Method for producing amine adduct of polyaspartic acid and method for producing crosslinked polyaspartic acid

Abstract

Provided are a method for producing an amine adduct of polyaspartic acid, in which an amine addition reaction can be performed without using an organic solvent and an amine adduct of polyaspartic acid having a high amine addition ratio and a high weight-average molecular weight can be obtained, and a method for producing a polyaspartic acid crosslinked body using the amine adduct of polyaspartic acid obtained by the production method.SOLUTION: This method for producing the amine addition product of the polyaspartic acid comprises a process (A) for reacting a polysuccinimide with a compound having a primary amino group in an aqueous medium under conditions of ≤ 20 °C reactional temperature and ≤ pH12 reactional temperature.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing an amine adduct of polyaspartic acid and a method for producing a crosslinked polyaspartic acid. [Background technology]

[0002] Water-absorbent resins are resins that can absorb tens to thousands of times their own weight in water, and are used in a wide range of fields, including sanitary products, disposable diapers, and medical supplies such as patches. Acrylic acid-based water-absorbent resins are a typical example (Patent Document 1). However, acrylic acid-based water-absorbent resins have low biodegradability, and their disposal (incineration and disposal) after use is becoming an issue. Therefore, there is a strong demand for novel biodegradable water-absorbent resins.

[0003] Polyaspartic acid has water retention properties and is expected to be used as a water-absorbent resin. When used as a water-absorbent resin, a crosslinked polyaspartic acid crosslinked with a crosslinking agent is used. For example, Patent Document 2 describes a water-absorbent resin containing a crosslinked polyaspartic acid crosslinked with an epoxy compound. A manufacturing method is also described. Patent Document 3 describes a water-absorbent resin containing a polymer having a polyaspartic acid skeleton crosslinked with a diamine. Patent Document 4 describes a water-absorbent resin containing a crosslinked polyaspartic acid crosslinked with an epoxy compound and a diamine compound.

[0004] Polyaspartic acid is also expected to be used as a thickener. For example, Patent Document 5 describes the use of polyaspartic acid crosslinked with polyamines as a thickener. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-112474 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-063511 [Patent Document 3] Japanese Patent Application Publication No. 2019-089898 [Patent Document 4] International Publication No. 2023 / 155523 [Patent Document 5] Japanese Patent Application Publication No. 2023-053737 Summary of the Invention [Problem to be solved by the invention]

[0006] Amine adducts of polyaspartic acid obtained by reacting polysuccinimide with amine compounds are expected to be used as thickeners or water-absorbent resins.

[0007] In the reaction between polysuccinimide and an amine compound, a polar organic solvent such as dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) is usually used as the reaction solvent. Therefore, a process for recovering the organic solvent after the reaction and a process for treating the recovered organic solvent are required. If an aqueous solvent containing no organic solvent could be used as the reaction solvent, the workload and environmental load could be reduced.

[0008] Furthermore, when an amine adduct of polyaspartic acid is used as a thickener or water absorbent, the thickening or water retention tends to be higher as the amine compound addition rate and weight-average molecular weight increase, and therefore, in the reaction of polysuccinimide with an amine compound, it is desirable to obtain an amine adduct of polyaspartic acid having a high amine compound addition rate and weight-average molecular weight.

[0009] Therefore, an object of the present invention is to provide a method for producing an amine adduct of polyaspartic acid, which can carry out an amine addition reaction without using an organic solvent and can produce an amine adduct of polyaspartic acid having a high amine addition rate and a high weight-average molecular weight, and a method for producing a crosslinked polyaspartic acid using the amine adduct of polyaspartic acid obtained by the production method. [Means for solving the problem]

[0010] The present invention includes the following aspects. [1] A method for producing an amine adduct of polyaspartic acid, comprising step (A) reacting polysuccinimide with a compound having a primary amino group in an aqueous solvent at a reaction temperature of 20°C or less and a reaction pH of 12 or less. [2] The method for producing an amine adduct of polyaspartic acid according to [1], wherein in the step (A), the mass ratio of the polysuccinimide to the aqueous solvent (polysuccinimide / aqueous solvent) is in the range of 1 / 1 to 1 / 2. [3] The method for producing an amine adduct of polyaspartic acid according to [1] or [2], wherein the polysuccinimide is polysuccinimide particles that have passed through a sieve with an opening of 500 μm. [4] The method for producing an amine adduct of polyaspartic acid according to [3], wherein the polysuccinimide is polysuccinimide particles that have passed through a sieve with an opening of 150 μm. [5] The method for producing an amine adduct of polyaspartic acid according to any one of [1] to [4], wherein the reaction temperature in the step (A) is 15°C or lower. [6] The method for producing an amine adduct of polyaspartic acid according to any one of [1] to [5], wherein the compound having a primary amino group is a polyfunctional amine. [7] The method for producing an amine adduct of polyaspartic acid according to [6], wherein the polyfunctional amine has a first primary amino group and a second primary amino group, and the first secondary amino group is a polyfunctional amine having lower reactivity with the polysuccinimide than the first primary amino group. [8] The method for producing an amine adduct of polyaspartic acid according to [7], wherein the polyfunctional amine is at least one selected from the group consisting of lysine, ornithine, and arginine. [9] A method for producing a crosslinked polyaspartic acid, comprising a step of reacting a crosslinking agent with the polyaspartic acid amine adduct obtained by the method for producing an amine adduct of polyaspartic acid according to any one of [1] to [8] to carry out a crosslinking reaction. [Effects of the Invention]

[0011] According to the present invention, there are provided a method for producing an amine adduct of polyaspartic acid, which can carry out an amine addition reaction without using an organic solvent and can produce an amine adduct of polyaspartic acid having a high amine addition rate and a high weight-average molecular weight, and a method for producing a crosslinked polyaspartic acid using the amine adduct of polyaspartic acid obtained by the above production method. DETAILED DESCRIPTION OF THE INVENTION

[0012] A numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0013] [Method for producing amine adduct of polyaspartic acid] A first aspect of the present disclosure is a method for producing an amine adduct of polyaspartic acid, which includes step (A) of reacting polysuccinimide with a compound having a primary amino group in an aqueous solvent at a reaction temperature of 20°C or less and a reaction pH of 12 or less.

[0014] <Process (A)> (Polysuccinimide) Polysuccinimide is a polymer represented by the following formula (1).

[0015] [ka]

[0016] In the formula (1), n ​​represents the number of repeating succinimide monomer units, and is an integer of 2 or more, for example, an integer of 10 to 10,000.

[0017] Polysuccinimide can be produced by known methods. For example, polysuccinimide can be produced by heating aspartic acid in the presence of phosphoric acid at 170 to 190°C in a vacuum to cause dehydration condensation. To obtain a polysuccinimide with a higher molecular weight, the polysuccinimide obtained as described above can be treated with a condensing agent such as dicyclohexylcarbodiimide. The weight-average molecular weight of polysuccinimide is, for example, 20,000 or more, preferably 50,000 or more, more preferably 70,000 or more, and even more preferably 10 or more. The weight-average molecular weight of polysuccinimide is preferably 500,000 or less, more preferably 200,000 or less. The weight-average molecular weight is a converted value measured by GPC using polystyrene as a standard substance.

[0018] After obtaining the reaction product as described above, the polysuccinimide may be obtained by pulverizing the reaction product and washing it with distilled water or the like until the filtrate has a pH of 2 or less to 7. After washing, the polysuccinimide can be obtained by vacuum drying at 70 to 90°C.

