JP2011140534A - High water-absorbing polymer - Google Patents

Abstract

The present invention provides a highly water-absorbing polymer comprising an ionic group-containing cellulose derivative that exhibits all the performances of water absorption after centrifugal dehydration, liquid passage speed under pressure, and water absorption speed in a well-balanced manner.
(1) A superabsorbent polymer obtained by reacting an ionic group-containing cellulose derivative (A) with a water-soluble crosslinking agent (B), wherein the ionic group-containing cellulose derivative (A) A superabsorbent polymer having an average degree of substitution of 1.1 or more and a viscosity in a 1% by mass aqueous solution of 130 mPa · s or more, and (2) the superabsorbent polymer and a hydrophilic inorganic compound. It is a superabsorbent polymer composition.
[Selection figure] None

Description

  The present invention relates to a superabsorbent polymer and a superabsorbent polymer composition using the same.

Superabsorbent polymers are used in the sanitary products field as superabsorbents in absorbent articles such as disposable diapers for infants, adults, and incontinents, and sanitary napkins for women. At present, polyacrylic acid-based water-absorbing polymers occupy the mainstream as high water-absorbing polymers. However, since the polyacrylic acid-based water-absorbing polymer uses petroleum as a raw material, there is a problem that the amount of CO ₂ emitted during production and disposal is large and the load on the global environment is large. Therefore, a highly water-absorbing polymer using plant-derived raw materials such as polysaccharides has been proposed.

For example, Patent Literature 1 discloses a crosslinked gel obtained by thermally crosslinking a carboxyalkyl cellulose derivative having an acidification rate of 79% or more and an absorbent body using the same, and Patent Literature 2 discloses an alkali metal of carboxymethyl cellulose. An absorptive material obtained by crosslinking a salt with a degree of crosslinking of 0.005 to 0.07 per glucose unit is disclosed. Patent Document 3 discloses an essential component of an alkali metal salt of a crosslinked carboxymethyl cellulose having a water absorption ratio of 100 times or more. An absorbent is disclosed.
Patent Document 4 discloses a highly water-absorbing and substantially granular carboxymethyl cellulose material prepared from a cellulose material having a degree of polymerization of 1000 or more and having an average degree of substitution of 0.2 to 0.9. Yes.

Patent Document 5 discloses a biodegradation made of cellulose polyvalent carboxylate, in which a part of cellulose skeleton includes glucose polyvalent glucose in which a part of hydroxyl groups of glucose ring constituting cellulose is substituted with polyvalent carboxylic acid. A water-absorbing material is disclosed.
Patent Document 6 also discloses that carboxyalkyl cellulose obtained from a pulp having a kappa value of about 1 to about 65 is reacted with a sufficient amount of a crosslinking agent to render the carboxyalkyl cellulose insoluble in water. The resulting superabsorbent composition is disclosed.
However, it is difficult to say that any of the above superabsorbent polymers has sufficient performance for use in absorbent articles such as sanitary goods, and particularly when superabsorbent polymers are used in absorbent articles. A highly water-absorbing polymer that exhibits all the performances of the water absorption amount after centrifugal dehydration, the liquid flow rate under pressure, and the water absorption rate, which are indicators of the above, in good balance has not been obtained.

JP 2008-247975 A JP-A-56-28755 JP-A-58-25160 JP-A-61-261301 JP-A-10-204101 JP 2006-199956 A

  It is an object of the present invention to provide a highly water-absorbing polymer comprising an ionic group-containing cellulose derivative that exhibits all the performances of water absorption after centrifugal dehydration, liquid passage speed under pressure, and water absorption speed in a well-balanced manner.

The present inventors have found that a superabsorbent polymer obtained by crosslinking an ionic group-containing cellulose derivative having a specific average degree of substitution and viscosity with a water-soluble crosslinking agent can solve the above problems.
That is, the present invention provides the following (1) and (2).
(1) A superabsorbent polymer obtained by reacting an ionic group-containing cellulose derivative (A) with a water-soluble crosslinking agent (B), wherein the average substitution degree of the ionic group-containing cellulose derivative (A) is A superabsorbent polymer having a viscosity of 1.1 or more and a viscosity in a 1% by mass aqueous solution of 130 mPa · s or more.
(2) A superabsorbent polymer composition comprising the superabsorbent polymer of (1) and a hydrophilic inorganic compound.

