JPWO2018062501A1 - Composition - Google Patents

Abstract

An object of the present invention is to provide a cellulose fiber-containing sheet which is a bulky cellulose fiber-containing sheet and has a sufficiently high water retention capacity and a high water absorption rate. The present invention is a composition comprising a cellulose fiber having a phosphate group or a phosphate group-derived substituent, wherein at least a part of the cellulose fiber is crosslinked with a phosphate group or a phosphate group-derived substituent. In addition, the present invention relates to a 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 with respect to the total mass of the composition is 50% by mass or less. Number of crosslinking points = (strong acid group amount contained in cellulose fiber−weak acid group amount contained in cellulose fiber) / 2 Formula (1)

Description

  The present invention relates to a composition. Specifically, the present invention relates to a cellulose fiber-containing composition comprising cellulose fibers having phosphate groups.

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

  For example, when a cellulose fiber is used for an absorbent article, a cellulose fiber comprises the various members of an absorbent article in the form of a nonwoven fabric etc. In such a case, the nonwoven fabric is required to have high water absorbability. In the past, in order to increase the water absorbability of non-woven fabrics containing cellulose fibers, it has been carried out that cellulose fibers carry a highly water-absorbent resin such as SAP. In addition, it is also studied to increase the water absorbability of the non-woven fabric by crosslinking and modifying the cellulose fiber.

  Patent Document 1 discloses a fabric containing cross-linked modified cellulose fibers. Here, formaldehyde, a nitrogen-containing cyclic compound, etc. are used as a crosslinking agent used for crosslinking modification. Further, in Patent Document 2, a water-swellable cellulose derivative having a carboxyl group and crosslinked is immersed in an aqueous solution of a strong acid, and then the cellulose derivative is alkali in an organic solvent compatible with water. No. 6,095,095 and a method of producing a water-absorbent cellulose material excellent in salt water absorption speed by converting acid type carboxyl group back to salt type and drying it. Here too, it is considered to increase the water absorption of the cellulose material by crosslinking the cellulose fiber.

  Patent Document 3 discloses a surface cross-linked water-absorbent resin that contains a polymer obtained by polymerizing a monomer aqueous solution containing an acid group-containing unsaturated monomer as an essential component and cellulose. Here, a phosphorylated and crosslinked cellulose is described as the cellulose, and an N-methylol compound such as dimethylol ethylene urea and dimethylol dihydroxy ethylene urea is described as the crosslinking agent.

JP 2000-129575 A Japanese Patent Application Publication No. 08-243388 JP, 2011-213759, A

  Generally, 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 retentivity of cellulose fibers to decrease. For this reason, even if it is a bulky cellulose fiber containing sheet, development of a cellulose fiber containing sheet with sufficiently high water retention is desired. In addition, in the case of a cellulose fiber-containing sheet, it has also been studied to increase the water absorption rate.

  Therefore, in order to solve the problems of the prior art, the present inventors have a sufficiently high water retention even when a bulky sheet is formed from a composition containing a cellulose fiber, and exhibit an excellent water absorption rate. Investigations were advanced for the purpose of providing a cellulose fiber-containing composition that can be used.

As a result of earnestly examining in order to solve said subject, the present inventors make the amount of crosslinked-structures of a phosphated cellulose fiber more than predetermined amount in the composition containing the phosphated cellulose fiber which has a crosslinked structure. 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 a cellulose fiber having a phosphate group or a substituent derived from a phosphate group, wherein at least a part of the cellulose fiber is crosslinked by a phosphate group or a substituent derived from a phosphate group The composition having a crosslinking point of 0.20 mmol / g or more of cellulose fiber calculated by the following formula (1) and a water content of 50% by mass or less based on the total mass of the composition.
Number of crosslinking points = (amount of strongly acidic group contained in cellulose fiber−amount of weakly acidic group contained in cellulose fiber) / 2 Formula (1)
[2] The composition according to [1], which is a non-woven fabric.
[3] The composition is used as a strip sample having a width of 5 mm and a length of 50 mm, and the end region up to 5 mm from the longitudinal edge of the strip sample is immersed in ion exchange water (electrical conductivity 2 μS / cm or less) When the time taken for ion exchange water to reach a distance point of 45 mm in the longitudinal direction from the direction edge is measured, the water absorption speed (mm / sec) calculated by the following equation (2) is 2.5 mm / sec. The composition according to [1] or [2], which is sec or more and 100 mm / sec or less;
Water absorption speed (mm / sec) = 40 (mm) / t (sec) Formula (2)
In Formula (2), t represents the time (sec) taken by the ion-exchanged water to reach a distance point of 45 mm in the longitudinal direction from the longitudinal edge of the strip 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 degree of water retention (%) of the cellulose fiber calculated by the following formula is 150% or more.
Water retention (%) = (weight of cellulose fiber after centrifugation treatment-absolute weight of cellulose fiber) / absolute weight of cellulose fiber × 100
In the above equation, the degree of water retention is measured according to SCAN-C 62:00, but the conditions for centrifugation are 15 ° C. and weight acceleration 3950 g during centrifugation for 15 minutes.

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

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

  Hereinafter, the present invention will be described in detail. The description of the configuration requirements described below may be made based on typical 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 phosphate group or a substituent derived from a phosphate group (hereinafter, also simply referred to as a phosphate group). Here, at least a part of the cellulose fiber, the phosphate group or the substituent derived from the phosphate group is crosslinked. And the number of crosslinking points of the cellulose fiber calculated by Formula (1) is 0.20 mmol / g or more.
Number of crosslinking points = (amount of strongly acidic group contained in cellulose fiber−amount of weakly acidic group contained in cellulose fiber) / 2 Formula (1)
Moreover, the water content with respect to the total mass of the composition of this invention is 50 mass% or less. In the present specification, a composition containing cellulose fiber can be referred to as a cellulose fiber-containing composition.

