TW202246360A - Water-absorbent resin - Google Patents

Abstract

The present invention provides a water-absorbent resin having excellent water-absorbing performance and water-retaining performance and high production efficiency. The present invention relates to a water-absorbent resin including a crosslinked product of a water-soluble polymer obtained by introducing an acidic group into a partial decomposition product of starch having a weight average molecular weight of 7.5 million or less.

Description

Absorbent resin

The present invention relates to a water-absorbent resin.

Water-absorbent resins are widely used in various fields such as hygiene products, food, agriculture and forestry, and civil engineering. As the water-absorbent resin, partially neutralized salts of polyacrylic acid or polymethacrylic acid are widely used, and water-absorbent resins using polysaccharides such as starch as raw materials are also known.

Patent Document 1 discloses a method for producing a water-absorbent resin by heating and drying carboxyalkylated starches to crosslink the starches. It is described that when the carboxyalkylation reaction is performed, it is preferable to suppress the reduction of the molecular weight of starch.

Patent Document 2 discloses a method of surface-treating carboxyalkylated polysaccharide particles with non-cross-linking acids such as hydrochloric acid, and then heating and drying or allowing a cross-linking agent to act to cross-link the polysaccharides to produce water-absorbent particles. The method of permanent resin.

Patent Document 3 discloses a method for producing a water-absorbent material by reacting starch and an anhydride of a polybasic acid in an extruder. It is described that when reacting with an anhydride of a polybasic acid, it is preferable to suppress a decrease in the molecular weight of starch. prior art literature patent documents

Patent Document 1: Specification of US Patent No. 5,079,354 Patent Document 2: Japanese PCT Publication No. 2010-504414 Patent Document 3: Japanese PCT Publication No. 2007-222704

[Problem to be Solved by the Invention]

Conventional water-absorbent resins that use polysaccharides as raw materials do not have sufficient water-absorbing performance. In addition, since it is produced from high-molecular-weight polysaccharides, the viscosity of the material is high, and there are problems in handling during production. An object of the present invention is to provide a water-absorbent resin having excellent water absorption performance and water retention performance and high production efficiency. [Technical means to solve the problem]

The present inventors paid attention to the molecular weight of starch used as a raw material of a water-absorbent resin, and completed the present invention. That is, the present invention relates to a water-absorbent resin comprising a cross-linked product of a water-soluble polymer having an acidic group introduced into a partial decomposition product of starch having a weight average molecular weight of 7.5 million or less.

The weight average molecular weight of the partial starch decomposition product is preferably 50,000 or more.

The degree of dispersion (weight average molecular weight/number average molecular weight) of the partially decomposed starch product is preferably 5 or more.

The pullulan conversion weight average molecular weight of the water-soluble polymer analyzed by aqueous size exclusion chromatography is preferably 500,000 to 50 million.

The above-mentioned acidic group is preferably carboxyalkyl, carboxyalkenyl, or sulfoalkyl.

The above-mentioned water-absorbent resin preferably has the following characteristics: (a) The non-pressurized water absorption rate of ion-exchanged water is 100-400 g/g; (b) The water retention rate of ion-exchanged water is 80-300 g/g; (c) The non-pressurized water absorption capacity of normal saline is 20-70 g/g; and/or (d) The water retention rate of normal saline is 7-60 g/g.

The ratio (A/B) of the non-pressurized absorption capacity (A) of ion-exchanged water to the non-pressurized absorption capacity (B) of physiological saline is preferably 7 or less.

The content of water and/or a hydrophilic solvent in the water-absorbent resin is preferably from 0.1 to 10%.

The above-mentioned water-absorbent resin preferably does not have an internal crosslinking structure formed by covalent bonds.

Also, the present invention relates to a method for decomposing a water-absorbing resin, which includes the step of subjecting the above-mentioned water-absorbing resin to an alkali treatment.

Also, the present invention relates to an article containing the above-mentioned water-absorbent resin.

Also, the present invention relates to a water-soluble polymer obtained by introducing acidic groups into partially decomposed starch with a weight average molecular weight of 7.5 million or less.

The degree of dispersion (weight average molecular weight/number average molecular weight) of the partially decomposed starch of the water-soluble polymer is preferably 5 or more.

The pullulan conversion weight average molecular weight (Mw) of the water-soluble polymer analyzed by aqueous size exclusion chromatography is preferably 500,000-50 million.

The above-mentioned acidic group is preferably carboxyalkyl, carboxyalkenyl, or sulfoalkyl.

Also, the present invention relates to a resin composition for producing a water-absorbent resin containing the above-mentioned water-soluble polymer. [Effect of Invention]

The water-absorbent resin of the present invention is excellent in water absorption performance and water retention performance. Moreover, since the viscosity at the time of manufacture is low, workability is excellent and production efficiency improves.

＜＜Absorbent resin＞＞ The water-absorbent resin of the present invention is characterized by containing a water-soluble polymer having an acidic group introduced into a partially decomposed starch product having a weight average molecular weight of 7.5 million or less.

＜Partial decomposition of starch＞ Partially decomposed starch is mainly a product in which a part of the glycosidic bond between α-glucose molecules constituting starch has been hydrolyzed, but the location where the decomposition occurs and the form of the decomposition are not limited. The type of starch used as the raw material is not particularly limited, and examples include waxy corn starch, tapioca starch, potato starch, corn starch (including waxy corn starch and high amylose), wheat starch, rice starch, and sweet potato starch.

The weight average molecular weight of the partially decomposed starch product is 7.5 million or less, preferably 5 million or less, more preferably 4.5 million or less, further preferably 4 million or less, still more preferably 3.5 million or less. When the weight-average molecular weight exceeds 7.5 million, the viscosity becomes high, and thus the reaction at the time of introducing an acidic group or the workability in the purification step tends to decrease, and the water-absorbing performance of the water-absorbent resin tends to decrease. The lower limit of the weight average molecular weight of the partially decomposed starch product is not particularly limited, but it is preferably 50,000 or more, more preferably 200,000 or more. When the weight average molecular weight is less than 50,000, the water retention property of the water-absorbent resin tends to decrease. Furthermore, the method of measuring the weight average molecular weight is not particularly limited, for example, it can be obtained based on a calibration curve of molecular weight and dissolution time prepared by using pullulan whose molecular weight has been known by aqueous size exclusion chromatography.

The number average molecular weight of the partially decomposed starch product is not particularly limited, but it is preferably 1 million or less in consideration of viscosity. In addition, the lower limit of the number average molecular weight of the partially decomposed starch product is preferably at least 10,000, more preferably at least 50,000. Furthermore, the method for measuring the number average molecular weight is not particularly limited, for example, it can be obtained based on a calibration curve of molecular weight and dissolution time prepared by pullulan with known molecular weight in aqueous size exclusion chromatography.

The weight average molecular weight or the number average molecular weight of the partial starch decomposition product can also be adjusted by mixing the partial starch decomposition product of 2 or more types. In this case, the weight average molecular weight or number average molecular weight of the mixture preferably satisfies the above numerical range.

The degree of dispersion (weight average molecular weight/number average molecular weight) of the partially decomposed starch product is not particularly limited, but is preferably 5 or more, more preferably 7 or more. The upper limit of the degree of dispersion (weight average molecular weight/number average molecular weight) of the partially decomposed starch product is not particularly limited, but is usually 70 or less. The viscosity of the partially decomposed starch product is not particularly limited.

＜Water-soluble polymer＞ The water-soluble polymer is formed by introducing acidic groups into the partially decomposed starch with a weight average molecular weight of 7.5 million or less. The acidic group is not particularly limited as long as it is a protonic acid, and examples thereof include acidic groups having a carboxyl group such as carboxyalkyl and carboxyalkenyl; acidic groups having a sulfonic acid group such as sulfoalkyl and sulfoalkenyl. ; Phosphoalkyl (phosphoalkyl), phosphoalkenyl (phosphoalkenyl) and other acidic groups with phosphoric acid groups.

Carboxyalkyl is an alkyl group substituted with a carboxyl group. The carbon number of the alkyl group substituted with a carboxyl group is preferably 1-8, more preferably 1-5. The alkyl group may be either linear or branched. Specific examples of the alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, second-butyl, third-butyl, n-pentyl, 1-methyl Base-n-butyl, 2-methyl-n-butyl, 3-methyl-n-butyl, 1,1-dimethyl-n-propyl, 1,2-dimethyl-n-propyl, 2, 2-Dimethyl-n-propyl, 1-ethyl-n-propyl, etc.

Specific examples of carboxyalkyl include carboxymethyl, carboxyethyl, carboxypropyl, carboxybutyl, carboxypentyl and the like.

Carboxyalkenyl is alkenyl substituted with carboxy. The carbon number of the alkenyl substituted with a carboxyl group is preferably 2-8, more preferably 2-4. The alkenyl group may be either linear or branched. Specific examples of alkenyl include vinyl, 1-propenyl, 2-propenyl, 1-methyl-1-vinyl, 1-butenyl, 2-butenyl, and 3-butene group, 2-methyl-1-propenyl, 2-methyl-2-propenyl, 1-ethylvinyl, 1-methyl-1-propenyl, 1-methyl-2-propenyl, etc.

Specific examples of carboxyalkenyl group include carboxyvinyl group, carboxypropenyl group, carboxybutenyl group and the like.

A sulfoalkyl group is an alkyl group substituted with a sulfo group. The alkyl group substituted with a sulfonic acid group may, for example, be the alkyl group described above for the carboxyalkyl group. As a specific example of a sulfoalkyl group, a sulfomethyl group, a sulfoethyl group, a sulfopropyl group, etc. are mentioned.

A sulfoalkenyl group is an alkenyl group substituted with a sulfonic acid group. As the alkenyl group substituted with a sulfonic acid group, the alkenyl group described for the carboxyalkenyl group can be used. Specific examples of the sulfoalkenyl group include a sulfoethenyl group, a sulfopropenyl group, and the like.

A phosphoalkyl group is an alkyl group substituted with a phosphate group. As the alkyl group substituted with a phosphoric acid group, the alkyl group described for the carboxyalkyl group can be used. As a specific example of a phosphoalkyl group, a phosphomethyl group, a phosphoethyl group, a phosphopropyl group, etc. are mentioned.

Phosphoalkenyl is an alkenyl group substituted with a phosphoric acid group. As the alkenyl group substituted with a phosphoric acid group, the alkenyl group described for the carboxyalkenyl group can be used. As a specific example of a phosphoalkenyl group, a phosphovinyl group, a phosphopropenyl group, etc. are mentioned.

Among the acidic groups, acidic groups having a carboxyl group and a sulfonic acid group are preferable, carboxyalkyl groups, carboxyalkenyl groups, and sulfoalkyl groups are more preferable, and even more Preferably, it is a carboxyalkyl group having 1 to 5 carbon atoms.