  ADVANTAGE OF THE INVENTION According to this invention, the superabsorbent polymer manufactured from the plant-derived raw material excellent in the water absorption amount after centrifugal dehydration, the liquid flow rate under pressure, and the water absorption rate is provided. By using the superabsorbent polymer of the present invention for a water-absorbent article, it is possible to provide a water-absorbent article that exhibits excellent water absorption after centrifugal dehydration, liquid passing speed under pressure, water absorption speed, and has comfort. it can.

(A) is a schematic sectional drawing of the state which decomposed | disassembled the filtration cylindrical tube of the liquid-flow rate measurement apparatus under pressure of a super absorbent polymer, (b) is a schematic sectional drawing of the weight rod of this apparatus. It is the schematic which shows the measuring apparatus of the water absorption rate of the super absorbent polymer used in the Example and the comparative example. It is the figure which plotted the water absorption after centrifugal dehydration of the superabsorbent polymer obtained in Examples 1 to 10 and Comparative Examples 1 to 7 and 9 to 11 on the horizontal axis and the flow rate under pressure on the vertical axis. .

The superabsorbent polymer of the present invention is a superabsorbent polymer obtained by reacting an ionic group-containing cellulose derivative (A) with a water-soluble crosslinking agent (B), the ionic group-containing cellulose derivative (A ) Is an average substitution degree of 1.1 or more, and its viscosity in a 1% by mass aqueous solution is 130 mPa · s or more.
Although the reason why the superabsorbent polymer of the present invention is excellent in the water absorption after centrifugal dehydration, the liquid passing rate under pressure, and the water absorption rate is not clear, the ionic group-containing cellulose derivative having a high aqueous solution viscosity has a high molecular weight. The crosslinked polymer is a highly water-absorbing polymer with a low water solubility compared to a polymer obtained by crosslinking an ionic group-containing cellulose derivative having a low aqueous solution viscosity. It is estimated that the liquid speed is improved.
In addition, a highly water-absorbing polymer comprising an ionic group-containing cellulose derivative having a high average substitution degree increases the density of ionic groups per unit mass and increases charge repulsion between polymer chains during water absorption. It is considered that the water absorption after centrifugal dehydration and the water absorption speed are improved as compared with a highly water-absorbing polymer comprising an ionic group-containing cellulose derivative having a low ionic group.

[Ionic group-containing cellulose derivative (A)]
The ionic group-containing cellulose derivative (A) used in the present invention contains, as an ionic group, an anionic group such as a carboxyl group, a sulfonic acid group, or a phosphoric acid group, or a cationic group such as an ammonium group. Derivatives can be used.

Specific examples of the ionic group-containing cellulose derivative (A) used in the present invention include carboxymethyl cellulose, carboxyethyl cellulose, carboxymethyl hydroxyethyl cellulose, carboxymethyl hydroxypropyl cellulose, carboxyethyl hydroxyethyl cellulose, carboxyethyl hydroxypropyl cellulose, sulfuric acid. Cellulose derivatives such as sulfonated cellulose, sulfated hydroxyethyl cellulose, sulfated hydroxypropyl cellulose, seurouronic acid, cationized hydroxyethyl cellulose, and cationized hydroxypropyl cellulose, and alkali metal salts thereof.
Among these ionic group-containing cellulose derivatives (A), from the viewpoint of production cost, carboxyalkyl cellulose having an alkyl group having 1 to 3 carbon atoms such as carboxymethyl cellulose and carboxyethyl cellulose, and alkali metal salts thereof are preferable.
Said ionic group containing cellulose derivative (A) can be used individually or in combination of 2 or more types.

(Neutralization degree of ionic group-containing cellulose derivative (A))
In order for the ionic group-containing cellulose derivative (A) to improve the affinity with water, it is desirable that a part of the ionic group is an alkali metal salt. In that case, the degree of neutralization can be arbitrarily adjusted, but from the viewpoint of reactivity with the crosslinking agent, the degree of neutralization is preferably lower than 100%, more preferably 98 to 80%, 95 More preferably, it is -85%. The degree of neutralization is calculated from the following formula.
Degree of neutralization = [(number of moles of alkali metal salt of ionic group per unit mass) / (number of moles of all ionic groups)] × 100 (%)

