmol relative to 1.0 g of pulp to initiate the reaction. A 0.5 M aqueous solution of sodium hydroxide was added dropwise during the reaction, maintaining the pH between 10 and 10.5. The reaction was considered complete when no change in pH was observed.

[0389] [Cleaning process]

[0390] Next, the obtained TEMPO oxidized pulp was cleaned. The cleaning process was performed by repeatedly performing the following steps: after dehydrating the TEMPO oxidized pulp to obtain dehydrated sheets, 5000 parts by weight of ion-exchanged water were added, stirred to ensure uniform dispersion, and then filtered for dehydration. The cleaning endpoint was defined as the point at which the conductivity of the filtrate fell below 100 μS / cm.

[0391] [Additional oxidation treatment]

[0392] The following procedure was used to further oxidize the residual aldehyde groups on the dehydrated sheets. 100 parts by weight of the dehydrated sheets were dispersed in 10,000 parts by weight of 0.1 mol / L acetate buffer (pH 4.8). Then, 113 parts by weight of 80% sodium chlorite were added, and the mixture was immediately sealed. The mixture was then stirred at 500 rpm with a magnetic stirrer at room temperature for 48 hours to obtain the pulp slurry.

[0393] [Cleaning process]

[0394] Next, the resulting TEMPO oxidized pulp, after additional oxidation, was washed. The washing process was performed by repeatedly performing the following steps: after dehydrating the oxidized pulp to obtain dehydrated sheets, 5000 parts by weight of ion-exchanged water were added, stirred to ensure uniform dispersion, and then filtered for dehydration. The washing endpoint was defined as the point at which the conductivity of the filtrate fell below 100 μS / cm.

[0395] The TEMPO oxidized pulp obtained in this way was found to contain 1.30 mmol / g of carboxyl groups using the method described later. Furthermore, X-ray diffraction analysis of the obtained TEMPO oxidized pulp confirmed the presence of cellulose type I crystals by identifying typical peaks at two positions: approximately 2θ = 14° to 17° and approximately 2θ = 22° to 23°.

[0396] [Fiber Debonding Process]

[0397] Ion-exchanged water was added to the obtained TEMPO oxidized pulp to prepare a pulp with a solids content of 2% by mass. The pulp was treated six times at a pressure of 200 MPa using a wet micronization apparatus (SUGINO MACHINE, STAR BURST) to obtain a microfibrillated cellulose dispersion (D) containing microfibrillated cellulose. X-ray diffraction confirmed that the microfibrillated cellulose maintained type I cellulose crystals. Furthermore, the fiber width of the microfibrillated cellulose was measured using transmission electron microscopy, and the result was 3–5 nm. It should be noted that the carboxyl group content measured using the method described later was 1.30 mmol / g.

[0398] <Manufacturing Example 5>

[0399] [Sulfur-containing oxygen acidification treatment]

[0400] Using 38 parts by mass of amide sulfuric acid instead of ammonium dihydrogen phosphate, the same procedure as in Manufacturing Example 1 was performed to obtain sulfated pulp. The heating time in the hot air dryer was set to 20 minutes.

[0401] The resulting sulfated pulp was subjected to infrared absorption spectroscopy using FT-IR. The results showed that the absorption spectrum was within the range of 1220–1260 cm⁻¹. -1 The observation of sulfate-based absorption nearby confirms that sulfate groups were added to the pulp.

[0402] [Fiber Debonding Process]

[0403] Ion-exchanged water was added to the obtained sulfated pulp, and the mixture was stirred to prepare a 2% by mass pulp. The pulp was treated six times at a pressure of 200 MPa using a wet micronization apparatus (SUGINO MACHINE, STAR BURST) to obtain a microfibrillated cellulose dispersion (E) containing microfibrillated cellulose. X-ray diffraction confirmed that the microfibrillated cellulose maintained type I cellulose crystals. Furthermore, the fiber width of the microfibrillated cellulose was measured using transmission electron microscopy and found to be 2–5 nm. It should be noted that the sulfate content, measured using the method for determining the oxyacid content of sulfur described later, was 1.47 mmol / g.