The molecular weight of the water-soluble polymer is not particularly limited, and the weight average molecular weight of the pullulan conversion obtained by aqueous size exclusion chromatography is preferably 500,000 to 50 million, more preferably 500,000 to 46 million, and even more preferably The best range is 700,000 to 20 million. When the said weight average molecular weight is less than 500,000, the water retention property of a water-absorbent resin will tend to fall, and if it exceeds 50 million, the water-absorbent performance of a water-absorbent resin will tend to fall. Furthermore, the pullulan-equivalent weight average molecular weight obtained by aqueous size exclusion chromatography analysis can be based on the calibration of molecular weight and dissolution time prepared by pullulan with known molecular weight in aqueous size exclusion chromatography Find the curve.

The total acid value of the water-soluble polymer is preferably 50-350 mgKOH/g, more preferably 70-300 mgKOH/g. The total acid value refers to the acid value measured after returning the neutralized acid groups to the unneutralized state, and represents the introduction amount of all the acid groups introduced into the water-soluble polymer. If the total acid value is less than 50 mgKOH/g or exceeds 350 mgKOH/g, the water-absorbent resin tends to lower the water absorption performance of aqueous solutions containing electrolytes such as physiological saline.

In the case of introducing an acidic group on a water-soluble polymer by reacting a haloalkyl group having an acidic group with a hydroxyl group of starch or a partially decomposed starch, the amount of the acidic group introduced can also be expressed by the degree of etherification. The degree of etherification of the water-soluble polymer is preferably from 0.1 to 2.0, more preferably from 0.2 to 1.5. The degree of etherification can be determined by ashing titration or the like. In addition, the total acid value is detected by introducing acidic groups. When the raw material starch or starch partial decomposition does not contain acidic groups, it can be regarded as the acidic group detected by the measurement of the total acid value. Equal to those introduced by etherification. Therefore, when there is no acidic group in the starch or starch partial decomposition product of the raw material, it can be simply calculated from the numerical value of the above-mentioned total acid value by calculation. For example, when the acidic groups are carboxymethyl groups and all of them are neutralized into sodium salts, it can be calculated by etherification degree=(162×total acid value)÷(56100-80×total acid value). In addition, the unit of the total acid value at this time is mgKOH/g.

The free acid number of the water-soluble polymer is preferably 5-30 mgKOH/g, more preferably 7-25 mgKOH/g. Free acid value is the acid value measured against unneutralized acid groups. If the free acid value is less than 5 mgKOH/g, the strength of the water-absorbent resin tends to be insufficient, and if it exceeds 30 mgKOH/g, the water-absorbing performance tends to decrease.

The degree of dispersion (weight average molecular weight/number average molecular weight) of the water-soluble polymer is not particularly limited, but is preferably 5-110, more preferably 7-70. If it is less than 5 or more than 110, the water-absorbent performance of the water-absorbent resin tends to decrease. The number average molecular weight of the water-soluble polymer can be obtained by analyzing the aqueous size exclusion chromatography. The viscosity of the water-soluble polymer is not particularly limited.

＜Cross-linked structure of water-absorbent resin＞ The water-absorbent resin is a cross-linked product of the above-mentioned water-soluble polymer. Crosslinks consist of internal crosslinks and any surface crosslinks. The internal crosslinking structure is preferably formed by acidic groups contained in the water-soluble polymer. As the internal cross-linking structure, for example, an ionic bond formed between acidic groups existing in partially decomposed starch, and a coordination bond formed via a metal ion, when the acidic group is an acidic group having a carboxyl group, for example, For example, hydrogen bonds formed by dimerization of carboxyl groups, etc. As described below, from the viewpoint of decomposability, the water-absorbent resin preferably does not have an internal crosslinking structure formed by covalent bonds. Examples of internal crosslinking by covalent bonds include, but are not limited to, ester bonds, ether bonds, carbon-carbon single bonds (C-C bonds), and carbon-carbon double bonds (C=C bonds). . The structure of the surface crosslink and its formation method are as follows.

＜Any ingredients＞ The water-absorbent resin may optionally contain structural units other than the above-mentioned water-soluble polymers. As the structural unit other than the water-soluble polymer, polyacrylic acid (salt) such as a partially neutralized polyacrylic acid cross-linked product, a self-crosslinking partially neutralized polyacrylic acid, and a starch-acrylic acid graft polymer may be mentioned, for example. As a salt of acrylic acid, sodium salt, potassium salt, ammonium salt, etc. are mentioned. Structural units other than partial starch decomposition products include methacrylic acid, maleic acid, vinylsulfonic acid, styrenesulfonic acid, 2-(meth)acrylamide-2-methyl Anionic unsaturated monomers such as propanesulfonic acid, 2-(meth)acrylylethanesulfonic acid, 2-(meth)acrylylpropanesulfonic acid and their salts; acrylamide, methacrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide Amide, 2-Hydroxyethyl (meth)acrylate, 2-Hydroxypropyl (meth)acrylate, Methoxypolyethylene glycol (meth)acrylate, Polyethylene glycol mono(meth)acrylate , vinylpyridine, N-vinylpyrrolidone, N-acrylpiperidine, N-acrylpyrrolidine and other non-ionic unsaturated monomers containing hydrophilic groups; (meth)acrylic acid N,N -Dimethylaminoethyl, N,N-Diethylaminoethyl (meth)acrylate, N,N-Dimethylaminopropyl (meth)acrylate, N,N-Dimethylaminopropyl Cationic unsaturated monomers such as (meth)acrylamide and quaternary salts thereof; linear cellulose; poly(γ-glutamic acid), and the like.

When the water-absorbent resin contains a structural unit other than the water-soluble polymer, its content is preferably 90% by weight or less, more preferably 50% by weight, relative to the total amount of the water-soluble polymer used as the main component. % by weight or less, more preferably 20% by weight or less.

The water absorbent resin may also contain water and/or a hydrophilic solvent. Examples of hydrophilic solvents include methanol, ethanol, n-propanol, isopropanol, acetone, ethylene glycol, propylene glycol, diethylene glycol, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol Alcohol dimethyl ether, dimethyl sulfide, etc. The content of water and/or the hydrophilic solvent in the water-absorbent resin is preferably from 0.1 to 20%, more preferably from 1 to 19%. If it is less than 0.1%, the water absorption rate tends to decrease, and if it exceeds 20%, the water-absorbent resin particles tend to aggregate (came easily) during water absorption. The content of water and/or the hydrophilic solvent can be adjusted by heating or drying the water-absorbent resin.

＜Physical properties of water-absorbent resin＞ The water absorption capacity of the water-absorbent resin under no pressure can be determined by measuring the absorbency of physiological saline or ion-exchanged water when no load is applied to the water-absorbent resin by the method described in the Examples. In the solid state of the water-absorbent resin of the present invention, the water absorption capacity of ion-exchanged water without pressure is preferably 100-400 g/g, more preferably 120-350 g/g. In addition, the water-absorbent resin of the present invention preferably has a non-pressurized water absorption capacity of 20-70 g/g, more preferably 30-65 g/g of physiological saline.

The ratio (A/B) of the non-pressurized water absorption capacity (A) of the ion-exchanged water of the water-absorbent resin to the non-pressurized absorption capacity (B) of physiological saline is preferably 7 or less, more preferably 5 or less .

The water retention rate of the water-absorbent resin can be determined by measuring the absorbency of physiological saline or ion-exchanged water when the water-absorbent resin is subjected to a load of 150 G by the method described in the Examples. In the solid state of the water-absorbent resin of the present invention, the water retention rate of ion-exchanged water is preferably 80-300 g/g, more preferably 100-300 g/g. In addition, the water retention rate of physiological saline of the water-absorbent resin of the present invention is preferably 7-60 g/g, more preferably 10-60 g/g, still more preferably 20-60 g/g.

＜Manufacturing method of water-absorbent resin＞ The production method of the water-absorbent resin of the present invention is not particularly limited as long as it has the above structure. For example, it can be obtained by steps of partially decomposing starch, introducing acidic groups, and forming an internal crosslinked structure. Furthermore, the step of partially decomposing the starch and the step of introducing acidic groups may also be performed in different orders, and it does not matter which one is performed first.

In the step of partially decomposing starch, a part of the α-1,4-glycosidic bond of the α-glucose molecule constituting the starch is often partially hydrolyzed. The partial decomposition method is not particularly limited, and methods such as enzymatic treatment, acid treatment, and physical crushing of starch can be exemplified. In addition, these methods may be used in combination. As the reaction device, a reactor, an extruder, or the like can be used.

When the starch is decomposed by enzyme treatment, the enzyme used is not particularly limited as long as it can hydrolyze the starch. From the viewpoint of efficiently reducing the molecular weight, it is preferable to use an endo-type (endo) enzyme. -type) enzyme. Specific examples of enzymes include α-amylase, cyclomaltodextrin glucanotransferase, 4-α-glucanotransferase, 4,6-α-glucanotransferase Enzyme, maltose transglucosylase (amylomaltase), new pullulanase (neopullulanase), starch pullulanase (amylopullulanase), etc. These enzymes may also be used in combination. The pH during the enzyme treatment is not particularly limited, but is preferably pH 5.0 to 7.0. Adjustment of pH can be performed by adding hydrochloric acid, acetic acid, sodium hydroxide, potassium hydroxide, etc. Preferably, the starch is heated and kneaded at 70-110° C. to make it gelatinized, and the enzyme treatment is carried out at the same time. Enzyme treatment can be performed after gelatinization of starch, or simultaneously with gelatinization. As a method of carrying out enzyme treatment after gelatinization of starch, the method of carrying out an enzyme reaction by suspending starch in water first, heating and gelatinizing, adding an enzyme after that, is mentioned. In addition, as a method of performing enzyme treatment simultaneously with gelatinization of starch, the method of suspending starch in water, adding enzymes, and heating the obtained mixed solution within a temperature range that does not completely inactivate the enzymes can be mentioned. .

In the case of partially decomposing starch by acid treatment, the acid used is not particularly limited as long as it can hydrolyze starch. Specific examples include hydrochloric acid, sulfuric acid, oxalic acid, acetic acid, formic acid, and trifluoroacetic acid. Wait. The temperature during the acid treatment is preferably 150-160°C.

In the case of partially decomposing starch by physical crushing, specific methods include radiation irradiation, shearing, grinding, high-pressure treatment, ultrasonic waves, thermal decomposition, photolysis, and combinations thereof.