[0019] The powdered polysuccinimide may be fractionated using a sieve to remove particles with a large particle size. For example, polysuccinimide particles that have passed through a sieve with a mesh size of 500 μm can be used. Alternatively, for example, polysuccinimide particles that have passed through a sieve with a mesh size of 150 μm can be used. The smaller the particle size of the polysuccinimide particles, the higher the amine addition rate and the higher the weight-average molecular weight of the polyaspartic acid amine adduct obtained by the production method of this embodiment.

[0020] (Compound having a primary amino group: Compound (A)) A compound having a primary amino group (-NH2) (hereinafter also referred to as "compound (A)") is a compound having one or more primary amino groups. In addition to one or more primary amino groups, compound (A) may also have one or more secondary amino groups, or one or more tertiary amino groups.

[0021] The number of primary amino groups contained in compound (A) may be, for example, 1 to 4, preferably 1 to 3, and more preferably 1 or 2. Compound (A) may be a monofunctional amine or a polyfunctional amine. A polyfunctional amine is an amine compound having two or more amino groups selected from the group consisting of primary amino groups and secondary amino groups. When a monofunctional amine is used, the amine adduct of polyaspartic acid obtained by the production method of this embodiment can be used as a thickener. When a polyfunctional amine is used, the amine adduct of polyaspartic acid obtained by the production method of this embodiment can be used as a thickener or a water-absorbing resin.

[0022] Examples of the compound (A) include water-soluble amine compounds having 1 to 22 carbon atoms. The compound (A) may be an aliphatic amine or an aromatic amine. Examples of the water-soluble amine compound include amine compounds having a LogP (n-octanol / water partition coefficient) of less than 3.

[0023] Examples of the aliphatic amine having one primary amino group include alkyl monoamines, alkanol monoamines, and alkenyl monoamines.

[0024] Examples of alkyl monoamines include alkyl monoamines having an alkyl group having 1 to 22 carbon atoms. The alkyl group of the alkyl monoamine may be linear, branched, or may have a ring structure. Specific examples of alkyl monoamines include linear alkyl monoamines such as methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, dodecylamine, and octadecylamine; branched alkyl monoamines such as isopropylamine, isobutylamine, isopentylamine, and isohexylamine; cycloalkyl monoamines such as cyclopropylamine, cyclobutylamine, cyclopentylamine, and cyclohexylamine; and cycloalkyl alkyl monoamines such as cyclobutylmethylamine, cyclopentylmethylamine, cyclohexylmethylamine, cyclobutylethylamine, cyclopentylethylamine, cyclohexylethylamine, cyclobutylpropylamine, cyclopentylpropylamine, cyclohexylpropylamine, cyclobutylbutylamine, cyclopentylbutylamine, and cyclohexylbutylamine, but are not limited to these.

[0025] Examples of alkanol monoamines include alkanol monoamines having an alkyl group having 1 to 22 carbon atoms. The alkyl group of the alkanol monoamine may be linear, branched, or may contain a ring structure. Specific examples of alkanol monoamines include linear alkanol monoamines such as methanolamine, ethanolamine, propanolamine, butanolamine, pentanolamine, hexanolamine, heptanolamine, and octanolamine; branched alkanol monoamines such as isopropanolamine, isobutanolamine, isopentanolamine, and isohexanolamine; and cycloalkanol monoamines such as aminomethylcyclopropanol, aminomethylcyclobutanol, and cis-4-amino-1-methylcyclohexanol, but are not limited to these.

[0026] Examples of alkenyl monoamines include alkenyl monoamines having an alkenyl group having 2 to 22 carbon atoms. The alkenyl group of the alkenyl monoamine may be linear, branched, or may contain a ring structure. Specific examples of alkenyl monoamines include 2-butenylamine, 3-butenylamine, 4-pentenylamine, and 5-hexenylamine.

[0027] Examples of the aliphatic amine having two primary amino groups include alkyldiamine, polyetherdiamine, polyalkylenepolyamine, and diamine compounds containing a disulfide bond.

[0028] Examples of alkyldiamines include alkyldiamines having an alkyl group having 1 to 22 carbon atoms. The alkyl group of the alkyldiamine may be linear, branched, or may have a ring structure. Specific examples of alkyldiamines include, but are not limited to, linear alkyldiamines such as ethylenediamine and hexamethylenediamine; and alicyclic diamines such as norbornenediamine, 1,3-bis(aminomethyl)cyclohexane, and 1,4-bis(aminomethyl)cyclohexane.

[0029] Examples of polyetherdiamines include polyetherdiamines having a poly(oxyalkylene) group having 1 to 22 carbon atoms. The poly(oxyalkylene) group of the polyetherdiamine may be linear, branched, or may contain a ring structure. The alkylene chain in the poly(oxyalkylene) chain may have 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, and more preferably an ethylene group or a propylene group. Specific examples of polyetherdiamines include, but are not limited to, 1,2-bis(2-aminoethoxy)ethane, diethylene glycol bis(3-aminopropyl) ether, polyoxyethylenediamine, and polyoxypropylenediamine.

[0030] Examples of polyalkylene polyamines include polyalkylene polyamines having 1 to 22 carbon atoms. Specific examples of polyethylene polyamines include, but are not limited to, polyethylene amines such as diethylene triamine, triethylene tetramine, tetraethylene pentamine, and pentaethylene hexamine.

[0031] Examples of the diamine compound containing a disulfide bond include compounds in which monoamines having one primary amino group are bonded by a disulfide bond. Specific examples of the diamine compound containing a disulfide bond include, but are not limited to, cystine and cystamine.

[0032] Examples of aliphatic amines having three primary amino groups include tris(2-aminoalkyl)amines. Examples of tris(2-aminoalkyl)amines include tris(2-aminoalkyl)amines having an alkyl group having 1 to 5 carbon atoms. Specific examples of tris(2-aminoalkyl)amines include, but are not limited to, tris(2-aminoethyl)amine and tris(3-aminopropyl)amine.

[0033] Examples of aromatic amines include aromatic amines having one or more amino groups or aminoalkylene groups bonded to an aromatic ring. The aminoalkylene group may be linear, branched, or may contain a ring structure. The alkylene group in the aminoalkylene group may be an alkylene group having 1 to 6 carbon atoms. Examples of the aromatic ring include a benzene ring, a naphthalene ring, and a biphenyl ring. Specific examples of aromatic amines include aromatic monoamines such as aniline, benzylamine, phenethylamine, 3-phenylpropylamine, o-toluidine, p-toluidine, 2,4,6-trimethylaniline, 2-naphthylamine, and 1-naphthylamine; and aromatic diamines such as m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-xylylenediamine, o-xylylenediamine, and p-xylylenediamine.

[0034] The compound (A) may be a compound having a primary amino group (a1) as a first functional group and a second functional group (a2) that is less reactive with polysuccinimide than the primary amino group (a1) (hereinafter also referred to as "compound (A1)").

[0035] The primary amino group (a1) in the compound (A1) is preferably a primary amino group bonded to a methylene group (NH2-CH2-).

[0036] The second functional group (a2) in the compound (A1) is preferably a primary amino group or a phosphonooxy group ((OH)P(=O)-O-), more preferably a primary amino group. When the second functional group (a2) is a primary amino group, the amino group of the second functional group (a2) is preferably an amino group in a structure represented by the following general formula (2):

[0037] [ka] [In the formula, G represents a carboxy group or a carboxylate group, and * represents a bond.]

[0038] When G is a carboxylate group, it may form a salt with a cation. Examples of such salts include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as calcium salts and magnesium salts; organic base salts such as amine salts; and basic amino acid salts such as lysine salts and arginine salts. Among these, alkali metal salts are preferred, and sodium salts or potassium salts are more preferred.

