Kit for nonwoven fabric impregnated with cellulose fiber water dispersion and method for producing nonwoven fabric impregnated with cellulose fiber water dispersion

Abstract

To provide a kit for a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose, which gives a nonwoven fabric having a large water retention amount, and to provide a method for producing a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose.SOLUTION: A kit for a cellulose fiber water dispersion-impregnated nonwoven fabric, comprising a cellulose fiber water dispersion and a nonwoven fabric, wherein a viscosity η [mPa·s] of the cellulose fiber water dispersion in a stationary state is 1, 000mPa·s or more, and a natural logarithm Ln (η) of the viscosity η [mPa·s] and a thickness t [mm] of the nonwoven fabric satisfy the following formula (I): T ≤ -0. 87Ln (η) + 11 (I) SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a kit for producing a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose and a method for producing a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose. [Background technology]

[0002] Nonwoven fabrics have excellent breathability, water absorption, moisture retention, etc., and can be used in a wide range of applications. Cellulose fibers also have excellent hydrophilicity, flexibility, etc. In recent years, various products have been produced by combining nonwoven fabrics having these properties with cellulose fibers to form composites. For example, Patent Document 1 describes a wet wipe sheet impregnated with a medicinal solution, which is made by impregnating a nonwoven fabric with a medicinal solution for the purpose of improving the ability to wipe away dirt such as muddy baby stools, and which is characterized in that the medicinal solution contains cellulose nanofibers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-86203 Summary of the Invention [Problem to be solved by the invention]

[0004] Wet tissues or wet sheets are used for various purposes such as sterilization, cleaning, makeup, moisturizing, gardening, and medical care, and in some cases it is desirable to increase the water retention capacity of the nonwoven fabric in order to improve quality or performance. An object of the present invention is to provide a kit for impregnating a nonwoven fabric with an aqueous dispersion of fibrous cellulose, and a method for producing a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose, which can produce a nonwoven fabric with a high water retention capacity. [Means for solving the problem]

[0005] The present inventors have found that the above-mentioned problems can be solved by providing a kit for a nonwoven fabric impregnated with an aqueous fibrous cellulose dispersion, which kit includes an aqueous fibrous cellulose dispersion and a nonwoven fabric, in which the viscosity η [mPa s] of the aqueous fibrous cellulose dispersion in a stationary state is set to a specific value or more, and the natural logarithm Ln(η) of the viscosity η [mPa s] and the thickness t [mm] of the nonwoven fabric satisfy a specific relationship. The present invention provides the following <1> ~ <7> Regarding. <1> A kit for impregnating a nonwoven fabric with an aqueous fibrous cellulose dispersion, comprising an aqueous fibrous cellulose dispersion and a nonwoven fabric, the viscosity η [mPa s] of the fibrous cellulose aqueous dispersion in a static state is 1,000 mPa s or more; A kit for a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose, wherein the natural logarithm Ln(η) of the viscosity η [mPa·s] and the thickness t [mm] of the nonwoven fabric satisfy the following formula (I): t≦-0.87Ln(η)+11 (I) <2> The viscosity η of the fibrous cellulose aqueous dispersion in a static state is 100,000 mPa s or less. <1> A kit for producing a nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose described in 1. <3> The thickness t of the nonwoven fabric is 0.8 mm or more. <1> or <2> A kit for producing a nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose described in 1. <4> The density of the nonwoven fabric is 0.02 g / cm 3 More than 0.25g / cm 3 Below is the <1> ~ <3> 10. A kit for producing a nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose according to any one of the above. <5> The content of fibrous cellulose in the fibrous cellulose aqueous dispersion is 0.15% by mass or more and 1.5% by mass or less. <1> ~ <4> 10. A kit for producing a nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose according to any one of the above. <6> The nonwoven fabric is a nonwoven fabric containing cellulose fibers. <1> ~ <5> 10. A kit for producing a nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose according to any one of the above. <7> A method for producing a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose, comprising the step of impregnating a nonwoven fabric with an aqueous dispersion of fibrous cellulose, the viscosity η [mPa s] of the fibrous cellulose aqueous dispersion in a static state is 1,000 mPa or more; A method for producing a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose, wherein the natural logarithm Ln(η) of the viscosity η [mPa·s] and the thickness t [mm] of the nonwoven fabric satisfy the following formula (I): t≦-0.87Ln(η)+11 (I) [Effects of the Invention]

[0006] According to the present invention, there are provided a kit for producing a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose and a method for producing a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose, which can produce a nonwoven fabric having a high water retention capacity. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fine fibrous cellulose having phosphorus oxo acid groups and pH. [Figure 2] 1 is a graph showing the relationship between the amount of NaOH dropped onto a slurry containing fibrous cellulose having a carboxy group and pH. DETAILED DESCRIPTION OF THE INVENTION

[0008] In this specification, a numerical range represented by "X to Y" means a numerical range including X as the lower limit and Y as the upper limit. When a numerical range is described in stages, the upper and lower limits of each numerical range can be combined in any way.

[0009] [Kit for impregnating nonwoven fabric with fibrous cellulose aqueous dispersion] The kit for a nonwoven fabric impregnated with an aqueous fibrous cellulose dispersion of this embodiment (hereinafter simply referred to as "kit") comprises an aqueous fibrous cellulose dispersion and a nonwoven fabric, wherein the viscosity η [mPa·s] of the aqueous fibrous cellulose dispersion in a stationary state is 1,000 mPa·s or more, and the natural logarithm Ln(η) of the viscosity η [mPa·s] and the thickness t [mm] of the nonwoven fabric satisfy the following formula (I): t≦-0.87Ln(η)+11 (I) The reason why the kit of this embodiment can produce a nonwoven fabric with a high water retention capacity is not clear, but is presumed to be as follows. As described above, the kit of this embodiment has a viscosity η of a specific value or more, and the natural logarithm of the viscosity η, Ln(η), and the thickness of the nonwoven fabric satisfy formula (I). Therefore, when the nonwoven fabric is impregnated with an aqueous dispersion of fibrous cellulose, the aqueous dispersion penetrates uniformly into the nonwoven fabric, and the viscosity of the aqueous dispersion itself and the hydrophilicity of the fibrous cellulose contribute to making it easier for water to be retained in the voids of the nonwoven fabric. The kit of this embodiment will be described in detail below.

[0010] [Aqueous dispersion of fibrous cellulose] The kit of this embodiment contains an aqueous dispersion of fibrous cellulose.

[0011] <Fibrous cellulose> The fibrous cellulose is not particularly limited, and any known fibrous cellulose can be used. The fiber width of the fibrous cellulose is preferably 2 nm or more and 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, and even more preferably 25 μm or less.

[0012] From the viewpoint of water retention capacity, the number average fiber width of the fibrous cellulose is preferably 2 nm or more and 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, and even more preferably 25 μm or less, and from the viewpoint of ease of production, it is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and even more preferably 15 μm or more.

[0013] The number-average fiber width of fibrous cellulose is measured in accordance with ISO 16065-2 or using an electron microscope. When using ISO 16065-2, the number-average fiber width can be measured using a Valmet FS5 or an ABB Fiber Tester. When using an electron microscope, the measurement is performed as follows: First, an aqueous suspension of fibrous cellulose with a concentration of 0.01% to 0.1% by mass is prepared, and this suspension is cast onto a hydrophilically treated carbon film-coated grid to prepare a sample for transmission electron microscope (TEM) observation. When wide fibers are included, scanning electron microscope (SEM) images of the surface cast onto glass may be observed. Next, electron microscope images are observed at magnifications of 1,000x, 5,000x, 10,000x, or 50,000x, depending on the width of the fibers to be observed. The sample, observation conditions, and magnification must be adjusted to meet the following conditions. (1) Draw a line X at any point in the observed image, and 20 or more fibers intersect with the line X. (2) Draw a line Y that intersects the line perpendicularly within the same image, and 20 or more fibers intersect the line Y.

[0014] For observation images that satisfy the above conditions, the widths of 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 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 of the read fiber widths is then taken as the number-average fiber width of the fibrous cellulose.

[0015] The fiber length of the fibrous cellulose is not particularly limited, but is preferably 0.1 μm or more and 1,000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and even more preferably 0.1 μm or more and 700 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 by image analysis using, for example, TEM, SEM, or atomic force microscope (AFM).

[0016] The fibrous cellulose preferably has a type I crystal structure. The presence of a type I crystal structure in fibrous cellulose can be identified from a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ=1.5418 Å) monochromated with graphite. Specifically, the presence of typical peaks at two positions, around 2θ=14° to 17° and around 2θ=22° to 23°, can be used for identification. The proportion of type I crystal structure in the fibrous cellulose is, for example, preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. This allows for the nonwoven fabric to be expected to have even better water retention. 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).

[0017] The axial ratio (fiber length / fiber width) of the fibrous cellulose is not particularly limited, but is preferably, for example, 20 to 10,000, and more preferably 25 to 1,000. By setting the axial ratio to the above lower limit or more, a sheet containing the fibrous cellulose can be easily formed. 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 an aqueous dispersion, handling such as dilution becomes easier.