As a method of introducing an acidic group into a partially decomposed starch product, the partially decomposed starch product is reacted with an acidic group-containing compound or its precursor. Water-soluble polymers can be obtained by introducing acidic groups into the hydroxyl groups of partially decomposed starch products. The acidic group-containing compound is not particularly limited as long as it can introduce the above-mentioned acidic group, and examples thereof include haloalkyl compounds having acidic groups, haloalkenyl compounds having acidic groups, acid anhydrides, and salts thereof. Examples of the halogen constituting the haloalkyl compound and the haloalkenyl compound include chlorine and bromine.

Specific examples of acidic group-containing compounds include: monochloroacetic acid, monobromoacetic acid, 3-bromopropionic acid, 6-bromohexanoic acid, succinic anhydride, maleic anhydride, vinylsulfonic acid, phosphoric acid Chlorine, ethyl monochloroacetate, and their sodium salts, potassium salts, etc. Specific examples of the salt include sodium monochloroacetate, potassium monochloroacetate, and sodium vinylsulfonate.

Acrylonitrile etc. are mentioned as a precursor of an acidic group containing compound. As a method of using acrylonitrile, for example, the following method can be exemplified: first, reacting acrylonitrile and a starch partial decomposition product under alkaline conditions, introducing a cyanoethyl group, and then inducing the cyanoethyl group into an amide group (Synthesis; 1989 (12): 949-950), alkaline hydrolysis of the obtained amide.

The outline of the reaction to produce a water-soluble polymer by reacting partial decomposition of starch with monochloroacetic acid is shown in formula (I).

The outline of the reaction to produce a water-soluble polymer by reacting partial decomposition of starch with 3-bromopropionic acid is shown in formula (II).

The outline of the reaction to produce a water-soluble polymer by reacting partial decomposition of starch with 6-bromohexanoic acid is shown in formula (III).

The outline of the reaction to produce a water-soluble polymer by reacting partial decomposition of starch with succinic anhydride is shown in formula (IV).

The outline of the reaction to produce a water-soluble polymer by reacting a partial decomposition product of starch with maleic anhydride is shown in formula (V).

The outline of the reaction to produce a water-soluble polymer by reacting partial decomposition of starch with sodium vinylsulfonate is shown in formula (VI).

In the formulas (I) to (VI), a water-soluble polymer in which the 6-hydroxyl group of the glucose unit is completely introduced into the sodium salt of the acidic group is shown, but the hydroxyl group not introduced into the acidic group may remain. Furthermore, acidic groups which have not been neutralized by salts may also be present. The introduction position of the acidic group is not limited as long as it is a hydroxyl group present in the partially decomposed starch product, and may be any of the 1-position, 2-position, 3-position, 4-position, and 6-position hydroxyl groups.

The reaction conditions of the partially decomposed starch product and the acidic group-containing compound are not particularly limited, but it is preferably carried out under alkaline conditions. When using a haloalkyl compound or a haloalkenyl compound as an acidic group-containing compound, it is preferable to use 1 to 1.5 equivalents of the alkali agent with respect to the haloalkyl compound or the haloalkenyl compound. The alkaline agent may, for example, be sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia or sodium carbonate. The acidic group introduced into the partially decomposed starch product preferably forms a salt with sodium, potassium, lithium, ammonia, etc. derived from an alkaline agent. Therefore, it is preferable to use a haloalkyl compound, a haloalkenyl compound and a starch moiety as an alkali agent. The amount required for the reaction of decomposition products and the neutralization of the acidic groups of haloalkyl compounds and haloalkenyl compounds. For example, when using chloroacetic acid as an acidic group-containing compound, it is theoretically preferable to use 2 equivalents or more of an alkali agent with respect to chloroacetic acid. When sodium chloroacetate is used, acid groups are neutralized in advance, so it is preferable to use 1 equivalent or more of an alkali agent with respect to sodium chloroacetate.

The usage-amount of the compound containing an acidic group can be set arbitrarily according to the target total acid value (etherification degree) of a water-soluble polymer. Usually, it is preferably 0.5 to 5 equivalents, more preferably 0.5 to 2.0 equivalents with respect to 1 mole of hydroxyl groups of the partially decomposed starch product. When a haloalkyl compound such as chloroacetic acid is used to prepare an aqueous solution for the reaction, the introduction reaction of the acidic group competes with the hydrolysis reaction of the haloalkyl compound, so the haloalkyl compound must be used in excess of the theoretical value. The excess amount of the haloalkyl compound in the aqueous solution reaction is preferably set to 5 equivalents or less relative to the theoretical value.

The reaction temperature of the partially decomposed starch product and the acidic group-containing compound is not particularly limited, but is preferably 0 to 120°C. The reaction time is not particularly limited, but is preferably 1 to 24 hours. The reaction can be carried out in water, but it can also be carried out in water and alcohols such as methanol, ethanol, isopropanol, butanol, ethylene glycol, diethylene glycol, propylene glycol, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, etc. Carry out in mixed solvents such as alcohol ethers, etc., and disperse the powder of dried starch partial decomposition products in alcohols such as methanol, ethanol, isopropanol, butanol, glycol ethers such as ethylene glycol dimethyl ether, etc. in neutral solvents. When using a mixed solvent, the proportion of solvents other than water is preferably 50% by volume or less in the mixed solvent. As the reaction device, a reactor, an extruder, or the like can be used.

When using a haloalkyl compound such as chloroacetic acid or a salt thereof as an acidic group-containing compound, the reaction temperature with a partially decomposed starch product is not particularly limited, but is preferably 0 to 100°C.

In particular, when chloroacetic acid or its salt is used as the haloalkyl compound, it is preferably performed at 25 to 90° C. in order to prevent hydrolysis due to water in the reaction solution. The reaction time is preferably the time until the haloalkyl compound as a raw material is consumed, and is more preferably 1 to 12 hours for the stability of the haloalkyl compound and the efficiency of the production process. The reaction can be carried out in water, but it can also be carried out in a mixed solvent of water and alcohols such as methanol, ethanol, isopropanol, butanol, glycol ethers such as ethylene glycol dimethyl ether, etc., or the dried starch Partially decomposed powder is dispersed in hydrophilic solvents such as alcohols such as methanol, ethanol, isopropanol, butanol, and glycol ethers such as ethylene glycol dimethyl ether. When using a mixed solvent, the proportion of solvents other than water is preferably 50% by volume or less in the mixed solvent. As the reaction device, a reactor, an extruder, or the like can be used.

Also, in the case of using an acid anhydride as an acidic group-containing compound, the reaction can proceed only by mixing the partially decomposed starch product with the acid anhydride and heating, but in order to accelerate the reaction, sodium carbonate and sodium hydroxide can also be used. tertiary amines such as triethylamine, imidazoles such as 2-methylimidazole, quaternary ammonium salts such as tetrabutylammonium bromide, and phosphonium salts such as tetrabutylphosphonium bromide are used as catalysts. The addition amount of these catalysts is preferably 0.1 equivalent or less with respect to the acidic group-containing compound. These catalysts may be used alone or in combination of two or more.

The reaction time is preferably the time until the acid anhydride as a raw material is consumed, more preferably 1 to 12 hours. The end point of the reaction can be judged by acid value measurement or IR measurement. The reaction can be carried out in water, but in order to prevent the hydrolysis and alcoholysis of the acid anhydride, the reaction solvent is preferably dimethylsulfide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, etc. Protic solvent. When using a mixed solvent, the proportion of solvents other than water is preferably 50% by volume or more in the mixed solvent. When the reaction is carried out without a solvent, the acid anhydride can function as a solvent, so the reaction temperature is preferably carried out at or above the melting point of the acid anhydride. When a solvent is used for the reaction, the reaction temperature is preferably from 50 to 100°C, more preferably from 70 to 90°C. As the reaction device, a reactor, an extruder, or the like can be used.

It is preferable to partially neutralize the salt of the acidic group added to the partially decomposed starch product. By neutralization, a part of the acidic groups forming the salt is converted into free acidic groups. For example, when monochloroacetic acid is used as the above-mentioned acidic group-containing compound and sodium hydroxide is used as the alkaline agent, the sodium salt of the carboxyl group is added to the partially decomposed starch. By adding an acid thereto, a part of the carboxyl group is converted into a free carboxylic acid.

The acid used for neutralization is not particularly limited. When the acidic group is a carboxyl group, it is preferably an acid having a pKa equal to or less than that of the carboxyl group. Examples include: hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, acetic acid, formic acid, tris Chloroacetic acid, etc. When neutralizing the sulfonic acid group or phosphoric acid group, it is preferable to use a strong acid, such as a mineral acid such as hydrochloric acid or sulfuric acid, or a strongly acidic ion exchange resin. Neutralization can be carried out using known devices such as reactors and extruders. After adding an acid, it is preferable to perform stirring at 0-50 degreeC for 0.2-1 hour in order to perform a neutralization reaction. The neutralization reaction is preferably carried out under the condition of pH 6.8-7.2.

In the step of introducing an acidic group or the subsequent neutralization reaction, a salt may be formed between a halogen derived from an acidic group-containing compound and a metal or ammonia derived from an alkaline agent, so desalting is preferably performed. As the desalination method, a method of washing by dissolving a water-soluble polymer in water is exemplified, and the aqueous solution is added dropwise to a hydrophilic product such as methanol, ethanol, isopropanol, acetone, or acetonitrile. In the solvent, the water-soluble polymer is re-precipitated, filtered and recovered, and then the water-soluble polymer recovered by filtration is re-dispersed in aqueous methanol (the water content is about 70-90%), stirred, and then filtered to recover the water-soluble polymer. Particles of permanent polymers. Moreover, as a desalination method, the method of treating the aqueous solution of a hydrophilic polymer with the filter which has an ultrafiltration membrane is mentioned. As a cleaning solution for desalination, water or a mixture of water and a hydrophilic organic solvent such as methanol, ethanol, propanol, acetone, or acetonitrile can be used. Desalination is preferably carried out until the salt concentration in the water-soluble polymer becomes 1% or less.

In the step of forming the internal crosslinked structure, the water-soluble polymers are crosslinked with each other. The crosslinking can be formed by heating and drying, for example, a water-soluble polymer in which a part of the acidic groups are free acidic groups under an aqueous condition without using a crosslinking agent. The water-soluble polymer at the point when heat drying starts may be an aqueous solution, or may be a wet powder containing an aqueous solvent with a water content of 1% by weight or more. When drying a wet powder containing an aqueous solvent, the moisture content in the wet powder at the start of the drying is preferably 1 to 85% by weight, more preferably 20 to 80% by weight, and still more preferably 55 to 75% by weight. weight%. Furthermore, the so-called moisture content here refers to the ratio of the total amount of water and hydrophilic solvent in the wet powder. The temperature during heating is preferably from 50 to 150°C, more preferably from 60 to 130°C. The drying method is not particularly limited, and may be performed using a tumble dryer, a spray dryer, a conical screw mixer, or the like.