[0404] <Measurement>

[0405] [Determination of the content of oxyacid groups in phosphorus]

[0406] The content of phosphorus oxyacid groups in microfibrillated cellulose (equal to the content of phosphorus oxyacid groups in phosphorus oxyacidified pulp) was determined by the following procedure: ion-exchanged water was added to the microfibrillated cellulose dispersion containing the object, the content was set to 0.2% by mass, and after treatment with ion-exchange resin, titration was performed using alkali.

[0407] The treatment based on ion exchange resin is carried out as follows: 1 / 10 by volume of a strong acid ion exchange resin (Amberjet 1024; manufactured by ORGANO, already balanced) is added to the above slurry containing microfibrillary cellulose. After shaking for 1 hour, the resin is injected onto a 90μm mesh screen to separate it from the slurry.

[0408] Additionally, the titration using alkali was performed as follows: In a slurry containing fine fibrous cellulose treated with ion exchange resin, 10 μL of a 0.1N sodium hydroxide aqueous solution was added every 5 seconds, while the change in pH value displayed by the slurry was measured. It should be noted that nitrogen gas was blown into the slurry 15 minutes before the start of the titration. In this neutralization titration, in the curve obtained by plotting the measured pH against the amount of alkali added, two points were observed where the increment (the differential value of pH relative to the amount of alkali added) reached its maximum. The point where the maximum increment was first obtained at the start of alkali addition is called the first endpoint, and the point where the maximum increment was obtained subsequently is called the second endpoint. Figure 1The amount of alkali required from the start of titration to the first endpoint is equal to the amount of the first dissociated acid in the slurry used for titration. Furthermore, the amount of alkali required from the start of titration to the second endpoint is equal to the amount of total dissociated acid in the slurry used for titration. It should be noted that the amount of alkali (mmol) required from the start of titration to the first endpoint is divided by the solids content (g) in the slurry being titrated, and the resulting value is taken as the amount of phosphorus oxyacid groups (first dissociated acid content) (mmol / g). Additionally, the amount of alkali (mmol) required from the start of titration to the second endpoint is divided by the solids content (g) in the slurry being titrated, and the resulting value is taken as the total dissociated acid content (mmol / g).

[0409] [Determination of Carboxyl Content]

[0410] The carboxyl content of the microfibrillated cellulose (equal to the carboxyl content of TEMPO oxidized pulp) was determined by adding ion-exchanged water to the microfibrillated cellulose dispersion containing the microfibrillated cellulose, setting the content to 0.2% by mass, treating it with an ion-exchange resin, and then titrating it with an alkali.

[0411] The treatment based on ion exchange resin is carried out as follows: 1 / 10 by volume of a strong acid ion exchange resin (Amberjet 1024; manufactured by ORGANO, already balanced) is added to 0.2% by mass of a slurry containing fine fibrous cellulose. After shaking for 1 hour, the resin is injected onto a 90 μm mesh screen to separate it from the slurry.

[0412] Additionally, titration using an alkali is performed as follows: While adding a 0.1N aqueous solution of sodium hydroxide to a slurry containing fibrous cellulose treated with an ion exchange resin, the change in pH value of the slurry is measured. If the pH change is observed while adding the sodium hydroxide aqueous solution, the following is obtained: Figure 2 The titration curve shown is as depicted. Figure 2 As shown, in this neutralization titration, in the curve obtained by plotting the measured pH values ​​relative to the amount of alkali added, a point is observed where the increment (the differential value of pH relative to the amount of alkali added) reaches its maximum. This maximum point of increment is called the first endpoint. Here, we will... Figure 2 The region from the start of titration to the first endpoint is called the first region. The amount of alkali required for the first region is equal to the amount of carboxyl groups in the slurry used for titration. Furthermore, the amount of alkali (mmol) obtained from the first region of the titration curve is divided by the solid content (g) in the slurry containing the fine fibrous cellulose to be titrated, thereby calculating the amount of carboxyl groups introduced (mmol / g).

[0413] It should be noted that the above carboxyl group introduction amount (mmol / g) indicates that the counter ion of the carboxyl group is the hydrogen ion (H+). + The amount of substituents in 1g of fibrous cellulose (hereinafter referred to as the amount of carboxyl groups (acid type)).

