JP2020172738A - Sheet and manufacturing method for sheet - Google Patents

Abstract

To provide a sheet containing fibrous cellulose having a fiber width of 10 μm or more and fine fibrous cellulose having a fiber width of 1 μm or less, in which the occurrence of twisting is suppressed.SOLUTION: A sheet of the present invention includes: a first cellulose fiber having a phosphorous acid group or a substituent derived from a phosphorous acid group and having a fiber width of 10 μm or more; and a second cellulose fiber having a fiber width of 1000 nm or less.SELECTED DRAWING: None

Description

The present invention relates to a sheet and a method for producing the sheet.

In recent years, due to the substitution of petroleum resources and heightened environmental awareness, materials using reproducible natural fibers have been attracting attention. Among natural fibers, fibrous cellulose having a fiber diameter of 10 to 50 μm, particularly fibrous cellulose (pulp) derived from wood, has been widely used mainly as paper products.

As the fibrous cellulose, fine fibrous cellulose having a fiber diameter of 1 μm or less is also known. Fine fibrous cellulose is attracting attention as a new material, and its uses are diverse. For example, development of sheets, non-woven fabrics, and resin composites containing fine fibrous cellulose is underway.

For example, Patent Document 1 discloses a microporous membrane made of cellulose fibers in which fibers having a thickness of 1 μm or more are contained in an amount of 1% by weight or more based on the total weight of the cellulose fibers. There is. Further, Patent Document 2 describes a first fiber having a number average fiber width of 2 nm or more and less than 1000 nm, and a second fiber having a number average fiber width of 1000 nm or more and 100,000 nm or less and a number average fiber length of 0.1 to 20 mm. Nonwoven fabrics containing fibers are disclosed. Further, Patent Document 3 discloses a non-woven fabric containing cellulose fibers having an average fiber diameter of 0.1 to 50 μm and polyolefin fibers having an average fiber diameter of 1.5 μm or less.

Japanese Unexamined Patent Publication No. 2014-210987 JP-A-2015-4140 Japanese Unexamined Patent Publication No. 2012-036518

As described above, films and non-woven fabrics containing various cellulose fibers are known. However, when the present inventors produce a sheet containing fibrous cellulose (pulp) having a fiber width of 10 μm or more and fine fibrous cellulose having a fiber width of 1 μm or less, twisting occurs in the obtained sheet. I found out that there are cases.
Therefore, the present invention provides a sheet containing fibrous cellulose (pulp) having a fiber width of 10 μm or more and fine fibrous cellulose having a fiber width of 1 μm or less, in which the occurrence of twisting is suppressed. The purpose.

As a result of diligent studies to solve the above problems, the present inventors have found that in a sheet containing a first cellulose fiber having a fiber width of 10 μm or more and a second cellulose fiber having a fiber width of 1000 nm or less. It has been found that by using a first cellulose fiber having a phosphorous acid group or a substituent derived from a phosphorous acid group, a sheet in which the occurrence of twisting is suppressed can be obtained.
Specifically, the present invention has the following configuration.

[1] Includes a first cellulose fiber having a phosphorous acid group or a substituent derived from a phosphorous acid group and having a fiber width of 10 μm or more, and a second cellulose fiber having a fiber width of 1000 nm or less. Sheet.
[2] The sheet according to [1], wherein the second cellulose fiber has a phosphorous acid group or a substituent derived from a phosphorous acid group.
[3] The sheet according to [1] or [2], wherein the content of the first cellulose fiber is 10% by mass or more with respect to the total mass of the cellulose fiber.
[4] The sheet according to any one of [1] to [3], which has a haze of 20% or more.
[5] The sheet according to any one of [1] to [4], which has a total light transmittance of 80% or more.
[6] The sheet according to any one of [1] to [5], which has a basis weight of 40 g / m ² or less.
[7] The sheet according to any one of [1] to [6], which has an air permeability of 10,000 seconds or more.
[8] The sheet according to any one of [1] to [7], wherein the water retention degree of the first cellulose fiber is 220% or more.
[9] The first cellulose fiber having a water retention degree of 220% or more, a fiber width of 10 μm or more, a phosphorous acid group or a substituent derived from a phosphorous acid group, and a fiber width of 1000 nm or less. A method for producing a sheet, which comprises a step of forming a sheet from a slurry containing a second cellulose fiber.
[10] The method for producing a sheet according to [9], wherein the second cellulose fiber has a phosphorous acid group or a substituent derived from a phosphorous acid group.

According to the present invention, a sheet in which the occurrence of twisting is suppressed can be obtained.

FIG. 1 is a graph showing the relationship between the amount of NaOH added dropwise and the pH of a fibrous cellulose-containing slurry having a phosphorus oxo acid group. FIG. 2 is a graph showing the relationship between the amount of NaOH added dropwise to the fibrous cellulose-containing slurry having a carboxy group and the pH. FIG. 3 is a photograph showing an example of twisting generated in the sheet of the comparative example.

Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be based on typical embodiments or specific examples, but the present invention is not limited to such embodiments.

(Sheet)
The present invention comprises a first cellulose fiber having a phosphorous acid group or a substituent derived from a phosphorous acid group and having a fiber width of 10 μm or more, and a second cellulose fiber having a fiber width of 1000 nm or less. Regarding the including sheet. In the present specification, cellulose fibers having a fiber width of 1000 nm or less may be referred to as fine fibrous cellulose.

Since the sheet of the present invention has the above-mentioned structure, twisting of the sheet is suppressed in the sheet manufacturing process. Therefore, the sheet of the present invention has a good appearance and a highly homogeneous sheet can be obtained.

The haze of the sheet of the present invention is preferably 20% or more. The haze of the sheet of the present invention may be higher than that of a sheet containing mainly fine fibrous cellulose as cellulose fibers. Further, the haze of the sheet of the present invention may be 90% or less, 85% or less, or 80% or less. By setting the haze of the sheet of the present invention to the above upper limit value or less, a sheet having excellent transparency as compared with conventional glassine paper or graphan paper can be obtained.
The total light transmittance of the sheet of the present invention is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. Here, the haze of the sheet is a value measured using, for example, a haze meter (manufactured by Murakami Color Technology Research Institute, HM-150) in accordance with JIS K 7136. The total light transmittance of the sheet is a value measured using, for example, a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute) in accordance with JIS K 7361.

Further, the sheet of the present invention is also excellent in barrier property. In the sheet of the present invention, a first cellulose fiber having a fiber width of 10 μm or more and having a phosphorous acid group or a substituent derived from a phosphorous acid group and a second cellulose fiber having a fiber width of 1000 nm or less are used. Since it is used in combination, the cellulose fibers can be made denser, and as a result, the barrier property is enhanced. Specifically, the air permeability of the sheet of the present invention is preferably 10,000 seconds or more, more preferably 50,000 seconds or more, and even more preferably 100,000 seconds or more. The air permeability of the sheet is determined by, for example, J. It can be calculated according to the Oken-type air permeability method of TAPPI-5.

The sheet of the present invention has a low basis weight and is therefore lightweight. Conventionally, when manufacturing glassine paper or graphan paper, it has been considered to increase the density of cellulose fibers in order to improve transparency and barrier properties, and a calendar treatment is performed after the papermaking process. Was practiced as a conventional method. However, in order to ensure the workability of calendar processing, there is a limit to reducing the basis weight. On the other hand, in the sheet of the present invention, the first cellulose fiber having a fiber width of 10 μm or more and having a phosphorous acid group or a substituent derived from a phosphorous acid group and a second cellulose having a fiber width of 1000 nm or less. Since the fibers are used in combination, a sheet having excellent transparency and barrier properties can be obtained without performing calendar treatment, and as a result, the basis weight can be reduced. Therefore, the weight reduction of the seat is achieved. In this way, the present invention can achieve both low basis weight and high barrier properties, which are usually in a trade-off relationship. Specifically, the basis weight of the sheet of the present invention is preferably 40 g / m ² or less, more preferably 30 g / m ² or less, and even more preferably 20 g / m ² or less. The basis weight of the sheet can be calculated according to, for example, JIS P 8124. The basis weight of the sheet can be appropriately adjusted according to the performance required for the sheet.

The thickness of the sheet of the present invention is preferably 5 μm or more, more preferably 10 μm or more, and further preferably 20 μm or more. The upper limit of the thickness of the sheet is not particularly limited, but may be, for example, 1000 μm. The thickness of the sheet is measured according to, for example, JIS P 8118.

The density of the sheet of the present invention is preferably 0.1 g / cm ³ or more, more preferably 0.2 g / cm ³ or more, and further preferably 0.3 g / cm ³ or more. The upper limit of the density of the sheet is not particularly limited, but is preferably 5.0 g / cm ³ or less, for example. Here, the density of the sheet is calculated from these values by measuring the basis weight according to JIS P 8124 and measuring the thickness of the sheet according to JIS P 8118. The density of the sheet can be appropriately adjusted according to the performance required for the sheet, for example, by performing calendar processing or the like.

(First cellulose fiber)
The sheet of the present invention contains a first cellulose fiber. Here, the first cellulose fiber is a cellulose fiber having a phosphorous acid group or a substituent derived from a phosphorous acid group and having a fiber width of 10 μm or more. The fiber width of the first cellulose fiber may be 10 μm or more, but is preferably 15 μm or more, and more preferably 20 μm or more. The fiber width of the first cellulose fiber is preferably 100 μm or less. In the present specification, the first cellulose fiber is also referred to as a coarse cellulose fiber.

The fiber width of the first cellulose fiber can be measured using a Kajaani fiber length measuring device (FS-200 type) manufactured by Kajaani Automation Co., Ltd. Here, the fiber width of the first cellulose fiber is the fiber width of the trunk fiber of the cellulose fiber. For example, when the cellulose fiber is a fibril cellulose fiber, the fiber width of the trunk fiber constituting the main shaft is referred to as the fiber width of the first cellulose fiber, not the fiber width of the fibrillated and branched fiber.

It is preferable to use pulp as the fiber raw material of the first cellulose fiber. Examples of pulp include wood pulp, non-wood pulp and deinked pulp. The wood pulp is not particularly limited, but is, for example, broadleaf kraft pulp (LBKP), coniferous kraft pulp (NBKP), sulfite pulp (SP), dissolved pulp (DP), soda pulp (AP), and unbleached kraft pulp (UKP). ) And chemical pulp such as oxygen bleached kraft pulp (OKP), semi-chemical pulp such as semi-chemical pulp (SCP) and chemiground wood pulp (CGP), crushed wood pulp (GP) and thermomechanical pulp (TMP, BCTMP), etc. Examples include mechanical pulp. The non-wood pulp is not particularly limited, and examples thereof include cotton pulp such as cotton linter and cotton lint, and non-wood pulp such as hemp, straw and bagasse. The deinking pulp is not particularly limited, and examples thereof include deinking pulp made from used paper. As the first cellulose fiber, one of the above may be used alone, or two or more of them may be mixed and used.

