JP2017048296A - Water-absorbing resin and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polysaccharide-based water-absorbing resin which can be produced with a simple method without modification of a resin and contamination of an additive, is excellent in speed of water absorption, and has high water absorption to an electrolyte aqueous solution, and to provide a method for producing the same.SOLUTION: There is provided a polysaccharide-based water-absorbing resin which is a water-absorbing resin having a bulk density of 0.10-0.28 g/cm, and is obtained by crosslinking polysaccharides, where the polysaccharides are a cellulose derivative.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a polysaccharide water-absorbing resin that is excellent in water absorption speed, that is, absorbs liquid quickly and has high water absorption with respect to an aqueous electrolyte solution, and a method for producing the same. More specifically, the present invention relates to a polysaccharide water-absorbing resin which is not accompanied by resin modification or additive mixing and has a high water absorption rate produced by a simple method and has a high water absorption with respect to an aqueous electrolyte solution, and a method for producing the same. .

  The water-absorbent resin absorbs several tens to several hundred times as much water as its own weight. As the water-absorbent resin, a polyacrylic acid crosslinked product is mainly used, and it is widely used in sanitary products such as paper diapers and sanitary products, civil engineering, food, and agriculture. In particular, when using water-absorbing resin in paper diapers and sanitary products, if the resin absorbs the liquid quickly, the time for the liquid to touch the skin of the user of the paper diaper or sanitary product is shortened. Can be reduced. Thus, there is a demand for a water-absorbing resin that has a high water absorption rate, that is, a rate of absorbing a predetermined amount of liquid. In general, the water absorption speed of a water-absorbent resin is affected by the surface area of particles, capillary action, mamako formation, surface wettability, and the like. Therefore, in improving the water absorption speed of the acrylic acid-based water-absorbing resin, the resin is made porous (Patent Document 1), the resin and the inorganic substance are mixed (Patent Document 2), or the resin is coated with a surfactant (Patent Document 3). ) Etc. are taken.

  On the other hand, as a water-absorbing resin having high water absorption with respect to an aqueous solution containing an electrolyte, a crosslinked carboxymethyl cellulose (Patent Document 4), a crosslinked carboxyethyl cellulose (Patent Document 5), a crosslinked guar gum, a crosslinked carrageenan (Patent Document 6), and the like. A polysaccharide cross-linked product of has been studied. These have attracted attention as water-absorbing resins for hygiene products because they have high water absorption with respect to electrolyte solutions and are excellent in biodegradability.

US Pat. No. 5,314,420 JP-A-61-58657 Japanese Patent Laid-Open No. 3-62745 International Publication No. 2012/147225 JP 2010-18670 A JP 2003-154262 A

Sanyo Kasei News, 2010 No. 458

  Acrylic acid SAP (Super Absorbent Polymer) is usually pulverized after drying (Non-patent Document 1). Therefore, it has a polyhedral surface shape composed of a relatively flat surface of particles. It is conceivable that the water absorption rate of the water-absorbent resin increases as the surface area of the resin increases. Regarding the method for improving the water absorption rate of an acrylic acid-based water-absorbent resin, making the resin porous (Patent Document 1) increases the manufacturing cost due to an increase in manufacturing steps. In addition, mixing of the resin and the inorganic substance (Patent Document 2) reduces the proportion of the water-absorbing resin component in the product due to the addition of the additive to the resin. Further, coating of a resin with a surfactant (Patent Document 3) is accompanied by a decrease in water absorption due to modification of the resin.

  On the other hand, the polysaccharide water-absorbing resin has high water absorption with respect to the electrolyte solution and is suitable for hygiene products. However, the polysaccharide water-absorbing resin is inferior in water absorption rate as compared with the acrylic acid water-absorbing resin. For this reason, the method of improving the water absorption speed | rate of the polysaccharide water absorbing resin with high water absorption with respect to electrolyte aqueous solution is calculated | required.

  The present invention provides a polysaccharide-based water-absorbing resin produced by a simple method without modification of the resin and mixing of additives, having an excellent water absorption rate and having high water absorption with respect to an aqueous electrolyte solution, and a method for producing the same Is to provide.