[0414] [Determination of the content of oxyacid groups of sulfur]

[0415] The obtained fibrous cellulose was wet-ashed using perchloric acid and concentrated nitric acid, then diluted at an appropriate ratio, and the sulfur content was determined by ICP emission spectroscopy. The sulfur content was divided by the absolute dry mass of the fibrous cellulose used in the test as the oxyacid content of sulfur (unit: mmol / g).

[0416] [Determination of Urea Content]

[0417] The urea content of microfibrillated cellulose was determined by administering freeze-dried and pulverized samples to a TN-110 trace total nitrogen analyzer manufactured by Mitsubishi Chemical Analytech Co., Ltd. It should be noted that ionic nitrogen was removed during neutralization and washing processes. The amount of urea introduced per unit mass of microfibrillated cellulose (mmol / g) was calculated by dividing the nitrogen content per unit mass of microfibrillated cellulose (g / g) obtained in the trace nitrogen analysis by the atomic weight of nitrogen.

[0418] <Example 1>

[0419] [Dissolution of cellulose ethers]

[0420] Methylcellulose (manufactured by Shin-Etsu Chemical Industry Co., Ltd., METOLOSE SM-25, weight average molecular weight: 6.0 × 10⁻⁶) was used. 4 The methoxyl content (1.8%) was added to the ion-exchanged water at a concentration of 2% by mass and stirred at room temperature for 1 hour to dissolve. Following the above steps, an aqueous solution of cellulose ether (A) was obtained.

[0421] [Sheet production]

[0422] The fine fibrous cellulose dispersion (A) and the above-mentioned cellulose ether aqueous solution (A) were each diluted with deionized water to a solid content concentration of 0.5% by mass. Then, the diluted cellulose ether aqueous solution was mixed with 70 parts by mass of the diluted fine fibrous cellulose dispersion to a concentration of 30 parts by mass, to obtain a mixture.

[0423] Therefore, the final basis weight of the sheet is 32 g / m². 2The mixture was measured and spread on a commercially available acrylic sheet. It should be noted that a blocking frame (internal dimensions: 250mm × 250mm, height: 5cm) was placed on the acrylic sheet to achieve a specified basis weight. The sheet was then dried in a desiccator at 100°C for 1 hour and peeled off from the acrylic sheet, thereby obtaining a sheet containing fine fibrous cellulose. The sheet thickness was 25μm.

[0424] <Example 2>

[0425] In Example 1, [Dissolution of Cellulose Ethers], methylcellulose (manufactured by Shin-Etsu Chemical Industry Co., Ltd., METOLOSE SM-400, weight-average molecular weight: 1.4 × 10⁻⁶) was dissolved. 5 A cellulose ether aqueous solution (B) with a substitution degree (methoxyl content): 1.8 was prepared. In addition, sheets containing fine fibrous cellulose were obtained in the same manner as in Example 1.

[0426] <Example 3>

[0427] In Example 1, [Dissolution of Cellulose Ethers], hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Industry Co., Ltd., METOLOSE 65SH-50, weight-average molecular weight: 7.5 × 10⁻⁶) was dissolved. 4 A cellulose ether aqueous solution (D) with a substitution degree (methoxy group): 1.8 and a substitution molar number (hydroxypropoxy group): 0.15 was prepared. Otherwise, sheets containing fine fibrous cellulose were obtained in the same manner as in Example 1.

[0428] <Example 4>

[0429] In Example 1, [Dissolution of Cellulose Ethers], hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Industry Co., Ltd., METOLOSE 65SH-400, weight-average molecular weight: 1.4 × 10⁻⁶) was dissolved. 5 A cellulose ether aqueous solution (E) with a substitution degree (methoxy group): 1.8 and a substitution molar number (hydroxypropoxy group): 0.15 was prepared. In addition, sheets containing fine fibrous cellulose were obtained in the same manner as in Example 1.

[0430] <Example 5>

[0431] In Example 1, [Dissolution of Cellulose Ethers], hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Industry Co., Ltd., METOLOSE 65SH-1500, weight-average molecular weight: 2.2 × 10⁻⁶) was dissolved. 5 A cellulose ether aqueous solution (F) with a substitution degree (methoxy group): 1.8 and a substitution molar number (hydroxypropoxy group): 0.15 was prepared. Otherwise, sheets containing fine fibrous cellulose were obtained in the same manner as in Example 1.

