Sheet

Abstract

To provide a sheet having high surface smoothness.SOLUTION: A sheet contains a fibrous cellulose having a fiber width of 1,000 nm or less and a resin, wherein the fibrous cellulose has an anionic group, a content of the anionic group is 0.50 mmol / g or more, the fibrous cellulose has an organic onium ion as a counter ion of the anionic group, and satisfies the following conditions (A) and (B). (A) A tensile elastic modulus is 1.10 GPa or more, and (B) a haze is less than 2.0%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a sheet. Specifically, the present invention relates to a sheet comprising fine fibrous cellulose and a resin. [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] Generally, fine fibrous cellulose is stably dispersed in aqueous solvents, and therefore is often provided in the form of an aqueous dispersion and used for various purposes. On the other hand, when fine fibrous cellulose is mixed with a resin component to produce a composite or the like, there is also a demand for mixing the fine fibrous cellulose with an organic solvent. To meet this demand, a technique for producing a fine fibrous cellulose-containing dispersion in which fine fibrous cellulose is dispersed in a dispersion medium containing an organic solvent has been investigated (Patent Documents 1 to 4).

[0004] Furthermore, Patent Documents 5 and 6 disclose resin compositions containing fine fibrous cellulose and a resin. The resin composition of Patent Document 5 contains an organic onium ion as a counter ion of a phosphate group or a substituent derived from a phosphate group, and the resin composition of Patent Document 6 contains an organic onium ion as a counter ion of a carboxy group. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-140738 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-188375 [Patent Document 3] Japanese Patent Application Publication No. 2019-49091 [Patent Document 4] Japanese Patent Publication No. 2020-76054 [Patent Document 5] International Publication No. 2019 / 098331 [Patent Document 6] Japanese Patent Application Laid-Open No. 2015-143336 Summary of the Invention [Problem to be solved by the invention]

[0006] When a resin composition containing fine fibrous cellulose and a resin is formed into a sheet, high surface smoothness may be required for the intended use. However, in sheets containing fine fibrous cellulose and a resin obtained by conventional techniques, the dispersibility of the fine fibrous cellulose in the resin may be insufficient, and the surface smoothness of the sheet may be poor.

[0007] Therefore, in order to solve the problems of the conventional techniques, the present inventors have carried out investigations with the aim of providing a sheet having high surface smoothness. [Means for solving the problem]

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

[0009] [1] A sheet containing fibrous cellulose and a resin having a fiber width of 1000 nm or less, The fibrous cellulose has anionic groups, and the content of the anionic groups is 0.50 mmol / g or more; The fibrous cellulose has an organic onium ion as a counter ion of the anionic group, A sheet that meets the following conditions (A) and (B); (A) Tensile modulus of elasticity is 1.10 GPa or more; (B) Haze is less than 2.0%. [2] The sheet according to [1], wherein the arithmetic mean roughness (Ra) of at least one surface is 200 nm or less. [3] The sheet according to [1] or [2], wherein the fiber width of the fibrous cellulose is 10 nm or less. [4] The sheet according to any one of [1] to [3], wherein the anionic group is a group introduced into the fibrous cellulose via an ester bond or an ether bond. [Effects of the Invention]

[0010] According to the present invention, a sheet having excellent surface smoothness can be obtained. [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] (sheet) This embodiment relates to a sheet containing fibrous cellulose having a fiber width of 1000 nm or less and a resin. Here, the fibrous cellulose has anionic groups, and the content of the anionic groups is 0.50 mmol / g or more. The fibrous cellulose also has organic onium ions as counterions of the anionic groups. The sheet of this embodiment satisfies the following conditions (A) and (B): (A) The tensile modulus is 1.10 GPa or more. (B) Haze is less than 2.0%. 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] The present embodiment has the above-described configuration, making it possible to provide a sheet with excellent surface smoothness. Specifically, a sheet with a small arithmetic mean roughness (Ra) value on the sheet surface can be obtained. The arithmetic mean roughness (Ra) of at least one surface of the sheet is preferably 200 nm or less, more preferably 180 nm or less, even more preferably 160 nm or less, even more preferably 140 nm or less, even more preferably 120 nm or less, and particularly preferably 100 nm or less. The lower limit of the arithmetic mean roughness (Ra) of the sheet surface is not particularly limited, but is preferably, for example, 5 nm or more. Here, the arithmetic mean roughness (Ra) of the sheet surface is a value measured in accordance with JIS B 0601:1994. In this case, the surface on which the arithmetic mean roughness (Ra) of the sheet surface is measured is the surface that is not in contact with the release film or base film during sheet production. An example of an instrument for measuring the arithmetic mean roughness (Ra) is the SE-3C manufactured by Kosaka Laboratory Co., Ltd.

[0015] In the sheet of this embodiment, the tensile modulus and haze each falling within a predetermined numerical range indicate that the fine fibrous cellulose is uniformly dispersed in the sheet. That is, the sheet of this embodiment is a uniformly dispersed sheet in which the fine fibrous cellulose is uniformly dispersed in the resin component. As such, in the sheet of this embodiment, since the fine fibrous cellulose is uniformly dispersed, a sheet with excellent surface smoothness can be obtained. Furthermore, the sheet of this embodiment is a sheet with excellent tensile strength and high transparency.

[0016] In this embodiment, the fine fibrous cellulose is uniformly dispersed in the dispersion (coating liquid) forming the sheet. Therefore, the dispersion (coating liquid) forming the sheet can exhibit high thixotropy. When the dispersion (coating liquid) has high thixotropy, it is possible to reduce the viscosity during coating, making it less likely that the coating surface will become uneven during coating. However, since the viscosity increases after coating, the coating surface tends to become smoother.

[0017] The tensile modulus of the sheet may be 1.10 GPa or more, preferably 1.20 GPa or more, and more preferably 1.30 GPa or more. The upper limit of the tensile modulus of the sheet is not particularly limited, but is preferably 30 GPa or less. Here, the tensile modulus of the sheet is measured in accordance with JIS P 8113:2006, except that the test specimen size is changed to 75 mm × 15 mm and the extension rate is changed to 1 mm / min. When measuring the tensile modulus, the test specimen is conditioned at 23°C and 50% relative humidity for 24 hours. For example, a Tensilon tensile tester manufactured by A&D Co., Ltd. can be used to measure the tensile modulus.

[0018] The haze of the sheet may be less than 2.0%, preferably 1.9% or less, more preferably 1.8% or less, and even more preferably 1.7% 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.

[0019] The total light transmittance of the sheet is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. The upper limit of the total light transmittance of the sheet is not particularly limited, and may be 100%. 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 the total light transmittance, for example, a haze meter (HM-150) manufactured by Murakami Color Research Laboratory Co., Ltd. can be used.

[0020] The thickness of the sheet is not particularly limited, but is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, and particularly preferably 30 μm or more. The thickness of the sheet is preferably 10,000 μm or less, more preferably 5,000 μm or less, even more preferably 3,000 μm or less, and even more preferably 1,000 μm or less. The thickness of the sheet is preferably adjusted appropriately depending on the application. The thickness of the sheet can be measured using a stylus-type constant pressure thickness gauge (Millitron 1202DPG-02, manufactured by Mahl TECLOCK CORPORATION). The thickness of the sheet is measured according to the following method. A sheet cut into a size of 50 mm square or more is conditioned at 23°C and 50% relative humidity for 24 hours, and the thickness is measured at four random points, and the average value is used as the sheet thickness.

[0021] The basis weight of the sheet is not particularly limited, but is preferably 5 g / m 2 It is preferable that the content is 10 g / m or more. 2 More preferably, it is 20 g / m or more. 2 More preferably, it is 30 g / m or more. 2 It is more preferable that the basis weight of the sheet is 10,000 g / m or more. 2 Preferably, it is 5000 g / m or less. 2 More preferably, it is 3000 g / m or less. 2 More preferably, it is 1000 g / m or more. 2The 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.

