Fibrous cellulose, dispersions and sheets

Abstract

To provide a microfibrous cellulose that is less prone to discoloration even under a high-temperature environment.SOLUTION: This invention relates to a fibrous cellulose that has a fiber width of 1000 nm or less and includes a substituent represented by the formula (11). In the formula (11), R1 and R2 each denote a hydrogen atom, a saturated-linear hydrocarbon group, saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched hydrocarbon group, an unsaturated-cyclic hydrocarbon group, an aromatic group, or a group derived from any of them.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to fibrous cellulose, dispersions and sheets. [Background technology]

[0002] Cellulose fibers have traditionally been widely used in clothing, absorbent articles, paper products, and other applications. In addition to fibrous cellulose with a fiber diameter of 10 μm to 50 μm, microfibrous cellulose with a fiber diameter of 1 μm or less is also known as a cellulose fiber. Microfibrous cellulose has attracted attention as a new material, and its applications are diverse. For example, development of sheets, resin composites, and thickeners containing microfibrous cellulose is underway.

[0003] Fine fibrous cellulose can be produced by defibrating cellulose fibers. However, because cellulose fibers are strongly bonded to each other by hydrogen bonds, simply defibrating the fibers requires a huge amount of energy to obtain fine fibrous cellulose. For this reason, it is known that in order to produce fine fibrous cellulose with less defibration energy, it is effective to perform pretreatment such as chemical treatment or enzyme treatment in addition to the defibration treatment. For example, it is known that introducing ionic substituents into cellulose fibers by chemical treatment of cellulose fibers facilitates finer cellulose fibers and further improves dispersion stability after finer cellulose fibers.

[0004] Furthermore, when mixing fine fibrous cellulose with a resin, it is sometimes required that the fine fibrous cellulose exhibit high dispersibility in an organic solvent or a resin. For example, as disclosed in Patent Document 1, in order to improve the dispersibility of fine cellulose fibers in a resin, development of a fine cellulose fiber-containing material containing fine cellulose fibers and a nitrogen-containing compound exhibiting basicity is underway. Furthermore, Patent Document 2 discloses a fine cellulose fiber dispersion containing fine cellulose fibers and ammonia or an organic alkali. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-227639 [Patent Document 2] International Publication No. 2011 / 111612 Summary of the Invention [Problem to be solved by the invention]

[0006] Sheets and dispersions containing fine fibrous cellulose have a wide range of uses, and in these uses, the sheets and dispersions may be exposed to high-temperature environments. Furthermore, in the process of producing a sheet containing fine fibrous cellulose, the fine fibrous cellulose may be subjected to a heat treatment. However, when fine fibrous cellulose obtained by conventional techniques is used, the fine fibrous cellulose contained in the sheet or dispersion may change color, and improvements have been sought.

[0007] Therefore, in order to solve the problems of the conventional techniques, the present inventors have conducted studies with the aim of providing fine fibrous cellulose that undergoes little change in color even in a high-temperature environment. [Means for solving the problem]

[0008] Specifically, the present invention has the following configuration.

[0009] [1] Fibrous cellulose having a fiber width of 1000 nm or less and having a substituent represented by the following formula (11): [ka] In formula (11), R1 and R2 each represent a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived therefrom. [2] The fibrous cellulose according to [1], further having an ionic substituent other than the substituent represented by formula (11). [3] The fibrous cellulose according to [2], wherein the ionic substituent is at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxy group, a substituent derived from a carboxy group, a sulfur oxoacid group, a substituent derived from a sulfur oxoacid group, a xanthate group, and a substituent derived from a xanthate group. [4] The fibrous cellulose according to [2] or [3], wherein the ionic substituent is a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group. [5] The fibrous cellulose according to any one of [1] to [4], wherein the fibrous cellulose has a fiber width of 10 nm or less. [6] The fibrous cellulose according to any one of [1] to [5], wherein the amount of the substituent represented by formula (11) introduced is 0.10 to 15.00 μmol / g. [7] The fibrous cellulose according to any one of [1] to [6], wherein the nitrogen concentration in the filtrate obtained by the following measurement method is 100 ppm or less; (Measurement method) Distilled water is added so that the fibrous cellulose concentration becomes 0.2% by mass, and after stirring for 24 hours, the mixture is filtered using a filter medium with a pore size of 0.45 μm to obtain a filtrate; the nitrogen concentration (ppm) in the filtrate is measured by trace nitrogen analysis. [8] A dispersion containing the fibrous cellulose according to any one of [1] to [7]. [9] The dispersion according to [8], wherein the dispersion has a total light transmittance of 95.0% or more when it contains 0.2% by mass of fibrous cellulose.

[10] The dispersion according to [8] or [9], wherein the haze of the dispersion containing 0.2% by mass of fibrous cellulose is 5.0% or less.

[11] A sheet comprising the fibrous cellulose according to any one of [1] to [7].

[12] The sheet according to

[11] , wherein when the sheet is heated at 160°C for 6 hours, the YI increase rate calculated by the following formula is 1500% or less; YI increase rate (%) = (yellowness of sheet after heating - yellowness of sheet before heating) / yellowness of sheet before heating × 100 In the above formula, the yellowness of the sheet is measured in accordance with JIS K 7373:2006.

[13] The sheet according to

[11] or

[12] , which has a total light transmittance of 90.0% or more.

[14] The sheet according to any one of

[11] to

[13] , which has a haze of 5.0% or less. [Effects of the Invention]

[0010] According to the present invention, fine fibrous cellulose can be obtained which shows little change in color even in a high-temperature environment. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having phosphorus oxo acid groups and pH. [Figure 2] FIG. 2 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a carboxy group and the pH. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below. The following description of the components may be based on representative embodiments and specific examples, but the present invention is not limited to such embodiments.

[0013] (fine fibrous cellulose) The present embodiment relates to a fibrous cellulose having a fiber width of 1000 nm or less and having a substituent represented by the following formula (11). [ka] In formula (11), R1 and R2 each represent a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived therefrom. In this specification, fibrous cellulose having a fiber width of 1000 nm or less is also referred to as fine fibrous cellulose or CNF.

[0014] Because the present embodiment has the above-described configuration, it is possible to provide fine fibrous cellulose that exhibits little change in color even in a high-temperature environment. For example, even when a sheet containing the fine fibrous cellulose of the present embodiment is formed and heated, coloring (yellowing) of the sheet can be suppressed. Specifically, in the present embodiment, when a sheet containing the fine fibrous cellulose is formed and heated at 160°C for 6 hours, the YI increase rate can be suppressed.

[0015] For example, when a sheet containing fine fibrous cellulose is formed and heated at 160°C for 6 hours, the YI increase is preferably 1500% or less, more preferably 1400% or less, even more preferably 1300% or less, still more preferably 1250% or less, and particularly preferably 1200% or less. The lower limit of the YI increase is not particularly limited and may be 0%. Here, the YI increase is a value calculated by the following formula: YI increase rate (%) = (yellowness of sheet after heating - yellowness of sheet before heating) / yellowness of sheet before heating × 100 In the above formula, the yellowness index of the sheet is the yellowness index measured in accordance with JIS K 7373:2006, the yellowness index of the sheet after heating is the yellowness index after the sheet is heated at 160° C. for 6 hours, and the yellowness index of the sheet before heating is the yellowness index before the sheet is heated at 160° C. Similarly, in the dispersion, the YI increase rate is kept low.

[0016] In this embodiment, ammonia, a primary amine, or the like is added to a dispersion containing fibrous cellulose and heated, whereby the ketone groups and aldehyde groups present at the terminals of the fibrous cellulose are iminated to form a structure represented by the above formula (11). That is, the ketone groups and aldehyde groups present at the terminals of the fibrous cellulose are iminated and blocked with groups (imino groups) represented by the above formula (11). This is presumably to suppress decomposition of the fibrous cellulose during heating, etc., and as a result, to suppress discoloration of the fibrous cellulose. In fibrous cellulose into which a substituent represented by the above formula (11) has been introduced, decomposition during heating, etc. is suppressed, and therefore discoloration (yellowing) is presumably suppressed.

[0017] The substituent represented by the above formula (11) is a substituent having an imino group (=NR), and in this specification, the substituent represented by the above formula (11) may be referred to as an imino group. That is, this embodiment relates to fine fibrous cellulose having an imino group. In the above formula (11), R1 and R2 each represent a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived therefrom. R1 and R2 each represent 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, or an aromatic group, preferably 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, or an aromatic group, more preferably a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, or an aromatic group, and even more preferably a hydrogen atom, a saturated linear hydrocarbon group, or a saturated branched hydrocarbon group. In addition, in the above formula (11), it is also a preferred embodiment that both R1 and R2 are hydrogen atoms. Furthermore, the substituent represented by the above formula (11) is preferably a non-ionic substituent.

[0018] In the above formula (11), when R1 and R2 are each a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, an unsaturated linear hydrocarbon group, or an unsaturated branched hydrocarbon group, the number of carbon atoms in each of R1 and R2 is preferably 1 to 12, more preferably 1 to 6, even more preferably 1 to 4, and particularly preferably 1 to 3. Furthermore, in the above formula (11), when R1 and R2 are each a saturated cyclic hydrocarbon group or an unsaturated cyclic hydrocarbon group, the number of carbon atoms in each of R1 and R2 is preferably 3 to 20, more preferably 3 to 12, and even more preferably 3 to 6. In particular, R1 and R2 are each preferably a hydrogen atom, a saturated linear hydrocarbon group having 1 to 3 carbon atoms, or a saturated branched hydrocarbon group having 1 to 3 carbon atoms, and particularly preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

[0019] The amount of the substituent represented by formula (11) introduced into the fibrous cellulose is preferably 0.10 μmol / g or more, more preferably 0.50 μmol / g or more, even more preferably 1.00 μmol / g or more, even more preferably 1.20 μmol / g or more, even more preferably 1.50 μmol / g or more, and particularly preferably 2.00 μmol / g or more. Furthermore, the amount of the substituent represented by formula (11) introduced into the fibrous cellulose is preferably 15.00 μmol / g or less, more preferably 10.00 μmol / g or less, even more preferably 8.00 μmol / g or less, and particularly preferably 5.00 μmol / g or less. By keeping the amount of the substituent represented by formula (11) introduced into the fibrous cellulose within the above range, discoloration of the fibrous cellulose in a high-temperature environment can be more effectively suppressed.

[0020] The amount of the substituent (imino group) represented by formula (11) introduced into fibrous cellulose can be calculated by quantifying the amount of 2-picoline borane that reacts with the imino group when the imino group is reduced with 2-picoline borane. Specifically, the amount of imino group introduced can be calculated using the following procedure. First, 1 mmol of 2-picoline borane is dissolved in 1 L of acetic acid to obtain a 2-picoline borane solution. Next, 10 mL of the 2-picoline borane solution is added to 100 g of a 1% by mass fibrous cellulose dispersion and heated in a 65°C water bath for 1 hour to allow the reduction reaction of the imino group to proceed. After the reaction, 10 parts by mass of 1N sulfuric acid is added, followed by the dropwise addition of a 1 mmol / L potassium permanganate aqueous solution. After the dropwise addition, the amount of unreacted 2-picoline borane is quantified at the endpoint when the clear solution turns slightly red. The amount of 2-picoline borane reacted with imino groups is calculated by subtracting the amount of unreacted 2-picoline borane from the amount of 2-picoline borane tested. Specifically, the amount of imino groups in fibrous cellulose (unit: μmol / g) is calculated using the following formula. Amount of imino group (µmol / g) = 3 x [0.01 - 0.001 x amount of potassium permanganate added (mL) x (5 / 6)] x 1000

[0021] In this embodiment, the amount of free nitrogen contained in the fibrous cellulose and the amount of free nitrogen attached to the fibrous cellulose are preferably small. Specifically, the nitrogen concentration in the filtrate obtained by the following measurement method is preferably 100 ppm or less, more preferably 80 ppm or less, even more preferably 70 ppm or less, even more preferably 60 ppm or less, even more preferably 50 ppm or less, even more preferably 40 ppm or less, and particularly preferably 30 ppm or less. The nitrogen concentration in the filtrate may be 0 ppm. Since free nitrogen contained in fibrous cellulose causes coloration, maintaining the nitrogen concentration in the filtrate within the above range can more effectively suppress coloration (yellowing) of dispersions and sheets containing fibrous cellulose. The nitrogen concentration in the filtrate is measured as follows: First, distilled water is added to the fibrous cellulose so that the concentration is 0.2% by mass. After stirring for 24 hours, the mixture is filtered using a filter medium with a pore size of 0.45 μm to obtain a filtrate. The nitrogen concentration (ppm) in the filtrate is then measured by trace nitrogen analysis.

[0022] In this embodiment, the fiber width of the fibrous cellulose may be 1000 nm or less, preferably 100 nm or less, more preferably 50 nm or less, even more preferably 20 nm or less, and particularly preferably 10 nm or less.

[0023] The average fiber width of the fibrous cellulose is, for example, 1000 nm or less. The average fiber width of the fibrous cellulose is, for example, preferably 1 nm or more and 1000 nm or less, more preferably 1 nm or more and 100 nm or less, even more preferably 1 nm or more and 50 nm or less, even more preferably 1 nm or more and 20 nm or less, and particularly preferably 1 nm or more and 10 nm or less. The fibrous cellulose is, for example, monofilament cellulose.

[0024] The fiber width of fibrous cellulose is measured, for example, using an electron microscope as follows. First, an aqueous suspension of fibrous cellulose with a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for TEM observation. When wide fibers are included, an SEM image of the surface cast onto glass may be observed. Next, electron microscope images are observed at magnifications of 1000x, 5000x, 10000x, or 50000x, depending on the width of the fibers to be observed. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions.

[0025] (1) Draw a line X at any point in the observed image, and 20 or more fibers intersect with the line X. (2) Draw a line Y that intersects the line perpendicularly within the same image, and 20 or more fibers intersect the line Y.

[0026] For observation images that satisfy the above conditions, the widths of the fibers intersecting with lines X and Y are visually read. In this way, three or more sets of observation images of at least the surface portions that do not overlap each other are obtained. Next, for each image, the widths of the fibers intersecting with lines X and Y are read. In this way, the widths of at least 20 fibers x 2 x 3 = 120 fibers are read. The average value of the read fiber widths is then taken as the average fiber width of the fibrous cellulose.

[0027] The fiber length of the fibrous cellulose is not particularly limited, but is preferably 0.1 μm or more and 1000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and even more preferably 0.1 μm or more and 600 μm or less. By setting the fiber length within the above range, destruction of the crystalline regions of the fibrous cellulose can be suppressed. It also becomes possible to set the slurry viscosity of the fibrous cellulose within an appropriate range. The fiber length of the fibrous cellulose can be determined, for example, by image analysis using TEM, SEM, or AFM.