[0018] In this embodiment, the fibrous cellulose preferably has at least one of an ionic substituent and a nonionic substituent. From the viewpoint of improving the dispersibility of fibers in a dispersion medium and increasing the defibration efficiency in the defibration treatment, it is more preferable that the fibrous cellulose has an ionic substituent. The ionic substituent may include, for example, either an anionic group or a cationic group, or both. Furthermore, the nonionic substituent may include, for example, an alkyl group and an acyl group. In this embodiment, it is particularly preferable that the ionic substituent has an anionic group. Furthermore, the ionic substituent is preferably a group that is introduced into the fibrous cellulose via an ester bond or an ether bond, and more preferably a group that is introduced into the fibrous cellulose via an ester bond. In this case, the ester bond is preferably formed by dehydration condensation between the fibrous cellulose and a compound that becomes the ionic substituent. The fibrous cellulose does not necessarily have to be subjected to a treatment for introducing an ionic substituent.

[0019] Examples of anionic groups as ionic substituents 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 (sometimes simply referred to as 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 group is preferably at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxy groups, carboxymethyl groups, carboxyethyl groups, sulfur oxoacid groups and substituents derived from sulfur oxoacid groups, xanthate groups, and sulfonic acid groups; more preferably at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxy groups, sulfur oxoacid groups, substituents derived from sulfur oxoacid groups, and xanthate groups; even more preferably at least one selected from the group consisting of phosphorus oxoacid groups, substituents derived from phosphorus oxoacid groups, carboxy groups, sulfur oxoacid groups, and substituents derived from sulfur oxoacid groups; and particularly preferably a phosphorus oxoacid group. Introducing a phosphorus oxoacid group as the anionic group can further enhance the dispersibility of fibrous cellulose, for example, even under alkaline or acidic conditions, making it easier to obtain nonwoven fabrics with high water retention. Examples of cationic groups as ionic substituents include ammonium groups, phosphonium groups, and sulfonium groups.

[0020] 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.

[0021] [ka]

[0022] In formula (1), a, b, and n are natural numbers, and m is an arbitrary number (where a=b×m). At least one of n α and α′ (preferably a) 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. Each 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 from any of these. α in formula (1) may be a group derived from a cellulose molecular chain. Furthermore, in formula (1), n ​​is preferably 1.

[0023] 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. In addition, the derivative group in R is a carboxy group, a carboxylate group (-COO -Examples of functional groups include, but are not limited to, functional groups to which at least one functional group selected from the group consisting of a hydroxyl group, an amino group, and the like is added or substituted. 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, which facilitates penetration into the fiber raw material and increases the yield of fibrous cellulose. When multiple Rs are present in formula (1) or when multiple types of substituents represented by formula (1) are introduced into the fibrous cellulose, the multiple Rs may be the same or different.

[0024] β b+ is a monovalent or higher cation made of an organic or inorganic substance. Examples of 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, but are not limited to, ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. These can be used alone or in combination of two or more types. Note that in formula (1), β b+ When a plurality of β b+ may be the same or different. The monovalent or higher cations made of organic or inorganic substances include β b+ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0025] More specifically, examples of phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups include phosphate groups (-POH), salts of phosphate groups, phosphite groups (phosphonic acid groups) (-POH), and salts of phosphite groups (phosphonic acid groups). Furthermore, phosphorus oxoacid groups or substituents derived from phosphorus oxoacid groups may be groups in which a phosphate group is condensed (e.g., a pyrophosphate group), groups in which a phosphonic acid group is condensed (e.g., a polyphosphonic acid group), phosphate ester groups (e.g., a monomethyl phosphate group, a polyoxyethylene alkyl phosphate group), or alkyl phosphonic acid groups (e.g., a methyl phosphonic acid group). Among these, the phosphate group is preferred.

[0026] The sulfur oxoacid group (a sulfur oxoacid group or a substituent derived from a sulfur oxoacid group) is, for example, a substituent represented by the following formula (2). A plurality of substituents represented by the following formula (2) may be introduced into each fibrous cellulose. In this case, the introduced plurality of substituents represented by the following formula (2) may be the same or different.

[0027] [ka]

[0028] In formula (2), 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 formula (2), β b+is a monovalent or higher cation composed of an organic or inorganic substance. Examples of the monovalent or higher cation composed of an organic substance include organic onium ions. Examples of the organic onium ions include organic ammonium ions and organic phosphonium ions. Examples of the organic ammonium ions include aliphatic ammonium ions and aromatic ammonium ions, and examples of the organic phosphonium ions include aliphatic phosphonium ions and aromatic phosphonium ions. Examples of the monovalent or higher cation composed of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, ions of divalent metals such as calcium or magnesium, hydrogen ions, ammonium ions, etc. Note that when multiple types of substituents represented by the above formula (2) are introduced into the fibrous cellulose, the multiple β b+ may be the same or different. The monovalent or higher cations made of organic or inorganic substances include β b+ Sodium or potassium ions are preferred because they are less likely to yellow when the fiber raw material containing the cation is heated and are easy to use industrially, but there is no particular limitation.

[0029] The amount of ionic substituent introduced into fibrous cellulose is, for example, preferably 0.05 mmol / g or more and 5.20 mmol / g or less per gram (mass) of fibrous cellulose, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, particularly preferably 1.00 mmol / g or more, and more preferably 3.65 mmol / g or less, even more preferably 3.50 mmol / g or less, and even more preferably 3.00 mmol / g or less. By setting the amount of ionic substituent (preferably anionic group) introduced within the above range, it is possible to easily refine the fiber raw material and improve the stability of the fibrous cellulose. Here, the denominator in the unit mmol / g is the value of the counter ion of the ionic substituent, which is a hydrogen ion (H +) indicates the mass of fibrous cellulose when

[0030] The amount of ionic substituents introduced into the fibrous cellulose can be measured, for example, by neutralization titration, which involves adding an alkali such as an aqueous sodium hydroxide solution to a slurry containing the obtained fibrous cellulose and measuring the change in pH to measure the amount introduced.

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

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

[0033] The above-mentioned amount of carboxy groups introduced (mmol / g) indicates the amount of carboxy groups in the acid-form fibrous cellulose (hereinafter referred to as the amount of carboxy groups (acid form)) because the denominator is the mass of the acid-form fibrous cellulose. On the other hand, when the counter ions of the carboxy groups are substituted with any cation C so as to be charge equivalent, the amount of carboxy groups in the fibrous cellulose with the cation C as the counter ion (hereinafter referred to as the amount of carboxy groups (C form)) (mmol / g) can be determined by converting the denominator to the mass of the fibrous cellulose when the cation C is the counter ion. That is, it is calculated using the following formula. Amount of carboxyl group (C type) = Amount of carboxyl group (acid type) / {1 + (W - 1) × (Amount of carboxyl group (acid type)) / 1000} W: Formula weight per valence of cation C (for example, Na is 23, Al is 9)

[0034] When measuring the amount of substituents by titration, adding too many drops of sodium hydroxide or titrating too quickly can result in lower than expected amounts of substituents, leading to inaccurate values. For example, a suitable amount and interval is recommended: titrating 10-50 μL of 0.1 N sodium hydroxide every 5-30 seconds. To eliminate the influence of carbon dioxide dissolved in the fibrous cellulose-containing slurry, it is recommended to perform measurements while blowing an inert gas such as nitrogen into the slurry from 15 minutes before the start of titration until the end of titration.

[0035] The amount of sulfur oxoacid or sulfonic acid groups introduced into fibrous cellulose can be calculated by freeze-drying a slurry containing fibrous cellulose and then pulverizing the sample to measure the sulfur content. Specifically, the slurry containing fibrous cellulose is freeze-dried and pulverized, and the resulting sample is subjected to pressure-heat decomposition with nitric acid in a sealed container, appropriately diluted, and the sulfur content is measured by ICP-OES. The value calculated by dividing the value by the bone-dry mass of the fibrous cellulose used is taken as the amount of sulfur oxoacid or sulfonic acid groups (unit: mmol / g) of the fibrous cellulose.

[0036] (Method of producing fibrous cellulose) <Fiber materials containing cellulose> Fibrous cellulose is produced from fibrous raw materials containing cellulose. The cellulose-containing fiber raw material is not particularly limited, but pulp is preferred due to its availability and low cost. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, 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 may be, for example, deinked pulp made from recycled paper. The pulp of this embodiment may be one of the above types alone or a mixture of two or more types. Among the above pulps, wood pulp and deinked pulp are preferred from the viewpoint of availability. Furthermore, among wood pulps, chemical pulp is more preferred, and kraft pulp and sulfite pulp are even more preferred, from the viewpoint of a high cellulose content, a high yield of fibrous cellulose during defibration treatment, and the fact that decomposition of cellulose in the pulp is minimal and long-fiber fibrous cellulose with a large axial ratio can be obtained. Note that the use of long-fiber fibrous cellulose with a large axial ratio tends to increase viscosity. As a fiber raw material containing cellulose, for example, cellulose contained in sea squirts and bacterial cellulose produced by acetic acid bacteria can be used. Furthermore, instead of fiber raw materials containing cellulose, fibers formed from linear nitrogen-containing polysaccharide polymers such as chitin and chitosan can also be used.

[0037] To obtain fibrous cellulose having an ionic substituent introduced therein, it is preferable to have an ionic substituent introduction step for introducing an ionic substituent into the above-mentioned cellulose-containing fiber raw material, a washing step, an alkali treatment step (neutralization step), and a defibration step in this order, and an acid treatment step may be included instead of or in addition to the washing step. Examples of the ionic substituent introduction step include a phosphorus oxo acid group introduction step, a carboxy group introduction step, a sulfur oxo acid group introduction step, a xanthate group introduction step, a phosphonic or phosphine group introduction step, a sulfonic group introduction step, and a cationic group introduction step. Each of these steps will be explained below.