[0039] When the second functional group (a2) in the compound (A1) is a primary amino group, the primary amino group in the second functional group (a2) is a primary amino group that is less reactive with polysuccinimide (PSI) than the primary amino group (a1). Examples of the compound (A1) having such a primary amino group (a1) and a second functional group (a2) include diamines having different terminal structures containing the respective amino groups. For example, asymmetric diamines are included.

[0040] The compound (A1) may be a compound in which the primary amino group (a1) is an amino group of NH2-CH2- and the second functional group (a2) is an amino group in the structure represented by the above general formula (2). Such a compound (A1) may be a compound represented by the following general formula (3).

[0041] [ka] [In the formula, L represents a divalent linking group.]

[0042] In the general formula (3), examples of the divalent linking group for L include a linear or branched alkylene group, a combination of a linear or branched alkylene group with an ether bond, a combination of a methylene group with an ester bond, etc. L is preferably a linear alkylene group, and the linear alkylene group preferably has 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, and even more preferably 2 to 5 carbon atoms.

[0043] In compound (A1), the carboxy group of the compound represented by general formula (3) may form a salt. Examples of such salts include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as calcium salts and magnesium salts; organic base salts such as amine salts; and basic amino acid salts such as lysine salts and arginine salts. Among these, alkali metal salts are preferred, and sodium salts or potassium salts are more preferred.

[0044] The compound (A1) may be a compound represented by the following general formula (4).

[0045] [ka] [In the formula, n represents an integer of 1 to 10.]

[0046] In the formula (4), n is preferably an integer of 2 to 8, and more preferably an integer of 3 to 5.

[0047] In compound (A1), the carboxy group of the compound represented by general formula (4) may form a salt. In this case, examples of the salt include alkali metal salts such as sodium salt and potassium salt; alkaline earth metal salts such as calcium salt and magnesium salt; organic base salts such as amine salt; and basic amino acid salts such as lysine salt and arginine salt. Among these, alkali metal salts are preferred, and sodium salts or potassium salts are more preferred.

[0048] Examples of the compound (A1) in which the second functional group (a2) is a phosphonooxy group ((OH)2P(=O)-O-) group include compounds represented by the following general formula (5).

[0049] [ka] [In the formula, L represents a divalent linking group.]

[0050] Examples of the divalent linking group for L in the general formula (5) include the same as the divalent linking group for L in the formula (3). L in the formula (5) is preferably a linear alkylene group, and the linear alkylene group preferably has 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, and even more preferably 3 to 5 carbon atoms.

[0051] In compound (A1), the phosphonooxy group of the compound represented by formula (5) may form a salt. Examples of such salts include alkali metal salts such as sodium salts and potassium salts; alkaline earth metal salts such as calcium salts and magnesium salts; organic base salts such as amine salts; and basic amino acid salts such as lysine salts and arginine salts. Among these, alkali metal salts are preferred, and sodium salts or potassium salts are more preferred.

[0052] Specific examples of the compound (A1) include lysine, ornithine, arginine, and phosphorylethanolamine.

[0053] Compound (A1) may be a dipeptide. Examples of the dipeptide include dipeptides having a basic amino acid residue at the C-terminus, such as glycine-lysine (isopeptide bond), alanine-lysine (isopeptide bond), glycine-ornithine (isopeptide bond), and alanine-ornithine (isopeptide bond); and dipeptides having a basic amino acid residue at the N-terminus, such as lysine-glycine, lysine-alanine, ornithine-glycine, and ornithine-alanine.

[0054] Compound (A) may be in the form of an acid salt. Examples of the acid salt of compound (A) include, but are not limited to, hydrochloride and sulfate.

[0055] (aqueous solvent) An aqueous solvent is a solvent whose main component is water and does not include organic solvents. An "organic solvent" is an organic compound that is liquid at room temperature and normal pressure (e.g., 20 to 30°C, 1 atmosphere). An example of an aqueous solvent is water. Examples of water that can be used include distilled water and deionized water.

[0056] The aqueous solvent may contain components other than water (excluding organic solvents), such as inorganic salts.

[0057] (Reaction temperature) The reaction temperature is 20°C or lower, preferably 15°C or lower. The reaction temperature is preferably 0°C or higher. The reaction temperature range is preferably 0 to 20°C, more preferably 0 to 15°C. When the reaction temperature is within the above range, the amine addition rate in the amine adduct of polyaspartic acid obtained by the production method of this embodiment is increased, and the weight-average molecular weight is increased. In addition, the water retention of the crosslinked polyaspartic acid obtained by crosslinking the amine adduct of polyaspartic acid is improved. Furthermore, when the reaction temperature is closer to 0°C, the amine addition rate in the amine adduct of polyaspartic acid is increased, and the weight-average molecular weight tends to be increased. Therefore, the reaction temperature may be 0 to 10°C or 0 to 5°C.

[0058] (pH) The pH during the reaction (reaction pH) is preferably 12 or less, more preferably 11.5 or less. During the reaction, it is preferable to adjust the pH using a basic compound such as sodium hydroxide so that the pH does not exceed an upper limit set within the range of 12 or less. The upper limit of the reaction pH is preferably set in the range of 10 to 12, more preferably in the range of 10 to 11.5, and even more preferably in the range of 11 to 11.5. When the upper limit of the reaction pH is within the above range, the amine addition rate in the amine adduct of polyaspartic acid obtained by the production method of this embodiment is increased, and the weight-average molecular weight is increased. In addition, the water retention of the crosslinked polyaspartic acid obtained by crosslinking the amine adduct of polyaspartic acid is improved. The lower limit of the reaction pH is, for example, 8, preferably 9, and more preferably 10.

[0059] (Reaction method) In step (A), it is preferable to first dissolve compound (A) in an aqueous solvent to obtain an aqueous solution of compound (A). Next, it is preferable to add polysuccinimide to the aqueous solution of compound (A). Polysuccinimide has low solubility in aqueous solvents. Therefore, polysuccinimide is dispersed in the aqueous solution of compound (A). Before dispersing polysuccinimide in the aqueous solution of compound (A), polysuccinimide particles with large particle sizes may be removed using a sieve or the like.

[0060] The ratio of the aqueous solvent to the compound (A) is, for example, preferably 5 to 50 parts by mass, more preferably 7 to 15 parts by mass, per 1 part by mass of the compound (A).

[0061] The mass ratio of polysuccinimide to aqueous solvent (polysuccinimide / aqueous solvent) can be in the range of 1 / 1 to 1 / 2, preferably 1 / 1.2 to 1 / 2, and more preferably 1 / 1.4 to 1 / 2. When the mass ratio of polysuccinimide to aqueous solvent is within the above range, the amine addition rate in the amine adduct of polyaspartic acid obtained by the production method of this embodiment is increased, and the weight-average molecular weight is increased. In addition, the water retention of the crosslinked polyaspartic acid obtained by crosslinking the amine adduct of polyaspartic acid is improved.

[0062] The molar ratio of polysuccinimide to compound (A) (polysuccinimide / compound (A)) is 100 / 0.1 to 100 / 30, preferably 100 / 0.2 to 100 / 20, and more preferably 100 / 0.3 to 100 / 15.

[0063] It is preferable to add an inorganic base such as sodium hydroxide to the reaction mixture obtained by dispersing polysuccinimide in an aqueous solution of compound (A) to adjust the pH to a basic range (for example, pH 9 or higher, preferably pH 10 or higher). At this time, the pH of the reaction mixture is adjusted to 12 or lower.

[0064] The reaction between polysuccinimide and compound (A) is carried out by reacting the reaction mixture under conditions of a reaction temperature of 20°C or less and a reaction pH of 12 or less. During the reaction, it is preferable to appropriately adjust the pH of the reaction mixture to basic using an inorganic base such as sodium hydroxide. At this time, the pH of the reaction mixture is adjusted to pH 12 or less. It is preferable to stir the reaction mixture during the reaction. The reaction time is not particularly limited, but may be, for example, 3 to 50 hours.