[0028] The fibrous cellulose preferably has a type I crystal structure. The presence of type I crystal structure in fibrous cellulose can be identified by a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromated with graphite. Specifically, it can be identified by the presence of two typical peaks at two positions: 2θ=14° to 17° and 2θ=22° to 23°. The proportion of type I crystal structure in the fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. This can be expected to provide even better performance in terms of heat resistance and low linear thermal expansion coefficient. The degree of crystallinity can be determined by measuring the X-ray diffraction profile and using the pattern in a conventional manner (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0029] The axial ratio (fiber length / fiber width) of the fibrous cellulose is not particularly limited, but is preferably, for example, from 20 to 10,000, and more preferably from 50 to 1,000. By setting the axial ratio to the above lower limit or more, a sheet containing fibrous cellulose can be easily formed. Furthermore, by setting the axial ratio to the above upper limit or less, it is preferable in that, for example, when treating the fibrous cellulose as a dispersion, handling such as dilution becomes easier.

[0030] Fibrous cellulose has, for example, both crystalline and amorphous regions. Fibrous cellulose having both crystalline and amorphous regions and having an axial ratio within the above range can be realized by the method for producing fine fibrous cellulose described below.

[0031] The fibrous cellulose preferably further has an ionic substituent other than the substituent represented by the above formula (11) (imino group). The fibrous cellulose may contain, for example, either an anionic group or a cationic group, or both, as the ionic substituent. In this embodiment, it is particularly preferable that the ionic substituent has an anionic group. Furthermore, the ionic substituent is preferably a group that is introduced into the fibrous cellulose via an ester bond or an ether bond, and more preferably a group that is introduced into the fibrous cellulose via an ester bond. In this case, the ester bond is preferably formed by dehydration condensation of a hydroxyl group of the fibrous cellulose and a compound that becomes the ionic substituent.

[0032] Examples of the anionic group include a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group (sometimes simply referred to as a phosphorus oxo acid group), a carboxy group or a substituent derived from a carboxy group (sometimes simply referred to as a carboxy group), a sulfur oxo acid group or a substituent derived from a sulfur oxo acid group (sometimes simply referred to as a sulfur oxo acid group), a xanthate group or a substituent derived from a xanthate group (sometimes simply referred to as a xanthate group), a phosphonic group or a substituent derived from a phosphonic group, a phosphine group or a substituent derived from a phosphine group, a sulfonic group or a substituent derived from a sulfonic group, and a carboxyalkyl group (including a carboxymethyl group). Among these, the anionic group is preferably at least one selected from the group consisting of a phosphorus oxo acid group, a substituent derived from a phosphorus oxo acid group, a carboxy group, a substituent derived from a carboxy group, a sulfur oxo acid group, a substituent derived from a sulfur oxo acid group, a xanthate group, and a substituent derived from a xanthate group, more preferably at least one selected from the group consisting of a phosphorus oxo acid group, a substituent derived from a phosphorus oxo acid group, a carboxy group, a substituent derived from a carboxy group, a sulfur oxo acid group, and a substituent derived from a sulfur oxo acid group, and particularly preferably a phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group. By appropriately selecting the anionic group, it is possible to obtain a dispersion or sheet having excellent transparency and suppressed coloration.

[0033] The phosphorus oxo acid group or the substituent derived from the phosphorus oxo acid group is, for example, a substituent represented by the following formula (1). A plurality of substituents represented by the following formula (1) may be introduced into each fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (1) may be the same or different.

[0034] [ka]

[0035] In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (where a=b×m). At least one of the n α and α' is O. - and the rest are R or OR. Note that all of α and α' are O - The n α's may all be the same or may be different. b+ is a cation of one or more valences consisting of organic or inorganic substances.

[0036] R is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated branched hydrocarbon group, an unsaturated cyclic hydrocarbon group, an aromatic group, or a group derived therefrom. In formula (1), n is preferably 1.

[0037] Examples of saturated linear hydrocarbon groups include, but are not limited to, methyl, ethyl, n-propyl, and n-butyl groups. Examples of saturated branched hydrocarbon groups include, but are not limited to, i-propyl and t-butyl groups. Examples of saturated cyclic hydrocarbon groups include, but are not limited to, cyclopentyl and cyclohexyl groups. Examples of unsaturated linear hydrocarbon groups include, but are not limited to, vinyl and allyl groups. Examples of unsaturated branched hydrocarbon groups include, but are not limited to, i-propenyl and 3-butenyl groups. Examples of unsaturated cyclic hydrocarbon groups include, but are not limited to, cyclopentenyl and cyclohexenyl groups. Examples of aromatic groups include, but are not limited to, phenyl and naphthyl groups.

[0038] In addition, the derivative group in R is a carboxy group, a carboxylate group (-COO - ), a hydroxy group, an amino group, an ammonium group, or another functional group to which at least one functional group has been added or substituted, but is not particularly limited. Furthermore, the number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R within the above range, the molecular weight of the phosphorus oxoacid group can be set within an appropriate range, facilitating penetration into the fiber raw material and increasing the yield of fine cellulose fibers. When multiple Rs are present in formula (1) or when multiple types of substituents represented by the above formula (1) are introduced into the fibrous cellulose, the multiple Rs may be the same or different.

[0039] β b+is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic onium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. It should be noted that in formula (1), β b+ When a plurality of β b+ may be the same or different. The monovalent or higher cations consisting of organic or inorganic substances include β b+ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0040] More specifically, examples of the phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group include a phosphate group (-POH), a salt of a phosphate group, a phosphorous acid (phosphonic acid) group (-POH), and a salt of a phosphite (phosphonic acid) group. The phosphorus oxo acid group or a substituent derived from a phosphorus oxo acid group may also be a group in which a phosphate group is condensed (e.g., a pyrophosphate group), a group in which a phosphonic acid is condensed (e.g., a polyphosphonic acid group), a phosphate ester group (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), or an alkyl phosphonic acid group (e.g., a methylphosphonic acid group).

[0041] The sulfur oxoacid group (a sulfur oxoacid group or a substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). A plurality of substituents represented by the following formula (2) may be introduced into each fibrous cellulose. In this case, the plurality of introduced substituents represented by the following formula (2) may be the same or different.

[0042] [ka]

[0043] In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (where 1 = b × m). When n is 2 or more, multiple p's may be the same number or different numbers. In the above structural formula, β b+ is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic onium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic onium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. Note that when multiple types of substituents represented by the above formula (2) are introduced into the fibrous cellulose, the multiple β b+ may be the same or different. The monovalent or higher cations consisting of organic or inorganic substances include β b+ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0044] The content (amount introduced) of the ionic substituent is, for example, preferably 0.50 mmol / g or more per 1 g (mass) of fibrous cellulose, more preferably 0.60 mmol / g or more, even more preferably 0.80 mmol / g or more, and particularly preferably 1.00 mmol / g or more. The content (amount introduced) of the ionic substituent is, for example, preferably 5.20 mmol / g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol / g or less, even more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, and particularly preferably 2.00 mmol / g or less. Here, the denominator in the unit mmol / g is calculated based on the fact that the counter ion of the ionic substituent (anionic group) is a hydrogen ion (H + By setting the amount of ionic substituents introduced within the above range, it is possible to obtain a dispersion or sheet that is excellent in transparency and suppresses coloration.

[0045] The amount of ionic substituents introduced into the fibrous cellulose can be measured, for example, by neutralization titration, which involves measuring the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to a slurry containing the obtained fibrous cellulose.

[0046] 1 is a graph showing the relationship between the amount of NaOH added dropwise to a slurry containing fibrous cellulose having phosphorus oxo acid groups and pH. The amount of phosphorus oxo acid groups introduced into the fibrous cellulose is measured, for example, as follows. First, a slurry containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement object may be subjected to a defibration treatment similar to the defibration treatment step described below before the treatment with the strongly acidic ion exchange resin. Next, the change in pH is observed while adding aqueous sodium hydroxide solution, and a titration curve like the one shown in the upper part of Figure 1 is obtained. The titration curve shown in the upper part of Figure 1 plots the measured pH against the amount of alkali added, while the titration curve shown in the lower part of Figure 1 plots the pH increment (derivative value) (1 / mmol) against the amount of alkali added. In this neutralization titration, two points of maximum increment (derivative value of pH with respect to the amount of alkali added) are confirmed on the curve plotting the measured pH against the amount of alkali added. Of these, the first maximum increment obtained after starting to add alkali is called the first endpoint, and the next maximum increment obtained is called the second endpoint. The amount of alkali required from the start of titration to the first endpoint is equal to the amount of first dissociated acid of the fibrous cellulose contained in the slurry used for titration; the amount of alkali required from the first endpoint to the second endpoint is equal to the amount of second dissociated acid of the fibrous cellulose contained in the slurry used for titration; and the amount of alkali required from the start of titration to the second endpoint is equal to the total amount of dissociated acid of the fibrous cellulose contained in the slurry used for titration. The value obtained by dividing the amount of alkali required from the start of titration to the first endpoint by the solids content (g) of the slurry to be titrated is the amount of phosphorus oxo acid groups introduced (mmol / g). Note that the term "amount of phosphorus oxo acid groups introduced" simply refers to the amount of first dissociated acid. In Figure 1, the region from the start of titration to the first endpoint is referred to as Region 1, and the region from the first endpoint to the second endpoint is referred to as Region 2. For example, if the phosphorus oxoacid group is a phosphate group and this phosphate group undergoes condensation, the apparent amount of weakly acidic groups in the phosphorus oxoacid group (also referred to herein as the second dissociated acid amount) decreases, and the amount of alkali required in Region 2 is less than the amount required in Region 1. On the other hand, the amount of strongly acidic groups in the phosphorus oxoacid group (also referred to herein as the first dissociated acid amount) corresponds to the amount of phosphorus atoms regardless of whether condensation occurs. Furthermore, if the phosphorus oxoacid group is a phosphite group, the phosphorus oxoacid group no longer contains weakly acidic groups, and the amount of alkali required in Region 2 is reduced or may even be zero. In this case, there is only one point on the titration curve where the pH increment is maximized.

[0047] The above-mentioned amount of introduced phosphorus oxoacid groups (mmol / g) indicates the amount of phosphorus oxoacid groups in the acid-form fibrous cellulose (hereinafter referred to as the amount of phosphorus oxoacid groups (acid form)) because the denominator indicates the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the phosphorus oxoacid groups are substituted with an arbitrary cation C so as to be charge equivalent, the amount of phosphorus oxoacid groups in the fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of phosphorus oxoacid groups (C form)) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula. Amount of phosphorus oxoacid group (C type) = Amount of phosphorus oxoacid group (acid type) / {1 + (W - 1) × A / 1000} A [mmol / g]: total amount of anions derived from phosphorus oxoacid groups in fibrous cellulose (total amount of dissociated acid from phosphorus oxoacid groups) W: Formula weight per valence of cation C (e.g., Na is 23, Al is 9)

[0048] 2 is a graph showing the relationship between the amount of NaOH added dropwise to a dispersion containing fibrous cellulose having carboxy groups as ionic substituents and pH. The amount of carboxy groups introduced into the fibrous cellulose is measured, for example, as follows. First, a dispersion containing fibrous cellulose is treated with a strongly acidic ion exchange resin. If necessary, the measurement object may be subjected to a defibration treatment similar to the defibration treatment step described below before the treatment with the strongly acidic ion exchange resin. Next, the change in pH was observed while adding aqueous sodium hydroxide solution, and a titration curve like the one shown in the upper part of Figure 2 was obtained. The titration curve shown in the upper part of Figure 2 plots the measured pH against the amount of added alkali, while the titration curve shown in the lower part of Figure 2 plots the pH increment (derivative value) (1 / mmol) against the amount of added alkali. In this neutralization titration, a single point was identified in the curve plotting the measured pH against the amount of added alkali, where the increment (derivative value of pH with respect to the amount of added alkali) reached a maximum. This maximum point is called the first endpoint. Here, the region from the start of the titration to the first endpoint in Figure 2 is called the first region. The amount of alkali required in the first region is equal to the amount of carboxyl groups in the dispersion used for titration. The amount of alkali required in the first region of the titration curve (mmol) is then divided by the solids content (g) in the dispersion containing the fibrous cellulose to be titrated to calculate the amount of carboxyl groups introduced (mmol / g).

[0049] The above-mentioned amount of carboxy groups introduced (mmol / g) indicates the amount of carboxy groups in the acid-form fibrous cellulose (hereinafter referred to as the amount of carboxy groups (acid form)), since the denominator is the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the carboxy groups are substituted with an arbitrary cation C so as to be charge equivalent, the amount of carboxy groups in the fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of carboxy groups (C form)) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula: Amount of carboxyl group (C type) = Amount of carboxyl group (acid type) / {1 + (W - 1) × (Amount of carboxyl group (acid type)) / 1000} W: Formula weight per valence of cation C (e.g., Na is 23, Al is 9)

[0050] When measuring the amount of ionic substituents by titration, adding too many drops of sodium hydroxide or titrating too quickly can result in lower ionic substituents than expected, leading to inaccurate values. An appropriate amount and interval is, for example, titrating 10–50 μL of 0.1 N sodium hydroxide every 5–30 seconds. To eliminate the influence of carbon dioxide dissolved in the fibrous cellulose-containing slurry, it is also recommended to measure the amount of ionic substituents while blowing an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration until the end of titration.

[0051] The amount of sulfur oxoacid or sulfonic acid groups introduced into fibrous cellulose can be calculated by wet ashing the fibrous cellulose using perchloric acid and concentrated nitric acid, diluting it at an appropriate ratio, and measuring the amount of sulfur by ICP atomic emission spectrometry. The amount of sulfur oxoacid or sulfonic acid groups (unit: mmol / g) is calculated by dividing the amount of sulfur by the bone dry mass of the fibrous cellulose tested.