[0038] <Ionic Substituent Introduction Step> -Phosphorus oxoacid group introduction process- The phosphorus oxo acid group introduction step involves reacting a cellulose-containing fiber raw material with at least one compound (hereinafter also referred to as "compound A") selected from compounds capable of introducing phosphorus oxo acid groups by reacting with hydroxyl groups in the cellulose-containing fiber raw material, thereby obtaining a phosphorus oxo acid group-introduced fiber. In the 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. One example of a method for reacting compound A with a fiber raw material in the presence of compound B is to mix compound A and compound B with a fiber raw material in a dry, wet, or slurry state. Among these methods, using a dry or wet fiber raw material is preferred because of the high uniformity of the reaction, and using a dry fiber raw material is particularly preferred. The form of the fiber raw material is not particularly limited, but is preferably a cotton-like or thin sheet form. Compound A and compound B may be added to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state heated to or above their melting point. Among these methods, adding compound A and compound B in the form of a solution dissolved in a solvent, 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 solution form, the fiber raw material may be immersed in the solution and allowed to absorb the liquid before being removed, or the solution may be added dropwise to the fiber raw material. Alternatively, the required amounts of compound A and compound B may be added to the fiber raw material, or excess amounts of compound A and compound B may be added to the fiber raw material, and then the excess compound A and compound B may be removed by squeezing or filtration.

[0039] The compound A used in this embodiment may be any compound that has a phosphorus atom and can form an ester bond with cellulose, including, but not limited to, phosphoric acid or a salt thereof, phosphorous acid or a salt thereof, dehydrated condensed phosphoric acid or a salt thereof, and phosphoric anhydride (diphosphorus pentoxide). Phosphoric acid can be used with various purities, such as 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid. Phosphorous acid can be, for example, 99% phosphorous acid (phosphonic acid). Dehydrated condensed phosphoric acid is formed by the condensation of two or more molecules of phosphoric acid through a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates, phosphites, and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts, and ammonium salts of phosphoric acid, phosphorous acid, or dehydrated condensed phosphoric acid, which can be neutralized to various degrees. Among these, phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts of phosphoric acid are preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, and ammonium dihydrogen phosphate are more preferred, from the viewpoints of high efficiency in introducing phosphorus oxoacid groups, easier improvement of defibration efficiency in the defibration treatment step described below, low cost, and ease of industrial application. The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted into the amount of phosphorus atoms, the amount of phosphorus atoms added to 100 parts by mass of the fiber raw material (bone dry mass) is preferably 0.5 parts by mass or more and 100 parts by mass or less, more preferably 1 part by mass or more and 50 parts by mass or less, and even more preferably 2 parts by mass or more and 30 parts by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of 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.

[0040] As described above, the compound B used in this embodiment is at least one selected from urea and its derivatives. Examples of the compound B include urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea. From the viewpoint of improving the uniformity of the reaction, it is preferable to use an aqueous solution of compound B. Furthermore, from the viewpoint of further improving the uniformity of the reaction, it is preferable to use an aqueous solution in which both compound A and compound B are dissolved. The amount of compound B added per 100 parts by mass (bone dry mass) of the fiber raw material is not particularly limited, but is preferably, for example, 1 part by mass or more and 500 parts by mass or less, more preferably 10 parts by mass or more and 400 parts by mass or less, and even more preferably 100 parts by mass or more and 350 parts by mass or less.

[0041] In the reaction of a fiber material containing cellulose with compound A, the reaction system may contain, in addition to compound B, amides or amines, for example. Examples of amides include formamide, dimethylformamide, acetamide, and dimethylacetamide. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, triethylamine is known to function as a particularly good reaction catalyst.

[0042] In the phosphorus oxo acid group introduction step, it is preferable to add or mix compound A or the like with the fiber raw material and then heat-treat the fiber raw material. The heat treatment temperature is preferably selected so that the phosphorus oxo acid group can be efficiently introduced while suppressing thermal decomposition and hydrolysis of the fiber. The heat treatment temperature is preferably, for example, from 50°C to 300°C, more preferably from 100°C to 250°C, and even more preferably from 130°C to 200°C. Furthermore, various types of equipment having heat transfer media can be used for the heat treatment, including, for example, a stirring dryer, a rotary dryer, a disk dryer, a roll-type heater, a plate-type heater, a fluidized-bed dryer, a band-type dryer, a filtration dryer, a vibration fluidized-bed dryer, a flash dryer, a reduced-pressure dryer, an infrared heater, a far-infrared heater, a microwave heater, and a high-frequency dryer.

[0043] 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 the fiber raw material and compound A may be heated while being kneaded or stirred using 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). Furthermore, the heating device used for the heat treatment is preferably one that can constantly discharge, to the outside of the system, moisture contained in the slurry and moisture generated during the dehydration condensation (phosphorylation) reaction between compound A and hydroxyl groups contained in cellulose or the like in the fiber raw material. Examples of such a heating device include an oven with a blower system. Constantly discharging moisture from the system not only suppresses the hydrolysis of phosphate ester bonds, which is the reverse reaction of phosphate esterification, but also suppresses acid hydrolysis of sugar chains in the fiber. This makes it possible to obtain fibrous cellulose with a high axial ratio. The heat treatment time is, for example, preferably from 1 second to 300 minutes after the water content has been substantially removed from the fiber raw material, more preferably from 1 second to 1,000 seconds, and even more preferably from 10 seconds to 800 seconds. In this embodiment, the amount of phosphorus oxo acid groups introduced can be kept within a preferred range by setting the heating temperature and heating time within appropriate ranges.

[0044] The amount of phosphorus oxoacid groups introduced into the fiber raw material is, for example, preferably 0.05 mmol / g or more and 5.20 mmol / g or less per gram (mass) of fibrous cellulose, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, particularly preferably 1.00 mmol / g or more, more preferably 3.65 mmol / g or less, and even more preferably 3.00 mmol / g or less. By keeping the amount of phosphorus oxoacid groups introduced within the above range, it is possible to facilitate the pulverization of the fiber raw material and improve the stability of the fibrous cellulose.

[0045] -Carboxy group introduction process- The carboxyl group introduction process is carried out by treating a fiber raw material containing cellulose with an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, or TEMPO oxidation treatment, or with a compound having a carboxylic acid-derived group or a derivative thereof, or an acid anhydride of a compound having a carboxylic acid-derived group or a derivative thereof. 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.

[0046] The acid anhydride of a compound having a group derived from carboxylic acid is not particularly limited, but 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, but examples thereof include acid anhydrides of compounds having carboxy groups such as dimethylmaleic anhydride, diethylmaleic anhydride, diphenylmaleic anhydride, etc. in which at least some of the hydrogen atoms have been substituted with substituents such as alkyl groups or phenyl groups.

[0047] When TEMPO oxidation treatment is performed in the carboxyl group introduction step, it is preferable to perform the treatment under conditions of pH 6 or higher and 8 or lower. This type of treatment is also called neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment can be performed, for example, by adding pulp as the fiber raw material, a nitroxy radical such as TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) as a catalyst, and sodium hypochlorite as a sacrificial reagent to a sodium phosphate buffer solution (pH = 6.8). Furthermore, by adding sodium chlorite, aldehydes generated during the oxidation process can be efficiently oxidized to carboxyl groups. The TEMPO oxidation treatment may also be carried out under conditions of a pH of 10 to 11. This type of treatment is also called alkaline TEMPO oxidation treatment. The alkaline TEMPO oxidation treatment can be carried out, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a co-catalyst, and sodium hypochlorite as an oxidizing agent to pulp as a fiber raw material. The amount of carboxyl groups introduced into the fiber raw material varies depending on the type of substituent. For example, when carboxyl groups are introduced by TEMPO oxidation, the amount is preferably 0.05 mmol / g to 3.65 mmol / g per gram (mass) of fibrous cellulose, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, particularly preferably 0.90 mmol / g or more, and more preferably 3.00 mmol / g or less, even more preferably 2.50 mmol / g or less, even more preferably 2.20 mmol / g or less, and particularly preferably 2.00 mmol / g or less. Alternatively, when the substituent is a carboxymethyl group, the amount may be 5.8 mmol / g or less per gram (mass) of fibrous cellulose. By keeping the amount of carboxyl groups introduced within the above range, cellulose fiber fineness in the fine-fining treatment step can be facilitated and the stability of the fibrous cellulose can be improved.

[0048] -Sulfur oxoacid group introduction process- The process for producing fibrous cellulose may include, for example, a sulfur oxoacid group introduction step as an ionic substituent introduction step, in which hydroxyl groups in a cellulose-containing fiber raw material react with sulfur oxoacids to obtain cellulose fibers having sulfur oxoacid groups (sulfur oxoacid group-introduced fibers).

[0049] In the sulfur oxo acid group introduction step, instead of compound A in the above-described <Phosphorus oxo acid group introduction step>, at least one compound (hereinafter also referred to as "compound C") selected from compounds capable of introducing sulfur oxo acid groups by reacting with hydroxyl groups in cellulose-containing fiber raw materials is used. Compound C may be any compound containing a sulfur atom and capable of forming an ester bond with cellulose, including, but not limited to, sulfuric acid or its salts, sulfurous acid or its salts, and sulfuric acid amides. Sulfuric acid of various purities can be used, for example, 96% sulfuric acid (concentrated sulfuric acid). Sulfurous acid can be 5% aqueous sulfurous acid. Sulfates or sulfites include lithium, sodium, potassium, and ammonium salts of sulfates or sulfites, which can be neutralized to various degrees. Sulfamic acid or the like can be used as the sulfuric acid amide. In the sulfur oxo acid group introduction step, it is preferable to use compound B in the above-described <Phosphorus oxo acid group introduction step> as well.

