WO2018062501A1

WO2018062501A1 - Composition

Info

Publication number: WO2018062501A1
Application number: PCT/JP2017/035524
Authority: WO
Inventors: 雄右轟; 裕一野口; 郁絵本間; 孟晨趙
Original assignee: 王子ホールディングス株式会社
Priority date: 2016-09-30
Filing date: 2017-09-29
Publication date: 2018-04-05
Also published as: US20190276959A1; EP3521505A1; KR102210597B1; KR20190049857A; JP7044067B2; CN109952398A; EP3521505A4; JPWO2018062501A1

Abstract

The present invention addresses the problem of providing a bulky cellulose fiber-containing sheet wherein cellulose fibers have sufficiently high water retainability and high water absorption rate. The present invention relates to a composition which contains cellulose fibers having a phosphoric acid group or a substituent derived from a phosphoric acid group, and wherein: the phosphoric acid group or the substituent derived from a phosphoric acid group is crosslinked in at least some of the cellulose fibers; the number of crosslinking points of the cellulose fibers as calculated by formula (1) is 0.20 mmol/g or more; and the water content relative to the total mass of the composition is 50% by mass or less. (Number of crosslinking points) = ((amount of strongly acidic groups contained in cellulose fibers) - (amount of weakly acidic groups contained in cellulose fibers))/2 Formula (1)

Description

Composition

The present invention relates to a composition. Specifically, this invention relates to the cellulose fiber containing composition containing the cellulose fiber which has a phosphate group.

Conventionally, cellulose fibers have been widely used in clothing, absorbent articles, paper products and the like. As the cellulose fiber, in addition to fibrous cellulose having a fiber diameter of 10 μm or more and 50 μm or less, fine fibrous cellulose having a fiber diameter of 1 μm or less is also known.

For example, when cellulose fiber is used for the absorbent article, the cellulose fiber constitutes various members of the absorbent article in the form of a nonwoven fabric or the like. In such a case, the nonwoven fabric is required to have high water absorption. Conventionally, in order to improve the water absorption of the nonwoven fabric containing a cellulose fiber, superabsorbent resin, such as SAP, is carried on the cellulose fiber. In addition, it has been studied to increase the water absorption of the nonwoven fabric by modifying the crosslinking of cellulose fibers.

Patent Document 1 discloses a fabric containing cross-linked modified cellulose fibers. Here, formaldehyde, a nitrogen-containing cyclic compound, or the like is used as a crosslinking agent used for crosslinking modification. In Patent Document 2, a water-swellable cellulose derivative having a carboxyl group and cross-linked is immersed in an aqueous solution of a strong acid, and then the cellulose derivative is alkalinized in an organic solvent compatible with water. Is added, and after returning the acid-type carboxyl group to the salt form, a method of producing a water-absorbing cellulose material having an excellent salt water absorption rate by drying is disclosed. Also here, it is studied to increase the water absorption of the cellulose material by crosslinking the cellulose fibers.

Patent Document 3 discloses a surface-crosslinked water-absorbing resin containing a polymer obtained by polymerizing an aqueous monomer solution containing an acid group-containing unsaturated monomer as an essential component and cellulose. Here, phosphorylated and crosslinked cellulose is described as cellulose, and N-methylol compounds such as dimethylolethyleneurea and dimethyloldihydroxyethyleneurea are described as crosslinking agents.

JP 2000-129575 A Japanese Patent Laid-Open No. 08-243388 JP 2011-213759 A

Usually, when cellulose fibers are crosslinked, the cellulose fiber-containing sheet tends to be bulky. However, in such a bulky cellulose fiber-containing sheet, there is a tendency for the water retention of the cellulose fibers to decrease. For this reason, even if it is a bulky cellulose fiber containing sheet | seat, development of the cellulose fiber containing sheet | seat with sufficiently high water retention is desired. Moreover, in the cellulose fiber containing sheet | seat, raising the water absorption speed is also examined.

Therefore, in order to solve such problems of the prior art, the present inventors have a sufficiently high water retention even when a bulky sheet is formed from a cellulose fiber-containing composition and exhibits an excellent water absorption rate. A study was carried out for the purpose of providing a composition containing cellulose fibers.

As a result of intensive studies to solve the above-mentioned problems, the present inventors set the amount of the crosslinked structure of the phosphorylated cellulose fiber to a predetermined amount or more in the composition containing the phosphorylated cellulose fiber having a crosslinked structure. Thus, it has been found that even when a bulky sheet is formed from the composition, sufficiently high water retention and excellent water absorption speed are exhibited.
Specifically, the present invention has the following configuration.

[1] A composition comprising cellulose fibers having a phosphate group or a phosphate group-derived substituent, wherein the phosphate group or the phosphate group-derived substituent is crosslinked in at least a part of the cellulose fiber. The composition in which the number of crosslinking points of the cellulose fiber calculated by the following formula (1) is 0.20 mmol / g or more and the water content is 50% by mass or less with respect to the total mass of the composition.
Number of crosslinking points = (strong acid group content contained in cellulose fiber−weak acid group content contained in cellulose fiber) / 2 Formula (1)
[2] The composition according to [1], which is a nonwoven fabric.
[3] A strip sample having a width of 5 mm and a length of 50 mm is used as the composition, and the end region from the longitudinal edge of the strip sample to 5 mm is immersed in ion-exchanged water (electric conductivity 2 μS / cm or less), When measuring the time required for the ion exchange water to reach a distance point of 45 mm in the longitudinal direction from the direction edge, the water absorption speed (mm / sec) calculated by the following formula (2) is 2.5 mm / sec. The composition according to [1] or [2], which is not less than sec and not more than 100 mm / sec;
Water absorption speed (mm / sec) = 40 (mm) / t (sec) Formula (2)
In Expression (2), t represents the time (sec) required for the ion-exchanged water to reach a distance point of 45 mm in the longitudinal direction from the longitudinal edge of the strip-shaped sample.
[4] The composition according to any one of [1] to [3], wherein the amount of strongly acidic groups contained in the cellulose fiber is 1.60 mmol / g or more;
[5] The composition according to any one of [1] to [4], wherein the cellulose fiber has a water retention (%) calculated by the following formula of 150% or more.
Water retention (%) = (weight of cellulose fiber after centrifugation-absolute dry weight of cellulose fiber) / absolute dry weight of cellulose fiber × 100
In the above formula, the water retention is measured according to SCAN-C 62:00, but the conditions for the centrifugation treatment are 20 ° C. and the weight acceleration at the time of centrifugation is 3950 g for 15 minutes.

According to the present invention, even when a bulky sheet is formed, it is possible to obtain a cellulose fiber-containing composition that has sufficiently high water retention and can exhibit an excellent water absorption rate.

FIG. 1 is a graph showing the relationship between the NaOH dripping amount and the pH relative to the fiber raw material.

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

(Composition)
The present invention relates to a composition comprising a cellulose fiber having a phosphoric acid group or a substituent derived from a phosphoric acid group (hereinafter also simply referred to as a phosphoric acid group). Here, the phosphoric acid group or the substituent derived from the phosphoric acid group is crosslinked in at least a part of the cellulose fiber. And the crosslinking point number of the cellulose fiber calculated by Formula (1) is 0.20 mmol / g or more.
Number of crosslinking points = (strong acid group content contained in cellulose fiber−weak acid group content contained in cellulose fiber) / 2 Formula (1)
Moreover, the moisture content with respect to the total mass of the composition of this invention is 50 mass% or less. In addition, in this specification, the composition containing a cellulose fiber can be called a cellulose fiber containing composition.