(Average substitution degree of ionic group-containing cellulose derivative (A))
Methods for measuring the average degree of substitution of the ionic group-containing cellulose derivative include a neutralization titration method, an ash alkali method, and a high performance liquid chromatography (HPLC) method. In the present invention, the average substitution degree was calculated by a neutralization titration method. Use the average degree of substitution.
The “average degree of substitution (DS)” is the average degree of substitution of the monosaccharide units constituting the polysaccharide with respect to the hydroxyl group.
The average degree of substitution of the ionic group-containing cellulose derivative according to the present invention is 1.1 or more, preferably 1.15 to 3.0. When the average degree of substitution is greater than 1.1, the ionic group density per unit mass increases, and charge repulsion between polymer chains during water absorption increases, which is preferable for use as a highly water-absorbing polymer.

(Viscosity of ionic group-containing cellulose derivative (A))
The viscosity of the 1% by weight aqueous solution of the ionic group-containing cellulose derivative (A) is such that a 200 ml aqueous solution of the ionic group-containing cellulose derivative is prepared so that the solid content is 1% by weight, and the condition of B is 25 ° C. and 60 rpm. It is the value of the viscosity measured with a type viscometer.
The 1 mass% aqueous solution viscosity of the ionic group-containing cellulose derivative (A) according to the present invention is 130 mPa · s or more, preferably 400 to 10000 mPa · s, more preferably 450 to 9000 mP · s, still more preferably 600 to 8000 mP · s, particularly preferably 850 to 5000 mPa · s. If the viscosity of a 1% by weight aqueous solution is within the above range, the highly water-absorbing polymer obtained by cross-linking this solution has less water-soluble content and is less likely to cause lumps during water absorption. The speed is thought to improve.
In addition, the shape of the ionic group-containing cellulose derivative (A) as a raw material can be appropriately selected according to the desired gel shape and the like, for example, powder (powder), granule, fiber, etc. It may be in the form of a sheet (or film) or cloth (nonwoven fabric, woven fabric, etc.).
A commercial item may be used for the said ionic group containing cellulose derivative, and what was manufactured using the conventional method (or application) may be used for it.

  Among the ionic group-containing cellulose derivatives, carboxyalkyl cellulose is, for example, cellulose (wood pulp, linter pulp, etc.) in a known method, for example, a step of producing alkali cellulose by reacting with alkali, and the obtained alkali. It can be produced through a step of reacting cellulose with an etherifying agent (carboxyalkyl etherifying agent). The cellulose used as a raw material may be in the form of powder, fiber, or the like.

As the step of producing the alkali cellulose, for example, a known method such as a slurry method or a kneader method can be used. Examples of the alkali used in the step of producing alkali cellulose include alkali metal hydroxides such as lithium, potassium and sodium, alkaline earth metal hydroxides such as magnesium, calcium and barium, and ammonia. It is done. In these, an alkali metal hydroxide is preferable and sodium hydroxide is more preferable.
The alkali is usually used in the form of an aqueous solution. In addition, the usage-amount of an alkali is 10-100 mass parts normally with respect to 100 mass parts of cellulose, Preferably it is 30-80 mass parts, More preferably, it is 40-70 mass parts.

The etherifying agent used in the step of reacting with the etherifying agent can be selected according to the type of carboxyalkyl cellulose, and examples thereof include monochloroacetic acid and monochloropropionic acid.
Usually, an alkali metal salt of carboxyalkyl cellulose is obtained after the etherification step.

  A carboxyalkyl cellulose having both a particularly high degree of substitution and a high viscosity as used in the present invention is not commercially available. However, for example, using a commercially available carboxyalkyl cellulose having a low degree of substitution as a raw material, after immersing the cellulose in an aqueous solution of the etherifying agent for several hours, add the required amount of sodium hydroxide while crushing and stirring with a crusher And can be produced by performing an etherification reaction (see separate chemical series 34-4, water-soluble polymer (new supplement 3rd edition), published by Chemical Industry Co., Ltd., p. 47).

