Method for producing water-absorbent resin

Abstract

To improve water absorption performance and stability of the water absorption performance of a polysaccharide-based water-absorbing resin using a polysaccharide as a raw material.SOLUTION: A method for producing a polysaccharide-based water-absorbing resin obtained by crosslinking a polysaccharide, the method comprising a crosslinking step of crosslinking the polysaccharide with a crosslinking agent, wherein the crosslinking agent contains a crosslinking agent A having an acid dissociation constant pKa of 7 or more and 13 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-absorbent resin. [Background technology]

[0002] A water-absorbent resin is a resin that can absorb tens to thousands of times its own weight in water, and examples thereof include polyacrylic acid-based water-absorbent resins. These water-absorbent resins are widely used in disposable sanitary products due to their high water-absorbing properties. However, most sanitary products containing these water-absorbent resins are incinerated after use, raising concerns that the carbon dioxide generated during incineration may contribute to global warming. Under these circumstances, there is a demand for biodegradable polysaccharide-based water-absorbent resins made from polysaccharides as raw materials.

[0003] Patent Document 1 below proposes a starch-based water-absorbing material made from starch as a raw material (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-506022 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional polysaccharide-based water-absorbent resins made from polysaccharides as raw materials have room for improvement in terms of water absorption performance and stability of water absorption performance.

[0006] An object of the present invention is to improve the water absorption capacity and stability of the water absorption capacity of a polysaccharide-based water-absorbent resin in which polysaccharides are used as raw materials. [Means for solving the problem]

[0007] The present invention provides a method for producing a polysaccharide-based water-absorbent resin obtained by crosslinking a polysaccharide, a crosslinking step of crosslinking the polysaccharide with a crosslinking agent, The crosslinking agent contains a crosslinking agent A having an acid dissociation constant pKa of 7 or more and 13 or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to improve the water absorption capacity and stability of the water absorption capacity of a polysaccharide-based water-absorbent resin in which polysaccharides are used as raw materials. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Method for producing polysaccharide-based water-absorbent resin> The method for producing a polysaccharide-based water absorbent resin of the present embodiment is a method for producing a water absorbent resin obtained by crosslinking a polysaccharide, and includes a crosslinking step of crosslinking the polysaccharide with a crosslinking agent, and the crosslinking agent contains a crosslinking agent A having an acid dissociation constant pKa of 7 or more and 13 or less. According to the method for producing a polysaccharide-based water absorbent resin of the present embodiment, it is possible to improve the water absorption performance and stability of the water absorption performance of a polysaccharide-based water absorbent resin in which a polysaccharide is used as a raw material.

[0010] [Polysaccharides] From the viewpoint of improving water absorption performance, the polysaccharide is preferably one or more selected from the group consisting of starch, cellulose, dextrin, pectin, carrageenan, gum arabic, and modified products thereof, and more preferably one or more selected from the group consisting of modified starch and modified cellulose.

[0011] Examples of starches include one or more selected from the group consisting of corn starch, potato starch, wheat starch, tapioca starch, and rice starch. Examples of cellulose include one or more selected from the group consisting of cotton, wood-derived pulp, bacterial cellulose, and lignocellulose.

[0012] From the viewpoint of improving water absorption performance, the modified product is preferably a polysaccharide into which a carboxyalkyl group has been introduced, and is preferably one or more selected from the group consisting of carboxyalkyl starch and carboxyalkyl cellulose, and more preferably one or more selected from the group consisting of carboxymethyl starch and carboxymethyl cellulose.

[0013] [Crosslinking process] From the viewpoint of improving water absorption performance, the crosslinking agent contains a crosslinking agent A having an acid dissociation constant pKa of 7 or more and 13 or less. In this specification, the acid dissociation constant pKa can be a value listed in the Bordwell pKa table (https: / / organicchemistrydata.org / hansreich / resources / pka / ).

[0014] The acid dissociation constant of the crosslinking agent A is 7 or more from the viewpoint of improving the stability of water absorption performance, and from the same viewpoint, it is 13 or less, more preferably 10 or less. If the acid dissociation constant of the crosslinking agent is less than 7, the crosslinking agent tends to be unevenly dispersed when added during the production process of the polysaccharide-based water absorbent resin, and the water absorption performance of the obtained polysaccharide-based water absorbent resin varies greatly depending on the amount of crosslinking agent added, making the water absorption performance of the polysaccharide-based water absorbent resin unstable. In addition, it is difficult to imagine a crosslinking agent with an acid dissociation constant greater than 13 that can be used for the polysaccharide-based water absorbent resin of the present invention.

