JP2021188245A - Redispersible pulp and redispersible pulp composition - Google Patents

Abstract

To provide a redispersible pulp which can exhibit excellent dispersibility even in a dehydratied or dry state, and a redispersible pulp composition.SOLUTION: A redispersible pulp involves a sulfonated pulp in which hydroxy groups of cellulose constituting a cellulose fiber are at least partially substituted with sulfo groups. An introduction amount of sulfo groups in the sulfonated pulp is 0.1 mmol/g or over and 5.0 mmol/g or under. A sheet of the sulfonated pulp is prepared by using a 100-mesh wire net in accordance with JIS P 8222 so as to have a thickness of 0.05 mm-3.0 mm and a basis weight of 45 g/m2-1000 g/m2, and the sheet shows an ease of disentanglement of 15 s or under in a measuring method in accordance with JIS P 4501. The redispersible pulp includes a sulfonated pulp which exhibits an ease of disentanglement that is equal to or lower than a predetermined value in a sheet state, thereby exhibiting excellent dispersibility even in a state of low moisture percentage.SELECTED DRAWING: Figure 1

Description

The present invention relates to redispersible pulp and redispersible pulp compositions. More specifically, the present invention relates to a redispersible pulp and a redispersible pulp composition that exhibit excellent dispersibility when redispersed in water or the like.

In the papermaking process, pulp obtained from raw wood is prepared as a pulp slurry dispersed in a large amount of water, and then paper is produced as it is using a paper machine or the like. On the other hand, the pulp slurry is dehydrated and dried to prepare dry pulp, wet pulp (wet pulp sheet, thickness of about 3 mm to 5 mm), and stored or shipped. In the papermaking process, such wet pulp or the like is dispersed again in a dispersion medium such as water to prepare a pulp slurry, and then paper is manufactured using a paper machine or the like. However, preparing a pulp slurry from such wet pulp or the like has a problem that it is very laborious and costly as compared with the case of directly preparing from pulp obtained from a raw material. Specifically, since the wet pulp and the like have a low water content, the bonds between the pulps (hydrogen bonds) are strong. For this reason, conventionally, in the process of preparing a pulp slurry using the above-mentioned wet pulp or the like, it is difficult to disperse the pulp slurry, and a lumpy substance may remain. Therefore, a special device or the like is used to prepare an appropriate pulp slurry. It is used (Non-Patent Document 1).

On the other hand, conventionally, as a technique for suppressing a decrease in redispersibility of wet pulp or the like, a method of adding a dispersant for suppressing the bond between pulps to a pulp slurry (for example, Patent Document 1) or a special method for wet pulp. A method of providing an embossed structure (for example, Patent Document 2) has been proposed.

International Publication No. 2019/130968 JP-A-2015-205508

Pulp and Paper Manufacturing Technology Series 5 "Preparation of Paper Charges", Published by Pulp and Paper Technology Association, 1992, pp. 3-11

However, when the conventional dispersant is added to the pulp slurry, the use of the pulp is limited by the added dispersant, and the economic burden is increased due to the increase in the processing equipment for providing the treatment for removing the dispersant. There are problems such as complicated processing. Further, when the conventional wet pulp sheet or the like is dissociated by a special device, there is a problem that the economic burden for providing the special device increases. That is, in the conventional technique, a dispersant is added to the pulp to chemically dehydrate or dry the pulp, or a special stirrer or the like is used to physically redisperse the dehydrated or dried pulp. Although the technology is disclosed, the technology that makes the pulp itself exhibit redispersibility is not disclosed.
Also, in the field of papermaking, it is a common common knowledge among those skilled in the art that pulp in a state where the pulp slurry is dehydrated or dried to have a low water content is inferior in redispersibility. Conventionally, there is no known pulp that can be easily redispersed from a dehydrated or dried state.

In view of the above circumstances, it is an object of the present invention to provide a redispersible pulp capable of exhibiting excellent dispersibility even from a dehydrated or dried state, and a redispersible pulp composition containing the redispersible pulp. And.

As a result of diligent studies to solve the above problems, the present inventors have found that the above problems can be solved in the sulfonated pulp obtained by introducing a predetermined amount of sulfo groups into the pulp, and completed the present invention. I arrived.

The redispersible pulp of the first invention contains a sulfonated pulp in which at least a part of the hydroxyl group of the cellulose constituting the cellulose fiber is substituted with a sulfo group, and the sulfonated pulp contains the introduction of the sulfo group. The amount is 0.1 mmol / g or more and 5.0 mmol / g or less, and the basis weight is 45 g / m ^{2 to} 1000 g / m ² and the thickness is 0.05 mm using a 100 mesh wire mesh in accordance with JIS P 8222. A redispersible pulp characterized in that the looseness measured by the following (1) or (2) on a sheet prepared to be ~ 3.0 mm is 15 seconds or less.
It is characterized by being characterized by that.

(1) In the case of a sheet prepared to have a basis weight of 45 g / m ² or more and less than 100 g / m ² and a thickness of 0.05 mm to 3.0 mm, the ease of loosening is measured in accordance with JIS P 4501.
(2) In the case of a sheet prepared to have a basis weight of 100 g / m ² or more and less than 1000 g / m ² and a thickness of 0.05 mm to 3.0 mm, follow the procedures of (i) and (ii) below in accordance with JIS P 4501. Measure.
(I) Put the rotor in a 1L glass beaker containing 1L of pure water, and adjust the rotation speed of the rotor to 600 rpm.
(Ii) Measure the time from when the test piece is inserted until the rotation speed of the rotor recovers to 450 rpm.

The redispersible pulp of the second invention is based on JIS 811-2 (2012) in the measurement dispersion liquid in which the sulfonated pulp is dispersed in water to a solid content concentration of 0.3% by mass in the first invention. It is characterized in that the standard filtrate degree based on the measuring method is 60 mL or more.
The redispersible pulp of the third invention is characterized in that, in the first invention or the second invention, the sulfonated pulp has a moisture content of 60% or less in the sheet in the measurement of easiness of loosening.
The redispersible pulp composition of the fourth invention is a solid composition containing the redispersible pulp according to any one of the first invention, the second invention or the third invention, and water, and is a fiber. It is one of the following, cotton-like, lump-like, block-like, sheet-like, granular, powder-like, wax-like, sponge-like, gel-like, paste-like, and cream-like. basis weight ^45g / ^{m 2 ~1000g} / m 2 using a wire net, following in thickness was prepared 0.05mm~3.0mm sheet (1) or 100 seconds unraveling ease as measured by (2) It is characterized by the following.

(1) In the case of a sheet prepared to have a basis weight of 45 g / m ² or more and less than 100 g / m ² and a thickness of 0.05 mm to 3.0 mm, the ease of loosening is measured in accordance with JIS P 4501.
(2) In the case of a sheet prepared to have a basis weight of 100 g / m ² or more and less than 1000 g / m ² and a thickness of 0.05 mm to 3.0 mm, follow the procedures of (i) and (ii) below in accordance with JIS P 4501. Measure.
(I) Put the rotor in a 1L glass beaker containing 1L of pure water, and adjust the rotation speed of the rotor to 600 rpm.
(Ii) Measure the time from when the test piece is inserted until the rotation speed of the rotor recovers to 450 rpm.

The redispersible pulp composition of the fifth invention is characterized in that, in the fourth invention, the water content of the composition is 0.5% by mass or more and 97% by mass or less.
In the fourth or fifth invention, the redispersible pulp composition of the sixth invention has the moisture content in the fibrous, cotton-like, lumpy, block-like, sheet-like, granular, powdery or waxy state. It is characterized by being 0.5% by mass or more and 60% by mass or less.
The redispersible pulp composition of the seventh invention is the redispersibility according to any one of the first invention, the second invention or the third invention in any of the inventions of the fourth invention, the fifth invention or the sixth invention. The content of the sulfonated pulp contained in the pulp redisperable pulp is 3% by mass or more.
The redispersible pulp composition of the eighth invention contains pulp for papermaking in any one of the inventions of the fourth invention, the fifth invention, the sixth invention or the seventh invention, and the content ratio of the pulp for papermaking. However, the solid content of the sulfonated pulp is 1 part by mass or more and 900 parts by mass or less with respect to 100 parts by mass.
The redispersible pulp composition of the ninth invention is dispersed in water at a solid content concentration of 0.3% by mass in any one of the fourth invention, the fifth invention, the sixth invention, the seventh invention or the eighth invention. It is characterized in that the standard freeness is 60 mL or more and 800 mL or less based on the measurement method according to JIS 811-2 (2012) in the measured dispersion liquid.

According to the first invention, since the sulfonated pulp that exhibits the easiness of unraveling to a predetermined value or less from the sheet-like state is contained, it is possible to exhibit excellent dispersibility even from a low water content state. can.
According to the second invention, since the sulfonated pulp having a free water content of a predetermined value or more is contained, it is possible to improve the handleability while exhibiting excellent dispersibility.
According to the third invention, excellent dispersibility can be exhibited even from a state similar to the dehydrated state.
According to the fourth and fifth inventions, since the predetermined redispersible pulp is contained, excellent dispersibility can be exhibited even in the solid state.
According to the sixth invention, excellent dispersibility can be exhibited even in a state where the water content is low.
According to the seventh invention, since the predetermined sulfonated pulp is contained in a predetermined value or more, excellent dispersibility can be appropriately exhibited.
According to the eighth invention, since the pulp for papermaking is contained, the strength can be improved.
According to the ninth invention, since the sulfonated pulp having a freeness of water of a predetermined value or more is contained, it is possible to improve the handleability while exhibiting excellent dispersibility.

It is a schematic flow chart of the manufacturing method of the pulp of this embodiment. It is a figure which shows the experimental result (experiment 1), and is the table which showed the dispersibility of the redispersed pulp and the water decomposability of the sulfonated pulp containing the redispersible pulp. It is a figure which shows the experimental result (experiment 2), and is the table which showed the dispersibility of the redispersed pulp and the water decomposability of the sulfonated pulp containing the redispersible pulp. It is a figure which shows the experimental result, and is the graph which showed the relationship between the pulp sheet, its hydrolyzability (seconds), and the amount of a functional group introduced. It is a figure which shows the experimental result, and is the graph which showed the relationship between the pulp sheet, its hydrolyzability (seconds), and the amount of a functional group introduced. It is a figure which shows the experimental result, and is the graph which showed the relationship between the pulp sheet, its hydrolyzability (seconds), and the amount of a functional group introduced. It is a figure which shows the experimental result, and is the graph which showed the relationship between the predetermined pulp sheet in FIG. 3 and its hydrolyzability (seconds). It is a figure which shows the experimental result, and is the table which showed the characteristic (physical property) of the mixed sheet made by mixing the sulfonated pulp and the papermaking pulp. It is a figure which shows the experimental result, and is the photograph which showed the property of the redispersible pulp and the redispersible pulp composition. It is a figure which shows the experimental result, and is the photograph which showed the property of the redispersible pulp and the redispersible pulp composition.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The redispersible pulp of the present embodiment contains a sulfonated pulp in which at least a part of the hydroxyl groups of the cellulose constituting the pulp is substituted with a sulfo group, so that the redispersible pulp has excellent dispersibility (hydrolysis) even in a low water state. It is characterized by being able to exert. The redispersible pulp composition of the present embodiment is a composition containing the redispersible pulp of the present embodiment, and by containing the redispersible pulp of the present embodiment, even from a state of low water content. It is characterized by being able to exhibit excellent dispersibility (water-decomposability).