Since the cellulose fiber-containing composition of the present invention has the above-described configuration, it can form a bulky cellulose fiber-containing sheet. In this case, the water retention of the cellulose fiber can be kept sufficiently high. Moreover, when the cellulose fiber containing composition of this invention is made into a sheet form, the outstanding water absorption speed | velocity | rate can be exhibited. This invention succeeded in obtaining the cellulose fiber containing composition which can exhibit a new physical property by controlling appropriately the crosslinked structure and the amount of crosslinked structures of a phosphorylated cellulose fiber.

The water content with respect to the total mass of the cellulose fiber-containing composition of the present invention is 50% by mass or less. This means that the cellulose fiber-containing composition of the present invention is preferably not in a slurry form but in a solid form. The cellulose fiber-containing composition of the present invention is preferably in the form of a gel, a sheet or a powder, for example, and more preferably in the form of a sheet. Especially, it is preferable that the cellulose fiber containing composition of this invention is a nonwoven fabric. In addition, in this specification, when a cellulose fiber containing composition is a sheet form, a cellulose fiber containing composition can also be called a cellulose fiber containing sheet, and a cellulose fiber containing sheet is one Embodiment of a cellulose fiber containing composition. It is.

The water content with respect to the total mass of the cellulose fiber-containing composition of the present invention may be 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, and 20% by mass or less. More preferably, it is particularly preferably 15% by mass or less. In the present invention, the moisture content of the cellulose fiber-containing composition may be 0% by mass.
Here, the moisture content was determined by measuring the weight of the cellulose fiber-containing composition adjusted to an equilibrium state at 23 ° C. and a relative humidity of 50%, and then dried at 105 ° C. overnight. The weight of the composition can be measured and calculated using the following formula.
Water content (%) = (weight before drying at 105 ° C.−weight after drying at 105 ° C.) / Weight before drying at 105 ° C. × 100

When the cellulose fiber-containing composition of the present invention is in sheet form, the density of the cellulose fiber-containing sheet is preferably 1.2 g / cm ³ or less, more preferably 1.0 g / cm ³ or less, More preferably, it is 0.8 g / cm ³ or less. The density of the cellulose fiber-containing sheet is preferably 0.05 g / cm ³ or more. When the cellulose fiber-containing composition of the present invention is a nonwoven fabric, the density of the nonwoven fabric is preferably within the above range. When the cellulose fiber-containing composition of the present invention is in the form of a sheet, the density of the cellulose fiber-containing sheet is preferably within the above range, and a bulky sheet can be obtained by adjusting the density to the above range.

When the cellulose fiber-containing composition of the present invention is in sheet form, the basis weight of the cellulose fiber-containing sheet is preferably 30 g / m ² or more, more preferably 50 g / m ² or more, and 100 g / m. More preferably, it is ² or more. The basis weight of the cellulose fiber-containing sheet is preferably 1000 g / m ² or less. By setting the basis weight of the cellulose fiber-containing sheet within the above range, water absorption can be more effectively exhibited.

When the cellulose fiber-containing composition of the present invention is in sheet form, the thickness of the cellulose fiber-containing sheet is preferably 5 μm or more, more preferably 10 μm or more, and further preferably 15 μm or more. Moreover, it is preferable that the thickness of a cellulose fiber containing sheet | seat is 50 mm or less, It is more preferable that it is 40 mm or less, It is further more preferable that it is 30 mm or less.

When the cellulose fiber-containing composition of the present invention is in the form of a sheet, the water absorption rate (mm / sec) calculated by the following formula (2) is preferably 2.5 mm / sec or more and 100 mm / sec or less. The water absorption rate (mm / sec) is more preferably 3.0 mm / sec or more, and further preferably 3.5 mm / sec or more.

Here, the water absorption speed (mm / sec) calculated by the following formula (2) is a water absorption speed measured by the following procedure. First, a sheet-like cellulose fiber-containing composition is formed into a strip-shaped sample having a width of 5 mm and a length of 50 mm, and the end region from the longitudinal edge of the strip-shaped sample to 5 mm is ion-exchanged water (electric conductivity 2 μS / cm). Soak in) Thereafter, the time required for the ion-exchanged water to reach a distance point of 45 mm in the longitudinal direction from the longitudinal edge is measured. Then, the water absorption rate (mm / sec) is calculated from the obtained time using the following formula (2).
Water absorption speed (mm / sec) = 40 (mm) / t (sec) Formula (2)
In Expression (2), t represents the time (sec) required for the ion-exchanged water to reach a distance point of 45 mm in the longitudinal direction from the longitudinal edge of the strip-shaped sample.

(Cellulose fiber)
The cellulose fiber-containing composition of the present invention contains a cellulose fiber having a phosphate group as a main component. Here, the state in which cellulose fibers having a phosphate group are contained as a main component means that the content of cellulose fibers having a phosphate group is 50% by mass or more with respect to the total mass of the cellulose fiber-containing composition. Say. The content of the cellulose fiber having a phosphate group is preferably 60% by mass or more, more preferably 70% by mass or more, and more preferably 80% by mass or more with respect to the total mass of the cellulose fiber-containing composition. More preferably it is.

Although it does not specifically limit as a cellulose raw material for obtaining a cellulose fiber, It is preferable to use a pulp from the point that it is easy to acquire and it is cheap. Examples of the pulp include wood pulp, non-wood pulp, and deinked pulp. Examples of wood pulp include hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolved pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), oxygen bleached craft Chemical pulps such as pulp (OKP) are listed. Moreover, semi-chemical pulps such as semi-chemical pulp (SCP) and chemi-ground wood pulp (CGP), mechanical pulps such as ground wood pulp (GP), thermomechanical pulp (TMP, BCTMP) and the like can be mentioned, but are not particularly limited. Non-wood pulp includes cotton pulp such as cotton linter and cotton lint, non-wood pulp such as hemp, straw and bagasse, cellulose isolated from sea squirts and seaweed, chitin, chitosan, etc., but is not particularly limited. . The deinking pulp includes deinking pulp made from waste paper, but is not particularly limited. The pulp of this embodiment may be used alone or in combination of two or more. Among the above pulps, wood pulp containing cellulose and deinked pulp are preferable in terms of availability.

In the present invention, the fiber width of the cellulose fiber having a phosphate group is not particularly limited. For example, the fiber width of the cellulose fiber having a phosphate group may be greater than 1000 nm, or 1000 nm or less. Moreover, the cellulose fiber whose fiber width is larger than 1000 nm and the cellulose fiber whose fiber width is 1000 nm or less may be mixed. In addition, when the fiber width of a cellulose fiber is 1000 nm or less, such a cellulose fiber may be called a fine fibrous cellulose.

In addition, the cellulose fiber-containing composition of the present invention may contain cellulose fibers not having a phosphate group in addition to cellulose fibers having a phosphate group. In this case, the content of the cellulose fiber having no phosphate group is preferably 20% by mass or less, and more preferably 10% by mass or less with respect to the total mass of the fiber raw material.