  The cellulose fiber-containing composition of the present invention can form a bulky cellulose fiber-containing sheet because it has the above-described constitution, but also 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 can be exhibited. The present invention has succeeded in obtaining a cellulose fiber-containing composition capable of exhibiting new physical properties by appropriately controlling the cross-linked structure and the cross-linked structure amount of the phosphorylated cellulose fiber.

  The water content relative 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 in a solid state, not in a slurry state. The cellulose fiber-containing composition of the present invention is, for example, preferably in the form of gel, sheet or powder, and more preferably in the form of sheet. Among them, the cellulose fiber-containing composition of the present invention is preferably a non-woven 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 relative 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 Is more preferably, and particularly preferably 15% by mass or less. In the present invention, the water content of the cellulose fiber-containing composition may be 0% by mass.
Here, after the weight of the cellulose fiber-containing composition which has been conditioned to an equilibrium state at 23 ° C. and a relative humidity of 50% is measured, the water content is cellulose fiber-containing after being dried overnight at 105 ° C. The weight of the composition can be measured and calculated using the following equation:
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 a sheet, 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. Also when the cellulose fiber containing composition of this invention is a nonwoven fabric, it is preferable that the density of a nonwoven fabric is in the said range. When the cellulose fiber containing composition of this invention is a sheet form, it is preferable that the density of a cellulose fiber containing sheet exists in the said range, and it can be set as a bulky sheet | seat by adjusting a density to the said range.

When the cellulose fiber-containing composition of the present invention is a sheet, 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 2 More preferably, it is ² or more. Further, 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 in the above range, the water absorption can be more effectively exhibited.

  When the cellulose fiber-containing composition of the present invention is in the form of a sheet, the thickness of the cellulose fiber-containing sheet is preferably 5 μm or more, more preferably 10 μm or more, and still more preferably 15 μm or more. The thickness of the cellulose fiber-containing sheet is preferably 50 mm or less, more preferably 40 mm or less, and still more preferably 30 mm or less.

  When the cellulose fiber containing composition of this invention is a sheet form, it is preferable that the water absorption speed (mm / sec) calculated by following formula (2) is 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 still more preferably 3.5 mm / sec or more.

Here, the water absorption rate (mm / sec) calculated by the following equation (2) is a water absorption rate measured by the following procedure. First, a sheet-like cellulose fiber-containing composition is used as a strip sample having a width of 5 mm and a length of 50 mm, and the end region up to 5 mm from the longitudinal edge of this strip sample is ion exchanged water (electrical conductivity 2 μS / cm) Soak in). After that, the time taken for the ion exchanged water to reach from the longitudinal end to the distance point of 45 mm in the longitudinal direction is measured. And water absorption speed (mm / sec) is computed using the following formula (2) from the obtained time.
Water absorption speed (mm / sec) = 40 (mm) / t (sec) Formula (2)
In Formula (2), t represents the time (sec) taken by the ion-exchanged water to reach a distance point of 45 mm in the longitudinal direction from the longitudinal edge of the strip sample.

(Cellulose fiber)
The cellulose fiber containing composition of this invention contains the cellulose fiber which has a phosphoric acid group as a main component. Here, the state in which the cellulose fiber having a phosphate group is contained as the main component means that the content of the cellulose fiber 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 based on the total mass of the cellulose fiber-containing composition. It is further preferred that

  The cellulose raw material for obtaining cellulose fibers is not particularly limited, but it is preferable to use pulp from the viewpoint of availability and low cost. The pulp may include wood pulp, non-wood pulp and deinked pulp. As wood pulp, for example, hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), oxygen bleached kraft Chemical pulp, such as pulp (OKP), etc. are mentioned. In addition, semichemical pulp such as semichemical pulp (SCP), chemiground wood pulp (CGP), mechanical pulp such as ground pulp (GP), thermomechanical pulp (TMP, BCTMP), etc. may be mentioned, but it is not particularly limited. Non-wood pulps include cotton-based pulps such as cotton linters and cotton lint, non-wood-based pulps such as hemp, straw and bagasse, celluloses isolated from ascidians and seaweeds, chitin, chitosan and the like, but are not particularly limited . Examples of the deinked pulp include, but not particularly limited to, deinked pulp made from waste paper. The pulp of this embodiment may be used singly or in combination of two or more. Among the above-mentioned pulps, wood pulps containing cellulose and deinked pulps 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 larger than 1000 nm, and may be 1000 nm or less. Moreover, the cellulose fiber whose fiber width | variety is larger than 1000 nm, and the cellulose fiber whose fiber width | variety 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.

  Moreover, the cellulose fiber which does not have a phosphoric acid group may be contained in the cellulose fiber containing composition of this invention other than the cellulose fiber which has a phosphoric acid group. In this case, the content of the cellulose fiber not having a phosphate group is preferably 20% by mass or less, and more preferably 10% by mass or less, based on the total mass of the fiber raw material.

  Here, the fiber width of the cellulose fiber can be measured by the following method by electron microscope observation. 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 this suspension is cast on a hydrophilized carbon film-coated grid 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 fiber to be constructed. However, the sample, observation conditions and magnification are adjusted to satisfy the following conditions.

(1) One straight line X is drawn at an arbitrary position in the observation image, and 20 or more fibers cross the straight line X.
(2) Draw a straight line Y intersecting perpendicularly with the straight line in the same image, and 20 or more fibers cross the straight line Y.

  With respect to the observation image satisfying the above conditions, the width of the fiber intersecting with the straight line X and the straight line Y is visually read. Thus, three or more sets of images of at least non-overlapping surface portions are observed, and for each image, the width of the fiber intersecting the straight line X and the straight line Y is read. Thus, a fiber width of at least 20 x 2 x 3 = 120 is read.