[Water-soluble crosslinking agent (B)]
There is no restriction | limiting in particular in water-soluble crosslinking agent (B), Well-known compounds, such as a methylenebisacrylamide, epichlorohydrin, a polyglycidyl compound, an aldehyde compound, polycarboxylic acid, a vinyl ether compound, a methylol compound, polyisocyanate, a polyoxazoline compound Can be used.
Preferred examples of the water-soluble crosslinking agent (B) include (a) a compound having two or more hydroxyl groups in the molecule, (b) a compound having two or more polymerizable double bonds, and (c) two or more epoxies. And a compound having a group.
(A) As a compound having two or more hydroxyl groups in the molecule, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, polyglycerin, propylene glycol, diethanolamine, polyoxypropylene, sorbitan fatty acid ester, trimethylolpropane, Examples include pentaerythritol, 1,3-propanediol, and sorbitol.
(B) Examples of the compound having two or more polymerizable double bonds in the molecule include bis (meth) acrylamide, allyl (meth) acrylamide, and (meth) acrylic acid di- or polyester (for example, diethylene glycol diacrylate). , trimethylolpropane triacrylate, and polyethylene glycol diacrylate), C ₁ -C ₁₀ derived from the reaction of a polyhydric alcohol and 2-8 C ₂ -C ₄ alkylene oxide per hydroxyl group, unsaturated with polyols Examples thereof include di- or polyester of mono- or polycarboxylic acid (for example, ethoxylated trimethylolpropane triacrylate) and the like.

(C) As a compound having two or more epoxy groups in the molecule, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin triglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether And polyglycidyl ethers such as trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, and hydrogenated bisphenol A type diglycidyl ether.
Among these, from the viewpoint of reactivity and water absorption performance of the resulting polymer, (b) a compound having two or more polymerizable double bonds in the molecule, and (c) two or more epoxy groups in the molecule. (C) a compound having two or more epoxy groups in the molecule is more preferable, polyglycidyl ether is more preferable, and ethylene glycol diglycidyl ether is particularly preferable.

[Production of superabsorbent polymer]
The production method of the superabsorbent polymer of the present invention is not particularly limited as long as it is a method obtained by reacting the ionic group-containing cellulose derivative (A) and the water-soluble crosslinking agent (B).
The ratio of the ionic group-containing cellulose derivative (A) and the water-soluble crosslinking agent (B) is arbitrary, but the ratio of the water-soluble crosslinking agent (B) is 100 parts by mass of the ionic group-containing cellulose derivative (A). On the other hand, it is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, still more preferably 7 parts by mass or less, and most preferably 5 parts by mass or less. When the ratio is within these ratios, a highly water-absorbing polymer having sufficient gel strength is obtained, and the water absorption after centrifugal dehydration is high, which is preferable.
The superabsorbent polymer of the present invention may be a superabsorbent polymer containing a solvent (for example, water).
The superabsorbent polymer of the present invention does not include a gel obtained by crosslinking the ionic group-containing cellulose derivative (A) with heat without using the water-soluble crosslinking agent (B). This is because the gel crosslinked by heat in this way is not preferable in using as a highly water-absorbing polymer, such as not only having sufficient water absorption performance but also being colored by heating.

In producing the highly water-absorbing polymer of the present invention, in order to obtain a highly water-absorbing polymer exhibiting all the performance of the water absorption amount after centrifugal dehydration, the liquid flow rate under pressure, and the water absorption rate in a particularly high level with a good balance, The gel obtained by reacting the ionic group-containing cellulose derivative (A) with the water-soluble crosslinking agent (B) and crosslinking the ionic group-containing cellulose derivative (A) is once saturated and swollen with water, and then acetone or the like. A method of removing water from the gel using a water miscible solvent is effective.
The reason why it is possible to obtain a highly water-absorbing polymer that exhibits all the performances of the water absorption amount after centrifugal dehydration, the liquid flow rate under pressure, and the water absorption rate at a particularly high level in a well-balanced manner is not clear. I think so.
It is known that polysaccharides such as cellulose derivatives are physically cross-linked by dehydration and drying after hydration. One cause of this physical cross-linking is due to the formation of intermolecular hydrogen bonds between polysaccharides by removing water molecules held between the molecules by dehydration. Therefore, usually, when the gel obtained by crosslinking the ionic group-containing cellulose derivative (A) is water-containing and heat-dried, the water absorption after centrifugal dehydration is greatly reduced.
When the gel obtained by crosslinking the ionic group-containing cellulose derivative (A) is once saturated and swollen with water and dehydrated with a water-miscible solvent, free water is removed from the gel, but bound water is removed. Therefore, the physical cross-linking between the ionic group-containing cellulose derivatives (A) is suppressed, a high water absorption after centrifugal dehydration can be achieved, and the high liquid pressure and water absorption rates under pressure can be achieved at a particularly high level. It is believed that a water-absorbing polymer can be obtained.