[0050] 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.

[0051] 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 seconds to 10,000 seconds. For the heat treatment, various devices having a heat medium can be used, such as an agitator dryer, rotary dryer, disk dryer, roll-type heater, plate-type heater, fluidized-bed dryer, band-type dryer, filtration dryer, vibration fluidized dryer, flash dryer, reduced-pressure dryer, infrared heater, far-infrared heater, microwave heater, and high-frequency dryer.

[0052] The amount of sulfur oxoacid groups introduced into the cellulose raw material is preferably 0.05 mmol / g or more and 5.00 mmol / g or less, more preferably 0.10 mmol / g or more, even more preferably 0.20 mmol / g or more, even more preferably 0.50 mmol / g or more, particularly preferably 0.90 mmol / g or more, and more preferably 3.00 mmol / g or less. By keeping the amount of sulfur oxoacid groups introduced within the above range, it is possible to easily pulverize the fiber raw material and improve the stability of the fibrous cellulose.

[0053] -Oxidation step using a chlorine-based oxidizing agent (second carboxyl group introduction step)- The ionic substituent introduction step may include an oxidation step using a chlorine-based oxidizing agent, in which a chlorine-based oxidizing agent is added to a wet or dry fiber raw material having a hydroxyl group to cause a reaction, thereby introducing a carboxyl group into the fiber raw material.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] -Xanthate group introduction process (xanthogen acid esterification process)- The ionic substituent introduction step may include, for example, a xanthate group introduction step (hereinafter also referred to as a xanthation 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 a xanthate group into the fiber raw material. Specifically, carbon disulfide is added to a fiber raw material that has been converted into alkali cellulose by the method described below, and the reaction is carried out.

[0058] ((Alkali cellulose)) When introducing ionic substituents into a fiber raw material, it is preferable to convert the cellulose contained in the fiber raw material into alkali cellulose by treating the cellulose with an alkaline solution. This treatment causes ionic dissociation of some of the hydroxyl groups in the cellulose, thereby increasing the nucleophilicity (reactivity). The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. Due to their high versatility, it is preferable to use, for example, sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, or tetrabutylammonium hydroxide. The conversion into alkali cellulose may be carried out simultaneously with the introduction of ionic substituents, before the introduction, or at both the same time.

[0059] 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.

[0060] 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.

[0061] The treatment time for alkali cellulose formation is preferably 1 minute or more and 6 hours or less, more preferably 10 minutes or more, even more preferably 30 minutes or more, and more preferably 5 hours or less, even more preferably 4 hours or less.

[0062] 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 fibrous cellulose.

[0063] When the introduction of ionic substituents and the conversion to alkali cellulose are not carried out simultaneously, the conversion to alkali cellulose is preferably carried out before the introduction of ionic substituents. In this case, the alkali cellulose obtained by the conversion to alkali cellulose is preferably subjected to solid-liquid separation by a common deliquoring method such as centrifugation or filtration to remove water. This improves the reaction efficiency in the subsequent ionic substituent introduction step. The cellulose fiber concentration after solid-liquid separation is preferably 5% to 50%, more preferably 10% to 40%, and even more preferably 15% to 35%.

[0064] -Phosphonic or phosphine group introduction step (phosphoalkylation step)- The ionic substituent introduction step may include a phosphonic or phosphine group introduction step (phosphoalkylation step). In the phosphoalkylation step, a compound having a reactive group and a phosphonic or phosphine group (compound E) is used as an essential component. A ), an optional alkali compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having hydroxyl groups and reacted to introduce phosphonic or phosphine groups into the fiber raw material.

[0065] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Compound E AExamples of suitable compounds include vinylphosphonic acid, phenylvinylphosphonic acid, and phenylvinylphosphinic 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.

[0066] Compound E A When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] -Sulfonic acid group introduction step (sulfoalkylation step)- The ionic substituent introduction step may include a sulfone group introduction step (sulfoalkylation step). In the sulfoalkylation, a compound having a reactive group and a sulfone group (compound E) is used as an essential component. B ) and, as an optional component, an alkali compound and 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.

[0071] 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.

[0072] Compound E B When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or 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.

[0073] 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.

[0074] 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.

[0075] 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 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.

[0076] -Carboxyalkylation step (third carboxy group introduction step)- The ionic substituent introduction step may include a carboxyalkylation step. As an essential component, a compound having a reactive group and a carboxy group (compound E C ), an optional alkaline compound, and compound B selected from the aforementioned urea and its derivatives are added to a wet or dry fiber raw material having a hydroxyl group and reacted to introduce a carboxyl group into the fiber raw material.

[0077] 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.

[0078] Compound E CWhen adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] -Cationic group introduction step (cationization step)- As an essential component, a compound having a reactive group and a cationic group (compound E D ), an optional alkaline compound, and a compound B selected from the above-mentioned urea and its derivatives are added to a wet or dry fiber raw material having hydroxyl groups and reacted to introduce cationic groups into the fiber raw material.

[0083] Examples of the reactive group include a halogenated alkyl group, a vinyl group, and an epoxy group (glycidyl group). Examples of the cationic group include an ammonium group, a phosphonium group, a sulfonium group, etc. Among these, the cationic group is preferably an ammonium group. Compound E D As the alkyl group, glycidyl trimethyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, etc. are preferred from the viewpoints of the efficiency of introducing substituents, and therefore the defibration efficiency, cost, and ease of handling. Furthermore, it is also preferable to use the compound B in the above-mentioned <Phosphorus oxo acid group introduction step> as an optional component in the same manner. The amount added is also preferably as described above.

[0084] Compound E D When adding, it may be added to the fiber raw material as a reagent (solid or liquid) as is, or 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.

[0085] 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.

[0086] Compound E D The amount added per 100 parts by mass of the fiber raw material is preferably 1 part by mass or more and 100,000 parts by mass or less, more preferably 2 parts by mass or more and 10,000 parts by mass or less, and even more preferably 5 parts by mass or more and 1,000 parts by mass or less.

[0087] The reaction time may vary depending on the reaction temperature, but is preferably from 1 minute to 1,000 minutes, more preferably from 5 minutes to 500 minutes, and even more preferably from 10 minutes to 400 minutes. After the reaction, excess reaction reagents, by-products, etc. may be washed and removed with water by filtration or the like.

[0088] <Cleaning process> In the method for producing fibrous cellulose according to the present embodiment, a washing step can be carried out on the ionic substituent-introduced fibers as needed. The washing step is carried out by washing the ionic substituent-introduced fibers with water or an organic solvent, for example. The washing step may be carried out after each step described below, and the number of washing steps carried out in each washing step is not particularly limited.

[0089] <Alkaline treatment (neutralization treatment) process> When producing fibrous cellulose, the fiber raw material may be subjected to an alkali treatment (neutralization treatment) between the ionic substituent introduction step and the defibration treatment step described below. The alkali treatment method is not particularly limited, but an example thereof is a method in which the ionic substituent-introduced fiber is immersed in an alkali solution. The alkaline compound contained in the alkaline solution is not particularly limited and may be an inorganic alkaline compound or an organic alkaline compound. In this embodiment, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of their high versatility. The solvent contained in the alkaline solution may be either water or an organic solvent. Among these, the solvent contained in the alkaline solution is preferably water or a polar solvent including a polar organic solvent such as an alcohol, and more preferably an aqueous solvent including at least water. As the alkaline solution, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of their high versatility. The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably, for example, from 5°C to 80°C, and more preferably from 10°C to 60°C. The immersion time of the ionic substituent-introduced fiber in the alkaline solution in the alkaline treatment step is not particularly limited, but is, for example, preferably from 5 minutes to 30 minutes, and more preferably from 10 minutes to 20 minutes. The amount of alkaline solution used in the alkaline treatment is not particularly limited, but is, for example, preferably from 100% by mass to 100,000% by mass, and more preferably from 1,000% by mass to 10,000% by mass, based on the bone dry mass of the ionic substituent-introduced fiber.

[0090] In order to reduce the amount of alkaline solution used in the alkali treatment step, the ionic substituent-introduced fiber may be washed with water or an organic solvent after the ionic substituent-introducing step and before the alkali treatment step. From the viewpoint of improving handleability, it is preferable to wash the alkali-treated ionic substituent-introduced fiber with water or an organic solvent after the alkali treatment step and before the defibrating step.

[0091] <Acid treatment process> When producing fibrous cellulose, the fiber raw material may be subjected to an acid treatment between the step of introducing an ionic substituent and the defibration treatment step described below. For example, the step of introducing an ionic substituent, the acid treatment step, the alkali treatment step, and the defibration treatment step may be performed in this order. The acid treatment method is not particularly limited, but examples include a method of immersing the fiber raw material in an acid-containing acid solution. The concentration of the acid solution used is not particularly limited, but is preferably 10% by mass or less, and more preferably 5% by mass or less. The pH of the acid solution used is also not particularly limited, but is preferably 0 to 4, and more preferably 1 to 3. Examples of the acid contained in the acid solution include inorganic acids, sulfonic acids, and carboxylic acids. Examples of inorganic acids include sulfuric acid, nitric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, and boric acid. Examples of sulfonic acids include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and trifluoromethanesulfonic acid. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, and tartaric acid. Among these, hydrochloric acid or sulfuric acid is particularly preferred. The temperature of the acid solution in the acid treatment is not particularly limited, but is preferably, for example, 5°C to 100°C, and more preferably 20°C to 90°C. The immersion time in the acid solution in the acid treatment is not particularly limited, but is, for example, preferably 5 minutes to 120 minutes, and more preferably 10 minutes to 60 minutes. The amount of the acid solution used in the acid treatment is not particularly limited, but is, for example, preferably 100% by mass to 100,000% by mass, and more preferably 1,000% by mass to 10,000% by mass, based on the bone dry mass of the fiber raw material.

