JP7119609B2 - Sheet and sheet manufacturing method - Google Patents

Description

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

BACKGROUND ART In recent years, attention has been paid to materials using reproducible natural fibers due to the replacement of petroleum resources and the growing awareness of the environment. Among natural fibers, fibrous cellulose having a fiber diameter of 10 to 50 μm, particularly wood-derived fibrous cellulose (pulp) has been widely used mainly as paper products.

As 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 wide-ranging. For example, sheets, nonwoven fabrics, and resin composites containing fine fibrous cellulose are being developed.

For example, Patent Document 1 discloses a microporous membrane made of cellulose fibers and containing 1% by weight or more of fibers having a thickness of 1 μm or more based on the total weight of the cellulose fibers. there is Further, Patent Document 2 discloses 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 100000 nm or less and a number average fiber length of 0.1 to 20 mm. A nonwoven fabric comprising fibers is disclosed. Furthermore, Patent Document 3 discloses a nonwoven fabric containing cellulose fibers with an average fiber diameter of 0.1 to 50 μm and polyolefin fibers with an average fiber diameter of 1.5 μm or less.

JP 2014-210987 A Japanese Patent Application Laid-Open No. 2015-4140 JP 2012-036518 A

As noted above, membranes and nonwovens containing various cellulosic fibers are known. However, the present inventors found that when producing a sheet containing fibrous cellulose (pulp) with a fiber width of 10 μm or more and fine fibrous cellulose with a fiber width of 1 μm or less, the obtained sheet is twisted. I figured out that there is a case.
Therefore, the present invention provides a sheet containing fibrous cellulose (pulp) with a fiber width of 10 μm or more and fine fibrous cellulose with a fiber width of 1 μm or less, wherein the occurrence of twisting is suppressed. aim.

As a result of intensive studies to solve the above problems, the present inventors found that a sheet containing first cellulose fibers having a fiber width of 10 μm or more and second cellulose fibers having a fiber width of 1000 nm or less, The present inventors have found that by using the first cellulose fibers having an ionic substituent, it is possible to obtain a sheet in which the occurrence of twisting is suppressed.
Specifically, the present invention has the following configurations.

[1] A sheet comprising first cellulose fibers having an ionic substituent and having a fiber width of 10 μm or more and second cellulose fibers having a fiber width of 1000 nm or less.
[2] The sheet according to [1], wherein the second cellulose fibers have an ionic substituent.
[3] The sheet according to [1] or [2], wherein the content of the first cellulose fibers is 10% by mass or more with respect to the total mass of the cellulose fibers.
[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 10000 seconds or more.
[8] The sheet according to any one of [1] to [7], wherein the amount of the ionic substituent introduced into the first cellulose fibers is 0.3 mmol/g or more.
[9] The sheet according to any one of [1] to [8], wherein the water retention of the first cellulose fibers is 220% or more.
[10] A step of forming a sheet from a slurry containing first cellulose fibers having a water retention rate of 220% or more and a fiber width of 10 μm or more and second cellulose fibers having a fiber width of 1000 nm or less. Sheet manufacturing method.
[11] The method for producing a sheet according to [10], wherein the second cellulose fibers have an ionic substituent.

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 dropped NaOH and the pH for fiber raw materials having a phosphate group. FIG. 2 is a graph showing the relationship between the amount of dropped NaOH and electrical conductivity with respect to fiber raw materials having carboxyl groups. FIG. 3 is a graph showing the relationship between the amount of dropped NaOH and electrical conductivity with respect to fiber raw materials having phosphate groups. FIG. 4 is a photograph showing an example of twist generated in a sheet of a comparative example.

The present invention will be described in detail below. Although the constituent elements described below may be described based on representative embodiments and specific examples, the present invention is not limited to such embodiments.

(sheet)
TECHNICAL FIELD The present invention relates to a sheet containing first cellulose fibers having an ionic substituent and having a fiber width of 10 μm or more and second cellulose fibers having a fiber width of 1000 nm or less. In this specification, cellulose fibers having a fiber width of 1000 nm or less are sometimes referred to as fine fibrous cellulose.

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

The sheet of the present invention preferably has a haze of 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 be equal to or less than the above upper limit, a sheet having excellent transparency as compared with conventional glassine paper or graphane paper can be obtained.
The total light transmittance of the sheet of the invention is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. Here, the haze of the sheet conforms to JIS K 7136 and is a value measured using, for example, a haze meter (HM-150, manufactured by Murakami Color Research Laboratory). Further, the total light transmittance of the sheet is a value measured according to JIS K 7361, for example, using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory).

Furthermore, the sheet of the present invention also has excellent barrier properties. In the sheet of the present invention, since the first cellulose fibers having a fiber width of 10 μm or more and the second cellulose fibers having a fiber width of 1000 nm or less are used in combination, the cellulose fibers can be densified. As a result, barrier properties are 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, for example, by J.P. It can be calculated according to the Oken air permeability method of TAPPI-5.

The sheet of the present invention is lightweight due to its low basis weight. Conventionally, when manufacturing glassine paper or graphane paper, it has been considered to increase the density of cellulose fibers in order to improve transparency and barrier properties, and calendering is performed in the post-papermaking process. was practiced as usual. However, there is a limit to reducing the basis weight in order to ensure workability in calendering. On the other hand, in the sheet of the present invention, since the first cellulose fibers having a fiber width of 10 μm or more and the second cellulose fibers having a fiber width of 1000 nm or less are used in combination, transparency and barrier properties can be obtained without calendering. A sheet having excellent properties can be obtained, and as a result, a low basis weight can be achieved. Therefore, the weight of the seat can be reduced. Thus, the present invention can achieve both a low basis weight and a high barrier property, 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 JIS P 8124, for example. Note that the basis weight of the sheet can be appropriately adjusted according to the performance required of the sheet.

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

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 even more preferably 0.3 g/cm ³ or more. Although the upper limit of the density of the sheet is not particularly limited, it is preferably 5.0 g/cm ³ or less, for example. Here, the density of the sheet is calculated from the basis weight measured in accordance with JIS P 8124, the thickness of the sheet measured in accordance with JIS P 8118, and these values. The density of the sheet can be appropriately adjusted by subjecting the sheet to calendering, for example, depending on the performance required of the sheet.

(First cellulose fiber)
The sheet of the present invention comprises first cellulosic fibers. Here, the first cellulose fibers are cellulose fibers having ionic substituents and having a fiber width of 10 μm or more. The fiber width of the first cellulose fibers may be 10 µm or more, preferably 15 µm or more, and more preferably 20 µm or more. The width of the first cellulose fibers is preferably 100 µm or less. The first cellulose fibers are also referred to herein as coarse cellulose fibers.

The fiber width of the first cellulose fiber can be measured using a Kajaani fiber length measuring instrument (FS-200 type) manufactured by Kajaani Automation. Here, the fiber width of the first cellulose fiber is the fiber width of the stem fiber of the cellulose fiber. For example, when the cellulose fibers are fibril cellulose fibers, the fiber width of the trunk fibers forming the main axis is referred to as the fiber width of the first cellulose fibers, not the fiber width of fibrillated and branched fibers.

Pulp is preferably used as the fiber raw material for the first cellulose fibers. Pulp includes, for example, wood pulp, non-wood pulp and deinked pulp. Examples of wood pulp include, but are not limited to, hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP). ) and chemical pulp such as oxygen bleached kraft pulp (OKP), semi-chemical pulp such as semi-chemical pulp (SCP) and chemigroundwood pulp (CGP), groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP) A mechanical pulp etc. are mentioned. Non-wood pulps include, but are not limited to, cotton-based pulps such as cotton linters and cotton lints, and non-wood-based pulps such as hemp, straw, and bagasse. Examples of deinked pulp include, but are not limited to, deinked pulp made from waste paper. As the first cellulose fiber, one of the above cellulose fibers may be used alone, or two or more of them may be mixed and used.