[0022] The density of the sheet is not particularly limited, but is preferably 0.5 g / cm 3 It is preferable that the concentration is 0.75 g / cm or more. 3 More preferably, it is 0.85 g / cm or more. 3 It is more preferable that the density of the sheet is 2.5 g / cm or more. 3 Preferably, it is 1.8 g / cm or less. 3 More preferably, it is 1.5 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.

[0023] (resin) The sheet of this embodiment contains a resin. The type of resin contained in the sheet is not particularly limited, but examples thereof include thermoplastic resins and thermosetting resins.

[0024] Examples of the resin include acrylic resins, polystyrene resins, polyolefin resins, polycarbonate resins, polyester resins, polyamide resins, polyacrylonitrile resins, silicone resins, fluorine-based resins, chlorine-based resins, epoxy resins, melamine resins, phenolic resins, polyurethane resins, diallyl phthalate resins, alcohol-based resins, and cellulose derivatives. Examples of the cellulose derivatives include carboxymethyl cellulose, methyl cellulose, and hydroxyethyl cellulose. Among these, the resin is preferably a hydrophobic and transparent resin, and is preferably at least one selected from the group consisting of acrylic resins, polystyrene resins, polyolefin resins, polycarbonate resins, polyester resins, polyamide resins, silicone resins, fluorine-based resins, chlorine-based resins, epoxy resins, and polyurethane resins. It is more preferably at least one selected from the group consisting of acrylic resins and polystyrene resins, and is particularly preferably an acrylic resin. In this embodiment, since the fine fibrous cellulose has organic onium ions as counter ions of the anionic groups, even when the sheet contains a hydrophobic resin, the fine fibrous cellulose can be uniformly dispersed in the resin. Furthermore, by using an acrylic resin as the resin, it is easier to obtain a sheet with excellent transparency and surface smoothness.

[0025] When an acrylic resin is used as the resin, the glass transition temperature (Tg) of the acrylic resin is preferably −80° C. or higher, more preferably −30° C. or higher, and even more preferably 20° C. or higher. The upper limit of the glass transition temperature of the acrylic resin is not particularly limited, but may be 120° C. or lower.

[0026] When producing a sheet, the above-mentioned resin and fine fibrous cellulose may be mixed together and then the sheet may be formed. Furthermore, when producing a sheet, the above-mentioned resin precursor may be mixed with fine fibrous cellulose instead of at least a portion of the resin, and then the sheet may be formed. When forming a sheet after mixing the resin precursor with fine fibrous cellulose, it is preferable to allow the polymerization or crosslinking reaction of the resin precursor to proceed during the sheet production process. In this specification, the term "resin precursor" refers to a monomer or an oligomer with a relatively low molecular weight used to produce a resin. The type of resin precursor is not particularly limited, but examples include precursors of thermoplastic resins and thermosetting resins. Such resin precursors undergo a polymerization reaction or crosslinking reaction due to the action of light, heat, a curing agent, etc., to become the above-mentioned resin.

[0027] The resin content relative to the total mass of solids in the sheet is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 97% by mass or more. Furthermore, the resin content relative to the total mass of solids in the sheet is preferably 99.5% by mass or less, more preferably 99% by mass or less, and even more preferably 98% by mass or less. By setting the resin content within the above range, the specific elastic modulus of the sheet can be more effectively increased, and the haze of the sheet can be more effectively reduced. Furthermore, by setting the resin content within the above range, it becomes easier to obtain a sheet with even better surface smoothness.

[0028] (fine fibrous cellulose) The sheet of this embodiment contains fibrous cellulose having a fiber width of 1000 nm or less. The fiber width of the fibrous cellulose contained in the sheet is preferably 100 nm or less, more preferably 50 nm or less, even more preferably 20 nm or less, even more preferably 10 nm or less, and particularly preferably 8 nm or less.

[0029] The average fiber width of the fibrous cellulose contained in the sheet 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.

[0030] 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.

[0031] (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.

[0032] 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.

[0033] The fiber width of the fibrous cellulose contained in the sheet may be measured by the above-mentioned method for the fibrous cellulose contained in the dispersion liquid from which the sheet is formed, and the measured value may be used. Alternatively, the fiber width may be measured by the above-mentioned method after isolating the fibrous cellulose contained in the sheet.

[0034] 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.

[0035] 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 fine fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. This can be expected to provide even better performance in terms of heat resistance and low linear thermal expansion coefficient. The degree of crystallinity can be determined by measuring the X-ray diffraction profile and using the pattern in a conventional manner (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

[0036] 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 fine 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 the fibrous cellulose is used as a dispersion, handling such as dilution becomes easier.

[0037] Fibrous cellulose has, for example, both crystalline and amorphous regions. Fine 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.

[0038] The fibrous cellulose has anionic groups. Examples of the anionic groups include phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups (sometimes simply referred to as phosphorus oxoacid groups), carboxy groups or substituents derived from carboxy groups (sometimes simply referred to as carboxy groups), sulfur oxoacid groups or substituents derived from sulfur oxoacid groups (sometimes simply referred to as sulfur oxoacid groups), xanthate groups or substituents derived from xanthate groups, phosphonic groups or substituents derived from phosphonic groups, phosphine groups or substituents derived from phosphine groups, sulfonic groups or substituents derived from sulfonic groups, and carboxyalkyl groups. Among these, the anionic groups are preferably groups introduced into the fibrous cellulose via ester or ether bonds, and more preferably groups introduced into the fibrous cellulose via ester bonds. In this case, the ester bonds are preferably formed by dehydration condensation of the fibrous cellulose and a compound that becomes the anionic group. The anionic group is preferably 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 carboxyalkyl group, and a sulfonic acid group. It is more preferably at least one selected from the group consisting of a phosphorus oxoacid group, a substituent derived from a phosphorus oxoacid group, a sulfur oxoacid group, and a substituent derived from a sulfur oxoacid group. It is particularly preferably at least one selected from the group consisting of a phosphorus oxoacid group and a substituent derived from a phosphorus oxoacid group. By appropriately selecting the anionic group, the tensile modulus of the sheet can be increased and the haze of the sheet can be reduced, thereby more effectively improving the surface smoothness of the sheet. Furthermore, by using at least one anionic group selected from the group consisting of a phosphorus oxoacid group and a substituent derived from a phosphorus oxoacid group, it is possible to obtain a sheet with superior transparency and heat resistance.

[0039] 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.

[0040] [ka]

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] β b+is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation made of an inorganic substance include 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.

[0046] 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).

[0047] 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.

[0048] [ka]

[0049] In the above structural formula, b and n are natural numbers, p is 0 or 1, and m is an arbitrary number (where 1 = b × m). When n is 2 or more, multiple p's may be the same number or different numbers. In the above structural formula, β b+ is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. Note that when multiple types of substituents represented by the above formula (2) are introduced into the fibrous cellulose, the multiple β b+ may be the same or different. The monovalent or higher cations 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.

[0050] The content (amount introduced) of the anionic group may be, for example, 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 anionic group 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 anionic group is a hydrogen ion (H + By setting the amount of anionic groups introduced within the above range, the content of organic onium ions that the fibrous cellulose can contain can be set within an appropriate range, thereby more effectively improving the dispersibility of the fibrous cellulose in organic solvents and resins.

[0051] The amount of anionic groups introduced into the fibrous cellulose can be measured, for example, by neutralization titration, which involves measuring the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to a slurry containing the obtained fibrous cellulose.

[0052] 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.

[0053] 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 groups (C type) = Amount of phosphorus oxoacid groups (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)

[0054] 2 is a graph showing the relationship between the amount of NaOH added dropwise to a dispersion containing fibrous cellulose having carboxy groups as anionic groups 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).

[0055] 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)

[0056] When measuring the amount of anionic groups using titration, adding too much sodium hydroxide solution or titrating too quickly can result in a lower than expected amount of anionic groups, leading to inaccurate results. An appropriate amount and titration interval is, for example, titrating 10 to 50 μL of 0.1 N sodium hydroxide solution every 5 to 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 anionic groups 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.

[0057] 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.

[0058] (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.