[0052] The amount of xanthate groups introduced into fibrous cellulose can be measured using the Bredee method as follows. First, 40 mL of saturated ammonium chloride solution is added to 1.5 parts by mass (bone dry mass) of fibrous cellulose. The sample is crushed with a glass rod and mixed thoroughly. After leaving for approximately 15 minutes, the sample is filtered through GFP filter paper (GS-25, manufactured by Advantec) and thoroughly washed with saturated ammonium chloride solution. Next, the sample, including the GFP filter paper, is placed in a 500 mL tall beaker, and 50 mL of 0.5 M sodium hydroxide solution (5 °C) is added, stirred, and left for 15 minutes. Phenolphthalein solution is added until the solution turns pink, and then 1.5 M acetic acid is added. The point at which the solution changes from pink to colorless is considered the neutralization point. After neutralization, 250 mL of distilled water is added and stirred thoroughly. 10 mL of 1.5 M acetic acid and 10 mL of 0.05 mol / L iodine solution are added using a volumetric pipette. Then, this solution is titrated with 0.05 mol / L sodium thiosulfate solution, and the amount of xanthate groups is calculated using the following formula from the titration amount of sodium thiosulfate and the bone dry mass of the fibrous cellulose. Amount of xanthate group (mmol / g) = (0.05 × 10 × 2 - 0.05 × sodium thiosulfate titration (mL)) / 1000 / bone-dry mass of fibrous cellulose (g)

[0053] (Method of producing fine fibrous cellulose) <Fiber raw materials> Fine fibrous cellulose is produced from a cellulose-containing fiber raw material. While the cellulose-containing fiber raw material is not particularly limited, pulp is preferably used due to its availability and low cost. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not limited to, chemical pulps such as hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), and oxygen-bleached kraft pulp (OKP); semi-chemical pulps such as semi-chemical pulp (SCP) and chemi-ground wood pulp (CGP); and mechanical pulps such as groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP). Examples of non-wood pulp include, but are not limited to, cotton-based pulps such as cotton linters and cotton lint, and non-wood pulps such as hemp, wheat straw, and bagasse. The deinked pulp is not particularly limited, but examples thereof include deinked pulp made from waste paper. The pulp of this embodiment may be one of the above types used alone, or two or more types may be used in combination. Among the above pulps, wood pulp and deinked pulp are preferred from the viewpoint of ease of availability. Furthermore, among wood pulps, chemical pulp is more preferred, and kraft pulp and sulfite pulp are even more preferred, from the viewpoints of having a high cellulose ratio and a high yield of fine fibrous cellulose during defibration treatment, and of obtaining long-fiber fine fibrous cellulose with a large axial ratio due to minimal decomposition of cellulose in the pulp. Note that the viscosity tends to increase when long-fiber fine fibrous cellulose with a large axial ratio is used.

[0054] Examples of cellulose-containing fiber raw materials include cellulose contained in sea squirts and bacterial cellulose produced by acetic acid bacteria.Furthermore, fibers formed from linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can also be used instead of cellulose-containing fiber raw materials.

[0055] <Phosphorus oxoacid group introduction step> The process for producing fine fibrous cellulose may include a step of introducing an ionic substituent. An example of the step of introducing an ionic substituent is a step of introducing a phosphorus oxo acid group. The step of introducing a phosphorus oxo acid group is a step of reacting a cellulose-containing fiber raw material with at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing a phosphorus oxo acid group by reacting with a hydroxyl group possessed by the cellulose-containing fiber raw material. This step results in the production of a fiber into which a phosphorus oxo acid group has been introduced.

[0056] In the phosphorus oxoacid group introduction step according to this embodiment, the reaction of the cellulose-containing fiber raw material with compound A may be carried out in the presence of at least one selected from urea and its derivatives (hereinafter also referred to as "compound B"). Alternatively, the cellulose-containing fiber raw material with compound A may be reacted in the absence of compound B.

[0057] An example of a method for reacting compound A with a fiber raw material in the presence of compound B is a method in which compound A and compound B are mixed with a fiber raw material in a dry, wet, or slurry state. Among these, using a fiber raw material in a dry or wet state is preferred because of the high uniformity of the reaction, and using a fiber raw material in a dry state is particularly preferred. The form of the fiber raw material is not particularly limited, but is preferably, for example, in a cotton-like or thin sheet form. Examples of methods include adding compound A and compound B to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state heated to or above the melting point. Among these, adding compound A and compound B in the form of a solution dissolved in a solvent, particularly an aqueous solution, is preferred because of the high uniformity of the reaction. Compound A and compound B may be added to the fiber raw material simultaneously, separately, or as a mixture. The method for adding compound A and compound B is not particularly limited. When compound A and compound B are in the form of a solution, the fiber raw material may be immersed in the solution to absorb the liquid and then removed, or the solution may be added dropwise to the fiber raw material. Alternatively, the required amounts of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material, and then the excess compound A and compound B may be removed by squeezing or filtration.

[0058] The compound A used in this embodiment may be any compound that has a phosphorus atom and is capable of forming an ester bond with cellulose, and examples thereof include, but are not limited to, phosphoric acid or a salt thereof, phosphorous acid or a salt thereof, dehydrated condensed phosphoric acid or a salt thereof, and phosphoric anhydride (diphosphorus pentoxide). Phosphoric acid may be used in a variety of purities, such as 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid. Phosphorous acid may be 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acid is formed by condensing two or more molecules of phosphoric acid through a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, which may be neutralized to various degrees. Among these, from the viewpoints of high efficiency of introduction of phosphorus oxoacid groups, ease of further improving defibration efficiency in the defibration step described below, low cost, and ease of industrial application, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid, or phosphorous acid, sodium salt of phosphorous acid, potassium salt of phosphorous acid, ammonium salt of phosphorous acid are preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, or phosphorous acid, sodium phosphite are more preferred.

[0059] The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted into the amount of phosphorus atoms, the amount of phosphorus atoms added to the fiber raw material (bone dry mass) is preferably 0.5% by mass or more and 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of fine fibrous cellulose can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to the above upper limit or less, a balance can be achieved between the yield improvement effect and costs.

[0060] As described above, compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. Furthermore, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved.

[0061] The amount of compound B added relative to the fiber raw material (bone dry mass) is not particularly limited, but is preferably, for example, 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, and even more preferably 100% by mass or more and 350% by mass or less.

[0062] In the reaction of a fiber raw material containing cellulose with compound A, the reaction system may contain, in addition to compound B, for example, amides or amines. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is known to function as a particularly good reaction catalyst.

[0063] In the phosphorus oxo acid group introduction step, it is preferable to add or mix compound A or the like to the fiber raw material and then heat-treat the fiber raw material. The heat treatment temperature is preferably selected so that the phosphorus oxo acid group can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is, for example, preferably 50°C to 300°C, more preferably 100°C to 250°C, and even more preferably 130°C to 200°C. Furthermore, various types of equipment having heat transfer media can be used for the heat treatment, including, for example, a hot air dryer, agitator dryer, rotary dryer, disk dryer, roll-type heater, plate-type heater, fluidized-bed dryer, band-type dryer, filtration dryer, vibration fluidized dryer, flash dryer, reduced-pressure dryer, infrared heater, far-infrared heater, microwave heater, and high-frequency dryer.

[0064] In the heat treatment according to this embodiment, for example, compound A may be added to a thin sheet-like fiber raw material by impregnation or other methods, followed by heating, or heating while kneading or stirring the fiber raw material and compound A in a kneader or the like. This makes it possible to suppress unevenness in the concentration of compound A in the fiber raw material and more uniformly introduce phosphorus oxoacid groups onto the surface of the cellulose fibers contained in the fiber raw material. This is thought to be because, when water molecules move to the surface of the fiber raw material as it dries, dissolved compound A is attracted to the water molecules by surface tension, preventing it from migrating to the surface of the fiber raw material (i.e., causing unevenness in the concentration of compound A).

[0065] Furthermore, the heating device used for the heat treatment is preferably one that can constantly discharge, to the outside of the device system, for example, the water retained in the slurry and the water generated in the dehydration condensation (phosphorylation) reaction between compound A and hydroxyl groups contained in cellulose or the like in the fiber raw material. Examples of such heating devices include an oven with a blower system. Constantly discharging the water from the device system can suppress the hydrolysis reaction of phosphate ester bonds, which is the reverse reaction of phosphate esterification, as well as the acid hydrolysis of sugar chains in the fiber. This makes it possible to obtain fine fibrous cellulose with a high axial ratio.

[0066] The heat treatment time is, for example, preferably from 1 second to 300 minutes after the water content has been substantially removed from the fiber raw material, more preferably from 1 second to 1,000 seconds, and even more preferably from 10 seconds to 800 seconds. In this embodiment, by setting the heating temperature and heating time within appropriate ranges, the amount of phosphorus oxo acid groups introduced can be kept within a preferred range.

[0067] The phosphorus oxo acid group introduction step may be carried out at least once, but may also be carried out twice or more. By carrying out the phosphorus oxo acid group introduction step twice or more, a large number of phosphorus oxo acid groups can be introduced into the fiber raw material.

[0068] The amount of phosphorus oxoacid groups introduced into the fiber raw material is, for example, preferably 0.50 mmol / g or more per 1 g (mass) of fiber raw material, more preferably 0.60 mmol / g or more, even more preferably 0.80 mmol / g or more, and particularly preferably 1.00 mmol / g or more. The content (amount introduced) of phosphorus oxoacid groups is, for example, preferably 5.20 mmol / g or less per 1 g (mass) of fibrous cellulose, more preferably 3.65 mmol / g or less, even more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, and particularly preferably 2.00 mmol / g or less. By keeping the amount of phosphorus oxoacid groups introduced within the above range, dispersions and sheets with excellent transparency and reduced coloration can be obtained.

[0069] <Carboxy group introduction step> The process for producing fine fibrous cellulose may include a carboxyl group introduction step as an ionic substituent introduction step, which is carried out by subjecting a cellulose-containing fiber raw material to an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, or TEMPO oxidation treatment, or by treating the cellulose-containing fiber raw material with a compound having a carboxylic acid-derived group or a derivative thereof, or an acid anhydride of a compound having a carboxylic acid-derived group or a derivative thereof.

[0070] The compound having a group derived from carboxylic acid is not particularly limited, but examples thereof 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, the derivative of the compound having a group derived from carboxylic acid is not particularly limited, but examples thereof include imidized products of acid anhydrides of compounds having carboxy groups, and derivatives of acid anhydrides of compounds having carboxy groups. The imidized products of acid anhydrides of compounds having carboxy groups are not particularly limited, but examples thereof include imidized products of dicarboxylic acid compounds such as maleimide, succinimide, and phthalimide.

[0071] The acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, and examples thereof include acid anhydrides of dicarboxylic acid compounds such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride, etc. Furthermore, the derivative of an acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, and examples thereof include acid anhydrides of compounds having carboxy groups such as dimethyl maleic anhydride, diethyl maleic anhydride, diphenyl maleic anhydride, etc., in which at least some of the hydrogen atoms have been substituted with a substituent such as an alkyl group or a phenyl group.

[0072] When TEMPO oxidation treatment is performed in the carboxyl group introduction step, it is preferable to perform the treatment under conditions of, for example, pH 6 or higher and pH 8 or lower. This type of treatment is also called neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment can be performed, for example, by adding pulp as the fiber raw material, a nitroxy radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to a sodium phosphate buffer solution (pH = 6.8). Furthermore, by adding sodium chlorite, aldehydes generated during the oxidation process can be efficiently oxidized to carboxyl groups. The TEMPO oxidation treatment may also be performed under conditions of pH 10 or higher and pH 11 or lower. This type of treatment is also called alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be performed, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp as the fiber raw material.

[0073] The amount of carboxyl groups introduced into the fiber raw material varies depending on the type of substituent. For example, when carboxyl groups are introduced by TEMPO oxidation, the amount is preferably 0.50 mmol / g or more per gram (mass) of fiber raw material, more preferably 0.60 mmol / g or more, even more preferably 0.80 mmol / g or more, and particularly preferably 1.00 mmol / g or more. Furthermore, the amount of carboxyl groups introduced into the fibrous cellulose is preferably 3.65 mmol / g or less, more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, and even more preferably 2.00 mmol / g or less. Furthermore, when the substituent is a carboxymethyl group, the amount of carboxyl groups introduced may be 5.8 mmol / g or less per gram (mass) of fine fibrous cellulose. By keeping the amount of carboxyl groups introduced within the above range, dispersions and sheets with excellent transparency and reduced coloration can be obtained.

[0074] <Sulfur oxoacid group introduction step> The process for producing fine fibrous cellulose may include a sulfur oxoacid group introduction step as an ionic substituent introduction step, in which hydroxyl groups in a cellulose-containing fiber raw material react with sulfur oxoacids to obtain cellulose fibers having sulfur oxoacid groups (sulfur oxoacid group-introduced fibers).

[0075] In the sulfur oxo acid group introduction step, instead of compound A in the above-described <Phosphorus oxo acid group introduction step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfur oxo acid groups by reacting with hydroxyl groups in cellulose-containing fiber raw materials is used. Compound C may be any compound containing a sulfur atom and capable of forming an ester bond with cellulose, including, but not limited to, sulfuric acid or its salts, sulfurous acid or its salts, and sulfuric acid amides. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid). Sulfurous acid can be 5% aqueous sulfurous acid. Sulfates or sulfites can be lithium, sodium, potassium, or ammonium salts of sulfates or sulfites, which can be neutralized to various degrees. Sulfamic acid or the like can be used as the sulfuric acid amide. In the sulfur oxo acid group introduction step, it is preferable to use compound B in the above-described <Phosphorus oxo acid group introduction step> as well.

[0076] In the sulfur oxoacid group introduction step, the cellulose raw material is preferably mixed with an aqueous solution containing a sulfur oxoacid and urea and / or a urea derivative, and then the cellulose raw material is subjected to a heat treatment. The heat treatment temperature is preferably selected so that the sulfur oxoacid groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 150°C or higher. The heat treatment temperature is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

[0077] In the heat treatment step, heating is preferably performed until substantially all moisture is removed. Therefore, the heat treatment time varies depending on the amount of moisture contained in the cellulose raw material and the amount of aqueous solution containing sulfur oxoacid and urea and / or a urea derivative added, but is preferably, for example, 10 to 10,000 seconds. For the heat treatment, various devices having a heat medium can be used, such as a hot air dryer, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized dryer, an airflow dryer, a reduced-pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, or a high-frequency dryer.

[0078] The amount of sulfur oxoacid groups introduced into the cellulose raw material is preferably 0.50 mmol / g or more, more preferably 0.60 mmol / g or more, even more preferably 0.80 mmol / g or more, and particularly preferably 1.00 mmol / g or more per gram (mass) of fibrous cellulose. The amount of sulfur oxoacid groups introduced is preferably 5.00 mmol / g or less, more preferably 3.00 mmol / g or less per gram (mass) of fibrous cellulose. By keeping the amount of sulfur oxoacid groups introduced within the above range, dispersions and sheets with excellent transparency and reduced coloration can be obtained.

[0079] <Oxidation step using a chlorine-based oxidizing agent (second carboxyl group introduction step)> The process for producing fine fibrous cellulose may include an oxidation step using a chlorine-based oxidizing agent as an ionic substituent introduction step. In the oxidation step using a chlorine-based oxidizing agent, the chlorine-based oxidizing agent is added to a wet or dry fiber raw material having a hydroxyl group to cause a reaction, thereby introducing a carboxyl group into the fiber raw material.