  The average fiber length of the cellulose fiber 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. When the average fiber length of the cellulose fiber is in the above range, the strength of the sheet can be enhanced when the cellulose fiber-containing composition is formed into a sheet. Here, the average fiber length of the cellulose fiber can be determined, for example, by measuring the length-weighted average fiber length using a Kajaani fiber length measuring device (type FS-200) manufactured by Kajaani Automation. Moreover, it can also measure using a scanning electron microscope (SEM), a transmission electron microscope (TEM), etc. according to the length of a fiber.

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

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

The phosphate group in the phosphorylated cellulose fiber is a divalent functional group corresponding to phosphoric acid from which a hydroxyl group has been removed. It is specifically a group represented by -PO ₃ H _2. The substituent derived from the phosphate group includes a substituent obtained by condensation polymerization of a phosphate group, a salt of a phosphate group, a phosphate ester group and the like, 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 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 each α n and α ′ may be O-. When n is 2 or more and α 'is R or OR, at least one of each α n is O- and the remainder is R or OR. When n is 2 or more and α ′ is O—, each α n may be all R or all OR, and at least one is O— and the rest is R or OR It may be R is each 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 carbonization Hydrogen, unsaturated-cyclic hydrocarbon, aromatic, and derivatives thereof.

  Although a methyl group, an ethyl group, n-propyl group, or n-butyl group etc. are mentioned as a saturated-linear hydrocarbon group, It does not specifically limit. Examples of the saturated-branched hydrocarbon group include i-propyl group and t-butyl group, but are not particularly limited. Although a cyclopentyl group, a cyclohexyl group, etc. are mentioned as a saturated cyclic hydrocarbon group, It does not specifically limit. Examples of the unsaturated-linear hydrocarbon group include, but are not particularly limited to, a vinyl group, an allyl group and the like. Examples of unsaturated-branched hydrocarbon groups include i-propenyl group and 3-butenyl group, but are not particularly limited. Although a cyclopentenyl group, a cyclohexenyl group, etc. are mentioned as unsaturated-cyclic hydrocarbon group, It does not specifically limit. As an aromatic group, although a phenyl group or a naphthyl group etc. are mentioned, it does not specifically limit.

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

  β b + is a monovalent or more cation composed of an organic substance or an inorganic substance. The monovalent or more monovalent cations of organic substances include aliphatic ammonium or aromatic ammonium, and the monovalent or more monovalent cations of inorganic substances include ions of alkali metals such as sodium, potassium or lithium, Examples thereof include cations of divalent metals such as calcium or magnesium, or hydrogen ions, but not particularly limited. These can also be applied combining 1 type or 2 or more types. The monovalent or more monovalent cation composed of an organic substance or an inorganic substance is preferably an ion of sodium or potassium which is not easily yellowed when the fiber material containing β is heated and which is industrially easy to use, but is not particularly limited.

  The content of the phosphate group of the cellulose fiber is preferably 0.10 mmol / g or more, more preferably 0.20 mmol / g or more, and more preferably 0.50 mmol / g or more per 1 g (mass) of cellulose fiber. 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 It is most preferable that it is / g or more. Further, the content of the phosphoric acid group is preferably 3.65 mmol / g or less, more preferably 3.5 mmol / g or less, and still more preferably 3.0 mmol / g or less. In addition, in this specification, content of the phosphoric acid group which cellulose fiber has is equal to the strong acidic radical weight of the phosphoric acid group which cellulose fiber has, as mentioned later.

  The content of the phosphate group contained in the cellulose fiber can be measured by the neutralization titration method. In the case of measurement by the neutralization titration method, the phosphate group is completely converted to the acid form, and then refinement is carried out by the mechanical treatment step (micronization step) to obtain the obtained fine fibrous cellulose-containing slurry, The amount introduced is determined by determining the change in pH while adding an aqueous sodium hydroxide solution.

  The phosphoric acid group is converted to the acid form by diluting the obtained phosphorylated cellulose fiber with ion-exchanged water so that the cellulose fiber concentration is 2% by mass, and while stirring, a sufficient amount of 1N aqueous hydrochloric acid solution is slightly added. Do this by adding In the conversion of the phosphate group to the acid form, the above-mentioned cellulose fiber-containing slurry is dewatered to obtain a dewatered sheet, which is then diluted again with ion exchange water, and the operation of adding 1N hydrochloric acid aqueous solution is repeated to repeat the cellulose fiber It is preferable to completely change the phosphate group contained in the acid form to the acid form. And after the conversion process to the acid type of a phosphoric acid group, after stirring the obtained cellulose fiber containing slurry and making it disperse | distribute uniformly, it is excess by repeating the operation which obtains filtration dehydration and obtains a dehydration sheet. It is preferable to wash away the hydrochloric acid sufficiently.

  In the mechanical treatment step (the refining step), ion-exchanged water is poured into the obtained dewatered sheet to obtain a cellulose fiber-containing slurry having a cellulose fiber concentration of 0.3% by mass, and the slurry is subjected to disintegration processing (M Processing is performed at 21500 rpm for 30 minutes using Technics Inc., Claire Mix-2.2 S). Thus, a fine fibrous cellulose-containing slurry is obtained.

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

  FIG. 1 illustrates a curve obtained by plotting the measured pH against the amount of alkali (aqueous sodium hydroxide solution) added in the neutralization titration. The area up to the first end point is called a first area, and the area up to the second end point is called a second area. Note that there is a third area after the second area. That is, three regions 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 It becomes equal to.