[Form of superabsorbent polymer]
There is no restriction | limiting in particular in the shape of the super absorbent polymer of this invention, According to a use, it can select suitably. For example, it may be granular (powder), granule, fiber, etc., and may be a sheet (or film), cloth (nonwoven fabric, woven fabric, etc.). In order to increase the absorption rate, the sheet-like gel may be made porous by phase separation, or may be roughened to a matte surface on the surface. The gel may be composed of two or more different types of gels.
Examples of the powdery absorbent polymer include an indeterminate type, a block type, a bowl type, a spherical aggregation type, and a spherical type because of the difference in shape.
The average particle size of the powdery superabsorbent polymer is usually 0 from the viewpoint of obtaining excellent liquid permeability, water absorption, water absorption speed, and from the point of view of not causing discomfort when touching the human body in actual use. 0.1 to 1000 μm, preferably 1 to 950 μm, more preferably 10 to 900 μm, and still more preferably 100 to 850 μm. The average fiber length of the fibrous superabsorbent polymer is usually about 0.05 to 100 mm, preferably about 0.1 to 50 mm, and more preferably about 0.5 to 30 mm.
The average thickness of the sheet-like superabsorbent polymer is usually 0.01 to 100 mm, preferably 0.1 to 50 mm, more preferably 0.5 to 30 mm.

[Superabsorbent polymer composition]
The superabsorbent polymer composition of the present invention comprises the superabsorbent polymer of the present invention and a hydrophilic inorganic compound.
A hydrophilic inorganic compound is mix | blended from the viewpoint of the solidification performance of a bodily fluid, and a liquid return prevention property. Examples of such hydrophilic inorganic compounds include metal oxides such as silica, titanium oxide, aluminum oxide, magnesium oxide, and zinc oxide, and composite oxides such as zeolite. Among these, silica is preferable, amorphous silica is more preferable, and fumed silica is more preferable. The hydrophilic inorganic compound may be porous or non-porous.
The average primary particle size of the hydrophilic inorganic compound is preferably 3 to 30 nm, more preferably 5 to 20 nm, and still more preferably 5 to 15 nm, from the viewpoints of solidification performance of body fluids and liquid return prevention properties, and handling properties. is there.
Although the specific surface area of the hydrophilic inorganic compound is not particularly limited, from the same viewpoint as above, preferably 10~2000m ² / g, more preferably 50~1200m ² / g, more preferably 100~1000m ² / g It is.
The content of the hydrophilic inorganic compound is preferably 4 to 40% by mass, more preferably based on the total amount of the superabsorbent polymer composition, from the viewpoints of solidification performance of body fluid, anti-return properties, and moldability. 6 to 30% by mass.

Hereinafter, “parts” indicating the blending amounts all represent “solid mass parts”, and “%” is all “solid mass%”. The water absorption amount after centrifugal dehydration of the polymer, the liquid flow rate under pressure, and the water absorption rate were measured by the following methods.
(1) Measurement of average substitution degree of ionic group-containing cellulose derivative 1.0 g of 100% neutralized product of ionic group-containing cellulose derivative was once converted into an acid form with an excess of 1M aqueous hydrochloric acid, and then 0.1M hydroxylated. It was dissolved in 25 mL of an aqueous sodium solution, and excess sodium hydroxide was adjusted with a 0.1 M aqueous hydrochloric acid solution. Here, the parameter A was calculated from the amount of hydrochloric acid required for proper determination by the following formula. Here, A is the amount (ml) of 1N hydrochloric acid aqueous solution necessary for neutralizing 1 g of the ionic group-containing cellulose derivative in acid form.
Parameter A (ml / g) = 0.1 × {25 × (factor of 0.1M aqueous sodium hydroxide) − (amount of 0.1M hydrochloric acid required for determination (ml)) × (0.1M aqueous hydrochloric acid) Factor)} / (absolute dry weight of acid type ionic group-containing cellulose derivative (g))
Next, parameter A was substituted into the following formula, and the average degree of substitution of the ionic group-containing cellulose derivative was calculated.
Average substitution degree of ionic group-containing cellulose derivative = (0.162 × A) / (1−0.058A)

(2) Measurement of viscosity of 1% by weight aqueous solution of ionic group-containing cellulose derivative 200 mL of an aqueous solution was prepared so that the solid content of the aqueous solution of the ionic group-containing cellulose derivative was 1% by weight. (Manufactured by Tokyo Keiki Co., Ltd.) was used to measure the viscosity at 25 ° C. and 60 rpm.