The redispersible pulp of the present embodiment means not only an aggregate in a state where a plurality of fibers are aggregated, but also individual fibers constituting these aggregates. That is, unless otherwise specified in the present specification, both the one in the state of one fiber and the one in the aggregate of a plurality of fibers are simply referred to as the redispersible pulp of the present embodiment. When not particularly limited, the aggregate of a plurality of fibers is referred to as the redispersible pulp of the present embodiment.

The fact that the redispersible pulp of the present embodiment exhibits dispersibility in a state of low water content means that the redispersible pulp of the present embodiment, which will be described later, exhibits dispersibility with respect to a dispersion medium. do. Although the details are vertical, the redispersible pulp composition contained in the redispersible pulp of the present embodiment is in a solid state when the water content is lower than 100%, and exhibits dispersibility when added to a dispersion medium. It is possible to make it.

The excellent dispersibility of the redispersible pulp of the present embodiment means that the redispersible pulp composition of the present invention described later is used as a dispersion medium in a state where the water content is reduced as described above. It means that the dispersibility in a dispersion medium such as water is good when it is put into the water.
The dispersibility for the dispersion medium here means that when it comes into contact with a large amount of water, the bonds between the fibrous pulps that are in close contact with each other are loosened and completely separated into the dispersion medium, as well as some loosening. It also includes a state in which a small amount of fibers in the state of being in contact with each other are close to each other.

The dispersibility of the redispersible pulp of this embodiment is described in the water-decomposability evaluation method of the sulfonated pulp described later and the water-decomposability test described in Examples (the test method of easiness of loosening specified in JIS P 4501). Can be evaluated at. Details will be described later.

The ease of loosening here includes not only a state in which the bonds between the fibers of the test piece are weakened and loosened and separated into small pieces, but also a state in which the fibers are separated into water. That is, in the present specification, the dispersibility of the redispersible pulp of the present embodiment has the same meaning as the hydrolyzability of the sheet-shaped pulp as well as the fibrous pulp being separated into the dispersion medium. But it can also be used.

(Sulfonized pulp contained in the redispersible pulp of the present embodiment)
The sulfonated pulp contained in the redispersible pulp of the present embodiment is a fibrous member in which a plurality of cellulose fibers are aggregated, and the cellulose (D-glucose is β (1 → 4) glycoside) constituting the contained cellulose fibers. At least a part of the hydroxyl group (-OH group) of the bonded chain polymer) is sulfonated by the sulfo group represented by the following formula (1). That is, the sulfonated pulp in the redispersible pulp of the present embodiment is a pulp in which some of the hydroxyl groups of the cellulose fibers constituting the pulp are substituted with sulfo groups.

(-SO3-) r · Zr + (1)
(Here, r is an independent natural number of 1 to 7, and Zr + is a hydrogen ion, an alkali metal cation, a monovalent transition metal ion, an ammonium ion, an aliphatic ammonium ion, when r = 1. It is at least one selected from the group consisting of aromatic ammonium ions and cationic polymers. When r = 2 or more, cations of alkaline earth metals, cations of polyvalent metals, and cations such as diamines. It is at least one selected from the group consisting of compounds containing two or more sex functional groups in the molecule.)

In the present specification, the fibers of one sulfonated pulp and the aggregate of the fibers of a plurality of sulfonated pulps are both simply referred to as sulfonated pulps contained in the redispersible pulp of the present embodiment. In the present specification, the sulfonated pulp without particular limitation refers to an aggregate of a plurality of sulfonated pulps.

(Amount of sulfo group introduced in sulfonated pulp)
The sulfonated pulp in the redispersible pulp of the present embodiment is adjusted so that the sulfo group is within a predetermined range. By containing the sulfonated pulp in which the sulfo group is adjusted within a predetermined range, excellent hydrolyzability can be imparted to the redispersible pulp of the present embodiment (see Examples).

For example, the amount of sulfo groups introduced per 1 g (solid content mass) of sulfonated pulp is adjusted to be higher than 0.1 mmol / g. It is preferably 0.2 mmol / g or more, more preferably 0.4 mmol / g or more, still more preferably 0.5 mmol / g or more, and even more preferably 1.0 mmol / g or more.

In particular, it is preferable that the amount of sulfo groups introduced per 1 g (solid content mass) of the sulfonated pulp is 1.0 mmol / g or more from the viewpoint of tensile strength.
For example, when the introduction amount of the sulfo group is 1.0 mmol / g or more, the sheet made of the redispersible pulp composition containing the redispersible pulp of the present embodiment adjusted by the method described later has a tear length described later. Is strong and the strength in the pulling direction is strong, so that the sheet can be easily wound into a roll. Then, if the redisperable pulp composition of the present embodiment in the form of a sheet rolled into a roll is put into water, it can be easily dispersed in a dispersion medium.

Although the upper limit is not particularly limited, there is a concern that the crystallinity will decrease as the amount of sulfo group introduced per 1 g (solid content mass) of the sulfonated pulp approaches 9.9 mmol / g, and when sulfur is introduced. Costs also tend to increase. Therefore, the upper limit value is preferably 9.9 mmol / g or less, and preferably 5.0 mmol / g or less from the viewpoint of cost.

The amount of sulfo group introduced into the sulfonated pulp in the redispersible pulp of the present embodiment can be evaluated by the amount of sulfur introduced due to the sulfo group or by directly measuring the sulfo group. As the latter measuring method, for example, it can be calculated by the electric conductivity measurement described in Examples described later.

(Hydrolytic property of sulfonated pulp)
The sulfonated pulp contained in the redispersible pulp of the present embodiment has a predetermined ease of loosening (that is, dispersibility (hydrolyzability)).
For example, in the sheet prepared by the looseness measurement in the above measuring method, the looseness in the test method is 15 seconds or less. It is preferably 14 seconds or less, more preferably 12 seconds or less, still more preferably 11 seconds or less, and even more preferably 10 seconds or less.
The dispersibility of the sulfonated pulp contained in the redispersible pulp of the present embodiment can be evaluated by the hydrolyzability test (test method for easiness of loosening specified in JIS P 4501) described in Examples described later. can. Details will be described in Examples described later, and the outline thereof will be shown below.

For example, the sulfonated pulp is formed into a sheet having a basis weight of 45 g / m ² or more and less than 100 g / m ² and a thickness of 0.05 mm to 3.0 mm, and is easily loosened (that is, hydrolyzed) in accordance with JIS P 4501. Sex) is measured.
Alternatively, the sulfonated pulp is formed into a sheet having a basis weight of 100 g / m ² or more and less than 1000 g / m ² and a thickness of 0.05 mm to 3.0 mm, and is easily loosened (that is, hydrolyzed) in accordance with JIS P 4501. Sex) is measured.

In the latter method, it is desirable to measure by the following procedures (i) and (ii).
First, (i) a rotor is placed in a 1 L glass beaker containing 1 L of pure water, and the rotation speed of the rotor is adjusted to 600 rpm. Then, (ii) measure the time from the loading of the test piece until the rotation speed of the rotor recovers to 450 rpm.

As described above, since the redispersible pulp of the present embodiment contains the sulfonated pulp having water solubility as described above, it has excellent dispersibility (hydrolysis) even in a state where the water content is low. You will be able to demonstrate it.
Further, the redispersible pulp of the present embodiment is a completely new pulp that cannot be assumed by the common general technical knowledge in the papermaking field at the time of filing. Specifically, according to the common technical knowledge in the papermaking field at the time of filing, it is said that if the pulp slurry prepared in the papermaking process is dehydrated or dried to reduce the water content, the pulp is inferior in redispersibility. It is a common recognition among those skilled in the art that it is difficult to easily redisperse such dehydrated or dried pulp even if it is put into water. However, the redispersible pulp of the present embodiment is a pulp capable of exhibiting excellent redispersibility (water-decomposability) even if the water content is lowered as in the case of conventional dry pulp and the like as described above. , Can be used as a very good pulp in the papermaking process.

(Sulfone pulp filtrate)
The sulfonated pulp contained in the redispersible pulp of the present embodiment preferably has a predetermined freeness from the viewpoint of handleability.
For example, the sulfonated pulp has a freeness of 60 mL or more, preferably 100 mL or more, more preferably 300 mL or more, and further preferably 500 mL or more. On the other hand, if the freeness exceeds 800 mL, the handleability when made into a sheet or the like is deteriorated. Therefore, from the viewpoint of handleability, it is preferable to use the sulfonated pulp adjusted so that the lower limit value is 60 mL or more and the upper limit value is 800 mL or less.

Further, the sulfonated pulp does not particularly limit the length of the fiber. For example, in order to improve the handleability, the average fiber length of the sulfonated pulp is preferably 2.0 mm or more. The upper limit is not particularly limited, but from the viewpoint of dispersibility, it is preferably 20 mm or less, more preferably 15 mm or less, still more preferably 10 mm or less, still more preferably 5 mm or less.
The average fiber length can be measured by a method using a fiber tester described in Examples described later.

(Content ratio of sulfonated pulp in redispersible pulp of this embodiment)
The redispersible pulp of the present embodiment may be mixed with other pulp (for example, pulp for papermaking). The pulp for papermaking refers to mechanical pulp processed by a grinder, used paper pulp, chemical pulp, chemically modified pulp into which functional groups other than sulfonated are actively introduced, and the like.

The blending ratio (content ratio) of the sulfonated pulp contained in the redispersible pulp of the present embodiment is not particularly limited.
For example, the content ratio of the sulfonated pulp contained in the redispersible pulp of the present embodiment may be 1% by mass or more, preferably 3% by mass or more, and more preferably 10% by mass or more in terms of solid content mass%. , More preferably 30% by mass or more, still more preferably 50% by mass or more, still more preferably 70% by mass or more.
When the content ratio of the sulfonated pulp is 90% by mass or more in terms of solid content, the dispersibility (water-decomposability) of the redispersible pulp of the present embodiment is about the same as the physical property value of the sulfonated pulp that is easy to loosen. Indicates a value. On the other hand, from the viewpoint of tensile strength, it is preferable that the content ratio of the sulfonated pulp is small.
When the content ratio of the sulfonated pulp is 100% by mass in terms of solid content (that is, when the redispersible pulp of the present embodiment is made of the sulfonated pulp), it is naturally the physical property value of the sulfonated pulp. The redispersible pulp of this embodiment becomes the same.

The solid content mass% was calculated by the following formula. The details of the "solid content mass (g)" in the formula will be described later.

Solid mass% = (solid mass (g) / total mass at the time of measurement (g)) × 100

(Regarding the redispersible pulp composition of this embodiment)
Next, the redispersible pulp composition of the present embodiment will be described.
The redispersible pulp composition of the present embodiment is a solid composition containing the redispersible pulp of the present embodiment as described above.
Specifically, the redispersible pulp composition of the present embodiment is in the form of a solid having a water content of less than 100%, and is, for example, fibrous, cottony, lumpy, blocky, granular, powdery. It is a solid composition such as a sheet, a wax, a sponge, a gel, a paste, and a cream.

Here, the gel state means a general elastic semi-solid state, and means a state in which a dispersion medium such as water containing a solid component loses fluidity and becomes a solid state, or becomes a liquid. It is in a non-fluid state by adding a solid component.

Further, for example, when it is formed into a sheet shape, it ^{can be adjusted so that the basis weight (g / m 2} ) is 40 g / m ² or more and 1500 g / m ² and the thickness is 0.05 mm (50 μm) or more and 5 mm or less. Can be prepared to be. The density (g / cm ³ ) in the sheet can be calculated by dividing the basis weight (g / m ² ) by (thickness (mm) × 1000). When the thickness is in units of μm, the density (g / cm ³ ) in each sheet can be calculated by dividing the basis weight (g / m ² ) by the thickness (μm).