Here, the fiber width of the cellulose fiber can be measured by the following method by observation with an electron microscope. First, a cellulose fiber aqueous suspension having a concentration of 0.05% by mass or more and 0.1% by mass or less is prepared, and the suspension is cast on a carbon film-coated grid subjected to a hydrophilic treatment to obtain a sample for TEM observation. . At this time, an SEM image of the surface cast on glass may be observed. Observation with an electron microscope image is performed at a magnification of 1000 times, 5000 times, 10000 times, or 50000 times depending on the width of the constituent fibers. However, the sample, observation conditions, and magnification are adjusted to satisfy the following conditions.

(1) One straight line X is drawn at an arbitrary location in the observation image, and 20 or more fibers intersect the straight line X.
(2) A straight line Y perpendicular to the straight line is drawn in the same image, and 20 or more fibers intersect the straight line Y.

The width of the fiber intersecting with the straight line X and the straight line Y is visually read from the observation image satisfying the above conditions. In this way, at least three sets of images of the surface portion that do not overlap each other are observed, and the width of the fiber intersecting with the straight line X and the straight line Y is read for each image. Thus, at least 20 × 2 × 3 = 120 fiber widths are read.

The average fiber length of the cellulose fibers is not particularly limited, but is preferably 0.1 mm or more, and more preferably 0.6 mm or more. Moreover, it is preferable that it is 5 mm or less, and it is more preferable that it is 2 mm or less. By setting the average fiber length of the cellulose fibers within the above range, the strength of the sheet can be increased when the cellulose fiber-containing composition is formed into a sheet. Here, the average fiber length of the cellulose fibers can be determined by measuring the length-weighted average fiber length using, for example, a Kajaani fiber length measuring device (FS-200 type) manufactured by Kajaani Automation. Moreover, it can also measure using a scanning microscope (SEM), a transmission electron microscope (TEM), etc. according to the length of a fiber.

When the cellulose fiber is fine fibrous cellulose, the fine fibrous cellulose preferably has an I-type crystal structure. Here, the fact that the fine fibrous cellulose has a type I crystal structure can be identified in a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ = 1.5418Å) monochromatized with graphite. Specifically, it can be identified by having typical peaks at two positions of 2θ = 14 ° to 17 ° and 2θ = 22 ° to 23 °.
The proportion of the I-type crystal structure in the fine fibrous cellulose is preferably 30% or more, more preferably 50% or more, and further preferably 70% or more. In this case, further superior performance can be expected in terms of heat resistance and low linear thermal expansion coefficient. The degree of crystallinity is obtained by measuring an X-ray diffraction profile and determining the crystallinity by a conventional method (Seagal et al., Textile Research Journal, 29, 786, 1959).

In this specification, the cellulose fiber has a phosphate group (a phosphate group or a substituent derived from the phosphate group). In the present invention, such cellulose fibers are sometimes referred to as phosphorylated cellulose fibers.

The phosphoric acid group in the phosphorylated cellulose fiber is a divalent functional group corresponding to the phosphoric acid obtained by removing the hydroxyl group. Specifically, it is a group represented by —PO ₃ H ₂ . The substituent derived from the phosphate group includes a substituent such as a group obtained by polycondensation of the phosphate group, a salt of the phosphate group, and a phosphate ester group, and is preferably an ionic substituent.

In the present invention, the phosphate group or the substituent derived from the phosphate group may be a substituent represented by the following formula (1).

In the formula (1), a, b and n are natural numbers (however, a = b × m). At least one of α1, α2,..., αn and α 'is O-, and the rest is either R or OR. All of αn and α 'may be O-. When n is 2 or more and α 'is R or OR, at least one of each αn is O- and the rest is R or OR. When n is 2 or more and α ′ is O—, all αn may be R, all may be OR, or at least one is O— and the rest is R or OR. It may be. R is a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched hydrocarbon group, respectively. A hydrogen group, an unsaturated-cyclic hydrocarbon group, an aromatic group, and derivatives thereof.

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

The derivative in R is a functional group in which at least one of functional groups such as a carboxy group, a hydroxy group, or an amino group is added to or substituted for the main chain or side chain of the various hydrocarbon groups. Although group is mentioned, it is not specifically limited. Further, the number of carbon atoms constituting the main chain of R is not particularly limited, but is preferably 20 or less, more preferably 10 or less. When the number of carbon atoms constituting the main chain of R exceeds 20, the molecule of the Roxo oxo acid group containing R becomes so large that it is difficult to penetrate into the fiber raw material and the yield of fine cellulose fibers may be reduced. .

Βb + is a monovalent or higher cation made of an organic or inorganic substance. Examples of the monovalent or higher cation made of an organic substance include aliphatic ammonium or aromatic ammonium. Examples of the monovalent or higher cation made of an inorganic substance include ions of alkali metals such as sodium, potassium, or lithium, Examples include, but are not particularly limited to, a cation of a divalent metal such as calcium or magnesium, or a hydrogen ion. These can be applied alone or in combination of two or more. The monovalent or higher cation composed of an organic substance or an inorganic substance is preferably a sodium ion or potassium ion which is not easily yellowed when heated to a fiber raw material containing β and is industrially useful, but is not particularly limited.

The phosphoric acid group content of the cellulose fiber is preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, and 0.50 mmol / g or more per 1 g (mass) of cellulose fibers. Is more preferably 1.00 mmol / g or more, still more preferably 1.20 mmol / g or more, particularly preferably 1.30 mmol / g or more, 1.60 mmol. / G or more is most preferable. Moreover, it is preferable that content of a phosphate group is 3.65 mmol / g or less, It is more preferable that it is 3.5 mmol / g or less, It is further more preferable that it is 3.0 mmol / g or less. In addition, in this specification, content of the phosphate group which a cellulose fiber has is equal to the strongly acidic group amount of the phosphate group which a cellulose fiber has so that it may mention later.

The phosphate group content of the cellulose fiber can be measured by a neutralization titration method. In the measurement by the neutralization titration method, after completely converting the phosphate group to the acid form, it is refined by a mechanical treatment process (a refinement process), and the resulting fine fibrous cellulose-containing slurry is The amount introduced is determined by determining the change in pH while adding aqueous sodium hydroxide.

The phosphoric acid group is converted into an acid form by diluting the obtained phosphorylated cellulose fiber with ion-exchanged water so that the cellulose fiber concentration becomes 2% by mass, and stirring a sufficient amount of 1N aqueous hydrochloric acid solution. This is done by adding them one by one. In the conversion of the phosphoric acid group into an acid form, the cellulose fiber-containing slurry is dehydrated to obtain a dehydrated sheet, which is then diluted again with ion-exchanged water, and the operation of adding a 1N aqueous hydrochloric acid solution is repeated, thereby producing cellulose fibers. It is preferable to completely change the phosphate group contained in the acid form. Then, after the step of converting the phosphoric acid group into an acid form, the obtained cellulose fiber-containing slurry is stirred and dispersed uniformly, and then the operation of obtaining a dehydrated sheet by filtration and dehydration is repeated, so that surplus It is preferable to wash away hydrochloric acid sufficiently.

In the mechanical treatment process (miniaturization process), ion-exchanged water is poured into the obtained dehydration sheet to obtain a cellulose fiber-containing slurry having a cellulose fiber concentration of 0.3% by mass. Using Cleamix-2.2S manufactured by Technic Co., Ltd., treatment is performed for 30 minutes at 21500 rpm. In this way, a fine fibrous cellulose-containing slurry is obtained.