The first cellulose fibers have ionic substituents. The ionic substituents can include, for example, either one or both of an anionic group and a cationic group. Examples of the anionic group include, for example, a phosphate group or a substituent derived from a phosphate group (sometimes simply referred to as a phosphate group), a carboxyl group or a substituent derived from a carboxyl group (sometimes simply referred to as a carboxyl group), and a sulfone group or a substituent derived from a sulfone group (sometimes referred to simply as a sulfone group), and at least one selected from a phosphate group and a carboxyl group. More preferably, it is particularly preferably a phosphate group.

A phosphate group is a divalent functional group, for example, phosphoric acid with the hydroxyl group removed. Specifically, it is a group represented by —PO ₃ H ₂ . Substituents derived from a phosphate group include substituents such as salts of phosphate groups and phosphate ester groups. The substituent derived from a phosphoric acid group may be contained in the first cellulose fiber as a condensed phosphoric acid group (for example, a pyrophosphate group).
A phosphoric acid group or a substituent derived from a phosphoric acid group is, for example, a substituent represented by the following formula (1).

In formula (1), a, b and n are natural numbers (where a=b×m). a of α ^{1 , α 2} , . Note that all of αn and α′ may be O 2 ⁻ . Each R is a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated linear hydrocarbon group, an unsaturated-branched hydrocarbon group A hydrogen group, an unsaturated-cyclic hydrocarbon group, an aromatic group, or a derivative group thereof.

Examples of the saturated straight-chain hydrocarbon group include, but are not limited to, methyl group, ethyl group, n-propyl group, n-butyl group, and the like. The saturated-branched hydrocarbon group includes i-propyl group, t-butyl group and the like, but is not particularly limited. The saturated cyclic hydrocarbon group includes, but is not particularly limited to, a cyclopentyl group, a cyclohexyl group, and the like. The unsaturated straight-chain hydrocarbon group includes, but is not particularly limited to, a vinyl group, an allyl group, and the like. The unsaturated-branched hydrocarbon group includes i-propenyl group, 3-butenyl group and the like, but is not particularly limited. The unsaturated-cyclic hydrocarbon group includes, but is not limited to, a cyclopentenyl group, a cyclohexenyl group, and the like. The aromatic group includes, but is not particularly limited to, a phenyl group, a naphthyl group, or the like.

In addition, as the derivative group for R, at least one functional group such as a carboxyl group, a hydroxyl group, or an amino group is added or substituted with respect to the main chain or side chain of the various hydrocarbon groups described above. Examples include, but are not limited to, groups. Although the number of carbon atoms constituting the main chain of R is not particularly limited, it is preferably 20 or less, more preferably 10 or less. By setting the number of carbon atoms constituting the main chain of R to the above range, the molecular weight of the phosphate group can be set to an appropriate range, facilitating penetration into the fiber raw material, and yielding the first cellulose fiber. can also be increased.

β ^b+ is a monovalent or higher cation composed of an organic substance or an inorganic substance. Examples of monovalent or higher-valent cations composed of organic substances include aliphatic ammonium and aromatic ammonium. Examples include cations of divalent metals such as calcium and magnesium, hydrogen ions, and the like, but are not particularly limited. These may be applied singly or in combination of two or more. As the cation having a valence of 1 or more composed of an organic substance or an inorganic substance, sodium or potassium ions are preferable, but not particularly limited, because they are less likely to turn yellow when fiber raw materials containing β are heated and are easily industrially available.

The amount of the ionic substituent introduced into the first cellulose fiber is preferably 0.3 mmol/g or more, more preferably 0.4 mmol/g or more, more preferably 0.5 mmol/g (mass) of cellulose fiber. /g or more, more preferably 0.7 mmol/g or more, and particularly preferably 1.0 mmol/g or more. In addition, the amount of the ionic substituent 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 cellulose fiber. It is more preferably .0 mmol/g or less. Here, the unit mmol/g indicates the amount of substituents per 1 g mass of fibrous cellulose when the counter ion of the anionic group is hydrogen ion (H ⁺ ), for example. By setting the amount of the ionic substituent to be introduced within the above range, it is possible to more effectively suppress the occurrence of twisting in the sheet in the manufacturing process of the sheet.

The introduction amount of the ionic substituent into the first cellulose fiber can be measured, for example, by a neutralization titration method as described below.
FIG. 1 is a graph showing the relationship between the amount of dropped NaOH and pH for the first cellulose fibers having a phosphate group. The amount of phosphate groups introduced into the first cellulose fibers is measured, for example, as follows. First, the first cellulose fiber is diluted with ion-exchanged water, and 1N hydrochloric acid is added while stirring. After that, the first cellulose fibers are recovered by filtration and dehydration. This operation is repeated while appropriately changing the amount of 1N hydrochloric acid added to completely convert the phosphoric acid groups of the first cellulose fibers into the acid form. After the step of converting the phosphate groups into the acid form, the first cellulose fibers obtained are diluted with ion-exchanged water, followed by filtration and dehydration to obtain a dehydrated sheet. thoroughly wash away. Next, to a suspension obtained by diluting the obtained first cellulose fibers (acid form) with ion-exchanged water, while adding an aqueous sodium hydroxide solution, the change in pH is observed to obtain a titration curve as shown in FIG. . As shown in FIG. 1, there are two points at which the pH increment (the differential value of the pH with respect to the amount of alkali dropped) is maximum (the point where the increment is the largest and the point where the increment is the second largest). Among these, the region from the beginning of the addition of alkali to the maximum point of the increment obtained first (hereinafter referred to as the first end point) is called the first region, and the maximum point of the increment obtained next from the first end point (hereinafter referred to as the 1st end point). 2 end point) is called a second region, and after the second region there is a third region. The first endpoint is obtained while the pH is between 4 and 7 and the second endpoint is between pH 9 and 10. Of these, the amount of alkali required in the first region is equal to the amount of strong acid groups in the slurry used for titration, and the amount of alkali required in the second region is the amount of weak acid groups in the slurry used for titration. be equal. When the phosphate groups condense, the weakly acidic groups are apparently lost, and the amount of alkali required for the second region becomes smaller than the amount of alkali required for the first region. On the other hand, the amount of strongly acidic groups coincides with the amount of phosphorus atoms regardless of the presence or absence of condensation. Therefore, the amount of phosphate groups introduced (or the amount of phosphate groups) or the amount of substituents introduced (or the amount of substituents) means the amount of strongly acidic groups. Therefore, the value obtained by dividing the alkali amount (mmol) required in the first region of the titration curve obtained above by the solid content (g) in the first cellulose fiber suspension to be titrated is It is the amount of phosphate group introduced (mmol/g).

When the first cellulose fibers and the second cellulose fibers are mixed, they are separated and recovered by centrifugation, and the amount of phosphate group introduced is measured by the method described above or the method described later. Centrifugation is performed by adjusting the cellulose dispersion in which the first cellulose fiber and the second cellulose fiber are mixed to a solid content concentration of 0.2% by mass, using a cooling high-speed centrifuge (Kokusan Co., H-2000B), It is carried out under the conditions of 12000 G and 10 minutes. After that, the sedimented solid content obtained is recovered as the first cellulose fibers, and the supernatant liquid is recovered as the second cellulose fibers.