[0092] <Defibrillation process> The ionic substituent-introduced fibers are defibrated in a defibration treatment step to obtain fibrous cellulose. In the defibration treatment step, for example, a defibration treatment device can be used. The defibration treatment device is not particularly limited, but examples that can be used include a high-speed defibrator, a grinder (stone mill-type grinder), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision grinder, a ball mill, a bead mill, a disk-type refiner, a conical refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater.

[0093] In the defibration process, it is preferable to dilute the ionic substituent-introduced fibers with a dispersion medium to form a slurry. The dispersion medium can be one or more selected from water and organic solvents such as polar organic solvents. The polar organic solvent is not particularly limited, but examples thereof include alcohols, polyhydric alcohols, ketones, ethers, esters, and aprotic polar solvents. Examples of alcohols include methanol, ethanol, isopropanol, n-butanol, and isobutyl alcohol. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, and glycerin. Examples of ketones include acetone and methyl ethyl ketone (MEK). Examples of ethers include diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether. Examples of esters include ethyl acetate and butyl acetate. Examples of aprotic polar solvents include dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), and N-methyl-2-pyrrolidinone (NMP).

[0094] The solid content concentration of the fibrous cellulose during the defibration treatment can be set appropriately. The slurry obtained by dispersing the phosphorus oxo acid group-introduced fibers in a dispersion medium may contain solid components other than the phosphorus oxo acid group-introduced fibers, such as urea having hydrogen bonding properties.

[0095] As the fibrous cellulose, fibrous cellulose containing an ionic group and unmodified fibrous cellulose may be used in combination.

[0096] The content of fibrous cellulose in the fibrous cellulose aqueous dispersion is preferably 0.15% by mass or more and 1.5% by mass or less, more preferably 0.25% by mass or more, even more preferably 0.35% by mass or more, and even more preferably 0.45% by mass or more, from the viewpoint of achieving a desired viscosity for the fibrous cellulose aqueous dispersion and increasing the water retention capacity of the nonwoven fabric.

[0097] [Nonwoven fabric] The kit of this embodiment includes a nonwoven fabric. The nonwoven preferably comprises cellulose fibers. Examples of raw materials for cellulose fibers include wood pulp (softwood pulp, hardwood pulp), rag pulp, linter pulp, linen pulp, non-wood pulp such as paper mulberry, mitsumata pulp, and gampi pulp, and recycled paper pulp; and fluff pulp, which is made by mechanically defibrating these pulps into fibers. The method for pulping the raw pulp is not particularly limited, and cellulose fibers can be obtained by pulping using a conventionally known method.

[0098] <Heat-fusible adhesive> The nonwoven fabric may contain a heat-fusible adhesive. The heat-fusible adhesive may be supplied in particulate form as a heat-fusible powder, or may be supplied by spraying in a state where it is dissolved or dispersed in a solvent, or may be supplied in fibrous form as a heat-fusible fiber. However, the heat-fusible adhesive is preferably supplied to the nonwoven fabric in fibrous form. That is, the heat-fusible adhesive is more preferably a heat-fusible fiber. Examples of components of heat-sealable adhesives include, but are not limited to, polyethylene (PE), polypropylene (PP), polyethylene-vinyl acetate copolymer, polyamide, and polyesters such as polyethylene terephthalate (PET).

[0099] The heat-fusible fibers are not particularly limited as long as they are at least partially melted by heat treatment after forming the web and function as a binder. The heat-fusible fiber may be a sheath-core type obtained by combining two types of resins with different melting points, in which the fiber is partially melted. Heat-fusible fibers with a sheath-core type structure have a core made of a resin with a high melting point surrounded by a sheath made of a resin with a low melting point. Specific examples include fibers that combine two types of resins with different melting points (PET / PET composite fiber, PE / PE composite fiber, PP / PP composite fiber, PE / PET composite fiber, PP / PET composite fiber, PE / PP composite fiber).

[0100] The content of the heat-fusible adhesive in the nonwoven fabric is not particularly limited, but from the viewpoint of imparting strength to the nonwoven fabric, it is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more, even more preferably 15% by mass or more, and more preferably 30% by mass or less, even more preferably 25% by mass or less. Note that the above content does not include the content of the raw fiber.

[0101] <Other ingredients> The nonwoven fabric of the present invention may contain other components in addition to the pulp and the heat-fusible adhesive described above. Specific examples include functional powders, functional fibers, functional liquids, etc. The functional powders, functional fibers, and functional liquids are preferably those having one or more functions such as deodorizing function, antibacterial function, antiviral function, antiallergen function, antifungal function, fragrance function, and flame-retardant component, and examples thereof include zeolite, activated carbon, chitin, chitosan, scallop shells, titanium oxide, titanium dioxide, magnesium oxide, plant extracts, mushroom extracts, catechin, flavonol, cyclodextrin, collagen fiber, iron oxide, citric acid, zinc pyrithione, copper pyrithione, hinokitiol, eucalyptus extract, and flame retardant particles such as halogen bromine-based, hydrated metal oxide-based, antimony oxide-based, phosphorus-based, and phosphorus-nitrogen-based condensates.

[0102] When the nonwoven fabric of the present invention contains other components, the total amount of the other components in the nonwoven fabric is not particularly limited, but is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. There is no particular lower limit for the content of the other components. Note that the above content does not include the content of the raw fiber.

[0103] In the present invention, the average fiber diameter of all fibers (raw fiber) constituting the nonwoven fabric is preferably 5 to 80 μm, more preferably 10 to 60 μm. It is preferable that the average fiber diameter of the fibers constituting the nonwoven fabric is within the above range, since this increases the water retention capacity of the nonwoven fabric. The average fiber diameter can be measured by microscopic observation in the case of synthetic fibers, and the average fiber diameter can be measured by image analysis using a fiber length measuring device (e.g., KAAJAANI Fiber Lab.) in the case of pulp fibers.

[0104] In the present invention, the average fiber length of all fibers (raw fibers) constituting the nonwoven fabric is preferably 0.5 to 150 mm. When the nonwoven fabric is an airlaid nonwoven fabric, the average fiber length of all fibers (raw fibers) constituting the nonwoven fabric is preferably 0.5 to 10 mm, more preferably 0.5 to 6 mm. Having the average fiber length of all fibers constituting the nonwoven fabric within the above range is preferable because it reduces the bulk density of the nonwoven fabric and increases the water retention capacity of the nonwoven fabric. The average fiber length can be measured by microscopic observation in the case of synthetic fibers, and can be measured by a fiber length measuring device (e.g., KAAJAANI Fiber Lab.) in the case of pulp fibers.

[0105] <Nonwoven fabric manufacturing method> The method for producing the nonwoven fabric preferably includes a web forming step of forming a sheet-like web from raw material fibers, and a fiber bonding step of bonding the raw material fibers in the obtained web.

[0106] In the present invention, the nonwoven fabric may be either a wetlaid nonwoven fabric or a drylaid nonwoven fabric, and specific examples include airlaid nonwoven fabrics, air-through nonwoven fabrics, spunlace nonwoven fabrics, needle-punched nonwoven fabrics, resin-bonded nonwoven fabrics, etc. From the viewpoint of increasing the water retention capacity of the nonwoven fabric, the nonwoven fabric is preferably a drylaid nonwoven fabric, i.e., a nonwoven fabric obtained by a dry manufacturing method, and more preferably an airlaid nonwoven fabric. In airlaid nonwoven fabrics, the raw fibers are randomly oriented in three dimensions, creating many voids and resulting in a nonwoven fabric with a high water retention capacity.

[0107] An air-laid nonwoven fabric is a nonwoven fabric in which a web is formed by an air-laid method, in which fibers constituting the nonwoven fabric are randomly layered in three dimensions using an air flow. Airlaid nonwoven fabrics are produced, for example, as follows: First, a gas-permeable carrier sheet is placed on a mesh-like endless belt, and then, using an airlaid web-forming device, the fibers that make up the nonwoven fabric are deposited on the gas-permeable carrier sheet while being dispersed in air to form a web. Next, the web is thermally bonded by heating using the heat-fusible adhesive contained in the web (thermal bonding method). The formed air-laid web may be heat-treated by a common thermal bonding method, such as a method of introducing the air-laid web into a heating furnace or a method of treating the air-laid web with hot air. Furthermore, a sheet may be placed on the surface of the nonwoven fabric before or after heat sealing. When the surface on which the breathable carrier sheet is placed is considered the back surface, the sheet is placed on the other surface (front surface). Here, the sheet placed on the front surface is not limited to a breathable sheet, and various sheets can be placed. The front surface sheet may be the same as the breathable carrier sheet on the back surface.

[0108] Examples of hot air treatment include a method in which the web is heat-treated by passing it through a through-air dryer equipped with a rotating drum with breathable surface (hot air circulating rotary drum method), and a method in which the web is heat-treated by passing it through a box-type dryer that can pass hot air through the web (hot air circulating conveyor oven method). The heat treatment temperature should be equal to or higher than the melting point of the heat-fusible adhesive. If the heat-fusible adhesive is made of two or more resins, the heat treatment temperature should be equal to or higher than the melting point of the resin with the lowest melting point. When heated to a temperature equal to or higher than the melting point of the heat-fusible adhesive, the heat-fusible adhesive melts, and the fibrous raw materials are bonded together via the molten heat-fusible adhesive.