[0059] As a fiber raw material containing cellulose, for example, cellulose contained in sea squirts or bacterial cellulose produced by acetic acid bacteria can be used.Furthermore, instead of a fiber raw material containing cellulose, fibers formed from linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can also be used.

[0060] <Phosphorus oxoacid group introduction step> The process for producing fine fibrous cellulose includes an anionic group introduction step. An example of the anionic group introduction step is a phosphorus oxo acid group introduction step. The phosphorus oxo acid group introduction step is a step in which at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing phosphorus oxo acid groups by reacting with hydroxyl groups in a cellulose-containing fiber raw material is allowed to act on the cellulose-containing fiber raw material. This step results in the production of phosphorus oxo acid group-introduced fibers.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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).

[0070] 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.

[0071] 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.

[0072] 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.

[0073] The amount of phosphorus oxoacid groups introduced into the fiber raw material may be, for example, 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 (introduced amount) 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 controlling the amount of phosphorus oxoacid groups introduced within the above range, the content of organic onium ions that the fibrous cellulose may contain can be controlled within an appropriate range, thereby more effectively improving the dispersibility of the fibrous cellulose in organic solvents and resins. Furthermore, by controlling the amount of phosphorus oxoacid groups introduced within the above range, a sheet with excellent surface smoothness can be obtained.

[0074] <Carboxy group introduction step> The process for producing fine fibrous cellulose may include a carboxyl group introduction step as an anionic group 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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 per gram (mass) of fiber raw material is 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. 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 5.80 mmol / g or less per gram (mass) of fine fibrous cellulose. By adjusting the amount of carboxyl groups introduced within the above range, the content of organic onium ions that the fine fibrous cellulose may contain can be adjusted to an appropriate range, thereby more effectively improving the dispersibility of the fibrous cellulose in organic solvents and resins. Furthermore, by keeping the amount of carboxyl groups introduced within the above range, a sheet with excellent surface smoothness can be obtained.

[0079] <Sulfur oxoacid group introduction step> The process for producing fine fibrous cellulose may include a sulfur oxoacid group introduction step as an anionic group introduction step, in which hydroxyl groups in a cellulose-containing fiber raw material react with sulfur oxoacid to obtain cellulose fibers having sulfonic groups (sulfonic group-introduced fibers).

[0080] 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.

[0081] 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.

[0082] 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.

[0083] The amount of sulfur oxo groups introduced into the cellulose raw material should be 0.50 mmol / g or more per gram (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 amount of sulfur oxo acid groups introduced is preferably 5.00 mmol / g or less per gram (mass) of fibrous cellulose, more preferably 3.00 mmol / g or less. By adjusting the amount of sulfur oxo acid groups introduced within the above range, the content of organic onium ions contained in the fine fibrous cellulose can be adjusted to an appropriate range, thereby more effectively improving the dispersibility of the fibrous cellulose in organic solvents and resins. Furthermore, by adjusting the amount of sulfur oxo acid groups introduced within the above range, a sheet with excellent surface smoothness can be obtained.

[0084] <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 anionic group 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 hydroxyl groups to cause a reaction, thereby introducing carboxyl groups into the fiber raw material.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] <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 anionic group 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.

[0089] <<Alkali cellulose>> When introducing anionic groups into a fiber raw material, it is preferable to convert the cellulose contained in the fiber raw material into alkali cellulose by treating it with an alkaline solution. This treatment causes ionic dissociation of some of the hydroxyl groups in the cellulose, thereby increasing its nucleophilicity (reactivity). The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. Due to their high versatility, it is preferable to use, for example, sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, or tetrabutylammonium hydroxide. The conversion into alkali cellulose may be carried out simultaneously with the introduction of anionic groups, before the introduction, or at both the same time.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] When anionic group introduction and alkali cellulose formation are not performed simultaneously, alkali cellulose formation is preferably performed prior to the introduction of anionic groups. In this case, the alkali cellulose obtained by the alkali cellulose formation treatment is preferably subjected to solid-liquid separation and water removal using a common deliquoring method such as centrifugation or filtration. This improves the reaction efficiency in the subsequent anionic group introduction step. The cellulose fiber concentration after solid-liquid separation is preferably 5% to 50%, more preferably 10% to 40%, and even more preferably 15% to 35%.

[0095] <Phosphonic or Phosphine Group Introduction Step (Phosphoalkylation Step)> The process for producing fine fibrous cellulose may include a phosphonic or phosphine group introduction step (phosphoalkylation step) as an anionic group 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] <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 anionic group 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.

[0102] 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 olefin sulfonates include sodium 2-chloroethanesulfonate, sodium vinylsulfonate, sodium p-styrenesulfonate, and 2-acrylamido-2-methylpropanesulfonic acid. Among these, compound E is particularly preferred in terms of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. B is preferably sodium vinyl sulfonate. Furthermore, as an optional component, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> in the same manner, and the amount added is also preferably as described above.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] <Carboxyalkylation step (third carboxy group introduction step)> The process for producing fine fibrous cellulose may include a carboxyalkylation step as an anionic group introduction step. 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] <Cleaning process> In the method for producing fine fibrous cellulose, a washing step can be carried out on the anionic group-introduced fibers as needed. The washing step is carried out by washing the anionic group-introduced fibers with water or an organic solvent, for example. The washing step may be carried out after each step described below, and the number of washings carried out in each washing step is not particularly limited.

[0114] <Alkali treatment process> When producing fine fibrous cellulose, the fiber raw material may be subjected to an alkali treatment between the anionic group introduction step and the defibration step described below. The alkali treatment method is not particularly limited, but examples thereof include a method of immersing anionic group-introduced fibers in an alkali solution.

[0115] 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.

[0116] The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably from 5°C to 80°C, and more preferably from 10°C to 60°C. The immersion time of the anionic group-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably from 5 minutes to 30 minutes, and more preferably from 10 minutes to 20 minutes. The amount of alkaline solution used in the alkaline treatment is not particularly limited, but is preferably from 100% by mass to 100,000% by mass, and more preferably from 1,000% by mass to 10,000% by mass, based on the absolute dry mass of the anionic group-introduced fiber.

[0117] In order to reduce the amount of alkaline solution used in the alkaline treatment step, the anionic group-introduced fiber may be washed with water or an organic solvent after the anionic group-introducing step and before the alkaline treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkaline-treated anionic group-introduced fiber with water or an organic solvent after the alkaline treatment step and before the defibrating treatment step.

[0118] <Acid treatment process> When producing fine fibrous cellulose, the fiber raw material may be subjected to an acid treatment between the step of introducing anionic groups and the defibration treatment step described below. For example, the anionic group introduction step, acid treatment, alkali treatment, and defibration treatment may be performed in this order.

[0119] 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.

[0120] 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 mass% to 100,000 mass%, and more preferably, 1,000 mass% to 10,000 mass%, based on the absolute dry mass of the fiber raw material.

[0121] <Defibrillation process> The anionic group-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), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision grinder, a ball mill, a bead mill, a disk 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.

[0122] In the defibration process, for example, the anionic group-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).

[0123] The solid content concentration of the fine fibrous cellulose during the defibration treatment can be appropriately set. In addition, the slurry obtained by dispersing the anionic group-introduced fibers in a dispersion medium may contain solids other than the anionic group-introduced fibers, such as urea having hydrogen bonding properties.

[0124] (organic onium ions) The fine fibrous cellulose contains organic onium ions as counter ions of the anionic groups. In this embodiment, at least a portion of the organic onium ions are present as counter ions of the fibrous cellulose, but free organic onium ions may also be present in the sheet. Note that the organic onium ions do not form covalent bonds with the fibrous cellulose.

[0125] The organic onium ion preferably satisfies at least one of the following conditions (a) and (b): (a) Contains a hydrocarbon group having 5 or more carbon atoms. (b) The total number of carbon atoms is 17 or more. That is, the fibrous cellulose preferably contains, as a counter ion of the anionic group, at least one selected from an organic onium ion containing a hydrocarbon group having 5 or more carbon atoms and an organic onium ion having a total carbon number of 17 or more. By using an organic onium ion that satisfies at least one of the conditions (a) and (b) above, the dispersibility of the fine fibrous cellulose in organic solvents and resins can be more effectively improved.