(Moisture content of redispersible pulp composition)
The redispersible pulp composition of the present embodiment is solid as described above, and is not particularly limited as long as the water content is lower than 100%.
For example, the redispersible pulp composition of the present embodiment has a moisture content in a solid state of less than 100%, preferably 97% or less, more preferably 95% or less, still more preferably 90%. It is less than or equal to, and more preferably 80% or less.
The lower limit of the water content of the redispersible pulp composition of the present embodiment is not particularly limited unless it is in an absolutely dry state. For example, the redispersible pulp composition of the present embodiment may be prepared to have a moisture content of 10% or less using a dryer or the like, or may be adjusted to about 2 to 3%, and has a moisture content of about 2 to 3%. It may be 1%.
Therefore, the redispersible pulp composition of the present embodiment has a water content of more than 0% and 97% or less in the solid state. It is preferably 0.5% to 95%, more preferably 0.5% to 90%, still more preferably 0.5% to 85%, and even more preferably 0.5% to 80%. , More preferably 0.5% to 70%, still more preferably 0.5% to 60%.
For example, the water content of the redispersible pulp composition of the present embodiment in the form of gel, paste or cream is 50% by mass to 97% by mass. Further, for example, the water content of the redispersible pulp composition of the present embodiment, which is fibrous, cotton-like, lump-like, block-like, granular, powder-like, sheet-like, wax-like, or sponge-like, is 0.5% by mass or more. It is 60% by mass.

If the water content of the redispersible pulp composition of the present embodiment is low, the redisperable pulp composition has transportability, storability, uniformity of solid content concentration (quality stability), antifungal property, putrefaction resistance, and suppression of fiber decomposition ( The advantage of being able to improve (inhibition of hydrolysis) and the like can be obtained. On the other hand, if the water content is high, there are advantages that the dispersibility in the liquid can be improved, the dispersion time in the liquid can be shortened (workability), and the like.
For example, the redispersible pulp composition of the present embodiment has a water content of 0.5% by mass in a fibrous, cottony, lumpy, blocky, sheety, granular, powdery, sponge-like or waxy state. As described above, when it is 60% by mass or less, the handleability can be improved while exhibiting excellent dispersibility.

The term "absolutely dry state" as used herein means a state in which the moisture content is approximately 0.4% or less. Examples of the method for making this absolute dry include a method of depressurizing and drying with a desiccator containing a desiccant such as calcium chloride or diphosphorus pentoxide. In other words, it is possible to obtain the redispersible pulp composition of the present embodiment having a low water content by drying by a method that does not use such a drying method for making an absolute dry state.

The water content in the present specification means the ratio of water content to the entire measurement sample, and is calculated using the following formula. The detailed measurement method is described in Examples.

Moisture content (%) = 100- (sample solid content mass (g) / sample (g) at the time of water content measurement) × 100 = {(sample (g) at the time of water content measurement-solid content mass (g) at the sample )) / Sample at the time of water content measurement (g)} × 100

The solid content mass (g) in the sample in the above formula means the dry weight of the sample.
Specifically, it refers to a dry weight adjusted to be constant by drying a sample at 105 ° C. using a dryer or the like. Details are shown in the description of the examples.
For example, the redispersible pulp composition is placed in a dryer, dried under predetermined drying conditions (for example, temperature 105 ° C., 2 hours) and measured to dry after water is removed from the redispersible pulp. It is possible to calculate the weight of the product.
Further, the constant amount means a state in which the moisture in the atmosphere and the moisture in the raw material in the treatment facility apparently do not enter and exit. Specifically, it means that after drying for a certain period of time (for example, 2 hours), the amount of change in the weight measured twice in succession is within 1% of the weight at the start of drying (however). Second, the second weight measurement shall be at least half of the drying time required for the first time).

(Dispersibility of redispersible pulp composition (hydrolyzability))
The excellent dispersibility of the redispersible pulp composition of the present embodiment means that, like the sulfonated pulp contained in the redispersible pulp of the present embodiment described above, a dispersion medium having a low water content is used. It means that the dispersibility with respect to the dispersion medium is good when it is put into. That is, the redispersible pulp composition of the present embodiment has a predetermined ease of loosening (that is, dispersibility (hydrolyzability)).
Specifically, similarly to the dispersibility (hydrolyzability) of the sulfonated pulp described above, first, a sheet is prepared by the method described in Examples described later (method according to JIS P 8222). Then, the ease of loosening (that is, dispersibility) of this sheet can be evaluated by using the hydrolyzability test method (test method based on the measurement method based on JIS P 4501) described in Examples described later.

For example, the dispersibility of the redispersible pulp composition is determined to have excellent dispersibility (that is, water decomposability) if the hydrolyzability of the sheet prepared by the looseness measurement in the above measurement method is 100 seconds or less. be able to. More specifically, the dispersibility of the redispersible pulp composition of the present embodiment may be as long as the water-decomposability value of the sheet is 100 seconds or less, preferably 90 seconds or less, and more preferably 80 seconds. It is more preferably 70 seconds or less, still more preferably 50 seconds or less, still more preferably 30 seconds or less, still more preferably 20 seconds or less, still more preferably 10 seconds or less.

The ease of loosening here is the same as that of the above-mentioned sulfonated pulp.

As described above, by containing the redispersible pulp of the present embodiment having the above-mentioned dispersibility, the redispersible pulp composition of the present embodiment is excellent even in a solid state having a low water content. It will be possible to exert a good dispersibility (water-decomposability).

Therefore, if the redispersible pulp composition of the present embodiment is mixed with water in a dried or dehydrated state in the same manner as the conventional dry pulp or wet pulp in the papermaking process, it will be compared with the conventional dry pulp or the like. Can be easily dispersed.
Moreover, it is possible to suppress the generation of lumpy lumps as compared with the case where conventional dry pulp or the like is mechanically dispersed. That is, since the energy required for redispersing the conventional dry pulp or the like can be reduced, the amount of carbon dioxide emitted in such a step can be suppressed. Moreover, the use of additives and the like for improving dispersibility can be suppressed. Further, as the obtained pulp slurry, it is possible to prepare a pulp slurry having a higher quality than that obtained by redispersing conventional dry pulp or the like.
Therefore, if the redispersible pulp composition of the present embodiment is used in the papermaking process in the papermaking process, it is possible to produce papermaking that is economically and excellent in quality.

Further, as described above, the redispersible pulp composition of the present embodiment contains the redispersible pulp of the present embodiment, which is a completely new pulp that cannot be assumed by the common general technical knowledge in the papermaking field at the time of filing. be.
Therefore, as described above, the redispersible pulp composition of the present embodiment can exhibit excellent redispersibility (water-decomposability) even if the water content is lowered as in the case of conventional dry pulp and the like. It is a composition and can be used as a very excellent pulp composition in the papermaking process.

(Freeness of redispersible pulp composition)
The redispersible pulp composition of the present embodiment preferably has a predetermined freeness from the viewpoint of handleability.
For example, the redispersible pulp composition of the present embodiment has a freeness of 60 mL or more, preferably 100 mL or more, more preferably 300 mL or more, and further preferably 500 mL or more. If the degree of water permeability is lowered, the entanglement of the fibers can be improved, so that the strength of the aggregate such as a sheet can be improved. Further, if the water solubility is lowered, the glossiness of the surface can be improved. On the contrary, the productivity can be improved by increasing the free water content. On the other hand, when the freeness exceeds 800 mL, the handleability when made into a sheet or the like tends to deteriorate.
Therefore, from the viewpoint of handleability, it is preferable to use the redispersible pulp of this embodiment adjusted so that the lower limit value is 60 mL or more and the upper limit value is 800 mL or less.
The freeness of the present specification is calculated by using the measuring method described in Examples (measurement method according to JIS 811-2 (2012)) in the same manner as the above-mentioned sulfonated pulp.

The length of the pulp fibers contained in the redispersible pulp composition of the present embodiment is not particularly limited.
For example, in order to improve the handleability, the average fiber length of the pulp in the redispersible pulp composition of the present embodiment is preferably 0.2 mm or more. The lower limit is preferably 0.5 mm or more, more preferably 1.0 mm or more, still more preferably 1.5 mm or more, still more preferably, from the viewpoint of improving the strength of the composition due to the entanglement of the fibers. Is 2.0 mm or more. The upper limit is not particularly limited, but from the viewpoint of dispersibility, it is preferably 20 mm or less, more preferably 15 mm or less, still more preferably 10 mm or less, still more preferably 5 mm or less.
The average fiber length can be measured by a method using a fiber tester described in Examples described later or by observation with an optical microscope.

(Content ratio of sulfonated pulp in the redispersible pulp composition of the present embodiment)
In the redispersible pulp composition of the present embodiment, the content ratio of the above-mentioned sulfonated pulp is preferably 3% by mass or more in terms of solid content mass%. That is, if the redispersible pulp composition of the present embodiment is in a solid state and is adjusted so that the content of the sulfonated pulp described above is equal to or higher than the above value while containing water, the above-mentioned shape can be obtained. It is possible to appropriately exert excellent dispersibility while maintaining it. The formula for calculating "solid content mass%" is the same as the above-mentioned formula.

The content ratio of the above-mentioned sulfonated pulp in the redispersible pulp composition of the present embodiment is not particularly limited as long as it is 3% by mass or more in terms of solid content mass. For example, the content ratio of the sulfonated pulp is 3% by mass or more in terms of solid content mass%, preferably 5% by mass or more, and more preferably 10% by mass.

When the content ratio of the sulfonated pulp is 100% by mass in terms of solid content mass% (that is, when the redispersible pulp composition of the present embodiment is made of the sulfonated pulp), it is formed by the sulfonated pulp. The resulting sheet corresponds to the sheet of the redispersible pulp composition of the present embodiment.

The redispersible pulp composition of the present embodiment may consist only of sulfonated pulp as described above, or may be mixed with other pulp (for example, the above-mentioned papermaking pulp). good.
The content ratio of other pulp such as papermaking pulp contained in the redispersible pulp composition of the present embodiment is not particularly limited.
For example, the content ratio of other pulp in the redispersible pulp composition of the present embodiment is adjusted to be 1 part by mass or more and 900 parts by mass or less with respect to 100 parts by mass of the solid content of the sulfonated pulp. can do.
The lower limit of the content ratio of the other pulp is not particularly limited as long as it is 1 part by mass or more with respect to 100 parts by mass of the solid content of the sulfonated pulp. For example, it is 10 parts by mass or more, preferably 40 parts by mass or more, more preferably 100 parts by mass or more, still more preferably 200 parts by mass or more, still more preferably 500 parts by mass or more.

The redispersible pulp composition of the present embodiment may be adjusted to contain the sulfonated pulp having predetermined physical properties according to the state of the water content of the redispersible pulp composition.

For example, when the water content of the redispersible pulp composition of the present embodiment is about several tens to 80%, the sulfonated pulp contained thereof is preferably one having the following characteristics. In this case, even the redispersible pulp composition of the present embodiment, which has been dehydrated and molded by a press or the like, can appropriately exhibit excellent dispersibility.
The sulfonated pulp contained in the redispersible pulp composition of the present embodiment having the moisture content is the moisture content in a sheet prepared by the method described in Examples described later (method according to JIS P 8222). Is within a predetermined range, and the hydrolyzability of the sheet is within the above-mentioned range.
The moisture content in the sheet refers to the moisture content of the sheet in measuring the easiness of loosening of the sulfonated pulp. For example, the moisture content of the sheet is preferably 30% or more and 70% or less, and more preferably 40% or more and 60% or less.