The first cellulose fiber has a phosphorous acid group or a substituent derived from a phosphorous acid group (also simply referred to as a phosphorous acid group). The phosphorous acid group or the substituent derived from the phosphorous acid group is, for example, a substituent represented by the following formula (2).

In equation (2), b is a natural number, m is an arbitrary number, and b × m = 1. α is a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched chain hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched chain hydrocarbon group. , An unsaturated-cyclic hydrocarbon group, an aromatic group, or an inducing group thereof. Above all, it is particularly preferable that α is a hydrogen atom. The α in the formula (2) does not include a group derived from the cellulose molecular chain.

Examples of the saturated-linear hydrocarbon group represented by α in the formula (2) include a methyl group, an ethyl group, an n-propyl group, an n-butyl group and the like, but are not particularly limited. Examples of the saturated-branched chain hydrocarbon group include an i-propyl group and a t-butyl group, but are not particularly limited. Examples of the saturated-cyclic hydrocarbon group include, but are not limited to, a cyclopentyl group, a cyclohexyl group and the like. Examples of the unsaturated-linear hydrocarbon group include a vinyl group, an allyl group and the like, but are not particularly limited. Examples of the unsaturated-branched chain hydrocarbon group include an i-propenyl group and a 3-butenyl group, but are not particularly limited. Examples of the unsaturated-cyclic hydrocarbon group include, but are not limited to, a cyclopentenyl group, a cyclohexenyl group and the like. Examples of the aromatic group include a phenyl group and a naphthyl group, but the group is not particularly limited.

Further, as the inducing group in α, a functional group in which at least one of functional groups such as a carboxy group, a hydroxy group, or an amino group is added or substituted with respect to the main chain or side chain of the above-mentioned various hydrocarbon groups. The group is mentioned, but is not particularly limited. The number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, and more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R to the above range, the molecular weight of the phosphorous acid group can be set to an appropriate range, and penetration into the fiber raw material is facilitated.

Β ^{b +} in the formula (2) is a monovalent or higher cation composed of an organic substance or an inorganic substance. Examples of monovalent or higher cations composed of organic substances include aliphatic ammonium or aromatic ammonium, and examples of monovalent or higher valent cations composed of inorganic substances include ions of alkali metals such as sodium, potassium, and lithium. Examples thereof include cations of divalent metals such as calcium and magnesium, hydrogen ions, and the like, but the present invention is not particularly limited. These may be applied alone or in combination of two or more. The monovalent or higher cation composed of an organic substance or an inorganic substance is preferably sodium or potassium ion which is hard to yellow when the fiber raw material containing β is heated and is easily industrially used, but is not particularly limited.

The first cellulose fiber may have a phosphorous acid group or a group derived from the phosphorous acid group in addition to the phosphorous acid group or the substituent derived from the phosphorous acid group. The phosphoric acid group or the group derived from the phosphoric acid group is, for example, a substituent represented by the following formula (1) or (3). The phosphoric acid group or the group derived from the phosphoric acid group may be a condensed phosphorus oxo acid group as represented by the following formula (3).

In the formula (1), a and b are natural numbers, and m is an arbitrary number (where a = b × m). Of α and α', a are O ⁻ and the rest are OR. Here, R is a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched chain hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, or an unsaturated-branched chain. A hydrocarbon group, an unsaturated-cyclic hydrocarbon group, an aromatic group, or an inducing group thereof. In addition, α in the formula (1) may be a group derived from a cellulose molecular chain.

In the formula (3), a and b are natural numbers, m is an arbitrary number, and n is a natural number of 2 or more (where a = b × m). Of α ¹ , α ² , ..., α ⁿ and α', a are O ⁻ , and the rest are either R or OR. Here, R is a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched chain hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, or an unsaturated-branched chain. A hydrocarbon group, an unsaturated-cyclic hydrocarbon group, an aromatic group, or an inducing group thereof. In addition, α in the formula (3) may be a group derived from a cellulose molecular chain.

The specific examples of each group in the formulas (1) and (3) are the same as the specific examples of each group in the formula (2). Further, the formula (1) and specific examples beta ^{b +} a in (3) are the same as specific examples of beta ^{b +} in equation (2).

The fact that the first cellulose fiber has a phosphorous acid group as a substituent means that the infrared absorption spectrum of the dispersion containing the first cellulose fiber is measured, and the tautomerism of the phosphorous acid group is measured in the vicinity of 1210 cm ^-1. It can be confirmed by observing the P = O-based absorption of the body phosphonate group. In addition, the fact that the first cellulose fiber has a phosphoric acid group as a substituent means that the infrared absorption spectrum of the dispersion containing the first cellulose fiber is measured, and P = O of the phosphoric acid group is measured in the vicinity of 1230 cm ^-1. It can be confirmed by observing the absorption based on. Further, the fact that the first cellulose fiber has a phosphorous acid group or a phosphorous acid group as a substituent can be confirmed by a method of confirming a chemical shift by using NMR, a method of combining titration with elemental analysis, or the like.

The amount of the phosphorous acid group introduced into the first cellulose fiber is preferably 0.1 mmol / g or more, more preferably 0.3 mmol / g or more per 1 g (mass) of the first cellulose fiber, for example. , 0.5 mmol / g or more, more preferably 0.7 mmol / g or more, and particularly preferably 1.0 mmol / g or more. The amount of the phosphorous acid group introduced into the first cellulose fiber is preferably 3.65 mmol / g or less, more preferably 3.5 mmol / g or less per 1 g (mass) of the cellulose fiber. More preferably, it is 0.0 mmol / g or less. Here, the unit mmol / g indicates, for example, the amount of substituents per 1 g of mass of the first cellulose fiber when the counter ion of the phosphite group is a hydrogen ion (H ⁺ ).

The amount of a phosphorous acid group (including a phosphorous acid group) introduced into the first cellulose fiber can be measured by, for example, a neutralization titration method. In the measurement by the neutralization titration method, the introduction amount is measured by determining the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to the obtained first cellulose fiber-containing slurry.

FIG. 1 is a graph showing the relationship between the amount of NaOH added dropwise and the pH of the first cellulose fiber-containing slurry having a phosphoric acid group. The amount of the phosphorus oxo acid group introduced into the first cellulose fiber is measured, for example, as follows.
First, the slurry containing the first cellulose fiber is treated with a strongly acidic ion exchange resin. If necessary, the defibration treatment similar to the defibration treatment step described later may be performed on the measurement target before the treatment with the strongly acidic ion exchange resin.
Next, the change in pH is observed while adding an aqueous sodium hydroxide solution, and a titration curve as shown in the upper part of FIG. 1 is obtained. The titration curve shown in the upper part of FIG. 1 plots the measured pH with respect to the amount of alkali added, and the titration curve shown in the lower part of FIG. 1 plots the pH with respect to the amount of alkali added. The increment (differential value) (1 / mmol) is plotted. In this neutralization titration, two points are confirmed in which the increment (differential value of pH with respect to the amount of alkali dropped) becomes maximum in the curve plotting the measured pH with respect to the amount of alkali added. Of these, the maximum point of the increment obtained first when alkali is added is called the first end point, and the maximum point of the increment obtained next is called the second end point. The amount of alkali required from the start of titration to the first end point is equal to the amount of first dissociated acid of the first cellulose fiber contained in the slurry used for titration, and is required from the first end point to the second end point. The amount of alkali used for titration becomes equal to the amount of second dissociating acid of the first cellulose fiber contained in the slurry used for titration, and the amount of alkali required from the start of titration to the second end point is contained in the slurry used for titration. It is equal to the total amount of dissociated acid of the first cellulose fiber. Then, the value obtained by dividing the amount of alkali required from the start of titration to the first end point by the solid content (g) in the slurry to be titrated is the amount of phosphorus oxo acid group introduced (mmol / g). The amount of phosphorus oxo acid group introduced (or the amount of phosphorus oxo acid group) simply means the amount of the first dissociated acid.
In FIG. 1, the region from the start of titration to the first end point is referred to as a first region, and the region from the first end point to the second end point is referred to as a second region. For example, when the phosphoric acid group is a phosphoric acid group and the phosphoric acid group causes condensation, the amount of weakly acidic groups in the phosphoric acid group (also referred to as the second dissociated acid amount in the present specification) is apparently It decreases, and the amount of alkali required for the second region is smaller than the amount of alkali required for the first region. On the other hand, the amount of strongly acidic groups in the phosphorus oxo acid group (also referred to as the first dissociated acid amount in the present specification) is the same as the amount of phosphorus atoms regardless of the presence or absence of condensation. Further, when the phosphorous acid group is a phosphorous acid group, the weakly acidic group does not exist in the phosphorous acid group, so that the amount of alkali required for the second region is reduced or the amount of alkali required for the second region is reduced. May be zero. In this case, the titration curve has one point where the pH increment is maximized.

Since the denominator of the above-mentioned phosphorus oxo acid group introduction amount (mmol / g) indicates the mass of the acid-type cellulose fiber, the phosphorus oxo acid group amount (hereinafter, acid) of the acid-type cellulose fiber (hereinafter, acid) Type)) is shown. On the other hand, when the counterion of the phosphorus oxo acid group is replaced with an arbitrary cation C so as to have a charge equivalent, the denominator is converted to the mass of the cellulose fiber when the cation C is the counterion. Then, the amount of phosphorus oxo acid groups (hereinafter, the amount of phosphorus oxo acid groups (C type)) possessed by the cellulose fibers whose cation C is a counterion can be obtained.
That is, it is calculated by the following formula.
Phosphoric acid group amount (C type) = Phosphoric acid group amount (acid type) / {1+ (W-1) x A / 1000}
A [mmol / g]: Total anion amount derived from the phosphorus oxo acid group of the first cellulose fiber (total dissociated acid amount of the phosphorus oxo acid group)
W: Formula amount per valence of cation C (for example, Na is 23, Al is 9)

In the measurement of the amount of phosphorus oxo acid groups by the titration method, if the amount of one drop of the sodium hydroxide aqueous solution is too large or the titration interval is too short, the amount of phosphorus oxo acid groups will be lower than the original value. It may not be obtained. As an appropriate dropping amount and titration interval, for example, it is desirable to titrate 10 to 50 μL of a 0.1 N sodium hydroxide aqueous solution every 5 to 30 seconds. Further, in order to eliminate the influence of carbon dioxide dissolved in the first cellulose fiber-containing slurry, for example, measurement is performed while blowing an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration to the end of titration. desirable.