烷、四氫呋喃及甲氧基(聚)乙二醇等醚類；ε-己內醯胺及N,N-二甲基甲醯胺等醯胺類。全部溶劑中除水以外之溶劑所占之比率較佳為根據溶劑之沸點來調整，於溶劑之沸點為100℃以下之情形時，較佳為70體積%以上，於高於100℃之情形時，較佳為30體積%以下。When forming a crosslinked structure, in addition to water, a solvent other than water may be used together. Examples of solvents other than water include lower aliphatic alcohols such as methanol, ethanol, n-propanol, and isopropanol; ketones such as acetone;

Ethers such as alkane, tetrahydrofuran and methoxy (poly)ethylene glycol; amides such as ε-caprolactam and N,N-dimethylformamide. The proportion of solvents other than water in all solvents is preferably adjusted according to the boiling point of the solvent. When the boiling point of the solvent is below 100°C, it is preferably more than 70% by volume. When the boiling point of the solvent is higher than 100°C , preferably 30% by volume or less.

唑啉化合物、碳二醯亞胺化合物、矽烷偶合劑、多元金屬化合物等。The internal crosslinked structure can be formed without using a crosslinking agent as described above, but a crosslinking agent can also be used. Examples of the crosslinking agent include epoxy compounds, polyol compounds, polyamine compounds, polyisocyanate compounds, alkylene carbonate compounds, halo epoxy compounds, halohydrin compounds, polyvalent

Azoline compounds, carbodiimide compounds, silane coupling agents, polymetallic compounds, etc.

Examples of the epoxy compound include glycidyl succinate, sorbitol polyglycidyl ether, trimethylolpropane polyglycidyl ether, polyethylene glycol diglycidyl ether, and glycerol polyglycidyl ether. , Diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, dehydrated glycerol, etc.

Examples of the polyhydric alcohol compound include ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propylene glycol, dipropylene glycol, 2,2, 4-Trimethyl-1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanediol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene , oxyethylene-oxypropylene block copolymer, neopentylitol, sorbitol, etc.

Examples of the polyamine compound include ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethylene Amines, inorganic or organic salts of these polyamine compounds (azinium salts, etc.), polysaccharides with amine groups such as chitin, etc.

唑啉化合物，例如可例舉1,2-伸乙基雙

唑啉等。As the above-mentioned polyisocyanate compound, for example, 2,4-toluene diisocyanate, hexamethylene diisocyanate, etc.;

Azoline compounds, for example, 1,2-ethylene bis

oxazoline etc.

烷-2-酮、4-甲基-1,3-二

烷-2-酮、4,6-二甲基-1,3-二

烷-2-酮等。Examples of the alkylene carbonate compound include: 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one, 4,5-dimethyl Base-1,3-dioxolane-2-one, 4,4-dimethyl-1,3-dioxolane-2-one, 4-ethyl-1,3-dioxolane- 2-keto, 4-hydroxymethyl-1,3-dioxolan-2-one, 1,3-di

Alkan-2-one, 4-methyl-1,3-di

Alkan-2-one, 4,6-dimethyl-1,3-di

Alkanes-2-ones etc.

As said halogenated epoxy compound, epichlorohydrin, epibromohydrin, (alpha)-methyl epichlorohydrin, or its polyamine adduct (For example, KYMENE (registered trademark) by Hercules company) etc. are mentioned, for example.

In addition, as other known crosslinking agents, water-based carbodiimide compounds (for example, Carbodilite manufactured by Nisshinbo Chemical Co., Ltd.), γ-glycidoxypropyltrimethoxysilane, γ-amine Silane coupling agents such as propyltriethoxysilane, or multiple metal compounds such as hydroxides or chlorides of zinc, calcium, magnesium, aluminum, iron, zirconium, etc.

When producing a water-absorbent resin, surface crosslinking may be performed in addition to internal crosslinking. The strength of the water-absorbent resin can be increased by surface cross-linking. As the crosslinking agent used for surface crosslinking, the same crosslinking agent as described above for internal crosslinking can be used. Among them, epoxy compounds are preferable, and ethylene glycol diglycidyl ether, sorbitol polyglycidyl ether, and glycidyl succinate are more preferable.

Surface cross-linking can be formed by the following method: spray the surface cross-linking agent onto the water-absorbing resin, and then use a cylindrical mixer, V-shaped mixer, ribbon mixer, spiral mixer, double-arm mixer Kneader, pulverizing kneader, etc. are mixed by a known method, and then crosslinked. When spraying and mixing, surfactants can be added as needed.

Furthermore, the water-absorbent resin may contain disinfectants, deodorants, antibacterial agents, fragrances, various inorganic powders, foaming agents, pigments, dyes, hydrophilic short fibers, fertilizers, oxidizing agents, and reducing agents in order to impart various functions. , water, and salts and other additives. The amount of addition thereof can be appropriately selected by those skilled in the art.

＜＜Decomposition method of water-absorbent resin＞＞ The method for decomposing a water-absorbent resin of the present invention is characterized by including the step of subjecting the above-mentioned water-absorbent resin to an alkali treatment. In the step of performing alkali treatment, the water-absorbent resin is placed under conditions of preferably pH 9 or higher, more preferably pH 10 or higher. By alkali treatment, the cross-linked structure or glycosidic bonds of the water-absorbent resin are decomposed into water-soluble polymers, which can reduce the environmental load when discarded.

The alkali agent used for alkali treatment is not specifically limited, For example, sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia, sodium carbonate, potassium carbonate, etc. are mentioned. The temperature at the time of alkali treatment is not specifically limited, For example, it can carry out under the conditions of 5-50 degreeC.

＜＜Articles containing water-absorbent resin＞＞ The article of the present invention contains the above-mentioned water-absorbent resin. Examples of such articles include sanitary materials such as disposable diapers, sanitary products, incontinence pads, portable toilets, waste disposal bags, animal excrement treatment agents, medical treatment materials, and wound dressing materials. ; Agricultural materials such as fertilizers; Civil engineering materials such as soil modifiers, sludge curing agents, and waterproof materials. As an example of sanitary products, a laminate in which a base sheet, an absorber, and a top sheet are laminated in this order may be mentioned. The above-mentioned absorber contains the water-absorbent resin of the present invention, and may further contain water-absorbent paper or pulp if necessary.

＜＜Resin composition for water-absorbent resin＞＞ The resin composition for water-absorbent resins of the present invention contains the above-mentioned water-soluble polymer. The content of the water-soluble polymer in the resin composition is preferably 5-80% by weight, more preferably 25-60% by weight.

The resin composition may contain optional components such as a solvent and a crosslinking agent in addition to the water-soluble polymer. As a solvent, water, methanol, ethanol, isopropanol, etc. mentioned above as the solvent used for forming a crosslinked structure can be used. As the crosslinking agent, those exemplified above as the internal crosslinking agent or the surface crosslinking agent can be used.

By heating and drying the resin composition of the present invention under the condition of containing water, an internal cross-linked structure of water-soluble polymers can be formed to obtain a water-absorbent resin. Heating and drying can be performed by the conditions described above for the step of forming the internal crosslinked structure of the water-soluble polymer. [Example]

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to the following examples. Hereinafter, "parts" or "%" represent "parts by weight" or "% by weight", respectively, unless otherwise specified.

(1) Materials used (1-1) Starch raw material corn starch cassava waxy corn potato

(1-2) Hydrolytic enzymes α-Amylase (Spitase (registered trademark) HK/R manufactured by Nagase Chemical Co., Ltd.), 12,200 units/g Branching enzyme (Branchzyme (registered trademark) manufactured by Novozyme), 25,000 units/g Maltose glucosylase: aerobically cultivated Thermus thermophilus, centrifuged the crushed extract of the recovered bacteria, and used the supernatant as a crude enzyme solution. Conventionally, the crude enzyme solution is subjected to column chromatography, and the single sample purified by electrophoresis is used as the purified enzyme solution.

Furthermore, regarding the activity of maltose transglucosylase, the following method was carried out. The reaction solution 1 containing 10 w/v% maltotriose, 50 mM sodium acetate buffer (pH 6.0) and enzyme was incubated at 60°C for 20 minutes. Thereafter, the reaction was terminated after heating at 100° C. for 10 minutes. The amount of glucose in the reaction solution was determined by the glucose oxidase method. Regarding the unit amount of maltose glucosylase, the activity of maltose glucosylase which produces 1 μmol of glucose in 1 minute was defined as 1 unit.

(2) Production of partially decomposed starch (Production Examples 1 to 17 and Production Example 54) A partially decomposed starch product was produced by the following method. In addition, the weight average molecular weight of the partial starch decomposition product obtained was calculated|required based on the calibration curve of molecular weight and dissolution time prepared with the pullulan whose molecular weight is known in aqueous size exclusion chromatography.

Production Example 1: Partially Decomposed Starch Derived from Corn Starch Starch milk was prepared by suspending corn starch in 20 mM acetic acid buffer (pH 6.0) at a concentration of 15% (w/w). In this starch milk, add maltose transglucosylase crude enzyme liquid in the manner of reaching 0.8 units per gram of starch solids, and add branching enzyme in a manner of reaching 20 units per gram of starch solids, and store in room After stirring at temperature for 30 minutes, it was kept at 80° C. for 6 hours while stirring, and reacted to prepare liquefied starch. The weight average molecular weight of the obtained partially decomposed starch was 810,000.

Production Example 2: Partially Decomposed Starch Derived from Corn Starch Starch milk was prepared by suspending corn starch in 20 mM acetic acid buffer (pH 6.0) at a concentration of 15% (w/w). To the starch milk, add maltose-transglucosylase crude enzyme liquid in such a way that it reaches 1.6 units per gram of starch solids, stir at room temperature for 30 minutes, and keep stirring at 90°C for 3 hours. Furthermore, it was kept at 80 degreeC for 17 hours, it was made to react, and the liquefied starch was prepared. The weight average molecular weight of the obtained partially decomposed starch was 663,000.

Production Example 3: Partially Decomposed Starch Derived from Corn Starch Starch milk was prepared by suspending corn starch in 20 mM acetic acid buffer (pH 6.0) at a concentration of 15% (w/w). To the starch milk, add maltose glucosylase purified enzyme liquid in a manner that reaches 1.6 units per gram of starch solids, stir at room temperature for 30 minutes, and keep stirring at 80°C for 8 hours. It reacts to prepare liquefied starch. The weight average molecular weight of the partially decomposed starch obtained was 720,000.