[0109] After the fiber bonding step, a heat pressing treatment may be carried out for the purpose of finely adjusting the density of the formed nonwoven fabric, etc. In this case, the pressing pressure is preferably 44 kg / cm or less, more preferably 10 kg / cm or less, in terms of linear pressure, which is lower than the pressure in the heat pressing step that is generally carried out as a fiber bonding step for bonding fibers together.

[0110] The nonwoven fabric may be a commercially available product, and examples of commercially available products include Hatosheet series, KS-40, and K-60 (manufactured by Oji Kinocloth Co., Ltd.).

[0111] (Properties of fibrous cellulose aqueous dispersion and nonwoven fabric) <<Viscosity of fibrous cellulose aqueous dispersion in a stationary state>> From the viewpoint of increasing the water retention capacity of the nonwoven fabric, the viscosity η [mPa·s] of the aqueous dispersion of fibrous cellulose in a stationary state is 1,000 mPa·s or more, preferably 1,000 mPa·s or more and 100,000 mPa·s or less, more preferably 1,500 mPa·s or more, even more preferably 2,000 mPa·s or more, and more preferably 80,000 mPa·s or less, even more preferably 50,000 mPa·s or less, still more preferably 20,000 mPa·s or less, and even more preferably 18,000 mPa·s or less. The viscosity η [mPa s] of a fibrous cellulose aqueous dispersion in a stationary state can be adjusted, for example, by adjusting the concentration of the fibrous cellulose aqueous dispersion or the degree of defibration treatment or polymerization degree of the fibrous cellulose. The viscosity of a fibrous cellulose aqueous dispersion tends to decrease as the concentration is reduced. Furthermore, the viscosity tends to increase as the defibration of fibrous cellulose progresses, and decreases as the degree of polymerization decreases. Examples of treatments to reduce the degree of polymerization include ozone treatment, enzyme treatment, and hypochlorous acid treatment. The viscosity η of the fibrous cellulose dispersion in a stationary state is measured by the method described in the examples.

[0112] <Thickness of nonwoven fabric> From the viewpoint of increasing the water retention capacity of the nonwoven fabric, the thickness t [mm] of the nonwoven fabric is preferably 0.8 mm or more and 6 mm or less, more preferably 0.9 mm or more, and more preferably 5 mm or less, and even more preferably 4.5 mm or less. The thickness t [mm] of the nonwoven fabric is measured by the method described in the Examples.

[0113] When the thickness t of the nonwoven fabric is 0.8 mm or more and 1.5 mm or less, the viscosity η [mPa·s] of the fibrous cellulose aqueous dispersion in a stationary state is preferably 1,000 mPa·s or more and 100,000 mPa·s or less, more preferably 1,500 mPa·s or more, even more preferably 2,000 mPa·s or more, and more preferably 80,000 mPa·s or less, even more preferably 50,000 mPa·s or less, still more preferably 20,000 mPa·s or less, and even more preferably 18,000 mPa·s or less.

[0114] When the thickness t of the nonwoven fabric is more than 1.5 mm and not more than 2.5 mm, the viscosity η [mPa s] of the fibrous cellulose aqueous dispersion in a stationary state is preferably 1,000 mPa s or more and 30,000 mPa s or less, more preferably 1,500 mPa s or more, even more preferably 2,000 mPa s or more, and more preferably 20,000 mPa s or less, even more preferably 18,000 mPa s or less.

[0115] When the thickness t of the nonwoven fabric is more than 2.5 mm and not more than 4.2 mm, the viscosity η [mPa·s] of the fibrous cellulose aqueous dispersion in a stationary state is preferably 1,000 mPa·s or more and 18,000 mPa·s or less, more preferably 1,500 mPa·s or more, and even more preferably 2,000 mPa·s or more.

[0116] <Nonwoven fabric density> The density of the nonwoven fabric is preferably 0.02 g / cm from the viewpoint of increasing the water retention capacity of the nonwoven fabric. 3 More than 0.3g / cm 3 More preferably, it is 0.03 g / cm or less. 3 More preferably, it is 0.25 g / cm or more. 3 The following is the result. The density of the nonwoven fabric is calculated by the method described in the Examples.

[0117] <Formula (I)> The natural logarithm Ln(η) of the viscosity η [mPa·s] and the thickness t [mm] of the nonwoven fabric satisfy the following formula (I). t≦-0.87Ln(η)+11 (I) Formula (I) was derived from the viewpoint of determining the maximum amount of water that can be impregnated (retained) in a nonwoven fabric by effectively utilizing the hydrophilicity of fibrous cellulose while ensuring the fluidity of the aqueous dispersion of fibrous cellulose when impregnating the nonwoven fabric.

[0118] [Method of manufacturing nonwoven fabric impregnated with aqueous dispersion of fibrous cellulose] The method for producing a nonwoven fabric impregnated with an aqueous fibrous cellulose dispersion of the present invention (hereinafter also referred to as the "production method of the present invention") comprises a step of impregnating a nonwoven fabric with an aqueous fibrous cellulose dispersion, wherein the viscosity η [mPa s] of the aqueous fibrous cellulose dispersion in a stationary state is 1,000 mPa or more, and the natural logarithm Ln(η) of the viscosity η [mPa s] and the thickness t [mm] of the nonwoven fabric satisfy the following formula (I): t≦-0.87Ln(η)+11 (I)

[0119] The fibrous cellulose aqueous dispersion and nonwoven fabric used in the manufacturing method of this embodiment can be the fibrous cellulose aqueous dispersion and nonwoven fabric contained in the kit of this embodiment, and it is preferable to use the kit of this embodiment for the manufacturing method of this embodiment.

[0120] In the manufacturing method of this embodiment, the step of impregnating the nonwoven fabric with the aqueous fibrous cellulose dispersion itself can be carried out by a conventional method. For example, the aqueous fibrous cellulose dispersion may be applied to one or both sides of the nonwoven fabric to impregnate the nonwoven fabric with the aqueous fibrous cellulose dispersion, or the nonwoven fabric may be immersed in the aqueous fibrous cellulose dispersion to impregnate the nonwoven fabric with the aqueous fibrous cellulose dispersion. From the viewpoint of increasing the water retention capacity of the nonwoven fabric, it is preferable to immerse the nonwoven fabric in the aqueous fibrous cellulose dispersion. The temperature of the fibrous cellulose aqueous dispersion when it is impregnated into the nonwoven fabric is, for example, 10°C or higher and 50°C or lower. The time for immersing the nonwoven fabric in the aqueous dispersion of fibrous cellulose can be appropriately selected depending on the shape, density, etc. of the nonwoven fabric, and is, for example, from 5 seconds to 30 minutes.

[0121] The production method of the present invention preferably includes a step of sealing the obtained nonwoven fabric impregnated with an aqueous fibrous cellulose dispersion, from the viewpoint of maintaining the water retention capacity of the nonwoven fabric. The container for sealing the nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose may be made of, for example, plastic, glass, silicon, aluminum, or paper. The temperature at which the sealed nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose is stored is, for example, 5°C or higher and 50°C or lower, and preferably 10°C or higher and 40°C or lower.

[0122] (Application) A nonwoven fabric impregnated with an aqueous fibrous cellulose dispersion obtained using the kit of this embodiment and a nonwoven fabric impregnated with an aqueous fibrous cellulose dispersion obtained by the production method of this embodiment can be suitably used in applications requiring the nonwoven fabric to contain a large amount of water, such as wet tissues or wet sheets used in various applications such as sterilization, cleaning, cosmetics, moisturizing, gardening, medical care, etc. Specifically, a nonwoven fabric impregnated with an aqueous fibrous cellulose dispersion obtained using the kit of this embodiment and a nonwoven fabric impregnated with an aqueous fibrous cellulose dispersion obtained by the production method of this embodiment can be suitably used for sterilization wet tissues or wet sheets, floor cleaning wet sheets, moisture-retaining sheets for eyeglasses (to prevent dry eyes), cosmetics (for example, face masks), nonwoven sheets for gardening, nonwoven sheets for cut flowers, wet sheets for raising insects, medical sheets, etc. [Example]

[0123] 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 details, 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 interpreted as being limited by the specific examples shown below. Unless otherwise specified, the following operations were carried out at room temperature (23°C) and a relative humidity of 50%.

[0124] <Production Example 1> [Phosphorus oxoacid group introduction step] The raw pulp used was softwood kraft pulp (solid content 93% by mass, basis weight 245 g / m) manufactured by Oji Paper Co., Ltd. 2 Sheet-type 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 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 total weight 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. [Cleaning process] The resulting phosphorylated pulp was then washed. 100 g (bone dry mass) of phosphorylated pulp was mixed with 10 L of ion-exchanged water to obtain a pulp dispersion. The pulp was stirred to uniformly disperse the pulp, and then repeatedly filtered and dehydrated. The washing was completed when the electrical conductivity of the filtrate reached 100 μS / cm or less. [Neutralization process] 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.

[0125] The infrared absorption spectrum of the obtained phosphorylated pulp was measured using FT-IR. -1 Absorption due to the P=O of phosphate groups was observed around 2θ = 14° to 17° and 2θ = 22° to 23°, confirming the addition of phosphate groups to the pulp. Furthermore, when the obtained phosphorylated 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. The amount of phosphate groups (amount of first dissociated acid) measured by the method described below in [Measurement of phosphorus oxo acid group amount] was 1.45 mmol / g. The total amount of dissociated acid was 2.45 mmol / g.