In addition, which of the phosphite, the phosphoric acid, and the condensed phosphoric acid is the phosphoric acid detected when the phosphoric acid group, the condensed phosphoric acid group, or both is contained in addition to the phosphite group? As a method for distinguishing between, for example, a method of performing a treatment for cutting the condensed structure such as acid hydrolysis and then performing the above-mentioned titration operation, or a treatment for converting a phosphite group into a phosphate group such as an oxidation treatment. Examples thereof include a method of performing the above-mentioned titration operation after the operation.

When the first cellulose fiber and the second cellulose fiber are mixed, the amount of phosphorous acid group introduced (phosphorous acid group amount) is measured by the method described above after separating and recovering by the centrifugation method. For centrifugation, a cellulose dispersion in which the first cellulose fiber and the second cellulose fiber are mixed is adjusted to a solid content concentration of 0.2% by mass, and a high-speed cooling centrifuge (Kokusan Co., Ltd., H-2000B) is used. Perform under the conditions of 12000G and 10 minutes. Then, the obtained precipitated solid content is recovered as the first cellulose fiber, and the supernatant is recovered as the second cellulose fiber.

The water retention degree of the first cellulose fiber is preferably 220% or more, more preferably 230% or more, further preferably 240% or more, further preferably 250% or more, and 280. % Or more is particularly preferable. Moreover, the water retention degree of the first cellulose fiber is preferably 600% or less. The water retention of the first cellulose fiber is determined by J. It is a value measured according to TAPPI-26. The water retention degree of the first cellulose fiber is the water retention degree of the first cellulose fiber before sheet formation, but the water retention degree of the first cellulose fiber after sheet formation satisfies the above range. May be good.

The content of the first cellulose fiber is preferably 10% by mass or more, more preferably 20% by mass or more, and more preferably 30% by mass or more, based on the total mass of the cellulose fibers contained in the sheet. Is even more preferable. The content of the first cellulose fiber is preferably 99% by mass or less, more preferably 95% by mass or less, and 90% by mass or less, based on the total mass of the cellulose fibers contained in the sheet. It is more preferably 80% by mass or less, and particularly preferably 75% by mass or less.

<First cellulose fiber manufacturing process>
<Phosphorous acid group introduction process>
The first cellulose fiber manufacturing step includes a phosphite group introduction step. In the phosphite group introduction step, at least one compound (hereinafter, also referred to as “compound A”) selected from compounds capable of introducing a phosphorous acid group by reacting with a hydroxyl group of a fiber raw material containing cellulose is introduced. , A step of acting on a fiber raw material containing cellulose. By this step, a phosphite group-introduced fiber can be obtained.

In the phosphorous acid group introduction step according to the present embodiment, the reaction between the fiber raw material containing cellulose and Compound A is carried out in the presence of at least one selected from urea and its derivatives (hereinafter, also referred to as “Compound B”). You may go. On the other hand, the reaction of the fiber raw material containing cellulose with the compound A may be carried out in the absence of the compound B.

As an example of the method of allowing the compound A to act on the fiber raw material in the coexistence with the compound B, a method of mixing the compound A and the compound B with the fiber raw material in a dry state, a wet state or a slurry state can be mentioned. Of these, since the reaction uniformity is high, it is preferable to use a fiber raw material in a dry state or a wet state, and it is particularly preferable to use a fiber raw material in a dry state. The form of the fiber raw material is not particularly limited, but is preferably cotton-like or thin sheet-like, for example. Examples of the compound A and the compound B include a method of adding the compound A and the compound B to the fiber raw material in the form of a powder or a solution dissolved in a solvent, or in a state of being heated to a melting point or higher and melted. Of these, since the reaction is highly homogeneous, it is preferable to add the mixture in the form of a solution dissolved in a solvent, particularly in the form of an aqueous solution. Further, the compound A and the compound B may be added to the fiber raw material at the same time, may be added separately, or may be added as a mixture. The method for adding the compound A and the compound B is not particularly limited, but when the compound A and the compound B are in the form of a solution, the fiber raw material may be immersed in the solution to absorb the liquid and then taken out, or the fiber raw material may be taken out. The solution may be dropped into the water. Further, the required amounts of Compound A and Compound B may be added to the fiber raw material, or after the excess amounts of Compound A and Compound B are added to the fiber raw material, respectively, the excess Compound A and Compound B are added by pressing or filtering. It may be removed.

The compound A used in this embodiment is at least one selected from a compound having a phosphorous acid group and a salt thereof. Examples of the compound having a phosphorous acid group include phosphorous acid, and examples of phosphorous acid include 99% phosphorous acid (phosphonic acid). Examples of the salt of the compound having a phosphorous acid group include a lithium salt, a sodium salt, a potassium salt, and an ammonium salt of phosphorous acid, and these can have various neutralization degrees. Of these, phosphorous acid, sodium salt of phosphorous acid, potassium salt of phosphorous acid, or sub-phosphorous acid, from the viewpoint of high efficiency of introduction of phosphorous acid group, low cost, and easy industrial application. An ammonium salt of phosphoric acid is preferably used.

The amount of compound A added to the fiber raw material is not particularly limited, but for example, when the amount of compound A added is converted to the phosphorus atomic weight, the amount of phosphorus atom added to the fiber raw material (absolute dry mass) is 0.5% by mass or more. It is preferably 100% by mass or less, more preferably 1% by mass or more and 50% by mass or less, and further preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atom added to the fiber raw material within the above range, the yield of the first cellulose fiber can be further improved. On the other hand, by setting the addition amount of phosphorus atoms to the fiber raw material to be equal to or less than the above upper limit value, the effect of improving the yield and the cost can be balanced.

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

The amount of compound B added to the fiber raw material (absolute dry mass) is not particularly limited, but is preferably 1% by mass or more and 500% by mass or less, and more preferably 10% by mass or more and 400% by mass or less. It is more preferably 100% by mass or more and 350% by mass or less.

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

In the phosphorous acid group introduction step, it is preferable to add or mix the compound A or the like to the fiber raw material and then heat-treat the fiber raw material. As the heat treatment temperature, it is preferable to select a temperature at which the phosphite group can be efficiently introduced while suppressing the thermal decomposition and hydrolysis reaction of the fiber. The heat treatment temperature 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 further preferably 130 ° C. or higher and 200 ° C. or lower. In addition, equipment having various heat media can be used for the heat treatment, for example, a stirring drying device, a rotary drying device, a disk drying device, a roll type heating device, a plate type heating device, a fluidized layer drying device, and an air stream. A drying device, a vacuum drying device, an infrared heating device, a far infrared heating device, a microwave heating device, and a high frequency drying device can be used.

In the heat treatment according to the present embodiment, for example, a method of adding compound A to a thin sheet-shaped fiber raw material by a method such as impregnation and then heating, or a method of heating while kneading or stirring the fiber raw material and compound A with a kneader or the like. Can be adopted. This makes it possible to suppress uneven concentration of compound A in the fiber raw material and more uniformly introduce the phosphorous acid group onto the surface of the cellulose fiber contained in the fiber raw material. This is because when the water molecules move to the surface of the fiber raw material due to drying, the dissolved compound A is attracted to the water molecules by the surface tension and also moves to the surface of the fiber raw material (that is, the concentration unevenness of the compound A is caused. It is considered that this is due to the fact that it can be suppressed.

Further, the heating device used for the heat treatment always keeps the water content retained by the slurry and the water content generated by the dehydration condensation (phosphate esterification) reaction between the compound A and the hydroxyl group contained in the cellulose or the like in the fiber raw material. It is preferable that the device can be discharged to the outside of the device system. Examples of such a heating device include a ventilation type oven and the like. By constantly discharging the water in the apparatus system, it is possible to suppress the hydrolysis reaction of the phosphate ester bond, which is the reverse reaction of the phosphate esterification, and also to suppress the acid hydrolysis of the sugar chain in the fiber. it can.

The heat treatment time is preferably 1 second or more and 300 minutes or less, more preferably 1 second or more and 1000 seconds or less, and 10 seconds or more and 800 seconds or less after the water is substantially removed from the fiber raw material. Is more preferable. In the present embodiment, the amount of phosphite group introduced can be within a preferable range by setting the heating temperature and the heating time within appropriate ranges.

The phosphorous acid group introduction step may be performed at least once, but may be repeated twice or more. By performing the phosphorous acid group introduction step two or more times, many phosphorous acid groups can be introduced into the fiber raw material. In the present embodiment, as an example of a preferable embodiment, there is a case where the phosphite group introduction step is performed twice.

<Washing process>
In the first method for producing cellulose fibers in the present embodiment, a washing step can be performed on the phosphorous acid group-introduced fibers, if necessary. The cleaning step is performed, for example, by cleaning the phosphite group-introduced fibers with water or an organic solvent. Further, the cleaning step may be performed after each step described later, and the number of cleanings performed in each cleaning step is not particularly limited.

<Alkaline treatment process>
In the first method for producing cellulose fibers in the present embodiment, if necessary, the washed phosphite group-introduced fibers may be treated with an alkali. In this case, it is preferable to adjust the pH to 12 or more and 13 or less by diluting the washed phosphite group-introduced fiber with 10 L of ion-exchanged water and then adding a 1 N alkaline solution little by little with stirring. .. 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 the present embodiment, for example, sodium hydroxide or potassium hydroxide is preferably used as the alkaline compound because of its high versatility. Further, the solvent contained in the alkaline solution may be either water or an organic solvent. Among them, the solvent contained in the alkaline solution is preferably a polar solvent containing water or a polar organic solvent exemplified by alcohol, and more preferably an aqueous solvent containing at least water. As the alkaline solution, for example, an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide is preferable because of its high versatility.

The temperature of the alkaline solution in the alkaline treatment step is not particularly limited, but is preferably 5 ° C. or higher and 80 ° C. or lower, and more preferably 10 ° C. or higher and 60 ° C. or lower. The immersion time of the phosphorous acid group-introduced fiber in the alkaline solution in the alkali treatment step is not particularly limited, but is preferably 5 minutes or more and 30 minutes or less, and more preferably 10 minutes or more and 20 minutes or less. The amount of the alkaline solution used in the alkaline treatment is not particularly limited, but is preferably 100% by mass or more and 100,000% by mass or less, and 1000% by mass or more and 10000% by mass or less, based on the absolute dry mass of the phosphorous acid group-introduced fiber. The following is more preferable.
The cleaning step described above may be further provided after the alkali treatment step.