The crosslinked structure is considered to be formed by dehydration condensation of the phosphate groups introduced into the cellulose fiber. That is, the crosslinked structure is a structure in which a glucose unit of cellulose is linked via an O atom, one to two P atoms of pyrophosphate. Therefore, when the crosslinked structure is formed, the weakly acidic groups are apparently lost, and the amount of alkali required until the second end point is smaller than the amount of alkali required until the first end point. Here, when the phosphoric acid groups introduced into the cellulose fibers are not condensed at all, the amount of strongly acidic groups introduced into the cellulose fibers is equal to the amount of weakly acidic groups. Therefore, the value obtained by dividing the amount of weakly acidic groups lost due to the formation of the crosslinked structure by 2 represents the amount of crosslinked structure (the number of crosslinking points). That is, the amount of cross-linked structure (the number of crosslinking points) is obtained by dividing the difference between the amount of alkali required for the first end point (the amount of first dissociated alkali) and the amount of alkali required for the second end point (the second dissociated alkali amount) by 2. It is equal to the The amount of crosslinking structure (the number of crosslinking points) is represented by the following formula (1).
Cross-linked structure amount (cross-linking score) = (strongly acidic group content in cellulose fiber-weakly acidic group content in cellulose fiber) / 2 Formula (1)

  In the present invention, the crosslinked structure amount (the 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, 0. It is more preferable that it is 25 mmol / g or more. The upper limit value of the amount of crosslinking structure (the number of crosslinking points) is, for example, 1.82 mmol / g or less because it is a value obtained by dividing the amount of strongly acidic groups contained in the cellulose fiber by 2.

The water retention of the cellulose fiber is preferably 150% or more, more preferably 170% or more, and still more preferably 200% or more. The upper limit value of the water retention degree of the cellulose fiber is not particularly limited, but may be, for example, 1000%. Here, the water retention degree of the cellulose fiber is a value measured according to SCAN-C 62:00, and is a value calculated by the following equation. In the case of measuring the water retention of cellulose fiber, the cellulose fiber is subjected to centrifugal separation treatment at 20 ° C. and 4400 rpm (weight acceleration at the time of centrifugation: 3950 g) for 15 minutes. The amount of cellulose fiber to be subjected to centrifugation is 0.5 g (a basis weight of 1700 ± 100 g / m ² ) in terms of dry weight per measurement. As a centrifuge, for example, H-3R manufactured by Koksan can be used. The larger the water retention value, the higher the affinity between the cellulose fiber and water.
Water retention (%) = (weight of cellulose fiber after centrifugation treatment-absolute weight of cellulose fiber) / absolute 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 the inorganic ions, monovalent metal ions represented by alkali metal ions, divalent metal ions represented by alkaline earth metal ions, and other nonmetal cations, ammonium ions, aluminum ions, tin ions, Other examples include base metal ions such as lead ions, and transition metal ions such as silver ions, copper ions, and iron ions. The organic ions include organic ammonium ions and organic phosphonium ions. When it is desired to increase the degree of water retention, it is preferable to use a monovalent cation as a counter ion, and from the viewpoint of versatility, it is more preferable to use an ammonium ion and an alkali metal ion as a counter ion, and sodium ion and ammonium ion More preferably, it is a counter ion. On the other hand, when it is desired to impart functions such as deodorizing and antibacterial, it is preferable to use functional cations such as copper ions, silver ions and organic ammonium ions as counter ions.

(Optional ingredient)
The cellulose fiber-containing composition of the present invention may contain optional components other than cellulose fiber. Optional components include, for example, antifoaming agents, lubricants, surfactants, UV absorbers, dyes, pigments, fillers, stabilizers, organic solvents miscible with water such as alcohols, preservatives, organic particles, inorganic particles And resins (in the form of pellets, fibers) and the like.

(Method of producing composition)
In the method for producing a composition (method for producing a cellulose fiber-containing composition), a phosphoric acid group or a substituent derived from a phosphoric acid group is introduced into a cellulose fiber, and the crosslinking score of the cellulose fiber calculated by the following formula (1) is And a step of crosslinking the phosphate group or a substituent derived from the phosphate group to be 0.20 mmol / g or more. The water content of the composition thus obtained is 50% by mass or less.
Number of crosslinking points = (amount of strongly acidic group contained in cellulose fiber−amount of weakly acidic group contained in cellulose fiber) / 2 Formula (1)

<Phosphoric acid group introduction process>
The step of introducing a phosphate group or a substituent derived from a phosphate group into the cellulose fiber can be called a phosphate group introducing step. The step of crosslinking at least a part of the phosphate group or the substituent derived from the phosphate group is also included in the phosphate group introducing step. That is, the phosphate group introducing step includes a step of phosphorylating cellulose fiber and a step of crosslinking at least a part of the phosphate group or the substituent derived from the phosphate group.

  In the phosphoric acid group introducing step, at least one selected from a compound having a phosphoric acid group or a substituent derived from a phosphoric acid group and a salt thereof to cellulose fiber (hereinafter also referred to as "phosphorylating agent" or "compound A" Reaction can be carried out. Such phosphorylating agent may be mixed with dry or wet cellulose fiber in the form of powder or aqueous solution. As another example, a powder or an aqueous solution of a phosphating agent may be added to a cellulose fiber slurry. That is, the phosphoric acid group introducing step includes at least the step of mixing the cellulose fiber and the phosphorylating agent.

  The phosphoric acid group introducing step can be carried out by reacting a cellulose fiber with a phosphorylating agent, and this reaction is carried out of at least one selected from urea and derivatives thereof (hereinafter also referred to as "compound B") It may be performed in the presence.