[0126] The hydrocarbon group having 5 or more carbon atoms is preferably an alkyl group having 5 or more carbon atoms or an alkylene group having 5 or more carbon atoms, more preferably an alkyl group having 6 or more carbon atoms or an alkylene group having 6 or more carbon atoms, even more preferably an alkyl group having 7 or more carbon atoms or an alkylene group having 7 or more carbon atoms, and particularly preferably an alkyl group having 10 or more carbon atoms or an alkylene group having 10 or more carbon atoms. Of these, the organic onium ion preferably has an alkyl group having 5 or more carbon atoms, and more preferably an organic onium ion that includes an alkyl group having 5 or more carbon atoms and has a total of 17 or more carbon atoms.

[0127] The organic onium ion is preferably an organic onium ion represented by the following general formula (A).

[0128] [ka]

[0129] In the general formula (A), M is referred to as the central element of the organic onium ion. M is preferably a nitrogen atom or a phosphorus atom. R1 to R4 each independently represent a hydrogen atom or an organic group. However, it is preferable that at least one of R1 to R4 is an organic group having 5 or more carbon atoms, or that the total number of carbon atoms of R1 to R4 is 17 or more. Among these, M is preferably a nitrogen atom. That is, the organic onium ion is preferably an organic ammonium ion. Furthermore, it is preferable that at least one of R1 to R4 is an alkyl group having 5 or more carbon atoms, and that the total number of carbon atoms of R1 to R4 is 17 or more.

[0130] Examples of organic onium ions include lauryltrimethylammonium, cetyltrimethylammonium, stearyltrimethylammonium, octyldimethylethylammonium, lauryldimethylethylammonium, didecyldimethylammonium, lauryldimethylbenzylammonium, tributylbenzylammonium, methyltri-n-octylammonium, hexylammonium, n-octylammonium, dodecylammonium, tetradecylammonium, hexadecylammonium, stearylammonium, N,N-dimethyldodecylammonium, N,N-dimethyltetradecylammonium, N,N-dimethylhexadecylammonium, N,N-dimethyl-n-octadecylammonium, dihexylammonium, di(2 (-ethylhexyl)ammonium, di-n-octylammonium, didecylammonium, didodecylammonium, didecylmethylammonium, N,N-didodecylmethylammonium, polyoxyethylenedodecylammonium, alkyldimethylbenzylammonium, di-n-alkyldimethylammonium, behenyltrimethylammonium, tetraphenylphosphonium, tetraoctylphosphonium, acetonyltriphenylphosphonium, allyltriphenylphosphonium, amyltriphenylphosphonium, benzyltriphenylphosphonium, ethyltriphenylphosphonium, diphenylpropylphosphonium, triphenylphosphonium, tricyclohexylphosphonium, tri-n-octylphosphonium, etc. The alkyl group in alkyldimethylbenzylammonium and di-n-alkyldimethylammonium can be a linear alkyl group having from 8 to 18 carbon atoms.

[0131] As shown in general formula (A), the central element of an organic onium ion is bonded to a total of four groups or hydrogen atoms. In the names of the organic onium ions mentioned above, if there are fewer than four groups bonded, the remaining groups are bonded to hydrogen atoms to form the organic onium ion. For example, in the case of N,N-didodecylmethylammonium, it can be determined from the name that two dodecyl groups and one methyl group are bonded. In this case, a hydrogen atom is bonded to the remaining group to form the organic onium ion.

[0132] When the organic onium contains O atoms, the larger the mass ratio of C atoms to O atoms (C / O ratio), the better, and for example, C / O > 5. By making the C / O ratio greater than 5, it becomes easier to obtain a fibrous cellulose concentrate when organic onium ions or compounds that form organic onium ions upon neutralization are added to a slurry containing fine fibrous cellulose.

[0133] The molecular weight of the organic onium ion is preferably 2000 or less, more preferably 1800 or less. By setting the molecular weight of the organic onium ion within the above range, the handleability of the fibrous cellulose can be improved. Furthermore, by setting the molecular weight of the organic onium ion within the above range, a decrease in the content of fibrous cellulose in the sheet can be suppressed.

[0134] The content of organic onium ions is preferably 0.5 to 2 times the molar amount of the anionic groups contained in the fine fibrous cellulose, but is not particularly limited thereto. The content of organic onium ions can be measured by tracking the atoms typically contained in the organic onium ions. Specifically, if the organic onium ions are ammonium ions, the amount of nitrogen atoms is measured, and if the organic onium ions are phosphonium ions, the amount of phosphorus atoms is measured. Note that if the fine fibrous cellulose contains nitrogen atoms or phosphorus atoms in addition to organic onium ions, it is sufficient to measure the amount of the target atoms after performing a method of extracting only the organic onium ions, such as an extraction operation using an acid.

[0135] The organic onium ion is preferably an ion that exhibits hydrophobicity. That is, the fine fibrous cellulose in this embodiment exhibits hydrophobicity due to the presence of the organic onium ion. As a result, dispersibility in organic solvents and resins is improved, and a sheet exhibiting the desired viscosity tensile modulus and haze can be obtained. Furthermore, such a sheet has high surface smoothness.

[0136] (optional ingredient) The sheet of this embodiment may be a sheet made of the above-mentioned fine fibrous cellulose and resin, or may contain optional components in addition to the above-mentioned fine fibrous cellulose and resin, such as surfactants, organic ions, coupling agents, inorganic layered compounds, inorganic compounds, leveling agents, preservatives, antifoaming agents, organic particles, lubricants, antistatic agents, UV protection agents, dyes, pigments, stabilizers, magnetic powders, alignment promoters, plasticizers, dispersants, and crosslinking agents.

[0137] The sheet may also contain an organic solvent used in the production process as an optional component. When the above-mentioned fine fibrous cellulose and resin are dispersed in an organic solvent in the production process, the organic solvent contained in the dispersion may remain in the sheet. In this way, the sheet may contain the component used in the production process.

[0138] (Sheet manufacturing method) The sheet manufacturing method preferably includes the steps of: adding organic onium ions or compounds that form organic onium ions upon neutralization to the fine fibrous cellulose-containing slurry obtained through the above-described defibration step to obtain a fibrous cellulose aggregate (concentrate); obtaining a dispersion containing the fibrous cellulose aggregate (concentrate) and a resin; and forming a sheet from the dispersion. In the step of obtaining the dispersion containing the fibrous cellulose aggregate (concentrate) and a resin, a resin precursor may be used instead of the resin. In addition, the step of obtaining the dispersion containing the fibrous cellulose aggregate (concentrate) and a resin may include a step of dispersing the fibrous cellulose aggregate (concentrate) in an organic solvent.

[0139] In the step of obtaining a fibrous cellulose aggregate (concentrate), the above-mentioned organic onium ions or a compound (hydrophobizing agent) that forms organic onium ions upon neutralization is added to the fine fibrous cellulose-containing slurry obtained in the above-mentioned defibration treatment step. In this case, the organic onium ions are preferably added as a solution containing the organic onium ions, and more preferably as an aqueous solution containing the organic onium ions.

[0140] An aqueous solution containing an organic onium ion usually contains the organic onium ion and a counter ion (anion). When preparing an aqueous solution of an organic onium ion, if the organic onium ion and the corresponding counter ion have already formed a salt, the organic onium ion can be dissolved in water as is. When preparing an aqueous solution of an organic onium ion, if the organic onium ion and the corresponding counter ion have already formed a salt, the organic onium ion can be dissolved in water or hot water.

[0141] In addition, organic onium ions may be generated only after neutralization with an acid, such as dodecylamine. In this case, the organic onium ions are obtained by the reaction of a compound that forms an organic onium ion upon neutralization with an acid. In this case, examples of acids used for neutralization include inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as lactic acid, acetic acid, formic acid, and oxalic acid. In the aggregation step, a compound that forms an organic onium ion upon neutralization may be directly added to the fibrous cellulose-containing slurry, and the anionic groups contained in the fibrous cellulose may be used as counterions to convert the compound into an organic onium ion.