The redisperable pulp composition of the present embodiment has a water content of about several tens of percent to 80%, for example, a filter press device, a belt press machine, a screw press device, a simple press machine, a disc filter, or a disc. Examples thereof include those in a state of being dehydrated and molded by a disk-type dehydration / concentrator such as a thickener, a drum-type dehydration / concentrator such as a drum screen, or the like.

Further, for example, the redispersible pulp composition of the present embodiment has a moisture content close to a dry state (a moisture content higher than 0% to several tens of percent, that is, a dry state excluding those in an absolutely dry state). ), The sulfonated pulp contained is preferably one having the following characteristics. In this case, even the redispersible pulp composition of the present embodiment, which has been dried by a dryer or the like, can appropriately exhibit excellent dispersibility.
The sulfonated pulp contained in the redispersible pulp composition of the present embodiment having the moisture content is the moisture content in a sheet prepared by the method described in Examples described later (method according to JIS P 8222). Is within a predetermined range, and the hydrolyzability of the sheet is within the above-mentioned range.
The moisture content in the sheet refers to the moisture content of the sheet in measuring the easiness of loosening of the sulfonated pulp, for example, it is preferably 20% or less, more preferably 15% or less, still more preferably 10%. It is less than or equal to, and even more preferably 5% or less.

(Manufacturing method of sulfonated pulp)
The method for producing the sulfonated pulp contained in the redispersible pulp of the present embodiment can be produced by the following production method (sulfonated pulp production method), but is not limited to such a production method.

As shown in FIG. 1, the outline of this sulfonated pulp manufacturing method is that the sulfonated pulp contained in the redispersible pulp of the present embodiment by subjecting a fiber raw material containing cellulose (for example, wood pulp) to a chemical treatment step (for example, wood pulp). Hereinafter, it is a method for producing (simply referred to as sulfonated pulp).

As shown in FIG. 1, in this chemical treatment step, the supplied fiber raw material is brought into contact with the reaction solution (contact step S1) and then subjected to a heating reaction (reaction step S2) to sulfonate the hydroxyl group of cellulose. The method.
In the present specification, the fiber raw material refers to fibrous pulp or the like containing cellulose molecules. Pulp is a fibrous member in which a plurality of cellulose fibers are aggregated. This cellulose fiber is a collection of a plurality of fine fibers (for example, microfibrils and the like). The fine fibers are a collection of a plurality of cellulose molecules (hereinafter, may be simply referred to as cellulose) which are chain polymers in which D-glucose is β (1 → 4) glycosidic bonded.

The fiber raw material used is preferably washed in advance. For example, it is desirable to filter and dehydrate using water on a sieve of 200 mesh or 235 mesh because fine fibers and dust can be eliminated and the handleability at the time of manufacturing is improved. In other words, pulp is an aggregate of cellulose fibers having a size that can be a residue of 200 mesh or 235 mesh. The details of the fiber raw material will be described later.

As described above, the chemical treatment step includes a contact step S1 in which sulfamic acid, which is a sulfating agent having a sulfo group, and urea are brought into contact with cellulose fibers of a fiber raw material containing cellulose such as pulp, and a contact step S1 after the contact step S1. It includes a reaction step S2 in which a sulfo group is substituted and introduced into at least a part of the hydroxyl group of the cellulose fiber contained in the pulp. Hereinafter, each step will be described in order.

(Contact step S1)
The contact step S1 is a step of bringing sulfamic acid and urea into contact with a fiber raw material containing cellulose. The contact step S1 is not particularly limited as long as it is a method capable of causing the contact.
For example, the fiber raw material (for example, wood pulp) may be immersed in a reaction solution in which sulfamic acid and urea are dissolved in a solvent to impregnate the fiber raw material with the reaction solution, or the reaction solution may be applied to the fiber raw material. It may be applied, or the fiber raw material may be individually coated with sulfamic acid and urea, impregnated, or spray-sprayed. For example, if a method of immersing the fiber raw material in the reaction solution and impregnating the fiber raw material with the reaction solution is adopted, there is an advantage that sulfamic acid and urea can be uniformly brought into contact with the fiber raw material.

The solvent that dissolves sulfamic acid and urea is not particularly limited. For example, in the case of only water (including pure water such as ion-exchanged water and distilled water, as well as tap water, etc.), protons such as ethanol, methanol, acetic acid, polar acid, 2-propanol, nitromethane, and ammonia water. Polar protic solvents, aprotic polar solvents such as acetone, ethyl acetate, tetrahydrofuran (THF), dimethylformamide (DMF), acetonitrile, dimethylsulfoxide (DMSO), dimethylsulfide (DMS), dimethylacetamide (DMA), etc. Non-polar solvents such as diethyl ether, benzene, toluene, hexane, chloroform, 1,4-dioxane and the like can be mentioned, and these may be used alone or a mixture of two or more thereof may be used. May be. In particular, water is preferable from the viewpoint of easily dissolving sulfamic acid and urea.

(Mixing ratio of reaction solution)
When a method of immersing the fiber raw material in the reaction solution and impregnating the fiber raw material with the reaction solution is adopted, the mixing ratio of sulfamic acid and urea contained in the reaction solution is not particularly limited. For example, the mixing ratio described in Examples described later can be used.
For example, the sulfonate and urea or / and its derivatives are in a concentration ratio (g / L) of 4: 1 (1: 0.25), 2: 1 (1: 0.5), 1: 1, 2 It can be adjusted to be: 3 (1: 1.5) and 1: 2.5.

(Contact amount of reaction solution)
The amount of the reaction solution to be brought into contact with the fiber raw material is such that sulfamic acid and urea in the reaction solution are brought into contact with the fiber raw material in a predetermined ratio.
For example, in a state where the reaction solution is in contact with the fiber raw material, the sulfonate contained in the reaction solution is 1 part by weight to 20,000 parts by weight with respect to 100 parts by weight of the dry weight of the fiber raw material, and the reaction solution. The urea or / and its derivative contained in the above can be prepared to be 1 part by weight to 100,000 parts by weight with respect to 100 parts by weight of the dry weight of the fiber raw material.

(Reaction step S2)
The fiber raw material impregnated with the reaction solution prepared in the contact step S1 as described above is supplied to the reaction step S2 in the next step.
In this reaction step S2, the cellulose fiber contained in the fiber raw material supplied from the contact step S1 is reacted with sulfamic acid and urea to replace the sulfo group of sulfamic acid with the cellulose hydroxyl group in the cellulose fiber. This is a step of introducing a sulfo group into the cellulose fiber contained in the fiber raw material. That is, this reaction step S2 is a step of performing a sulfonation reaction in which a sulfo group is substituted for the cellulose hydroxyl group in the cellulose fiber contained in the fiber raw material impregnated with the reaction solution.

The reaction step S2 is not particularly limited as long as it is a method capable of a sulfonation reaction in which the hydroxyl group of the cellulose fiber in the fiber raw material is substituted with a sulfo group. For example, a method of accelerating the sulfonate reaction by heating the fiber raw material can be adopted. Hereinafter, a case where the sulfonation reaction is carried out by this heating method will be described as a representative.

(Reaction temperature in reaction step S2)
The reaction temperature in the reaction step S2 is not particularly limited as long as it is a temperature at which a sulfo group can be introduced into the cellulose fibers constituting the fiber raw material while suppressing the thermal decomposition and hydrolysis reaction of the fibers.
For example, the atmospheric temperature of the fiber raw material supplied to the reaction step S2 is adjusted to be 100 ° C. or higher and 200 ° C. or lower. The atmospheric temperature is preferably 120 ° C. or higher and 200 ° C. or lower. When the atmospheric temperature at the time of heating becomes higher than 200 ° C., thermal decomposition of the fiber occurs and the progress of discoloration of the fiber becomes faster. On the other hand, when the reaction temperature is lower than 100 ° C., the transparency of the obtained sulfonated pulp tends to decrease.
Therefore, from the viewpoint of the transparency of the obtained sulfonated pulp, the reaction temperature (specifically, the atmospheric temperature) in the reaction step S2 is 100 ° C. or higher and 200 ° C. or lower, preferably 120 ° C. or higher and 180 ° C. or lower. More preferably, it is 120 ° C. or higher and 160 ° C. or lower.

The heater or the like used in the reaction step S2 is not particularly limited as long as it can directly or indirectly heat the fiber raw material after the contact step S1 while satisfying the above requirements.
For example, a hot press method using a known dryer, a vacuum dryer, a microwave heating device, an autoclave, an infrared heating device, a heat press machine (for example, AH-2003C manufactured by AS ONE Co., Ltd.) is adopted. Can be done. In particular, from the viewpoint of operability, it is preferable to use a circulation blower type dryer because gas may be generated in the reaction step S2.

(Reaction time in reaction step 2)
The heating time (that is, the reaction time) when the above heating method is adopted as the reaction step is not particularly limited as long as the sulfo group can be appropriately introduced into the cellulose fiber as described above. For example, the reaction time in the reaction step S2 is adjusted to be 1 minute or more when the reaction temperature is adjusted to be within the above range. It is preferably 5 minutes or longer, more preferably 10 minutes or longer, and even more preferably 15 minutes or longer.
When the reaction time is shorter than 1 minute, it is presumed that the substitution reaction of the sulfo group with respect to the hydroxyl group of the cellulose fiber has hardly proceeded. On the other hand, even if the heating time is too long, it tends not to be expected to improve the amount of sulfo group introduced.
Therefore, the reaction time when the above heating method is adopted as the reaction step S2 is not particularly limited, but is preferably 5 minutes or more and 300 minutes or less, more preferably 5 minutes or more and 120 minutes or less, from the viewpoint of reaction time and operability. It is better to say.

(Fiber raw material)
The fiber raw material used in the sulfonated pulp production method is not particularly limited as long as it contains cellulose as described above. For example, what is generally called pulp may be used, or a material containing cellulose isolated from sea squirts, seaweed, etc. can be used as a fiber raw material, but if it is composed of cellulose molecules, it can be used. , Can be anything.
Examples of the above-mentioned pulp include wood-based pulp (hereinafter simply referred to as wood pulp), melted pulp, cotton-based pulp such as cotton linter, straw, bagus, 楮, sansho, hemp, kenaf, and fruits. Examples include, but are not limited to, non-wood pulp, used newspaper pulp, used paper pulp produced from used magazine paper and used cardboard paper, and the like. From the viewpoint of easy availability, wood pulp is easy to use as a fiber raw material.

There are various types of this wood pulp, but the use is not particularly limited. For example, papermaking pulp such as softwood kraft pulp (NBKP), hardwood kraft pulp (LBKP), and thermomechanical pulp (TMP) can be mentioned. When the above-mentioned pulp is used as the fiber raw material, one of the above-mentioned types of pulp may be used alone, or two or more of them may be mixed and used.

(Washing step after reaction step S2)
After the reaction step S2 in the chemical treatment step, a washing step of washing the sulfonated pulp after introducing the sulfo group may be included.
The surface of the sulfonated pulp after introducing the sulfo group is acidic due to the influence of the sulfonate agent. In addition, an unreacted reaction solution is also present. Therefore, if a washing step is provided to ensure that the reaction is terminated and the excess reaction solution is removed to bring the reaction solution into a neutral state, the handleability can be improved.