[0015] From the viewpoint of improving the stability of water absorption performance, inorganic acids and inorganic acid salts can be used as the crosslinking agent A, and these may be used alone or in combination of two or more. The inorganic acids and inorganic acid salts are preferably at least one selected from the group consisting of boric acid, boronic acid, ammonium salts, and dihydrogen phosphate salts, more preferably at least one selected from the group consisting of boric acid, potassium dihydrogen phosphate, sodium dihydrogen phosphate, calcium dihydrogen phosphate, magnesium dihydrogen phosphate, ammonium chloride, ammonium dihydrogen phosphate, ammonium nitrate, ammonium acetate, ammonium formate, ammonium lactate, and ammonium sulfate, and even more preferably at least one selected from the group consisting of boric acid, potassium dihydrogen phosphate, and sodium dihydrogen phosphate.

[0016] From the viewpoint of improving the stability of water absorption performance, the content of the crosslinking agent A in the crosslinking agent is preferably 80% by mass or more, more preferably substantially 100% by mass, and even more preferably 100% by mass. In this specification, "substantially" means that the crosslinking agent A may be contained in an amount equivalent to that of an impurity.

[0017] In the crosslinking step, the amount of the crosslinking agent added is preferably 0.001 mmol or more, more preferably 0.1 mmol or more, per 1 g of the polysaccharide from the viewpoint of improving water absorption performance, and from the same viewpoint, is preferably 5 mmol or less, more preferably 2 mmol or less, per 1 g of the polysaccharide.

[0018] The crosslinking of the polysaccharide can be carried out by mixing the polysaccharide with the crosslinking agent and heating the mixture. Examples of a method for mixing the polysaccharide with the crosslinking agent include a method in which the polysaccharide and the crosslinking agent are uniformly mixed using a mixing device such as a cylindrical mixer, a screw mixer, a screw extruder, a turbulizer, a Nauta mixer, a double-arm kneader, a fluid mixer, a V-type mixer, a mincing mixer, a ribbon mixer, an airflow mixer, a rotating disk mixer, a conical blender, or a roll mixer.

[0019] The temperature at which the polysaccharide and the crosslinking agent are mixed is not particularly limited, but is preferably 10 to 150°C, more preferably 20 to 100°C, and particularly preferably 25 to 80°C.

[0020] After mixing the polysaccharide and the crosslinking agent, it is preferable to carry out a heat treatment. From the viewpoint of improving water absorption performance, the heating temperature in the heat treatment is 100 to 200°C, more preferably 110 to 170°C, and particularly preferably 120 to 160°C. The heating time in the heat treatment can be appropriately set depending on the heating temperature, but from the viewpoint of improving water absorption performance, it is preferably 5 to 100 minutes, more preferably 10 to 60 minutes.

[0021] [Shredding process] The method for producing a polysaccharide-based water absorbent resin of the present embodiment may include a shredding step of shredding the polysaccharide-based water absorbent resin, if necessary. The size (longest diameter) of the shredded polysaccharide-based water absorbent resin is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and particularly preferably 1 mm to 1 cm.

[0022] The shredding can be carried out by a known method, and can be carried out using a shredding device (for example, a Becks mill, a rubber chopper, a Farma mill, a mincing machine, an impact crusher, or a roll crusher).

[0023] In the pulverization step, the method for pulverizing the water absorbent resin composition containing the crosslinked polymer (A) is not particularly limited, and pulverization devices (for example, hammer pulverizers, impact pulverizers, roll pulverizers, and Schett airflow pulverizers) can be used. The particle size of the shredded polysaccharide water absorbent resin can be adjusted by sieving, etc., if necessary.

[0024] <Absorbent> The polysaccharide-based water-absorbent resin can be used to obtain an absorbent. The water-absorbent resin composition may be used alone or in combination with other materials. The structure and manufacturing method of the absorbent are similar to those known in the art (see, for example, JP 2003-225565 A, JP 2006-131767 A, and JP 2005-097569 A).