(Second cellulose fiber)
The sheet of the present invention contains a second cellulose fiber (fine fibrous cellulose) having a fiber width of 1000 nm or less. The fiber width of the second cellulose fiber can be measured, for example, by observation with an electron microscope. The second cellulose fiber is, for example, a single fibrous cellulose.

The fiber width of the second cellulose fiber may be 1000 nm or less, preferably 500 nm or less, more preferably 300 nm or less, further preferably 200 nm or less, and further preferably 100 nm or less. It is more preferably 50 nm or less, and particularly preferably 10 nm or less. In the sheet of the present invention, fine fibrous cellulose having such a small fiber width is used in combination with a first cellulose fiber (coarse cellulose fiber) having a phosphorous acid group or a substituent derived from a phosphorous acid group. , It is possible to suppress the occurrence of twisting of the sheet in the sheet manufacturing process.

The fiber width of the second cellulose fiber is measured as follows, for example, using an electron microscope. First, an aqueous suspension of a second cellulose fiber having a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and this suspension is cast on a hydrophilized carbon film-coated grid for TEM observation. Use as a sample for use. If it contains wide fibers, an SEM image of the surface cast on the glass may be observed. Next, observation is performed using an electron microscope image at a magnification of 1000 times, 5000 times, 10000 times, or 50,000 times depending on the width of the fiber to be observed. However, the sample, observation conditions and magnification should be adjusted so as to satisfy the following conditions.
(1) A straight line X is drawn at an arbitrary position in the observation image, and 20 or more fibers intersect the straight line X.
(2) A straight line Y that intersects the straight line perpendicularly is drawn in the same image, and 20 or more fibers intersect the straight line Y.
The width of the fiber intersecting the straight line X and the straight line Y is visually read with respect to the observation image satisfying the above conditions. In this way, at least three sets of observation images of surface portions that do not overlap each other are obtained. Next, for each image, the width of the fiber intersecting the straight line X and the straight line Y is read.

The fiber length of the second cellulose fiber is not particularly limited, but is preferably 0.1 μm or more and 1000 μm or less, more preferably 0.1 μm or more and 800 μm or less, and 0.1 μm or more and 600 μm or less. Is even more preferable. By setting the fiber length within the above range, the destruction of the crystal region of the second cellulose fiber can be suppressed. It is also possible to set the slurry viscosity of the second cellulose fiber in an appropriate range. The fiber length of the second cellulose fiber can be obtained by, for example, image analysis by TEM, SEM, or AFM.

The second cellulose fiber preferably has an I-type crystal structure. Here, the fact that the second cellulose fiber has an I-type crystal structure can be identified in the diffraction profile obtained from the wide-angle X-ray diffraction photograph using CuKα (λ = 1.5418 Å) monochromatic with graphite. Specifically, it can be identified by having typical peaks at two positions, 2θ = 14 ° or more and 17 ° or less and 2θ = 22 ° or more and 23 ° or less.

The ratio of the type I crystal structure to the second cellulose fiber is, for example, preferably 30% or more, more preferably 40% or more, and further preferably 50% or more. As a result, even better performance can be expected in terms of heat resistance and low coefficient of linear thermal expansion. The crystallinity is determined by a conventional method from the X-ray diffraction profile measured and the pattern (Seagal et al., Textile Research Journal, Vol. 29, p. 786, 1959).

The axial ratio (fiber length / fiber width) of the second cellulose fiber is not particularly limited, but is preferably 20 or more and 10000 or less, and more preferably 50 or more and 1000 or less. By setting the axial ratio to the above lower limit value or more, it is easy to form a sheet containing the second cellulose fiber. By setting the axial ratio to the above upper limit value or less, for example, when the second cellulose fiber is treated as an aqueous dispersion, it is preferable in that handling such as dilution becomes easy.

The second cellulose fiber in the present embodiment has, for example, both a crystalline region and a non-crystalline region. In particular, the second cellulose fiber having both a crystalline region and a non-crystalline region and having a high axial ratio is realized by a method for producing fine fibrous cellulose described later.

The second cellulose fiber in this embodiment preferably has an ionic substituent. The ionic substituent can include, for example, either one or both of an anionic group and a cationic group. Examples of the anionic group include a phosphoric acid group or a substituent derived from a phosphoric acid group (sometimes simply referred to as a phosphoric acid group), a carboxy group or a substituent derived from a carboxy group (sometimes simply referred to as a carboxy group), and the like. And at least one selected from a sulfone group or a substituent derived from a sulfone group (sometimes simply referred to as a sulfone group), and at least one selected from a phosphorus oxo acid group and a carboxy group. More preferably, it is a phosphorusoxo acid group, and particularly preferably. The phosphorous acid group may be, for example, a phosphoric acid group or a phosphorous acid group.

The amount of the ionic substituent introduced into the second cellulose fiber is preferably 0.3 mmol / g or more, more preferably 0.4 mmol / g or more, and 0.5 mmol per 1 g (mass) of the cellulose fiber. It is more preferably / g or more, more preferably 0.7 mmol / g or more, and particularly preferably 1.0 mmol / g or more. The amount of the ionic substituent introduced in the second cellulose fiber is preferably 3.65 mmol / g or less, more preferably 3.5 mmol / g or less per 1 g (mass) of the cellulose fiber. More preferably, it is 0.0 mmol / g or less. Here, the unit mmol / g indicates, for example, the amount of substituents per 1 g of mass of the second cellulose fiber when the counter ion of the anionic group is a hydrogen ion (H ⁺ ). By setting the amount of the ionic substituent introduced within the above range, it is possible to more effectively suppress the occurrence of twisting of the sheet in the sheet manufacturing process.

The amount of the ionic substituent introduced into the second cellulose fiber can be measured by, for example, a neutralization titration method. In the measurement by the neutralization titration method, the introduction amount is measured by determining the change in pH while adding an alkali such as an aqueous sodium hydroxide solution to the obtained slurry containing the second cellulose fiber.

FIG. 1 is a graph showing the relationship between the amount of NaOH added dropwise and the pH of a slurry containing a second cellulose fiber having a phosphorus oxo acid group. The amount of the phosphorus oxo acid group introduced into the second cellulose fiber is measured, for example, as follows.
First, the slurry containing the second cellulose fiber is treated with a strongly acidic ion exchange resin. If necessary, the defibration treatment similar to the defibration treatment step described later may be performed on the measurement target before the treatment with the strongly acidic ion exchange resin.
Next, the change in pH is observed while adding an aqueous sodium hydroxide solution, and a titration curve as shown in the upper part of FIG. 1 is obtained. The titration curve shown in the upper part of FIG. 1 plots the measured pH with respect to the amount of alkali added, and the titration curve shown in the lower part of FIG. 1 plots the pH with respect to the amount of alkali added. The increment (differential value) (1 / mmol) is plotted. In this neutralization titration, two points are confirmed in which the increment (differential value of pH with respect to the amount of alkali dropped) becomes maximum in the curve plotting the measured pH with respect to the amount of alkali added. Of these, the maximum point of the increment obtained first when alkali is added is called the first end point, and the maximum point of the increment obtained next is called the second end point. The amount of alkali required from the start of titration to the first end point is equal to the amount of first dissociated acid of the second cellulose fiber contained in the slurry used for titration, and is required from the first end point to the second end point. The amount of alkali used for titration becomes equal to the amount of second dissociating acid of the second cellulose fiber contained in the slurry used for titration, and the amount of alkali required from the start of titration to the second end point is contained in the slurry used for titration. It is equal to the total amount of dissociated acid of the first cellulose fiber. Then, the value obtained by dividing the amount of alkali required from the start of titration to the first end point by the solid content (g) in the slurry to be titrated is the amount of phosphorus oxo acid group introduced (mmol / g). The amount of phosphorus oxo acid group introduced (or the amount of phosphorus oxo acid group) simply means the amount of the first dissociated acid.
In FIG. 1, the region from the start of titration to the first end point is referred to as a first region, and the region from the first end point to the second end point is referred to as a second region. For example, when the phosphoric acid group is a phosphoric acid group and the phosphoric acid group causes condensation, the amount of weakly acidic groups in the phosphoric acid group (also referred to as the second dissociated acid amount in the present specification) is apparently It decreases, and the amount of alkali required for the second region is smaller than the amount of alkali required for the first region. On the other hand, the amount of strongly acidic groups in the phosphorus oxo acid group (also referred to as the first dissociated acid amount in the present specification) is the same as the amount of phosphorus atoms regardless of the presence or absence of condensation. Further, when the phosphorous acid group is a phosphorous acid group, the weakly acidic group does not exist in the phosphorous acid group, so that the amount of alkali required for the second region is reduced or the amount of alkali required for the second region is reduced. May be zero. In this case, the titration curve has one point where the pH increment is maximized.

Since the denominator of the above-mentioned phosphorus oxo acid group introduction amount (mmol / g) indicates the mass of the acid-type fibrous cellulose, the phosphorus oxo acid group amount of the acid-type fibrous cellulose (hereinafter referred to as the phosphorus oxo acid group amount). (Called (acid type))). On the other hand, when the counterion of the phosphorus oxo acid group is replaced with an arbitrary cation C so as to have a charge equivalent, the denominator is converted to the mass of fibrous cellulose when the cation C is a counterion. This makes it possible to determine the amount of phosphorus oxo acid groups (hereinafter, the amount of phosphorus oxo acid groups (C type)) possessed by fibrous cellulose in which the cation C is a counterion.
That is, it is calculated by the following formula.
Phosphoric acid group amount (C type) = Phosphoric acid group amount (acid type) / {1+ (W-1) x A / 1000}
A [mmol / g]: Total anion amount derived from the phosphorus oxo acid group of the second cellulose fiber (total dissociated acid amount of the phosphorus oxo acid group)
W: Formula amount per valence of cation C (for example, Na is 23, Al is 9)

FIG. 2 is a graph showing the relationship between the amount of NaOH added dropwise and the pH of a slurry containing a second cellulose fiber having a carboxy group. The amount of the carboxy group introduced into the second cellulose fiber is measured, for example, as follows.
First, the slurry containing the second cellulose fiber is treated with a strongly acidic ion exchange resin. If necessary, the defibration treatment similar to the defibration treatment step described later may be performed on the measurement target before the treatment with the strongly acidic ion exchange resin.
Next, the change in pH is observed while adding an aqueous sodium hydroxide solution, and a titration curve as shown in the upper part of FIG. 2 is obtained. The titration curve shown in the upper part of FIG. 2 plots the measured pH with respect to the amount of alkali added, and the titration curve shown in the lower part of FIG. 2 plots the pH with respect to the amount of alkali added. The increment (differential value) (1 / mmol) is plotted. In this neutralization titration, in the curve plotting the pH measured with respect to the amount of alkali added, one point was confirmed where the increment (differential value of pH with respect to the amount of alkali dropped) became the maximum, and this maximum point was the first. Called one end point. Here, the region from the start of titration to the first end point in FIG. 2 is referred to as a first region. The amount of alkali required in the first region is equal to the amount of carboxy groups in the slurry used for titration. Then, the amount of alkali (mmol) required in the first region of the titration curve is divided by the solid content (g) in the slurry containing the second cellulose fiber to be titrated, whereby the amount of carboxy group introduced ( mmol / g) is calculated.
The above-mentioned amount of carboxy group introduced (mmol / g) is the amount of substituents per 1 g of mass of the second cellulose fiber when the counterion of the carboxy group is hydrogen ion (H ⁺ ) (hereinafter, the amount of carboxy group). (Called (acid type)).