(3) Measurement of the degree of neutralization of the superabsorbent polymer A sodium hydroxide solution is appropriately added dropwise to the ion-exchange aqueous solution of the superabsorbent polymer, and a pH meter (manufactured by Horiba, Ltd., pH ion meter D53, electrode type). 6583) was used to measure the pH of the solution. At this time, the degree of neutralization (mol%) was calculated from the number of moles of carboxy groups in the superabsorbent polymer and the number of moles of sodium hydroxide added, and the degree of neutralization was plotted on the horizontal axis and the pH plotted on the vertical axis. A neutralization titration curve was drawn.
Next, 0.1 g of the superabsorbent polymer was put into 20 ml of ion-exchanged water, and after stirring for 10 minutes, the pH of the stirred solvent was measured. From the obtained pH value, the neutralization titration curve was used. The target degree of neutralization was calculated.

(4) Measurement of water absorption after centrifugal dehydration of superabsorbent polymer 1 g of polymer particles were swollen with 150 mL of physiological saline (0.9% NaCl aqueous solution, manufactured by Otsuka Pharmaceutical Co., Ltd.) for 30 minutes, and then 250 mesh nonwoven fabric. Put in a bag, dehydrate in a centrifuge at 143 G for 10 minutes, and measure the total mass (total mass) after dehydration. And the amount of water absorption after centrifugal dehydration is measured according to the following formula.
Water absorption after centrifugal dehydration (g / g) = [(total weight−weight of nonwoven fabric bag−weight of polymer particles−remaining amount of nonwoven fabric bag liquid) / (weight of polymer particles)]
Here, the remaining amount of nonwoven fabric bag liquid = (weight of nonwoven fabric after centrifugal dehydration−weight of nonwoven fabric bag).

(5) Measurement of under-pressurization liquid passing speed of superabsorbent polymer Moreover, the under-pressurization liquid passing speed of superabsorbent polymer can be measured using the measuring apparatus shown in FIG. FIG. 1A is a schematic cross-sectional view of a state in which a filtration cylindrical tube of a liquid flow rate measuring device under pressure is disassembled, and FIG. 1B is a schematic cross-sectional view of a weight bar of the device. This measuring device is composed of a cylindrical tube (1), a wire mesh (2), a filtration cylindrical tube (a) composed of a narrow tube (4) with a cock (3), and a weight bar (b).
The procedure for measuring the flow rate under pressure using this measuring apparatus is as follows.
In a 200 mL glass beaker, a sufficient amount of physiological saline to swell 0.32 ± 0.005 g of the water-absorbing polymer as a measurement sample (for example, 0.9 mass that is 5 times or more the saturated absorption amount of the water-absorbing polymer) (Sodium chloride solution) and leave it for 30 minutes.
At the lower end of the vertically opened cylinder (1) (inner diameter 25.4 mm), a wire mesh (2) (mesh opening 150 μm, Biocolumn sintered stainless steel filter 30SUS sold by Sansho Co., Ltd.) and cock (3) A filtration cylindrical tube (a) provided with a thin tube (4) (inner diameter: 2 mm) (inner diameter: 4 mm, length: 8 cm) was prepared and swollen in the cylinder (1) with the cock (3) closed. All the contents of the beaker including the measurement sample are charged. Open the cock (3) and adjust the liquid level in the cylinder (1) to 5 cm above the 60 mL scale line. Next, a cylindrical rod (6) having a diameter of 2 mm with a metal mesh (5) (aperture 150 μm, diameter 25 mm) at the tip is inserted into the cylinder (1) so that the metal mesh (5) and the measurement sample are in contact with each other. Further, a weight (7) is placed so that a load of 2.0 kPa is applied to the measurement sample. After leaving in this state for 1 minute, the cock (3) is opened to allow the liquid to flow, and the time T ₁ (second) until the liquid level in the cylinder (1) decreases by 20 mL is measured. The flow rate of physiological saline under pressure is calculated.
Flow rate under pressure (mL / min) = 20 × 60 / (T ₁ −T ₀ )
In the formula, T ₁ (second) indicates the time required for 20 ml of physiological saline to pass with the absorbent polymer placed in the filtration cylindrical tube, and T ₀ (second) indicates the absorbency in the filtration cylindrical tube. It shows the time required for 20 ml of physiological saline to pass with no polymer added.
The measurement was performed five times, and the average value of the remaining three points was taken as the measured value, except for the values at the upper and lower points.