The present invention relates to a water absorbent resin having a bulk density of 0.10 to 0.28 g / cm ³ .

  Moreover, this invention relates to the said water absorbing resin whose water absorption rate is 1.00 g / gs or more.

  The present invention also relates to the above water-absorbent resin in which a polysaccharide is crosslinked.

  Moreover, this invention relates to the said water absorbing resin whose said polysaccharide is a cellulose derivative.

  Moreover, this invention relates to the said water absorbing resin whose said cellulose derivative is carboxymethylcellulose.

  The present invention also relates to a method for producing a water-absorbent resin, characterized by pulverizing a swollen gel.

  Moreover, this invention relates to the manufacturing method of the said water absorbing resin using the gel obtained by bridge | crosslinking a polysaccharide.

  Moreover, this invention relates to the manufacturing method of the said water absorbing resin whose said polysaccharide is a cellulose derivative.

  Moreover, this invention relates to the manufacturing method of the said water absorbing resin whose said cellulose derivative is carboxymethylcellulose.

  Moreover, this invention relates to the manufacturing method of the said water absorbing resin which performs swelling of resin with the liquid mixture which is compatible with water.

  Moreover, this invention relates to the manufacturing method of the said water absorbing resin whose mass% of the water in the said liquid mixture is 50 to 90%.

  Moreover, this invention relates to the manufacturing method of the said water absorbing resin whose swelling degree of a gel is 30-90 g / g.

  Moreover, this invention relates to the manufacturing method of the said water absorbing resin which stirs and grind | pulverizes a gel.

Moreover, this invention relates to the manufacturing method of the said water absorbing resin obtained by substituting the resin after grinding | pulverization with the organic solvent compatible with water, and drying.

  According to the present invention, since the additive is not mixed, the water absorption speed can be improved without reducing the ratio of the water absorbent resin in the product.

  In addition, since the chemical composition of the resin is not modified, the water absorption rate can be improved without reducing the water absorption of the resin.

In addition, since the step of improving the water absorption rate of the resin also serves as the resin crushing step, the water absorption rate can be improved without increasing the synthesis step.

It is a figure which shows the surface shape which has the unevenness | corrugation of the water absorbing resin obtained in Example 1. FIG. It is a figure which shows the surface shape which has the unevenness | corrugation of the water absorbing resin obtained in Example 2. FIG. It is a figure which shows the flat surface shape of the water absorbing resin obtained by the comparative example 1. FIG. It is a figure which shows the flat surface shape of the water absorbing resin obtained in the comparative example 2.

  The present invention relates to a polysaccharide water-absorbing resin having an excellent water absorption rate and high water absorption with respect to an aqueous electrolyte solution and a method for producing the same. More specifically, the present invention relates to a polysaccharide water-absorbing resin that is excellent in water absorption speed and is highly water-absorbing with respect to an aqueous electrolyte solution, and a method for producing the same.

  First, the water absorbent resin will be described. A water-absorbing resin is a resin that can absorb water several to several hundred times its own weight. The water-absorbing resin may be used alone or in combination.

  The water-absorbing resin may be any water-absorbing resin containing an anionic functional group such as a carboxyl group or a sulfone group, and a water-absorbing resin obtained by crosslinking a polymer such as a polysaccharide or a synthetic polymer can be used. These resins may be used alone or in combination.

  When the polysaccharide is cross-linked, examples of the polysaccharide include, but are not limited to, polysaccharides, polysaccharide derivatives, and alkali metal salts such as sodium salts and potassium salts thereof. Examples of polysaccharides and polysaccharide derivatives include cellulose, methylcellulose, ethylcellulose, cellulose nitrate, cellulose sulfate, cellulose acetate, hydroxymethylcellulose, cationized cellulose, hydroxyethylcellulose, hydroxypropylcellulose, ethylhydroxycellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, carboxy Ethylcellulose, gum arabic, guar gum, locust bean gum, pectin, tragacanth, corn starch, xanthan gum, dextrin, gelatin, casein, sodium chondroitin sulfate, starch, oxidized starch, acetylated starch, phosphorylated starch, agar, carrageenan, alginic acid, hyaluron Examples include sodium acid. These sodium salts and potassium salts are also included. In particular, carboxymethyl cellulose is preferable from the viewpoint of water absorption with respect to the aqueous electrolyte solution.