Production Example 4: Partially Decomposed Starch Derived from Corn Starch Starch milk was prepared by suspending corn starch in 20 mM acetic acid buffer (pH 6.0) at a concentration of 15% (w/w). In the starch milk, maltose transglucosylase purified enzyme liquid was added in a manner of 0.6 units per gram of starch solids, and α-amylase was added in a manner of 0.03 units per gram of starch solids, After stirring at room temperature for 30 minutes, while stirring, it kept at 90 degreeC for 4.5 hours, and also kept it at 100 degreeC for 1.5 hours and made it react, and prepared the liquefied starch. The weight average molecular weight of the obtained partially decomposed starch was 1.46 million.

Production Example 5: Partially Decomposed Starch Derived from Tapioca Starch Starch milk was prepared by suspending tapioca starch in 20 mM acetic acid buffer (pH 6.0) at a concentration of 15% (w/w). Add maltose-transglucosylase crude enzyme solution to the starch milk in such a way that it reaches 1.6 units per gram of starch solids, stir at room temperature for 30 minutes, and keep stirring at 80°C for 20 hours. It reacts to prepare liquefied starch. The weight average molecular weight of the obtained partially decomposed starch was 200,000.

Production Example 6: Partially Decomposed Starch Derived from Tapioca Starch Starch milk was prepared by suspending tapioca starch in 20 mM acetic acid buffer (pH 6.0) at a concentration of 15% (w/w). To the starch milk, add maltose-transglucosylase crude enzyme solution in such a way that it reaches 0.4 units per gram of starch solids, stir at room temperature for 30 minutes, and keep stirring at 80°C for 9 hours. It reacts to prepare liquefied starch. The weight average molecular weight of the obtained partially decomposed starch was 1.18 million.

Production Example 7: Partially decomposed starch derived from tapioca starch Starch milk was prepared by suspending tapioca starch in 20 mM acetic acid buffer (pH 6.0) at a concentration of 15% (w/w). In this starch milk, add maltose transglucosylase purified enzyme solution in such a way that it reaches 0.4 units per gram of starch solids, stir at room temperature for 30 minutes, and keep it at 80°C for 3 hours while stirring. It reacts to prepare liquefied starch. The weight average molecular weight of the obtained partially decomposed starch was 1.96 million.

Production Example 8: Partially Decomposed Starch Derived from Waxy Corn Starch Waxy cornstarch was suspended in tap water, calcium chloride was added so that the final concentration reached 1 mM, and the pH was adjusted to 6.0 to prepare starch milk with a concentration of about 15% by mass. To this starch milk, α-amylase was added so as to reach 0.78 units per gram of starch solids, stirred for 30 minutes, and then passed into a continuous liquefaction device at a flow rate of 1 L/min. The starch milk was heated at 100° C. for 25 minutes in a continuous liquefaction device, and then heated at 140° C. for 5 minutes to prepare liquefied starch. The weight average molecular weight of the partially decomposed starch obtained was 610,000.

Production Example 9: Partially Decomposed Starch Derived from Waxy Corn Starch Prepared by the same method as Production Example 8, changing the amount of enzyme added to 0.36 U. The weight average molecular weight of the obtained partially decomposed starch was 1.33 million.

Production Example 10: Partially Decomposed Starch Derived from Potato Starch Starch milk was prepared by suspending potato starch in 20 mM acetic acid buffer (pH 6.0) at a concentration of 15% (w/w). In this starch milk, add maltose transglucosylase purified enzyme solution in such a way that it reaches 0.8 units per gram of starch solids, stir at room temperature for 30 minutes, and keep stirring at 80°C for 4 hours. It reacts to prepare liquefied starch. The weight average molecular weight of the partially decomposed starch obtained was 1.53 million.

Production Example 11: Partially Decomposed Starch Derived from Corn Starch Starch milk was prepared by suspending corn starch in 20 mM acetic acid buffer (pH 6.0) at a concentration of 15% (w/w). In the starch milk, maltose transglucosylase purified enzyme liquid was added in a manner of 0.6 units per gram of starch solids, and α-amylase was added in a manner of 0.03 units per gram of starch solids, After stirring at room temperature for 30 minutes, while stirring, it kept at 90 degreeC for 4.5 hours, and also kept it at 100 degreeC for 1.5 hours and made it react, and prepared the liquefied starch. The weight average molecular weight of the obtained partially decomposed starch was 1.46 million.

Production Example 12: Partially Decomposed Starch Derived from Corn Starch Starch milk was prepared by suspending corn starch in 20 mM acetic acid buffer (pH 6.0) at a concentration of 15% (w/w). In the starch milk, maltose transglucosylase purified enzyme liquid was added in a manner of 0.6 units per gram of starch solids, and α-amylase was added in a manner of 0.03 units per gram of starch solids, After stirring at room temperature for 30 minutes, it was made to react at 80 degreeC for 6 hours, stirring, and the liquefied starch was prepared. The weight average molecular weight of the obtained partially decomposed starch was 1.04 million.

Production Example 13: Partially Decomposed Starch Derived from Tapioca Starch Starch milk was prepared by suspending tapioca starch in 20 mM acetic acid buffer (pH 6.0) at a concentration of 15% (w/w). In this starch milk, add maltose transglucosylase purified enzyme liquid in such a way that it reaches 1.6 units per gram of starch solids, stir at room temperature for 30 minutes, and keep it at 80°C for 20 hours while stirring. It reacts to prepare liquefied starch. The weight average molecular weight of the obtained partially decomposed starch was 190,000.

Production Example 14: Partially Decomposed Starch Derived from Corn Starch Starch milk was prepared by suspending corn starch in 20 mM acetic acid buffer (pH 6.0) at a concentration of 15% (w/w). In this starch milk, add maltose transglucosylase purified enzyme solution in a manner that reaches 8.0 units per gram of starch solids, stir at room temperature for 30 minutes, and keep stirring at 90°C for 3.0 hours. Furthermore, it was kept at 80 degreeC for 21 hours, it was made to react, and the liquefied starch was prepared. The weight average molecular weight of the partially decomposed starch obtained was 270,000.

(Manufacture Example 15) Partially decomposed starch derived from corn starch After suspending cornstarch in tap water so as to have a concentration of 30% (w/w), 1 N sodium hydroxide was added to adjust the pH to 6.0 to obtain starch milk. To the starch milk, add maltose-transglucosylase crude enzyme solution in such a way that it reaches 0.2 units per gram of starch solids, stir at room temperature for 30 minutes, and then carry out 6 hours at 80°C while stirring. reaction to produce liquefied starch. The weight average molecular weight of the partially decomposed starch obtained was 6.07 million, and the degree of dispersion was 35.4.

(Manufacturing example 16) Corn starch was suspended in tap water so as to have a concentration of 30% (w/w), and then 1 N sodium hydroxide was added to adjust the pH to 6.0 to obtain starch milk. In this starch milk, maltose transglucosylase crude enzyme solution was added in a manner of 0.15 units per gram of starch solids, and α-amylase was added in a manner of 0.04 units per gram of starch solids, After stirring at room temperature for 30 minutes, the reaction was carried out at 80° C. for 6 hours while stirring to prepare liquefied starch. The weight average molecular weight of the partially decomposed starch obtained was 1.34 million, and the degree of dispersion was 10.6. The obtained aqueous solution of partially decomposed starch was vacuum-dried at 80° C., the obtained dried product was pulverized, and a dry powder product passing through a 1 mm mesh was recovered. The moisture content of dry powder product is 2.7%.

(Manufacturing example 17) Corn starch was suspended in tap water so as to have a concentration of 15% (w/w), and then 1 N sodium hydroxide was added to adjust the pH to 6.0 to obtain starch milk. Add α-amylase to the starch milk at a rate of 0.5 units per gram of starch solids, stir at room temperature for 30 minutes, and then react at 100°C for 20 minutes while stirring to prepare liquefaction starch. The weight average molecular weight of the partially decomposed starch obtained was 1.37 million, and the degree of dispersion was 65.6.

(Manufacturing Example 54) Corn starch was suspended in tap water so as to have a concentration of 30% (w/w), and then 1 N sodium hydroxide was added to adjust the pH to 6.0 to obtain starch milk. To the starch milk, add maltose-transglucosylase crude enzyme solution in such a way that it reaches 0.2 units per gram of starch solids, stir at room temperature for 30 minutes, and then carry out 6 hours at 80°C while stirring. reaction to produce liquefied starch. The weight average molecular weight of the partially decomposed starch obtained was 1.91 million, and the degree of dispersion was 10.1.

(3) Production of water-soluble polymers (Production Examples 18 to 34 and Production Example 55) (3-1) Manufacturing Example 18 125 g of the 15% by weight aqueous solution of the partially decomposed starch product produced in Production Example 1 (the hydroxyl group of the partially decomposed starch product is 0.35 mol) was added to a 500 ml separable flask equipped with a stirrer, a thermometer, and a condenser. Next, add 42.7 g of 48.8% sodium hydroxide aqueous solution (0.52 mol, 1.5 equivalents relative to the hydroxyl group of the partially decomposed starch product), and stir the solution below 60°C until it is completely uniform. After confirming that the solution becomes uniform, add dropwise at 50-60°C within 30 minutes. Dissolve 60.7 g of sodium monochloroacetate (0.52 mol, 1.5 equivalents to the hydroxyl group of partially decomposed starch) in 78.4 g of ion-exchanged water of aqueous solution. After adding the sodium monochloroacetate aqueous solution, the temperature was adjusted to 80 to 85° C., and stirring was performed for 1 hour. The end point of the reaction meets the following conditions: Sampling the reaction solution, using 0.01 N silver nitrate solution, and measuring the chloride ion content in the reaction solution by potentiometric titration, to achieve the calculation of the chloride ion content when all sodium monochloroacetate has reacted More than 98% of the value of 6.0%. In this production example, the chlorine content was 6.2%.

After the reaction, the reaction solution was diluted with 28 g of ion-exchanged water. The diluted reaction solution was cooled to room temperature, and added to 1 L of methanol within about 30 minutes to precipitate and reprecipitate the water-soluble polymer. After adding all the reaction solution, stirring was performed for 30 minutes, and the water-soluble polymer dispersed in methanol was separated into solid and liquid by filtration under reduced pressure.

Then, in order to remove the sodium chloride contained in the water-soluble polymer, the recovered water-soluble polymer was re-dispersed in 0.7 L of methanol/water with a volume ratio of 80/20 (volume ratio) in aqueous methanol at room temperature After stirring for 30 minutes and washing, the solid-liquid separation was carried out by filtration under reduced pressure, and the water-soluble polymer was recovered again. The chlorine content of the recovered water-soluble polymer was measured by potentiometric titration using a 0.01 N silver nitrate solution, and the washing process was repeated until the chlorine content became less than 1%. The total acid value of the obtained water-soluble polymer was 182 mgKOH/g, and the degree of etherification calculated from the total acid value was 0.71.