(6) Measurement of water absorption rate of superabsorbent polymer The water absorption rate of superabsorbent polymer was measured by the DW method. As a device for carrying out the DW method, a water absorption rate measuring device (10) (Demand Wettability Tester) shown in FIG. 2 is used, and a polymer spray table (11) in which the surface of the physiological saline W is set at the same level as the burette (12). ) (70 mmφ, No. 2 filter paper placed on glass filter No. 1), 0.3 g of superabsorbent polymer P is sprayed, and the superabsorbent polymer is sprinkled with water absorption of 0, 60 After a second, the amount of decrease in the level of the physiological saline W was read from the scale of the burette (12), and the amount of water absorption was measured to obtain the water absorption rate (mL / min).

Production Example 1 (Production of ionic group-containing cellulose derivative 1)
In a 2 L separable flask, 498 g of 2-propanol, 68.4 g of sodium hydroxide, 81.8 g of ion-exchanged water, an ionic group-containing cellulose derivative (Nippon Paper Chemical Co., Ltd., carboxymethyl cellulose, trade name: Sun 100 g of Rose A300SH) was charged, stirred at room temperature for 1 hour, and then heated to 60 ° C. over 30 minutes. To this was added a mixture of 107.75 g of monochloroacetic acid and 107 g of 2-propanol, and after stirring for 1 hour at 60 ° C., a mixture of 22.8 g of sodium hydroxide and 15.2 g of ion-exchanged water was added. , Reacted at 70 ° C. for 90 minutes. The reaction solution was filtered, and the resulting powder was washed 3 times in 2 L of 80% methanol, finally washed with 2 L of methanol, and dried under reduced pressure in a 60 ° C. dryer for 12 hours to obtain a white powder. 100 g (100% neutralization degree) of the white powder obtained as described above was dispersed in 500 g of an 80% aqueous methanol solution in a 1 L beaker. 60 ml of 1M hydrochloric acid was added thereto, and after stirring for 30 minutes with a stirring blade, filtration was performed. The obtained white powder was washed with 500 ml of 80% aqueous methanol solution three times. Finally, it was washed with 500 ml of methanol and dried under reduced pressure for 4 hours or more in a 50 ° C. dryer to obtain an ionic group-containing cellulose derivative 1.

Production Examples 2 to 7 (Production of ionic group-containing cellulose derivatives 2 to 7)
In a 1 L beaker, commercially available ionic group-containing cellulose derivatives listed in Table 1 (Nippon Paper Chemical Co., Ltd., carboxymethylcellulose, “Sunrose” series, or Daicel Chemical Industries, Ltd., carboxymethylcellulose sodium, trade name: 100 g of Ernest gum FDM (degree of neutralization 100%) was dispersed in 500 g of an 80% aqueous methanol solution. A predetermined amount of 1M hydrochloric acid was added thereto, and after stirring for 30 minutes with a stirring blade, filtration was performed. The obtained white powder was washed with 500 ml of 80% aqueous methanol solution three times. Finally, it was washed with 500 ml of methanol and dried under reduced pressure for 4 hours or more in a 50 ° C. dryer to obtain ionic group-containing cellulose derivatives 2 to 7. The amount of 1M hydrochloric acid to be added was adjusted so as to achieve the neutralization degree shown in Table 1.