[0142] The amount of organic onium ion added is preferably 2% by mass or more, more preferably 10% by mass or more, even more preferably 50% by mass or more, and particularly preferably 100% by mass or more, based on the total mass of the fibrous cellulose, and is preferably 1000% by mass or less, based on the total mass of the fibrous cellulose. The number of moles of organic onium ions to be added is preferably at least 0.2 times, more preferably at least 0.5 times, and even more preferably at least 1.0 times the amount (molar number) of inorganic oxo acid groups contained in the fibrous cellulose multiplied by the valence, and is preferably no more than 10 times the amount (molar number) of inorganic oxo acid groups contained in the fibrous cellulose multiplied by the valence.

[0143] When organic onium ions are added and stirred, aggregates are generated in the fibrous cellulose-containing slurry. These aggregates are formed by agglomeration of fibrous cellulose having organic onium ions as counter ions. In this specification, such aggregates are also referred to as fibrous cellulose concentrates. The fibrous cellulose-containing slurry in which aggregates have been generated can be filtered under reduced pressure to recover the fibrous cellulose aggregates (concentrates).

[0144] The obtained fibrous cellulose aggregate may be washed with ion-exchanged water. Repeated washing of the fibrous cellulose aggregate with ion-exchanged water can remove excess organic onium ions and the like contained in the fibrous cellulose aggregate.

[0145] The solid content concentration of the obtained fibrous cellulose aggregate is preferably 5% by mass or more, more preferably 15% by mass or more, and even more preferably 25% by mass or more, and may be 100% by mass.

[0146] The moisture content of the fibrous cellulose aggregate may be 0% by mass, 0.5% by mass or more, 1% by mass or more, 3% by mass or more, or 5% by mass or more, based on the total mass of the fibrous cellulose aggregate. The moisture content of the fibrous cellulose aggregate is preferably 20% by mass or less, more preferably 15% by mass or less, based on the total mass of the fibrous cellulose aggregate. The moisture content of the fibrous cellulose aggregate can be measured by placing 200 mg of the fibrous cellulose aggregate on a moisture meter (MS-70, manufactured by A&D Co., Ltd.) and heating at 140°C. The moisture content of the fibrous cellulose aggregate can be calculated from the measured moisture content.

[0147] The fibrous cellulose agglomerate may be one that has further undergone a drying process, an aging process, a spray drying process, a granulation process, a sheeting process, a heating process, a wetting process, a grinding process, a spraying process, a dipping process, a filtration process, a freezing process, a sublimation process, a water squeezing process, a pressurized dehydration process, a centrifugal dehydration process, a surface treatment process, etc. Among these, the fibrous cellulose agglomerate is preferably one that has undergone a drying process, which allows for the production of a fibrous cellulose agglomerate with a low water content.

[0148] In the step of obtaining a dispersion containing fibrous cellulose aggregates (concentrate) and a resin, the fibrous cellulose aggregates (concentrate) obtained in the step of obtaining the fibrous cellulose aggregates (concentrate) described above are mixed with a resin to obtain a fibrous cellulose resin dispersion. In this case, the resin dispersion may contain an organic solvent. For example, in the step of obtaining a dispersion containing fibrous cellulose aggregates (concentrate) and a resin, the fibrous cellulose aggregates (concentrate) and the resin may be simultaneously dispersed in a single organic solvent, the fibrous cellulose aggregates (concentrate) may be dispersed in an organic solvent and then mixed with the resin, the resin may be dispersed in an organic solvent and then mixed with the fibrous cellulose aggregates (concentrate), or the fibrous cellulose aggregates (concentrate) and the resin may be dispersed in separate organic solvents and then the respective dispersions may be mixed. This dispersion step is also referred to as a redispersion step, since it involves redispersing the fibrous cellulose aggregates (concentrate) in a resin or solvent.

[0149] In the re-dispersion step, a resin precursor may be used instead of the resin, or both the resin and the resin precursor may be used. Examples of resin precursors include the monomers and oligomers that constitute the above-mentioned resins. When the resin or resin precursor is liquid, the fibrous cellulose aggregate (concentrate) may be dispersed in the liquid resin or resin precursor using a high-pressure homogenizer or the like to form a dispersion. In this case, the liquid resin or resin precursor can serve as a dispersion medium for the fibrous cellulose aggregate (concentrate), so the resulting resin dispersion does not need to contain an organic solvent.

[0150] When an organic solvent is used in the re-dispersion step, the relative dielectric constant of the organic solvent used at 25°C is preferably 60 or less, more preferably 50 or less. Since the fibrous cellulose in this embodiment can exhibit excellent dispersibility even in an organic solvent with a low relative dielectric constant, the relative dielectric constant of the organic solvent at 25°C may be 45 or less, 40 or less, or 35 or less.

[0151] In addition, the Hansen solubility parameter (HSP) δd of the organic solvent is 5 MPa. 1 / 2 More than 20MPa 1 / 2 Preferably, it is 10 MPa or less. 1 / 2 Over 19MPa 1 / 2 It is preferable that Δh is 1 MPa or less. 1 / 2 More than 40MPa 1 / 2 Preferably, it is 2 MPa or less. 1 / 2 More than 30MPa 1 / 2 It is more preferable that Δp is 0 MPa or less. 1 / 2 More than 4MPa 1 / 2 The range is as follows: δh is 0 MPa 1 / 2 More than 6MPa 1 / 2 It is also preferable that the following ranges are simultaneously satisfied.

[0152] Examples of organic solvents include methanol (dielectric constant 32.6), ethanol (dielectric constant 24.3), n-propyl alcohol (dielectric constant 20.1), isopropyl alcohol (IPA) (dielectric constant 18.62), 1-butanol (dielectric constant 18), m-cresol (dielectric constant 11.8), glycerin (dielectric constant 42.5), acetic acid (dielectric constant 6.15), pyridine (dielectric constant 12.3), tetrahydrofuran (THF) (dielectric constant 7.5), acetone (dielectric constant 20.7), methyl ethyl ketone (MEK) (dielectric constant 15.45), and ethyl acetate ( Examples of suitable organic solvents include toluene (dielectric constant 2.4), hexane (dielectric constant 2.3), styrene (dielectric constant 2.3 to 3.4), diethyl ether (dielectric constant 4.3), and chloroform (dielectric constant 4.8). Among these, the organic solvent is preferably at least one selected from the group consisting of toluene, xylene, and styrene.

[0153] When an organic solvent is used in the redispersion step, the organic solvent is added in an amount of preferably 30% by mass or more, more preferably 45% by mass or more, and even more preferably 60% by mass or more, based on the total mass of the dispersion. The amount of organic solvent added is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less, based on the total mass of the dispersion.

[0154] The resulting dispersion may contain water in addition to the organic solvent, but the water content relative to the total mass of the dispersion is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. In this embodiment, it is preferable that the dispersion medium does not substantially contain water, and it is particularly preferable that the water content relative to the total mass of the dispersion is 0% by mass.

[0155] The dispersing device used to disperse fibrous cellulose aggregates (concentrates) in an organic solvent, liquid resin, or resin precursor can be, for example, the same as the defibration processing device described above. Among these, when dispersing fibrous cellulose aggregates (concentrates) in an organic solvent, liquid resin, or resin precursor, it is preferable to use a high-pressure homogenizer or ultra-high-pressure homogenizer. Using a high-pressure homogenizer in the redispersion step improves the redispersibility of the fibrous cellulose aggregates (concentrates), resulting in a sheet with a high tensile modulus and reduced haze. As a result, a sheet with excellent surface smoothness can be obtained.