In the measurement of the amount of substituents introduced by the titration method, if the amount of one drop of the sodium hydroxide aqueous solution is too large or the titration interval is too short, the amount of phosphoroxoic acid groups will be lower than the original amount. May not be obtained. As an appropriate dropping amount and titration interval, for example, it is desirable to titrate 10 to 50 μL of a 0.1 N sodium hydroxide aqueous solution every 5 to 30 seconds. Further, in order to eliminate the influence of carbon dioxide dissolved in the slurry containing the second cellulose fiber, for example, measurement is performed while blowing an inert gas such as nitrogen gas into the slurry from 15 minutes before the start of titration to the end of titration. Etc. are desirable.

The second cellulose fiber may have a phosphorous acid group or a substituent derived from a phosphorous acid group (also simply referred to as a phosphorous acid group) as an ionic substituent. In this case, the phosphorous acid group or the substituent derived from the phosphorous acid group is, for example, the substituent represented by the above-mentioned formula (2). The second cellulose fiber may have a phosphorous acid group or a group derived from the phosphorous acid group in addition to the phosphorous acid group or the substituent derived from the phosphorous acid group. The phosphoric acid group or the group derived from the phosphoric acid group is, for example, a substituent represented by the above-mentioned formula (1) or (3).

When the second cellulose fiber has a phosphorous acid group or a substituent (phosphorous acid group) derived from the phosphorous acid group, the amount of the phosphorous acid group introduced into the second cellulose fiber is, for example, the second cellulose. It is preferably 0.3 mmol / g or more, more preferably 0.4 mmol / g or more, further preferably 0.5 mmol / g or more, and 0.7 mmol / g or more per 1 g (mass) of the fiber. Is more preferable, and 1.0 mmol / g or more is particularly preferable. The amount of the phosphorous acid group introduced into the second cellulose fiber is preferably 3.65 mmol / g or less, more preferably 3.5 mmol / g or less per 1 g (mass) of the cellulose fiber. More preferably, it is 0.0 mmol / g or less. Here, the unit mmol / g indicates, for example, the amount of substituents per 1 g of mass of the second cellulose fiber when the counter ion of the anionic group is a hydrogen ion (H ⁺ ). By setting the amount of the phosphorous acid group introduced within the above range, it is possible to more effectively suppress the occurrence of twisting of the sheet in the sheet manufacturing process.

The content of the second cellulose fiber is preferably 1% by mass or more, more preferably 5% by mass or more, and 10% by mass or more, based on the total mass of the cellulose fibers contained in the sheet. More preferably, it is more preferably 15% by mass or more, and particularly preferably 30% by mass or more. The content of the second cellulose fiber is preferably 90% by mass or less, more preferably 80% by mass or less, and 70% by mass or less, based on the total mass of the cellulose fibers contained in the sheet. Is more preferable.

<Manufacturing process of fine fibrous cellulose>
<Fiber raw material>
Fine fibrous cellulose is produced from a fiber raw material containing cellulose. The fiber raw material containing cellulose is not particularly limited, but pulp is preferably used because it is easily available and inexpensive. Examples of pulp include wood pulp, non-wood pulp, and deinked pulp. The wood pulp is not particularly limited, but is, for example, broadleaf kraft pulp (LBKP), coniferous kraft pulp (NBKP), sulfite pulp (SP), dissolved pulp (DP), soda pulp (AP), and unbleached kraft pulp (UKP). ) And chemical pulp such as oxygen bleached kraft pulp (OKP), semi-chemical pulp such as semi-chemical pulp (SCP) and chemiground wood pulp (CGP), crushed wood pulp (GP) and thermomechanical pulp (TMP, BCTMP), etc. Examples include mechanical pulp. The non-wood pulp is not particularly limited, and examples thereof include cotton pulp such as cotton linter and cotton lint, and non-wood pulp such as hemp, straw and bagasse. The deinking pulp is not particularly limited, and examples thereof include deinking pulp made from used paper. As the pulp of the present embodiment, one of the above types may be used alone, or two or more types may be mixed and used.
Among the above pulps, for example, wood pulp and deinked pulp are preferable from the viewpoint of availability. Further, among wood pulps, from the viewpoint of high cellulose ratio and high yield of fine fibrous cellulose during defibration treatment, long fiber fine fibrous cellulose having a small decomposition of cellulose in pulp and a large axial ratio can be obtained. From the viewpoint, for example, chemical pulp is more preferable, and kraft pulp and sulfite pulp are further preferable.

As the fiber raw material containing cellulose, for example, cellulose contained in ascidians and bacterial cellulose produced by acetobacter can be used. Further, instead of the fiber raw material containing cellulose, a fiber formed by a linear nitrogen-containing polysaccharide polymer such as chitin or chitosan can also be used.

<Linoxo acid group introduction process>
When the second cellulose fiber has a phosphorus oxo acid group as an ionic substituent, the process for producing the second cellulose fiber includes a step of introducing a phosphorus oxo acid group. When the second cellulose fiber has a phosphorous acid group, the following compounds can be used as the compound A in the above-mentioned <phosphorous acid group introduction step>. Examples of the compound A include phosphoric acid or a salt thereof, phosphorous acid or a salt thereof, dehydration condensed phosphoric acid or a salt thereof, and anhydrous phosphoric acid (diphosphorus pentoxide), but are not particularly limited. As the phosphoric acid, those having various puritys can be used, and for example, 100% phosphoric acid (normal phosphoric acid) or 85% phosphoric acid can be used. The dehydration-condensed phosphoric acid is one in which two or more molecules of phosphoric acid are condensed by a dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Examples of the phosphate and the dehydration-condensation phosphate include lithium salts, sodium salts, potassium salts and ammonium salts of phosphoric acid or dehydration-condensation phosphoric acid, and these can have various degrees of neutralization. Examples of phosphorous acid include 99% phosphorous acid (phosphonic acid). Examples of the salt of the compound having a phosphorous acid group include a lithium salt, a sodium salt, a potassium salt, and an ammonium salt of phosphorous acid, and these can have various neutralization degrees. Of these, phosphoric acid and phosphite are highly efficient in introducing phosphoric acid groups, are more likely to improve defibration efficiency in the defibration process described later, are low in cost, and are easy to apply industrially. , Sodium salt of phosphoric acid or phosphite, potassium salt of phosphoric acid or phosphite, or ammonium salt of phosphoric acid or phosphite is preferred, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, or Ammonium dihydrogen phosphate is more preferred.
The other procedure is the same as the above-mentioned <Phosphorous acid group introduction step>.

<Carboxylic acid group introduction process>
When the second cellulose fiber has a carboxy group as an ionic substituent, the step of producing the fine fibrous cellulose includes a step of introducing a carboxy group. The carboxy group introduction step has an oxidation treatment such as ozone oxidation, oxidation by the Fenton method, TEMPO oxidation treatment, a compound having a group derived from carboxylic acid or a derivative thereof, or a group derived from carboxylic acid with respect to the fiber raw material containing cellulose. This is done by treating with an acid anhydride of the compound or a derivative thereof.

The compound having a group derived from a carboxylic acid is not particularly limited, but for example, a dicarboxylic acid compound such as maleic acid, succinic acid, phthalic acid, fumaric acid, glutaric acid, adipic acid, itaconic acid, citric acid, aconitic acid and the like. Examples include tricarboxylic acid compounds. The derivative of the compound having a group derived from a carboxylic acid is not particularly limited, and examples thereof include an imide of an acid anhydride of a compound having a carboxy group and a derivative of an acid anhydride of a compound having a carboxy group. The imide of the acid anhydride of the compound having a carboxy group is not particularly limited, and examples thereof include an imide of a dicarboxylic acid compound such as maleimide, succinateimide, and phthalateimide.

The acid anhydride of the compound having a group derived from carboxylic acid is not particularly limited, but for example, a dicarboxylic acid compound such as maleic anhydride, succinic anhydride, phthalic anhydride, glutaric anhydride, adipic anhydride, itaconic anhydride and the like. Acid anhydride can be mentioned. The derivative of the acid anhydride of the compound having a group derived from carboxylic acid is not particularly limited, but for example, a compound having a carboxy group such as dimethylmaleic acid anhydride, diethylmaleic acid anhydride, diphenylmaleic acid anhydride and the like. Examples thereof include those in which at least a part of hydrogen atoms of the acid anhydride is substituted with a substituent such as an alkyl group or a phenyl group.

When the TEMPO oxidation treatment is carried out in the carboxy group introduction step, it is preferable to carry out the treatment under conditions of pH 6 or more and 8 or less, for example. Such a treatment is also referred to as a neutral TEMPO oxidation treatment. Neutral TEMPO oxidation treatment includes, for example, sodium phosphate buffer (pH = 6.8), pulp as a fiber raw material, and TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl) as a catalyst. This can be done by adding a nitroxy radical and sodium hypochlorite as a sacrificial reagent. Further, by coexisting sodium chlorite, the aldehyde generated in the oxidation process can be efficiently oxidized to the carboxy group.

Further, the TEMPO oxidation treatment may be carried out under the condition that the pH is 10 or more and 11 or less. Such a treatment is also referred to as an 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. ..

<Washing process>
In the method for producing fine fibrous cellulose in the present embodiment, a washing step can be performed on the ionic substituent-introduced fiber, if necessary. The washing step is the same step as the washing step in the first cellulose fiber manufacturing step.

<Alkaline treatment process>
In the case of producing fine fibrous cellulose, an alkali treatment may be performed on the fiber raw material between the step of introducing an ionic substituent and the step of defibration treatment described later. The alkaline treatment method is the same as the alkaline treatment method in the first cellulose fiber manufacturing process.
The cleaning step described above may be further provided after the alkali treatment step.