  When cross-linking polysaccharides, as a cross-linking agent, polyhydric epoxy compounds having two or more functional groups, polyhydric aldehydes, polycarboxylic acids, polyvalent isocyanates, polyvalent vinyls, polyvalent acrylates, Examples include polyvalent methacrylates and polyvalent halogens, but substances having different functional groups such as epichlorohydrin and glycidyl methacrylate can also be used, but are not limited thereto.

  For example, polyhydric epoxies such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polyhydric aldehydes such as glutaraldehyde, glyoxal and terephthalaldehyde. Polyhydric carboxylic acids such as malic acid, citric acid, tartaric acid, polyacrylic acid, maleic acid and succinic acid, polyvalent isocyanates such as diphenylmethane diisocyanate, hexamethylene diisocyanate, toluene diisocyanate and isophorone diisocyanate, and many such as divinylsulfone -Valent vinyls, polyvalent acrylates such as polyethylene glycol diacrylate, polyethylene glycol dimethacrylate Polyvalent methacrylates such rate or the like on halo such as epichlorohydrin, although polyvalent halogens include, but are not limited thereto. Since a hydroxyl group which is a hydrophilic functional group is formed after the reaction, a polyvalent epoxy compound is preferable from the viewpoint of the hydrophilicity of the generated compound. In particular, ethylene glycol diglycidyl ether is preferred from the viewpoint of the high proportion of the epoxy group in the molecular structure, that is, the low epoxy equivalent.

  Cross-linked synthetic polymers include cross-linked polyacrylic acid neutralized products, self-crosslinked polyacrylic acid neutralized products, saponified vinyl acetate-acrylic acid ester copolymers, and acrylate-acrylamide copolymers. One or more water-absorbing resins such as a crosslinked polymer, a crosslinked product of acrylic acid-2-acrylamido-2methylpropanesulfonic acid copolymer salt, and a crosslinked product of isobutylene-maleic anhydride copolymer salt are listed. . In the above, examples of the salt include water absorbent resin particles such as sodium salt, potassium salt, ammonium salt, amine salt (alkylamine salt such as methylamine and trimethylamine; alkanolamine salt such as triethanolamine and diethanolamine). Can be mentioned.

  When the water absorbent resin is carboxyalkyl cellulose, the weight average molecular weight is preferably 1000 or more, more preferably 10,000 or more, and further preferably 100,000 or more. The weight average molecular weight is preferably 10 million or less, more preferably 5 million or less, and further preferably 4 million or less. If the weight average molecular weight is 1000 or more, sufficient water absorption performance can be secured, and if it is 10 million or less, it is easy to knead during synthesis.

  When the water absorbent resin is carboxyalkyl cellulose, the substitution degree of the carboxyl group is preferably 0.1 or more, more preferably 0.3 or more, and further preferably 0.5 or more. Further, the degree of substitution of the carboxyl group is preferably 2.5 or less, more preferably 1.4 or less, and even more preferably 1.1 or less. If the degree of substitution of the carboxy group is 0.1 or more, water absorption as the water absorbent resin particles tends to be sufficiently achieved. Further, if the degree of substitution of the carboxy group is 2.5 or less, crosslinking proceeds sufficiently and water-insoluble resin particles insoluble in water tend to be obtained. In addition, a substitution degree shows the average value of the number by which the hydroxyl group per glucose ring was substituted by the carboxy group.