This washing step is not particularly limited as long as the sulfonated pulp after the introduction of the sulfo group can be made substantially neutral.
For example, a method of washing with pure water or the like until the sulfonated pulp after introducing the sulfo group becomes neutral can be adopted. Further, neutralization washing using alkali or the like may be performed. When such neutralization cleaning is performed, examples of the alkaline compound contained in the alkaline solution include an inorganic alkaline compound and an organic alkaline compound. Examples of the inorganic alkali compound include hydroxides, carbonates and phosphates of alkali metals. Examples of the organic alkaline compound include ammonia, an aliphatic amine, an aromatic amine, an aliphatic ammonium, an aromatic ammonium, a heterocyclic compound, and a hydroxide of a heterocyclic compound.

Next, the present invention will be described in more detail by way of examples. However, the present invention is not limited by the following examples.
In the following examples, the redispersible pulp of the present invention and the redispersible pulp composition of the present invention are obtained by having the sulfonated pulp contained in the redispersible pulp of the present invention having predetermined characteristics (water-decomposable). It was confirmed that it had excellent dispersibility.

(Experiment 1)
In Experiment 1, the characteristics (hydrolytic property) of the sulfonated pulp possessed by the redispersible pulp of the present invention were confirmed.

Unbeaten softwood kraft pulp (NBKP) was used as the fiber raw material.
In the following, NBKP used in the experiment will be described simply as pulp.
Pulp is a large amount of ion-exchanged water (the range of electrical conductivity values measured by an ORGANO electric conductivity meter (model number RG-12) is 0.1 to 0.2 μS / cm, hereinafter referred to as pure water). After washing with, the water was drained with a stainless steel sieve having an opening of 75 μm (200 mesh), a part of the sample was taken, and the solid content concentration was measured by the method described later (solid content concentration 21.6% by mass).
When the pulp characteristics of the washed pulp were evaluated by the method described later, it was found to have a freeness of 720 mL and an average fiber length of 2.54 mm.

(Chemical treatment process)
The pulp was added to the reaction solution prepared as follows, and the reaction solution was impregnated into the pulp.
The step of impregnating the pulp with the reaction solution corresponds to the "contact step" in the present embodiment.

(Preparation of reaction solution)
Using sulfamic acid (purity 99.8%, manufactured by Fuso Chemical Industries, Ltd.) and urea solution (purity 99.0%, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., model number; special grade reagent), the mixing ratio of the two is the concentration ratio. At (g / L), 2: 1 (200 g / L: 100 g / L), 1: 1 (200 g / L: 200 g / L), 1: 1.5 (200 g / L: 300 g / L), 1: 2 (200 g / L: 400 g / L) and 2: 2.5 (200 g / L: 500 g / L) were mixed to prepare each reaction solution (for samples A to E).

(Contact process)
The prepared reaction solution was used to contact the pulp.
1000 g of each reaction solution was separated, and 20 g of this reaction solution and 20 g of pulp (solid content mass) were brought into contact with each other. As the contact method, an impregnation method was used.

The "solid content mass (g)" of the pulp means the dry weight of the pulp itself to be measured.
The weight of the dried pulp was measured by using a dryer (manufactured by Yamato Scientific Co., Ltd., model number; DKN602) at a temperature of 105 ° C. for 2 hours, and dried until the moisture content reached an equilibrium state. The method for evaluating the equilibrium state in the experiment is to dry the temperature of the constant temperature bath at a predetermined temperature (for example, 50 ° C. or 105 ° C.) for 1 hour in the above-mentioned dryer, and then measure the weight twice in succession. The state in which the amount of change was within 1% of the weight at the start of drying was considered to be in the equilibrium state (however, the second weight measurement was set to be more than half of the drying time required for the first time).
In the following description, where the model number of the dryer is not described, the same model as the above dryer was used.
The water content was measured by the following formula.

Moisture content (%) = 100- (Pulp solid content mass (g) / Pulp weight (g) when measuring moisture content) x 100

After contacting the reaction solution and the pulp for 10 minutes, the dispersion liquid in which the reaction solution and the pulp were mixed was suction-filtered using a filter paper (manufactured by Advantec, No. 2) and dehydrated (dehydration filtration). Filtration was continued until the solution stopped dripping. After suction filtration, the pulp was peeled off from the filter paper, and the pulp was placed in a dryer under an atmosphere of 50 ° C. and dried for 24 hours. Drying was carried out until the moisture content in the pulp reached an equilibrium state (at this time, the moisture content was 5% or less).

(Reaction process)
The pulp impregnated with the reaction solution prepared in the contact step was subjected to a heating reaction in the reaction step of the next step. In this heating reaction, the pulp is brought into contact with the reaction solution, and heat is applied to the fibers of the pulp while retaining or supporting sulfamic acid and urea in the reaction solution to promote the heating reaction and carry out the cellulose in the pulp. This is a step of introducing a sulfo group into a fiber.
The step of heating the pulp impregnated with this reaction solution to introduce a sulfo group corresponds to the "reaction step" in the present embodiment.

The reaction conditions for the heating reaction were as follows.
For heating, the temperature of the constant temperature bath of the dryer using the dryer: 120 ° C., heating time: 25 minutes

The heated pulp was washed until it became neutral to obtain sulfonated pulp (samples A to E) in which the cellulose fibers constituting the pulp were sulfonated.

The obtained sulfonated pulp corresponds to the sulfonated pulp contained in the redispersed pulp of the present embodiment.

The washing treatment of the heated pulp until it became neutral was carried out as follows.
First, a large amount of pure water was added to the reacted pulp to prepare a pulp slurry. Then, sodium hydrogen carbonate (purity 99.5%, manufactured by Nacalai Tesque) was added until no bubbles were formed to neutralize the mixture.
This neutralization treatment and the step of washing the neutralized pulp slurry described later with a large amount of pure water correspond to the "cleaning step in the chemical treatment step" of the present embodiment.

(Measurement of sulfo group introduction amount by electrical conductivity measurement)
The amount of sulfo groups introduced in the prepared sulfonated pulp was measured by measuring the electrical conductivity.

The prepared sulfonated pulp is a salt in which Na is bound by electrostatic interaction due to the influence of sodium hydrogen carbonate used for neutralization. In this state, the electrical conductivity cannot be measured, so it is necessary to remove the Na salt once to form an H-type with protons bonded. Therefore, first, the prepared sulfonated pulp was converted into H-type as follows, and then measured by titration with an aqueous sodium hydroxide solution.

First, a sulfonated pulp dispersion (pulp slurry for measurement) to be used for measurement was prepared.
A pulp slurry obtained by dispersing the sulfonated pulp obtained by the above method in pure water is poured onto a stainless steel sieve having an opening of 63 μm (235 mesh) and washed with a large amount of pure water (the end point of washing is the electricity of the filtrate). A pulp slurry for measurement was prepared so that the solid content concentration of the sulfonated pulp was 1.0% by mass (assuming that the conductivity was 100 μS / cm or less).

The solid content concentration was calculated by the following formula.

Solid content concentration (%) = (mass of solid content of pulp (g) / mass of pulp slurry (g)) × 100

50 g of pulp slurry for measurement (solid content mass 0.5 g) was placed in a beaker, and hydrochloric acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., model number; special grade reagent) was diluted with pure water in this beaker to adjust to 0.5 M. 250 mL was added. The shaking process was performed for 1 hour or more. Then, after pouring it on an opening of 46 μm (330 mesh), it was washed with a large amount of water to prepare H-type sulfonated pulp.
The prepared H-type sulfonated pulp was placed in a beaker so that the solid content mass was 0.2 g, and pure water was added to make the total amount 50 g. This beaker was set on an electric conductivity meter (a water quality meter (manufactured by DKK-TOA Corporation, model number; MM-43X) and an electric conductivity electrode (manufactured by DKK-TOA Corporation, model number; CT-58101B)) to introduce a functional group. The amount was measured.

For titration using alkali, 20 μL to 100 μL of 5 M sodium hydroxide solution (manufactured by Fuji Film Wako Junyaku Co., Ltd., product name; 5 mol / L sodium hydroxide solution) diluted with pure water to 1 M is added dropwise. The change in the value of the electric conductivity meter was measured, plotted on the vertical axis as the electric conductivity and the horizontal axis as the titration of sodium hydroxide droplets to obtain a curve, and the turning point was confirmed from the obtained curve. At the initial stage of dripping, the electric conductivity meter decreases, but at a certain point, it shows an inflection. Since the quantification of sodium hydroxide required to reach this turning point corresponds to the amount of sulfo groups, the amount of sodium hydroxide at this turning point can be divided by the mass of the pulp solid content of the sulfonated pulp used for measurement. , The amount of sulfo groups in the sulfonated pulp, that is, the amount of sulfo groups introduced was measured.

(Measurement of average fiber length of sulfonated pulp)
A pulp slurry for measurement (solid content mass 0.1 g) was placed in a glass beaker, and water was added to the beaker to prepare a diluted pulp slurry having a total volume of 300 mL. The average fiber length of the sulfonated pulp in the dilute pulp slurry was measured using a fiber tester (CODE912, manufactured by Lorenzen & Bettley) for this dilute pulp slurry. At that time, the count number (number of fibers) of the fibers detected by the fiber tester was 9000 to 20000.

(Measurement of freeness)
The freeness was measured by a measuring method according to JIS P 811-2 Canadian standard freezing method (2012). In the test, the pulp slurry for measurement in 1.0% by mass was diluted with pure water to 0.3% by mass, and 1000 mL (20 ° C.) was prepared. This prepared solution was used for measurement using a freeness tester (manufactured by Kumagai Riki Kogyo Co., Ltd., serial number; 02098077).

(Preparation of pulp sheet and test of ease of loosening (hydrolysis))
The dispersibility evaluation of redispersibility pulp, firstly, JIS P 8222 Pulp - process for the preparation of test handsheet papers - (2015) by handsheet sheet (basis weight of about ^{48g / m 2 ~63g / m 2} , moisture content of about 10 %, Thickness of about 80 μm to 0.2 mm). Test pieces having a size of 11.4 × 11.4 cm were prepared from this pulp sheet.

A specific method for producing a hand-drawn sheet will be described below.
The method for producing the hand-drawn sheet was as follows.
3.75 g of the pulp slurry for measurement was weighed in a 5 L plastic container by mass of solid content, and tap water was added until the solid content concentration reached 0.2 to 0.5% by mass and dispersed well. Using the hand paper machine described in JIS P 8222 Pulp-Preparation Method for Hand Paper for Testing- (2015), this diluted slurry was used to make a wire mesh with an opening of 0.154 mm (100 mesh, size; 25 cm x 25 cm). A hand-drawn sheet was prepared by a method conforming to JIS P 8222 except that it was used. That is, the sheet was prepared using a wire mesh of 100 mesh according to JIS P 8222.
The obtained sheet was subjected to humidity control in accordance with JIS P 8111, and then cut to a size of 11.4 cm on a side. After humidity control, the moisture content of the sheet was measured by the method described above, and the thickness of the sheet was measured according to JIS P 8118. For details, refer to Micron level pulp sheet thickness measurement described later.

Then, using this test piece, the hydrolyzability of the pulp sheet (that is, the dispersibility of the redispersible pulp) was evaluated according to JIS P 4501 toilet paper (1993).
A glass beaker (manufactured by Shibata Scientific Technology, product name; 300 mL of beaker (with standard scale)) containing 300 mL (20 ° C) of pure water is placed on a magnetic stirrer (manufactured by AS ONE, model number; HS-30DN), and a rotor (rotor). The rotation speed of the stirrer star-shaped crosshead PTFE coating (diameter 35 mm, height 12 mm) manufactured by AS ONE Co., Ltd. was adjusted to 600 rpm. I put a test piece in it and started measuring the time with a stopwatch.
After the sheet was put in, the rotation speed decreased, and as the test piece was loosened, the rotation speed increased, and when the speed recovered to 540 rpm, the stopwatch was stopped and the time was recorded in units of 1 second.