[0156] In the sheet manufacturing method of this embodiment, it is preferable to include a step of heating the suspension obtained by dispersing fibrous cellulose aggregates (concentrate) in an organic solvent, a liquid resin, or a resin precursor during or before the redispersion step. That is, the sheet manufacturing method preferably further includes a step of suspending at least the fibrous cellulose aggregates (concentrate) in an organic solvent, a liquid resin, or a resin precursor to obtain a suspension, and a step of heating the suspension and treating it with a high-pressure homogenizer or an ultra-high-pressure homogenizer to obtain a dispersion. In this case, the sheet manufacturing method preferably includes a step of adding an organic onium ion or a compound that forms an organic onium ion by neutralization to the fine fibrous cellulose-containing slurry obtained through the above-mentioned defibration step to obtain fibrous cellulose aggregates (concentrate), a step of suspending the fibrous cellulose aggregates (concentrate) in an organic solvent, a liquid resin, or a liquid resin precursor to obtain a suspension, and a step of heating the suspension and treating it with a high-pressure homogenizer or an ultra-high-pressure homogenizer. Among these, the sheet manufacturing method preferably includes the steps of: adding organic onium ions or a compound that forms organic onium ions upon neutralization to a slurry containing fine fibrous cellulose obtained through the above-mentioned defibration step to obtain a fibrous cellulose aggregate (concentrate), suspending the fibrous cellulose aggregate (concentrate) in an organic solvent to obtain a suspension, heating the suspension and treating it with a high-pressure homogenizer or an ultra-high-pressure homogenizer to obtain a first dispersion, mixing the first dispersion with a resin or a resin precursor to obtain a second dispersion, and forming a sheet from the second dispersion. Before the step of mixing the first dispersion with the resin or the resin precursor to obtain the second dispersion, a step of dispersing the resin or the resin precursor in an organic solvent may be provided.

[0157] The suspension may contain an organic solvent and a resin and / or a resin precursor, and in this case, the suspension containing the fibrous cellulose aggregate (concentrate), the resin and / or the resin precursor, and the organic solvent may be heated. That is, the sheet manufacturing method may include the steps of: adding an organic onium ion or a compound that forms an organic onium ion by neutralization to the fine fibrous cellulose-containing slurry obtained through the above-mentioned defibration step to obtain a fibrous cellulose aggregate (concentrate), suspending the fibrous cellulose aggregate (concentrate) and the resin and / or the resin precursor in an organic solvent to obtain a suspension, heating the suspension and treating it with a high-pressure homogenizer or an ultra-high-pressure homogenizer to obtain a dispersion, and forming a sheet from the dispersion.

[0158] In the step of heating the suspension, the suspension is preferably heated to 40°C or higher. In the heating step, the temperature of the suspension is preferably 100°C or lower. By heating the suspension to the above temperature, the redispersibility of the fibrous cellulose aggregates (concentrate) is improved, and a sheet with a high tensile modulus and reduced haze is obtained. As a result, a sheet with excellent surface smoothness is easily obtained.

[0159] Conventionally, in the redispersion step, cooling has usually been carried out to prevent thermal denaturation of the fibrous cellulose aggregates (concentrates). However, in this embodiment, a heating step is intentionally provided in the redispersion step or before the redispersion step. By providing such a heating step, it has been possible to successfully obtain a sheet with a higher tensile modulus and less haze.

[0160] When the suspension is heated in the redispersion step or before the redispersion step, it is preferable that the liquid temperature after passing through the dispersion device be 40°C or higher. When a high-pressure homogenizer or ultra-high-pressure homogenizer is used as the dispersion device, it is preferable that the liquid temperature after passing through the grinding mechanism be 40°C or higher. In order to raise the liquid temperature after passing through the dispersion device to 40°C or higher, for example, it is possible to increase the pressure during passage through the dispersion device, reduce the inner diameter of the internal flow path of the grinding treatment unit, increase the pumping speed, heat the grinding treatment unit before and / or after passing through the pump, or heat the suspension to be tested in advance.

[0161] In this specification, the step of preheating the suspension to be tested is sometimes referred to as a preheating step. In the preheating step, the suspension is preferably heated to a liquid temperature of 40°C or higher and 100°C or lower. In this embodiment, it is preferable to provide such a preheating step. By preheating the suspension before treatment with the high-pressure homogenizer to 40°C or higher, the dispersibility of the fine fibrous cellulose in organic solvents and resins is further improved, making it easier to obtain a sheet with a higher tensile modulus and lower haze.

[0162] The step of obtaining the dispersion may further include a step of dispersing an optional component in the obtained dispersion. The optional component used in this step may include the optional components described above.

[0163] 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. In the re-dispersion step, if the dispersion contains a resin precursor instead of a resin, or if the dispersion contains both a resin and a resin precursor, polymerization or crosslinking of the resin precursor may be allowed to proceed in the sheet-forming step.

[0164] <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.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] <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.

[0172] 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.

[0173] 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.

[0174] 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.

[0175] (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.

[0176] <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.

[0177] Examples of natural resins include rosin-based resins such as rosin, rosin ester, and hydrogenated rosin ester.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] <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.

[0184] 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.

[0185] 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.

[0186] (Application) The sheet of this embodiment has a high tensile modulus and reduced haze, and therefore may be used for optical components. For example, it can be used as a light-transmitting substrate for various display devices, various solar cells, and the like, various protective films, and various decorative films. The laminate sheet of the present invention is also suitable for applications such as substrates for electronic devices, lenses, lens covers, components for home appliances, window materials for various vehicles and buildings, interior materials, exterior materials, and packaging materials. [Example]

[0187] 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.

[0188] <Manufacturing example A> [Phosphorylation] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper. 2A sheet-like pulp (with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012) was used. This raw pulp was subjected to a phosphorus oxo-oxidation 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 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, to obtain a chemical-impregnated pulp. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165°C for 250 seconds to introduce phosphate groups into the cellulose in the pulp, thereby obtaining a phosphorylated pulp. The phosphate groups were introduced into the cellulose via ester bonds.

[0189] 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.

[0190] 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 and washed to obtain a neutralized phosphorylated pulp.

[0191] The infrared absorption spectrum of the obtained phosphorylated pulp was measured using FT-IR. -1 The absorption due to the P=O of the phosphate group was observed around the 2θ=14° to 17° and the 2θ=22° to 23° angle, confirming that the pulp had phosphate groups. The phosphorylated pulp was analyzed using an X-ray diffractometer, and typical peaks were observed at two positions, around 2θ=14° to 17° and 2θ=22° to 23°, confirming the presence of cellulose type I crystals.

[0192] Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2% by mass. This slurry was treated six times with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (A) containing fine fibrous cellulose.

[0193] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of phosphate groups (amount of first dissociated acid groups, strong acid groups) measured by the method described below in [Measurement of amount of phosphorus oxo acid groups] was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0194] <Manufacturing example B> [Phosphorous] A phosphite pulp was obtained by the same procedure as in Production Example A, except that 33 parts by mass of phosphorous acid (phosphonic acid) was used instead of ammonium dihydrogen phosphate. The phosphorous acid group was introduced into the cellulose via an ester bond.

[0195] The infrared absorption spectrum of the obtained phosphorous-oxidized pulp was measured using FT-IR. -1 The absorption due to P=O of the phosphonic acid group, which is a tautomer of the phosphorous acid group, was observed near the α-axis, confirming that the phosphorous acid group (phosphonic acid group) had been added to the pulp. Furthermore, when the obtained phosphorous-oxidized pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ=14° to 17° and around 2θ=22° to 23°, confirming the presence of cellulose type I crystals.

[0196] The obtained phosphited pulp was treated in a wet pulp-forming apparatus in the same manner as in Production Example A to obtain a fine fibrous cellulose dispersion (B) containing fine fibrous cellulose.

[0197] X-ray diffraction confirmed that this fine fibrous cellulose maintained cellulose type I crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of phosphorous acid groups (amount of first dissociated acid) measured by the method described below in [Measurement of phosphorus oxo acid group amount] was 1.51 mmol / g. The total amount of dissociated acid was 1.54 mmol / g.