[0432] <Example 6>

[0433] In Example 5, the mixing amount of the diluted microfibrillated cellulose dispersion (A) was set to 50 parts by mass, and the mixing amount of the diluted cellulose ether aqueous solution (F) was changed to 50 parts by mass. Otherwise, the same operation as in Example 5 was performed to obtain a sheet containing microfibrillated cellulose.

[0434] <Example 7>

[0435] In Example 5, the amount of the diluted microfibrillated cellulose dispersion (A) was set to 30 parts by mass, and the amount of the diluted cellulose ether aqueous solution (F) was changed to 70 parts by mass. Otherwise, the same procedure as in Example 5 was followed to obtain a sheet containing microfibrillated cellulose.

[0436] <Example 8>

[0437] In Example 5, the amount of the diluted microfibrillated cellulose dispersion (A) was set to 10 parts by mass, and the amount of the diluted cellulose ether aqueous solution (F) was changed to 90 parts by mass. Otherwise, the same procedure as in Example 5 was followed to obtain a sheet containing microfibrillated cellulose.

[0438] <Example 9>

[0439] In Example 5, the final basis weight was changed to 180 g / m³. 2 Otherwise, the same procedure as in Example 5 was followed to obtain a sheet containing microfibrillated cellulose with a thickness of 150 μm.

[0440] <Example 10>

[0441] In Example 6, the final basis weight was changed to 180 g / m³. 2 Otherwise, the same procedure as in Example 5 was followed to obtain a sheet containing microfibrillated cellulose with a thickness of 150 μm.

[0442] <Example 11>

[0443] Using a microfibrillated cellulose dispersion (B), except as otherwise described in Example 5, sheets containing microfibrillated cellulose were obtained.

[0444] <Example 12>

[0445] Using a microfibrillated cellulose dispersion (B), except as otherwise described in Example 6, sheets containing microfibrillated cellulose were obtained.

[0446] <Example 13>

[0447] Using a microfibrillated cellulose dispersion (C), except as otherwise described in Example 5, sheets containing microfibrillated cellulose were obtained.

[0448] <Example 14>

[0449] Using a microfibrillated cellulose dispersion (D), except as otherwise described in Example 5, sheets containing microfibrillated cellulose were obtained.

[0450] <Example 15>

[0451] Using a microfibrillated cellulose dispersion (E), except as otherwise described in Example 5, sheets containing microfibrillated cellulose were obtained.

[0452] <Example 16>

[0453] The sheet containing microfibrillated cellulose obtained in Example 9 was subjected to the following treatment, except that the operation was the same as in Example 9, to obtain a laminate in which resin layers are laminated on both sides of the sheet containing microfibrillated cellulose.

[0454] [Formation of the resin layer]

[0455] 8.5 parts by weight of modified polycarbonate resin (Iupizeta FPC-2136, manufactured by Mitsubishi Gas Chemical Co., Ltd.), 60 parts by weight of toluene, and 30 parts by weight of methyl ethyl ketone were mixed to obtain a resin coating solution. Next, 1.5 parts by weight of an isocyanate compound (DURANATE TPA-100, manufactured by Asahi Kasei Chemicals Co., Ltd.) as an adhesive additive was added to the above resin coating solution and mixed. The resin coating solution was then applied to one side (the side in contact with the acrylic sheet) of a sheet containing microfibrillated cellulose using a rod coater. Subsequently, the resin coating solution was cured by heating at 100°C for 1 hour to form a resin layer. Then, following the same procedure, a resin layer was also formed on the opposite side of the microfibrillated cellulose sheet to obtain a laminate. The thickness of the resin layer on each side was 3 μm.

[0456] <Comparative Example 1>

[0457] In Example 1, [Dissolution of Cellulose Ethers], methylcellulose (manufactured by Shin-Etsu Chemical Industry Co., Ltd., METOLOSE SM-8000, weight-average molecular weight: 3.6 × 10⁻⁶) was dissolved. 5 A cellulose ether aqueous solution (C) with a substitution degree (methoxyl content): 1.8 was prepared. In addition, sheets containing fine fibrous cellulose were obtained in the same manner as in Example 1.