In the titration using an alkali, a change in pH value indicated by the dispersion is measured while adding a 0.1N aqueous sodium hydroxide solution to the fine fibrous cellulose-containing slurry. In this neutralization titration, two points are obtained where the increment (differential value of pH with respect to the amount of alkali dropped) is maximized in the curve plotting the measured pH against the amount of alkali (sodium hydroxide aqueous solution) added. (The point with the largest increment and the second largest point). Of these, the amount of alkali required up to the maximum point of increment obtained first after adding alkali (hereinafter referred to as the first end point) is equal to the amount of strongly acidic groups in the dispersion used for titration, The amount of alkali required up to the maximum point of increase obtained (hereinafter referred to as the second end point) becomes equal to the amount of weakly acidic groups in the dispersion used for titration. The alkali amount (mmol) required up to the first end point is divided by the solid content (g) in the fine fibrous cellulose-containing slurry to be titrated to obtain the first dissociated alkali amount (mmol / g). Is the phosphate group content of the cellulose fiber.

FIG. 1 shows an example of a curve plotting pH measured against the amount of alkali (sodium hydroxide aqueous solution) added in neutralization titration. The region up to the first end point is referred to as the first region, and the region up to the second end point is referred to as the second region. There is a third region after the second region. That is, three areas appear. In FIG. 1, the amount of alkali required in the first region is equal to the amount of strongly acidic groups in the slurry used for titration, and the amount of alkali required in the second region is the amount of weakly acidic groups in the slurry used for titration. Is equal to

The crosslinked structure is considered to be formed by dehydration condensation between phosphate groups introduced into the cellulose fiber. That is, the crosslinked structure is a structure in which a glucose unit of cellulose is bonded to each of two P atoms of pyrophosphate via O atoms. Therefore, when a crosslinked structure is formed, the weakly acidic group is apparently lost, and the amount of alkali required by the second end point is reduced compared to the amount of alkali required by the first end point. Here, when the phosphate groups introduced into the cellulose fiber are not condensed at all, the amount of the strongly acidic group introduced into the cellulose fiber is the same as the amount of the weakly acidic group. For this reason, the value obtained by dividing the amount of weakly acidic groups lost by forming a crosslinked structure by 2 represents the amount of crosslinked structure (number of crosslinking points). That is, the amount of cross-linking structure (number of cross-linking points) is obtained by dividing the difference between the alkali amount required until the first end point (first dissociated alkali amount) and the alkali amount required until the second end point (second dissociated alkali amount) by 2. Is equal to The amount of cross-linking structure (number of cross-linking points) is represented by the following formula (1).
Cross-linked structure amount (number of cross-linking points) = (strong acid group amount contained in cellulose fiber−weak acid group amount contained in cellulose fiber) / 2 Formula (1)

In the present invention, the crosslinked structure amount (number of crosslinking points) of the cellulose fiber calculated by the above formula (1) may be 0.20 mmol / g or more, preferably 0.22 mmol / g or more. More preferably, it is 25 mmol / g or more. In addition, since the upper limit of the amount of crosslinking structures (number of crosslinking points) is a value obtained by dividing the amount of strongly acidic groups contained in cellulose fibers by 2, it is, for example, 1.82 mmol / g or less.

The water retention of the cellulose fiber is preferably 150% or more, more preferably 170% or more, and further preferably 200% or more. In addition, there is no restriction | limiting in particular in the upper limit of the water retention of a cellulose fiber, For example, it can be 1000%. Here, the water retention of the cellulose fiber is a value measured according to SCAN-C 62:00, and is a value calculated by the following equation. When measuring the water retention of the cellulose fiber, the cellulose fiber is centrifuged for 15 minutes at 20 ° C. and 4400 rpm (weight acceleration during centrifugation: 3950 g). The amount of cellulose fiber used for the centrifugation treatment is 0.5 g (prepared basis weight 1700 ± 100 g / m ² ) in terms of dry weight per measurement. As a centrifuge, for example, H-3R manufactured by Kokusan Co., Ltd. can be used. In addition, it means that affinity with a cellulose fiber and water is so high that the numerical value of a water retention is large.
Water retention (%) = (weight of cellulose fiber after centrifugation-absolute dry weight of cellulose fiber) / absolute dry weight of cellulose fiber × 100

The cellulose fiber may have a counter ion. The counter ion may be an inorganic ion or an organic ion. As inorganic ions, monovalent metal ions typified by alkali metal ions, divalent metal ions typified by alkaline earth metal ions, ammonium ions, aluminum ions, tin ions, which are nonmetallic cations, Examples include base metal ions such as lead ions, and other transition metal ions such as silver ions, copper ions, and iron ions. Examples of the organic ions include organic ammonium ions and organic phosphonium ions. When it is desired to increase the water retention, it is preferable to use a monovalent cation as a counter ion. From the viewpoint of versatility, it is more preferable to use an ammonium ion or an alkali metal ion as a counter ion. More preferably, it is a counter ion. On the other hand, when it is desired to provide functions such as deodorization and antibacterial functions, it is preferable to use a functional cation such as copper ion, silver ion, or organic ammonium ion as a counter ion.

(Optional component)
The cellulose fiber-containing composition of the present invention may contain optional components other than cellulose fibers. Optional components include, for example, defoaming agents, lubricants, surfactants, UV absorbers, dyes, pigments, fillers, stabilizers, organic solvents miscible with water such as alcohol, preservatives, organic fine particles, and inorganic fine particles. , Resin (pellet, fiber) and the like.

(Method for producing composition)
The production method of the composition (the production method of the cellulose fiber-containing composition) introduces a phosphate group or a phosphate group-derived substituent into the cellulose fiber, and the number of crosslinking points of the cellulose fiber calculated by the following formula (1) is A step of crosslinking a phosphate group or a substituent derived from the phosphate group so as to be 0.20 mmol / g or more. In addition, the water content of the composition obtained in this way is 50 mass% or less.
Number of crosslinking points = (strong acid group content contained in cellulose fiber−weak acid group content contained in cellulose fiber) / 2 Formula (1)

<Phosphate group introduction process>
The step of introducing a phosphate group or a substituent derived from a phosphate group into a cellulose fiber can be referred to as a phosphate group introduction step. In addition, the process of bridge | crosslinking at least one part of the phosphate group or the substituent derived from a phosphate group is also contained in a phosphate group introduction | transduction process. That is, the phosphoric acid group introducing step includes a step of phosphorylating cellulose fibers and a step of crosslinking at least a part of the phosphoric acid group or a substituent derived from the phosphoric acid group.

In the phosphoric acid group introduction step, at least one selected from a phosphoric acid group or a compound having a substituent derived from a phosphoric acid group and a salt thereof (hereinafter referred to as “phosphorating agent” or “compound A”) is used for the cellulose fiber. Can be performed by reacting. Such a phosphorylating agent may be mixed in dry or wet cellulose fibers in the form of powder or aqueous solution. As another example, a phosphoric acid powder or an aqueous solution may be added to the cellulose fiber slurry. That is, the phosphate group introduction step includes at least a step of mixing the cellulose fiber and the phosphorylating agent.

The phosphate group introduction step can be performed by reacting a cellulose fiber with a phosphorylating agent. This reaction is performed by at least one selected from urea and derivatives thereof (hereinafter also referred to as “compound B”). You may carry out in presence.