[0198] <Manufacturing example C> [Sulfation] Sulfated pulp was obtained in the same manner as in Production Example A, except that 38 parts by mass of amidosulfuric acid (sulfamic acid) was used instead of ammonium dihydrogen phosphate and the heating time was extended to 20 minutes. The sulfate ester group was introduced into the cellulose via an ester bond.

[0199] The infrared absorption spectrum of the obtained sulfated pulp was measured using FT-IR. -1 The absorption due to the S=O of the sulfate ester group was observed around the α-axis, confirming that sulfate ester groups had been added to the pulp. Furthermore, when the obtained sulfated pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ=14° to 17° and around 2θ=22° to 23°, confirming the presence of cellulose type I crystals.

[0200] Ion-exchanged water was added to the obtained sulfated pulp and stirred to prepare a slurry with a solids concentration (fibrous cellulose concentration) of 2% by mass. This slurry was treated six times in a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (C) containing fine fibrous cellulose.

[0201] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3-5 nm. The amount of sulfur oxoacid groups measured by the method described below in [Measurement of sulfur oxoacid and sulfonic acid groups] was 1.47 mmol / g.

[0202] <Manufacturing example D> [Maleic acid esterification] A sheet (solids concentration 90% by mass) made from softwood bleached kraft pulp (NBKP) was mixed for 15 seconds at 20,000 rpm using a hand mixer (Osaka Chemical, Labo Millser PLUS) to produce a fluffy fluffing pulp (solids concentration 90% by mass). 100 parts by mass of the fluffy fluffing pulp and 50 parts by mass of maleic anhydride were placed in an autoclave and treated at 150°C for 2 hours to obtain carboxyl-introduced pulp. The carboxyl groups were introduced into the cellulose via ester bonds.

[0203] The resulting carboxylated pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting carboxylated 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.

[0204] The infrared absorption spectrum of the obtained carboxyl-introduced pulp was measured using FT-IR. -1 Absorption due to carboxyl groups was observed around 2θ = 14° to 17° and 2θ = 22° to 23°, confirming that the pulp had been maleated. Furthermore, when the carboxyl-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0205] Ion-exchanged water was added to the obtained carboxyl-introduced pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated six times with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (D) containing fine fibrous cellulose.

[0206] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxyl groups measured by the method described below in "Measurement of Carboxy Group Amount" was 1.22 mmol / g.

[0207] <Production Example E> [Carboxyethylated] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper. 2 A sheet-like pulp (with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured according to JIS P 8121-2:2012) was used. A chemical solution consisting of 250 parts by mass of 12N NaOH aqueous solution, 163 parts by mass of 2-chloropropionic acid, and 140 parts by mass of ion-exchanged water (total 553 parts by mass) was added to 100 parts by mass (bone dry mass) of this raw pulp to obtain a chemical-impregnated pulp. The resulting chemical-impregnated pulp was then heated in a hot air dryer at 165°C for 10 minutes to introduce carboxyethyl groups (carboxy groups) into the cellulose in the pulp, yielding a carboxy-introduced pulp. The carboxy groups were introduced into the cellulose via ether bonds.

[0208] The resulting carboxylated pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting carboxylated 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.

[0209] Next, the washed carboxylated pulp was neutralized as follows: First, the washed carboxylated pulp was diluted with 10 L of ion-exchanged water, and then a 1 N aqueous sodium hydroxide solution was added little by little while stirring to obtain a carboxylated pulp slurry with a pH of 12 to 13. Next, the carboxylated pulp slurry was dehydrated and washed to obtain a neutralized carboxylated pulp.

[0210] When the carboxyl-group-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming that it contained cellulose type I crystals.

[0211] Ion-exchanged water was added to the obtained carboxyl-introduced pulp to prepare a slurry with a solid content of 2% by mass. This slurry was treated six times with a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (E) containing fine fibrous cellulose.

[0212] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxyl groups measured by the method described below in [Measurement of Carboxy Group Amount] was 1.41 mmol / g.

[0213] <Manufacturing example F> [Sulfoethylation] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper. 2A sheet-like pulp (with a Canadian Standard Freeness (CSF) of 700 ml when disintegrated and measured in accordance with JIS P 8121-2:2012) was used. A chemical solution consisting of 180 parts by mass of a 2N NaOH aqueous solution and 780 parts by mass of a 25% by mass sodium vinyl sulfonate aqueous solution (total 960 parts by mass) was added to 100 parts by mass (bone dry mass) of this raw pulp to obtain a chemical solution-impregnated pulp. The resulting chemical solution-impregnated pulp was then heated in a hot air dryer at 165°C for 16 minutes to introduce sulfoethyl groups (sulfonic groups) into the cellulose in the pulp, yielding sulfoethyl group-introduced pulp (sulfonic group-introduced pulp). The sulfoethyl groups were introduced into the cellulose via ether bonds.

[0214] The resulting sulfoethyl group-introduced pulp was then washed. The washing process involved pouring ion-exchanged water over the resulting sulfoethyl group-introduced pulp to obtain a pulp dispersion, which was then stirred to uniformly disperse the pulp, followed by filtration and dehydration. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less.

[0215] When the sulfoethyl group-introduced pulp was analyzed using an X-ray diffractometer, typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0216] Ion-exchanged water was added to the obtained sulfoethyl group-introduced pulp to prepare a slurry with a solid content of 2% by mass. This slurry was treated six times with a wet atomization device (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a fine fibrous cellulose dispersion (F) containing fine fibrous cellulose.

[0217] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystal structure. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3-5 nm. The amount of sulfur oxoacid groups measured by the method described below in [Measurement of sulfur oxoacid and sulfonic acid groups] was 1.48 mmol / g.

[0218] <Manufacturing example G> [TEMPO oxidation] Softwood kraft pulp (undried) manufactured by Oji Paper Co., Ltd. was used as the raw pulp. This raw pulp was subjected to an alkaline TEMPO oxidation treatment as follows: First, 100 parts by weight of the raw 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 10 mmol per 1.0 g of pulp 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, and the reaction was considered complete when no further change in pH was observed. The carboxyl group was introduced by oxidation of the hydroxyl group at the C6 position of cellulose.

[0219] 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.

[0220] The remaining aldehyde groups in this dehydrated sheet were further oxidized as follows: 100 parts by weight of the dehydrated sheet (dry mass equivalent) was dispersed in 10,000 parts by weight of 0.1 mol / L acetate buffer (pH 4.8). 113 parts by weight of 80% by weight sodium chlorite was then added, the container was immediately sealed, and the mixture was stirred at 500 rpm using a magnetic stirrer while reacting at room temperature for 48 hours to obtain a pulp slurry.

[0221] The resulting TEMPO-oxidized pulp was then washed. The pulp slurry after the additional 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.

[0222] The obtained TEMPO-oxidized pulp was analyzed using an X-ray diffractometer. Typical peaks were observed at two positions, around 2θ = 14° to 17° and around 2θ = 22° to 23°, confirming the presence of cellulose type I crystals.

[0223] Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solid content of 2% by mass. This slurry was treated six times at a pressure of 200 MPa in a wet pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion (G) containing fine fibrous cellulose.

[0224] X-ray diffraction confirmed that the obtained fine fibrous cellulose maintained cellulose type I crystals. Furthermore, the fiber width of the fine fibrous cellulose was measured using a transmission electron microscope and found to be 3 to 5 nm. The amount of carboxyl groups measured by the method described below in [Measurement of Carboxy Group Amount] was 1.80 mmol / g.

[0225] [Measurement of phosphorus oxoacid group content] In measuring the amount of phosphorus oxo acid groups (amount of phosphate groups or amount of phosphite groups) in fine fibrous cellulose, 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 fine fibrous cellulose dispersion was treated with an ion-exchange resin and then titrated with an alkali to measure the amount of phosphorus oxo acid 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 dispersion, 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 the slurry while adding 10 μL of 0.1 N sodium hydroxide solution every 5 seconds to the fine fibrous cellulose dispersion after ion exchange resin treatment. 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 curve plotting the measured pH against the amount of alkali added. Of these, the first maximum point of increment after starting the alkali addition is called the first endpoint, and the second maximum point of increment 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).