  As an example of the method of causing compound A to act on cellulose fiber in the coexistence of compound B, a method of mixing powder or an aqueous solution of compound A and compound B with dry or wet cellulose fiber can be mentioned. Moreover, the method of adding the powder and aqueous solution of the compound A and the compound B to a cellulose fiber containing slurry as another example is mentioned. Among these, since the reaction uniformity is high, a method of adding an aqueous solution of Compound A and Compound B to cellulose fiber in a dry state, or adding a powder or an aqueous solution of Compound A and Compound B to cellulose fiber in a wet state The method is preferred. Compound A and Compound B may be added simultaneously or separately. Alternatively, the compound A and the compound B to be tested first may be added as an aqueous solution, and excess chemical solution may be removed by pressing. The form of the cellulose fiber is preferably cotton-like 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 phosphoric acid, lithium salts of phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, ammonium salts of phosphoric acid and the like, but are not particularly limited. Examples of lithium salts of phosphoric acid include lithium dihydrogen phosphate, dilithium hydrogen phosphate, trilithium phosphate, lithium pyrophosphate, lithium polyphosphate and the like. Examples of sodium salts of phosphoric acid include sodium dihydrogenphosphate, disodium hydrogenphosphate, trisodium phosphate, sodium pyrophosphate, sodium polyphosphate and the like. Examples of potassium salts of phosphoric acid include potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, and potassium polyphosphate. Examples of ammonium salts of phosphoric acid include ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium polyphosphate and the like. Among them, phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts 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 enhanced and the efficiency of phosphate group introduction is further enhanced. 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 the phosphoric acid group increases, and from the viewpoint of suppressing hydrolysis of cellulose fiber, pH 3 or more and pH 7 or less Is more preferred. The pH of the aqueous solution of the compound A may be adjusted by, for example, using a compound having a phosphoric acid group in combination of a compound exhibiting acidity and a compound exhibiting alkalinity, and changing its quantitative ratio. The pH of the aqueous solution of the phosphorylating agent (compound A) may be adjusted by adding an inorganic alkali or an organic alkali to a compound having an acid group among the compounds having a phosphoric acid group.

  The addition amount of the phosphorylation agent (compound A) to the cellulose fiber is not particularly limited, but when the addition amount of the phosphorylation agent (compound A) is converted to phosphorus atomic weight, the addition amount of phosphorus atom to the cellulose fiber (absolute dry mass) 0.5 to 100 mass% is preferable, 1 to 50 mass% is more preferable, and 2 to 30 mass% is the most preferable. If the addition amount of phosphorus atoms to the cellulose fiber is within the above range, the yield of the phosphorylated cellulose fiber can be further improved. By making the addition amount of the phosphorus atom with respect to a cellulose fiber into 100 mass% or less, the effect of a yield improvement and cost can be balanced. On the other hand, the yield can be increased by setting the addition amount of phosphorus atoms to the cellulose fiber to the above lower limit value or more.

  As compound B used in this embodiment, urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, 1-ethylurea and the like can be mentioned.

  The compound B is preferably used as an aqueous solution like the compound A. Further, it is preferable to use an aqueous solution in which both the compound A and the compound B are dissolved, because the uniformity of the reaction is enhanced. It is preferable that the addition amount of the compound B with respect to a cellulose fiber (absolute dry mass) is 1 mass% or more and 500 mass% or less, more preferably 10 mass% or more and 400 mass% or less, 100 mass% or more and 350 mass% It is more preferable that it is the following, and it is especially preferable that it is 150 to 300 mass%.

  In addition to the compound A and the compound B, amides or amines may be included in the reaction system. Examples of the 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 phosphoric acid group introduction step preferably includes a heating step (hereinafter also referred to as a heat treatment step). By providing the heat treatment step, a phosphoric acid group can be efficiently introduced into the cellulose fiber, and at least a part of the phosphoric acid group or a substituent derived from the phosphoric acid 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 phosphating agent, and the process of heating the mixture of a cellulose fiber and a phosphating agent.

  As the heat treatment temperature in the heat treatment step, it is preferable to select a temperature at which the phosphoric acid group can be efficiently introduced while suppressing the thermal decomposition or hydrolysis reaction of the cellulose fiber. Moreover, heat processing temperature selects the temperature which bridge | crosslinks the substituent derived from a phosphoric acid group or a phosphoric acid group so that the crosslinking score of the cellulose fiber calculated by Formula (1) mentioned above may be 0.20 mmol / g or more. It is preferable to do. Specifically, the heat treatment temperature is preferably 50 ° C. or more and 300 ° C. or less, more preferably 100 ° C. or more and 250 ° C. or less, and still more preferably 130 ° C. or more and 200 ° C. or less. For heating, a vacuum dryer, an infrared heater, or a microwave heater may be used.

  During the heat treatment, while water is contained in the cellulose fiber-containing slurry to which Compound A is added, when the time for which the cellulose fiber is allowed to stand for a long time, Compound A dissolved with water molecules along with drying is on the cellulose fiber surface. Moving. Therefore, unevenness may occur in the concentration of the compound A in the cellulose fiber, and there is a possibility that the introduction of the phosphoric acid group to the cellulose fiber surface does not progress uniformly. In order to suppress the occurrence of uneven concentration of Compound A in the cellulose fiber due to drying, use a very thin sheet of cellulose fiber or heat dry or vacuum dry while kneading or stirring the cellulose fiber and Compound A with a kneader etc. You should take the method.