As an example of a method of causing Compound A to act on cellulose fibers in the presence of Compound B, there may be mentioned a method of mixing Compound A and Compound B powders or aqueous solutions with dry or wet cellulose fibers. Another example is a method of adding powders and aqueous solutions of Compound A and Compound B to the cellulose fiber-containing slurry. Among these, since the uniformity of the reaction is high, a method of adding an aqueous solution of Compound A and Compound B to dry cellulose fibers, or a powder or an aqueous solution of Compound A and Compound B to wet cellulose fibers The method is preferred. Moreover, the compound A and the compound B may be added simultaneously, or may be added separately. Moreover, you may add the compound A and the compound B first used for reaction as aqueous solution, and remove an excess chemical | medical solution by pressing. The form of the cellulose fiber is preferably cotton or thin sheet, but is not particularly limited.

The phosphorylating agent (compound A) is at least one selected from a compound having a phosphate group and a salt thereof. Examples of the compound having a phosphate group include, but are not limited to, phosphoric acid, lithium salt of phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, ammonium salt of phosphoric acid, and the like. Examples of the lithium salt of phosphoric acid include lithium dihydrogen phosphate, dilithium hydrogen phosphate, trilithium phosphate, lithium pyrophosphate, and lithium polyphosphate. Examples of the sodium salt of phosphoric acid include sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, and sodium polyphosphate. Examples of the potassium salt of phosphoric acid include potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, and potassium polyphosphate. Examples of the ammonium salt of phosphoric acid include ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium polyphosphate. Among these, phosphoric acid, sodium salt of phosphoric acid, potassium salt of phosphoric acid, and ammonium salt of phosphoric acid are preferably used.

The phosphorylating agent (compound A) is preferably used as an aqueous solution because the uniformity of the reaction is increased and the efficiency of introducing phosphate groups is further increased. The pH of the aqueous solution of the phosphorylating agent (compound A) is not particularly limited, but is preferably 7 or less because the efficiency of introduction of phosphoric acid groups is increased. Is more preferable. The pH of the aqueous solution of Compound A may be adjusted by, for example, using a phosphoric acid group-containing compound that exhibits acidity and an alkalinity, and changing the amount ratio thereof. You may adjust pH of the aqueous solution of a phosphorylating agent (compound A) by adding an inorganic alkali or an organic alkali to what shows acidity among the compounds which have a phosphoric acid group.

Although the addition amount of the phosphorylating agent (compound A) with respect to a cellulose fiber is not specifically limited, When the addition amount of a phosphorylating agent (compound A) is converted into a phosphorus atomic weight, the addition amount of the phosphorus atom with respect to a cellulose fiber (absolute dry mass) Is preferably 0.5 to 100% by mass, more preferably 1 to 50% by mass, and most preferably 2 to 30% by mass. If the addition amount of the phosphorus atom with respect to a cellulose fiber is in the said range, the yield of a phosphorylated cellulose fiber can be improved more. By making the addition amount of phosphorus atoms to the cellulose fiber 100% by mass or less, it is possible to balance the effect of improving the yield and the cost. On the other hand, a yield can be raised by making the addition amount of the phosphorus atom with respect to a cellulose fiber more than the said lower limit.

Compound B used in this embodiment includes urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, 1-ethylurea and the like.

Compound B is preferably used as an aqueous solution in the same manner as Compound A. Moreover, since the uniformity of reaction increases, it is preferable to use the aqueous solution in which both compound A and compound B are dissolved. The amount of Compound B added to the cellulose fiber (absolute dry mass) is preferably 1% by mass or more and 500% by mass or less, more preferably 10% by mass or more and 400% by mass or less, and 100% by mass or more and 350% by mass or less. More preferably, it is more preferably 150% by mass or more and 300% by mass or less.

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

The phosphate group introduction step preferably includes a heating step (hereinafter also referred to as a heat treatment step). By providing the heat treatment step, a phosphate group can be efficiently introduced into the cellulose fiber, and at least a part of the phosphate group or a substituent derived from the phosphate group can be crosslinked. That is, it is preferable that the manufacturing method of the composition of this invention includes the process of mixing a cellulose fiber and a phosphorylating agent, and the process of heating the mixture of a cellulose fiber and a phosphorylating agent.

The heat treatment temperature in the heat treatment step is preferably selected to be a temperature at which phosphate groups can be efficiently introduced while suppressing thermal decomposition and hydrolysis reaction of cellulose fibers. In addition, the heat treatment temperature is a temperature at which the phosphoric acid group or the substituent derived from the phosphoric acid group is crosslinked so that the number of crosslinking points of the cellulose fiber calculated by the above formula (1) is 0.20 mmol / g or more. It is preferable to do. Specifically, the heat treatment temperature is preferably 50 ° C. or higher and 300 ° C. or lower, more preferably 100 ° C. or higher and 250 ° C. or lower, and further preferably 130 ° C. or higher and 200 ° C. or lower. Moreover, you may use a vacuum dryer, an infrared heating apparatus, and a microwave heating apparatus for a heating.

During the heat treatment, while water is contained in the cellulose fiber-containing slurry to which compound A has been added, if the time for which the cellulose fibers are allowed to stand is increased, the compound A that dissolves with water molecules along with the drying is deposited on the cellulose fiber surface. Moving. Therefore, the concentration of the compound A in the cellulose fiber may be uneven, and the introduction of phosphate groups on the surface of the cellulose fiber may not proceed uniformly. In order to suppress the occurrence of uneven density of Compound A in the cellulose fiber due to drying, a very thin sheet-like cellulose fiber is used, or the cellulose fiber and Compound A are kneaded or stirred with a kneader or the like and dried by heating or drying under reduced pressure. The method should be taken.

The heating device used for the heat treatment is preferably a device that can always discharge the moisture retained by the slurry and the moisture generated by the addition reaction of the fibers such as phosphate groups to the hydroxyl group of the fiber, such as a blower oven. Etc. are preferred. If the moisture in the system is always discharged, the hydrolysis reaction of the phosphate ester bond, which is the reverse reaction of the phosphorylation, can be suppressed, and the acid hydrolysis of the sugar chain in the cellulose fiber can be suppressed. it can.

The heat treatment time (heating time) is also affected by the heating temperature, but it is preferably 1 second or more and 300 minutes or less after the phosphorylating agent and the cellulose fiber are mixed and exposed to a heat source, and 5 seconds or more. It is more preferably 270 minutes or less, and further preferably 10 seconds or more and 15000 seconds or less. For example, when the heating temperature is 100 ° C. or more and 250 ° C. or less, the heating time is preferably 10 seconds or more, more preferably 20 seconds or more, and further preferably 30 seconds or more. When the heat treatment temperature is 100 ° C. or more and 250 ° C. or less, the upper limit of the heating time is preferably 15000 seconds or less. In the present invention, by introducing the heat treatment temperature and the heating time within an appropriate range, the amount of phosphate groups introduced can be within a preferred range.

The phosphate group introduction step may be performed at least once, but may be repeated a plurality of times. In this case, more phosphoric acid groups are introduced, which is preferable.