  The water absorption ratio of the water absorbent resin is preferably 40 g / g or more with respect to 1 g of the water absorbent resin. When the water absorption ratio is 40 g / g or more, there is a tendency that a sufficient water absorption amount can be achieved while suppressing the amount of water-absorbing resin particles used. 50 g / g or more is more preferable, and 60 g / g or more is more preferable. There is no particular upper limit for the water absorption ratio, but 3000 g / g or less is preferable because the strength of the gel is lowered and the handleability at the time of water absorption is deteriorated. In addition, a water absorption magnification is obtained by the measuring method mentioned later.

The water retention ratio of the water absorbent resin is preferably 40 g / g or more with respect to 1 g of the water absorbent resin. When the water absorption ratio is 40 g / g or more, there is a tendency that a sufficient water absorption amount can be achieved while suppressing the amount of water-absorbing resin particles used. 50 g / g or more is more preferable, and 60 g / g or more is more preferable. There is no particular upper limit for the water retention ratio, but it is preferably 3000 g / g or less because the strength of the gel is reduced and the handleability during water absorption is poor. The water retention ratio is a numerical value of the characteristic that water is not re-released even when pressurized.

When the bulk density of the water absorbent resin is 0.10 to 0.28 g / cm ³ , a good water absorption rate can be exhibited. Further, more preferably 0.17~0.23g / cm ^3, more preferably 0.15~0.25g / cm ^3.

  If the water absorption rate of the water-absorbent resin is 1.00 g / gs or more, urine can be rapidly absorbed when mounted on a diaper. Moreover, 1.50 g / gs or more is more preferable, and it is further more preferable if it is 2.00 g / gs or more. There is no particular upper limit for the water absorption rate.

Next, the swelling process will be described. In the present invention, the swelling of the water-absorbent resin is carried out by stirring the high-grade aqueous resin in water or a mixed solution of an organic solvent that is compatible with water using a stirring blade for 5 minutes at 100 min ⁻¹ and allowing to stand for 1 hour. To swell.

In the present invention, the degree of swelling is defined as follows. The mass of the resin dried at 60 ° C. for 3 hours or more was defined as (A), and the water absorbent resin was swollen with water or a mixed solution of water and an organic solvent. The mass of the resin after swelling was taken as (B), and the mass (C) after putting it in a bag of nylon 20 cm in size of 20 cm × 10 cm and hanging down for 15 minutes was measured. The value obtained from the following formula (1) was defined as the degree of swelling of the resin. When the resin is swollen in advance, the resin mass at the measured value is used as the mass of the resin.
Swelling degree of resin [g / g] = (C-A-B) / A (1)
When the swelling degree in the swelling step is 30 to 90 g / g, irregularities are formed on the particle surface when pulverized, and dehydration is facilitated. When it is 30 g / g or more, irregularities are formed on the particle surface when pulverized. Moreover, dehydration becomes easy as it is 90 g / g or less.
The degree of swelling is further preferably 35 to 85 g / g, and more preferably 40 to 80 g / g.

  Next, the organic solvent will be described. In the present invention, the organic solvent only needs to be compatible with water.

  Examples of the organic solvent include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, acetonitrile and the like, and one or a mixture of two or more thereof. Can be used.

  If the ratio of the water in the liquid mixture of water and an organic solvent is 50-90 mass%, the water | moisture content in a gel can be easily dehydrated at a subsequent dehydration process. When the ratio of water is 50% by mass or more, the gel swells. Moreover, when it is 90 mass% or less, the quantity of the organic solvent used for dehydration can be reduced.

  Moreover, the ratio of water in the mixed liquid of water and organic solvent is more preferably 55 to 85% by mass, and further preferably 60 to 80% by mass.

  Next, the grinding process will be described. In the present invention, the pulverization method may be any method as long as the resin is pulverized. Examples of the pulverization method include stirring, cutting, and ultrasonic irradiation, but are not limited thereto. Further, pulverization by stirring is simple and more preferable. By stirring in water, irregularities are formed on the particle surface.

  Next, the size of the resin after pulverization in water will be described. Since the resin after pulverization has irregularities, the long diameter portion was measured. If the resin after pulverization has a major axis of 470 to 4500 mm, the yield is preferable. When it is 400 mm or more, it becomes easy to recover the resin after drying. Moreover, drying becomes easy as it is 4500 mm or less.