[0080] Examples of chlorine-based oxidizing agents include hypochlorous acid, hypochlorites, chlorous acid, chlorites, chloric acid, chlorates, perchloric acid, perchlorates, and chlorine dioxide. From the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling, the chlorine-based oxidizing agent is preferably sodium hypochlorite, sodium chlorite, or chlorine dioxide. When adding a chlorine-based oxidizing agent, it may be added directly to the fiber raw material as a reagent (solid or liquid), or may be dissolved in an appropriate solvent and then added.

[0081] The concentration of the chlorine-based oxidizing agent in the solution in the oxidation step using the chlorine-based oxidizing agent, converted into an effective chlorine concentration, is preferably 1 to 1,000% by mass, more preferably 5 to 500% by mass, and even more preferably 10 to 100% by mass. The amount of the chlorine-based oxidizing agent added per 100 parts by mass of the fiber raw material is preferably 1 to 100,000 parts by mass, more preferably 10 to 10,000 parts by mass, and even more preferably 100 to 5,000 parts by mass.

[0082] The reaction time with the chlorine-based oxidizing agent in the oxidation step using the chlorine-based oxidizing agent varies depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. The pH during the reaction is preferably from 5 to 15, more preferably from 7 to 14, and even more preferably from 9 to 13. At the start of the reaction, the pH is preferably maintained constant (for example, pH 11) during the reaction by appropriately adding hydrochloric acid or sodium hydroxide. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0083] <Xanthate group introduction step (xanthogen acid esterification step)> The process for producing fine fibrous cellulose may include a xanthate group introduction step (hereinafter also referred to as a xanthation step) as an ionic substituent introduction step. In the xanthation step, carbon disulfide and an alkali compound are added to a wet or dry fiber raw material having a hydroxyl group to cause a reaction, thereby introducing xanthate groups into the fiber raw material. Specifically, carbon disulfide is added to a fiber raw material that has been converted into alkali cellulose by the method described below, and the reaction is carried out.

[0084] <<Alkali cellulose>> When introducing ionic substituents into a fiber raw material, it is preferable to convert the cellulose contained in the fiber raw material into alkali cellulose by treating the cellulose with an alkaline solution. This treatment causes ionic dissociation of some of the hydroxyl groups in the cellulose, thereby increasing the nucleophilicity (reactivity). The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. Due to their high versatility, it is preferable to use, for example, sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, or tetrabutylammonium hydroxide. The conversion into alkali cellulose may be carried out simultaneously with the introduction of ionic substituents, before the introduction, or at both the same time.

[0085] 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.

[0086] The alkali concentration in the alkaline solution is preferably 0.01 mol / L to 4 mol / L in molar concentration, more preferably 0.1 mol / L to 3 mol / L in molar concentration, and even more preferably 1 mol / L to 2.5 mol / L in molar concentration. In particular, when the treatment temperature for alkali cellulose formation is less than 10° C., the alkali concentration is preferably 1 mol / L to 2 mol / L in molar concentration.

[0087] The treatment time for alkali cellulose formation is preferably 1 minute or more, more preferably 10 minutes or more, and even more preferably 30 minutes or more, and the alkali treatment time is preferably 6 hours or less, more preferably 5 hours or less, and even more preferably 4 hours or less.

[0088] By adjusting the type of alkaline solution, treatment temperature, concentration, and immersion time as described above, it is possible to suppress the penetration of the alkaline solution into the crystalline regions of cellulose, making it easier to maintain the crystalline structure of cellulose type I, and increasing the yield of fine fibrous cellulose.

[0089] When the introduction of ionic substituents and the conversion to alkali cellulose are not carried out simultaneously, the conversion to alkali cellulose is preferably carried out before the introduction of ionic substituents. In this case, the alkali cellulose obtained by the conversion to alkali cellulose treatment is preferably subjected to solid-liquid separation by a common deliquoring method such as centrifugation or filtration to remove water. This improves the reaction efficiency in the subsequent ionic substituent introduction step. The cellulose fiber concentration after solid-liquid separation is preferably 5% to 50%, more preferably 10% to 40%, and even more preferably 15% to 35%.

[0090] <Phosphonic or Phosphine Group Introduction Step (Phosphoalkylation Step)> The process for producing fine fibrous cellulose may include a step of introducing a phosphonic or phosphine group (phosphoalkylation step) as an ionic substituent introduction step. In the phosphoalkylation step, a compound having a reactive group and a phosphonic or phosphine group (compound E) is used as an essential component. A ), an optional alkali compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having hydroxyl groups and reacted to introduce phosphonic or phosphine groups into the fiber raw material.

[0091] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E A Examples of suitable compounds include vinyl phosphonic acid, phenyl vinyl phosphonic acid, and phenyl vinyl phosphinic acid. From the viewpoints of the efficiency of introducing substituents, the defibration efficiency, cost, and ease of handling, Compound E A is preferably vinylphosphonic acid. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0092] Compound E A When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0093] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0094] Compound E A The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0095] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0096] <Sulfonic acid group introduction step (sulfoalkylation step)> The process for producing fine fibrous cellulose may include a sulfonic acid group introduction step (sulfoalkylation step) as an ionic substituent introduction step. In the sulfoalkylation, a compound having a reactive group and a sulfonic acid group (compound E) is used as an essential component. B ) and, as an optional component, an alkali compound and a compound B selected from the aforementioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a sulfonic acid group into the fiber raw material.

[0097] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E B Examples of suitable vinyl compounds include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, and 2-acrylamido-2-methylpropanesulfonic acid. Among these, vinyl compound E is preferred in terms of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. B is preferably sodium sulfonate. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0098] Compound E B When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0099] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0100] Compound E BThe amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0101] The reaction time may vary depending on the reaction temperature, but is preferably, for example, from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 15 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0102] <Carboxyalkylation step (third carboxy group introduction step)> The process for producing fine fibrous cellulose may include a carboxyalkylation step as an ionic substituent introduction step. As an essential component, a compound having a reactive group and a carboxy group (compound E C ), an optional alkaline compound, and compound B selected from the aforementioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a carboxyl group into the fiber raw material.

[0103] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E C As the chloroisothiazolinone, monochloroacetic acid, sodium monochloroacetate, 2-chloropropionic acid, 3-chloropropionic acid, sodium 2-chloropropionate, and sodium 3-chloropropionate are preferred from the standpoints of efficiency in introducing substituents, and therefore defibration efficiency, cost, and ease of handling. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0104] Compound E CWhen adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0105] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0106] Compound E C The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0107] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 3 minutes to 500 minutes, and even more preferably from 5 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0108] <Cationic group introduction step (cationization step)> The process for producing fine fibrous cellulose may include a cationic group introduction step as an ionic substituent introduction step. D ), an optional alkaline compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having hydroxyl groups and reacted to introduce cationic groups into the fiber raw material.

[0109] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Examples of the cationic group include an ammonium group, a phosphonium group, a sulfonium group, etc. Among these, the cationic group is preferably an ammonium group. Compound E D As the alkyl group, glycidyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, etc. are preferred from the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> as an optional component in the same manner. The amount added is also preferably as described above.

[0110] Compound E D When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or it may be dissolved in an appropriate solvent and added. The fiber raw material is preferably converted into alkali cellulose in advance or simultaneously with the reaction. The method for converting into alkali cellulose is as described above.

[0111] The temperature during the reaction is, for example, preferably 50°C or higher and 300°C or lower, more preferably 100°C or higher and 250°C or lower, and even more preferably 130°C or higher and 200°C or lower.

[0112] Compound E D The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0113] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 10 minutes to 500 minutes, and even more preferably from 20 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0114] <Cleaning process> In the method for producing fine fibrous cellulose, a washing step can be carried out on the ionic substituent-introduced fibers as needed. The washing step is carried out by washing the ionic substituent-introduced fibers with water or an organic solvent, for example. The washing step may be carried out after each step described below, and the number of washing steps carried out in each washing step is not particularly limited.

[0115] <Alkali treatment process> When producing fine fibrous cellulose, the fiber raw material may be subjected to an alkali treatment between the step of introducing an ionic substituent and the defibration treatment step described below. The alkali treatment method is not particularly limited, but examples thereof include a method of immersing the ionic substituent-introduced fiber in an alkali solution.

[0116] The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. In this embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of its high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. Among these, the solvent contained in the alkaline solution is preferably a polar solvent including water or a polar organic solvent such as an alcohol, and more preferably an aqueous solvent including at least water. As the alkaline solution, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of its high versatility.

[0117] The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably, for example, from 5°C to 80°C, and more preferably from 10°C to 60°C. The immersion time of the ionic substituent-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is, for example, preferably from 5 minutes to 30 minutes, and more preferably from 10 minutes to 20 minutes. The amount of alkaline solution used in the alkaline treatment is not particularly limited, but is, for example, preferably from 100% by mass to 100,000% by mass, and more preferably from 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the ionic substituent-introduced fiber.

[0118] In order to reduce the amount of alkaline solution used in the alkali treatment step, the ionic substituent-introduced fiber may be washed with water or an organic solvent after the ionic substituent-introducing step and before the alkali treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkali-treated ionic substituent-introduced fiber with water or an organic solvent after the alkali treatment step and before the defibrating step.

[0119] <Acid treatment process> When producing fine fibrous cellulose, the fiber raw material may be subjected to an acid treatment between the step of introducing an ionic substituent and the defibration treatment step described below. For example, the step of introducing an ionic substituent, the acid treatment, the alkali treatment, and the defibration treatment may be performed in this order.

[0120] The acid treatment method is not particularly limited, but examples include a method of immersing the fiber raw material in an acid-containing acid solution. The concentration of the acid solution used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less. The pH of the acid solution used is also not particularly limited, but is preferably 0 to 4, and more preferably 1 to 3. Examples of the acid contained in the acid solution include inorganic acids, sulfonic acids, and carboxylic acids. Examples of inorganic acids include sulfuric acid, nitric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid. Among these, hydrochloric acid or sulfuric acid is particularly preferred.

[0121] The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably, for example, 5°C to 100°C, and more preferably 20°C to 90°C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is, for example, preferably 5 minutes to 120 minutes, and more preferably 10 minutes to 60 minutes. The amount of the acid solution used in the acid treatment is not particularly limited, but is, for example, preferably 100% by mass to 100,000% by mass, and more preferably 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the fiber raw material.

[0122] <Nitrogen removal treatment> The process for producing fine fibrous cellulose may further include a step of reducing the amount of nitrogen (nitrogen removal treatment step). However, nitrogen contained in imino groups is not included in the nitrogen removed in this step. In this step, by reducing the amount of nitrogen other than nitrogen contained in imino groups, fine fibrous cellulose that can further suppress discoloration can be obtained. The nitrogen removal treatment step may be performed after the defibration treatment step described below, but is preferably performed before the defibration treatment step described below.

[0123] In the nitrogen removal treatment step, it is preferable to adjust the pH of the slurry containing the ionic substituent-introduced fiber to 10 or more and then perform a heat treatment. In the heat treatment, the liquid temperature of the slurry is preferably 50°C or more and 100°C or less, and the heating time is preferably 15 minutes or more and 180 minutes or less. When adjusting the pH of the slurry containing the ionic substituent-introduced fiber, it is preferable to add an alkali compound that can be used in the above-mentioned alkali treatment step to the slurry.

[0124] After the nitrogen removal treatment step, the ionic substituent-introduced fiber may be subjected to a washing step, if necessary. The washing step is carried out by washing the ionic substituent-introduced fiber with, for example, water or an organic solvent. The number of washing steps to be carried out in each washing step is not particularly limited.

[0125] <Defibrillation process> The ionic substituent-introduced fibers are defibrated in a defibration treatment step to obtain fine fibrous cellulose. In the defibration treatment step, for example, a defibration treatment device can be used. The defibration treatment device is not particularly limited, but examples that can be used include a high-speed defibrator, a grinder (stone mill-type grinder), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision grinder, a ball mill, a bead mill, a disk-type refiner, a conical refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater. Among the above defibration treatment devices, it is more preferable to use a high-speed defibrator, a high-pressure homogenizer, or an ultra-high-pressure homogenizer, which are less affected by the grinding media and have less risk of contamination.

[0126] The processing conditions in the defibration processing step are not particularly limited, but for example, when a high-pressure homogenizer is used, the pressure during processing is preferably 1 MPa or more and 350 MPa or less, more preferably 10 MPa or more and 300 MPa or less, and even more preferably 50 MPa or more and 250 MPa or less.

[0127] In the defibration treatment step, for example, the ionic substituent-introduced fibers are preferably diluted with a dispersion medium to form a slurry. The dispersion medium can be one or more selected from water and organic solvents such as polar organic solvents. The polar organic solvent is not particularly limited, but examples thereof include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

[0128] The solid content concentration of the fine fibrous cellulose during the defibration treatment can be appropriately set. The slurry obtained by dispersing the ionic substituent-introduced fibers in a dispersion medium may contain solids other than the ionic substituent-introduced fibers, such as urea having hydrogen bonding properties.

[0129] <Imination treatment step> After the defibration treatment step, it is preferable to provide a step of introducing a substituent (imino group) represented by the above formula (11) into the obtained fibrous cellulose. In this specification, the step of introducing a substituent (imino group) represented by the above formula (11) into the fibrous cellulose is also referred to as an imination treatment step. In the imination treatment step, at least one selected from ammonia and a primary amine is added to a dispersion containing fibrous cellulose, and the mixture is heated. At this time, it is preferable that the solvent in the dispersion contains water.

[0130] The heating temperature after adding at least one selected from ammonia and primary amines to the dispersion containing fibrous cellulose is preferably 70° C. or higher, more preferably 80° C. or higher, and even more preferably 90° C. or higher. The heating temperature is preferably 100° C. or lower.

[0131] The amounts of ammonia and primary amine added in the imination treatment step are preferably 0.25 mmol or more, more preferably 0.5 mmol or more, and even more preferably 1 mmol or more, per gram of fibrous cellulose contained in the dispersion, and are preferably 100 mmol or less, more preferably 50 mmol or less, and even more preferably 25 mmol or less, per gram of fibrous cellulose contained in the dispersion.

[0132] The pH of the dispersion in the imination treatment step is preferably 8 or higher, more preferably 9 or higher, and even more preferably 10 or higher. The pH of the dispersion is preferably 14 or lower, and even more preferably 13 or lower. By adjusting the pH of the dispersion within the above range, the imination treatment can be carried out efficiently.

[0133] After the imination treatment step (after heat treatment), it is preferable to provide a step for removing free nitrogen, such as ammonia or primary amines, remaining in the system. The free nitrogen removal step preferably involves, for example, ion exchange resin treatment or washing with water or an organic solvent. When ion exchange resin treatment is performed in the free nitrogen removal step, free nitrogen can be removed from the dispersion by adding a strongly acidic ion exchange resin and a strongly basic ion exchange resin to the dispersion, shaking the dispersion, and then separating the resin from the dispersion. In this case, the amount of each of the strongly acidic ion exchange resin and the strongly basic ion exchange resin added is preferably 1 part by volume or more, more preferably 5 parts by volume or more, and even more preferably 10 parts by volume or more, per 100 parts by volume of the dispersion. By providing a free nitrogen removal step after the imination treatment step (after heat treatment), the amount of free nitrogen contained in the fibrous cellulose and the amount of free nitrogen attached to the fibrous cellulose can be reduced, and as a result, color change in a dispersion or sheet containing fibrous cellulose can be more effectively suppressed.