[0025] <Absorbent articles> The water-absorbent resin composition can be used to obtain an absorbent article. Specifically, the absorbent body described above is used. The absorbent article can be used not only for sanitary goods such as disposable diapers and sanitary napkins, but also for various applications such as anti-condensation agents, agricultural and horticultural water retention agents, waste blood solidification agents, disposable body warmers, and the like, for absorbing and retaining various aqueous liquids in various industrial fields, and as a gelling agent. The manufacturing method of the absorbent article is the same as known methods (disclosed in JP-A Nos. 2003-225565, 2006-131767, and 2005-097569, etc.). [Example]

[0026] The present invention will be further explained below with reference to examples and comparative examples, but the present invention is not limited thereto. The water retention capacity and other properties of the polysaccharide-based water-absorbent resin were measured in a room at 25±2°C and 50±5% RH using the following method. The polysaccharide-based water-absorbent resin was left to stand for 24 hours in a room at 25±2°C and 50±5% RH after production to reduce the water content to 3% by weight, and was used for each measurement. The acid dissociation constant pKa was determined using values ​​listed in Bordwell's pKa table (https: / / organicchemistrydata.org / hansreich / resources / pka / ).

[0027] <Measurement method> [Method for measuring water retention capacity] 1.00 g of a polysaccharide-based water-absorbent resin was placed in a tea bag (20 cm long, 10 cm wide) made from nylon mesh with a mesh size of 63 μm (JIS Z8801-1:2006), and the bag was immersed in 1,000 ml of ion-exchanged water for 1 hour without stirring, then removed and hung for 15 minutes to drain. The tea bag was then placed in a centrifuge and centrifuged at 150 G for 90 seconds to remove excess ion-exchanged water, and the mass (h1) including the tea bag was measured, and the water retention capacity was calculated using the following formula. Water retention amount (g / g)=(h1)-(h2) (h2) is the weight of the tea bag measured in the same manner as above, but without a measurement sample.

[0028] [Method for measuring the absorption capacity of ion-exchanged water] 1.00 g of a water-absorbent resin composition as a measurement sample was placed in a tea bag (20 cm long, 10 cm wide) made of nylon mesh with a mesh size of 63 μm (JIS Z8801-1:2006), and the bag was immersed in 1,000 ml of ion-exchanged water for 1 hour without stirring, then pulled out and hung for 15 minutes to drain. Thereafter, the weight (w1) including the tea bag was measured. The weight (w2) of the tea bag without the measurement sample was measured in the same manner as above. The absorption capacity of ion-exchanged water was calculated using the measured (w1) and (w2) and the following formula. Absorption capacity of ion-exchanged water (g / g) = (w1) - (w2)

[0029] [Evaluation of the degree of change in the physical properties of the water-absorbent resin with respect to the amount of crosslinking agent added] The absorption capacity (g / g) of the water-absorbent resin produced using each amount of crosslinking agent added was plotted on a graph with the horizontal axis representing "the amount of crosslinking agent added (mmol) per 1 g of polysaccharide" and the vertical axis representing "the absorption capacity (g / g) of the water-absorbent resin." A regression line was determined from these points by the least squares method, and the slope of the line was taken as "the degree of change in the physical properties of the water-absorbent resin relative to the amount of crosslinking agent added." It can be said that the smaller the value of "the degree of change in the physical properties of the water-absorbent resin relative to the amount of crosslinking agent added," the smaller the degree of change in the physical properties relative to the amount of crosslinking agent added, and the more stable the water-absorbent performance.

[0030] <Example> Example 1-1 7.2 parts of carboxymethyl starch as a polysaccharide and 0.144 parts of boric acid as crosslinker A were placed in a 300 ml glass beaker, and ion-exchanged water was added so that the total weight of the compounds in the beaker was 100 parts. The mixture was kneaded using a glass rod at one rotation per second for a total of 10 minutes until homogeneous. The kneaded mixture was dried at 140°C for 60 minutes to evaporate the water, yielding an absorbent (unmolded body). The absorbent was then crushed in a crusher and molded.

[0031] Example 1-2 A polysaccharide-based water-absorbent resin 1-2 was obtained in the same manner as in Example 1-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 1.

[0032] Examples 1-3 A polysaccharide-based water-absorbent resin 1-3 was obtained in the same manner as in Example 1-1, except that the amount of the crosslinking agent added was changed to the amount shown in Table 1.

[0033] Example 2-1 A polysaccharide-based water-absorbent resin 2-1 was obtained in the same manner as in Example 1-1, except that the type of crosslinking agent was changed to one shown in Table 1.