FIG. 2 is a graph showing the relationship between the amount of NaOH dropped onto the first cellulose fibers having carboxyl groups and the electrical conductivity. The amount of carboxyl groups introduced into the first cellulose fibers is measured, for example, as follows.
First, the first cellulose fiber is diluted with ion-exchanged water, and 1N hydrochloric acid is added while stirring. After that, the first cellulose fibers are recovered by filtration and dehydration. This operation is repeated while appropriately changing the amount of 1N hydrochloric acid added to completely convert the carboxyl groups of the first cellulose fibers to acid forms. After the step of converting the carboxyl groups into the acid form, the first cellulose fibers obtained are diluted with ion-exchanged water, filtered and dehydrated to obtain a dehydrated sheet, and this operation is repeated to remove excess hydrochloric acid. Rinse thoroughly. Next, a suspension obtained by diluting the obtained first cellulose fibers (acid form) with ion-exchanged water was observed for a change in electrical conductivity while adding an aqueous sodium hydroxide solution, resulting in a titration curve as shown in FIG. get In addition, if necessary, a defibration treatment similar to the fibrillation treatment step to be described later may be performed on the object to be measured. As shown in FIG. 2, the titration curve has a first region where the increment (slope) of the conductivity becomes almost constant after the electrical conductivity decreases, and then the increment (slope) of the conductivity increases. It is divided into a second area. The boundary point between the first region and the second region is defined as the point where the second differential value of the conductivity, that is, the amount of change in the increment (slope) of the conductivity becomes maximum. Then, the value obtained by dividing the alkali amount (mmol) required in the first region of the titration curve by the solid content (g) in the first cellulose fiber-containing slurry to be titrated is the introduction amount of the carboxyl group. (mmol/g).
In addition, since the denominator of the amount of carboxyl group introduced (mmol/g) is the mass of the acid-type first cellulose fiber, the amount of carboxyl groups possessed by the acid-type first cellulose fiber (hereinafter referred to as carboxyl group amount (referred to as acid form)). On the other hand, when the counterion of the carboxyl group is substituted with an arbitrary cation C so as to have a charge equivalent, the denominator is converted to the mass of the first cellulose fiber when the cation C is the counterion. By doing so, it is possible to determine the amount of carboxyl groups (hereinafter referred to as the amount of carboxyl groups (C type)) possessed by the first cellulose fibers whose counterions are the cations C.
That is, the amount of carboxyl group introduced is calculated by the following formula.
Carboxyl group amount (C type) = carboxyl group amount (acid form) / {1 + (W-1) x (carboxyl group amount (acid form)) / 1000}
W: Formula weight per valence of cation C (for example, 23 for Na and 9 for Al)
In addition, in the measurement of the amount of substituents by the titration method, if the titration interval of the aqueous sodium hydroxide solution is too short, the amount of substituents may be lower than originally. It is desirable to titrate the sodium aqueous solution by 50 μL in 30 seconds.

The water retention of the first cellulose fibers is preferably 220% or more, more preferably 230% or more, still more preferably 240% or more, even more preferably 250% or more, and 280%. % or more is particularly preferable. Also, the water retention of the first cellulose fibers is preferably 600% or less. The water retention of the first cellulose fiber is described in J. Am. 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 sheeting, and the water retention degree of the first cellulose fiber after sheeting satisfies the above range. good too.

The content of the first cellulose fibers is preferably 10% by mass or more, more preferably 20% by mass or more, and 30% by mass or more, relative to the total mass of the cellulose fibers contained in the sheet. is more preferred. In addition, the content of the first cellulose fibers is preferably 99% by mass or less, more preferably 95% by mass or less, and 90% by mass or less with respect to the total mass of the cellulose fibers contained in the sheet. is more preferably 80% by mass or less, and particularly preferably 75% by mass or less.

<Manufacturing process of the first cellulose fiber>
<Phosphate group introduction step>
When the first cellulose fiber has a phosphate group as an ionic substituent, the manufacturing process of the first cellulose fiber includes a phosphate group introduction step. In the step of introducing a phosphate group, at least one compound selected from compounds capable of introducing a phosphate group (hereinafter also referred to as "compound A") is added to cellulose by reacting with a hydroxyl group possessed by a fiber raw material containing cellulose. It is a step of acting on a fiber raw material containing. Through this step, a phosphate group-introduced fiber is obtained.

In the phosphate group-introducing step according to the present embodiment, the reaction between the fiber material containing cellulose and compound A is performed in the presence of at least one selected from urea and derivatives thereof (hereinafter also referred to as "compound B"). may On the other hand, the reaction between the cellulose-containing fiber raw material and the compound A may be carried out in the absence of the compound B.

An example of the method of allowing the compound A to act on the fiber raw material in the presence of the compound B includes 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. Among these, 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, because the uniformity of the reaction is high. Although the form of the fiber material is not particularly limited, it is preferably in the form of cotton or a thin sheet, for example. The compound A and the compound B can be added to the fiber raw material in the form of a powder, a solution dissolved in a solvent, or a melted state by heating to a melting point or higher. Among these, it is preferable to add in the form of a solution dissolved in a solvent, particularly in the form of an aqueous solution, since the uniformity of the reaction is high. Moreover, the compound A and the compound B may be added simultaneously to the fiber raw material, may be added separately, or may be added as a mixture. The method of adding the compound A and the compound B is not particularly limited, but when the compound A and the compound B are in 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 added dropwise to the Further, the necessary amount of compound A and compound B may be added to the fiber raw material, or after adding excessive amounts of compound A and compound B to the fiber raw material, the excess compound A and compound B are removed by pressing or filtering. may be removed.

Examples of the compound A used in this embodiment include phosphoric acid or its salts, dehydrated condensed phosphoric acid or its salts, phosphoric anhydride (phosphorus pentoxide) and the like, but are not particularly limited. Phosphoric acid of various purities can be used, for example, 100% phosphoric acid (orthophosphoric acid) or 85% phosphoric acid can be used. Dehydration-condensed phosphoric acid is obtained by condensing two or more molecules of phosphoric acid by dehydration reaction, and examples thereof include pyrophosphoric acid and polyphosphoric acid. Phosphates and dehydrated condensed phosphates include lithium salts, sodium salts, potassium salts and ammonium salts of phosphoric acid or dehydrated condensed phosphates, and these can have various degrees of neutralization. Among these, the efficiency of introducing a phosphate group is high, the fibrillation efficiency is easily improved in the fibrillation step described later, the cost is low, and it is easy to apply industrially. Sodium salt, potassium salt of phosphate, or ammonium salt of phosphate are preferred, and phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, or ammonium dihydrogen phosphate are more preferred.

The amount of compound A added to the fiber raw material is not particularly limited. For example, when the amount of compound A added is converted to the phosphorus atomic weight, the amount of phosphorus atoms 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 even more preferably 2% by mass or more and 30% by mass or less. By setting the amount of phosphorus atoms added to the fiber raw material within the above range, the yield of the first cellulose fibers can be further improved. On the other hand, by setting the amount of phosphorus atoms added to the fiber raw material to be equal to or less than the above upper limit, it is possible to balance the effect of improving the yield and the cost.

Compound B used in this embodiment is at least one selected from urea and derivatives thereof as described above. Compound B includes, for example, urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, and 1-ethylurea.
From the viewpoint of improving the uniformity of the reaction, compound B is preferably used as an aqueous solution. 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, more preferably 10% by mass or more and 400% by mass or less, More preferably, it is 100% by mass or more and 350% by mass or less.

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

In the phosphate group-introducing step, it is preferable to heat-treat the fiber raw material after adding or mixing the compound A or the like to the fiber raw material. As the heat treatment temperature, it is preferable to select a temperature at which the phosphate 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 even more preferably 130° C. or higher and 200° C. or lower. In addition, for the heat treatment, equipment having various heat media can be used. A drying device, a vacuum drying device, an infrared heating device, a far infrared heating device, or a microwave heating device can be used.