(3-2) Production Examples 19 to 32 A water-soluble polymer was obtained by reacting in the same manner as in Production Example 18 except that the raw materials and addition amounts described in Table 1 were changed.

[Table 1] water soluble polymer Manufacturing example 18 Manufacturing Example 19 Manufacturing example 20 Manufacturing example 21 Manufacturing example 22 Manufacturing Example 23 Manufacturing Example 24 Manufacturing Example 25 Manufacturing Example 26 Manufacturing example 27 Manufacturing example 28 Manufacturing example 29 Manufacturing Example 30 Manufacturing example 31 Manufacturing example 32 Partial starch hydrolyzate 1 Manufacturing example 1 Manufacturing example 2 Manufacturing example 3 Manufacturing example 4 Manufacturing Example 5 Manufacturing example 6 Manufacturing example 7 Manufacturing example 7 Manufacturing example 8 Manufacturing example 8 Manufacturing example 9 Manufacturing example 10 Manufacturing example 11 Manufacturing Example 12 Manufacturing Example 15 Aqueous solution concentration (%) 15 15 15 15 15 15 15 15 25 25 25 15 15 15 30 Aqueous solution volume (g) 125.0 115.0 125.0 125.0 100.0 96.4 125.0 114.8 82.5 95.2 93.7 115.0 112.5 77 66.3 Partial starch hydrolyzate 2 - - - - - - - Manufacturing Example 13 - - - - Manufacturing Example 14 - - Aqueous solution concentration (%) - - - - - - - 15 - - - - 15 - - Aqueous solution volume (g) - - - - - - - 12.8 - - - - 12.5 - - alkaline agent 48.8% NaOH aqueous solution (g) 42.7 27.5 42.7 42.7 23.9 32.9 42.7 43.6 5.5 47.4 53.4 27.5 29.9 - 23.4 48% KOH aqueous solution (g) - - - - - - - - - - - - - 75 - Aqueous solutions containing compounds containing ionic functional groups Na monochloroacetic acid (g) 60.7 44.7 60.7 60.7 38.9 46.8 60.7 61.9 8.9 77.0 75.8 44.7 48.5 - - Monochloroacetic acid (g) - - - - - - - - - - - - - 30.3 13.0 Water used to dissolve compounds containing ionic functional groups (g) 78.4 63.9 78.4 78.4 55.6 59.7 78.4 79.9 10.4 150.0 150.0 63.9 69.4 40.4 3.3 Reaction solution dilution water (g) 28 0 150 150 0 25 28 125 73 0 0 0 80 77 200 Methanol for reprecipitation (L) 1.0 0.8 1.5 1.5 0.7 0.8 1.0 1.4 0.6 1.0 1.0 0.8 1.2 1.0 1.0 Wash with aqueous methanol (L) 0.7 0.6 0.7 1.3 0.5 0.5 0.7 0.8 0.3 0.5 0.5 0.7 0.7 0.7 0.5

(Manufacturing example 33) Add 20.0 g of the powder of partially decomposed starch produced in Production Example 16 (the hydroxyl group of the partially decomposed starch is 0.36 mol) and 110 g of dimethylsulfoxide (DMSO) to a 300 ml pot equipped with a stirrer, a thermometer, and a condenser tube. Detachable flask for dissolution. Next, 10.6 g of maleic anhydride (0.11 mol, 0.30 equivalent to the hydroxyl group of the partially decomposed starch product) was added, and stirred at 90 to 95° C. for 3 hours to react. The reaction solution after the stirring was sampled, and neutralized and titrated with 0.1 N NaOH. As a result, the acid value of the reaction solution was 70 mgKOH/g (theoretical end-point acid value was 43 mgKOH/g).

After the reaction, the reaction solution was added to 2.5 L of acetone within about 30 minutes to precipitate and reprecipitate the water-soluble polymer. After adding all the reaction solution, stirring was carried out for 30 minutes, and the water-soluble polymer dispersed in acetone was separated into solid and liquid by filtration under reduced pressure and recovered.

Then, in order to remove the unreacted maleic anhydride contained in the water-soluble polymer and the maleic acid generated by hydrolysis, the recovered water-soluble polymer was redispersed in 500 mL of acetone, and the After stirring and washing at room temperature for 30 minutes, solid-liquid separation was performed by filtration under reduced pressure, and the water-soluble polymer was recovered again. The total acid value of the obtained water-soluble polymer was 90 mgKOH/g. The weight average molecular weight of the obtained water-soluble polymer was 3.1×10 ⁶ , and the degree of dispersion was 39.6.

(Manufacturing example 34) Add 27.2 g of the powder of partially decomposed starch produced in Production Example 17 (the hydroxyl group of the partially decomposed starch is 0.47 mol) and 58.1 g of dimethylsulfoxide (DMSO) to a 300 ml pot equipped with a stirrer, a thermometer, and a condenser. Detachable flask for dissolution. Next, 14.2 g (0.14 mol, 0.30 equivalent to the hydroxyl group of the partially decomposed starch product) of succinic anhydride was added. It stirred at 70-75 degreeC for 1 hour, and made it react. The reaction liquid after the stirring was sampled, and neutralized and titrated with 0.1 N NaOH. As a result, the acid value of the reaction liquid was 85 mgKOH/g (theoretical end point acid value was 80.1 mgKOH/g).

After the reaction was completed, 125 g of ion-exchanged water was added to the reaction solution for dilution. Further, 10.8 g (0.13 mol) of 48% NaOH aqueous solution was added to neutralize 93% of the theoretical amount of carboxylic acid introduced by the reaction with succinic anhydride to prepare a sodium salt. Then, the obtained solution was added to 750 ml of methanol within about 30 minutes to precipitate and reprecipitate the water-soluble polymer. After adding all the reaction solution, stirring was carried out for 30 minutes, and the water-soluble polymer dispersed in methanol was separated into solid and liquid by filtration under reduced pressure and recovered.

Next, in order to remove the unreacted succinic anhydride contained in the water-soluble polymer and the succinic acid produced by hydrolysis, the recovered water-soluble polymer was re-dispersed in 500 mL of methanol and carried out at room temperature for 30 minutes. After stirring and washing, solid-liquid separation was carried out by filtration under reduced pressure, and the water-soluble polymer was recovered again. As a result of measuring the total acid value and free acid value of the obtained water-soluble polymer, it was confirmed that the total acid value was 138 mgKOH/g and the free acid value was partially neutralized 37 mgKOH/g. The weight average molecular weight of the obtained water-soluble polymer was 3.7×10 ⁶ , and the degree of dispersion was 13.8.

[Table 2] water soluble polymer Manufacturing example 33 Manufacturing example 34 Partial starch hydrolyzate 1 Manufacturing Example 16 Manufacturing Example 17 Powder weight (g) 20 27.2 DMSO (g) 110 58.1 Anhydride (g) Succinic anhydride - 14.2 maleic anhydride 10.6 - Reaction temperature (°C) 90～95 70～75 Reaction solution dilution water (g) - 125 48% NaOH aqueous solution (g) - 10.8 Solvent for reprecipitation (L) Methanol - 0.75 acetone 2.5 - Solvent for cleaning (L) Methanol - 0.5 acetone 0.5 - Physical properties of water-soluble polymers Mw (×10 ⁶ ) 3.1 3.7 Mw/Mn 39.6 13.8 Total acid value (mgKOH/g) 90 138 Free acid value (mgKOH/g) - 37

(Manufacturing Example 55) 200 g of the 30% by weight aqueous solution of the partially decomposed starch product produced in Production Example 54 (the hydroxyl group of the partially decomposed starch product is 1.11 mol) was added to a 500 ml separable flask equipped with a stirrer, a thermometer, and a condenser. Next, add 48.8% sodium hydroxide aqueous solution 79.4 g (0.96 mol, 0.86 equivalent relative to the hydroxyl group of the partially decomposed starch product), and stir the solution below 60°C until it is completely uniform. After confirming that the solution became uniform, 89.9 g (0.46 mol, 0.4 equivalent to the hydroxyl group of partially decomposed starch) crystals of 6-bromohexanoic acid were added little by little over 30 minutes at 50 to 60°C. After adding 6-bromohexanoic acid, the temperature was adjusted to 45 to 50° C., and stirring was performed for 10 hours. The end point of the reaction meets the following conditions: the reaction solution is sampled, and the bromide ion content in the reaction solution is measured by potentiometric titration using a 0.01 N silver nitrate solution, and the content of the bromide ion when all 6-bromohexanoic acid has reacted reaches More than 98% of the calculated value of 9.8%. In this production example, the bromine content was 10.1%.

After the reaction, the reaction solution was diluted with 250 g of ion-exchanged water. The diluted reaction solution was cooled to room temperature, and added to 1.6 L of ethanol within about 30 minutes to precipitate and reprecipitate the water-soluble polymer. After adding all the reaction solution, stirring was carried out for 30 minutes, and the water-soluble polymer dispersed in ethanol was separated into solid and liquid by filtration under reduced pressure.

Then, in order to remove the sodium bromide contained in the water-soluble polymer, the recovered water-soluble polymer was re-dispersed in 0.5 L of ethanol/water with a volume ratio of 90/10 (volume ratio) in aqueous ethanol, at room temperature After stirring and washing for 30 minutes, solid-liquid separation was carried out by vacuum filtration, and the water-soluble polymer was recovered again. The bromine content of the recovered water-soluble polymer was measured by potentiometric titration using 0.01 N silver nitrate solution, and the washing process was repeated until the bromide ion content became less than 1%. The total acid value of the obtained water-soluble polymer was 145 mgKOH/g, and the degree of etherification calculated from the total acid value was 0.64.

(4) Production of water-absorbent resin (Production Examples 35 to 51) Put 35 g of the water-soluble polymer obtained in Production Example 18 (wet product containing methanol, with a moisture content of 65%) into a 300 ml beaker, and then add 100 ml of methanol/water = 80/20 (volume ratio) of aqueous methanol to disperse the water-soluble polymer. To this, while stirring with a magnetic stirrer, 3.7 ml of 1 N hydrochloric acid was slowly added with a measuring pipette. After adding hydrochloric acid, stir for 15 minutes, perform vacuum suction filtration, and recover the water-soluble polymer partially neutralized into free acid. The recovered water-soluble polymers are wet crystals containing hydrous alcohol. The wet crystals were transferred to a petri dish, put into an air dryer set at 70° C., and dried for 12 hours to perform cross-linking treatment. During the drying process, methanol volatilizes at the initial stage, and the water-soluble polymer temporarily dissolves in water and becomes caramel-like, so after drying, it becomes a spongy solid. The spongy solid was pulverized with a mortar and sieved through a sieve with a mesh size of 150 μm and 850 μm to recover particles with a particle diameter of 150 to 850 μm.