  Further, the size of the resin after pulverization is more preferably a major axis of 480 to 4000 mm, and further preferably 490 to 3800 mm.

  Next, the dehydration method will be described. Dehydration is performed by immersing the swollen gel in a hydrophilic organic solvent. Examples of the organic solvent include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, acetonitrile, and the like.

(Water absorption ratio)
The water absorption magnification was measured with reference to JIS-K-7223-1996. 150 ml of artificial urine in a 200 ml beaker was stirred at 100 min ⁻¹ using a stirrer chip having a central diameter of 8 mm and a length of 30 mm and a magnetic stirrer, and about 0.5 g (A) of a water absorbent resin was added. Stirring was continued for 5 minutes and then allowed to stand for 55 minutes. Thereafter, the contents of the beaker were put into a bag having a size of 20 cm × 10 cm made of nylon 255 mesh, and the mass (B) after being suspended for 15 minutes was measured. Similarly, the mass (C) of only the bag was measured in the same manner. The water absorption magnification was determined from the formula (2). The composition of the artificial urine is used by dissolving 200 g of urea, 80 g of sodium chloride, 8 g of magnesium sulfate heptahydrate, and 6 g of calcium chloride dihydrate in 10 L of ion exchange water.
Artificial urine water absorption [g / g] = (B-A-C) / A (2)

(Water retention ratio)
After measuring the water absorption ratio by the above method, put the water absorbent resin after measuring the water absorption capacity into a 500 ml wide mouth bottle (made by Tech Jam Co., Ltd.), and the bottom of the nylon bag is from the bottom of the wide mouth bottle. The lid was closed so as to hold the bag with the lid so as to come to the 1/3 position. Subsequently, the jar was centrifuged at 1000 min ⁻¹ for 90 seconds using a centrifuge (SPREMA23, manufactured by Tommy Seiko Co., Ltd.). A nylon bag was taken out and the mass (D) was measured so as not to touch the water accumulated at the bottom of the wide-mouth bottle. Only the bag was centrifuged in the same manner, and the mass (C ′) was measured. The water retention magnification was determined from the equation (3).
Water retention magnification of artificial urine [g / g] = (D-A-C ') / A (3)

(Water absorption speed)
It carried out according to JIS-K-7224-1996. About 25 g (A) of artificial urine in a 50 ml beaker is stirred at 600 min ⁻¹ using a stirrer chip having a central diameter of 8 mm and a length of 30 mm and a magnetic stirrer, and about 1.0 g (B) of a water absorbent resin Was introduced. The timer was started simultaneously with the addition of the water-absorbent resin, and the time (C) required was measured with the point where the inclination of the vortex of the rotating liquid approached the plane as the end point. The water absorption rate was obtained from the equation (4).
Water absorption rate of artificial urine [(g / gs) = (A / B) / C (4)

(The bulk density)
In the present invention, the bulk density is measured as follows. 5 ml of the sample was put into a 5 ml graduated cylinder, and the mass of the sample was measured (A). Then, using a device with a mechanical tapping mechanism using a cam, tap the graduated cylinder until the sample volume becomes constant under the conditions of a height of 10 ± 1 mm and a tap speed of 180 times / minute or less, and measure the sample volume. (B). The bulk density was determined from the following formula (5).
Bulk density of sample [g / cm ³ ] = A / B (5)

  The bulk density becomes lower as the particle surface has more irregularities, that is, more voids. For this reason, it seems that the surface shape and the bulk density have a close correlation.

  Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the following examples.

[Measurement of weight average molecular weight]
The weight average molecular weight was measured by gel permeation chromatography (GPC) under the following conditions. The measurement solution was prepared by dissolving the sample in the eluent and filtering with a 0.45 μm membrane filter. The calibration curve was approximated by a cubic equation using pullulan and polyethylene glycol.
Apparatus: “RID-10A” (manufactured by Shimadzu Corporation, trade name)
Column: Gelpack (registered trademark) GL-W540 and Gelpack (registered trademark) GL-W560 (two in total) (manufactured by Hitachi Chemical Co., Ltd., trade name)
Eluent: 0.2Mol / l NaCl aqueous solution Sample concentration: 4mg / ml
Elution rate: 1 ml / min
Measurement temperature: 40 ° C
In addition, unless otherwise indicated, the molecular weight measurement in a present Example was performed on the same conditions as the above.