In the heat treatment according to the present embodiment, for example, the compound A is added to a thin sheet-like fiber raw material by a method such as impregnation, and then heated, or the fiber raw material and the compound A are heated while kneading or stirring with a kneader or the like. method can be adopted. This makes it possible to suppress concentration unevenness of the compound A in the fiber raw material and to more uniformly introduce phosphate groups to the surface of the cellulose fibers contained in the fiber raw material. This is because when water molecules move to the surface of the fiber material during drying, the dissolved compound A is attracted to the water molecules by surface tension and similarly moves to the surface of the fiber material (that is, the concentration unevenness of the compound A is It is thought that this is due to the fact that it is possible to suppress the occurrence of

In addition, the heating device used for the heat treatment always removes the moisture retained by the slurry and the moisture generated due to the dehydration condensation (phosphorylation) reaction between the compound A and the hydroxyl groups contained in the cellulose etc. in the fiber raw material. It is preferable that the device can be discharged to the outside of the device system. As such a heating device, for example, an air-blowing oven can be used. By constantly draining the water in the device system, it is possible to suppress the hydrolysis reaction of the phosphate ester bond, which is the reverse reaction of phosphorylation, and to suppress the acid hydrolysis of the sugar chains in the fiber. can. Therefore, it is possible to obtain the first cellulose fibers having a high axial ratio.

The heat treatment time is, for example, 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 water is substantially removed from the fiber raw material. is more preferable. In the present embodiment, the introduction amount of the phosphate group can be set within a preferable range by setting the heating temperature and the heating time within appropriate ranges.

The step of introducing a phosphate group may be performed at least once, but may be performed repeatedly two or more times. By performing the phosphate group-introducing step two or more times, many phosphate groups can be introduced into the fiber raw material. In the present embodiment, one example of a preferred aspect is the case where the phosphate group introduction step is performed twice.

<Carboxyl Group Introduction Step>
When the first cellulose fiber has a carboxyl group as an ionic substituent, the manufacturing process of the first cellulose fiber includes a carboxyl group introduction step. In the step of introducing a carboxyl group, the fiber raw material containing cellulose is subjected to oxidation treatment such as ozone oxidation, oxidation by the Fenton method, TEMPO oxidation treatment, a compound having a carboxylic acid-derived group or a derivative thereof, or a carboxylic acid-derived group. This is done by treating the compound with an acid anhydride or a derivative thereof.

The compound having a carboxylic acid-derived group is not particularly limited. Examples include tricarboxylic acid compounds. Derivatives of compounds having a carboxylic acid-derived group are not particularly limited, but include, for example, imidized acid anhydrides of compounds having a carboxyl group and derivatives of acid anhydrides of compounds having a carboxyl group. Examples of imidized acid anhydrides of compounds having a carboxyl group include, but are not particularly limited to, imidized dicarboxylic acid compounds such as maleimide, succinimide and phthalimide.

The acid anhydride of the compound having a group derived from carboxylic acid is not particularly limited. acid anhydrides; In addition, the acid anhydride derivative of the compound having a carboxylic acid-derived group is not particularly limited. Acid anhydrides in which at least some of the hydrogen atoms are substituted with substituents such as alkyl groups and phenyl groups can be mentioned.

When the TEMPO oxidation treatment is performed in the carboxyl group introduction step, it is preferable to perform the treatment under the condition of pH 6 or more and 8 or less. Such treatment is also referred to as 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-tetramethylpiperidine-1-oxyl) as a catalyst. This can be done by adding sodium hypochlorite as a nitroxy radical, sacrificial reagent. Furthermore, coexistence of sodium chlorite enables efficient oxidation of aldehydes generated in the process of oxidation to carboxyl groups.

Moreover, the TEMPO oxidation treatment may be performed under the condition that the pH is 10 or more and 11 or less. Such treatment is also called alkali TEMPO oxidation treatment. Alkaline TEMPO oxidation treatment can be performed, for example, by adding a nitroxy radical such as TEMPO as a catalyst, sodium bromide as a cocatalyst, and sodium hypochlorite as an oxidizing agent to pulp as a fiber raw material. .

<Washing process>
In the first method for producing cellulose fibers in the present embodiment, the ionic substituent-introduced fibers can be subjected to a washing step, if necessary. The washing step is performed by washing the ionic substituent-introduced fiber with, for example, water or an organic solvent. Moreover, the washing process may be performed after each process described later, and the number of times of washing performed in each washing process is not particularly limited.

<Alkali treatment process>
In the first method for producing cellulose fibers in the present embodiment, alkali treatment may be performed on the ionic substituent-introduced fibers after washing, if necessary. In this case, it is preferable to adjust the pH to 12 or more and 13 or less by diluting the washed ionic substituent-introduced fiber with 10 L of ion-exchanged water, and then gradually adding a 1N alkaline solution while 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, it is preferable to use, for example, sodium hydroxide or potassium hydroxide as the alkaline compound because of its high versatility. Moreover, 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 water or a polar solvent including a polar organic solvent exemplified by alcohol, and more preferably an aqueous solvent including at least water. As the alkaline solution, for example, an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable because of its high versatility.

Although the temperature of the alkaline solution in the alkaline treatment step is not particularly limited, it is preferably 5° C. or higher and 80° C. or lower, more preferably 10° C. or higher and 60° C. or lower. The immersion time of the ionic substituent-introduced fiber in the alkali solution in the alkali treatment step is not particularly limited, but is preferably 5 minutes or more and 30 minutes or less, 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 for example, it is preferably 100% by mass or more and 100000% by mass or less, and 1000% by mass or more and 10000% by mass with respect to the absolute dry mass of the ionic substituent-introduced fiber. The following are more preferable.
In addition, after the alkali treatment step, the cleaning step described above may be further provided.

(Second cellulose fiber)
The sheet of the present invention contains second cellulose fibers (fine fibrous cellulose) having a fiber width of 1000 nm or less. The fiber width of the second cellulose fibers can be measured, for example, by electron microscopic observation. The second cellulose fiber is, for example, monofilament-like 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, even more preferably 200 nm or less, and even more preferably 100 nm or less. It is preferably 50 nm or less, more preferably 10 nm or less. The sheet of the present invention can be obtained by using fine fibrous cellulose with a small fiber width in combination with the first cellulose fibers (coarse cellulose fibers) having an ionic substituent, thereby twisting the sheet into a sheet in the manufacturing process of the sheet. It is possible to suppress the occurrence of leakage.

The fiber width of the second cellulose fibers is measured using, for example, an electron microscope as follows. First, an aqueous suspension of the second cellulose fibers having a concentration of 0.05% by mass or more and 0.1% by mass or less was prepared, and this suspension was cast on a hydrophilized carbon film-coated grid and observed by TEM. Use as a sample. SEM images of surfaces cast on glass may be observed if they contain wide fibers. Then, an electron microscope image is observed at a magnification of 1,000, 5,000, 10,000, or 50,000 times depending on the width of the fiber to be observed. However, the sample, observation conditions and magnification are adjusted so as to satisfy the following conditions.
(1) A single straight line X is drawn at an arbitrary point in the observed image, and 20 or more fibers intersect the straight line X.
(2) Draw a straight line Y that intersects the straight line perpendicularly in the same image, and 20 or more fibers intersect the straight line Y.
Widths of fibers intersecting the straight lines X and Y are visually read from the observation image satisfying the above conditions. In this way, at least three sets of observed images of surface portions that do not overlap each other are obtained. Then, for each image, the width of the fiber that crosses straight line X and straight line Y is read.

The fiber length of the second cellulose fiber is not particularly limited, but for example, it 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 more preferred. By setting the fiber length within the above range, it is possible to suppress breakage of the crystal regions of the second cellulose fibers. Also, it is possible to set the slurry viscosity of the second cellulose fibers within an appropriate range. The fiber length of the second cellulose fibers can be determined by image analysis using TEM, SEM, or AFM, for example.

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

The proportion of the I-type crystal structure in the second cellulose fibers is, for example, preferably 30% or more, more preferably 40% or more, and even more 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 degree of crystallinity is determined by a conventional method from the pattern of X-ray diffraction profiles (Seagal et al., Textile Research Journal, vol. 29, p. 786, 1959).

Although the axial ratio (fiber length/fiber width) of the second cellulose fibers is not particularly limited, it is preferably 20 or more and 10,000 or less, more preferably 50 or more and 1,000 or less. A sheet containing the second cellulose fibers can be easily formed by making the axial ratio equal to or higher than the above lower limit. By setting the axial ratio to be equal to or less than the above upper limit, for example, when the second cellulose fiber is treated as an aqueous dispersion, it is preferable in terms of ease of handling such as dilution.