  The heating device used for the heat treatment is preferably a device capable of constantly discharging the water held by the slurry and the water produced by the addition reaction to the hydroxyl groups of the fibers such as phosphoric acid groups, for example, an air-blowing oven. Etc. is preferred. In addition to being able to suppress the hydrolysis reaction of the phosphate ester bond which is the reverse reaction of phosphoric acid esterification by always draining the water in the device system, it is also possible to suppress the acid hydrolysis of the sugar chain in the cellulose fiber 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 phosphating agent and the cellulose fiber are mixed and exposed to the heat source, and preferably 5 seconds or more It is more preferable that it is 270 minutes or less, and it is further more preferable that they are 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 still more preferably 30 seconds or more. When the heat treatment temperature is 100 ° C. or more and 250 ° C. or less, it is preferable to set the upper limit of the heating time to 15000 seconds or less. In the present invention, by setting the heat treatment temperature and the heating time to an appropriate range, the introduction amount of the phosphate group can be set to a preferable range.

  The phosphate group introduction step may be performed at least once, but can be repeated multiple times. In this case, more phosphate groups are introduced, which is preferable.

<Disintegration and cleaning process>
It is preferable that a disintegration step is provided after the phosphoric acid group introduction step, and a washing step is further preferably provided after the disintegration step. The disaggregation process is performed according to JIS P 8220. That is, the disaggregation process is a process for making the phosphated cellulose fiber obtained in the phosphoric acid group introduction process into a uniform pulp suspension. In this step, the phosphorylated cellulose fiber is preferably about the same size as a general paper pulp (for example, width 20 μm to 30 μm, length average fiber length 0.1 mm to 3.0 mm) . In the case where a suspension in which the phosphorylated cellulose fibers are sufficiently dispersed can be obtained without performing the disaggregation step, the disaggregation step may be omitted.

  In the washing step, excess chemical solution such as a phosphating agent is washed away. In the washing step, it is preferable to repeat the operation of filtering and dewatering the phosphorylated cellulose fiber which has been subjected to the disaggregation treatment, pouring the ion-exchanged water, and stirring and uniformly dispersing.

<Alkali treatment process>
It is preferable to provide an alkali treatment step after the phosphoric acid group introduction step and the disaggregation step. By providing the alkali treatment step, it is possible to variously change the counter ion of the phosphorylated cellulose fiber. For example, when sodium hydroxide is selected as the alkali, the counter ion of the phosphorylated cellulose fiber can be made 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, and in this case, one counter ion of the phosphoric acid group of phosphorylated cellulose fiber is an ammonium ion, The counter ion of is hydrogen ion.

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

The temperature of the alkali solution in the alkali treatment step is not particularly limited, but is preferably 5 ° C. or more and 80 ° C. or less, and more preferably 10 ° C. or more and 60 ° C. or less.
The immersion time in the alkali solution in the alkali treatment step is not particularly limited, but is preferably 5 minutes to 30 minutes, and more preferably 10 minutes to 20 minutes.
The use amount of the alkali solution in the alkali treatment is not particularly limited, but it is preferably 100% by mass or more and 100000% by mass or less, and preferably 1000% by mass or more and 10000% by mass or less based on the dry weight of the phosphorylated cellulose fiber. Is more preferred.

  In order to reduce the amount of alkali 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 the handleability.

<Other counter ion change processing>
The counter ion can also be changed by contacting the salt of inorganic alkali or the salt of organic alkali with the phosphorylated cellulose fiber instead of the above-mentioned alkali treatment step. For example, when sodium chloride is selected as the salt of inorganic alkali, the counter ion of phosphorylated cellulose fiber can be sodium. In addition, when alkyl ammonium chloride is selected as the salt of organic alkali, the counter ion of the phosphorylated cellulose fiber can be made to be alkyl ammonium.

<Disintegration processing>
When the cellulose fiber used in the present invention is a fine fibrous cellulose having a fiber width of 1000 nm or less, a defibration treatment step may be provided after the alkali treatment step. In the defibration treatment step, fibers are usually defibrated using a defibration treatment device to obtain a fine fibrous cellulose-containing slurry, but the treatment device and treatment method are not particularly limited.
As the defibration processing apparatus, a high-speed fibrillation machine, a grinder (millstone type crusher), a high pressure homogenizer, an ultrahigh pressure homogenizer, a high pressure collision type crusher, a ball mill, a bead mill, etc. can be used. Alternatively, use an apparatus for wet grinding such as a disc refiner, a conical refiner, a twin screw kneader, a vibration mill, a homomixer under high speed rotation, an ultrasonic disperser, or a beater as a defibration treatment apparatus. You can also. The defibration processing apparatus is not limited to the above. As a preferable defibration treatment method, a high-speed fibrillation machine, a high pressure homogenizer, and an ultrahigh pressure homogenizer, which are less affected by the grinding media and less likely to be contaminated, can be mentioned.

<Sheet forming 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 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 non-woven fabric. In the step of forming a sheet using phosphorylated cellulose fiber, the forming method may be appropriately selected according to the nature and the shape of the sheet. In the present embodiment, for example, a method such as a wet papermaking method or a dry papermaking method can be employed.

  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 a wet papermaking method is demonstrated.

First, in the wet paper making process, ion-exchanged water is added to the phosphorylated cellulose fiber obtained in the process described above 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 fourdrinier paper machine, twin wire paper machine, cylinder paper machine, inclined wire paper machine, single mesh paper machine, Yankee paper machine and the like. Alternatively, papermaking may be performed using a hand-drawing device.

  The sheet obtained in the wet papermaking process is preferably subjected to a dewatering and drying process. In the dehydration step, dehydration may be performed by pressing the sheet. The pressure at this time is preferably 1 MPa or more, more preferably 5 MPa or more, and still more 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 can be easily obtained even when pressure is applied under the above conditions in the dehydration step.

  In the sheet forming step, in the case of using a dry papermaking method, the phosphorylated cellulose fibers are uniformly mixed in the air, the air flow containing the phosphorylated cellulose fibers, and the mesh endless belt provided with a suction box on the lower side. To form a sheet. That is, the dry papermaking method is a method including the step of mixing and depositing the phosphorylated cellulose fiber 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 dewatering and drying step of the sheet is not particularly limited. In addition, as a heat transfer medium, a method such as bringing a metal plate or metal roll into direct contact with the sheet can be appropriately employed.