Examples 1 to 10 and Comparative Examples 1 to 11 (Production of superabsorbent polymer)
In a 250 ml Teflon (registered trademark) container, as an ionic group-containing cellulose derivative (A), ionic group-containing cellulose derivatives 1 to 7 obtained in Production Examples 1 to 7, water-soluble crosslinking agent (B) as ethylene Glycol diglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-810, epoxy equivalent: 113) and ion-exchanged water were charged so as to have the concentrations and amounts of cross-linking agent shown in Table 2, and a hybrid mixer (manufactured by Keyence Corporation, HM-500) for 10 minutes. Reaction was performed by heating the obtained ionic group-containing cellulose derivative aqueous solution in a 70 ° C. oven for the time shown in Table 2. The hydrogel obtained after the reaction was pulverized with a pulverizer to obtain hydrogel fragments.
The hydrogel fragments were charged into a 5 L container made of SUS equipped with a stirring blade, added with 4.5 L of ion exchange water, stirred for 30 minutes, filtered, and the swollen gel on the filter paper was collected. The swollen gel was again immersed in 4.5 L of ion-exchanged water, and filtered after 30 minutes to collect the swollen gel. Add twice the mass of acetone to the collected swollen gel in a 5 L beaker, add the swollen gel while stirring with a stirring blade, stir for 1 hour, filter, and add the powdered gel on the filter paper. It was collected. The obtained powdered gel was immersed in 1 L of acetone, stirred for 1 hour, and then filtered to collect the powdered gel on the filter paper. The obtained powdery gel was pulverized with a pulverizer and washed twice with 500 g of acetone to obtain a powdery gel of a superabsorbent polymer.
The obtained powdery gel was classified with a sieve having an aperture of 850 μm and 106 μm, and a powdery gel having a particle size of 106 μm or more and 850 μm or less was obtained. 0.5% by mass of fumed silica (manufactured by Nippon Aerosil Co., Ltd., trade name: Aerosil # 200, average primary particle size: 14 nm, specific surface area: 200 m ² / g) is mixed with the obtained powdered gel. A superabsorbent polymer composition was obtained. Table 2 and FIG. 3 show the results of measuring the production conditions of the superabsorbent polymer, the water absorption after centrifugal dehydration, and the water absorption speed.

  From Table 2 and FIG. 3, the superabsorbent polymer of the example has the same water absorption rate as that of the superabsorbent polymer of the comparative example, but is superior in the water absorption amount after centrifugal dehydration and the liquid passing rate under pressure. I understand that.

The superabsorbent polymer of the present invention is a superabsorbent polymer excellent in water absorption after centrifugal dehydration, water absorption speed and liquid permeability under pressure. Therefore, the superabsorbent polymer of the present invention is useful for sanitary materials such as sanitary napkins, disposable diapers, adult sheets, tampons, and sanitary cotton. In addition, since the raw material of the superabsorbent polymer is derived from a plant, the amount of CO ₂ emitted during production and disposal is small, and the burden on the global environment is small. Furthermore, the superabsorbent polymer is expected to be applied to cosmetics where it is important to be manufactured from natural raw materials.

a: Filtration cylindrical tube of measuring device for measuring the flow rate of superabsorbent polymer under pressure b: Weight bar 1: Cylinder Wire mesh Cock 4. 4. Tubular with cock Wire mesh Cylindrical bar 7. Weight W: Saline P: Superabsorbent polymer 10: Measuring device for water absorption rate of superabsorbent polymer 11: Polymer spray table 12: Burette

Claims (6)

  A superabsorbent polymer obtained by reacting an ionic group-containing cellulose derivative (A) with a water-soluble crosslinking agent (B), wherein the average degree of substitution of the ionic group-containing cellulose derivative (A) is 1.1. A superabsorbent polymer having a viscosity of 130 mPa · s or higher in a 1% by mass aqueous solution.   The superabsorbent polymer according to claim 1, wherein the ionic group-containing cellulose derivative (A) is carboxyalkyl cellulose and an alkali metal salt thereof.   The superabsorbent polymer according to claim 1 or 2, wherein the viscosity of a 1% by mass aqueous solution of the ionic group-containing cellulose derivative (A) is 400 to 10,000 mPa · s.   The superabsorbent polymer according to any one of claims 1 to 3, wherein the water-soluble crosslinking agent (B) is a compound having two or more epoxy groups in the molecule.   The superabsorbent polymer in any one of Claims 1-4 whose ratio of a water-soluble crosslinking agent (B) is 20 mass parts or less with respect to 100 mass parts of ionic group containing cellulose derivatives (A).   A superabsorbent polymer composition comprising the superabsorbent polymer according to any one of claims 1 to 5 and a hydrophilic inorganic compound.

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