The second cellulose fibers in this embodiment have, for example, both crystalline and amorphous regions. In particular, the second cellulose fibers having both a crystalline region and an amorphous region and having a high axial ratio are realized by the method for producing fine fibrous cellulose described later.

The second cellulose fiber in this embodiment preferably has an ionic substituent. The ionic substituents can include, for example, either one or both of an anionic group and a cationic group. Examples of the anionic group include, for example, a phosphate group or a substituent derived from a phosphate group (sometimes simply referred to as a phosphate group), a carboxyl group or a substituent derived from a carboxyl group (sometimes simply referred to as a carboxyl group), and a sulfone group or a substituent derived from a sulfone group (sometimes referred to simply as a sulfone group), and at least one selected from a phosphate group and a carboxyl group. More preferably, it is particularly preferably a phosphate group. The phosphate group is the same as the phosphate group that the first cellulose fiber may have.

The amount of the ionic substituent introduced into the second cellulose fibers is, for example, preferably 0.1 mmol/g or more, more preferably 0.3 mmol/g or more per 1 g (mass) of the second cellulose fibers. , is more preferably 0.5 mmol/g or more, still more preferably 0.7 mmol/g or more, and particularly preferably 1.0 mmol/g or more. In addition, the amount of the ionic substituent 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 cellulose fiber. It is more preferably .0 mmol/g or less. Here, the unit mmol/g indicates the amount of substituents per 1 g of mass of the second cellulose fiber when the counter ion of the anionic group is hydrogen ion (H ⁺ ), for example.

The amount of anionic groups introduced into the second cellulose fibers can be measured, for example, by conductivity titration. In the measurement by the conductivity titration method, the introduced amount is measured by determining the change in conductivity while adding an alkali such as an aqueous sodium hydroxide solution to the obtained slurry containing the second cellulose fibers.

FIG. 3 is a graph showing the relationship between the amount of NaOH dripped onto the second cellulose fiber having a phosphate group and the electrical conductivity. The amount of phosphate groups introduced into the second cellulose fiber is measured, for example, as follows. First, the slurry containing the second cellulose fibers is treated with a strongly acidic ion exchange resin. In addition, before the treatment with the strongly acidic ion exchange resin, a defibration treatment similar to the fibrillation treatment step described below may be performed on the object to be measured, if necessary. Next, change in electrical conductivity is observed while adding sodium hydroxide aqueous solution, and a titration curve as shown in FIG. 3 is obtained. As shown in FIG. 3, the electrical conductivity drops sharply at first (hereinafter referred to as "first region"). After that, the conductivity starts to rise slightly (hereinafter referred to as "second region"). After that, the increment of conductivity increases (hereinafter referred to as "third region"). The boundary point between the second region and the third region is defined as the point where the second derivative of the conductivity, that is, the amount of change in the increment (slope) of the conductivity is maximized. Thus, three regions appear in the titration curve. Of these, the amount of alkali required in the first region is equal to the amount of strong acid groups in the slurry used for titration, and the amount of alkali required in the second region is the amount of weak acid groups in the slurry used for titration. be equal. When the phosphate groups condense, the weakly acidic groups are apparently lost, and the amount of alkali required for the second region becomes smaller than the amount of alkali required for the first region. On the other hand, the amount of strongly acidic groups coincides with the amount of phosphorus atoms regardless of the presence or absence of condensation. Therefore, the amount of phosphate group introduced (or the amount of phosphate group) or the amount of substituent group introduced (or the amount of substituent group) means the amount of strongly acidic group. Therefore, the value obtained by dividing the alkali amount (mmol) required in the first region of the titration curve obtained above by the solid content (g) in the slurry to be titrated is the amount of phosphate group introduced (mmol/ g).

The amount of carboxyl groups introduced into the second cellulose fiber is measured, for example, as follows. First, the slurry containing the second cellulose fibers is treated with a strongly acidic ion exchange resin. In addition, before the treatment with the strongly acidic ion exchange resin, a defibration treatment similar to the fibrillation treatment step described below may be performed on the object to be measured, if necessary. Next, the change in electrical conductivity is observed while adding an aqueous sodium hydroxide solution to obtain a titration curve similar to that in FIG. The titration curve is divided into a first region in which the conductivity increment (slope) becomes almost constant after the electrical conductivity decreases, and a second region in which the conductivity increment (slope) increases thereafter. The boundary point between the first region and the second region is defined as the point where the second differential value of the conductivity, that is, the amount of change in the increment (slope) of the conductivity becomes maximum. Then, the value obtained by dividing the alkali amount (mmol) required in the first region of the titration curve by the solid content (g) in the second cellulose fiber-containing slurry to be titrated is the introduction amount of the carboxyl group. (mmol/g).

The amount of carboxyl groups introduced above (mmol/g) is the amount of substituents per 1 g of the mass of the second cellulose fiber when the counter ion of the carboxyl group is hydrogen ion (H ⁺ ) (hereinafter referred to as the amount of carboxyl group (acid form)). On the other hand, when the counterion of the carboxyl group is substituted with an arbitrary cation C so as to have a charge equivalent, the denominator is converted to the mass of the second cellulose fiber when the cation C is the counterion. By doing so, it is possible to determine the amount of carboxyl groups (hereinafter referred to as the amount of carboxyl groups (C-type)) possessed by the second cellulose fibers in which the cation C is the counterion.
That is, the amount of carboxyl group introduced is calculated by the following formula.
Amount of carboxyl groups introduced (type C) = amount of carboxyl groups (acid form) / [1 + (W-1) x (amount of carboxyl groups (acid form)) / 1000]
W: Formula weight per valence of cation C (for example, 23 for Na and 9 for Al)

The content of the second cellulose fibers is preferably 1% by mass or more, more preferably 5% by mass or more, and 10% by mass or more, relative to the total mass of the cellulose fibers contained in the sheet. is more preferable, 15% by mass or more is even more preferable, and 30% by mass or more is particularly preferable. In addition, the content of the second cellulose fibers is preferably 90% by mass or less, more preferably 80% by mass or less, and 70% by mass or less with respect to the total mass of the cellulose fibers contained in the sheet. is more preferable.

<Manufacturing process of fine fibrous cellulose>
<Textile raw material>
Microfibrous cellulose is produced from fibrous raw materials containing cellulose. The fibrous raw material containing cellulose is not particularly limited, but pulp is preferably used because it is readily available and inexpensive. Pulp includes, for example, wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include, but are not limited to, hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving 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 chemigroundwood pulp (CGP), groundwood pulp (GP) and thermomechanical pulp (TMP, BCTMP) A mechanical pulp etc. are mentioned. Non-wood pulps include, but are not limited to, cotton-based pulps such as cotton linters and cotton lints, and non-wood-based pulps such as hemp, straw, and bagasse. Examples of deinked pulp include, but are not limited to, deinked pulp made from waste paper. The pulp of this embodiment may be used alone or in combination of two or more.
Among the above pulps, wood pulp and deinked pulp are preferred, for example, from the viewpoint of availability. In addition, among wood pulps, the cellulose ratio is high and the yield of fine fibrous cellulose at the time of defibration is high, and the decomposition of cellulose in the pulp is small, and fine fibrous cellulose of long fibers with a large axial ratio can be obtained. From the point of view, for example, chemical pulp is more preferable, and kraft pulp and sulfite pulp are more preferable.

As the fiber raw material containing cellulose, for example, cellulose contained in sea squirts and bacterial cellulose produced by acetic acid bacteria can be used. Fibers formed by straight-chain nitrogen-containing polysaccharide polymers such as chitin and chitosan can also be used instead of fiber raw materials containing cellulose.