<Fiber processing>
By defibrating the fibers in the defibration treatment step, fine fibrous cellulose (second cellulose fiber) can be obtained. In the defibration treatment step, for example, a defibration treatment apparatus can be used. The defibrating apparatus is not particularly limited, but for example, a high-speed defibrator, a grinder (stone mill type crusher), a high-pressure homogenizer or an ultra-high pressure homogenizer, a high-pressure collision type crusher, a ball mill, a bead mill, a disc type refiner, a conical refiner, and a twin shaft. A kneader, a vibration mill, a homomixer under high speed rotation, an ultrasonic disperser, or a beater can be used. Among the above-mentioned defibration processing devices, it is more preferable to use a high-speed defibrator, a high-pressure homogenizer, and an ultra-high-pressure homogenizer, which are less affected by crushed media and less likely to cause contamination.

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

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

(ratio)
The mass ratio of the first cellulose fiber to the second cellulose fiber (first cellulose fiber: second cellulose fiber) is preferably 30:70 to 90:10, preferably 40:60 to 90:10. More preferably. Here, the first cellulose fiber in the sheet can be observed with, for example, a scanning electron microscope (S-3600N, manufactured by Hitachi High-Technologies Corporation). The second cellulose fiber can be observed with, for example, a high-resolution field emission scanning electron microscope (manufactured by Hitachi, Ltd., S-5200). Based on such observation, the mass ratio may be calculated from the volume ratio of each fiber. However, the mixing ratio of each cellulose fiber in the sheet manufacturing process as described later is equivalent to the ratio of the first cellulose fiber and the second cellulose fiber in the sheet.

(Other fibers)
The sheet of the present invention may contain other cellulose fibers in addition to the first cellulose fibers and the second cellulose fibers. Examples of other cellulose fibers include highly beaten pulp in which the first cellulose fiber is beaten to make the fiber width larger than 1 μm and less than 10 μm. Here, the fiber width of the other fibers is the fiber width of the trunk fiber of the cellulose fiber. For example, when the other fiber is a fibrillated cellulose fiber, the fiber width of the trunk fiber is referred to as the fiber width of the other fiber, not the fiber width of the fibrillated and branched fiber.

Beating of other cellulose fibers can be performed using, for example, a defibration treatment apparatus. The defibrating processing device is not particularly limited. Examples thereof include a high-speed defibrator, a grinder (stone mill type crusher), a high-pressure homogenizer, an ultra-high pressure homogenizer, a clear mix, a high-pressure collision type crusher, a ball mill, a bead mill, a disc type refiner, and a conical refiner. In addition, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, a beater, or a wet pulverizer can be appropriately used.

(Water-soluble polymer)
The sheet of the present invention may further contain a water-soluble polymer. Examples of the water-soluble polymer include carboxyvinyl polymer, polyvinyl alcohol, alkyl methacrylate / acrylic acid copolymer, polyvinylpyrrolidone, sodium polyacrylate, polyethylene glycol, diethylene glycol, triethylene glycol, polyethylene oxide, propylene glycol and dipropylene glycol. Synthetic water-soluble polymers such as polypropylene glycol, isoprene glycol, hexylene glycol, 1,3-butylene glycol, and polyacrylamide; xanthan gum, guar gum, tamarind gum, carrageenan, locust bean gum, quince seed, alginic acid, purulan , Carrageenan, and thickening polysaccharides such as pectin; cellulose derivatives such as carboxymethyl cellulose, methyl cellulose, and hirodoxyethyl cellulose; cationized starch, raw starch, oxidized starch, etherified starch, esterified starch, etc. , And starches such as amylose; glycerins such as glycerin, diglycerin, and polyglycerin; hyaluronic acid, metal salts of hyaluronic acid, and the like.

(Paper power enhancer)
The sheet of the present invention preferably further contains a paper strength enhancer. This makes it possible to further improve the strength of the sheet. Examples of the paper strength enhancer include a dry paper strength agent and a wet paper strength agent. Examples of the dry paper strength agent include cationized starch, polyacrylamide (PAM), carboxymethyl cellulose (CMC), acrylic resin and the like. Examples of the wet paper strength agent include polyamide epihalohydrin, urea, melamine, and heat-crosslinkable polyacrylamide. Above all, the sheet of the present invention preferably contains polyamine polyamide epihalohydrin.

Polyamine polyamide epihalohydrin is a cationic thermosetting resin obtained by heat-condensing an aliphatic dibasic carboxylic acid or a derivative thereof with a polyalkylene polyamine to synthesize a polyamide polyamine, and then reacting the polyamide polyamine with epihalohydrin. Is. Since the polyamine polyamide epihalohydrin is an aqueous resin, the polyamine polyamide epihalohydrin can be added as an aqueous solution to the sheet-forming slurry.

Examples of the polyamine polyamide epihalohydrin include polyamine polyamide epichlorohydrin, polyamine polyamide epibromohydrin, and polyamine polyamide epiiodehydrin.

The content of the paper strength enhancer in the sheet is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and 0.5 parts by mass with respect to 100 parts by mass of the cellulose fibers. It is more preferable to have more than one part. The content of the paper strength enhancer is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and further preferably 30 parts by mass or less with respect to 100 parts by mass of the cellulose fiber. preferable. By setting the content of the paper strength enhancer within the above range, the strength of the sheet can be improved more effectively.

(Optional ingredient)
The sheet of the present invention may contain any component other than the above-mentioned components. Optional ingredients include, for example, preservatives, defoamers, lubricants, UV absorbers, dyes, pigments, stabilizers, surfactants, sizing agents, coagulants, yield improvers, bulking agents, drainage improvers, etc. Examples thereof include pH adjusters, fluorescent whitening agents, pitch control agents, slime control agents, defoaming agents, water retention agents, dispersants and the like.

The content of the optional component contained in the sheet is preferably 50% by mass or less, more preferably 40% by mass or less, and more preferably 30% by mass or less, based on the total mass of the sheet. More preferred.

(Sheet manufacturing method)
The method for producing a sheet of the present invention comprises a first cellulose fiber having a fiber width of 10 μm or more and having a phosphorous acid group or a substituent derived from a phosphorous acid group, and a second cellulose having a fiber width of 1000 nm or less. It comprises the step of forming a sheet from a slurry containing fibers. Here, the water retention degree of the first cellulose fiber is 220% or more. Further, the second cellulose fiber is preferably a cellulose fiber having an ionic substituent, and the ionic substituent may be a phosphorous acid group or a substituent derived from a phosphorous acid group.

When preparing the slurry, the dispersion liquid in which the first cellulose fiber and the second cellulose fiber are dispersed is diluted as necessary. At this time, the solid content concentration contained in the diluted slurry is preferably 10% by mass or less, and more preferably 5% by mass or less. Further, the solid content concentration contained in the diluted slurry is preferably 0.01% by mass or more. In the sheet manufacturing process of the present invention, by using the first cellulose fiber having a water retention rate of 220% or more, a slurry in which the fiber is uniformly dispersed can be obtained. Further, by using the first cellulose fiber having a water retention degree of 220% or more, it is possible to suppress the aggregation of the cellulose fiber even in the slurry having a high cellulose fiber concentration.

The water retention degree of the first cellulose fiber is preferably 220% or more, more preferably 230% or more, and further preferably 240% or more. Moreover, the water retention degree of the first cellulose fiber is preferably 600% or less. The water retention of the first cellulose fiber is determined by J.I. It is a value measured according to TAPPI-26.

The step of forming a sheet from the slurry includes a coating step of coating the slurry on a base material or a papermaking step of making the slurry. The sheet manufacturing method of the present invention preferably does not include a calendering process as a post-process of the coating process or the papermaking process.

<Coating process>
In the coating step, for example, a slurry (coating liquid) containing fibrous cellulose is applied onto a base material, and the sheet formed by drying the slurry (coating liquid) is peeled off from the base material to obtain a sheet. Further, by using a coating device and a long base material, sheets can be continuously produced.

The material of the base material used in the coating process is not particularly limited, but a material having high wettability to the slurry may be able to suppress shrinkage of the sheet during drying, but a sheet formed after drying is easy. It is preferable to select one that can be peeled off. Of these, a resin film or plate or a metal film or plate is preferable, but is not particularly limited. For example, resin films and plates such as polypropylene, acrylic, polyethylene terephthalate, vinyl chloride, polystyrene, polycarbonate, and polyvinylidene chloride, metal films and plates of aluminum, zinc, copper, and iron plates, and their surfaces are oxidized. , Stainless film or plate, brass film or plate, etc. can be used.

In the coating process, when the viscosity of the slurry is low and it develops on the base material, a dammed frame is fixed on the base material to obtain a sheet with a predetermined thickness and basis weight. You may. The frame for damming is not particularly limited, but it is preferable to select, for example, a frame in which the end portion of the sheet that adheres after drying can be easily peeled off. From this point of view, a resin plate or a metal plate molded is more preferable. In the present embodiment, for example, a resin plate such as a polypropylene plate, an acrylic plate, a polyethylene terephthalate plate, a vinyl chloride plate, a polystyrene plate, a polycarbonate plate, a polyvinylidene chloride plate, or a metal plate such as an aluminum plate, a zinc plate, a copper plate, or an iron plate. , And those whose surfaces are oxidized, stainless steel plates, brass plates and the like can be used.
The coating machine for coating the slurry on the base material is not particularly limited, and for example, a roll coater, a gravure coater, a die coater, a curtain coater, an air doctor coater, or the like can be used. A die coater, a curtain coater, and a spray coater are particularly preferable because the thickness of the sheet can be made more uniform.

The slurry temperature and the atmospheric temperature when the slurry is applied to the substrate are not particularly limited, but are preferably, for example, 5 ° C. or higher and 80 ° C. or lower, more preferably 10 ° C. or higher and 60 ° C. or lower, and 15 ° C. It is more preferably 50 ° C. or lower, and particularly preferably 20 ° C. or higher and 40 ° C. or lower. When the coating temperature is equal to or higher than the above lower limit, the slurry can be coated more easily. When the coating temperature is not more than the above upper limit value, volatilization of the dispersion medium during coating can be suppressed.

In the coating process, the slurry is based so that the finished basis weight of the sheet is preferably 5 g / m ² or more and 100 g / m ² or less, and more preferably 10 g / m ² or more and 60 g / m ² or less. It is preferable to coat the material. By coating so that the basis weight is within the above range, a uniform sheet can be obtained without twisting, so that the sheet can be thinned.

As described above, the coating step includes a step of drying the slurry coated on the substrate. The step of drying the slurry is not particularly limited, but is performed by, for example, a non-contact drying method, a method of drying while restraining the sheet, or a combination thereof.