As Comparative Example 1, by subjecting the pulp to the beating treatment described below instead of the sulfonated pulp, the easiness of loosening (hydrolysis) was improved as in the experiment except that the beating pulp showing a low water content was used. It was measured.

(Comparative Example 1; Method for preparing beaten pulp)
After adjusting the solid content concentration of the pulp to 2.0% by mass, 200 g of the pulp was put into a mixer (manufactured by Panasonic Corporation, model number; MX-X701, container; attached mixer having a rated capacity of 1000 mL). The mixer rotation was set at "high speed" and mixed for 10 minutes.

The experimental results are shown in FIG.
As shown in FIG. 2, the sulfonated pulp contained in the redispersible pulp was compared with Comparative Example 1 even when the sheet prepared by the looseness measurement in the above measuring method had a low water content. We were able to demonstrate excellent dispersibility (water-decomposability).
In general, pulp (particularly pulp exhibiting low water content) produces stronger bonds as the physical entanglement between pulp fibers and the hydrogen bonds between celluloses increase and the water content decreases. As a result, it takes time to absorb water even if water is given again to improve the water content.
However, when the sample A having the same degree of freeness and having a sulfo group and the comparative example 1 having no sulfo group were compared as the absorbed pulp, the comparative example 1 did not show redispersibility. As a result of further investigation of the hydrolyzable effect of the sulfo group, it was found that the hydrolyzability can be imparted without affecting the water solubility.
In the past, in order to impart redispersibility to pulp, it was necessary to add a chemical called a dispersant to improve dispersibility. However, it was confirmed that if the redispersible pulp of the present invention is used, excellent dispersibility can be exhibited without using a dispersant or the like.
Therefore, from the results of Experiment 1, it was confirmed that when the redispersible pulp is formed only from the sulfonated pulp, it has excellent dispersibility (hydrolyzability). It was also confirmed that the redispersible pulp composition in the form of a sheet also had excellent dispersibility (hydrolyzability).
Therefore, in Experiment 2, the hydrolyzability when the basis weight, thickness and moisture content of the sheet were increased was confirmed.

(Experiment 2)
In Experiment 2, in the preparation of the sulfonated pulp, the mixing ratio of sulfamic acid and urea in the contact step was 2: 1 {(69 g / L: 35 g / L, sample 1), (139 g / L: 69 g / L, sample 2). ), (278 g / L: 139 g / L, sample 4)} and 2: 3 {(278 g / L: 400 g / L, sample 3). ..

(Preparation of reaction solution)
An example of preparation of the reaction solution (Sample 1) is shown.
Sulfamic acid (purity 99.8%, manufactured by Fuso Chemical Industries) and urea (purity 99.0%, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., model number; special grade reagent) were completely dissolved in 720 mL of pure water (with sulfamic acid). The mixing ratio of urea is 69 (g / L): 35 (g / L)).

(Preparation of sulfonated pulp for sample 1)
Pulp obtained by drying an NBKP sheet (moisture content 50%, basis weight 6000 g / m2, thickness 0.7 mm) manufactured by Marusumi Paper Co., Ltd. in a 105 ° C. dryer to a moisture content of about 1% using the entire amount of the above reaction solution. The sheet was uniformly impregnated with 400 g. The impregnated sheet was dried in a dryer at 105 ° C. for 3.5 hours. Then, the reaction was carried out in a dryer at 140 ° C. for 25 minutes. The obtained reaction product was neutralized with a large amount of sodium hydrogencarbonate (purity 99.5%, manufactured by Nakaraitesk Co., Ltd.) on a stainless steel sieve with an opening of 63 μm (235 mesh), and then a large amount of pure water was used. A sulfonated pulp (sulfonated pulp for sample 1) was obtained by washing with.

The end points of neutralization and washing were set until the filtrate became neutral and no bubbles were generated for neutralization, and when the electrical conductivity of the filtrate became 1.0 mS / m or less for washing.

The obtained sulfonated pulp was measured by the above-mentioned method and had a functional group introduction amount of 0.13 mmol / g (for the measurement of the functional group introduction amount of sample 1, a 5 M sodium hydroxide solution (Fuji Film Wako Pure Chemical Industries, Ltd.). (Product name; 5 mol / L sodium hydroxide solution) was diluted to 0.1 M with pure water by the same method), the freeness was 680 mL, and the average fiber length was Was 2.53 mm.

(Preparation of sulfonated pulp for sample 2)
The adjustment ratio of the reaction solution was 720 mL of pure water, 100 g of sulfamic acid, and 50 g of urea (the mixing ratio of sulfamic acid and urea was 139 (g / L): 69 (g / L)), and the prepared reaction solution was used for sample 1. The sulfonated pulp for sample 2 was prepared by performing the same operation as the preparation of the sulfonated pulp for sample 2. The physical characteristics of the prepared sulfonated pulp for sample 2 were evaluated in the same manner as for the sulfonated pulp for sample 1.

(Preparation of sulfonated pulp for sample 3)
The adjustment ratio of the reaction solution was 720 mL of pure water, 200 g of sulfamic acid, and 288 g of urea (the mixing ratio of sulfamic acid and urea was 278 (g / L): 400 (g / L)), and the total amount of the prepared reaction solution was used. The sulfonated pulp for sample 3 was prepared by performing the same operation as the preparation of the sulfonated pulp for sample 1. The physical characteristics of the prepared sulfonated pulp for sample 3 were evaluated in the same manner as for the sulfonated pulp for sample 1.

(Preparation of sulfonated pulp for sample 4)
The adjustment ratio of the reaction solution was 720 mL of pure water, 200 g of sulfamic acid, and 100 g of urea (the mixing ratio of sulfamic acid and urea was 278 (g / L): 139 (g / L)), and the prepared reaction solution was used for sample 1. The sulfonated pulp for sample 4 was prepared by performing the same operation as the preparation of the sulfonated pulp for sample 4. The physical characteristics of the prepared sulfonated pulp for sample 4 were evaluated in the same manner as for the sulfonated pulp for sample 1.

(Preparation of sheet used for loosening easiness measurement)
A pulp slurry was prepared from each of the obtained sulfonated pulps (sulfonated pulp for sample 1, sulfonated pulp for sample 2, sulfonated pulp for sample 3, and sulfonated pulp for sample 4), and JIS P was prepared. 8222 Pulp-Preparation method for hand-made test paper- (2015) Follow the procedure shown below to make a pulp sheet (pulp sheet for sample 1; ES4-1 to ES4-4, pulp sheet for sample 2; ES3-1 to ES3-4). , Pulp sheet for sample 3; ES1-1 to ES1-4, pulp sheet for sample 4; ES2-1 to ES2-4) were prepared.
When the hand-made paper was prepared, it was prepared by a method conforming to JIS P 8222 using a wire mesh having an opening of 0.154 mm (100 mesh, size; 25 cm × 25 cm) in the same manner as in the above-mentioned case except for the above.

Weigh 625 g (solid content mass 6.25 g) of pulp slurry for measurement prepared using each sulfonated pulp (for sample 1 to sample 4), and tap water until the solid content concentration reaches 0.2 to 0.5 mass%. Water was added and dispersed well. Using the hand paper machine described in JIS P 8222 Pulp-Preparation Method of Hand Paper for Testing- (2015), the wire mesh was set and a hand paper sheet was prepared by the method described in JIS. ..

(Preparation of pulp sheets ES1-1, ES2-1, ES3-1, ES4-1)
The prepared sheet is press-dehydrated, collected from a drying plate, and then placed in a dryer at 105 ° C. and dried for about 10 minutes to have a moisture content of 1%, a water-containing sheet basis weight of 100 g / m ² , and a thickness of about 0. A 5.5 mm pulp sheet was prepared.

(Preparation of pulp sheets ES1-2, ES2-2, ES3-2, ES4-2)
The produced sheet was subjected to press dehydration treatment and then recovered from a drying plate to ^{obtain a pulp sheet having a water content of 50%, a sheet basis weight of 200 g / m 2} when contained in water, and a thickness of about 0.5 mm.

(Preparation of pulp sheets ES1-3, ES2-3, ES3-3, ES4-3)
^{A pulp sheet having a water content of 50% and a water-containing sheet basis weight of 1000 g / m 2 was} prepared by the same method as the pulp sheet ES1-1 except that the amount of the pulp slurry was changed to 3125 g (solid content mass 31.3 g). After the pulp sheet was obtained, the pulp sheet was placed in a dryer at 105 ° C. and dried for about 30 minutes to obtain a pulp sheet having a water content of 1%, a water-containing sheet basis weight of 500 g / m ² , and a thickness of about 3 mm.

(Preparation of pulp sheets ES1-4, ES2-4, ES3-4, ES4-4)
By the same method as the pulp sheet ES1-3, a pulp sheet having a water content of 50%, a water-containing sheet basis weight of 1000 g / m ² , and a thickness of about 3 mm was produced.

(Measurement of pulp sheet thickness)
The thickness of the pulp sheet was measured using a digital micrometer (manufactured by Niigata Seiki Co., Ltd., model number; MCD130-25). The measured value indicates the position where the measurement surface of the micrometer is in contact with the pulp sheet and the pulp sheet is not crushed.
The same applies to the pulp sheet of the preliminary test described above, the pulp sheet prepared of the phosphoric acid esterified pulp having the phosphoric acid ester group introduced, and the pulp sheet made of the pulp having no functional group introduced, which is a comparative example described later. It was measured by the method of.

(Easy to loosen (hydrolyzable) test)
First, a test piece having a size of 11.4 × 11.4 cm was prepared from each of the prepared pulp sheets.
Using each of these test pieces, the hydrolyzability of the pulp sheet (that is, the dispersibility of the redispersible pulp) was evaluated with reference to JIS P 4501.

In addition, as a comparative example described later, a pulp sheet prepared with an introduction amount of a sulfo group of less than 0.1 mmol / g (Comparative Example 2) and a pulp sheet prepared with a phosphoric acid esterified pulp having a phosphoric acid ester group introduced (Comparative Example 2). Comparative Examples 3 and 4) and a pulp sheet prepared from pulp having no functional group introduced (Comparative Example 5) were also measured by the same method.

Further, if the sheet having a moisture content of 1% is left unattended after being taken out from the dryer, it absorbs moisture and the moisture content increases. Therefore, in this experiment, the hydrolyzability (that is, the hydrolyzability of the sulfonated pulp contained in the redispersible pulp) was evaluated by using the sheet immediately after taking out the dryer.

The operation method of the test for ease of loosening (hydrolysis) was as follows.
A 1L glass beaker containing 1L (20 ° C) of pure water (manufactured by Shibata Scientific Technology, product name; beaker (with standard scale) 1000 mL) is placed on a magnetic stirrer (manufactured by AS ONE, model number; HS-30DN) and a rotor. The rotation speed of (manufactured by AS ONE, product name; stirrer star-shaped crosshead PTFE coating, diameter 35 mm, height 12 mm) was adjusted to 600 rpm. A test piece cut to a side of 11.4 cm was put into it, and time measurement was started with a stopwatch.
After the sheet was put in, the rotation speed decreased, and as the test piece was loosened, the rotation speed increased. When the speed recovered to 450 rpm, the stopwatch was stopped and the time was recorded in units of 1 second. Further, when the stirring was continued for 10 minutes or more but the rotation speed did not return to 450 rpm, it was judged as "no hydrolyzability" (that is, no dispersibility). In other words, in the case of a sheet with a basis weight of 100 g / m ² or more and less than 1000 g / m ² and a thickness of 0.05 mm to 3.0 mm, the 300 mL glass beaker was changed to a 1 L glass beaker, and the amount of pure water was changed from 300 mL to 1 L. The easiness of unraveling was measured by a measuring method compliant with JIS P 4501 except that the time point for recovering the rotation speed of the rotor after the test piece was changed was changed from 540 rpm to 450 rpm.