<Phosphate group introduction step>
When the fine fibrous cellulose has a phosphate group, the process for producing the fine fibrous cellulose includes a phosphate group introduction step. The phosphate group-introducing step is the same as the phosphate group-introducing step in the first cellulose fiber production step.

<Carboxyl Group Introduction Step>
When the fine fibrous cellulose has a carboxyl group, the production process of the fine fibrous cellulose includes a carboxyl group introduction step. The carboxyl group-introducing step is the same step as the carboxyl group-introducing step in the first cellulose fiber manufacturing process.

<Washing process>
In the method for producing fine fibrous cellulose according to the present embodiment, the phosphate group-introduced fibers can be washed if necessary. The washing step is the same step as the first washing step in the manufacturing process of the cellulose fibers.

<Alkali treatment process>
When producing fine fibrous cellulose, the fiber raw material may be subjected to alkali treatment between the ionic substituent introduction step and the fibrillation treatment step described later. The alkali treatment method is the same as the alkali treatment method in the first manufacturing process of the cellulose fibers.
In addition, after the alkali treatment step, the cleaning step described above may be further provided.

<Fibrillation treatment>
Fine fibrous cellulose is obtained by defibrating the fibers in the fibrillation treatment step. In the defibration treatment process, for example, a fibrillation treatment device can be used. The fibrillation treatment device is not particularly limited, but includes, for example, a high-speed fibrillator, a grinder (stone mill mill), a high-pressure homogenizer, an ultra-high-pressure homogenizer, a high-pressure collision-type pulverizer, a ball mill, a bead mill, a disk-type refiner, a conical refiner, and a biaxial refiner. A kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, a beater, or the like can be used. Among the above defibration equipment, it is more preferable to use a high-speed fibrillation machine, a high-pressure homogenizer, and an ultrahigh-pressure homogenizer, which are less affected by the grinding media and less likely to cause contamination.

In the fibrillation treatment step, the fibers are preferably diluted with a dispersion medium to form a slurry. As the dispersion medium, one or more selected from organic solvents such as water and polar organic solvents can be used. The polar organic solvent is not particularly limited, but alcohols, polyhydric alcohols, ketones, ethers, esters, aprotic 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 and glycerin. 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 esters include ethyl acetate and butyl acetate. Aprotic polar solvents include dimethylsulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidinone (NMP) and the like.

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

(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, and 40:60 to 90:10. It is more preferable to have Here, the first cellulose fibers in the sheet can be observed, for example, with a scanning electron microscope (S-3600N, manufactured by Hitachi High-Technologies Corporation). Also, the second cellulose fibers can be observed, for example, with a high-resolution field emission scanning electron microscope (S-5200, manufactured by Hitachi, Ltd.). 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, which will be described later, is the same as 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. Other cellulose fibers include, for example, highly beaten pulp obtained by beating the first cellulose fibers to a fiber width of more than 1 μm and less than 10 μm. Here, the fiber width of other fibers is the fiber width of trunk fibers of cellulose fibers. For example, when the other fibers are fibrillated cellulose fibers, the fiber width of the other fibers is not the fiber width of the fibrillated and branched fibers but the fiber width of the stem fibers.

Beating of other cellulose fibers can be performed, for example, using a defibration treatment apparatus. The fibrillation treatment device is not particularly limited. Examples thereof include high-speed defibrators, grinders (stone mill-type grinders), high-pressure homogenizers, ultra-high-pressure homogenizers, CLEARMIX, high-pressure collision-type grinders, ball mills, bead mills, disk-type refiners, and conical refiners. In addition, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, a beater, or a wet pulverizing device can be used as appropriate.

(water-soluble polymer)
The sheet of the present invention may further contain a water-soluble polymer. Examples of water-soluble polymers include carboxyvinyl polymer, polyvinyl alcohol, alkyl methacrylate/acrylic acid copolymer, polyvinylpyrrolidone, sodium polyacrylate, polyethylene glycol, diethylene glycol, triethylene glycol, polyethylene oxide, propylene glycol, dipropylene glycol, Synthetic water-soluble polymers exemplified by 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, pullulan , carrageenan, and pectin; cellulose derivatives, such as carboxymethylcellulose, methylcellulose, and hydroxyethylcellulose; cationized starch, raw starch, oxidized starch, etherified starch, esterified starch , and starches exemplified by amylose; glycerins exemplified by glycerin, diglycerin, and polyglycerin; hyaluronic acid, metal salts of hyaluronic acid, and the like.

(paper strength agent)
The sheet of the present invention preferably further contains a paper strength agent. This makes it possible to further improve the strength of the sheet. Paper strength agents include dry strength agents and wet strength agents. Examples of dry paper strength agents include cationized starch, polyacrylamide (PAM), carboxymethyl cellulose (CMC), and acrylic resins. Examples of wet paper strength agents include polyamide epihalohydrin, urea, melamine, and thermally crosslinkable polyacrylamide. Among others, the sheet of the present invention preferably contains polyamine polyamide epihalohydrin.

Polyamine polyamide epihalohydrin is a cationic thermosetting resin obtained by subjecting an aliphatic dibasic carboxylic acid or a derivative thereof and a polyalkylene polyamine to thermal condensation 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 polyamine polyamide epihalohydrin include polyamine polyamide epichlorohydrin, polyamine polyamide epibromohydrin, and polyamine polyamide epiiodohydrin.

The content of the paper strength agent 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 cellulose fibers. More preferably, it is at least 1 part. In addition, the content of the paper strength agent 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 agent within the above range, the strength of the sheet can be improved more effectively.

(Optional component)
The sheet of the present invention may contain optional components other than the components described above. Optional components include, for example, preservatives, antifoaming agents, lubricants, UV absorbers, dyes, pigments, stabilizers, surfactants, sizing agents, coagulants, retention improvers, bulking agents, drainage improvers, pH adjusters, fluorescent whitening agents, pitch control agents, slime control agents, antifoaming agents, water retention agents, dispersing agents and the like can be mentioned.

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 30% by mass or less, relative to the total mass of the sheet. More preferred.

(Manufacturing method of sheet)
The sheet manufacturing method of the present invention includes a step of forming a sheet from a slurry containing first cellulose fibers having a fiber width of 10 μm or more and second cellulose fibers having a fiber width of 1000 nm or less. Here, the water retention of the first cellulose fibers is 220% or more. Also, the second cellulose fiber is preferably a cellulose fiber having an ionic substituent.

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

The water retention of the first cellulose fibers is preferably 220% or more, more preferably 230% or more, and even more preferably 240% or more. Also, the water retention of the first cellulose fibers is preferably 600% or less. Note that the water retention of the first cellulose fiber is described in J. Am. It is a value measured according to TAPPI-26.

The step of forming a sheet from slurry includes a coating step of coating the slurry onto a substrate or a papermaking step of papermaking the slurry. In addition, it is preferable that the method for producing a sheet of the present invention does not include a calendering process as a process after 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 substrate, dried, and the formed sheet is peeled off from the substrate to obtain a sheet. In addition, sheets can be continuously produced by using a coating device and a long base material.

The material of the base material used in the coating process is not particularly limited, but a material with high wettability to the slurry can suppress the shrinkage of the sheet during drying, but the sheet formed after drying is easy. It is preferable to select a material that can be easily peeled off. Among them, 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 such as aluminum, zinc, copper, and iron plates, and those whose surfaces have been oxidized. , a stainless steel film or plate, a brass film or plate, or the like can be used.