[0226] [Measurement of Carboxy Group Amount] In measuring the amount of carboxy groups in fine fibrous cellulose, 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 fine fibrous cellulose dispersion was treated with an ion-exchange resin, and then titrated with an alkali to measure the amount of carboxy 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 dispersion, shaking for 1 hour, and then pouring it onto a mesh with 90 μm openings to separate the resin from the slurry. The alkali titration was carried out by adding 50 μL of 0.1 N sodium hydroxide solution to the fine fibrous cellulose dispersion after treatment with the ion exchange resin every 30 seconds, while measuring the change in the pH value of the dispersion. The amount of carboxyl groups (mmol / g) was calculated by dividing the amount of alkali (mmol) required in the region corresponding to the first region shown in Figure 2 by the solid content (g) of the slurry to be titrated.

[0227] [Measurement of sulfur oxoacid and sulfonic acid groups] The amount of sulfur oxoacid groups or sulfonic groups in the fine fibrous cellulose 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).

[0228] Example 1 100 g of a 2.73 mass% aqueous solution of di-n-stearyldimethylammonium chloride (hereinafter also referred to as DSDMA) as a hydrophobizing agent was added to 100 g of fine fibrous cellulose dispersion (A) and stirred for 5 minutes, resulting in the formation of aggregates in the fine fibrous cellulose dispersion. The fine fibrous cellulose dispersion containing the aggregates was filtered under reduced pressure to obtain fine fibrous cellulose aggregates. The obtained fine fibrous cellulose aggregates were repeatedly washed with ion-exchanged water to remove excess di-n-stearyldimethylammonium chloride and eluted ions contained in the fine fibrous cellulose aggregates, thereby obtaining a fine fibrous cellulose concentrate. The obtained fine fibrous cellulose concentrate was air-dried to obtain a fine fibrous cellulose concentrate (A) with a solids concentration of 90 mass%.

[0229] Toluene was added to the fine fibrous cellulose concentrate (A) to give a suspension with a solids concentration (fibrous cellulose concentration) of 6% by mass. This suspension was then preheated in a hot water bath until the temperature of the suspension reached 40°C. The preheated suspension was treated five times at 100 MPa using a high-pressure homogenizer (Beryu-Mini, manufactured by Biryu Co., Ltd.). The liquid temperature after passing through the pulverization treatment section was measured. A toluene dispersion of fine fibrous cellulose was thus obtained.

[0230] Toluene was added to acrylic resin (1) (manufactured by DIC Corporation, Acrydic A-181) so that the acrylic resin concentration was 40% by mass, and the mixture was stirred to obtain an acrylic resin (1) solution.

[0231] 20.8 parts by mass of the toluene dispersion of fine fibrous cellulose, 59.4 parts by mass of the acrylic resin (1) solution, and 19.8 parts by mass of toluene were mixed to obtain a resin-containing fine fibrous cellulose dispersion. The ratio of the fine fibrous cellulose (A) to the acrylic resin (1) in the resin-containing fine fibrous cellulose dispersion was 5:95.

[0232] The resin-containing fine fibrous cellulose dispersion was applied to a release film using an applicator and dried for 10 minutes in a hot air dryer at 100°C to obtain a sheet. The film thickness of the obtained sheet was 70 μm. The haze, tensile modulus, and arithmetic mean roughness of the obtained sheet were measured using the methods described below.

[0233] [Haze Measurement] A test piece measuring 50 mm square was cut out from the sheet, and the haze of the test piece was measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K 7136:2000.

[0234] [Measurement of tensile modulus] The tensile modulus of the sheet was measured using a Tensilon tensile tester (manufactured by A&D Co., Ltd.) in accordance with JIS P 8113:2006, except that the test specimen size was changed to 75 mm × 15 mm and the extension rate was changed to 1 mm / min. When measuring the tensile modulus, the test specimens were conditioned at 23°C and 50% relative humidity for 24 hours.

[0235] [Measurement of arithmetic mean roughness] The arithmetic mean roughness (Ra) of the sheet surface was measured in accordance with JIS B 0601:1994 using a surface roughness meter (SE-3C, manufactured by Kosaka Laboratory Co., Ltd.). The measurement surface of the sheet was the surface that was not in contact with the release film. The measurement conditions for the surface roughness meter were a cutoff value of 0.8 mm and an evaluation length of 25 mm.

[0236] <Examples 2 to 7> Sheets were obtained in the same manner as in Example 1, except that the fine fibrous cellulose dispersion and the DSDMA aqueous solution having the concentration shown in the table below were used.

[0237] Example 8 A sheet was obtained in the same manner as in Example 1, except that the toluene suspension was not preheated before treatment with the high-pressure homogenizer.

[0238] Example 9 A sheet was obtained in the same manner as in Example 1, except that xylene was used instead of toluene as the dispersion medium for the fine fibrous cellulose.

[0239] Example 10 A sheet was obtained in the same manner as in Example 1, except that a 1.68 mass % aqueous solution of didecyldimethylammonium chloride (hereinafter also referred to as DDDMA) was used instead of the 3.86 mass % aqueous solution of di-n-stearyldimethylammonium chloride.

[0240] Example 11 A sheet was obtained in the same manner as in Example 1, except that acrylic resin (2) (NeoCryl B-734, manufactured by Kusumoto Chemicals Co., Ltd.) was used instead of acrylic resin (1).

[0241] Example 12 A sheet was obtained in the same manner as in Example 1, except that 8.3 parts by mass of the toluene dispersion of fine fibrous cellulose, 61.3 parts by mass of the acrylic resin (1) solution, and 30.4 parts by mass of toluene were mixed to obtain a resin-containing fine fibrous cellulose dispersion. The ratio of the fine fibrous cellulose (A) to the acrylic resin (1) in the resin-containing fine fibrous cellulose dispersion was 2:98.

[0242] Example 13 A sheet was obtained in the same manner as in Example 1, except that polystyrene (manufactured by Sigma-Aldrich Japan, weight average molecular weight 350,000, number average molecular weight 170,000) was used instead of the acrylic resin (1).

[0243] <Comparative Example 1> A sheet was obtained in the same manner as in Example 1, except that the toluene suspension was not preheated before treatment with the high-pressure homogenizer, and the toluene suspension was treated for 10 minutes using an ultrasonic homogenizer (Hielscher, UP400S) instead of the high-pressure homogenizer.

[0244] [Table 1]

[0245] [Table 2]

[0246] DSDMA: Di-n-stearyldimethylammonium chloride DDDMA: Didecyldimethylammonium chloride Acrylic resin (1): Acrydic A-181 (Tg: 35°C), manufactured by DIC Corporation Acrylic resin (2): NeoCryl B-734 (Tg: 45°C), manufactured by Kusumoto Chemicals Co., Ltd.

[0247] In the examples, sheets having a predetermined tensile modulus and haze were obtained, and as a result, sheets having excellent surface smoothness were obtained.

Claims

1. A sheet containing fibrous cellulose having a fiber width of 1000 nm or less and a resin, the fibrous cellulose has anionic groups, and the content of the anionic groups is 0.50 mmol / g or more; the fibrous cellulose has an organic onium ion as a counter ion of the anionic group, A sheet satisfying the following conditions (A) and (B) (however, excluding a sheet containing an acrylic polymer including a structure derived from at least one compound selected from an isocyanate compound, a carbodiimide compound, and an oxazoline compound, and a structure derived from an aqueous acrylic polyol); (A) the tensile modulus is 1.10 GPa or more; (B) Haze is less than 2.0%.

2. The sheet according to claim 1, wherein at least one surface has an arithmetic mean roughness (Ra) of 200 nm or less.

3. 3. The sheet according to claim 1 or 2, wherein the fiber width of the fibrous cellulose is 10 nm or less.

4. The sheet according to any one of claims 1 to 3, wherein the anionic group is a group introduced into the fibrous cellulose via an ester bond or an ether bond.

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