The water-absorbent resins of Production Examples 36 to 51 were obtained in the same manner as in Production Example 35, except that the raw materials and addition amounts described in Table 3 were changed.

[table 3] Absorbent resin Manufacturing example 35 Manufacturing example 36 Manufacturing example 37 Manufacturing example 38 Manufacturing example 39 Manufacturing Example 40 Manufacturing example 41 Manufacturing example 42 Manufacturing example 43 Manufacturing example 44 Manufacturing Example 45 Manufacturing example 46 Manufacturing example 47 Manufacturing example 48 Manufacturing Example 49 Manufacturing Example 50 Manufacturing example 51 water soluble polymer Manufacturing example 18 Manufacturing example 19 Manufacturing example 20 Manufacturing Example 21 Manufacturing example 21 Manufacturing Example 22 Manufacturing Example 23 Manufacturing Example 24 Manufacturing Example 24 Manufacturing Example 25 Manufacturing Example 26 Manufacturing Example 27 Manufacturing example 28 Manufacturing example 29 Manufacturing Example 30 Manufacturing example 31 Manufacturing example 32 Weight (g) 35 45 50 27 25 45 45 35 35 25 45 45 45 45 20 25 25 Moisture content (%) 65 69 69 64 64 66 66 65 65 67 68 63 73 60 69 66 66 Aqueous methanol (ml) 100 120 125 123 122 120 123 123 122 123 122 121 123 121 123 122 83 1N hydrochloric acid (ml) 3.7 4.9 2.3 1.7 3.1 4.8 2.3 2.4 3.5 1.8 3.0 4.3 2.5 3.6 1.6 2.8 1.0

(Manufacturing example 52) Put 20 g of the water-soluble polymer obtained in Production Example 33 (wet product containing water and acetone, with a moisture content of 61%) into a 300 ml beaker, and then add 60 ml of acetone/water=90/10 (volume ratio) of water-containing acetone to disperse the water-soluble polymer. There, while stirring with a magnetic stirrer, 19.3 ml of 1 N NaOH was slowly added with a measuring pipette. After adding the aqueous NaOH solution, the mixture was stirred for 15 minutes, and vacuum filtration was performed to recover a water-soluble polymer in which a part of the carboxylic acid introduced by maleic anhydride was neutralized into a sodium salt. The recovered water-soluble polymer was wet crystals containing aqueous acetone. The wet crystals were transferred to a Petri dish, put into an air dryer set at 70° C., and dried for 12 hours to perform cross-linking treatment. The solid obtained after the treatment was pulverized with a mortar, sieved with a sieve with a mesh size of 150 μm and 850 μm, and particles with a particle size of 150-850 μm were recovered.

(Manufacturing Example 53) Transfer 25 g of the water-soluble polymer obtained in Production Example 34 (wet product containing methanol, moisture content: 63%) (wet crystallization) to a Petri dish, and put it into an air dryer set at 70°C for Dry for 12 hours, and carry out cross-linking treatment. After the treatment, the obtained solid was pulverized with a mortar, sieved with a sieve with a mesh size of 150 μm and 850 μm, and particles with a particle size of 150-850 μm were recovered.

(Manufacturing Example 56) Put 25 g of the water-soluble polymer obtained in Production Example 55 (wet product containing ethanol, with a moisture content of 61%) into a 300 ml beaker, and then add 80 ml of ethanol/water=90/10 (volume ratio) of hydrous ethanol to disperse the water-soluble polymer. To this, while stirring with a magnetic stirrer, 12.1 ml of 1 N hydrochloric acid was slowly added with a measuring pipette. After adding hydrochloric acid, stir for 15 minutes, perform vacuum suction filtration, and recover the water-soluble polymer partially neutralized into free acid. The recovered water-soluble polymers are wet crystals containing hydrous alcohol. The wet crystals were transferred to a Petri dish, put into an air dryer set at 150° C., and dried for 1 hour to perform cross-linking treatment. The solid obtained after the treatment was pulverized with a mortar, sieved with a sieve with a mesh size of 150 μm and 850 μm, and particles with a particle size of 150-850 μm were recovered.

(5) Production of water-absorbent resin (comparative production examples 1 and 2) According to the procedure disclosed in Example (EXAMPLE) 2 of Patent Document 1 (US Patent No. 5,079,354), corn starch without low molecular weight was carboxymethylated, and heated and dried under alkaline conditions to produce a comparative example. 1. Water absorbent resin.

According to the sequence disclosed in Example 1 (paragraphs [0146] to [0147]) of Patent Document 2 (Japanese Special Publication No. 2010-504414), after using epichlorohydrin to cross-link the potato starch without low molecular weight, carry out Carboxymethylation was carried out to produce the water-absorbent resin (obtained by hydrochloric acid treatment) of Comparative Production Example 2.

(6) Viscosity evaluation method of partially decomposed starch The viscosity at the time of performing the operation of mixing with NaOH aqueous solution about the partial starch decomposition product was evaluated based on the following reference|standard. The mixing operation was carried out as follows: According to the addition ratios described in Manufacturing Examples 15-28, in a 500 ml separable flask, a glass-made anchor-type stirring blade (blade diameter: 60 mm) was installed on a mechanical stirrer (Shinto Scientific The device obtained from Sany Motor BL600 manufactured by Co., Ltd. The evaluation results are shown in Table 4. ○: Liquid viscosity is low and can be mixed uniformly. Δ: The liquid viscosity is high, or the viscosity becomes high during mixing, so it cannot be mixed uniformly. ×: The liquid viscosity is high, or the viscosity becomes high during mixing, so it cannot be mixed.

(7) Evaluation method of water-soluble polymer (7-1) Total acid value of water-soluble polymers Here, the method of measuring the total acid value of the water-soluble polymer which has carboxymethyl group as an acidic group is demonstrated. Accurately weigh about 0.3 g of water-soluble polymer into a 100 ml beaker, and dissolve it in 40 ml of ion-exchanged water. This aqueous solution was set in a potentiometric titration device (AT-610, manufactured by Kyoto Denshi Kogyo Co., Ltd.) equipped with a glass electrode (C-171, manufactured by Kyoto Denshi Kogyo Co., Ltd.). When the sample is all sodium salt, at this stage, the potential appears to be below 30 mV, so add 1 N hydrochloric acid until the potential reaches above 320 mV, so that all the carboxylic acid groups in the water-soluble polymer become free acids. state (into a state of excess hydrochloric acid). After confirming that the potential reached 320 mV or more, neutralization titration was performed with a 0.1 N NaOH aqueous solution. In this titration, two inflection points were detected, the first inflection point was detected near 220 mV, and the second inflection point was detected near 0 to -30 mV. The former is the neutralization point of excess hydrochloric acid in the sample, and the latter is the neutralization point of carboxylic acid in the water-soluble polymer. Therefore, the total acid value was calculated by the following formula 1. Total acid value (mgKOH/g) = [{(Vb－Va)×0.1×fa×56.11}÷Sa]/(1－wr) (Formula 1) Here, Va is the capacity (ml) of 0.1 N NaOH consumed before reaching the first inflection point, Vb is the capacity (ml) of 0.1 N NaOH consumed before reaching the second inflection point, and fa is 0.1 The power value of NaOH of N, Sa is the amount of sample taken. wr is the moisture content of the water-soluble polymer measured by the following method.

(7-2) Degree of etherification of water-soluble polymers Using the value of the said total acid value, it calculated by following Formula 2. Degree of etherification = (162×TAV) ÷ (56100－80×TAV) (Formula 2) Here, TAV is the total acid value (unit: mgKOH/g) of a water-soluble polymer.

(7-3) Moisture content of water-soluble polymer The moisture content refers to the weight loss ratio (%) relative to the initial weight of the sample when the sample is dried at a drying temperature of 130° C. using a halogen moisture meter. In this example, 0.5-1.0 g of water-soluble polymer was placed in the Halogen Moisture Meter HC103 manufactured by Mettler-Toledo Co., Ltd., at a drying temperature of 130°C, a shutdown standard of 1 mg/50 seconds, and %MC mode (display MC value = (sample initial weight - dry weight) ÷ sample initial weight × 100 mode) to measure. Set the displayed MC value as the moisture content.

(7-4) Free acid value of water-soluble polymer The free acid value is the acid value defined in the case of crosslinking of the water-soluble polymer by acid treatment. In the examples, since the cross-linked polymer was produced following the acid treatment, it was difficult to directly quantify by titration, so the value calculated by the following calculation was defined as the free acid value. In the acid treatment, an acid having a lower pKa than the carboxylic acid of the water-soluble polymer is used for the treatment, so the amount of acid added in the acid treatment is substantially equal to the free acid value. Therefore, the free acid value was calculated by the following formula 3. Free acid value (mgKOH/g) = (Vc×N×fb×56.11) ÷ Sb (Formula 3) Here, Vc is the capacity (ml) of the aqueous acid solution used for the acid treatment, N is the equivalent concentration of the acid solution, fb is the molarity of the acid solution, and Sb is the weight of the water-soluble polymer added in the acid treatment (purity ).

(8) Evaluation method of water-absorbent resin (8-1) Water absorption rate without pressure (physiological saline) Put 1.0 g of the measurement sample into a tea bag (20 cm in length and 10 cm in width) made of nylon mesh with a mesh size of 63 μm (JIS Z8801-1:2006), and put it in 1,000 ml of physiological saline (saline Concentration is 0.9% by weight), impregnation was carried out for 3 hours without stirring, and then hung for 10 minutes to control the water. Measure the weight (h1) including the tea bag, and calculate the water retention according to the following formula. Furthermore, the temperature of the physiological saline used and the measurement environment is 25°C±2°C. FSC (g/g) = (h1) - (h2) In addition, (h2) is the weight of the tea bag measured by the same operation as above about the case where there is no measurement sample. Here, FSC is the abbreviation of Free Swell Capacity, which means free swelling capacity, and refers to the water absorption capacity without pressure.