In the coating process, when the viscosity of the slurry is low and it spreads on the base material, a dam frame is fixed on the base material in order to obtain a sheet with a predetermined thickness and basis weight. may The frame for damming is not particularly limited, but it is preferable to select, for example, one that allows easy peeling of the edge of the sheet that adheres after drying. From such a point of view, a molded resin plate or metal plate is more preferable. In the present embodiment, for example, resin plates such as polypropylene plates, acrylic plates, polyethylene terephthalate plates, vinyl chloride plates, polystyrene plates, polycarbonate plates, and polyvinylidene chloride plates, and metal plates such as aluminum plates, zinc plates, copper plates, iron plates, etc. , and those whose surfaces have been oxidized, and those obtained by molding a stainless steel plate, a brass plate, or the like can be used.
The coating machine for coating the slurry on the base material is not particularly limited, but for example, a roll coater, gravure coater, die coater, curtain coater, air doctor coater, etc. can be used. A die coater, a curtain coater, and a spray coater are particularly preferred because they can make the thickness of the sheet more uniform.

The slurry temperature and the ambient temperature when the slurry is applied to the substrate are not particularly limited, but are preferably 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 higher, and particularly preferably 20° C. or higher and 40° C. or lower. If the coating temperature is at least the above lower limit, the slurry can be more easily coated. When the coating temperature is equal to or lower than the above upper limit, volatilization of the dispersion medium during coating can be suppressed.

In the coating step, the slurry is applied so that the finished basis weight of the sheet is preferably 5 g/m ² or more and 100 g/m ² or less, more preferably 10 g/m ² or more and 60 g/m ² or less. It is preferable to apply it to 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 made thinner.

The coating step includes the step of drying the slurry applied onto the substrate, as described above. The step of drying the slurry is not particularly limited, but may be 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, but for example, a method of drying by heating with hot air, infrared rays, far infrared rays, or near infrared rays (heat drying method), or a method of drying in a vacuum (vacuum drying method) 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.

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

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

The papermaking process is carried out by filtering the slurry with a wire and dehydrating it to obtain a wet paper sheet, which is then pressed and dried. The filter cloth used for filtering and dewatering 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. Although such filter cloth is not particularly limited, for example, sheets, fabrics, and porous membranes made of organic polymers are preferable. Although the organic polymer is not particularly limited, non-cellulose organic polymers such as polyethylene terephthalate, polyethylene, polypropylene, and polytetrafluoroethylene (PTFE) are preferred. In this embodiment, for example, a polytetrafluoroethylene porous film having a pore size of 0.1 μm or more and 20 μm or less, or a polyethylene terephthalate or polyethylene fabric having a pore size of 0.1 μm or more and 20 μm or less can be used.

In the sheeting process, a method for producing a sheet from a slurry includes, for example, a water squeezing section for discharging a slurry containing cellulose fibers onto the upper surface of an endless belt and squeezing a dispersion medium from the discharged slurry to form a web; A drying section that dries the web to form a sheet. An endless belt is provided from the water squeezing section to the drying section, and the web produced in the water squeezing 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, but includes, for example, dehydration methods commonly used in the manufacture of paper. Among these, the method of dehydrating with a fourdrinier, a circular net, an inclined wire, or the like and then further dehydrating with a roll press is preferable. The drying method used in the papermaking process is not particularly limited, but includes, for example, methods used in the manufacture of paper. Among these, a drying method using a cylinder dryer, Yankee dryer, hot air drying, near-infrared heater, infrared heater, or the like is more preferable.

(Application)
The use of the sheet of the present invention is not particularly limited. For example, sheets include wrapping paper, tracing paper, cooking sheet, medicine packaging paper, battery separator, filter, liner for total heat exchange, diaphragm, press molding member, flexible substrate, resin composite, reinforced fiber plastic laminate, Suitable for applications such as

EXAMPLES The characteristics of the present invention will be described more specifically below with reference to examples and comparative examples. The materials, amounts used, proportions, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed to be limited by the specific examples shown below. In the following, Example 13 shall be read as Reference Example 13.

(Example 1)
<Preparation of first cellulose fiber (1)>
[Preparation of phosphorylated pulp]
As raw material pulp, softwood kraft pulp manufactured by Oji Paper Co., Ltd. (solid content 93% by mass, basis weight 208 g / m ² sheet, defiberized and Canadian standard freeness (CSF) measured according to JIS P 8121 700 ml) It was used. The raw material pulp was subjected to a phosphorylation treatment as follows. First, a mixed aqueous solution of ammonium dihydrogen phosphate and urea is added to 100 parts by mass (absolute dry mass) of the raw material pulp to obtain 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of water. A chemical-impregnated pulp was obtained by adjusting as follows. Next, the resulting chemical solution-impregnated pulp was heated in a hot air dryer at 165° C. for 200 seconds to introduce phosphoric acid groups into cellulose in the pulp to obtain phosphorylated pulp.

[Washing process]
Then, the obtained phosphorylated pulp was washed. In the washing treatment, a pulp dispersion liquid obtained by pouring 10 L of ion-exchanged water into 100 g (absolute dry mass) of phosphorylated pulp is stirred so that the pulp is uniformly dispersed, and then filtration and dehydration are repeated. gone. The washing was finished when the electric conductivity of the filtrate became 100 μS/cm or less.

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

[Washing process]
Next, the washing treatment was performed on the phosphorylated pulp after the neutralization treatment. The phosphorylated pulp thus obtained was subjected to infrared absorption spectrum measurement using FT-IR. As a result, absorption due to phosphate groups was observed near 1230 cm ^-1 , confirming that phosphate groups were added to the pulp. In addition, when the obtained phosphorylated pulp was tested and analyzed with an X-ray diffraction device, it was found that the A typical peak was confirmed, confirming that it had cellulose type I crystals. Moreover, the fiber width measured by the measuring method described later was 29 μm. The amount of phosphate groups (strongly acidic group amount) measured by the method described later was 1.2 mmol/g. Ion-exchanged water was added to the obtained phosphorylated pulp to obtain a first cellulose fiber dispersion (1) containing first cellulose fibers (1) having a solid content concentration of 2% by mass.

<Preparation of second cellulose fiber (1)>
[Miniaturization]
The first cellulose fiber dispersion (1) obtained by the above method is treated twice with a wet atomization device (Starburst, manufactured by Sugino Machine Co., Ltd.) at a pressure of 200 MPa to obtain a second cellulose fiber (1 ) to obtain a second cellulose fiber dispersion (1). X-ray diffraction confirmed that the second cellulose fibers (1) maintained cellulose type I crystals. Further, the fiber width measured by the measuring method described later was 3 to 5 nm. The amount of phosphate groups (strongly acidic group amount) measured by the method described later was 1.2 mmol/g.

<Measurement of phosphate group content of first cellulose fiber>
The phosphate group content of the first cellulose fiber was measured by a neutralization titration method. First, the first cellulose fibers were diluted with ion-exchanged water, 1N hydrochloric acid was added while stirring, and then the first cellulose fibers were collected by filtration and dehydration. This operation was repeated to completely convert the phosphoric acid groups of the first cellulose fibers to the acid form. After diluting the obtained first cellulose fibers with ion-exchanged water, excess hydrochloric acid was sufficiently washed away by repeating the operation of obtaining a dehydrated sheet by filtration and dehydration. After that, to a suspension obtained by diluting the first cellulose fiber (acid form) with ion-exchanged water, the change in pH was observed while adding an aqueous sodium hydroxide solution to obtain a titration curve as shown in FIG. rice field. The amount of alkali (mmol) required in the first region of the obtained titration curve is divided by the solid content (g) in the first cellulose fiber suspension to be titrated to obtain the amount of phosphate group introduced (mmol/ g).