<Disaggregation / cleaning process>
A disaggregation step is preferably provided after the phosphate group introduction step, and a washing step is preferably further provided after the disaggregation step. The disaggregation process is performed in accordance with JIS P 8220. That is, a disaggregation process is a process for making the phosphorylated cellulose fiber obtained at the phosphate group introduction | transduction process into uniform pulp suspension. In this step, it is preferable that the phosphorylated cellulose fibers have a size comparable to that of general paper pulp (for example, a width of 20 μm to 30 μm and a length average fiber length of 0.1 mm to 3.0 mm). . In addition, even if a disaggregation process is not performed, when a suspension in which phosphorylated cellulose fibers are sufficiently dispersed is obtained, the disaggregation process may be omitted.

In the washing process, excess chemicals such as phosphorylating agents are washed away. In the washing step, it is preferable to repeat the operation of filtering and dewatering the phosphorylated cellulose fiber subjected to the disaggregation treatment, pouring ion-exchanged water and stirring to uniformly disperse.

<Alkali treatment process>
It is preferable to provide an alkali treatment step after the phosphate group introduction step and the disaggregation step. By providing the alkali treatment step, various counter ions of the phosphorylated cellulose fiber can be changed. For example, if sodium hydroxide is selected as the alkali, the counter ion of the phosphorylated cellulose fiber can be a sodium ion. In addition, in the manufacturing method of the cellulose fiber containing composition of this invention, it is not necessary to provide an alkali treatment process. In this case, one counter ion of the phosphoric acid group of phosphorylated cellulose fiber is an ammonium ion, and the other The counter ion becomes a hydrogen ion.

Although it does not specifically limit as a method of an alkali treatment, For example, the method of immersing a phosphorylated cellulose fiber in an alkaline solution is mentioned.
The alkali compound contained in the alkali solution is not particularly limited, but may be an inorganic alkali compound or an organic alkali compound. The solvent in the alkaline solution may be either water or an organic solvent. The solvent is preferably a polar solvent (polar organic solvent such as water or alcohol), and may be an aqueous solvent. Of the alkaline solutions, a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution is particularly preferred because of its high versatility.

Although the temperature of the alkali solution in an alkali treatment process is not specifically limited, 5 to 80 degreeC is preferable and 10 to 60 degreeC is more preferable.
The immersion time in the alkaline solution in the alkali treatment step is not particularly limited, but is preferably 5 minutes or longer and 30 minutes or shorter, and more preferably 10 minutes or longer and 20 minutes or shorter.
Although the usage-amount of the alkaline solution in an alkali treatment is not specifically limited, It is preferable that it is 100 mass% or more and 100,000 mass% or less with respect to the absolute dry mass of a phosphorylated cellulose fiber, and it is 1000 mass% or more and 10000 mass% or less. Is more preferable.

In order to reduce the amount of alkaline solution used in the alkali treatment step, the phosphorylated cellulose fiber may be washed with water or an organic solvent before the alkali treatment step. After the alkali treatment, it is preferable to wash the alkali-treated phosphorylated cellulose fiber with water or an organic solvent in order to improve handleability.

<Other counter ion change processing>
Instead of the alkali treatment step described above, the counter ion can be changed by bringing the inorganic alkali salt or organic alkali salt into contact with the phosphorylated cellulose fiber. For example, if sodium chloride is selected as the inorganic alkali salt, the counter ion of the phosphorylated cellulose fiber can be sodium. Further, if alkyl ammonium chloride is selected as the organic alkali salt, the counter ion of the phosphorylated cellulose fiber can be alkyl ammonium.

<Defibration processing>
When the cellulose fiber used in the present invention is fine fibrous cellulose having a fiber width of 1000 nm or less, a defibrating treatment step may be provided after the alkali treatment step. In the defibrating process, the fiber is usually defibrated using a defibrating apparatus to obtain a fine fibrous cellulose-containing slurry, but the processing apparatus and the processing method are not particularly limited.
As the defibrating apparatus, a high-speed defibrator, a grinder (stone mill type pulverizer), a high-pressure homogenizer, an ultra-high pressure homogenizer, a high-pressure collision type pulverizer, a ball mill, a bead mill, or the like can be used. Alternatively, as a defibrating apparatus, a device for wet grinding such as a disk type refiner, a conical refiner, a twin-screw kneader, a vibration mill, a homomixer under high-speed rotation, an ultrasonic disperser, or a beater should be used. You can also. The defibrating apparatus is not limited to the above. Preferable defibrating treatment methods include a high-speed defibrator, a high-pressure homogenizer, and an ultra-high pressure homogenizer that are less affected by the grinding media and less worried about contamination.

<Sheet formation process>
It is preferable that the manufacturing method of the cellulose fiber containing composition of this invention further includes the process of forming a sheet | seat using the phosphorylated cellulose fiber mentioned above. In this case, the cellulose fiber-containing composition is in the form of a sheet and is preferably a nonwoven fabric. In the step of forming a sheet using phosphorylated cellulose fibers, a forming method can be appropriately selected according to the properties and shape of the sheet. In this embodiment, it is possible to employ methods such as a wet papermaking method and a dry papermaking method.

The step of forming a sheet using cellulose fibers may be a step of forming a sheet by a wet papermaking method. Below, an example in the case of forming a sheet | seat by the wet papermaking method is demonstrated.

First, in the wet papermaking process, ion-exchanged water is added to the phosphorylated cellulose fiber obtained in the above-described process to obtain a cellulose fiber-containing slurry.
Next, the cellulose fiber-containing slurry is subjected to a wet papermaking process. Examples of the paper machine used in the wet paper making process include a long net paper machine, a twin wire paper machine, a circular net paper machine, an inclined wire type paper machine, a single net paper machine, and a Yankee paper machine. Further, paper making may be performed using a hand-making machine.

The sheet obtained in the wet papermaking process is preferably subjected to a dehydration drying process. In the dehydration step, dehydration may be performed by pressurizing the sheet. The pressure at this time is preferably 1 MPa or more, more preferably 5 MPa or more, and further preferably 10 MPa or more. The pressure is preferably 100 MPa or less. Since the cellulose fiber-containing composition of the present invention is excellent in compression resistance, a bulky sheet is easily obtained even when pressure is applied under the above conditions in the dehydration step.

When using the dry paper making method in the sheet forming process, the phosphorylated cellulose fibers are uniformly mixed in the air, and the air flow containing the phosphorylated cellulose fibers is placed on a mesh endless belt having a suction box on the lower side. To form a sheet. That is, the dry papermaking method is a method including a step of mixing and depositing phosphorylated cellulose fibers in the air. In the dry papermaking method, the above operation may be repeated a plurality of times as necessary.

The drying method in the dehydration drying process of the sheet is not particularly limited, but hot air, steam, infrared rays, microwaves, etc. can be used as appropriate. Further, as a heat transfer medium, a technique such as directly contacting a metal plate or a metal roll with the sheet can be appropriately employed.

You may further pressurize with respect to the sheet | seat after a dehydration drying process. The pressure at this time is preferably 1 MPa or more, more preferably 5 MPa or more, and further preferably 10 MPa or more. The pressure is preferably 100 MPa or less. By this operation, the thickness and density of the sheet can be appropriately adjusted. Moreover, since the cellulose fiber containing composition of this invention is excellent in compression resistance, even if it is a case where it pressurizes on the said conditions, a bulky sheet | seat is easy to be obtained.