  A pressing operation may be further performed on the sheet after the dehydration and drying step. The pressure at this time is preferably 1 MPa or more, more preferably 5 MPa or more, and still more 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 pressure | voltages on the said conditions, a bulky sheet | seat is easy to be obtained.

(Use)
The application 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 non-woven fabric. The cellulose fiber-containing composition is used, for example, as a component of absorbent articles such as sweat, urine, menstrual blood, harmful chemicals, etc. in the state of fluff pulp or non-woven fabric, or used as sanitary paper, filter material, buffer material, etc. Be done.

  The features of the present invention will be more specifically described below with reference to examples and comparative examples. The materials, amounts used, proportions, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as limited by the specific examples shown below.

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

<Disintegration and cleaning process>
Ion-exchanged water was poured to the obtained phosphorylated cellulose fiber A so that the cellulose fiber concentration would be 2% by mass, and the mixture was subjected to disaggregation treatment with a 2 L-volume tabletop disintegrator for 20 minutes. The obtained pulp slurry is filtered and dewatered to obtain a dewatered sheet, and then ion-exchanged water is poured again, and stirring and uniform dispersion are repeated to wash away excess chemical solution sufficiently, and phosphated cellulose fiber B I got

<Alkali treatment process>
The obtained phosphorylated cellulose fiber B is diluted with ion exchanged water so that the cellulose fiber concentration is 2% by mass, 1N aqueous sodium hydroxide solution is added little by little while stirring, and the pH is 12 ± 0.2. Pulp slurry was obtained. Thereafter, the pulp slurry is dewatered to obtain a dewatered sheet, and then ion-exchanged water is poured again, and after stirring and dispersing uniformly, filtration dewatering to obtain a dewatered sheet is repeated to obtain excess water. The sodium oxide was thoroughly washed away to obtain phosphorylated cellulose fiber C containing phosphorylated cellulose. And the water retention degree of the phosphorylated cellulose fiber C was measured by the method mentioned later. Moreover, the content of the phosphate group introduction amount and the cross-linked structure of the phosphorylated cellulose fiber C was measured by the method described later.

<Sheet formation / press 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 I got a sheet. The cellulose fiber-containing sheet was dried in a humidity control room at 23 ° C. and a relative humidity of 50% until the weight became constant. Next, a 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 sheet density was calculated in accordance with JIS P 8118: 1998. In addition, as a paper thickness gauge, a high bridge paper thickness gauge (No. 735 manufactured by Takahashi Manufacturing Co., Ltd.) was used. Moreover, the water content (water content) and water absorption speed of the cellulose fiber containing sheet A were measured by the method mentioned 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. The same measurement as in Example 1 was performed for the obtained phosphorylated cellulose fiber and cellulose fiber-containing sheet.

(Example 3)
Example 1 and Example 1 except that in the above-mentioned <phosphorylation reaction step> the drying and heat treatment time is 300 seconds, and in the above <breaking and washing step>, the disintegration time in the disintegrator is 15 minutes. Similarly, a phosphated cellulose fiber and a cellulose fiber-containing sheet were obtained. The same measurement as in Example 1 was performed for the obtained phosphorylated cellulose fiber and cellulose fiber-containing sheet.

(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. The same measurement as in Example 1 was performed for the obtained phosphorylated cellulose fiber and cellulose fiber-containing sheet.

(Comparative example 1)
<Disintegration process>
As softwood kraft pulp, pulp manufactured by Oji Paper Co., Ltd. (solid content 96 mass%, basis weight 213 g / m ² sheet) was used as a raw material. Ion-exchanged water was poured so that the cellulose fiber concentration would be 2% by mass, and the mixture was deaggregated for 5 minutes with a 2 L desktop disintegrator. The obtained pulp slurry was filtered and dewatered to obtain a cellulose fiber A '. The water retention of cellulose fiber A 'was measured by the method described later.

<Sheet formation / press 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. The cellulose fiber-containing sheet was dried in a humidity control room at 23 ° C. and a relative humidity of 50% until the weight became constant. Subsequently, the cellulose fiber containing sheet A 'was obtained by pressing for 60 seconds under pressure 11.57 Mpa. By measuring the thickness after pressing, the density of the cellulose fiber-containing sheet A ′ was calculated. Moreover, the water content (water content) and water absorption speed of cellulose fiber containing sheet A 'were measured by the method mentioned later.

(Comparative example 2)
In the above-mentioned <phosphorylation reaction step>, the drying and heat treatment time is set to 200 seconds, and in the above <decomposition and washing step>, the same procedure as in Example 1 is carried out except that the treatment with the disintegrator is not performed. A sheet containing phosphorylated cellulose fiber and cellulose fiber was obtained. The same measurement as in Example 1 was performed for the obtained phosphorylated cellulose fiber and cellulose fiber-containing sheet. In Comparative Example 2, ion exchanged water was added, and only slight manual stirring was performed, and the phosphocellulose fiber was uniformly dispersed in water, and therefore the disintegrator was not 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. The same measurement as in Example 1 was performed for the obtained phosphorylated cellulose fiber and cellulose fiber-containing sheet.
In Comparative Example 3, ion exchanged water was added, and only slight manual stirring was performed, and the phosphated cellulose fiber was uniformly dispersed in water, and therefore the disintegrator was not used.