[0065] The above reaction causes ring-opening of polysuccinimide to produce polyaspartic acid. Furthermore, compound (A) is bonded to one or more of the aspartic acid units of polyaspartic acid to produce an amine adduct of polyaspartic acid. Examples of the aspartic acid unit bonded to compound (A) include the structural unit represented by the following general formula (6):

[0066] [ka] [In the formula, R 1 is a monovalent organic group.

[0067] R in the general formula (6) 1 is a group derived from compound (A).

[0068] When the compound (A) is a polyfunctional amine, the amine adduct of polyaspartic acid may contain a structure in which aspartic acid units are crosslinked with the polyfunctional amine.

[0069] The amine addition rate in the amine adduct of polyaspartic acid obtained in step (A) can be, for example, 55% or more. The amine addition rate may be, for example, 58 to 95%, or 58 to 90%. The amine addition rate is the proportion (%) of aspartic acid units to which compound (A) is bonded to all aspartic acid units in the amine adduct of polyaspartic acid. The amine addition rate can be determined from the ratio (Ib / Ia) of the integral value Ia of the peak derived from the protons of -CH2- in the main chain of polyaspartic acid to the integral value Ib of the peak derived from the protons of -CH2- in compound (A) in proton NMR. Alternatively, it can be determined from the ratio (Ic × 2 / Ia) of the integral value Ia of the peak derived from the protons of -CH2- in compound (A) to twice the integral value Ic of the peak derived from the protons of -CH2- in compound (A).

[0070] The weight-average molecular weight of the polyaspartic acid amine adduct obtained in step (A) depends on the weight-average molecular weight of the polysuccinimide used in the reaction. For example, the weight-average molecular weight of the polyaspartic acid amine adduct is preferably increased by 5% or more relative to the weight-average molecular weight of the polysuccinimide.

[0071] The amine adduct of polyaspartic acid obtained in step (A) can be isolated by known ordinary isolation procedures such as recrystallization, reprecipitation, filtration, concentration, and the like.

[0072] In the production method of this embodiment, polysuccinimide and compound (A) are reacted in an aqueous solvent containing no organic solvent. Therefore, a step of removing the organic solvent and a step of treating the organic solvent are not required. This reduces the workload and the environmental impact.

[0073] The production method of this embodiment can produce an amine adduct of polyaspartic acid with a high amine addition rate and a high weight-average molecular weight. This is thought to be because, under favorable conditions such as a relatively low reaction temperature of 20°C or less and a constant basic environment, the polymer decomposition reaction of polyaspartic acid (the amide bond in the main chain is the decomposition site) does not proceed very well, while the addition reaction of polysuccinimide with compound (A) mainly proceeds.

[0074] [Method of manufacturing crosslinked polyaspartic acid] A second aspect of the present disclosure is a method for producing a crosslinked polyaspartic acid, which includes a step (hereinafter also referred to as "step (B)") of reacting a crosslinking agent with the polyaspartic acid amine adduct obtained by the method for producing a polyaspartic acid amine adduct according to the first aspect to perform a crosslinking reaction.

[0075] In the reaction between the amine adduct of polyaspartic acid and the crosslinking agent, the amine adduct moiety of the amine adduct of polyaspartic acid (i.e., R 1 The crosslinking agent may be bonded to a part of the amine adduct of polyaspartic acid, that is, a carboxyl residue of the part to which the amine is not added (i.e., a carboxyl group of an aspartic acid unit to which no amine is bonded). The amine adduct of polyaspartic acid produced by the production method according to the first aspect may be reacted with a compound other than compound (A) or a compound corresponding to compound (A) that was not used in the production of the amine adduct, followed by a crosslinking reaction using a crosslinking agent. Alternatively, the amine adduct of polyaspartic acid may be reacted with a crosslinking agent to perform a crosslinking reaction, followed by a compound other than compound (A) or a compound corresponding to compound (A) that was not used in the production of the amine adduct.

[0076] <Process (B)> (Amine adduct of polyaspartic acid) The amine adduct of polyaspartic acid can be obtained by the method for producing the amine adduct of polyaspartic acid according to the first aspect. Therefore, the production method of this embodiment may include a step of obtaining the amine adduct of polyaspartic acid according to the method for producing the amine adduct of polyaspartic acid according to the first aspect.

[0077] (Crosslinking agent) The crosslinking agent is not particularly limited as long as it can crosslink the amine adduct of polyaspartic acid. The crosslinking agent may be a crosslinking agent capable of crosslinking aspartic acid units to which compound (A) is not added, or a crosslinking agent capable of crosslinking aspartic acid units to which compound (A) is added. Examples of the crosslinking agent include a polyfunctional amine compound and a polyfunctional epoxy compound.

[0078] <Multifunctional amine compounds> The polyfunctional amine compound may be an aliphatic amine or an aromatic amine, and examples of the polyfunctional amine compound include the above-mentioned aliphatic amine having two primary amino groups, aliphatic amine having three primary amino groups, aromatic diamine, and compound (A1).

[0079] <Multifunctional epoxy compounds> A polyfunctional epoxy compound is a compound containing two or more epoxy groups. Examples of polyfunctional epoxy compounds include polyglycidyl ethers of alkane polyols (e.g., having 2 to 6 carbon atoms) or poly(alkylene glycols) (e.g., having 2 to 6 carbon atoms), such as ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, and butanediol diglycidyl ether; sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, erythritol polyglycidyl ether, and trimethylolethane polyglycidyl ether. Examples include polyglycidyl ethers of alkane polyols (e.g., having 2 to 6 carbon atoms) and poly(alkylene glycols) (e.g., having 2 to 6 carbon atoms), such as glycidyl ether and trimethylolpropane polyglycidyl ether; diepoxyalkanes (e.g., having 4 to 8 carbon atoms), such as 1,2,3,4-diepoxybutane, 1,2,4,5-diepoxypentane, 1,2,5,6-diepoxyhexane, 1,2,7,8-diepoxyoctane, and 1,4- and 1,3-divinylbenzene epoxide; and polyphenol polyglycidyl ethers (e.g., having 6 to 15 carbon atoms), such as 4,4'-isopropylidenediphenol diglycidyl ether (bisphenol A diglycidyl ether) and hydroquinone diglycidyl ether. Commercially available polyfunctional epoxy compounds include the Denacol (registered trademark) series (EX-810, EX-861, EX-313, EX-614B, EX-512, etc.) manufactured by Nagase ChemteX Corporation. The polyfunctional epoxy compound is preferably a difunctional epoxy compound, more preferably alkylene glycol diglycidyl ether, and even more preferably ethylene glycol diglycidyl ether.

[0080] (Crosslinking reaction) The crosslinking reaction can be carried out by a known method depending on the type of crosslinking agent. The amount of the crosslinking agent to be added can be, for example, 0.1 to 10 parts by mass, preferably 0.5 to 5 parts by mass, and more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the amine adduct of polyaspartic acid.

[0081] The amine adduct of polyaspartic acid may be a solid amine adduct obtained by isolating the amine adduct of polyaspartic acid from the reaction solution obtained in the above step (A). In this case, it is preferable to prepare an aqueous solution of the amine adduct of polyaspartic acid before adding the crosslinking agent.

[0082] The polyaspartic acid amine adduct may be used in the form of a solution without being isolated from the reaction solution obtained in the step (A). In this case, a crosslinking agent may be added to the reaction solution obtained in the step (A).