<Measurement of phosphate group content of second cellulose fiber>
The amount of phosphate groups in the second cellulose fiber was measured by conductivity titration. First, to a fibrous cellulose-containing slurry prepared by diluting a second cellulose fiber dispersion liquid (1) containing target fine fibrous cellulose with ion-exchanged water so that the content becomes 0.2% by mass, , after treatment with an ion-exchange resin, was measured by titration with an alkali.
The ion-exchange resin treatment is carried out by adding 1/10 by volume of a strongly acidic ion-exchange resin (Amberjet 1024; Organo Co., Ltd., conditioned) to the fibrous cellulose-containing slurry and shaking for 1 hour. , by pouring it onto a mesh with an opening of 90 μm to separate the resin and the slurry.
In addition, titration with an alkali is carried out by adding a 0.1 N sodium hydroxide aqueous solution to the fibrous cellulose-containing slurry after treatment with an ion exchange resin, and adding 50 μL each time once every 30 seconds. This was done by measuring the change in the value of The amount of phosphate group (mmol/g) is obtained by dividing the alkali amount (mmol) required in the region corresponding to the first region shown in FIG. 3 among the measurement results by the solid content (g) in the slurry to be titrated. calculated by

<Measurement of Fiber Width of First Cellulose Fiber>
The fiber width of the first cellulose fiber was obtained by measurement using a Kajaani fiber length measuring instrument (FS-200 type) manufactured by Kajaani Automation.

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

<Sheeting>
The first cellulose fiber (1) is 50 parts by mass, the second cellulose fiber (1) is 50 parts by mass, the polyvinyl alcohol is 10 parts by mass, and the polyamine polyamide/epichlorohydrin is 5 parts by mass. Cellulose fiber dispersion (1) of 1, second cellulose fiber dispersion (1), polyvinyl alcohol solution (manufactured by Nippon Synthetic Chemical Industry, Gohsenex Z-200), and 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 Coating Liquid 1 was adjusted to 0.5% by mass.
Next, the coating liquid 1 was weighed so that the basis weight of the obtained sheet (layer composed of the solid content of the coating liquid) was 10 g/m ² , coated on a commercially available acrylic plate, and heated at 50°C. was dried in a constant temperature dryer. A metal frame for damming (a metal frame with an inner dimension of 180 mm×180 mm and a height of 5 cm) was arranged on the acrylic plate so as to obtain a predetermined basis weight. Next, the dried sheet was separated from the acrylic plate to obtain a sheet containing the first cellulose fibers and the second cellulose fibers.

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

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

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

(Example 5)
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. were mixed to obtain a coating liquid 2. A sheet was obtained in the same manner as in Example 1 except that Coating Liquid 2 was used instead of Coating Liquid 1 used in the sheet forming step.

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

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

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

(Example 9)
<Production of first cellulose fiber (2)>
In [Preparation of phosphorylated pulp] of Example 1, the first cellulose fiber (1) was prepared in the same manner as the first cellulose fiber (1), except that the chemical-impregnated pulp was heated with a hot air dryer for 150 seconds to obtain a phosphorylated pulp. A cellulose fiber (2) was obtained. The obtained first cellulose fibers (2) had a fiber width of 29 μm and a phosphate group content (strong acid group content) of 0.7 mmol/g.

<Preparation of second cellulose fiber (2)>
[Miniaturization]
Second cellulose fibers (2) were obtained in the same manner as in [Refining] of Example 1, except that the first cellulose fibers (2) were used. The obtained second cellulose fibers (2) had a fiber width of 3 to 5 nm and a phosphate group content (strong acid group content) of 0.7 mmol/g.

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

(Example 10)
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. were 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 sheet forming step was used as coating liquid 4, and the coating liquid 4 was measured so that the basis weight of the sheet was 25 g/m ² . .

(Example 11)
<Preparation of first cellulose fiber (3)>
In the preparation of the phosphorylated pulp, the first cellulose fiber (3) was prepared 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 a phosphorylated pulp. Obtained. The obtained first cellulose fibers (3) had a fiber width of 29 μm and a phosphate group content (strong acid group content) of 0.5 mol/g.

<Preparation of second cellulose fiber (3)>
[Miniaturization]
Second cellulose fibers (3) were obtained in the same manner as in [Refining] of Example 1, except that the first cellulose fibers (3) were used. The obtained second cellulose fibers (3) had a fiber width of 3 to 5 nm and a phosphate group content (strong acid group content) of 0.5 mmol/g.

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

(Example 12)
80 parts by mass of the first cellulose fibers (3), 20 parts by mass of the second cellulose fibers (3), 10 parts by mass of polyvinyl alcohol, and 5 parts by mass of polyamine polyamide/epichlorohydrin. were 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 sheet forming step was Coating Liquid 5, and the Coating Liquid 5 was measured so that the basis weight of the sheet was 25 g/m ² . .

(Example 13)
<Preparation of second cellulose fiber (4)>
Softwood bleached kraft pulp (NBKP) was beaten with a double disc refiner until the irregular freeness reached 100 ml to obtain a pulp dispersion with a solid content concentration of 2% by mass. The pulp dispersion is diluted with ion-exchanged water so that the solid content concentration is 0.2% by mass, and the high-pressure homogenizer "Panda Plus 2000" manufactured by NiroSoavi Co. performs three times of refining treatment at a treatment pressure of 120 MPa. A second cellulose fiber dispersion (4) containing cellulose fibers (4) was obtained. The obtained second cellulose fibers (4) had a fiber width of 130 nm and a phosphate group content (strong acid group content) of 0.03 mmol/g.

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

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

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

(Comparative example 2)
A sheet was obtained in the same manner as in Example 6, except that the first cellulose fibers (4) obtained above were used as the first cellulose fibers in the sheet forming step.

(Comparative Example 3)
<Preparation of first cellulose fiber (5)>
Water was added to the softwood bleached kraft pulp so that the solid content concentration was 4.0% by mass, and after dispersion, the mixture was treated once with a double disc refiner to obtain first cellulose fibers (5). The fiber width of the first cellulose fibers (5) was 16 µm.
A sheet was obtained in the same manner as in Example 2, except that the first cellulose fibers (5) were used as the first cellulose fibers 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 fibers (5) were used as the first cellulose fibers 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 fibers (5) were used as the first cellulose fibers 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 fibers (5) were used as the first cellulose fibers 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 P8118.

(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 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 Research Laboratory Co., Ltd.) in accordance with JIS K 7136. Further, the total light transmittance was measured using a haze meter (HM-150, manufactured by Murakami Color Research Laboratory Co., Ltd.) in accordance with JIS K 7361.

(seat appearance)
The number of twists in 20 prepared sheets (size: 18 cm long, 18 cm wide) (total area: 0.648 m ² ) was confirmed visually. It was converted into the number of twists per 1 m ² and evaluated according to the following criteria. "Twisting" refers to white lumps observed on the surface of the sheet as shown in the dotted line frame in FIG.
◎: No twist (0/m ² )
○: Number of twists 1/ ^m2 or more and less than ² /m2 △: Number of twists ² or more/m2 and less than 10/ ^m2 ×: Number of twists 10/ ^m2 or more

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

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

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

Claims (9)

A first cellulose fiber having a phosphate group or a substituent derived from a phosphate group and having a fiber width of 10 μm or more, and a phosphate group or a substituent derived from a phosphate group and having a fiber width and second cellulose fibers of 1000 nm or less. 2. The sheet according to claim 1 , wherein the content of the first cellulose fibers is 10% by mass or more relative to the total mass of the cellulose fibers. 3. The sheet according to claim 1, which has a haze of 20% or more. The sheet according to any one of claims 1 to 3 , which has a total light transmittance of 80% or more. The sheet according to any one of claims 1 to 4 , which has a basis weight of 40 g/m ² or less. The sheet according to any one of claims 1 to 5 , which has an air permeability of 10000 seconds or more. The sheet according to any one of claims 1 to 6 , wherein the introduction amount of the phosphate groups of the first cellulose fibers or the substituents derived from the phosphate groups is 0.3 mmol/g or more. The sheet according to any one of claims 1 to 7 , wherein the first cellulose fibers have a water retention rate of 220% or more. a first cellulose fiber having a water retention of 220% or more, having a phosphate group or a substituent derived from a phosphate group, and having a fiber width of 10 μm or more;
A method for producing a sheet, comprising a step of forming a sheet from a slurry containing a second cellulose fiber having a phosphoric acid group or a substituent derived from a phosphoric acid group and having a fiber width of 1000 nm or less.

Images