(Production Example 1)
28.4 g of carboxymethyl cellulose (weight average molecular weight 1.1 million, substitution degree 0.75) was dissolved in 255 mL of a 1.5 Mol / l sodium hydroxide aqueous solution. To this aqueous solution, 5.23 g of ethylene glycol diglycidyl ether was added and mixed with stirring at 30 ° C. for 2 hours. Thereafter, the mixture was allowed to stand at 60 ° C. for 6 hours to be heated and gelled. This gel was extruded with a potato masher having pores with a diameter of 2 mm, and cut to an appropriate size. The crushed gel was immersed in 500 mL of methanol for 3 hours, and water was removed with methanol. This operation was repeated twice. Then, it was made to dry at 60 degreeC with a vacuum dryer for 3 hours, and the carboxymethylcellulose crosslinked body was obtained.

(Production Example 2)
The carboxymethylcellulose crosslinked product produced in Production Example 1 is further pulverized, and sieves with sieve openings of 150 and 710 μm are stacked. A methylcellulose crosslinked product was obtained. Table 1 shows the bulk density, the water retention magnification with respect to the artificial urine fluid, and the water absorption rate.

Example 1
In a 3 L beaker, 540 ml of water was added, 6 g of the crosslinked carboxymethyl cellulose described in Production Example 1 was added, stirred, and then allowed to stand at room temperature for 1 hour to swell. It was 90 g / g when the swelling degree of the bridge | crosslinking carboxymethylcellulose sodium salt in this swelling condition was measured. To this mixture, 540 ml of acetone was further added, and stirring was performed at 600 min ⁻¹ for 1 hour using a stirring blade to grind the gel. Thereafter, the mixture was filtered to separate the gel, and the separated gel was dispersed in 900 ml of acetone and allowed to stand for 1 hour. Further, this mixed solution is filtered through a sieve having an opening of 150 μm to separate the gel, and the gel is dispersed in 540 ml of acetone and left to stand for 6 hours. A powdery water-absorbent resin was obtained as particles with a sieve opening between 150 and 710 μm. Table 1 shows the bulk density, the water retention magnification with respect to the artificial urine fluid, and the water absorption rate. Moreover, what observed the surface shape is shown in FIG. The surface of the resin produced in Example 1 had a structure with many irregularities.

(Example 2)
In a 1 L beaker, 120 ml of water and 80 ml of acetone were added and mixed. 6 g of the carboxymethylcellulose crosslinked product described in Production Example 1 was added to this mixed solution, stirred, and then allowed to stand at room temperature for 1 hour to swell. It was 31 g / g when the swelling degree of the bridge | crosslinking carboxymethylcellulose sodium salt in this swelling condition was measured. To this mixture, 70 ml of acetone was further added, and stirring was performed at 600 min ⁻¹ for 1 hour using a stirring blade to chop the gel. Thereafter, the mixture was filtered to separate the gel, and the separated gel was dispersed in 120 ml of acetone and then allowed to stand for 1 hour to replace most of the water in the gel with acetone. Further, this mixed solution is filtered to separate the gel, and the gel is dispersed in 120 ml of acetone and left to stand for 6 hours to sufficiently replace the water in the gel with acetone, and then the gel is filtered and dried. After that, the powder was lightly pulverized to have a particle size of 150 to 710 μm to obtain a powdery water absorbent resin. Table 1 shows the bulk density, the water retention magnification with respect to the artificial urine fluid, and the water absorption rate. Moreover, what observed the surface shape is shown in FIG. The surface of the resin produced in Example 2 had a structure with many irregularities.

  In the comparative example, since there is no resin pulverization step, the resin of Production Example 2 having a particle diameter of 150 to 710 μm was used.