[0134] After the iminization treatment step (after the heat treatment), it is preferable to carry out a pH adjustment step for the dispersion containing fibrous cellulose. By carrying out the pH adjustment step, color changes in the dispersion containing fibrous cellulose and the sheet can be more effectively suppressed. The pH of the dispersion is preferably 4 or higher, more preferably 5 or higher, and even more preferably 6 or higher.

[0135] The means for adjusting the pH is not particularly limited, and for example, an acid component or an alkali component may be added to a slurry containing fine fibrous cellulose. The acid component may be either an inorganic acid or an organic acid. Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. Examples of organic acids include formic acid, acetic acid, citric acid, malic acid, lactic acid, adipic acid, sebacic acid, stearic acid, maleic acid, succinic acid, tartaric acid, fumaric acid, and gluconic acid. The alkali component may be an inorganic alkali compound or an organic alkali compound. Examples of inorganic alkali compounds include lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, lithium bicarbonate, potassium carbonate, potassium bicarbonate, sodium carbonate, and sodium bicarbonate. Examples of organic alkali compounds include ammonia, hydrazine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, dipropylamine, butylamine, diaminoethane, diaminopropane, diaminobutane, diaminopentane, diaminohexane, cyclohexylamine, aniline, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, pyridine, and N,N-dimethyl-4-aminopyridine.

[0136] In addition, in the pH adjustment step, an ion exchange treatment may be performed to adjust the pH. A strong acid cation exchange resin or a weak acid ion exchange resin can be used in the ion exchange treatment. By treating with an appropriate amount of cation exchange resin for a sufficient time, a slurry containing fine fibrous cellulose with the desired pH can be obtained. Furthermore, in the pH adjustment step, the addition of an acid component or an alkali component may be combined with the ion exchange treatment.

[0137] <Uniform dispersion treatment process> The imination treatment step may be followed by a step of uniformly dispersing the fibrous cellulose contained in the obtained dispersion. In the imination treatment step, some of the fibrous cellulose in the dispersion may aggregate, so by providing a uniform dispersion treatment step after the imination treatment step, the aggregated fine fibrous cellulose can be uniformly dispersed again.

[0138] In the uniform dispersion treatment step, for example, a high-speed defibrator, grinder (stone mill type grinder), high-pressure homogenizer, high-pressure collision type grinder, ball mill, bead mill, disk type refiner, conical refiner, twin-screw kneader, vibration mill, homomixer under high-speed rotation, ultrasonic disperser or beater can be used. Among the above-mentioned uniform dispersion treatment devices, it is more preferable to use a high-speed defibrator or high-pressure homogenizer.

[0139] The treatment conditions in the uniform dispersion treatment step are not particularly limited, but it is preferable to increase the maximum movement speed of the fibrous cellulose during treatment and the pressure during treatment. In a high-speed defibrator, the peripheral speed is preferably 20 m / sec or more, more preferably 25 m / sec or more, and even more preferably 30 m / sec or more. A high-pressure homogenizer is more preferably used because it has a higher maximum movement speed of the fibrous cellulose during treatment and a higher pressure during treatment than a high-speed defibrator. In treatment with a high-pressure homogenizer, the pressure during treatment is preferably 1 MPa or more and 350 MPa or less, more preferably 10 MPa or more and 300 MPa or less, and even more preferably 50 MPa or more and 250 MPa or less.

[0140] (dispersion) This embodiment also relates to a dispersion containing the above-mentioned fibrous cellulose. The dispersion of this embodiment contains fibrous cellulose having a fiber width of 1000 nm or less and having a substituent represented by the above formula (11).

[0141] The total light transmittance of the dispersion is preferably 95.0% or more, more preferably 96.0% or more, even more preferably 97.0% or more, and particularly preferably 98.0% or more. The upper limit of the total light transmittance of the dispersion is not particularly limited and may be 100.0%. The total light transmittance is measured assuming a concentration of fibrous cellulose contained in the dispersion of 0.2% by mass. The measurement is performed using a haze meter and a glass cell for liquids with a 1 cm optical path length in accordance with JIS K 7361-1:1997. Zero-point measurement is performed using ion-exchanged water placed in the same glass cell. That is, the total light transmittance measured using ion-exchanged water alone is taken as 100%. The temperature of the dispersion during measurement is 23°C. The haze meter may be an HM-150 manufactured by Murakami Color Research Laboratory Co., Ltd., and the glass cell for liquid may be an MG-40 (reverse optical path) manufactured by Fujiwara Seisakusho Co., Ltd.

[0142] The haze of the dispersion is preferably 5.0% or less, more preferably 4.0% or less, even more preferably 3.0% or less, even more preferably 2.0% or less, and particularly preferably 1.0% or less. The lower limit of the haze of the dispersion is not particularly limited and may be 0.0%. The haze is measured assuming a concentration of fibrous cellulose contained in the dispersion of 0.2% by mass. The measurement is performed using a haze meter and a glass cell for liquids with an optical path length of 1 cm in accordance with JIS K 7136:2000. Zero-point measurement is performed using ion-exchanged water placed in the same glass cell. The temperature of the dispersion during measurement is 23°C. The haze meter may be an HM-150 manufactured by Murakami Color Research Laboratory, and the glass cell for liquids may be an MG-40 (reverse optical path) manufactured by Fujiwara Seisakusho.

[0143] In the dispersion of this embodiment, when the concentration of fine fibrous cellulose is 0.4% by mass, the viscosity of the dispersion at 23°C is preferably 100 mPa·s or more, more preferably 1000 mPa·s or more, and even more preferably 2000 mPa·s or more. Furthermore, the viscosity of the dispersion at 23°C is preferably 200,000 mPa·s or less, and more preferably 100,000 mPa·s or less. The viscosity of a dispersion with a fine fibrous cellulose concentration of 0.4% by mass can be measured using a Brookfield T-LVT type viscometer. The measurement conditions are 23°C, a rotation speed of 3 rpm, and the viscosity is measured 3 minutes after the start of measurement. Furthermore, the dispersion to be measured is allowed to stand for 24 hours in an environment of 23°C and 50% relative humidity, and the liquid temperature of the dispersion is set to 23°C.

[0144] The content of fibrous cellulose in the dispersion is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more, based on the total mass of the dispersion. The upper limit of the content of fibrous cellulose in the dispersion is not particularly limited, but can be, for example, 20% by mass.

[0145] The water content of the dispersion is preferably 99.99% by mass or less, more preferably 99.90% by mass or less, and even more preferably 99.8% by mass or less, based on the total mass of the dispersion. The water content of the dispersion is preferably 80% by mass or more, based on the total mass of the dispersion. The dispersion may contain an organic solvent. Examples of organic solvents include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP), etc. When an organic solvent is contained in the dispersion, it is preferable that the total content of water and the organic solvent is within the above range.

[0146] The dispersion may contain optional components (additives) in addition to a solvent such as water and fibrous cellulose. Examples of optional components include surfactants, coupling agents, inorganic layered compounds, inorganic compounds, leveling agents, preservatives, antifoaming agents, organic particles, lubricants, antistatic agents, UV protection agents, dyes, pigments, stabilizers, magnetic powders, alignment promoters, plasticizers, dispersants, and crosslinking agents. The dispersion may also contain optional components such as hydrophilic polymers, hydrophilic low-molecular-weight compounds, and organic ions.

[0147] Examples of hydrophilic polymers include carboxyvinyl polymers, polyvinyl alcohol, alkyl methacrylate-acrylic acid copolymers, polyvinylpyrrolidone, polyvinyl methyl ether, polyacrylates such as sodium polyacrylate, alkyl acrylate copolymers, urethane copolymers, modified polyesters, modified polyimides, polyalkylene glycols such as polyethylene glycol and polypropylene glycol, polycations such as polyacrylamide and polyethyleneimine, polyanions, amphoteric polymers, xanthan gum, guar gum, tamarind gum, carrageenan, locust bean gum, quince seed, alginic acid, and alginic acid. Examples of the thickening polysaccharides include metal salts of glutamic acid, pullulan, sacran and pectin; cellulose derivatives (excluding the above-mentioned fibrous cellulose) include carboxymethylcellulose, carboxyethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose and hydroxyethylcellulose; starches include cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, dextrin and amylose; glycerins such as polyglycerin; hyaluronic acid, metal salts of hyaluronic acid; proteins such as casein.The hydrophilic polymer may also be a copolymer of these hydrophilic polymers.

[0148] The hydrophilic low-molecular-weight compound is preferably a hydrophilic oxygen-containing organic compound, more preferably a polyhydric alcohol, such as glycerin, sorbitol, or ethylene glycol.

[0149] Examples of organic ions include tetraalkylammonium ions and tetraalkylphosphonium ions. Examples of tetraalkylammonium ions include tetramethylammonium ions, tetraethylammonium ions, tetrapropylammonium ions, tetrabutylammonium ions, tetrapentylammonium ions, tetrahexylammonium ions, tetraheptylammonium ions, tributylmethylammonium ions, lauryltrimethylammonium ions, cetyltrimethylammonium ions, stearyltrimethylammonium ions, octyldimethylethylammonium ions, lauryldimethylethylammonium ions, didecyldimethylammonium ions, lauryldimethylbenzylammonium ions, and tributylbenzylammonium ions. Examples of tetraalkylphosphonium ions include tetramethylphosphonium ions, tetraethylphosphonium ions, tetrapropylphosphonium ions, tetrabutylphosphonium ions, and lauryltrimethylphosphonium ions. Examples of tetrapropylonium ions and tetrabutylonium ions include tetra-n-propylonium ions and tetra-n-butylonium ions, respectively.

[0150] In addition, when the optional component is a component having a ketone group or an aldehyde group, a substituent represented by the above formula (11) may also be introduced into the optional component. The method for introducing the substituent represented by the above formula (11) into the optional component can be the same as the method for introducing the substituent represented by the above formula (11) into the fibrous cellulose. When introducing the substituent represented by the above formula (11) into the optional component, the substituent represented by the above formula (11) may be introduced into the fibrous cellulose and the optional component separately, or the substituent represented by the above formula (11) may be introduced into both the fibrous cellulose and the optional component simultaneously. By introducing the substituent represented by the above formula (11) into the optional component, coloration of the optional component, such as the resin component contained in the sheet or dispersion, can be more effectively suppressed.

[0151] (sheet) This embodiment also relates to a sheet containing the above-mentioned fibrous cellulose. The sheet of this embodiment contains fibrous cellulose having a fiber width of 1000 nm or less and having a substituent represented by the above formula (11).

[0152] The content of fibrous cellulose relative to the total mass of solids in the sheet is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. Furthermore, the content of fibrous cellulose relative to the total mass of solids in the sheet is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. By keeping the content of fibrous cellulose within the above range, it becomes easier to obtain a sheet with excellent transparency and suppressed coloration.

[0153] In this embodiment, the sheet preferably contains a resin in addition to the above-described fibrous cellulose. The type of resin is not particularly limited, but examples thereof include thermoplastic resins and thermosetting resins.

[0154] Examples of resins include acrylic resins, polystyrene resins, polycarbonate resins, polyester resins, polyamide resins, silicone resins, fluorine-based resins, chlorine-based resins, epoxy resins, melamine resins, phenolic resins, polyurethane resins, diallyl phthalate resins, alcohol-based resins, cellulose derivatives, and precursors of these resins. Examples of cellulose derivatives include carboxymethyl cellulose, methyl cellulose, and hydroxyethyl cellulose. The type of resin precursor is not particularly limited, but examples include precursors of thermoplastic resins and thermosetting resins. A thermoplastic resin precursor refers to a monomer or a relatively low-molecular-weight oligomer used to produce a thermoplastic resin. A thermosetting resin precursor refers to a monomer or a relatively low-molecular-weight oligomer that can undergo a polymerization or crosslinking reaction under the action of light, heat, or a curing agent to form a thermosetting resin. When the sheet contains a resin precursor, the polymerization or crosslinking reaction of the resin precursor may be promoted by the action of light, heat, or a curing agent in a subsequent process or during use, depending on the application mode.

[0155] The resin content relative to the total mass of solids in the sheet is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. Furthermore, the resin content relative to the total mass of solids in the sheet is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. By keeping the resin content within the above range, it becomes easier to obtain a sheet with excellent transparency and suppressed coloration.

[0156] In the present embodiment, the sheet may contain optional components in addition to the above-described fibrous cellulose and resin. Examples of optional components include the optional components that may be contained in the dispersion liquid.

[0157] The total light transmittance of the sheet is preferably 90.0% or more, and more preferably 91.0% or more. The upper limit of the total light transmittance of the sheet is not particularly limited, and may be 100.0%. Here, the total light transmittance of the sheet is a value measured in accordance with JIS K 7361-1:1997. As an instrument for measuring haze, for example, a haze meter (HM-150) manufactured by Murakami Color Research Laboratory Co., Ltd. can be used.

[0158] The haze of the sheet is preferably 5.0% or less, more preferably 4.0% or less, even more preferably 3.0% or less, even more preferably 2.0% or less, and particularly preferably 1.0% or less. The lower limit of the haze of the sheet is not particularly limited, and may be 0.0%. Here, the haze of the sheet is a value measured in accordance with JIS K 7136:2000. As an instrument for measuring haze, for example, a haze meter (HM-150) manufactured by Murakami Color Research Laboratory Co., Ltd. can be used.

[0159] The yellowness index (YI) of the sheet is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.0 or less. The lower limit of the yellowness index (YI) of the sheet is not particularly limited, but may be 0.0. The yellowness index (YI) of the sheet is the yellowness index (YI) before the sheet is heated.

[0160] Furthermore, when the sheet is heated at 160°C for 6 hours, the YI increase rate is preferably 1500% or less, more preferably 1400% or less, even more preferably 1300% or less, even more preferably 1250% or less, and particularly preferably 1200% or less. The lower limit of the YI increase rate is not particularly limited and may be 0%. Here, the YI increase rate is a value calculated by the following formula. YI increase rate (%) = (yellowness of sheet after heating - yellowness of sheet before heating) / yellowness of sheet before heating × 100 In the above formula, the yellowness of the sheet is the yellowness measured in accordance with JIS K 7373:2006, the yellowness of the sheet after heating is the yellowness after the sheet is heated at 160°C for 6 hours, and the yellowness of the sheet before heating is the yellowness before the sheet is heated at 160°C for 6 hours.