[0083] The reaction temperature and reaction time of the crosslinking reaction can be appropriately set depending on the type of crosslinking agent. The reaction temperature can be, for example, 30° C. to 100° C. The reaction time can be, for example, 40 minutes to 600 minutes.

[0084] The crosslinked polyaspartic acid produced by the reaction can be isolated by known ordinary isolation procedures such as recrystallization, reprecipitation, filtration, concentration, etc.

[0085] <Other processes> The production method of this embodiment may include other steps in addition to the step (B) described above, such as a step of reacting an amine adduct of polyaspartic acid with a compound other than a crosslinking agent (hereinafter also referred to as "step (a)") before the step (B), and a step of reacting a crosslinked polyaspartic acid with a compound other than a crosslinking agent after the step (B) (hereinafter also referred to as "step (b)").

[0086] (Step (a)) <Compounds other than crosslinking agents> The compound other than the crosslinking agent (hereinafter also referred to as "compound (B)") is a compound that does not form a crosslinked structure when reacted with the amine adduct of polyaspartic acid. The compound (B) used in step (a) is not particularly limited as long as it has a functional group capable of reacting with the functional group (amino group, carboxy group) possessed by the amine adduct of polyaspartic acid. Examples of the functional group possessed by compound (B) include a hydroxy group, an amino group, a thiol group, and an epoxy group. Compound (B) preferably has only one functional group capable of reacting with the functional group possessed by the amine adduct of polyaspartic acid. Compound (B) may be compound (A) that was not used in the production of the amine adduct of polyaspartic acid. For example, compound (B) may be a monoamine compound having one primary amino group.

[0087] The reaction temperature and reaction time of the reaction between the amine adduct of polyaspartic acid and compound (B) can be appropriately set depending on the type of compound (B). The reaction temperature can be, for example, 30° C. to 100° C. The reaction time can be, for example, 40 minutes to 600 minutes.

[0088] (Step (b)) The compound (B) used in step (b) is not particularly limited as long as it has a functional group capable of reacting with the functional group (amino group, carboxy group, or functional group introduced by a crosslinking agent) of the crosslinked polyaspartic acid. Examples of the functional group of the compound (B) include the same functional groups as those listed in step (a).

[0089] The reaction temperature and reaction time for the reaction between the crosslinked polyaspartic acid and compound (B) can be appropriately set depending on the type of compound (B). The reaction temperature can be, for example, 30° C. to 100° C. The reaction time can be, for example, 40 minutes to 600 minutes.

[0090] In the production method of this embodiment, a polyaspartic acid crosslinked product having excellent water retention properties can be obtained by using the amine adduct of polyaspartic acid obtained by the production method of the amine adduct of polyaspartic acid according to the first aspect.

[0091] <Applications of crosslinked polyaspartic acid> The polyaspartic acid crosslinked material produced by the production method of this embodiment can be used as a water-absorbing composition that constitutes an absorbent material in absorbent articles such as diapers, sanitary products, etc. When the polyaspartic acid crosslinked material is used as a water-absorbing composition, the size (average particle size) is preferably 1 to 5000 μm, more preferably 10 to 1000 μm, and even more preferably 100 to 800 μm.

[0092] The crosslinked polyaspartic acid can be used as a thickening composition. When used as a crosslinked polyaspartic acid, the size (average particle size) is preferably 150 μm or less, more preferably 100 μm or less, and even more preferably 80 μm or less.

[0093] (Water absorbent resin) The water-absorbing resin contains a crosslinked polyaspartic acid obtained by the production method of the present embodiment. The water-absorbing resin may contain other resins than the crosslinked polyaspartic acid, other known additives, etc., as necessary. When the crosslinked polyaspartic acid is in the form of a hydrogel, the crosslinked polyaspartic acid is dried as needed and typically pulverized before or after drying to form a water-absorbent resin. The drying method is not particularly limited, and any known method, such as heat drying, freeze drying, reduced pressure (vacuum) drying, or reduced pressure heat drying, may be used. Since the particle shape may vary depending on the drying method, the drying method should be selected according to the purpose. In the case of heat drying, the drying temperature is typically 60°C to 250°C, preferably 80°C to 220°C, and more preferably 100°C to 200°C. In the case of reduced pressure heat drying, the drying temperature is typically 50°C to 200°C, preferably 60°C to 150°C, and more preferably 70°C to 120°C. The drying time depends on the surface area and moisture content of the hydrogel crosslinked product, and the type of dryer, and is selected to achieve the desired moisture content. It is difficult to reduce the moisture content of a water absorbent resin to zero, and therefore, in the case where a water absorbent resin contains a small amount of water (for example, 0.3 to 15% by weight, further 0.5 to 10% by weight) and can be handled as a powder, the water absorbent resin containing this small amount of water is also referred to as a water absorbent resin in this specification. In the water-absorbing resin, the content of the crosslinked polyaspartic acid is preferably 50% by mass to 100% by mass, more preferably 70% by mass to 100% by mass, and further preferably 90% by mass to 100% by mass. The water-absorbing resin may be a crosslinked polyaspartic acid.

[0094] (Water-absorbing resin particles) Examples of the shape of the water-absorbent resin particles include substantially spherical, crushed, granular, etc. The size (average particle size) of the water-absorbent resin particles is preferably 1 to 5000 μm, more preferably 10 to 1000 μm, and even more preferably 100 to 800 μm. The particle size distribution of the water-absorbent resin particles may be adjusted by performing an operation such as particle size adjustment using classification with a sieve.

[0095] The water-absorbent resin particles can be subjected to crosslinking (surface crosslinking) of the surface portion of the crosslinked hydrogel using a crosslinking agent. By performing surface crosslinking, it is easy to control the water absorption properties of the water-absorbent resin particles. The surface crosslinking is preferably performed at a timing when the crosslinked hydrogel reaches a specific water content.

[0096] Examples of the crosslinking agent (surface crosslinking agent) for surface crosslinking include crosslinking agents used in producing crosslinked polyaspartic acid. Other examples include compounds having two or more reactive functional groups. The crosslinking agents may be used alone or in combination of two or more.

[0097] After the surface cross-linking, water or the water-containing solvent is distilled off by a known method, whereby cross-linked particles, which are a surface-cross-linked, dry product, can be obtained.

[0098] The water-absorbent resin particles may be composed solely of the crosslinked particles, but may further contain various additional components selected from, for example, a gel stabilizer, a metal chelating agent, and a flowability improver (lubricant). The additional components may be located inside the crosslinked particles, on the surface of the crosslinked particles, or both. As the additional component, a flowability improver (lubricant) is preferred, and among them, inorganic particles are more preferred. Examples of inorganic particles include silica particles such as amorphous silica, talc, and mica.

[0099] The water-absorbent resin particles may contain a plurality of inorganic particles arranged on the surface of the crosslinked particles. For example, the inorganic particles can be arranged on the surface of the crosslinked particles by mixing the crosslinked particles with the inorganic particles. The inorganic particles may be silica particles such as amorphous silica. When the water-absorbent resin particles contain inorganic particles arranged on the surface of the crosslinked particles, the ratio of the inorganic particles to the mass of the crosslinked particles may be 0.2% by mass or more, 0.5% by mass or more, 1.0% by mass or more, or 1.5% by mass or more, and may be 5.0% by mass or less, or 3.5% by mass or less. When the amount of inorganic particles added is within the above-mentioned range, water-absorbent resin particles having suitable water absorption properties are easily obtained.

[0100] The water-absorbent resin particles can be used in various products that require water absorption, moisture absorption, and the like.