(Analysis and evaluation)
<Measurement of water retention>
The water retention of the cellulose fiber was measured according to SCAN-C 62:00. In the case of measuring the water retention of the cellulose fiber, the cellulose fiber was subjected to centrifugation for 15 minutes under conditions of 20 ° C. and 4400 rpm (weight acceleration at the time of centrifugation: 3950 g). The amount of cellulose fibers used in the centrifugation treatment was 0.5 g (a basis weight of 1700 ± 100 g / m ² ) in bone dry weight per measurement. As a centrifuge, H-3R manufactured by Koksan Corporation was used. The water retention rate was calculated by the following equation.
Water retention (%) = (weight of cellulose fiber after centrifugation treatment-absolute weight of cellulose fiber) / absolute weight of cellulose fiber × 100
The larger the water retention value, the higher the affinity between the cellulose fiber and water.

<Measurement of phosphate group introduction amount>
The introduced amount of phosphate group was measured by the neutralization titration method. Specifically, the phosphate group contained in the cellulose fiber is completely converted to an acid form, and then refining is carried out by the mechanical processing step (the refining step). The amount introduced was determined by determining the change in pH exhibited by the slurry (dispersion liquid) while adding an aqueous 1 N sodium hydroxide solution.
In conversion of the phosphate group to the acid form, dilute the obtained phosphorylated cellulose fiber with ion-exchanged water so that the concentration of cellulose fiber is 2% by mass, and while stirring, add a small amount of 1N aqueous hydrochloric acid solution for a while Was added one by one. Next, the cellulose fiber-containing slurry is stirred for 15 minutes and then dewatered to obtain a dewatered sheet, which is then diluted again with ion exchanged water, and the operation of adding 1 N hydrochloric acid aqueous solution is repeated to obtain phosphoric acid contained in cellulose fiber. The group was completely converted to the acid form. Furthermore, the cellulose fiber-containing slurry was stirred to be dispersed uniformly, and then the operation of obtaining a dewatered sheet by filtration dewatering was repeated to wash away excess hydrochloric acid sufficiently.
In the mechanical treatment step, ion-exchanged water was poured into the obtained dewatered sheet to obtain a cellulose fiber-containing slurry having a cellulose fiber concentration of 0.3% by mass. This slurry was treated for 30 minutes at 21500 revolutions / minute using a fibrillation treatment apparatus (manufactured by Emtechnic Co., Ltd., Clearmix-2.2 S). In the titration using an alkali, the change in the pH value of the dispersion was measured while adding a 0.1 N aqueous solution of sodium hydroxide to the fine fibrous cellulose-containing slurry.

In this neutralization titration, in the curve obtained by plotting the measured pH against the amount of addition of alkali, two points at which the increment (the differential value of the pH with respect to the alkali dropping amount) is maximized are given (the point at which the increment is maximized) And the second largest point). Among them, the amount of alkali required up to the maximum point of the incrementally obtained (hereinafter referred to as the first end point) obtained by adding alkali first is equal to the amount of strongly acidic groups in the dispersion used for titration. The amount of alkali required until the maximum point of the incremental 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 amount of alkali (mmol) required until the first end point is divided by the solid content (g) in the dispersion to be titrated to obtain a first amount of dissociated alkali (mmol / g). It was introduced amount.

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

<Measurement of water content>
The moisture content is the weight of a cellulose fiber-containing sheet after drying to a balance state at 23 ° C. and a relative humidity of 50% in a humidity control chamber and then dried at 105 ° C. overnight. Was calculated and calculated using the following equation.
Moisture 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>
With regard to the water absorption rate, a cellulose fiber-containing sheet is cut into a strip-shaped sample having a width of 5 mm and a length of 50 mm, and the end region up to 5 mm from the longitudinal edge of this strip-shaped sample is ion exchanged water (electrical conductivity 2 μS / cm) Dipped below). Thereafter, the time required for the ion-exchanged water to reach a distance point of 45 mm in the longitudinal direction from the longitudinal direction edge was measured, and the water absorption speed (mm / sec) was calculated using the following equation (2).
Water absorption speed (mm / sec) = 40 (mm) / t (sec) Formula (2)
In Formula (2), t represents the time (sec) taken by the ion-exchanged water to reach a distance point of 45 mm in the longitudinal direction from the longitudinal edge of the strip sample.

  The cellulose fibers obtained in the examples had high water retention, and the cellulose fiber-containing sheet 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), both excellent water retention and high water absorption speed were compatible.

Claims (5)

A composition comprising a cellulose fiber having a phosphate group or a substituent derived from a phosphate group,
The phosphate group or the substituent derived from the phosphate group is cross-linked in at least a part of the cellulose fiber,
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 = (amount of strongly acidic group contained in cellulose fiber−amount of weakly acidic group contained in cellulose fiber) / 2 Formula (1)   The composition according to claim 1, which is a non-woven fabric. The composition is used as a strip sample having a width of 5 mm and a length of 50 mm, and the end region up to 5 mm from the longitudinal edge of the strip sample is immersed in ion exchange water (electrical conductivity 2 μS / cm or less) The water absorption speed (mm / sec) calculated by the following equation (2) is 2.5 mm / sec when the time taken for the ion exchange water to reach the 45 mm distance point in the longitudinal direction from the edge is measured. The composition according to claim 1 or 2, which is at least 100 mm / sec.
Water absorption speed (mm / sec) = 40 (mm) / t (sec) Formula (2)
In Formula (2), t represents the time (sec) taken by the ion-exchanged water to reach a distance point of 45 mm in the longitudinal direction from the longitudinal edge of the strip 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 (%) of the cellulose fiber calculated by the following formula is 150% or more.
Water retention (%) = (weight of cellulose fiber after centrifugation treatment-absolute weight of cellulose fiber) / absolute weight of cellulose fiber × 100
In the above equation, the degree of water retention is measured according to SCAN-C 62:00, but the conditions for centrifugation are 15 ° C. and weight acceleration 3950 g during centrifugation for 15 minutes.

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