[0161] The thickness of the sheet is not particularly limited, but is preferably 5 μm or more, more preferably 7 μm or more, even more preferably 10 μm or more, even more preferably 15 μm or more, and particularly preferably 20 μm or more. The thickness of the sheet is preferably 100 μm or less.

[0162] The basis weight of the sheet is not particularly limited, but is preferably 10 g / m 2 It is preferable that the weight is 20 g / m or more. 2 The basis weight of the sheet is more preferably 200 g / m or more. 2 Preferably, it is 150 g / m or less. 2 The basis weight of the sheet is a value calculated according to the following method: A sheet cut into a size of 50 mm square or larger is conditioned at 23°C and a relative humidity of 50% for 24 hours, and then the weight is measured and divided by the area of the cut sheet to calculate the basis weight of the sheet.

[0163] The density of the sheet is not particularly limited, but is preferably 0.5 g / cm 3 It is preferable that the concentration is 1.0 g / cm or more. 3 More preferably, it is 1.2 g / cm or more. 3 It is more preferable that the density of the sheet is 3.0 g / cm or more. 3 Preferably, it is 2.0 g / cm or less. 3 More preferably, it is 1.8 g / cm or less. 3 It is more preferable that the density of the sheet is calculated by dividing the basis weight of the sheet by its thickness.

[0164] (Laminate) This embodiment may also relate to a laminate having a structure in which another layer is further laminated on the above-mentioned sheet. Such another layer may be provided on both surfaces of the sheet, or may be provided only on one surface of the sheet. Examples of the other layer laminated on at least one surface of the sheet include a resin layer and an inorganic layer.

[0165] <Resin layer> The resin layer is a layer whose main component is a natural resin or a synthetic resin. Here, the main component refers to a component that is contained in an amount of 50% by mass or more relative to the total mass of the resin layer. The resin content is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more relative to the total mass of the resin layer. The resin content may be 100% by mass or may be 95% by mass or less.

[0166] Examples of natural resins include rosin-based resins such as rosin, rosin ester, and hydrogenated rosin ester.

[0167] Examples of synthetic resins include polyolefin resins, cyclic olefin resins, polycarbonate resins, polyethylene terephthalate resins, polyethylene naphthalate resins, polyimide resins, polystyrene resins, acrylic resins, etc. Among these, the synthetic resin is preferably a polyolefin resin, and preferably contains at least one selected from polyethylene resins and polypropylene resins.

[0168] Examples of the polycarbonate resin constituting the resin layer include aromatic polycarbonate resins and aliphatic polycarbonate resins. Specific examples of these polycarbonate resins are known, such as the polycarbonate resins described in JP-A-2010-023275.

[0169] The resin layer may be made of a single resin, a copolymer obtained by copolymerization or graft polymerization of multiple resin components, or a blend material obtained by mixing multiple resin components by a physical process.

[0170] An adhesive layer may be provided between the sheet and the resin layer, or the sheet and the resin layer may be directly adhered to each other without providing an adhesive layer. When an adhesive layer is provided between the sheet and the resin layer, an acrylic resin may be used as the adhesive. Examples of adhesives other than acrylic resins include vinyl chloride resins, (meth)acrylic ester resins, styrene / acrylic ester copolymer resins, vinyl acetate resins, vinyl acetate / (meth)acrylic ester copolymer resins, urethane resins, silicone resins, epoxy resins, ethylene / vinyl acetate copolymer resins, polyester resins, polyvinyl alcohol resins, ethylene-vinyl alcohol copolymer resins, and rubber emulsions such as SBR and NBR.

[0171] When no adhesive layer is provided between the sheet and the resin layer, the resin layer may contain an adhesion aid, and the surface of the resin layer may be subjected to a surface treatment such as hydrophilization. Examples of the adhesion aid include a compound containing at least one selected from an isocyanate group, a carbodiimide group, an epoxy group, an oxazoline group, an amino group, and a silanol group, and an organosilicon compound. Among these, the adhesion aid is preferably at least one selected from a compound containing an isocyanate group (isocyanate compound) and an organosilicon compound. Examples of the organosilicon compound include a silane coupling agent condensate and a silane coupling agent. Examples of the surface treatment method include corona treatment, plasma discharge treatment, UV irradiation treatment, electron beam irradiation treatment, and flame treatment.

[0172] <Inorganic layer> The material constituting the inorganic layer is not particularly limited, but examples thereof include aluminum, silicon, magnesium, zinc, tin, nickel, and titanium; their oxides, carbides, nitrides, oxycarbides, oxynitrides, and oxycarbonitrides; and mixtures thereof. From the viewpoint of stably maintaining high moisture resistance, silicon oxide, silicon nitride, silicon oxide carbide, silicon oxynitride, silicon oxycarbonitride, aluminum oxide, aluminum nitride, aluminum oxide carbide, aluminum oxynitride, and mixtures thereof are preferred.

[0173] The method for forming the inorganic layer is not particularly limited. Generally, methods for forming thin films are roughly divided into chemical vapor deposition (CVD) and physical vapor deposition (PVD), and either method may be employed. Specific examples of CVD methods include plasma CVD, which uses plasma, and catalytic chemical vapor deposition (Cat-CVD), which uses a heated catalyst to catalytically decompose a material gas. Specific examples of PVD methods include vacuum deposition, ion plating, and sputtering.

[0174] Atomic layer deposition (ALD) can also be used to form inorganic layers. ALD is a method for forming thin films atomically by alternately supplying the source gases of each element that make up the film to be formed to the surface on which the layer is to be formed. While it has the drawback of a slow film formation speed, it has the advantage of being able to coat even complex surfaces more cleanly than plasma CVD, and to deposit thin films with fewer defects. ALD also has the advantage of being able to control film thickness at the nanometer level, making it relatively easy to cover large surfaces. Furthermore, the use of plasma in ALD is expected to improve reaction speed, enable lower processing temperatures, and reduce unreacted gases.

[0175] (Sheet manufacturing method) The sheet manufacturing method preferably includes a step of forming a sheet from the dispersion obtained by the above-described method. The step of forming a sheet from the dispersion preferably includes a coating step of coating the dispersion onto a substrate, or a papermaking step of making paper from the dispersion.

[0176] <Coating process> In the coating step, the dispersion obtained in the dispersion obtaining step is coated on a substrate, and the coated substrate is dried to form a sheet, which can be peeled off from the substrate to obtain a sheet. In addition, by using a coating device and a long substrate, sheets can be produced continuously.

[0177] The material of the substrate used in the coating process is not particularly limited, but a substrate with high wettability with the dispersion liquid can suppress shrinkage of the sheet during drying, but it is preferable to select a substrate from which the sheet formed after drying can be easily peeled off. Among these, resin films or plates or metal films or plates are preferred, but are not particularly limited. For example, resin films or plates such as acrylic, polyethylene terephthalate, vinyl chloride, polystyrene, and polyvinylidene chloride, metal films or plates such as aluminum, zinc, copper, and iron plates, and those with their surfaces oxidized, stainless steel films or plates, brass films or plates, etc. can be used.

[0178] In the coating process, if the viscosity of the dispersion is low and it spreads on the substrate, a blocking frame may be fixed to the substrate to obtain a sheet of a predetermined thickness and basis weight. The blocking frame is not particularly limited, but it is preferable to select one that allows the edge of the sheet to be easily peeled off after drying. From this perspective, molded resin or metal plates are more preferable. In this embodiment, for example, resin plates such as acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, and polyvinylidene chloride plates, metal plates such as aluminum plates, zinc plates, copper plates, and iron plates, and plates with their surfaces oxidized, stainless steel plates, brass plates, etc. can be used.

[0179] The coater used to coat the dispersion onto the substrate is not particularly limited, and examples thereof include a roll coater, gravure coater, die coater, curtain coater, air doctor coater, etc. Die coaters, curtain coaters, and spray coaters are particularly preferred because they can make the thickness of the sheet more uniform.

[0180] The dispersion temperature and the ambient temperature when applying the dispersion to the substrate are not particularly limited, but are preferably, for example, from 5°C to 80°C, more preferably from 10°C to 60°C, even more preferably from 15°C to 50°C, and particularly preferably from 20°C to 40°C. If the application temperature is at least the lower limit, the dispersion can be applied more easily. If the application temperature is at most the upper limit, evaporation of the dispersion medium during application can be suppressed.

[0181] In the coating process, the finished basis weight of the sheet is preferably 10 g / m 2 More than 200g / m 2 More preferably, 20 g / m 2 More than 150g / m 2 It is preferable to coat the dispersion onto the substrate so that the coating is carried out so that the basis weight falls within the above range, thereby obtaining a sheet with excellent strength.

[0182] As described above, the coating process includes a step of drying the dispersion liquid coated on the substrate. The step of drying the dispersion liquid is not particularly limited, but can be carried out by, for example, a non-contact drying method, a method of drying while restraining the sheet, or a combination thereof. Non-contact drying methods are not particularly limited, but include, for example, a method of drying by heating with hot air, infrared rays, far-infrared rays, or near-infrared rays (heat drying method), or a method of drying in a vacuum (vacuum drying method). While heat drying and vacuum drying may be combined, heat drying is usually used. Drying with infrared rays, far-infrared rays, or near-infrared rays can be carried out using, for example, an infrared device, a far-infrared device, or a near-infrared device. The heating temperature in the heat drying method is not particularly limited, but is preferably, for example, 20°C to 150°C, and more preferably, 25°C to 105°C. Setting the heating temperature at or above the lower limit allows the dispersion medium to volatilize quickly. Setting the heating temperature at or below the upper limit allows for reduced heating costs and suppressed heat-induced discoloration of the fibrous cellulose.

[0183] <Paper making process> The papermaking process is carried out by making paper from the dispersion using a papermaking machine. The papermaking machine used in the papermaking process is not particularly limited, but examples thereof include continuous papermaking machines such as Fourdrinier, cylinder, and tilting types, and multi-layer papermaking machines that combine these. In the papermaking process, known papermaking methods such as handmaking may also be used.

[0184] The papermaking process involves filtering and dehydrating the dispersion through a wire to obtain a wet sheet, which is then pressed and dried. The filter cloth used to filter and dehydrate the dispersion is not particularly limited, but it is preferable that it does not allow fibrous cellulose to pass through and that the filtration rate does not become too slow. Such filter cloths are not particularly limited, but are preferably sheets, woven fabrics, or porous membranes made of organic polymers. The organic polymer is not particularly limited, but is preferably a non-cellulose organic polymer such as polyethylene terephthalate, polyethylene, polypropylene, or polytetrafluoroethylene (PTFE). In this embodiment, examples include porous membranes made of polytetrafluoroethylene with a pore size of 0.1 μm to 20 μm, and woven fabrics made of polyethylene terephthalate or polyethylene with a pore size of 0.1 μm to 20 μm.

[0185] In the sheet-forming step, a method for producing a sheet from a dispersion can be carried out using, for example, a production apparatus including a water squeezing section in which a dispersion containing fine fibrous cellulose is discharged onto an endless belt and the dispersion medium is squeezed out of the discharged dispersion to produce a web, and a drying section in which the web is dried to produce a sheet. An endless belt is disposed between the water squeezing section and the drying section, and the web produced in the water squeezing section is transported to the drying section while remaining on the endless belt.

[0186] The dehydration method used in the papermaking process is not particularly limited, but examples thereof include dehydration methods commonly used in paper manufacturing. Among these, methods of dehydrating using a Fourdrinier, cylinder, or inclined wire, followed by further dehydration using a roll press, are preferred. Furthermore, the drying method used in the papermaking process is not particularly limited, but examples thereof include methods used in paper manufacturing. Among these, drying methods using a cylinder dryer, Yankee dryer, hot air dryer, near-infrared heater, infrared heater, etc. are more preferred.

[0187] (Application) The fibrous cellulose of this embodiment can be used as an additive for, for example, foods, cosmetics, cement, paints (for painting vehicles such as automobiles, ships, and aircraft, for building materials, for daily necessities, etc.), inks, pharmaceuticals, etc. Furthermore, the fine fibrous cellulose of this embodiment can also be applied to daily necessities by being added to resin-based materials or rubber-based materials.

[0188] The sheet containing the fibrous cellulose of this embodiment may also be used for optical components. For example, it can be used as a light-transmitting substrate for various display devices, various solar cells, etc. The laminate sheet of the present invention is also suitable for applications such as substrates for electronic devices, components for home appliances, window materials for various vehicles and buildings, interior materials, exterior materials, and packaging materials. [Example]

[0189] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0190] <Production Example 1> [Phosphorylation] Hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd. was used as the raw material pulp. This raw material pulp was subjected to a phosphating treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea was added to 100 parts by mass (bone dry mass) of the raw material pulp to adjust the composition to 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water, thereby obtaining a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 200 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining a phosphorylated pulp.

[0191] The resulting phosphorylated pulp was then washed. 100 g (bone dry mass) of phosphorylated pulp was mixed with 10 L of ion-exchanged water to obtain a pulp dispersion. The pulp was stirred to uniformly disperse the pulp, and then repeatedly filtered and dehydrated. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0192] Next, the washed phosphorylated pulp was neutralized as follows. First, the washed phosphorylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous solution of sodium hydroxide was added little by little while stirring to obtain a phosphorylated pulp slurry with a pH of 12 to 13. Next, the phosphorylated pulp slurry was dehydrated to obtain a neutralized phosphorylated pulp. Next, the neutralized phosphorylated pulp was subjected to the above-mentioned washing treatment.

[0193] The infrared absorption spectrum of the phosphorylated pulp obtained was measured using FT-IR. -1 Absorption due to phosphate groups was observed near the pulp, confirming that phosphate groups had been added to the pulp.

[0194] [Fiber defibration processing] Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was processed six times using a high-pressure homogenizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that this fine fibrous cellulose maintained cellulose type I crystallinity. The amount of phosphate groups (amount of first dissociated acid) measured by the measurement method described below in the measurement of [amount of phosphorus oxo acid group] was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, and the number-average fiber width was 3 nm.

[0195] <Production Example 2> [Phosphorous Treatment] A phosphite pulp was obtained by the same procedure as in Production Example 1, except that 33 parts by mass of phosphorous acid (phosphonic acid) was used instead of ammonium dihydrogen phosphate in the phosphating treatment.

[0196] The infrared absorption spectrum of the obtained phosphorous pulp was measured using FT-IR. -1 Absorption due to P=O of the phosphonic acid group, which is a tautomer of the phosphorous acid group, was observed near the nucleus, confirming that phosphorous acid groups (phosphonic acid groups) had been added to the pulp.

[0197] The resulting phosphite pulp was treated with a high-pressure homogenizer in the same manner as in Production Example 1 to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that the resulting fine fibrous cellulose maintained cellulose type I crystals. The amount of phosphite groups (amount of first dissociated acid) measured by the method described below in [Measurement of amount of phosphorus oxo acid group] was 1.51 mmol / g, and the total amount of dissociated acid was 1.54 mmol / g. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, and the number average fiber width was 3 nm.