[0033] Examples of uses of the water absorbent resin particles include medical products and hygiene products such as sanitary products, diapers, breast milk pads, incontinence pads, portable toilets, wet tissues, medical underpads, medical blood absorbers, and wound protection dressings; cleaning products such as disposable dustcloths; pet supplies such as pet sheets; daily necessities and clothing such as disposable body warmers, sweat-absorbent fibers, and deodorizing and moisture-removing sheets; food-related products such as food freshness-preserving agents, dehydrating agents in the food field, food packaging materials such as drip-absorbent sheets, and transportation materials such as water-absorbent sheets for transporting fresh vegetables; construction-related products such as anti-condensation building materials and waterproofing agents for concrete; gasoline dehydrating agents, gasoline moisture removers, oil dehydrating agents, or oil moisture removers; water retention materials, soil conditioners, floral foam (material for immobilizing cut flowers), seedling beds for raising seedlings, hydroponic vegetation sheets, seed tapes, fluid seeding media, anti-condensation agricultural sheets, and agricultural products such as irrigation solutions.

[0101] (absorber) The absorbent body includes the water-absorbent resin particles and a fiber layer containing fibrous material. The absorbent body is, for example, a mixture containing water-absorbent resin particles and fibrous material. The absorbent body may have a configuration in which the water-absorbent resin particles and fibrous material are uniformly mixed, a configuration in which the water-absorbent resin particles are sandwiched between fibrous material formed in a sheet or layer shape, or another configuration.

[0102] The mass proportion of the water-absorbent resin particles in the absorbent body may be 2 to 100 mass %, 10 to 90 mass %, or 10 to 80 mass % relative to the total mass of the water-absorbent resin particles and fibrous materials.

[0103] The shape of the absorbent body is not particularly limited and may be, for example, a sheet, a cylinder, a film, or a fiber. The thickness of the absorbent body (for example, the thickness of a sheet-shaped absorbent body) may be, for example, 0.1 to 50 mm, or 0.3 to 30 mm.

[0104] The absorbent contains the water-absorbent resin particles. The absorbent may contain other known water-absorbent resin particles in addition to the water-absorbent resin particles. It is preferable that the absorbent contains only the water-absorbent resin particles.

[0105] The content of the water-absorbent resin particles in the absorbent body is set to 50 to 2000 g per square meter of the absorbent body (i.e., 50 to 2000 g / m) from the viewpoint of more easily obtaining sufficient liquid absorption performance when the absorbent body is used in an absorbent article described later. 2 ), and more preferably 100 to 1000 g / m 2 In order to ensure that the absorbent article has sufficient liquid absorption performance and, in particular, to prevent liquid leakage, the content of the water-absorbent resin particles is 50 g / m 2 From the viewpoint of suppressing the occurrence of the gel blocking phenomenon, exhibiting the liquid diffusion performance as an absorbent article, and further improving the liquid permeation speed, the content of the water-absorbent resin particles is preferably 2000 g / m or more. 2 It is preferable that:

[0106] [Fibrous material] The fibrous material is not particularly limited, but includes pulverized wood pulp, cotton, cotton linters, rayon, cotton, wool, acetate, vinylon, cellulosic fibers such as cellulose acetate, synthetic fibers such as polyamide, polyester, polyolefin, and mixtures of these fibers. One type of fibrous material may be used alone, or two or more types may be used in combination. Hydrophilic fibers can be used as the fibrous material.

[0107] The content of the fibrous material is set to 50 to 800 g per square meter of the absorbent body (i.e., 50 to 800 g / m) from the viewpoint of obtaining sufficient liquid absorption performance when the absorbent body is used in an absorbent article described later. 2 ), and more preferably 100 to 600 g / m 2 , and more preferably 150 to 500 g / m 2In order to ensure that the absorbent article exhibits sufficient liquid absorption performance, in particular by suppressing the occurrence of gel blocking to enhance the liquid diffusion performance, and furthermore, to enhance the strength of the absorbent body after absorbing liquid, the content of the fibrous material is set to 50 g or more per square meter of the absorbent body (i.e., 50 g / m 2 In particular, from the viewpoint of suppressing return of the absorbent body after absorbing the liquid, the content of the fibrous material is preferably 800 g or less per square meter of the absorbent body (i.e., 800 g / m 2 (see below) is preferred.

[0108] To improve the shape retention of the absorbent body before and during use, an adhesive binder may be added to the fibrous material to bond the fibers together. Examples of adhesive binders include heat-fusible synthetic fibers, hot-melt adhesives, and adhesive emulsions. The adhesive binders may be used alone or in combination of two or more.

[0109] Examples of heat-fusible synthetic fibers include full-melt binders such as polyethylene, polypropylene, and ethylene-propylene copolymers; and non-full-melt binders having a side-by-side or core-sheath structure of polypropylene and polyethylene. In the above-mentioned non-full-melt binders, only the polyethylene portion can be heat-fused.

[0110] Examples of hot melt adhesives include mixtures of base polymers such as ethylene-vinyl acetate copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene-styrene block copolymer, styrene-ethylene-butylene-styrene block copolymer, styrene-ethylene-propylene-styrene block copolymer, and amorphous polypropylene with tackifiers, plasticizers, antioxidants, and the like.

[0111] The adhesive emulsion may be, for example, a polymer of at least one monomer selected from the group consisting of methyl methacrylate, styrene, acrylonitrile, 2-ethylhexyl acrylate, butyl acrylate, butadiene, ethylene, and vinyl acetate.

[0112] [Additives] The absorbent may contain various additives commonly used in the technical field. Examples of additives include inorganic powders, deodorants, pigments, dyes, fragrances, antibacterial agents, adhesives, etc. By incorporating additives, it is possible to impart various functions to the absorbent. Examples of the inorganic powders include silicon dioxide, zeolite, mica, kaolin, clay, etc. When the water-absorbing agent contains inorganic particles, the absorbent may contain the inorganic powder in addition to the inorganic particles in the water-absorbing agent.

[0113] (Absorbent articles) The absorbent article includes a liquid-impermeable sheet, the absorber, and a liquid-permeable sheet. In the absorbent article, the liquid-impermeable sheet, the absorber, and the liquid-permeable sheet are arranged in this order. In the absorbent article, the liquid-permeable sheet is arranged at the outermost side on the side from which the liquid to be absorbed penetrates. The liquid-impermeable sheet is arranged at the outermost side on the side opposite to the side from which the liquid to be absorbed penetrates. Examples of absorbent articles include diapers (e.g., disposable diapers), toilet training pants, incontinence pads, urine absorption sheets, urine absorption liners, sanitary materials (sanitary napkins, tampons, etc.), sweat pads, pet sheets, portable toilet components, and animal waste disposal materials.

[0114] In the absorbent article, a liquid-impermeable sheet, an absorbent body, and a liquid-permeable sheet are laminated in this order.

[0115] The absorbent article may contain other known absorbent bodies in addition to the absorbent body described above. It is preferable that the absorbent article uses only the absorbent body described above as the absorbent body.

[0116] [Liquid-permeable sheet] The liquid-permeable sheet is disposed on the outermost side of the absorbent body, on the side into which the liquid to be absorbed penetrates. The liquid-permeable sheet has, for example, a main surface that is wider than the main surface of the absorbent body, and the outer edge of the liquid-permeable sheet extends around the absorbent body.