[0458] <Comparative Example 2>

[0459] In Example 1, [Dissolution of Cellulose Ethers], hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Industry Co., Ltd., METOLOSE 65SH-15000, weight-average molecular weight: 4.3 × 10⁻⁶) was dissolved. 5 A cellulose ether aqueous solution (G) with a substitution degree (methoxy group): 1.8 and a substitution molar number (hydroxypropoxy group): 0.15 was prepared. In addition, sheets containing fine fibrous cellulose were obtained in the same manner as in Example 1.

[0460] <Comparative Example 3>

[0461] In Example 1, the [dissolution of cellulose ether] was changed as follows, but otherwise the same procedure as in Example 1 was followed to obtain a sheet containing fine fibrous cellulose.

[0462] [Dissolution of polyvinyl alcohol]

[0463] Polyvinyl alcohol (manufactured by Kuraray, Poval 5-74LLA, degree of polymerization: 500, degree of saponification: 74 mol%) was added to ion-exchanged water at a concentration of 12% by mass, and stirred at 95°C for 1 hour to dissolve. Following the above steps, an aqueous solution of polyvinyl alcohol (A) was obtained.

[0464] <Comparative Example 4>

[0465] In Example 1, the [dissolution of cellulose ether] was changed as follows, but otherwise the same procedure as in Example 1 was followed to obtain a sheet containing fine fibrous cellulose.

[0466] [Dissolution of polyvinyl alcohol]

[0467] Polyvinyl alcohol (manufactured by Kuraray, Poval 5-98, degree of polymerization: 500, degree of saponification: 99 mol%) was added to deion-exchanged water at a concentration of 12% by mass, and stirred at 95°C for 1 hour to dissolve. Following the above steps, an aqueous solution of polyvinyl alcohol (B) was obtained.

[0468] <Comparative Example 5>

[0469] In Example 1, the [dissolution of cellulose ether] was changed as follows, but otherwise the same procedure as in Example 1 was followed to obtain a sheet containing fine fibrous cellulose.

[0470] [Dissolution of polyethylene oxide]

[0471] Polyethylene oxide (manufactured by Sumitomo Seikan, PEO-18, viscosity-average molecular weight: 4.3 × 10⁻⁶) was used. 6 Add the ethylene oxide solution to the ion-exchange water at a concentration of 2% by mass, stir for 1 hour at room temperature, and dissolve. Following the above steps, an aqueous solution of polyethylene oxide is obtained.

[0472] <Comparative Example 6>

[0473] In Example 11, the [dissolution of cellulose ether] was changed as follows, but otherwise the same procedure as in Example 11 was followed to obtain a sheet containing fine fibrous cellulose.

[0474] [Dissolution of polyvinyl alcohol]

[0475] Polyvinyl alcohol (manufactured by Kuraray, Poval 5-98, degree of polymerization: 500, degree of saponification: 99 mol%) was added to deion-exchanged water at a concentration of 12% by mass, and stirred at 95°C for 1 hour to dissolve. Following the above steps, an aqueous solution of polyvinyl alcohol (B) was obtained.

[0476] <Evaluation>

[0477] [Measurement of Total Light Transmittance of Sheets]

[0478] The total light transmittance of the sheet was measured according to JIS K 7361-1:1997 using a haze meter (Murakami Color Technology Research Institute Co., Ltd., HM-150).

[0479] [Haze Measurement of Sheets]

[0480] The haze of the sheet was measured in accordance with JIS K 7136:2000 using a haze meter (Murakami Color Technology Research Institute Co., Ltd., HM-150).

[0481] [Tensive Properties of Sheets]

[0482] The tensile modulus of elasticity, tensile strength, and tensile elongation were determined according to JIS P 8113:2006 using a TENSILON tensile testing machine (manufactured by A&D). It should be noted that samples conditioned for 24 hours at 23°C and 50% relative humidity were used as test pieces. Furthermore, the tensile modulus of elasticity was calculated based on the maximum positive slope value in the SS curve.

[0483] [Yellowness Measurement of Sheet Before and After Heating]

[0484] The yellowness (YI) of the sheet before and after heating was determined according to JIS K 7373:2006 using a Colour Cute i (manufactured by Suga Test Instruments). It should be noted that the YI after heating is defined as the YI of the sheet after heating at 160°C for 6 hours. Furthermore, the change in YI before and after heating (ΔYI) was calculated using the following method.