[0198] <Production Example 3> The same operation as in Production Example 1 was performed except that the following xanthate treatment was performed instead of the phosphate treatment to obtain xanthated pulp.

[0199] [Xanthate treatment] To 100 parts by mass (bone dry mass) of raw pulp (hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd.), 2500 parts by mass of an 8.5% by mass aqueous solution of sodium hydroxide was added, and the mixture was stirred at room temperature for 3 hours to perform an alkali treatment. The pulp after this alkali treatment was subjected to solid-liquid separation by centrifugation (filter cloth 400 mesh, 3000 rpm for 5 minutes) to obtain a dehydrated alkali cellulose. To 10 parts by mass (bone dry mass) of the obtained alkali cellulose, 3.5 parts by mass of carbon disulfide was added, and the sulfurization reaction was carried out at room temperature for 4.5 hours to perform a xanthate formation treatment.

[0200] The obtained xanthated pulp was treated with a high-pressure homogenizer in the same manner as in Production Example 1 to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. The amount of xanthate groups measured by the measurement method described in [Measurement of xanthate group amount] below was 1.73 mmol / g. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, and the number average fiber width was 3 nm.

[0201] <Production Example 4> [Sulfation treatment] Sulfated pulp was obtained in the same manner as in Production Example 1, except that 38 parts by mass of amidosulfuric acid (sulfamic acid) was used instead of ammonium dihydrogen phosphate in the phosphorylation treatment and the heating time was extended to 20 minutes.

[0202] The infrared absorption spectrum of the sulfated pulp obtained was measured using FT-IR. -1 Absorption due to sulfate groups was observed in the vicinity, confirming that sulfate groups had been added to the pulp.

[0203] The obtained sulfated pulp was treated with a high-pressure homogenizer in the same manner as in Production Example 1 to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. The amount of sulfate groups measured by the measurement method described below in "Measurement of sulfur oxoacid group amount" was 1.47 mmol / g. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, and the number average fiber width was 3 nm.

[0204] <Production Example 5> Maleated pulp was obtained in the same manner as in Production Example 1, except that the following maleic oxidation treatment was carried out instead of the phosphating treatment.

[0205] [Maleic oxidation treatment] Raw material pulp (hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd.) was dried at 105°C for 3 hours to obtain dried pulp with a moisture content of 3% by mass or less. Next, 100 parts by mass of the dried pulp and 50 parts by mass of maleic anhydride were charged into an autoclave and treated at 150°C for 2 hours to carry out maleic oxidation treatment.

[0206] The infrared absorption spectrum of the maleated pulp obtained was measured using FT-IR. -1 Absorption due to carboxyl groups was observed near the pulp, confirming that carboxyl-containing substituents (maleic acid groups) were added to the pulp.

[0207] The resulting maleated pulp was treated with a high-pressure homogenizer in the same manner as in Production Example 1 to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that the resulting fine fibrous cellulose maintained cellulose type I crystals. The carboxyl group amount measured by the method described in "Measurement of Carboxy Group Amount" below was 1.22 mmol / g. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, and the number average fiber width was 3 nm.

[0208] <Production Example 6> A TEMPO oxidized pulp was obtained in the same manner as in Production Example 1, except that the following TEMPO oxidation treatment was carried out.

[0209] [TEMPO oxidation treatment] Hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd. was used as the raw material pulp. This raw material pulp was subjected to an alkaline TEMPO oxidation treatment as follows: First, 100 parts by weight of the raw material pulp (dry mass equivalent), 1.6 parts by weight of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl), and 10 parts by weight of sodium bromide were dispersed in 10,000 parts by weight of water. Next, a 13% by weight aqueous solution of sodium hypochlorite was added to 1.0 g of pulp to achieve a concentration of 3.8 mmol to initiate the reaction. During the reaction, a 0.5 M aqueous solution of sodium hydroxide was added dropwise to maintain the pH at 10 to 10.5. The reaction was considered complete when no further change in pH was observed.

[0210] The resulting TEMPO-oxidized pulp was then washed. The pulp slurry after TEMPO oxidation was dehydrated to obtain a dehydrated sheet, to which 5,000 parts by mass of ion-exchanged water was added, and the sheet was stirred to uniformly disperse the pulp. This process was repeated until the electrical conductivity of the filtrate reached 100 μS / cm or less, marking the end of the washing process.

[0211] The obtained TEMPO-oxidized pulp was treated with a high-pressure homogenizer in the same manner as in Production Example 1 to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. The amount of carboxyl groups measured by the measurement method described below was 1.30 mmol / g. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, and the number average fiber width was 3 nm.

[0212] <Production Example 7> The same procedure as in Production Example 1 was carried out except that the following hypochlorite oxidation treatment was carried out to obtain hypochlorite oxidized pulp.

[0213] [Hypochlorous acid oxidation treatment] The raw pulp (hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd.) was mixed for 15 seconds at 20,000 rpm using a hand mixer (Lab Millser PLUS manufactured by Osaka Chemical Co., Ltd.) to produce a fluffy fluffing pulp (solids concentration: 90% by mass). Sodium hypochlorite pentahydrate was then added to ion-exchanged water to prepare an aqueous solution with a sodium hypochlorite solids concentration of 22% by mass. 9,000 parts by mass of a 22% by mass aqueous sodium hypochlorite solution was added to 100 parts by mass of the fluffy fluffing pulp, and the mixture was reacted for 2 hours in a warm bath at 30°C to produce hypochlorite-oxidized pulp. During the reaction, the pH was maintained at 11 by adding 1N aqueous sodium hydroxide solution as needed.

[0214] The resulting hypochlorite-oxidized pulp was then washed. The resulting hypochlorite-oxidized pulp was poured into ion-exchanged water to obtain a pulp dispersion. The pulp was stirred to uniformly disperse the pulp, and then filtered and dehydrated. This was repeated until the electrical conductivity of the filtrate reached 100 μS / cm or less, marking the end point of the washing.

[0215] The obtained hypochlorite-oxidized pulp was treated with a high-pressure homogenizer in the same manner as in Production Example 1 to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. The amount of carboxyl groups measured by the measurement method described below was 0.70 mmol / g. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, and the number-average fiber width was 3 nm.

[0216] <Production Example 8> Carboxyethylated pulp was obtained in the same manner as in Production Example 1, except that the following carboxyethylation treatment was carried out.

[0217] [Carboxyethylation treatment] A chemical solution (553 parts by mass in total) consisting of 250 parts by mass of 12N NaOH aqueous solution, 163 parts by mass of 2-chloropropionic acid, and 140 parts by mass of ion-exchanged water was added to 100 parts by mass (bone dry mass) of raw pulp (hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd.) to obtain a chemical solution-impregnated pulp. The obtained chemical solution-impregnated pulp was then heated in a hot air dryer at 165°C for 10 minutes to introduce carboxyethyl groups (carboxy groups) into the cellulose in the pulp, obtaining a carboxyethylated pulp.

[0218] The resulting carboxyethylated pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting carboxyethylated pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0219] Next, the washed carboxyethylated pulp was neutralized as follows: First, the washed carboxyethylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous solution of sodium hydroxide was added little by little while stirring to obtain a carboxyethylated pulp slurry with a pH of 12 to 13. Next, the carboxyethylated pulp slurry was dehydrated and washed to obtain a neutralized carboxyethylated pulp.

[0220] The resulting carboxyethylated pulp was treated with a high-pressure homogenizer in the same manner as in Production Example 1 to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that the resulting fine fibrous cellulose maintained cellulose type I crystals. The amount of carboxy groups measured by the measurement method described below was 1.41 mmol / g. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, and the number average fiber width was 3 nm.

[0221] <Production Example 9> A sulfoethylated pulp was obtained in the same manner as in Production Example 1, except that the following sulfoethylation treatment was carried out.

[0222] [Sulfoethylation treatment] A chemical solution (total 960 parts by mass) consisting of 180 parts by mass of 2N NaOH aqueous solution and 780 parts by mass of a 25% by mass sodium vinyl sulfonate aqueous solution was added to 100 parts by mass (bone dry mass) of raw pulp (hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd.) to obtain a chemical solution-impregnated pulp. The obtained chemical solution-impregnated pulp was then heated in a hot air dryer at 165°C for 16 minutes to introduce sulfoethyl groups into the cellulose in the pulp, obtaining a sulfoethylated pulp.

[0223] The resulting sulfoethylated pulp was then washed. The resulting sulfoethylated pulp was poured into ion-exchanged water to obtain a pulp dispersion. The pulp was stirred to uniformly disperse the pulp, and then filtered and dehydrated. This washing process was repeated until the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0224] The obtained sulfoethylated pulp was treated with a high-pressure homogenizer in the same manner as in Production Example 1 to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. The amount of sulfoethyl groups (amount of sulfonic groups) measured by the measurement method described below was 1.48 mmol / g. The fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, and the number average fiber width was 3 nm.

[0225] <Production Example 10> A cationized pulp was obtained in the same manner as in Production Example 1, except that the following cationization treatment was carried out.

[0226] [Cationization treatment] To 100 parts by mass (bone dry mass) of raw pulp (hardwood dissolving pulp (dry sheet) manufactured by Oji Paper Co., Ltd.), a chemical solution consisting of 180 parts by mass of 1N NaOH aqueous solution and 325 parts by mass of a cationizing agent (Catiomaster G manufactured by Yokkaichi Synthetic Co., Ltd., glycidyl trimethylammonium chloride, purity 73.1% by mass, moisture content 20.2% by mass) (total 505 parts by mass) was added to obtain a chemical-impregnated pulp. The obtained chemical-impregnated pulp was then heated in a hot air dryer at 165°C for 12 minutes to introduce cationic groups into the cellulose in the pulp, yielding a cationized pulp.

[0227] The resulting cationized pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting cationized pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0228] Next, the washed cationized pulp was neutralized as follows: First, the washed cationized pulp was diluted with 10 L of ion-exchanged water, and then 1 N hydrochloric acid was added little by little while stirring to obtain a cationized pulp slurry with a pH of 1 to 2. Next, the cationized pulp slurry was dehydrated and washed to obtain neutralized cationized pulp.

[0229] The resulting cationized pulp was treated with a high-pressure homogenizer in the same manner as in Production Example 1 to obtain a fine fibrous cellulose dispersion containing fine fibrous cellulose. X-ray diffraction confirmed that the resulting fine fibrous cellulose maintained cellulose type I crystals. Furthermore, trace nitrogen analysis was performed on the resulting fine fibrous cellulose, and the amount of cationic groups calculated using the following formula was 1.45 mmol / g. (Amount of cationic groups) [mmol / g] = (amount of nitrogen) / 14 × 1000 / (amount of fine fibrous cellulose tested) Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope, and the number average fiber width was found to be 3 nm.

[0230] [Table 1]

[0231] Example 1 [Imino group introduction treatment] The fine fibrous cellulose dispersion obtained in Production Example 1 was diluted to a solids concentration of 1% by mass. 0.68 parts by mass of a 25% by mass aqueous ammonia solution was added to 100 parts by mass of the resulting dispersion. 1N aqueous NaOH solution was then added and stirred to adjust the pH to 12, and the mixture was then heated in a water bath at 95°C for 1 hour to introduce imino groups (-CH=NH) into the fine fibrous cellulose. After heating, 1 / 5 by volume of a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) and 1 / 5 by volume of a strongly basic ion exchange resin (Amberjet 4400; Organo Corporation, conditioned) were added to the heated dispersion, and the mixture was shaken for 1 hour. The treatment solution was then poured onto a 90 μm mesh to separate the resin from the dispersion, thereby removing free nitrogen from the dispersion. 0.1N aqueous NaOH solution was added to the resulting dispersion and stirred to obtain a fine fibrous cellulose dispersion with imino groups introduced therein, adjusted to pH 7.5.

[0232] [Uniform dispersion processing] The obtained dispersion of imino group-introduced fine fibrous cellulose was treated three times with a high-pressure homogenizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa.

[0233] [Sheet production] Acetoacetyl group-modified polyvinyl alcohol (Gosenex Z-300, manufactured by Mitsubishi Chemical Corporation) was added to ion-exchange water to a concentration of 12% by mass, and the mixture was stirred at 95°C for 1 hour to dissolve. An aqueous polyvinyl alcohol solution was obtained by the above procedure. The imino group-introduced fine fibrous cellulose dispersion and the above polyvinyl alcohol aqueous solution were each diluted with ion-exchange water to a solids concentration of 0.6% by mass. Next, 70 parts by mass of the diluted imino group-introduced fine fibrous cellulose dispersion were mixed with 30 parts by mass of the diluted polyvinyl alcohol aqueous solution to obtain a mixed solution. Furthermore, the finished basis weight of the sheet was 35 g / m 2 The mixture was weighed out so that the weight was 100g and spread on a commercially available acrylic plate. A damming frame (inner dimensions 250mm x 250mm, height 5cm) was placed on the acrylic plate to achieve the specified basis weight. The sheet was then dried in a dryer at 70°C for 24 hours and peeled off from the acrylic plate to obtain a sheet containing imino group-introduced fine fibrous cellulose. The sheet had a thickness of 25µm.

[0234] <Example 2> An imino group-introduced fine fibrous cellulose dispersion and an imino group-introduced fine fibrous cellulose-containing sheet were obtained in the same manner as in Example 1, except that in the [imino group introduction treatment], the amount of aqueous ammonia solution added was 0.34 parts by mass.

[0235] Example 3 An imino group-introduced fine fibrous cellulose dispersion and an imino group-introduced fine fibrous cellulose-containing sheet were obtained in the same manner as in Example 1, except that in the [imino group introduction treatment], the amount of aqueous ammonia solution added was 0.17 parts by mass.

[0236] Example 4 An imino group-introduced fine fibrous cellulose dispersion and an imino group-introduced fine fibrous cellulose-containing sheet were obtained in the same manner as in Example 1, except that in the [imino group introduction treatment], the amount of aqueous ammonia added was 0.09 parts by mass.

[0237] <Example 5> In the [imino group introduction treatment], the same procedure as in Example 1 was repeated except that 1.24 parts by mass of 25% by mass methylamine was added instead of the aqueous ammonia solution, to obtain a dispersion of imino group (-CH=N-CH3)-introduced fine fibrous cellulose and a sheet containing imino group-introduced fine fibrous cellulose.

[0238] Example 6 In the [imino group introduction treatment], the same procedure as in Example 1 was repeated except that 0.59 parts by mass of isopropylamine was added instead of the aqueous ammonia solution, to obtain a dispersion of imino group (-CH=N-CH-(CH3)2)-introduced fine fibrous cellulose and a sheet containing imino group-introduced fine fibrous cellulose.