[0117] The liquid-permeable sheet may be a sheet formed from a resin or fiber commonly used in the art. From the viewpoints of liquid permeability, flexibility, and strength when used in absorbent articles, the liquid-permeable sheet may contain, for example, polyolefins such as polyethylene (PE) and polypropylene (PP), polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polylactic acid, polyester, such as polyhydroxyalkanoate, polyamides such as nylon, and rayon, or synthetic resins or synthetic fibers containing these synthetic resins. Alternatively, the liquid-permeable sheet may be natural fibers such as cotton, silk, hemp, or pulp (cellulose). From the viewpoints of increasing the strength of the liquid-permeable sheet, the liquid-permeable sheet may contain synthetic fibers. The synthetic fibers may be, in particular, polyolefin fibers, polyester fibers, or a combination thereof. These materials may be used alone or in combination of two or more materials.

[0118] The liquid-permeable sheet may be a nonwoven fabric, a porous sheet, or a combination thereof. A nonwoven fabric is a sheet in which fibers are intertwined without being woven. The nonwoven fabric may be a nonwoven fabric made of short fibers (i.e., staple) (short fiber nonwoven fabric) or a nonwoven fabric made of long fibers (i.e., filaments) (long fiber nonwoven fabric). The staple may generally have a fiber length of several hundred mm or less, although this is not limited thereto.

[0119] The liquid-permeable sheet may be at least one type of nonwoven fabric selected from the group consisting of thermal-bonded nonwoven fabric, air-through nonwoven fabric, resin-bonded nonwoven fabric, spunbonded nonwoven fabric, melt-blown nonwoven fabric, spunbonded / melt-blown / spunbonded nonwoven fabric, air-laid nonwoven fabric, spunlace nonwoven fabric, and point-bonded nonwoven fabric, and is preferably at least one type of nonwoven fabric selected from the group consisting of thermal-bonded nonwoven fabric, air-through nonwoven fabric, spunbonded nonwoven fabric, and spunbonded / melt-blown / spunbonded nonwoven fabric.

[0120] The liquid-permeable sheet may be a thermal-bonded nonwoven fabric, an air-through nonwoven fabric, a resin-bonded nonwoven fabric, a spunbonded nonwoven fabric, a melt-blown nonwoven fabric, an air-laid nonwoven fabric, a spunlace nonwoven fabric, a point-bonded nonwoven fabric, or a laminate of two or more nonwoven fabrics selected from these. These nonwoven fabrics may be formed, for example, from the synthetic fibers or natural fibers described above. A laminate of two or more nonwoven fabrics may be, for example, a spunbond / meltblown / spunbonded nonwoven fabric, which is a composite nonwoven fabric having a spunbonded nonwoven fabric, a meltblown nonwoven fabric, and a spunbonded nonwoven fabric laminated in this order. Among these, from the viewpoint of suppressing liquid leakage, a thermal-bonded nonwoven fabric, an air-through nonwoven fabric, a spunbonded nonwoven fabric, or a spunbonded / meltblown / spunbonded nonwoven fabric is preferably used.

[0121] It is desirable that the nonwoven fabric used as the liquid-permeable sheet has an appropriate degree of hydrophilicity from the viewpoint of the liquid absorption performance of the absorbent article.

[0122] The hydrophilic nonwoven fabric described above may be formed from fibers exhibiting moderate hydrophilicity, such as rayon fibers, or from fibers obtained by hydrophilizing hydrophobic chemical fibers, such as polyolefin fibers or polyester fibers. Methods for obtaining nonwoven fabrics containing hydrophilically treated hydrophobic chemical fibers include, for example, a method in which a hydrophilizing agent is mixed with hydrophobic chemical fibers to obtain a nonwoven fabric by the spunbonding method, a method in which a hydrophilizing agent is added when producing a spunbond nonwoven fabric from hydrophobic chemical fibers, and a method in which a hydrophilizing agent is impregnated into a spunbond nonwoven fabric obtained from hydrophobic chemical fibers. Examples of hydrophilizing agents include anionic surfactants such as aliphatic sulfonates and higher alcohol sulfate ester salts, cationic surfactants such as quaternary ammonium salts, nonionic surfactants such as polyethylene glycol fatty acid esters, polyglycerin fatty acid esters, and sorbitan fatty acid esters, silicone surfactants such as polyoxyalkylene-modified silicones, and stain release agents made from polyester, polyamide, acrylic, or urethane resins.

[0123] The liquid-permeable sheet is preferably a nonwoven fabric that is moderately bulky and has a large basis weight, from the viewpoint of imparting good liquid permeability, flexibility, strength, and cushioning properties to the absorbent article, and from the viewpoint of increasing the liquid permeation rate of the absorbent article.

[0124] [Liquid-impermeable sheet] The liquid-impermeable sheet is disposed on the outermost side of the absorbent article, opposite the liquid-permeable sheet. The liquid-impermeable sheet has, for example, a major surface wider than the major surface of the absorbent body, and the outer edge of the liquid-impermeable sheet extends around the periphery of the absorbent body. The liquid-impermeable sheet prevents liquid absorbed by the absorbent body from leaking out from the liquid-impermeable sheet side.

[0125] Examples of liquid-impermeable sheets include sheets made of resins such as polyethylene, polypropylene, polyvinyl chloride, polylactic acid, and polyhydroxyalkanoate; sheets made of nonwoven fabrics such as spunbond / meltblown / spunbond (SMS) nonwoven fabrics in which a water-resistant meltblown nonwoven fabric is sandwiched between high-strength spunbond nonwoven fabrics; and sheets made of composite materials of these resins and nonwoven fabrics (e.g., spunbond nonwoven fabrics and spunlace nonwoven fabrics). Liquid-impermeable sheets are preferably breathable, as this reduces stuffiness when worn and can alleviate discomfort for the wearer. A sheet made of a synthetic resin primarily composed of low-density polyethylene (LDPE) resin can be used as the liquid-impermeable sheet.

[0126] The size relationship between the absorbent body, the liquid-permeable sheet, and the liquid-impermeable sheet is not particularly limited, and may be adjusted appropriately depending on the intended use of the absorbent article, etc.

[0127] Although specific embodiments of the present invention have been described above in detail, the present invention is not limited to the above-described embodiments. Various modifications, alterations, and combinations of the respective configurations, elements, and features may be adopted without departing from the spirit of the present invention. Unless otherwise specified, the words "comprise" and "have" do not exclude the presence of elements other than those referred to as the object of the word, and these terms can be used interchangeably. The contents of each document mentioned in this specification are hereby incorporated by reference as if they were part of this specification. [Example]

[0128] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0129] [Water retention measurement] The water retention capacity was evaluated by measuring the water absorption capacity using the tea bag method (JIS K-7223) using physiological saline, then dehydrating the tea bags in a centrifugal dehydrator at 25°C and 150G for 2 minutes, and measuring the weight of the tea bags after dehydration. The water retention capacity was calculated using the following formula. Water retention [g / g] = {(weight after dehydration) - (blank weight after dehydration) - (sample weight)} / (sample weight)

[0130] [Synthesis Example 1: Synthesis of Polysuccinimide Reaction Product] 160 parts of aspartic acid and 83 parts of 85 wt % phosphoric acid were mixed in a mortar, transferred to a tray, and reacted at 190°C and 1.3 kPa for 6 hours. The reaction mixture was pulverized, washed with distilled water until the filtrate reached a pH of 2.0 or less, and then vacuum dried at 80°C to obtain 115 parts of polysuccinimide having a weight-average molecular weight of 138,000.