(Use)
The use of the cellulose fiber-containing composition of the present invention is not particularly limited. The cellulose fiber-containing composition is preferably in the form of a sheet, and more preferably a nonwoven fabric. Cellulose fiber-containing compositions are used, for example, as components of absorbent articles such as sweat, urine, menstrual blood, and harmful chemicals in the state of fluff pulp and non-woven fabric, and used as sanitary paper, filter materials, cushioning materials, etc. Is done.

Hereinafter, the features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

Example 1
<Phosphorylation reaction process>
Oji Paper's pulp (solid content: 96% by mass, basis weight: 213 g / m ² sheet form) was used as a raw material as the softwood kraft pulp. 100 parts by mass of the above-mentioned softwood kraft pulp (absolute dry mass) is impregnated with a mixed aqueous solution of ammonium dihydrogen phosphate and urea to obtain 45 parts by mass of ammonium dihydrogen phosphate, 120 parts by mass of urea, and 150 parts by mass of ion-exchanged water. The resulting solution was pressed to obtain a chemical-impregnated pulp. The obtained chemical-impregnated pulp was dried and heat-treated for 350 seconds with a hot air dryer at 165 ° C. to introduce phosphoric acid groups and a phosphoric acid cross-linked structure into cellulose in the pulp to obtain phosphorylated cellulose fibers A.

<Disaggregation / cleaning process>
To the obtained phosphorylated cellulose fiber A, ion-exchanged water was poured so that the cellulose fiber concentration was 2% by mass, and the disaggregation treatment was carried out for 20 minutes with a 2 L desktop disintegrator. The obtained pulp slurry is filtered and dehydrated to obtain a dehydrated sheet, and then the ion-exchanged water is poured again, and the operation of stirring and dispersing uniformly is repeated to sufficiently wash away the excess chemical solution, and phosphorylated cellulose fiber B Got.

<Alkali treatment process>
The obtained phosphorylated cellulose fiber B is diluted with ion-exchanged water so that the cellulose fiber concentration becomes 2% by mass, and 1N sodium hydroxide aqueous solution is added little by little while stirring, so that the pH is 12 ± 0.2. A pulp slurry was obtained. Then, after dehydrating this pulp slurry and obtaining a dehydrated sheet, after adding ion-exchanged water again, stirring and uniformly dispersing, and repeating the operation of obtaining a dehydrated sheet by filtration and dewatering, excess water is obtained. Sodium oxide was thoroughly washed away to obtain phosphorylated cellulose fiber C containing phosphorylated cellulose. And the water retention of the phosphorylated cellulose fiber C was measured by the method mentioned later. Moreover, the amount of phosphoric acid groups introduced into the phosphorylated cellulose fiber C and the content of the crosslinked structure were measured by the method described later.

<Sheet making / pressing process>
The obtained cellulose fibers C, poured deionized water as cellulose fibers concentration of 0.3 mass%, the area 0.0043M ² by dehydration filtration, cellulose fiber content of the basis weight of 200 g / m ² A sheet was obtained. This cellulose fiber-containing sheet was dried in a humidity control chamber at 23 ° C. and a relative humidity of 50% until the weight became constant. Next, the cellulose fiber-containing sheet A (cellulose fiber-containing composition) was obtained by pressing at a pressure of 11.57 MPa for 60 seconds. The density of the cellulose fiber-containing sheet A was calculated by measuring the thickness after pressing. The density of the sheet was calculated according to JIS P 8118: 1998. In addition, as a paper thickness gauge, a high bridge paper thickness gauge (No. 735 manufactured by Takahashi Seisakusho Co., Ltd.) was used. Moreover, the water content (water content) and the water absorption rate of the cellulose fiber-containing sheet A were measured by the method described later.

(Example 2)
A phosphorylated cellulose fiber and a cellulose fiber-containing sheet were obtained in the same manner as in Example 1 except that the above <alkali treatment step> was not performed. About the obtained phosphorylated cellulose fiber and the cellulose fiber containing sheet | seat, the measurement similar to Example 1 was performed.

(Example 3)
Example 1 except that the drying / heating treatment time was set to 300 seconds in the above <phosphorylation reaction step> and that the disaggregation treatment time in the disintegrator was set to 15 minutes in the above <disaggregation / washing step>. Similarly, phosphorylated cellulose fibers and cellulose fiber-containing sheets were obtained. About the obtained phosphorylated cellulose fiber and the cellulose fiber containing sheet | seat, the measurement similar to Example 1 was performed.

Example 4
A phosphorylated cellulose fiber and a cellulose fiber-containing sheet were obtained in the same manner as in Example 3 except that the above <alkali treatment step> was not performed. About the obtained phosphorylated cellulose fiber and the cellulose fiber containing sheet | seat, the measurement similar to Example 1 was performed.

(Comparative Example 1)
<Disaggregation process>
Oji Paper's pulp (solid content: 96% by mass, basis weight: 213 g / m ² sheet form) was used as a raw material as the softwood kraft pulp. Ion exchange water was poured so that the cellulose fiber concentration would be 2% by mass, and the mixture was disaggregated for 5 minutes using a 2 L desktop disintegrator. The obtained pulp slurry was filtered and dehydrated to obtain cellulose fiber A ′. The water retention of the cellulose fiber A ′ was measured by the method described later.

<Sheet making / pressing process>
The obtained cellulose fibers A ', was poured deionized water so cellulose fibers concentration of 0.3 mass%, the area 0.0043M ² by dehydration filtration, a basis weight of 200 g / m ² cellulosic fibers A containing sheet was obtained. This cellulose fiber-containing sheet was dried in a humidity control chamber at 23 ° C. and a relative humidity of 50% until the weight became constant. Next, a cellulose fiber-containing sheet A ′ was obtained by pressing at a pressure of 11.57 MPa for 60 seconds. By measuring the thickness after pressing, the density of the cellulose fiber-containing sheet A ′ was calculated. Moreover, the water content (water content) and the water absorption rate of the cellulose fiber-containing sheet A ′ were measured by the method described later.

(Comparative Example 2)
In the above <phosphorylation reaction step>, the drying / heating treatment time is 200 seconds, and in the above <disaggregation / washing step>, except that the treatment with a disintegrator is not performed, the same as in Example 1, A phosphorylated cellulose fiber and a cellulose fiber-containing sheet were obtained. About the obtained phosphorylated cellulose fiber and the cellulose fiber containing sheet | seat, the measurement similar to Example 1 was performed. In Comparative Example 2, since the phosphorylated cellulose fibers were uniformly dispersed in water only by adding ion-exchanged water and performing slight hand stirring, no disaggregator was used.

(Comparative Example 3)
A phosphorylated cellulose fiber and a cellulose fiber-containing sheet were obtained in the same manner as in Comparative Example 2 except that the above <alkali treatment step> was not performed. About the obtained phosphorylated cellulose fiber and the cellulose fiber containing sheet | seat, the measurement similar to Example 1 was performed.
In Comparative Example 3, since ion-exchanged water was added and only slight hand stirring was performed, the phosphorylated cellulose fiber was uniformly dispersed in the water, and thus the disaggregator was not used.