(Comparative Example 1)
In a 3 L beaker, 540 ml of water was added, and 6 g of the crosslinked carboxymethyl cellulose described in Production Example 2 was added. After stirring, the mixture was allowed to stand at room temperature for 1 hour to swell. It was 90 g / g when the swelling degree of the bridge | crosslinking carboxymethylcellulose sodium salt in this swelling condition was measured. A further 900 ml of acetone was added to this mixture, and then this was dispersed in 900 ml of acetone, and then allowed to stand for 1 hour to replace most of the water in the gel with acetone. Further, the mixture is filtered to separate the gel, and the gel is dispersed in 540 ml of acetone and left for 6 hours to sufficiently replace the water in the gel with acetone, and then the gel is filtered and dried. After that, the partially agglomerated particles were lightly pulverized and the particle size was adjusted to 150 to 710 μm to obtain a powdery water absorbent resin. Table 1 shows the bulk density, the water retention magnification with respect to the artificial urine fluid, and the water absorption rate. Moreover, what observed the surface shape is shown in FIG. The surface of the resin produced in Comparative Example 1 was smoother than the surfaces produced in Examples 1 and 2.

(Comparative Example 2)
A 300 ml beaker was mixed with 120 ml of water and 80 ml of acetone. To this, 2 g of potassium chloride was dissolved. 6 g of the carboxymethylcellulose crosslinked product described in Production Example 2 was added to this mixed solution, stirred, and then allowed to stand at room temperature for 1 hour to swell. It was 31 g / g when the swelling purity of the bridge | crosslinking carboxymethylcellulose sodium salt in this swelling condition was measured. Thereafter, this was dispersed in 120 ml of acetone and allowed to stand for 1 hour, and most of the water in the gel was replaced with acetone. Further, this mixed solution is filtered to separate the gel, and the gel is dispersed in 120 ml of acetone and left to stand for 6 hours to sufficiently replace the water in the gel with acetone, and then the gel is filtered and dried. After that, the partially agglomerated particles were lightly pulverized and the particle size was adjusted to 150 to 710 μm to obtain a powdery water absorbent resin. Table 1 shows the bulk density, the water retention magnification with respect to the artificial urine fluid, and the water absorption rate. Moreover, what observed the surface shape is shown in FIG. The surface of the resin produced in Comparative Example 2 was smoother than the surfaces produced in Examples 1 and 2.

Claims (14)

A water absorbent resin having a bulk density of 0.10 to 0.28 g / cm ³ .   The water absorbent resin according to claim 1, wherein the water absorption rate is 1.00 g / gs or more.   The water-absorbent resin according to claim 1 or 2, wherein a polysaccharide is crosslinked.   The water absorbent resin according to any one of claims 1 to 3, wherein the polysaccharide is a cellulose derivative.   The water-absorbent resin according to claim 1, wherein the cellulose derivative is carboxymethyl cellulose.   A method for producing a water-absorbent resin, comprising pulverizing a swollen gel in a liquid.   The method for producing a water absorbent resin according to claim 6, wherein the gel is a cross-linked polysaccharide.   The method for producing a water absorbent resin according to claim 7, wherein the polysaccharide is a cellulose derivative.   The method for producing a water-absorbent resin according to claim 8, wherein the cellulose derivative is carboxymethylcellulose.   The method for producing a water-absorbent resin according to any one of claims 6 to 9, wherein the swollen gel absorbs water and a mixed solution compatible with water.   The method for producing a water-absorbent resin according to any one of claims 6 to 10, wherein a mass% of water in the mixed solution is 50 to 90%.   The method for producing a water-absorbent resin according to any one of claims 6 to 11, wherein the swelling degree of the swollen gel is 30 to 90 g / g.   The method for producing a water-absorbent resin according to any one of claims 6 to 12, wherein the pulverization in the liquid is stirred in the mixed liquid.   The method for producing a water-absorbent resin according to any one of claims 6 to 13, which is obtained by replacing the pulverized resin with an organic solvent compatible with water and drying.

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