[0131] [Measurement of weight-average molecular weight of polysuccinimide] The weight-average molecular weight (Mw) of polysuccinimide was measured by GPC (gel permeation chromatography) using polysaccharide polymer (pullulan) as the standard, after dissolving the polysuccinimide in 15% aqueous sodium hydroxide solution and then diluting it with 0.1 M saline. Equipment: HLC-8420GPC (Tosoh Corporation) Detector: differential refractometer Column: Shodex Asahipak Guard column GF-1G 7B, GF-7MHQ x 3, Reference column: SB-800HQ x 3 Solvent: 0.1M saline Concentration: 0.2 to 1.0 wt% Injection volume: 10μL Flow rate: 1.0ml / min

[0132] [Synthesis Example 2: Synthesis of polyaspartic acid lysine adduct] Example 1 The polysuccinimide obtained in Synthesis Example 1 was fractionated using a 500 μm mesh sieve (JIS Z 8801 stainless steel test sieve, manufactured by Tokyo Screen Co., Ltd.), and polysuccinimide particles that passed through the sieve were isolated. 30 parts by mass of the polysuccinimide particles, 5.64 parts by mass of L-lysine hydrochloride (Tokyo Chemical Industry Co., Ltd.), and 58.50 parts by mass of distilled water were placed in a four-neck glass flask and stirred. Then, 25.23 parts of a 48% aqueous solution of NaOH was added dropwise with stirring at 15°C while adjusting the pH to an upper limit of 11.5 using a pH electrode / monitor (Horiba, Ltd.). After the dropwise addition was completed, the mixture was stirred for an additional 18 hours at 15°C. The resulting reaction solution was filtered through a 59 μm nylon mesh to obtain a solution (solids content: 41%) of a lysine adduct of sodium polyaspartate (hereinafter referred to as "polyaspartic acid lysine adduct").

[0133] (Examples 2 to 11, Comparative Examples 1 to 3) A solution of a polyaspartic acid lysine adduct was obtained in the same manner as in Example 1, except that the mesh size of the sieve used to obtain the polysuccinimide particles, the mass ratio of polysuccinimide to distilled water, the temperature conditions, the upper limit of pH during the reaction, the weight-average molecular weight of the polysuccinimide used, and the molar ratio of polysuccinimide particles to L-lysine were changed as shown in Table 1.

[0134] [Table 1]

[0135] In Table 1, "PSI" represents polysuccinimide. "<500 μm" and "<150 μm" represent the fraction that passed through a 500 μm sieve and the fraction that passed through a 150 μm sieve, respectively. "500-250 μm" represents the fraction that passed through a 500 μm sieve and did not pass through a 250 μm sieve. "250-150 μm" represents the fraction that passed through a 250 μm sieve and did not pass through a 150 μm sieve. "Mw" represents the weight-average molecular weight.

[0136] [Measurement of weight-average molecular weight of polyaspartic acid-lysine adduct] The weight-average molecular weight (Mw) of the polyaspartic acid-lysine adduct was measured by GPC (gel permeation chromatography) using polysaccharide polymer (pullulan) as a standard and diluting the polyaspartic acid-lysine adduct in 0.1 M saline. Equipment: HLC-8420GPC (Tosoh Corporation) Detector: differential refractometer Column: Shodex Asahipak Guard column GF-1G 7B, GF-7MHQ x 3, Reference column: SB-800HQ x 3 Solvent: 0.1M saline Concentration: 0.2 to 1.0 wt% Injection volume: 10μL Flow rate: 1.0ml / min

[0137] [Lysine addition rate measurement] The proportion of aspartic acid units to which lysine was added (lysine addition rate) of the polyaspartic acid lysine adduct obtained in Synthesis Example 2 was measured by NMR. Sample preparation: Polyaspartic acid lysine adduct was mixed with heavy water (Kanto Chemical Co., Inc.) in a ratio of 0.2 parts by mass:0.9 parts by mass, and the sample was then subjected to 1H-NMR measurement using a JEOL ECZ-400S. The obtained spectrum was processed using Delta (NMR software) manufactured by JEOL Ltd., and the area ratio between the broad peak near 3.3 ppm (corresponding to the added lysine) and the sharp peak near 3.2 ppm (corresponding to the unreacted lysine) was calculated and expressed as the "lysine addition rate (%)," as shown in Table 2. Lysine addition rate (%) = broad peak area around 3.3 ppm / (broad peak area around 3.3 ppm + sharp peak area around 3.2 ppm) × 100

[0138] [Water retention measurement] <Production of crosslinked polyaspartic acid> 4.64 parts of the solution of the polyaspartic acid lysine adduct obtained in Synthesis Example 2 above and 0.106 parts of polyfunctional epoxy compound EX-810 (manufactured by Nagase ChemteX) were mixed and reacted by heating at 60°C.

[0139] The gel composition obtained after 110 minutes of reaction was freeze-dried, and the dried composition was pulverized in a mortar and passed through a stainless steel sieve (JIS Z-8801) with a mesh size of 710 μm, and the fraction that did not pass through a sieve with a mesh size of 150 μm was collected. This was used as water-absorbent resin particles (SAP) of crosslinked polyaspartic acid, and its water retention was measured.

[0140] <Water retention measurement> Water retention was evaluated by measuring water absorption using the tea bag method (JIS K-7223) using physiological saline, followed by dehydration in a centrifugal dehydrator at 25°C and 150G for 2 minutes, and then measuring the weight of the tea bag after dehydration. Water retention was calculated using the following formula. The results are shown in Table 2 as "SAP water retention (g / g)." Water retention [g / g] = {(weight after dehydration) - (blank weight after dehydration) - (sample weight)} / (sample weight)

[0141] [Table 2]

[0142] In Examples 1 to 11, both the weight-average molecular weight and the lysine addition rate of the obtained lysine adducts of sodium polyaspartate were improved compared to Comparative Examples 1 to 3. The water retention properties of the SAPs produced from the lysine adducts of sodium polyaspartate obtained in Examples 1 to 11 were also improved compared to Comparative Examples 1 to 3. [Industrial Applicability]

[0143] According to the present invention, there are provided a method for producing an amine adduct of polyaspartic acid, which can carry out an amine addition reaction without using an organic solvent and can produce an amine adduct of polyaspartic acid having a high amine addition rate and a high weight-average molecular weight, and a method for producing a crosslinked polyaspartic acid using the amine adduct of polyaspartic acid obtained by the above production method.

Claims

1. The method includes a step (A) of reacting polysuccinimide with a compound having a primary amino group in an aqueous solvent under conditions of a reaction temperature of 20°C or less and a reaction pH of 12 or less, A method for producing an amine adduct of polyaspartic acid.

2. In the step (A), the mass ratio of the polysuccinimide to the aqueous solvent (polysuccinimide / aqueous solvent) is in the range of 1 / 1 to 1 / 2. A method for producing the amine adduct of polyaspartic acid according to claim 1.

3. The polysuccinimide is polysuccinimide particles that have passed through a sieve with an opening of 500 μm. A method for producing the amine adduct of polyaspartic acid according to claim 1 or 2.

4. The polysuccinimide is polysuccinimide particles that have passed through a sieve with an opening of 150 μm. A method for producing the amine adduct of polyaspartic acid according to claim 3.

5. the reaction temperature in the step (A) is 15°C or less; A method for producing the amine adduct of polyaspartic acid according to claim 1 or 2.

6. the compound having a primary amino group is a polyfunctional amine; A method for producing the amine adduct of polyaspartic acid according to claim 1 or 2.

7. the polyfunctional amine has a first primary amino group and a second primary amino group, and the first secondary amino group has lower reactivity with the polysuccinimide than the first primary amino group; A method for producing the amine adduct of polyaspartic acid according to claim 6.

8. The polyfunctional amine is at least one selected from the group consisting of lysine, ornithine, and arginine. A method for producing the amine adduct of polyaspartic acid according to claim 7.

9. A method for producing a crosslinked polyaspartic acid, comprising a step of reacting a crosslinking agent with the polyaspartic acid amine adduct obtained by the method for producing the polyaspartic acid amine adduct according to claim 1 or 2 to carry out a crosslinking reaction.

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