[0126] [Fiber defibration process] Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solids concentration of 3% by mass. This slurry was processed five times in a single-disc refiner to obtain a phosphorylated microfibril cellulose fiber dispersion. The fiber width of the phosphorylated microfibril cellulose fiber dispersion was measured using a Valmet FS5 and found to be 20 μm.

[0127] X-ray diffraction confirmed that the phosphorylated microfibril cellulose maintained cellulose type I crystallinity.

[0128] <Production Example 2> Phosphorylated pulp was obtained in the same manner as in Production Example 1. Ion-exchanged water was added to the obtained phosphorylated pulp to prepare a slurry with a solids concentration of 2% by mass. This slurry was treated six times at a pressure of 150 MPa in a wet atomization device (manufactured by Sugino Machine Co., Ltd.) to obtain a cellulose nanofiber dispersion containing phosphorylated cellulose nanofibers. The fiber width of the phosphorylated cellulose nanofibers was measured using a transmission electron microscope and was found to be 3 to 5 nm.

[0129] X-ray diffraction confirmed that the phosphorylated cellulose nanofibers maintained cellulose type I crystals.

[0130] Example 1 Ion-exchanged water was added to the phosphorylated microfibril cellulose fiber dispersion obtained in Production Example 1 so that the solids concentration was diluted to 0.5% by mass. An electronically controlled stirrer (Eurostar, manufactured by IKA) was used as the stirrer, and the mixture was stirred at 4,000 rpm for 5 minutes to obtain a diluted phosphorylated microfibril cellulose fiber dispersion (aqueous fibrous cellulose dispersion). The viscosity measured by the measurement method described in [Viscosity Measurement] below was 2,400 mPa s.

[0131] As described later in [Calculation of water retention capacity], the obtained 0.5% by mass phosphorylated microfibril cellulose fiber dispersion was added to a 5 cm square piece cut into a thickness of 4 mm and a density of 0.15 g / cm.3 A dry air-laid nonwoven fabric (Hatosheet XCA-4, manufactured by Oji Kinocloth Co., Ltd.) was soaked in the water to obtain a nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose, and the water retention capacity was measured. The water retention capacity was 1.4 g / cm. 3 "Dry airlaid nonwoven fabric" is a dry nonwoven fabric formed by the airlaid method using cellulose fibers.

[0132] <Example 2> In Example 1, the thickness is 4 mm and the density is 0.15 g / cm 3 Instead of dry airlaid nonwoven fabric (Hatosheet XCA-4, manufactured by Oji Kinocloth Co., Ltd.), a thickness of 2 mm and a density of 0.20 g / cm 3 A nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose was obtained in the same manner as in Example 1, except that a dry air-laid nonwoven fabric (Hatosheet XCA-2, manufactured by Oji Kinocloth Co., Ltd.) was used, and the water retention capacity was determined. The water retention capacity was 1.7 g / cm. 3 It was.

[0133] Example 3 Ion-exchanged water was added to the phosphorylated microfibril cellulose fiber dispersion obtained in Production Example 1 so that the solids concentration was diluted to 1.0% by mass. An electronically controlled stirrer (Eurostar, manufactured by IKA) was used as the stirrer, and the mixture was stirred at 4,000 rpm for 5 minutes to obtain a diluted phosphorylated microfibril cellulose fiber dispersion (aqueous fibrous cellulose dispersion). The viscosity measured by the measurement method described in [Viscosity Measurement] below was 13,000 mPa s.

[0134] As described later in [Calculation of water retention capacity], the obtained 1.0 mass% phosphorylated microfibril cellulose fiber dispersion was added to a 5 cm square piece cut into a thickness of 2 mm and a density of 0.20 g / cm. 3 A dry air-laid nonwoven fabric (Hatosheet XCA-2, manufactured by Oji Kinocloth Co., Ltd.) was soaked in the water to obtain a nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose, and the water retention capacity was measured. The water retention capacity was 2.1 g / cm. 3 It was.

[0135] Example 4 Ion-exchanged water was added to dilute the cellulose nanofiber dispersion obtained in Production Example 2 to a solids concentration of 0.5% by mass. An electronically controlled stirrer (Eurostar, manufactured by IKA) was used, and the mixture was stirred at 4,000 rpm for 5 minutes to obtain a diluted phosphorylated microfibril cellulose fiber dispersion (aqueous fibrous cellulose dispersion). The viscosity measured by the measurement method described in [Viscosity Measurement] below was 15,500 mPa s.

[0136] As described later in [Water retention calculation], the obtained 0.5% by mass cellulose nanofiber dispersion was added to a 5 cm square piece cut into a thickness of 2 mm and a density of 0.20 g / cm. 3 A dry air-laid nonwoven fabric (Hatosheet XCA-2, manufactured by Oji Kinocloth Co., Ltd.) was immersed in the solution to obtain a nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose, and the water retention capacity was measured. The water retention capacity was 1.5 g / cm. 3 It was.

[0137] <Example 5> In Example 1, the thickness is 4 mm and the density is 0.15 g / cm 3 Instead of dry airlaid nonwoven fabric (Hatosheet XCA-4, manufactured by Oji Kinocloth Co., Ltd.), a thickness of 1 mm and a density of 0.04 g / cm 3 A nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose was obtained in the same manner as in Example 1, except that a dry air-laid nonwoven fabric (KS-40, manufactured by Oji Kinocloth Co., Ltd.) was used, and the water retention capacity was determined. The water retention capacity was 1.9 g / cm. 3 It was.

[0138] Example 6 In Example 1, the thickness is 4 mm and the density is 0.15 g / cm 3 Instead of dry airlaid nonwoven fabric (Hatosheet XCA-4, manufactured by Oji Kinocloth Co., Ltd.), a thickness of 1.4 mm and a density of 0.04 g / cm 3 A nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose was obtained in the same manner as in Example 1, except that a dry air-laid nonwoven fabric (K-60, manufactured by Oji Kinocloth Co., Ltd.) was used, and the water retention capacity was determined. The water retention capacity was 1.7 g / cm. 3 It was.

[0139] <Comparative Example 1> Ion-exchanged water was added to dilute the cellulose nanofiber dispersion obtained in Production Example 2 to a solids concentration of 0.2% by mass. An electronically controlled stirrer (Eurostar, manufactured by IKA) was used, and the mixture was stirred at 4,000 rpm for 5 minutes to obtain a diluted phosphorylated microfibril cellulose fiber dispersion (aqueous fibrous cellulose dispersion). The viscosity measured by the measurement method described in [Viscosity Measurement] below was 350 mPa s.

[0140] As described later in [Calculation of water retention capacity], the obtained 0.2 mass% cellulose nanofiber dispersion was added to a 5 cm square piece cut into a thickness of 2 mm and a density of 0.20 g / cm. 3 A dry air-laid nonwoven fabric (Hatosheet XCA-2, manufactured by Oji Kinocloth Co., Ltd.) was soaked in the water to obtain a nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose, and the water retention capacity was measured. The water retention capacity was 1.3 g / cm. 3 It was.

[0141] <Comparative Example 2> In Comparative Example 1, the thickness was 2 mm and the density was 0.20 g / cm 3 Instead of dry airlaid nonwoven fabric (Hatosheet XCA-2, manufactured by Oji Kinocloth Co., Ltd.), a thickness of 4 mm and a density of 0.15 g / cm 3 A nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose was obtained in the same manner as in Comparative Example 1, except that a dry airlaid nonwoven fabric (Hatosheet XCA-4, manufactured by Oji Kinocloth Co., Ltd.) was used, and the water retention capacity was determined. 3 It was.

[0142] <Comparative Example 3> Ion-exchanged water was added to dilute the cellulose nanofiber dispersion obtained in Production Example 2 to a solids concentration of 0.3% by mass. An electronically controlled stirrer (Eurostar, manufactured by IKA) was used and the mixture was stirred at 4,000 rpm for 5 minutes to obtain a diluted phosphorylated microfibril cellulose fiber dispersion (aqueous fibrous cellulose dispersion). The viscosity measured by the method described in [Viscosity Measurement] below was 4,000 mPa s.

[0143] As described later in [Water retention calculation], the obtained 0.3 mass% cellulose nanofiber dispersion was added to a 5 cm square cut out of cellulose nanofiber with a thickness of 4 mm and a density of 0.15 g / cm. 3 A dry air-laid nonwoven fabric (Hatosheet XCA-4, manufactured by Oji Kinocloth Co., Ltd.) was soaked in the aqueous dispersion of fibrous cellulose to obtain a nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose, and the water retention capacity was measured. The water retention capacity was 1.1 g / cm 3 It was.

[0144] <Comparative Example 4> In Example 1, the thickness is 4 mm and the density is 0.15 g / cm 3 Instead of dry airlaid nonwoven fabric (Hatosheet XCA-4, manufactured by Oji Kinocloth Co., Ltd.), a thickness of 8 mm and a density of 0.12 g / cm 3 A nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose was obtained in the same manner as in Example 1, except that a dry airlaid nonwoven fabric (Hatosheet XCA-8, manufactured by Oji Kinocloth Co., Ltd.) was used. The water retention capacity was 0.9 g / cm. 3 It was.

[0145] <Comparative Example 5> In Example 4, a nonwoven fabric impregnated with the aqueous fibrous cellulose dispersion was obtained in the same manner as in Example 4, except that the solids concentration of the cellulose nanofiber dispersion (aqueous fibrous cellulose dispersion) was 1.0 mass %, and the water retention capacity was determined. The viscosity of the aqueous fibrous cellulose dispersion, measured by the measurement method described in [Viscosity Measurement] below, was 67,000 mPa s. The water retention capacity was 0.7 g / cm. 3 It was.