The non-contact drying method is not particularly limited, and for example, a method of heating and drying with hot air, infrared rays, far infrared rays or near infrared rays (heat drying method) or a method of vacuum drying (vacuum drying method) is applied. can do. Although the heat drying method and the vacuum drying method may be combined, the heat drying method is usually applied. Drying with infrared rays, far infrared rays, or near infrared rays is not particularly limited, but can be performed using, for example, an infrared device, a far infrared device, or a near infrared device.

The heating temperature in the heat drying method is not particularly limited, but is preferably 20 ° C. or higher and 150 ° C. or lower, and more preferably 25 ° C. or higher and 105 ° C. or lower. When the heating temperature is at least the above lower limit value, the dispersion medium can be rapidly volatilized. Further, when the heating temperature is not more than the above upper limit value, it is possible to suppress the cost required for heating and suppress the discoloration due to the heat of the cellulose fibers.

<Papermaking process>
The papermaking process is performed by making a slurry with a paper machine. The paper machine used in the paper making process is not particularly limited, and examples thereof include continuous paper machines such as a long net type, a circular net type, and an inclined type, and a multi-layer paper making machine combining these. In the papermaking process, a known papermaking method such as hand-making may be adopted.

The papermaking process is performed by filtering and dehydrating the slurry with a wire to obtain a wet paper sheet, and then pressing and drying the sheet. The filter cloth used for filtering and dehydrating the slurry is not particularly limited, but it is more preferable that, for example, fibrous cellulose does not pass through and the filtration rate does not become too slow. Such a filter cloth is not particularly limited, but for example, a sheet made of an organic polymer, a woven fabric, or a porous membrane is preferable. The organic polymer is not particularly limited, but non-cellulosic organic polymers such as polyethylene terephthalate, polyethylene, polypropylene, and polytetrafluoroethylene (PTFE) are preferable. In the present embodiment, for example, a porous membrane of polytetrafluoroethylene having a pore size of 0.1 μm or more and 20 μm or less, polyethylene terephthalate having a pore size of 0.1 μm or more and 20 μm or less, a polyethylene woven fabric, or the like can be mentioned.

In the sheeting step, a method of producing a sheet from a slurry includes, for example, a water-squeezed section in which a slurry containing cellulose fibers is discharged onto the upper surface of an endless belt and a dispersion medium is squeezed from the discharged slurry to generate a web. This can be done using a manufacturing apparatus that includes a drying section that dries the web to produce a sheet. An endless belt is arranged from the watering section to the drying section, and the web generated in the watering section is conveyed to the drying section while being placed on the endless belt.

The dehydration method used in the papermaking process is not particularly limited, and examples thereof include a dehydration method usually used in the production of paper. Among these, a method of dehydrating with a long net, a circular net, an inclined wire or the like and then further dehydrating with a roll press is preferable. Further, the drying method used in the papermaking process is not particularly limited, and examples thereof include a method used in the production of paper. Among these, a drying method using a cylinder dryer, a Yankee dryer, hot air drying, a near infrared heater, an infrared heater, or the like is more preferable.

(Use)
The use of the sheet of the present invention is not particularly limited. For example, the sheet includes wrapping paper, tracing paper, parchment paper, medicine wrapping paper, battery separator, filter, total heat exchange liner, vibrating plate, press molding member, flexible substrate, resin composite material, reinforced plastic laminate, etc. Suitable for applications such as.

The features of the present invention will be described in more detail with reference to Examples and Comparative Examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Therefore, the scope of the present invention should not be construed as limiting by the specific examples shown below.

(Example 1)
<Preparation of the first cellulose fiber (1)>
[Preparation of subphosphorylated pulp]
As a raw material pulp, softwood kraft pulp made by Oji Paper (solid content 93% by mass, basis weight 245 g / m ² sheets, separated and measured according to JIS P 8121, Canadian standard drainage degree (CSF) is 700 ml) It was used.

The raw material pulp was subjected to phosphorus oxo oxidation treatment as follows. First, a mixed aqueous solution of phosphorous acid (phosphonic acid) and urea is added to 100 parts by mass (absolute dry mass) of the raw material pulp to add 33 parts by mass of phosphorous acid (phosphonic acid), 120 parts by mass of urea, and 150 parts of water. The amount was adjusted to be parts by mass, and a chemical-impregnated pulp was obtained. Next, the obtained chemical-impregnated pulp was heated in a hot air dryer at 165 ° C. for 250 seconds to introduce a phosphorous acid group into the cellulose in the pulp to obtain a phosphorylated pulp.

Then, the obtained subphosphorylated pulp was washed. In the washing treatment, the pulp dispersion obtained by pouring 10 L of ion-exchanged water into 100 g (absolute dry mass) of subphosphorized pulp is stirred so that the pulp is uniformly dispersed, and then filtration and dehydration are repeated. Was done by. When the electrical conductivity of the filtrate became 100 μS / cm or less, the washing end point was set.

Next, the washed subphosphorylated pulp was neutralized as follows. First, the washed subphosphorylated pulp is diluted with 10 L of ion-exchanged water, and then a 1N aqueous sodium hydroxide solution is added little by little with stirring to obtain a subphosphorylated pulp slurry having a pH of 12 or more and 13 or less. Obtained. Next, the subphosphorylated pulp slurry was dehydrated to obtain a neutralized subphosphorylated pulp. Next, the subphosphorylated pulp after the neutralization treatment was subjected to the above washing treatment.

The infrared absorption spectrum of the obtained subphosphorylated pulp was measured using FT-IR. As a result, absorption based on P = O of the phosphonic acid group, which is a tautomer of the phosphite group, was observed around 1210 cm ^-1 , and the phosphite group (phosphonic acid group) was added to the pulp. Was confirmed. Further, when the obtained subphosphorylated pulp was tested and analyzed by an X-ray diffractometer, two positions were found: 2θ = 14 ° or more and 17 ° or less and 2θ = 22 ° or more and 23 ° or less. A typical peak was confirmed in, and it was confirmed that it had cellulose type I crystals. The amount of phosphite group (first dissociated acid amount) measured by the measuring method described in [Measurement of phosphite group amount] described later for the obtained phosphorous acid pulp was 1.40 mmol / g. It was. The total amount of dissociated acid was 1.43 mmol / g. Ion-exchanged water was added to the obtained subphosphorylated pulp to obtain a first cellulose fiber dispersion liquid (1) containing the first cellulose fiber (1) having a solid content concentration of 2% by mass.

<Preparation of the second cellulose fiber (1)>
[Miniaturization]
The first cellulose fiber dispersion liquid (1) obtained by the above method was treated twice with a wet atomizing device (manufactured by Sugino Machine Limited, Starburst) at a pressure of 200 MPa, and the second cellulose fiber (1) was treated. ), A second cellulose fiber dispersion (1) was obtained. By X-ray diffraction, it was confirmed that the second cellulose fiber (1) maintained the cellulose type I crystal. The fiber width measured by the measuring method described later was 3 to 5 nm.

[Measurement of phosphite group amount]
The amount of phosphite groups in the first cellulose fiber and the second cellulose fiber is a slurry prepared by diluting a dispersion containing each cellulose fiber with ion-exchanged water so that the content is 0.2% by mass. On the other hand, the measurement was carried out by performing a treatment with an ion exchange resin and then performing a titration with an alkali. The first cellulose fiber was miniaturized by the same procedure as the above-mentioned [miniaturization] step, and then subjected to treatment with an ion exchange resin.
For the treatment with the ion exchange resin, a strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) having a volume of 1/10 was added to the fine fibrous cellulose-containing slurry, and the mixture was shaken for 1 hour. After that, it was poured on a mesh having a mesh size of 90 μm to separate the resin and the slurry.
In addition, titration using alkali changes the pH value indicated by the slurry while adding 10 μL of 0.1 N sodium hydroxide aqueous solution to the fine fibrous cellulose-containing slurry treated with an ion exchange resin every 5 seconds. It was done by measuring. The titration was carried out while blowing nitrogen gas into the slurry from 15 minutes before the start of the titration. In this neutralization titration, two points are observed where the increment (differential value of pH with respect to the amount of alkali dropped) becomes maximum in the curve plotting the measured pH with respect to the amount of alkali added. Of these, the maximum point of the increment obtained first when alkali is added is called the first end point, and the maximum point of the increment obtained next is called the second end point (FIG. 1). The amount of alkali required from the start of the titration to the first end point is equal to the amount of the first dissociated acid in the slurry used for the titration. Further, the amount of alkali required from the start of titration to the second end point becomes 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 end point divided by the solid content (g) in the slurry to be titrated was defined as the amount of phosphite groups (mmol / g).

<Measurement of fiber width of the first cellulose fiber>
The fiber width of the first cellulose fiber was determined by measuring using a Kajaani fiber length measuring device (FS-200 type) manufactured by Kajaani Automation Co., Ltd.

<Measurement of fiber width of the second cellulose fiber>
The fiber width of the second cellulose fiber was measured by the following method. The supernatant of the fine fibrous cellulose dispersion obtained by treatment with a wet atomizing device is mixed with water so that the concentration of the fine fibrous cellulose is 0.01% by mass or more and 0.1% by mass or less. It was added dropwise to the diluted and hydrophilized carbon grid film. This was dried, stained with uranyl acetate, and observed with a transmission electron microscope (JEOL-2000EX, manufactured by JEOL Ltd.).

<Sheet>
The first cellulose fiber (1) is 50 parts by mass, the second cellulose fiber (1) is 50 parts by mass, polyvinyl alcohol is 10 parts by mass, and polyamine polyamide / epichlorohydrin is 5 parts by mass. 1 Cellulose Fiber Dispersion Solution (1), 2nd Cellulose Fiber Dispersion Solution (1), Polyvinyl Alcohol Solution (Gosenex Z-200, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), Polyamine Polyamide / Epichlorohydrin Solution (Arakawa) Arafix 255) manufactured by Kagaku Kogyo Co., Ltd. was mixed to obtain a coating liquid 1. The solid content concentration of the coating liquid 1 was adjusted to 0.5% by mass.
Next, the coating liquid 1 is weighed so that the basis weight of the obtained sheet (layer composed of the solid content of the coating liquid) is 10 g / m ² , and the coating liquid 1 is coated on a commercially available acrylic plate at 50 ° C. It was dried in a constant temperature dryer. A metal frame for damming (a gold frame having an inner dimension of 180 mm × 180 mm and a height of 5 cm) was placed on the acrylic plate so as to have a predetermined basis weight. Next, the dried sheet was peeled off from the acrylic plate to obtain a sheet containing the first cellulose fiber and the second cellulose fiber.

(Example 2)
In the sheet forming step, a sheet was obtained in the same manner as in Example 1 except that the coating liquid 1 was weighed so that the basis weight of the sheet was 15 g / m ² .