[0485] Change in YI before and after heating (ΔYI) = (Yellowness of the sheet after heating) - (Yellowness of the sheet before heating)

[0486] [Sheet Appearance]

[0487] In addition, the appearance of the sheet is evaluated according to the following criteria based on the YI before and after heating.

[0488] A: The change in YI (ΔYI) before and after heating is less than 1.5.

[0489] B: The change in YI (ΔYI) before and after heating is greater than 1.5 and less than 5.0.

[0490] C: The change in YI (ΔYI) before and after heating is greater than 5.0.

[0491] [Sheet Formability]

[0492] Cut the sheet into 5cm x 5cm test pieces and conditioned them for 24 hours at 23℃ and 50% relative humidity. Figure 3 As shown, the test piece is bent until θ reaches 0°, and then evaluated according to the following criteria.

[0493] A: The sheet does not break when bent.

[0494] B: The sheet breaks when bent.

[0495] [Table 1-1]

[0496] Table 1-1

[0497]

[0498] [Table 1-2]

[0499] Table 1-2

[0500]

[0501] The sheets obtained in Examples 1-16 exhibit low haze, high total light transmittance, and excellent transparency. Furthermore, the YI value before heating is low, thus suppressing the increase in YI caused by heating. Consequently, they possess high tensile modulus of elasticity and tensile strength, excellent rigidity, high tensile elongation, and excellent flexibility.

[0502] On the other hand, the weight-average molecular weight of cellulose derivatives exceeds 3.0 × 10⁻⁶. 5In Comparative Examples 1 and 2, gelation occurred, making it impossible to form sheets 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 the case using cellulose derivatives. Consequently, the elongation at break was low, the sheets cracked upon bending, and the formability was poor.

Claims

1. A sheet material comprising: Fine fibrous cellulose with a fiber width of less than 10 nm; and The weight-average molecular weight is 1.0 × 10⁻⁶. 4 Above and 3.0×10 5 The following cellulose derivatives, The cellulose derivative is a water-soluble cellulose ether. In the solid composition of the sheet, the total content of fine fibrous cellulose and cellulose derivatives is 60% by mass or more. The fine fibrous cellulose has anionic groups.

2. The sheet according to claim 1, wherein, The microfibrillated cellulose has phosphorus oxyacid groups or groups derived from phosphorus oxyacid groups.

3. The sheet according to claim 1 or 2, wherein, The amount of anionic groups in the microfibrillated cellulose is less than 0.50 mmol / g.

4. The sheet according to claim 1 or 2, wherein, The amount of anionic groups in the microfibrillated cellulose is above 0.80 mmol / g.

5. The sheet according to claim 1 or 2, wherein, The microfibrillary cellulose contains urea groups.

6. The sheet according to claim 1, wherein, The water-soluble cellulose ether is nonionic.

7. The sheet according to claim 1 or 2, wherein, The water-soluble cellulose ether has at least one functional group selected from the group consisting of methoxy and hydroxypropoxy.

8. The sheet according to claim 1 or 2, wherein, The water-soluble cellulose ether is selected from the group consisting of methylcellulose and hydroxypropyl methylcellulose.

9. The sheet according to claim 1 or 2, wherein, In the solid composition of the sheet, the total content of microfibrillated cellulose and cellulose derivatives is more than 90% by mass.

10. The sheet according to claim 1 or 2, wherein, In the solid composition of the sheet, the content of microfibrillated cellulose is 50% or more by mass.

11. The sheet according to claim 1 or 2, wherein, The yellow index of the sheet changed to less than 1.5 before and after heating it at 160°C for 6 hours.

12. The sheet according to claim 1 or 2, wherein, The haze of the sheet is below 5%.

13. The sheet according to claim 1 or 2, wherein, The total light transmittance of the sheet is over 90%.

14. The sheet according to claim 1 or 2, wherein, The tensile modulus of elasticity of the sheet is above 6.5 GPa.

15. The sheet according to claim 1 or 2, wherein, The sheet has a tensile elongation of 3% or more.

16. A laminate having a sheet as described in any one of claims 1 to 15, and having a resin layer on at least one side of the sheet.

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