[0146] <Comparative Example 6> In Example 4, a nonwoven fabric impregnated with the aqueous fibrous cellulose dispersion was obtained in the same manner as in Example 4, except that the solid content concentration of the cellulose nanofiber dispersion (aqueous fibrous cellulose dispersion) was changed to 0.1 mass %, and the water retention capacity was determined. The viscosity of the aqueous fibrous cellulose dispersion, measured by the measurement method described in [Viscosity Measurement] below, was 10 mPa s. The water retention capacity was 1.2 g / cm. 3 It was.

[0147] <Comparative Example 7> Ion-exchanged water was added to sodium carboxymethylcellulose (Tokyo Chemical Industry Co., Ltd.) so that the solids concentration was 1.0% by mass. An electronically controlled stirrer (Eurostar, IKA) was used and the mixture was stirred at 3,000 rpm for 10 minutes to obtain an aqueous solution of sodium carboxymethylcellulose. The viscosity measured using the method described in the "Viscosity Measurement" section below was 60 mPa s.

[0148] As described later in [Calculation of water retention capacity], the obtained 1.0 mass% sodium carboxymethylcellulose aqueous solution was added to a 5 cm square piece cut into a thickness of 2 mm and a density of 0.20 g / cm. 3 A dry airlaid nonwoven fabric (Hatosheet XCA-2, manufactured by Oji Kinocloth Co., Ltd.) was immersed in the solution, and the water retention capacity of the nonwoven fabric after immersion was measured. The water retention capacity was 1.3 g / cm. 3 It was.

[0149] <Comparative Example 8> As described in the "Water retention calculation" below, a 5cm square piece of 4mm thick porcelain with a density of 0.15g / cm was placed in ion-exchanged water. 3 A dry air-laid nonwoven fabric (Hatosheet XCA-4, manufactured by Oji Kinocloth Co., Ltd.) was soaked in the aqueous dispersion of fibrous cellulose to obtain a nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose, and the water retention capacity was measured. The water retention capacity was 1.1 g / cm 3 It was.

[0150] <Comparative Example 9> As described in the "Water retention calculation" below, a 5cm square piece of 2mm thick porcelain with a density of 0.20g / cm3 was placed in ion-exchanged water. 3 A dry air-laid nonwoven fabric (Hatosheet XCA-2, manufactured by Oji Kinocloth Co., Ltd.) was soaked in the water to obtain a nonwoven fabric impregnated with the aqueous dispersion of fibrous cellulose, and the water retention capacity was measured. The water retention capacity was 1.1 g / cm. 3 It was.

[0151] [Measurement of phosphorus oxoacid group content] Ion-exchanged water was added to the phosphate-group-introduced pulp obtained in Production Example 1 to prepare a slurry with a solids concentration of 2% by mass. This slurry was then treated twice at a pressure of 150 MPa in a wet pulverization device (Starburst, manufactured by Sugino Machine Co., Ltd.) to obtain a fine fibrous cellulose dispersion. The fine fibrous cellulose dispersion was diluted with ion-exchanged water to a concentration of 0.2% by mass to prepare a fibrous cellulose-containing slurry, which was then treated with an ion-exchange resin and titrated with an alkali to measure the content. 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 fibrous cellulose-containing slurry, shaking for 1 hour, and then pouring it onto a mesh with 90 μm openings to separate the resin from the slurry. In addition, alkali titration was performed by measuring the change in the pH of a slurry containing fine fibrous cellulose after ion exchange resin treatment while adding 10 μL of 0.1 N sodium hydroxide solution every 5 seconds. Nitrogen gas was bubbled through the slurry 15 minutes before the start of the titration. In this neutralization titration, two maximum points of increment (the derivative of pH with respect to the amount of alkali added) were observed on the plot of pH versus the amount of alkali added. The first maximum point of increment after starting the addition of alkali is called the first endpoint, and the second maximum point is called the second endpoint (Figure 1). The amount of alkali required from the start of the titration to the first endpoint is equal to the amount of first dissociated acid in the slurry used for titration. The amount of alkali required from the start of the titration to the second endpoint is equal to the total amount of dissociated acid in the slurry used for titration. The amount of alkali (mmol) required from the start of titration to the first endpoint was divided by the solid content (g) in the slurry to be titrated, and the value was taken as the amount of phosphorus oxo acid groups (mmol / g).

[0152] [Viscosity measurement] The aqueous dispersions of fibrous cellulose obtained in Examples 1 to 6 and Comparative Examples 1 to 5 were allowed to stand at 23°C for 24 hours, and then their viscosities were measured using a Brookfield viscometer (LV-2T viscometer). The measurement conditions were 23°C, and the viscosity was measured after rotating at 3 rpm for 3 minutes. The viscosity was also measured in the same manner as above, except that the rotation speed was 30 rpm for the aqueous dispersion of fibrous cellulose obtained in Comparative Example 6 and 12 rpm for the aqueous solution of sodium carboxymethylcellulose obtained in Comparative Example 7.

[0153] [Measurement of nonwoven fabric thickness] The thickness of the nonwoven fabric was measured in accordance with "6.1.1 Method A" of JIS L 1913:2010.

[0154] [Calculating the density of nonwoven fabric] The density of the nonwoven fabric was calculated from the relationship between the basis weight of the nonwoven fabric measured in accordance with "6.2 Mass per unit area (ISO method)" of JIS L 1913:2010 and the thickness of the nonwoven fabric.

[0155] [Water retention calculation] The mass (W1) (g) of a nonwoven fabric cut into a 5 cm square was measured. A container was filled with a fibrous cellulose aqueous dispersion, a carboxymethyl cellulose sodium aqueous solution, or ion-exchanged water, and the 5 cm square nonwoven fabric was immersed for 30 minutes to obtain a fibrous cellulose aqueous dispersion-impregnated nonwoven fabric or a ion-exchanged water-impregnated nonwoven fabric. The immersed nonwoven fabric was removed from the liquid with tweezers, and the liquid was allowed to drip off for 30 seconds, after which the mass (W2) (g) was measured. The water retention capacity was calculated using the following formula, where T (cm) is the thickness of the nonwoven fabric after immersion, and C (mass%) is the concentration of the fibrous cellulose aqueous dispersion, the carboxymethyl cellulose sodium aqueous solution, or the ion-exchanged water. Water retention amount (g / cm 3 )=(W2-W1)×(100-C) / 100 / (5×5×T)

[0156] [Table 1]

[0157] Table 1 shows that nonwoven fabrics with high water retention capacity can be obtained by using the kit for producing nonwoven fabrics impregnated with an aqueous fibrous cellulose dispersion of the present invention (Examples 1 to 6). In contrast, when a kit having an aqueous fibrous cellulose dispersion with a viscosity (η) of less than 1,000 mPa·s was used (Comparative Examples 1 and 2), when a kit not satisfying formula (I) was used (Comparative Examples 3 to 5), or when a kit having an aqueous fibrous cellulose dispersion with a viscosity (η) of less than 1,000 mPa·s and not satisfying formula (I) was used (Comparative Example 6), the water retention capacity of the resulting nonwoven fabric was found to be low. Furthermore, when an aqueous solution of sodium carboxymethylcellulose or ion-exchanged water was used instead of the aqueous fibrous cellulose dispersion (Comparative Examples 7 to 9), the water retention capacity of the resulting nonwoven fabric was found to be low.

Claims

1. A kit for impregnating a nonwoven fabric with an aqueous fibrous cellulose dispersion, comprising an aqueous fibrous cellulose dispersion and a nonwoven fabric, the viscosity η [mPa s] of the fibrous cellulose aqueous dispersion in a static state is 1,000 mPa s or more; A kit for a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose, wherein the natural logarithm Ln(η) of the viscosity η [mPa·s] and the thickness t [mm] of the nonwoven fabric satisfy the following formula (I): t≦-0.87Ln(η)+11...(I)

2. 2. The kit for producing a nonwoven fabric impregnated with an aqueous fibrous cellulose dispersion according to claim 1, wherein the viscosity η of the aqueous fibrous cellulose dispersion in a static state is 100,000 mPa·s or less.

3. 3. The kit for producing a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose according to claim 1, wherein the thickness t of the nonwoven fabric is 0.8 mm or more.

4. The density of the nonwoven fabric is 0.02 g / cm ３ 0.25g / cm or more ３ 3. The kit for producing a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose according to claim 1 or 2, wherein:

5. 3. The kit for producing a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose according to claim 1, wherein the content of fibrous cellulose in the aqueous dispersion of fibrous cellulose is 0.15% by mass or more and 1.5% by mass or less.

6. 3. The kit for producing a nonwoven fabric impregnated with an aqueous fibrous cellulose dispersion according to claim 1, wherein the nonwoven fabric is a nonwoven fabric containing cellulose fibers.

7. A method for producing a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose, comprising the step of impregnating a nonwoven fabric with an aqueous dispersion of fibrous cellulose, the viscosity η [mPa s] of the fibrous cellulose aqueous dispersion in a static state is 1,000 mPa or more; a method for producing a nonwoven fabric impregnated with an aqueous dispersion of fibrous cellulose, wherein the natural logarithm Ln(η) of the viscosity η [mPa s] and the thickness t [mm] of the nonwoven fabric satisfy the following formula (I): t≦-0.87Ln(η)+11...(I)

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