(Analysis and evaluation)
<Measurement of water retention>
The water retention of the cellulose fibers was measured according to SCAN-C 62:00. When measuring the water retention of the cellulose fibers, the cellulose fibers were centrifuged for 15 minutes at 20 ° C. and 4400 rpm (weight acceleration during centrifugation: 3950 g). The amount of cellulose fiber used for the centrifugation treatment was 0.5 g (prepared basis weight 1700 ± 100 g / m ² ) in terms of absolute dry weight per measurement. As a centrifuge, H-3R manufactured by Kokusan Co., Ltd. was used. The water retention was calculated by the following formula.
Water retention (%) = (weight of cellulose fiber after centrifugation-absolute dry weight of cellulose fiber) / absolute dry weight of cellulose fiber × 100
In addition, it means that affinity with a cellulose fiber and water is so high that the numerical value of a water retention is large.

<Measurement of phosphate group introduction amount>
The amount of phosphate group introduced was measured by neutralization titration. Specifically, after completely converting the phosphoric acid group contained in the cellulose fiber into an acid form, it is refined by a mechanical treatment process (a refinement process), and the resulting fine fibrous cellulose-containing slurry is 0. The amount introduced was determined by determining the change in pH indicated by the slurry (dispersion) while adding a 1N aqueous sodium hydroxide solution.
In converting the phosphoric acid group into an acid form, the obtained phosphorylated cellulose fiber is diluted with ion-exchanged water so that the cellulose fiber concentration becomes 2% by mass, and a sufficient amount of 1N hydrochloric acid aqueous solution is slightly added while stirring. Added in increments. Next, the cellulose fiber-containing slurry is stirred for 15 minutes and then dehydrated to obtain a dehydrated sheet. Then, the slurry is diluted again with ion-exchanged water, and a 1N hydrochloric acid aqueous solution is added to repeat the phosphoric acid contained in the cellulose fiber. The group was completely changed to the acid form. Furthermore, the cellulose fiber-containing slurry was stirred and dispersed uniformly, and then the operation of obtaining a dehydrated sheet by filtration and dehydration was repeated to sufficiently wash away excess hydrochloric acid.
In the mechanical treatment process, ion-exchanged water was poured into the obtained dehydration sheet to obtain a cellulose fiber-containing slurry having a cellulose fiber concentration of 0.3% by mass. This slurry was processed for 30 minutes under the condition of 21500 rotations / minute using a defibrating apparatus (Cleamix-2.2S, manufactured by M Technique Co., Ltd.). In the titration using an alkali, a change in pH value indicated by the dispersion was measured while adding a 0.1N sodium hydroxide aqueous solution to the fine fibrous cellulose-containing slurry.

This neutralization titration gives two points where the increment (differential value of pH with respect to the amount of alkali dropped) is maximized in the curve plotting the measured pH against the amount of alkali added (the point at which the increment is maximum). And the second largest point). Of these, the amount of alkali required up to the maximum incremental point (hereinafter referred to as the first end point) obtained for the first time after adding alkali is equal to the amount of strongly acidic group in the dispersion used for titration. The amount of alkali required up to the maximum point of increment obtained (hereinafter referred to as the second end point) is equal to the amount of weakly acidic groups in the dispersion used for titration.
The alkali amount (mmol) required up to the first end point is divided by the solid content (g) in the titration target dispersion to obtain the first dissociated alkali amount (mmol / g). The amount introduced was taken.

<Measurement of the number of crosslinking points>
The crosslinked structure is considered to be formed by dehydration condensation between phosphate groups introduced into the cellulose fiber. That is, the crosslinked structure is a structure in which a glucose unit of cellulose is bonded to each of two P atoms of pyrophosphate via O atoms. Therefore, when the crosslinked phosphate group is formed, the weakly acidic group is apparently lost, and the amount of alkali required by the second end point is reduced as compared with the amount of alkali required by the first end point. That is, the number of crosslinking points is equal to a value obtained by dividing the difference between the alkali amount required until the first end point (first dissociated alkali amount) and the alkali amount required until the second end point (second dissociated alkali amount) by 2.

<Measurement of moisture content>
The moisture content is the weight of the cellulose fiber-containing sheet after drying at 105 ° C. overnight after measuring the weight of the cellulose fiber-containing sheet dried to an equilibrium state in a humidity control chamber at 23 ° C. and 50% relative humidity. Was calculated using the following formula.
Water content (%) = (sheet weight before drying at 105 ° C.−sheet weight after drying at 105 ° C.) / Sheet weight before drying at 105 ° C. × 100

<Measurement of water absorption rate>
The water absorption rate is obtained by cutting the cellulose fiber-containing sheet into a strip-shaped sample having a width of 5 mm and a length of 50 mm, and ion-exchanged water (electric conductivity: 2 μS / cm) from the end region of the strip-shaped sample from the longitudinal edge to 5 mm. Dipped below). Thereafter, the time required for the ion-exchanged water to reach the distance point of 45 mm in the longitudinal direction from the longitudinal side edge was measured, and the water absorption rate (mm / sec) was calculated using the following formula (2).
Water absorption speed (mm / sec) = 40 (mm) / t (sec) Formula (2)
In Expression (2), t represents the time (sec) required for the ion-exchanged water to reach a distance point of 45 mm in the longitudinal direction from the longitudinal edge of the strip-shaped sample.

The cellulose fibers obtained in the examples have a high water retention, and the cellulose fiber-containing sheets exhibited an excellent water absorption rate. Although the cellulose fiber-containing sheet obtained in the examples was a bulky sheet (a sheet having a small density), excellent water retention and a high water absorption rate were compatible.

Claims

A composition comprising cellulose fibers having a substituent derived from a phosphate group or a phosphate group,
In at least a part of the cellulose fiber, the phosphate group or a substituent derived from the phosphate group is crosslinked,
The number of crosslinking points of the cellulose fiber calculated by the following formula (1) is 0.20 mmol / g or more,
The composition whose water content with respect to the total mass of the said composition is 50 mass% or less.
Number of crosslinking points = (strong acid group content contained in cellulose fiber−weak acid group content contained in cellulose fiber) / 2 Formula (1)
The composition according to claim 1, which is a non-woven fabric.
The composition is made into a strip-shaped sample having a width of 5 mm and a length of 50 mm, and the end region from the longitudinal edge of the strip-shaped sample to 5 mm is immersed in ion-exchanged water (electric conductivity of 2 μS / cm or less), and the longitudinal direction. When measuring the time required for the ion exchange water to reach a distance point of 45 mm in the longitudinal direction from the end side, the water absorption speed (mm / sec) calculated by the following formula (2) is 2.5 mm / sec. The composition according to claim 1, wherein the composition is 100 mm / sec or less.
Water absorption speed (mm / sec) = 40 (mm) / t (sec) Formula (2)
In Expression (2), t represents the time (sec) required for the ion-exchanged water to reach a distance point of 45 mm in the longitudinal direction from the longitudinal edge of the strip-shaped sample.
The composition according to any one of claims 1 to 3, wherein the amount of strongly acidic group contained in the cellulose fiber is 1.60 mmol / g or more.
The composition according to any one of claims 1 to 4, wherein the water retention (%) calculated by the following formula of the cellulose fiber is 150% or more.
Water retention (%) = (weight of cellulose fiber after centrifugation-absolute dry weight of cellulose fiber) / absolute dry weight of cellulose fiber × 100
In the above formula, the water retention is measured according to SCAN-C 62:00, but the conditions for the centrifugation treatment are 20 ° C. and the weight acceleration at the time of centrifugation is 3950 g for 15 minutes.