(Evaluation test of the dispersed state of pulp)
At the end point of the water-decomposability test of the test piece, the dispersed state of the pulp sheet (water-decomposability of the sulfonated pulp contained in the redispersible pulp) was visually observed. The evaluation criteria are as follows.
◯: A completely dispersed state was observed.
Δ: Although it did not have a sheet shape, a lumpy one having a diameter of about several millimeters was observed.
×: It is observed that the rotation speed returns to 450 rpm, but about 20% maintains the sheet shape, or the rotation speed does not return to 450 rpm and more than 50% maintains the sheet shape. Was done.

(Comparative example)
As a comparative example, the conditions of the reaction solution and pulp having different functional groups introduced were prepared.
In Comparative Example 2, a sulfonated pulp having a sulfo group introduction amount of less than 0.1 mmol / g was prepared by the same method as in Sample 1 of Experiment 2, and the characteristics of the pulp and the pulp sheet (CS4-1) were the same as in Experiment 2. The characteristics of ~ CS4-4) were evaluated.
In Comparative Examples 3 and 4, a phosphoric acid esterified pulp into which a phosphoric acid group was introduced was prepared, and the characteristics of the pulp and the pulp sheet (CS1-1 to CS1-4, CS2-1 to CS2-4) were prepared in the same manner as in Experiment 2. )) The characteristics were evaluated.
In Comparative Example 5, the characteristics of the pulp and the characteristics of the pulp sheet (CS3-1 to CS3-4) were evaluated in the same manner as in Experiment 2 using a pulp having no functional group introduced (general pulp).

(Comparative Example 2; Sulfonized pulp in which the amount of sulfo group introduced is less than 0.1 mmol / g)
In Comparative Example 2, the prepared reaction solution was used with the adjustment ratio of the reaction solution being 720 mL of pure water, 20 g of sulfamic acid, and 10 g of urea (mixing ratio of sulfamic acid and urea was 28 g / L): 14 (g / L). By performing the same operation as the preparation of the sulfonated pulp for sample 1, a sulfonated pulp having an introduction amount of less than 0.1 mmol / g of sulfo groups was prepared, and the characteristics of the pulp and the pulp sheet were the same as in Experiment 2. The characteristics of (CS4-1 to CS4-4) were evaluated.

When the amount of sulfo group introduced was less than 0.1 mmol / g, it was possible to detect (qualitatively) the amount of sulfo group introduced, but it was within the error range in the electrical conductivity titration and was below the lower limit of quantification. means.
The qualitativeness of the sulfo group was confirmed by an infrared spectrophotometer (Fourier transform infrared spectrophotometer manufactured by JASCO Corporation, model number FT / IR-4200).
The measurement of the infrared spectrophotometer was performed under the following conditions.
Measurement sample: Measured using a sample from which water has been removed in an atmosphere of 40 ° C. Measurement conditions: ATR method, integration count 100 times, resolution 4 cm-1
Observed wavenumber derived from sulfo group: around 810 cm-1 (derived from SO)

(Comparative Examples 3 and 4; Phosphate Esterified Pulp)
First, in 720 mL of pure water, 144 g of ammonium dihydrogen phosphate (purity 99.0%, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd., model number; special grade reagent) and 72 g of urea (purity 99.0%, manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) The model number; special grade reagent) was completely dissolved (the mass ratio of ammonium dihydrogen phosphate to urea was 200 (g / L): 100 (g / L)).

Pulp obtained by drying an NBKP sheet (moisture content 50%, basis weight 6000 g / m2, thickness 0.7 mm) manufactured by Marusumi Paper Co., Ltd. in a 105 ° C. dryer to a moisture content of about 1% using the entire amount of the above reaction solution. The sheet was uniformly impregnated with 400 g. The impregnated sheet was dried in a dryer at 105 ° C. for 3.5 hours. Then, the reaction was carried out in a dryer at 140 ° C. for 25 minutes. The obtained reaction product was neutralized with a large amount of sodium hydrogen carbonate (purity 99.5%, manufactured by Nakaraitesk Co., Ltd.) on a stainless steel sieve with an opening of 63 μm (235 mesh), and then a large amount of pure water was used. Phosphate esterified pulp was obtained by washing with. The end points of neutralization and washing were set until the filtrate became neutral and no bubbles were generated for neutralization, and when the electrical conductivity of the filtrate became 1.0 mS / m or less for washing.

After washing, the phosphoric acid esterified pulp was adjusted to a solid content concentration of 1.0% by mass using pure water to prepare a pulp slurry for measurement. The obtained phosphoric acid esterified pulp (Comparative Example 1) was found to be 0.67 mmol / g when the amount of functional groups introduced was measured by the method described later.
The reaction solution was prepared with 720 mL of pure water, 144 g of ammonium dihydrogen phosphate, and 360 g of urea (mass ratio of ammonium dihydrogen phosphate to urea was 200 (g / L): 500 (g / L)). A phosphoric acid esterified pulp (Comparative Example 2) of 1.74 mmol / g was also prepared by performing the same operation as above using the reaction solution.
As described above, the phosphoric acid esterified pulp was evaluated for its physical properties and the pulp sheet was prepared and evaluated under the same conditions as the sulfonated pulp of Experiment 2.

(Comparative Example 5; General Pulp)
^{50 g of NBKP sheet (moisture content 50%, basis weight 6000 g / m 2} , thickness 7 mm) manufactured by Marusumi Paper Co., Ltd. in a standard pulp dissociator containing 3000 mL of pure water (manufactured by Kumagai Riki Kogyo Co., Ltd., serial number; 9107182). Put in and dissociated for 3 minutes. The dissociated pulp was placed on a stainless sieve having a mesh size of 63 μm (235 mesh) and washed with a large amount of pure water to obtain a pulp having no functional group introduced. The end point of washing was when the electrical conductivity of the filtrate was 1.0 mS / m or less.
After washing, the pulp having no functional group introduced was adjusted to a solid content concentration of 1.0% by mass using pure water to prepare a pulp slurry for measurement. As described above, the pulp into which no functional group was introduced was evaluated for its physical properties and the preparation and evaluation of a pulp sheet under the same conditions as the sulfonated pulp of Experiment 2.

(Experimental result)
The experimental results are shown in FIGS. 3 to 7.
(A) of FIGS. 4 to 7 is a graph showing the hydrolyzability of each sheet.
FIGS. 4 to 7B are graphs showing the relationship between the hydrolyzability of the sheet used in the measurement of looseness and the amount of functional group introduced.

From the experimental results, it is possible that the sulfonation contained in the redispersible pulp exhibits excellent hydrolyzability even when the sheet is thicker than in Experiment 1 and the water content is also reduced. It was confirmed that it could be done. That is, from the results of Experiment 2, it was confirmed that when the redispersible pulp is formed only from the sulfonated pulp, it has excellent dispersibility (hydrolyzability). Similarly, the redispersible pulp composition in the form of a sheet also has excellent dispersibility (hydrolyzability) even in a state where the thickness of the sheet is thicker than that in Experiment 1 and the water content is also reduced. ) Was confirmed.

In the experiment, in order to investigate the difference in sheet water solubility due to the introduction of a functional group into the pulp, a comparison was made between a sulfo group and a phosphate ester group capable of introducing the functional group into the pulp by a method similar to sulfonation. ..
As a result, it was shown that the sulfonated pulp sheet into which the sulfo group was introduced was superior in water solubility to the phosphate esterified pulp sheet into which the phosphate ester group was introduced under all the sheet preparation conditions. In addition, the sulfonated pulp sheet tended to improve its hydrolyzability as the amount of functional group introduced increased, while the phosphoric acid esterified pulp sheet tended to decrease in water solubility as the amount of functional group introduced increased. ..
This effect was considered from the characteristics of functional groups. Phosphoric acid esterification to pulp is usually carried out at 140 ° C. or higher. On the other hand, the phosphoric acid ester group (-PO3H2) is known as a functional group that exhibits dehydration condensation at high temperature, and a crosslinked structure (-PO2H-O-PO2H-) is formed by the dehydration condensation reaction.
Therefore, it is foreseen that most of the phosphoric acid ester groups introduced during the reaction are introduced non-crosslinked, but some form a crosslinked structure. On the other hand, the sulfo group did not form a crosslinked structure and was converted to the Na type by neutralization and washing, so that the water solubility was improved as the affinity for water was improved. From this, it was suggested that the sulfonated pulp is a pulp having excellent redispersibility.

The redispersible pulp and the redispersible pulp composition of the present invention showed dispersibility (hydrolyzability) even when formed into a thick sheet (thickness 3 mm) (FIGS. 6 and 7).
In the conventional technique, as a method of imparting water solubility to the sheet, an embossing method of making unevenness on the sheet surface can be mentioned. The embossing method can impart water solubility to the sheet surface portion. If it is a thin sheet, it can be expected that the water solubility will be improved because the inside of the sheet will be uneven.
However, in the thick sheet as carried out in the present invention, only embossing the CS3-3 and CS3-4 of Comparative Example 5 which did not show water solubility does not impart unevenness to the inside of the sheet, so that the water solubility is improved. It cannot be expected that it will be improved, and it will cause the embossing machine to become complicated.
From this, it is an unprecedented effect that hydrolyzability could be exhibited even with a high basis weight sheet only by introducing a sulfo group.

(Experiment 3)
In Experiment 3, the redispersible pulp composition and the redispersible pulp composition appropriately exhibited dispersibility by setting the mixing ratio (content ratio) of the sulfonated pulp within a predetermined range, and moreover, the pulp for papermaking. It was confirmed that the strength can be improved by adjusting the mixing ratio of.

(Making a mixed sheet)
The mixed sheet-making pulp includes the sulfonated pulp (Samples A to E) prepared in Experiment 1 and the broad-leaved bleached kraft pulp beaten with a refiner for papermaking (LBKP (manufactured by Marusumi Paper Co., Ltd., freeness 276 mL, hereinafter papermaking). A hand-made sheet (each sheet of Samples 5 to 9) was prepared by the same method as in Experiment 2 Experiment 1 using a slurry in which (described as pulp)) was mixed in a predetermined ratio.

The solid content mass% of the sulfonated pulp contained in the sheet was calculated by the following formula.

Mass% of solid content of sulfonated pulp contained in the sheet = (mass of solid content of sulfonated pulp (g)) / (mass of solid content of pulp used for sheet preparation (g)) × 100

For example, when the mass ratio of the sample (sulfonated pulp) to the pulp for papermaking is 5: 5, the content ratio of the sulfonated pulp of the sheet means 50% by mass. In other words, the content ratio of the papermaking pulp is 100 parts by mass with respect to 100 parts by mass of the solid content of the sulfonated pulp.

As a comparative example, a pulp sheet (Comparative Example 6) using pulp for papermaking was produced in the same manner. That is, a pulp sheet having a sulfonated pulp content of 0% was prepared.