(8-2) Water absorption rate without pressure (ion-exchanged water) Except for putting 0.2 g of the measurement sample into a tea bag and using ion-exchanged water instead of saline, measure the weight including the tea bag after immersion in the same manner as the water absorption capacity under no pressure (physiological saline) ( h1'), and calculate the water retention capacity according to the following formula. In addition, (h2') is the weight of the tea bag measured by the operation similar to the above about the case where there is no measurement sample. FSC (g/g) = {(h1')-(h2')}/0.2

(8-3) Water retention rate (normal saline) After the above water absorption rate measurement without pressure, set it together with the tea bag in a centrifugal separator, perform centrifugal dehydration at 150 G for 90 seconds to remove the remaining liquid components, and measure the weight including the tea bag (h3) , according to the following formula to find the water retention. CRC (g/g) = (h3) - (h4) In addition, (h4) is the weight of the tea bag measured by the same operation as above about the case where there is no measurement sample. Here, CRC is the abbreviation of Centrifuge Retention Capacity, which means centrifuge retention capacity and refers to water retention rate.

(8-4) Water retention rate (ion exchanged water) After the measurement of the water absorption rate under no pressure, set it together with the tea bag in a centrifugal separator, perform centrifugal dehydration at 150 G for 90 seconds to remove the remaining liquid components, and measure the weight including the tea bag (h3' ), and calculate the water retention according to the following formula. CRC (g/g) = {(h3') - (h4')}/0.2 In addition, (h4') is the weight of the tea bag measured by the operation similar to the above about the case where there is no measurement sample.

(8-5) Alkali decomposability About 5 g of the water-absorbing gel subjected to the water retention test with physiological saline was put into a 200 ml beaker, and several drops of 48.8% NaOH aqueous solution were added thereon. Thereafter, the mixture was stirred with a stainless steel pharmaceutical spoon, and the mixture was spread thinly on the bottom of the beaker, and the dissolved state was visually confirmed. When it disintegrates in a gel state, the insoluble matter disappears, and becomes a transparent solution, it is evaluated as "dissolved", and when the gel state is maintained or a part of the insoluble matter remains, it is evaluated as "insoluble".

(9) Evaluation of water-absorbent resin (Examples 1-20, Comparative Examples 1-2) Water absorption performance and alkali decomposability were measured for each of the water-absorbent resins obtained in Production Examples 35 to 53, Production Example 56, and Comparative Production Examples 1 to 2. The results are shown in Table 4.

[Table 4] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12 Example 13 Example 14 Example 15 Example 16 Example 17 Example 18 Example 19 Example 20 Comparative example 1 Comparative example 2 water soluble polymer Manufacturing Example 18 Manufacturing Example 19 Manufacturing Example 20 Manufacturing Example 21 Manufacturing Example 21 Manufacturing Example 22 Manufacturing Example 23 Manufacturing Example 24 Manufacturing Example 24 Manufacturing Example 25 Manufacturing example 26 Manufacturing example 27 Manufacturing example 28 Manufacturing example 29 Manufacturing Example 30 Manufacturing example 31 Manufacturing example 32 Manufacturing example 33 Manufacturing example 34 Manufacturing example 55 Comparative Manufacturing Example 1 Comparative Manufacturing Example 2 Absorbent resin Manufacturing example 35 Manufacturing example 36 Manufacturing example 37 Manufacturing example 38 Manufacturing example 39 Manufacturing Example 40 Manufacturing example 41 Manufacturing example 42 Manufacturing example 43 Manufacturing example 44 Manufacturing Example 45 Manufacturing example 46 Manufacturing example 47 Manufacturing example 48 Manufacturing Example 49 Manufacturing Example 50 Manufacturing example 51 Manufacturing example 52 Manufacturing Example 53 Manufacturing example 56 Starch type corn starch corn starch corn starch corn starch corn starch cassava cassava cassava cassava cassava waxy corn waxy corn waxy corn potato corn starch corn starch corn starch corn starch corn starch corn starch corn starch potato Cross-linking (acid or base) HCl HCl HCl HCl HCl HCl HCl HCl HCl HCl HCl HCl HCl HCl HCl HCl HCl NaOH NaOH HCl none (Epichlorohydrin) Partial starch hydrolyzate 1 Manufacturing example 1 Manufacturing example 2 Manufacturing example 3 Manufacturing Example 4 Manufacturing Example 4 Manufacturing Example 5 Manufacturing example 6 Manufacturing example 7 Manufacturing example 7 Manufacturing example 7 Manufacturing example 8 Manufacturing example 8 Manufacturing example 9 Manufacturing example 10 Manufacturing example 11 Manufacturing example 12 Manufacturing example 15 Manufacturing Example 16 Manufacturing example 17 Manufacturing example 54 - - Amount used (weight%) 100 100 100 100 100 100 100 100 100 90 100 100 100 100 90 100 100 100 100 100 - - Mw (×10 ⁶ ) 0.81 0.66 0.72 1.46 1.46 0.20 1.18 1.96 1.96 1.96 0.61 0.61 1.33 1.53 1.46 1.04 6.07 1.34 1.37 1.91 - - Mw/Mn 6.4 7.4 8.7 9.8 9.8 2.9 22.6 8.0 8.0 8.0 35.2 35.2 19.1 9.9 9.8 10.6 35.4 10.6 65.6 10.1 - - Partial starch hydrolyzate 2 - - - - - - - - - Manufacturing Example 13 - - - - Manufacturing Example 14 - - - - - - - Amount used (weight%) 0 0 0 0 0 0 0 0 0 10 0 0 0 0 10 0 0 0 0 0 - - Mw (×10 ⁶ ) - - - - - - - - - 0.19 - - - - 0.27 - - - - - - - Mw/Mn - - - - - - - - - 2.94 - - - - 4.40 - - - - - - - counter cation sodium sodium sodium sodium sodium sodium sodium sodium sodium sodium sodium sodium sodium sodium sodium Potassium sodium sodium sodium sodium sodium sodium Physical properties of water-soluble polymers Mw (×10 ⁶ ) 3.4 2.0 2.3 4.0 4.0 0.8 5.3 11.5 11.5 9.4 1.6 2.3 4.5 9.3 3.4 1.9 45.6 3.1 3.7 4.8 - - Mw/Mn 9.3 8.7 8.5 7.2 7.2 10.1 16.8 19.3 19.3 25.3 7.4 22.3 14.6 20.9 16.1 11.2 104.9 39.6 13.8 14.0 - - Total acid value (mgKOH/g) 182 170 180 161 161 142 165 170 170 172 71 192 191 162 134 138 154 90 138 145 - - degree of etherification 0.71 0.65 0.70 0.60 0.60 0.51 0.62 0.65 0.65 0.66 0.23 0.76 0.76 0.61 0.48 0.50 0.57 0.32 (*1) 0.57 (*2) 0.64 - - Free acid value (mgKOH/g) 17 twenty two 11 11 twenty two 17 8 8 11 11 11 17 8 17 11 17 11 17 37 11 - - viscosity ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ Δ Δ water absorption FSC (ion exchanged water) 179 140 216 227 156 212 268 331 185 289 152 171 251 228 216 233 143 40 160 62 69 292 CRC (ion exchanged water) 147 112 131 160 127 154 172 186 152 184 122 130 145 182 160 140 112 twenty one 63 39 twenty one 81 FSC (Normal Saline) 43 36 34 51 41 42 63 64 44 58 twenty three 29 53 48 52 47 27 11 25 20 15 29 CRC (Normal Saline) 39 33 29 44 38 36 55 50 41 51 twenty one 27 42 44 46 39 twenty four 7 twenty two 14 5 26 Alkali decomposition to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve to dissolve insoluble insoluble *1: The degree of esterification using maleic anhydride = (162*total acid value (mgKOH/g))/(56100-120*total acid value (mgKOH/g)) *2: The degree of esterification using succinic anhydride = (162* total acid value (mgKOH/g))/(56100-122* total acid value (mgKOH/g))

As shown in Table 4, compared with Comparative Examples 1-2, the water-absorbent resins of Examples 1-20 are superior in water-absorbing performance.

Moreover, the water-soluble polymer used as the raw material of Examples 1-20 was low in viscosity compared with Comparative Examples 1-2, and it was excellent in workability|operativity at the time of manufacturing a water-absorbent resin. The higher the viscosity, the more difficult it is to mix uniformly, and the choice of manufacturing equipment may be limited, or the quality may vary. In addition, in order to mix uniformly, it is necessary to increase the degree of dilution, and there is a concern that production efficiency will decrease. .

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Claims (16)

A water-absorbent resin comprising a cross-linked product of a water-soluble polymer having an acidic group introduced into a partially decomposed starch product having a weight average molecular weight of 7.5 million or less. The water-absorbent resin according to claim 1, wherein the weight average molecular weight of the partially decomposed starch product is 50,000 or more. The water-absorbent resin according to claim 1 or 2, wherein the degree of dispersion (weight average molecular weight/number average molecular weight) of the partially decomposed starch product is 5 or more. The water-absorbent resin according to any one of claims 1 to 3, wherein the water-soluble polymer has a pullulan-equivalent weight-average molecular weight of 500,000 to 50 million as analyzed by aqueous size exclusion chromatography. The water-absorbent resin according to any one of claims 1 to 4, wherein the acidic group is a carboxyalkyl group, a carboxyalkenyl group, or a sulfoalkyl group. The water-absorbent resin according to any one of Claims 1 to 5, which has the following characteristics: (a) The non-pressurized water absorption rate of ion-exchanged water is 100-400 g/g; (b) The water retention rate of ion-exchanged water is 80-300 g/g; (c) The non-pressurized water absorption capacity of normal saline is 20-70 g/g; and/or (d) The water retention rate of normal saline is 7-60 g/g. The water-absorbent resin according to any one of Claims 1 to 6, the ratio (A/B) of the unpressurized water absorption capacity (A) of ion-exchanged water to the unpressurized absorption capacity (B) of physiological saline ) is 7 or less. The water-absorbent resin according to any one of claims 1 to 7, wherein the content of water and/or the hydrophilic solvent is 0.1 to 10%. The water-absorbent resin according to any one of claims 1 to 8, which does not have an internal crosslinking structure formed by covalent bonds. A method for decomposing a water-absorbent resin, comprising the step of treating the water-absorbent resin according to any one of claims 1 to 9 with alkali. An article comprising the water-absorbent resin according to any one of claims 1 to 9. A water-soluble polymer, which is formed by introducing acidic groups into partially decomposed starch with a weight average molecular weight of less than 7.5 million. The water-soluble polymer according to claim 12, wherein the degree of dispersion (weight average molecular weight/number average molecular weight) of the partially decomposed starch product is 5 or more. The water-soluble polymer according to claim 12 or 13, wherein the pullulan-equivalent weight average molecular weight (Mw) analyzed by aqueous size exclusion chromatography is 500,000 to 50 million. The water-soluble polymer according to any one of claims 12 to 14, wherein the acidic group is carboxyalkyl, carboxyalkenyl, or sulfoalkyl. A resin composition for producing a water-absorbent resin, comprising the water-soluble polymer according to any one of claims 12 to 15.