[0034] Example 2-2 A polysaccharide-based water-absorbent resin 2-2 was obtained in the same manner as in Example 2-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 1.

[0035] Example 2-3 A polysaccharide-based water-absorbent resin 2-3 was obtained in the same manner as in Example 2-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 1.

[0036] Example 3-1 A polysaccharide-based water-absorbent resin 3-1 was obtained in the same manner as in Example 1-1, except that the type of crosslinking agent was changed to one shown in Table 1.

[0037] Example 3-2 A polysaccharide-based water-absorbent resin 3-2 was obtained in the same manner as in Example 3-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 1.

[0038] Example 3-3 A polysaccharide-based water-absorbent resin 3-3 was obtained in the same manner as in Example 3-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 1.

[0039] Example 4-1 A polysaccharide-based water-absorbent resin 4-1 was obtained in the same manner as in Example 1-1, except that the type of crosslinking agent was changed to one shown in Table 1.

[0040] Example 4-2 A polysaccharide-based water-absorbent resin 4-2 was obtained in the same manner as in Example 4-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 1.

[0041] Example 4-3 A polysaccharide-based water-absorbent resin 4-3 was obtained in the same manner as in Example 4-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 1.

[0042] Example 4-4 A polysaccharide-based water-absorbent resin 4-4 was obtained in the same manner as in Example 4-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 1.

[0043] [Example 4-5] A polysaccharide-based water-absorbent resin 4-5 was obtained in the same manner as in Example 4-1, except that the amount of the crosslinking agent added was changed to the amount shown in Table 1.

[0044] Example 5-1 A polysaccharide-based water-absorbent resin 5-1 was obtained in the same manner as in Example 1-1, except that the type of crosslinking agent was changed to one shown in Table 2.

[0045] Example 5-2 A polysaccharide-based water-absorbent resin 5-2 was obtained in the same manner as in Example 5-1, except that the amount of the crosslinking agent added was changed to the amount shown in Table 2.

[0046] Example 5-3 A polysaccharide-based water-absorbent resin 5-3 was obtained in the same manner as in Example 5-1, except that the amount of the crosslinking agent added was changed to the amount shown in Table 2.

[0047] Example 6-1 A polysaccharide-based water-absorbent resin 6-1 was obtained in the same manner as in Example 1-1, except that the type of crosslinking agent was changed to one shown in Table 2.

[0048] Example 6-2 A polysaccharide-based water-absorbent resin 6-2 was obtained in the same manner as in Example 6-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 2.

[0049] Example 6-3 A polysaccharide-based water-absorbent resin 6-3 was obtained in the same manner as in Example 6-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 2.

[0050] Comparative Example 1-1 A polysaccharide-based water-absorbent resin C1-1 was obtained in the same manner as in Example 1-1, except that the type and amount of the crosslinking agent were changed to those shown in Table 2.

[0051] Comparative Example 1-2 A polysaccharide-based water-absorbent resin C1-2 was obtained in the same manner as in Comparative Example 1-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 2.

[0052] Comparative Examples 1-3 A polysaccharide-based water-absorbent resin C1-3 was obtained in the same manner as in Comparative Example 1-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 2.

[0053] Comparative Example 2-1 A polysaccharide-based water-absorbent resin C2-1 was obtained in the same manner as in Example 1-1, except that the type and amount of the crosslinking agent were changed to those shown in Table 2.

[0054] Comparative Example 2-2 A polysaccharide-based water-absorbent resin C2-2 was obtained in the same manner as in Comparative Example 2-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 2.

[0055] Comparative Example 2-3 A polysaccharide-based water-absorbent resin C2-3 was obtained in the same manner as in Comparative Example 2-1, except that the amount of crosslinking agent added was changed to the amount shown in Table 2.

[0056] The evaluation results are shown in Table 1 or Table 2 below.

[0057] [Table 1]

[0058] [Table 2]

Claims

1. A method for producing a polysaccharide-based water-absorbent resin obtained by crosslinking a polysaccharide, comprising: a crosslinking step of crosslinking the polysaccharide with a crosslinking agent, The method for producing a polysaccharide-based water-absorbent resin, wherein the crosslinking agent contains a crosslinking agent A having an acid dissociation constant pKa of 7 or more and 13 or less.

2. 2. The method for producing a polysaccharide-based water-absorbent resin according to claim 1, wherein the polysaccharide is at least one selected from the group consisting of starch, amylopectin, amylose, cellulose, and modified products thereof.

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