First, weigh a total of 3.75 g (solid content mass) of the pulp slurry for measurement and pulp for papermaking in a 5 L plastic container, add tap water until the solid content concentration reaches 0.2 to 0.5 mass%, and disperse well. I let you. Using the hand paper machine described in JIS P 8222 Pulp-Preparation Method for Test Hand Paper- (2015), this diluted slurry was used in the same manner as described above, with an opening of 0.154 mm (100 mesh, size; A mixed sheet was prepared by a method conforming to JIS P 8222 except that a wire mesh of 25 cm × 25 cm) was used.

An example of a slurry preparation example (pulp sheet of sample 5) is shown below.
Sample A (solid content mass 2.63 g) and papermaking pulp (solid content mass 1.12 g) are mixed to prepare a total of 3.75 g, and a slurry for making a sheet having a sulfonated pulp content of 70%. (Sample A: pulp for papermaking = 7: 3 (mass ratio)).
Water was added to the prepared mixed pulp to prepare a slurry having a solid content concentration in the range of 0.2 to 0.5% by mass.

The obtained sheet was humidity-controlled according to JIS P 8111 to have a moisture content of 7 to 15%, and then the sheet cut to a size of 11.4 cm on a side was subjected to a hydrolyzability test by the same method as in the above experiment. gone.
In addition, those cut to a size of 1.5 x 23 cm conformed to JIS P 8113 except that the distance between the gripping tools was set to 10 cm using an autograph (manufactured by Shimadzu Corporation, model number; AG-I500N). It was measured by the method.

(Measurement of tear length of pulp sheet)
Even when pulps with the same tensile strength are used, the results differ depending on the basis weight at the time of sheet preparation and cannot be compared uniformly. Therefore, the product of the obtained tensile strength (kN / m) and the coefficient (gravitational acceleration). Was divided by the basis weight (g / m ² ) to calculate the tear length (km). Specifically, the tear length was calculated using the following formula.

Fracture length (km) = tensile strength (kN / m) x 9.8067 / basis weight (g / m ² )

(Measurement of pulp sheet thickness)
The sheet thickness measurement at the micron level (μm level) was performed as follows.
Measured in accordance with JIS P 8118 using a paper thickness measuring instrument (paper pressure measuring instrument composed of a measuring instrument (manufactured by CITIZEN, model number; MEI-11) and an indicator (manufactured by CITIZEN, model number; SA-CD1)). did.

(Measurement of water resistance of pulp sheet)
The water resistance of the pulp sheet is measured by the following method with reference to the water drop method (Choichi Nakamura, "Paper Size" P.389 "6.1 / 8 Water Floating Method" Kitao Book Trading (1962)). did.
A glass preparation, which is generally used for microscopic observation, was used as a test table, and a pulp sheet cut into 45 mm × 85 mm was fixed on it with cellophane tape at both ends so as not to cause wrinkles. Place the slide on which the pulp sheet is fixed on a horizontal table, and use a syringe (JIS T 3101 (injection needle) H5 compliant) to drop 1 drop of pure water (20 ° C) from a position 10 mm above the pulp sheet. (Approximately 8 mg) was added dropwise. The time was started from the time when the dropped pure water came into contact with the pulp sheet using a stopwatch, and the time (seconds) until the pure water dropped on the pulp sheet surface was completely absorbed into the pulp sheet was measured.

The experimental results are shown in FIG.
As shown in FIG. 8, it was confirmed that the redispersible pulp exhibited excellent dispersibility (hydrolyzability) even when the sulfonated pulp and the papermaking pulp were mixed in a predetermined ratio. Moreover, it was confirmed that the strength can be improved by increasing the ratio of the pulp for papermaking. That is, from the results of Experiment 3, the redispersible pulp composition formed into a sheet containing the redispersible pulp has excellent dispersibility even when the sulfonated pulp and the papermaking pulp are mixed in a predetermined ratio. It was confirmed that it exhibits water solubility).

In the conventional technique, as a method of imparting water solubility to the sheet, a method of adding a dispersant in addition to the above-mentioned embossing method can be mentioned. Since the method of adding a dispersant adds chemicals other than pulp, it may not be usable depending on the application (for example, a dispersant unsuitable for food applications). Therefore, in the conventional method using dispersibility, it is necessary to consider the application destination of the application.
However, it has been shown that when the redispersible pulp and the redispersible pulp composition of the present invention are used, excellent dispersibility is exhibited without using a dispersant.

(Experiment 4)
In Experiment 4, since the redispersible pulp composition was in a solid state, its state was confirmed.

In the experiment, a screw tube bottle (manufactured by Maruem Co., Ltd., volume; 110 mL) was used, and 40 g of the redispersible pulp composition adjusted so that the sulfonated pulp had a predetermined solid content concentration was placed therein. Then, the state when the state was changed from the standing state (the state in which the sample was put and allowed to stand for 5 minutes) to the lying state (the state in which the sample was placed and left standing for 5 minutes) was confirmed.
The redispersible pulp composition of the experiment has a solid content concentration of 3% by mass (corresponding to the "solid content mass%" of the redispersible pulp or the redispersible pulp composition in the embodiment) of the sulfonated pulp (in the photograph). Redispersible pulp 3%) and 5% by mass (redispersible pulp 5% in the photograph) were used.

As a comparative example, pure water, the solid content concentration of the sulfonated pulp is 1% by mass (indicated as 1% in the photo), 2% by mass (indicated as 2% in the photo), and the solid content of the papermaking pulp. The one having a component concentration of 2% by mass (denoted as 2% pulp in the photograph) was used.

The experimental results are shown in FIGS. 9 and 10.
FIG. 9A shows an outline of the shooting direction of the photograph.
FIG. 9B shows a photograph of a side view (X direction) in an inverted state.
FIG. 10 shows a side view (Y direction, Z direction) photograph of the inverted state, in which (A) is a redispersible pulp composition having a solid content concentration of 5% by mass of the sulfonated pulp, (B). ) Is a redisperable pulp composition having a solid content concentration of 3% by mass of the sulfonated pulp, (C) is a composition having a solid content concentration of 2% by mass of the sulfonated pulp of the comparative example, and (D) is the sulfone of the comparative example. It is a side view photograph of the inverted state in which the solid content concentration of the converted pulp is 1% by mass, and (E) is the solid content concentration of 2% by mass of the papermaking pulp of the comparative example.
From the results of FIG. 10, the redispersible pulp composition containing the redispersible pulp of the example ((A), (B) in FIG. 10) was taken after the bottle was tilted (photograph in the direction of (Z)). In addition, the dispersion did not flow into the bottle as in Comparative Examples ((C) to (E) in FIG. 10) and remained. It has been found that this feature is a peculiar property of the solid shape redispersible pulp composition.
Therefore, it was confirmed that the redispersible pulp composition was in a solid state when the solid content concentration of the sulfonated pulp was 3% by mass or more.

In recent years, chemical denaturation to cellulose has been developed for the production of transparent, jelly-like gel-like materials called cellulose nanofibers. On the other hand, cellulose nanofibers obtained from chemically modified pulp have been produced at a low solid content concentration of 0.01 to 2% by mass (comparative example).
The redispersible pulp and the redispersible pulp composition of the present invention are characterized by a new shape in which the pulp exhibits a specific solid state in a state of 3% by mass or more (Example) having a concentration higher than 2% by mass. Was able to be linked to the physical property of redispersion.

The redispersed pulp and the redispersible pulp composition of the present invention are used to redisperse those having a low water content in various fields such as medical field, food field, environmental field, industrial field and paper manufacturing field. Suitable as pulp to be made.

S1 contact process S2 reaction process

Claims (9)

It contains sulfonated pulp in which at least a part of the hydroxyl groups of cellulose constituting the cellulose fiber is substituted with a sulfo group.
The sulfonated pulp is
The amount of the sulfo group introduced is 0.1 mmol / g or more and 5.0 mmol / g or less.
According to the following (1) or (2) in a sheet prepared according to JIS P 8222 with a basis weight of 45 g / m ^{2 to} 1000 g / m ^{2 and a thickness of 0.05 mm to 3.0 mm using a 100 mesh wire mesh.} A redispersible pulp characterized by a measured looseness of 15 seconds or less.

(1) In the case of a sheet prepared to have a basis weight of 45 g / m ² or more and less than 100 g / m ² and a thickness of 0.05 mm to 3.0 mm, the ease of loosening is measured in accordance with JIS P 4501.
(2) In the case of a sheet prepared to have a basis weight of 100 g / m ² or more and less than 1000 g / m ² and a thickness of 0.05 mm to 3.0 mm, follow the procedures of (i) and (ii) below in accordance with JIS P 4501. Measure.
(I) Put the rotor in a 1L glass beaker containing 1L of pure water, and adjust the rotation speed of the rotor to 600 rpm.
(Ii) Measure the time from when the test piece is inserted until the rotation speed of the rotor recovers to 450 rpm. The sulfonated pulp is
Claim 1 is characterized in that the standard freeness is 60 mL or more based on a measurement method based on JIS 811-2 (2012) with a measurement dispersion liquid dispersed in water to a solid content concentration of 0.3% by mass. The redispersible pulp described. The sulfonated pulp is
The redispersible pulp according to claim 1 or 2, wherein the moisture content of the sheet in the looseness measurement is 60% or less. A solid composition containing the redispersible pulp according to any one of claims 1, 2 or 3 and water, which is fibrous, cottony, lumpy, blocky, sheety, granular, or powdery. It is one of the following, which is selected from the form of wax, sponge, gel, paste, and cream.
According to the following (1) or (2) in a sheet prepared according to JIS P 8222 with a basis weight of 45 g / m ^{2 to} 1000 g / m ^{2 and a thickness of 0.05 mm to 3.0 mm using a 100 mesh wire mesh.} A redispersible pulp composition characterized by a measured looseness of 100 seconds or less.

(1) In the case of a sheet prepared to have a basis weight of 45 g / m ² or more and less than 100 g / m ² and a thickness of 0.05 mm to 3.0 mm, the ease of loosening is measured in accordance with JIS P 4501.
(2) In the case of a sheet prepared to have a basis weight of 100 g / m ² or more and less than 1000 g / m ² and a thickness of 0.05 mm to 3.0 mm, follow the procedures of (i) and (ii) below in accordance with JIS P 4501. Measure.
(I) Put the rotor in a 1L glass beaker containing 1L of pure water, and adjust the rotation speed of the rotor to 600 rpm.
(Ii) Measure the time from when the test piece is inserted until the rotation speed of the rotor recovers to 450 rpm.
The redispersible pulp composition according to claim 4, wherein the water content of the composition is 0.5% by mass or more and 97% by mass or less. The moisture content in the fibrous, cotton-like, lump-like, block-like, sheet-like, granular, powder-like, wax-like or sponge-like states is 0.5% by mass or more and 60% by mass or less. The redispersible pulp composition according to claim 4 or 5. The redispersion according to claim 4, 5 or 6, wherein the content ratio of the sulfonated pulp contained in the redispersible pulp according to any one of claims 1, 2 or 3 is 3% by mass or more. Sex pulp composition. Contains pulp for papermaking
The fourth, fifth, sixth or seventh aspect of the present invention, wherein the content ratio of the papermaking pulp is 1 part by mass or more and 900 parts by mass or less with respect to 100 parts by mass of the solid content of the sulfonated pulp. Redispersible pulp composition. It is characterized by having a standard freeness of 60 mL or more and 800 mL or less based on a measurement method based on JIS 811-2 (2012) with a measurement dispersion liquid dispersed in water to a solid content concentration of 0.3% by mass. The redispersible pulp composition according to claim 4, 5, 6, 7 or 8.

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