[0239] Example 7 In the [imino group introduction treatment], the same procedure as in Example 1 was repeated except that 0.93 parts by mass of aniline was added instead of the aqueous ammonia solution, to obtain a dispersion of imino group (-CH=N-Ph)-introduced fine fibrous cellulose and a sheet containing imino group-introduced fine fibrous cellulose.

[0240] <Examples 8 to 16> An imino group-introduced fine fibrous cellulose dispersion and an imino group-introduced fine fibrous cellulose-containing sheet were obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion shown in Table 2 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 1.

[0241] Example 17 An imino group-introduced fine fibrous cellulose dispersion and an imino group-introduced fine fibrous cellulose-containing sheet were obtained in the same manner as in Example 1, except that the imino group-introduced fine fibrous cellulose dispersion was not subjected to the [uniform dispersion treatment].

[0242] Example 18 In the [imino group introduction treatment], the amounts of strongly acidic ion exchange resin and strongly basic ion exchange resin added to the dispersion after heating were each 1 / 20 by volume, but the same procedures as in Example 1 were carried out to obtain an imino group-introduced fine fibrous cellulose dispersion and an imino group-introduced fine fibrous cellulose-containing sheet.

[0243] <Comparative Example 1> A fine fibrous cellulose dispersion and a fine fibrous cellulose-containing sheet were obtained in the same manner as in Example 1, except that the [imino group introduction treatment] and [uniform dispersion treatment] were not carried out.

[0244] <Comparative Examples 2 to 10> A fine fibrous cellulose dispersion and a fine fibrous cellulose-containing sheet were obtained in the same manner as in Comparative Example 1, except that the fine fibrous cellulose dispersion shown in Table 3 was used instead of the fine fibrous cellulose dispersion obtained in Production Example 1.

[0245] (Measurement and Evaluation) The dispersions and sheets obtained in the examples and comparative examples were evaluated by the following methods.

[0246] [Fiber width measurement] The fiber width of the fine fibrous cellulose was measured using the following method. The fine fibrous cellulose dispersion was diluted with water to a cellulose concentration of 0.01% by mass to 0.1% by mass and cast onto a hydrophilically treated carbon film-coated grid. After drying, the grid was stained with uranyl acetate and observed under a transmission electron microscope (TEM, JEOL-2000EX, manufactured by JEOL Ltd.). The obtained image was visualized with arbitrary vertical and horizontal axes representing the image width, and the magnification was adjusted so that 20 or more fibers intersected these axes. After obtaining observation images satisfying these conditions, two random axes were drawn vertically and horizontally per image, and the fiber widths of the fibers intersecting the axes were visually determined. Three unique observation images were taken for each dispersion, and the fiber widths of the fibers intersecting each of the two axes were determined (20 or more × 2 × 3 = 120 or more). The number-average fiber width was calculated from the fiber widths obtained in this manner.

[0247] [Measurement of phosphorus oxoacid group content] In measuring the amount of phosphorus oxoacid groups (amount of phosphate groups or phosphite groups), ion-exchanged water was first added to the target fine fibrous cellulose to prepare a slurry with a solids concentration of 0.2% by mass. The resulting slurry was treated with an ion-exchange resin and then titrated with an alkali to measure the amount of phosphorus oxoacid groups. Treatment with ion exchange resin was carried out by adding 1 / 10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) to the above-mentioned fine fibrous cellulose-containing slurry, shaking for 1 hour, and then pouring it onto a mesh with 90 μm openings to separate the resin from the slurry. In addition, alkali titration was performed by measuring the change in the pH of a slurry containing fine fibrous cellulose after ion exchange resin treatment while adding 10 μL of 0.1 N sodium hydroxide solution every 5 seconds. Nitrogen gas was bubbled through the slurry 15 minutes before the start of the titration. In this neutralization titration, two maximum points of increment (the derivative of pH with respect to the amount of alkali added) were observed on the plot of pH versus the amount of alkali added. The first maximum point of increment after starting the addition of alkali is called the first endpoint, and the second maximum point is called the second endpoint (Figure 1). The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of first dissociated acid in the slurry used for titration. The amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid in the slurry used for titration. The amount of alkali (mmol) required from the start of titration to the first endpoint was divided by the solid content (g) in the slurry to be titrated, and the value was taken as the amount of phosphorus oxo acid groups (mmol / g).

[0248] [Measurement of sulfur oxoacid and sulfonic acid groups] The amount of sulfur oxoacid groups or sulfonic groups was measured as follows. The obtained fine fibrous cellulose (solid content obtained by heating and drying the dispersion) was wet ashed using perchloric acid and concentrated nitric acid, then diluted at an appropriate ratio and the amount of sulfur was measured by ICP atomic emission spectrometry. The amount of sulfur was divided by the bone dry mass of the fine fibrous cellulose tested, and the value was taken as the amount of sulfur oxoacid groups or sulfonic groups (unit: mmol / g).

[0249] [Measurement of xanthate group content] The xanthate group content was measured using the Bredee method. Specifically, 40 mL of saturated ammonium chloride solution was added to 1.5 parts by mass (bone-dry mass) of fine fibrous cellulose (solid content obtained by heating and drying the dispersion). The sample was crushed with a glass rod and mixed thoroughly. After leaving the mixture for approximately 15 minutes, it was filtered through GFP filter paper (GS-25, manufactured by Advantec) and thoroughly washed with saturated ammonium chloride solution. The sample, along with the GFP filter paper, was placed in a 500 mL tall beaker, and 50 mL of 0.5 M sodium hydroxide solution (5 °C) was added and stirred. After leaving the mixture for 15 minutes, phenolphthalein solution was added until the solution turned pink, followed by 1.5 M acetic acid. The point at which the solution changed from pink to colorless was designated as the neutralization point. After neutralization, 250 mL of distilled water was added and stirred thoroughly. 10 mL of 1.5 M acetic acid and 10 mL of 0.05 mol / L iodine solution were added using a volumetric pipette. This solution was then titrated with 0.05 mol / L sodium thiosulfate solution. The amount of xanthate groups was calculated from the titration amount of sodium thiosulfate and the bone dry mass of the fine fibrous cellulose using the following formula. Amount of xanthate group (mmol / g) = (0.05 × 10 × 2 - 0.05 × sodium thiosulfate titration (mL)) / 1000 / bone-dry mass of fine fibrous cellulose (g)

[0250] [Measurement of carboxyl group content] The amount of carboxy groups in the fine fibrous cellulose was measured by adding ion-exchanged water to a fine fibrous cellulose dispersion containing the target (maleic oxidized, TEMPO oxidized, hypochlorite oxidized, or carboxyethylated) fine fibrous cellulose to make the content 0.2 mass%, treating the dispersion with an ion-exchange resin, and then titrating the dispersion with an alkali. Treatment with ion exchange resin was carried out by adding 1 / 10 by volume of a strongly acidic ion exchange resin (Amberjet 1024; manufactured by Organo Corporation, conditioned) to a 0.2% by mass slurry containing fine fibrous cellulose, shaking for 1 hour, and then pouring the mixture onto a mesh with 90 μm openings to separate the resin from the slurry. In addition, alkali titration was performed by measuring the change in pH of the fibrous cellulose-containing slurry after treatment with an ion exchange resin while adding 0.1 N aqueous sodium hydroxide. Observing the change in pH while adding aqueous sodium hydroxide yielded a titration curve like the one shown in Figure 2. As shown in Figure 2, in this neutralization titration, a single point was observed where the increment (the differential value of pH with respect to the amount of alkali added) reached a maximum on the curve plotting the measured pH against the amount of alkali added. This maximum increment was called the first endpoint. The region from the start of the titration to the first endpoint in Figure 2 is called the first region. The amount of alkali required in the first region was equal to the amount of carboxyl groups in the slurry used for titration. The amount of alkali (mmol) required in the first region of the titration curve was divided by the solids content (g) of the fine fibrous cellulose-containing slurry to be titrated to calculate the amount of carboxyl groups introduced (mmol / g). The amount of carboxyl groups introduced (mmol / g) is calculated based on the amount of carboxyl groups introduced (mmol / g) when the counter ions of the carboxyl groups are hydrogen ions (H + ) (hereinafter referred to as the amount of carboxy groups (acid type)) per 1 g of fibrous cellulose.

[0251] [Measurement of imino group content] The amount of imino groups introduced into the fine fibrous cellulose was calculated by quantifying the amount of 2-picoline borane that reacted with the imino groups when the imino groups were reduced with 2-picoline borane. Specifically, 1 mmol of 2-picoline borane was dissolved in 1 L of acetic acid to obtain a 2-picoline borane solution. 10 mL of the 2-picoline borane solution was added to 100 g of a 1% by mass fine fibrous cellulose dispersion and heated in a 65°C water bath for 1 hour to allow the reduction reaction of the imino groups to proceed. After the reaction, 10 parts by mass of 1N sulfuric acid was added, followed by the dropwise addition of a 1 mmol / L aqueous potassium permanganate solution. The amount of unreacted 2-picoline borane was quantified at the point where the clear solution turned slightly red after the dropwise addition. The amount of 2-picoline borane that reacted with the imino groups was calculated by subtracting the amount of unreacted 2-picoline borane from the amount of 2-picoline borane tested. Specifically, the amount of imino groups in the fibrous cellulose (unit: μmol / g) was calculated from the following formula. Amount of imino group (µmol / g) = 3 x [0.01 - 0.001 x amount of potassium permanganate added (mL) x (5 / 6)] x 1000

[0252] [Measurement of Haze of Dispersion] The haze of the fine fibrous cellulose dispersion was measured by diluting the dispersion with ion-exchanged water to 0.2% by mass, and then measuring the haze in accordance with JIS K 7136:2000 using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory) and a glass cell for liquids with a 1 cm optical path length (MG-40, manufactured by Fujiwara Seisakusho, reverse optical path) with ion-exchanged water in the same glass cell. The dispersion to be measured was allowed to stand for 24 hours in an environment of 23°C and 50% relative humidity before measurement. The liquid temperature of the dispersion during measurement was 23°C.

[0253] [Measurement of total light transmittance of dispersion liquid] The total light transmittance of the fine fibrous cellulose dispersion was measured by diluting the dispersion with ion-exchanged water to 0.2% by mass, and then measuring it with a haze meter (HM-150, manufactured by Murakami Color Research Laboratory) using a glass cell for liquids with a 1 cm optical path length (MG-40, reverse optical path, manufactured by Fujiwara Seisakusho) in accordance with JIS K 7361-1:1997. Zero-point measurement was performed using ion-exchanged water placed in the same glass cell. In other words, the total light transmittance measured with ion-exchanged water alone was taken as 100%. The dispersion to be measured was allowed to stand for 24 hours in an environment of 23°C and 50% relative humidity before measurement. The liquid temperature of the dispersion during measurement was 23°C.

[0254] [Measurement of nitrogen concentration in filtrate] Distilled water was added to the fine fibrous cellulose dispersion so that the fine fibrous cellulose concentration was 0.2% by mass, and the mixture was stirred for 24 hours. After stirring, a filtrate was obtained using a filter medium with a pore size of 0.45 μm. The nitrogen concentration (ppm) in the filtrate was measured by trace nitrogen analysis.

[0255] [Sheet Haze] The haze of the fine fibrous cellulose-containing sheet was measured in accordance with JIS K 7136:2000 using a haze meter ("HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd.).

[0256] [Total light transmittance of sheet] The total light transmittance of the fine fibrous cellulose-containing sheet was measured in accordance with JIS K 7361-1: 1997 using a haze meter ("HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd.).

[0257] [YI measurement before and after heating the sheet] According to JIS K 7373:2006, the YI (yellowness index) of the fine fibrous cellulose-containing sheet was measured before and after heating using Colour Cute i (manufactured by Suga Test Instruments Co., Ltd.) The yellowness index after heating was the yellowness index of the sheet heated at 160°C for 6 hours. The YI increase rate was measured using the following method. YI increase rate (%) = (yellowness of sheet after heating - yellowness of sheet before heating) / yellowness of sheet before heating × 100

[0258] [Table 2]

[0259] [Table 3]

[0260] The imino group-introduced fine fibrous cellulose-containing sheets obtained in the Examples showed little change in color after heating, whereas the imino group-free sheets obtained in the Comparative Examples showed a large change in color after heating, and coloring was observed after heating.

Claims

1. The fiber width is 1000 nm or less, and the fiber has a substituent represented by the following formula (11) and an ionic substituent other than the substituent represented by the formula (11), fibrous cellulose, wherein the ionic substituent other than the substituent represented by formula (11) is at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a carboxy group, a sulfur oxoacid group, and a xanthate group; 【Chemical 1】 In formula (11), R １ is a hydrogen atom, and R ２ is a hydrogen atom, a saturated linear hydrocarbon group, a saturated branched hydrocarbon group, a saturated cyclic hydrocarbon group, or an aromatic group.

2. The fibrous cellulose according to claim 1 , wherein the ionic substituent is a phosphorus oxoacid group or a substituent derived from a phosphorus oxoacid group.

3. 3. The fibrous cellulose according to claim 1, wherein the fiber width of the fibrous cellulose is 10 nm or less.

4. The fibrous cellulose according to any one of claims 1 to 3, wherein the amount of the substituent represented by formula (11) introduced is 0.10 to 15.00 µmol / g.

5. 5. The fibrous cellulose according to claim 1 , wherein the nitrogen concentration in the filtrate obtained by the following measurement method is 100 ppm or less. (Measurement method) Distilled water is added so that the fibrous cellulose concentration becomes 0.2% by mass, and after stirring for 24 hours, the mixture is filtered using a filter medium with a pore size of 0.45 μm to obtain a filtrate; the nitrogen concentration (ppm) in the filtrate is measured by trace nitrogen analysis.

6. A dispersion comprising the fibrous cellulose according to any one of claims 1 to 5.

7. The dispersion according to claim 6, wherein the dispersion contains 0.2% by mass of the fibrous cellulose and has a total light transmittance of 95.0% or more.

8. The dispersion according to claim 6 or 7, wherein the haze of the dispersion is 5.0% or less when the dispersion contains 0.2% by mass of the fibrous cellulose.

9. A sheet comprising the fibrous cellulose according to any one of claims 1 to 5.

10. 10. The sheet according to claim 9, wherein when the sheet is heated at 160°C for 6 hours, the YI increase rate calculated by the following formula is 1500% or less: YI increase rate (%)=(yellowing index of sheet after heating−yellowing index of sheet before heating) / yellowing index of sheet before heating×100 In the above formula, the yellowness of the sheet is the yellowness measured in accordance with JIS K 7373:2006.

11. The sheet according to claim 9 or 10, having a total light transmittance of 90.0% or more.

12. The sheet according to any one of claims 9 to 11, having a haze of 5.0% or less.

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