(Example 3)
In the sheet forming step, a sheet was obtained in the same manner as in Example 1 except that the coating liquid 1 was weighed so that the basis weight of the sheet was 25 g / m ² .

(Example 4)
In the sheet forming step, a sheet was obtained in the same manner as in Example 1 except that the coating liquid 1 was weighed so that the basis weight of the sheet was 30 g / m ² .

(Example 5)
Each liquid has 75 parts by mass of the first cellulose fiber (1), 25 parts by mass of the second cellulose fiber (1), 10 parts by mass of polyvinyl alcohol, and 5 parts by mass of polyamine polyamide / epichlorohydrin. Was mixed to obtain a coating liquid 2. A sheet was obtained in the same manner as in Example 1 except that the coating liquid 1 used in the sheeting step was used as the coating liquid 2.

(Example 6)
In the sheet forming step, a sheet was obtained in the same manner as in Example 5 except that the coating liquid 2 was weighed so that the basis weight of the sheet was 25 g / m ² .

(Example 7)
Each liquid has 90 parts by mass of the first cellulose fiber (1), 10 parts by mass of the second cellulose fiber (1), 10 parts by mass of polyvinyl alcohol, and 5 parts by mass of polyamine polyamide / epichlorohydrin. Was mixed to obtain a coating liquid 3. A sheet was obtained in the same manner as in Example 1 except that the coating liquid 1 used in the sheeting step was the coating liquid 3.

(Example 8)
In the sheet forming step, a sheet was obtained in the same manner as in Example 7 except that the coating liquid 3 was weighed so that the basis weight of the sheet was 25 g / m ² .

(Example 9)
<Preparation of the first cellulose fiber (2)>
In [Preparation of Subphosphorized Pulp] of Example 1, the chemical solution-impregnated pulp was heated in a hot air dryer for 150 seconds to obtain subphosphorylated pulp, but the first was the same as that of the first cellulose fiber (1). 1 Cellulose Fiber (2) was obtained. The fiber width of the obtained first cellulose fiber (2) was 29 μm, and the amount of phosphorous acid groups (strongly acidic groups) was 0.8 mmol / g.

<Preparation of the second cellulose fiber (2)>
[Miniaturization]
A second cellulose fiber (2) was obtained in the same manner except that the first cellulose fiber (2) was used in [Miniaturization] of Example 1. The fiber width of the obtained second cellulose fiber (2) was 3 to 5 nm, and the amount of phosphorous acid groups (strongly acidic groups) was 0.8 mmol / g.

[Sheet]
A sheet was obtained in the same manner as in Example 4 except that the first cellulose fiber (2) and the second cellulose fiber (2) obtained above were used in the sheeting step.

(Example 10)
Each liquid has 80 parts by mass of the first cellulose fiber (2), 20 parts by mass of the second cellulose fiber (2), 10 parts by mass of polyvinyl alcohol, and 5 parts by mass of polyamine polyamide / epichlorohydrin. Was mixed to obtain a coating liquid 4. A sheet was obtained in the same manner as in Example 9 except that the coating liquid used in the sheeting step was the coating liquid 4 and the coating liquid 4 was weighed so that the basis weight of the sheet was 25 g / m ² . ..

(Example 11)
<Preparation of the first cellulose fiber (3)>
In the preparation of the sulfite pulp, the first cellulose fiber (3) was obtained in the same manner as the first cellulose fiber (1) except that the chemical impregnated pulp was heated in a hot air dryer for 125 seconds to obtain the subphosphor oxide pulp. ) Was obtained. The fiber width of the obtained first cellulose fiber (3) was 29 μm, and the amount of phosphorous acid groups (strongly acidic groups) was 0.6 mol / g.

<Preparation of the second cellulose fiber (3)>
[Miniaturization]
A second cellulose fiber (3) was obtained in the same manner except that the first cellulose fiber (3) was used in [Miniaturization] of Example 1. The fiber width of the obtained second cellulose fiber (3) was 3 to 5 nm, and the amount of phosphorous acid groups (strongly acidic groups) was 0.6 mmol / g.

[Sheet]
In the sheeting step, the first cellulose fiber (3) and the second cellulose fiber (3) obtained above were used, and the coating liquid was weighed so that the basis weight was 30 g / m ^2. , A sheet was obtained in the same manner as in Example 4.

(Example 12)
Each liquid has 80 parts by mass of the first cellulose fiber (3), 20 parts by mass of the second cellulose fiber (3), 10 parts by mass of polyvinyl alcohol, and 5 parts by mass of polyamine polyamide / epichlorohydrin. Was mixed to obtain a coating liquid 5. A sheet was obtained in the same manner as in Example 11 except that the coating liquid used in the sheeting step was the coating liquid 5 and the coating liquid 5 was weighed so that the basis weight of the sheet was 25 g / m ² . ..

(Example 13)
<Preparation of the second cellulose fiber (4)>
The softwood bleached kraft pulp (NBKP) was beaten with a double disc refiner until the irregular freeness reached 100 ml to obtain a pulp dispersion having a solid content concentration of 2% by mass. The pulp dispersion was diluted with ion-exchanged water so that the solid content concentration became 0.2% by mass, and the pulp dispersion was finely divided three times at a processing pressure of 120 MPa with a high-pressure homogenizer "Panda Plus2000" manufactured by NiroSoavi. A second cellulose fiber dispersion (4) containing the cellulose fiber (4) was obtained. The fiber width of the obtained second cellulose fiber (4) was 130 nm, and the amount of phosphorus oxo acid groups (the amount of strongly acidic groups) was 0.03 mmol / g.

[Sheet]
A sheet was obtained in the same manner as in Example 3 except that the second cellulose fiber (4) was used as the second cellulose fiber in the sheet forming step.

(Example 14)
Each liquid is mixed and coated so that the first cellulose fiber (1) is 50 parts by mass, the second cellulose fiber (1) is 50 parts by mass, and the polyamine polyamide / epichlorohydrin is 5 parts by mass. Liquid 6 was obtained. A sheet was obtained in the same manner as in Example 3 except that the coating liquid 1 used in the sheeting step was the coating liquid 6.

(Comparative Example 1)
As the first cellulose fiber, softwood bleached kraft pulp, which is an unmodified pulp that has not been subjected to any chemical modification treatment, was used. The fiber width of the first cellulose fiber (4) was 29 μm.
A sheet was obtained in the same manner as in Example 3 except that the first cellulose fiber (4) was used as the first cellulose fiber in the sheet forming step.

(Comparative Example 2)
In the sheeting step, a sheet was obtained in the same manner as in Example 6 except that the first cellulose fiber (4) obtained above was used as the first cellulose fiber.

(Comparative Example 3)
<Preparation of the first cellulose fiber (5)>
Water was added to the softwood bleached kraft pulp so that the solid content concentration became 4.0% by mass, dispersed, and then treated once with a double disc refiner to obtain the first cellulose fiber (5). The fiber width of the first cellulose fiber (5) was 16 μm.
A sheet was obtained in the same manner as in Example 2 except that the first cellulose fiber (5) was used as the first cellulose fiber in the sheet forming step.

(Comparative Example 4)
A sheet was obtained in the same manner as in Example 3 except that the first cellulose fiber (5) was used as the first cellulose fiber in the sheet forming step.

(Comparative Example 5)
A sheet was obtained in the same manner as in Example 5 except that the first cellulose fiber (5) was used as the first cellulose fiber in the sheet forming step.

(Comparative Example 6)
A sheet was obtained in the same manner as in Example 6 except that the first cellulose fiber (5) was used as the first cellulose fiber in the sheet forming step.

(Evaluation and analysis)
(Basis weight)
Basis weight was measured according to JIS P 8124.

(Paper thickness)
The thickness of the sheet was measured according to JIS P 8118.

(density)
The basis weight was measured according to JIS P 8124, the thickness of the sheet was measured according to JIS P 8118, and the density was calculated from these values.

(Air permeability)
J. The air permeability was measured according to the Oken-type air permeability method of TAPPI-5.

(Haze and total light transmittance)
The haze was measured using a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute) in accordance with JIS K 7136. In addition, the total light transmittance was measured using a haze meter (HM-150, manufactured by Murakami Color Technology Research Institute) in accordance with JIS K 7361.

(Sheet appearance)
The number of twists in 20 sheets (size 18 cm in length and 18 cm in width) (total area: 0.648 m for ² minutes) was visually confirmed. It was converted into the number of twists per 1 m ² and evaluated according to the following criteria. In addition, "twist" means a white lump portion confirmed on the sheet surface as shown in the dotted line frame of FIG.
◎: No twist (0 pieces / m ² )
◯: Number of twists 1 piece / m ² or more and less than 2 pieces / m ² Δ: Number of twists 2 pieces / m ² or more and less than 10 pieces / m ² ×: Number of twists 10 pieces / m ² or more

(Observation of fibers in the sheet)
The first cellulose fiber in the sheet was confirmed by a scanning electron microscope (S-3600N, manufactured by Hitachi High-Technologies Corporation). The second cellulose fiber in the sheet was confirmed by a high-resolution field emission scanning electron microscope (S-5200, manufactured by Hitachi, Ltd.).

(Water retention)
J. The water retention was measured according to TAPPI-26.

In the sheets obtained in the examples, the occurrence of twisting was suppressed. On the other hand, in the sheet obtained in the comparative example, many twists were generated.

Claims (10)

A sheet containing a first cellulose fiber having a phosphorous acid group or a substituent derived from a phosphorous acid group and having a fiber width of 10 μm or more, and a second cellulose fiber having a fiber width of 1000 nm or less. The sheet according to claim 1, wherein the second cellulose fiber has a phosphorous acid group or a substituent derived from a phosphorous acid group. The sheet according to claim 1 or 2, wherein the content of the first cellulose fiber is 10% by mass or more with respect to the total mass of the cellulose fiber. The sheet according to any one of claims 1 to 3, wherein the haze is 20% or more. The sheet according to any one of claims 1 to 4, wherein the total light transmittance is 80% or more. The sheet according to any one of claims 1 to 5, which has a basis weight of 40 g / m ² or less. The sheet according to any one of claims 1 to 6, wherein the air permeability is 10,000 seconds or more. The sheet according to any one of claims 1 to 7, wherein the water retention degree of the first cellulose fiber is 220% or more. A first cellulose fiber having a water retention degree of 220% or more and a fiber width of 10 μm or more and having a phosphorous acid group or a substituent derived from a phosphorous acid group, and a second cellulose fiber having a fiber width of 1000 nm or less. A method for producing a sheet, which comprises a step of forming a sheet from a slurry containing cellulose fibers. The method for producing a sheet according to claim 9, wherein the second cellulose fiber has a phosphorous acid group or a substituent derived from a phosphorous acid group.

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